A Model for Quantum Stochastic Absorption in Absorbing Disordered Media

Wave propagation in coherently absorbing disordered media is generally modeled by adding a complex part to the real part of the potential. In such a case, it is already understood that the complex potential plays a duel role; it acts as an absorber as well as a reflector due to the mismatch of the phase of the real and complex parts of the potential. Although this model gives expected results for weakly absorbing disordered media, it gives unphysical results for the strong absorption regime where it causes the system to behave like a perfect reflector. To overcome this issue, we develop a model here using stochastic absorption for the modeling of absorption by "fake", or "side", channels obviating the need for a complex potential. This model of stochastic absorption eliminates the reflection that is coupled with the absorption in the complex potential model and absorption is proportional to the magnitude of the absorbing parameter. Solving the statistics of the reflection coefficient and its phase for both the models, we argue that stochastic absorption is a potentially better way of modeling absorbing disordered media.Comment: 5 pages, 4 figure

Needs in tuberculosis research

Tuberculosis is still a major health problem in developing countries. It is also emerging as a major infectious disease in the developed countries due to AIDS epidemic. Its pathogenesis, immunology and molecular biology are still incompletely understood. The development of new drugs to fight tuberculosis ceased over two decades ago. The variable efficacy of BCG, found in different trials, still remains an enigma. And, it is likely that its epidemiology is also different, in some aspects, in developing countries compared with the developed ones. Sometime ago, it was said that the application of current knowledge about tuberculosis was lagging so far behind its application in the field that the focus should shift from more and more research in tuberculosis. That saying appears to have lost its validity under the present circumstances, especially when the WHO has declared a global war on the “neglected epidemic”. The following horizons in different aspects of tuberculosis can be recognised in respect of research needs in tuberculosis

Tuberculosis - the continuing scourge of India

Epidemiological picture of tuberculosis in India is complex with wide variation in the annual risk of infection and prevalence of disease. The concentration of the disease among younger age groups makes tuberculosis a major socio-economic burden in India. The disability adjusted life years (DALYS) is estimated to be around 63 and 46 lakhs of years of life lost in men and women respectively. The burden is likely to increase with HIV epidemic with an increase of cases with dual infection, increase in morbidity and mortality due to tuberculosis. Management of drug resistant tuberculosis is a major hurdle in tuberculosis control and is a major step in cutting the chain of transmission to those with HIV infection, AIDS and immunodeficiency. Development of new therapeutic modalities to address this problem are also urgently required. Poor patient compliance has been the reason for failure of many control programmes. Operational research studies conducted by the TRC have resulted in elucidation of socio-behavioural aspects of patients’ which need further investigation for remedial measures. Studies to improve drug delivery and to measure the impact of health education and mass media on compliance are areas which need to be concentrated. Newer techniques such as DNA fingerprinting need to employed to improve knowledge of the patterns of transmission in communities. The impact of HIV infection on tuberculosis and the role of chemoprophylaxis in HIV infected individuals in high risk populations, children in close contact with newly diagnosed patients and HIV infected individuals need to be urgently explored. improved methods for diagnosis of Mycobacterium tuberculosis infection must await considerable advance in the understanding of basic immunology, mycobacterial antigenic structure and host-parasitic interaction

Does decentralization work? Forest conservation in the Himalayas

This paper studies the effect of decentralization of management and control on forest conservation in the central Himalayas. The density of forest cover (measured with satellite images and field surveys) in forests managed by village councils is compared with that in state-managed forests and in unmanaged village commons. Geographic proximity and historical and ecological information are used to identify the effects of the three types of management regimes. Village council management does no worse, and possibly better, at conservation than state management and costs an order of magnitude less per unit area. Relative to unmanaged commons, village council management raises crown cover in broadleaved forests (the type of forest that may provide the most benefits to villagers under the rules) but not in pine forests.

Gaussian approximation for finitely extensible bead-spring chains with hydrodynamic interaction

The Gaussian Approximation, proposed originally by Ottinger [J. Chem. Phys., 90 (1) : 463-473, 1989] to account for the influence of fluctuations in hydrodynamic interactions in Rouse chains, is adapted here to derive a new mean-field approximation for the FENE spring force. This "FENE-PG" force law approximately accounts for spring-force fluctuations, which are neglected in the widely used FENE-P approximation. The Gaussian Approximation for hydrodynamic interactions is combined with the FENE-P and FENE-PG spring force approximations to obtain approximate models for finitely-extensible bead-spring chains with hydrodynamic interactions. The closed set of ODE's governing the evolution of the second-moments of the configurational probability distribution in the approximate models are used to generate predictions of rheological properties in steady and unsteady shear and uniaxial extensional flows, which are found to be in good agreement with the exact results obtained with Brownian dynamics simulations. In particular, predictions of coil-stretch hysteresis are in quantitative agreement with simulations' results. Additional simplifying diagonalization-of-normal-modes assumptions are found to lead to considerable savings in computation time, without significant loss in accuracy.Comment: 26 pages, 17 figures, 2 tables, 75 numbered equations, 1 appendix with 10 numbered equations Submitted to J. Chem. Phys. on 6 February 200

Damage Mechanisms in Tapered Composite Structures Under Static and Fatigue Loading

In this work an integrated computational/experimental approach was developed to validate the predictive capabilities of State-of-the-Art (SoA) Progressive Damage Analysis (PDA) methods and tools. Specifically, a tapered composite structure incorporating ply-drops typical in the aerospace industry to spatially vary structural thickness was tested under static tension and cyclic tension fatigue loads. The data acquired from these tests included quantitative metrics such as pre-peak stiffness, peak load, location of delamination damage onset, and growth of delaminations as functions of applied static and fatigue loads. It was shown that the PDA tools were able to predict the pre-peak stiffness and peak load within 10% of experimental average, thereby meeting and exceeding the pre-defined success criteria. Additionally, it was shown that the PDA tools were able to accurately predict the location of delamination onset and satisfactorily predict delamination growth under static tension loading. Overall, good correlations were achieved between modeling and experiments

Significance of thermal fluctuations and hydrodynamic interactions in receptor-ligand mediated adhesive dynamics of a spherical particle in wall bound shear flow

The dynamics of adhesion of a spherical micro-particle to a ligand-coated wall, in shear flow, is studied using a Langevin equation that accounts for thermal fluctuations, hydrodynamic interactions and adhesive interactions. Contrary to the conventional assumption that thermal fluctuations play a negligible role at high P$\acute{e}$clet numbers, we find that for particles with low surface densities of receptors, rotational diffusion caused by fluctuations about the flow and gradient directions aids in bond formation, leading to significantly greater adhesion on average, compared to simulations where thermal fluctuations are completely ignored. The role of wall hydrodynamic interactions on the steady state motion of a particle, when the particle is close to the wall, has also been explored. At high P$\acute{e}$clet numbers, the shear induced force that arises due to the stresslet part of the Stokes dipole, plays a dominant role, reducing the particle velocity significantly, and affecting the states of motion of the particle. The coupling between the translational and rotational degrees of freedom of the particle, brought about by the presence of hydrodynamic interactions, is found to have no influence on the binding dynamics. On the other hand, the drag coefficient, which depends on the distance of the particle from the wall, plays a crucial role at low rates of bond formation. A significant difference in the effect of both the shear force and the position dependent drag force, on the states of motion of the particle, is observed when the P$\acute{e}$let number is small.Comment: The manuscript has been accepted as an article in Physical Review E Journa

Follow-up of patients discharged against medical advice in tuberculous meningitis studies in children

A total of 395 TB meningitis patients were admitted for treatment comprising regimens containing Rifampicin with and without Pyrazinamide. Of these, 50 patients were discharged against medical advice before completing the prescribed therapy, most being too sick and put on dangerously ill list. On follow-up, all such patients were found to have died. Discharges due to other reasons like migration, economic and domestic problems etc., were low, i.e., 6%. Drop out of patients, thus, was not a serious problem in TB meningitis studies despite the fact that 62% of the patients were from outside Madras City. This was possible due to the initial and periodic motivation of the patients

Niacin production test in mycobacteria: Replacement of benzidine - cyanogen bromide reagent by o-tolidne - cyanogen bromide

The identification of M. tuberculosis depends primarily on the niacin production test. Runyon and others (1959) described a method based on the observations of Konno (1956) using aniline as the reagent. However, the aniline reagent gives a yellow colour which can cause difficulty in the interpretation of the results, particularly in the case of the chromogenic mycobacteria. Hence several workers prefer the test employing benzidine (Medveczky, 1960) or o-tolidine (Guttierrez-Vazquez, 1960), since the pink colour produced in these tests is easier to read. The standard method for niacin production test at this Centre has been the one using benzidine. However, satisfactory supplies of benzidine are no longer available, as the manufacture of this compound’ has recently been stopped. Hence it was decided to investigate the test using o-tolidine. Though other workers (Tarshis, 1960, 1961; Gangadharam and Droubi, 1971) have compared the benzidine and o-tolidine methods on small numbers of cultures, no large scale investigation of these two methods has been reported. Therefore a direct controlled comparison of these two methods was undertaken, the results of which are reported here