000114   Kudo T;Ohba I (Department of Physics, Advanced Research Centre for Science and Technology, Waseda Universit, Tokyo 169-8555, Japan) : Derivation of relativistic wave equation from the Poisson process. Pramana J Phys 2002, 59(2), 413-16.

A Poisson process is one of the fundamental descriptions for relativistic particles: both fermions and bosons. A generalized linear photon wave equation in dispersive and homogeneous medium with disipation is derived using the formulation of the Poisson process. This formulation provides a possible interpretation of the passage time of a photon moving in the medium, which never exceeds the speed of light in vacuum.

8 ref

000113   Kedar Singh;Saxena N S;Thomas S;Sreekala M S (Condensed Matter Physics Laboratory, Department of Physics, University of Rajasthan, Jaipur-302 004) : Structural relaxation of hybrid composite of phenol formaldehyde. Indian J Engng Mater Sci 2003, 10(1), 65-8.

Glass-palm fibre reinforced hybrid phenol formaldehyde (PF) composites have been studied at constant heating rate by using differential scanning calorimetry (DSC). Sample under investigation is annealed for different times and temperatures. Glass transition temperature (Tg), crystallization temperature (Tc) and heat absorbed (ΔH) in glass transition region have been calculated for glass palm fibre reinforced hybrid phenol formaldehyde composite. It is found that Tc-Tg and ΔH are maximum at annealing time of 60 min and temperature of 60°C. This composite is found to be more thermally stable at these annealing time and temperature due to structural relaxation.

1 illus, 2 tables, 35 ref

000112   Kawazoe Y (NO, Institute for Materials Research (IMR), Thoku University, Sendai 980-8577, Japan) : Realization of prediction of materials properties by ab initio computer simulation. Bull Mater Sci 2003, 26(1), 13-7.

Ab initio treatment is becoming realistic to predict physical, chemical, and even mechanical properties of academically and industrially interesting materials. There is, however, some limitation in size and time of the system up to the order of several hundred atoms and <126> 1 pico second, even if the fastest supercomputer is used efficiently. Therefore, it is very difficult to simulate realistic materials with grain boundaries and important reactions like diffusion in materials. To improve this situation, two ways have been invented. One way is to upgrade approximations to match the necessary levels according to inhomogeneous electron gas theory beyond the present day standard, i.e. local density approximation (LDA). The reason is simply that the system is composed of many particles interacting with Coulomb forces governed by quantum mechanics. Another is to extract the necessary parameters from the ab initio calculations on systems with limited number of atoms, and apply these results into cluster variation, direct, or any other sophisticated methods based on classical concepts such as statistical mechanics. Several typical examples recently worked out are introduced to indicate that these methodologies are actually possible to be successfully used to predict materials properties before experiments based on the present day state-of-art supercomputing systems.

7 illus, 9 ref

000111   Kandpal H C;Anand S (NO, Optical Radiation Standards, National Physical Laboratory, New Delhi-110012) : Analomous behavior of spectra at wavefront dislocations. MAPAN 2003, 18(Jan-Mar), 267-73.

Remarkable spectral modifications and shift in the neighbourhood of a phase singularity produced by a zone plate (circular, an Archimedean or limacon variation zone plate) near the focus of a converging spatially fully coherent polychromatic wave are reported. It is found that the spectrum of a wave on the zone plate consisting of a single spectral profile splits into two peaks at the on-axis point and shows redshift and blueshift around the phase singularity.

4 illus, 4 ref

000110   Jayannavar A M;Benjamin C (Institute of Physics, , Sachivalaya Marg, Bhubaneswar-751 005) : Wave attenuation model for dephasing and measurement of conditional time. Pramana J Phys 2002, 59(2), 385-95.

Inelastic scattering induces dephasing in mesoscopic systems. An analysis of previous models to simulate inelastic scattering in such systems in presented and a relatively new model based on wave attenuation is introduced. The problem of aharonov-Bohm (AB) oscillations in conductance of a mesoscopic ring is studied. Show that the conductance is symmetric under flux reveal and the visibility of AB oscillations decasys to zero as a function of the incoherence parameter, signaling dephasing. Further the wave attenuation model is applied to a fundamental problem in quantum mechanics, that of the conditional (reflection/transmission) times spent in a given region of space by a quantum particle before scattering off from that region.

6 illus, 24 ref

000109   Hari Dass N D;Sathiapalan B;Kalyanarama (Institute of Methematical Sciences, , C I T Campus, Taramani, Chennai-600 113) : Passage from a pure state description to the microcanonical ensemble description for closed quantum systems. Pramana J Phys 2002, 59(2), 303-9.

Addressed the foundational issue of how a macroscopic quantum system starting off as a pure state tends towards a mixed state described by the microcanonical ensemble. The earlier works of von Neumann and Van Kampen are also reviewed. A simple criterion is given as a to when the above mentioned passage can take place.

1 ref

000108   Hari Dass N D;Ganesh P (Institute of Mathematical Sciences, , C I T Campus, Chennai-600 113) : Information cloning of harmonic oscillator coherent states. Pramana J Phys 2002, 59(2), 263-7.

Shows that in the case of unknown harmonic oscillator coherent states it is possible to achieve what call perfect information cloning. Means that it is still possible to make arbitrary number of copies of a state which as exactly the same information content as the original unknown coherent state. By making use of this perfect information cloning it would be possible to estimate the original state through measurements and make arbitrary number of copies of the estimator.Define the notion of a measurements fidelity and calculate it for our case as well as for the Gaussian cloners.

6 ref

000107   Harbola M K;Sen K D (Physics Dep, Indian Institute of Technology, Kanpur-208 016) : Obtaining Kohn-Sham potential without taking the functional derivative. Bull Mater Sci 2003, 26(1), 69-74.

Over the past decade and a half, many new accurate density functionals, based on the generalized gradient approximation, have been proposed, and they give energies close to chemical accuracy. However, accuracy of the energy functional does not guarantee that its functional derivative, which gives the corresponding potential, is also accurate all over space. For example, although the Becke88 exchange-energy functional gives very good exchange energies, its functional derivative goes as -1/2 in comparison to the corect -1/r for r→∞, where r is the distance of the electron from a finite system. On the other hand, accuracy of the potential is of prime importance if one is interested in properties other than the total energy; properties such as optical response depend crucially on the potential in the outer regions of a system. A different approach has been presented, based on the ideas of Harbola and Sahni, to obtain the potential directly from the energy density of a given approximation, without taking recourse to the functional derivative route. This leads to a potential that is as accurate as the functional itself. The accuracy of the approach by presenting some results obtained from the Becke88 functional has been demonstrated.

1 illus, 2 tables, 29 ref

000106   Hara K;Ohba I (Department of Physics, Advanced Research Centre for Science and Technology, Waseda Universit, Tokyo-169-8555, Japan) : Tunneling time distribution by means of Nelson's quantum mechanics and wave-particle duality. Pramana J Phys 2002, 59(2), 405-8.

Constructs a tunneling time distribution by means of Nelson's quantum mechanics and investigate statistical properties of the tunneling time distribution. as a result, finds that the relationship between the average and the variance of the tunneling time shows `wave-particle duality'.

1 illus, 6 ref

000105   Hanke R;Kolling A;Melcher J (NO, Physikalisch- Technische Bundesanstal, 38116 Braunschweig , Germany) : Inductance calibration in the frequency range from 50 Hz to 1 MHz at PTB. MAPAN 2003, 18(Jan-Mar), 255-9.

Inductance calibration at PTB are carried out with a Maxwell-Wein bridge. This bridge has the advantage that the first order bridge equation (1) is independent of frequency which means that the bridge has the potential to be operated in a large frequency range. However, the actual frequency range, from power frequencies up to 1 MHz, requires an investigation of higher order effects.

2 illus, 1 table, 6 ref

000104   Gupta N K;Godwal B K (High Pressure Physics Div, BARC, Mumbai-400 085) : Effects on non-local thermodynamic equilibrium conditions on numerical simulations of inertial confinement fusion plasmas. Pramana J Phys 2002, 59(1), 33-51.

14 illus, 44 ref

000103   Goswami D (Tata Institute of Fundamental Research, , Homi Bhahaa Road, Mumbai-400 005) : Decoherence control in quantum computing with simple chirped pulses. Pramana J Phys 2002, 59(2), 235-42.

Shows how the use of optimally shaped pulses to guide the time evolution of a system (`coherent control') can be an effective approach towards quantum computation logic. Demonstrates this with selective control of decoherence for a multilevel system with a simple linearly chirped pulse. Uses multiphoton density-matrix approach to explore the effects of ultrafast shaped pulses for two-level systems that do not have a single photon resonance, and shows that many multiphoton results are surprisingly similar to the single-photon results. Finally chooses two specific chirped pulses: one that always generates inversion and the other that always generates self-induced transparency to demonstrate an ensemble CNOT gate.

4 illus, 1 table, 10 ref

000102   Godwal B K;Modak P;Rao R A (High Pressure Physics Div, Bhabha Atomic Research Centre, Mumbai-400 085) : On the electronic structure and equation of state in high pressure studies of solids. Bull Mater Sci 2003, 26(1), 175-81.

The high pressure beaviour of zinc as an interesting example of controversy, and of extensive interplay between theory and experiment have been discussed. Its room temperature electronic structure calculations have been presented to study the temperature effect on the occurrence of its controversial axial ratio (c/a) anomaly under pressure, and the related electronic topolotical transition (ETT). A dense 63x63x29 k-point sampling of the Brillouin zone was employed and it was found that the small (c/a) anomaly near 10 GPa pressure persisted at room temperature. A weak signature of the anomaly can be seen in the pressure-volume curve, which gets enhanced in the universal equation of state, along with that of K-point ETTs. The change of slope is attributed to the universal equation of state near 10 GPa pressure, mainly to hybridization effects. The temperature effect in fact enhances the possibility of L-point ETT. It was found that the L-point was very sensitive to exchange correlation terms, and hence it is suggested that further refinements in the theoretical techniques are needed to resolve the controversies on the ETT in Zn.

6 illus, 48 ref

000101   Ghosh S K (Chemistry Group, Atomic Research Centre, Mumbai-400 085) : Density functional theory and multiscale materials modeling. Bull Mater Sci 2003, 26(1), 3-12.

One of the vital ingredients in the theoretical tools useful in materials modeling at all the length scales of interest is the concept of density. In the microscopic length scale, it is the electron density that has played a major role in providing a deeper understanding of chemical binding in atoms, molecules and solids. In the inermediate mesoscopic length scale, an appropriate picture of the equilibrium and dynamical processes has been obtained through the single particle number density for the constituent atoms or molecules. A wide class of problems involving nanomaterials, interfacial science and soft condensed matter has been addressed using the density based theoretical formalism as well as atomistic simulation in this regime. In the macroscopic length scale, however, matter is usually treated as a continuous medium and a description using local mass density, energy density and other related density functions has been found to be quite appropriate. A unique single unified theoretical framework that emerges through the density concept at these diverse length scales and is applicable to both quantum and classical systems is the so called density functional theory (DFT) which essentially provides a vehicle to project the many-particle picture to a single particle one.

4 illus, 61 ref

000100   Ghosh R (School of Physical Sciences, Jawaharlal Nehru University, New Delhi-110 067) : Probing magnetochirality. Pramana J Phys 2002, 59(2), 189-94.

Magnetochiral anisotropy refers to the phenomenon that when light is passed through a chiral medium placed in an external magnetic field, the refractive index, or equivalenty, the absorption encountered by the light differs depending on whether it travels parallel or antiparallel to the magnetic field. It is a very small effect, the change in refractive index because of this effect alone being of the order of 10<^>11. This effect has recently been masured in an active ring laser interferometer in which the detection scheme convincingly eliminates the contributions from natural optical activity, the Faraday effect and other stray anisotropies in the system. The phenomenon is important in the context of fundamental interactions between light and matter and the governing symmetry principles, and also in biochemistry as one possible explanation for the homochirality of life.