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Showing papers by "National University of Cuyo published in 1992"


Journal ArticleDOI
27 Mar 1992-Science
TL;DR: Results indicate that GTP-binding proteins are required for endosome fusion and in particular that a G protein is involved, and may provide insight into the mechanism by which endosomal vesicles become competent for fusion after their formation at the cell surface.
Abstract: Several steps in the transport of macromolecules along the endocytic and exocytic pathways are mediated by carrier vesicles. The mechanism by which vesicles recognize and fuse with the target compartment is poorly understood.

132 citations


Journal ArticleDOI
TL;DR: In this paper, the stability between the high temperature β phase and the 2H martensite was analyzed in single crystals of a high electron concentration around 1.52, and the equilibrium temperatures and entropy differences were determined.
Abstract: The stability between the high temperature β phase and the 2H martensite is analyzed in CuZnAl single crystals of a high electron concentration around 1.52. The results are compared with those deduced from previous reports, and the equilibrium temperatures and entropy differences are determined. A phenomenological model for the stress induced transformation explains well the observed crystallography.

46 citations


Journal ArticleDOI
TL;DR: In this article, the stability between the close packed martensitic structures 6R, 18R and 2H in CuZnAl single crystals is analyzed.
Abstract: The stability between the close packed martensitic structures 6R, 18R and 2H in CuZnAl single crystals is analysed. Experimental results for high electron concentrations (e/a > 1.50) and data from the literature for lower e/a are used, covering a wide range of compositions. Numerical values for the stacking fault energies and the differences of enthalpy are reported. The thermodynamic stability of the orthorhombic 18R structure with respect to 6R and 2H in a wide composition range is established.

35 citations


Journal ArticleDOI
TL;DR: Data suggest that POA is linked to the ipsilateral HPC through histaminergic influence to control behavioral patterns induced by novelty, and shows that HA in POA exerted an inhibitory influence on general motor behaviors and also on goal-directed activity.

16 citations


Journal ArticleDOI
TL;DR: Pachytenes display a regular geometric array of pore aggregation with striking clustering, whereas diplotene nuclear pores takes on a random distribution, whereas leptotene and zygotene spermatocytes show a more homogeneous distribution of nuclear pores.
Abstract: Transilluminated seminiferous tubules were staged and utilized to determine the distribution of nuclear pore complexes in seminiferous tubules of the rat. Segments of seminiferous tubules of adult albino rats were separated and identified (in stages VII–VIII, IX–XI, XII–XIV, and V–VI), and then processed by freeze-fracture. Type A spermatogonia, the only spermatogonia located in seminiferous segments possessing stages IX–XI and XII–XIV, are oval cells in contact with the basal lamina. They either exhibit a random distribution of nuclear pores or a slight degree of clumping. Type B spermatogonia, found in segments possessing stages V–VI, exhibit, instead, a noticeable pore clustering. The identification of intermediate spermatogonia was not undertaken in this study. Preleptotene spermatocytes are easily identified in freeze-fracture by their location in segments with stages VII–VIII, by their arrangement in numerous groups between the basal lamina and the pachytene spermatocytes, and by their comparatively small size. They exhibit noticeable pore clustering. Leptotene (segments containing stages IX–XI) and zygotene (XII–XIV) spermatocytes show a more homogeneous distribution of nuclear pores. Pachytene spermatocytes are identified by their large size, by consistent detachment from the basal lamina and by being rather numerous and found in all the stages explored. Diplotene spermatocytes have the largest nuclei of all germ cells. They are always detached from the basal lamina and found only in seminiferous segments containing stage XIII. Pachytenes display a regular geometric array of pore aggregation with striking clustering, whereas diplotene nuclear pores take on a random distribution. Secondary spermatocytes, only present in stage XIV intermingled with metaphaseanaphase profiles, are characterized in replicas by a paucity of evenly distributed nuclear pores.

10 citations


Journal ArticleDOI
TL;DR: In this paper, the authors consider four-dimensional string models obtained by tensoring N = 2 coset theories with noniagonal modular invariants and present results from a systematic analysis including moddings by discrete symmetries.
Abstract: We consider four-dimensional string models obtained by tensoring N=2 coset theories with nondiagonal modular invariants. We present results from a systematic analysis including moddings by discrete symmetries.

8 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a canonical transformation to eliminate the states containing Cu + and Cu +3 by means of a standard canonical transformation, and diagonalized the resulting effective Hamiltonian for a Cu 4 O 8 cluster with periodic boundary conditions, for zero and one added holes.

7 citations


Journal ArticleDOI
TL;DR: There exists a proteinic factor in the intestine of the vector that promotes metacyclogenesis and is incorporated by the parasite and the possible binding of the differentiation factor to the parasite surface was inhibited.

6 citations


Journal ArticleDOI
TL;DR: Results give support to the concept that PRL may have a regulatory role in CUS, as PRL levels in intact rats were low as expected and the C response due to CUS was significantly increased.
Abstract: The probable role of prolactin (PRL) on the behavioral responses evoked by chronic unpredictable stress (CUS) was studied in adult male rats. Three experiments were performed examining the effect of CUS on behavioral performance in: (i) intact rats with normal endogenous PRL levels, (ii) rats with high endogenous PRL levels, and (iii) rats with low endogenous PRL levels. Behavioral parameters studied were: locomotion, head-dipping, rearing and grooming. Endocrine parameters studied were: PRL and corticosterone (C) plasma concentrations. In Experiment (i) results showed that CUS inhibited significantly locomotion, head-dipping and rearing activity. No variations in PRL plasma levels were found but a significant increase in C was detected. In Experiment (ii) the hyperprolactinaemia induced by pituitary transplants in the kidney capsule blocked partially the inhibition of locomotion due to CUS. No modifications on head-dipping, rearing and grooming were observed. PRL levels in these rats were consistently high as expected and CUS regimen did not change the hormone concentrations in blood. The C response due to CUS, however was completely blocked in the pituitary-implanted group. In Experiment (iii), repeated treatment with bromocriptine (5 mg/kg i.p.) significantly increased the inhibitory effect of CUS on locomotion, head-dipping and rearing. Grooming was also decreased in CUS-treated rats. PRL levels in these animals was low as expected and the C response due to CUS was significantly increased. Results give support to the concept that PRL may have a regulatory role in CUS.

6 citations


Journal ArticleDOI
TL;DR: Nickel tracing proved to delineate cell contours more intensely and less interruptedly than lanthanum and to be more applicable to seasonal variations in adult galea.
Abstract: With the purpose of evaluating a new intercellular tracer, nickel-K ferrocyanide, we compared results yielded by lanthanum with information provided by nickel. This was done in the seminiferous epithelium of Holtzman rats of several postnatal ages and in a wild local seasonal breeder Galea musteloides. Tissues were studied with transmission electron microscopy and freeze-fracture replications. Nickel tracing proved to delineate cell contours more intensely and less interruptedly than lanthanum. With regard to seasonal variations in adult galea, the limits of the barrier were similar to those described in other mammals: spermatogonia, preleptotene, and leptotene spermatocytes were surrounded by the tracer in the basal compartment. The zygotenepachytenes were contained in the lumenal compartment and tracers were stopped at the inter-Sertoli cell tight junctions. During the inactive spermatogenic phase in winter, the seminiferous epithelium contained Sertoli cells and occasional germ cells, never beyond the spermatocyte stage. The tracer filled intercellular spaces, indicating that the barrier was incompetent. Some resting germ cells showed nuclear hyperchromasia, karyolysis, organelle loss, cell shrinkage, and cell fusion leading to a multinucleated cells. The inter-Sertoli tight junctions were scanty and had randomly oriented and discontinuous junctional strands. Moreover, inter-Sertoli cell gap junctions proliferated. During the active spermatogenic phase in summer, junctions were numerous. Their junctional strands were parallel to each other, and continuous.

5 citations


Journal ArticleDOI
TL;DR: In this paper, the stacking fault energy is reduced due to an additional lattice distortion which depends on the ordering energy of the f.c.t. lattice, and the stacking faults interact, leading to a small increase in energy.
Abstract: The close-packed martensitic phases in Cu–Zu–Al alloys can be described as an f.c.t. ordered lattice into which stacking faults are introduced. The stacking fault energy would be essentially the same as for the disordered α-phase, but is reduced due to an additional lattice distortion which depends on the ordering energy of the f.c.t. lattice. In the 2 H martensite with a stacking fault on each second plane, the stacking faults interact, leading to a small increase in energy. Thus, in these ordered martensites the stacking fault energy depends not only on the composition, but also on the ordering energy and on the lattice distortion associated with it. These observations can be relevant to understand the dislocation mobility in other f.c.t. long-range ordered alloys. Die dichtest gepackten Martensitphasen in Cu–Zn–Al-Legierungen konnen beschrieben werden als flachenzentrierte Strukturen, in die Stapelfehler eingefuhrt werden. Die Stapelfehlerenergie ware im wesentlichen dieselbe wie in der ungeordneten α-Phase, wenn sie nicht durch eine zusatzliche Gitterverzerrung, die von der Ordnungsenergie in der f.c.t. Struktur abhangt, vermindert wurde. Fur den 2 H-Martensit mit Stapelfehlern auf jeder zweiten Ebene mus noch eine Wechselwirkung zwischen Stapelfehlern berucksichtigt werden, die zu einer Energieerhohung fuhrt. In diesen geordneten Martensitstrukturen hangt die Stapelfehlerenergie nicht nur von der Legierungszusammensetzung, sondern auch von der Ordnungsenergie und der Gitterverzerrung ab. Diese Ergebnisse konnen unter Umstanden auch die Versetzungsbeweglichkeit in anderen geordneten Legierungen erklaren.