2,639 research outputs found
Double-peak spectral energy density of GRBs and the true identity of GRB 031203
A double-peak spectral-energy-density of gamma-rays, similar to that observed
in blazars, is expected in gamma-ray bursts (GRBs) produced in supernova (SN)
explosions. The second peak, which is formed by inverse Compton scattering of
ambient SN light by cosmic ray electrons accelerated by the jets from the SN
explosion, has a much higher peak-energy than the first ordinary peak. However,
in X-ray flashes (XRFs), which in the cannonball (CB) model are normal GRBs
viewed farther off axis, the first peak-energy is shifted to the soft X-ray
region while the second peak-energy moves to the MeV range. In far-off-axis
GRBs, such as GRBs 980425 and 031203, the second peak may have been confused
with the normal GRB peak. In most GRBs, which have been observed so far, the
gamma-ray detectors ran out of statistics far below the second peak. However,
in bright GRBs, the two peaks may be resolved by simultaneous measurements with
SWIFT and GLAST.Comment: The estimated soft X-ray fluence in GRB 031203 was replaced in the
text and Fig. 3 with the correct estimate by Vaughan et al. Corrected typo
The cannonball model of long GRBs - overview
During the past ten years, the predictions of the cannonball (CB) model of
gamma ray bursts (GRBs) were repeatedly confronted with the mounting data from
space- and ground-based observations of GRBs and their afterglows (AGs). The
two underlying radiation mechanisms of the model, inverse Compton scattering
(ICS) and synchrotron radiation (SR), provided an accurate description of the
prompt and afterglow emission in all of the many well-sampled GRBs that were
studied. Simple as they are, these two mechanisms and the burst environment
were shown to generate the observed rich structure of the GRB light-curves at
all observed frequencies and times.Comment: Invited talk, to be published in the proceedings of Cefalu 2009
workshop `Probing stellar populations out to the distant universe', Cefalu,
Sicily, Italy, September 7-19, 200
Role of electrolytes and unmeasured anions in the metabolic acid-base abnormalities in dogs with parvoviral enteritis
Background: The strong ion model (SIM) is an alternative paradigm in the characterization of acidâbase disturbances particularly in complex disorders.
Hypothesis/Objectives: To compare the acidâbase changes in dogs with parvoviral enteritis (PE) using the HendersonâHasselbalch (HH) approach, with 2 strong ion approaches.
Animals: Fortyâfour dogs with PE, and 16 ageâmatched control dogs.
Methods: Prospective controlled observational study. Acidâbase status was evaluated using the HH model, FenclâStewart (FS) approach and a validated strong ion model (VDM). The acidâbase changes according to each model were classified and compared. Statistical correlations between pH, CO2, and various SIM variables were performed, as well as between the sum of effects (SOE) of the SIM and the individual variables comprising the SOE.
Results: The HH model identified acidâbase disorders in 31/44 cases of which 16/31 were mixed with metabolic acidosis and concurrent respiratory alkalosis the most common (10/31). Using the FS approach, metabolic changes were present 36/42 cases, with changes in free water (FW), chloride, and unmeasured anions (UA) being the most prevalent. Both FW and UA correlated well with pH; however, UA were most consistently abnormal in severe acidemia. Similarly to the HH, the VDM detected acidâbase disturbances in 28/44 cases. Major contributors to the acidâbase changes were hyponatremia, hypochloremia, and Atot acidosis because of elevated globulins and increased UA.
Conclusions and Clinical Importance: Acidâbase changes are common and complex in dogs with PE, and were easier to understand using a SIM paradigm. Increases in UA have not been documented in PE in dogs
Numerical modeling of Bridgman growth of PbSnTe in a magnetic field
In this work we study heat and mass transport, fluid motion, and solid/liquid phase change in the process of steady Bridgman growth of Pb(.8)Sn(.2)Te (LTT) in an axially-imposed uniform magnetic field under terrestrial and microgravity conditions. In particular, this research is concerned with the interrelationships among segregation, buoyancy-driven convection, and magnetic damping in the LTT melt. The main objectives are to provide a quantitative understanding of the complex transport phenomena during solidification of the nondilute binary of LTT, to provide estimates of the strength of magnetic field required to achieve the desired diffusion-dominated growth, and to assess the role of magnetic damping for space and earth based control of the buoyancy-induced convection. The problem was solved by using FIDAP and numerical results for both vertical and horizontal growth configurations with respect to the acceleration of gravity vector are presented
On the X-ray lines in the afterglows of GRBs
The observation of X-ray lines in the afterglow of GRB 011211 has been
reported, and challenged. The lines were interpreted as blue-shifted X-rays
characteristic of a set of photoionized ``metals'', located in a section of a
supernova shell illuminated by a GRB emitted a couple of days after the
supernova explosion. We show that the most prominent reported lines coincide
with the ones predicted in the ``cannonball'' model of GRBs. In this model, the
putative signatures are Hydrogen lines, boosted by the (highly relativistic)
motion of the cannonballs (CBs). The corresponding Doppler boost can be
extracted from the fit to the observed I-, R- and V-band light-curves of the
optical afterglow of GRB 011211, so that, since the redshift is also known, the
line energies are --in the CB model-- predicted. We also discuss other GRBs of
known redshift which show spectral features generally interpreted as Fe lines,
or Fe recombination edges. The ensemble of results is very encouraging from the
CB-model's point of view, but the data on each individual GRB are not good
enough to draw (any) objectively decisive conclusions. We outline a strategy
for X-ray observers to search for lines which, in the CB model, move
predictably from higher to lower energies.Comment: Accepted for publication in Ap
Optimum Small Optical Beam Displacement Measurement
We derive the quantum noise limit for the optical beam displacement of a
TEM00 mode. Using a multimodal analysis, we show that the conventional split
detection scheme for measuring beam displacement is non-optimal with 80%
efficiency. We propose a new displacement measurement scheme that is optimal
for small beam displacement. This scheme utilises a homodyne detection setup
that has a TEM10 mode local oscillator. We show that although the quantum noise
limit to displacement measurement can be surpassed using squeezed light in
appropriate spatial modes for both schemes, the TEM10 homodyning scheme
out-performs split detection for all values of squeezing.Comment: 13 pages, 7 figure
Expression Analysis of the Ligands for the Natural Killer Cell Receptors NKp30 and NKp44
BACKGROUND: The natural cytotoxicity receptors (NCR) are important to stimulate the activity of Natural Killer (NK) cells against transformed cells. Identification of NCR ligands and their level of expression on normal and neoplastic cells has important implications for the rational design of immunotherapy strategies for cancer. METHODOLOGY/PRINCIPAL FINDINGS: Here we analyze the expression of NKp30 ligand and NKp44 ligand on 30 transformed or non-transformed cell lines of different origin. We find intracellular and surface expression of these two ligands on almost all cell lines tested. Expression of NKp30 and NKp44 ligands was variable and did not correlate with the origin of the cell line. Expression of NKp30 and NKp44 ligand correlated with NKp30 and NKp44-mediated NK cell lysis of tumor cells, respectively. The surface expression of NKp30 ligand and NKp44 ligand was sensitive to trypsin treatment and was reduced in cells arrested in G(2)/M phase. CONCLUSION/SIGNIFICANCE: These data demonstrate the ubiquitous expression of the ligands for NKp30 and NKp44 and give an important insight into the regulation of these ligands
- âŠ