1,722,819 research outputs found
Inhibition of the human erythrocytic glutathione-S-transferase T1 (GST T1) by thimerosal
No full textWe have investigated the interaction of thimerosal, a widely used antiseptic and preservative, with the human erythrocytic GST TI (glutathione-S-transferase TI). This detoxifying enzyme is expressed in the erythrocytes of solely the human species and it displays a genetic polymorphism. Due to this polymorphism about 25 % of the individuals of the caucasian population lack this activity ("non-conjugators"), while 75 % show it ("conjugators") (Hallier, E., et al., 1993). Using our newly developed HPLC-fluorescence detection assay (Mueller, M., et al., 2001) we have profiled the kinetics of enzyme inhibition in erythrocyte lysates of two individuals previously identified as "normal conjugator" (medium enzyme activity) and "super-conjugator" (very high activity). For the normal conjugator we have determined a 2.77 mM thimerosal concentration to inhibit 50 % of the GST TI activity. In the case of the super-conjugator a 2.3 mM thimerosal concentration causes a 50 % inhibition of the enzyme activity. For both phenotypes a 14.8 mM thimerosal concentration results in residual enzyme activities equal to those typically detected in non-conjugator lysates. Thus, sufficiently high doses of thimerosal may be able to change the phenotypic status of an individual - at least in vitro - by inhibition of the GST T1 enzyme
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Concurrent coupling between a particle simulation and a continuum description
No full textWe introduce a numerical scheme that concurrently couples a particle simulation of a multi-component polymer melt to
a continuum description. We use a soft, coarse-grained model in the particle simulation and a time-dependent Ginzburg-Landau approach for the
continuum description. The coupling between the particle coordinates and the order-parameter field, m, allows us to estimate the
parameters the free-energy functional, ,
of the Ginzburg-Landau approach and it makes the particle model follow the time-evolution of the order-parameter field. The
algorithm exploits the time-scale separation between the fast kinetics of the order-parameter field and the slow temporal variations
of the parameters of the free-energy functional. A detailed analysis is presented for the spinodal decomposition of a binary polymer
blend based on the Random-Phase Approximation and Monte-Carlo simulations
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Temperature dependence of the slip length in polymer melts at attractive surfaces
No full textUsing Couette and Poiseuille flows, we extract the temperature dependence of the slip length, delta, from molecular dynamics simulations of a coarse-grained polymer model in contact with an attractive surface. delta is dictated by the ratio of bulk viscosity and surface mobility. At weakly attractive surfaces, lubrication layers form; delta is large and increases upon cooling. Close to the glass transition temperature T(g), very large slip lengths are observed. At a more attractive surface, a sticky surface layer is built up, giving rise to small slip lengths. Upon cooling, delta decreases at high temperatures, passes through a minimum, and grows for T -> T(g). At strongly attractive surfaces, the Navier-slip condition fails to describe Couette and Poiseuille flows simultaneously. The simulations are corroborated by a schematic, two-layer model suggesting that the observations do not depend on details of the computational model
Sulfhydryl oxidation: A potential strategy to achieve neuroprotection during severe hypoxia?
No full textPreviously we reported that sulfhydryl (SH) modulation affects the susceptibility of rat hippocampal slices to severe hypoxia. SH-oxidation by DTNB (5,5'-dithiobis 2-nitrobenzoic acid) or H2O2 postponed the onset of hypoxia-induced spreading depression (HSD), thereby delaying the loss of neuronal function, whereas SH-reduction by DTT (1,4-dithio-DL-threitol) hastened HSD onset. To judge the neuroprotective merit that might arise from a postponement of HSD by oxidants, we have extended our earlier observations by multiparametric recordings and screened for changes in the extracellular K+ accumulation, HSD propagation velocity, and its maximum spread. As parameters for neuronal network function, the failure of synapses during hypoxia and their posthypoxic recovery were analyzed. DTNB (2 mM) or H2O2 (5 mM) postponed HSD but did not attenuate the rise in extracellular K+ concentration ([K+](o)), HSD propagation velocity or its maximum spread. H2O2 slightly postponed the synaptic failure during hypoxia; the posthypoxic recovery of synapses was, however, incomplete. DTNB slowed the synaptic recovery upon reoxygenation. DTT (2 mM) hastened HSD onset, but HSD propagation velocity and tissue invasion were not affected. Upon reoxygenation, however, normalization of [K+](o) was disturbed and synaptic recovery failed. Therefore, SH-reducing conditions at the onset of HSD proved to be devastating for the hippocampal network. In conclusion, the only merit of DTNB or H2O2 treatment is a delayed HSD onset, i.e. some extra time before neuronal function is lost during severe hypoxia. Attenuation of the severe changes during HSD or an improved outcome was not observed. Nevertheless, combination of SH-oxidants with established neuroprotectants might be a potential therapeutic approach. (c) 2008 IBRO. Published by Elsevier Ltd. All rights reserved
Dynamic recording of cell death in the in vitro dorsal vagal nucleus of rats in response to metabolic arrest
No full textAnoxic/ischemic neuronal death is usually assessed in cell cultures or in vivo within a time window of 24 h to several days using the nucleic acid stain propidium iodide or histological techniques. Accordingly, there is limited information on the time course of such neuronal death. We loaded acute rat brain stem slices with propidium iodide for dynamic fluorometric recording of metabolic arrest-related cell death in the dorsal vagal nucleus. This model was chosen because dorsal vagal neurons show a graded response to metabolic inhibition: anoxia and aglycemia cause a sustained hyperpolarization, whereas ischemia induces a glutamate-mediated, irreversible depolarization. We found that the number of propidium iodide-labeled cells increased from 27% to 43% of total cell count within 1-7 h after preparation of slices. Compared with these untreated control slices, cyanide-induced anoxia (30 min) or aglycemia (1 h) did not cause further cell death, whereas 3-h aglycemia destroyed an additional 13% of cells. Ischemia (1 h) due to cyanide plus iodoacetate immediately labeled an additional 20% of cells, and an additional 48% of cells were destroyed within the following 3 h of postischemia. Continuous recording of propidium iodide fluorescence showed that loss of membrane integrity started within 25 min after onset of the ischemic depolarization and the concomitant intracellular Ca(2+) rise. The results show that propidium iodide can be used to monitor cell death in acute brain slices. Our findings suggest that pronounced cell death occurs within a period of 1-4 h after onset of metabolic arrest and is apparently due to necrotic/oncotic mechanisms
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