Showing papers by "National University of Cuyo published in 1986"

Correlation functions of the antiferromagnetic Heisenberg model using a modified Lanczos method.

Abstract: Using a modified Lanczos algorithm, we study the correlation functions in the ground state of the one-dimensional antiferromagnetic Heisenberg model. %'e obtain numerical results for rings up to 24 sites. There are no indications of the anomalous behavior of these correlation functions recently observed in chains with 16 sites. %'e also present a pedagogical description of the hashing technique which is an efficient algorithm for searching and storage purposes.

Immunochemical localization of epididymal protein DE on rat spermatozoa: Its fate after induced acrosome reaction

Abstract: The localization of rat epididymal protein DE on cauda epididymis spermatozoa was studied with a specific antibody and the peroxidase antiperoxidase (PAP) immunocyto-chemical reaction. At the light microscopic level, all spermatozoa appeared to be labeled over the dorsal portion of the head, whereas tails were negative. This observation was confirmed using scanning electron microscopy. A large number of particles were seen on the external surface of the plasma membrane covering the acrosomal region and a smaller number on the postacrosomal portion. Flagella appeared free of particles. Sperm suspensions were incubated in conditions that induce capacitation and the acrosome reaction, and, in this instance, the permanence of protein DE on the vesicles and the postacrosomal region of the membrane were observed. The localization of this epididymal protein on the sperm surface is compatible with a role in the gamete interaction process.

A permeability barrier in the testis of an insect Triatoma: A freeze-fracture and lanthanum tracer study.

Abstract: In vertebrates, the testicular permeability barrier has been the subject of numerous studies. Some recent observations also indicate the existence of such a barrier in some invertebrates, e.g. insects and worms. With the aim of determining whether the morphological features of the blood-testis barrier generally found in vertebrates can be extended to other animals, we studied the testis of the insect Triatoma infestans using electron-dense tracers and freeze-fracture techniques. This organ is divided into cysts timed in synchroneous maturation. The intercellular tracer (lanthanum hydroxide) freely penetrates the basal areas of the seminiferous epithelium surrounding spermatogonia and spermatocytes devoid of synaptonemal complexes (pre-leptotene and leptone). Zygotene spermatocytes indicate the establishment of the barrier. Freeze-fracture techniques exhibit the morphological correlate of the barrier consisting of 9-10 nm particle rows on the P faces of the Sertoli cell membranes. These rows are relatively loose showing an undulating disposition and correspond to the septate junctions found in thin sections. The percolation of intercellular tracers demonstrates that septate junctions between the basal membraneous areas of Sertoli cells possess the barrier properties.

First outbreak of botulism caused by Clostridium botulinum subtype Af

Abstract: In December 1982 an outbreak of foodborne botulism presumably produced by the ingestion of home-made pickled trout occurred in San Rafael, province of Mendoza, Argentina. The toxin detected in blood serum and feces samples of the sole affected patient was preliminarily typed as a plain type A. A strain of Clostridium botulinum was isolated from feces which, after culture by the dialysis method, produced 1 x 10(7) LD50/mouse per ml. Quantitative neutralization tests carried out at different levels of toxin concentration, showed that this toxin consists of a major type A antigenic component (about 99% of the complex) and a minor type F component, defining its identity as a subtype Af. A rabbit antiserum obtained from this toxin neutralizes A and F reference toxins. Despite the antitoxic and supportive treatment, the patient died as a consequence of the poisoning. The polyvalent antiserum administered contained A, B and E antitoxins. Death could be due to the lethal effect of the A fraction, the F fraction or to a combined effect of both toxic components of the toxin. This is the first detection of an outbreak produced by C. botulinum subtype Af, serotype described in Argentina fifteen years ago, and not detected until now in other parts of the world.(ABSTRACT TRUNCATED AT 250 WORDS)

Bethe-ansatz solution of a model for a mixed valent impurity with two magnetic configurations: II. Numerical solution of the thermodynamic equations

Abstract: A mixed valence impurity with two magnetic configurations of total angular momentumJ2 andJ1=J2+1/2, respectively, coupled by conduction electrons with total angular momentum 1/2 via a hybridization matrix element is considered. The thermodynamic Bethe-ansatz equations derived previously are solved numerically for various values ofJ2. Thef-level occupation, the entropy, the magnetic susceptibility and the specific heat are obtained as a function of temperature for variousf-level positions. The magnetic field dependence is also discussed in the limit of integer valence (exchange model).

Effect of Coulomb repulsion between localized and extended states in the Anderson model.

Abstract: The effect of the Coulomb repulsion between localized and extended states in the thermodynamic properties of the asymmetric Anderson model is studied. The magnetic susceptibility is calculated by means of the renormalization-group approach. It is shown that the properties of the model with f-d Coulomb repulsion can be mapped into the properties of a model without f-d repulsion and renormalized parameters. A brief discussion of the effect of direct exchange between localized and extended states is also included.

Kininogenase from rat vascular tissue.

Abstract: A kininogenase resembling glandular kallikrein ws partially purified from vascular tissue and characterized. Saline perfused rat tail arteries and veins were homogenized in 0.25 M sucrose containing 10 mM Tris-HC1 (pH 7.4). The homogenate was centrifuged at 105,000 x g for 60 min and a vascular kininogenase was purified from the supernatant by chromatofocusing, affinity chromatography on immobilized antibodies against rat urinary kallikrein, and gel filtration on Sephadex G-100. The inhibitory effects of antibodies against rat urinary kallikrein were tested using equivalent kininforming concentrations of rat urinary kallikrein and vascular kininogenase. Kininogenase activities of both enzymes were similarly inhibited by urinary kallikrein antibodies. Aprotinin (1,000 KIU) completely inhibited vascular kininogenase activity while soybean trypsin inhibitor (100 µg) did not modify its kinin-forming activity. Vascular kininogenase and rat urinary kallikrein had the same elution volume when chromatographed on a Sephadex G-100 column and had similar mobilities in 10% polyacrylamide gel electrophoresis. Kinins released by vascular kininogenase were identified as bradykinin by reverse-phase high performance liquid chromatography. Rat vascular kininogenase appears to be similar to glandular kallikrein. Kinins released locally by vascular kininogenase may contribute to the regulation of vascular tone.

Diffraction of low-energy ion-induced secondary electrons emitted in the forward direction from a solid foil

Abstract: By the measurement of doubly differential distributions of electrons emitted downstream when 170-keV protons pass through thin carbon foils, besides the convoy electron peak and the characteristic ridge, centered in the beam direction and found also in gas targets, a lateral structure is observed at larger angles. The location of this structure can be uniquely and quantitatively attributed to electron diffraction in the three-dimensional reticule of the polycrystalline foil. Electrons in the central ridge are found to diffract, while the convoy electrons do not.

Inelasticity corrections in thermal neutron scattering by molecules using a synthetic (incoherent) scattering function

Abstract: Recently a synthetic scattering law has been developed to describe the interaction of thermal neutrons with molecular gases. Although this function does not contain a detailed description of the atomic motions in the molecular unit (nor pair correlations), the main features of the molecular dynamics are retained through the introduction of effective quantities which are directly related to the basic properties of the system. In this work we present evaluations of inelasticity corrections using the synthetic model for both reactor and pulsed neutron diffraction experiments. Predictions are made of differential cross sections (self component) for light and heavy water and these are compared with available experimental results.

Classical unified fields: physical space

Abstract: We develop a general unified theory of classical mechanics and classical electromagnetism in a gravitational field on Friedman-Schouten space-time (FSS). In this formalism (i) local equations of a charged fluid in an electromagnetic field are the same as in classical mechanics, (ii) local equations for a moving charged fluid are the same as in electromagnetism, (iii) the path of a charged particle under gravity and electromagnetism is a geodesic of the four-dimensional FSS, and (iv) the strong equivalence principle and a nonzero torsion coexist without conflict.

Ultrastructural effects of cadmium on the epididymis of the cryptorchid rat.

Abstract: The short-term (90 min) effect of an intraperitoneal injection of cadmium chloride (3 mumol/100 g body weight) was studied with the electron microscope in the epididymis of mature rats rendered unilaterally cryptorchid 60 days before injection. It was found that the endothelium of the epididymal capillaries of the cryptorchid organ, at this low dose and short time, showed neither separation of cytoplasmic leaflets, nor platelet damage, nor extravasation, which are the lesions previously described by us and which were present in the contralateral, scrotal epididymis. The possible mechanisms for the protective action of cryptorchidism against the effects of cadmium on capillary endothelia are discussed.

The Parallel Transport of a Vector: Its Physical Meaning in Three Geometrical Unified Field Theories

Abstract: The physical interpretation of the parallel transport of a vector is analyzed in three classical geometric unified field theories: the theory of physical space and the theories of Weyl and Infeld. In physical space it is found to be a Fermi-Walker transport in the presence of electromagnetic interactions.