020062   Luo W F;Zhao X X;Sun Q B;Gao C X;Tang J;Wang H J;Zhao W (State Key Laboratory of Transient Optics and Photonics, Xi' an Institute Optics and Precision Mechanisc, Chinese Academy of Science, Xi'an 710119, China, Email: luowf@opt.ac.cn) : Characteristics of the aluminum alloy plasma produced by a 1064 nm Nd: YAG laser with different irradiances. Pramana J Phys 2010, 74(6), 945-59.

The plasma generated by 1064 nm Nd:YAG laser irradiation of aluminum alloy in air at atmospheric pressure was studied spectroscopically. The electron density inferred by measuring the Stark-broadened line profile of Si (I) 288.16 nm decreases with increasing distance from the target surface. The electron temperature was determined using the Boltzmann plot method with nine strong neutral aluminum lines. Due to the thermal conduction towards the solid target and radiative cooling of the plasma as well as conversion of thermal energy into kinetic energy, the electron temperature decreases both at the plasma edge and close to the target surface. Electron density and electron temperature were also studied as functions of laser power density. At the same time, the validity of the assumption of local thermodynamic equilibrium and the effect of self-absorption were discussed in light of the results obtained.

8 illus, 1 table, 37 ref

020061   Lo C Y (NO, Applied and Pure Research Institute, 7 Taggart Drive, Unit E, Nashua, NH 03060) : Physical measurments in general relativity and requirements on a physical Riemannian space time. Bull pure appl Sci-Sect D 2010, 29(1), 1-23.

The spatial invariant line element, which is regarded as the local distance in Einstein's theory of measurement, is actually a space contraction measured from a local Minkowski space, resting but at free fall. It is shown that Einstein's theory of measurement is actually based on only invalid applications of special relativity; and is not an integral part of general relativity. In addition to theoretical difficulties pointed out by Whitehead, Einstein's approach seems to necessitate his covariance principle that creates further problems. It is shown that a physical Riemannian space-time must have a frame of reference with the Euclidean-like structure that is compatible with physical measurements. Thus, the invariant line element provides the space contractions while the Euclidean-like structure provides the measurement of local distance. Furthermore, the notion of gauge invariant measurable quantity is proven an illusion in mathematics only. For instance, in the light deflection, the impact parameter and the shortest distance from the sun cannot be gauge invariant when measurements are involved.

58 ref

020060   Lo C Y (NO, Applied and Pure Research Institute, 7 Taggart Drive, Unit E, Nashua, NH 03060 USA) : Principle of causality and the requirement for weak gravity versus Einstein's covariance principle. Bull pure appl Sci-Sect D 2010, 29(2), 81-103.

Consideres their unbounded metric as a weak wave from a distant source, but they were unaware that their "wave" violates the principle of causality. However, the claim of the Royal Society on the inconsistency between Einstein's "covariance principle" and Einstein's requirement for weak gravity is valid. Although his requirement is crucial for having agreements with observations, it may not be compatible with a Lorentz manifold. Thus, there was no general consensus. However, the principle of causality enables us to show that Einstein's requirement is valid on source-induced gravity. Moreover, there are counter examples for Einstein's covariance principle although it is needed for Einstein's theory of measurement, whose justifications are actually based on invalid applications of special relativity. Einstein's covariance principle is also inconsistent with his equivalence principle. It is pointed out that not only his theory of measurement is not used in his predictions, but also leads to disagreement with observations and theoretical inconsistency. The valid spatial measurement is based on the Euclidean-like structure; and this is what Einstein actually practiced in his calculations.

64 ref

020059   Lo C Y (NO, Applied and Pure Research Institute, 7 Taggart Drive Unit E, Nashua, NH 03060 USA) : Precession formulas for gravity probe-B and its complementary experiments of local light speeds. Bull pure appl Sci-Sect D 2009, 28(1), 67-85.

Calculation shows that different gauges lead to different formulas of the de Sitter precession. Therefore, gauge invariance for a given frame of reference is clearly invalid, and thus general relativity remains to be completed. In fact, the claim of diffeomorphic solutions being the same in physics, just as Einstein's "covariance principle," is due to an inadequate ability to distinguish the physics from mathematics. Moreover, since the Stanford experiment, Gravity Probe-B, measures only the accumulated effects of the de Sitter precession, it would be very difficult for gravity Probe-B to distinguish these three formulas because of the time averaging effect. Although the radial gauge has an arbitrary integral constant in the related formula, Gravity Probe-B is unable to show whether such a gauge or Whitehead's theory is invalid. However, as Zhou conjectured, an experiment on local light speeds would further support the Maxwell-Newton Approximation, in addition to tell whether Whitehead's theory is valid although his experiment is not sensitive to the globe's rotation. Concurrently, it is pointed out that the so-called physically measurable gauge invariant values are merely mathematical illusions.

48 ref

020058   Liu Y O (Physics and Electronics Dep, Xinzhou Teachers Univ, Xinzhou, 034000, China, Email: yqliu_phy@yahoo.com.cm) : Magnons interaction of spinor Bose-Einstein condensates in an optical lattice. Pramana J Phys 2009, 73(6), 1105-10.

Study the interaction of magnons in dipolar spinor Bose-Einstein conden-sates in an optical lattice. By means of Holstein-Primakoff and Fourier transformations the energy spectra of the ground and the excited states is obtained analytically. Our results show that the collision of magnons is elastic which is expressed by the conservation of wave numbers in the process of collision. At last, we found that the interaction of magnons is attractive which tends to self-localization to form spin waves, i.e., a cluster of a macroscopic number of coherent magnons. Because of the attraction, the instability of spin wave brings about the existence of solitary wave.

14 ref

020057   Li J;Chen L;Sun F (Postgraduate School, Naval Univ of Engineering, Wuhan, 430033, People's Republic of China, Email: lgchenna@yahoo.com) : Fundamental optimal relation of generalized irreversible carnot heat pump with complex heat transfer law. Pramana J Phys 2010, 74(2), 219-30.

The fundamental optimal relation between heating load and coefficient of performance (COP) of a generalized irreversible Carnot heat pump is derived based on a new generalized heat transfer law, which includes the generalized convective heat transfer law and generalized radiative heat transfer law, q α (ΔTⁿ)^m. The generalized irreversible Carnot heat pump model incorporates several internal and external irreversibilities, such as heat resistance, bypass heat leakage, friction, turbulence and other undesirable irre-versibility factors. The added irreversibilities besides heat resistance are characterized by a constant parameter and a constant coefficient. The effects of heat transfer laws and various loss terms are analysed. The heating load vs. COP characteristic of a generalized irreversible Carnot heat pump is a parabolic-like curve, which is consistent with the experimental result of thermoelectric heat pump. The obtained results include those obtained in many literatures and indicated that the analysis results of the generalized irreversible Carnot heat pump were more suitable for engineering practice than those of the endoreversible Carnot heat pump.

2 illus, 58 ref

020056   Li G Z;Yang W M;Cheng X F;Fan J;Guo X D (Physics Dep, Shaanxi Normal Univ, Xi'an, Shaanxi, 710062, China, Email: wm-yang@sohu.com) : Fabrication of single-grain GdBa₂Cu₃O_7-x bulk superconductors with a new kind of liquid source by the top seeded infiltration and growth technique. Pramana J Phys 2010, 74(5), 827-32.

Compared to the conventional melt growth (MG) method, the top seeded infiltration and growth (TSIG) process is an effective way for preparing bulk REBa₂Cu₃O_7-x (RE-123) with finely dispersed RE₂BaCuO₅ (RE-211) particles. However, it is more complicated and time-consuming, because three kinds of precursor powders, namely, RE-211, RE-123 and BaCuO2, have to be prepared for the conventional TSIG process. In this paper, a new liquid source (NLS) composed of RE-211 and Ba₃Cu₅O₈, was proposed for simplifying the TSIG process, which is different from the regular liquid source (RLS) composed of RE-123 and Ba₃Cu₅O₈. In this modified TSIG technique, we need to prepare only RE-211 and BaCuO₂ powders. Single-grain GdBa₂Cu₃O_7-x (GdBCO) bulk superconductors have been fabricated using the RLS and NLS separately. The morphology, microstructure and levitatiori force of the bulk GdBCO have also been investigated. The results indicate that the NLS can be used to simplify the process flow and improve the efficiency on the fabrication of single-grain GdBCO superconductors.

4 illus, 20 ref

020055   Levai G (NO, Institute of Nuclear Research of the Hungarian Academy of Sciences(ATO, P.O. Box 51, H-4001 Debrecen, Hungary, Email: levai@namafia.atomki.hu) : Spontaneous breakdown of PT symmetry in the complex Coulomb potential. Pramana J Phys 2009, 73(2), 329-35.

The PT symmetry of the Coulomb potential and its solutions are studied along trajectories satisfying the PT symmetry requirement. It is shown that with appropriate normalization constant the general solutions can be chosen PT-symmetric if the L parameter that corresponds to angular momentum in the Hermitian case is real. PT symmetry is spontaneously broken, however, for complex L values of the form L = - 1/2 + iλ. In this case the potential remains PT-symmetric, while the two independent solutions are transformed to each other by the PT operation and at the same time, the two series of discrete energy eigenvalues turn into each other's complex conjugate.

18 ref

020054   Leiva G (Departamento de Fisica, Facultad de Ciencias, Universidad de Tarapaca, Casilla 7-D, Arica, Chile, Email: cleivas@uta.cl) : Harmonic oscillator in snyder space: the classical case and the quantum case. Pramana J Phys 2010, 74(2), 169-75.

The harmonic oscillator in Snyder space is investigated in its classical and quantum versions. The classical trajectory is obtained and the semiclassical quantization from the phase space trajectories is discussed. An effective cut-off to high frequencies is found. The quantum version is developed and an equivalent usual harmonic oscillator is obtained through an effective mass and an effective frequency introduced in the model. This modified parameters give us a modified energy spectrum also.

2 illus, 13 ref

020053   Kushwaha V S;Mehta N;Kumar N (Physics Dep, Kanpur institute of Technology, Kanpur-208 007, Email: dr_neeraj_mehta@yahoo.co.in) : Observation of Meyer-Neldel rule in thermally activated poole-frenkel photoconduction in a-Se₇₀Te_30-xCd_x thin films. Pramana J Phys 2010, 74(3), 475-80.

In the present paper, we report the compensation effect on photoconductivity of thin films of Se₇₀Te_30-xCd_x (x = 2, 4, 6) alloys for high field conduction. Steady state photoconductivity measurements have been made in thin films for different electric fields. The photoconduction was found to be ohmic at low fields and Poole-Frenkel type at high fields. Meyer-Neldel rule (MN rule) for the pre-exponential factor (σph)₀ and activation energy (Δph) of photoconduction in thin films of Se₇₀Te_30-xCd_x is observed in the study.

3 illus, 27 ref

020052   Kurian M J;Jyothi S;Leju S K;Isaac M; Venugopal C;Renuka G (School of Pure and Applied Physics, Mahatma Gandhi Univ, Priyadarshini Hills, P.O., Kottayam-686 560, Email: cvgmphysics@yahoo.co.in) : Stability of electrostatic ion cyclotron waves in a multi-ion plasma. Pramana J Phys 2009, 73(6), 1111-22.

Studied the stability of the electrostatic ion cyclotron wave in a plasma consisting of isotropic hydrogen ions (H⁺) and temperature-anisotropic positively (O⁺) and negatively (O^-) charged oxygen ions, with the electrons drifting parallel to the magnetic field. Analytical expressions have been derived for the frequency and growth/damping rate of ion cyclotron waves around the first harmonic of both hydrogen and oxygen ion gyrofrequencies. We find that the frequencies and growth/damping rates are dependent on the densities and temperatures of all species of ions. A detailed numerical study, for parameters relevant to comet Halley, shows that the growth rate is dependent on the magnitude of the frequency. The ion cyclotron waves are driven by the electron drift parallel to the magnetic field; the temperature anisotropy of the oxygen ions only slightly enhance the growth rates for small values of temperature anisotropies. A simple explanation, in terms of wave exponentiation times, is offered for the absence of electrostatic ion cyclotron waves in the multi-ion plasma of comet Halley.

3 illus, 19 ref

020051   Kuriakose S;Vijayan K K;Nair K P R;Rasheed T M A (Physics Dep, Research Centre, Maharaja's College, Ernakulam, Kochi-682 011, Email: sunnykuriakose1@gmail.com) : Vibrational overtone spectra of phenol, o-chlorophenol and p-chlorophenol - effect of conntration on conformations of o-chlorophenol. Asian J Spectrosc 2010, 14(3-4), 93-100.

Vibrational overtone absorption spectra of liquid phase phenol, o-chlorophenol and p-chlorophenol in the near infrared region are reported. The analysis of the observed aryl CH and OH local mode mechanical frequency values confirm the presence of intramolecular hydrogen bonding between the OH group and the chlorine atom in o-chlorophenol. This observation supports the conclusion drawn from electronic spectroscopic studies reported earlier. The near infrared overtone spectra of o-chlorophenol at different concentrations in CC1₄ are also reported and the analysis of the spectra of o-chlorophenol at different concentrations indicate that the intramolecular bonding present in o-chlorophenol is only slightly affected by concentration and intermolecular hydrogen bonding is weakened by concentration. The bonding at lower concentrations is due to both intramolecular and intermolecular interactions.

5 illus, 2 tables, 18 ref

020050   Kumar A;Bhatt M K;Singh Shivender K;Singh S K;Bhatt R J;Karimi N A (Physics Dep, B.N. College, Patna, Bihar) : Synthesis and characterisation of ZnO nano particles by different methods. Bull pure appl Sci-Sect D 2010, 29(2), 161-7.

Nanoparticles of Zinc Oxide have been synthesized by sol-gel method by decomposition of Zinc Sulphate through Sodium Hydroxide route. The particles were prepared by different methods (A) and (B) which differ in process of mixing, heat treatment and stirring time etc. The natures of particles i.e. crystallinity and size etc were assigned by Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD) pattern. The images obtained by SEM show that the particles prepared by method (A) exist in cluster form where as images obtained from method (B) do not exist in that form but appear in the form of a sheet. The particles prepared by this process are named as ZnO-A and ZnO-B. The peaks obtained by XRD pattern clearly indicate that the particles are highly crystalline in nature but crystallinity of ZnO-A is less than ZnO-B. The sizes of particles have been calculated by Debye Scherrer formula from the values of FWHM of peaks. The sizes of ZnO-A and ZnO-B were found lOnm and 7.7nm respectively. Hence the process B is more effective for the preparation of ZnO nanoparticles.

2 illus, 25 ref

020049   Krishna B M;Jhon M P;Nandakumaran V M (Spohhisticated Test and Instrumentation Centre, Cohin Univ of Science and Technology, Cohin-682 022, Email: bindum2cusat.ac.in) : Bidirectional communication using delay coupled chaotic directly modulated semiconducter laser. Pramana J Phys 2010, 74(2), 177-88.

Chaotic synchronization of two directly modulated semiconductor lasers with negative delayed optoelectronic feedback is investigated and this scheme is found to be useful for efficient bidirectional communication between the lasers. A symmetric bidirectional coupling is identified as a suitable method for isochronal synchronization of such lasers. The optimum values of coupling and feedback strength that can provide maximum quality of synchronization are identified. This method is successfully employed for encoding/decoding both analog and digital messages. The importance of a symmetric coupling is demonstrated by studying the variation of decoding efficiency with respect to asymmetric coupling.

8 illus, 1 table, 54 ref

020048   Khare A;Mandal B P (Physics Institute, Sachivalaya Marg, Bhubaneswar-751 005, Email: bhabani.mandal@gmail.com) : New quasi-exactly solvable Hermitian as well as non-hermitian PT-invariant potentials. Pramana J Phys 2009, 73(2), 387-95.

Start with quasi-exactly solvable (QES) Hermitian (and hence real) as well as complex PT-invariant, double sinh-Gordon potential and show that even after adding perturbation terms, the resulting potentials, in both cases, are still QES potentials. Further, by using anti-isospectral transformations, obtains Hermitian as well as TT-invariant complex QES periodic potentials. Studies in detail the various properties of the corresponding Bender-Dunne polynomials.

13 ref

020047   Ketabi S A;Ghane T;Shahtahmasebi N (Physics School, Damghan Univ Of Basic Sciences, Damghan, Iran, Email: saketabi@dubs.ac.ir) : Influence of solitons on the conductance properties of double-stranded deoxyribonucleic acid. Pramana J Phys 2010, 74(1), 143-52.

A numerical study is presented to investigate the role of solitons in the electronic states of double-stranded DNA (dsDNA) molecule in the metal/DNA/metal system. Based on tight-binding Hamiltonian model and within the framework of a generalized Green's function technique, we consider a ladder model for poly(dG)-poly(dC) DNA molecule containing M cells with four sites (two base pair sites and two backbone sites) in each cell. In the presence of a sublattice of solitons, our results show that the homogeneous soliton distributions induce the electronic states in the band gap of DNA molecule. In addition, the room temperature current-voltage characteristic of the system shows a linear and ohmic-like behaviour.

4 illus, 40 ref

020046   Kayacan O (Physics Dep, Faculty of Arts and Sciences, Celal Bayar Univ, 45030 Muradiye, Manisa, Turkey, Email: ozhan.kayacan@bayar.edu.tr) : Linear polymerized photopolymer orienting a nematic liquid crystal within nonextensive formalism. Pramana J Phys 2010, 74(5), 781-91.

The distribution function of photogenerated cross-links in thin films of poly(vinyl cinnamate) or poly(vinyl 4-methoxy-cinnamate) is investigated within nonex-tensive statistics, in terms of the irradiation time of these films with linearly polarized UV light. The scalar order parameter is obtained from the generalized distribution function, and is compared to the measured birefringence for some values of the entropic index q. The exposure time dependence of the nematogen scalar order parameter is plotted, and the effect of the nonextensive formalism on its exposure time dependence is presented.

6 illus, 16 ref

020045   Karumuri S B;Choudhury J;Sarkar N K; Bhattacharjee R (Physics Dep, Post-Graduate Centre, P.B. Siddhartha College of Arts and Science, Vijayawada-520 010, Email: srinivasa_karumuri@rediffmail.com) : Vibrational spectroscopy of C_m-C/C_b-C_b stretching vibrations of copper tetramesityl prophyrin: an algebraic approach. Pramana J Phys 2010, 74(1), 57-66.

Using Lie algebraic techniques and simpler expressions of the matrix elements of Majorana and Casimir operators given by us, we obtain an effective Hamiltonian operator which conveniently describes stretching vibrations of biomolecules. For a copper tetramesityl porphyrin molecule, the higher excited vibrational levels are calculated by applying the U(2) algebraic approach.

2 illus, 2 tables, 7 ref

020044   Kanak Kumari;Mahto D;Chandra G;Sah R K;Singh K M (Physics Dep, T.M. B.University, Bhagalpur, Bihar) : Study of Schwarzschid's radius with reference to the non-spinning black holes. Bull pure appl Sci-Sect D 2010, 29(2), 183-7.

Tried to convert the radius of the event horizon of non-spinning black holes of Schwarzschild's radius given by the equation Rs= 2GM/C² in terms of an another standard parameter known as Chandrashekhar limit (Mch), which is the largest unit of mass, where G = Gravitational constant, M=Mass of the Non-spinning Black hole, c = velocity of light. Also tries to derive an expression relating the energy of black holes and Schwarzschild's radius including a constant term designated by Black hole constant(KBH) for non-spinning black holes and also calculated the value of Black hole constant (K_BH).

15 ref

020043   Kalamse V;Gaikwad S;Chaudhari A (School of Physical Sciences, Swami Ramanand Teerth Marathwada Univ, Nanded-431 606, Email: ajaychau5@yahoo.com) : Computational study of 5d transition metal mononitrides and monoborides using density functional method. Bull Mater Sci 2010, 33(3), 233-8.

5d-metal mononitrides and monoborides viz. X-N and X-B (X = La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg) are studied using density functional method based B3LYP functional with LANL2DZ and SDD basis set. The lowest spin state, electron affinities, ionization potentials and binding energies for mononitrides and monoborides are obtained. The electronic state and electronic configuration of mononitrides and monoborides are discussed. Orbitals involved in bond formation are identified. The properties of mononitrides and monoborides are compared, it is found that 5rf-metal atoms form stronger bond with nitrogen atom than the boron atom. The range of binding energy, electron affinity and ionization potential is wider for mononitrides than that for monoborides. The properties of 5rf-metal mononitrides and 3rf-metal mononitrides are also compared. The binding energies for the former are lower than those for the latter.

7 tables, 41 ref

020042   Joshi K P;Saraf K B (Physics Dep, Shri J.J.T. Univ, Chudella-333 001) : Growth of acrylic starlites crystals copper iodate and it's characterisation. Asian J chem envir Res 2011, 4(1), 28-32.

Starlites of copper iodate have been grown by a simple gel technique at ambient temperature. The optimum conditions were established by varying various parameters such as concentrations of reactant, gel setting time etc. star shaped crystals of copper iodate were obtained. The crystals were characterized by XRD and FTIR.

4 illus, 3 table, 11 ref

020041   Joshi B N;More M A;Mahajan A M (Electronics Dep, North Maharashtra Univ, Jalgaon-425 001, Email: ammahajan@nmu.ac.in ) : Growth and characterisation of MMA/SiO₂ hybrid low-k thin films for interlayer dielectric applications. Bull Mater Sci 2010, 33(3), 197-201.

The methylmethacrylate (MMA) incorporated SiO₂ thin films having low dielectric constant (k = 2-97) were deposited successfully to realize new interlayer material for the enhancement of electrical performance of on-chip wiring in very large scale integrated (VLSI) circuits. We have successfully incorporated MMA monomer and eliminated the polymerization step to lower the dielectric constant of deposited thin film. The presence of peak of C=C bond in Fourier transform infrared (FTIR) spectra and carbon peak in energy dispersive (EDAX) spectra confirms the incorporation of carbon in the film due to MMA. The concentration of MMA has great impact on the peak area and full width at half maxima (FWHM) of the Si-O-Si bond, which decreases the density by low atomic weight elements and consequently decreases the dielectric constant. The surface morphology analysed by scanning electron microscopic (SEM) image shows excellent uniformity of the film. The refractive index of 1-31 was measured by ellipsometer for 0-5 ml MMA concentration film. These deposited thin films having low refractive index and dielectric constant are widely applicable for the optical interconnects and interlayer applications in integrated optical circuits and VLSI circuits.

5 illus, 3 tables, 24 ref

020040   Joshi B C;Mathew M;Joshi B C;Kumar D; Dhanavantri C (Optoelectronic Devices Group, Central Electronics Engineering Research Institute, CEERI (Council of Scientific and Industrial Research, CSIR), Pilani-333 031, Email: bhubesh@ceeri.ernet.in) : Characterization of GaN/AlGaN epitaxial layers grown by metalorganic chemical vapour deposition for high electron mobility transistor applications. Pramana J Phys 2010, 74(1), 135-41.

GaN and AlGaN epitaxial layers are grown by a metalorganic chemical vapour deposition (MOCVD) system. The crystalline quality of these epitaxially grown layers is studied by different characterization techniques. PL measurements indicate band edge emission peak at 363.8 nni and 312 nm for GaN and AlGaN layers respectively. High resolution XRD (HRXRD) peaks show PWHM of 272 and 296 arcsec for the (0002) plane of GaN and GaN in GaN/AlGaN respectively. For GaN buffer layer, the Hall mobility is 346 cm2/V-s and carrier concentration is 4.5 x 1016/cm3. AFM studies on GaN buffer layer show a dislocation density of 2 X 108/cm2 by wet etching in hot phosphoric acid. The refractive indices of GaN buffer layer on sapphire at 633 nm are 2.3544 and 2.1515 for TE and TM modes respectively.

8 illus, 14 ref

020039   Jain S R;Srivastava S C L (Nuclear Physics Division, Van De Graaff Building, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, Email: srjain@barc.gov.in) : Random matrix theory for pseudo-hermitian systems: cyclic blocks. Pramana J Phys 2009, 73(6), 989-97.

Discusses the relevance of random matrix theory for pseudo-Hermitian systems, and, for Hamiltonians that break parity P and time-reversal invariance T. In an attempt to understand the random Ising model, we present the treatment of cyclic asymmetric matrices with blocks and show that the nearest-neighbour spacing distributions have the same form as obtained for the matrices with scalar entries. We also summarize the theory for random cyclic matrices with scalar entries. We have also found that for block matrices made of Hermitian and pseudo-Hermitian sub-blocks of the form appearing in Ising model depart from the known results for scalar entries. However, there is still similarity in trends even in log-log plots.

6 illus, 16 ref

020038   Jain S R (Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai-400 085, Email: srjain@barc.gov.in) : Statistical features of quantum evolution. Pramana J Phys 2009, 73(2), 251-7.

It is shown that the integral of the uncertainty of energy with respect to time is independent of the particular Hamiltonian of the quantum system for an arbitrary pseudo-unitary (and hence PT-) quantum evolution. The result generalizes the time-energy uncertainty principle for pseudo-unitary quantum evolutions. Further, employing random matrix theory developed for pseudo-Hermitian systems, time correlation functions are studied in the framework of linear response theory. The results given here provide a quantum brachistochrone problem where the system will evolve in a thermodynamic environment with spectral complexity that can be modelled by random matrix theory.

19 ref

020037   Honorato C G;Toscano J J (Facculted de Ciencias Fisico Mathematicas, Benemerita Universidsd Autonoma de Puebla, Apartado Postal 1152,Puebla, Mexico, Email: jtoscano@fcfm.buap.mx ) : Ue(1)-covariant Rξ gauge for the two-Higgs doublet model. Pramana J Phys 2009, 73(6), 1023-39.

A U_e(l)-covariant R₇₄ gauge for the two-Higgs doublet model based on BRST (Becchi-Rouet-Stora-Tyutin) symmetry is introduced. This gauge allows one to remove a significant number of nonphysical vertices appearing in conventional linear gauges, which greatly simplifies the loop calculations, since the resultant theory satisfies QED-like Ward identities. The presence of four ghost interactions in these types of gauges and their connection with the BRST symmetry are stressed. The Feynman rules for those new vertices that arise in this gauge, as well as for those couplings already present in the linear R_ξ gauge but that are modified by this gauge-fixing procedure, are presented.

6 table, 22 ref

020036   Hatano N;Kawamoto T;Feinberg J (Industrial Science Institute, Tokyo Univ, Komaba, Meguro, Tokyo 153-8505, Japan, Email: hatano@iis.u-tokyo.ac.jp) : Probabilistic interpretation of resonant states. Pramana J Phys 2009, 73(3), 553-64.

Provides probabilistic interpretation of resonant states. We do this by showing that the integral of the modulus square of resonance wave functions (i.e., the conventional norm) over a properly expanding spatial domain is independent of time, and therefore leads to probability conservation. This is in contrast with the conventional employment of a bi-orthogonal basis that precludes probabilistic interpretation, since wave functions of resonant states diverge exponentially in space. On the other hand, resonant states decay exponentially in time, because momentum leaks out of the central scattering area. This momentum leakage is also the reason for the spatial exponential divergence of resonant state. It is by combining the opposite temporal and spatial behaviours of resonant states that we arrive at our probabilistic interpretation of these states. The physical need to normalize resonant wave functions over an expanding spatial domain arises because particles leak out of the region which contains the potential range and escape to infinity, and one has to include them in the total count of particles.

5 illus, 53 ref

020035   Gupta V K;Jangid R A;Yadav S (Microwave Research Lab, Physics Dep, Raj Rishi Autonomous Govt. P.G. College, Alwar-301 001, Email: contactvkg@yahoo.co.in) : Emission and scattering behavior of soil of alwar contaminated with crude oil at microwave frequencies. Bull pure appl Sci-Sect D 2010, 29(1), 63-72.

The real and imaginary parts of dielectric constant ε' and ε" of soil of Alwar contaminated with crude oil are determined at different low levels of contamination. ε' and ε" are measured by wave-guide cell method at a single microwave frequency 9.78 GHz and at constant temperature 33°C. In view of passive and active microwave remote sensing Microwave emissivity and radar backscattering coefficient of contaminated soil with crude oil is estimated by model calculations. It is observed that the horizontal component of emissivity (e_h) decreases as percentage concentration of contamination of crude oil increases at all observation angles. The vertical component of emissivity (e_v} decreases as percentage concentration of contamination for the observation angle up to 0° -60° then variation of (e_v) at higher observation angle (θ <62> 60°) shows quite different behavior. Further, the contamination effect on radar backscattering coefficient is not much significant for horizontal polarization, (σ⁰_hh) increases slightly w.r.t contamination for all observation angle (0°-80°) while (σ⁰_vv) increases slightly w.r.t contamination for all observation angle (0° -60°) then decreases for higher observation angles.

5 illus, 9 ref

020034   Gupta U;Ghoshal S K;Gill K S;Devendra Mohan (Applied Physics Dep, G.J. Univ of Sc. and Technology, Hisar, Email: umeshgupta2006@gmail.com) : Synthesis and characterization of sol-gel derived superconducting material: YBCO. Asian J Spectrosc 2010, 14(3-4), 77-84.

The YBCO material is synthesized under the controlled environment by the sol-gel method. Standard characterization techniques like FTIR, UV/VIS/NIR spectroscopy, XRD and TGA have been employed to understand the phase transition during the growth of the sample. YBCO shows some interesting results about the properties related to different phases of formation as two different crystalline phases are observed in the sol form before annealing. Various optical and crystalline properties during the phase transition are investigated and an attempt is made to study the dynamics of the phase transition.

8 illus, 46 ref

020033   Gupta S K;Azam A;Akhter J (Applied Physics Dep, Z.H. College of Engineering and Technology, Aligarh Muslim Univ, Aligarh-202 002, Email: sanjeev@ceeri.ernet.in) : Experimental analysis of current conduction through thermally grown SiO₂ on thick epitaxial 4H-SiC employing Poole-frenkal machanism. Pramana J Phys 2010, 74(2), 325-30.

Electrical properties of SiO² grown on the Si-face of the epitaxial 4H-SiC substrate by wet thermal oxidation technique have been experimentally investigated in metal oxide-silicon carbide (MOSiC) structure with varying oxide thicknesses employing Poole-Frenkel (P-F) conduction mechanism. The quality of SiO₂ with increasing thickness in MOSiC structure has been analysed on the basis of variation in multiple oxide traps due to effective P-F conduction range. Validity of Poole-Frenkel conduction is established quantitatively employing electric field and the oxide thickness using forward I-V characteristics across MOSiC structures. From P-F conduction plot (In(J/E) vs. E^1/2), it is revealed that Poole-Frenkel conduction retains its validation after a fixed electric field range. The experimental methodology adopted is useful for the characterization of oxide films grown on 4H-SiC substrate.

4 illus, 12 ref

020032   Garg I;Deo N (Physics & Astrophysics Dep, Delhi Univ, Delhi-110 007, Email: ndeo@physics.du.ac.in) : Random matrix approach to RNA folding with interaction. Pramana J Phys 2009, 73(3), 533-41.

In the matrix model of RNA [G Vernizzi, H Orland and A Zee, Phys. Rev, Lett. 94, 168103 (2005)] we introduce external interactions on n bases in the action of the partition function where n ≤ L and L is the length of the polymer chain. The RNA structures found in the model can be separated into two regimes: (i) 0 ≤α≤ 1, n <60> L and 0 ≤ α <60> 1, n = L where unpaired and paired base structures exist and (ii) a = 1, n - L with only completely paired base structures. Figures for the genus distribution functions show differences at small lengths. We consider the situation when the strength of external perturbation is different on different bases in the polymer chain.

4 illus, 1 tables, 12 ref

020031   Garai S K;Mukhopadhyay S (Physics Dep, M.U.C. Women's College, Burdwan-713 104, Email: sisir-garai@yahoo.co.in) : Method of implementing frequency-encoded NOT, OR and NOR logic operations using lithium niobate waveguide and reflecting semiconductor optical amplifiers. Pramana J Phys 2009, 73(5), 901-12.

Optics has already proved its strong potentiality for the conduction of parallel logic, arithmetic and algebraic operations. In the last few decades several all-optical data processors were proposed. To implement these processors different data encoding/decoding techniques have been reported. In this context, polarization encoding technique, intensity-based encoding technique, tristate and quaternary logic operation, multivalued logic operations, symbolic substitution techniques etc. may be mentioned. Very recently, frequency encoding/decoding technique has drawn interest from the scientific community. Frequency is the fundamental character of any signal; and it remains unaltered in reflection, refraction, absorption etc. during the propagation and transmission of the signal. This is the most important advantage of frequency encoding technique over the conventional encoding techniques. In this communication the authors propose a new scheme for implementing NOT, OR and NOR logic operations. For this purpose co-propagating beams having different frequencies in C-band (1535-1560 nm) have been used for generating cascaded sum and difference frequency, exploiting the nonlinear response character of periodically poled LiNbO₃ waveguide. The cross-gain modulation property of the semiconductor optical amplifier (SOA) and the wavelength conversion property of the reflecting semiconductor optical amplifiers (RSOA) are exploited here to implement the desired optical logic and arithmetic operations.

6 illus, 3 tables, 22 ref

020030   Ganai P A;Sheikh J A;Maqbool I;Singh R P (Physics Dep, Kashmir Univ, Srinagar-190 006, Email: prince-ganai@yahoo.co.uk) : Temperature and angular momentum dependence of the quadrupole deformation in sd-shell. Pramana J Phys 2009, 73(5), 839-46.

Temperature and angular momentum dependence of the quadrupole deformation is studied in the middle of the sd-shell for ²⁸Si and ²⁷Si isotopes using the spherical shell model approach. The shell model calculations have been performed using the standard universal sd-shell (USD) interaction and the canonical partition function constructed from the calculated eigensolutions. It is shown that the extracted average quadrupole moments show a transitional behaviour as a function of temperature and the infered transitional temperature is shown to vary with angular momentum. The quadrupole deformation of the individual eigenstate is also analysed.

3 illus, 24 ref

020029   Firdous A;Quasim I;Ahmad M M;Kotru P N (Physics and Electronics Dep, Jammu Univ, Jammu-180 006, Email: pnkotru@rediffmail.com) : Dielectric and thermal studies on gel grown strontium tartrate pentahydrate crystals. Bull Mater Sci 2010, 33(4), 377-82.

Results of dielectric and thermal studies on strontium tartrate pentahydrate crystals are described. The value of dielectric constant is shown to be independent of temperature till 360 K at all the frequencies (110-700 kHz) of the applied a.c. field. It increases abruptly achieving a peak value of 25.5 at 100 kHz; the peak value being strongly dependent on frequency. In the temperature range, 87 <60> T <60> 117°C, the value of ε' falls suggesting a transition at around 100°C or so. The dielectric constant, ε', of the material is shown to be frequency dependent but temperature independent in the pre- or post-T_c range 87 <60> T <60> 117°C, suggesting that the contribution towards polarization may be due to ionic or space charge polarization which gets eliminated at higher frequencies. The ferroelectric transition is supported by the results of thermoana-lytical studies. It is explained that crystallographic change due to polymorphic phase transition may be occurring in the material, besides the change due to loss of water molecules, which leads to the dielectric anomaly at around 100°C. Coats-Redfern approximation method is applied for obtaining non-isothermal kinetic parameters leading to calculation of activation energies corresponding to three decomposition stages of material in the temperature ranging from 379-1113 K.

8 illus, 21 ref

020028   Feinberg J (Physics Dep, Haifa at Oranim Univ, Tivon 36006, Israel, Email: joshua@physics.technion.ac.il) : Statistics of resonances in one-dimensional continuous systems. Pramana J Phys 2009, 73(3), 565-72.

Study the average density of resonances (DOR) of a disordered one-dimensional continuous open system. The disordered system is semi-infinite, with white-noise random potential, and it is coupled to the external world by a semi-infinite continuous perfect lead. Our main result is an integral representation for the DOR which involves the probability density function of the logarithmic derivative of the wave function at the contact point.

21 ref

020027   Eraiah B (Physics dep, Bangalore Univ, Bangalore-560 056, Email: eraiah@rediffmail.com) : Optical properties of lead-tellurite glasses doped with samarium trioxide. Bull Mater Sci 2010, 33(4), 391-4.

The optical properties of a new family of xSm₂O₃-(40-x)PbO-60TeO₂ glasses are investigated. The optical absorption spectra were recorded at room temperature in the UV-visible region. From the absorption edge studies, the values of optical bandgap energies have been evaluated. The refractive index, molar refraction and polarizability of oxide ions have been calculated by using Lorentz-Lorentz relations. The non-linear variations of the above optical parameters are discussed with respect to samarium concentration.

6 illus, 19 ref

020026   Elahi P;Morshedi S (Physics Dep, College of Science, Shiraz Univ of Technology, Shiraz, Iran, Email: elahi@sutech.ac.ir) : Double-end-pumped cubic Nd:YVO₄ laser: temperature distribution and thermal stress. Pramana J Phys 2010, 74(1), 67-74.

Thermal effects of a double-end-pumped cubic Nd:YVO₄ laser crystal are investigated in this paper. A detailed analysis of temperature distribution and thermal stress in cubic crystal with circular shape pumping is discussed. It has been shown that by considering the total input powers as constant, the double-end-pumped configurations with equal pump power can be considered as having a minimum thermal effect with respect to the other end-pumped configuration.

8 illus, 12 ref

020025   Dutta D;Chakraborty S (NO, CGGV Veritas Services India Pvt. Ltd, 504-B, DELPHI Building Wing 5th Floor, Hiranandani Business Park, Powai, Mumbai, Email: debabrata.dutta@cggveritas.com) : Bifurcation diagrams in relation to synchronization in chaotic systems. Pramana J Phys 2010, 74(6), 919-29.

Numerically study some of the three-dimensional dynamical systems which exhibit complete synchronization as well as generalized synchronization to show that these systems can be conveniently partitioned into equivalent classes facilitating the study of bifurcation diagrams within each class. We demonstrate how bifurcation diagrams may be helpful in predicting the nature of the driven system by knowing the bifurcation diagram of driving system and vice versa. The study is extended to include the possible generalized synchronization between elements of two different equivalent classes by taking the Rossler-driven-Lorenz-system as an example.

5 illus, 11 ref

020024   Divakara S;Madhu S;Somashekar R (Studies in Physics Dep, Mysore Univ, Manasagangotri, Mysore-570 006, Email: rs@physics.uni-mysore.ac.in) : Stacking faults and microstructural parameters in non-mulberry silk fibres. Pramana J Phys 2009, 73(5), 927-38.

Analysed the broadening of X-ray reflections observed in non-mulberry silk fibres in terms of stacking faults and microstructural parameters using a single-order method and have, with these parameters, developed, for the first time, a procedure to compute the whole pattern of these silk fibres. The essential deviations in the values of microstructural parameters obtained from line profile and whole pattern fitting procedures are discussed in this paper.

7 illus, 2 tables, 32 ref

020023   Dhriendra Kumar;Nayak P;Jha L (Physics Dep, Mithila Janta Inter College, Madhubani-847 211) : Theoretical study of multiband microstrip antenna. Bull pure appl Sci-Sect D 2009, 28(1), 13-19.

In the present paper on the basis of concept of inserting slot arrays following a known antenna distribution a theoretical study of a multi-wideband microstrip-patch anteena has been made. The design of anteena included the insertion of rectangular slots following a Chebyshev distribution around a central rectangular slot in addition to a triangular slot. These slots engraved in rectangular and triangular patch are joined together and fed by one probe feed. A close agreement was found when theoretical results were compared with simulated results.

5 illus, 7 ref

020022   Dhar V K;Tickoo A K;koul R;Dubey B P (Astrophysical Sciences Div, Bhabha Atomic Research Centre, Mumbai-400 085, Email: veer@barc.gov.in) : Comprative performance of some popular artificial neural network algorithms on benchmark and function approximation problems. Pramana J Phys 2010, 74(2), 307-24.

Reports an inter-comparison of some popular algorithms within the artificial neural network domain (viz., local search algorithms, global search algorithms, higher-order algorithms and the hybrid algorithms) by applying them to the standard benchmarking problems like the IRIS data, XOR/N-bit parity and two-spiral problems. Apart from giving a brief description of these algorithms, the results obtained for the above benchmark problems are presented in the paper. The results suggest that while Levenberg-Marquardt algorithm yields the lowest RMS error for the N-bit parity and the two-spiral problems, higher-order neuron algorithm gives the best results for the IRIS data problem. The best results for the XOR problem are obtained with the neuro-fuzzy algorithm. The above algorithms were also applied for solving several regression problems such as cos(x) and a few special functions like the gamma function, the complimentary error function and the upper tail cumulative x²-distribution function. The results of these regression problems indicate that, among all the ANN algorithms used in the present study, Levenberg-Marquardt algorithm yields the best results. Keeping in view the highly nonlinear behaviour and the wide dynamic range of these functions, it is suggested that these functions can also be considered as standard benchmark problems for function approximation using artificial neural networks.

5 illus, 7 table, 43 ref

020021   Delgado G E;Mora A J;Grima-Gallardo P;Duran S;Munoz M;Quintero M (Laboratorio de Cristalografia, Departamento de Quimica, Facultad de Ci, Universidad de Los Andes, Merida 5101, Venezuela, Email: gerzon@ula.ve) : Preparation and crystal structure characterization of CuNiGaSe₃ and CuNiInSe₃ quaternary compounds. Bull Mater Sci 2010, 33(5), 637-40.

Samples of the quaternary chalcogenide compounds, CuNiGaSe₃ and CuNiInSe₃, prepared by direct fusion and annealing method, were characterized by X-ray powder diffraction. In each case, the crystal structure was refined using the Rietveld method. Both compounds were found to crystallize in the tetragonal system, space group P42c (N°112), with unit cell parameter values a = 5.6213(1) Angustrum, c = 11.0282(3) Angustrum, V = 348.48(1) Angustrum³ and a = 5.-7857(2) Angustrum, c = 11.6287(5) Angustrum, V= 389.26(3) Angustrum³ for CuNiGaSe₃ and CuNiInSe₃, respectively. These compounds have a normal adamantane structures and are isostructural with CuFelnSe₃.

2 illus, 3 tables, 24 ref

020020   Delgado G E;Mora A J;Contreras J E;Betancourt L (Laboratorio de Cristalografia, Departamento de Quimica, Universidad de Los Andes, Merida 5101, Venezuela, Email: gerzon@ula.ve) : Synthesis and characterization of ternary compound, Mn₂SnTe₄. Bull Mater Sci 2010, 33(3), 247-9.

Mn₂SnTe₄ was synthesized by direct fusion using the anneal method. X-ray powder diffraction analysis indicated that this material crystallizes in the olivine-type structure, space group Pnnta, Z = 4, with unit cell parameters: a = 14.020(2) Angustrum, b = 8.147(1) Angustrum, c = 6.607(1) Angustrum, V= 754.7(2) Angustrum³. The Rietveld refinement converged to the figures of merit, R_p = 6.9%, R_wp = 8.5%, R_exp = 6.0%, x₂ = 2.0 and S=1.4.

2 illus, 2 tables, 20 ref

020019   Deepak N K (Physics Dep, Pure and Applied Physics School, Kannur Univ, Payyanur Campus, Payyanur-670 327, Email: deepakg_nk@yahoo.com) : Lattice location of dopant atoms: an N-body model calculation. Pramana J Phys 2010, 74(3), 421-40.

The channelling and scattering yields of I MeV α-particles in the (100), (110} and (111} directions of silicon implanted with bismuth and ytterbium have been simulated using JV-body model. The close encounter yield from dopant atoms in silicon is determined from the flux density, using the Bontemps and Fontenille method. All previous works reported in literature so far have been done with computer programmes using a statistical analytical expression or by a binary collision model or a continuum model. These results at the best gave only the transverse displacement of the lattice site from the concerned channelling direction. Here we applied the superior N-body model to study the yield from bismuth in silicon. The finding that bismuth atom occupies a position close to the silicon substitutional site is new. The transverse displacement of the suggested lattice site from the channelling direction is consistent with the experimental results. The above model is also applied to determine the location of ytterbium in silicon. The present values show good agreement with the experimental results.

16 illus, 4 tables, 15 ref

020018   Dashora A;Marwal A;Soni K R;Ahuja B L (Physics Dep, Science Univ College, M.L. Sukhadia Univ, Udaipur-313 001) : Electronic property and compton profiles of silver iodide. Pramana J Phys 2010, 74(6), 1017-27.

Authors have carried out an extensive study of electronic properties of silver iodide in β- and γ-phases. The theoretical Compton profiles, energy bands, density of states and anisotropies in momentum densities are computed using density functional theories. We have also employed full-potential linearized augmented plane-wave method to derive the energy bands and the density of states. To compare our theoretical data, isotropic Compton profile measurement on γ-AgI using ^137>Cs Compton spectrometer at an intermediate resolution of 0.38 a.u. has been undertaken. The theoretical anisotropies are also interpreted on the basis of energy bands.

6 illus, 3 tables, 37 ref

020017   Das B;Ghosh D;Chatterjee P (Mathematics Dep, Siksha Bhavana, Visva Bharati Univ, Santiniketan-731 235, Email: brindabandas2006@rediffmail.com) : Large-amplitude double layers in a dusty plasma with an arbitrary streaming ion beam. Pramana J Phys 2010, 74(6), 973-81.

Formation of large-amplitude double layers in a dusty plasma whose constituents are electrons, ions, warm dust grains and positive ion beam are studied using Sagdeev's pseudopotential technique. Existence of double layers is investigated. It is found that both the temperature of dust particles and ion beam temperature play significant roles in determining the region of the existence of double layers.

5 illus, 32 ref

020016   Cruz J C;Kumar C N;Pathak K N;Bosse J (Physics Dep, Panjab Univ, Chandigarh-160 0146, Email: pathak@pu.ac.in) : Density excitations of harmonically trapped ideal gas. Pramana J Phys 2010, 74(1), 83-96.

The dynamic structure factor S(q, w) of a harmonically trapped Bose gas has been calculated well above the Bose-Einstein condensation temperature by treating the gas cloud as a canonical ensemble of non-interacting classical particles. The static structure factor is found to vanish αq² in the long-wavelength limit. We also incorporate a relaxation mechanism phenomenologically by including a stochastic friction force to study S(q, wJ). A significant temperature dependence of the density fluctuation spectra is found. The Debye-Waller factor has been calculated for the trapped thermal cloud as a function of q and the number N of atoms, A substantial difference is found for small- and largeN clouds.

6 illus, 14 ref

020015   Choudhury J;Karumuri S R;Sarkar N K; Bhattacharjee R (Physics Dep, Assam Univ, Silchar-788 011, Email: choudhuryjoy@rediffmail.com) : Vibrational spectrum of CF₄ isotopes in an algebraic model. Pramana J Phys 2009, 73(5), 881-7.

In this paper the stretching vibrational modes of CF4 isotopes are calculated up to first overtone using the one-dimensional vibron model for the first time. The model Hamiltonian so constructed seems to describe the C-F stretching modes accurately using a relatively small set of well-defined parameters.

1 illus, 2 tables, 25 ref

020014   Chen A;Li J;Li C;Zhang Y (Center of Nonlinear Science Studies, Kunming Univ of Science and Technology, Kunming, Yunnan, 650093, People's Republic of China, Email: aiyongchen@163.com) : From bell-shaped solitary wave to W/M-shaped solitary wave solutions in an integrable nonlinear wave equation. Pramana J Phys 2010, 74(1), 19-26.

The bifurcation theory of dynamical systems is applied to an integrable nonlinear wave equation. As a result, it is pointed out that the solitary waves of this equation evolve from bell-shaped solitary waves to W/M-shaped solitary waves when wave speed passes certain critical wave speed. Under different parameter conditions, all exact explicit parametric representations of solitary wave solutions are obtained.

3 illus, 10 ref

020013   Chawla P;Sharma G;Lochab S P;Singh N (Physics Dep, Kurukshetra Univ, Kurukshetra-136 119, Email: ranu.puja@gmail.com) : Effect of solvent-induced structural modifications on optical properties of CdS nanoparticles. Bull Mater Sci 2010, 33(5), 535-41.

Investigated the effects of solvent used during synthesis on structural and optical properties of CdS quantum dots. Different methods of synthesis for the production of CdS quantum dots are presented. These are: (a) wet chemical co-precipitation in non-aqueous medium (i.e. methanol); (b) wet chemical co-precipitation in aqueous medium (deionized water) and (c) solid state reaction. It is demonstrated that the use of methanol as solvent leads to a strong enhancement of PL intensity of CdS quantum dots for use in optoelectronic devices. These products were characterized by X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). The change in band-gap with size-quantization was investigated by UV-V1S absorption spectroscopy. CdS nanocrystals prepared in non-aqueous medium have narrow size distribution than those prepared in aqueous medium and solid state reaction. Phase transformation of CdS nanocrystals from a cubic to hexagonal structure was observed in methanol solution. The formation of CdS/Cd(OH)₂ nanostructure was also confirmed using X-ray diffraction pattern. This suggests that the strong enhancement of the PL intensity may have originated from the remarkable reduction of non-radiative recombination process, due to surface defects of quantum dots. The red shift of the Raman peaks compared to that for bulk CdS may be attributed to optical phonon confinement.

6 illus, 1 table, 28 ref