GRB 060218: The nature of the optical-UV component

The optical-UV component in GRB 060218 is assumed to be due to optically thick cyclotron emission. The key aspect of this model is the high temperature of the absorbing electrons. The heat input derives from nuclei accelerated in semi-relativistic internal shocks, like in ordinary gamma-ray bursts. Coulomb collisions transfer part of that energy to electrons. Inverse Compton cooling on the X-ray photons leads to electron temperatures around 100 keV. Such a high brightness temperature for the optical-UV emission implies an emitting area roughly equal to that of the thermal X-ray component. This suggests a model in which the radio, optical-UV and thermal X-ray emission are closely related: Although the optical-UV and thermal X-ray emission are two separate spectral components, it is argued that they both come from the photosphere of a quasi-spherical, continuous outflow, whose interaction with the circumstellar medium gives rise to the radio emission. The properties of GRB 060218, as measured in the co-moving frame, are similar to those of ordinary gamma-ray burst; i.e., the main difference is the much lower value of the bulk Lorentz factor in GRB 060218. The cyclotron absorption implies a magnetic field in rough equipartition with the matter energy density in the outflow. Hence, the magnetic field could have a dynamically important role, possibly with a magnetar as the central engine.Comment: 16 pages, 1 figure, accepted to Ap

Swift Identification of Dark Gamma-Ray Bursts

We present an optical flux vs. X-ray flux diagram for all known gamma-ray bursts (GRBs) for which an X-ray afterglow has been detected. We propose an operational definition of dark bursts as those bursts that are optically subluminous with respect to the fireball model, i.e., which have an optical-to-X-ray spectral index beta_OX < 0.5. Out of a sample of 52 GRBs we identify 5 dark bursts. The definition and diagram serve as a simple and quick diagnostic tool for identifying dark GRBs based on limited information, particularly useful for early and objective identification of dark GRBs observed with the Swift satellite.Comment: 4 pages, 1 figure. ApJ Letters, in pres

Paravertebral Block for Post-Operative Analgesia after Breast Cancer Surgery, Effects of Adding Morphine: Double Blind, Randomised Clinical Trial

To access publisher's full text version of this article, please click on the hyperlink in Additional Links field or click on the hyperlink at the top of the page marked Files. This article is open access.Introduction: Thoracic paravertebral block (PVB) block is frequently used in breast cancer surgery for postoperative pain management. Adding opioids to local anaesthetics has been shown to have beneficial effects during epidural analgesia. Our hypothesis was that adding morphine to bupivacaine for PVB would improve analgesia provided by this procedure. Methods: 60 patients (25 - 75 years) undergoing elective surgery for breast cancer were randomly assigned to one of two groups. Both groups received a single injection thoracic paravertebral block; group BAM with 20 ml 0.5% bupivacaine, epinephrine and morphine while group BA received identical block except morphine was given subcutaneously. All patients had general anaesthesia. Results: Severity of pain and nausea was low in both groups. Pain scores remained below 20/100 after the first 2 hours throughout the 72 hours of the study. There was no significant difference between the groups in pain scores, consumption of additional morphine or nausea scores. Shoulder mobility was also very good in both groups. Conclusion: Thoracic paravertebral block with bupivacaine and epinephrine was associated with good postoperative analgesic effects and low incidence of nausea and vomiting. The addition of morphine to the local anaesthetic solution in paravertebral block did not have any additional analgesic effects

Boomerang returns unexpectedly

Experimental study of the anisotropy in the cosmic microwave background (CMB) is gathering momentum. The eagerly awaited Boomerang results have lived up to expectations. They provide convincing evidence in favor of the standard paradigm: the Universe is close to flat and with primordial fluctuations which are redolent of inflation. Further scrutiny reveals something even more exciting however -- two hints that there may be some unforeseen physical effects. Firstly the primary acoustic peak appears at slightly larger scales than expected. Although this may be explicable through a combination of mundane effects, we suggest it is also prudent to consider the possibility that the Universe might be marginally closed. The other hint is provided by a second peak which appears less prominent than expected. This may indicate one of a number of possibilities, including increased damping length or tilted initial conditions, but also breaking of coherence or features in the initial power spectrum. Further data should test whether the current concordance model needs only to be tweaked, or to be enhanced in some fundamental way.Comment: 11 pages, 3 figures, final version accepted by Ap

Inducers of Friend leukaemic cell differentiation in vitro--effects of in vivo administration.

Studies were conducted of the in vivo therapeutic potential of compounds which induce the differentiation of Friend leukaemia cells (FLC) in vitro. DBA2/J mice were inoculated with Friend leukaemia cells grown in tissue culture and at various times thereafter were treated with either N-methylacetamide, dimethylacetamide, or tetramethylurea. While survival was only occasionally prolonged, in every study these agents significantly inhibited leukaemia cell proliferation in the spleen and to a lesser extent in the marrow. These agents had no effect on the rate of proliferation of FLC growing subcutaneously nor on the proliferation of myeloid leukaemia in RFMS mice. These studies indicate that the administration of inducing agents to mice bearing Friend leukaemia can alter the proliferation characteristics of the leukaemia cells and hence suggest that these agents may have therapeutic potential

A multi-feedzone wellbore simulator

A multi-feedzone wellbore simulator has been developed. This computer code is quite general as it enables one to compute downhole conditions in wells with an arbitrary number of feedzones during discharge or injection. The simulator is applied to flowing pressure and temperature surveys from various wells in Mexico, Iceland and Kenya. It is demonstrated that such a model can be used to estimate flow rates and enthalpies of individual feedzones

Self-Organized Criticality in Compact Plasmas

Compact plasmas, that exist near black-hole candidates and in gamma ray burst sources, commonly exhibit self-organized non-linear behavior. A model that simulates the non-linear behavior of compact radiative plasmas is constructed directly from the observed luminosity and variability. The simulation shows that such plasmas self organize, and that the degree of non-linearity as well as the slope of the power density spectrum increase with compactness. The simulation is based on a cellular automaton table that includes the properties of the hot (relativistic) plasmas, and the magnitude of the energy perturbations. The plasmas cool or heat up, depending on whether they release more or less than the energy of a single perturbation. The energy release depends on the plasmas densities and temperatures, and the perturbations energy. Strong perturbations may cool the previously heated plasma through shocks and/or pair creation. New observations of some active galactic nuclei and gamma ray bursters are consistent with the simulationComment: 9 pages, 5 figures, AASTeX, Submitted to ApJ