• Volume 11, Issue 5

November 1978,   pages  519-671

• An automated high precision calorimeter for the temperature range 200K–400K. Part 1: Design and performance

A fully automated calorimeter has been designed and tested over the temperature range 200K–400K. The system may be used for measurements with an absolute accuracy of 0.2% of samples of approximate mass 50g and thermal capacity 15 JK−1. The temperature of the sample is determined by a quartz crystal thermometer of resolution 100 µK which is not in direct thermal contact with the sample. The performance of the system is illustrated by results obtained on high purity copper, distilled water and K2PbCu(NO2)6 which exhibits very sharp first order phase transitions at about 273.4K and 281.8K.

• Green’s functions in quantum chemistry II. Improving the Σ perturbation approach

Two methods, which are expected to lead to results better than those of theΣ perturbation approach given earlier are investigated. Within the algebraic approximation, the methods are applied to the hydrogen molecule and to ethylene in the Pariser-Parr-Pople (PPP) approximation. Both the methods are seen to suffer from the defect of not conserving the number of particles in the system. The methods are (a) the use of a partitioning other than Hartee-Fock. Due to the non-conservation of particle number, the method does not seem to be suited for the calculation of the ground state energy, but it gives good results for ionisation potentials. The investigation reveals that the only partitioning which conserves the number of particles is the Hartree-Fock partitioning (b) the renormalisedΣ perturbation method, suggested by Csnak and others. For ethylene in the PPP approximation, the method does conserve the number of particles (but not in general). However, the energy obtained is not as good as that in theΣ perturbation method. This method therefore seems to be of limited applicability in molecular calculations.

• Infrared absorption spectra of 2,3- and 3,5-dichloroaniline

The infrared absorption spectra of 2,3- and 3,5-dichloroanilines have been recorded in the region 250–4000 cm−1. The spectra of the latter are recorded in solid phase (KBr and Nujol mull) and in CS2/CCl4 and CHCl3 solutions while that of the former in thin film only. The spectra have been analysed assuming C3 and C2v point group symmetry respectively and a tentative assignment of the observed bands to different fundamental modes has been made.

• A phenomenological, kinematical model of the coronal magnetic fields in terms of thin flux tubes rising from the photosphere

A kinematical model is necessary for understanding the gross structure of the coronal magnetic field and its slow evolution in consistency with the small scale structure of the photospheric fields. Here we have developed a preliminary phenomenological model in terms of flux tubes of flux amounts ≈ 1017 − 1018.5 Mx rising across the inner corona in the form of arches and opening out in the outer corona. In contrast to Parker’s estimate, this model is consistent with the observed spans of the chromospheric fibrils and x-ray arches. It is also consistent with the number of flux tubes present above the photosphere as estimated from the observed abundance of spicules.

• Scaling hypothesis, relativistic statistics and critical mass of dwarf stars

Assuming that field theoretic Green’s functions scale, expressions for correlation function, number density, pressure are obtained for a relativistic statistical many-body system. The scaling parameter is related to anomalous dimension and is a measure of interaction. The effect of this interaction on the critical mass of dwarf stars is studied and is not found to be insignificant. A mass radius relation is deduced. The Chandrasekhar limit is reproduced in the limit of non-interaction.

• Statistical mechanics of bosons with attractive interaction

In order to obtain meaningful results for a system of bosons interacting via a potential containing a long-ranged attraction, the coupling of low momentum particles with high momentum particles has to be taken into account. The method of thermal Green’s functions applied to this problem leads to involved graphical calculations even for temperatures close to the absolute zero. It is shown that the problem can be tackled much more simply and profitably by obtaining an effective hamiltonian for low momentum particles in a manner similar to that adopted in the recent renormalisation group approach to critical phenomena. The occurrence of anomalous pairings is avoided by performing suitable Bogolubov transformations. The procedure gives the quasiparticle spectrum besides yielding an explicit expression for the free energy in the low temperature limit. The results agree with those derived by Green’s function methods using partial summations.

• Systematics of asymmetry in fission based on order-disorder model

According to Order-Disorder Model (ODM), in the early stages of fission, the charges in a fissioning nucleus gets polarised into two impending parts along with corresponding most stable neutrons which are calculated from the minimum in isobaric mass parabola. This polarisation into two most stable configuration leaves a small number of neutrons as balance neutrons i.e.Nbal. The distribution of theseNbal for various polarisation modes, shows a very profound correlation with the yield distribution. Judging from this striking correlation between these two distributions, it can be predicted that the asymmetry in fission decreases gradually and ultimately disappear for nuclei havingZ ⋍ 102 but reappears again for the nuclei in super heavy region.

• Neutron induced reactions in antimony isotopes at 14 MeV

Neutron activation cross-sections in antimony isotopes were measured at an incident neutron energy of 14.2±0.2 MeV. The versatile mixed powder technique and high resolution Ge(Li) detector gamma ray spectroscopy were employed. The measured cross-sections were compared with those reported in literature. The total (n, 2n) cross-sections were compared with the estimates based on statistical theory. The experimental values were found to be smaller than the statistical theory estimates and the resulting diminution was attributed to the precompound effects in (n, 2n) reactions at 14 MeV.

• Transverse momenta of secondaries from 200 GeV/c proton-nucleus interactions

A study of 100 interactions, produced by secondary particles from 200 GeV/c proton interactions in nuclear emulsions, has been made to estimate the transverse momenta of the secondary particles. The data have been analysed by different methods of energy estimation and the weighted average values ofpt have been compared as estimated from various methods. An average value ofpt equal to 0.38 ± 0.03 GeV/c, in proton-nucleus interactions at 200 GeV/c, has been obtained from the production mechanism method.

• Neutral current cross-sections for neutrinos on protons

Defining the ratiosrp =σ(vpvx)/σ(vpμx) and$$\bar r_p = \sigma (\bar \nu p \to \bar \nu x)/\sigma (\bar \nu p \to \mu ^ + x)$$ we obtain the bounds 0.28 ⩽rp ⩽ 0.61 and$$0 \cdot 15 \leqslant \bar r_p \leqslant 0 \cdot 37$$ using only the parton model and the data of CDHS group with iron target. We also give the complete set of parton-model relations which would allow the determination of all the neutral-current coupling constants from inclusive cross sections alone.

• Scale breaking in neutrino scattering

We consider two types of scale breaking models—one based on asymptotically free gauge theory and the other phenomenological—which have already been fitted to the electron and muon data. Their predictions for the neutrino scattering are worked out and the sensitivity on the model parameters and the input electron data studied. The effects of scale breaking at very lowQ2 and of a finite longitudinal cross-section are incorporated in analogy withep data. The predictions are compared with the recent neutrino scattering data.

• Density matrix formalism for anelastic relaxation

A density matrix formalism is developed for anelastic (mechanical) relaxation in crystalline materials with point defects characterized by elastic dipoles. The time-dependent approach to equilibrium of the strain response under the action of a constant applied stress is deduced. The formalism parallels the one used in nuclear magnetic relaxation. The anelastic relaxation time is determined as a function of the parameters occurring in the defect hopping term in the Hamiltonian. This term is responsible for the dissipation of the anelastic ‘potential’ energy into the host lattice. In a lengthy concluding section, the following aspects are discussed point by point: the advantages of the formalism presented, its scope and special cases; the physical implications of the expression obtained for the relaxation time; the similarities and differences between magnetic relaxation and anelastic relaxation, etc.

• Electron neutral collision frequency from breakdown measurements in crossed electric and magnetic fields

A simplified method of determining the electron-neutral collision frequency at unit pressurev0 is presented in a number of gases (hydrogen, argon and air) in crossed electric and magnetic fields utilising the sparking voltage data and equivalent pressure concept. The values ofv0 for lowH/p are found to agree with those reported by other authors. But at highH/p, the estimated values ofv0 are appreciably higher for all the three gases. The increase in the values ofv0 possibly occurs due to the change of the electron energy distribution at higherH/p.

• # Pramana – Journal of Physics

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• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019