High contrast electromagnetically induced transparency in a nitrogen filled Rb vapour cell

We observe the electromagnetically induced transparency (EIT) spectra inside a nitrogen filled Rb vapour cell (Rb-N₂) in a five-level Λ-type system of D₂ transition of Rb atom. The high contrast EIT resonance in buffer gas filled Rb cell is obtained under our experimental conditions. The effect of velocity changing coherence preserving collisions to obtain the contrast resonance in buffer gas cell has been discussed. We measured the dependence of EIT width and height on pump intensity and find that the EIT width (FWHM) and peak height have a linear dependence on pump intensity. Our experimental results show that the presence of N2 buffer gas reduces the power broadening of the observed resonances.     

Analysis of short-pulse laser photon transport through tissues for optical tomography

We describe a method for analyzing short-pulse laser propagation through tissues for the detection of tumors and inhomogeneities in tissues with the goal of developing a time-resolved optical tomography system. Traditional methods for analyzing photon transport in tissues usually involve the parabolic or diffusion approximation, which implies infinite speed of propagation of the optical signal. To overcome such limitations we calculate the transmitted and reflected intensity distributions, using the damped-wave hyperbolic P(1) and the discrete-ordinates methods, for a wide range of laser, tissue, and tumor parameters. The results are compared with the parabolic diffusion P(1) approximation.     

Carbon-13 NMR signals of some benzodiazepine drugs

Some carbon-13 NMR signal assignments of diazepam, flurazepam, clonazepam and chlordiazepoxide have been revised and the assignments of nitrazepam are reported. The assignments of the various resonances were made by considering the changes in chemical shifts produced by the change of substituents and also by comparison with the chemical shifts of model compounds.     

Lattice dynamical calculation of the second Grüneisen constant of CsBr

The second order Grüneisen constant constitutes an additional measure of the anharmonicity in a solid (the Grüneisen constant itself being the first measure). This quantity and the corresponding second mode-Grüneisen parameters are calculated for CsBr using a modified rigid ion model of lattice dynamics. The model parameters are deduced from the three elastic constants and the long wavelength optical mode frequencies. Using the first and second order pressure dependences of these physical observables, the individual second mode-Grüneisen parameters are obtained as a function of wave vector. The temperature variation of the second Grüneisen constant is then deduced in a quasi-harmonic approximation. The second Grüneisen constant is also calculated from available thermodynamic data and is in reasonable agreement with the present theoretical prediction.     

Velocity autocorrelation in liquid sodium

The expression for the memory function of Corngold et al. has been modified using an effective potential for liquid sodium to calculate the velocity autocorrelation function and the coefficient of self diffusion. The results are found in good agreement with computer experiment results of Schiff.     

Change of force constant around a point defect in a solid

The local or gap mode frequencies of a host lattice-point defect system. XY:Z may be predicted from the properties of the end member pure crystals XY and XZ alone whenever pertinent data on pure crystals are available, without invoking any arbitrary force constant softening. In this instance the molecular model has been used, and relevant examples from alkali halides are presented. A modification of the Green's function technique is also discussed.     

Is multiscaling an artifact in the stochastically forced Burgers equation?

We study turbulence in the one-dimensional Burgers equation with a white-in-time, Gaussian random force that has a Fourier-space spectrum approximately 1/k, where k is the wave number. From very high-resolution numerical simulations, in the limit of vanishing viscosity, we find evidence for multiscaling of velocity structure functions which cannot be falsified by standard tests. We find a new artifact in which logarithmic corrections can appear disguised as anomalous scaling and conclude that bifractal scaling is likely.     

Dynamics of passive-scalar turbulence

We present the first study of the dynamic scaling or multiscaling of passive-scalar turbulence. For the Kraichnan version of passive-scalar turbulence we show analytically, in both Eulerian and quasi-Lagrangian frameworks, that simple dynamic scaling is obtained but with different dynamic exponents. By developing the multifractal model we show that dynamic multiscaling occurs in passive-scalar turbulence only if the advecting velocity field is itself multifractal. We substantiate our results by detailed numerical simulations in shell models of passive-scalar advection.     

Varieties of dynamic multiscaling in fluid turbulence

We show that different ways of extracting time scales from time-dependent velocity structure functions lead to different dynamic-multiscaling exponents in fluid turbulence. These exponents are related to equal-time multiscaling exponents by different classes of bridge relations, which we derive. We check this explicitly by detailed numerical simulations of the Gledzer-Ohkitani-Yamada shell model for fluid turbulence. Our results can be generalized to any system in which both equal-time and time-dependent structure functions show multiscaling.