Migration efficiency of paired sperm in the tract of the peri-ovulatory female grey short-tailed opossum (Monodelphis domestica)

American marsupials are the only mammals known to ejaculate paired spermatozoa, which confer a motility advantage in vitro over single spermatozoa in viscous environments. In the only American marsupial examined, the Virginian opossum (Didelphidae), relatively low numbers of spermatozoa are ejaculated (106), but transport is extremely efficient with ~1 in 20 spermatozoa reaching the site of fertilization compared to ~1 in 10,000 in the rabbit. This study examined the post-copulatory distribution and state (paired or single) of spermatozoa at various times in the female reproductive tract of another didelphid, the polyovular grey short-tailed opossum (Monodelphis domestica). After a single mating, the reproductive tracts of 19 females were dissected at 0.5 (n=4), 6 (n=4), 12 (n=3), 18 (n=3) and 24h (n=5) post coitum (p.c.). Each tract was dissected into 8 major anatomical sections and spermatozoa were recovered by flushing. Mating occurred 5.4 ± 0.4d (mean ± SEM; n=19) after pairing, copulation lasted 4.4 ± 0.2 min (n=18) and ovulation occurred 18.0 - 24.1h p.c. (n=5). Shortly after mating (0.5h p.c.) the tract contained 1.2 ± 0.2g of seminal gel (n=2) and 2.0 ± 1.3 x106 spermatozoa (n=3; 38% of which were paired) found predominantly in the anterior vaginal culs de sac. A uterine sperm reservoir was never observed, but spermatozoa reached the isthmus and ampulla within 6 and 18h p.c. respectively. Paired spermatozoa localized almost exclusively in the isthmus from 6h p.c., and pairing decreased to only 4% of the total sperm population in the tract by the start of ovulation. In total ~1 in 300 ejaculated spermatozoa (~6.5 x103; n=9) reached the oviduct. In conclusion, sperm pairing appears to confer effective colonization of the isthmus in M. domestica and, like the Virginian opossum, transport of spermatozoa is relatively efficient

Efficient Recursion Method for Inverting Overlap Matrix

A new O(N) algorithm based on a recursion method, in which the computational effort is proportional to the number of atoms N, is presented for calculating the inverse of an overlap matrix which is needed in electronic structure calculations with the the non-orthogonal localized basis set. This efficient inverting method can be incorporated in several O(N) methods for diagonalization of a generalized secular equation. By studying convergence properties of the 1-norm of an error matrix for diamond and fcc Al, this method is compared to three other O(N) methods (the divide method, Taylor expansion method, and Hotelling's method) with regard to computational accuracy and efficiency within the density functional theory. The test calculations show that the new method is about one-hundred times faster than the divide method in computational time to achieve the same convergence for both diamond and fcc Al, while the Taylor expansion method and Hotelling's method suffer from numerical instabilities in most cases.Comment: 17 pages and 4 figure

One-way multigrid method in electronic structure calculations

We propose a simple and efficient one-way multigrid method for self-consistent electronic structure calculations based on iterative diagonalization. Total energy calculations are performed on several different levels of grids starting from the coarsest grid, with wave functions transferred to each finer level. The only changes compared to a single grid calculation are interpolation and orthonormalization steps outside the original total energy calculation and required only for transferring between grids. This feature results in a minimal amount of code change, and enables us to employ a sophisticated interpolation method and noninteger ratio of grid spacings. Calculations employing a preconditioned conjugate gradient method are presented for two examples, a quantum dot and a charged molecular system. Use of three grid levels with grid spacings 2h, 1.5h, and h decreases the computer time by about a factor of 5 compared to single level calculations.Comment: 10 pages, 2 figures, to appear in Phys. Rev. B, Rapid Communication

Against all odds? Forming the planet of the HD196885 binary

HD196885Ab is the most "extreme" planet-in-a-binary discovered to date, whose orbit places it at the limit for orbital stability. The presence of a planet in such a highly perturbed region poses a clear challenge to planet-formation scenarios. We investigate this issue by focusing on the planet-formation stage that is arguably the most sensitive to binary perturbations: the mutual accretion of kilometre-sized planetesimals. To this effect we numerically estimate the impact velocities $dv$ amongst a population of circumprimary planetesimals. We find that most of the circumprimary disc is strongly hostile to planetesimal accretion, especially the region around 2.6AU (the planet's location) where binary perturbations induce planetesimal-shattering $dv$ of more than 1km/s. Possible solutions to the paradox of having a planet in such accretion-hostile regions are 1) that initial planetesimals were very big, at least 250km, 2) that the binary had an initial orbit at least twice the present one, and was later compacted due to early stellar encounters, 3) that planetesimals did not grow by mutual impacts but by sweeping of dust (the "snowball" growth mode identified by Xie et al., 2010b), or 4) that HD196885Ab was formed not by core-accretion but by the concurent disc instability mechanism. All of these 4 scenarios remain however highly conjectural.Comment: accepted for publication by Celestial Mechanics and Dynamical Astronomy (Special issue on EXOPLANETS

Basis Functions for Linear-Scaling First-Principles Calculations

In the framework of a recently reported linear-scaling method for density-functional-pseudopotential calculations, we investigate the use of localized basis functions for such work. We propose a basis set in which each local orbital is represented in terms of an array of `blip functions'' on the points of a grid. We analyze the relation between blip-function basis sets and the plane-wave basis used in standard pseudopotential methods, derive criteria for the approximate equivalence of the two, and describe practical tests of these criteria. Techniques are presented for using blip-function basis sets in linear-scaling calculations, and numerical tests of these techniques are reported for Si crystal using both local and non-local pseudopotentials. We find rapid convergence of the total energy to the values given by standard plane-wave calculations as the radius of the linear-scaling localized orbitals is increased.Comment: revtex file, with two encapsulated postscript figures, uses epsf.sty, submitted to Phys. Rev.

Structure and Dynamics of Liquid Iron under Earth's Core Conditions

First-principles molecular dynamics simulations based on density-functional theory and the projector augmented wave (PAW) technique have been used to study the structural and dynamical properties of liquid iron under Earth's core conditions. As evidence for the accuracy of the techniques, we present PAW results for a range of solid-state properties of low- and high-pressure iron, and compare them with experimental values and the results of other first-principles calculations. In the liquid-state simulations, we address particular effort to the study of finite-size effects, Brillouin-zone sampling and other sources of technical error. Results for the radial distribution function, the diffusion coefficient and the shear viscosity are presented for a wide range of thermodynamic states relevant to the Earth's core. Throughout this range, liquid iron is a close-packed simple liquid with a diffusion coefficient and viscosity similar to those of typical simple liquids under ambient conditions.Comment: 13 pages, 8 figure

Preferred Healthy Food Nudges, Food Store Environments, and Customer Dietary Practices in 2 Low-Income Southern Communities

Objective To examine how food store environments can promote healthful eating, including (1) preferences for a variety of behavioral economics strategies to promote healthful food purchases, and (2) the cross-sectional association between the primary food store where participants reported shopping, dietary behaviors, and body mass index. Methods Intercept survey participants (n = 342) from 2 midsized eastern North Carolina communities completed questionnaires regarding preferred behavioral economics strategies, the primary food store at which they shopped, and consumption of fruits, vegetables, and sugary beverages. Results Frequently selected behavioral economic strategies included: (1) a token and reward system for fruit and vegetable purchases; and (2) price discounts on healthful foods and beverages. There was a significant association between the primary food store and consumption of fruits and vegetables (P = .005) and sugary beverages (P = .02). Conclusions and Implications Future studies should examine associations between elements of the in-store food environment, purchases, and consumption

Computational Physics on Graphics Processing Units

The use of graphics processing units for scientific computations is an emerging strategy that can significantly speed up various different algorithms. In this review, we discuss advances made in the field of computational physics, focusing on classical molecular dynamics, and on quantum simulations for electronic structure calculations using the density functional theory, wave function techniques, and quantum field theory.Comment: Proceedings of the 11th International Conference, PARA 2012, Helsinki, Finland, June 10-13, 201