1,960 research outputs found
Habitat selection of an endangered primate, the samango monkey (Cercopithecus albogularis schwarzi): integrating scales to prioritise habitat for wildlife management
Aim: As habitat loss continues to accelerate with global human population growth, identifying landscape characteristics that influence species occurrence is a key conservation priority in order to prevent global biodiversity loss. In South Africa, the arboreal samango monkey (Cercopithecus albogularis sp.) is threatened due to loss and fragmentation of the indigenous forests it inhabits. The aim of this study was to determine the habitat preferences of the samango monkey at different spatial scales, and to identify key conservation areas to inform management plans for this species. Location: This study was carried out in the western Soutpansberg Mountains, which represents the northernmost population of samango monkeys within South Africa, and the only endangered subspecies (C. a. schwarzi). Methods: We used sequentially collected GPS points from two samango monkey groups followed between 2012 – 2017 to quantify the used and available habitat for this species within the western Soutpansberg Mountains. We developed 2nd (selection of ranging area), 3rd (selection within range) and 4th (feeding site selection) order resource selection functions (RSFs) to identify important habitat features at each scale. Through scale integration, we identified three key conservation areas for samango monkeys across Limpopo Province, South Africa. Results: Habitat productivity was the most important landscape variable predicting probability of use at each order of selection, indicating the dependence of these arboreal primates on tall-canopy indigenous forests. Critical habitat across Limpopo was highly fragmented, meaning complete isolation between subpopulations is likely. Main conclusions: Understanding the habitat characteristics that influence samango monkey distribution across South Africa is crucial for prioritising critical habitat for this species. Our results indicated that large, contiguous patches of tallcanopy indigenous forest are fundamental to samango monkey persistence. As such, protected area expansion of large forest patches and creation of forest corridors are identified as key conservation interventions for this species
Absence of a dose-rate effect in the transformation of C3H 10T1/2 cells by α-particles
The findings of Hill et al. (1984) on the greatly enhanced transformation frequencies at very low dose rates of fission neutrons induced us to perform an analogous study with -particles at comparable dose rates. Transformation frequencies were determined with γ-rays at high dose rate (0·5 Gy/min), and with -particles at high (0·2 Gy/min) and at low dose rates (0·83-2·5 mGy/min) in the C3H 10T1/2 cell system.
α-particles were substantially more effective than γ-rays, both for cell inactivation and for neoplastic transformation at high and low dose rates. The relative biological effectiveness (RBE) for cell inactivation and for neoplastic transformation was of similar magnitude, and ranged from about 3 at an -particle dose of 2 Gy to values of the order of 10 at 0·25 Gy. In contrast to the experiments of Hill et al. (1984) with fission neutrons, no increased transformation frequencies were observed when the -particle dose was protracted over several hours
Simultaneous Projectile-Target Excitation in Heavy Ion Collisions
We calculate the lowest-order contribution to the cross section for
simultaneous excitation of projectile and target nuclei in relativistic heavy
ion collisions. This process is, to leading order, non-classical and adds
incoherently to the well-studied semi-classical Weizs\"acker-Williams cross
section. While the leading contribution to the cross section is down by only
from the semiclassical process, and consequently of potential
importance for understanding data from light projectiles, we find that phase
space considerations render the cross section utterly negligible.Comment: 9 pages, LA-UR-94-247
Elastic properties of a tungsten-silver composite by reconstruction and computation
We statistically reconstruct a three-dimensional model of a tungsten-silver
composite from an experimental two-dimensional image. The effective Young's
modulus () of the model is computed in the temperature range 25-1060^o C
using a finite element method. The results are in good agreement with
experimental data. As a test case, we have reconstructed the microstructure and
computed the moduli of the overlapping sphere model. The reconstructed and
overlapping sphere models are examples of bi-continuous (non-particulate)
media. The computed moduli of the models are not generally in good agreement
with the predictions of the self-consistent method. We have also evaluated
three-point variational bounds on the Young's moduli of the models using the
results of Beran, Molyneux, Milton and Phan-Thien. The measured data were close
to the upper bound if the properties of the two phases were similar ().Comment: 23 Pages, 12 Figure
Electromagnetic Dissociation of Nuclei in Heavy-Ion Collisions
Large discrepancies have been observed between measured Electromagnetic
Dissociation(ED) cross sections and the predictions of the semiclassical
Weiz\"acker-Williams-Fermi(WWF) method. In this paper, the validity of the
semiclassical approximation is examined. The total cross section for
electromagnetic excitation of a nuclear target by a spinless projectile is
calculated in first Born approximation, neglecting recoil. The final result is
expressed in terms of correlation functions and convoluted densities in
configuration space. The result agrees with the WWF approximation to leading
order(unretarded electric dipole approximation), but the method allows an
analytic evaluation of the cutoff, which is determined by the details of the
electric dipole transition charge density. Using the Goldhaber-Teller model of
that density, and uniform charge densities for both projectile and target, the
cutoff is determined for the total cross section in the nonrelativistic limit,
and found to be smaller than values currently used for ED calculations. In
addition, cross sections are calculated using a phenomenological momentum space
cutoff designed to model final state interactions. For moderate projectile
energies, the calculated ED cross section is found to be smaller than the
semiclassical result, in qualitative agreement with experiment.Comment: 28 page
Cosmological Tracking Solutions
A substantial fraction of the energy density of the universe may consist of
quintessence in the form of a slowly-rolling scalar field. Since the energy
density of the scalar field generally decreases more slowly than the matter
energy density, it appears that the ratio of the two densities must be set to a
special, infinitesimal value in the early universe in order to have the two
densities nearly coincide today.
Recently, we introduced the notion of tracker fields to avoid this initial
conditions problem. In the paper, we address the following questions: What is
the general condition to have tracker fields? What is the relation between the
matter energy density and the equation-of-state of the universe imposed by
tracker solutions? And, can tracker solutions explain why quintessence is
becoming important today rather than during the early universe
The flip flop nozzle extended to supersonic flows
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76293/1/AIAA-1992-2724-750.pd
Optical Hall conductivity of systems with gapped spectral nodes
We calculate the optical Hall conductivity within the Kubo formalism for
systems with gapped spectral nodes, where the latter have a power-law
dispersion with exponent n. The optical conductivity is proportional to n and
there is a characteristic logarithmic singularity as the frequency approaches
the gap energy. The optical Hall conductivity is almost unaffected by thermal
fluctuations and disorder for n=1, whereas disorder has a stronger effect on
transport properties if n=2
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