Showing papers by "National University of Cuyo published in 1995"
TL;DR: In this article, a model that has been shown to undergo a purely noise induced transition, from a monostable regime to a bistable one, when it is submitted to a white or colored noise source is analyzed.
Abstract: We analyze a model that has been shown to undergo a purely noise induced transition, from a monostable regime to a bistable one, when it is submitted to a white or colored noise source. We show, using a consistent interpolating Markovian approximation for the colored noise case, that for large values of the correlation time, the system undergoes a new transition to a monostable state, indicating a reentrancelike phenomenon in its phase diagram. Numerical results support our findings.
74 citations
TL;DR: In this article, the dependence of the pair interchange energies on the composition of alloy compositions along the ternary phase diagram is investigated, together with other data taken from the literature, are analyzed in terms of a model, based on the pair exchange energies, developed by Ahlers.
Abstract: The Cu-Mn-Al alloys exhibit, in a certain range of composition, an A2 (BCC) phase which is stable at high temperatures (around 1,050 K). Two ordering reactions take place on lowering the temperature A2 {yields} B2 and B2 {yields} L2{sub 1}, with a distribution of antiphase domains. Spinodal decomposition can be found in the as quenched specimen for some compositions, as shown by Sato et al. In addition a martensitic transformation can also occur, with an Ms strongly dependent on the composition. In this work the dependence of the Ms on composition is investigated, for alloy compositions along the Cu{sub 3} Al-Cu{sub 3}Mn{sub 2} line of the ternary phase diagram. The results, together with other data taken from the literature, are analyzed in terms of a model, based on the pair interchange energies, developed by Ahlers.
51 citations
TL;DR: A comprehensive method for BoNTs typing is proposed based on the in vivo response expected on quantitative BoNT-antitoxin systems and the actual and the hypothetical antigenic makeup of BoNT subtypes.
44 citations
TL;DR: It is reported that fusion can proceed at very low Ca2+ concentrations, and evidence is presented that Zn2+ depletion blocks endosome fusion, suggesting that this ion is necessary for the function of one or more factors involved in the fusion process.
Abstract: Fusion among endosomes is an important step for transport and sorting of internalized macromolecules. Working in a cell-free system, we previously reported that endosome fusion requires cytosol and ATP, and is sensitive to N-ethylmaleimide. Fusion is regulated by monomeric and heterotrimeric GTP-binding proteins. We now report that fusion can proceed at very low Ca2+ concentrations, i.e. < 30 nM. Moreover, fusion is not affected when intravesicular Ca2+ is depleted by preincubation of vesicles with calcium ionophores (5 microM ionomycin or A23187) in the presence of calcium chelators (5 mM EGTA or 60 mM EDTA). The results indicate that fusion can proceed at extremely low concentrations of intravesicular and extravesicular Ca2+. However, BAPTA [1,2-bis-(o-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid], a relatively specific Ca2+ chelator, inhibits fusion. BAPTA binds other metals besides Ca2+. We present evidence that BAPTA inhibition is due not to Ca2+ chelation but to Zn2+ depletion. TPEN [N,N,N',N'-tetrakis-(2-pyridylmethyl) ethylenediamine], another metal-ion chelator with low affinity for Ca2+, also inhibited fusion. TPEN- and BAPTA-inhibited fusions were restored by addition of Zn2+. Zn(2+)-dependent fusion presents the same characteristics as control fusion. In intact cells, TPEN inhibited transport along the endocytic pathway. The results indicate that Zn2+ depletion blocks endosome fusion, suggesting that this ion is necessary for the function of one or more factors involved in the fusion process.
36 citations
TL;DR: Results suggest that HA may be involved in memory retrieval processes in the hippocampus and showed that HA increased significantly the LT and this effect was grossly dose-dependent.
Abstract: The possible role of histamine (HA) locally applied into the hippocampus on memory mechanisms of the rats was studied. The acquisition of a one-way active avoidance response to an ultrasonic 40 kHz sinus-wave tone anticipating an electric shock was used as experimental model. Learning sessions consisted in placing animals into a two compartment cage were they learnt to escape to the safe compartment after an ultrasonic tone anticipating an electric feet shock. After acquiring the conditioned avoidance response, animals were implanted with microinjection cannulae and injected with 1 μl of saline, or increasing doses of histamine (9, 22.5, 45, and 90nmol) into the hippocampus. In the experimental sessions, 4 trials before (PRE) and 4 trials afterward treatment (POST), the percentage of conditioned avoidance responses (% CAR) and the latency time to escape (LT) were measured. Results showed that HA increased significantly the LT and this effect was grossly dose-dependent. % CAR was also affected and the score was significantly inhibited by the imidazolamine administration. Results suggest that HA may be involved in memory retrieval processes in the hippocampus.
33 citations
TL;DR: A piecewise linear version of a one-component, one-dimensional reaction-diffusion bistable model is studied, with the aim of analyzing the effect of boundary conditions on the formation and stability of stationary patterns.
Abstract: We study a piecewise linear version of a one-component, one-dimensional reaction-diffusion bistable model, with the aim of analyzing the effect of boundary conditions on the formation and stability of stationary patterns. The analysis proceeds through the study of the behavior of the Lyapunov functional in terms of a control parameter: the reflectivity at the boundary. We show that, in this example, this functional has a very simple and direct geometrical interpretation.
31 citations
TL;DR: In this paper, the major GA-like substance in roots of potato cuttings was identified as GA3 by gas-chromatography-mass spectrometry (GC-MS), which might be the root factor responsible for delaying tuberization in potato.
Abstract: Cuttings of potato shoots treated with the plant growth retardant 2-chloroethyltrimethyl ammonium chloride (CCC) form tubers earlier and have less biologically-active gibberellin (GA)-like substances in the roots than control cuttings. The major GA-like substance in roots of potato cuttings was identified as GA3 by gas-chromatography-mass spectrometry (GC-MS). The content of GA3 in roots of control cuttings, estimated by GC-MS-selected ion monitoring (SIM) using [17, 17-2H]GA3 as a quantitative internal standard, was 38.8 ng per g fresh weight (fw), and in roots of CCC-treated cuttings, in which tuberization was promoted, was 0.6 ng per g fw. Gibberellin A1, GA8 and GA20 were also indicated as minor components of roots from both control and CCC-treated cuttings. The comparatively high GA3 content in roots of control cuttings might be the ‘root factor’ responsible for delaying tuberization in potato.
22 citations
TL;DR: This paper presents a theory for the absorption probability density for a walker in the presence of a dynamic trap by using the multistate continuous-time random-walk approach, finding excellent agreement for symmetric and nonsymmetric switching-time densities.
Abstract: There have been a number of recent investigations of diffusing particles in the presence of traps. Among many applications of this process, we find phenomena such as reaction rates, biological models, and dielectric relaxation. In this paper we present a theory for the absorption probability density for a walker in the presence of a dynamic trap by using the multistate continuous-time random-walk approach. The results are exact for every switching-time probability density of the trap. The deterministic and Markovian cases can be obtained by selecting the appropriate switching-time density for the trap. Siegert's result is reobtained in the static case. We perform Monte Carlo simulations, and compare these results with our analytical prediction, finding excellent agreement for symmetric and nonsymmetric switching-time densities.
20 citations
TL;DR: It is demonstrated that beta-glucuronidase from rat preputial glands binds with high affinity to spermatozoa from the cauda epididymis, and the existence of phosphomannosyl receptors on the sperm plasma membrane suggests strongly that maturing spermutozoa could be a target for glycosidases secreted into the lumen of the cauds, which then become bound to these cells via different ligand-receptor systems.
Abstract: Summary
This study demonstrates that β-glucuronidase from rat preputial glands binds with high affinity to spermatozoa from the cauda epididymis. The binding was calcium-independent and was inhibited by mannose-6-phosphate, but not by other phosphorylated or non-phosphorylated sugars. Binding was also inhibited by α-mannosidase from Dictyostelium discoideum, an enzyme known to have mannose-6-phosphate as the ligand. From solubilized sperm membranes, a protein of >200 kDa and one of 45 kDa, were adsorbed to a column of D. discoideum enzyme and to a phosphomannan column respectively, and eluted with mannose-6-phosphate. According to histochemical observations at the light and the electron microscopic level, gold particles coated with the enzyme became bound to the external surface of the plasmalemma in the acrosomal region of caudal spermatozoa. Similar labelling was observed using gold particles coated with antibodies against the rat 300 kDa phosphomannosyl receptor. The existence of phosphomannosyl receptors on the sperm plasma membrane, and our previous demonstration of the presence of affinity sites for epididymal β-galactosidase on these gametes which is inhibited by phosphofructosyl derivatives, suggest strongly that maturing spermatozoa could be a target for glycosidases secreted into the lumen of the cauda epididymis, which then become bound to these cells via different ligand-receptor systems.
15 citations
TL;DR: The results indicate that activation of heterotrimeric GTP-binding proteins is sufficient to trigger acrosome exocytosis in human spermatozoa.
Abstract: Summary
The acrosome reaction is a specialized exocytotic process. In the mouse there is compelling evidence that receptor-mediated activation of GTP-binding proteins by factors in the zona pellucida of oocytes is a central event in the acrosome reaction. Several reagents are able to affect GTP-binding proteins directly, bypassing the receptor–ligand step for activation. We have assessed the effect of several of these compounds on human spermatozoa, monitoring cell vitality and the acrosome reaction simultaneously using the triple-stain technique. GTPγS and aluminium fluoride complexes promote sperm activation very efficiently; amphiphilic peptides capable of activating Go and Gi, also elicit the acrosome reaction. The results indicate that activation of heterotrimeric GTP-binding proteins is sufficient to trigger acrosome exocytosis in human spermatozoa.
12 citations
21 Apr 1995-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, the total cross section of Teflon has been measured for energies between 3.8 × 10 −4 eV and 5.9 × 10 2 eV by the transmission method with pulsed neutron time-of-flight techniques.
Abstract: The neutron total cross section of Teflon has been measured for energies between 3.8 × 10 −4 eV and 5.9 × 10 2 eV by the transmission method with pulsed neutron time-of-flight techniques. In order to cover that wide energy range, two independent measurements were performed on samples with different thicknesses and employing as neutron moderator a conventional polyethylene slab for the epithermal region and a liquid nitrogen cooled paraffin block for the cold/thermal region. Due to some inhomogeneities in the sample material, the transmission data were normalized using the best available values of the scattering lengths and incoherent cross sections for carbon and fluorine.
TL;DR: In this paper, the EPR and magnetization for Gd2BaNiO5 single crystals were reported and the high-temperature susceptibility gave μeff = 79μB/mol Gd and ΘGd = 11 K (JGdGd/kB = 06 K).
TL;DR: The results suggest that some hydrolytic enzymes—specific for each species—are hormone dependent in the epididymis and may play a role in the processing of cell surface glycoproteins of maturing spermatozoa and in the involution of the epidIDymis during the period of sexual inactivity.
TL;DR: The results suggest that the FPR-binding system belongs to a peculiar transport route that permits maturing spermatozoa to acquire hydrolytic enzymes secreted by the epididymal epithelium.
Abstract: This study reports on the binding of beta-galactosidase obtained from different organs of the rat urogenital tract to membranes of these organs. Homologous and cross binding saturation assays indicated that: (1) high-affinity sites that recognize fructose-6-phosphate derivates (FPR) are present in spermatozoa from the rete testis, epididymal membranes and testes, although the latter may reflect binding to testicular spermatozoa; (2) the membranes of the other organs studied do not have FPR; (3) the FPR of the epididymis does not recognize enzymes purified from other organs of the reproductive tract. These results suggest that the FPR-binding system belongs to a peculiar transport route that permits maturing spermatozoa to acquire hydrolytic enzymes secreted by the epididymal epithelium. In the epididymis and seminal vesicles more than 50% of the enzymatic activity of beta-galactosidase was recovered in cytosol, suggesting that the enzyme is located mainly in the secretory fluid of these organs.
TL;DR: In this paper, cyclic permutation symmetries are applied to four-dimensional strings, built from N=2 coset models of the type CPm = SU(m+1)/[SU(m)×U(1)].
Abstract: Moddings by cyclic permutation symmetries are performed on four-dimensional strings, built from N=2 coset models of the type CPm=SU(m+1)/[SU(m)×U(1)]. For some illustrative cases, the massless chiral and antichiral states of E6 are computed. The extent of the equivalence between different conformal invariant theories which possess equal chiral rings is analyzed.
TL;DR: Experimental results strongly support the hypothesis of an independent ``saddle-point'' ionization mechanism for intermediate ion-atom collision velocities and suggest that they may have observed a remnant of convoy-cusp electrons, which subsists at an emission angle of 10\ifmmode^\circ\textdegree\fi{}.
Abstract: Irby et al. [Phys. Rev. A 47, 2957 (1993)] claim that their experimental results, obtained with ${\mathrm{C}}^{+}$, ${\mathrm{C}}^{2+}$, and ${\mathrm{C}}^{3+}$ projectiles on He and Ne targets, strongly support the hypothesis of an independent ``saddle-point'' ionization mechanism for intermediate ion-atom collision velocities. They state that in previous measurements, in which single-stage electron analyzers were used, this process has been obscured by reflected and secondary electrons. We present experimental evidence that this effect exists, but is insignificant. We suggest that they may have observed a remnant of convoy-cusp electrons, which subsists at an emission angle of 10\ifmmode^\circ\else\textdegree\fi{}.
TL;DR: It is suggested that either local enzyme immaturity or the abdominal temperature (5 degrees C than scrotal temperature) may protect zinc enzymes against displacement by cadmium.
Abstract: Ninety minutes after i.p. injection of 3 mumol of cadmium chloride/100 g body weight into immature, 15 day-old rats, the endothelial intercellular junctions of the caput epididymis capillaries showed none of the lesions such as loss of junctional associated ectoplasmic microfilaments, separation of interdigitated leaflets, disassembling of interendothelial tight junctions, passage of blood plasma and cells into the pericapillary space, platelet clumping and disintegration, and intracapillary clotting, which after the same dose are found in sexually mature rat epididymides. The resistance of the immature, physiologically intraabdominal epididymal capillary endothelium reminds one of the protection against cadmium that is brought about by surgical cryptorchidism in adult mature rats. We suggest that either local enzyme immaturity or the abdominal temperature (5 degrees C than scrotal temperature) may protect zinc enzymes against displacement by cadmium.
Journal Article•
TL;DR: The utilization of hospitalization criteria together with the risk factors for a complicated course, specifically when two or more factors per patient are present, permit the identification of a population with CAP that needs hospitalization with 71.4% sensitivity and 100% specificity.
Abstract: To evaluate the admission criteria and to select indicators that identify patients for whom hospitalization is not necessary, we studied 75 patients with community acquired pneumonia (CAP) who were admitted to a clinical service. According to Appropriateness Evaluation Protocol (AEP) only 60% of our patients justified their hospitalization (Group A) while 40% did not (Group B). The most frequent hospitalization criteria found in Group A were tachypnea (> 30x min.) (40%), respiratory failure (38%) and encefalopathy (18%). The average age in Group A was 62 versus 47 in Group B (p < 0.001). Comorbid conditions were present in 100% of Group A and 71% had two or more while only 33% of patients in Group B had two or more (p < 0.01). During the evolution, Group A had more organ failure than B (53 vs. 17%) (p < 0.001) and a longer period of hospitalization (14 vs. 9 days) (p < 0.01). The differences between groups A and B is best visualized in the incidence of sepsis (4 vs. 0%), and mortality rates (15% vs. 0%) (p < 0.05). Using the Fine risk criteria for a complicated course, we selected 14 patients from Group B, with one or more criteria (Group C) that were compared with 16 patients without them (Group D). The presence of a poor clinical status at admission was the only difference between Group D and C (79 vs. 0%) (p < 0.001). When three or more risk factors were present the differences were significant (79 vs. 6%) (p < 0.001). We conclude that the utilization of hospitalization criteria together with the risk factors for a complicated course, specifically when two or more factors per patient are present, permit the identification of a population with CAP that needs hospitalization with 71.4% sensitivity and 100% specificity. The presence of two or less risk factors in patients without admission criteria has a highly predictable negative value (100%) and anticipates an uneventful evolution without complications.
TL;DR: The activity of five acid hydrolases in the adrenal gland at the perinatal stage in adult rats was measured here and changes in alpha-mannosidase and N-acetyl-beta-D- glucosaminidase activity were detected, suggesting that the enzymatic activity and development of the Adrenal gland may be correlated during the first week after birth.
TL;DR: The present results suggest that in the rat AD might modulate the hippocampal-mediated expression of some motor and stereotyped behaviours induced by unknown environments.
Abstract: The possible effects of Adenosine (AD), locally applied into the ventral Hippocampus (HPCv) on the expression of general motor activity and some stereotyped behaviours were studied in adult male rats. Locomotion display was recorded in a hole-board equiped with automatic infrared animal activity detectors. Stereotyped behaviours were measured by direct inspection by two observers. Animals were implanted with microinjection cannulae into the HPCv and 72 h later they were injected with saline, or increasing doses of AD. In one experiment rats were microinjected once with saline or Adenosine and general motor activity and exploration were examined. In other experiment, rats were injected into the HPCv twice with saline, the AD-receptors antagonist 1,3-dipropil-methyl-xanthine (DMX) or AD and only stereotyped behaviours were examined. Results of Experiment 1 showed that the 40 nMol dose of AD was significantly effective to inhibit by about 30% several motor activities such as vertical, horizontal and ambulatory behaviours. Results of Experiment 2, showed that grooming was not modified by AD but the dose of 10 nMol increased the time of immobility by about 3 times over controls. DMX was able to block completely the AD effects on immobility. The present results suggest that in the rat AD might modulate the hippocampal-mediated expression of some motor and stereotyped behaviours induced by unknown environments.
TL;DR: In this paper, different electroweak strings with axionic content, including non-topological configurations calculated numerically, were described and shown their possible influence on baryogenesis indicating that they may constitute a mechanism competitive to that of bubble nucleation with two Higgs-doublets.
Abstract: We describe different electroweak strings with axionic content, including non-topological configurations calculated numerically, and show their possible influence on baryogenesis indicating that they may constitute a mechanism competitive to that of bubble nucleation with two Higgs-doublets.
TL;DR: In this article, a path integral representation of the probability density and the use of an influence functional are proposed for the nonadiabatic elimination of variables in stochastic processes, based on the path integral model.
Abstract: We present a novel scheme for the non-adiabatic elimination of variables in stochastic processes, based on a path integral representation of the probability density and the use of an influence functional. We analyze in particular the case of multivariate Fokker-Planck equations, or equivalently a set of coupled Langevin equations driven by white noises, and discuss some examples where exact or approximate results are obtained.
01 Dec 1995
TL;DR: Rat brain tubulin in a proper buffered solution became insoluble in the presence of 10 mM NiCl2, and sedimented at centrifugal forces as low as 500 x g for 30 min, and both nickel-sedimented and microtubular tubulin conserved 65% of colchicine binding activity after 25 days of storage at -20 degrees C.
Abstract: Rat brain tubulin in a proper buffered solution became insoluble in the presence of 10 mM NiCl2, and sedimented at centrifugal forces as low as 500 x g for 30 min. Both nickel-sedimented and microtubular tubulin conserved 65% of colchicine binding activity after 25 days of storage at -20 degrees C. However in brain cytosol, only 9% of the initial binding activity was conserved. The electrophoretic mobility of tubulin recovered from aggregates also remained unaltered. Therefore the aggregates formed with Ni2+ share important physicochemical properties with microtubules.
TL;DR: In this article, the chiral Wess-Zumino term was constructed as a solution for the Batalin-Vilkovisky master equation for anomalous two-dimensional gauge theories, working in an extended field-antifield space.
Abstract: We construct the chiral Wess-Zumino term as a solution for the Batalin-Vilkovisky master equation for anomalous two-dimensional gauge theories, working in an extended field-antifield space, where the gauge group elements are introduced as additional degrees of freedom. We analyze the Abelian and the non-Abelian cases, calculating in both cases the BRST generator in order to show the physical equivalence between this chiral solution for the master equation and the usual (nonchiral) one.
01 Jan 1995
TL;DR: Recent data suggest that heterotrimeric G proteins and monomeric GTP-binding proteins are involved in endosome-endosome fusion and in endocytic transport.
Abstract: GTP-binding proteins or GTPases are versatile cyclic molecular switches (Gilman, A.G. 1987 ; Bourne et al., 1990, 1992). In the past few years there has been an explosion of interest in unraveling the role of GTPases in membrane traffic (Balch et al., 1990; Bourne, H.R., 1988). GTP-binding proteins are classified into two broad families: ras-like monomeric GTP-binding proteins and the heterotrimeric G proteins. Evidences from genetics, immunolocalization, and functional assays has established that two subfamilies of monomeric GTP-binding proteins, the Rab and ARF subfamilies, are required for membrane traffic (Pfeffer, S.R., 1992; Rothman, J.E. and Orci, L., 1992). More recently, attention has turned to the role of heterotrimeric G proteins in membrane traffic (Balch et al., 1992; Barr et al., 1992). This review will focus solely on the recent data that suggest that heterotrimeric G proteins and monomeric GTP-binding proteins are involved in endosome-endosome fusion and in endocytic transport.
TL;DR: In this paper, an EPR study on the Nd 2− x Sr x NiO y system with 0 ≤ x ≤ 0.6 at 100 ≤ T (K) ≤ 500.
Abstract: We present an EPR study on the Nd 2− x Sr x NiO y system with 0 ≤ x ≤ 0.6 at 100 ≤ T (K) ≤ 500. Samples were prepared by the ceramic method and reduced in a thermogravimetric balance. Three series were studied: (a) air-prepared samples containing Ni 2+ and Ni 3+ , (b) reduced samples in which Ni 2+ and Ni 1+ coexist, and (c) reduced single valence Ni 2+ samples. No EPR signal was observed in the oxidized samples. For the reduced samples, a correlation between the EPR intensity and the oxygen content was found.