260 research outputs found
Neutron star properties in the quark-meson coupling model
The effects of internal quark structure of baryons on the composition and structure of neutron star matter with hyperons are investigated in the quark- meson coupling (QMC) model. The QMC model is based on mean-field description of nonoverlapping spherical bags bound by self-consistent exchange of scalar and vector mesons. The predictions of this model are compared with quantum hadrodynamic (QHD) model calibrated to reproduce identical nuclear matter saturation properties. By employing a density dependent bag constant through direct coupling to the scalar field, the QMC model is found to exhibit identical properties as QHD near saturation density. Furthermore, this modified QMC model provides well-behaved and continuous solutions at high densities relevant to the core of neutron stars. Two additional strange mesons are introduced which couple only to the strange quark in the QMC model and to the hyperons in the QHD model. The constitution and structure of stars with hyperons in the QMC and QHD models reveal interesting di erences. This suggests the importance of quark structure e ects in the baryons at high densities. PACS number(s): 26.60.+c, 21.65.+f, 12.39.Ba, 24.85.+
Catastrophic rearrangement of a compact star due to the quark core formation
We study properties of compact stars with the deconfinement phase transition
in their interiors. The equation of state of cold baryon-rich matter is
constructed by combining a relativistic mean-field model for the hadronic phase
and the MIT Bag model for the deconfined phase. In a narrow parameter range two
sequences of compact stars (twin stars), which differ by the size of the quark
core, have been found. We demonstrate the possibility of a rapid transition
between the twin stars with the energy release of about ergs. This
transition should be accompanied by the prompt neutrino burst and the delayed
gamma-ray burst.Comment: Latex, 14 pages including five postscript figure
Strange matter in rotating compact stars
We have constructed equations of state involving various exotic forms of
matter with large strangeness fraction such as hyperon matter, Bose-Einstein
condensates of antikaons and strange quark matter. First order phase
transitions from hadronic to antikaon condensed and quark matter are considered
here. The hadronic phase is described by the relativistic field theoretical
model. Later those equations of state are exploited to investigate models of
uniformly rotating compact stars. The effect of rotation on the third family
branch for the equation of state involving only antikaon condensates is
investigated. We also discuss the back bending phenomenon due to a first order
phase transition from condensed to quark matter.Comment: 8 pages, 4 figures; Plenary talk delivered at Strangeness in Quark
Matter (SQM) 2004 held in Cape Town, South Africa from 15-20 September;
Accepted for publication in the proceedings in Journal of Physics
Phase II trial of the oral platinum complex JM216 in non-small-cell lung cancer: An EORTC early clinical studies group investigation
Background JM216 is a new oral platinum complex with dose-limiting toxicity myelosuppresssion, now undergoing phase II evaluation. Patients and methods JM216 was evaluated as first line therapy in non-small-cell lung cancer. Seventeen patients received 120 mg/m2/day for five days repeated every three weeks. Results Toxicity was manageable, the commonest side-effects being nausea, vomiting, diarrhoea, constipation and asthenia. Myelososuppression was generally grade <2 and there were no cases of neutropenic sepsis or bleeding. Thirteen patients were fully evaluable for response. No sustained objective responses were reported. One patient was reported as stable disease had a partial response after three courses but was progressing again after four. An additional five patients had stable disease (46.2%). Conclusions Although some patients may have had useful palliation, JM216 did not appear to have significant antitumour activity in non-small-cell lung cance
Neutron star properties in a chiral SU(3) model
We investigate various properties of neutron star matter within an effective
chiral model. The predictions of this model are
compared with a Walecka-type model. It is demonstrated that the importance of
hyperon degrees are strongly depending on the interaction used, even if the
equation of state near saturation density is nearly the same in both models.
While the Walecka-type model predicts a strange star core with strangeness
fraction , the chiral model allows only for
and predicts that , and will not exist in star, in
contrast to the Walecka-type model.Comment: 13 pages, Revtex, 5 figs include
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