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

Saturation with chiral interactions and consequences for finite nuclei

We explore the impact of nuclear matter saturation on the properties and systematics of finite nuclei across the nuclear chart. Using the ab initio in-medium similarity renormalization group (IM-SRG), we study ground-state energies and charge radii of closed-shell nuclei from $^4$He to $^{78}$Ni, based on a set of low-resolution two- and three-nucleon interactions that predict realistic saturation properties. We first investigate in detail the convergence properties of these Hamiltonians with respect to model-space truncations for both two- and three-body interactions. We find one particular interaction that reproduces well the ground-state energies of all closed-shell nuclei studied. As expected from their saturation points relative to this interaction, the other Hamiltonians underbind nuclei, but lead to a remarkably similar systematics of ground-state energies. Extending our calculations to complete isotopic chains in the $sd$ and $pf$ shells with the valence-space IM-SRG, the same interaction reproduces not only experimental ground states but two-neutron-separation energies and first excited $2^+$ states. We also calculate radii with the valence-space IM-SRG for the first time. Since this particular interaction saturates at too high density, charge radii are still too small compared with experiment. Except for this underprediction, the radii systematics is, however, well reproduced. Our results highlight the importance of nuclear matter as a theoretical benchmark for the development of next-generation chiral interactions.Comment: 11 pages, 15 figures, 1 tabl

Algorithms for polycyclic-by-finite groups

A set of fundamental algorithms for computing with polycyclic-by-finite groups is presented. Polycyclic-by-finite groups arise naturally in a number of contexts; for example, as automorphism groups of large finite soluble groups, as quotients of finitely presented groups, and as extensions of modules by groups. No existing mode of representation is suitable for these groups, since they will typically not have a convenient faithful permutation representation. A mixed mode is used to represent elements of such a group, utilising either a power-conjugate presentation or a polycyclic presentation for the elements of the normal subgroup, and a permutation representation for the elements of the quotient

Transforming Student and Staff Experiences with Active Learning Tutorials in Advanced Chemistry Courses

In order to increase student engagement and provide more opportunities for students to develop their creativity in the context of three large advanced chemistry courses, we have introduced active learning designs in the courses’ tutorial sessions. The tutorial designs focused on collaborative learning, student-generated content and real-world industrial situations. The tutorial activities, carefully scaffolded, focussed on students generating their own problems from scratch, dealing with situations that mimic what might happen on an industrial design team, and writing a short question following the typical format of a final exam question. The tutorial sessions lasted one hour each, and were delivered during the time lapse of three weeks. Most of the students had none or very limited previous experience with active learning instruction. Despite this, students adapted immediately to the active learning format, displaying good collaborative learning skills and a higher level of engagement and attendance to the sessions with respect to traditional taught tutorials. In the post instruction surveys, students reported an increased positive experience, recognising that the sessions allowed them to apply their knowledge to new situations, and stimulated them to learn more on the topics while practising transferable skills in peer discussions. Lecturers who delivered the sessions with active learning for the first time, reported a positive transformation on their own teaching experience. This article discusses the details of the active learning design, the student perceptions and staff teaching experience, highlighting how active learning can be a positive transformative experience not only for the students but also for the academic staff

Identification of mixed-symmetry states in an odd-mass nearly-spherical nucleus

The low-spin structure of 93Nb has been studied using the (n,n' gamma) reaction at neutron energies ranging from 1.5 to 3.0 MeV and the 94Zr(p,2n gamma)93Nb reaction at bombarding energies from 11.5 to 19 MeV. States at 1779.7 and 1840.6 keV, respectively, are proposed as mixed-symmetry states associated with the coupling of a proton hole in the p_1/2 orbit to the 2+_1,ms state in 94Mo. These assignments are derived from the observed M1 and E2 transition strengths to the symmetric one-phonon states, energy systematics, spins and parities, and comparison with shell model calculations.Comment: 5 pages, 3 figure

Evolution of Iron Kα_{\alpha} Line Emission in the Black Hole Candidate GX 339-4

GX 339-4 was regularly monitored with RXTE during a period (in 1999) when its X-ray flux decreased significantly (from 4.2$\times 10^{-10}$ erg cm$^{-2} s^{-1}$ to 7.6$\times 10^{-12}$ erg cm$^{-2}$s$^{-1}$ in the 3--20 keV band), as the source settled into the ``off state''. Our spectral analysis revealed the presence of a prominent iron K$_{\alpha}$ line in the observed spectrum of the source for all observations. The line shows an interesting evolution: it is centered at $\sim$6.4 keV when the measured flux is above 5$\times 10^{-11}$ erg cm$^{-2} s^{-1}$, but is shifted to $\sim$6.7 keV at lower fluxes. The equivalent width of the line appears to increase significantly toward lower fluxes, although it is likely to be sensitive to calibration uncertainties. While the fluorescent emission of neutral or mildly ionized iron atoms in the accretion disk can perhaps account for the 6.4 keV line, as is often invoked for black hole candidates, it seems difficult to understand the 6.7 keV line with this mechanism, because the disk should be less ionized at lower fluxes (unless its density changes drastically). On the other hand, the 6.7 keV line might be due to recombination cascade of hydrogen or helium like iron ions in an optically thin, highly ionized plasma. We discuss the results in the context of proposed accretion models.Comment: 18 pages, 2 figures, accepted for publication in the ApJ in v552n2p May 10, 2001 issu

Towards hardware acceleration of neuroevolution for multimedia processing applications on mobile devices

This paper addresses the problem of accelerating large artificial neural networks (ANN), whose topology and weights can evolve via the use of a genetic algorithm. The proposed digital hardware architecture is capable of processing any evolved network topology, whilst at the same time providing a good trade off between throughput, area and power consumption. The latter is vital for a longer battery life on mobile devices. The architecture uses multiple parallel arithmetic units in each processing element (PE). Memory partitioning and data caching are used to minimise the effects of PE pipeline stalling. A first order minimax polynomial approximation scheme, tuned via a genetic algorithm, is used for the activation function generator. Efficient arithmetic circuitry, which leverages modified Booth recoding, column compressors and carry save adders, is adopted throughout the design