Showing papers by "National University of Cuyo published in 2000"

Analytical modelling of infilled frame structures

Abstract: The analytical modelling of infilled frames is a complex issue because these structures exhibit a highly non- linear inelastic behaviour resulting from the interaction of the masonry infill panel and the surrounding frame. This paper presents a general review of the different procedures used for the analysis of infilled frames, which can be grouped in local or micro-models and simplified or macro-models, depending on the degree of refinement used to represent the structure. The finite element formulation and the equivalent truss mechanism are the typical examples of each group. The advantages and disadvantages of each procedure are pointed out, and practical recommendations for the implementation of the different models are indicated.

Intracellular Trafficking of Brucella abortus in J774 Macrophages

Abstract: Brucella abortus is a facultative intracellular bacterium capable of surviving inside professional and nonprofessional phagocytes. The microorganism remains in membrane-bound compartments that in several cell types resemble modified endoplasmic reticulum structures. To monitor the intracellular transport of B. abortus in macrophages, the kinetics of fusion of phagosomes with preformed lysosomes labeled with colloidal gold particles was observed by electron microscopy. The results indicated that phagosomes containing live B. abortus were reluctant to fuse with lysosomes. Furthermore, newly endocytosed material was not incorporated into these phagosomes. These observations indicate that the bacteria strongly affect the normal maturation process of macrophage phagosomes. However, after overnight incubation, a significant percentage of the microorganisms were found in large phagosomes containing gold particles, resembling phagolysosomes. Most of the Brucella bacteria present in phagolysosomes were not morphologically altered, suggesting that they can also resist the harsh conditions prevalent in this compartment. About 50% colocalization of B. abortus with LysoSensor, a weak base that accumulates in acidic compartments, was observed, indicating that the B. abortus bacteria do not prevent phagosome acidification. In contrast to what has been described for HeLa cells, only a minor percentage of the microorganisms were found in compartments labeled with monodansylcadaverine, a marker for autophagosomes, and with DiOC6 (3,3′-dihexyloxacarbocyanine iodide), a marker for the endoplasmic reticulum. These results indicate that B. abortus bacteria alter phagosome maturation in macrophages. However, acidification does occur in these phagosomes, and some of them can eventually mature to phagolysosomes.

Calcium-triggered acrosomal exocytosis in human spermatozoa requires the coordinated activation of Rab3A and N-ethylmaleimide-sensitive factor

Abstract: The acrosome reaction of spermatozoa is a complex, calcium-dependent, regulated exocytosis. Fusion at multiple sites between the outer acrosomal membrane and the cell membrane causes the release of the acrosomal contents and the loss of the membranes surrounding the acrosome. However, very little is known about the molecules that mediate and regulate this unique fusion process. Here, we show that N-ethylmaleimide-sensitive factor (NSF), a protein essential for most fusion events, is present in the acrosome of several mammalian spermatozoa. Moreover, we demonstrate that calcium-dependent exocytosis of permeabilized sperm requires active NSF. Previously, we have shown that the addition of the active (GTP-bound) form of the small GTPase Rab3A triggers exocytosis in permeabilized spermatozoa. In the present report we show that Rab3A is necessary for calcium-dependent exocytosis. The activation of Rab3A protects NSF from N-ethylmaleimide inhibition and precludes the exchange of the endogenous protein with recombinant dominant negative mutants of NSF. Furthermore, Rab3A activation of acrosomal exocytosis requires active NSF. Our results suggest that, upon calcium stimulation, Rab3A switches to its active GTP-bound form, triggering the formation of a protein complex in which NSF is protected. This process is suggested to be an essential part of the molecular mechanism of membrane fusion leading to the release of the acrosomal contents.

Rab3A triggers the acrosome reaction in permeabilized human spermatozoa

Abstract: The acrosome reaction is a regulated exocytotic process leading to a massive fusion between the outer acrosomal membrane and the cell membrane. In spite of the great amount of information available related to the acrosome reaction in several species, there is a remarkable paucity about the role of monomeric guanosine triphosphatases (GTPases) of the Rab family—wellestablished participants in exocytosis in other cell types—in the acrosome reaction. Western blot and immunofluorescence analysis indicate that Rab3A is present in human spermatozoa and localizes to the acrosomal region in the sperm head. One difficulty in studying the role of proteins in intact cells is the fact that they are unable to cross the cell membrane. Therefore, we established a working model of streptolysin O-permeabilized human spermatozoa. Permeabilized spermatozoa were able to respond in a regulated way to different stimuli, such as G protein activators and calcium. An acrosomal reaction was also triggered by a Rab3A peptide corresponding to the effector region. More important, recombinant Rab3A protein in the GTP-bound form caused acrosome exocytosis. The same protein loaded with GDP or Rab11 in the GTP-bound form was inactive. Also, recombinant GDI (GDP dissociation inhibitor)—a protein that releases Rab proteins from membrane—inhibited a GTPgS-stimulated acrosome reaction. Our results indicate that 1) permeabilized spermatozoa can be used to study the role of macromolecules in the acrosome reaction, 2) Rab3A is present in human spermatozoa, and 3) Rab3A or another Rab3 isoform is involved in the exocytosis of the acrosomal granule in human spermatozoa.

The dileucine motif within the tail of MPR46 is required for sorting of the receptor in endosomes.

Abstract: The cytoplasmic tail of MPR46 carries a leucine-based motif that is required for the sorting of lysosomal enzymes by the receptor. In addition, it is one of three independent, but functionally redundant, internalization signals present in the cytoplasmic tail of MPR46. We have analyzed a mutant of MPR46, in which the dileucine pair was replaced by alanines (MPR46 LL/AA) with respect to its intracellular distribution and trafficking. Ultrastructural analysis of cells expressing the MPR46 LL/AA mutant revealed that the substitution of the dileucine pair causes a shift of the receptor distribution from the TGN, where it is packaged into AP1-containing vesicles, to vesicular structures distributed throughout the cytoplasm. The vesicles could be identified as early endosomes with internalized BSA-gold and rab5 as markers. By analyzing the receptor trafficking biochemically, we found that return of the LL/AA mutant receptor from the plasma membrane/endosome pool back to the TGN was impaired, while recycling from endosomes to the plasma membrane was enhanced. In conclusion, our data indicate that the dileucine motif in the MPR46 tail is required for a sorting event in endosomes.

Classification of wild tomatoes: a review

Abstract: Wild tomatoes are native to western South America. The generic status of wild tomatoes within the Solanaceae has been controversial since the eighteen century. Linnaeus in 1753 placed tomatoes in Solanum while Miller, a contemporary ofLinnaeus, classified tomatoes in a new genus Lycopersicon. The majority of later botanists have followed Miller. Differing numbers of species and conflicting supraspecific classifications have been proposed, based on morphology or crossing studies. Two major crossability groups have been identified, one that includes mainly self-compatible species that easily cross with the cultivated tomato, and another that comprises self-incompatible species not easily cross with the cultivated tomato. Recent molecular investigations using appropriate outgroups have shown that tomatoes and potatoes are close related phylogenetically, and support the inclusion of tomatoes within Solanum, the classification advocated here. We discuss the conflicting goals of classifications based on predictivity versus stability, a continuing controversy in systematics.

The sesquiterpene lactone dehydroleucodine (DhL) affects the growth of cultured epimastigotes of Trypanosoma cruzi.

Abstract: Here,we report an inhibitory effect of a sesquiterpene lactone dehydroleucodine (DhL) on the growth of Trypanosoma cruzi in culture. At concentrations of the drug between 5 and 10 µg/ml in the medium,the parasites remained alive for at least 4 days. Higher concentrations of DhL were lethal for the parasites within a few hours. The effect of DhL is irreversible. Morphological changes induced by DhL were also observed in the parasites. The effect of DhL was blocked by the presence of reducing substrates such as glutathione or dithiothreitol, but these agents were not able to reverse the effect of DhL if added 2 days after the start of drug exposure.

Calorimetry in Cu–Zn–Al alloys under different structural and microstructural conditions

Abstract: Calorimetric measurements have been carefully performed on four kinds of Cu–Zn–Al samples, arising from the combination of different martensitic structures and from the presence or not of grain boundaries. The differences found in the transformation behaviour, characteristic transformation temperatures and in the corresponding thermodynamic properties (enthalpy and entropy changes) have been analyzed. The remarkable finding was that the transformation to 2H in the polycrystalline samples couldn’t go on completion. On the other hand, this behaviour was not observed for the transition to 18R, within the experimental scatter.

Colloid in the pituitary pars distalis of viscacha (Lagostomus maximus maximus): ultrastructure and occurrence in relation to season, sex, and growth.

Abstract: Randomly distributed extracellular colloidal accumulations were observed in the pars distalis of viscacha (Lagostomus maximus maximus). They were preferentially located in the peripheral zone of the gland and showed variability in shape and size. Two different types of colloidal accumulations were found by electron microscopy: 1) those surrounded by nongranulated follicular cells that correspond to characteristic follicles, and 2) those surrounded by granulated cells. In the follicles lined by nongranulated follicular cells, long, prominent microvilli and cytoplasmic processes protruded into the lumen. The frequency of these accumulations varies during the year in adult male animals, showing an increase in number during summer and a decrease during winter. The lowest value was registered in August (winter). The mean follicular diameter did not vary seasonally. The number of colloidal accumulations did not vary seasonally in adult female viscachas, but a significant difference in the mean follicular diameter between pregnant and non-pregnant females was observed. Pituitaries of immature animals contain fewer colloidal accumulations than those of adults. In fetuses, these accumulations were absent. The administration of melatonin provoked a decrease in the number of these structures. The numeric changes of the colloidal accumulations observed in this study are associated with: 1) the seasonal reproductive activity in adult males, and 2) the reproductive condition, body weight and sexual maturity in males and females. The fact that melatonin administration decreases the population of colloidal accumulations in males suggests participation of the pineal gland in these changes.

Constitutive expression of heat shock proteins hsp25 and hsp70 in the rat oviduct during neonatal development, the oestrous cycle and early pregnancy.

Abstract: Certain heat shock proteins are regulated by steroid hormones and are associated with oestrogen receptor function in reproductive tissues, indicating that these proteins have a role during implantation, decidualization and placentation. In the present study, the expression of hsp25, hsp70 and oestrogen receptor α were examined by immunohistochemistry in oviducts from rats during neonatal development, the oestrous cycle and during early pregnancy. Oestrogen receptor α was the first protein observed in the neonatal oviduct, and its expression preceded that of hsp70 and hsp25. Although these heat shock proteins have been associated with the oestrogen receptor, this study showed that during early development of the oviduct, the receptor protein was not associated with the concomitant expression of hsp25 and hsp70. However, these heat shock proteins were expressed when oviductal cells became differentiated. In the adult oviduct, hsp70 was more abundant than hsp25, moreover, there were no significant modifications in expression of hsp25 during the oestrous cycle. In contrast, the expression of hsp70 was significantly higher in epithelial cells during dioestrus, when the maximum amount of oestrogen receptor α was also observed. Therefore, the present study shows that hsp70, but not hsp25, is an oviductal protein modulated by the oestrous cycle and that it is a protein marker for specific phases of the oestrous cycle. In addition, hsp70 was more responsive to the hormonal changes in the infundibulum and ampullar regions of the oviduct. During early pregnancy, hsp25 expression was downregulated (unlike in the endometrium), whereas hsp70 was relatively abundant in the oviduct. hsp70 was observed in all functional segments of the oviduct during pregnancy, indicating that in the oviduct, this protein is modulated by oestrogens and progesterone and possibly by other pregnancy-related hormones.

Biased diffusion in anisotropic disordered systems

Abstract: We investigate a diffusion process into an anisotropic disordered medium in the presence of a bias. The medium is modeled by a two-dimensional square lattice in which the anisotropic disorder is represented by a bond percolation model with different occupation probabilities on each direction. The biased diffusion process is mapped by a random walk with unequal transition probabilities along and against the field ~in the @1,1# direction! by performing Monte Carlo simulations. We observe a transition from pure to drift diffusion when the bias reaches a threshold Bc . In order to estimate this Bc ,a neffective exponent is used to characterize the diffusion process. This Bc is also compared with another estimation for the critical field.

Resonant Raman scattering and optical transmission studies of Cu(II) and Fe(III) impurities in crystalline L -alanine

Abstract: A comparative study by means of resonant Raman scattering and optical transmission spectroscopy between the different color centers originating from Fe~III! and Cu~II! doping of L-alanine crystals is presented. In both samples we find a selective resonant enhancement of Raman active modes related to vibrations of the lattice and carboxyl group. We found that Cu~II!- and Fe~III!-doped samples have qualitatively similar electronic absorptions, but they display different effects on the resonant profiles of the phonons. Fe~III!-doped samples show an antiresonance behavior for some modes, something that is not observed in samples with Cu~II! impurities.

Oxygen diffusive barriers of rat distal colon: role of subepithelial tissue, mucosa, and mucus gel layer.

Abstract: The contributions of subepithelial tissue, mucosa, and mucus gel layer as restraints for oxygen diffusion in rat distal colon in vitro were assessed by comparing oxygen transfer through preparations of isolated submucosa, isolated mucosa with and without the superficial mucus gel layer, and mucosa-submucosa mounted as flat sheets in a diffusion chamber One side of the chamber was gassed with 95% O2-5% CO2 while the time course of oxygen concentration rise was measured in the continuously stirred opposite side, initially equilibrated with near-zero oxygen solution The procedure does not affect epithelial viability Diffusion in isolated mucosa was the same before and after KCN (5 mM) treatment, suggesting that epithelial oxygen consumption does not influence transfer rates Subepithelial tissue, mucosa, and mucus gel layer are roughly responsible, respectively, for 12%, 56%, and 32% of oxygen diffusive hindrance Diffusion coefficients range from 13% (mucosa-submucosa) to 54% (isolated submucosa) of that of water Subepithelial tissue accounts for about 12% of total diffusive restraint

Follow-up of steroid-resistant nephrotic syndrome: tubular proteinuria and enzymuria

Abstract: The aim of this study was to examine the compromise of proximal tubule cells in steroid-resistant nephrotic syndrome patients with a histologic diagnosis of focal segmental glomerulosclerosis (FSGS) through assessment of the urinary levels of beta 2-microglobulin (beta 2M) and N-acetyl-beta-D-glucosaminidase (NAG) during active disease and remission over a follow-up period of 3 years. We studied 34 children with nephrotic syndrome: 12 with steroid-resistant nephrotic syndrome (SRNS) and massive proteinuria, 7 with steroid-dependent nephrotic syndrome (SDNS) and 15 with steroid-sensitive nephrotic syndrome (SSNS). Of the SSNS patients, 8 children were in remission (RM) and 7 were in relapse (RL). Seven healthy children were included as controls. Urinary beta 2M, measured by enzyme-linked immunosorbent assay, was significantly increased in the SRNS group as compared to the SDNS group (P < 0.01), SSNS in remission (P < 0.01), and controls (P < 0.01). There were no differences between the SRNS group and SSNS in relapse. Analysis of urinary N-acetyl-beta-D-glucosaminidase (U-NAG) by colorimetric assay showed significantly higher values in the SRNS group of patients than in SDNS, SSNS, and control groups. A positive correlation between U-NAG and proteinuria was demonstrated (r = 0.73, P < 0.01). The SRNS group of patients (n = 12, 11 with a histologic diagnosis of FSGS and one with diffuse mesangial proliferation) was treated with the same protocol of i.v. methylprednisone and oral cyclophosphamide. Long-term follow-up showed a progressive decrease in U-beta 2M and U-NAG excretion to control values in the 3rd year, except in one patient who did not respond to the treatment. In the FSGS patients, evaluation of the contribution of structural interstitial histological abnormalities, including each of the histological parameters considered in interstitial scarring to the functional tubule abnormalities assessed by beta 2M and NAG excretion, was performed by multiple regression analysis. The r2 values for beta 2M and NAG were 53.99%, P = 0.19, and 57.90%, P = 0.14, respectively; neither was significant. We conclude that: (1) proximal tubule cell dysfunction, partially affected by massive albuminuria, may account for the higher values of beta 2M and NAG excretion in the SRNS patients and (2) urine beta 2M and NAG levels are not helpful in identifying histological evidence of structural tubulointerstitial damage in children with steroid-resistant nephrotic syndrome.

Development of the electroweak phase transition and baryogenesis

Abstract: We investigate the evolution of the electroweak phase transition, using a one-Higgs effective potential that can be regarded as an approximation for the Minimal Supersymmetric Standard Model. The phase transition occurs in a small interval around a temperature T_t below the critical one. We calculate this temperature as a function of the parameters of the potential and of a damping coefficient related to the viscosity of the plasma. The parameters that are relevant for baryogenesis, such as the velocity and thickness of the walls of bubbles and the value of the Higgs field inside them, change significantly in the range of temperatures where the first-order phase transition can occur. However, we find that in the likely interval for T_t there is no significant variation of these parameters. Furthermore, the temperature T_t is in general not far below the temperature at which bubbles begin to nucleate.

Development of the electroweak phase transition and baryogenesis

Abstract: We investigate the evolution of the electroweak phase transition, using a one-Higgs effective potential that can be regarded as an approximation for the Minimal Supersymmetric Standard Model. The phase transition occurs in a small interval around a temperature Tt below the critical one. We calculate this temperature as a function of the parameters of the potential and of a damping coefficient related to the viscosity of the plasma. The parameters that are relevant for baryogenesis, such as the velocity and thickness of the walls of bubbles and the value of the Higgs field inside them, change significantly in the range of temperatures where the first-order phase transition can occur. However, we find that in the likely interval for Tt there is no significant variation of these parameters. Furthermore, the temperature Tt is in general not far below the temperature at which bubbles begin to nucleate.

Xenopus laevis embryo development: arrest of epidermal cell differentiation by the chelating agent 1,10-phenanthroline.

Abstract: The embryonic epidermis of stage 35 Xenopus laevis embryos is a highly differentiated structure composed of four cell types arranged in a regular architecture. Each type is distinguished by its distinct morphological characteristics. Some cells are ciliated (type 1); others have their surfaces covered by abundant, secreted vesicles of 0.1 μm diameter (type 2), or multiple linear aggregates of spherical subunits on their apical surfaces (type 3) or large secreted vesicles that emanate from prominent apical holes of 1 μm diameter (type 4). In contrast, the macroscopic appearance of embryos exposed to 10 μM 1,10-phenanthroline (OP) as well as the ultramicroscopic structure and organization of their epidermal cells are markedly altered. The most predominant cells of the embryonic epidermis are undifferentiated and of heterogeneous size. They lack any characteristic morphology and are arranged irregularly. Ghost cells are also identified. The recognizable differentiated cells are decreased in number and present in a scattered arrangement. These are identified as either type 1 or 2 cells but with ciliae that are shorter and thicker than control or with only a few vesicles larger than 0.1 μm in diameter on their surface. No cells with linear aggregates or prominent apical holes are identified. Except for the altered epidermis, the embryos do not develop any other major organs and exhibit axial abnormalities with an average dorso-anterior index of three. Thus, the chelating agent OP perturbs metal dependent processes essential for terminal differentiation that may likely account for the resultant abnormalities of embryo organogenesis and morphogenesis. Mol. Reprod. Dev. 55:75–82, 2000. © 2000 Wiley-Liss, Inc.

HIGH-AFFINITY SITES FOR beta-D-GALACTOSIDASE ON MEMBRANE-BOUND VESICLES ISOLATED FROM RAT EPIDIDYMAL FLUID

Abstract: Glycosidases in rat epididymal fluid are secreted under androgen stimulation and possess receptors on the sperm surface. One of these enzymes, beta-D-galactosidase (gal), was found in the epididymal fluid as a soluble enzyme and also in a heterogeneous population of membrane bound vesicles (mbv). beta-D-Galactosidase was specifically localized to a subpopulation of larger, electron-dense mbv. The aim of this study was to analyze the high-affinity sites for gal on the membrane of mbv using two different methods: classical fluorometric assay (used in previous papers) and colloidal gold (20 nm) conjugated to gal as a marker in ultrastructural studies. beta-D-Galactosidase bound to mbv with high-affinity (Kd in a nanomolar range) are in a saturable form. Furthermore, 25 mM fructose-1,6-diphosphate (f-1,6-dip), a sugar that competes for the binding site, showed 50% inhibition of the binding. The gold conjugates were mostly observed on the surface of the large, electron-dense mbv but not on the small, electronl...

Changes in Distribution of Phosphomannosyl Receptors During Maturation of Rat Spermatozoa

Abstract: The aim of the present work was to study the distribution of the cation-independent (CI) and cation-dependent (CD) mannose-6-phosphate receptors (MPRs) in spermatozoa obtained from either rete testis or three regions of rat epididymis. We observed that both receptors underwent changes in distribution as spermatozoa passed from rete testis to cauda epididymis. CI-MPR was concentrated in the dorsal region of the head in rete testis sperm and that this labeling extended to the equatorial segment of epididymal spermatozoa. CD-MPR, however, changed from a dorsal distribution in rete testis, caput, and corpus to a double labeling on the dorsal and ventral regions in cauda spermatozoa. The percentages of spermatozoa that showed staining for either CI-MPR or CD-MPR increased from rete testis to epididymis. The observed changes were probably the result of a redistribution during transit rather than an unmasking of receptors. The fluorescence corresponding to CD-MPR and CI-MPR on the dorsal region disappea...

Nonisotropic effective-medium approximation for diffusion problems in random media

Abstract: We present the nonisotropic effective-medium approximation to solve diffusion problems in a twodimensional anisotropic random media. The problem has been worked out by introducing a generalization of the well-known effective-medium approximation. A set of coupled nonlinear self-consistent equations must be solved to find the effective rates in each direction. We have considered ~analytically! some particular models in short and large frequency limits. The dc conductivity is also compared against the isotropic case. The ac conductivity and Cole-Cole diagrams for the nonisotropic random bond percolation model have been analyzed in terms of the physical parameters that characterize the anisotropy and the disorder in the media. A monoparametric nonisotropic bond disordered model (a model! has also been worked out to show the applicability of the present approach in the context of weak or strong disorder. Such a model of disorder leads the system to show a quasi-one-dimensional behavior, proper of nonisotropic materials.

Violation of the equivalence principle oscillation solutions to the solar neutrino problem

Abstract: We study the solar neutrino problem within the framework of a parametrized post-Newtonian formulation for the gravitational interaction, which incorporates a violation of the equivalence principle (VEP), and examine the more important VEP effects using the current data on the rates and the energy spectrum. We find two possible solutions for the neutrino rate, one of them involving the MSW effect in matter and the other corresponding to a vacuum oscillation. In both cases, a semi-annual seasonal modulation of the neutrino flux is predicted, because of the anisotropic contributions to the gravitational effects. Our analysis provides new constraints for some VEP parameters.

Coupling between molecular vibrations and liquid crystalline order parameters.

Abstract: Specific Raman active modes in two prototype cyanobiphenyl liquid crystals are shown to display a temperature dependent softening proportional to either the nematic or smectic order parameters, while other vibrations ~like the CwN stretch mode! remain unaltered. This selective coupling between intramolecular vibrations and the liquid crystalline order is related to the intrinsic symmetry of the modes. The method provides a simple, microscopic, noninvasive optical technique with which the liquid crystalline order parameters can be qualitatively mapped out. Inelastic light scattering provides a myriad of information on different sorts of phase transitions @1#. This is achieved by either the direct observation of scattering from excitations related to the phase transition itself, or by indirectly monitoring the coupling of the order parameters to other excitations with a finite Raman cross section like phonons. Extensive examples of this sort exist in the literature about magnetic materials @2,3#. Liquid crystals ~LC’s ! are characterized by complex phase transitions which may involve one or several order parameters in different temperature ranges @4#. One may argue that the internal vibrations of an individual LC molecule should not be the same when the molecule is placed in the average molecular fields ~MF’s ! which are responsible for the different LC phases. Small changes in the electronic structure of the molecule coming from its interaction with the average MF within the LC should produce, accordingly, variations in the intramolecular modes. These changes are expected to be small, for the interactions characterizing the LC state are weak. A typical interaction energy is of the order of ;kBTc;10‐30 meV, which should be compared with a typical electronic excitation energy ;3 ‐5 eV. Thus one could a priori expect changes which should be no larger than Dv/v;10 22 ‐10 23 . Moreover, the fact that the LC state is characterized by one or several macroscopic order parameters should impose well defined symmetry restrictions to the coupling between the macroscopic order and the phonons, as we shall show later. In this Brief Report, we show that small but measurable frequency changes (Dv/v;10 23 ) in specific Raman active modes are seen in different phases of two prototype cyanoalkylbiphenyl LC’s. Moreover, we show that while some modes are sensitive to the presence of a nematic order parameter, others respond only to the smectic order, or remain unchanged. This selective coupling of intramolecular vibrations to the different order parameters of the LC’s not only adds another example to the field of inelastic light scattering of indirect monitoring of a phase transition, but also provides a powerful tool to qualitatively measure the LC order parameters themselves with a noninvasive microscopic technique like Raman scattering. In this sense, it may provide a useful method to monitor phase transitions in LC’s in situations where other experimental techniques may turn out to be difficult. Raman scattering has been used in the past both to characterize the intramolecular vibrations of different LC compounds and to study the orientational statistics of the nematic state @5#. These experiments use the fact that anisotropic Raman tensors can be associated with well defined vibrations ~like the CwN stretch!, and that the average orientation of the bonds can be probed by an appropriate choice of the incident and scattered polarizations. No changes in the frequencies of Raman active vibrations have been reported so far in the nematic phase. More recently @6#, ample changes (;15 cm 21 ) in Raman active modes have been reported for

Comunicología latinoamericana: disciplina a la búsqueda de objeto

Abstract: "Comunicology" is a very important scientific discipline, because of the decisive influence of mass media in actual life. But there are problems for composing its own thematical space, and for defining its theoretical object. We may advertise it in the confussional relations with another sciences (linguistic, anthropology, sociology, and so on). One of the factors that make influence, is the students' way of thinking: their expectatives are massmediatic ones, not academical ones. It's evident in the behavior we see at Communicology 's congresses. Also the indefition about limits of the discipline, has taken in Latin America to a total identification between communicology and "cultural studies". The impossibility of thinking the precise place of those studies for communicology, shows the problems for constitution of the discipline.

Changes in gastroduodenal 5-hydroxytryptamine-containing cells induced by dehydroleucodine.

Abstract: In previous work, we demonstrated that dehydroleucodine (DhL), a lactone isolated from Artemisia douglasiana Besser, prevents gastroduodenal damage induced by absolute ethanol (EtOH). The present study examined the effects of DhL - applied alone or before EtOH - on gastroduodenal cells containing 5-hydroxytryptamine (5-HT), to clarify the mechanism of action of the drug. Mice were divided into four groups: (I) control; (II) DhL; (III) EtOH, and (IV) DhL + EtOH. Stomachs and duodena were studied by immunohistochemistry and image analysis. EtOH decreased the immunopositive cell number and the area occupied by these cells. This effect was prevented by DhL. DhL alone did not affect the gastric immunopositive cell number and area. Duodena treated only with DhL exhibited a reduction of immunopositive cell number, but no change in area was observed. We propose that the drug probably inhibits the release of the inflammatory mediator 5-HT from endocrine cells, acting as a 'cell stabilizer' in response to injury.

Spin dynamics in perovskites, pyrochlores, and layered manganites

Abstract: High temperature electron spin resonance (ESR) and magnetic susceptibility (χ) are analyzed for manganites related with colossal magnetoresistance (CMR). The properties of compounds with different crystalline structures: three-dimensional (3D) perovskites, pyrochlore, and La1.2Sr1.8Mn2O7, a two-dimensional layer, are compared. In the paramagnetic regime, and outside the critical regions associated with phase transitions, the temperature dependence of the ESR linewidth presents a universal behavior dominated by the variations of χ(T), ΔHpp(T)=[C/Tχ(T)]ΔHpp(∞). The high temperature limit of the linewidth, ΔHpp(∞), is related to the parameters of the Hamiltonian describing the interactions of the spin system. The role played by magnetic anisotropy, isotropic superexchange, and double exchange is revealed and discussed in the analysis of the experimental data. In CMR and non-CMR pyrochlores, ΔHpp(∞)∝ωp2/J where J is proportional to the Curie–Weiss temperature, including the hybridization mechanism producing C...