STUDENT ABSTRACTS

We have built and tested a new experimental apparatus for performing differential phase shift spectroscopy of the forbidden 6P_1/2 —> 6P_3/2 1283nm E2/M1 transition in atomic thallium, detecting two relatively frequency-shifted laser beams after passing in counter-propagating directions in a three-mirror Fabry-Pérot ring cavity. A separate laser locking system has achieved frequency stabilization to a better than 0.3 MHz; when used in conjunction with the ring cavity’s length stabilization apparatus, the optical system can resolve a differential phase sensitivity of ~ 10 µrad/√Hz. In addition to addressing these experimental details, modeling of differential phase shift measurements made with a thallium atomic beam intersecting one pass of each probe beam predicts a signal size within this resolution for the mentioned weak transition. This work is one of a number of preliminary steps toward a future experiment which will attempt to measure a fundamental T-odd P-even force that would represent physics beyond the Standard Model (adapted from an experiment proposal by [Koz89]). Future experimental steps are described at the end of this work.

This thesis reports the results of the MIT-Williams collaboration to observe Charon occultation C313.2. We provide a historical overview of past stellar occultations by objects in the Solar System, with particular emphasis on occultations by Pluto, Charon, and Kuiper Belt Objects. We develop a method by which the vital parameters of an occulting body, such as physical size and atmospheric variables, can be determined by comparison with a theoretical model. We will also describe a means of predicting the path of an occultation on the Earth given certain parameters provided by a suite of Mathematica software at MIT. From our observations of C313.2, we measure a radius of Charon of 606±8 km, implying a bulk density of 1.72±0.15 g/cm³ and rock-mass fraction of 0.63±0.05, consistent with a collisional formation scenario for the Pluto-Charon system. We also discuss the results of other teams that observed C313.2.

We present the results of a study of the physical properties of solar spicules observed with the Transition Region and Coronal Explorer satellite and the Swedish 1-m Solar Telescope on La Palma in 2004 and 2005. We have developed and improved an IDL routine, followspicule, capable of measuring the heights, velocities, and inclinations from images taken in three wavelengths: H, Ca II H, and 1600 Å. We report spicule heights and inclinations for 490 spicules in H, 28 in Ca II H, and 67 in 1600 Å. Comparing parabolic and linear curve fits of spicule trajectories, we attempt to confirm either ballistic or constant velocity spicule behavior. In addition, we examine the intensity changes and apparent motion of individual spicules to infer chromospheric heat flow and mass transfer and search for evidence of sheathed vs. monolithic spicule models.

We conduct a study of flares for multiple young stellar clusters using ANCHORS (An Archive of Chandra Observations of Regions of Star Formation) data and flare criteria derived previously from COUP (Chandra Orion Ultradeep Project). Stellar flares are strong disturbances in magnetic field structure in stellar atmospheres that result in violent outbursts of plasma and radiation. Understanding flares and identifying stars and young stellar objects that flare aids in understanding stellar magnetic field structures as well as evolution of protoplanetary disks and stellar environments. As a part of the ANCHORS data base creation, we subject our sources’ light curves to Bayesian Blocks analysis, which allows us to search for flaring behavior. While COUP presents a large catalog of stars with extensive variability sampling from the Orion Cloud region, ANCHORS data offers a complimentary sample from a variety of environments. We present the results of our study in a form of select light curves, detailed description of flaring detection algorithm, and a summary of flares found and some of their physical properties. The ANCHORS project is supported by Chandra archival grant AR5-6002A and NASA contract NAS8-39073. (http://cxc.harvard.edu/symposium_2005/proceedings/stars_wd.html - abs04)

BIOLOGY

Prochlorococcus belongs to the cyanobacterial lineage and is a dominant member of the photosynthetic biomass in subtropical and tropical regions of the world’s open oceans. One area our laboratory is focusing on involves the impacts of environmental stress on the photosynthetic physiology and biochemistry of Prochlorococcus. The research in this thesis examines the effects of high light stress on Prochlorococcus strain MIT9313, which represents a major Prochlorococcus ecotype in the world’s oceans. Specifically, the work in this project characterizes the effects of light stress on cell division and pigment levels of Prochlorococcus MIT9313, and its capacity for recovery. When shifted from a growth irradiance of 20 µmol photons m-2s-1 to 100 µmol photons m-2s-1, high light-stressed MIT9313 cells exhibited significant decreases in both cell numbers and chlorophyll concentrations compared to controls. Although light-stressed cells did not exhibit immediate recovery upon return to the original growth conditions, preliminary data suggest that over longer time periods, recovery might occur. In addition, both the duration of the light stress treatment and the irradiance level of the actual light stress, have significant effects on the extent of the light stress-induced decrease in cell and chlorophyll concentrations. As part of this research project, comparative genomic analyses of several peripheral proteins in the Photosystem I reaction center complex — PsaF, PsaJ, PsaK, PsaL, and PsaM — were also conducted. These polypeptides play an important role in protein-protein and pigment interactions in the photosynthetic apparatus. Knowledge of the molecular responses of Prochlorococcus to environmental stress is critical given the abundance of this photosynthetic prokaryote in the world’s oceans and its importance in global biogeochemical cycles.

A single base-pair substitution in the ALDH2 gene causes an inability to process alcohol. The ALDH2 deficiency allele shows an unusual geographic distribution across human populations previously hypothesized to be under selection (Peterson, 1999 & Oota, 2004). Signatures of recent positive selection were not detected using multi-site analysis of LD through tests of Extended Haplotype Homozygosity. Re-sequencing a 5.8kb region surrounding the ALDH2 deficiency allele showed no signs of recent positive selection or balancing selection using tests of the frequency spectrum. However, using HapMap data, a highly unusual pattern of gender specific differences in allele frequencies were observed over an approximately 1Mb region suggesting that this pattern is occurring as result of sex-specific selection on a surrounding gene.

Agrobacterium tumefaciens is a soil-dwelling bacterium that infects a wide range of dicotyledonous plants, inciting crown gall tumors. A. tumefaciens carries a large tumor-inducing plasmid bearing a virulence regulon that encodes a Type 4 Secretion System (T4SS). The bacterium transfers a strand of DNA, the T-strand, through the T4SS to the plant host. The T-strand stably integrates into the plant cell genome and the cell expresses the genes therein. The T-strand includes genes inducing plant cell division and the synthesis of a carbon/nitrogen source for the bacteria, thereby providing the bacteria with a unique, permanent ecological niche. By substituting the T-strand DNA with genes that suit human purposes, A. tumefaciens has been used successfully to create genetically modified plants. Only the plants that are susceptible to infection by A. tumefaciens can be genetically modified by it. Of the operons in the virulence regulon, the virC operon consists of two genes, virC1 and virC2, and is a host range determinant. An intact virC operon expands the range of plant species that Agrobacterium can successfully infect. VirC1 and VirC2 enhance the T-strand production and virulence of Agrobacterium tumefaciens. We tested for an interaction between VirC1 and VirC2 by co-purifying the proteins in vitro with affinity agarose. VirC2 bound to VirC1 irrespective of changes to the VirC1 ATPase motif. Affinity purification of VirC1 with ATP-agarose showed that VirC1 binds ATP. Site-directed mutagenesis altering the conserved ATP-binding lysine in the VirC1 ATPase motif to glutamine did not affect the ability of VirC1 to bind ATP. The interaction between VirC1 and VirC2 modulates the affinity of VirC1 for ATP.

Birdsong is a learned vocal behavior consisting of stereotyped syllables arranged in a sequence. Analysis of different species’ song shows that these sequences are characteristic of individual species and that there are two major classes of sequence types: linear and non-linear. After presenting a method to classify birdsong according to sequence type, this thesis aims to model the neural mechanisms that generate the motor pattern controlling vocal sequences. The main focus in constructing this model was to make it consistent with current anatomical and physiological evidence. Furthermore, the model accounts for the effects that various lesions to nuclei within the song-production pathway have on song sequence. The presence of sequential bursts in various song system nuclei suggested the hypothesis that a synfire chain could generate temporal sequences (Hahnloser et al., 2002). Computer simulations using single compartment Hodgkin-Huxley neurons demonstrated that the stable propagation of multiple sizes of bursts along a synfire chain is possible (Li & Greenside, 2005). Given the proposed synfire chain model, this thesis then examines the role of nuclei afferent to the proposed synfire chain, proposing a possible mechanism for the synchronous initiation of the bilaterally represented synfire chain. Finally, the model was revised to account for the two types of vocal sequences observed. While the original synfire chain model is used for linear sequences, in order to model nonlinear sequences, a series of interconnected synfire chains is postulated, with similar patterns of initiation by afferent nuclei.

The sawfly Empria obscurata is one of the few transparent terrestrial organisms. Larvae of E.obscurata can maintain cryptic coloration on different backgrounds because their transparent skin exposes the food in their gut, allowing them to turn to color of whatever they have been eating. We studied the adaptive significance of its transparency by raising hatched larvae on three different diets: flowers, leaves, or both flowers and leaves. Larvae that mix their diets (eating both green leaves and yellow flowers) on their native host plant, Potentilla fruticosa, have significantly higher fitness than those raised on either leaves or flowers alone. Those fed both leaves and flowers develop quicker, grow larger, have higher survivorship and longer adult longevity. None of the larvae fed flowers survived to diapause with 50% dying before their first molt. Larvae fed leaves took longer to develop and had higher mortality during diapause than those fed both leaves and flowers. The transparency of Empria obscurata larvae would also allow them the switch host plants without compromising their crypsis. We observed switching of E.obscurata from Potentilla fruticosa to P.tridentata in the field. We raised larvae on four alternate Rosaceous foods: P.tridentata, P.norvegica, Fragaria sp., and Rosa sp. Those raised on P.norvegica, an introduced plant, had the highest mortality with 58% dying before their first molt and none surviving to diapause. Those raised on Rosa, P.tridentata and Fragaria had slower development, lower weights, lower survivorship, and shortened adult longevity. Empria obscurata has co-evolved with P.fruticosa and is best adapted to eating it. This suggests that currently host shift is most useful as a way to temporarily supplement Potentilla fruticosa food sources. However, should P.fruticosa become rare, E.obscurata could shift and develop a new evolving line.

Cyanobacteria are ubiquitous photosynthetic microorganisms. Prochlorococcus is a dominant genus in the world‚s oceans, and possibly one of the most abundant photosynthetic organisms on Earth. In this project, two Prochlorococcus strains (MIT9313 and MED4) were selected for study, as these strains represent major Prochlorococcus ecotypes. The molecular responses of these two strains to temperature and light stress were characterized, and we expect that differences in the responses of these and other Prochlorococcus strains (ecotypes) to environmental stress could influence niche differentiation in the oceans. Growth rates of MIT9313 and MED4 were not identical at all temperatures, and although these strains grow at comparable rates at 21°C, MIT9313 grows faster at 26°C. Following 24 hours of heat stress, an increase in the levels of saturated fatty acids was observed in both strains, suggesting an increase in membrane rigidity in response to high temperatures. After 24 hours of exposure to high light stress, MIT9313, but not MED4, exhibited distinct changes to the internal membranes, likely representing controlled membrane degradation. Additionally, both strains increased membrane fluidity by decreasing levels of 18-C fatty acids. Neither strain exhibited any changes in their levels of the key photosynthetic apparatus proteins, PsaC and PsbA, following 24 hours of high light stress. Genomic analyses of the chlorophyll binding proteins Pcb, IsiA, and CP43 revealed important sequence differences among strains. Understanding the molecular responses of Prochlorococcus to environmental stress promises to advance our understanding of how these ecologically important microorganisms will continue to contribute to global carbon and nitrogen cycles as global warming continues to increase ocean temperatures.

Tetrahymena thermophila is a single-celled, ciliated protist with two nuclei: the smaller, diploid, and transcriptionally silent micronucleus, and the larger, polyploid, and expressed macronucleus. T. thermophila reproduces both sexually through conjugation and asexually by binary fission. During conjugation, the macronucleus develops from a mitotic copy of the micronucleus. In this process, the five pairs of micronuclear chromosomes are fragmented into 250-300 smaller chromosomes by breakage at the 15-bp chromosome breakage sequence (Cbs) and telomere addition. These chromosomes are then replicated to ~45 copies, and are maintained at this copy number during vegetative division, even though there is no precise means to equally partition the chromosomes. A yet-unidentified mechanism is hypothesized to count and selectively replicate each chromosome to its correct copy number following division. This project aimed to construct a vector that, when introduced into T. thermophila, would fragment a targeted chromosome by homologous recombination and processing of an included Cbs element. Studies with such a vector would hopefully lead to insights about copy number control, as well as genome balance. Two improvements were made to MNC (Flynn, 2004), an earlier version of a fragmentation vector. A section of T. thermophila DNA was inserted into MNC to allow for fragmentation at the homologous site in the T. thermophila genome, and the pLitmus28 polylinker was added to MNC to create additional sites at which T. thermophila DNA can be inserted. In the future, these vectors can be used to transform T. thermophila and as a starting point for further improvements.

Examination of slc4a1 and gypc DNA sequences, which encode Band 3 and Glycophorin C proteins respectively, in five Great Ape species (H. sapiens, P. troglodytes, P. paniscus, G. gorilla, and P. pygmaeus) and an outgroup (H. leucogenys) using maximum likelihood and pair-wise comparison methods yielded evidence of adaptive evolution in the 5’ ends of both genes throughout the lineage, with the 3’ ends much more highly conserved. These genes encode erythrocyte membrane proteins, mutations of which are associated with malaria-resistant phenotypes in humans. Stronger selection signals came from deeper in the tree around the split of orangutans and gorillas from the human/chimpanzee branch, but there is also evidence from the comparison of humans with chimpanzees and bonobos of continuing adaptive evolution into the present. This suggests that selective pressure, possibly mediated by a Plasmodium malaria parasite, has been acting in the long-term, contradicting the agriculture hypothesis of the arrival of malaria as a human pathogen, and continues today as a dynamic host-pathogen relationship.

The ant-membracid system is ideal for studying the role of space in mediating a mutualistic interaction. Of particular interest are the processes that generate membracid aggregation, since the degree of aggregation determines the benefit accrued by individual membracids. A unique mark/multiple re-observation experiment suggests that having oviposited and being tended by ants play dominant roles in the movement decisions of female membracids. Models are developed to describe the mechanisms that may generate aggregation and these models are confronted with data from enclosure experiments. The Ant Stick model, in which membracids move at random until encountering an ant-discovered ramet, is provisionally supported as the process that generates observed patterns of aggregation.

This study examines the effect of the invasive ant, Myrmica rubra, both on the mutualism with the native treehopper Publilia concava, and on the diversity of the native insect community. Baseline data were determined for the current range of M. rubra, which appears to be concentrated along the Hoosic River from North Adams, MA to Hoosic Falls, NY. Closeness to the river, and the presence of Japanese knotweed and goldenrod were the strongest predictors of M. rubra presence. Increased densities of M. rubra were negatively correlated with the number of other ant species present in an area, but did not significantly impact non-ant insect diversity. M. rubra, which is smaller, recruits in significantly higher numbers to treehopper aggregations than the local, larger ant, Camponotus sp., although the overall benefit to the treehoppers is not significantly different. M. rubra is less efficient on a per-capita basis, perhaps due to its smaller size. Finally, performance of M. rubra appeared to be higher when its protein diet was supplemented with honeydew compared to a protein-only diet. In the future, M. rubra’s range and its effect on the local insect community should be closely monitored, as many invasive species can produce dramatic and irreversible effects on local ecosystems. This thesis provides critical baseline data for future studies.

As essential components of eukaryotic cells, sphingolipids play diverse roles in plants. They serve as structural components of cellular membranes and their metabolites play a role in cell signaling and regulation. Fully elucidating these roles in plants requires an understanding of the plant sphingolipid metabolic pathway and the numerous genes involved. Plant genes involved in the metabolism of sphingolipids have been identified based on their homology to yeast sphingolipid genes and characterized through the heterologous expression of candidate genes in yeast transformants. Here we characterize two kinases, encoded by two genes found in tandem at the At4g21535 (A-2) and At4g21540 (A-1) loci in A. thaliana. Yeast transformant strains carrying putative Arabidopsis kinase genes were monitored for kinase activity using non-radioactive enzyme assays and the properties of the kinases were characterized. Results showed that both genes indeed encoded kinases that were able to phosphorylate several long-chain bases including synthetic ones. Both A-1 and A-2 preferred dihydroxy LCBs over trihydroxy LCBs. We observed a significant difference in GTP utilization by A-1 and A-2 leading us to propose that these kinases may play different roles in sphingolipid metabolism. The identity of these genes was verified by the observation that lysates from T-DNA insertional mutants had reduced kinase activity compared to wild-type plants. This project and previous work together demonstrate that at least three long-chain base kinases are involved in Arabidopsis sphingolipid metabolism.

The forests of Williamstown, Massachusetts support a diverse community of herbaceous plants. Herb layer composition varies widely between individual forested stands, and has been linked with environmental conditions created by elevation, slope, and aspect. Such factors include soil moisture, pH, nutrient availability, and organic content, as well as characteristics of the canopy. The composition of herb communities has also been linked with the land-use history of the region. Much of Williamstown was cleared for agriculture in the early nineteenth century, and abandoned by the mid-1800s. Present-day forests consist of a mosaic of woodlot types: secondary forests that have regrown upon abandoned agricultural land, and primary forests that have never been cleared for agriculture. While current tree communities do not differ significantly between primary and secondary stands, their respective herb layers exhibit marked discrepancies. Agriculture affects herbs through long-term alteration of physical conditions, including many of the same parameters influenced by topography. Agriculture furthermore destroys microhabitat variation, leveling the heterogeneous microtopography that develops as forests age. Finally, agriculture removes herbaceous populations and seed sources, restricting herb dispersal. The herbs most affected by this process are dispersal-limited species such as the myrmecochorous (ant-dispersed) spring ephemerals. This survey, incorporating forested sites all over Williamstown, corroborates the importance of land-use in controlling herb distribution. Primary sites were richer and more diverse than secondary sites, due largely to the preclusion of dispersal-limited herbs from post-agricultural land. Soil moisture also proved to be fundamental in determining the biogeography of herbs. Herb richness and diversity were greatest in moist soils, and many individual herbaceous species were associated positively or negatively with moisture levels. This study demonstrated that numerous environmental and historical factors interact to influence herbaceous plants at a species-specific level, resulting in an array of unique herb communities throughout Williamstown forests.

Sphingolipids are a ubiquitous class of lipids that serve important structural and functional roles in all eukaryotic organisms. Though sphingolipids are known to be involved in a multitude of crucial cellular processes, plants harboring mutations in some genes important to the synthesis and metabolism of these compounds are often indistinguishable from wild-type plants under normal growth conditions. Here we describe an effort to identify phenotypes of Arabidopsis thaliana sphingolipid mutants in response to exogenous stressors. We develop a method to screen plants for signs of damage after exposure to any of a number of compounds previously shown in other organisms to inhibit specific steps in sphingolipid metabolism. We show that the range of phenotypes displayed by different mutant lines in response to a single inhibitor can be quite large, focusing on the response of plants carrying an insertion mutation in the AtDPL1 locus that causes loss of long-chain base phosphate lyase enzyme activity. Such plants are shown to be hypersensitive to Fumonisin B₁, a potent inhibitor of ceramide synthesis, and N,N-Dimethylsphingosine, an inhibitor of long-chain base kinases. Much of this work is preliminary in nature, and we present several possible avenues for future research.

Agrobacterium tumefaciens infects a wide variety of plants by transferring a portion of its tumor inducing plasmid known as the T-strand into the host cell genome via the VirB transport apparatus. Integration of the T-DNA into the host cell’s genome results in the creation of a unique ecological niche and the synthesis of substances that provide nutrition for the bacterium. The T-strand consists of a 20,000 base-pair sequence flanked by 25 base-pair border sequence repeats. Adjacent to the right border is another conserved 24 base-pair sequence called overdrive (OD) that assists in the formation of tumors by enhancing T-DNA processing. Disruption of the OD core sequence leads to inefficient T-DNA transmission. OD is believed to promote T-DNA cleavage at the RB sequence by its interaction with the VirD2 protein. OD function is further enhanced by interaction with VirC1, one of the proteins encoded by the two open reading frames of the virC locus (the other being VirC2). We set out to test the hypothesis that VirC1 acts to tether the pTi to the pole of the bacterium, in close proximity to the VirB pore. This localization would facilitate movement of the T-DNA through the pore and into the host. To this end, we have designed an experimental strategy by which the pTi can be directly visualized in vivo. The design involves binding of a GFP-LacI reporter construct under vir promoter control to a tandem array of lac operator sequences inserted within the T-DNA region. Progress was made in constructing a plasmid with the lac operator insert that will be integrated into the pTi by recombination. Future work will focus on preparing the GFP-LacI reporter and observing its behavior in wild type and virC1 mutants in vivo. A separate goal of this thesis was the purification of the VirC2 protein in order to raise antibodies for its identification in vivo. Attempts to obtain the pure protein were successful and are outlined.

Oxyntomodulin (OXM), a postprandially released intestinal hormone, inhibits food intake via the glucagon-like peptide-1 receptor (GLP-1R). Using telemetry to measure heart rate (HR) in conscious and freely moving mice, we tested 1) whether OXM affects HR, and 2) whether this effect is also mediated by the GLP-1R. We found that peripherally administered OXM significantly increased HR in wild-type mice, raising HR by over 200 bpm to a maximum of 728 ± 11 bpm. To test the hypothesis that the HR effects of OXM are mediated through the sympathetic nervous system, we measured the HR effects of OXM in Dbh-/- mice that lack epinephrine and norepinephrine and in wild-type mice pretreated with metoprolol and atropine, which block input to the heart from both arms of the autonomic nervous system (ANS). OXM induced an increase in HR of 192 ± 13 bpm in Dbh-/- mice indicating that the HR effects of OXM are independent of catecholamines. HR increased by 44±3% in autonomically blocked mice, indicating that OXM acts independently of the ANS, increasing intrinsic HR directly. Intrinsic HR increased by 40±7% in Glp-1R-/- mice, demonstrating that the HR effects of OXM are independent of the GLP-1R. Interestingly, while the HR effects of OXM are independent of the GLP-1R, peripheral OXM inhibited activity and lowered T_b via GLP-1R dependent mechanisms. We hypothesize that OXM increases intrinsic HR through direct actions on the heart via either the glucagon receptor or an unidentified OXM specific receptor.

This thesis compared the forest-floor invertebrate communities in secondary (post-agricultural) and primary (never completely cleared) eastern deciduous woodlots in northwestern Massachusetts. Invertebrates were extracted with an enhanced Tullgren-Berlese funnel from litter and soil samples collected at 77 forest plots. Individuals greater than 2mm in any dimension were identified to order. Spiders (Araneida) were significantly more abundant in primary woodlots than in secondary woodlots, but overall invertebrate density did not differ significantly between forest types. Spiders, as the top predator in the invertebrate food web, can serve as indicators of overall community structure. Their dearth in secondary woodlots suggests that the forest-floor communities are less complex on post-agricultural land, with less energy reaching the upper trophic levels. Quality of leaf litter in primary woodlots may explain this difference. Spider density increases with leaf litter depth in primary woodlots, but has no relationship with litter depth in secondary woodlots. Sugar maple (Acer saccharum) is more abundant in primary woodlots, whereas red maple (Acer rubrum) and paper birch (Betula papyrifera) favor secondary woodlots. Soils are more alkaline in primary woodlots and this is linked to forest-canopy composition. Despite differences in spider densities, significant overall differences were not found between the invertebrate communities in primary and secondary woodlots. The order level of taxonomic resolution may not have been fine enough to show the community differences beyond that of spider density.

CHEMISTRY

The self-assembly behavior of self-assembling amphiphilic copolymer systems can be exploited for the purposes of drug delivery. Polyesters such as poly-ε-caprolactone show great potential for use in these systems, as their ester linkages are hydrolytically degradable, but few polyesters are water-soluble, limiting their role to the hydrophobic segment of the copolymer. To this end, the synthesis of functionalized derivatives of ε-caprolactone has been accomplished, including monomers that will ultimately lead to polymers with alcohol and carboxylic acid functionalities. One amine-functionalized monomer is made, and the other is one step from completion. It is hoped that these hydrogen bonding moieties will confer water solubility on the poly-ε-caprolactone backbone, permitting its use as the hydrophilic segment of an amphiphilic copolymer system. Alternatively, the monomers can be reacted with pentapeptide groups before polymerization to yield graft copolymers that will significantly alter the weight ratio of hydrophobic to hydrophilic material once the amphiphilic systems are generated.

After developing the mathematics of stability analysis, we choose five simple chemically relevant models and, using dimensionless equations, we study analytically and numerically their transitions from stable steady states to oscillatory states. We use MATHEMATICA to visualize the oscillatory behavior of these five systems and we then generalize these results into a simple two-variable model with either a linear or an enzymatic removal term. Next, we consider a generalized two-variable model of a self-complementary self-replicating system that includes both catalyzed and uncatalyzed formation of the template. Since most self-replicating systems adhere to the so-called square root rate law, we focus on this rate in our analysis of the spatial and temporal aspects of this system and again use MATHEMATICA to visualize its oscillatory behavior.

Three poly(ethylene glycol) (PEG) polyamide copolymers, amphiphilic molecules made by coupling hydrophobic polyamides to hydrophilic PEG (10 kDa), were synthesized via one of two methods. PEG-polyvaline and PEG-poly(2-ethyl-oxazoline) were synthesized by ring opening polymerization of the valine N-carboxyanhydride and 2-ethyl-oxazoline monomers with PEG as a macroinitiator, while PEG-polyphenylalanine was synthesized by directly coupling L-polyphenylalanine (2-5 kDa) to an intermediate linker form of PEG. Solvent and temperature effects were explored in each synthesis, and ¹H NMR was used to determine the relative sizes of the copolymer segments. Fluorimetry studies were performed with the probe Nile Red to investigate micelle formation in aqueous solution; further tuning of the composition and length of the hydrophobic block is required as no aggregation was observed for these three copolymers.

Streptomyces coelicolor belongs to the genus of soil-dwelling bacteria known as streptomycetes. S. coelicolor has a complex but well characterized life cycle involving mycelium formation, production of secondary metabolites like antibiotics, and sporulation to produce the next generation. This study focuses on a mutant form of the bacterium, called bld, that lacks the ability to form an aerial mycelium thus halting development of the organism and preventing progression through the remainder of the cycle. The particular bld mutant used in this study, NY415, is believed to result from the absence of the anti-sigma factor, RsuA that normally regulates the sigma factor SigU. Therefore, in this strain, SigU is free to bind RNA polymerase and turn on transcription of the sigU regulon.

The transcription of genes in the mutant that are not normally transcribed in the WT suggests that there are resulting proteins that are unique to the mutant. Two-dimensional gel electrophoresis, in-gel tryptic digestion and MALDI-TOF mass spectrometry were used to separate, digest and identify the secreted proteins in both the bld and the WT strains of the bacterium. The results of these experiments illustrated that the bld mutant produces a more diverse set of proteins than the WT. Protein identification also showed that the bld mutant produces and secretes several predicted proteases, so a BSA digestion experiment was carried out to assess protease activity in both strains. The culture supernatant form the bld but not the WT caused BSA degradation. In addition, it was hypothesized that SigU is activated in the WT when the organism is responding to some form of stress condition in the environment, thus forming the bld mutant. As a result, studies were carried out in which the WT strain was grown on kanamycin plates in the presence of potential stressors, after fusing the sigU promoter gene with a kanamycin resistance reporter gene. Acidic conditions were found to elicit transcription from the sigU promoter.

An efficient synthesis of the C₁–C₁₅ bisoxazole fragment of the antiviral marine natural product hennoxazole A is completed in 7 steps from a bisoxazole dimethyl acetal in a 9.9% overall yield. Notable features of this synthesis include a novel application of a diastereoselective aldol-like reaction between an N-acetyl thiazolidinethione and a dimethyl acetal to establish the stereocenter of the C₈ methoxy group, and an elegant approach to pyran ring systems via an acetoacetate displacement of the chiral auxiliary. Central to the asymmetric total synthesis of hennoxazole A is the coupling between the C₁–C₁₅ bisoxazole system and the C₁₆–C₂₅ triene fragment. This novel strategy took advantage of the natural reactivity of the intact bisoxazole core and allowed for this relatively simple, inert heterocyclic system to be carried through a variety of synthetic transformations unaffected. Overall, hennoxazole A was prepared in a longest linear sequence of 17 steps starting from commercially available serine methyl ester hydrochloride and ethyl acetimidate hydrochloride in a 1.6% overall yield.

I performed laser spectroscopy and electronic structure calculations to probe inter and intramolecular, red- and blue-shifting H^...F interactions in hydrofluorocarbons. I constructed a photoacoustic spectroscopy (PAS) apparatus and used it to record the CH-stretching vibrational overtone spectra of 1,1,1,2,3,3,4,4,4-nonafluorobutane, pentafluoroethane, and tetrafluoroethane in the 4^th and 5^th CH-stretching vibrational overtone regions. Based on temperature- and pressure-dependent overtone spectra of the 5^th CH-stretching vibrational overtone of pentafluoroethane, I conclude that the lower energy, lower intensity transition in that overtone manifold is due to a dimer involving a red-shifting, intermolecular hydrogen bond. Assignment of the 5^th CH-stretching overtone of 1,1,1,2,3,3,4,4,4-nonafluorobutane to gauche, gauche and zigzag conformers using density functional theory harmonic frequency calculations and similar calculations for perfluorobutane and 1,1,1,2,2,3,3,4,4-nonafluorobutane lead me to conclude that fluorine interactions play a larger role in the relative stability of gauche conformations in hydrofluorocarbons than was previously understood. Natural Bond Orbital (NBO) and Natural Localized Molecular Orbital (NLMO) calculations support previous assignment of the vibrational overtone spectrum of 1,1,1,2,2,3,3,4,4-nonafluorobutane using a 3 conformer model that includes a blue-shifting, intramolecular hydrogen bond in the gauche conformer. I also predict a blue-shifting, intramolecular hydrogen bond in the gauche conformer of 1-fluorobutane.

Streptomycetes are pharmaceutically important bacteria due to the wide selection of antibiotics and other secondary metabolites produced by the various species. Streptomyces coelicolor is the representative of this genus due to its well-characterized and sequenced genome. It undergoes a complex life cycle involving several stages of morphological differentiation, one of which is sporulation. WhiJ ORF3 and ORF5 mutants are two of the identified sporulation mutants. The WhiJ ORF3 protein possesses a helix-turn-helix motif, which is a characteristic of DNA binding proteins. No such motif has been identified in the WhiJ ORF5 protein. Previous work has suggested that the ORF3 protein does bind to DNA and appears to do so in the presence of the ORF5 protein.

The aim of the following set of experiments was to identify DNA and protein binding partner(s) of the ORF3 and ORF5 proteins respectively. The BacterioMatch II Two-Hybrid System was used in the identification of the protein-binding partner(s) of the ORF5 protein. The protocol employed precluded the procurement of conclusive results. The construction of a cDNA library would help produce more conclusive results. The Systematic Evolution of Ligands by Exponential Enrichment (SELEX) was the protocol used to identify the DNA binding partner of the ORF3 protein. The DNA gel of samples of elution buffer eluants suggested that the ORF3 protein does indeed bind to DNA. Sequencing analysis will determine the exact region of the S. coelicolor genome to which the ORF3 protein binds specifically.

Dennstaedtia punctilobula, also known as hay-scented fern, is a perennial plant that proliferates in large dense patches in forests throughout the northeast. Its invasive behavior seems to discourage other plant species from living amongst it. This growth pattern has led chemists to the theory that hay-scented fern uses allelopathy, or the release of harmful chemicals, to compete for resources with other plants by inhibiting their growth or germination. Past studies have involved isolation and purification procedures that somewhat separated a putative allelochemical from other plant components. The most recent previous study showed that bioactivity was being produced in fern extract solutions that contained sucrose, glucose, and fructose. Although initial field studies searching for allelopathy in hay-scented fern were not able to recreate the hypothesized bioactivity, an experiment conducted in the greenhouse with soil harvested from an active hay-scented patch showed increased bioactivity (or inhibited growth) with soil taken from where hay-scented grew the densest.

Pyran-based natural products offer both medicinal potential and interesting synthetic challenges. An efficient and general method for the asymmetric synthesis of pyranoid moieties has been developed. We have demonstrated that it is possible to synthesize a diverse array of magnesium nucleophiles from commercially available reagents and add these to a variety of aldol adducts via imidazole-mediated displacement of a thiazolidinethione chiral auxiliary. The product can then be cyclized to give the desired pyran-based ring system. Functional groups may be modified, either before or after a cyclization step, depending on the structure of the target molecule. This thesis work has shown applicability to the syntheses of the antiviral marine natural product hennoxazole A, the cytotoxic cyanobacterial metabolite acutiphycin, and the anticancer plant styrylpyrone derivative goniothalamin. We also envision that this method might be applied to the synthesis of a wide variety of pyran-based natural products as well as other polyacetate- and polypropionate-derived systems.

The SOS DNA repair system in the bacterium Bacillus subtilis comprises more than 30 genes that are coordinately induced by DNA damage to provide for cellular survival in response to DNA assault. The SOS response to DNA damage is known to include enhanced DNA repair capacity, enhanced mutagenesis, and inhibition of cell division; however, the functions of most of the SOS gene products remain unknown. I discovered that the damage-inducible YqjY protein, an SOS gene product that shares homology with the GNAT family of histone acetyltransferases (HATs), catalyzes the acetylation of eukaryotic histones and purified B. subtilis HBsu protein in vitro. The HBsu protein was identified as a potential substrate for YqjY because it belongs to a group of highly conserved histone-like proteins in bacteria, represented by the well-studied Escherichia coli HU protein. In addition to its homology with histones, the E. coli HU protein is functionally analogous to eukaryotic HMG proteins, which are also acetylated by HATs, in that it binds preferentially to distorted or damaged DNA structures and to recombinational repair intermediates. Corresponding to a potential role for HBsu in DNA repair, I showed that HBsu binds at least 500 times tighter to Holliday junction structures than to linear DNA.

Recent studies have shown that eukaryotic HAT complexes contain more than a dozen distinct proteins, including DNA repair proteins and transcription factors, suggesting that acetylation of histones and HMG proteins may serve to recruit these activities to specific DNA sites. Thus, the role of YqjY may be to recruit DNA repair proteins to a damaged or partially repaired site. In preliminary studies aimed at identifying proteins associated with YqjY and HBsu in vivo, I used anti-GFP antibody to immunoprecipitate an HBsu-GFP fusion protein from induced cells. Although the technique worked, initial results as assessed by SDS PAGE were inconclusive.

COMPUTER SCIENCE

A collection of recorded and transcribed telephone conversations clearly demonstrates the universality of small talk and other socially motivated utterances. Building on theories about the linguistics of conversational speech, I consider various ways of describing each utterance, including which words were used, their part-of-speech, and the proximity to the beginning of the conversation. In order to better understand which of these features are most useful, I create a system for automatically distinguishing between on- and off-topic utterances and compare its performance when using different combinations of these features. The central hypothesis is that conversational speech contains sufficient low-level clues to separate on- and off-topic utterances with an automatic classifier. I find that the overall structure of conversations is predictable, and automatic classification can indeed be done with better-than-chance accuracy, but distinguishing more reliably between on-and off-topic utterances will probably require deeper knowledge of the context and overall topic.

Modern computer hardware is capable of supporting virtualization as a means of overcoming the restrictions of physical machines. Operating system virtualization has gained popularity in the past several years as a solution to the very important problem of resource under-utilization in so-called “server farm” environments. This technique provides a virtual hardware interface on top of which can run unmodified or slightly modified versions of operating systems like Windows XP or Linux. The Xen Virtual Machine Monitor is an implementation of operating system virtualization that additionally supports migration, the act of moving a virtual operating system from one physical machine to another. We have utilized this capability to implement a load-balancing daemon in Python that attempts to equalize the load on all nodes in a group of machines running Xen. In addition, we have implemented a simulator for testing balancing algorithms. Experiments using these tools have suggested a number of conclusions about the future of virtual operating system load balancing.

GEOSCIENCES

This study investigates the potential connection between marine productivity and nutrients delivered to the Bay of Bengal via rivers. Since the Bay of Bengal is strongly influenced by the monsoon season, the amount of fluvial input and associated nutrients varies on both seasonal and twenty thousand year timescales, providing an excellent background against which to compare productivity changes. Present seasonal changes in marine productivity are investigated using sediment traps, and past changes in productivity are investigated using sediment from ocean cores dated from about 190 ky to 90 ky b.p., spanning the glacial-interglacial transition between marine isotope stages 6 and 5. Calculations of coccolith flux to the sediment trap show that the months of the summer southwest monsoon are the periods when the most coccoliths are exported to the traps. Chemical analyses of the coccolith Sr/Ca ratios indicate that, for some species, however, the greatest nutrient-stimulated productivity occurs during the northeast monsoon. Coccolith Sr/Ca ratios and Ba/Ti ratios from sediment cores indicate that productivity is highest during periods of strong southwest monsoon and enhanced eddy pumping, as indicated by other proxy records for the cores. Neodymium isotopes from sediment cores indicate that during the glacial marine isotope stage 6, there was a switch in the source of sediment to the Bay, possibly reflecting a restriction of the intertropical convergence zone due to northern hemisphere ice. Finally, a two-box model is used to assess the effect of changes in river discharge on nutrient concentrations in the surface waters and export of organic carbon to deep waters. Sensitivity tests of the model imply that the upwelling of nutrients from the deep water has a greater effect on carbon export and surface nutrient concentration than river input. The combined results from the sediment traps, the sediment cores, and the numerical model all imply that, in terms of stimulating marine productivity, river-derived nutrients are less important than nutrients pumped to the surface from the deep ocean.

The motivation for this project was research previously conducted by the Keck Geology Consortium and others in the Tobacco Root Mountains, just east of the areas of the current study. Two major metamorphic events were recognized in the Tobacco Root Mountains: a previously known Archean orogeny and the newly characterized Early Proterozoic Big Sky Orogeny. In the Tobacco Root Mountains, Mogk and others (2004) used geochemistry, petrology, and field evidence to classify the quartzofeldspathic gneisses as felsic members of one or more bimodal volcanic associations extruded in an active continental margin or continental arc setting ca. 3.3 Ga.

Gneiss samples from the Highland Mountains contain abundant plagioclase and little or no microcline. Conversely, samples from Alder Gulch and the Greenhorn Range contain abundant microcline and up to 25% plagioclase. All of the quartzofeldspathic gneisses of this study range from 67 to 76 wt% SiO₂. Samples from the Highland Mountains are typically sodic (wt% Na₂O > wt% K₂O) and samples from the Greenhorn Range and Alder Gulch are typically potassic (wt% K₂O > wt% Na₂O). Gneisses from all three areas are relatively enriched in P, Nb, and Ti and depleted in K and Pb when normalized against primitive mantle and are enriched in LREE and depleted in Eu when normalized against chondrites. Geochemical classification diagrams characterize the protolith of the gneisses as rhyolite or dacite. Most samples from the Highland Mountains plot in the volcanic-arc granite region of tectonic discriminant diagrams after Pearce et al. (1984) and samples from the Greenhorn Range and Alder Gulch plot near the intersection of the volcanic-arc, within-plate, and syn-collisional granite regions.

Mogk and others (2004) find that potassic alteration, likely due to Tertiary granitic plutons, of quartzofeldspathic gneisses of the Tobacco Root Mountains limits the distinction of the protolith and tectonic setting for sodic and potassic gneisses. The gneisses of the current study do not appear to be altered, and the sodic and potassic samples have distinctive trace element signatures. Data from the current study are consistent with an evolving back-arc setting in which sodic protoliths of gneisses from the Highland Mountains formed earlier and potassic protoliths of gneisses from the Greenhorn Range and Alder Gulch formed later. Analyses of interlayered mafic gneisses (Siegel, 2006) support a back-arc interpretation.

Discharge records and suspended sediment samples from a glacial stream in Svalbard, analyzed in the context of climatic conditions, provide a better understanding of the processes controlling glacial lake sedimentation under transport-limited sediment conditions. Comparisons between monitoring sites at opposite ends of the glacial stream Linnéelva confirm the presence of a significant sediment sink during periods of low streamflow. During higher flows, remobilization of stored sediment contributes to higher concentrations of suspended sediment in Linnéelva. A direct relationship between discharge and suspended sediment concentration, even at the highest sampled discharges, implies that sediment transport to the glacial lake Linnévatnet is primarily controlled by discharge. During the mid-late summer, glacial baseflow does not provide enough streamflow to transport significant amounts of sediment. The highest summer discharges, and thus the majority of summer sediment transport towards Linnévatnet, occur following summer rainfall events. Fluctuations in summer rainfall should therefore be reflected in Linnévatnet’s sediment record. Although previous research has shown that Linnébreen controls sediment transport and lake sedimentation over the long-term, the glacier at the present time does not appear to be the major factor controlling summer sediment transport to Linnévatnet.

MATHEMATICS

Biological models have been criticized for not being able to take into account stochasticity found in biological data, particularly variations in time delays. In this paper, I show how to implement stochasticity, using the Naor process, into time delays in discrete differential equation models. The Naor process was implemented in the red blood cell model of cyclic hemolytic anemia proposed by Mahaffy, Belair, and Mackey in 1998. The introduction of stochasticity into the red blood cell model significantly decreases the size of the red blood cell cycles and the size of the period of the cycles. The introduction of stochasticity also has a minor effect on the bifurcation point of where the cycles start to occur. These results indicate that stochasticity is an important consideration when trying to model the size and the period of cyclic diseases.

We then examine two relatively unexplored continued fraction representation systems, focusing especially on the expansions of real quadratic irrationals. It is well known that a number is a real quadratic irrational if and only if its simple continued fraction is eventually periodic. Here we show that, with a fixed integer numerator, all quadratic irrationals can be written periodically with a period of length one. We also explore Diophantine approximation issues within the context of these new expansions. We further investigate whether a similar period-one expansion holds for a system of non-simple continued fractions in which each numerator depends on the previous denominator. Using the dynamics of a related map to study this system, we offer preliminary results and conjectures in this direction, and place these in context with what is currently known.

PHYSICS

In this thesis, we propose an SU(3) flavor symmetric extension to the standard supersymmetric model. We replace the single pair of Higgs fields in the standard supersymmetric model with multiplets of Higgs fields that transform non-trivially under SU(3) flavor transformations to make the Lagrangian flavor symmetric. We break the flavor symmetry by introducing multiplets of scalar fields that get vacuum expectation values in the flavor symmetry scale, _F ~ 10¹⁶ GeV. By coupling these scalar fields to the Higgs, we are able to make all but one pair of Higgs fields heavy, thereby preventing excessive fermion flavor mixings. Our model accommodates all the experimental constraints from past collider experiments, including bounds on the masses of the Higgs fields and known fermion masses and mixings. Lastly, we show that the new particles we introduce in our model are detectable by collecting more data than was done in previous e⁺e^- colliders without the need to increase the collision energy.

We have created BECs of 10⁵ ⁸⁷Rb atoms. Previous work developed methods to transfer ~ 10⁶ atoms from a magneto-optical trap (MOT) to a CO₂ laser dipole trap and to image these clouds through optical depth measurements. We have improved dipole trap loading through the installation of an adjustable telescope allowing us to modify dipole trap curvature. Trap geometries with greater curvature exhibit a higher elastic collision rate, allowing us to run evaporation at faster rates and avoid losses to background collisions. A new evaporation scheme allows us to conduct efficient evaporation, avoiding unnecessary losses. Our most recent data shows unambiguous evidence of condensation through observation of predicted BEC signatures.

PSYCHOLOGY

When a person suffers a failure experience, makes an internal attribution of that failure to him or herself, and experiences the disagreeable feelings of self-awareness that then arise, he or she may wish to “escape” from him or herself. This thesis explores one escape path that has not been previously investigated: conformity. The present thesis attempts to investigate the connection between self-awareness, failure, and conformity as an escape from self – namely, conformity as a means to escape self-awareness. Study 1 investigates conformity using the degree of change between participants’ pre-tested responses to a variety of opinion questions, and their response to the same items in the laboratory when it appears that their views run counter to those of other participants. Study 2 addresses conformity by presenting fictitious group norms, with which most participants are likely to disagree, and measures the effect of these bogus group norms on participants’ responses in each condition. Study 2 also introduces a new behavioral measure of conformity, namely choosing a pen with the same ink color as ostensibly chosen by other participants. Study 3 utilizes a slightly different manifestation of the success/failure variable, and also serves to replicate Study 2. Overall, although results vary from study to study, the studies indicate that there does appear to be a link between self-awareness and conformity, with the effect emerging the most reliably in the behavioral measure (pen choice). Additional research is needed to further probe the dynamics of that relationship.

In recent years, the clinical literature concerning the role of ovarian hormones in the modulation of cognition has become particularly controversial. Animal studies suggest that estradiol, under particular circumstances, can have both beneficial and deleterious effects on learning and memory using a variety of behavioral measures. While most of these studies track the performance of intact, cycling females or examine the effect of chronic hormone replacement administered to ovariectomized females, little work has examined the time course over which acute estradiol influences cognition. Furthermore, the long-term consequences of dramatic changes in the hormonal milieu (e.g., pregnancy and lactation) have not been well studied. This study consists of two experiments examining these issues. In Experiment 1, ovariectomized female rats were given acute administrations of estradiol. Following delays of 10 minutes, 1 day, 2 days, or 9 days, they were tested on the elevated plus maze and on a simple place learning task. Rats primed with estradiol exhibited improvements in place learning when tested 1 day following priming, but not at other time points indicating that estradiol positively influences place learning in a very transitory fashion. In Experiment 2, the effect of estradiol or oil priming was examined in nulliparous and primiparous female rats that had been ovariectomized following weaning. These data revealed a trend towards impaired place learning associated with parity that was no longer evident following priming with estradiol, further suggesting that motherhood may adversely affect place learning ability and alter sensitivity to estradiol within this neural system.

Many types of psychotherapy exist, ranging from insight-oriented therapies to behavioral therapies. To the extent that therapies differ, both in their theoretical base and technical diversity, certain therapies might be more appealing than others. Yet, limited research has examined preferences for different types of therapy and no research has considered preferences for various couple therapies. The current study addressed this gap in the literature, examining sex differences in preferences for Cognitive-Behavioral Couple Therapy (CBCT), Emotion-Focused Couple Therapy (EFT), and Solution-Focused Couple Therapy (SFT) among 67 individuals involved in a committed heterosexual or homosexual relationship. Participants read descriptions of each therapy and completed a 7-item questionnaire regarding their impressions of each type as well as a rank-ordering of the three types. They also completed the Bem Sex Role Inventory (BSRI), Emotional Expressiveness Questionnaire (EEQ), and Psychological Mindedness (PM) scale to determine whether scores on these measures predicted affinity for each type. Results indicated that heterosexual men and women differed in their preferences, particularly with regard to EFT, though homosexual men and women showed no distinct preferences. Among heterosexual participants, emotional expressiveness was a marginally significant predictor of affinity for EFT and masculinity was a significant predictor of affinity for SFT, and psychological mindedness was a significant predictor of affinity for EFT among homosexual participants. The study indicated that variability exists in therapy preferences and that they are predicted by certain personality characteristics. Methodological limitations and future research directions are also discussed.

A longitudinal study currently in progress formed the basis for an investigation of the prevalence, stability, and associated abilities of imaginary companions (ICs) in preschool children aged 2.5 to 5 years. To date, twenty-seven children have returned at the final time point (60 months) where they received a full assessment of both belief understanding (theory-of-mind) and emotion understanding (Test of Emotion Comprehension, Pons & Harris, 2000). At previous time points (24 months, 36 months, and 48 months), children were assessed on pretense, language, symbolic representation, role-play, and simple theory-of-mind tasks. In addition, at 36, 48, and 60 months the children were questioned about having an IC. Over the three time points that ICs were studied (36 to 60 months), the percentage of children who had ICs increased steadily from 11 percent at 36 months to 30 percent at 60 months. ICs were found to be relatively brief in duration, typically lasting no longer than one year. At 48 months (Time 3), where there are data on 46 children, those with an IC by this time point performed better on measures of role-play, language, and theory of mind than those who did not have an IC. This finding is corroborated by the results of the 27 children who have completed the study to date. In this smaller sample, those children who had an IC at any point during the study had higher scores on role-play, language, and emotion comprehension than did those children who had never possessed an IC. Overall, these results suggest that imaginary companions are found among children who have strong language abilities, a good understanding of the beliefs and emotions of others, and the capacity to engage in role-play.

Beck’s Cognitive Theory of depression holds that dysfunctional (i.e., inflexibly negative) beliefs are a causal factor in the development and onset of unipolar depression. Dysfunctional beliefs are traditionally assessed with the Dysfunctional Attitudes Scale (DAS). The 40-item Form A of the DAS is the most widely used and thoroughly validated measure of dysfunctional beliefs. Studies have consistently demonstrated that DAS scores are elevated among depression-prone individuals when they are clinically depressed. But between depressive episodes, such individuals exhibit elevated DAS scores only if the scale is administered following some kind of mood or construct prime. A common interpretation is that dysfunctional beliefs are a hallmark of depression-proneness, as proposed in Beck's theory, but become latent during asymptomatic periods and can only be detected during those periods if somehow reactivated. While the ability to demonstrate persistence of dysfunctional beliefs in depression-prone individuals supports one of the theory's predictions, the theory further implies that dysfunctional beliefs are present in some form before initial onset of depression. Testing that prediction has proven much more of a challenge to date, in large part because of the practical and ethical difficulties of administering individualized mood primes to all participants in large, longitudinal studies. One possible way to resolve that challenge would be to have participants report their strongest dysfunctional beliefs during a recent time interval in which they presumably experienced periods of both positive and negative mood. In essence, it may be possible for never-depressed individuals to report whether their dysfunctional beliefs tend to grow much stronger during negative moods, and to use differences in such reports to predict future vulnerability to depression. To this end, we created two versions of the DAS with modified instructions; each version instructed participants to estimate how strongly they would have endorsed each statement during their most discouraged mood period of the past week. We then examined these measures across two studies. In Study 1, we determined that both modified versions of the DAS were more strongly associated with self-reported depression-proneness than was the unmodified DAS. Study 2 further tested one of the modified versions of the DAS from Study 1, the DAS-RANGE, by examining its association with self-reported depression-proneness, and its predictive validity as determined by self-reported fluctuations in dysfunctional beliefs reported on a daily basis. The DAS-RANGE did not detect latent dysfunctional beliefs more effectively than the Conventional DAS in Study 2. However, contrary to previous studies of depression-proneness, across both studies our results suggested that the Conventional DAS was effective at detecting latent dysfunctional beliefs in high-risk for depression individuals, even beyond the variance accounted for by current depressive symptoms. Possible implications of this pattern for future research on cognitive vulnerability to depression are explored.

The field of family therapy has witnessed tremendous growth over the past 30 years. Therapy models have evolved to include a multicultural perspective and to cater to different family types. Because research on client preferences for therapy has been limited to individual therapy, the current study was undertaken as an exploration of preferences for three different types of family therapy: Cognitive Behavioral Family Therapy (CBFT), Solution-Focused Family Therapy (SFT), and Functional Family Therapy (FFT). In particular, the study purports to determine if cultural values, socioeconomic status (SES), and personality (specifically openness, agreeableness, and conscientiousness) can predict ratings of effectiveness of and preferences for these three types of family therapy. With regard to cultural values, the study examined the associations between certain cultural values and perceived successfulness of and willingness to utilize these three types of family therapy. Two hundred thirty seven college students rated and ranked the three therapies, and completed cultural family values and personality measures. The results revealed that cultural values, personality, and SES were not significant predictors of ratings of effectiveness for the three types of family therapies. However, SES was found to be significantly correlated with preference for SFT. Overall, FFT was the most preferred family therapy regardless of standings on the three personality variables, how strongly one adhered to certain cultural values, or the socioeconomic status of the participant’s family. Limitations of the study and implications for further research are discussed.

STUDENT ABSTRACTS

ASTROPHYSICS

BIOLOGY

CHEMISTRY

COMPUTER SCIENCE

GEOSCIENCES

MATHEMATICS

PHYSICS

PSYCHOLOGY