5,257 research outputs found
3-d resistive MHD simulations of magnetic reconnection and the tearing mode instability in current sheets
Magnetic reconnection plays a critical role in many astrophysical processes
where high energy emission is observed, e.g. particle acceleration,
relativistic accretion powered outflows, pulsar winds and probably in
dissipation of Poynting flux in GRBs. The magnetic field acts as a reservoir of
energy and can dissipate its energy to thermal and kinetic energy via the
tearing mode instability. We have performed 3d nonlinear MHD simulations of the
tearing mode instability in a current sheet. Results from a temporal stability
analysis in both the linear regime and weakly nonlinear (Rutherford) regime are
compared to the numerical simulations. We observe magnetic island formation,
island merging and oscillation once the instability has saturated. The growth
in the linear regime is exponential in agreement with linear theory. In the
second, Rutherford regime the island width grows linearly with time. We find
that thermal energy produced in the current sheet strongly dominates the
kinetic energy. Finally preliminary analysis indicates a P(k) 4.8 power law for
the power spectral density which suggests that the tearing mode vortices play a
role in setting up an energy cascade.Comment: 4 pages, 8 figures, accepted for publication in the International
Journal of Modern Physics D, proceedings of HEPRO meeting, held in Dublin, in
September 200
A multi-flow model for microquasars
We present a new picture for the central regions of Black Hole X-ray
Binaries. In our view, these central regions have a multi-flow configuration
which consists in (1) an outer standard accretion disc down to a transition
radius r_J, (2) an inner magnetized accretion disc below r_J driving (3) a non
relativistic self-collimated electron-proton jet surrounding, when adequate
conditions for pair creation are met, (4) a ultra relativistic
electron-positron beam. This accretion-ejection paradigm provides a simple
explanation to the canonical spectral states, from radio to X/gamma-rays, by
varying the transition radius r_J and disc accretion rate independently. Large
values of r_J and low accretion rate correspond to Quiescent and Hard states.
These states are characterized by the presence of a steady electron-proton MHD
jet emitted by the disc below r_J. The hard X-ray component is expect to form
at the jet basis. When r_J becomes smaller than the marginally stable orbit
r_i, the whole disc resembles a standard accretion disc with no jet,
characteristic of the Soft state. Intermediate states correspond to situations
where r_J ~ r_i. At large accretion rate, an unsteady pair cascade process is
triggered within the jet axis, giving birth to flares and ejection of
relativistic pair blobs. This would correspond to the luminous intermediate
state, with its associated superluminal motions.Comment: 12 pages, 3 figures. Proceedings of ``High Energies in the
Highlands'', Fort-William, 27 June-1 July 200
008 BONE MARROWLESIONS, CARTILAGE LOSS, AND PAIN IN KNEE OSTEOARTHRITIS: RESULTS FROM A RANDOMIZED CONTROLLED CLINICAL TRIAL USING MRI
Search For Oxygen in Cool DQ White Dwarf Atmospheres
We report new infrared spectroscopic observations of cool DQ white dwarfs by
using Coolspec on the 2.7m Harlan-Smith Telescope. DQs have helium-rich
atmospheres with traces of molecular carbon thought to be the result of
convective dredge-up from their C/O interiors. Recent model calculations
predict that oxygen should also be present in DQ atmospheres in detectable
amounts. Our synthetic spectra calculations for He-rich white dwarfs with
traces of C and O indicate that CO should be easily detected in the cool DQ
atmospheres if present in the expected amounts. Determination of the oxygen
abundance in the atmosphere will reveal the C/O ratio at the core/envelope
boundary, constraining the important and uncertain ^{12}C(alpha,gamma)^{16}O
reaction rate.Comment: 2 pages, 2 figures, to appear in proceedings of the 13th European
Workshop on White Dwarf
Cytokine Reduction in the Treatment of Joint Conditions
The destruction of joints caused by rheumatoid arthritis and
osteoarthritis is characterized by an imbalance of enzyme catalysed
cartilage breakdown and regeneration. A complex cytokine network
perpetuates joint conditions by direct regulation of
metalloproteases, by indirect recruitment of cells that secrete
degradative enzymes, and by inhibition of reparative processes. The
destructive action of cytokines such as interleukin-1, interleukin-6
and tumour necrosis factor-α can be modulated at multiple
points associated either with cytokine production or with cytokine
action. Potential agents for cytokine reduction include selective
anti-cytokine antibodies, anticytokine receptor antibodies, cytokine
receptor antagonist proteins, and soluble and chimeric cytokine
receptor molecules. Pharmacologic regulation of IL-1 and TNFα
remain primary targets for treatment of arthritis, and results of
early clinical trials are promising. However, the results of
long-term clinical trials will be required to support the value of
anti-cytokine therapy in treatment of arthritis
Reduction in the structural changes of experimental osteoarthritis by a nitric oxide inhibitor
AbstractObjectiveTo evaluate the in-vivo therapeutic efficacy ofN-iminoethyl-L-Lysine (L-NIL), a selective inhibitor of inducible nitric oxide synthase (iNOS) in a dose response study, on the progression of lesions in the experimental osteoarthritic (OA) dog model.DesignThe sectioning of the anterior cruciate ligament of the right stifle joint of mongrel dogs was done by a stab wound. Dogs were separated into experimental groups: Group 1 received no treatment, Groups 2, 3, and 4 received oral L-NIL (0.3, 1 or 10mg/kg/day, respectively) starting immediately after surgery. The OA dogs were killed at 12 weeks after surgery.ResultsMacroscopically, L-NIL decreased the size of the cartilage lesions on condyles and plateaus. The histologic severity of the cartilage lesions was decreased in the L-NIL-treated dogs. This effect was more pronounced at the highest dosage tested (3 and 10mg/kg/day).ConclusionsThis study confirms the effectiveness of L-NIL, a selective inhibitor of iNOS, in attenuating the progression of experimental OA. It also clearly shows that the effect is dose-dependent
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