Topological Field Theory and Rational Curves

We analyze the superstring propagating on a Calabi-Yau threefold. This theory naturally leads to the consideration of Witten's topological non-linear sigma-model and the structure of rational curves on the Calabi-Yau manifold. We study in detail the case of the world-sheet of the string being mapped to a multiple cover of an isolated rational curve and we show that a natural compactification of the moduli space of such a multiple cover leads to a formula in agreement with a conjecture by Candelas, de la Ossa, Green and Parkes.Comment: 20 page

Genome-Wide Association Study for Type 2 Diabetes in Indians Identifies a New Susceptibility Locus at 2q21

Indians undergoing socioeconomic and lifestyle transitions will be maximally affected by epidemic of type 2 diabetes (T2D). We conducted a two-stage genome-wide association study of T2D in 12,535 Indians, a less explored but high-risk group. We identified a new type 2 diabetes–associated locus at 2q21, with the lead signal being rs6723108 (odds ratio 1.31; P = 3.32 3 1029 ). Imputation analysis refined the signal to rs998451 (odds ratio 1.56; P = 6.3 3 10212) within TMEM163 that encodes a probable vesicular transporter in nerve terminals. TMEM163 variants also showed association with decreased fasting plasma insulin and homeostatic model assessment of insulin resistance, indicating a plausible effect through impaired insulin secretion. The 2q21 region also harbors RAB3GAP1 and ACMSD; those are involved in neurologic disorders. Forty-nine of 56 previously reported signals showed consistency in direction with similar effect sizes in Indians and previous studies, and 25 of them were also associated (P , 0.05). Known loci and the newly identified 2q21 locus altogether explained 7.65% variance in the risk of T2D in Indians. Our study suggests that common susceptibility variants for T2D are largely the same across populations, but also reveals a population-specific locus and provides further insights into genetic architecture and etiology of T2D

John William Trevan’s concept of Median Lethal Dose (LD50/LC50) – more misused than used

Introduction: Median lethal dose (MLD) has been a controversial subject among biologists and animal ethicists since its inception in 1927 by Trevan. Toxicologists use MLD (LD50) as the first step to assess the toxicity of a substance. Animal ethicists criticize LD50 tests because animals suffer pain, and LD50 is irreproducible. The disadvantage of classifying chemicals based on LD50, the importance of the ‘characteristics’ proposed by Trevan, and the ideal mortality range for determining the best estimate of LD50 are also discussed. Objective: The aim of this review was to understand Trevan’s concept of LD50 and the method of Litchfield and Wilcoxon (L and W), and Finney’s probit analysis for LD50 determination Materials and method: A literature survey was conducted using Google search and Pubmed. Simulated data set was used for identifying the ideal mortality range for calculating the ‘best estimate’ of LD50. Brief description of the state of knowledge: After Trevan, the extensively used classical methods for LD50 determination are Finney’s probit analysis and the L and W method. Animal ethicists questioned LD50, because of its irreproducibility. Presently used methods for LD50 tests do not provide information on the dose-response, hence assessing the complete spectrum of toxicity is not possible. However, LD50 is used to classify chemicals. Conclusions: 'The 'characteristic' is more specific than the slope or LD50 of a dose-response curve. LD50 does not manifest the exact nature of the toxicity of a substance; hence, classifying chemicals based on LD50s may have little relevanc