151 research outputs found
Seasonal activity patterns of the frog, Crinia signifera (Anura: Myobatrachidae), in southern Tasmania, Australia
We investigated the seasonal adaptations of the myobatrachid frog Girard, 1863 in a commercial forest in southern Tasmania, Australia. Seasonal variation in activity patterns, body size and body condition was investigated. Although C does not hibernate over winter, activity levels arc much reduced during this time. Females trapped in summer were smaller than those captured throughout the remainder of the year. We interpreted seasonal variation in the condition of captured frogs as an indication that breeding in spring and
early summer is metabolically costly and fat stores are replenished by extensive foraging in summer. Fat stores accumulated in summer and autumn by males are used for body maintenance over winter and breeding in the following spring
Electronic and phononic properties of the chalcopyrite CuGaS2
The availability of ab initio electronic calculations and the concomitant
techniques for deriving the corresponding lattice dynamics have been profusely
used for calculating thermodynamic and vibrational properties of
semiconductors, as well as their dependence on isotopic masses. The latter have
been compared with experimental data for elemental and binary semiconductors
with different isotopic compositions. Here we present theoretical and
experimental data for several vibronic and thermodynamic properties of CuGa2, a
canonical ternary semiconductor of the chalcopyrite family. Among these
properties are the lattice parameters, the phonon dispersion relations and
densities of states (projected on the Cu, Ga, and S constituents), the specific
heat and the volume thermal expansion coefficient. The calculations were
performed with the ABINIT and VASP codes within the LDA approximation for
exchange and correlation and the results are compared with data obtained on
samples with the natural isotope composition for Cu, Ga and S, as well as for
isotope enriched samples.Comment: 9 pages, 8 Figures, submitted to Phys. Rev
Low-Afterglow, High-Refractive-Index Liquid Scintillators for Fast-Neutron Spectrometry and Imaging Applications
For ion and neutron spectrometry and imaging applications at a high intensity
pulsed laser facility, fast liquid scintillators with very low afterglow are
required. Furthermore, neutron imaging with fiber (or liquid-core) capillary
arrays calls for scintillation materials with high refractive index. To this
end, we have examined various combinations of established mixtures of fluors
and solvents, that were enriched alternatively with nitrogen or oxygen.
Dissolved molecular oxygen is known to be a highly effective quenching agent,
that efficiently suppresses the population of the triplet states in the fluor,
which are primarily responsible for the afterglow. For measuring the glow
curves of scintillators, we have employed the time-correlated single photon
counting (TCSPC) technique, characterized by high dynamic range of several
orders of magnitude in light intensity. In this paper we outline the
application for the fast scintillators, briefly present the scintillation
mechanism in liquids, describe our specific TCSPC method and discuss the
results.Comment: 5 pages, Contribution to SORMA WEST 2008. To be published in IEEE
TNS, 200
Electronic, vibrational, and thermodynamic properties of ZnS (zincblende and rocksalt structure)
We have measured the specific heat of zincblende ZnS for several isotopic
compositions and over a broad temperature range (3 to 1100 K). We have compared
these results with calculations based on ab initio electronic band structures,
performed using both LDA and GGA exchange- correlation functionals. We have
compared the lattice dynamics obtained in this manner with experimental data
and have calculated the one-phonon and two-phonon densities of states. We have
also calculated mode Grueneisen parameters at a number of high symmetry points
of the Brillouin zone. The electronic part of our calculations has been used to
investigate the effect of the 3d core electrons of zinc on the spin-orbit
splitting of the top valence bands. The effect of these core electrons on the
band structure of the rock salt modification of ZnS is also discussed.Comment: 33pages, 16 Figures, submitted to Phys. Rev.
Heat Capacity of PbS: Isotope Effects
In recent years, the availability of highly pure stable isotopes has made
possible the investigation of the dependence of the physical properties of
crystals, in particular semiconductors, on their isotopic composition.
Following the investigation of the specific heat (, ) of monatomic
crystals such as diamond, silicon, and germanium, similar investigations have
been undertaken for the tetrahedral diatomic systems ZnO and GaN (wurtzite
structure), for which the effect of the mass of the cation differs from that of
the anion. In this article we present measurements for a semiconductor with
rock salt structure, namely lead sulfide. Because of the large difference in
the atomic mass of both constituents (= 207.21 and (=32.06 a.m.u., for the natural isotopic abundance) the effects of varying
the cation and that of the anion mass are very different for this canonical
semiconductor. We compare the measured temperature dependence of , and the corresponding derivatives with respect to ( and
), with \textit{\textit{ab initio}} calculations based on the
lattice dynamics obtained from the local density approximation (LDA) electronic
band structure. Quantitative deviations between theory and experiment are
attributed to the absence of spin-orbit interaction in the ABINIT program used
for the electronic band structure calculations.Comment: 17 pages including 10 Fig
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