477 research outputs found
Forest Landowner Short Courses at Mississippi State University
Extension forestry at Mississippi State University has been providing educational opportunities for forest landowners in Mississippi for more than 70 years. The first forest landowner short course was offered in 1984. Since then, the short course curriculum has grown to include 11 short courses taught throughout the state every year. Since 1987, these short courses have resulted in over 7,000 attendees owning or managing over 2,000,000 acres of forest land and valuing the information they received at over $115,00,000. The short course format described here will combine well with new and emerging technologies such as interactive video, the Internet, and live satellite broadcast
Introduction to forest valuation and investment analysis
Most foresters and forest landowners are aware that money has a time value. A dollar today is worth more than a dollar tomorrow. If you borrow 1,000 in 90 days. The term forest economists use for this concept is the t :!me value of money: the closer to today you receive a sum of money, the greater its present value
Hydrodynamic simulations of merging clusters of galaxies
We present the results of high-resolution AP3M+SPH simulations of merging clusters of galaxies. We find that the compression and shocking of the core gas during a merger can lead to large increases in bolometric X-ray luminosities and emission-weighted temperatures of clusters. Cooling flows are completely disrupted during equal-mass mergers, with the mass deposition rate dropping to zero as the cores of the clusters collide. The large increase in the cooling time of the core gas strongly suggests that cooling flows will not recover from such a merger within a Hubble time. Mergers with subclumps having one eighth of the mass of the main cluster are also found to disrupt a cooling flow if the merger is head-on. However, in this case the entropy injected into the core gas is rapidly radiated away and the cooling flow restarts within a few Gyr of the merger. Mergers in which the subcluster has an impact parameter of 500 kpc do not disrupt the cooling flow, although the mass deposition rate is reduced by ∼30 per cent. Finally, we find that equal mass, off-centre mergers can effectively mix gas in the cores of clusters, while head on mergers lead to very little mixing. Gas stripped from the outer layers of subclumps results in parts of the outer layers of the main cluster being well mixed, although they have little effect on the gas in the core of the cluster. None of the mergers examined here resulted in the intracluster medium being well mixed globally
Transport coefficients of multi-particle collision algorithms with velocity-dependent collision rules
Detailed calculations of the transport coefficients of a recently introduced
particle-based model for fluid dynamics with a non-ideal equation of state are
presented. Excluded volume interactions are modeled by means of biased
stochastic multiparticle collisions which depend on the local velocities and
densities. Momentum and energy are exactly conserved locally. A general scheme
to derive transport coefficients for such biased, velocity dependent collision
rules is developed. Analytic expressions for the self-diffusion coefficient and
the shear viscosity are obtained, and very good agreement is found with
numerical results at small and large mean free paths. The viscosity turns out
to be proportional to the square root of temperature, as in a real gas. In
addition, the theoretical framework is applied to a two-component version of
the model, and expressions for the viscosity and the difference in diffusion of
the two species are given.Comment: 31 pages, 8 figures, accepted by J. Phys. Cond. Matte
Perturbative Analysis of Adaptive Smoothing Methods in Quantifying Large-Scale Structure
Smoothing operation to make continuous density field from observed point-like
distribution of galaxies is crucially important for topological or
morphological analysis of the large-scale structure, such as, the genus
statistics or the area statistics (equivalently the level crossing statistics).
It has been pointed out that the adaptive smoothing filters are more efficient
tools to resolve cosmic structures than the traditional spatially fixed
filters. We study weakly nonlinear effects caused by two representative
adaptive methods often used in smoothed hydrodynamical particle (SPH)
simulations. Using framework of second-order perturbation theory, we calculate
the generalized skewness parameters for the adaptive methods in the case of
initially power-law fluctuations.
Then we apply the multidimensional Edgeworth expansion method and investigate
weakly nonlinear evolution of the genus statistics and the area statistics.
Isodensity contour surfaces are often parameterized by the volume fraction of
the regions above a given density threshold. We also discuss this
parameterization method in perturbative manner.Comment: 42 pages including 9 figure, ApJ 537 in pres
A marker of biological age explains individual variation in the strength of the adult stress response
This research was funded by the Biotechnology and Biological Sciences Research Council (BBSRC) under grants BB/J016446/1, BB/J015091/1 and BB/J016292/1. The project has also received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. AdG 666669 (D.N.) and 268926 (P.M.)) K.A.S. was also funded by a BBSRC David Phillips Research Fellowship. The raw data and R script from this experiment are publicly available at: https://doi.org/10.5281/zenodo.846830 [38].The acute stress response functions to prioritize behavioural and physiological processes that maximize survival in the face of immediate threat. There is variation between individuals in the strength of the adult stress response that is of interest in both evolutionary biology and medicine. Age is an established source of this variation-stress responsiveness diminishes with increasing age in a range of species-but unexplained variation remains. Since individuals of the same chronological age may differ markedly in their pace of biological ageing, we asked whether biological age-measured here via erythrocyte telomere length-predicts variation in stress responsiveness in adult animals of the same chronological age. We studied two cohorts of European starlings in which we had previously manipulated the rate of biological ageing by experimentally altering the competition experienced by chicks in the fortnight following hatching. We predicted that individuals with greater developmental telomere attrition, and hence greater biological age, would show an attenuated corticosterone (CORT) response to an acute stressor when tested as adults. In both cohorts, we found that birds with greater developmental telomere attrition had lower peak CORT levels and a more negative change in CORT levels between 15 and 30 min following stress exposure. Our results, therefore, provide strong evidence that a measure of biological age explains individual variation in stress responsiveness: birds that were biologically older were less stress responsive. Our results provide a novel explanation for the phenomenon of developmental programming of the stress response: observed changes in stress physiology as a result of exposure to early-life adversity may reflect changes in ageing.Publisher PDFPeer reviewe
Cluster scaling relations from cosmological hydrodynamic simulations in dark energy dominated universe
Clusters are potentially powerful tools for cosmology provided their observed
properties such as the Sunyaev-Zel'dovich (SZ) or X-ray signals can be
translated into physical quantities like mass and temperature. Scaling
relations are the appropriate mean to perform this translation. It is
therefore, important to understand their evolution and their modifications with
respect to the physics and to the underlying cosmology. In this spirit, we
investigate the effect of dark energy on the X-ray and SZ scaling relations.
The study is based on the first hydro-simulations of cluster formation for
diferent models of dark energy. We present results for four dark energy models
which differ from each other by their equations of state parameter, .
Namely, we use a cosmological constant model (as a reference), a perfect
fluid with constant equation of state parameter and one with and a scalar field model (or quintessence) with varying . We generate
N-body/hydrodynamic simulations that include radiative cooling with the public
version of the Hydra code, modified to consider an arbitrary dark energy
component. We produce cluster catalogues for the four models and derive the
associated X-ray and SZ scaling relations. We find that dark energy has little
effect on scaling laws making it safe to use the CDM scalings for
conversion of observed quantities into temperature and masses.Comment: 9 pages, 7 figures, submitted to A&
SPH Simulations of Negative (Nodal) Superhumps: A Parametric Study
Negative superhumps in cataclysmic variable systems result when the accretion
disc is tilted with respect to the orbital plane. The line of nodes of the
tilted disc precesses slowly in the retrograde direction, resulting in a
photometric signal with a period slightly less than the orbital period. We use
the method of smoothed particle hydrodynamics to simulate a series of models of
differing mass ratio and effective viscosity to determine the retrograde
precession period and superhump period deficit as a function of
system mass ratio . We tabulate our results and present fits to both
and versus , as well as compare the
numerical results with those compiled from the literature of negative superhump
observations. One surprising is that while we find negative superhumps most
clearly in simulations with an accretion stream present, we also find evidence
for negative superhumps in simulations in which we shut off the mass transfer
stream completely, indicating that the origin of the photometric signal is more
complicated than previously believed.Comment: 14 pages, 15 figures. Accepted for publication in MNRA
The Dynamical Evolution of Black Hole-Neutron Star Binaries in General Relativity: Simulations of Tidal Disruption
We calculate the first dynamical evolutions of merging black hole-neutron
star binaries that construct the combined black hole-neutron star spacetime in
a general relativistic framework. We treat the metric in the conformal flatness
approximation, and assume that the black hole mass is sufficiently large
compared to that of the neutron star so that the black hole remains fixed in
space. Using a spheroidal spectral methods solver, we solve the resulting field
equations for a neutron star orbiting a Schwarzschild black hole. The matter is
evolved using a relativistic, Lagrangian, smoothed particle hydrodynamics (SPH)
treatment. We take as our initial data recent quasiequilibrium models for
synchronized neutron star polytropes generated as solutions of the conformal
thin-sandwich (CTS) decomposition of the Einstein field equations. We are able
to construct from these models relaxed SPH configurations whose profiles show
good agreement with CTS solutions. Our adiabatic evolution calculations for
neutron stars with low compactness show that mass transfer, when it begins
while the neutron star orbit is still outside the innermost stable circular
orbit, is more unstable than is typically predicted by analytical formalisms.
This dynamical mass loss is found to be the driving force in determining the
subsequent evolution of the binary orbit and the neutron star, which typically
disrupts completely within a few orbital periods. The majority of the mass
transferred onto the black hole is accreted promptly; a significant fraction
(~30%) of the mass is shed outward as well, some of which will become
gravitationally unbound and ejected completely from the system. The remaining
portion forms an accretion disk around the black hole, and could provide the
energy source for short-duration gamma ray bursts.Comment: 32 pages, 16 figures, 2 tables, RevTeX, accepted by PR
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