Volume 14, Issue 4
April 1980, pages 233-320
pp 233-252 April 1980 Crystallography
Comparisons are made between calculations based on the double-helix and side-by-side models of DNA and data taken from the available x-ray diffraction measurements of the B form of DNA. The SBS model invoked here is an improvement on the one which was published earlier. In our estimation the fibre diffraction patterns do not significantly favour either model. However, the DH model is incompatible with the on-axis form of the cylindrically-averaged Patterson function, whereas the SBS model is compatible (this result is relatively insensitive to appreciable modifications to the SBS structure)—the crucial question is whether the quality of the data is sufficient to make this finding significant. It is shown that the maximum expected effect on the fibre pattern, of exchanging A-T base pairs for G-C base pairs, is less than the probable experimental error.
pp 253-262 April 1980 General Relativity
A solution of the Einstein-Maxwell equations corresponding to source-free electromagnetic field plus pure radiation is obtained. The solution is algebraically special. A particular case of the solution is considered which encompasses many known solutions. Among them is a radiating Ruban metric.
pp 263-269 April 1980 Solid State Physics
The general expression for the Anderson-Grüneisen parameterδ recently derived by Gupta and others, has been used to study the variation ofδ with the Grüneisen parameterγ employing the interaction approach. For this purpose four potential energy functions have been selected. It is found thatδ values evaluated by the modified Varshni-Shukla potential are better than other forms of overlap repulsive interaction. The variation ofδ withγ is also studied by plotting curves betweenδ andγ. The method of least-squares has been employed to yield the best fitted equation.
pp 271-287 April 1980 Plasma Physics
The role of a sequence of imploding spherical and cylindrical shocks is investigated in the context of laser-driven fusion in deuterium-tritium pellets. An approximate analytical treatment of a convergent sequence of shocks is presented within the framework of gas-dynamic equations for self-similar motion. These analytical solutions are compared with the exact numerical solutions. The solutions display an explicit dependence on the relative strength between the successive shocks and the ratio of the final to the initial pressure in the shocks. These solutions are employed to estimate the fusion yield for a given input shock energy.
pp 289-294 April 1980 Instrumentation
A modified electron bombardment type ion source suitable for use with mass spectrometer is described. Ion formation occurs throughout a relatively large volume in the ionisation box, since no magnetic field is used to collimate the ionising electrons. A sensitivity of 2 × 10−5 amp/torr is obtained for an ion extraction energy of 2 keV and 200 mass resolution. Trajectory tracing has been used to study the operation of the ion source. Capability of the ion source to analyse solid samples in microgram quantity was tested by studying evaporation of BaO from tungsten.
pp 295-302 April 1980 Nuclear And Particle Physics
Zero range DWBA analysis for two-particle (neutron and proton) transfer reactions is carried out, using simple shell model structure wave functions for54Fe,56Co and58Ni, with56Ni inert core. In this structure calculation, a microscopic set of two-body interaction matrix elements derived from the non-local separable potential of Tabakin are employed. These matrix elements include in the perturbation theory two corrections (i) the second-order Börn term and (ii) the appropriate core excitations. Unlike the situation in many two-particle transfer reactions, the fragmentation of the reaction strengths to the excited states with respect to the lowest states of same spin and parity in the above transfer processes is satisfactorily borne out from this analysis.
pp 303-313 April 1980 Nuclear And Particle Physics
Characteristics of the inelastic interactions of 9.38 GeV/c deuterons with nuclear emulsion nuclei have been studied. These have been compared with nucleon-nucleus interactions at a corresponding momentum. The probability of nucleon stripping in deuteron-nucleus interactions has been observed to be 0.5. The charged particle multiplicity in deuteron-nucleus interactions exhibitA-dependence of the typeAα with α=0.08. The experimental data disagree with KNO scaling.
pp 315-320 April 1980 Optics
Calculation of the diffracted amplitude for the diffracting aperture on a sphere is briefly reviewed. Explicit formulas are given to compute the diffracted amplitude. In these formulas the real wave and evanescent wave contributions are discussed.
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