Dephasing of Aharonov-Bohm oscillations in a mesoscopic ring with a magnetic impurity

We present a detailed analysis of the Aharonov-Bohm interference oscillations manifested through transmission of an electron in a mesoscopic ring with a magnetic impurity atom inserted in one of its arms. The electron interacts with the impurity through the exchange interaction leading to exchange spin-flip scattering. Transmission in the spin-flipped and spin-unflipped channels are explicitly calculated. We show that the spin-flipper acts as a dephasor in spite of absence of any inelastic scattering. The spin-conductance (related to spin-polarized transmission coefficient) is asymmetric in the flux reversal as opposed to the two probe conductance which is symmetric under flux reversal.Comment: 4 pages RevTex, 6 figures, brief repor

Quantum Stochastic Absorption

We report a detailed and systematic study of wave propagation through a stochastic absorbing random medium. Stochastic absorption is modeled by introducing an attenuation constant per unit length $\alpha$ in the free propagation region of the one-dimensional disordered chain of delta function scatterers. The average value of the logarithm of transmission coefficient decreases linearly with the length of the sample. The localization length is given by $\xi ~ = ~ \xi_w \xi_\alpha / (\xi_w + \xi_\alpha)$, where $\xi_w$ and $\xi_\alpha$ are the localization lengths in the presence of only disorder and of only absorption respectively. Absorption does not introduce any additional reflection in the limit of large $\alpha$, i.e., reflection shows a monotonic decrease with $\alpha$ and tends to zero in the limit of $\alpha\to\infty$, in contrast to the behavior observed in case of coherent absorption. The stationary distribution of reflection coefficient agrees well with the analytical results obtained within random phase approximation (RPA) in a larger parameter space. We also emphasize the major differences between the results of stochastic and coherent absorption.Comment: RevTex, 6 pages,2 column format, 9 .eps figures include

Modelling of Stochastic Absorption in a Random Medium

We report a detailed and systematic study of wave propagation through a stochastic absorbing random medium. Stochastic absorption is modeled by introducing an attenuation constant per unit length $\alpha$ in the free propagation region of the one-dimensional disordered chain of delta function scatterers. The average value of the logarithm of transmission coefficient decreases linearly with the length of the sample. The localization length is given by $\xi ~ = ~ \xi_w \xi_\alpha / (\xi_w + \xi_\alpha)$, where $\xi_w$ and $\xi_\alpha$ are the localization lengths in the presence of only disorder and of only absorption respectively. Absorption does not introduce any additional reflection in the limit of large $\alpha$, i.e., reflection shows a monotonic decrease with $\alpha$ and tends to zero in the limit of $\alpha\to\infty$, in contrast to the behavior observed in case of coherent absorption. The stationary distribution of reflection coefficient agrees well with the analytical results obtained within random phase approximation (RPA) in a larger parameter space. We also emphasize the major differences between the results of stochastic and coherent absorption.Comment: 7 pages RevTex, 9 eps figures included, modified version of cond-mat/9909327, to appear in PRB, mpeg simulations at http://www.iopb.res.in/~joshi/mpg.htm

Loss of interference in an Aharonov-Bohm ring

We study a simple model of dephasing of Aharonov-Bohm oscillations in the transmission of an electron across a mesoscopic ring. A magnetic impurity in one of the arms of the ring couples to the electron spin via an exchange interaction. This interaction leads to spin flip scattering and induces dephasing via entanglement. This is akin to the models evoked earlier to explain destruction of interference due to which-path information in double-slit experiments. Total transmission is found to be symmetric under flux reversal but not the spin polarization.Comment: 4 pages, latex/revtex, 4 eps figures. Proceedings of CMDAYS2K, held at Guru Ghasidas University, Bilaspur, Chattisgarh, India, Aug 29-31, 2

An investigation to observe the effect of DMSO and glycerol on the aggregation of lysozyme

Huntington’s disease, Parkinson’s disease, Alzheimer’s disease, Prions Disease are few among many diseases caused due to the aggregation of misfolded proteins, which eventually leads to the formation of amyloids. Amyloids contain a large amount of â – sheets which make it highly stable in the body environment, thus making its lysis difficult. It is reported that the misfolded proteins form amorphous aggregates first which contain less number of â – sheets. These aggregates would further form amyloids as the number â – sheets increase. Inhibiting the formation of aggregates can be regarded as a therapeutic approach in the treatment of above mentioned diseases. In the present investigation, two existing protocols for the formation of amorphous aggregates of lysozyme (Lys) were studied and a novel protocol for the same was proposed. This novel protocol showed high amounts of aggregate formation of lysozyme under laboratory conditions, as observed under Thioflavin T (ThT) assay. However, there was no formation of amyloids, as was observed under Congo Red assay. The effect of DMSO and Glycerol was investigated on the formation of Lysozyme aggregate. The results of these assays indicated that there was significant decrease in the amount of aggregation of lysozyme in solution. Thus, it was concluded that DMSO and Glycerol act as inhibitors for lysozyme aggregation