18,613 research outputs found
SNAKE ASSEMBLAGE STRUCTURES AND SEASONAL ACTIVITY PATTERNS ON A MILITARY BASE IN SOUTH-CENTRAL PENNSYLVANIA:: LAND MANAGEMENT IMPLICATIONS FOR SNAKE CONSERVATION
We ascertained the assemblage structures of snakes occurring in a mixed habitat matrix of natural and disturbed habitats during 2008–2011 at Letterkenny Army Depot (LEAD), a 7200 ha U.S. Army base in south-central Pennsylvania, to understand the patterns of species abundance as they related to habitat type of managed lands. We detected eight species in 12 sites comprising natural and disturbed habitats of wetlands, forest, and thicket and open fields. The Common Gartersnake (Thamnophis sirtalis) occurred in the most sites, the Red-bellied Snake (Storeria occipitomaculata) was the rarest species in the study. Two to six species occupied each site and were distributed unevenly. Dynamics of assemblages could be explained in part by habitat and also by the presence of the North American Racer (Coluber constrictor). All species for which data were available exhibited a unimodal pattern to their seasonal activity (mostly May and June); however, seasonal activity peaks differed between sexes. Sex ratios varied among species but were consistently female–biased in the Common Gartersnake and Ring-necked Snake (Diadophis punctatus) in Pennsylvania and surrounding areas. As elsewhere in Pennsylvania and the Northeast, body sizes of adults were larger for species syntopic with the North American Racer than for species not syntopic with this potential predator. We found a degree of predictability with respect to snake assemblage dynamics among habitats at LEAD, which in turn can prove useful in resource management of this large and protected human-impacted system
Two-fluid dust and gas mixtures in smoothed particle hydrodynamics II: an improved semi-implicit approach
We present an improved version of the Loren-Aguilar & Bate (2014) method to
integrate the two-fluid dust/gas equations that correctly captures the limiting
velocity of small grains in the presence of net differences (excluding the drag
force) between the accelerations of the dust and the gas. A series of
accelerated DUSTYBOX tests and a simulation of dust-settling in a
protoplanetary disc are performed comparing the performance of the new and old
methods. The modified method can accurately capture the correct limiting
velocity while preserving all the conservation properties of the original
method.Comment: Accepted for publication in MNRA
Sequential evacuation strategy for multiple rooms toward the same means of egress
This paper examines different evacuation strategies for systems where several
rooms evacuate trough the same means of egress, using microscopic pedestrian
simulation.As a case study, a medium-rise office building is considered. It was
found that the standard strategy, whereby the simultaneous evacuation of all
levels is performed, can be improved by a sequential evacuation, beginning with
the lowest floor and continuing successively with each one of the upper floors
after a certain delay. The importance of the present research is that it
provides the basis for the design and implementation of new evacuation
strategies and alarm systems that could significantly improve the evacuation of
multiple rooms trough a common means of escape.Comment: 8 pages, 4 figure
Two fluid dust and gas mixtures in SPH: A semi-implicit approach
A method to avoid the explicit time integration of small dust grains in the
two fluid gas/dust smoothed particle hydrodynamics (SPH) approach is proposed.
By assuming a very simple exponential decay model for the relative velocity
between the gas and dust components, all the effective characteristics of the
drag force can be reproduced. A series of tests has been performed to compare
the accuracy of the method with analytical and explicit integration results. We
find that the method performs well on a wide range of tests, and can provide
large speed ups over explicit integration when the dust stopping time is small.
We have also found that the method is much less dissipative than conventional
explicit or implicit two-fluid SPH approaches when modelling dusty shocks.Comment: 20 pages, 14 figures. Accepted for publication in MNRA
Toroidal vortices as a solution to the dust migration problem
In an earlier letter, we reported that dust settling in protoplanetary discs
may lead to a dynamical dust-gas instability that produces global toroidal
vortices. In this letter, we investigate the evolution of a dusty
protoplanetary disc with two different dust species (1 mm and 50 cm dust
grains), under the presence of the instability. We show how toroidal vortices,
triggered by the interaction of mm grains with the gas, stop the radial
migration of metre-sized dust, potentially offering a natural and efficient
solution to the dust migration problem.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
Competition interfaces and second class particles
The one-dimensional nearest-neighbor totally asymmetric simple exclusion
process can be constructed in the same space as a last-passage percolation
model in Z^2. We show that the trajectory of a second class particle in the
exclusion process can be linearly mapped into the competition interface between
two growing clusters in the last-passage percolation model. Using technology
built up for geodesics in percolation, we show that the competition interface
converges almost surely to an asymptotic random direction. As a consequence we
get a new proof for the strong law of large numbers for the second class
particle in the rarefaction fan and describe the distribution of the asymptotic
angle of the competition interface.Comment: Published at http://dx.doi.org/10.1214/009117905000000080 in the
Annals of Probability (http://www.imstat.org/aop/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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