Showing papers in "Acta Physica Hungarica in 1992"

Hall effect in the viscous flow of an ionized gas between two parallel walls under transverse magnetic field in a rotating system

Abstract: The equations of motion accounting for rigid rotation about an axis perpendicular to the flow have been given and exact solutions have been obtained for both velocities such as the primary flow as well as the secondary flow corresponding to the cases of non-conducting and conducting walls, taking into account the Hall currents. In case of non-conducting walls, it is found that these solutions foru, w are all independent of the partial pressure of the electron gas,s. The induced magnetic field is neglected under the assumption that the magnetic Reynolds number is small.

Dynamics of a binary metallic glass Cu57Zr43

Abstract: Computations of the frequencies of the longitudinal and transverse phonon modes in a binary metallic glass (Cu57Zr43) based on a simple model approach have been presented. The model assumes a central force effective between nearest neighbours, and a volume dependent force. Both types of excitations of phonons are computed for the self-consistent screening and are compared to those computed by Kobayashi and Takeuchi using recursion method.

Dielectric screenings and elastic and thermodynamic properties of metallic glasses

Abstract: The elastic and thermodynamic properties of metallic glasses (Ca70Mg30, Mg70Zn30, Cu57Zr43 and Pd77.5Si16.5Cu6) are obtained from dispersion relations in the low momentum region derived by us for various dielectric screenings, adopting a simple model given by Bhatia and Singh. This model assumes a central force, effective between nearest neighbours and a volume dependent force. For elastic properties, elastic constantsC 11 andC 44 are obtained from slopes of longitudinal and transverse dispersion relations, respectively, whereasC 12 is found by the requirement that elastic anisotropy for disordered systems, like metallic glass, is to be zero. For thermodynamic properties, Debye temperature is calculated for the glasses for various dielectric screenings.

Equation for cathodic glow sheath

Abstract: The classical one dimensional approach of cathodic glow discharge is extended into a two dimensional time dependent model. A radial ion transport equation is derived on the basis of the space charge balance. Axial effects are accounted for in a nonlinear source term. It is shown that the radial transport of the ions caused by the radial electric field can be described as a diffusion process with a cathode fall dependent diffusion coefficient. The effect of the motion of sheath boundary and the displacement current are also incorporated. The model exhibits all of the well-known macroscopic phenomena of glow discharges: subnormal, normal, anomal glow behaviour; pressure dependence of voltage current characteristics; (nearly) piecewise constant current density distributions; the effect of absorbing or reflecting walls; stability limits; subnormal glow oscillations; the lateral spread of glow discharge.

Magnetic effect on low Reynolds number flow in a heated tube of slowly varying section

Abstract: A mathematical model is advanced for blood flow in an axisymmetric heated tube in the presence of a uniform magnetic field. The radius of the tube is assumed to to vary slowly in the axial direction. Using asymptotic series analysis about a small parameter, e, solutions are obtained for the velocity components, temperature and pressure. The effect of the magnetic field on the axial velocity is discussed quantitatively.

Spectrometer corrections for a retarding field analyser used for elastic peak electron spectroscopy and auger electron spectroscopy

Abstract: Elastic peak electron spectroscopy using a retarding field analyser (RFA) proved to be an efficient tool for several applications. The advantage of RFA lies in its simultaneous LEED-AES application, in its large aperture averaging angular effects and in the possibility of surface analysis with the elastic peak. The difficulty of the RFA is its poor energy resolution integrating also the background adjacent to the peak observed (elastic or Auger peak) and producing peak distortion. Spectrometer correction was made by determining the spectral distribution function of the RFA energy window, using an approach of sum of Gaussians. Parameters of the Gaussian functions have been determined by decomposition of elastic peak spectra measured with an RFA Riber OPR-304 on Ag. Ag and Au elastic peaks at 1 and 2 keV energy were compared with highly resolved spectra obtained with a hemispherical analyser. Calculated elastic peak spectra exhibited reasonable agreement with experimental data obtained with the RFA spectrometer.

Lattice dynamical study of some fcc metals

Abstract: The Morse potential is modified to determine the two and three body forces in consistent manner. These forces are employed to build up the dynamical matrix, which predicts the qualitative features of phonon dispersion in some of the face centered cubic (fcc) metals.

The effect of magnetic field on the scintillation efficiency of organic scintillators

Abstract: The fluorescence of different organic plastic and liquid scintillators has been measured as a function of magnetic fieldH up to 13 mT (milli tesla). In the case of NE213, NE230 and stilbene, the percentage change in scintillation efficiency ΔE(%) increases with increasingH till it becomes maximum at an optimum valueH m, and then it decreases with further increase inH. However, in the case of pamolene crystal ΔE(%)) increases monotonically withH throughout the magnetic field range referred to.

Oppenheimer-Volkoff equation inD space-time dimensions

Abstract: The equations which describe the hydrostatic equilibrium of a relativistic stellar configuration inD space-time dimensions (D ≥/ 4) with a spherical symmetric gravitational field are obtained. With suitable transformations, the equations of mass continuity and of hydrostatic equilibrium are given in a non-dimensional form. With the obtained equations the homogeneous stellar model is studied and some stability criteria are obtained inD (D ≥/ 4) space-time dimensions.

Phonons and elastic constants for scandium, zirconium and magnesium

Abstract: The generalised exponential potential and the Born-Mayer potential are employed to describe the paired and the unpaired interactions in the hexagonally closed pack (hcp) metals These forces are found to explain simultaneously the phonon dispersion and the elastic behaviours of the metals like Scandium (Sc), Zirconium (Zr) and Magnesium (Mg) The input data for lattice constants inverse compressibility and cohesive energy give rise to such results on the said behaviour of the metals which compare satisfactorily with the experimental values

Stability of two superposed homogeneous fluids

Abstract: The stability of two homogeneous fluids under gravitational force has been discussed. A general perturbation in the horizontal planez=0 has been taken with wave numberkx, ky along and perpendicular to the streaming motion, respectively. It is found that critical wave numberk* lies on an ellipse in the first quadrant ofkx, ky plane.

Age-Hardening characteristics of an AlMgSi Alloy

Abstract: Age-hardening behaviour of an AIMgSi alloy was followed by hardness measurements during isochronal and isothermal ageing. The alloy is found to age-harden during natural ageing at room temperature after quenching from the solid solution temperature. The alloy exhibits peak hardness by artificial ageing at 200 °C for 2 hours. Isothermal ageing curves indicated that the rate of hardness increase at early stages of ageing, is dependent upon the ageing temperature in a manner which obeys an Arrhenius-type equation. An activation energy of 0.95±0.05 eV was calculated from the Arrhenius plot of the results. This activation energy shows that the process responsible for hardness increase in the early stages of ageing may be controlled by the migration of solute-vacancy complexes.

Level structure of154Gd

Abstract: The decay of154Eu to154Gd has been studied using H. P. Ge and H. P. Ge−NaI(Tl) spectrometers in coincidence measurements. 141 gamma transitions have been observed. One of these transitions is found to be new and has an energy of 202.5 keV. The 165.9, 202.5, 229.8 and 484.6 keV transitions are placed correctly in the decay scheme of154Eu. The levels from this and previous work are compared with those calculated by means of the unified model.

Analytic study of the classical equilibrium of highly rotating spheroidal polytropes

Abstract: We have considered some aspects of the structural features of the classical (Newtonian) equilibrium of a highly rotating spheroidal polytropen=1, governed by the equation of state:P=constantρ γ (P denotes the pressure, π the density and γ the adiabatic constant). Approximate analytical solutions to the equilibrium equations suitable for use in very short computer programs or on small calculators have been given in (u Θ,v Θ), (u p, vp), (u π,v π) and (ξ Θ, θ) planes for γ=2 following Pade (2,2) approximation technique. Under certain transformations, the equilibrium equation has been cast into first order differential equations in (u Θ,v Θ), (u p, vp), (u π,v π), (z Θ,y Θ), (z p, yp) and (z π,y π) planes. Transformations connecting solutions in these planes have been derived. Graphical material is included showing a comparative study of the runs ofu Θ withv Θ (Fig. 1),u p withv p (Fig. 2),u π withv π (Fig. 3), Θ withξ Θ (Fig. 4) and ζ with Δw (Fig. 5) for rotating (w=0.05 andw=0.15) and non-rotating (w=0) configurations. It has been found that the present method of approach is also more suitable for the study of both slowly and highly rotating configurations.

Structure of odd-odd Sb nuclei

Abstract: The structure of112,114,116,118Sb nuclei was studied with complex γ and electron spectroscopic methods via (p, nγ) and also (α,nγ) reactions (in the case of116Sb,118Sb)at 5.5–9.2 MeV proton and 14.5–16.0 MeV α-particle energies. New level schemes have been deduced. The energy splitting of the proton-neutron multiplet states of116,118,120,122,124Sb was calculated on the basis of the “parabolic rule”. Manyp−n multiplet states have been identified and conclusions have been drawn on the applicability of the parabolic rule as a simple guideline for experimental investigations. Detailed description of the energy spectra and electromagnetic properties of116,118,120,122,124Sb nuclei is given on the basis of the interactingboson-fermion-fermion/ odd-odd truncated quadrupole phonon model (IBFFM/OTQM). The calculations give account both of the “regular” and “irregular” behaviour of the energy splitting of thep−n multiplets, as well as of the electromagnetic moments, γ-branching and γ-mixing ratios. Conclusions have been drawn on the role of different interactions in the multiplet energy splitting. The IBFFM interpretation of the high-spin intruder bands and the spectroscopic factors of the neutron transfer reactions are also shortly discussed for Sb nuclei.

Energy levels of237Np

Abstract: The α decay of241 Am to237Np has been studied using Si(Li) and H.P.Ge−NaI(Tl) spectrometers in the low energy range 5–45 keV. Twelve gamma transitions have been observed. Two of these transitions are found to be new and have energies 28.52 and 40.44 keV. Furthermore, it was possible to confirm the placement of the 27.1 keV transition in the level scheme of237Np. The levels from this and previous work are compared with those calculated by means of the unified model and the extracted parameters are given.

Effect of aliphatic and aromatic substituents on the fluorescence of some polymers

Abstract: 7–8 dihydroxy-4-methyl coumarin A and its copolyesters A1 through A5 have been investigated here to study the effect of aliphatic and aromatic subtituents in the polymers, on the fluorescence of these compounds. It has been observed that along with other emissions 480 nm emission present in all the polymer specimens has been missing in the monomer specimen. The flourescence of these polymers is shown to depend on the aliphatic and aromatic substitutions at various positions.

Trajectory studies for the fusion of two heavy nuclei

Abstract: The dynamical aspects of two heavy nuclei colliding with energies above the Coulomb barrier are considered. The macroscopic aspects of the asymmetric and symmetric collisions have been studied. The classical trajectories for the fusing systems are numerically calculated. Effects due to increasing the initial kinetic energy or the initial asymmetry on the calculated trajectories are investigated. The results lead to three typical trajectories which correspond to the deep-inelastic, the quasifission and the formation of compound system reactions. It is found that the effect of the asymmetry plays the same role as that of the initial kinetic energy.

Quaternionic treatment of the electromagnetic wave equation

Abstract: After introducing the quaternions and some of their important properties the Maxwell Equations are translated by quaternion representation. The derivation of the wave equation is also discussed.

Examples of unconventional dimensional analysis

Abstract: It is shown that dimensional analysis can be used (i) to calculate the energy levels in a one-dimensional potentialV(x) ≈ |k, and (ii) to estimate the value of the gravitational constantG.

14.5-MeV Neutron capture cross-section measurements in160Gd with activation technique

Abstract: Activation cross-sections for neutron capture have been measured at an energy of 14.5 MeV for160Gd, relative to σ(160Gd(n, 2n)159Gd)=1975 mb. Gamma-ray spectra of the product nuclei were measured with a HP Ge-detector. By systematically varying the geometrical arrangement the corrections due to the influence of lower energy neutrons could be determined. The corrected activation capture cross-section at 14.5 MeV is found to be 1.0±0.2 mb.

A lattice gas model for enzyme kinetics with next-nearest neighbour interactions

Abstract: We have shown that, by using a one-dimensional lattice gas model with the next-nearest neighbour interactions and calculating the thermodynamic potential of the system by means of the transfer matrix method, we can find numerically for enzyme kinetics some new diagrams of saturation curve. These diagrams in the limit of no interactions between sites reduce to the classical Michaelis-Henri diagrams and in the limit of the nearest neighbour interactions to some other diagrams which we have obtained before by using a correlated walks theory. These new diagrams of saturation curve can be useful for the experimental investigation.

Lattice dynamical study of some fcc metals centered around a new scheme

Abstract: The present investigation used modified generalised Morse potential to explain the lattice dynamical behaviour of some fcc metals. This potential is controlled by factorP, used in the above modification. Theoretical and experimental findings are very close to each other and this agreement provides a satisfactory explanation of the above model.

The effect of temperature and pressure on the thermodynamic properties of rare gas solids in anharmonic approximation

Abstract: On the basis of the reduced second order self-consistent phonon approximation the temperature and pressure dependence of the thermodynamic functions of rare gas solids are computed and compared with experimental and other theoretical data in the high temperature region. The instability parameters are calculated also. The system of self-consistent equations is solved for the generalized form of the Lennard-Jones (n, m) interatomic potential.

Infrared behaviour of Green's function for fermions in supersymmetric Yang-Mills theories

Abstract: Infrared behaviour of the Green's function for fermions in supersymmetric Yang-Mills thebries is investigated. We show that only massless gauge vector fields give contributions to this behaviour.

Electron density of metallic surfaces by variation method

Abstract: In this paper variational calculation is performed for simple jellium metal surface electron density using the density functional theory. A trial function of the local electron density is proposed. The free parameters are obtained by minimization of the total energy functional. The effect of the high density gradient expansions of the kinetic emergy is studied (i.e. Kirzhnits energy). The results obtained are similar to those of Lang and Kohn, which use a more exact method.

Corrections for grad and markovian approximations in statistical derivation of nonequilibrium thermodynamics

Abstract: In previous work, non-linear phenomenological equations exhibiting reciprocity have been derived as first moments of a kinetic equation obtained from the Liouville equation via Grabert projection operators. In the derivation, a Markovian approximation and Gradtype ansatz based on information theory were used to derive self-consistent first-moment equations. It is possible to generalize the Grabert operators so that the previous derivation, after replacement of the old by the new operators, is free of these approximations.

Internal bremsstrahlung from204Tl

Abstract: The contiunous spectrum of internal bremsstrahlung from the unique first forbidden beta decay of204Tl was measured using the β stopper method with a multichannel analyzer and NaI (Tl) scintillation detector together with a standard geometrical arrangement. The raw spectrum was corrected for several factors using the step-by-step process of Liden and Starfeld and compared with theoretical results such as KUB (Knipp, Uhlenbeck and Bloch), LF (Lewis and Ford) and N (Nilsson) theories. The divergence between experiment and theory was found to increase with increasing energy.

Rotational energy transfer within theA 1Σ u + -state of Na2 induced by collisions with (2 S 1/2) Na

Abstract: The (v ′=34,J ′=14) level in theA 1Σ + electronic state of Na2 has been selectively populated by excitation with the 578.1 nm line of a ring dye-laser with rhodamine 6G. Through collisions with (2 S 1/2) Na atoms energy is transferred to neighbouring rotational levels in Na2 and the density of these levels is determined by observing fluorescence to the electronic ground state. From previous measurements of the lifetime of theA 1Σ + state and new measurements of the intensities of collision induced spectral lines, absolute collision cross sections for all rotational transitions up to ΔJ=±6 have been obtained; the total cross section for all rotational transitions observed is: $$_{rot} \sigma ^{total} = 0.41 \pm 0.11nm^2 $$ .

Dirac particle in a spatially periodic magnetic field

Abstract: The exact general solution of the Dirac equation in the steady periodic magnetic field along a fixed direction is obtained.