FACULTY PUBLICATIONS

We report on our observations of the occultation of the star P131.1 by Pluto in August 2002, and on the light curve we measured at the 2.2-m University of Hawaii telescope on Mauna Kea, as well as SpeX infrared observations with the NASA Infrared Telescope Facility and other observations with telescopes on Mauna Kea, on Haleakala, and at the Palomar Observatory and the Lick Observatory. We report on drastic changes in Pluto’s atmosphere since the 1988 observations of a Pluto occultation, including an overall expansion.

The Owl Nebula is a triple-shell planetary nebula with the outermost shell being a faint bow-shaped halo. We have obtained deep narrowband images and high-dispersion echelle spectra in the H, [O III], and [N II] emission lines to determine the physical structure of each shell in the nebula. These spatiokinematic data allow us to rule out hydrodynamic models that can reproduce only the nebular morphology. Our analysis shows that the inner shell of the main nebula is slightly elongated with a bipolar cavity along its major axis, the outer nebula is a filled envelope coexpanding with the inner shell at 40 km s-1, and the halo has been braked by the interstellar medium as the Owl Nebula moves through it. To explain the morphology and kinematics of the Owl Nebula, we suggest the following scenario for its formation and evolution. The early mass loss at the TP-AGB phase forms the halo, and the superwind at the end of the AGB phase forms the main nebula. The subsequent fast stellar wind compressed the superwind to form the inner shell and excavated an elongated cavity at the center, but this has ceased in the past. At the current old age the inner shell is backfilling the central cavity.

John Bevis produced a magnificently illustrated star atlas in about 1748, but his publisher went bankrupt, leaving only the copper plates. The plates were more detailed and included more constellations than Bayer’s epochal atlas of 1603. They were the first to show several important astronomical objects, including the Crab Nebula, which Bevis had discovered. (Bevis also observed the transits of Venus of 1761 and 1769 and the sole known transit of one planet in front of another for hundreds of years.) Both Bevis's and Bayer's plates were based on zodiacal, rather than equatorial coordinates. Some bound sets of the atlas, under the name Atlas Celeste, were sold in 1786. We incorporate and bring up to date the description of Bevis's accomplishments and the history of Bevis's publication laid out by William Ashworth in 1981. We describe, collate, and tabulate 23 existing atlases, not all complete, almost double the number known to Ashworth.

A popular description of how stars of different masses evolve, including their very different fates.

This paper is the fourth in a series whose purpose is to study the interstellar abundances of sulfur, chlorine, and argon in the Galaxy using a sample of 86 planetary nebulae. Here we present new high-quality spectrophotometric observations of 20 Galactic planetary nebulae with spectral coverage from 3700 to 9600 Å. A major feature of our observations throughout the entire study has been the inclusion of the near-infrared lines of [S III] 9069,9532, which allows us to calculate accurate S+2 abundances and to either improve upon or convincingly confirm results of earlier sulfur abundance studies. For each of the 20 objects here, we calculate ratios of S/O, Cl/O, and Ar/O and find average values of S/)=(1.1±1.1) x 10-2, Cl/O=(4.2±5.3) x 10-4, and Ar/O=(5.7±4.3) x 10-3. For six objects, we are able to compare abundances of S+3 calculated directly from available [S IV] 10.5m measurements with those inferred indirectly from the values of the ionization correction factors for sulfur. In the final paper of the series, we will compile results from all 86 objects, search for and evaluate trends, and use chemical evolution models to interpret our results.

Popular summaries of the asteroid extinction of the dinosaurs and other species, the broiling Sun we expect in a few million years, exploding stars (supernovae), and the accelerating Universe.

Review of Philip Glass, Arnold Weinstein, and Mary Zimmerman’s opera Galileo Galilei, as performed at the Brooklyn Academy of Music.

We discuss eight trecento (fourteenth century) paintings containing depictions of astronomical events to reveal the revolutionary advances made in both astronomy and naturalistic painting in early Renaissance Italy, noting that an artistic interest in naturalism predisposed these pioneering painters to make their scientific observations. In turn, the convincing representations of their observations of astronomical phenomena in works of art rendered their paintings more believable, convincing. Padua was already a renowned center for mathematics and nascent astronomy (which was separating from astrology) when Enrico Scrovegni commissioned the famous Florentine artist Giotto di Bondone to decorate his lavish family chapel (c. 1301-3). Giotto painted a flaming comet in lieu of the traditional Star of Bethlehem in the Adoration of the Magi scene. Moreover, he painted a historical apparition that he recently had observed with a great accuracy even by modern standards: Halley's Comet of 1301 (Olson, 1979). While we do not know the identity of the artist's theological advisor, we discuss the possibility that Pietro d'Abano, the Paduan medical doctor and "astronomer" who wrote on comets, might have been influential. We also compare Giotto's blazing comet with two others painted by the artist's shop in San Francesco at Assisi (before 1316) and account for the differences. In addition, we discuss Giotto's pupil, Taddeo Gaddi, reputed to have been partially blinded by a solar eclipse, whose calamity may find expression in his frescoes in Santa Croce, Florence (1328-30; 1338?). Giotto also influenced the Sienese painter Pietro Lorenzetti, two of whose Passion cycle frescoes at Assisi (1316-20) contain dazzling meteor showers that reveal the artist’s observed astronomical phenomena, such as the “radiant" effect of meteor showers, first recorded by Alexander von Humboldt in 1799 and only accepted in the nineteenth century. Lorenzetti also painted sporadic, independent meteors, which do not emanate from the radiant. It is also significant that these artists observed differences between comets and meteors, facts that were not absolutely established until the eighteenth century. In addition we demonstrate that artistic and scientific visual acuity were part of the burgeoning empiricism of the fourteenth century, which eventually yielded modern observational astronomy.

Storey Publications, North Adams, MA (2003)

Forest Ecol. and Management , 6250, 1-17 (2003

We investigated the effects of strip width, slope position, and soil scarification in a split–split plot design on the regeneration of northern hardwoods in northwestern Massachusetts. Whole plots of 20 and 40 m in width were cut in 1954 in a second growth forest dominated by Betula papyrifera. Slope position and soil scarification were the split and split–split plot treatments, respectively. We measured height for all tree species present in randomly located 4 m2 plots beginning in 1955 and at irregular intervals over the following 42-year period. We measured all trees in the cut strips in 1996. Prunus pensylvanica was the dominant species initially, but had nearly disappeared from the cut strips by 1996. Soil scarification significantly increased initial establishment of B. papyrifera, but density and basal area of this species did not differ by soil treatment in 1996. Tree composition in cut strips was weakly correlated with soil moisture, soil scarification, and initial tree density immediately following cutting, but high spatial variation in species composition and low replication made it difficult to detect any significant correlations among the distribution and abundance of different species and selected environmental variables. The canopy of the cut strips is even-aged; establishment of most canopy trees occurred within 5 years following cutting. A comparison of successional trends in adjacent uncut strips with the trends in the cut strips indicates that cutting has altered the sequence of successional changes in forest composition increasing the abundance of some species that were of low importance prior to cutting. In 1996, Acer rubrum and A. saccharum are replacing B. papyrifera in the canopy of the uncut strips. The canopy of the cut strips consists of a diverse and spatially varying mixture of intermediate hardwoods including Quercus rubra, Fraxinus americana, Betula lenta, Acer rubrum, B. papyrifera, and an understory of late successional hardwoods.

Life Science Ethics (G. Comsock, ed.) 269-271 Iowa State Press (2002)

Population Viability in Plants, (C.A. Brigham & M.W. Schwartz, eds.) 267-287 Berlin Heidelberg (2003)

Amer. J. Physiol, 283, R583-R590 (2002)

By performing multidisciplinary hands-on science research, 6-10 high school students each year develop their critical thinking, logical reasoning, scientific writing and presentation skills. Supervised by Williams College Electron Spin Resonance (ESR) Lab staff, students prepare teeth and other fossils from archaeological and paleontological sites for ESR dating. They are involved in the all aspects of the research, except those directly involving radiation, from selecting and preparing the fossil samples for dating, to running the Williams ESR spectrometer, and calculating ages. Mentored by the scientists, students prepare detailed reports to publish in scientific journals and present their data at scientific conferences, science fairs, and to science classes in their home schools.

Transient electronic absorption monitors the flow of vibrational energy in methylene iodide (CH2I2) following excitation of five C-H stretch and stretch-bend modes ranging in energy from 3000 cm-1 to 9000 cm-1. Intramolecular vibrational relaxation (IVR) occurs through a mechanism that is predominantly state-specific at the C-H stretch fundamental but closer to the statistical limit at higher excitation levels. The IVR times depend on the excitation energy for the fundamental and first C-H stretch overtone but are constant above the overtone. The intermolecular energy transfer (IET) times depend only weakly on the initial excitation level. Both the IVR and the IET times depend on the solvent (CCl4, CDCl3, C6D6, C6H6, or (CD3)2CO) and its interaction strength, yet there is no energy level dependence of the solvent influence.

Transient electronic absorption spectroscopy monitors the population of intermediate states in the vibrational relaxation of the iodo-substituted methanes, CHI3, CH2I2, and CH3I, in solution after excitation of the fundamental C-H stretching vibration. These experiments give times for both intra- and intermolecular energy flow for each molecule. The trend in intramolecular vibrational energy redistribution (IVR) times shows that the local vibrational state structure around the initially prepared states in each molecule, not the overall state density, controls IVR. Comparison of experiments in the solvents chloroform and acetone reveals the solvent role in IVR and shows a strong solvent effect on the intermolecular energy transfer (IET).

An upper level undergraduate inorganic chemistry experiment in which students synthesize a series of octahedral cobalt (III) complexes of the type Co(dmgH)2Br(L) and Co(dmgH)2Me(L), where L can be a variety of substituted pyridines or imidazoles is described. The electronic structure of the series of complexes can be examined using 1H NMR spectroscopy and cyclic voltammetry. Shifts in the 1H NMR methyl resonance can be directly correlated with the electron donating ability of the base and therefore the electron density at the metal center. Similarly, cyclic voltammetric studies reveal a significant shift in the reduction potentials, consistent with changes in the electron donating ability of the axial base, while the oxidation potentials are largely unaffected by the identity of the axial ligand.

To explain the inconsistency in the representation of the dz2 orbital in many textbooks, we considered the contour and polar representation of orbitals. Most introductory textbooks use the polar representation in their discussions, but the dz2 orbital seems to be most misrepresented orbital. In particular it is represented with a “lifesaver” middle section. We argue that this shape belongs to the contour representation and is inconsistent with the polar representation.

Methylcoenzyme M reductase (MCR), which contains a square planar nickel corphin cofactor, F430, catalyzes the final step in methane biosynthesis in methanogenic Archaea. Recent mechanistic proposals for this enzyme suggest that the putative organonickel intermediates may react via a free radical pathway. Benzylnickel complexes employing 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (tmc) have been prepared and their homolytic Ni–C bond dissociation energies determined by kinetic methods. The kinetics of decomposition of Ni–CH2Ph(tmc)+ in acetonitrile, in the presence of excess Ni(tmc)+, are consistent with reversible homolysis of the nickel benzyl bond followed by a recombination of benzyl radicals according to the rate law –d[Ni–CH2Ph(tmc)+]/dt = kobs[Ni–CH2Ph(tmc)+]2, where kobs = 2(k42k5)/(k–42)[Ni(tmc)+]2. From the activation parameters (benzyl: H‡obs = 40.6 ± 0.6 kcal/mol, S‡obs = 61.8 ± 2.0 cal/mol•K; p-fluorobenzyl: H‡obs = 38.4 ± 1.9 kcal/mol, S‡obs = 55.1 ± 6.5 cal/mol•K; p-chlorobenzyl: H‡obs = 34.2 ± 5.8 kcal/mol, S‡obs = 39.5 ± 20.2 cal/mol•K) the following Ni–C bond dissociation energies were deduced: benzyl, 19 ± 1 kcal/mol; p-fluorobenzyl, 18 ± 2 kcal/mol; p-chlorobenzyl, 16 ± 5 kcal/mol.

The Lower Beds at Olduvai Gorge are well known for containing early hominid fossils and Oldowan stone tools, and their ages have been established by 39Ar/40Ar dating and paleomagnetic stratigraphy. Ages are generally less certain for the upper deposits at Olduvai Gorge because of the scarcity of datable tuffs. The youngest archaeologically significant site at Olduvai is microlithic LSA, which lies in the type section of the Naisiusiu Beds. The age for the site is controversial, with 14C dates of 17.000-17,550 (Hay, 1976) and >42,000 BP (Manega, 1993). The tuff bed in the zone with artifacts does not contain materials datable by 39Ar/40Ar, and some other dating method was needed. In the summer of 2001, five equid teeth were collected from the type Naisiusiu site. Another tooth had previously been collected. ESR ages have been determined for three teeth from the archaeological level and their ages cluster around 62 ± 5 ka, assuming linear uranium uptake. Another tooth from a level without artifacts and believed to be significantly younger dated to 39 ± 5 ka, again assuming LU. These dates are considerably older than previous estimates and suggest that the East African MSA/LSA transition occurred very early.

Fossil teeth seem perfect chronometers for ESR dating. The signal is very stable, and hydroxyapatite (HAP) is a sensitive dosimeter, giving spectra with large and reproducible peaks. However, these assets are in part offset by various technical problems, especially the open system uranium uptake problem. Uranium appears to enter the enamel by simple diffusion from enamel (or, in some cases, directly from the sediment). Advances in several areas are reported here, but most emphasis in on new information about uptake. We have to approximate uptake by one of several relatively simply models. Model ages are most variable in older samples with larger internal dose effects, relative to external doses.

Skinner et al. (2001) reported that Q-band spectroscopy shows enamel fossilization is accompanied by crystal structure breakdown. Unlike diagenesis, this does not affect the signal intensity and the samples are still datable. However, then the uptake mechanism varies with time. Initial uptake experiments into modern dentine showed that uptake is rapid. However, some of this uranium is probably lost as the collagen breaks down and leaches out of the tooth. New results show differential uptake by modern and fossil dentine. There is also highly suggestive evidence that the rate of diffusion increases with age. Putting these conclusions together will allow more confident dating of old fossil teeth.

A model system for side chain fragment coupling to the core of hennoxazole A is investigated. Lateral metallation of a C13-TBS-protected bisoxazole, using lithium diethylamide, allows for selective and efficient alkylation at C15.

Several heteroaromatic systems, including oxazoles, pyrazoles, and thiophenes, are regioselectively alkylated using lithium diethylamide. Effects of substrate, base, and electrophile on the selectivity of this process are surveyed and interpreted.

PolyTOIL is a new statically-typed polymorphic object-oriented programming language that is provably type-safe. By separating the definitions of subtyping and inheritance, providing a name for the type of self, and carefully defining the type-checking rules, we have obtained a language that is very expressive while supporting modular type-checking of classes. The matching relation on types, which is related to F-bounded quantification, is used both in stating type-checking rules and expressing the bounds on type parameters for polymorphism. The design of PolyTOIL is based on a careful formal definition of type-checking rules and semantics. A proof of type safety is obtained with the aid of a subject reduction theorem.

This issue contains papers selected from the sixth Workshop on the Foundations of Object-Oriented Languages (FOOL), held in San Antonio, Texas on January 23, 1999, in conjunction with the 26th ACM Symposium on Principles of Programming Languages (POPL ’99). The workshop consisted of one-invited lectures, and seven contributed papers selected by the program committee. The four papers in this issue were selected from those presented at the workshop.

The Scrubber 3 system monitors problems in the local loop of the telephone network, making automated decisions on tens of millions of cases a year, many of which lead to automated actions. Scrubber saves Bell Atlantic millions of dollars annually, by reducing the number of inappropriate technician dispatches. Scrubber’s core knowledge base, the trouble isolation module (TIM) is a probability estimation tree constructed via several data mining processes. TIM currently is deployed in the Delphi system, which serves knowledge to multiple applications. As compared to previous approaches, TIM is more general, more robust, and easier to update when the network or user requirements chance. Under certain circumstances it also provides better classifications. In fact, TIM’s knowledge is general enough that it now serves a second deployed application. One of the most interesting aspects of the construction of TIM is that data mining was used not only in the traditional sense, namely, building a model from a warehouse of actual historical cases, but it was also used to produce an understandable model of the knowledge contained in an earlier, successful diagnostic system, which had evolved into opacity over years of operation.

Many important software systems are written in the C programming language. Unfortunately, the C language does not provide strong safety guarantees, and many common programming mistakes introduce type errors that are not caught by the compiler. These errors only manifest themselves at run time through unexpected program behavior, and it is often hard to isolate and identify their causes. This paper presents the Hobbes run-time type checker for compiled C programs. Our tool interprets compiled binaries, tracks type information for all memory and register locations, and reports warnings when a variety of type errors occur. Because the Hobbes type checker does not rely on source code, it is effective in many situations where similar tools are not, such as when full source code is not available or when C source is linked with program fragments written in assembly or other languages.

Proceedings of the 10th International Symposium on the Foundations of Software Engineering, Charleston, South Carolina, November 2002.

Dynamic load balancing is an essential tool for parallel adaptive computation. It has been an important research topic for more than a decade. The Zoltan library provides applications with a reusable, object-oriented interface to several load balancing algorithms, including coordinate bisection, octree/space filling curve methods, and multilevel graph partitioners. It allows run-time selection among balancing techniques, facilitating comparisons. It also provides a framework in which to modify existing algorithms or to implement new algorithms. We compare the performance of several available methods as mesh partitioners and as dynamic load balancers for an adaptive computation. Partition quality metrics and running times of the balancers and the solution process are measured for several methods. We also examine the effect of octant granularity for the Zoltan octree partitioning algorithm, and describe a modification of the recursive coordinate bisection algorithm that bisects along only one coordinate axis, to achieve a “slice” partitioning, designed to minimize interprocessor adjacency.

Quartzite, conglomerate and shale of the Mazatzal Group record filling of a Proterozoic intra-arc basin in central Arizona. U-Pb ages of zircons from rhyolite ash flow tuff indicate that deposition began at 1701 ± 2 Ma. Basal deposits of the newly defined Pine Creek Conglomerate formed in an alluvial fan setting, synchronous with the final phase of extrusive rhyolite volcanism and active faulting. After volcanic activity ceased, shallower-slope braided-stream environments developed in early Deadman Quartzite time. Subsequent marine transgression produced shallow subaqueous deposits of the upper part of the Deadman Quartzite. These were overlain by pro-delta sediments of the Maverick Shale, indicating a phase of basin deepening. Finally, the Mazatzal Peak Quartzite was deposited as the basin shoaled again, first to shallow marine and subsequently to fluvial conditions.

The quartzite is diagenetic quartz arenite, originally deposited as lithic arenite and lithic arkose. The provenance was initially restricted, and earliest sediment was derived mainly from the subjacent Red Rock Group. When tectonic activity ceased, however, the surrounding highlands were planed down by erosion and detritus from a wider variety of source rocks was funneled into the basin. This included contributions from arc-related supracrustal rocks of the Payson Ophiolite and East Verde River Formation, and finally a granitic basement input. Detrital quartz in the lower part of the Mazatzal Group is largely monocrystalline, and volcanic in origin. Polycrystalline quartz, associated with detrital feldspar and of probable continental affinity, is concentrated in the uppermost parts of the sequence.

The life span of the intra-arc basin was on the order of 30 m.y., from the formation of the Payson Ophiolite at 1.73 Ga to the deposition of the Mazatzal Peak Quartzite sometime after 1.70 Ga. The pre-Mazatzal Red Rock Group represents the last stages of volcanic arc activity, and the Mazatzal Group records the transition from orogenic to non-orogenic sedimentation in central Arizona.

Cosmogenic 26Al, 10Be, and 14C dating of fluvial fill terraces in steep canyons of the Colorado Front Range provide a temporal framework for analyzing episodic aggradation and incision. Results from Boulder Canyon show that terrace heights above the modern channel (grade) can be divided into (1) Bull Lake (> ~100 ka; 20 - 15 m above grade); (2) Pinedale (32-10 ka; 15 – 4 m above grade); and (3) Holocene age (<4 m above grade). No pre-Bull Lake deposits are preserved along Boulder Canyon and only three small remnants >15 m above grade record Bull Lake deposition. Well-preserved terraces of Pinedale age suggest that the range of terrace height above grade reflects short-term fluctuations in the river profile during periods of rapidly changing stream load and power. Net river incision apparently occurred during transitions to interglacial periods. Soil development and stratigraphic position, along with limited cosmogenic and 14C dating, suggest that ~130 ka terraces in Boulder Canyon correlate with the Louviers Alluvium, and that 32 to 10 ka fills in the Canyon correlate with the Broadway Alluvium on the adjacent High Plains. Late Pleistocene incision rates (~0.15 m ka-1) along Boulder Canyon exceed pre-late Pleistocene incision rates, and are higher than middle to late Pleistocene incision rates (~0.04 m ka-1) on the High Plains. This study provides an example of how modern geochronologic techniques allow us to understand better rivers that drain glaciated catchments.

Discharge and annual bedload measurements from the 1.25 km2 South Branch of Birch Brook, NW Massachusetts, show that the annual flux of bedload was 2.0 tons km-2 yr-1 from this forested basin between 1986 and 2000. Sediment transport by the South Branch is controlled by discharge events above bankfull (0.34 m3 s-1) and the relative availability of sediment in the stream channel, particularly material stored by organic debris dams. Peak discharge events explain 91% of the variance in measured sediment discharge on the South Branch during the period 1986 to 1996. After 1996, however, correlation is poor, reflecting a change in sediment availability after sediment year 1996, when sediment flux was 5 times average values.

Analyzing the sediment budget for the Birch Brook catchment permits us to speculate about how deforestation, grazing and cultivation in the 19th century affected hillslope erosion and stream sediment load. Higher sediment loads during the past century may have produced the low terraces that line the lower reaches of Birch Brook. The present rate of sediment transport from the Birch Brook catchment suggests that the erosion rate from forested catchments in NW Massachusetts is low.

Rates of long-term erosion across the Rocky Mountain region help to constrain the relative roles of tectonic uplift, climatic change and rock resistance in sculpting the modern landscape. We measured concentrations of cosmogenic nuclides in quartz extracted from stream sediment from 13 catchments to provide estimates of erosion rates at time scales from 103 to 105 yr. Preliminary analysis of 10Be activity from small (< 50 km2), upland catchments in Colorado and Wyoming indicates that the landscape is lowering at rates between 14 and 250 m/MY in this semiarid area. We sampled basins that: (1) have not been glaciated; (2) have only small volumes of sediment stored beneath terraces and in colluvium; and (3) display minimal evidence for anthropogenic disturbance. We measured the 10Be content of the 250 to 710 mm sand fraction collected in cross-channel transects. Our initial data do not show strong influence of basin relief, average slope, drainage area, tectonic environment, or climate. However, the range of erosion rates from different lithologies suggests that relative rock resistance exerts strong control on landform evolution in the Rocky Mountain region. Catchments draining weathered Precambrian basement (granites and gneisses) typical of the northern Front, Laramie and Medicine Bow Ranges give erosion rates of 18 to 30 (24 ± 6; n=9) m/MY. Weakly lithified Middle and Upper Cenozoic basin fill is eroding at rates of 45 to 250 m/MY at sites in southern Wyoming and northern Colorado. Precambrian quartzite exposed in the eastern Uinta Mountains gave a rate of 14 m/MY, the lowest we measured. Erosion rates measured in upland granitic and gneissic catchments in Colorado are comparable to those measured in other non-orogenic areas such as the southern Appalachians. If our initial measurements for erosion rates of weakly lithified basin fill are typical, most of the middle and late Cenozoic fill in the greater Wyoming area could have been stripped in the past 5 to 10 million years.

In the past two decades, retreat of the Mendenhall Glacier near Juneau, Alaska, has exposed a bedrock ridge spotted with “siltskins,” patchy coatings of calcite-cemented clay to sand-sized lithic grains. Coatings range from 0.5 to 20 mm thick and occur in two distinct morphologies. Striated siltskins are thin, located mainly on stoss faces, and preserve local striation direction. Thicker, corrugated skins preserved on lee faces consist of parallel microridges elongate downslope. Thin section analysis shows that siltskins consist of a basal, calcite-rich layer overlain by microlaminated layers of calcite-cemented lithic grains. Microstrata in layers of corrugated siltskins display complex internal structures including wavy microlaminae, truncated cross-bedding, convolute forms, and pockets of larger grains. SEM/EDS analysis of siltskin laminae and surfaces show laterally persistent Ca/Si differences. Isotopic values of ∆O18 and ∆C13 ranged from -19.52 to -12.74 and -6.18 to -3.44, respectively in five samples of cement, consistent with deposition from subglacial waters of varying isotopic concentrations and with derivation of carbon from inorganic sources. Regelation processes probably caused precipitation of the basal calcite layer from ice enriched in Ca. After the basal layer reached a limiting thickness, deposition of microlaminae of the upper layer dominated. The relatively thick corrugated siltskins we studied are depositional features enhanced by erosional processes. Wavelengths of parallel microridges generally range from 1 to 10 mm and apparently formed as sediment-rich water dripped or oozed down lee slope rock faces. Ice-rock separation, flow energy, and the amount and grain size of transported sediment controlled the layering and depositional forms. Deposition of siltskins depended on macro-scale processes in the glacier system, outcrop-scale features of the rock ridge, and micro-scale interactions of the ice, bedrock, and thin films of water in the regelation layer. Siltskins probably formed when a subglacial cavity system was active on the rock ridge, probably within the last 60 years. Siltskins provide clues about how micro-scale hydrologic processes interact with larger-scale subglacial systems.

Marine islands belong to discrete geographic realms attended by persistent patterns of oceanic and atmospheric circulation. Wet and dry vegetation zones on the opposite sides of Hawaii, for example, result from northeasterly trade winds in an open-ocean setting. Distinct windward and leeward shores are due to variations in wave exposure. The Channel Islands off southern California meet northwesterly winds that push the California Current and its associated upwelling along the west coast of North America. Other islands within the Gulf of California are influenced by seasonal shifts in winter and summer winds related to a semi-monsoonal pattern of atmospheric circulation. Ancient islands preserved in the rock record as drowned monadnocks provide a direct link to a comparable range of climatic and oceanographic interactions through Phanerozoic time. Exemplary case studies, one each from the Paleozoic, Mesozoic, and Cenozoic eras, are reviewed with respect to geography, ecology, and climate. They include the Ordovician Jens Munk Archipelago on Hudson Bay in Manitoba (Canada), the Cretaceous island group on the Pacific shores of northern Baja California (Mexico), and the Pliocene Santa Inés Archipelago from the Gulf of California in Baja California Sur (Mexico). Key physical features shared in common include sedimentary ramps with 6º–12º slopes constructed on basal conglomerates that incorporate debris from eroded basement rocks. Biological attributes shared in common are contrasting biofacies indicative of distinct windward and leeward environments.

The name Jens Munk Archipelago is proposed for a cluster of small monadnocks that rise a maximum of 45 m above present sea level on the shores of Hudson Bay in the Churchill area of northern Manitoba. Resistant Precambrian quartzite formed shoals and islands during the Late Ordovician and Early Silurian periods. Outcrop control in the present tundra environment of the Hudson Bay Lowlands is spotty at best, but the quartzitic monadnocks are fringed by Upper Ordovician and Lower Silurian ramp deposits, mainly carbonate in composition. Five isolated outliers of Ordovician-Silurian strata are described and the location of four other potential outliers is indicated. Ramp dip at any one site generally ranges from 10º to 15º and the surviving ramps on opposite flanks of paleoislands suggest preservation of near synsedimentary conditions. Extensive conglomerates of reworked quartzite are most abundant on a northern exposure within the islands. Ripple marks and oriented cephalopod debris are related to a vigorous long-shore current generated by northeasterly trade winds that emanated from a subtropical high-pressure cell in the Northern Hemisphere. A paleogeographic reconstruction links the Jens Munk Archipelago of Manitoba to a larger landmass with a Precambrian quartzite core centered over northern Saskatchewan. The general paleoecology of the Jens Munk Archipelago conforms to patterns of windward and leeward facies preserved on other paleoislands of various ages.

The Silurian continent of Baltica was a small-to-medium sized craton approximately 7.8 million km2 in size. Silurian outcrops cover one percent of the area of this former continent, although the extent of subsurface Silurian strata is appreciable. Stratigraphic patterns influenced by tectonic and eustatic cycles are documented from 25 lithologic and bathymetric profiles drawn from four principal areas in the Central Scandinavian, East Baltic, Dniester, and Timan–Pechora depressions. Baltica was bounded on its west flank by the developing Scandian orogen, which resulted from the closure of the Iapetus Ocean. On its southwest flank, Baltica underwent a collision with the microcontinent of Avalonia. The remaining continental margin was passive. Separate base maps for central Scandinavia, the combined East Baltic region and Dniester River area of Podolia, and the Timan–Pechora region of northwestern Russia allow reconstruction of approximately 35% of Baltica and its shelf margins. Paleogeographic maps are provided for Baltica through the Llandovery, Wenlock, and Ludlow series, but exclude the youngest Pridoli Series due to insufficient or unavailable data. Primary control of continental and marine sedimentation was exerted by tectonic factors, but the secondary imprint of eustasy is preserved in the stratigraphic record of Baltica’s mid-shelf sectors.

This road log describes three stops on the Loreto to Santa Rosalia transect [day 1] and five stops on the Santa Rosalia to Punta Chivato transect [day two], all in Baja California Sur, Mexico. Pliocene relationships are described at Arroyo Arce, the Bahia Concepción Basin at the base of the Concepción Peninsula, El Requeson, Arroyo El Purgatorio, Punta Cacarizo, Punta Cerotito, west flank of the Punta Chivato promontory, and Mesa Las Barracas.

A field trip guide to the Chester Dome, Vermont, area.

Tectonic models for the Devonian Acadian orogeny in the New England Appalachians typically invoke two major periods of crustal shortening: an early phase of recumbent folding followed by an upright doming event. In the western part of the Acadian orogen, Devonian deformation overprinted the Ordovician Taconic thrust belt. An alternative interpretation of the numerous domes in the western part of the Acadian orogen is that they record large-scale ductile extension. Evidence for extension includes dramatic tectonic thinning of Paleozoic units and synmetamorphic exhumation of footwall rocks. The best evidence for normal faulting is in the Chester dome in southeastern Vermont. There stratigraphic separation diagrams clearly show that Cambrian and Ordovician units have been excised by faulting; locally Middle Proterozoic basement rocks are separated from Silurian units by less than 0.5 km! Acadian extension occurred during garnet-grade metamorphism on low-angle, nearly planar normal faults. Kinematic indicators reveal that hanging wall rocks were displaced to the southwest. The Chester dome is defined by a folded mylonitic foliation. During dome-stage folding, the mylonitic foliation and the tops-to-the-southwest kinematic indicators, such as C-S fabrics and rotated porphyroclasts, were complexly overprinted by simple shear into different patterns on the east and west sides of the dome. Acadian extension was most likely the result of gravitational collapse following surface uplift and thermal weakening of the lower crust.

Two N-S trending sets of gneiss domes in New England dominate the western Acadian belt. One belt is west of the Connecticut Valley trough (CVT) and is cored by fragments of Laurentian basement and rocks of the Early Ordovician Shelburne Falls arc (SFA). The other is west of the Kearsarge-Central Maine trough (KCMT) and is cored by Late Proterozoic gneisses and rocks of the Late Ordovician Bronson Hill arc (BHA). The CVT and KCMT contain Silurian and Devonian metasediments that were rapidly deposited just before collision between Laurentia and Avalon. Collision caused dramatic shortening of the Silurian and Devonian basin deposits expressed as large-scale, west-verging nappes, which were overprinted during the doming phase of the Acadian orogeny. The domes are commonly elongated N-S and some preserve evidence for shear zones between the quartzo-feldspathic gneisses in the cores and the overlying metasediments. The western Acadian belt is narrow (~50 km) in Conn., Mass., and southern Vt.-N.H., but widens considerably in northern Vt.-N.H. and Maine.

Crustal shortening during collision between Laurentia and Avalon appears to have been greatest in southwestern New England and to have decreased northward. Middle to upper crustal rocks were extruded westward as nappes from the CVT and KCMT over the SFA and BHA, respectively. In contrast, more rigid lower crustal blocks, including rocks of the SFA, BHA, and fragments of Laurentian basement, were extruded northward relative to Laurentia. Early crustal thickening by nappe formation may have made extrusion of rigid blocks more energetically favorable than horizontal shortening in the lower crust. During northward extrusion the quartzo-feldspathic blocks moved upward relative to the overlying metasediments producing extensional shear zones with NNE-SSW displacement. Ongoing E-W compression lead to N-S elongation and steep dips on the E and W limbs of the domes. Extrusion also produced differential uplift recorded by large and abrupt E-W variations in P conditions of Acadian metamorphism.

Middle Proterozoic rocks of the Laurentian margin were thrust westward over Cambrian and Ordovician continental shelf deposits during the Taconic orogeny in the Berkshire massif. Dating this deformation would constrain the time of collision between Laurentia and the Ordovician Taconic arc and help discriminate between competing models for the orogeny. Discontinuous tabular bodies of alaskite were mapped by Ratcliffe (1984a,b; 1985) within the Berkshire massif and interpreted by him as syntectonic anatectic melts that intruded Taconic thrusts. The alaskite sills are most commonly found in the granitic Middle Proterozoic Tyringham Gneiss and many of the mapped Taconic thrusts within the massif closely follow the distribution of the alaskite bodies. We collected one sample of the Tyringham Gneiss and fourteen samples of alaskite, ranging in composition from granite to trondhjemite, for SHRIMP analysis to date the age of thrusting in the Berkshire massif. Zircons from the Tyringham gneiss contain cores with oscillatory zoning and thin homogeneous rims. The weighted average of eight 238U/206Pb analyses from the cores is 1179 + 9 Ma, while nine 238U/206Pb spot analyses from the rims yield an age of 1004 + 9 Ma; we interpret these to represent the crystallization age of the Tyringham Gneiss protolith and subsequent high grade metamorphism, respectively. Zircons from two samples of alaskite commonly contain xenocrystic cores that yield a wide range of ages from approximately 1050 to 1200 Ma surrounded by broad rims that commonly display oscillatory zoning. Many grains also show oscillatory zoning with no cores. The weighted average of sixteen 238U/206Pb analyses from grains without cores and rims of grains with cores in one alaskite sample is 997 + 5 Ma, and the weighted average of eight analyses from the second sample is 1004 + 19 Ma. We suggest that the alaskite bodies formed during the Ottawan phase of the Grenville orogeny and that they have no connection to the Taconic orogeny. The basal contact between Middle Proterozoic rocks of the Berkshire massif and underlying Early Paleozoic rocks is clearly a thrust, but many contacts within the Berkshire massif mapped as Taconic thrusts must either be Middle Proterozoic faults or, more likely, intrusive contacts between older basement gneisses and younger anatectic melts.

Uncertainties about the origin of the many disequilibrium or “vital effects” in a variety of calcifying organisms, and whether these effects are constant or variable, has hampered paleoceanographic application of carbon and oxygen isotopic ratios. Unraveling the source of these effects will improve paleoceanographic applications and may provide new information on changes in cell physiology and ecology. Culture of eight species of coccolithophorids, a dominant marine phytoplankton group, reveals a 5‰ array of disequilbrium or “vital effects” in both the carbon and oxygen isotopic composition of coccolith calcite. In moderate light and nutrient-replete cultures, oxygen isotopic fractionation (e18O) and carbon isotopic fractionation (e13C) correlates directly with cell division rates and correlates inversely with cell size across a range of species. However, when growth rates of a single species are increased or decreased by higher or lower light levels, e18O is relatively invariant. Likewise, growth rate variations as a function of temperature do not influence coccolith e18O; the slope of the e18O vs. temperature relation in cultures of both Gephyrocapsa oceanica and Helicosphaera carteri is the same as for abiogenic carbonates. These suggest a constant, species-specific isotopic fractionation, which does not vary with cell physiology. The constancy of vital effects suggests that coccolith stable isotopes will provide reliable phase for paleoceanographic reconstruction of temperature and seawater chemistry, as long monospecific fractions are analyzed or changes in nannofossil assemblages are accounted for with species-specific correction factors. We suspect that the cell size, and its constraints on the rate of CO2 diffusion relative to C fixation, may be the first order influence on coccolith stable isotope vital effects. A quantitative model of this process may provide important constraints on mechanisms of carbon acquisition of coccolithophorids in both modern and extinct species.

A major perturbation of the global carbon cycle ~55 million years ago, believed to result from release of 1000-2000 Gt of C from methane hydrates, correlates with an intense but transient greenhouse warming event known as the Paleocene Eocene Thermal Maximum (PETM). The rapid (105 yr) recovery of global temperatures reflects important negative feedbacks in the climate system and carbon cycle. Enhanced marine productivity may be one important feedback, but indicators for productivity changes have yielded conflicting results. Here we use a new independent indicator, Sr/Ca in coccolith carbonate which covaries with the productivity of coccolithophorid algae, to investigate the biotic response in the most complete PETM deep sea record which was recovered at ODP Site 690B in the Weddell Sea. In the dominant coccolithophorid genus Toweius, a large (40%) Sr/Ca increase immediately after the gas hydrate release signals a dramatic productivity increase. Productivity levels remain high for 60,000 years but decrease to pre-event levels by 120,000 years after the gas hydrate release. Productivity levels during the PETM are higher than observed at any other time in our -400,000 year record. Other coccolithophorid genera Chiasmolithus and Discoaster show a brief, modest (25% Sr/Ca increase) increase in productivity that lags behind the methane event by 50,000 years and is within the range of productivity variation elsewhere in the record. The timing of the Toweius productivity increase agrees well with Os isotope records of increased weathering intensity, which may have provided higher nutrient fluxes to stimulate algal productivity. If this type of productivity response occurred globally, it would also be consistent with the timing of C drawdown that may have returned temperatures to near pre-event levels.

The intense but transient greenhouse warming event known as the Paleocene Eocene Thermal Maximum (PETM) is linked with a major perturbation of the global carbon cycle, believed to result from release of 1000-2000 Gt of C from methane hydrates. Questions remain about the initial timing of warming and methane release and the nature of negative feedbacks in the carbon cycle which aided the rapid recovery of the climate system. Using Sr/Ca in coccolith carbonate, a new indicator of the productivity of coccolithophorid algae, we examine whether enhanced marine productivity may have been an important feedback in carbon cycle recovery. Recent advances in separating restricted fractions of coccoliths allow us to obtain species-specific Sr/Ca records across the PETM in sediments from ODP site 690 in the Weddell Sea and ODP 1209 at Shatsky Rise in the Pacific. At site 690, in the dominant coccolithophorid genus Toweius, a large (40%) Sr/Ca increase immediately after the carbon isotope excursion signals a dramatic productivity increase. Productivity levels remain high for 60,000 years but decrease to pre-event levels within 120,000 years. Productivity levels during the PETM are higher than observed at any other time in our -400,000 year record. Other coccolithophorid genera Chiasmolithus and Discoaster show a brief, modest (25% Sr/Ca increase) increase in productivity that lags behind the methane event by 50,000 years and is within the range of productivity variation elsewhere in the record. The timing of the Toweius productivity increase in Site 690 agrees well with Os isotope records of increased weathering intensity, which may have provided higher nutrient fluxes to stimulate algal productivity. If this type of productivity response occurred globally, it would also be consistent with the timing of C drawdown that may have returned temperatures to near pre-event levels. Results from ODP 1209 are pending.

Details of the relative timing of PETM warming and methane release are inferred from stable isotope records, but the onset of stable isotope shifts differ between coccolith-dominated bulk carbonate and single-specimen planktonic foraminiferal records. Using stable isotope analyses on separated Toweius fractions, we will be able to confirm or refute whether these discrepancies are due to changing coccolith assemblages and vital effects in the bulk records.

Geochim. Et Cosmochim. Acta, 66 (1), 719 (2003)

Nonequilibrium or “vital effects” on isotopic or elemental partitioning in biogenic carbonates have recently evolved from enemies to allies in a number of paleoceanographic applications. This transition has been especially pronounced in the chemistry of coccoliths, tiny calcite plates produced intracellularly by marine coccolithophorid algae. Recent culture experiments with a number of species have assessed the extent to which their chemistry is controlled by chemical kinetic versus biological factors.

Sr/Ca ratios of coccoliths show strong kinetic effects with coccolithophorid growth and calcification rates [1,2]. These trends are observed for different growth rates of a single species as well as among different species. A similar kinetic effect of Sr partitioning on crystal growth rates has been observed in abiogenic calcites and is hypothesized to reflect surface enrichment effects [3]. Models of crystal growth in coccoliths suggest that surface enrichment effects can explain some of the Sr/Ca variation observed in culture. Higher amplitude Sr/Ca variations observed in surface sediments require an additional mechanism, likely related to the kinetics of ion transport into and within the cell.

Stable isotope fractionation in coccoliths varies widely among different species. e18O is highly correlated to the different maximum growth rates of different species under light saturated and nutrient replete conditions [4]. Unlike the case for Sr/Ca, e18O is nearly constant over a range of growth rates for a single species and e18O is not correlated with different rates of calcite precipitation in different species. Consequently, similar mechanisms related to the kinetics of calcite precipitation cannot be applied for both elemental and isotopic effects. e18O covaries with e13C, with a break point to constant e13C but variable e18O at the lowest ratios. These patterns of covariation are tantalizingly similar to those observed in deep sea corals [5]. However, the mechanism of calcification rate-dependent supply of CO2 vs. “leak” of seawater HCO3- into the calcifying region proposed for corals [5] cannot be applied to intracellular calcification of coccolithophorids. The mechanism of stable isotopic effects in coccoliths remains a mystery, albeit a more clearly delineated one.

GSA Abstracts with Programs, 34 (6), 42 (2002)

The coastal Maine Magmatic Province exposes volcanic rocks that erupted onto and plutonic rocks that intruded into Avalonian crust prior to Acadian accretion. Correlation of the volcanic rocks within the province is problematic, hindering the development of robust tectonic models for this portion of Avalon. We present U-Pb dates from a key volcanic sequence exposed on and around Vinalhaven Island in Penobscot Bay that clarify regional correlation of volcanic units.

The volcanic sequence in the Vinalhaven area is interbedded with fossiliferous sedimentary rocks interpreted as Late Silurian to Early Devonian in age. However, these rocks are intruded by the Vinalhaven pluton which yields a U-Pb zircon date of 420.3 ± 0.5 Ludlovian age that is not consistent with ages interpreted from the fossiliferous units; specifically the Ames Knob Formation and the Seal Cove Formation. The Ames Knob Formation contains a diverse faunal assemblage interpreted as Wenlockian to Lockhovian (Berry & Boucot, 1970; Gates, 2001), whereas the stratigraphically higher Seal Cove Formation contains poorly preserved ostracodes interpreted to be Lockhovian (Brookins et al., 1974).

To investigate this temporal discrepancy, we determined U-Pb zircon dates from silicic volcanic rocks from Vinalhaven that stratigraphically bracket the fossiliferous units. A lithic-poor vitrophyre collected near the base of the section in the Polly Cove Formation (correlative to the Ames Knob Formation) yields a preliminary U-Pb zircon date of 425.8 ± 0.9. A lithic-poor welded tuff from the Vinalhaven rhyolite (stratigraphically higher than the Seal Cove Formation) yields a preliminary U-Pb zircon date of 420.2 ± 2.5. These dates are consistent with both the local field relationships and with published U-Pb ages of the Cadillac Mountain granite and the Cranberry Island volcanic series exposed on and around Mt. Desert Island, Maine (Seaman et al., 1995). Our initial results indicate that the Vinalhaven/North Haven layered sequence - from the basal Ames Knob Formation to the upper Vinalhaven rhyolite - was deposited/erupted (and folded) prior to ca. 420 Ma. These rocks and the fossils they contain are Silurian. If reevaluation of the fossil assemblages does not resolve the age discrepancy, then perhaps the Silurian time scale requires further calibration.

Volcanic rocks intruded by the Vinalhaven pluton are interbedded with the fossiliferous strata of the Ames Knob Formation and the Seal Cove Formation. The Ames Knob Formation contains a diverse faunal assemblage interpreted as Wenlockian to Lockhovian in age (Berry & Boucot, 1070; Gates, 2001), whereas the stratigraphically higher Seal Cove Formation contains poorly preserved ostracodes, corals and brachiopods interpreted to be Lockhovian in age (Brookins et al., 1974). However, a new U-Pb age for the Vinalhaven pluton (420.3 ± 0.5 Ma) apparently conflicts with the interpreted fossil ages. This apparent conflict is important to resolve because the fossil age of the Ames Knob Formation has been used to correlate volcanic units throughout the Coastal Volcanic Belt (CVB) of Maine and New Brunswick.

To investigate this temporal discrepancy, we determined U-Pb zircon ages for silicic volcanic units that stratigraphically bracket the Ames Knob Formation and the overlying Seal Cove Formation. The oldest silicic volcanic rock in the sequence occurs in the Polly Cove Formation, which is correlative with the Ames Knob Formation (Gates 2001). This lithic-poor welded tuff yields a U-Pb zircon date of 426 ± 1 Ma, indicating the Ames Knob fossil assemblages are of Wenlockian age. A lithic-poor welded tuff from the Vinalhaven rhyolite (stratigraphically higher than the Seal Cove Formation) yielded zircon crystals with complex growth histories, and our initial attempts to date the rock have produced a preliminary magmatic age. The zircon crystals appear to be binary mixtures of two growth domains: early Cambrian (ca. 540 Ma) cores and 420 ± 2 Ma magmatic mantles. The age of both the Ames Knob Formation and the Seal Cove Formation are no younger than the Pridolian.

We suggest three first-order implications. First, the range of the brachiopod genus Quadrifarius, described from a number of localities in the CVB (Berry & Boucot 1970), should be extended to Ludlovian time. Second, the strata on Vinalhaven are contemporaneous with the Cranberry Island volcanic series exposed on and around Mt. Desert Island, Maine (Seaman et al., 1995) and the Eastport volcanics (Gates & Moench, 1981). Finally because the volcanic strata were folded prior to intrusion of the pluton, the timing of deformation in this area is tightly constrained to about 420 Ma.

The cusp density of a hyperbolic 3-manifold is the ratio of the largest possible volume in a set of cusps with disjoint interiors to the volume in the manifold. It is known that all cusp densities fall in the interval [0, .853...]. It is shown that the cusp densities of finite volume orientable hyperbolic 3-manifolds are dense in this interval.

This paper is an introduction to supercrossing index for knots and links, which is related to crossing index in the same way that N. Kuiper's superbridge index is related to bridge index. A variety of results on supercrossing index and the associated crossing map are given.

An Italian translation of "The Shape of the Universe: Ten Possibilities", which appeared in American Scientist in 2001.

A Chinese version of this humorous supplement to calculus.

How mathematics can take over someone's life and turn them into a creature unlike anything seen before.

The battle lines are drawn. It is the students against the professors as they confront the final exam and fight for their lives.

How the birth of a new theorem parallels human birth.

How did Andrew Wiles come up with his proof of Fermat's Last Theorem? Just what was he doing in the attic all those years.

Here we construct U-numbers having pre-subscribed diophantine structure for which effective measures of irrationality are computed.

Here in a humor style, we give an introduction to p-adic numbers and construct infinite series that possess incredible convergence properties.

Here we answer a question posed by Davenport in 1947 regarding diophantine inequalities exhibiting only finitely many solutions. As a consequence of the results introduced here, a quantitative version of the classical Lagrange spectrum is found.

We create a moduli space tiled by cyclohedra, analogous to the Deligne-Mumford space of real stable curves of genus zero. We explore the structure of this space, coming from blow-ups of hyperplane arrangements, as well as discuss possibilities of its role in knot theory and mathematical physics.

A personal perspective on data mining.

Discussion of the scope of Data Mining and how it differs from Statistics.

Results from the NSF workshop on curriculum for a major in Statistics.

A paper showing no memory improvement for healthy participants taking recommended doses of Ginkgo Biloba.

Poster session at the 2003 annual meeting of the American College of Neuropsychiatrists.

It was previously unknown whether or not there existed an integral domain A such that A/I is complete for all nonzero ideals I, but the dimension of the generic formal fiber of A is not zero. In this paper, we construct such integral domains that are not only excellent, but we also show that the generic formal fiber of A can be forced to be local and conclude that the dimension of the generic formal fiber can be controlled.

In this paper, we construct examples of nonexcellent local domains for which tight closure and completion do not commute. In addition, we construct an example of a complete local normal Gorenstein domain which is not F-regular but is the completion of an F-regular local ring.

We show that a k-dimensional area-minimizing surface can pass through an acute conical singularity if and only if k  3. The larger k, the more acute the conical singularity can be.

We use the second variation formula to compute instabilities for certain cylindrical bubble clusters and compare to earlier simulations, experiments, and computations of Cox, Weaire, and Fortes.

In this paper, we find the best possible upper bound of the Hilbert transform (an operator important in harmonic analysis and the theory of differential equations), as an operator in weighted L2 space on the disk.

In this paper, we show that the continuous square function has a nice bound in weighted L2 space.

DNA beacons are short single-stranded chains which can form closed hairpin shapes through complementary base pairing at their ends. Contrary to the common polymer theory assumption that only their loop length matters, experiments show that their closing kinetics depend on the loop composition. We have modeled the closing kinetics and in so doing have obtained stacking enthalpies and entropies for single-stranded nucleic acids. The resulting change of persistence length with temperature effects the dynamics. With a Monte Carlo study we answer another polymer question, how the closing time scales with chain length, finding  ~ N2.44±0.02. There is a significant crossover for shorter chains, bringing the effective exponent into good agreement with experiment.

Optically excited semiconductors provide an ideal model system for the study of many body interactions. Recent breakthroughs in theory and experiment have revealed unique signatures of individual Coulomb-correlated many-body interactions, up to the six-particle level. Experiments are performed using ultrafast spectroscopy, so that the Coulomb-correlated quasi-particles can be measured on time scales short compared with their dephasing times. The simultaneous progress in theory and experiment in this field has resulted in a burst of collaborative activity, yielding detailed understanding of the influence of each many-body term. In this work we present the new experimental and theoretical techniques which have allowed such rapid progress. We also summarize the results which have been achieved thus far, and present the outstanding questions which are the subject of current study.

We have observed the formation of ground-state Na2 molecules via the spontaneous decay of excited molecules created by the photoassociation of ultracold atoms. We measure the binding energies created in three hyperfine components of the lowest singlet and triplet potentials of Na2 by two different methods. Two of the features are purely triplet a 3∑u+ (=15) (quasibound) states that have not been previously observed, while the third is a mixed X 1∑g+ —  3∑u+ state. The molecules are detected with high-resolution cw laser ionization techniques and binding energies are measured to within 10 MHz.

Using a thallium atomic beam apparatus and a stabilized, frequency-doubled diode laser system, we have measured the scalar Stark shift in the 6P1/2 — 7S1/2 transition of thallium. We determine the Stark shift to be ∆s = -103.23(39) kHz / (kV/cm)2 providing more than an order of magnitude improvement in precision over earlier measurements of this quantity. This measurement serves as a stringent new test of recently published thallium parity nonconservation calculations.

Consider an infinite collection of qubits arranged in a line, such that every pair of nearest neighbors is entangled: an “entangled chain.” In this paper we consider entangled chains with translational invariance and ask how large one can make the nearest neighbor entanglement. We find that it is possible to achieve an entanglement of formation equal to 0.285 ebits between each pair of nearest neighbors, and that this is the best one can do under certain assumptions about the state of the chain.

In a system of n quantum particles, we define a measure of the degree of irreducible n-way correlation, by which we mean the correlation that cannot be accounted for by looking at the states of n-1 particles. In the case of almost all pure states of three qubits, we show that there is no such correlation: almost every pure state of three qubits is completely determined by its two-particle reduced density matrices.

We show that almost every pure state of multiparty quantum systems (each of whose local Hilbert space has the same dimension) is completely determined by the state’s reduced density matrices of a fraction of the parties; this fraction is less than about two-thirds of the parties for state of large numbers of parties. In other words, once the reduced states of this fraction of the parties have been specified, there is no further freedom in the state.

This article defines a notion of a parallel transport in a lattice of quantum particles, such that the transformation associated with each link of the lattice is determined by the quantum state of the two particles joined by that link. We focus particularly on a one-dimensional lattice – a ring – of entangled rebits, which are binary quantum objects confined to a real state space. We consider states of the ring that maximize the correlation between nearest neighbors, and show that some correlation must be sacrificed in order to have non-trivial parallel transport around the ring. An analogy is made with lattice gauge theory, in which non-trivial parallel transport around closed loops is associated with a reduction in the probability of the field configuration. We discuss the possibility of extending our result to qubits and to higher dimensional lattices.

The von Neumann entropy and the subentropy of a mixed quantum state are upper and lower bounds, respectively, on the accessible information of any ensemble consistent with the given mixed stat. Here we define and investigate a set of quantities intermediate between entropy and subentropy.

The relation between the use of defense mechanisms and autonomic nervous system reactivity, under conditions of laboratory stress, was studied in 78 men and women. Both diastolic blood pressure (DBP) and skin conductance level (SCL) were monitored during exposure to ten stress tasks; concurrently, the use of three defense mechanisms was assessed by coding Thematic Apperception Test stories. Autonomic reactivity was found to be related to defenses; the nature of that relation differed across the defenses. DBP, typically found to be associated with cognitive work, was higher in those individuals who used more Identification, a defense that requires greater cognitive activity. The use of Projection, on the other hand, was associated with lower DBP. In addition, the use of Identification showed a tendency to be associated with lower SCL.

Evidence for both stability and change in Big 5 personality traits was found for both men and women over a 24 year time period. The use of the defense mechanisms of denial, projection and identification at early adulthood was found to be related to early adult personality traits, and to predict change in personality traits in middle adulthood and late middle age. Significantly, the importance of defense mechanisms for predicting personality change increased with age, while the importance of IQ decreased. The use of the immature defenses of denial and projection predicted increased Neuroticism, decreased Extraversion, and decreased Agreeableness. However, in interaction with IQ, defense mechanisms were found to have a compensatory effect, in that low IQ in combination with strong defense use predicted a more favorable personality outcome.

This study examined the effect of social context on the extent to which young men express their emotions, in particular, sadness. Sadness was induced in 87 college men, who were then brought into a room with two confederates (2 men or 2 women) and asked to talk about their feelings. This followed either expression of sadness by one confederate (while the second confederate listened either in a manner accepting of emotional expression or in a neutral manner) or withholding of sadness expression by the speaking confederate. The entire procedure was videotaped, and five aspects of participants’ sadness expression were coded or rated. In general, participants expressed significantly more sadness in the presence of expressive, accepting, and (to a lesser extent) male confederates. Clinical and research implications of these findings are discussed.

A two-phased experiment tested the hypothesis that the presumption of guilt that underlies police interrogations activates a process of behavioral confirmation. In Phase I, 52 suspects guilty or innocent of a mock theft were questioned by 52 interrogators led to believe that most suspects were guilty or innocent. Interrogators armed with guilty as opposed to innocent expectations selected more guilt-presumptive questions, used more interrogation techniques, judged the suspect to be guilty, and exerted more pressure to get a confession—particularly when paired with innocent suspects. In Phase II, neutral observers listened to audiotapes of the suspect, interrogator, or both. They perceived suspects in the guilty expectations condition as more defensive—and as somewhat more guilty. Results indicate that a presumption of guilt sets in motion a process of behavioral confirmation by which expectations influence the interrogator’s behavior, the suspect’s behavior, and ultimately the judgments of neutral observers.

Detecting deception is an inherently difficult task but one that plays a critical role for law enforcement investigators in the interrogation room. In general, research has failed to indicate that performance in this domain is improved by training or prior experience. We applied a signal detection framework to the paradigm in attempting to better conceptualize the influence of these factors. We found that while there was no effect on discrimination accuracy, there was an effect on response bias such that training and prior experience increase the likelihood of responding "deceit" as opposed to "truth". This "investigator bias" was observed both in a review of the literature and in the present study of North American law enforcement investigators who took part in a deception detection task. Possible theoretical mechanisms and practical implications of these findings are discussed

Previous research has consistently found that the decline in the present values of delayed rewards as delay increases is better fit by hyperbolic than by exponential delay-discounting functions. However, concave utility, transaction costs, and risk each could produce hyperbolic-looking data, even when the underlying discounting function is exponential. In Experiments 1 (n = 45) and 2 (n = 103) participants placed bids indicating their present values of real future monetary rewards in computer-based 2nd-price auctions. Both experiments suggest that utility is not sufficiently concave to account for the superior fit of hyperbolic functions. Experiment 2 provided no evidence that the effects of transaction costs and risk are large enough to account for the superior fit of hyperbolic functions.

Delay-discount rates (or rates of time preference) are associated with rates of consumption and a variety of impulsive behaviors. Despite the importance of discounting, little is known about its covariates. We estimated discount rates for money and candy rewards in each of four quarters for 154 Tsimane’ Amerindians (10 to 80 years of age). The Tsimane’ are a horticultural and foraging society in the tropical rain forest of Bolivia. Discount rates increased with age, decreased with educational levels and literacy, and tended to decrease as recent income rose. Rates were not associated with wealth, nutritional status, or moderate drug use. There were low but reliable correlations between discount rates across quarters, suggesting that a person’s discount rate is a somewhat stable characteristic that is also strongly influenced by situational factors.

Objective: Substance misusers are often considered impulsive, but it is unclear whether impulsivity precedes substance misuse or develops as a consequence of it. Because alcohol dependence has a clear familial component, a study comparing impulsivity in nonaffected individuals who differ with respect to paternal history of alcohol dependence may provide evidence of familial vulnerability to impulsivity. Method: 122 healthy individuals participated, none of whom misused alcohol or drugs; 58 were paternal history positive (PHP) and 64 were paternal history negative (PHN) for alcohol dependence. The paternal-history groups were balanced on gender, and the four paternal-history-by-gender groups were comparable with respect to demographic features. Participants were offered choices between monetary rewards (e.g., $34) available immediately and larger rewards (e.g., $50) available after delays ranging from 1 week to 6 months. This task measures a construct of impulsivity by assessing the rates at which individuals discount rewards delayed in time. Results: Although discount rates in PHP men did not differ reliably from those in PHN men, PHP women had higher discount rates than PHN women. Post hoc contrasts revealed that PHN women had lower discount rates than the other three groups. Similar results were obtained when age, education, socioeconomic status, and scores on a measure of sociopathy were used as covariates. Conclusions: Paternal history of alcohol dependence is associated with greater discount rates among women. The lack of an effect for men may suggest different mechanisms by which risk is transmitted from alcohol-dependent fathers to daughters compared with sons. Further research examining these relations and the implications that delay discounting has for drinking and related behaviors is warranted.

Female Sprague-Dawley rats received approximately 300 mg/kg per day of choline chloride through their drinking water on days 11 of pregnancy through birth and the level of nerve growth factor (NGF) in the hippocampus and frontal cortex of their male offspring was measured at 20 and 90 days of age. Prenatal choline supplementation caused significant increases in hippocampal NGF levels at 20 and 90 days of age, while levels of NGF in the frontal cortex were elevated in choline-supplemented rats at 20 days of age, but not 90 days of age. These results suggest that increases in NGF levels during development or adulthood may be one mechanism underlying improvements in spatial and temporal memory of adult rats exposed to elevated levels of choline chloride perinatally.

When people commit an embarrassing blunder, they typically overestimate how harshly they will be judged by others. This tendency can seem to fly in the face of research on the correspondence bias, which has established that observers are, in fact, quite likely to draw harsh dispositional inferences about others. These seemingly inconsistent literatures are reconciled by showing that actors typically neglect to consider the extent to which observers will moderate their correspondent inferences when they can easily adopt an actor’s perspective or imagine being in his or her shoes. These results help to explain why actors can overestimate the strength of observers’ dispositional inferences even when, as the literature on the correspondence bias attests, observers are notoriously prone to drawing those very inferences.

Recent reviews of cognitive theories of depression have noted that individualized assessment strategies might help to resolve mixed findings regarding the stability of depressotypic beliefs and attitudes. We describe encouraging results for an individualized measure of one such cognitive construct, irrational beliefs. Twenty depression-prone women (recurrent major depressives in full remission) and twenty closely matched never-depressed controls completed leading forced-choice measures of irrational beliefs (the Belief Scale; BS) and sociotropy-autonomy (The Revised Personal Style Inventory), as well as the Specific Demands on Self Scale (SDS). The BS requires participants to rate their agreement with twenty preselected statements of irrational beliefs, while the SDS focuses on whether participants harbor any strongly held irrational beliefs, even if uncommon or idiosyncratic. Consistent with previous research, there were no group differences on the traditional measure of irrational beliefs. In contrast, depression-prone participants strongly exceeded controls on the SDS, and this difference persisted after controlling for residual depression, anxiety symptoms, anxiety diagnoses, sociotropy, and autonomy. These findings provide some initial support for a key assumption of the rational-emotive model of depression, and, more broadly, suggest that individualized assessment strategies may help researchers capture the core negative beliefs of asymptomatic individuals, even in the absence of mood or cognitive priming.

Previous research has demonstrated dissociations between categorization and recognition performance in amnesic patients, supporting the idea that separate memory systems govern these tasks. However, previous research has also demonstrated that these dissociations are predicted by a single-system model that allows for reasonable parameter differences across groups. Generally, previous studies have employed categorization tasks that are less demanding than the recognition tasks. In the current study, the authors distinguish between single-system and multiple system accounts by testing two sets of memory-impaired individuals in a more demanding categorization task. These patients, just like previous amnesic participants, show dissociation between categorization and recognition when tested in previously employed paradigms. However, they display a categorization deficit when tested in the more challenging categorization task. The results are interpreted as support for a single-system framework in which categorization and recognition depend on one representational system.

J. D. Smith and colleagues (J. P. Minda & J. D. Smith, 2001; J. D. Smith & J. P. Minda, 1998, 2000; J. D. Smith, M. J. Murray, & J. P. Minda, 1997) presented evidence that they claimed challenged the predictions of exemplar models and that supported prototype models. In the authors' view, this evidence confounded the issue of the nature of the category representation with the type of response rule (probabilistic vs. deterministic) that was used. Also, their designs did not test whether the prototype models correctly predicted generalization performance. The present work demonstrates that an exemplar model that includes a response-scaling mechanism provides a natural account of all of Smith et al's experimental results. Furthermore, the exemplar model predicts classification performance better than the prototype models when novel transfer stimuli are included in the experimental designs.

R. M. Nosofsky and S. R. Zaki (2002) found that an exemplar similarity model provided better accounts of individual subject classification and generalization performance than did a mixed prototype model proposed by J. D. Smith and J. P. Minda (1998; J. P. Minda and J. M. Smith, 2001). However, these previous tests used a nonlinearly separable category structure. In the present work, the authors extend the previous findings by demonstrating a superiority for the exemplar generalization model over the mixed prototype model in a case involving a linearly separable structure. Because this structure has numerous features that Minda and Smith argued should be conducive to prototype-based processing, the results pose a significant challenge to the mixed prototype view.

Some of the behavioral deficits caused by prenatal or postnatal alcohol exposure have been demonstrated to be ameliorated by environmental manipulations such as handling or environmental enrichment. This experiment, in contrast, investigated whether behavioral deficits due to prenatal alcohol exposure could be exacerbated by a stressful experience, early weaning. Pregnant dams were given either a liquid diet with 35% of the calories derived from alcohol, a liquid diet without alcohol to control for any effects of the liquid diet administration, or ad libitum food and water. Half of each litter were weaned at 15 days of age (Early Weaning) and half were weaned at 21 days of age (Normally Weaned). Offspring were weighed, tested for activity in an open field at 18 days of age, and trained to find a hidden platform in the Morris water maze at 22 to 24 days of age. Alcohol exposed subjects who were weaned early were more impaired in spatial navigation ability than any other group. Similarly, the combination of early weaning and prenatal alcohol exposure caused the slowest growth. All subjects exposed to alcohol, regardless of weaning condition, had greater latencies to find the platform than those from the two control groups. There was no synergistic effect of alcohol and stress on activity levels, but all early-weaned females were more active than normally weaned females; males did not show this effect. Thus environmental stressors such as early weaning can compound detrimental symptoms of prenatal alcohol exposure. These results have implications for the understanding of the effects of the environment on neuronal plasticity.

The development of emotional behavior is dependent on the early experiences of the infant and the quality of maternal care. In these experiments, the effects of social isolation during the pre-weaning period on both pup behavior and maternal responsivity were examined. In the first study, the number of ultrasonic vocalizations (USVs) emitted after brief maternal separation was measured in neonatal rats with differing histories of social isolation. The social isolation procedure consisted of five days of daily separation from the dam and littermates for either three or six hours. At both ages tested, socially isolated pups vocalized significantly less than control pups. In the second study, the effects of prior isolation, either daily for five previous days (Chronic Isolation) or for four hours prior to testing (Acute Isolation) were examined in a T-maze choice test. Pup vocalizations in the presence of the dam and dams’ maternal behavior were assessed. When the dam was confined to the start box or during the maternal free access period, both Chronic and Acute Isolates vocalized less than pups who had never left the home nest. Dams spent more time with, and licked and groomed more frequently and for a longer time both Chronic and Acute Isolates compared to pups who had always been with dams in the home nest. These results suggest that early isolation experience can alter subsequent responses to separation stress in neonatal rats, and that maternal behavior is sensitive to the prior experiences of offspring.