Showing papers by "National University of Cuyo published in 1993"

Elastic constants of the monoclinic 18R martensite of a CuZnAl alloy

Abstract: The sound velocities of 15 propagation modes in an 18R single crystal of a CuZnAl alloy have been measured by the pulse-echo method. The elasticity equations have been solved using a numerical selfconsistent procedure, and the values of the 13 elastic constants of this monoclinic structure have been determined.

Ne ionization induced by the impact of 106-keV/u H+ and 3He2+: Two-center effects on the soft-electron emission.

Abstract: We present an experimental study of the electron emission induced by the collisional ionization of Ne gas by 106-keV/u ${\mathrm{H}}^{+}$ and $^{3}\mathrm{He}^{2+}$ projectiles. Cross sections, doubly differential in electron energy ${\mathit{E}}_{\mathit{e}}$ and angle \ensuremath{\theta}, were measured throughout the ranges 0.5\ensuremath{\le}${\mathit{E}}_{\mathit{e}}$\ensuremath{\le}440 eV and 0\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}\ensuremath{\theta}\ensuremath{\le}180\ifmmode^\circ\else\textdegree\fi{}. We show that measurements at electron energies down to 0.5 eV were possible after a reduction of the physical extension of the gas target to a minimum. We find a remarkable dependence of the measured distribution of soft electrons with the extension of the target. We try a model according to which this effect is attributed to the scattering of electrons into the acceptance cone defined by the detector. Our measurements enable us to perform a quantitative analysis of the shape of the soft-electron peak. Contrary to current belief, this peak is found to be strongly asymmetric. The magnitude of this asymmetry is comparable to that of the cusp resulting from electron capture into the continuum. This puts into evidence that, also for these low-energy electrons, the interaction with the two Coulomb centers, projectile and residual target ion, is essential. By analyzing the ratio of the emission obtained with $^{3}\mathrm{He}^{2+}$ and ${\mathrm{H}}^{+}$, we also study the dependence of the doubly differential cross section on the projectile charge.

The post-quench vacancy behavior in β-CuZnAl alloy

Abstract: Positron lifetime spectroscopy is used to study the long time room temperature behavior of defects retained after quench in β-CuZnAl single crystals. Quenching treatments are made in a temperature range from 493 to 1073 K. The decay in the defect concentration with the aging time is attributed to the motion of vacancies to sinks. Assuming the sinks as dislocations, a dislocation density is derived. This density increases with increasing quenching temperature. We find that after long time aging all vacancies disappear for all Tq used in this work except for 773 K. This behavior is associated to the existence of γ-phase precipitates which are known to be present after quench from this temperature.

Seasonal changes of the blood-testis barrier in viscacha (Lagostomus maximus maximus) : a freeze-fracture and lanthanum tracer study

Abstract: Adult male viscachas (Lagostomus maximus maximus) were gathered from their natural habitat during the period of complete spermatogenesis (June) and during the month of maximum testicular regression (August). The testes were processed by conventional electron microscopic technique using lanthanum nitrate (electron-dense intercellular tracer) to define the intercellular spaces below the inter-Sertoli tight junctions and by freeze-fracture techniques. During complete spermatogenesis the tracer surrounds spermatogonia, preleptotene, and leptotene spermatocytes and stops at the level of the inter-Sertoli tight junctions below all germ cells displaying synaptonemal complexes (zygotene-pachytene spermatocytes) and germ cells in more advanced stages of differentiation. Conversely, during testicular regression the tracer percolates all intercellular spaces between Sertoli cells and the remaining germ cells (spermatogonia and few preleptotene and leptotene spermatocytes.) During complete spermatogenesis, freeze-fracture replicas exhibit numerous inter-Sertoli tight junction strands parallel to each other and to the basal lamina. During spermatogenesis decay, the inter-Sertoli tight junctions are found to be short, tortuous, frequently interrupted, and often associated with extented membranous areas of gap junctions. © 1993 Wiley-Liss, Inc.

Stimulation of H3-Histamine Receptors Increases the Release of Prolactin in Male Rats

Abstract: Histamine (HA) stimulates prolactin secretion via H1 and H2 receptors. In the present study, we examined the role of a third subtype of receptor recently described in brain, the H3-HA receptor, on prolactin secretion in male rats. R(-)alpha-methyl-HA (alpha-MHA), a selective H3 receptor agonist, was injected into the lateral ventricle of the brain in freely moving rats. alpha-MHA produced a dose-dependent (1-5 micrograms) and long-lasting increase in plasma prolactin levels. This increase was observed from 15 to 60 min after injection of alpha-MHA. Its stimulatory action was prevented by thioperamide (20 micrograms i.v.t), a selective H3 antagonist. This compound, injected intraventricularly, lacked effect by itself on basal plasma prolactin levels. Neither pyrilamine (H1 antagonist; 60 micrograms i.v.t.) nor ranitidine (H2 antagonist; 60 micrograms i.v.t.) affected alpha-MHA-induced prolactin release. The stimulatory effect was still present when brain HA was depleted by alpha-fluoromethylhistidine (30 mg/kg i.p.). Our findings suggest that alpha-MHA evokes prolactin release by activation of postsynaptic H3 receptors.

Modified Riccati approach to partially solvable quantum Hamiltonians. III. Related families of Pöschl-Teller potentials.

Abstract: Within the modified Riccati approach developed elsewhere, we construct quasiexactly solvable potentials related to the P\"oschl-Teller and modified P\"oschl-Teller potentials. This is achieved by considering closed-form wave functions whose logarithmic derivatives are rational in the mapping u(x)=cosh(x) or u(x)=cos(x). With the hyperbolic mapping we construct an interesting four-parameter quasiexactly solvable confining potential with one, two, or three minima upon the value of its coupling constants. We give explicit expressions for the bound-state eigenfunctions and corresponding energy levels for some particular cases. The analytic continuation x\ensuremath{\rightarrow}ix transforms the previous potential into a periodic confining well, or a Kronig-Penney-like potential with an interesting structure of minima in each cell and a finite number of gaps. The energy levels in the last case are some of the band edges of the spectrum. In any case a finite but arbitrarily large number of energy levels and corresponding eigenfunctions are determined from the diagonalization of a finite matrix.

On the quantization of the n = 2 supersymmetric nonlinear sigma model

Abstract: A method for quantizing the bidimensional N = 2 supersymmetric nonlinear sigma model is developed. This method is both covariant under coordinate transformations (concerning the order relevant for calculation) and explicitly N = 2 supersymmetric. The operator product expansion of the supercurrent is computed accordingly, including also the dilaton. By imposing the N = 2 superconformal algebra the equations for the metric and the dilaton are obtained. In particular, they imply that the dilaton is a constant.

Spontaneous splenic hypofunction in systemic lupus erythematosus and primary Sjögren syndrome

Abstract: UNLABELLED The objective of this study was to evaluate hyposplenism in autoimmune diseases by the presence of Howell-Jolly bodies in blood erythrocytes and 99Tc spleen scan. Blood smears of 174 patients with autoimmune diseases and 126 controls were studied. Other possible causes for the presence of Howell-Jolly bodies were excluded. Evidence of hyposplenism was demonstrated in 4 of 79 patients with Systemic Lupus Erythematosus (SLE) and in 2 of 18 cases of primary Sjogren Syndrome (PSS), whereas no hyposplenism was found in the remaining cases of other autoimmune diseases. In one of the patients with SLE, hyposplenism was transient. Among the control cases, a patient with Chronic Lymphocytic Leukemia with splenomegaly presented hyposplenism. IN CONCLUSION 1) Hyposplenism is more frequently found in SLE and PSS than in other autoimmune diseases. 2) Hyposplenism in autoimmune diseases can be transient. 3) Splenomegaly and enlarged spleen scan do not exclude hyposplenism.

Quantization of massive chiral electrodynamics reexamined.

Abstract: We show that the models considered by Andrianov et al. [Phys. Rev. Lett. 63, 1554 (1989); and Phys. Rev. D 44, 2602 (1991)] are equivalent to other models where it is easily proved that the anomaly decouples and consequently the value of the chiral triangles amplitude is irrelvant for the unitarity of the S matrix.

Renal functional reserve and microalbuminuria excretion in vesicoureteral reflux after surgery correction.

Abstract: The acute effect of an oral protein load on glomerular filtration rate-renal functional reserve (RFR)- and albumin urinary excretion were evaluated in 9 patients with bilateral vesicoureteral grade IV reflux after surgical correction (Group I) and the results compared with 9 children with repeated urinary infection without reflux (Group II) and 6 healthy controls of similar age (Group III). Intravenous urography, performed in the year of the study, revealed renal scarring in 10 kidneys in Group 1 and 2 in Group II. All of them had normal values of plasma creatinine. Basal inulin clearance was significantly lower in vesicoureteral reflux patients. Good correlation was found between parenchymal area of both kidneys and baseline inulin. Following protein load an increase in creatinine and inulin clearance was recorded in urinary infection and control children. No change post load was observed in reflux patients. Microalbuminuria excretion was significantly higher in children with surgical correction during the control period. No changes were observed after load in any of the groups. We conclude that patients who had had bilateral vesicoureteral reflux grade IV showed an impaired renal response to a protein load. Long-term follow-up studies will confirm the value of this test for estimating the risk of further renal function deterioration in reflux nephropathy.

Neutron detection system for extremely low count rate calculation, construction and employment in search for “cold fusion”

Abstract: A 22% efficiency thermal neutron detection system was designed for the investigation of neutron emission from pulsed D2O electrolysis. Reasons are discussed for the choice of 10 atm 3He proportional counters. Optimization calculations carried out through standard reactor code system (AMPX-II) are presented along with construction details and characteristics of the associated electronics. Experimental verification of calculated efficiency and examples of measurements performed with the detector are included.

Seropositive polyarthritis as a presentation form of angioimmunoblastic lymphadenopathy

Abstract: We present a 59-year-old male who was admitted due to fever and generalized lymphadenopathy. The patient had polyclonal hypergammaglobulinemia, Coombs-positive anemia, positive rheumatoid factor (latex 1:1280-SCAT 1:128), hypocomplementemia, negative LE cells and FAN negative. He had a 2 months history of a rheumatoid arthritis-like polyarthritis with poor response to non-steroid antiinflammatory drugs. On physical examination a mild symmetrical polyarthritis of small and large joints was seen. A lymph node biopsy showed architectural effacement, absence of germinal centers, arborization of postcapillary venules and a polymorphonuclear infiltrate that included immunoblasts. Thus, this patient fulfills the morphologic criteria of angioimmunoblastic lymphadenopathy (AILD) (Fig. 1 and 2). Our purpose was to describe the association of seropositive polyarthritis with AILD as a presentation sign. Whether this represents a case of a rheumatoid arthritis with AILD or the polyarthritis which has been described as part of the clinical picture or AILD is difficult to say due to the short time evolution of the disease.

Nondiagonal CP(m) coset models and their Poincare polynomials

Abstract: N = 2 coset models of the type SU(m + 1)/SU(m) × U(1) with nondiagonal modular invariants for both SU(m + 1) and SU(m) are considered. Poincare polynomials of the the number of chiral generations of the associated string compactifications. Moddings corresponding chiral rings of these algebras are constructed. They are used to compute the number of chiral generations of the associated string compactifications. Moddings by discrete symmietries are also discussed.