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Dartmouth College

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2005

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Embryonic Stem Cell-Derived Hematopoietic Stem Cells, Yuan Wang, Frank Yates, Olaia Naveiras, Patricia Ernst, George Q. Daley Dec 2005

Embryonic Stem Cell-Derived Hematopoietic Stem Cells, Yuan Wang, Frank Yates, Olaia Naveiras, Patricia Ernst, George Q. Daley

Dartmouth Scholarship

Despite two decades of studies documenting the in vitro blood-forming potential of murine embryonic stem cells (ESCs), achieving stable long-term blood engraftment of ESC-derived hematopoietic stem cells in irradiated mice has proven difficult. We have exploited the Cdx-Hox pathway, a genetic program important for blood development, to enhance the differentiation of ESCs along the hematopoietic lineage. Using an embryonic stem cell line engineered with tetracycline-inducible Cdx4 , we demonstrate that ectopic Cdx4 expression promotes hematopoietic mesoderm specification, increases hematopoietic progenitor formation, and, together with HoxB4, enhances multilineage hematopoietic engraftment of lethally irradiated adult mice. Clonal analysis of retroviral integration sites …

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The Relationship Between Frq-Protein Stability And Temperature Compensation In The Neurospora Circadian Clock, Peter Ruoff, Jennifer J. Loros, Jay C. Dunlap Dec 2005

The Relationship Between Frq-Protein Stability And Temperature Compensation In The Neurospora Circadian Clock, Peter Ruoff, Jennifer J. Loros, Jay C. Dunlap

Dartmouth Scholarship

Temperature compensation is an important property of all biological clocks. In Neurospora crassa, negative-feedback regulation on the frequency (frq) gene's transcription by the FRQ protein plays a central role in the organism's circadian pacemaker. Earlier model calculations predicted that the stability of FRQ should determine the period length of Neurospora's circadian rhythm as well as the rhythm's temperature compensation. Here, we report experimental FRQ protein stabilities in frq mutants at 20 degrees C and 25 degrees C, and estimates of overall activation energies for mutant FRQ protein degradation. The results are consistent with earlier model predictions, i.e., temperature compensation of …

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Dynamical Control Of Qubit Coherence: Random Versus Deterministic Schemes, Lea F. Santos, Lorenza Viola Dec 2005

Dynamical Control Of Qubit Coherence: Random Versus Deterministic Schemes, Lea F. Santos, Lorenza Viola

Dartmouth Scholarship

We reexamine the problem of switching off unwanted phase evolution and decoherence in a single two-state quantum system in the light of recent results on random dynamical decoupling methods [L. Viola and E. Knill, Phys. Rev. Lett. 94, 060502 (2005)]. A systematic comparison with standard cyclic decoupling is effected for a variety of dynamical regimes, including the case of both semiclassical and fully quantum decoherence models. In particular, exact analytical expressions are derived for randomized control of decoherence from a bosonic environment. We investigate quantitatively control protocols based on purely deterministic, purely random, as well as hybrid design, and …

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Genetic And Molecular Analysis Of Phytochromes From The Filamentous Fungus Neurospora Crassa, Allan C. Froehlich, Bosl Noh, Richard D. Vierstra, Jennifer Loros, Jay C. Dunlap Dec 2005

Genetic And Molecular Analysis Of Phytochromes From The Filamentous Fungus Neurospora Crassa, Allan C. Froehlich, Bosl Noh, Richard D. Vierstra, Jennifer Loros, Jay C. Dunlap

Dartmouth Scholarship

Phytochromes (Phys) comprise a superfamily of red-/far-red-light-sensing proteins. Whereas higher-plant Phys that control numerous growth and developmental processes have been well described, the biochemical characteristics and functions of the microbial forms are largely unknown. Here, we describe analyses of the expression, regulation, and activities of two Phys in the filamentous fungus Neurospora crassa. In addition to containing the signature N-terminal domain predicted to covalently associate with a bilin chromophore, PHY-1 and PHY-2 contain C-terminal histidine kinase and response regulator motifs, implying that they function as hybrid two-component sensor kinases activated by light. A bacterially expressed N-terminal fragment of PHY-2 covalently …

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A Steerable, Untethered, 250x60 Micron Mems Mobile Micro-Robot, Bruce R. Donald, Christopher G. Levey, Craig D. Mcgray, Igor Paprotny, Daniela Rus Dec 2005

A Steerable, Untethered, 250x60 Micron Mems Mobile Micro-Robot, Bruce R. Donald, Christopher G. Levey, Craig D. Mcgray, Igor Paprotny, Daniela Rus

Computer Science Technical Reports

We present a steerable, electrostatic, untethered, MEMS micro-robot, with dimensions of 60 µm by 250 µm by 10 µm. This micro-robot is 1 to 2 orders of magnitude smaller in size than previous micro-robotic systems. The device consists of a curved, cantilevered steering arm, mounted on an untethered scratch drive actuator. These two components are fabricated monolithically from the same sheet of conductive polysilicon, and receive a common power and control signal through a capacitive coupling with an underlying electrical grid. All locations on the grid receive the same power and control signal, so that the devices can be operated …

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How Hard Is It To Cheat In The Gale-Shapley Stable Matching Algorithm, Chien-Chung Huang Dec 2005

How Hard Is It To Cheat In The Gale-Shapley Stable Matching Algorithm, Chien-Chung Huang

Computer Science Technical Reports

We study strategy issues surrounding the stable marriage problem. Under the Gale-Shapley algorithm (with men proposing), a classical theorem says that it is impossible for every liar to get a better partner. We try to challenge this theorem. First, observing a loophole in the statement of the theorem, we devise a coalition strategy in which a non-empty subset of the liars gets a better partner and no man is worse off than before. This strategy is restricted in that not everyone has the incentive to cheat. We attack the classical theorem further by means of randomization. However, this theorem shows …

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Crawdad: A Community Resource For Archiving Wireless Data At Dartmouth, David Kotz, Tristan Henderson Dec 2005

Crawdad: A Community Resource For Archiving Wireless Data At Dartmouth, David Kotz, Tristan Henderson

Dartmouth Scholarship

Wireless network researchers are seriously starved for data about how real users, applications, and devices use real networks under real network conditions. CRAWDAD (Community Resource for Archiving Wireless Data at Dartmouth) is a new National Science Foundation-funded project to build a wireless-network data archive for the research community. It will host wireless data and provide tools and documents to make collecting and using the data easy. This resource should help researchers identify and evaluate real and interesting problems in mobile and pervasive computing. To learn more about CRAWDAD and discuss its direction, about 30 interested people gathered at a workshop …

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The Caenorhabditis Elegans Heterochronic Regulator Lin-14 Is A Novel Transcription Factor That Controls The Developmental Timing Of Transcription From The Insulin/Insulin-Like Growth Factor Gene Ins-33 By Direct Dna Binding, Marta Hristova, Darcy Birse, Yang Hong, Victor Ambros Dec 2005

The Caenorhabditis Elegans Heterochronic Regulator Lin-14 Is A Novel Transcription Factor That Controls The Developmental Timing Of Transcription From The Insulin/Insulin-Like Growth Factor Gene Ins-33 By Direct Dna Binding, Marta Hristova, Darcy Birse, Yang Hong, Victor Ambros

Dartmouth Scholarship

A temporal gradient of the novel nuclear protein LIN-14 specifies the timing and sequence of stage-specific developmental events in Caenorhabditis elegans. The profound effects of lin-14 mutations on worm development suggest that LIN-14 directly or indirectly regulates stage-specific gene expression. We show that LIN-14 can associate with chromatin in vivo and has in vitro DNA binding activity. A bacterially expressed C-terminal domain of LIN-14 was used to select DNA sequences that contain a putative consensus binding site from a pool of randomized double-stranded oligonucleotides. To identify candidates for genes directly regulated by lin-14, we employed DNA microarray hybridization to compare …

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Dynamics Of A Nanomechanical Resonator Coupled To A Superconducting Single-Electron Transistor, M. P. Blencowe, J. Imbers, A. D. Armour Nov 2005

Dynamics Of A Nanomechanical Resonator Coupled To A Superconducting Single-Electron Transistor, M. P. Blencowe, J. Imbers, A. D. Armour

Dartmouth Scholarship

We present an analysis of the dynamics of a nanomechanical resonator coupled to a superconducting single-electron transistor (SSET) in the vicinity of Josephson quasi-particle (JQP) and double Josephson quasi-particle (DJQP) resonances. For weak coupling and wide separation of dynamical timescales, we find that for either superconducting resonances the dynamics of the resonator are given by a Fokker–Planck equation, i.e. the SSET behaves effectively as an equilibrium heat bath, characterized by an effective temperature, which also damps the resonator and renormalizes its frequency. Depending on the gate and drain–source voltage bias points with respect to the superconducting resonance, the SSET can …

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Visibility, Visual Awareness, And Visual Masking Of Simple Unattended Targets Are Confined To Areas In The Occipital Cortex Beyond Human V1/V2, Peter U. Tse, Susanna Martinez-Conde, Alexander A. Schlegel, Stephen L. Macknik Nov 2005

Visibility, Visual Awareness, And Visual Masking Of Simple Unattended Targets Are Confined To Areas In The Occipital Cortex Beyond Human V1/V2, Peter U. Tse, Susanna Martinez-Conde, Alexander A. Schlegel, Stephen L. Macknik

Dartmouth Scholarship

In visual masking, visible targets are rendered invisible by modifying the context in which they are presented, but not by modifying the targets themselves. Here, we localize the neuronal correlates of visual awareness in the human brain by using visual masking illusions. We compare monoptic visual masking activation, which we find within all retinotopic visual areas, with dichoptic masking activation, which we find only in those retinotopic areas downstream of V2. Because monoptic and dichoptic masking are equivalent in magnitude perceptually, the present results establish a lower bound for maintenance of visual awareness of simple unattended targets. Moreover, we find …

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Growth Factor–Induced Shedding Of Syndecan-1 Confers Glypican-1 Dependence On Mitogenic Responses Of Cancer Cells, Kan Ding, Martha Lopez-Burks, José A. Sánchez-Duran, Murray Korc, Arthur D. Lander Nov 2005

Growth Factor–Induced Shedding Of Syndecan-1 Confers Glypican-1 Dependence On Mitogenic Responses Of Cancer Cells, Kan Ding, Martha Lopez-Burks, José A. Sánchez-Duran, Murray Korc, Arthur D. Lander

Dartmouth Scholarship

The cell surface heparan sulfate proteoglycan (HSPG) glypican-1 is up-regulated by pancreatic and breast cancer cells, and its removal renders such cells insensitive to many growth factors. We sought to explain why the cell surface HSPG syndecan-1, which is also up-regulated by these cells and is a known growth factor coreceptor, does not compensate for glypican-1 loss. We show that the initial responses of these cells to the growth factor FGF2 are not glypican dependent, but they become so over time as FGF2 induces shedding of syndecan-1. Manipulations that retain syndecan-1 on the cell surface make long-term FGF2 responses glypican …

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Principal Component Analysis For Predicting Transcription-Factor Binding Motifs From Array-Derived Data, Yunlong Liu, Matthew P Vincenti, Hiroki Yokota Nov 2005

Principal Component Analysis For Predicting Transcription-Factor Binding Motifs From Array-Derived Data, Yunlong Liu, Matthew P Vincenti, Hiroki Yokota

Dartmouth Scholarship

The responses to interleukin 1 (IL-1) in human chondrocytes constitute a complex regulatory mechanism, where multiple transcription factors interact combinatorially to transcription-factor binding motifs (TFBMs). In order to select a critical set of TFBMs from genomic DNA information and an array-derived data, an efficient algorithm to solve a combinatorial optimization problem is required. Although computational approaches based on evolutionary algorithms are commonly employed, an analytical algorithm would be useful to predict TFBMs at nearly no computational cost and evaluate varying modelling conditions. Singular value decomposition (SVD) is a powerful method to derive primary components of a given matrix. Applying SVD …

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Low Magnetic Prandtl Number Dynamos With Helical Forcing, Pablo D. Mininni, David C. Montgomery Nov 2005

Low Magnetic Prandtl Number Dynamos With Helical Forcing, Pablo D. Mininni, David C. Montgomery

Dartmouth Scholarship

We present direct numerical simulations of dynamo action in a forced Roberts flow. The behavior of the dynamo is followed as the mechanical Reynolds number is increased, starting from the laminar case until a turbulent regime is reached. The critical magnetic Reynolds for dynamo action is found, and in the turbulent flow it is observed to be nearly independent on the magnetic Prandtl number in the range from ∼0.3 to ∼0.1. Also the dependence of this threshold with the amount of mechanical helicity in the flow is studied. For the different regimes found, the configuration of the magnetic and velocity …

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Human Immunodeficiency Virus Type 1-Induced Macrophage Gene Expression Includes The P21 Gene, A Target For Viral Regulation, Nancy Vazquez, Teresa Greenwell-Wild, Nancy J. Marinos, William D. Swaim, Salvador Nares, David E. Ott, Ulrich Schubert, Peter Henklein, Jan M. Orenstein, Michael B. Sporn, Sharon M. Wahl Nov 2005

Human Immunodeficiency Virus Type 1-Induced Macrophage Gene Expression Includes The P21 Gene, A Target For Viral Regulation, Nancy Vazquez, Teresa Greenwell-Wild, Nancy J. Marinos, William D. Swaim, Salvador Nares, David E. Ott, Ulrich Schubert, Peter Henklein, Jan M. Orenstein, Michael B. Sporn, Sharon M. Wahl

Dartmouth Scholarship

In contrast to CD4+ T cells, human immunodeficiency virus type 1 (HIV-1)-infected macrophages typically resist cell death, support viral replication, and consequently, may facilitate HIV-1 transmission. To elucidate how the virus commandeers the macrophage's intracellular machinery for its benefit, we analyzed HIV-1-infected human macrophages for virus-induced gene transcription by using multiple parameters, including cDNA expression arrays. HIV-1 infection induced the transcriptional regulation of genes associated with host defense, signal transduction, apoptosis, and the cell cycle, among which the cyclin-dependent kinase inhibitor 1A (CDKN1A/p21) gene was the most prominent. p21 mRNA and protein expression followed a bimodal pattern which was …

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Master’S Thesis Proposal: Computation Reuse In Stacking And Unstacking, Anne Loomis Nov 2005

Master’S Thesis Proposal: Computation Reuse In Stacking And Unstacking, Anne Loomis

Computer Science Technical Reports

Algorithms for dynamic simulation and control are fundamental to many applications, including computer games and movies, medical simulation, and mechanical design. I propose to explore efficient algorithms for finding a stable unstacking sequence -- an order in which we can remove every object from a structure without causing the structure to collapse under gravity at any step. We begin with a basic unstacking sequence algorithm: consider the set of all objects in a structure. Collect all possible subsets into a disassembly graph. Search the graph, testing the stability of each node as it is visited. Any path of stable nodes …

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Ecological Costs And Benefits Of Defenses In Nectar, Lynn S. Adler, Rebecca E. Irwin Nov 2005

Ecological Costs And Benefits Of Defenses In Nectar, Lynn S. Adler, Rebecca E. Irwin

Dartmouth Scholarship

The nectar of many plant species contains defensive compounds that have been hypothesized to benefit plants through a variety of mechanisms. However, the relationship between nectar defenses and plant fitness has not been established for any species. We experimentally manipulated gelsemine, the principal alkaloid of Carolina jessamine (Gelsemium sempervirens), in nectar to determine its effect on pollinator visitation, nectar robber visitation, and male and female plant reproduction. We found that nectar robbers and most pollinators probed fewer flowers and spent less time per flower on plants with high compared to low nectar alkaloids. High alkaloids decreased the donation of fluorescent …

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Detection Of Covert Channel Encoding In Network Packet Delays, Vincent Berk, Annarita Giani, George Cybenko Nov 2005

Detection Of Covert Channel Encoding In Network Packet Delays, Vincent Berk, Annarita Giani, George Cybenko

Computer Science Technical Reports

Covert channels are mechanisms for communicating information in ways that are difficult to detect. Data exfiltration can be an indication that a computer has been compromised by an attacker even when other intrusion detection schemes have failed to detect a successful attack. Covert timing channels use packet inter-arrival times, not header or payload embedded information, to encode covert messages. This paper investigates the channel capacity of Internet-based timing channels and proposes a methodology for detecting covert timing channels based on how close a source comes to achieving that channel capacity. A statistical approach is then used for the special case …

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Towards A Precision Measurement Of The Casimir Force In A Cylinder-Plane Geometry, M. Brown-Hayes, D. A.R. Dalvit, F. D. Mazzitelli, W. J. Kim, R. Onofrio Nov 2005

Towards A Precision Measurement Of The Casimir Force In A Cylinder-Plane Geometry, M. Brown-Hayes, D. A.R. Dalvit, F. D. Mazzitelli, W. J. Kim, R. Onofrio

Dartmouth Scholarship

We report on a proposal aimed at measuring the Casimir force in the cylinder-plane configuration. The Casimir force is evaluated including corrections due to finite parallelism, conductivity, and temperature. The range of validity of the proximity force approximation is also discussed. An apparatus to test the feasibility of a precision measurement in this configuration has been developed, and we describe both a procedure to control the parallelism and the results of the electrostatic calibration. Finally we discuss the possibility of measuring the thermal contribution to the Casimir force and deviations from the proximity force approximation, both of which are expected …

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Rhamnolipids Modulate Swarming Motility Patterns Of Pseudomonas Aeruginosa, Nicky C. Caiazza, Robert M. Q. Shanks, G. A. O'Toole Nov 2005

Rhamnolipids Modulate Swarming Motility Patterns Of Pseudomonas Aeruginosa, Nicky C. Caiazza, Robert M. Q. Shanks, G. A. O'Toole

Dartmouth Scholarship

Pseudomonas aeruginosa is capable of twitching, swimming, and swarming motility. The latter form of translocation occurs on semisolid surfaces, requires functional flagella and biosurfactant production, and results in complex motility patterns. From the point of inoculation, bacteria migrate as defined groups, referred to as tendrils, moving in a coordinated manner capable of sensing and responding to other groups of cells. We were able to show that P. aeruginosa produces extracellular factors capable of modulating tendril movement, and genetic analysis revealed that modulation of these movements was dependent on rhamnolipid biosynthesis. An rhlB mutant (deficient in mono- and dirhamnolipid production) and …

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Sympathetic Cooling Route To Bose-Einstein Condensate And Fermi-Liquid Mixtures, Robin Côté, Roberto Onofrio, Eddy Timmermans Oct 2005

Sympathetic Cooling Route To Bose-Einstein Condensate And Fermi-Liquid Mixtures, Robin Côté, Roberto Onofrio, Eddy Timmermans

Dartmouth Scholarship

We discuss a sympathetic cooling strategy that can successfully mitigate fermion-hole heating in a dilute atomic Fermi-Bose mixture and access the temperature regime in which the fermions behave as a Fermi liquid. We introduce an energy-based formalism to describe the temperature dynamics with which we study a specific and promising mixture, composed of 6Li and 87Rb. Analyzing the harmonically trapped mixture, we find that the favorable features of this mixture are further enhanced by using different trapping frequencies for the two species.

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The Changing Demographic, Legal, And Technological Contexts Of Political Representation, Benjamin Forest Oct 2005

The Changing Demographic, Legal, And Technological Contexts Of Political Representation, Benjamin Forest

Dartmouth Scholarship

Three developments have created challenges for political representation in the U.S. and particularly for the use of territorially based representation (election by district). First, the demographic complexity of the U.S. population has grown both in absolute terms and in terms of residential patterns. Second, legal developments since the 1960s have recognized an increasing number of groups as eligible for voting rights protection. Third, the growing technical capacities of computer technology, particularly Geographic Information Systems, have allowed political parties and other organizations to create election districts with increasingly precise political and demographic characteristics. Scholars have made considerable progress in measuring and …

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Assimilation And Differences Between The Settlement Patterns Of Individual Immigrants And Immigrant Households, Mark Ellis, Richard Wright Oct 2005

Assimilation And Differences Between The Settlement Patterns Of Individual Immigrants And Immigrant Households, Mark Ellis, Richard Wright

Dartmouth Scholarship

Analyses of immigrant settlement patterns typically rely on counts of foreign-born individuals by neighborhood, metropolitan area, state, or region. As an alternative, this study classifies immigrants and their descendents into household types to shift attention from individuals to relationships between individuals. The study uses pooled current population survey data to identify seven household types, six of which have various degrees of immigrant or second-generation presence. The research compares distributions of first- and second-generation immigrants with different types of households that include first- and second-generation immigrants. Our analysis shows that the geography of immigration based on households differs considerably from geographies …

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Noao Fundamental Plane Survey. Ii. Age And Metallicity Along The Red Sequence From Line‐Strength Data, Jenica E. Nelan, Russell J. Smith, Michael J. Hudson, Gary A. Wegner Oct 2005

Noao Fundamental Plane Survey. Ii. Age And Metallicity Along The Red Sequence From Line‐Strength Data, Jenica E. Nelan, Russell J. Smith, Michael J. Hudson, Gary A. Wegner

Dartmouth Scholarship

We present spectroscopic line-strength data for 4097 red-sequence galaxies in 93 low-redshift galaxy clusters and use these to investigate variations in average stellar populations as a function of galaxy mass. Our analysis includes an improved treatment of nebular emission contamination, which affects ~10% of the sample galaxies. Using the stellar population models of D. Thomas and collaborators, we simultaneously fit 12 observed line-strength-σ relations in terms of common underlying trends of age, [Z/H] (total metallicity), and [α/Fe] (α-element enhancement). We find that the observed line-strength-σ relations can be explained only if higher mass red-sequence galaxies are, on average, …

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Combinatorial Theorems About Embedding Trees On The Real Line, Amit Chakrabarti, Subhash Khot Oct 2005

Combinatorial Theorems About Embedding Trees On The Real Line, Amit Chakrabarti, Subhash Khot

Computer Science Technical Reports

We consider the combinatorial problem of embedding a tree metric into the real line with low distortion. For two special families of trees --- the family of complete binary trees and the family of subdivided stars --- we provide embeddings whose distortion is provably optimal, up to a constant factor. We also prove that the optimal distortion of a linear embedding of a tree can be arbitrarily low or high even when it has bounded degree.

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A Quasi-Ptas For Unsplittable Flow On Line Graphs, Nikhil Bansal, Amit Chakrabarti, Amir Epstein, Baruch Schieber Oct 2005

A Quasi-Ptas For Unsplittable Flow On Line Graphs, Nikhil Bansal, Amit Chakrabarti, Amir Epstein, Baruch Schieber

Computer Science Technical Reports

We study the Unsplittable Flow Problem (UFP) on a line graph, focusing on the long-standing open question of whether the problem is APX-hard. We describe a deterministic quasi-polynomial time approximation scheme for UFP on line graphs, thereby ruling out an APX-hardness result, unless NP is contained in DTIME(2^polylog(n)). Our result requires a quasi-polynomial bound on all edge capacities and demands in the input instance. Earlier results on this problem included a polynomial time (2+epsilon)-approximation under the assumption that no demand exceeds any edge capacity (the "no-bottleneck assumption") and a super-constant integrality gap if this assumption did not hold. Unlike most …

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Near-Infrared Characterization Of Breast Tumors In Vivo Using Spectrally-Constrained Reconstruction, Subhadra Srinivasan, Brian W. Pogue, Ben Brooksby, Shudong Jiang, Hamid Dehghani, Christine Kogel, Wendy A. Wells, Steven P. Poplack, Keith D. Paulsen Oct 2005

Near-Infrared Characterization Of Breast Tumors In Vivo Using Spectrally-Constrained Reconstruction, Subhadra Srinivasan, Brian W. Pogue, Ben Brooksby, Shudong Jiang, Hamid Dehghani, Christine Kogel, Wendy A. Wells, Steven P. Poplack, Keith D. Paulsen

Dartmouth Scholarship

Multi-wavelength Near-Infrared (NIR) Tomography was utilized in this study to non-invasively quantify physiological parameters of breast tumors using direct spectral reconstruction. Frequency domain NIR measurements were incorporated with a new spectrally constrained direct chromophore and scattering image reconstruction algorithm, which was validated in simulations and experimental phantoms. Images of total hemoglobin, oxygen saturation, water, and scatter parameters were obtained with higher accuracy than previously reported. Using this spectral approach, in vivo NIR images are presented and interpreted through a series of case studies (n=6 subjects) having differing abnormalities. The corresponding mammograms and ultrasound images are also evaluated. Three of six …

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Limits Of Quintessence, R. R. Caldwell, Eric V. Linder Sep 2005

Limits Of Quintessence, R. R. Caldwell, Eric V. Linder

Dartmouth Scholarship

We present evidence that the simplest particle-physics scalar-field models of dynamical dark energy can be separated into distinct behaviors based on the acceleration or deceleration of the field as it evolves down its potential towards a zero minimum. We show that these models occupy narrow regions in the phase plane of w and w′, the dark energy equation of state and its time derivative in units of the Hubble time. Restricting an energy scale of the dark energy microphysics limits how closely a scalar field can resemble a cosmological constant. These results, indicating a desired measurement resolution of order σ(w′)≈(1+w), …

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Hs 2331+3905: The Cataclysmic Variable That Has It All, S. Araujo-Betancor, B. T. Gänsicke, H.-J. Hagen, T. R. Marsh, E T. Harlaftis, J Thorstensen Sep 2005

Hs 2331+3905: The Cataclysmic Variable That Has It All, S. Araujo-Betancor, B. T. Gänsicke, H.-J. Hagen, T. R. Marsh, E T. Harlaftis, J Thorstensen

Dartmouth Scholarship

We report detailed follow-up observations of the cataclysmic variable HS 2331+3905, identified as an emission- line object in the Hamburg Quasar Survey. An orbital period of 81.08 min is unambiguously determined from the detection of eclipses in the light curves of HS 2331+3905. A second photometric period is consistently detected at P ≃ 83.38 min, ∼2.8% longer than Porb, which we tentatively relate to the presence of permanent superhumps. High time resolution photometry exhibits short-timescale variability on time scales of ≃5−6 min which we interpret as non-radial white dwarf pulsations, as well as a coherent signal at 1.12 min, which …

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The Effect Of Particles On Dynamic Recrystallization And Fabric Development Of Granular Ice During Creep, Min Song, Ian Baker, David M. Cole Sep 2005

The Effect Of Particles On Dynamic Recrystallization And Fabric Development Of Granular Ice During Creep, Min Song, Ian Baker, David M. Cole

Dartmouth Scholarship

The mechanical behavior and microstructural evolution of laboratory-prepared, particle-free fresh-water ice and ice with 1 wt.% (~0.43 vol.%) silt-sized particles were investigated under creep with a stress level of 1.45 MPa at −10°C. The particles were present both within the grains and along the grain boundaries. The creep rates of specimens with particles were always higher than those of particle-free ice. Dynamic recrystallization occurred for both sets of specimens, with new grains nucleating along grain boundaries in the early stages of creep. The ice with particles showed a higher nucleation rate. This resulted in a smaller average grain-size for the …

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A Drosophila Deg/Enac Channel Subunit Is Required For Male Response To Female Pheromones, Heping Lin, Kevin J. Mann, Elena Starostina, Ronald D. Kinser, Claudio W. Pikielny Sep 2005

A Drosophila Deg/Enac Channel Subunit Is Required For Male Response To Female Pheromones, Heping Lin, Kevin J. Mann, Elena Starostina, Ronald D. Kinser, Claudio W. Pikielny

Dartmouth Scholarship

Odorants and pheromones as well as sweet- and bitter-tasting small molecules are perceived through activation of G protein-coupled chemosensory receptors. In contrast, gustatory detection of salty and sour tastes may involve direct gating of sodium channels of the DEG/ENaC family by sodium and hydrogen ions, respectively. We have found that ppk25, a Drosophila melanogaster gene encoding a DEG/ENaC channel subunit, is expressed at highest levels in the male appendages responsible for gustatory and olfactory detection of female pheromones: the legs, wings, and antennae. Mutations in the ppk25 gene reduce or even abolish male courtship response to females in the dark, …

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