30,980 research outputs found
An Experimental Test of Buffer Utility as a Technique for Managing Pool-Breeding Amphibians
Vegetated buffers are used extensively to manage wetland-dependent wildlife. Despite widespread application, buffer utility has not been experimentally validated for most species. To address this gap, we conducted a six-year, landscape-scale experiment, testing how buffers of different widths affect the demographic structure of two amphibian species at 11 ephemeral pools in a working forest of the northeastern U.S. We randomly assigned each pool to one of three treatments (i.e., reference, 100m buffer, 30m buffer) and clearcut to create buffers. We captured all spotted salamanders and wood frogs breeding in each pool and examined the impacts of treatment and hydroperiod on breeding-population abundance, sex ratio, and recapture rate. The negative effects of clearcutting tended to increase as forest-buffer width decreased and be strongest for salamanders and when other stressors were present (e.g., at short-hydroperiod pools). Recapture rates were reduced in the 30m, but not 100m, treatment. Throughout the experiment for frogs, and during the first year post-cut for salamanders, the predicted mean proportion of recaptured adults in the 30m treatment was only 62% and 40%, respectively, of that in the reference treatment. Frog sex ratio and abundance did not differ across treatments, but salamander sex ratios were increasingly male-biased in both cut treatments. By the final year, there were on average, only about 40% and 65% as many females predicted in the 100m and 30m treatments, respectively, compared to the first year. Breeding salamanders at short-hydroperiod pools were about 10% as abundant in the 100m versus reference treatment. Our study demonstrates that buffers partially mitigate the impacts of habitat disturbance on wetland-dependent amphibians, but buffer width and hydroperiod critically mediate that process. We provide the first experimental evidence showing that 30-m-wide buffers may be insufficient for maintaining resilient breeding populations of pool-dependent amphibians, at least during the first six years post-disturbance
Derivation of SPH equations in a moving referential coordinate system
The conventional SPH method uses kernel interpolation to derive the spatial
semi-discretisation of the governing equations. These equations, derived using a
straight application of the kernel interpolation method, are not used in
practice. Instead the equations, commonly used in SPH codes, are heuristically
modified to enforce symmetry and local conservation properties. This paper
revisits the process of deriving these semi-discrete SPH equations. It is shown
that by using the assumption of a moving referential coordinate system and
moving control volume, instead of the fixed referential coordinate system and
fixed control volume used in the conventional SPH method, a set of new semi-
discrete equations can be rigorously derived. The new forms of semi-discrete
equations are similar to the SPH equations used in practice. It is shown through
numerical examples that the new rigorously derived equations give similar
results to those obtained using the conventional SPH equations
Universal monopole scaling near transitions from the Coulomb phase
Certain frustrated systems, including spin ice and dimer models, exhibit a
Coulomb phase at low temperatures, with power-law correlations and
fractionalized monopole excitations. Transitions out of this phase, at which
the effective gauge theory becomes confining, provide examples of
unconventional criticality. This work studies the behavior at nonzero monopole
density near such transitions, using scaling theory to arrive at universal
expressions for the crossover phenomena. For a particular transition in spin
ice, quantitative predictions are made through a duality mapping to the XY
model, and confirmed using Monte Carlo simulations.Comment: 4.5 pages, 4 figure
A study of the Haematological findings, Serum Proteins and Liver function tests in the Natal African in Health and in Amoebiasis
A notable feature of this century has been the introduction of medical science to large, undeveloped areas throughout the world. Backward, mainly tropical, regions have become fertile fields for study, particularly of nutritional and parasitic disorders, and the application of the modern biochemical methods have show that many inhabitants of these countries lack certain of the biochemical "normal" values seen in Europeans. One of the most striking differences is that of the serum proteins. Although by no means confined to this continent, these differences are commonly found in Africans
Higgs transitions of spin ice
Frustrated magnets such as spin ice exhibit Coulomb phases, where
correlations have power-law forms at long distances. Applied perturbations can
cause ordering transitions which cannot be described by the usual Landau
paradigm, and are instead naturally viewed as Higgs transitions of an emergent
gauge theory. Starting from a classical statistical model of spin ice, it is
shown that a variety of possible phases and transitions can be described by
this approach. Certain cases are identified where continuous transitions are
argued to be likely; the predicted critical behavior may be tested in
experiments or numerical simulations.Comment: 23 pages, 10 figures; v2: published version with minor changes;
ancillary file "Figures3D.nb" is a Mathematica (v7) notebook containing
figures as rotatable 3D graphics (see http://www.wolfram.com/cdf-player/ for
a free viewer
Improved high temperature resistant matrix resins
The objective was to develop organic matrix resins suitable for service at temperatures up to 644 K (700 F) and at air pressures up to 0.4 MPa (60 psia) for time durations of a minimum of 100 hours. Matrix resins capable of withstanding these extreme oxidative environmental conditions would lead to increased use of polymer matrix composites in aircraft engines and provide significant weight and cost savings. Six linear condensation, aromatic/heterocyclic polymers containing fluorinated and/or diphenyl linkages were synthesized. The thermo-oxidative stability of the resins was determined at 644 K and compressed air pressures up to 0.4 MPa. Two formulations, both containing perfluoroisopropylidene linkages in the polymer backbone structure, exhibited potential for 644 K service to meet the program objectives. Two other formulations could not be fabricated into compression molded zero defect specimens
Spin dynamics across the superfluid-insulator transition of spinful bosons
Bosons with non-zero spin exhibit a rich variety of superfluid and insulating
phases. Most phases support coherent spin oscillations, which have been the
focus of numerous recent experiments. These spin oscillations are Rabi
oscillations between discrete levels deep in the insulator, while deep in the
superfluid they can be oscillations in the orientation of a spinful condensate.
We describe the evolution of spin oscillations across the superfluid-insulator
quantum phase transition. For transitions with an order parameter carrying
spin, the damping of such oscillations is determined by the scaling dimension
of the composite spin operator. For transitions with a spinless order parameter
and gapped spin excitations, we demonstrate that the damping is determined by
an associated quantum impurity problem of a localized spin excitation
interacting with the bulk critical modes. We present a renormalization group
analysis of the quantum impurity problem, and discuss the relationship of our
results to experiments on ultracold atoms in optical lattices.Comment: 43 pages (single-column format), 8 figures; v2: corrected discussion
of fixed points in Section V
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Sphaerodactylus fantasticus
Number of Pages: 8Integrative BiologyGeological Science
A phenomenological model of the superconducting state of the Bechgaard salts
We present a group theoretical analysis of the superconducting state of the
Bechgaard salts, e.g., (TMTSF)_2PF_6 or (TMTSF)_2ClO_6. We show that there are
eight symmetry distinct superconducting states. Of these only the (fully
gapped, even frequency, p-wave, triplet) 'polar state' is consistent with the
full range of the experiments on the Bechgaard salts. The gap of the polar
state is d(k) (psi_uk,0,0), where psi_uk may be any odd parity function that is
translationally invariant.Comment: 4 pages, no figure
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