4,210 research outputs found
Duality Symmetry and the Cardy Limit
We study supersymmetric and non-supersymmetric extremal black holes obtained
in Type IIA string theory compactified on K3 X T^2, with duality group
O(6,22,Z) X SL(2,Z). In the Cardy limit an internal circle combines with the
AdS_2 component in the near horizon geometry to give a BTZ black hole whose
entropy is given by the Cardy formula. We study black holes carrying D0-D4 and
D0-D6 brane charges. We find, both in the supersymmetric and non-supersymmetric
cases, that a generic set of charges cannot be brought to the Cardy limit using
the duality symmetries. In the non-supersymmetric case, unlike the
supersymmetric one, we find that when the charges are large, a small fractional
change in them always allows the charges to be taken to the Cardy limit. These
results could lead to a microscopic determination of the entropy for extremal
non-supersymmetric black holes, including rotating cases like the extreme Kerr
black hole in four dimensions.Comment: 46 pages, Latex, Some comments added in Introduction and Conclusions.
Minor changes made in sections 3.4 and
Madras study of short-course chemotherapy in pulmonary tuberculosis
This article presents the results of a controlled clinical study of 3 shortcourse regimens conducted
at the Tuberculosis Research Centre, Madras, in collaboration with the British Medical Research
Council and the World Health Organization
Relapse in tuberculosis
At the outset, I would like to express my sincere gratitude to the Tuberculosis Association of India for having bestowed upon the coveted Wander-TAI Oration Award. When I think of the illustrious personalities who have preceded me I began to have doubts as to whether I will be able to do justice to today's occasion. If I fail to come up to your expectations it will not be because of lack of honest efforts on my part - it is because I neither have the scientific stature nor the gray hairs which my predecessors had. I sincerely hope you will view it in the proper spirit and condone any lapses in my presentation.
We are about to celebrate the centenary of the discovery of the tubercle bacilli by Robert Koch. It is less than 4 decades since we have had the benefits of chemotherapeutic agents with specific activity against tuberculosis. Nevertheless, the decades following the discovery of streptomycin by Waksman in 1943 have seen spectacular achievements in chemotherapy of tuberculosis. We now have several anti-tuberculosis drugs - isoniazid, rifampicin, streptomycin, pyrazinamide, PAS, ethambutol, thioacetazone, ethionamide, and a few other drugs. Isoniazid is by far the most potent and most effective drug with a bacteriological activity, with rifampicin being a close second. Streptomycin and pyrazinamide also have bactericidal activity, and like isoniazid and rifampicin, cause death of tubercle bacilli. Drugs such as PAS, ethambutol and thioacetazone have a bacteriostatic activity, that is, they prevent the multiplication of the bacilli, so that the elimination of the bacilli would depend upon the defense mechanism of the host; their utility is limited to their being companion drugs given in combination with isoniazid with the object of preventing the multiplication of isoniazid-resistant mutants. The present day management of tuberculosis consists of treatment with a combination of isoniazid with at least one other drug in appropriate dosages and rhythms for periods upto 24 months. With a judicatious choice of drug regimens containing isoniazid and other drugs it is possible to produce rapid sputum conversion to negativity and to eliminate the possibility of emergence of drug-resistance; further, patients attaining bacteriological quiescence continue to have quiescent disease even after stopping chemotherapy. With inadequate chemotherapy, on the other hand, failures may manifest in one or more ways - sputum may fail to become culture negative, drug-resistance may emerge, or sputum conversion occurs during treatment but culture becomes positive again after treatment is discontinued, that is, the patient has a bacteriological relapse. With the advent of highly effective chemotherapeutic regimens with practically 100% efficacy, bacteriological relapse has become the most crucial factor in determining the relative merits of chemotherapeutic regimens. I have, therefore, chosen the subject of relapse for today's oration
Axially magnetized Dark Energy cosmological model
We investigate the behaviour of the skewness parameters for an anisotropic
universe in the framework of General Relativity. Non interacting dark energy is
considered in presence of electromagnetic field. A time varying deceleration
parameter simulated by a hybrid scale factor is considered. The dynamics of the
universe is investigated in presence and absence of magnetic field. The
equation of state parameter of dark energy evolves within the range predicted
by the observations. Magnetic field is observed to have a substantial effect on
the cosmic dynamics and the skewness parameters. The models discussed here end
in a big rip and become isotropic at finite time.Comment: 9 pages, 13 figures, Version accepted for publication in Mod. Phys.
Lett.
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