Showing papers by "Federal University of Rio de Janeiro published in 1993"

Magnetic bistability in a metal-ion cluster

Abstract: MAGNETIC materials of mesoscopic dimensions (a few to many thousands of atoms) may exhibit novel and useful properties such as giant magnetostriction, magnetoresistivity and magnetocaloric effects1–4. Such materials also allow one to study the transition from molecular to bulk-like magnetic behaviour. One approach for preparing mesoscopic magnetic materials is to fragment bulk ferromagnets; a more controllable method is to take a 'bottom-up' approach, using chemistry to grow well defined clusters of metal ions5,6. Lis7 has described a twelve-ion manganese cluster in which eight of the Mn ions are in the +3 oxidation state (spin S=2) and four are in the +4 state (S=3/2). These ions are magnetically coupled to give an S=10 ground state8, giving rise to unusual magnetic relaxation properties8,9. Here we report that the magnetization of the Mn12 cluster is highly anisotropic and that the magnetization relaxation time becomes very long below a temperature of 4 K, giving rise to pronounced hysteresis. This behaviour is not, however, strictly analogous to that of a bulk ferromagnet, in which magnetization hysteresis results from the motion of domain walls. In principle, a bistable magnetic unit of this sort could act as a data storage device.

Pressure stability of proteins

Abstract: The stability of proteins toward temperature has been explored in much detail since the time that proteins were characterized as chemicals of constant composition, but the study of the effects of pressure upon pro­ teins is much more recent and has been much less frequent than that of temperature. However, there is every reason to expect that the effects of pressure would be more amenable to interpretation than those of tem­ perature: An increase in temperature changes both the energy content and the volume of the system, and because proteins are flexible polymers that maintain secondary, tertiary, and quatenary structure by bonds of strengths not much larger than the thermal energy, the internal interactions of the protein are changed by temperature in ways that cannot be easily foreseen. On the other hand, application of pressure affects internal inter­ actions exclusively by the changes in the distances (volumes) of the com­ ponents, whereas the total energy of the system remains almost constant. Hence, observations of pressure effects ought to precede those of tem­ perature in order to facilitate the interpretation of the more involved effects of the latter variable.

New concepts of instantaneous active and reactive powers in electrical systems with generic loads

Abstract: Conventional active and reactive power theory, valid for the steady-state analysis is reviewed. The instantaneous power theory, introduced by H. Akagi et al. (1983, 1984) is also presented. This instantaneous theory is valid for steady and transient states and for generic voltage and current waveforms. Some examples explaining the physical meaning of the new concepts are presented. By using the concepts of symmetrical components together with the new theory, the powers in an unbalanced system are analyzed, including the zero-sequence instantaneous power. An example showing how this theory can be used to design and control an active power filter is presented. Some simulation results are presented and discussed. >

Rapid DNA extraction protocol from soil for polymerase chain reaction‐mediated amplification

Abstract: A simple and rapid method of DNA extraction from soil was developed and DNA was made suitable for subsequent efficient amplification by the polymerase chain reaction (PCR). Key features of the extraction and purification were cold lysozyme- and SDS-assisted lysis with either freezing-thawing or bead beating, cold phenol extraction of the resulting soil suspension, CsCl and KAc precipitation and, finally, spermine-HCl or glass milk purification of DNA. Crude DNA preparations contained 4–20 μg DNA per g of soil extracted, and at least 50% of this was recovered in the final purified DNA preparations. The resulting DNA was pure enough to be restricted by various enzymes, and was amplifiable at concentrations of up to 20 ng of soil-derived DNA per 50 μl reaction mix. Amplification of a 683 bp target sequence, pat, was performed with different Taq DNA polymerases. Application of the protocol enabled us to detect target DNA derived from roughly 103 introduced Pseudomonas fluorescens (RP4 :: pat) cfu per g of soil. The fate of an introduced population in the soil could be followed to this limit with PCR-assisted detection of target DNA. In addition, target DNA was detected in soil 5 months after release, when the introduced organism was no longer detectable on selective agar plates. The extraction and purification protocol applied to various different soil types resulted in DNA of sufficient purity to permit amplification by PCR.

Cytokine regulation of neuronal differentiation of hippocampal progenitor cells

Abstract: The signalling mechanisms governing haematolymphopoiesis and those regulating neural development may be closely related, as indicated by similarities of higher-order structure and function of the cytokines involved, of the regional and temporal regulation of their transcription and translation, and of their bioactivity. Here we investigate this possible evolutionary connection using retroviral transduction of a temperature-sensitive mutant form of the SV40 large T antigen to develop conditionally immortalized murine embryonic hippocampal progenitor cell lines. Treatment of these cells with cytokines that are thought to participate in progressive lymphoid maturation, immunoglobulin synthesis and erythropoiesis causes progressive neuronal differentiation, as defined by morphological criteria, successive expression of increasingly mature neurofilament protein, and the generation of inward currents and action potentials. The cytokine interleukin(IL)-11 induces expression of action potentials that are insensitive to tetrodotoxin, which is indicative of developmentally immature sodium channels. By contrast, for expression of more mature action potentials (tetrodotoxin-sensitive) one of the interleukins IL-5, IL-7 or IL-9 must be applied in association with transforming growth factor-alpha after pretreatment with basic fibroblast growth factor. Our results suggest that the mechanisms regulating lineage commitment and cellular differentiation in the neural and haematopoietic systems are similar. Further, they define an in vitro model system that may facilitate molecular analysis of graded stages of mammalian neuronal differentiation.

Global analysis of antibody repertoires. II. Evidence for specificity, self-selection and the immunological "homunculus" of antibodies in normal serum.

Abstract: The serum IgM repertoires of C57BL/6, DBA/2 and BALB/c mouse strains were analyzed using a recently developed global and quantitative assay that measures antibody reactivities to a very large number of antigens. A characteristic repertoire could be assigned to each strain. The different repertoires could be successfully classified with multivariate statistics. Many common reactivities were also observed among the different strains, which allows the definition of a mouse-specific repertoire. Analysis of human sera support this notion. To investigate the impact of minor genetic differences on the serum IgM repertoire, the congenic strains B10.D2/oSn and B10.D2/nSn, which differ in the expression of the C5 component of complement, were analyzed. The two strains could be separated based on the reactivity profiles obtained. The analysis of the results reveals that many antigenic proteins are not recognized at all by natural antibodies, while others are disproportionately reactive, the resulting patterns giving rise to what could be the definition of an "immunological homunculus". The relevance of this type of analysis for clinical applications is discussed.

Electric field distribution and near-surface modifications in soda-lime glass submitted to a dc potential

Abstract: The laser-induced pressure pulse method (LIPP) is employed to investigate the electric field distribution in soda-lime glass samples after application of a dc potential (dc poling). The modifications of near-surface composition resulting from the dc polarization procedure were determined by means of three nuclear techniques for near-surface analysis: Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERD) and nuclear reaction analysis. An alkali-depleted layer is formed near the anode. This depletion layer persists for a long time after the dc poling. The electric field in this region is of the order of the intrinsic dielectric breakdown, and its configuration depends on the penetration, or not, of hydrogen. Based on these results, the conduction mechanism in the alkali-depleted layer is discussed. It is suggested that when hydrogen blocking electrodes are used ionized electrons are probably the charge carriers in the alkali-depleted layer.

Production of a potentially novel anti-microbial substance by Bacillus polymyxa.

Abstract: A bacterial strain, SCE2, identified as Bacillus polymyxa, produced an anti-microbial substance active against yeasts, fungi and different genera of Gram-positive and-negative bacteria, in liquid medium and in plate assays. This substance appeared to be an antibiotic different from the polymyxin group, mainly because of its action against the majority of Gram-positive bacteria tested and its lack of activity against Pseudomonas aeruginosa, a species usually killed by polymyxins. Preliminary characterization showed resistance to heat (65°C, 2 h), to proteases, trypsin, lysozyme, deoxyribonuclease I, ribonuclease A, phospholipase C, ethanol, acetone, chloroform, ether and to strong alkali treatment (2 M NaOH). The molecular weight was less than 3500. The B. polymyxa strain harboured a plasmid that did not correlate with antibiotic production; after curing experiments, a derivative strain, SCE2(46), was isolated that lacked the plasmid pES1, but showed the same inhibitory spectrum as the wild-type strain.

Cytochemical localization of carbohydrate residues in microfilariae of Wuchereria bancrofti and Brugia malayi.

Abstract: We investigated the localization of carbohydrate residues on the surface structures of microfilariae of Wuchereria bancrofti and Brugia malayi, using a panel of 10 different gold-labeled lectins and chitinase. The sheath, a structure that encloses the microfilariae, is not a homogeneous structure, presenting two clearly distinct layers. The outer layer is more electron dense and was not labeled with the lectins. The inner layer is less dense and was intensely labeled with lectins, especially those that recognize D-galactose and N-acetyl-D-galactosamine. Small differences were observed in the lectin labeling pattern of microfilariae of W. bancrofti and B. malayi. D-galactose and fucose were observed in the cuticle of both species. Chitin, as revealed with gold-labeled chitinase, was observed in the cuticle of microfilariae of W. bancrofti but not in B. malayi.

Inflorescence‐specific genes from Arabidopsis thaliana encoding glycine‐rich proteins

Abstract: Genomic and cDNA clones for three inflorescence-specific genes from Arabidopsis thaliana were isolated and characterized The genes are tandemly organized in the genome on a 10 kb fragment The expression of these genes is coordinately regulated in a developmental and organ-specific pattern They are expressed predominantly in anthers at the later stage of flower development The primary structure of the encoded gene products exhibits comparable features consisting of a hydrophobic domain at the N-terminal region followed by repeated glycine-rich motifs Little homology is observed either between the glycine-rich domain of the three genes or with previously described glycine-rich proteins from other plant species

Trophic Factors Produced by Retinal Cells Increase the Survival of Retinal Ganglion Cells In Vitro

Abstract: The naturally occurring neuron death of normal development has been shown to depend on trophic factors produced and released by target cells. It has also been shown that the afferent supply and local interactions play a role in the control of this degenerative phenomenon. We studied the effect of trophic factors produced by intrinsic retinal cells on the survival of retinal ganglion cells in vitro. Retinae of newborn hooded rats were retrogradely labelled with horseradish peroxidase injected into the superior colliculus to permit the identification of retinal ganglion cells in culture. We tested the effect of conditioned media either from aggregates or from explants of retinal cells from neonatal rats on the survival of ganglion cells in vitro. Our results showed that both conditioned media increased the survival of these cells. The trophic activity was dose-dependent, was maintained after dialysis against a 12 kDa membrane, was abolished by heating at 56 degrees C for 30 min, and was not found in conditioned medium from cerebral cortical explants. Conditioned medium obtained without fetal calf serum presented the same trophic effect. These results suggest that the local control of developmental neuron death by intrinsic retinal cells may be mediated by neurotrophic factors.

Prevalência de consumo de bebidas alcoólicas e de alcoolismo em uma região metropolitana do Brasil

Abstract: Foi realizado Inquerito epidemiologico com o objetivo de estimar o uso de substâncias psicoativas e a prevalencia de alcoolismo. Tomou-se como referencia a populacao de maiores de 13 anos de idade de regiao administrativa da cidade do Rio de Janeiro, RJ (Brasil), da qual se extraiu uma amostra aleatoria de 1.459 individuos. Os resultados referentes ao uso de bebidas alcoolicas e alcoolismo, identificados atraves do teste CAGE, mostraram: prevalencia de 51% para o consumo de alcool e de 3% para alcoolismo, sendo 4,9% em homens e 1,7% em mulheres; maior proporcao de consumidores de alcool e de alcoolistas entre homens de 30 e 49 anos; abstinencia mais frequente entre os viuvos, protestantes e individuos com niveis de renda inferiores.

Purification and characterization of highly active and stable polyphosphatase from Saccharomyces cerevisiae cell envelope.

Abstract: Saccharomyces cerevisiae cell envelope polyphosphatase was isolated in highly active and stable form by extraction from cells with zwittergent TM-314 followed by chromatography of the extract on phosphocellulose and QAE-Sephadex in the presence of 5 mM-MgCl2, 0.5 mM-EDTA and 0.1% Triton X-100. The enzyme possessed a specific activity of 220 U/mg and after 30 days retained 87% of its activity at -20 degrees C. Polyphosphatase molecular mass was determined to be about 40 kDa by gel filtration and polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The enzyme hydrolysed polyphosphates with various chain lengths (n = 3-208), had low activity for GTP and did not split pyrophosphate, ATP and p-nitrophenylphosphate. On polyphosphates with chain lengths n = 3, 9 and 208, Km values were 1.7 x 10(-4), 1.5 x 10(-5) and 8.8 x 10(-7) M respectively. Polyphosphatase was most active and stable at pH 6.0-8.0. The enzyme showed maximal activity at 50 degrees C. The time of half inactivation of polyphosphatase at 40, 45 and 50 degrees C was 45, 10 and 3 min, respectively. In the absence of divalent cations and also with Ca2+ or Cu2+, the enzyme showed practically no activity. The ability of divalent cations to activate polyphosphatase was reduced in the following order: Co2+ > Mg2+ > Mn2+ > Fe2+ > Zn2+. Polyphosphatase was completely inhibited by 1 mM-ammonium molybdate and 50 microM-Zn2+ or Cu2+ (in the presence of Mg2+).

TH1 and TH2 T-cell subsets are differentially activated by macrophages and B cells in murine leishmaniasis.

Abstract: The role of antigen-presenting cells in the differential expansion of TH1 and TH2 T cells in murine leishmaniasis was investigated. In general, macrophages preferentially induced gamma interferon and interleukin-2 secretion by syngeneic Leishmania-specific T cells, whereas B cells were more efficient in activating interleukin 4 production. B cells from susceptible BALB/c mice were better in inducing TH2 responses than B cells from resistant C57BL/6 mice, whereas macrophages from C57BL/6 mice were superior to BALB/c macrophages in inducing TH1 responses.

Faddeev-Jackiw Quantization of Non-Abelian Systems

Abstract: The Faddeev and Jackiw procedure for the quantization of constrained gauge systems is used on the analysis of non-Abelian symmetries. The key point is that the gauge algebra of the non-Abelian constraints under generalized brackets can be reconstructed. This follows from the singular matrix that defines the basic geometric structure of the model and its corresponding zero-modes. The attainment of this algebra, not previously found in the Faddeev-Jackiw formalism for constrained theories, leads to the correct transformation properties for the gauge fields. This construction shows that the zero-modes of the symplectic matrix and the generators of gauge symmetry are closely related. To illustrate the method studied here we consider a simple mechanical model with an underlying non-Abelian symmetry and the field theory of pure Chern-Simons theory in (2+1) dimensions.

Application of parallel processing techniques to the simulation of power system electromagnetic transients

Abstract: The authors propose the use of parallel techniques for the computation of power system electromagnetic transients in a multiprocessor environment. System partitioning and parallel solution methods are described. Questions regarding computational load balancing and communication overheads are discussed and techniques are presented to improve the proposed method with respect to those matters. In order to demonstrate the feasibility and to assess the performance of the proposed techniques, a parallel electromagnetic transients program for a multiprocessor environment has been developed. Tests using real power networks of different sizes, executed in an eight-processor hypercube machine, have shown promising performance indices. >