453 research outputs found
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The Use and Misuse of OxyContin
This paper examines the phenomenon of OxyContin abuse over the past two years. The prescription painkiller has been hailed as both a wonder drug and a killer. Both descriptions are accurate. The trouble is not with the pill itself but rather the environment into which it was released. The medical community lacked the experience with pain and addiction necessary to prescribe the powerful drug appropriately. As OxyContin was released in 1995, neither its manufacturer nor governmental agencies did anything to remedy these circumstances or protect against the eventual outcome. After nearly four successful years on the market, ubiquitous reports of addiction and overdoses filled the headlines. While in many ways the extent of the problem has been overstated by the media, that one exists is undeniable. Distinct from the concurrent growth of prescription drug abuse in general, OxyContin abuse has been particularly devastating to those individuals and areas affected. The best solutions focus on deterring and combating abuse and diversion, while ensuring access to the drug for the millions who benefit from it
Accretion discs models with the "beta"-viscosity prescription derived from laboratory experiments
We examine under which conditions one may apply, to steady state keplerian
accretion discs, the "beta"-viscosity prescription which has been derived from
rotating shear flow experiments (Richard & Zahn 1999). Using a vertically
averaged model, we show that this law may be suitable for all three families of
known systems: in young stellar objects, evolved binary stars and Active
Galactic Nuclei discs (except in their outer gas pressure dominated regions
where turbulence becomes hypersonic). According to the standard criterion for
viscous stability, "beta"-discs are always stable throughout. Using realistic
opacities and equation of state, we demonstrate that these discs are thermally
unstable in the temperature domain where hydrogen recombines, when they are
optically thick, and this could lead to limit cycle behavior. Radiation
pressure dominated regions are thermally stable, in contrast with
"alpha"-discs. This results in a fully stable solution for the innermost parts
of AGN discs.Comment: 8 pages, PostScript. accepted in Astron. & Astrophy
The growth of supermassive black holes fed by accretion disks
Supermassive black holes are probably present in the centre of the majority
of the galaxies. There is a consensus that these exotic objects are formed by
the growth of seeds either by accreting mass from a circumnuclear disk and/or
by coalescences during merger episodes.
The mass fraction of the disk captured by the central object and the related
timescale are still open questions, as well as how these quantities depend on
parameters like the initial mass of the disk or the seed or on the angular
momentum transport mechanism. This paper is addressed to these particular
aspects of the accretion disk evolution and of the growth of seeds.
The time-dependent hydrodynamic equations were solved numerically for an
axi-symmetric disk in which the gravitational potential includes contributions
both from the central object and from the disk itself. The numerical code is
based on a Eulerian formalism, using a finite difference method of
second-order, according to the Van Leer upwind algorithm on a staggered mesh.
The present simulations indicate that seeds capture about a half of the
initial disk mass, a result weakly dependent on model parameters. The
timescales required for accreting 50% of the disk mass are in the range 130-540
Myr, depending on the adopted parameters. These timescales permit to explain
the presence of bright quasars at z ~ 6.5. Moreover, at the end of the disk
evolution, a "torus-like" geometry develops, offering a natural explanation for
the presence of these structures in the central regions of AGNs, representing
an additional support to the unified model.Comment: 10 pages, 7 figures. Accepted for publication by Astronomy and
Astrophysic
Nuclear Magnetic Resonance to Detect Rumen Metabolites Associated with Enteric Methane Emissions from Beef Cattle
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Multi-omics of the gut microbial ecosystem in inflammatory bowel diseases.
Inflammatory bowel diseases, which include Crohn's disease and ulcerative colitis, affect several million individuals worldwide. Crohn's disease and ulcerative colitis are complex diseases that are heterogeneous at the clinical, immunological, molecular, genetic, and microbial levels. Individual contributing factors have been the focus of extensive research. As part of the Integrative Human Microbiome Project (HMP2 or iHMP), we followed 132 subjects for one year each to generate integrated longitudinal molecular profiles of host and microbial activity during disease (up to 24 time points each; in total 2,965 stool, biopsy, and blood specimens). Here we present the results, which provide a comprehensive view of functional dysbiosis in the gut microbiome during inflammatory bowel disease activity. We demonstrate a characteristic increase in facultative anaerobes at the expense of obligate anaerobes, as well as molecular disruptions in microbial transcription (for example, among clostridia), metabolite pools (acylcarnitines, bile acids, and short-chain fatty acids), and levels of antibodies in host serum. Periods of disease activity were also marked by increases in temporal variability, with characteristic taxonomic, functional, and biochemical shifts. Finally, integrative analysis identified microbial, biochemical, and host factors central to this dysregulation. The study's infrastructure resources, results, and data, which are available through the Inflammatory Bowel Disease Multi'omics Database ( http://ibdmdb.org ), provide the most comprehensive description to date of host and microbial activities in inflammatory bowel diseases
Rickettsia parkeri in Brazil
We report finding Rickettsia parkeri in Brazil in 9.7% of Amblyomma triste ticks examined. An R. parkeri isolate was successfully established in Vero cell culture. Molecular characterization of the agent was performed by DNA sequencing of portions of the rickettsial genes gltA, htrA, ompA, and ompB
The Gray Needle: Large Grains in the HD 15115 Debris Disk from LBT/PISCES/Ks and LBTI/LMIRcam/L' Adaptive Optics Imaging
We present diffraction-limited \ks band and \lprime adaptive optics images of
the edge-on debris disk around the nearby F2 star HD 15115, obtained with a
single 8.4 m primary mirror at the Large Binocular Telescope. At \ks band the
disk is detected at signal-to-noise per resolution element (SNRE) \about 3-8
from \about 1-2\fasec 5 (45-113 AU) on the western side, and from \about
1.2-2\fasec 1 (63-90 AU) on the east. At \lprime the disk is detected at SNRE
\about 2.5 from \about 1-1\fasec 45 (45-90 AU) on both sides, implying more
symmetric disk structure at 3.8 \microns . At both wavelengths the disk has a
bow-like shape and is offset from the star to the north by a few AU. A surface
brightness asymmetry exists between the two sides of the disk at \ks band, but
not at \lprime . The surface brightness at \ks band declines inside 1\asec
(\about 45 AU), which may be indicative of a gap in the disk near 1\asec. The
\ks - \lprime disk color, after removal of the stellar color, is mostly grey
for both sides of the disk. This suggests that scattered light is coming from
large dust grains, with 3-10 \microns -sized grains on the east side and 1-10
\microns dust grains on the west. This may suggest that the west side is
composed of smaller dust grains than the east side, which would support the
interpretation that the disk is being dynamically affected by interactions with
the local interstellar medium.Comment: Apj-accepted March 27 2012; minor correction
Highlights from the Pierre Auger Observatory
The Pierre Auger Observatory is the world's largest cosmic ray observatory.
Our current exposure reaches nearly 40,000 km str and provides us with an
unprecedented quality data set. The performance and stability of the detectors
and their enhancements are described. Data analyses have led to a number of
major breakthroughs. Among these we discuss the energy spectrum and the
searches for large-scale anisotropies. We present analyses of our X
data and show how it can be interpreted in terms of mass composition. We also
describe some new analyses that extract mass sensitive parameters from the 100%
duty cycle SD data. A coherent interpretation of all these recent results opens
new directions. The consequences regarding the cosmic ray composition and the
properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray
Conference, Rio de Janeiro 201
Evolutionary connectionism: algorithmic principles underlying the evolution of biological organisation in evo-devo, evo-eco and evolutionary transitions
The mechanisms of variation, selection and inheritance, on which evolution by natural selection depends, are not fixed over evolutionary time. Current evolutionary biology is increasingly focussed on understanding how the evolution of developmental organisations modifies the distribution of phenotypic variation, the evolution of ecological relationships modifies the selective environment, and the evolution of reproductive relationships modifies the heritability of the evolutionary unit. The major transitions in evolution, in particular, involve radical changes in developmental, ecological and reproductive organisations that instantiate variation, selection and inheritance at a higher level of biological organisation. However, current evolutionary theory is poorly equipped to describe how these organisations change over evolutionary time and especially how that results in adaptive complexes at successive scales of organisation (the key problem is that evolution is self-referential, i.e. the products of evolution change the parameters of the evolutionary process). Here we first reinterpret the central open questions in these domains from a perspective that emphasises the common underlying themes. We then synthesise the findings from a developing body of work that is building a new theoretical approach to these questions by converting well-understood theory and results from models of cognitive learning. Specifically, connectionist models of memory and learning demonstrate how simple incremental mechanisms, adjusting the relationships between individually-simple components, can produce organisations that exhibit complex system-level behaviours and improve the adaptive capabilities of the system. We use the term “evolutionary connectionism” to recognise that, by functionally equivalent processes, natural selection acting on the relationships within and between evolutionary entities can result in organisations that produce complex system-level behaviours in evolutionary systems and modify the adaptive capabilities of natural selection over time. We review the evidence supporting the functional equivalences between the domains of learning and of evolution, and discuss the potential for this to resolve conceptual problems in our understanding of the evolution of developmental, ecological and reproductive organisations and, in particular, the major evolutionary transitions
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