Validation of a method for measuring sperm quality and quantity in reproductive toxicity tests with pair-breeding male fathead minnows (Pimephales promelas)

This article originally appeared in the ILAR e-Journal. It is reprinted with permission from the ILAR Journal, Institute for Laboratory Animal Research, National Research Council, Washington DC (www.nationalacademies.org/ilar).The fathead minnow (Pimephales promelas) is an OECD-proposed test species routinely used in reproductive toxicity trials with suspected endocrine-disrupting compounds (EDCs). The basic fecundity, endocrinology, and histopathology of reproductively active male and female fathead minnows has been well characterized, but there are few studies of the utility of male sperm concentration and motility as endpoints for use in reproductive trials. The purpose of this study was to (1) characterize the baseline sperm concentration and motility of pair-breeding male fathead minnows over their spawning cycle and (2) determine whether a repeated and nondestructive sperm sampling protocol would influence the baseline fecundity of the fish. Pair-breeding male fathead minnows that underwent sampling for milt three times a week for 4 weeks exhibited no significant changes in milt volume, sperm concentration, or motility parameters up to 6 days after each spawning event. The repeated sperm sampling procedure did, however, cause a significant lowering of spawning frequencies, although this decline did not correlate with effects on fecundity as there were no significant changes in the mean total numbers of eggs laid, fertilization, and hatching successes. This study confirmed the presence of a stable background of sperm concentration and motility parameters of pair-breeding male fathead minnows under reference conditions. The absence of any inherent “cycling” in the magnitude of these parameters over the spawning period suggests that sperm concentration and motility could be useful measures of male reproductive toxicity at the termination of tests in which pair-breeding males are at varying days post spawn.The research described was funded by the EU project Comparative Research on Endocrine Disrupters (COMPRENDO) Institute of Zoology Regents Park, London, contract No. EVK1-CT-2002-00129E

Ratchet Effects for Vortices in Superconductors with Periodic Pinning Arrays

Using numerical simulations we show that novel transport phenomena can occur for vortices moving in periodic pinning arrays when two external perpendicular ac drives are applied. In particular, we find a ratchet effect where the vortices can have a net dc drift even in the absence of a dc drive. This ratchet effect can occur for ac drives which create orbits that break one or more reflection symmetries.Comment: 4 pages, 4 postscript figures; Proceedings of Third European Conference on Vortex Matter in Superconductor

Confinement and Quantization Effects in Mesoscopic Superconducting Structures

We have studied quantization and confinement effects in nanostructured superconductors. Three different types of nanostructured samples were investigated: individual structures (line, loop, dot), 1-dimensional (1D) clusters of loops and 2D clusters of antidots, and finally large lattices of antidots. Hereby, a crossover from individual elementary "plaquettes", via clusters, to huge arrays of these elements, is realized. The main idea of our study was to vary the boundary conditions for confinement of the superconducting condensate by taking samples of different topology and, through that, modifying the lowest Landau level E_LLL(H). Since the critical temperature versus applied magnetic field T_c(H) is, in fact, E_LLL(H) measured in temperature units, it is varied as well when the sample topology is changed through nanostructuring. We demonstrate that in all studied nanostructured superconductors the shape of the T_c(H) phase boundary is determined by the confinement topology in a unique way.Comment: 28 pages, 19 EPS figures, uses LaTeX's aipproc.sty, contribution to Euroschool on "Superconductivity in Networks and Mesoscopic Systems", held in Siena, Italy (8-20 september 1997

Applying Physical Education Methods to Skills Teaching of Law Students

[EN] We study to what extent the “constraints-led approach” (CLA) in physical education can also be applied to skills teaching for law students. In the CLA athletes are challenged to finding their own movement solutions in a dynamic setting rather than responding to verbal cues in a fixed environment. Similarly, we experimented with the implicit acquisition of policy analysis skills in law students in preparation for pro bono client work in so-called law clinics. Although the project was cut short due to Covid-19 circumstances, preliminary outcomes suggest students feel better equipped to working with clients. We provisionally conclude that CLA skills teaching has the potential to improve skill acquisition in clinical legal education.Sluijs, J.; Gilissen, HK.; Van Look, K. (2021). Applying Physical Education Methods to Skills Teaching of Law Students. En 7th International Conference on Higher Education Advances (HEAd'21). Editorial Universitat Politècnica de València. 1369-1376. https://doi.org/10.4995/HEAd21.2021.130471369137

Hall carrier density and magnetoresistance measurements in thin film vanadium dioxide across the metal-insulator transition

Temperature dependent magneto-transport measurements in magnetic fields of up to 12 Tesla were performed on thin film vanadium dioxide (VO2) across the metal-insulator transition (MIT). The Hall carrier density increases by 4 orders of magnitude at the MIT and accounts almost entirely for the resistance change. The Hall mobility varies little across the MIT and remains low, ~0.1cm2/V sec. Electrons are found to be the major carriers on both sides of the MIT. Small positive magnetoresistance in the semiconducting phase is measured

Ratchet Cellular Automata

In this work we propose a ratchet effect which provides a general means of performing clocked logic operations on discrete particles, such as single electrons or vortices. The states are propagated through the device by the use of an applied AC drive. We numerically demonstrate that a complete logic architecture is realizable using this ratchet. We consider specific nanostructured superconducting geometries using superconducting materials under an applied magnetic field, with the positions of the individual vortices in samples acting as the logic states. These devices can be used as the building blocks for an alternative microelectronic architecture.Comment: 4 pages, 3 figure