FACULTY PUBLICATIONS

Pasachoff, Jay M., and Alex Filippenko

Third edition (Brooks/Cole Publishing Company, http://info.brookscole.com/pasachoff)

A general survey textbook on astronomy

Pasachoff, Jay M., and John R. Percy

Cambridge University Press, eds.(2005) (http://www.cambridge.org/catalogue/catalogue.asp?isbn=052184262X)

Gulbis, A. A. S., J. L. Elliot, M. J. Person, and E.R. Adams (MIT), B. A. Babcock (Williams),
M. Emilio (Univ. Estadual de Ponta Grossa, Brazil), J. W. Gangestad (Williams), S.D. Kern and E. A. Kramer (MIT),
D. J. Osip (Observatories of the Carnegie Institution of Washington),
J. M. Pasachoff and S. P. Souza (Williams College), and T. Tuvikene (Vrije Univ., Belgium)

Nature; Jan. 5, 2006, issue, 439, pp. 48-51

The physical characteristics of Pluto and its moon, Charon, provide insight into the evolution of the outer Solar System. Although previous measurements have constrained the masses of these bodies, their radii and densities have remained uncertain. The observation of a stellar occultation by Charon in 1980 established a lower limit on its radius of 600 km (later refined to 601.5 km) and suggested a possible atmosphere. Subsequent, mutual event modeling yielded a range of 600-650 km, corresponding to a density of 1.56 ± 0.22 g cm^-3. Here we report multiple-station observations of a stellar occultation by Charon. From these data, we find a mean radius of 606 ± 8 km, a bulk density of 1.72 ± 0.15 g cm^-3, and rock-mass fraction 0.63 ± 0.05. We do not detect a significant atmosphere and place 3-sigma upper limits on atmospheric number densities for candidate gases. These results seem to be consistent with collisional formation for the Pluto—Charon system in which the precursor objects may have been differentiated, and they leave open the possibility of atmospheric retention by the largest objects in the outer solar system.
[See http://www.nature.com/nature/journal/v439/n7072/full/nature04276.html , analyzed in:
http://www.nature.com/nature/journal/v439/n7072/full/439024a.html

Schneider, G., J. M. Pasachoff, and Richard C. Willson, 2006

Astrophys. J. 641, 565-571 (April 10)

We have used the 2004 June 8 transit of Venus (ToV) as a surrogate to test observing methods, strategies, and techniques that are being contemplated for future space missions to detect and characterize extrasolar terrestrial planets (ETPs) as they transit their host stars, notably NASA’s Kepler mission, planned for 2008. As an analog to “Kepler-like” photometric transit observations, we obtained (spatially unresolved) radiometric observations with the ACRIM 3 instrument on board ACRIMSAT at a sampling cadence of 131 s to follow the effect of the ToV on the total solar irradiance (TSI). Contemporaneous high-resolution broadband imagery with NASA’s TRACE spacecraft provided, directly, measures of the stellar (solar) astrophysical noise that can intrinsically limit such transit observations. During the Venus transit, which lasted 5.5 hr, the planet’s angular diameter was approximately 1/32 the solar diameter, thus covering 0.1% of the stellar surface. With our ACRIM 3 data, we measure temporal changes in TSI with a 1 sigma per sample (unbinned) uncertainty of approximately 100 mW m^-2 (0.007%). A diminution in TSI of 1.4 W m^-2 (0.1%, closely corresponding to the geometrically occulted area of the photosphere) was measured at mid-transit compared with a mean pre-/post-transit TSI of 1365.9 W m^-2. The radiometric light curve is complex because of the parallactic motion of Venus induced by ACRIMSAT’s near-polar orbit, but exhibits the characteristic signature of photospheric limb darkening. These observations serve as a surrogate for future photometric observations of ETPs, such as Kepler will deliver. Detailed analysis of the ToV, a rare event within our own solar system, with time-resolved radiometry augmented with high-resolution imagery, provides a useful analog for investigating the detectability and characterization of ETPs from observations that are anticipated in the near future.

Lubowich, D. A., J. M. Pasachoff, H. R. Roberts, T. Millar, C. Henkel, and G. Brammer

Bull. Am. Astron. Soc. 38, #1, 186

The abundance of deuterium in the center of the Milky Way Galaxy, though relatively low compared with normal hydrogen, is higher than expected considering astration. We summarize the evidence and argue that the observed abundance largely results from in falling gas that is enriched in deuterium.

A.A.S. Gulbis, J.L. Elliot, M.J. Person, E.R. Adams, B.A. Babcock, M. Emilio, J.W. Gangestad, S.D. Kern, E.A. Kramer, D.J. Osip, J.M. Pasachoff, S.P. Souza, and T. Tuvikene

Nature, 439, 48-51, 5 January [2006]

The physical characteristics of Pluto and its moon, Charon, provide insight into the evolution of the outer Solar System. Although previous measurements have constrained the masses of these bodies, their radii and densities have remained uncertain. The observation of a stellar occultation by Charon in 1980 established a lower limit on its radius of 600 km (later refined to 601.5 km) and suggested a possible atmosphere. Subsequent, mutual event modelling yielded a range of 600–650 km, corresponding to a density of 1.56 ± 0.22 g cm^–3. Here we report multiple-station observations of a stellar occultation by Charon. From these data, we find a mean radius of 606 ± 8 km, a bulk density of 1.72 ± 0.15 g cm^–3, and rock-mass fraction 0.63 ±0.05. We do not detect a significant atmosphere and place 3-sigma upper limits on atmospheric number densities for candidate gases. These results seem to be consistent with collisional formation for the Pluto–Charon system in which the precursor objects may have been differentiated, and they leave open the possibility of atmospheric retention by the largest objects in the outer solar system.

Wareing, C.J., O’Brien, T.J., Zijlstra, A.A., Kwitter, K.B., Irwin, J., and Drew, J.E.

Sh2-188: ISM Shaping in Action, Mon. Not. R.A.S, 366, 387 [2006]

Sh 2-188 is an example of strong interaction between a planetary nebula (PN) and the interstellar medium (ISM). It shows a single arc-like structure, consisting of several filaments, which is postulated to be the result of motion through the ISM. We present new H images from the Isaac Newton Telescope Photometric H Survey of the Northern Galactic Plane that reveal structure behind the filamentary limb. A faint, thin arc is seen opposite the bright limb, in combination forming a closed ring. Behind the faint arc, a long wide tail is detected, doubling the size of the nebula. The nebula extends 15 arcmin on the sky in total. We have developed a ‘triple-wind’ hydrodynamical model, comprising of the initial ‘slow’ asymptotic giant branch (AGB) wind and the later ‘fast’ stellar wind (the interacting stellar winds model), plus a third wind reflecting the motion through the ISM. Simulations at various velocities of the central star relative to the ISM indicate that a high velocity of 125 km s^-1 is required to reproduce the observed structure. We find that the bright limb and the tail already formed during the AGB phase, prior to the formation of the PN. The closure of the ring arises from the slow-fast wind interaction. Most of the mass lost on the AGB has been swept downstream, providing a potential explanation of the missing-mass problem in PNe. We report a proper motion for the central star of 30 ± 10 mas yr^-1, the distance to the nebula is estimated to be 850⁺⁵⁰⁰_-420 pc, consistent with a spectroscopic distance to the star. Expansion velocities measured from spectroscopic data of the bright filaments are consistent with velocities measured from the simulation. Sh 2-188 is one of the largest PNe known, with an extent of 2.8 pc. The model shows that this size was already set during the AGB phase.

Kwitter, K.B.

An essay on the Helix Nebula and current ideas about its history, evolution and future

Sky & Telescope, ‘Spotlight on...’ essay [November 2005]

Barresi, M.J., Hutson, L.D., Assistant Professor, Chien, C.B., Karlstrom, R.O.

Development, 132(16), 3643-56 (2005)

Three major axon pathways cross the midline of the vertebrate forebrain early in embryonic development: the postoptic commissure (POC), the anterior commissure (AC) and the optic nerve. We show that a small population of Gfap+ astroglia spans the midline of the zebrafish forebrain in the position of, and prior to, commissural and retinal axon crossing. These glial “bridges” form in regions devoid of the guidance molecules slit2 and slit3, although a subset of these glial cells express slit1a. We show that Hh signaling is required for commissure formation, glial bridge formation, and the restricted expression of the guidance molecules slit1a, slit2, slit3 and sema3d, but that Hh does not appear to play a direct role in commissural and retinal axon guidance. Reducing Slit2 and/or Slit3 function expanded the glial bridges and caused defasciculation of the POC, consistent with a ;channeling' role for these repellent molecules. By contrast, reducing Slit1a function led to reduced midline axon crossing, suggesting a distinct role for Slit1a in midline axon guidance. Blocking Slit2 and Slit3, but not Slit1a, function in the Hh pathway mutant yot (gli2DR) dramatically rescued POC axon crossing and glial bridge formation at the midline, indicating that expanded Slit2 and Slit3 repellent function is largely responsible for the lack of midline crossing in these mutants. This analysis shows that Hh signaling helps to pattern the expression of Slit guidance molecules that then help to regulate glial cell position and axon guidance across the midline of the forebrain.

Morales, M.A., Assistant Professor, and A.L.H. Beal ’05

Annals of the Entomological Society of America, 99, 545-552 (2006)

Few studies have evaluated the relative importance of bottom-up regulation for the population dynamics of mutualism. To address this, we tested the hypothesis that host plant quality affects the strength of the mutualism between Publilia concava (Say) (Hemiptera: Membracidae) treehoppers feeding on Solidago altissima L. and ants. P. concava is a phloem-feeding treehopper that excretes a sugary waste product called honeydew. Ants collect this honeydew as a food resource, and treehoppers benefit both directly (e.g., feeding facilitation) and indirectly (e.g., protection from predators). We evaluated the effect of host plant quality on both the direct and indirect effects of this mutualism by using a factorial design that manipulated N-P-K fertilizer level and ant presence. For the experiment that focused on the direct effects of ant tending, both body size and survivorship were monitored. For the experiment that included the indirect effects of ant tending, only survivorship was monitored. Both host plant quality and ant tending increased the performance (survivorship and size) of Publilia treehoppers. However, we find no support for the hypothesis that host plant quality influences the strength of the mutualism in this system - there was no significant interaction between ant tending and fertilization for any measure of treehopper performance considered. We suggest that this result is explained by the independence of per capita tending levels with both host plant quality and treehopper density in this experiment.

M.M. Messina, S.A. Evans, Steven J. Swoap, Associate Professor, and J.M. Overton

Physiology & Behavior, 86(3), 324-30 (2005)

We studied the effect of arcuate nucleus (ARC) lesions induced pharmacologically by the perinatal treatment of monosodium L-glutamate (MSG) on the cardiovascular, metabolic, and behavioral responses to fasting. Saline and MSG-treated male Sprague-Dawley rats were instrumented with telemetry devices for measurement of mean arterial pressure (MAP) and heart rate (HR) and housed in room calorimeters at an ambient temperature (T_a) of 23°C for assessment of oxygen consumption (VO2). At baseline, controls and MSG-treated rats had similar MAP (control= 95 ± 4; MSG= 91 ± 2 mmHg), HR (control= 323 ± 4; MSG= 324 ± 2 bpm), and VO2 (control= 8.7 ± 0.3; MSG =8.6 ± 0.2 ml/min). There were no differences in fasting-induced reductions in body weight or in food intake upon refeeding. MSG-treatment significantly attenuated fasting-induced reductions in HR and VO2. This effect was specific to reduced caloric availability, as MSG-treated rats exhibited intact capacity to both increase and decrease HR and VO2 in response to cold (T_a=15°C) and to thermoneutrality (T_a=30°C). Additional studies were performed in saline- and MSG-treated rats chronically treated with β1-adrenergic receptor blockade (atenolol) prior to and during fasting. In controls, the cardiovascular responses to fasting during β1-blockade were blunted and generally mimicked the effects of MSG-treatment, while β1-blockade had no additional effect on MSG-treated rats. The results are consistent with the hypothesis that ARC neuronal signaling is requisite for intact homeostatic responses to fasting and may participate in fasting-induced withdrawal of cardiac sympathetic activity.

Steven J. Swoap, Associate Professor, M.J. Gutilla, L.C. Liles, R.O Smith ‘05 and D. Weinshenker

Journal of Neuroscience, 26, 241-245 (2006)

Torpor, a controlled rapid drop in metabolic rate and body temperature (T_b), is a hypometabolic adaptation to stressful environmental conditions, which occurs in many small mammals, marsupials, and birds. To date, signaling pathways required for torpor have not been identified. We examined the role of the sympathetic nervous system (SNS) in mediating the torpor adaptation to fasting by telemetrically monitoring the T_b of dopamine beta -hydroxylase knockout (Dbh) -/- mice which lack the ability to produce the SNS transmitters, norepinephrine (NE) and epinephrine (Epi). Control (Dbh +/-) mice readily reduced serum leptin levels and entered torpor after a fast in a cool environment. In contrast, Dbh -/- mice failed to reduce serum leptin and enter torpor under fasting conditions, whereas restoration of peripheral but not central NE lowered serum leptin levels and rescued the torpor response. Torpor was expressed in fasted Dbh -/- mice immediately after administration of either the non-selective alpha adrenergic receptor agonist, isoproterenol, or the beta3 AR specific agonist, CL316243, but not after administration of beta1, beta2, or alpha agonists. Importantly, the beta3-specific antagonist, SR 59230A, severely blunted fasting-induced torpor in control mice, whereas other AR antagonists were ineffective. These results define a critical role of peripheral SNS activity at beta3 AR-containing tissues in the torpor adaptation to limited energy availability and cool ambient temperature.

Sowden, G.L. ’06, Weishenker, D., Swoap, S.J., Associate Professor

FASEB Journal, 29(4), A313 Part 1 (2006)

Oxyntomodulin (OXM), a postprandially released gut hormone, inhibits food intake and stimulates metabolism in humans and rodents. Acting via the GLP-1 receptor, OXM functions as an incretin, stimulating release of insulin, a hormone known to stimulate the sympathetic nervous system (SNS). Using telemetry to measure heart rate (HR) in conscious and freely moving mice, we tested 1) whether OXM affects HR, and 2) whether the HR effects are mediated via insulin and SNS. Compared with saline, 15 μg of OXM increased HR in C57Bl mice by 121 ± 19 bpm (P<0.05, n=9) over the first 15 minutes up to 706 ± 9 bpm. To test the role of insulin, we administered OXM to streptazotocin-induced diabetic mice. OXM induced a similar increase in HR in type-I diabetic mice [an increase of 156 ±18 bpm, (P<0.05, n=9)], suggesting that the HR effects of OXM are independent of insulin. To test the hypothesis that the HR effects of OXM are mediated through the SNS, we measured the HR effects of OXM in Dbh-/- mice that lack epinephrine and norepinephrine. Dbh-/- mice did not respond to saline injections. However, Dbh-/- mice demonstrated a vigorous increase in HR within the first 15 min. after OXM administration [an increase of 164 ± 18 bpm, (P<0.05, n=6)], suggesting that OXM exerts its effects on HR independent of catecholamines. From our data, we can conclude that OXM exerts an effect on HR independent of insulin and SNS, and may act directly on the heart.

Swoap, S.J., Associate Professor, Gutilla, M.J., Liles, L.C., Smith, R.O. ’05, and Weinshenker, D.

FASEB Journal, 20(5), A828-A829, Part 2 (2006)

Torpor, a controlled rapid drop in metabolic rate and body temperature (Tb), is a hypometabolic adaptation to stressful environmental conditions, which occurs in many small mammals, marsupials, and birds. To date, signaling pathways required for torpor have not been identified. We examined the role of the sympathetic nervous system (SNS) in mediating the torpor adaptation to fasting by telemetrically monitoring the Tb of dopamine beta beta hydroxylase knockout (Dbh) -/- mice which lack the ability to produce the SNS transmitters, norepinephrine (NE) and epinephrine (Epi). Control (Dbh +/-) mice readily reduced serum leptin levels and entered torpor after a fast in a cool environment. In contrast, Dbh -/- mice failed to reduce serum leptin and enter torpor under fasting conditions, whereas restoration of peripheral but not central NE lowered serum leptin levels and rescued the torpor response. Torpor was expressed in fasted Dbh -/- mice immediately after administration of either the non-selective alpha adrenergic receptor agonist, isoproterenol, or the beta3 AR specific agonist, CL316243, but not after administration of beta1, beta2, or alpha antagonists. Importantly, a beta3-specific antagonist severely blunted fasting-induced torpor in control mice, whereas other AR antagonists were ineffective. These results define a critical role of peripheral SNS activity at beta3 AR-containing tissues in the torpor adaptation.

Young Jik Kwon, Stephany M. Standley, Sarah L. Goh, Assistant Professor of Chemistry,
and Jean M. J. Frechet

Journal of Controlled Release, 105, 199-212 (2005)

Acid-degradable cationic nanoparticles encapsulating a model antigen (i.e., ovalbumin) were prepared by inverse microemulsion polymerization with acid-cleavable acetal cross-linkers. Incubation of these degradable nanoparticles with dendritic cells derived from bone marrow (BMDCs) resulted in the enhanced presentation of ovalbumin-derived peptides, as quantified by B3Z cells, a CD8+ T cell hybridoma. The cationic nature of the particles contributed to the increased surface endocytosis (or phagocytosis) observed with BMDCs, which is the first barrier to overcome for successful antigen delivery. The acid sensitivity of the particles served to direct more ovalbumin antigens to be processed into the appropriately trimmed peptide fragments and presented via the major histocompatibility complex (MHC) class I pathway following hydrolysis within the acidic lysosomes. It was also shown that adjuvant molecules such as unmethylated CpG oligonucleotides (CpG ODN) and anti-interleukin-10 oligonucleotides (AS10 ODN) could be co-delivered with the protein antigen for maximized cellular immune response.

Eli S. Groban ’02, Martha B. Johnson ’97, Poopak Banky ’93, Peta-Gaye G. Burnett ’04,
Georgina L. Calderon ’05, Erica C. Dwyer ’03, Shakierah N. Fuller ’04, Biniam Gebre ’00,
Leah M. King ’04, Ila N. Sheren ’05, Lindi D. Von Mutius ’04, Thomas M. O’Gara,
and Charles M. Lovett, Professor of Chemistry

Nucleic Acids Res., 33, 6287-6295 (2005)

The Bacillus subtilis LexA protein represses the SOS response to DNA damage by binding as a dimer to the consensus operator sequence 5'-CGAACN₄GTTCG-3'. To characterize the requirements for LexA binding to SOS operators we determined the operator bases needed for site-specific binding as well as the LexA amino acids required for operator recognition. Using mobility shift assays to determine equilibrium constants for B. subtilis LexA binding to recA operator mutants, we found that several single base substitutions within the 14 base pair recA operator sequence destabilized binding enough to abolish site-specific binding. Our results show that the AT base pairs at the 3^rd and 4^th positions from the 5'- end of a 7 bp half site are essential and that the preferred binding site for a LexA dimer is 5'-CGAACATATGTTCG-3'. Binding studies with LexA mutants, in which the solvent accessible amino acid residues in the putative DNA binding domain were mutated, indicate that Arg-49 and His-46 are essential for binding and that Lys-53 and Ala-48 are also involved in operator recognition. Guided by our mutational analyses as well as hydroxyl radical footprinting studies of the dinC and recA operators we docked a computer model of B. subtilis LexA on the preferred operator sequence in silico. Our model suggests that binding by a LexA dimer involves bending of the DNA helix within the internal four base pairs of the operator.

Nora Au ’03, Elke Kuester-Schoeck, Veena Mandava ’00, Laura E. Bothwel ’02, Susan P. Canny ’02,
Karen Chachu ’01, Sierra A. Colavito ’02, Shakierah N. Fuller ’04, Eli S. Groban ’02, Laura A. Hensley ’02,
Theresa C. O'Brien ’02, Amish Shah ’01, Jessica T. Tierney ’02, Louise L. Tomm ’02, Thomas M. O'Gara,
Alexi I. Goranov, Alan D. Grossman, and Charles M. Lovett, Professor of Chemistry

J. Bacteriol. 187, 7655-7666 (2005)

The SOS response in bacteria includes a global transcriptional response to DNA damage. DNA damage is sensed by the highly conserved recombination protein RecA, which facilitates inactivation of the transcriptional repressor LexA. Inactivation of LexA causes induction (derepression) of genes of the LexA-regulon, many of which are involved in DNA repair and survival after DNA damage. To identify potential RecA-LexA regulated genes in Bacillus subtilis, we searched the genome for putative LexA binding sites within 300 bp upstream of the start codon of all annotated open reading frames. We found 62 genes that could be regulated by putative LexA binding sites. Using mobility shift assays, we found that LexA binds specifically to DNA in the regulatory regions of 54 of these genes, which are organized in 34 putative operons. Using DNA microarray analyses, we found that 33 of the genes with LexA binding sites exhibit RecA-dependent induction by both mitomycin C and UV radiation. Among these 33 SOS genes there are 22 distinct LexA binding sites preceding 18 putative operons. Alignment of the distinct LexA binding sites reveals an expanded consensus sequence for the B. subtilis operator: 5'- CGAACATATGTTCG-3'. Although the number of genes controlled by RecA and LexA in B. subtilis is similar to that of Escherichia coli, only 8 B. subtilis RecA-dependent SOS genes have homologous counterparts in E. coli.

J. Hodge Markgraf, Professor of Chemistry Emeritus, Adrian A. Dowst ’04,
Laurel A. Hensley ’03, Charles E. Jakobsche ’04, Cindy J. Kalter (Leiden University),
Peter J. Webb ’02, and Patrick W. Zimmerman ’03

Tetrahedron, 61, 9102-9110 (2005)

Benzocanthinone (1), a pentacyclic alkaloid, belongs to a large family of β-carboline derivatives, which exhibit a broad range of pharmacological activity. Compound 1 was synthesized by a new route, which was also used to prepare five isomers of 1. The key step was a radical-induced cyclization of N-aroyl derivatives of β-carboline and carbazole.

Kathleen M Beutel ’06 and Enrique Peacock-López, Professor of Chemistry

Journal of Chemical Physics, 124, 2449061 (2006)

Chemical self-replication of oligonucleotides and helical peptides show the so-called square root rate law. Based on this rate we extend our previous work on ideal replicators to include the square root rate and other possible nonlinearities, which we couple with an enzimatic sink. Although the nonlinearity is necessary for complex dynamics, the nature of the sink is the essential feature in the mechanism that allows temporal and spatial patterns. We obtain exact general relations for the Poincare-Adronov-Hopf and Turing bifurcations, and our generalized results include the Higgins, Autocatalator and Templator models as specific cases.

Enrique Peacock-López, Professor of Chemistry

The Chemical Educator, 11, 333-344 (2006)

For a symmetrical quantum double square well potential, we find analytical expressions satisfied by the quantized energies. Graphical or numerical solutions of the former relations allow us to calculate normalization constants and construct the first eight solutions of the Schrodinger equation. With these exact solutions, we analyze quantum tunneling across a potential barrier and compare our results with the experimental data for ammonia.

Elaine K. Denny ’04, Analia Sorribas ’06, and David P. Richardson, Professor of Chemistry

Northeastern Geology and Environmental Science, 27, 276-294 (2005)

Levels of polychlorinated biphenyls in river bank sediments, crayfish and brown trout were measured for samples taken from the Main and South Branches of the Hoosic River, which rises in western Massachusetts and flows through southwestern Vermont before emptying into the Hudson River. Sample sites were principally in Massachusetts but included Main Branch sites in Vermont and New York. The Hoosic is a fast flowing river, carrying sediment that is primarily fine sand (ca. 75%) mixed with silt and clay (ca. 15%).

Sediment samples were collected at 14 recreationally-relevant sites on a singe day (13 September 2003) to provide a snapshot of PCB levels that minimized variations caused by river level, flow rate, and other weather/season-dependent parameters. PCB contamination in the Hoosic originates at the site of the former Sprague Electric Company (SEC) plant in North Adams, MA where a capped waste dump has leaked Aroclors 1242 and 1254. Our measurements of Aroclor 1254 show that the average surface sediment PCB level downstream of the SEC is 0.1 ppm, varying from 0.020 to 0.235 ppm; subsurface sediments show the same average concentration but vary more widely, from 0.010 to 0.628 ppm. South Branch PCB levels, upstream of the SEC, are significantly lower (surface average: 0.025 ppm; subsurface average: 0.20 ppm) but indicate the presence of a diffuse, low level source of PCB contamination on this section of the Hoosic. While PCB levels measured in sediment samples appeared to vary somewhat randomly, normalization for percentage of fine sediment clearly showed local PCB spikes in the vicinity of the SEC and the dam in North Pownal, VT, and PCB dispersal along the length of the Hoosic.

Crayfish contained levels of Aroclor 1254 that were significant (0.08 to 0.37 ppm dry weight; almost no Aroclor 1242 was detected) but that may signal a decline in PCB levels compared to previous studies. Brown trout 1-2 years old showed roughly equivalent amounts of both Aroclors, with levels ranging from 0.1 to 0.4 ppm (wet weight). Older trout (4-7 years old) showed significantly higher levels of Aroclor 1242 relative to 1254 (2-5:1) with total PCB contamination greater than 2 ppm, exceeding the U.S. Environmental Protection Agency's consumption guidelines. These results do not indicate a significant decline in PCB levels compared to earlier studies. They also imply that brown trout bioaccumulate PCBs differently than crayfish and that local bans on consumption of Hoosic river fish should remain in force.

Brian G. Saar ’05, Geoff P. O’Donoghue ’06, Adam H. Steeves ’02,
and John W. Thoman, Jr., Professor of Chemistry

Chemical Physics Letters, 417, 159-163 (2006)

We demonstrate that the gauche conformation of 1H-nonafluorobutane contains a blue-shifting intramolecular hydrogen bond by recording its fifth overtone spectrum with cavity ringdown spectroscopy and performing electronic structure calculations. The magnitude of the blue-shift is enhanced in the overtone spectrum as compared to the fundamental. The energy difference between the gauche conformer and the lowest energy zigzag conformer is calculated to be 288 cm-1 using density functional theory and determined to be 280±30 cm-1 using temperature-dependent FTIR measurements. The -H^...F- bonding interaction in the gauche conformer leads to changes in bond lengths as compared to the non-hydrogen bonded conformers.

Stephen Freund, Assistant Professor of Computer Science, Martin Abadi, and Cormac Flanagan

ACM Transactions on Programming Languages and Systems, Volume 28(2), pp. 207-255 (2006)

This paper presents a static race-detection analysis for multithreaded shared-memory programs, focusing on the Java programming language. The analysis is based on a type system that captures many common synchronization patterns. It supports classes with internal synchronization, classes that require client-side synchronization, and thread-local classes. In order to demonstrate the effectiveness of the type system, we have implemented it in a checker and applied it to over 40,000 lines of hand-annotated Java code. We found a number of race conditions in the standard Java libraries and other test programs. The checker required fewer than 20 additional type annotations per 1,000 lines of code.

This paper also describes two improvements that facilitate checking much larger programs: an algorithm for annotation inference and a user interface that clarifies warnings generated by the checker. These extensions have enabled us to use the checker for identifying race conditions in large-scale software systems with up to 500,000 lines of code.

Stephen Freund, Assistant Professor of Computer Science, Cormac Flanagan, and Aaron Tomb

Proceedings of Workshop on Foundations and Developments of Object-Oriented Languages, 12 pages (2006)

To control the complexity of large object-oriented systems, objects should communicate via precisely-specified interfaces. Static type checking catches many interface violations early in the development cycle, but decidability limitations preclude checking all desired properties statically. In contrast, dynamic checking supports expressive specifications but may miss errors on execution paths that are not tested. We present a hybrid approach for checking precise object specifications that reasons statically, where possible, but also dynamically, when necessary. This hybrid approach supports a rich specification language with features such as object invariants and refinement types.

Stephen Freund, Assistant Professor of Computer Science and Cormac Flanagan

Proceedings of Workshop on Synchronization and Concurrency in Object-Oriented Languages, 10 pages (2005)

Multithreaded programs are notoriously prone to synchronization errors. Much prior work has tackled the problem of detecting such errors. This paper focuses on the subsequent problem of synchronization correction. We present a constraint-based analysis that, given an erroneous program, automatically infers (where possible) what additional locking operations should be inserted in order to yield a correctly-synchronized program. For performance reasons, our algorithm also attempts to minimize the number of additional lock acquires and the duration for which the acquired locks are held. We present experimental results that validate this approach on a number of standard Java library classes.

James D. Teresco, Assistant Professor of Computer Science, Karen D. Devine, and Joseph E. Flaherty

Chapter in Numerical Solution of Partial Differential Equations on Parallel Computers, Are Magnus Bruaset, Petter Bjørstad, Aslak Tveito, editors, © Springer-Verlag, 55-88 (2006)

In parallel simulations, partitioning and load-balancing algorithms compute the distribution of application data and work to processors. The effectiveness of this distribution greatly influences the performance of a parallel simulation. Decompositions that balance processor loads while keeping the applications communication costs low are preferred. Although a wide variety of partitioning and load-balancing algorithms have been developed, their effectiveness depends on the characteristics of the application using them. In this chapter, we review several partitioning algorithms, along with their strengths and weaknesses for various PDE applications. We also discuss current efforts toward improving partitioning algorithms for future applications and architectures.

James D. Teresco, Assistant Professor of Computer Science, Jamal Faik, and Joseph E. Flaherty

Applied Parallel Computing, State of the Art in Scientific Computation, Proceedings of the 7^th International Workshop, PARA 2004 Workshop, J. Dongarra, K. Madsen, J. Wasniewski, editors. Vol. 3732 of Lecture Notes in Computer Science, © Springer-Verlag, pp. 911-920 (2006)

Cluster and grid computing has made hierarchical and heterogeneous computing systems increasingly common as target environments for large-scale scientific computation. A cluster may consist of a network of multiprocessors. A grid computation may involve communication across slow interfaces. Modern supercomputers are often large clusters with hierarchical network structures. For maximum efficiency, software must adapt to the computing environment. We focus on partitioning and dynamic load balancing, in particular on hierarchical procedures implemented within the Zoltan Toolkit, guided by DRUM, the Dynamic Resource Utilization Model. Here, different balancing procedures are used in different parts of the domain. Preliminary results show benefits to using hierarchical partitionings on hierarchical systems.

B. G. Baarli, Research Associate, Rebecca R. Levine ’03, and Markes E. Johnson, Professor of Geosciences

Norwegian Journal of Geology, 86, 133-150 (2006)

The Smalfjord Formation in the Varangerfjorden areas of northern Norway was deposited as valley fill during an interglacial period of the Varangerian (Marinoan) glaciation. The paleovalley was initially cut by glacial erosion and braided rivers. Subsequent marine transgression due to glacial eustasy entered through the fjord valley mouth located to the present WNW and advanced across an irregular valley floor. As the initial transgression showed down, the shallow fjord acted as a normal storm-dominated eustuary and was filled by a prograding bay-head delta and flood-tidal delta prograding from opposite ends of the paleovalley. The final stage of fjord fill was completed by tidal sandflats and braided-river deposits. The latter was due to isostatic rebound in the hinterland. Renewed transgression resulted in a return to marine conditions in the succeeding Nyborg Formation, which spilled out of the paleovalley onto the surrounding areas.

Paul A. Skudder, III ’05, David H. Backus, Research Associate, D. H. Goodwin,
and Markes E. Johnson, Professor of Geosciences

Journal of Coastal Research, 22, 611-624 (2006)

Atmospheric and oceanographic conditions stimulate high productivity of marine organisms in the Gulf of California that are bulk producers of calcium carbonate. Due to prevailing winter winds, north-facing beaches receive vast amounts of shell debris derived from offshore clam banks above the 50 m isobath. As shells undergo mechanical abrasion, the smaller particles of carbonate material are transferred from beaches by the wind and sequestered in coastal dunes. This study reports on two dune fields from the midriff zone of the gulf. Sieve analysis is used to describe the grain size and sorting characteristics of seven samples from dunes at Cerro El Gallo near Mulegé and twelve samples from dunes farther south near San Nicolás. Dune sediments also were impregnated with epoxy to simulate rock samples from which thin sections were made to determine composition and relative abundances of constituent grains. The dunes at Cerro El Gallo are carbonate poor (5%–15 %) compared to those near San Nicolás (26%-51%) and possible factors contributing to regional variation are explored.

Another part of this study appraises the fecundity necessary to produce any carbonate fraction integrated by coastal dunes from seashells. One of the region’s more abundant clams, Megapitaria squalida, was used as a model to estimate the number of individuals of a given size and age class required to generate a cubic meter of pure carbonate sand. Satellite images of the dune fields at El Gallo and San Nicolás were viewed to map surface coverage. With input on the thickness of dune deposits and their composition, it is possible to roughly estimate the number of mature Megapitaria equal to the carbonate fraction of these dunes. The method may be applied to all coastal dunes on the Gulf of California, and could be used to assess a part of the region’s overall carbon budget heretofore unappreciated.

James M. Eros ’04, Markes E. Johnson, Professor of Geosciences, David H. Backus, Research Associate

Canadian Journal of Earth Sciences, 43, in press.

Arroyo Blanco Basin on Isla Carmen preserves a 157-m thick, nearly complete record of Pliocene-Pleistocene history in the Gulf of California. Examples of rocky-shore geomorphology occur on all margins of this trapezoidal-shaped, 3.3 km² basin. A shoreline is developed in low relief on Miocene andesite from the Comondú Group at the rear of the basin parallel to the island’s long axis. Two end-walls trace normal faults that stayed active during the life of the basin and maintained steep rocky shores. The basin is filled 64% by calcarudite and calcarenite derived from crushed rhodolith debris. Other facies include shell beds and stringers of andesite conglomerate that define a 4° to 6° ramp. The ramp expanded onshore through Pliocene time, based on a succession of overlapping range zones for 22 macrofossils typical of Lower through Upper Pliocene strata in the Gulf of California. The unconformity exposed 1 km inland at the rear of the basin is between Miocene volcanics and Pleistocene cap rock at an elevation 170 m above sea level. Whole rhodoliths encrusted on andesite pebbles occur above this unconformity. Presumably, the older Miocene-Pliocene unconformity is buried beneath the ramp. Four marine terraces with sea cliffs notched in Pliocene limestone occur at 68, 58, 37, and 12-m elevations. The 12-m terrace is associated regionally with the last interglacial epoch between 120,000 and 135,000 years ago. Juxtaposition of ramp and terrace features in the same exhumed basin support a long history of gradual Pliocene subsidence followed by episodic Pleistocene uplift.

Rónadh Cox, Associate Professor of Geosciences and A.F. Michel Rakotondrazafy

Geological Society of America Abstracts with Programs, 37, 234 (2005)

Madagascar's tectonically oversteepened, deeply weathered central highlands are eroding rapidly. The most visible manifestations of this process are lavakas: deep, vertical-sided groundwater-sapping features that develop in the thick saprolite and laterite of the microcontinent interior. Although widely reported to be of recent vintage and related to human activity, there are in fact few data on their rates of formation. The Miarinarivo area is a prime candidate for increasing erosion rates if lavaka formation is driven by human activity: it is only 100 km from the capital city, served by a paved main road, and the surrounding countryside is well populated and heavily used for grazing and cultivation. Field work in the Miarinarivo area confirms that individual lavakas grow very rapidly: one lavaka that initiated in October 2002 had grown by August 2004 to two big lobes, each about 50 m long, 12 m wide, and 15 m deep. The volume excavated from this single feature was about 10,000 m³ in 22 months, but the erosion rate decreased through time, from about 1300 m³/month in the first year to about 450 m³/month in the second (integrated across the whole year, although erosion is actually strongly concentrated in the 5-month rainy season). However, although the lavakas in the Miarinarivo area appear very fresh and recent, most of them are not. Of 240 lavakas in the mapping area in 2004, 227 appear on air photos taken in 1949, which means that the lavaka increase rate in this area is only 0.08%/year, or 0.1/km² yr^-1. Old lavakas are not significantly bigger than they were in 1949, although in many cases their headwalls remain vertical and vegetation-free. We infer that individual lavakas tend to reach a maximum size early on, with minimal growth thereafter. Sediment output declines exponentially, but limited sediment output may be maintained over many decades. The sediment comes mainly from small-scale headwall collapse, probably in the form of fluidized flows and low-density debris flows. Present data do not allow us to evaluate how long it takes for lavakas to become inactive, lose their vertical walls, and relax back to bowl-shaped depressions in the landscape; but cosmogenic isotope studies in progress will shed light on this timescale.

Rónadh Cox, Associate Professor of Geosciences, Lissa C.F. Ong ’04, and M. Arakawa, Hokkaido Univ.

36^th Lunar and Planetary Science Conference (2005)

Impact breaching of Europa's solid ice surface is not only possible, but probable. Estimates of crustal thickness range from a few 10’s of km down to a few km or even a few hundred m in places, and numerical simulations demonstrate that an ice shell 4-7 km thick or less is likely to be breached by 1 km diameter comets impacting at average speed. In addition, the larger impact structures Tyre, Callanish, and Mananàn (produced by bolides of about 1-2 km diameter, based on equations in Zahnle et al., have all been interpreted to represent partial breaching of the ice crust and leakage of fluid material from below. If 1-2 km diameter bolides split the crust, and 2 km is only the median diameter for impactors at Jupiter, larger bolides must produce full crustal penetration. Many chaos areas (equidimensional and sharply-bounded) may be a hitherto unrecognized record of full-crustal penetration by bolides.

Rónadh Cox, Associate Professor of Geosciences and Lissa C.F. Ong ’04

EOS Transactions of the AGU, Joint Assembly Supplement, 87, 33A-03 (2006)

Europa’s enigmatic chaos terrain probably represents breakage of the brittle surface ice and exposure of fluid material. Proposed explanations have focused on endogenic mechanisms and energy sources, but all are disputed. Crust-penetrating bolide impacts are an alternative mechanism by which chaos terrain could be produced, and primary evidence for this hypothesis comes from impact experiments. Additional insights come from analysis of the size-frequency distributions of chaos areas and craters, which combined appear to represent a unified impact production function for Europa. The impact size-frequency distribution at Europa is predicted to match that at Ganymede and Callisto (e.g. Schenk et al. 2004), but this has not been shown because of the lack of large impact craters. If, however, chaos areas are the expression of large impacts on Europa, then the impact database for Europa is dramatically increased, permitting examination of the production function. We show that the size-frequency distribution of chaos plus craters does indeed match production function at Ganymede and Callisto. From the expanded impact-retention record, we calculate an average surface age of 600 (-400/+855) Ma. This is substantially older than previous estimates, but still young by solar system standards, and similar to that of the Earth.

Elizabeth A. Gress ’06, Rónadh Cox. Associate Professor of Geosciences, A.F. Michel Rakotondrazafy

Geological Society of America Abstracts with Programs, 37, 540 (2006)

Lavakas are large gullies that form in the thick laterite and saprolite of Madagascar's deeply-weathered crystalline basement. Although little known outside of Madagascar, they are a common geologic hazard in this developing nation, causing the collapse of roads and the inundation of rice fields with debris flows. Conventional wisdom states that lavakas are directly related to human activities and to land mismanagement, but in fact, these claims are not based on scientific data collection. The origins of lavakas and the rates at which they grow and evolve are not yet understood, but research suggests that lavakas are a natural element of Madagascar's Holocene landscape. The Malagasy highlands are characterized by steep slopes, developed in saprolite up to 100 m thick; so the landscape is inherently unstable and prone to rapid erosion. While it is definitely true that some lavakas form due to human activities, the non-scientific alarmist portrayal of lavakas as wholly anthropogenic is unfounded, and damaging to both to national morale and international perception of the Malagasy people. By careful data collection and careful reporting, we hope to dispel some myths and increase general understanding of the fundamental causes of lavaka formation. Part of our goal is to make our findings widely available. We plan to provide practical guidance to infrastructure planners in Madagascar, by meeting local leaders and presenting our technical results in oral and report form. We also hope to provide the general public with a balanced picture of this complicated phenomenon, by constructing well-illustrated summaries of our results for submission to a variety of wide-readership and popular-science publications in English and in Malagasy. Wide dissemination of accurate information, based on scientific principles and high-quality data analysis, but framed clearly and interestingly, is especially important as Madagascar gains increasing international attention due to its prominence as a biodiversity hotspot. The challenge lies in presenting a nuanced understanding of a complicated phenomenon in which the roles of man and nature are intimately entangled.

Fara Christine Rasoazanamparany, Rónadh Cox, Associate Professor of Geosciences,
Sharron J. Macklin, and A.F. Michel Rakotondrazafy

EOS Transactions of the AGU, Joint Assembly Supplement, 87, H43F-01 (2006)

Madagascar's central highlands are deeply weathered, with 1-2 m of laterite overlying 10’s of meters of saprolite. These unstable materials sit at altitudes on the order of 1000 m in recently uplifted, steep terrain characterized by convex hills with slopes averaging 25 degrees and local ridge-valley elevation changes of 100-500 m. In many areas, these slopes bear numerous erosional features called lavakas, with mapped densities up to 25/km² in some areas. Lavakas are tadpole-shaped gullies with vertical sides and flat floors. They are wide at the headwall and taper to a narrow, deeply incised outfall, which connects to the valley drainage. They are not fed by overland flow, but develop by groundwater sapping and subterranean erosion in the porous and friable saprolite beneath the baked lateritic duracrust. The controls on lavaka formation are poorly understood. Interplay between climate, topography, and bedrock geology is known to be important, and human activity is also implicated. However, there are many areas with appropriate rainfall, hillslope geometry and geology where lavakas do not form. Likewise, lavakas form readily in some areas with little human activity, and do not form in other areas that are heavily used. Our analysis suggests that seismic activity may be a significant regional factor driving lavaka formation. Using GIS analysis, we compared the locations of recent earthquakes (1347 events with magnitudes 3.0-5.4, recorded between 1979 and 1995) with the distribution of zones where lavakas are abundant (as mapped by Henri Besairie in 1957), and found that they are strongly correlated. We cannot say whether individual seismic events are responsible for specific lavakas; but the observation that lavakas are most common in zones that are seismically active implies that earthquakes play a significant role. Repeated mild earth-shaking events might aid in loosening the saprolite and making it more vulnerable to lavaka-forming processes; or individual earthquakes might initiate collapse of slopes already weakened by groundwater sapping. More detailed work into the relationships between individual lavakas and local seismicity is needed to determine which of these mechanisms might be active. Our ongoing GIS analysis will quantify the relative importance of geology, topography, and seismicity in the location of lavaka-prone areas.

Nora L. Matell ’06 and Rónadh Cox, Associate Professor of Geosciences

36^th International Arctic Workshop, INSTAAR (2006)

Laminated lake sediments in Linnévatnet, on Spitsbergen, provide a high-resolution climate record of the Holocene (Svendsen and Mangerud, 1997; Werner, 1988). Sedimentation in Linnévatnet, like other Arctic lakes, depends on many variables, including winter snowpack, glacial ablation, and sediment availability (Hardy, 1996). A comprehensive understanding of current hydrology and sediment dynamics in the valley is essential to developing a detailed understanding of past climatic history. This study provides a detailed, if short duration, picture of the role of the Linné river braidplain as a sediment sink. Further quantification is vital to an understanding of sediment dynamics in the valley and sediment flux into the lake, but will require multi-year observations that also include the early meltwater floods. Other studies of suspended sediment flux in Arctic glacial systems have identified areas that act as sediment sinks during mid to late summer low flows, and sediment sources during early summer high flows (Hodgkins et al., 2003). It is still unknown whether this occurs in Linnédalen. However, it is clear that the valley braidplain plays a highly important role in sediment transport between Linnébreen and Linnévatnet.

David P. Dethier, Professor of Geosciences and Eli D. Lazarus ’04

Geomorphology, 75, 384-399 (2006)

Granitic regolith developed in the Boulder Creek catchment and adjacent areas records a history of deep weathering, some of which may predate Quaternary time. Field and well-log measurements of weathering, chemical denudation and erosion rates derived from ¹0Be cosmogenic radionuclide (CRN) data help to quantify rates of landscape change in the post-orogenic Rocky Mountains. The density of oxidized, fractured bedrock ranges from 2.7 to about 2.2 gm cm^-3, saprolite and grus have densities between ~2.0 and 1.8 gm cm^-3, and 30 soil samples averaged 1.6 ± 0.2 gm cm^-3. Highly weathered regolith in ~540 wells averages ~3.3 m thick, mean depth to bedrock in 1661 wells is ~7 m, and the weathered thickness exceeds 10 m in relatively large local areas east of the late Pleistocene glacial limit. Regolith thickness shows no simple relationship to rock type or structure, local slope, or distance from channels. Catchments in the vicinity of the Boulder Creek have an average CRN erosion rate of 2.2 ± 0.7 cm kyr^-1 for the past 10,000 to 40,000 years. Annual losses of cations and SiO₂ vary from about 2 to 5 g m^-2 over a runoff range of 10 to nearly 160 cm.

Using measured rates in simple box models shows that if a substantial fraction of void space is created by volume expansion in the weathering rock materials, ~7 meters of weathered rock materials could form in as little as 230 kyr. However, if density loss results mainly from chemical denudation and some volume expansion, the same weathering profile would take >1340 kyr to form. Erosion rates measured by CRN could be balanced by the rate of soil formation from saprolite if the annual solute loss from soil is 2.0 g m^-2 and 70% of the density decrease from saprolite to grus and soil results from strain. Saprolite, however, forms from oxidized bedrock at a far slower rate and rates of saprolite formation cannot balance soil and grus losses to erosion. The zone of thick weathered regolith is likely an eroding relict landscape. The undulating surface marked by relatively low relief and tors is not literally a topographic surface of Eocene, Oligocene or Miocene age unless it was covered with deposits that were removed in Pliocene or Quaternary time.

David P. Dethier, Professor of Geosciences, A.M. Sarna-Wojcicki, and R.J. Fleck

Geological Society of America Abstracts with Programs, 37(7), 180 (2005)

A new 40Ar/39Ar age and chemical analyses of dacitic pumice from pumice-rich alluvium at Blowers Bluff, central Whidbey Island, show that the interglacial deposits at that site have an age of about 120 ka. Pumice is found as thin beds, lenses as thick as 80 cm and bedded pumiceous alluvium in a 15 m-thick sequence of deposits that lies beneath two tills and middle Wisconsinan glaciomarine deposits at Blowers Bluff. Plagioclase separated from the pumice contained minor excess argon and gave a plateau age of 128 ± 9 ka and an isochron age of 120 ± 50 ka. The 40Ar/39Ar age is similar to a TL age estimate reported by Berger and Easterbrook (1993) from adjacent deposits. These ages suggest that the pumice deposits at Blowers Bluff are part of the Whidbey Formation, a widespread, mainly subsurface unit in the northern Puget lowland. The glass chemistry of the pumice does not match any known source, but Glacier Peak and Mt. Baker are likely candidates. During Whidbey Fm time, deep troughs of the modern northern Puget Sound area must have been filled with fluvial and lacustrine deposits, allowing volcanic-rich sediment to reach what is now Whidbey Island. Erosion of thick glacial and interglacial deposits occurred during ice retreat when a west-flowing lobe of Vashon ice carved what is now Penn Cove. Fragments and local cm-thick layers of an undated pumice crop out in latest Wisconsinan (Everson) glaciomarine deposits exposed in gravel pits on Ebey's Prairie, 10 to 15 km WSW of Blowers Bluff. Chemistry of the pumice suggests a Cascade source, but does not correlate with pumice chemistry from Blowers Bluff. Balanus fragments in the glaciomarine gravel gave 14C ages >40 ka, suggesting that they were reworked from stratigraphically and topographically lower deposits. The undated pumice could have been reworked from older deposits during erosion of Penn Cove and adjacent troughs or record an eruption at about 13 ka, when glaciomarine deposits were graded to a local relative sea level of ~70 m.

Jennifer E. Campbell ’05 and David P. Dethier, Professor of Geosciences

Geological Society of America Abstracts with Programs, 37(7), 430 (2005)

The chemistry of weathered materials and solute export values from the Middle Boulder Creek catchment, Colorado, allow us to measure slow weathering processes that produced thick regolith that locally mantles the Front Range. In areas outside the glacial limit, the weathered profile consists of 4 to 8 m of oxidized bedrock, saprolite, and grus, capped by a thin soil. We measured the density and chemistry of ~120 fresh and weathered granitic samples and the chemistry of ~30 water samples collected from small drainages in alpine and forested areas. Thin sections show that plagioclase, which comprises 15 to 35% of fresh Boulder Creek Granodiorite and Silver Plume Granite, is the main altered mineral. In thin section, biotite shows slight bleaching and expansion along cleavage planes, but plagioclase is more weathered. Microcline and quartz are little altered, suggesting the weathering sequence plagioclase>biotite>microcline>quartz. Mass balance analyses demonstrate that elemental loss increases up through the weathering profile as Ca>Mg>>Na>Si>K. Solute export in surface waters demonstrates significant losses of Ca and Mg, in addition to SiO₂ and Na. Depletion of Ca in weathering profiles and molar Ca/Na values >1 in surface water, however, indicate loss of Ca over Na in excess of that supported by congruent weathering of plagioclase. Decreased Ca/Na in weathering profiles may record rapid dissolution of minor hornblende or trace phases. Excess Ca in drainage water may reflect rapid weathering of minor amounts of calcic minerals derived from bedrock or from dustfall. Local catchments export dissolved cations + silica at rates from about 2 to 5 T m^-2 kyr^-1 over a runoff range of 10 to nearly 160 cm; average cosmogenic radionuclide (CRN) erosion rates in the vicinity are ~2.2 cm kyr^-1. Simple modeling shows that if 70% of the void space is created by volume expansion, CRN erosion rates could be balanced by grus + soil formation from saprolite if most of the annual solute loss comes from the soil zone. Rates of saprolite formation from oxidized bedrock, however, cannot balance soil and grus losses to erosion. Thick saprolite likely reflects a relict landscape that is eroding in the present climate. Better modeling of long-term processes requires clearer understanding of altering minerals and solute origin in the weathering profile.

Markes E. Johnson, Professor of Geosciences and G.B. Baarli

Journal of Coastal Research, 21, 887-899 (2005)

Modern and abandoned Pleistocene rocky shores are described for several of the Seychelles Islands in order to examine the range of erosional features typical of granite shores in a tropical setting and to gauge the prospects for their preservation at unconformities in the rock record. The proportion of sandy beaches to rocky shores is estimated for each of the various islands under consideration, including Mahé, Praslin, Ronde, La Digue, Grande Soœur, and Cocos. Aspects of physical geography related to the position of reefs and the variable width of lagoons that surround and buffer the islands is considered with respect to the regional pattern of prevailing winds and oceanic circulation. Literature on the erosion of granite landforms is reviewed and applied to the Seychelles Inner Islands and the Seychelles Bank on which they sit. Outcrops of Pleistocene limestone closely associated with granite surfaces were searched for body fossils that represent an intertidal rocky-shore biota. Coralline red algae and vermetid gastropods are the primary components of laminated limestone attached directly to granite surfaces as protective bioconstructions. Cemented limestone rubble includes the body fossils of a dozen different kinds of invertebrates also found extant on modern granite shores in the Seychelles. Among them are gastropods that represent a range of different life styles, as well as corals.

Markes E. Johnson, Professor of Geosciences

Geologiska Föreningens in Stockholm Förhandlingar, 128, 115-121 (2006)

Eight distinct highstands in sea level emerged from the author’s study of the Silurian System on a continent-to-continent basis during the 1980’s and 1990’s. Some emendations are needed to accommodate other trends recognized since that time, but the overall pattern is strong. Five major highstands and one minor highstand fit the Lower Silurian (Llandovery and Wenlock series). Three major highstands fit the Upper Silurian (Ludlow and Prídolí series). Three separate episodes of glaciation correspond to drops in sea level from the Lower Silurian but fluctuations recorded in the Upper Silurian have no clear cause. Many oceanic events share common trends when the relationship with sea-level fluctuations is tested against a tight biostratigraphic framework. The Sandvika Event correlates with a sea-level drop between the second and third highstands from the Llandovery Series. An unnamed secundo-primo event overlaps the fall between the third and fourth highstands. The Ireviken Event corresponds to a drop near the basal Wenlock. The Boge Event matches a minor draw down superimposed on the fifth rise from the Sheinwoodian Stage. The Mulde Event partly fits a drop in the Lower Homerian Stage. The Linde Event corresponds to the low between the sixth and seventh peaks from the Ludlow Series and the Klev Event fits the lowstand between the seventh and eighth peaks near the Ludlow-Pridolí boundary. The Lau Event, however, appears to adjoin the seventh highstand. No known event corresponds to the draw down between the first and second sea-level peaks recorded in the Llandovery Series.

Markes E. Johnson, Professor of Geosciences, J. Ledesma-Vázquez, Universidad Autónoma de Baja California,
and B.G. Baarli, Research Associate

Journal of Coastal Research, 22, 574-580 (2006)

The bones and teeth of vertebrates occur on shorelines in quantities sufficient to provide a guide to the range of animals that live both inland and offshore. Burial is necessary for any remains to enter the fossil record and coastal deposits representing intertidal and shallow subtidal environments are potential repositories of this record. A survey of 150 published reports on rocky shores from the Cambrian to the Pleistocene reveals approximately 5% in which vertebrate remains are listed and described. In all cases, the vertebrates involved are marine in habit but there is no reason to suppose that the remains of land-dwelling vertebrates should be excluded from such deposits. The potential for dinosaur remains to be incorporated in marine coastal deposits is appraised with particular attention to the Upper Cretaceous of Baja California (México) and southern California (USA). Newly discovered hadrosaur (duckbill) dinosaur bones from the Eréndira area on the Pacific coast of Baja California (México) are described as related to a Late Cretaceous rocky shoreline.

Paul A. Skudder, III ’05, David H. Backus, Research Associate, D. H. Goodwin,
and Markes E. Johnson, Professor of Geosciences

Journal of Coastal Research, 22, 611-624 (2006)

Atmospheric and oceanographic conditions stimulate high productivity of marine organisms in the Gulf of California that are bulk producers of calcium carbonate. Due to prevailing winter winds, north-facing beaches receive vast amounts of shell debris derived from offshore clam banks above the 50 m isobath. As shells undergo mechanical abrasion, the smaller particles of carbonate material are transferred from beaches by the wind and sequestered in coastal dunes. This study reports on two dune fields from the midriff zone of the gulf. Sieve analysis is used to describe the grain size and sorting characteristics of seven samples from dunes at Cerro El Gallo near Mulegé and twelve samples from dunes farther south near San Nicolás. Dune sediments also were impregnated with epoxy to simulate rock samples from which thin sections were made to determine composition and relative abundances of constituent grains. The dunes at Cerro El Gallo are carbonate poor (5%–15 %) compared to those near San Nicolás (26%-51%) and possible factors contributing to regional variation are explored.

Another part of this study appraises the fecundity necessary to produce any carbonate fraction integrated by coastal dunes from seashells. One of the region’s more abundant clams, Megapitaria squalida, was used as a model to estimate the number of individuals of a given size and age class required to generate a cubic meter of pure carbonate sand. Satellite images of the dune fields at El Gallo and San Nicolás were viewed to map surface coverage. With input on the thickness of dune deposits and their composition, it is possible to roughly estimate the number of mature Megapitaria equal to the carbonate fraction of these dunes. The method may be applied to all coastal dunes on the Gulf of California, and could be used to assess a part of the region’s overall carbon budget heretofore unappreciated.

Paul Karabinos, Professor of Geosciences, Ryan P. Gordon ’05, Joseph M. Pyle, Rensselaer Polytechnic Institute

Geological Society of America, Abstracts with Programs, 37(7), 20 (2005)

Field evidence clearly shows that Middle Proterozoic basement of the Berkshire massif in Massachusetts and Connecticut was thrust over early Paleozoic shelf rocks of the Laurentian margin. Furthermore, it is widely accepted that thrusting occurred during the Ordovician Taconic orogeny and that the massif was internally shortened by numerous thrusts, even though the evidence for these assertions is limited. Samples from well-exposed fault zones on the west margin of the massif are spectacular mylonites with a strong, recrystallized, planar foliation and a steep strain gradient. Sense-of-shear indicators are mostly consistent with westward thrusting, although textures suggest local reactivation into east-dipping normal faults. No clear evidence exists for internal thrusting within the massif; it apparently behaved as a rigid block during uplift. Silurian sills near the eastern margin of the massif are distal arc-related rocks that we suggest intruded normal faults that juxtaposed Late Proterozoic pelitic schist with basement rocks of the massif.

Electron microprobe dating of monazite does not support a Taconic age for thrusting. Monazite from a highly deformed quartzite exposed in the hanging-wall of the Dry Hill fault gives an age of 392 ± 14 Ma (1s.e., n=16). Quartz-rich schist from a fault zone at Umpachene Falls contains monazite grains with multiple age populations that peak at 530, 435, 380, and 290 Ma. Monazite grains in a graphitic schist from Benton Hill 200 m below a major thrust give a weighted average age of 436 ± 8 Ma (n=21). Two localities from Yale Farm near the western frontal thrust of the Berkshire massif give weighted average monazite ages of 401 ± 9 Ma (n=26) and 400 ± 10 (n=40). These preliminary monazite ages from well-exposed fault zones suggest that motion on faults along the western margin of the massif occurred during the Devonian or Silurian. So far, dating of monazite provides no evidence that faults were active during the Ordovician Taconic orogeny. However, one sample, collected more than 0.5 km from any major mapped fault, does show two peaks in monazite ages at 470 and 520 Ma. This sample apparently preserves evidence for Early Ordovician metamorphism, but more data are needed to confirm this older age.

Paul Karabinos, Professor of Geosciences and J.C. Hepburn

Geological Society of America, Abstracts with Programs, 38, 32 (2006)

Igneous rocks in western New England help constrain the tectonic setting of the Silurian Laurentian margin. In western CT, the Harrison and Newtown Gneiss together with the Brookfield Plutonic Suite appear to record arc magmatism during the interval 453 to 428 Ma (Sevigny and Hanson, 1993; 1995), and Grenville age inheritance in zircon suggests contamination by Laurentian crust. The granite at Yale Farm intruded Grenville rocks on the western edge of the Berkshire massif in northwestern CT at approximately 430 ± 10 Ma (Zartman et al., 1986). The granite of Beckey Quarry intruded Grenville rocks and the Hoosac Formation along the eastern margin of the Berkshire massif in southwestern MA at 434 ± 5 and 432 ± 2 Ma (Karabinos et al., 2003). The geochemistry of these two informal granite units suggests that they formed as arc magmas. The Dell Trondhjemite in northwestern MA has an arc geochemical signature (Kim and Jacobi, 1996) and intruded the Hawley Formation at 434 ± 8 Ma (Karabinos and Aleinikoff, 1991). A felsic sill intruded the Missisquoi Formation (MF) in Bridgewater, VT at 419 ± 1 Ma (Aleinikoff and Karabinos, 1990).

The Braintree Complex intruded the MF in Braintree, VT at 427 ± 4 Ma and geochemistry suggests an intraplate rift setting (Ratcliffe and Aleinikoff, 2000). In southeastern VT, the Standing Pond Volcanics (SPV) and possible feeder dikes to the SPV found in the MF preserve a back-arc basin geochemistry. A dike in the SPV constrains this unit to be older than 421 ± 2 Ma (Aleinikoff and Karabinos, 1990).

Thus, numerous isolated units in western New England provide evidence for a west-dipping subduction zone under the Laurentian margin at the end of the Ordovician Taconic orogeny through the Silurian. The limited volume of these arc-related rocks suggests a distal setting from the arc trench and a shallow dip of the subducting slab. This subduction zone was partly coeval with magmatism in the Bronson Hill arc in NH and MA. At ca. 430 to 425 Ma a transition occurred from arc magmatism to back-arc rifting that led to sedimentation in the Connecticut Valley trough. There are two viable models for the Bronson Hill arc. We suggest it formed above the west-dipping subduction zone near the Laurentian margin. However, it may be a peri-Gondwanan arc that was accreted in the Silurian (van Staal et al., 1998).

Paul Karabinos, Professor of Geosciences

Geological Society of America, Abstracts with Programs, 38, 20 (2006)

Compilation of numerous studies shows that western New England contains arc-related igneous rocks ranging in age from 496 to 428 Ma. Because arc terranes provide important constraints on along-strike correlations and the tectonic assembly of the Appalachians, it is critical to delineate separate arcs and to determine where they formed in Iapetus. For example, recent studies show that arc magmatism was widespread in the Appalachians and Caledonides between 480-470 Ma. Paleomagnetic and fossil evidence from Newfoundland, however, demonstrates that coeval arcs developed near Laurentia, near Gondwana, and within Iapetus (MacNiocaill and others, 1997); thus correlations based on age alone are tenuous. Karabinos et al. (1998) argued that the Shelburne Falls arc (SFA) formed on a rifted fragment of Laurentia and collided with the Laurentian mainland during the Taconic orogeny (470-455 Ma). They suggested that the younger Bronson Hill arc (BHA) (454-442 Ma, Tucker and Robinson, 1990) formed after a reversal in subduction polarity above a west-dipping subduction zone near Laurentia. In contrast, van Stall et al. (1998) correlated the BHA with the peri-Gondwanan Popelogan-Victoria arc and suggested a Late Ordovician collision with Laurentia. A lack of paleomagnetic and fossil data in western New England makes it difficult to test these models, and geochemical studies have been inconclusive. The following observations suggest, but do not prove, that the BHA formed near Laurentia: (1) in western CT and MA arc-related rocks (453-428 Ma) intruded Grenville basement and previously accreted SFA rocks, indicating that a west-dipping subduction zone existed under Laurentia, (2) volcanics rocks coeval with the SFA and BHA are separated by an unconformity in northern New Hampshire (Moench and Aleinikoff, 2003), (3) the Connecticut Valley trough, which separates the SFA and BHA, contains rift related volcanics that began to form soon after arc magmatism in the BHA ceased, consistent with a back-arc basin forming above a west-dipping subduction zone. To resolve the tectonic significance of the BHA, future studies should search for evidence of crustal contamination in arc-related igneous rocks and establish the provenance of sedimentary rocks intruded by arc plutons and interbedded with arc volcanics.

Paul Karabinos, Professor of Geosciences, David Morris ’05, Ryan Gordon ’05,
and Joseph Pyle, Rensselaer Polytechnic Institute

Geological Society of America, Abstracts with Programs, 38, 63 (2006)

Middle Proterozoic basement of the Berkshire massif in MA and CT was thrust westward over early Paleozoic shelf rocks of the Laurentian margin. Although, it is widely accepted that displacement on the frontal thrust occurred during the Ordovician Taconic orogeny, evidence for the age of thrusting is limited. We used zircon SHRIMP methods to date five felsic sills previously interpreted as syn-tectonic intrusives into Taconic thrusts. Two of these samples are from the eastern margin of the massif and give Silurian igneous crystallization ages of 432 ± 3 Ma (n=11) and 434 ± 5 Ma (n=8). Xenocrystic zircon cores (950 to 1250 Ma) indicate contamination by Grenville basement. Igneous zircon rims from three felsic sills located in the interior and western margin of the massif yield SHRIMP ages of 997 ± 10 Ma (n=16), 1004 ± 19 Ma (n=8), and 1003 ± 8 Ma (n=7). Cores from these zircons range from 1050 to 1230 Ma. Thus, none of the sills formed during the Ordovician Taconic orogeny.

The well-exposed frontal thrust zone on the western margin of the massif contains spectacular mylonites with steep strain gradients over tens to hundreds of meters. Electron microprobe dating of monazite from fault-zone samples does not support a Taconic age for thrusting. Monazite from a highly deformed quartzite exposed in the hanging-wall of the Dry Hill fault gives an age of 392 ± 14 Ma (1s.e., n=16). Quartz-rich schist from a fault zone at Umpachene Falls contains monazite grains with multiple age populations that peak at 530, 435, 380, and 290 Ma. Monazite grains in a graphitic schist from Benton Hill 200 m below a major thrust give a weighted average age of 436 ± 8 Ma (n=21). Two localities from Yale Farm near the western frontal thrust of the Berkshire massif give weighted average monazite ages of 401 ± 9 Ma (n=26) and 400 ± 10 (n=40).

The preliminary monazite ages from frontal thrust zone suggest that motion on faults along the western margin of the Berkshire massif occurred during the Acadian orogeny. We found no clear evidence for internal thrusting within the massif; it apparently behaved as a rigid block during uplift. Silurian sills near the eastern margin of the massif are distal arc-related rocks that appear to have intruded normal faults along the western margin of an incipient back-arc basin that evolved into the Connecticut Valley trough.

Andrea Burke ’06, Alicia Arevalos ’05, Seth Zeren ’05, P. Ziveri, N. Shimizu, and
Heather M. Stoll, Assistant Professor of Geosciences

EOS, Transactions of the American Geophysical Union, 86(52), OS51A-0550 (2005)

Coccolithophorid algae are important to the marine biologic carbon pump because their coccoliths are believed to be the dominant ballast increasing the transfer efficiency of organic carbon into the deep sea. Efforts to reconstruct coccolithophorid production from CaCO₃ accumulation are complicated by variable dissolution, hence we use sediment traps to explore coccolith chemistry (Sr/Ca and stable isotopes) as a proxy for coccolithophorid production. In biogenically dominated fluxes of the Arabian Sea, coccolith Sr/Ca covaries with primary productivity, coccolithophorid calcification, and coccolith export to shallow 1000m traps. However in Bay of Bengal traps lithogenic fluxes during the southwest monsoon dramatically increase export of all coccoliths during the southwest monsoon, although Sr/Ca and productivity of some species is highest in Northeast monsoon. In Quaternary coccoliths from the Bay of Bengal and Arabian Sea Sr/Ca variations closely track precessional monsoon cycles. In the Arabian Sea, strong summer monsoons drive high productivity due to increased upwelling intensity. In contrast in the Bay of Bengal high productivity during monsoon maxima likely reflects either shifts in chemical weathering intensity or in groundwater nitrate release due to increased vegetation and runoff.

Heather M. Stoll, Assistant Professor of Geosciences, P. Ziveri, Andrea Burke ’06,
Susanna Theroux ’05, N. Shimizu, and M. Conte

Geophysical Research Abstracts, 8. 10699 (2006)

Coccolithophorid CaCO₃ production can account for 20-80% of biogenic carbonate exported from the photic zone, and coccoliths are a dominant biogenic carbonate in many deep sea sediments. A new method for picking individual coccoliths from sediment traps and sediments for analysis using Secondary Ion Mass Spectrometry (ion probe) allows us to make precise Sr/Ca and Mg/Ca determinations on coccoliths from single species even in trap samples where material is very limited. There are large biological effects in Sr/Ca partitioning in coccoliths, which have been related to variations in coccolithophorid productivity. In sediment traps from Bermuda, Arabian Sea, and Bay of Bengal, we can identify Sr/Ca variations in several species, which are consistent with inferred seasonal variations in coccolithophorid productivity in surface waters. In the Arabian Sea, coccolith Sr/Ca ratios in Calcidiscus leptoporus and Helicosphaera carteri are lowest during the nonproductive intermonsoon and highest during the upwelling of southwest monsoon and nutrient entrainment from strong winds of northeast monsoon. Sr/Ca variations in C. leptoporus are larger, and this species also has the greater variation in export flux between southwest monsoon and intermonsoon seasons. At Bermuda, a 1996 fall bloom driven by passage of a warm mesoscale feature induced large change in Sr/Ca of C. leptoporus coincident with an increase of C. leptoporus export, but over an annual series for 2004 highest Sr/Ca ratios of C. leptoporus in the summer month match the typical summer peak in surface standing stock of this species but did not coincide with the highest export of C. leptoporus coccoliths. This method allows us to examine coccolith Sr/Ca in downcore settings with much better constraints on potential diagenetic alteration of carbonate chemistry. Coherent coccolithophorid productivity responses to precessional variations in monsoon intensity are tracked by coccolith Sr/Ca in the Bay of Bengal, Arabian Sea, and Eastern Mediterranean.

Heather M. Stoll, Assistant Professor of Geosciences, M. Jimenez, and Tyler Auer ’07

CuevaTur: 1 Congreso Español Sobre Cuevas Turisticas, 1, 7 (2006)

The Pindal Cave (Asturias, NW Spain) is hosted by limestones of the Barcaliente Formation 24 m above sea level and in close proximity (50m) to the coastal sea cliffs. For eleven months, dripwater flow was collected in 153 discrete samples each representing integrated flow over 48 hours. Dripwater flow rate is compared with precipitation and the major element chemistry of dripwaters. Dripwater flow rates vary dramatically from sample to sample, typically lagging precipitation peaks by 1-3 days. Overall dripwater flow is highest in the wet winter season and lowest in the dry summer season. Concentrations of Ca vary dramatically from sample to sample and are highly positively correlated with the daily-weekly variations in dripwater flow. Mean Ca concentrations are comparable during summer and winter months, despite lower summer drip flow, probably because higher soil CO2 during the summer growing season increases dissolution of host rock during infiltration, compensating for longer Ca residence times. Sr/Ca ratios and Mg/Ca ratios correlate inversely with dripwater flow rates, and together with Ca variations imply variable precipitation of calcite during aquifer throughflow. The concentration of Na in dripwaters reflects prevailing wind direction and transport of sea salt aerosols into the cave drainage basin and correlates with the NAO index, whereas concentrations of K are influenced by biological uptake and episodic anthropogenic inputs.

Heather M. Stoll, Assistant Professor of Geosciences

Nature, 441, 579-581 (2006)

The Arctic is one of the sensitive pressure-points for Earth’s climate. Core information now reveals much more about the region’s role in a long-term transition from “greenhouse” to “icehouse” conditions. Just as a white T-shirt keeps us cooler on a hot sunny day, a blanket of reflective snow and sea ice over the polar regions curbs the amount of sunlight the Earth absorbs. Ice and snow cover grows in response to cooling temperatures, and so acts as an amplifier of climate change, but the Arctic and the Antarctic were not always frozen and barren. Over the past 55 million years or so, the Earth has experienced a major cooling, from a greenhouse climate to the current icehouse climate. The results of a remarkable scientific project in the Arctic as reported in three papers in this issue^2–4, provide a detailed picture of the Arctic’s role in the long-term cooling, and its response during oscillations of the preceding greenhouse climates.

P. Ziveri, I. Probert, and Heather M. Stoll, Assistant Professor of Geosciences

Geophysical Research Abstracts, 8. 10697 (2006)

A main objective of the Euroclimate MERF* project is to reconstruct - the gradients in biological productivity, expected if nutrients entered the Mediterranean Sea from distinct sources such as rivers, and – the variations in the productivity of species in different ecological niches throughout the water column. The Mediterranean basin was selected since it is characterized by monsoon cycles, which increased nutrient fluxes to the ocean every 23,000 years. A suite of new proxy indicators derived largely from inorganic chemistry of primary producing coccolithophores (dominant calcareous phytoplankton group in the Mediterranean Sea), d15N and d13C of organic compounds, and C:P ratios in sediments, are all well-suited to this work. We will present here the first calibration from culture experiments of the carbonate chemical signatures with respect to the influence of major nutrients. We will discuss how the chemistry (d13C,d18O, Sr/Ca) and morphological and physiological characteristics (cell size, growth rates, calcification rates) of key species respond to variable nutrient levels (phosphate/nitrate) and temperature. The selected key species constitute an important component of modern and Quaternary sediments of the Mediterranean Sea. The culture calibrations will form the basis for continued calibration in surface sediments, ultimately yielding the means for improved proxy measurements of past environments.
* Quaternary marine ecosystem response to fertilization: Mediterranean sapropel events and implications for marine carbon uptake (MERF) (EUROCORESEUROCLIMATE)

L. Auliaherliaty, .P. Ziveri, S.R. Troelstra, M. Prins, and Heather M. Stoll, Assistant Professor of Geosciences

Geophysical Research Abstracts, 8, 00693 (2006)

The eastern Mediterranean Sea is an area where occasionally sapropel (organic-rich layers deposited under anoxic conditions) deposition took place. The area is influenced by the monsoon system involving changes in nutrient fluxes. Marine fertilization by aeolian and riverine input might also influence nutrient fluxes today. Detailed knowledge of these processes is important to understand the marine productivity cycle in this area, playing a role in modulating CO2 exchange with the atmosphere and also sequestrating it into the ocean as a major reservoir in the carbon cycle. Relatively little is known about the mechanisms behind these marine productivity cycles. In our research we use the inorganic chemistry of coccolithophores, a dominant calcareous phytoplankton group in the Mediterranean Sea, from surface sediment samples and gravity cores spanning several sapropel deposition events. Stable isotope and trace element data are used to reconstruct changes in nutrient flux, marine productivity, and oceanographic conditions. Our data will be combined with organic chemistry and sedimentologic results from the same samples. Furthermore, relationships obtained from culture studies will be applied to the sediment samples. This work is part of a EUROCORES-EUROCLIMATE, Project MERF (Quaternary Marine Ecosystem Response to Fertilization).

Donald deB. Beaver, Professor of History of Science

Proceedings of ISSI 2005, 10th International Conference of the International Society for Scientometrics and Informetrics, Stockholm, Sweden, July 24-28, 2005: pp. 727-730.

The vanishing single-authored paper seems to have hit a limit below which it will strongly resist further encroachment by collaboration or teamwork. That limit is about one paper in ten, but varies by field of science, being lower (~1 in 16) in chemistry, but higher in biology (~1 in 7). The prevalence of single authorship also varies between experimental (lesser) and theoretical (greater) research. The overall pattern of the growth of collaborative research now displays the shape of a logistic curve. Teamwork (6 or more authors) continues to grow in all fields at the expense of collaboration (5 or fewer authors), but the two patterns remain statistically distinct. The biological sciences came last to display the co-authorship pattern of teamwork.

Donald deB. Beaver, Professor of History of Science

Proceedings of International Workshop on Webometrics, Informetrics, and Scientometrics & Seventh COLLNET Meeting, COLLNET 2006, SRDI-INIST-CNRS-LORIA, Nancy, France, 10-12 May, 2006, pp. 2-3.

Colin Adams, Francis C. Oakley Third Century Professor of Mathematics

with A. Colestock, J. Fowler, W.D. Gillam, E. Katerman

Transactions of the A.M.S., Vol. 358, No. 2, 727-741 (2005)

Colin Adams, Francis C. Oakley Third Century Professor of Mathematics

with E. Schoenfeld

Geometriae Dedicata, Vol. 116, 723-247 (2005)

Colin Adams, Francis C. Oakley Third Century Professor of Mathematics

Ed. by W. Menasco and M. Thistlethwaite

The Handbook of Knot Theory, Elsevier, (August 2005)

Colin Adams, Francis C. Oakley Third Century Professor of Mathematics

Mathematical Intelligencer, Vol. 27, No. 2, 24-25 (2005)

Colin Adams, Francis C. Oakley Third Century Professor of Mathematics

with Lew Ludwig

Mathematical Intelligencer, Vol. 27, No. 3, 31-32 (2005)

Colin Adams, Francis C. Oakley Third Century Professor of Mathematics

Mathematical Intelligencer, Vol. 27, No. 4, 26-28 (2005)

Colin Adams, Francis C. Oakley Third Century Professor of Mathematics

Mathematical Intelligencer, Vol. 28, No. 1, 17-18 (2006)

Carsten Botts, Assistant Professor of Statistics

with Michael J. Daniels

Biometrika, Vol. 93, 179-195 (2006)

Thomas Garrity, Associate Professor of Mathematics

with S. Assaf, L. Chen, T. Cheslack-Postava ’00, B. Cooper ’01, A. Diesl, M. Lepinski and A. Schuyler

Integer: The Electronic Journal of Combinatorial Number Theory, 5 (2005)

A dual approach to defining the triangle sequence (a type of multidimensional continued fraction algorithm, initially developed in [Garrity1] for a pair of real numbers is presented, providing a new, clean geometric interpretation of the triangle sequence. We give a new criterion for when a triangle sequence uniquely describes a pair of numbers and give the first explicit examples of triangle sequences that do not uniquely describe a pair of reals.

Finally, this dual approach yields that the triangle sequence is topologically strongly mixing, meaning in particular that it is topologically ergodic.

Susan Loepp, Associate Professor of Mathematics with William Wootters

Cambridge University Press, (2006)

Frank Morgan, Webster Atwell Class of 1921 Professor of Mathematics

American Mathematical Society, (2005)

Based on a one-semester core real analysis course at Williams.

Frank Morgan, Webster Atwell Class of 1921 Professor of Mathematics

J. Geom. Anal., preprint at arvix.org, 321-341 (2005)

In the surface of a convex polytope P³ in R⁴, an area-minimizing surface avoids the vertices of P and crosses the edges orthogonally. In a smooth Riemannian manifold M with a group of isometries G, an area-minimizing G-invariant oriented hypersurface is smooth (except for a very small singular set in high dimensions). Already in 3D, area-minimizing G-invariant unoriented surfaces can have certain singularities, such as three orthogonal sheets meeting at a point. We also discuss flat chains modulo μ and soap films.

Frank Morgan, Webster Atwell Class of 1921 Professor of Mathematics

American Mathematical Society, (2005)

Streamlined, complete theory, plus applications in Fourier series and the calculus of variations, including physics (least action and Lagrange’s equations), economics (optimal production and maximal utility), Riemannian geometry, and general relativity.

Frank Morgan, Webster Atwell Class of 1921 Professor of Mathematics

Pacific J. of Math, 221, 123-146 (2005)

Perimeter-minimizing planar double soap bubbles in which regions are allowed to overlap with multiplicities meet in fours, fives, and sixes as well as threes. We further provide certain generalizations to immiscible fluids and higher dimensions, and an associated theory of calibrations. We work in the category of flat chains with coefficients in a normed group.

Frank Morgan, Webster Atwell Class of 1921 Professor of Mathematics, with Tom Garrity

Amer. Math. Soc., (2005)

Easy ways to be a better teacher.

Frank Morgan, Webster Atwell Class of 1921 Professor of Mathematics

Pacific J. of Math, 220, 379-387 (2005)

For the ‘hexagonal’ norm on R³, for which the isoperimetric shape is a hexagonal prism rather than a round ball, we give analogs of the compact immersed constant-mean-curvature surfaces of Kapouleas.

Frank Morgan, Webster Atwell Class of 1921 Professor of Mathematics

Notices Amer. Math. Soc., 52, 853-858 (2005)

We discuss the category of Riemannian manifolds with density and present easy generalizations of the volume estimate of Heinze and Karcher and thence of the isoperimetric inequality of Levy and Gromov.

Frank Morgan, Webster Atwell Class of 1921 Professor of Mathematics, with Manuel Ritoré, David Hoffman, Editor

Amer. Math. Soc., (2005)

Global Theory of Minimal Surfaces (Proc. Clay Inst., 2001 Summer School, MSRI)

Notes by Ritoré based on Morgan’s course at MSRI.

Allison Pacelli, Assistant Professor of Mathematics, with Yoonjin Lee

Proceedings of the American Math Society, 133, 2883-2889 (2005)

Allison Pacelli, Assistant Professor of Mathematics

Journal of Number Theory, 116, 311-323 (2006)

Cesar Silva, Professor of Mathematics, with S. Iams ‘04, B. Katz ‘03, B. Street, and K. Wickelgren

Colloq. Math. 103, 247-264 (2005)

Abstract: We study weak mixing and double ergodicity for nonsingular actions of locally compact Polish abelian groups. We show that if T is a nonsingular action of G, T is weakly mixing if and only if for all co-compact subgroups A of G the action of T restricted to A is weakly mixing. We show that a doubly ergodic nonsingular action is weakly mixing and construct an infinite measure-preserving flow that is weakly mixing but not doubly ergodic. We also construct an infinite measure-preserving flow whose Cartesian square is ergodic.

Mihai Stoiciu, Assistant Professor of Mathematics

Journal of Approximation Theory, 139, 29-64 (2006)

In this paper we consider random paraorthogonal polynomials on the unit circle defined by independent identically distributed random Verblusky coefficients. The zeros of these polynomials are random points on the unit circle. We prove that the local statistical distribution of these zeros is Poisson. This means that there is no local correlation between the zeros of the considered random paraorthogonal polynomials.

Daniel P. Aalberts, Associate Professor of Physics, Eric G. Daub ’04 and Jesse W. Dill ’04

Bioinformatics, 21, 3347 (2005)

Traditional bioinformatics methods scan primary sequences for local patterns. It is important to assess how accurate local primary sequence methods can be. We study the problem of donor pre-mRNA splice site recognition, where the sequence overlaps between real and decoy data sets can be quantified, exposing the intrinsic limitations of the performance of local primary sequence methods. We assess the accuracy of primary sequence methods generally by studying how they scale with dataset size and demonstrate that our new Primary Sequence Ranking methods have superior performance.

Kevin M. Jones, The William Edward McElfresh Professor of Physics, and colleagues at MIT and NIST

Physical Review A, 72, 043604 (2005)

The phase transition from a superfluid to a Mott insulator has been observed in a ²³Na Bose-Einstein condensate. A dye laser detuned ≈5 nm red of the Na 3S—>3P_1/2 transition was used to form the three-dimensional optical lattice. The heating effects of the small detuning as well as the three-body decay processes constrained the time scale of the experiment. Certain lattice detunings were found to induce a large loss of atoms. These loss features were shown to be due to photoassociation of atoms to vibrational levels in the Na₂ (1)³∑_g⁺ state.

Kevin M. Jones, The William Edward McElfresh Professor of Physics, and colleagues at NIST

Physical Review A, 72, 041801 (2005) (Rapid Communications)

By driving photoassociation transitions, we form electronically excited molecules (Na₂^*) from ultracold (50—300 µK) Na atoms. Using a second laser to drive transitions from the excited state to a level in the molecular ground state, we are able to split the photoassociation line and observe features with a width smaller than the natural linewidth of the excited molecular state. The quantum interference which gives rise to this effect is analogous to that which leads to electromagnetically induced transparency in three-level atomic -systems, but here one of the ground states is a pair of free atoms while the other is a bound molecule. The linewidth is limited primarily by the finite temperature of the atoms.

Kevin M. Jones, The William Edward McElfresh Professor of Physics, and colleagues at NIST

Reviews of Modern Physics, 78, 483 (2006)

Photoassociation is the process in which two colliding atoms absorb a photon to form an excited molecule. The development of laser-cooling techniques for producing gases at ultracold 1mK temperatures allows photoassociation spectroscopy to be performed with very high spectral resolution. Of particular interest is the investigation of molecular states whose properties can be related, with high precision, to the properties of their constituent atoms with the ‘complications’ of chemical binding accounted for by a few parameters. These include bound long-range or purely long-range vibrational states in which two atoms spend most or all of their time at large internuclear separations. Low-energy atomic scattering states also share this characteristic. Photoassociation techniques have made important contributions to the study of all of these. This review describes what is special about photoassociation spectroscopy at ultracold temperatures, how it is performed, and a sampling of results including the determination of scattering lengths, their control via optical Feshbach resonances, precision determinations of atomic lifetimes from molecular spectra, limits on photoassociation rates in a Bose-Einstein condensate, and briefly, production of cold molecules. Discussions are illustrated with examples on alkali-metal atoms as well as other species. Progress in the field is already past the point where this review can be exhaustive, but an introduction is provided on the capabilities of photoassociation spectroscopy and the techniques presently in use.

Kevin M. Jones, The William Edward McElfresh Professor of Physics, and colleagues at NIST

New Journal of Physics, 8, 64 (2006) (IOP Select)

We demonstrate an all-optical technique to evaporatively produce sodium Bose-Einstein condensates (BEC). We use a crossed-dipole trap formed from light near 1 µm, and a simple ramp of the intensity to force evaporation. In addition, we introduce photoassociation as diagnostic of the trap loading process, and show that it can be used to detect the onset of BEC. Finally, we demonstrate the straightforward production of multiple traps with condensates using this technique, and that some control over the spinor state of the BEC is achieved by positioning the trap as well.

Colin F. McCormick ’95, Kevin M. Jones, The William Edward McElfresh Professor of Physics,
and others (presented by McCormick)

Proceedings of CLEO/QUELS 2006, May 21-26 (2006)

We have observed high-contrast nonlinear optical ring formation in hot atomic vapor. The standard Kerr model fails to predict important qualitative features of these optical patterns, but a Doppler-broadened two-level model is extremely successful.

Colin F. McCormick’95, Kevin M. Jones, The William Edward McElfresh Professor of Physics,
and others (presented by V. Boyer)

Proceedings of CLEO/QUELS 2006, May 21-26 (2006)

We report our progress towards the realization of a tunable and narrow-band source of correlated photons for coherent manipulation of cold atoms, using a combination of four-wave mixing and electromagnetically induced transparency.

J.A. Kerckhoff ’05, C.D. Bruzewicz ’05, R. Uhl, and P.K. Majumder, Associate Professor of Physics

Rev. Sci. Instrum., 76, 093108 (2005)

We present a method of diode laser frequency stabilization based on the Faraday rotation of linearly polarized light passing through an atomic sample in the presence of a very modest 1 mT magnetic field. Near the zero crossing of this spectroscopic feature, an optical system capable of very precise polarimetry detects and corrects for very small frequency fluctuations via a feedback system, which keeps the rotation signal at zero. In our application, we have demonstrated robust frequency stabilization over time scales from 10 ms to 1 h at the 1 MHz level or below. We utilize this technique to lock our laser to a “forbidden” M1/E2 transition in thallium at 1283 nm, for which saturated absorption techniques are not straightforward. This technique has broad applicability to spectroscopy of various atomic systems as we also demonstrate using a Rb cell and a780 nm diode laser.

Ersen Bilgin ’06, Brian Patt, David Tucker-Smith, Assistant Professor of Physics, and Frank Wilczek

Phys. Lett. B, 634, 69-73 (2006)

We motivate and construct supersymmetric theories with continuous flavor symmetry, under which the electroweak Higgs doublets transform non-trivially. Flavor symmetry is spontaneously broken at a large mass scale in a sector of gauge-singlet fields; the light Higgs multiplets naturally emerge as special linear combinations that avoid acquiring the generic large mass. Couplings of the light Higgs doublets to light moduli field from the singlet sector could lead to important effects in the phenomenology of the Higgs sector at the LHC.

Martin Schmaltz and David Tucker-Smith, Assistant Professor of Physics

Ann. Rev. Nucl. Part. Sci. 55, 229 (2005)

Recently there has been renewed interest in the possibility that the Higgs particle of the Standard Model is a pseudo-Nambu-goldstone boson. This development was spurred by the observation that if certain global symmetries are broken only by the interplay between two or more coupling constants, then the Higgs mass-squared is free from quadratic divergences at one loop. This “collective symmetry” breaking is the essential ingredient in little Higgs theories, which are weakly coupled extensions of the Standard Model with little or no fine tuning, describing physics up to an energy scale ~ 10 TeV. Here we give a pedagogical introduction to little Higgs theories. We review their structure and phenomenology, focusing mainly on the SU(3) theory, the Minimal Moose, and the Littlest Higgs as concrete examples.

Z. Chacko, Yasunori Nomura and David Tucker-Smith, Assistant Professor of Physics

Nucl. Phys. B, 725, 207-250 (2005)

We construct supersymmetric theories in which the correct scale for electroweak symmetry breaking is obtained without significant fine-tuning. We calculate the fine-tuning parameter for these theories to be at the 20% level, which is significantly better than in conventional supersymmetry breaking scenarios. Supersymmetry breaking occurs at a low scale of order 100 TeV, and is transmitted to the supersymmetric standard-model sector through standard-model gauge interactions. The Higgs sector contains two Higgs doublets and a singlet field, with a superpotential that takes the most general form allowed by gauge invariance. An explicit model is constructed in 5D warped space with supersymmetry broken on the infrared brane. We perform a detailed analysis of electroweak symmetry breaking for this model, and demonstrate that the fine-tuning is in fact reduced. A new candidate for dark matter is also proposed which arises from the extended Higgs sector of the model. Finally, we discuss a purely 4D theory which may also significantly reduce fine-tuning.

William K. Wootters, Barclay Jermain Professor of Natural Philosophy

Foundations of Physics, (online 8 Feb. 2006)

A complete set of mutually unbiased bases for a Hilbert space of dimension N is analogous in some respects to a certain finite geometric structure, namely, an affine plane. Another kind of quantum measurement, known as a symmetric informationally complete positive-operator-valued measure, is, remarkably, also analogous to an affine plane, but with the roles of points and lines interchanged. In this paper I present these analogies and ask whether they shed any light on the existence or non-existence of such symmetric quantum measurements for a general quantum system with a finite-dimensional state space.

William K. Wootters, Barclay Jermain Professor of Natural Philosophy

International Journal of Quantum Information, 4, 219-232 (2006)

In a 1991 paper, Asher Peres and the author theoretically analyzed a set of unentangled bipartite quantum states that could apparently be distinguished better by a global measurement than by any sequence of local measurements on the individual subsystems. The present paper returns to the same example, and shows that the best result so far achieved can alternatively be attained by a measurement that, while still global, is “unentangled” in the sense that the operator associated with each measurement outcome is a tensor product.

Susan Loepp and William K. Wootters, Barclay Jermain Professor of Natural Philosophy

Cambridge University Press (2006)

Phebe Cramer, Professor of Psychology and Allison Tracy

Journal of Research in Personality, 11, 369 – 394 (2005)

In a prospective longitudinal study of 62 individuals from the Berkeley Guidance Study of the Institute of Human Development, we examined the pathway from early childhood personality to early adult adjustment and maladjustment. The results from a path analysis indicated that personality change between childhood and adulthood, influenced by the use of defense mechanisms, was the strongest predictor of adult adjustment. Increased Outgoingness, related to the use of the defense of projection, predicted better psychological health, less depression, but more anxiety. Increased Self-confidence, related to the use of the defense of identification, predicted better psychological health and less depression, but was not related to anxiety. A theoretical explanation of these relations is provided.

Phebe Cramer, Professor of Psychology

New York: Guilford Press (2006)

Integrating theory, research, and practical applications, this book provides a comprehensive examination of defense mechanisms and their role in both normal development and psychopathology. It describes how children and adults mobilize specific kinds of defenses to maintain their psychological equilibrium and preserve self-esteem, particularly in situations of trauma or stress. The impact of age, gender, personality differences, and psychotherapy are discussed.

Susan Engel, Senior Lecturer in Psychology

Cognitive Development, 20, 514-525 (2005)

This paper advances the hypothesis that young children use narrative play and stories to construct two types of fiction, the worlds of what is and what if. Heinz Werner's conceptualization of children's spheres of reality, in which actions, symbols, and events are constructed in particular ways, is used as a theoretical framework for understanding children's play and stories. Drawing on examples of children's spontaneous pretend play and story telling, the paper argues that, beginning in their second year, children use pretend play to differentiate the worlds of everyday-lived reality from an alternative pretend sphere; the world of as if. By their third year, children engage in play that hangs on a narrative framework. Such pretend play offers children further options: the fictional world of plausible make believe which simulates everyday life, what is, and the fictional world of more fantastic possibilities, what if. While the child's use of a narrative framework in her pretend play expands her range of psychological worlds, the developmental shift to purely verbal stories, sometimes during the child's third year, significantly adds to her ability to explore such worlds. An examination of the language young children use to accompany their narrative play and to tell stories demonstrates the ways in which children exploit the narrative form to contrast, compare, and traverse the constructed worlds of what is and what if.

Susan Engel, Senior Lecturer in Psychology

Cambridge, MA: Harvard University Press (2005)

Decades of work in psychology labs have vastly enhanced our knowledge about how children perceive, think, and reason. But it has also encouraged a distorted view of children, argues psychologist Susan Engel in this book--a view that has affected every parent who has tried to debate with a six-year-old. By focusing on the thinking processes prized by adults, too many expert opinions have rendered children as little adults. What has been lost is what is truly unique and mysterious--the childlike quality of a child's mind. Engel draws on keen observations and descriptive research to take us into the nearly forgotten, untidy, phantasmagorical world of children's inner lives. She reminds us that children fuse thought and emotion, play and reality; they swing wildly between different ways of interpreting and acting in the world. But just as a gawky child may grow into a beauty, illogical and sometimes maddening childishness can foreshadow great adult ability. Engel argues that the scientist in a crib view encourages parents and teachers to expect more logical reasoning and emotional self-control from children than they possess. She provides a concise and valuable overview of what modern developmental psychologists have learned about children's developing powers of perception and capacity for reasoning, but also suggests new ways of studying children that better capture the truth about their young minds.

Myrna L. Friedlander, Valentín Escudero, and Laurie Heatherington, Professor of Psychology

Washington, DC: American Psychological Association (2006)

The book demonstrates the crucial importance of healthy working relationships with clients in couple and family therapy. The authors’ conceptual model (System for Observing Family Therapy Alliances, or SOFTA) integrates theory, research, and practice related to the alliance in couple and family therapy. The authors demonstrate how to gather evidence about working alliances by tracking specific positive and negative behaviors in therapy sessions, including clients' as well as therapists' behavioral contributions to the alliance.

Myrna L. Friedlander, Valentín Escudero, Adam O. Horvath, Laurie Heatherington, Professor of Psychology,
Andrés Cabero, and Matthew P. Martens

Journal of Counseling Psychology, 53, 214-224 (2006)

To advance research and inform practice, the authors developed an observational rating system of client behavior reflecting strong and weak therapeutic alliances in couple and family therapy. The System for Observing Family Therapy Alliances (SOFTA), in both English and Spanish, has 2 dimensions that are common across therapy modalities (“emotional connection to the therapist” and “engagement in the therapeutic process”) and 2 dimensions that reflect the uniqueness of conjoint treatment (“safety within the therapeutic system” and “shared sense of purpose within the family”). Psychometric support is provided by 5 reliability studies, an exploratory factor analysis with data from 120 diverse English- and Spanish-speaking couples and families, and meaningful associations with various process and outcome indices. Recommendations are made for using the SOFTA in research, training, and (self-)supervision.

Robert D. Kavanaugh, Professor of Psychology

Child Psychology: A Handbook of Contemporary Issues, 153-166, L. Balter & C.S. Tamis-LeMonda (Eds.) NY: Psychology Press (2006)

This chapter discusses the relationship between children’s understanding of the thoughts and feelings of others and their linguistic and imaginative skills.

Robert D. Kavanaugh, Professor of Psychology

Handbook of Research on the Education of Young Children, 269-278, B. Spodek & O. N. Saracho (Eds.), Mahwah, NJ: Erlbaum (2006)

This chapter discusses the role of pretend play in the development of children’s literacy abilities and adult’s interest and involvement in fiction and the arts.

Kris N. Kirby, Professor of Psychology

Behavioural Processes, 72, 273-282 (2006)

In two experiments, human subjects were asked to estimate their present values of single delayed rewards and their present values of temporal sequences of three rewards. Present values were solicited by asking subjects to indicate an amount of money v for which they would be indifferent between receiving v at the end of the session and receiving the delayed reward(s). A procedure was used for which responding the true value of v was the optimal strategy, and the actual payoff that each subject received was determined by one randomly selected trial. In Experiment 1 (n = 29) each delayed reward was $9.90 in cash. In Experiment 2 (n = 19) the delayed rewards were dated $15 gift certificates to a local restaurant. In both experiments, the present values of the sequences were approximately equal to the sums of the present values of their component rewards. The presence of outliers suggests that a few subjects may have valued sequences less than the sums of their single rewards. Effects of a preference for uniform sequences, if any, were too small to be detected. Discounting of sequences was well-fit by a parallel hyperbolic discounting equation, consistent with Mazur’s (1986) results using multiple reinforcers.

Marlene J. Sandstrom, Associate Professor of Psychology & A. H. N. Cillessen

International Journal of Behavioral Development, 30,4 (2006)

In the current study, 466 children completed a peer nomination survey assessing both perceived and sociometric popularity at the end of the 5th grade. Measures of behavior problems were assessed through a composite of peer-, teacher-, and self- reports at the end of the 8th grade. Examination of the unique concurrent associations of each popularity type with peer nominated social characteristics in 5th grade demonstrated that sociometric popularity was positively associated with prosocial behavior and inclusive behavior, while perceived popularity was positively associated with overt and relational aggression. In addition to emerging as distinct conceptual constructs, these two dimensions of popularity also demonstrated unique associations with adjustment over time. Sociometric popularity in the 5th grade was associated with lower levels of externalizing behavior problems 3 years later, while perceived popularity was associated with higher levels of these problems over time. Interestingly, high levels of perceived popularity in the 5th grade were associated with less internalizing symptoms over time for boys, while high levels of sociometric popularity were associated with less internalizing symptoms over time for girls.

Noah J. Sandstrom, Assistant Professor of Psychology, J. H. Kim ’05, & M. A. Wasserman ’04

Hormones & Behavior, 50, 18-26 (2006)

Gonadal hormones have been shown to modulate memory retention in female rats. The current experiments examine the role of testicular hormones in modulating the performance of male rats on two spatial water maze tasks. In the first study, castrated and intact rats were trained on the visible platform and hidden platform versions of the Morris water maze task. Castration did not affect performance on either version of this reference memory task with castrated and intact rats demonstrating similar performance both during acquisition and on post-training probe trials. In the second experiment, castrated and intact rats were tested on a delayed-matching-to-place version of the water maze. Rats received a series of trial pairs in the maze with a hidden platform located in the same pool location on the exposure and retention trials of each pair; between pairs of trials, however, the platform was repositioned to a novel pool location. The interval between trials was either 10- or 60-min and memory retention, taken as the difference between the pathlengths on the exposure and retention trials, declined as the interval increased. Relative to intact males, castrated males demonstrated impaired working memory retention at 60-min but not at 10-min retention intervals. This interval-dependent impairment in working memory retention was reversed by physiologic levels of testosterone replacement. These findings indicate that castration does not significantly affect acquisition or probe trial performance on a classic reference memory task but does impair spatial working memory retention, an effect that is reversed by exogenous testosterone.

E. C. Dawson, Kenneth Savitsky, Associate Professor of Psychology, & D. Dunning

Journal of Applied Social Psychology, 36, 751-768 (2006)

Prominent theories of health-protective behavior predict increasing information seeking as a function of increasing disease severity, yet diagnostic screens for serious disease are notoriously underutilized. We suggest that in addition to severity, disease treatability impacts people’s willingness to submit to medical tests. In two studies, participants were relatively likely to seek a diagnostic test for a disease they believed to be serious and treatable (Study 1) and to avoid a test for a disease they believed to be serious but untreatable (Study 2). Implications for health-behavior models and persuasive health communication are discussed.

Kenneth Savitsky, Associate Professor of Psychology, L.D. Van Boven, N. Epley, & W.M. Wight ’00

Journal of Experimental Social Psychology, 41, 447-457 (2005)

Individuals tend to overestimate their relative contributions to collaborative endeavors. Thus, the sum of group members’ estimates of the percentage they each contributed to a joint task typically exceeds the logically allowable 100%. We suggest that this tendency stems partly from individuals’ inclination to regard their fellow group members collectively rather than individually, and that leading people to think about their group members as individuals should therefore reduce the perceived relative magnitude of their own contributions. Consistent with this account, four experiments demonstrate that individuals’ tendency to claim more than their fair share of the credit for a group task is attenuated when they “unpack” their collaborators, conceptualizing them as separate individuals, rather than as “the rest of the group.”

Ari Solomon, Assistant Professor of Psychology, J. Ruscio, J. R. Seeley, & , P. M. Lewinsohn

Psychological Medicine, 36, 973-985 (2006)

Background. The question of whether unipolar clinical depression differs categorically from limited depressive complaints has important implications for the disorder's assessment, treatment and research. This crucial issue has proven difficult to resolve, in part because many studies to date have relied on self-report measures or on clinically homogeneous samples. We therefore applied Meehl's taxometric method to a large, clinically heterogeneous sample, and examined the latent structure of depressive episodes using both self-report and structured clinical interview data. Method. Data were derived from the Oregon Adolescent Depression Project, a large longitudinal community study. All analyses involved more than 1400 participants. MAXEIG (MAXimum EIGenvalue) and base rate estimation were performed separately for Beck Depression Inventory (BDI) items and for DSM-IV-based major depressive episode (MDE) symptoms. Results. MAXEIG analyses of the BDI and MDE indicator sets appeared to converge on a taxonic structure for unipolar depression. Base rate estimates overall implied a latent depressive episode class that occurs more frequently than diagnosable MDEs but less frequently than persistent depressed or anhedonic mood. Conclusions. These findings provide tentative support for a categorical conceptualization and make it very clear that the continuity controversy regarding unipolar depression has not yet been decided in favor of dimensionality. To reconcile the conflicting reports to date, several data analytic and sampling issues need to be explored systematically

Brian A. Sundermeier, Visiting Assistant Professor of Psychology, S. M. Virtue, C. J. Marsolek, & P. van den Broek

Brian and Language, 95, 402-413 (2005)

In this study, we investigated whether the left and right hemispheres are differentially involved in causal inference generation. Participants read short inference-promoting texts that described either familiar or less-familiar scenarios. After each text, they performed a lexical decision on a letter string (which sometimes constituted an inference-related word) presented directly to the left or right hemisphere. Response-time results indicated that hemisphere of direct presentation interacted with type of inference scenario. When test stimuli were presented directly to the left hemisphere, lexical decisions were facilitated following familiar but not following less-familiar inference scenarios, whereas when test stimuli were presented directly to the right hemisphere, facilitation was observed in both familiar and less-familiar conditions. Thus, inferences may be generated in different ways depending on which of two dissociable neural subsystems underlies the activation of background information.

R. M. Nosofsky, R. D. Stanton, & Safa R. Zaki, Associate Professor of Psychology

Memory & Cognition, 33, 1256-1271 (2005)

Researchers have argued that an implicit procedural-learning system underlies performance for information integration category structures, whereas a separate explicit system underlies performance for rule-based categories. One source of evidence is a dissociation in which procedural interference harms performance in information integration structures, but not in rule-based ones. The present research provides evidence that some form of overall difficulty or category complexity lies at the root of the dissociation. The authors report studies in which procedural interference is observed for even simple rule-based structures under more sensitive testing conditions. Furthermore, the magnitude of the interference is large when the nature of the rule is made more complex. By contrast, the magnitude of interference is greatly reduced for an information integration structure that is cognitively simple. These results challenge the view that a procedural-learning system mediates performance on information integration categories, but not on rule-based ones.

Nicholas A. Bamat ’04, Susan A. Brunelli, Michelle M. Kron ’04, Andrew R. Schulte ’03, and
Betty Zimmerberg, Professor of Psychology

Neurotoxicology and Teratology, 27, 883-890 (2005)

Glue sniffing is epidemic among children living in poverty in Latin America. Previous research has shown that abused inhalants such as toluene share pharmacological properties with anxiolytic drugs, and that personality factors such as degree of anxiety have been proposed to modulate the effects of these drugs. To study this interaction in an animal model, rats selectively bred for high (High) or low (Low) rates of distress calls after maternal separation (ultrasonic vocalizations, USVs) were used to investigate toluene's acute and long-term effects on two measures of anxiety behavior. At ten days of age, neonatal subjects were administered toluene (1 g/kg i.p.) and USVs were recorded. The subjects were retested as juveniles on an elevated plus maze to examine sequela of earlier toluene exposure. Acute toluene administration reduced USVs relative to control groups in neonates of both lines, indicating anxiolysis. As expected, Lows had reduced USVs relative to Highs. At 28 days of age, Highs spent more time in the open arms of the elevated plus maze than Lows. However, prior neonatal toluene exposure blocked this reversal of behavioral phenotype. This suggests that early toluene exposure compromised a compensatory process occurring during this developmental period, which may have been maternally mediated. These results have implications for the effects of early drug exposure on plasticity in the developing nervous system.

Rosemary Eseh ’04 & Betty Zimmerberg, Professor of Psychology

Behavioural Brain Research, 164, 214-221 (2005)

Gestational iron deficiency (ID) has been linked to alterations in GABA neurotransmission, but whether these neuronal changes are mirrored in altered anxiety behavior in rats is not known. In this experiment, two tests of GABA-related affective behaviors in rats, ultrasonic vocalizations (USVs) and elevated plus maze (EPM) were used to investigate the consequences of maternal ID. Female rats were randomly assigned to one of three diet groups: low iron (10-20 ppm Fe), recommended (standard) iron control (60 ppm Fe) or lab chow (250 ppm Fe) control. Diets started 7 days prior to mating and continued until 10 days after birth (PN10). Maternal behavior and offspring growth and activity were also assessed. Blood samples taken on PN10 revealed a significant decrement in serum iron and an increase in total iron binding capacity in the low iron groups compared to the two control groups. Relative to the two control groups, the low iron group weighed less on PN1, and this weight difference persisted in adulthood. In neonates, the rate of USVs in the low iron group was significantly higher than the two control groups, and their general activity was significantly less than the controls. Maternal behavior was not significantly different across groups. By adulthood, anxiety behavior and motor activity in the low iron group were comparable to controls, although the iron deficient subjects habituated more slowly. This study shows that prenatal iron deficiency results in increased anxiety behavior in neonates that appears to be reversed with iron repletion but that some aspects of altered exploratory behavior and growth persist into adulthood.

Susan A. Brunelli, Rui Nie ’05, Clare Whipple ‘05, Vivian Winiger ‘05, Myron A. Hofer, Betty Zimmerberg, Professor of Psychology

Physiology and Behavior. 87, 527-536 (2006)

For over 25 generations, two lines of rats (High and Low USV lines) have been selectively bred for extreme rates of infantile (45 kHz) ultrasonic vocalizations (USV) in response to maternal separation at postnatal day (P)10. High and low line juveniles (P30-P40) were socially isolated and allowed to play in same-sex sibling pairs for 10 min per day over three days. Measures of play were nape contacts and pinning. Other social and nonsocial behaviors were also scored during the three sessions; two of these, 55 kHz USV and walk-overs, were statistically associated with play. Compared to the Random control line, both High and Low line juveniles showed deficits in play behavior. In the High line, play initiatory behavior (nape contacts) was reduced, but pinning, USV and walk-overs were relatively unchanged. In contrast, nape contacts, pinning, USV and walk-overs were all reduced in Low line juveniles compared to Random line controls. The results suggest that selection for extremes of infant USV rates has produced temperamental differences that are expressed in juvenile play in the High and Low USV lines.

C. Frye, K. Sumida, Betty Zimmerberg, Professor of Psychology, & S. A. Brunelli

Behavioral Neuroscience, 120, 281-289 (2006)

Duration and intensity of lordosis is mediated by actions of the progesterone (P) metabolite, 3 alpha-hydroxy-5 alpha-pregnan-20-one (3 alpha,5 alpha-THP) at GABA-sub(A) receptors in the midbrain ventral tegmental area. Because rats selectively bred for infantile vocalizations may differ in endogenous 3 alpha,5 alpha-THP secretion, their sexual behavior, midbrain, and plasma 3 alpha,5 alpha-THP levels as adult rats in behavioral estrus was examined. Rats bred for high rates of infantile vocalizations had shorter latencies and intervals between intromissions and ejaculation, higher lordosis quotients and ratings, more pacing of their sexual contacts, and had higher P and 3 alpha,5 alpha-THP levels in plasma and midbrain than did rats bred for low rats of infantile vocalizations. Thus, levels of 3 alpha,5 alpha-THP in the midbrain are associated with differences in sexual behavior of these rats.