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Showing papers by "National University of Cuyo published in 1981"


Journal ArticleDOI
TL;DR: In this article, the authors studied the dependence of electron yields from clean Cu and Au surfaces on the incidence angle theta of 5-50-keV He/sup +/, Ar/sup+/, and Xe /sup +/ projectiles, in the angular range 0--80 /sup 0/, and under ultrahigh-vacuum conditions.
Abstract: We have studied the dependence of electron yields ..gamma.. from clean Cu and Au surfaces on the incidence angle theta of 5--50-keV He/sup +/, Ar/sup +/, and Xe/sup +/ projectiles, in the angular range 0--80 /sup 0/, and under ultrahigh-vacuum conditions. We have found that, at small angles, ..gamma..proportionalsec/sup f/theta, with f generally different from unity. For Xe/sup +/ on Cu, ..gamma..(theta) presents an energy-dependence maximum, similar to that obtained for sputtering. The results are explained in terms of the anisotropy of the electron cascade in the solid, the depth distribution of the inelastic energy deposited by the projectile and by rapidly recoiling target atoms in the near-surface region of the solid.

48 citations


Journal ArticleDOI
TL;DR: In this paper, the deconfining phase transition at finite temperature in compact QED in lagrangian formulation is studied and the partition function in terms of topological excitations is explicitly shown that at large temperature these become the vortices of a system in one less dimension.

29 citations


Journal ArticleDOI
TL;DR: The results showed that a) the enzymes behave quite independently from each other, suggesting the existence of a specific regulation for each of them b) there were characteristic changes in enzymatic activity for each experimental condition.
Abstract: With the aim of gaining knowledge about the lysosomal apparatus of the rat epididymis, four acid hydrolases were analysed in homogenates of the whole organ and, in other experiments, in separated segments: proximal and distal caput, corpus and cauda. The activities were similar to those in the liver, and they were 50% recovered in a cytosol of 43 000 g x 60 min. Ten days after castration all segments showed similar changes, the activities of beta-glucuronidase and cathepsin D increased above normal levels while those of DNAase and acid phosphatase were found slightly decreased. After vasectomy region I (caput and corpus) showed decreased beta-glucuronidase activity and increased acid phosphatase activity. The activity of cathepsin D increased in both regions. In cryptorchid rats (90 days) the epididymis greatly decreased in weight, the activities of acid phosphatase and DNAase slightly decreased in region II (cauda) and in region I, respectively. In the abdominal epididymis (90 days) only region II decreased in weight. DNAase activity decreased in region I while cathepsin D did so in both regions. The results showed that a) the enzymes behave quite independently from each other, suggesting the existence of a specific regulation for each of them b) there were characteristic changes in enzymatic activity for each experimental condition.

18 citations


Journal ArticleDOI
TL;DR: In this paper, a canonical transformation of the Schrieffer-Wolff type is applied to the periodic Anderson model, and the resulting Hamiltonian contains terms up to fourth order describing several interaction processes including intersite spin and charge correlations, conduction-electron scattering, and excitonic interactions.
Abstract: A canonical transformation of the Schrieffer-Wolff type is applied to the periodic Anderson model. The case of infinitely correlated $f$-like orbitals is dealt with, and these are described through standard basis operators, including spin degeneracy only. First- and third-order terms in the mixing parameter are eliminated. The resulting Hamiltonian contains terms up to fourth order. These describe several interaction processes including intersite spin and charge correlations, conduction-electron scattering, and excitonic interactions. A detailed analysis of the modified Ruderman-Kittel-Kasuya-Yosida interaction obtained is given. Possible extensions of some of the results to higher orders are discussed. The method provides a way to evaluate the spin and charge susceptibilities of the conduction-electron gas in this model. The possible relevance of these functions to a theory of the phonon spectrum and of magnetic ordering of intermediate-valence systems is mentioned.

17 citations


Journal ArticleDOI
TL;DR: In this article, the effect of the continuous demagnetization of Ce on the superconductivity of the matrix is studied with a simple, exactly solvable model obtained as a zero-conduction-bandwidth limit of the Mueller-Hartmann and Zittartz and of the Wiecko-Lopez models.
Abstract: The effect of the continuous demagnetization of Ce on the superconductivity of the matrix is studied with a simple, exactly solvable model obtained as a zero-conduction-bandwidth limit of the Mueller-Hartmann and Zittartz and of the Wiecko-Lopez models. Phase diagrams are obtained from the exact free energies. This phase diagrams agree, within the limitations of the model, with those previously calculated by Mueller-Hartmann and Zittartz and by Wiecko and Lopez. The exact calculation of the free energy allows us to extend the Wiecko-Lopez results and to predict a normal phase at low temperatures which has not been observed before. The characteristic features observed in LaCe and (La/sub x/Th/sub 1-x/)Ce are reproduced. The phenomenon of reentrance emerges with a clear physical meaning as a competition for stability between two states with different occupation number of the ''conduction'' electrons which have different degeneracy (different contribution to the entropy).

13 citations



Journal ArticleDOI
TL;DR: In this article, temperature dependent penetration depth measurements can be used to characterize the superconductive behavior of amorphous metals, and the authors show that the measurements can also be used for superconductivity characterization.

9 citations


Journal ArticleDOI
TL;DR: The demagnetizing tensor formalism for the evaluation of magnetization and internal field in ellipsoidal bodies of isotropic materials is extended to the case of anisotropic materials and to the calculation of the field outside the body as discussed by the authors.
Abstract: The demagnetizing tensor formalism for the evaluation of magnetization and internal field in ellipsoidal bodies of isotropic materials is extended to the case of anisotropic materials and to the calculation of the field outside the body.

5 citations


01 Jan 1981

3 citations


Journal ArticleDOI
TL;DR: In this paper, it is shown that superconductivity is a useful tool to investigate the evolution of the amorphous state, when heat treatment below the crystallization temperature is performed.
Abstract: It is shown that superconductivity is a useful tool to investigate the evolution of the amorphous state, when heat treatment below the crystallization temperature.

2 citations


Journal ArticleDOI
TL;DR: In this paper, low field dc-magnetization measurements have been made over the 1.6 K -12 K temperature range on polycrystalline samples of Th l−x Gd x where x varies from 0.03 to 0.20 and the dc-susceptibility has a maximum at a freezing temperature T f that scales linearly with de Gd concentration.
Abstract: Low field dc-magnetization measurements have been made over the 1.6 K – 12 K temperature range on polycrystalline samples of Th l−x Gd x where x varies from 0.03 to 0.20. The dc-susceptibility has a maximum at a freezing temperature T f that scales linearly with de Gd concentration. Above T f the susceptibility follows a Curie-like law and below T f remanent magnetization and magnetic viscosity are observed. A detailed analysis of the data in the neighborhood of T f indicates that the time-dependent remanent effects extend to temperatures slightly above T f . A comparison with specific heat data shows that T f closely corresponds to the maximum of C p /T vs T.

Journal ArticleDOI
TL;DR: In this paper, it was shown that for a narrow band version of the Anderson Hamiltonian, the transformation of Schrieffer and Wolff can be carried out to all orders in the mixing parameter.

Journal ArticleDOI
TL;DR: In this paper, a Continuum limit of the two-dimensional ZN spin model is found and classical field equations are derived, and it is also shown that in its first approximation this field theory reduces to the Villain form of the spin system.

Journal ArticleDOI
TL;DR: In this article, weak field penetration depth measurements can be used to determine the change in the normal and superconducting behavior of amorphous samples, when heat-treated below the crystallization temperature.
Abstract: It is shown that weak field penetration depth measurements can be used to determine the change in the normal and superconducting behaviour of amorphous samples, when heat-treated below the crystallization temperature The results are used to discuss the validity of BCS-Gorkov relations, when applied to these materials