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

Short-course chemotherapy of pulmonary tuberculosis

The last four decades have seen spectacular developments in the management of pulmonary tuberculosis. The discovery of streptomycin in 1943 by Waksman was soon followed by other drugs with anti-tuberculosis activity, such as PAS, isoniazid, pyrazinamide, thioacetazone, ethambutol, rifampicin and others. The dis-covery of the anti-tuberculosis activity of isonia-zid in 1952 was a great land-mark which re-volutionalised the treatment of tuberculosis. Because of its high efficacy, low toxicity and low cost, isoniazid soon became the drug of choice in tuberculosis. Administered alone daily for 12 months, it has a potential of producing bacteri-ological quiescence in approximately 70% of pulmonary tuberculosis cases excreting isoniazid-sensitive cultures in their sputum. The con-comitant administration of thioacetazone or PAS daily for 1 year increases the efficacy of the regimen to about 85%. However, approximately 20% of the patients with quiescent disease at 1 year have a bacteriological relapse after stopping chemotherapy, so that the overall efficacy of the 2-drug regimens is reduced to less than 70% even among those patients who consume the drugs regularly. Such relapses can be prevented by continuing chemotherapy beyond 12 months for another 6-12 months. It is, therefore, customary to prescribe regimens of 8-24 months to tuberculosis patients