Measurement ofL-shell photoelectric cross sections in highZ elements at 60 keV

L-shell photoelectric cross sections have been measured at 60 keV for six elements in the range 74≤Z≤92. The measurements are found to agree with theoretical calculations.     

Observation of a topological relaxation mode in microemulsions

We report the observation of two diffusive relaxation modes in a very swollen microemulsion, measured by quasielastic light scattering experiments. In addition to a short-time diffusion process, we observe a long-time diffusive relaxation mode with unusual scaling behavior: the diffusion constant D is an exponential function of the characteristic length scale xi, D~exp(-xi). This observation provides experimental evidence for thermally activated topological relaxation of random fluid phases, as predicted by Milner et al. [J. Phys. (Paris) 51, 2629 (1990)]. We describe the activation energy of such a process by some simple microscopic model for the surfactant layer and give an estimation of the membrane elastic and Gaussian moduli kappa and kappa;, and its spontaneous curvature.     

A qualocation method for parabolic partial differential equations

In this paper a qualocation method is analysed for parabolicpartial differential equations in one space dimension. Thismethod may be described as a discrete H¹-Galerkin method inwhich the discretization is achieved by approximating the integralsby a composite Gauss quadrature rule. An O (h^4-i) rate of convergencein the W^i.p norm for i = 0, 1 and 1 p is derived for a semidiscretescheme without any quasi-uniformity assumption on the finiteelement mesh. Further, an optimal error estimate in the H² normis also proved. Finally, the linearized backward Euler methodand extrapolated Crank-Nicolson scheme are examined and analysed.     

On Rayleigh-Bénard convection with rotation and magnetic field

A sufficient condition for the validity of the principle of exchange of stabilities in the Rayleigh-Bénard convection problem under the simultaneous action of a uniform vertical rotation and magnetic field is derived. Furthermore the complex growth rate of an arbitrary oscillatory perturbation, neutral or unstable, is shown to lie inside a semicircle in the right half of the complexp-plane. These results are uniformly valid for all combinations of free insulating, rigid perfectly conducting and rigid insulating boundaries.

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Zusammenfassung Für die Gültigkeit des Prinzipes der Vertauschung der Stabilitäten im Rayleigh-Bénard-Konvektionsproblem mit simultanen Wirkungen einer gleichförmigen vertikalen Rotation und eines Magnetfeldes wird eine hinreichende Bedingung hergeleitet. Weiterhin wird gezeigt, daß die komplexe Anfachungsrate für eine beliebige oszillatorische Störung innerhalb eines Halbkreises in der rechten Hälfte der komplexenp-Ebene liegt. Diese Resultate sind gleichermaßen gültig für alle Kombinationen von freien isolierten, starren vollkommen leitenden und starren isolierten Begrenzungen.

     

Optical model analysis of (240–300) MeV K+-meson elastic scattering in nuclear emulsion

The differential elastic scatterings of (240–300) MeV K⁺-mesons in G-5 nuclear emulsions have been analysed in terms of exact diffuse-surface optical-model of the nucleus and the real nuclear volume potential integral per nucleon (I _v ) obtained. By making Chi square comparison between the experimental cross-sections and the theoretically calculated values for the optical model parameters R₀=1·07 F anda=0·57 F, I _v comes out to be (100±30) MeV F³. The analysis also confirms that for K⁺-nucleus scattering, repulsive potential is by far more probable than an attractive one. The K⁺-free nucleon cross-section has been estimated to lie in the range (13·5±1·7) mb.     

Pressure dependence of the E1 gap in GaSb: Resonant Raman technique

A new method to determine the pressure dependence of energy gaps with the help of the diamond anvil cell is reported. The method is based on resonance Raman scattering observed as the gap energies cross the photon energies of several laser line. The technique is illustrated by means of measurements of the pressure dependence of the E₁ gap of GaSb up to the phase transition (7.7 Gpa). A sublinear dependence of the E₁ gap on pressure and a linear dependence on lattice constant (dE₁/dlnV = 4.67 ± 0.1 eV) is obtained. These results are well explained by pseudopotential calculations.     

Measurement ofL-shell photoelectric cross-sections in lower intermediateZ elements at 6 keV

L-shell photoelectric cross-sections have been measured at 6 keV for eight elements in the range 40⩽Z⩽53. The measurements agree with theoretical calculations.     

Raman study of temperature dependence of lattice modes in calcite

The temperature dependence of the line width and the peak position of theE _g librational mode (of nominal frequency 285 cm⁻¹) and theE _g translational mode (of nominal frequency 155 cm⁻¹) in calcite (CaCO₃) have been studied by laser-Raman spectrometry. The role of orientational relaxation as a possible process contributing to the line width has been evaluated. It is concluded that reorientations do not play a major part in relation to the present observations. It is further shown that the latter can be understood on the basis of cubic and quartic anharmonic processes. The data also suggest that certain phonon interactions earlier considered insignificant for peak shift in calcite, do contribute significantly.     

Allenes—XXXV : The addition of allenic carbenes to oxygen heterocycles

Dimethylvinylidene carbene from 1-bromo-3-methylbutadiene and potassium t-butoxide adds to 2,5-dihydrofuran and 2,3-dihydropyran to give the corresponding allenic cyclopropanes. 1,4-Cycloaddition of the allenic carbene to furan followed by hydration during work up yields the bicyclic ketone 11.     

Infrared studies on ion irradiated quartz

Damage produced inα- and fused quartz bombarded with low energy (∼ 100 keV) D⁺, He⁺ and Ar⁺ ions, has been studied by observing the changes in their spectrum. Besides bulk reflectivity, the attenuated total reflection spectrum has also been studied, the latter with a view to obtaining the surface polariton frequencies. It is observed that for the same fluence, the changes following D⁺ irradiation are much higher compared to that for Ar⁺ irradiation. The variation of the surface polariton frequency inα-quartz with the damage energy deposited has the same trend as observed earlier for refractive index. Some annealing studies have also been performed in argon-irradiated samples. These studies indicate that whereas in fused quartz the damaged layer recovers completely, inα-quartz there is a residual amorphization even after annealing. A two-layer model is proposed which gives a reasonable simulation of the observedir properties.