4,524 research outputs found
The thermodynamics of collapsing molecular cloud cores using smoothed particle hydrodynamics with radiative transfer
We present the results of a series of calculations studying the collapse of
molecular cloud cores performed using a three-dimensional smoothed particle
hydr odynamics code with radiative transfer in the flux-limited diffusion
approximation. The opacities and specific heat capacities are identical for
each calculation. However, we find that the temperature evolution during the
simulations varies significantly when starting from different initial
conditions. Even spherically-symmetric clouds with different initial densities
show markedly different development. We conclude that simple barotropic
equations of state like those used in some previous calculations provide at
best a crude approximation to the thermal behaviour of the gas. Radiative
transfer is necessary to obtain accurate temperatures.Comment: 8 pages, 9 figures, accepted for publication in MNRA
A simplified model of the Martian atmosphere - Part 1: a diagnostic analysis
In this paper we derive a reduced-order approximation to the vertical and horizontal structure of a simplified model of the baroclinically unstable Martian atmosphere. The original model uses the full hydrostatic primitive equations on a sphere, but has only highly simplified schemes to represent the detailed physics of the Martian atmosphere, e.g. forcing towards a plausible zonal mean temperature state using Newtonian cooling. Three different norms are used to monitor energy conversion processes in the model and are then compared. When four vertical modes (the barotropic and first three baroclinic modes) are retained in the reduced-order approximation, the correlation norm captures approximately 90% of the variance, while the kinetic energy and total energy norms capture approximately 83% and 78% of the kinetic and total energy respectively. We show that the leading order Proper Orthogonal Decomposition (POD) modes represent the dominant travelling waves in the baroclinically-unstable, winter hemisphere. In part 2 of our study we will develop a hierarchy of truncated POD-Galerkin expansions of the model equations using up to four vertical modes
A simplified model of the Martian atmosphere - Part 2: a POD-Galerkin analysis
In Part I of this study Whitehouse et al. (2005) performed a diagnostic analysis of a simplied model of the Martian atmosphere, in which topography was absent and in which heating was modelled as Newtonian relaxation towards a zonally symmetric equilibrium temperature field. There we derived a reduced-order approximation to the vertical and the horizonal structure of the baroclinically unstable Martian atmosphere, retaining only the barotropic mode and the leading order baroclinic modes. Our objectives in Part II of the study are to incorporate these approximations into a Proper Orthogonal Decomposition-Galerkin expansion of the spherical quasi-geostrophic model in order to derive hierarchies of nonlinear ordinary differential equations for the time-varying coefficients of the spatial structures. Two different vertical truncations are considered, as well as three different norms and 3 different Galerkin truncations. We investigate each in turn, using tools from bifurcation theory, to determine which of the systems most closely resembles the data for which the original diagnostics were performed
FISH: A 3D parallel MHD code for astrophysical applications
FISH is a fast and simple ideal magneto-hydrodynamics code that scales to ~10
000 processes for a Cartesian computational domain of ~1000^3 cells. The
simplicity of FISH has been achieved by the rigorous application of the
operator splitting technique, while second order accuracy is maintained by the
symmetric ordering of the operators. Between directional sweeps, the
three-dimensional data is rotated in memory so that the sweep is always
performed in a cache-efficient way along the direction of contiguous memory.
Hence, the code only requires a one-dimensional description of the conservation
equations to be solved. This approach also enable an elegant novel
parallelisation of the code that is based on persistent communications with MPI
for cubic domain decomposition on machines with distributed memory. This scheme
is then combined with an additional OpenMP parallelisation of different sweeps
that can take advantage of clusters of shared memory. We document the detailed
implementation of a second order TVD advection scheme based on flux
reconstruction. The magnetic fields are evolved by a constrained transport
scheme. We show that the subtraction of a simple estimate of the hydrostatic
gradient from the total gradients can significantly reduce the dissipation of
the advection scheme in simulations of gravitationally bound hydrostatic
objects. Through its simplicity and efficiency, FISH is as well-suited for
hydrodynamics classes as for large-scale astrophysical simulations on
high-performance computer clusters. In preparation for the release of a public
version, we demonstrate the performance of FISH in a suite of astrophysically
orientated test cases.Comment: 27 pages, 11 figure
Improving procedural fairness in housing possession cases
This article offers an insight into the context and practice of housing possession hearings in which a social landlord seeks a possession order against a tenant who is in rent arrears. Drawing on the findings of the authors’ empirical research, supplemented by insights from the psychology of decision-making, this article questions whether judges are able to exercise discretion in a manner consistent with the fundamental demands of ‘procedural fairness’. We find that while the legal process requires judges to engage in rational decision-making, and while judges believe that this is what they are doing, the reality is very different: judges are likely to be relying on intuition. It is not that judges eschew engaging in more deliberative decision-making but rather that they are constrained by limits of the human mind as well as the conditions under which they make their decisions. In particular, the practice of housing possession is characterised by information deficits, low levels of legal representation and time constraints, and this does not facilitate decision-making that meets accepted standards of fairness. In response, we propose ways in which to enhance the consistency, transparency and accountability of decision-making while recognising the current climate of reform and diminishing resources within the legal system
On the spectral sequence associated to a multicomplex
A multicomplex, also known as a twisted chain complex, has an associated spectral sequence via a filtration of its total complex. We give explicit formulas for all the differentials in this spectral sequence
Toward three-dimensional simulations of stellar core collapse with magnetic fields
In spherical symmetry, very reliable models of stellar core collapse, bounce, and the postbounce phase can be constructed based on general relativistic Boltzmann neutrino transport. However, even if the time-integrated neutrino luminosity in the region between the surface of the protoneutron star and the stalled accretion shock is one or two orders of magnitude larger than the energy of a supernova explosion, it is generally accepted that the net energy transfer is not efficient enough to drive an explosion, unless the fluid instabilities in this regime are taken into account. Complementary to other groups, who are elaborating an extension of the accurate neutrino physics to axisymmetric simulations, we construct efficient parameterizations of the neutrino physics that enable three-dimensional magneto-hydrodynamics simulations that do not constrain the fluid instabilities by artificially imposed symmetries. We evaluate our approximations with respect to spherically symmetric Boltzmann neutrino transport, present preliminary MHD simulations with a resolution of 600 zones cubed, and illustrate the questions that can be addressed by this approac
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Effect of diet type on serum and faecal concentration of S100/calgranulins in the captive cheetah
Gastrointestinal disease is omnipresent in captive cheetahs (Acinonyx jubatus), in contrast to its freeranging populations. The current study aimed to evaluate the effect of diet type (meat-only whole prey) on gastrointestinal health in captive cheetahs by measuring faecal and serum concentrations of S100/calgranulins. This paper reports faecal S100A12 and calprotectin concentrations in 12 captive cheetahs fed supplemented beef versus whole rabbit for one month in a cross-over design. Also, serum S100A12 and calprotectin concentrations were determined in four cheetahs fed whole rabbit and six cheetahs fed supplemented beef, and these were compared to the faecal concentrations of the respective marker proteins. Both the immunoassay for canine calprotectin and canine S100A12 were precise and reproducible for use with serum samples and faecal extracts. Whereas the assay for S100A12 was linear and accurate, an inconsistent linearity of the canine calprotectin assay was observed and could be indicative of an insufficient cross-reactivity of the specific antibody used for this assay. Serum concentrations of S100A12 and calprotectin were not altered by diet type, and were not correlated with the respective concentrations in faeces. Numerically (P=0.241) greater calprotectin concentrations and greater (P=0.041) faecal S100A12 concentrations were detected in cheetahs fed supplemented beef compared with whole rabbit. These findings demonstrate that whole prey feeding may decrease intestinal inflammation in the captive cheetah. Consequently, the relation between diet type and intestinal inflammatory conditions in the captive cheetah warrants further investigation
Fermentation of animal components in strict carnivores: a comparative study with cheetah fecal inoculum
The natural diet of felids contains highly digestible animal tissues but also fractions resistant to small intestinal digestion, which enter the large intestine where they may be fermented by the resident microbial population. Little information exists on the microbial degradability of animal tissues in the large intestine of felids consuming a natural diet. This study aimed to rank animal substrates in their microbial degradability by means of an in vitro study using captive cheetahs fed a strict carnivorous diet as fecal donors. Fresh cheetah fecal samples were collected, pooled, and incubated with various raw animal substrates (chicken cartilage, collagen, glucosamine-chondroitin, glucosamine, rabbit bone, rabbit hair, and rabbit skin; 4 replicates per substrate) for cumulative gas production measurement in a batch culture technique. Negative (cellulose) and positive (casein and fructo-oligosaccharides; FOS) controls were incorporated in the study. Additionally, after 72 h of incubation, short-chain fatty acids (SCFA), including branched-chain fatty acids (BCFA), and ammonia concentrations were determined for each substrate. Glucosamine and glucosamine-chondroitin yielded the greatest OM cumulative gas volume (OMCV) among animal substrates (P < 0.05), whereas total SCFA production was greatest for collagen (P < 0.05). Collagen induced an acetate production comparable to FOS and a markedly high acetate-to-propionate ratio (8.41:1) compared to all other substrates (1.67:1 to 2.97:1)
Loudly sing cuckoo : More-than-human seasonalities in Britain
This research was funded by a grant from the Arts and Humanities Research Council, grant number AH/E009573/1.Peer reviewedPostprin
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