556 research outputs found
New southern geographical records of intertidal sea urchins (Echinodermata: Echinoidea), with notes on abundance
Ten species of epifaunal sea urchin were identified at Preslies Bay, Transkei, establishing new southern geographical distributions for seven of the species. Local distributions intertidally, subtidally, and within the Mtakatye estuary were documented. Estimates of abundance on the intertidal rocky shore indicated vertical separation between certain species
Security guidelines for field research in complex, remote and hazardous places
These guidelines assist researchers in conducting their field-based research or fieldwork in hazardous, remote or complex environments as safely and securely as possible. Fieldwork comes with risks, ranging from the mundane risks of car accidents to more exceptional risks of encountering violence. These risks may affect the security of the researcher and the research outcomes, as well as the security of the respondents, local assistants and interpreters, the home and host organizations, and research sponsors. Taking into account the risk environment should be
Blood thicker than water: Kinship, disease prevalence and group size drive divergent patterns of infection risk in a social mammal
The importance of social- and kin-structuring of populations for the transmission of wildlife disease is widely assumed but poorly described. Social structure can help dilute risks of transmission for group members, and is relatively easy to measure, but kin-association represents a further level of population sub-structure that is harder to measure, particularly when association behaviours happen underground. Here, using epidemiological and molecular genetic data from a wild, high-density population of the European badger (Meles meles), we quantify the risks of infection with Mycobacterium bovis (the causative agent of tuberculosis) in cubs. The risk declines with increasing size of its social group, but this net dilution effect conceals divergent patterns of infection risk. Cubs only enjoy reduced risk when social groups have a higher proportion of test-negative individuals. Cubs suffer higher infection risk in social groups containing resident infectious adults, and these risks are exaggerated when cubs and infectious adults are closely related. We further identify key differences in infection risk associated with resident infectious males and females. We link our results to parent– offspring interactions and other kin-biased association, but also consider the possibility that susceptibility to infection is heritable. These patterns of infection risk help to explain the observation of a herd immunity effect in badgers following low-intensity vaccination campaigns. They also reveal kinship and kin-association to be important, and often hidden, drivers of disease transmission in social mammals
A simple and efficient numerical scheme to integrate non-local potentials
As nuclear wave functions have to obey the Pauli principle, potentials issued
from reaction theory or Hartree-Fock formalism using finite-range interactions
contain a non-local part. Written in coordinate space representation, the
Schrodinger equation becomes integro-differential, which is difficult to solve,
contrary to the case of local potentials, where it is an ordinary differential
equation. A simple and powerful method has been proposed several years ago,
with the trivially equivalent potential method, where non-local potential is
replaced by an equivalent local potential, which is state-dependent and has to
be determined iteratively. Its main disadvantage, however, is the appearance of
divergences in potentials if the wave functions have nodes, which is generally
the case. We will show that divergences can be removed by a slight modification
of the trivially equivalent potential method, leading to a very simple, stable
and precise numerical technique to deal with non-local potentials. Examples
will be provided with the calculation of the Hartree-Fock potential and
associated wave functions of 16O using the finite-range N3LO realistic
interaction.Comment: 8 pages, 2 figures, submitted to Eur. Phys. J.
Snow petrel stomach-oil deposits as a new biological archive of Antarctic sea ice
Where snow petrels forage is predominantly a function of sea ice. They spit stomach oil in defence, and accumulated deposits at nesting sites are providing new opportunities to reconstruct their diet, and, in turn, the sea-ice environment over past millennia
Svestka's Research: Then and Now
Zdenek Svestka's research work influenced many fields of solar physics,
especially in the area of flare research. In this article I take five of the
areas that particularly interested him and assess them in a "then and now"
style. His insights in each case were quite sound, although of course in the
modern era we have learned things that he could not readily have envisioned.
His own views about his research life have been published recently in this
journal, to which he contributed so much, and his memoir contains much
additional scientific and personal information (Svestka, 2010).Comment: Invited review for "Solar and Stellar Flares," a conference in honour
of Prof. Zden\v{e}k \v{S}vestka, Prague, June 23-27, 2014. This is a
contribution to a Topical Issue in Solar Physics, based on the presentations
at this meeting (Editors Lyndsay Fletcher and Petr Heinzel
Ab initio Quantum and ab initio Molecular Dynamics of the Dissociative Adsorption of Hydrogen on Pd(100)
The dissociative adsorption of hydrogen on Pd(100) has been studied by ab
initio quantum dynamics and ab initio molecular dynamics calculations. Treating
all hydrogen degrees of freedom as dynamical coordinates implies a high
dimensionality and requires statistical averages over thousands of
trajectories. An efficient and accurate treatment of such extensive statistics
is achieved in two steps: In a first step we evaluate the ab initio potential
energy surface (PES) and determine an analytical representation. Then, in an
independent second step dynamical calculations are performed on the analytical
representation of the PES. Thus the dissociation dynamics is investigated
without any crucial assumption except for the Born-Oppenheimer approximation
which is anyhow employed when density-functional theory calculations are
performed. The ab initio molecular dynamics is compared to detailed quantum
dynamical calculations on exactly the same ab initio PES. The occurence of
quantum oscillations in the sticking probability as a function of kinetic
energy is addressed. They turn out to be very sensitive to the symmetry of the
initial conditions. At low kinetic energies sticking is dominated by the
steering effect which is illustrated using classical trajectories. The steering
effects depends on the kinetic energy, but not on the mass of the molecules.
Zero-point effects lead to strong differences between quantum and classical
calculations of the sticking probability. The dependence of the sticking
probability on the angle of incidence is analysed; it is found to be in good
agreement with experimental data. The results show that the determination of
the potential energy surface combined with high-dimensional dynamical
calculations, in which all relevant degrees of freedon are taken into account,
leads to a detailed understanding of the dissociation dynamics of hydrogen at a
transition metal surface.Comment: 15 pages, 9 figures, subm. to Phys. Rev.
Asymmetric rolling of interstitial-free steel using differential roll diameters. Part II : microstructure and annealing effects
The effects of annealing on the microstructure, texture, tensile properties, and R value evolution of an IF steel sheet after room-temperature symmetric and asymmetric rolling were examined. Simulations were carried out to obtain R values from the experimental textures using the viscoplastic self-consistent polycrystal plasticity model. The investigation revealed the variations in the textures due to annealing and symmetric/asymmetric rolling and showed that the R values correlate strongly with the evolution of the texture. An optimum heat treatment for the balance of strength, ductility, and deep drawability was found to be at 873 K (600 _C) for 30 minutes
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