A Computational Approach to Estimating Nondisjunction Frequency in Saccharomyces cerevisiae.

Errors segregating homologous chromosomes during meiosis result in aneuploid gametes and are the largest contributing factor to birth defects and spontaneous abortions in humans. Saccharomyces cerevisiae has long served as a model organism for studying the gene network supporting normal chromosome segregation. Measuring homolog nondisjunction frequencies is laborious, and involves dissecting thousands of tetrads to detect missegregation of individually marked chromosomes. Here we describe a computational method (TetFit) to estimate the relative contributions of meiosis I nondisjunction and random-spore death to spore inviability in wild type and mutant strains. These values are based on finding the best-fit distribution of 4, 3, 2, 1, and 0 viable-spore tetrads to an observed distribution. Using TetFit, we found that meiosis I nondisjunction is an intrinsic component of spore inviability in wild-type strains. We show proof-of-principle that the calculated average meiosis I nondisjunction frequency determined by TetFit closely matches empirically determined values in mutant strains. Using these published data sets, TetFit uncovered two classes of mutants: Class A mutants skew toward increased nondisjunction death, and include those with known defects in establishing pairing, recombination, and/or synapsis of homologous chromosomes. Class B mutants skew toward random spore death, and include those with defects in sister-chromatid cohesion and centromere function. Epistasis analysis using TetFit is facilitated by the low numbers of tetrads (as few as 200) required to compare the contributions to spore death in different mutant backgrounds. TetFit analysis does not require any special strain construction, and can be applied to previously observed tetrad distributions

Using Grid Cells for Navigation

SummaryMammals are able to navigate to hidden goal locations by direct routes that may traverse previously unvisited terrain. Empirical evidence suggests that this “vector navigation” relies on an internal representation of space provided by the hippocampal formation. The periodic spatial firing patterns of grid cells in the hippocampal formation offer a compact combinatorial code for location within large-scale space. Here, we consider the computational problem of how to determine the vector between start and goal locations encoded by the firing of grid cells when this vector may be much longer than the largest grid scale. First, we present an algorithmic solution to the problem, inspired by the Fourier shift theorem. Second, we describe several potential neural network implementations of this solution that combine efficiency of search and biological plausibility. Finally, we discuss the empirical predictions of these implementations and their relationship to the anatomy and electrophysiology of the hippocampal formation

Gauge Boson Exchange in AdSd+1AdS_{d+1}

We study the amplitude for exchange of massless gauge bosons between pairs of massive scalar fields in Anti-de Sitter space. In the AdS/CFT correspondence this amplitude describes the contribution of conserved flavor symmetry currents to 4-point functions of scalar operators in the boundary conformal theory. A concise, covariant (Y2K-compatible) derivation of the gauge boson propagator in \AdS_{d+1} is given. Techniques are developed to calculate the two bulk integrals over AdS space leading to explicit expressions or convenient, simple integral representations for the amplitude. The amplitude contains leading power and sub-leading logarithmic singularities in the gauge boson channel and leading logarithms in the crossed channel. The new methods of this paper are expected to have other applications in the study of the Maldacena conjecture.Comment: Corrections in (3.17) and (4.23); version to be published in Nuclear Physics B; 22 pages, 1 figure, using Plain TeX and BoxedEPS macros; email to [email protected]

Review of Child Neglect in Scotland

Neglect is damaging to children in the short and long term. Neglect is associated with some of the poorest outcomes. It affects children in the early years, but teenage neglect, often overlooked, is also damaging. Formulating an effective response to neglect still poses national and local challenges

An Assessment of Technical and Production Risks of Candidate Low-Cost Attitude/Heading Reference Systems(AHRS)

This report provides an assessment of technical and production risks of candidate low-cost attitude/heading reference systems (AHRS) for use in the Advanced General Aviation Transport Experiments (AGATE) airplanes. A low-cost AHRS is a key component of modem "glass cockpit" flight displays for General Aviation (GA) aircraft. The technical capabilities of several candidate low-cost AHRS were examined and described along with the technical issues involved with using all solid-state components for attitude measurement. An economic model was developed which describes the expected profit, rate of return, and volume requirements for the manufacture of low-cost AHRS for GA aircraft in the 2000 to 2020 time frame. The model is the result of interviews with GA airframe manufacturers, avionics manufacturers and historical analysis of avionics of similar complexity. The model shows that a manufacturer will break even after three years of AHRS production, realizing an 18 percent rate of return (23 percent profit) on an investment of $3.5M over the 20 year period. A start-up production estimate showed costs of$6-12M for a new company to build and certify an AHRS from scratch, considered to be a high-risk proposition, versus $0.25-0.75M for an experienced avionics manufacturer to manufacture a design under license, a low-risk proposition

Autonomous Golf Cart

Cedarville University’s Autonomous Golf Cart Senior Design Project’s mission is to provide engineering students with hands on experience with industry standard intelligent vehicle technologies, solve open-ended, multi-dimensional problems, and provide an autonomous transportation service to the greater campus community. Our autonomous technology will share the sidewalks; therefore, the public image of our autonomous routing service is critically linked with its technical performance. The autonomous golf cart has two major design areas: the cart’s hardware and its software. Within hardware, our team created functional braking and an H-Bridge for reversing. Within software, our team moved the codebase to a new software framework, implemented dynamic routing, and began obstacle avoidance using LiDAR

Playing poker with a committee : assessing the viability of coalitional coercive diplomacy

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Political Science, 2007.Includes bibliographical references.Since the end of the Cold War, 'coercive diplomacy', that is the strategic use of threats aimed at convincing an adversary to stop or undo 'hostile' actions, has become a principle crisis management tool of the Western powers. Yet as a strategy it has a relatively poor track record of success; a record that theorists have struggled to explain. Despite the fact that the majority of such engagements have been undertaken multilaterally, little work to date has focused on the impact that employing a coalitional 'coercing agent' has on the ability to craft a potent package of threats. This study aims to contribute to the debate by testing empirically the impact of coalitional dynamics on the ability of Western powers to employ coercive diplomacy. More specifically, it explores the theoretical tension between the anecdotal assumptions held by certain theorists regarding coalitional action problems (CAP) on the one hand and Jakobsen's four-point ideal policy of coercive diplomacy on the other. I explore this tension through two case studies: the employment of coercive diplomacy by NATO and the Contact Group aimed at halting Serbian aggression in Bosnia between 1992 and 1995 and the Western coalition's attempt to roll back the Iraqi invasion of Kuwait in 1990. The study finds that although CAP do arise as predicted, coalitions have effective mechanisms for overcoming them and thus are able to effectively implement coercive threat packages that approximate to Jakobsen's ideal policy.by Daniel Peter Burgess.S.M