Two-electron elastic tunneling in low-dimensional conductors

This article was published in the journal, Physical Review B [© American Physical Society]. It is also available at: http://link.aps.org/abstract/PRB/v65/e155209.We solve the Lippmann-Schwinger equation describing one-dimensional elastic scattering of preformed pairs (e.g., bipolarons) off a short-range scattering center, and find the two-particle transmission through a thin potential barrier. While the pair transmission is smaller than the single-electron transmission in the strong-coupling limit, it is remarkably larger in the weak-coupling limit. We also calculate current-voltage characteristics of a molecule-barrier-molecule junction. They show unusual temperature and voltage behaviors which are experimentally verifiable at low temperatures in bulk and nanoscale molecular conductors

Meta-analysis of type 2 Diabetes in African Americans Consortium

Type 2 diabetes (T2D) is more prevalent in African Americans than in Europeans. However, little is known about the genetic risk in African Americans despite the recent identification of more than 70 T2D loci primarily by genome-wide association studies (GWAS) in individuals of European ancestry. In order to investigate the genetic architecture of T2D in African Americans, the MEta-analysis of type 2 DIabetes in African Americans (MEDIA) Consortium examined 17 GWAS on T2D comprising 8,284 cases and 15,543 controls in African Americans in stage 1 analysis. Single nucleotide polymorphisms (SNPs) association analysis was conducted in each study under the additive model after adjustment for age, sex, study site, and principal components. Meta-analysis of approximately 2.6 million genotyped and imputed SNPs in all studies was conducted using an inverse variance-weighted fixed effect model. Replications were performed to follow up 21 loci in up to 6,061 cases and 5,483 controls in African Americans, and 8,130 cases and 38,987 controls of European ancestry. We identified three known loci (TCF7L2, HMGA2 and KCNQ1) and two novel loci (HLA-B and INS-IGF2) at genome-wide significance (4.15 × 10(-94)<P<5 × 10(-8), odds ratio (OR)  = 1.09 to 1.36). Fine-mapping revealed that 88 of 158 previously identified T2D or glucose homeostasis loci demonstrated nominal to highly significant association (2.2 × 10(-23) < locus-wide P<0.05). These novel and previously identified loci yielded a sibling relative risk of 1.19, explaining 17.5% of the phenotypic variance of T2D on the liability scale in African Americans. Overall, this study identified two novel susceptibility loci for T2D in African Americans. A substantial number of previously reported loci are transferable to African Americans after accounting for linkage disequilibrium, enabling fine mapping of causal variants in trans-ethnic meta-analysis studies.Peer reviewe

Genetic Parameters For Cow Weight And Height Using A Repeatability Model In American Angus Cattle

Estimates of genetic parameters were obtained from two samples of weights and heights of mature cows provided by the American Angus Association. The first sample consisted of 23,658 records for mature weight (MWT) and 13,012 for mature height (MHT) and the second sample consisted of 23,698 records for MWT and 13,310 for MHT. The four-generation pedigree file included 43,105 animals for the first sample and 44,141 animals for the second sample. Range in ages when cows were weighed was 2 to 11 years at the time of measurement. Variance components were estimated using the MTDFREML programs. Univariate and bivariate analyses were used to estimate genetic parameters for MWT, MHT, and the corresponding genetic correlation. The model included fixed effects of cow age and random cow permanent environmental, contemporary group (herd and year) and residual effects. Heritability estimates (SE) within contemporary group were 0.45 (0.012) for MWT and 0.64 (0.018) for MHT for sample 1 and 0.48 (0.011) for MWT and 0.62 (0.018) for MHT for sample 2. Estimates of repeatability were 0.64 and 0.77 for MWT and MHT, respectively for sample 1 and 0.66 and 0.70 for MWT and MHT, respectively for sample 2. The genetic and permanent environmental correlations between MWT and MHT were 0.80 and 0.75, respectively for sample 1 and 0.83 and 0.69 for sample 2. The estimates of genetic parameters will be used to estimate genetic changes in MWT and MHT from the complete data file