D-Branes and Spin^c Structures

It was recently pointed out by E. Witten that for a D-brane to consistently wrap a submanifold of some manifold, the normal bundle must admit a Spin^c structure. We examine this constraint in the case of type II string compactifications with vanishing cosmological constant, and argue that in all such cases, the normal bundle to a supersymmetric cycle is automatically Spin^c.Comment: 9 pages, LaTe

Machine Learning Techniques for the Development of a Stratego Bot

Stratego is a two-player, non-stochastic, imperfect-information strategy game in which players try to locate and capture the opponent\u27s flag. At the outset o f each game, players deploy their pieces in any arrangement they choose. Throughout play, each player knows the positions of the opponent’s pieces, but not the specific identities o f the opponent’s pieces. The game therefore involves deduction, bluffing, and a degree o f invention in addition to the sort o f planning familiar to perfect-information games like chess or backgammon. Developing a strong A.l. player presents three major challenges. Firstly, a Stratego program must maintain states o f belief about the opponent’s pieces as well as beliefs about the opponent’s beliefs. Beliefs must be updated according to in-game events. We propose to solve this using Bayesian probability theory and Bayesian networks. Secondly, any turn-based game-playing program must perform tree search as part o f its planning and move-making routine. Search in perfect-information games such as chess has been studied extensively and produced a wealth o f algorithms and heuristics to expedite the process. Stochastic and imperfect-information games, however, have received less general attention, though Schaeffer et al have made a significant effort to revisit this domain. Interestingly, the same family o f algorithms (Ballard’s Star-1 and Star-2) used in the stochastic perfect-information game of backgammon can be used in the deterministic, imperfect-information domain o f Stratego. The technical challenge here, just as in the stochastic domain, is to optimize node cutoffs. Thirdly, a strong Stratego program should have some degree o f inventiveness so that it can avoid predictable play. The game’s intricacy comes from information being concealed from the players. A program which plays too predictably (that is, according to known or obvious tactics) has a significant disadvantage against a more creative opponent. There is a balance, however, between tactics’ being novel and being foolish. Current, strong Stratego programs have been developed by human experts (such as Vincent deBoer), whose tactical preferences are hard-coded into those programs. Since we claim no especial talent for Stratego ourselves, part o f the development challenge will be to allow the program to discover tactical preferences and advantages on its own. Withholding explicitly programmed heuristics and allowing machines to discover tactics on their own has led to original and powerful computer play in the past (note Tesauro’s success with TD-Gammon). We hope our program will likewise learn to play competitively without depending on instruction from a mediocre or predictable player. Various techniques from machine learning, including both supervised and unsupervised learning, are applied to this objective. At our disposal are more than 50,000 match records from an online Stratego site. Part of developing a strong player will involve separating the truly advantageous features in these data from features which are merely frequent. The learning process must be objective enough to avoid bias and predictability, yet robust enough to exploit utility. We introduce a modeling method which allows partial instruction as guidelines for feature detection

Synergistic effects of ultraviolet radiation, thermal cycling, and atomic oxygen on altered and coated Kapton surfaces

The photovoltaic (PV) power system for Space Station Freedom (SSF) uses solar array blankets which provide structural support for the solar cells and house the electrical interconnections. In the low Earth orbital (LEO) environment where SSF will be located, surfaces will be exposed to potentially damaging environmental conditions including solar ultraviolet (UV) radiation, thermal cycling, and atomic oxygen. It is necessary to use ground based tests to determine how these environmental conditions would affect the mass loss and optical properties of candidate SSF blanket materials. Silicone containing, silicone coated, and SiO(x) coated polyimide film materials were exposed to simulated LEO environmental conditions to determine there durability and whether the environmental conditions of UV, thermal cycling and oxygen atoms act synergistically on these materials. A candidate PV blanket material called AOR Kapton, a polysiloxane polyimide cast from a solution mixture, shows an improvement in durability to oxygen atoms erosion after exposure to UV radiation or thermal cycling combined with UV radiation. This may indicate that the environmental conditions react synergistically with this material, and the damage predicted by exposure to atomic oxygen alone is more severe than that which would occur in LEO where atomic oxygen, thermal cycling and UV radiation are present together

Chromosome Axis Defects Induce a Checkpoint-Mediated Delay and Interchromosomal Effect on Crossing Over during Drosophila Meiosis

Crossovers mediate the accurate segregation of homologous chromosomes during meiosis. The widely conserved pch2 gene of Drosophila melanogaster is required for a pachytene checkpoint that delays prophase progression when genes necessary for DSB repair and crossover formation are defective. However, the underlying process that the pachytene checkpoint is monitoring remains unclear. Here we have investigated the relationship between chromosome structure and the pachytene checkpoint and show that disruptions in chromosome axis formation, caused by mutations in axis components or chromosome rearrangements, trigger a pch2-dependent delay. Accordingly, the global increase in crossovers caused by chromosome rearrangements, known as the “interchromosomal effect of crossing over,” is also dependent on pch2. Checkpoint-mediated effects require the histone deacetylase Sir2, revealing a conserved functional connection between PCH2 and Sir2 in monitoring meiotic events from Saccharomyces cerevisiae to a metazoan. These findings suggest a model in which the pachytene checkpoint monitors the structure of chromosome axes and may function to promote an optimal number of crossovers

SELECTED FACTORS INFLUENCING THE IMPLEMENTATION OF SUBSIDISED PUBLIC SECONDARY SCHOOL EDUCATION IN BURETI SUB- COUNTY, KERICHO COUNTY, KENYA

In the last decade, the government of Kenya has emphasized the provision of education as a leading policy initiative. As a result, the government instituted the Free Primary Education (FPE) in the year 2003, which resulted in high enrolment of the pupils at the Primary level. However, costly school fees were found to be a major reason that the vast majority of primary graduates could not attend Secondary schools because their families could not afford the cost. The provision of Subsidized Secondary Education (SSE) is very important in Kenya given that the country is a low income one. SSE policy was launched in 2008 with an aim of ensuring that all primary pupils from class eight are able to continue well with secondary education. There are limited studies on the SSE programme currently and it is against this background that this study sought to shed more light on the programme. The purpose of this study was to establish factors influencing implementation of SSE policy on access and retention of education in public secondary schools in Bureti Sub-County. The study aimed at establishing the factors that influence effective implementation of free secondary education in public schools in Buret Sub-County, in Kericho County, Kenya. The study adopted a descriptive survey research design. The target population was the school Principals/Deputy Principals, Teachers, Sub-County Director of Education, District Quality Assurance and Standard Officer. Simple random, systematic and stratified sampling procedures were used. Both qualitative and quantitative data was collected from the study. Data analysis was done using descriptive statistics after data cleaning and coding. Quantitative data was analyzed using frequency counts, means and percentages while qualitative data was analyzed thematically. Results of data analysis were presented using frequency distribution tables, bar graphs and pie charts. SPSS program was used in the analysis. The findings show that the major challenges facing implementation of FSE includes; Delay in disbursing the SSE funds, over enrolment of students leading to strained physical facilities, inadequate facilities, lack of funds from the government for expansion, acute teacher shortage, poor cost sharing strategies. Key intervention measures for mitigating the identified challenges includes; Government to release funds in good time to avoid straining relations between suppliers and schools management, increasing bursaries support from M.O.E, NGOS, CDF for continuing students, providing clear policy on fund disbursement and increasing FSE allocation per student among others

PGB: A PubMed Graph Benchmark for Heterogeneous Network Representation Learning

There has been a rapid growth in biomedical literature, yet capturing the heterogeneity of the bibliographic information of these articles remains relatively understudied. Although graph mining research via heterogeneous graph neural networks has taken center stage, it remains unclear whether these approaches capture the heterogeneity of the PubMed database, a vast digital repository containing over 33 million articles. We introduce PubMed Graph Benchmark (PGB), a new benchmark dataset for evaluating heterogeneous graph embeddings for biomedical literature. PGB is one of the largest heterogeneous networks to date and consists of 30 million English articles. The benchmark contains rich metadata including abstract, authors, citations, MeSH terms, MeSH hierarchy, and some other information. The benchmark contains three different evaluation tasks encompassing systematic reviews, node classification, and node clustering. In PGB, we aggregate the metadata associated with the biomedical articles from PubMed into a unified source and make the benchmark publicly available for any future works

My Way or the Highway: a More Naturalistic Model of Altruism Tested in an Iterative Prisoners' Dilemma

There are three prominent solutions to the Darwinian problem of altruism, kin selection, reciprocal altruism, and trait group selection. Only one, reciprocal altruism, most commonly implemented in game theory as a TIT FOR TAT strategy, is not based on the principle of conditional association. On the contrary, TIT FOR TAT implements conditional altruism in the context of unconditionally determined associates. Simulations based on Axelrod\'s famous tournament have led many to conclude that conditional altruism among unconditional partners lies at the core of much human and animal social behavior. But the results that have been used to support this conclusion are largely artifacts of the structure of the Axelrod tournament, which explicitly disallowed conditional association as a strategy. In this study, we modify the rules of the tournament to permit competition between conditional associates and conditional altruists. We provide evidence that when unconditional altruism is paired with conditional association, a strategy we called MOTH, it can out compete TIT FOR TAT under a wide range of conditions.Game Theory; Altruism; Prisoners' Dilemma; TIT FOR TAT; MOTH; Docking; Netlogo

Management of differences in sexual development: evolution of an approach for a resource-limited setting

Background: The approach to management of patients with disorders of sex development (DSD) has been refined over the past two decades. We sought to review DSD cases at our hospital and hypothesized that age at presentation would decline over time. Methods: A retrospective review of patients presenting to our hospital between January 1, 2005 and July 31, 2018, with findings of ambiguous genitalia was performed. Results: A total of 44 patients were identified, 3 with cloacal exstrophy. Of the 41 remaining patients, the majority (n = 24) had ovotesticular DSD. Three time periods in the evolution to a multidisciplinary team (MDT) approach were identified: Period 1 (2003–2009), Period 2 (2010– 2013), and Period 3 (2014–present). Median presenting age in Periods 1, 2, and 3 were 7 years (95% CI: 0.5–15), 6.5 years (95% CI: 1–19), and 11 years (95% CI: 2–17), respectively, and were not statistically different. Conclusion: Management of patients with DSD poses a challenge to healthcare providers across the globe. The gradual evolution of patient management with incorporation of MDTs and progression toward delayed surgery is seen in this study. There is indeed a need to set up regional centers of excellence, public awareness programs, and healthcare personnel training programs for optimal management of these patients in low- and middle-income countries (LMICs)

Apollo: A System for Tracking Internet Censorship

If it remains debatable whether the Internet has surpassed print media in making information accessible to the public, then it must nevertheless be conceded that the Internet makes the manipulation and censorship of information easier than had been on the printed page. In coming years and in an increasing number of countries, everyday producers and consumers of online information will likely have to cultivate a sense of censorship. It behooves the online community to learn how to detect and evade interference by governments, regimes, corporations, con-artists, and vandals. The contribution of this research is to describe a method and platform to study Internet censorship detection and evasion. This paper presents the concepts, initial theories, and future work