Showing papers by "University of Seville published in 1991"
TL;DR: In this article, the effect of the attractive anisotropic forces in stabilizing the orientationally ordered phases is also studied by performing simulations for a WCA-type Gay-Berne fluid.
Abstract: In this paper we report computer simulation results for bulk Gay-Berne fluids with anisotropy parameters κ = 3 and κ′ = 5. Using molecular dynamics simulations in the NVT ensemble, we identify isotropic fluid, nematic and smectic B phases. We observe that the nematic phase is only stable for reduced temperatures T* > 0·80. At lower temperatures, the isotropic phase directly evolves to the smectic B phase via a first order transition. We also give evidence of a weakly first order transition which involves a tilt of the molecular orientations with respect to the smectic planes. The effect of the attractive anisotropic forces in stabilizing the orientationally ordered phases is also studied by performing simulations for a WCA-type Gay-Berne fluid. When combined with previous studies of the vapour-liquid transition by Gibbs ensemble Monte Carlo simulations, and of the isotropic-nematic transition by thermodynamic integration, the results presented here provide quite a complete picture of the phase diagram for...
245 citations
TL;DR: The results indicate that the O2 sensor of type I cells is in the plasma membrane and suggest that environmental O2 interacts directly with the K+ channels.
Abstract: Type I cells of the carotid body are known to participate in the detection of O2 tension in arterial blood but the primary chemotransduction mechanisms are not well understood. Here we report the existence in excised membrane patches of type I cells of a single K+ channel type modulated by changes in PO2. Open probability of the O2-sensitive K+ channel reversibly decreased by at least 50% on exposure to hypoxia but single-channel conductance (approximately 20 pS) was unaltered. In the range between 70 and 150 mmHg (1 mmHg = 133 Pa) the decrease of single-channel open probability was proportional to the PO2 measured in the vicinity of the membrane patch. The inhibition of K+ channel activity by low PO2 was independent of the presence of non-hydrolyzable guanine triphosphate analogues at the internal face of the membrane. The results indicate that the O2 sensor of type I cells is in the plasma membrane and suggest that environmental O2 interacts directly with the K+ channels.
158 citations
TL;DR: In this article, a mixing model was proposed to explain the petrogenesis of the Hercynian calc-alkaline granodiorites of Iberia, and a modified classification of common plutonic rocks in orogenic environments was proposed.
141 citations
TL;DR: In this article, the Gay-Berne potential was used to locate the coexistence points corresponding to the isotropic-nematic transition by calculating the absolute free energy of each phase.
Abstract: Molecular dynamics computer simulations have been carried out on a system consisting of cylindrically symmetric molecules with length-to-breadth ratio k = 3 and well depth ratio k′ = 5 interacting through the Gay-Berne potential. For this system we have located the coexistence points corresponding to the isotropic-nematic transition by calculating the absolute free energy of each phase. Two temperatures, T* = 1·25 and 0·95, have been studied. In each case a weak first-order phase transition has been found, with a density change close to 2·5%. The isotropic-nematic coexistence densities are found to increase with increasing temperature.
126 citations
TL;DR: Experimental results from a CMOS prototype are given that show the suitability of the technique used, and their potential for biological CMOS system emulation.
Abstract: A CMOS circuit that emulates the FitzHugh-Nagumo neuron model is introduced. A complete derivation of the neuron model is presented, starting with the description of the fundamental biological mechanisms involved in the living neural cell, followed by the mathematical model formulation extracted from these mechanisms. A circuit theory technique for obtaining a physical IC suitable circuit that emulates the derived mathematical equations is then presented, culminating with the presentation of experimental results on a chip fabricated in a 2- mu m double-metal, double-poly CMOS process. It is emphasized that the FitzHugh-Nagumo model is very adequate for emulation of small biological systems. A reduced-complexity oscillatory model suitable for implementation of relatively large neural network architectures is also introduced with several corresponding CMOS realizations and measured results. >
123 citations
TL;DR: In this paper, a systematic method to obtain the bidimensional spectral dyadic Green's function of stratified planar structures with arbitrary complex bianisotropic layers is developed based on the uniqueness and equivalence electromagnetic theorems.
Abstract: A systematic method to obtain the bidimensional spectral dyadic Green's function of stratified planar structures with arbitrary complex bianisotropic layers is developed The method is based on the uniqueness and equivalence electromagnetic theorems A first-order partial differential formulation for the electromagnetic field inside each layer is used An explicit algorithm makes it possible to go from the single-layer formulas to the general multilayer matrix formulation The perturbative nature of the method provides good numerical efficiency and straightforward determination of asymptotic behavior >
94 citations
TL;DR: The kinetics of adherence of single isolates of Staphylococcus aureus, S. epidermidis, Pseudomonas aeruginosa and Escherichia coli to catheters made of polyvinyl chloride, Teflon, siliconised latex, polyurethane and Vialon was evaluated and it was concluded that bacterial adherence to catheter may depend in part on the nature of the biomaterial and that certain substances eluted from the cat
Abstract: Summary. The kinetics of adherence of single isolates of Staphylococcus aureus, S. epidermidis, Pseudomonas aeruginosa and Escherichia coli to catheters made of polyvinyl chloride (PVC), Teflon®, siliconised latex, polyurethane and Vialon® was evaluated by a radiometric assay. Radiolabelled bacteria (108 cfu/ml) were incubated in vials containing 1-cm lengths of catheter for up to 3 days. The peak of maximal adherence to each biomaterial was reached after 24 h for P. aeruginosa and after 72 h for the other strains. Bacterial adherence to PVC and siliconised latex was significantly higher (2–6 times; p≪0·05) than to the other biomaterials for all the strains. The lowest values of adherence were observed with polyurethane and Vialon® for the staphylococci but with Teflon® for E. coli and P. aeruginosa. Bacterial viability and growth was evaluated in eluates obtained from incubation of segments of each catheter in buffer for 24 h. None of the eluates affected the viability of the staphylococci. However, all of them, significantly increased the growth of E. coli and P. aeruginosa with the exception of the eluate from siliconised latex, in which the inoculum count was reduced to an undetectable level for E. coli. We conclude that bacterial adherence to catheters may depend in part on the nature of the biomaterial and that certain substances eluted from the catheters may affect the viability and growth of different micro-organisms.
94 citations
TL;DR: In this paper, the sphalerite leaching rate increased in a linear manner with increasing iron content, and activation energies in the 39 −81 kJ/mol range were observed in both systems.
93 citations
TL;DR: A detailed study of the lipid composition of sedimentary and water particulate samples of a dilute alkaline lake (Santa Olalla Lagoon, Guadalquivir Delta, southwestern Spain) has allowed the identification and quantification of about 300 compounds reflecting predominant inputs of organic matter and very early diagenetic processes as discussed by the authors.
91 citations
TL;DR: The differences in motoneuronal sensitivity coupled with structural variations in the lateral versus the medial rectus muscle suggest that symmetric nasal and temporal eye movements are preserved by different motor unit composition.
Abstract: 1. The discharge of antidromically identified medial rectus and abducens motoneurons was recorded in restrained unanesthesized goldfish during spontaneous eye movements and in response to vestibular and optokinetic stimulation. 2. All medial rectus and abducens motoneurons exhibited a similar discharge pattern. A burst of spikes accompanied spontaneous saccades and fast phases during vestibular and optokinetic nystagmus in the ON-direction. Firing rate decreased for the same eye movements in the OFF-direction. All units showed a steady firing rate proportional to eye position beyond their recruitment threshold. 3. Motoneuronal position (ks) and velocity (rs) sensitivity for spontaneous eye movements were calculated from the slope of the rate-position and rate-velocity linear regression lines, respectively. The averaged ks and rs values of medial rectus motoneurons were higher than those of abducens motoneurons. The differences in motoneuronal sensitivity coupled with structural variations in the lateral versus the medial rectus muscle suggest that symmetric nasal and temporal eye movements are preserved by different motor unit composition. Although the abducens nucleus consists of distinct rostral and caudal subgroups, mean ks and rs values were not significantly different between the two populations. 4. Every abducens and medial rectus motoneuron fired an intense burst of spikes during its corresponding temporal or nasal activation phase of the "eye blink." This eye movement consisted of a sequential, rather than a synergic, contraction of both vertical and horizontal extraocular muscles. The eye blink could act neither as a protective reflex nor as a goal-directed eye movement because it could not be evoked in response to sensory stimuli. We propose a role for the blink in recentering eye position. 5. Motoneuronal firing rate after ON-directed saccades decreased exponentially before reaching the sustained discharge proportional to the new eye position. Time constants of the exponential decay ranged from 50 to 300 ms. Longer time constants after the saccade were associated with backward drifts of eye position and shorter time constants with onward drifts. These postsaccadic slide signals are suggested to encode the transition of eye position to the new steady level. 6. Motoneurons modulated sinusoidally in response to sinusoidal head rotation in the dark, but for a part of the cycle they went into cutoff, dependent on their eye position recruitment threshold. Eye position (kv) and velocity (rv) sensitivity during vestibular stimulation were measured at frequencies between 1/16 and 2 Hz. Motoneuronal time constants (tau v = rv/kv) decreased on the average by 25% with the frequency of vestibular stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)
85 citations
TL;DR: In this article, a Gay-Berne fluid of prolate molecules with length-to-breadth ratio 3 is studied using molecular dynamics simulations, and it exhibits vapor, isotropic liquid, nematic, and smectic-B mesophases.
Abstract: A Gay-Berne fluid of prolate molecules with length-to-breadth ratio 3 is studied using molecular dynamics simulations. This fluid exhibits vapor, isotropic liquid, nematic, and smectic-B mesophases. For the bulk fluid we report new results along isochores that further delineate the smectic and nematic regions of the phase diagram; the effect of system size is also discussed. These studies lead to a rather complete description of the fluid part of the phase diagram. We have also studied the changes that occur when such a fluid is confined in a pore with parallel, homeotropic walls. Our molecular dynamics results show that the isotropic-nematic transition shifts to higher temperatures, or lower densities, i.e., the liquid crystal phase is stabilized relative to the bulk flild.
TL;DR: The main result is the Theorem 4.4 which transforms a deduction problem in a multi-valued logic to an equivalent problem about ideal membership in a polynomial ring.
TL;DR: Structural requirements of these receptors were studied and properties of these binding sites strongly support the concept that VIP could behave as regulatory peptide on the macrophage function.
TL;DR: Direct and indirect evidence point to consistently pollen-limited reproduction in this Mediterranean species, an evergreen, sclerophyllous shrub inhabiting the banks of temporary streams in all countries around the Mediterranean seaboard.
TL;DR: The results confirm the presence of melatonin binding sites in median eminence and show, for the first time, the existence ofMelatonin binding Sites in the Harderian gland, using [125I]melatonin.
TL;DR: Observations on various car mutants indicate that light prevents the normal inhibition of the pathway by the carA and carS gene products, which implies that the chromophore(s) for photocarotenogenesis are presumably flavins, and not carotenes.
Abstract: Blue light stimulates the accumulation of beta-carotene (photocarotenogenesis) in the fungus Phycomyces blakesleeanus. To be effective, light must be given during a defined period of development, which immediately precedes the cessation of mycelial growth and the depletion of the glucose supply. The competence periods for photocarotenogenesis and photomorphogenesis in Phycomyces are the same when they are tested in the same mycelium. Photocarotenogenesis exhibits a two-step dependence on exposure, as if it resulted from the additon of two separate components with different thresholds and amplitudes. The low-exposure component produces a small beta-carotene accumulation, in comparison with that of dark-grown mycelia. The high-exposure component has a threshold of about 100 J· m−2 blue light and produces a large beta-carotene accumulation, which is not saturated at 2·106 J·m−2. Exposure-response curves were obtained at 12 wavelengths from 347 to 567 nm. The action spectra of the two components share general similarities with one another and with those of other Phycomyces photoresponses. The small, but significant differences in the action spectra of the two components imply that the respective photosystems are not identical. Light stimulates the carotene pathway in the carB mutants, which contain the colourless precursor phytoene, but not beta-carotene. Carotenogenesis is not photoinducible in carA mutants, independently of their carotene content. This and other observations on various car mutants indicate that light prevents the normal inhibition of the pathway by the carA and carS gene products. The chromophore(s) for photocarotenogenesis are presumably flavins, and not carotenes.
TL;DR: In this paper, a marine sediment core from the Kattegat area (Sweden) has been studied for dating purposes, and the 137 Cs and 210 Pb profiles have been measured and described by a model of incomplete activity mixing.
TL;DR: This work has calculated the fraction of inhibited cyclase under each condition, the affinity constant of each inhibitor for the cyclase, and the probability that a rejected intermediate molecule will be readmitted and further metabolized in enzyme aggregates.
Abstract: The existence and the mode of operation of certain enzyme aggregates may be established from the concentrations of intermediates measured in the presence of specific inhibitors. beta-Carotene, the most abundant carotenoid pigment in the fungus Phycomyces blakesleeanus, arises from ring formation at both ends of lycopene. The inhibitors nicotine, imidazole, alpha-picoline, and 2-(4-chlorophenylthio)triethylamine lead to the simultaneous accumulation of lycopene, beta-carotene, and the one-ring intermediate gamma-carotene. The quantitative analytical values obey precise mathematical relationships: those expected from the operation of an enzyme aggregate with two cyclases equally sensitive to the inhibitors. The intermediates lycopene and gamma-carotene rejected by chemically inhibited enzymes may be readmitted to other cyclases in the wild type but not in heterokaryons containing a carA mutation. We have calculated the fraction of inhibited cyclase under each condition, the affinity constant of each inhibitor for the cyclase, and the probability that a rejected intermediate molecule will be readmitted and further metabolized. The probabilities for lycopene and gamma-carotene are identical and independent of the inhibitor responsible for the rejection. Our calculations suggest that each rejected intermediate molecule is readmitted to the enzyme aggregates two or three times on the average.
TL;DR: Results suggest that the intracellular distribution of the glycosylation enzymes is not only cell type-specific as previously shown (Roth, J., Taatjes, D. J., Weinstein, J. C., Greenwell, P., and Watkins, W. M.) but it might also vary depending on the stage of cell differentiation.
TL;DR: A direct relationship appears to exist between increasing Gle Mason grade and increasing glandular variability, and there is an inverse relationship between Gleason grade, gland lumen area, and the number of glandular nuclei, as assessed by a group of pathologists.
Abstract: Three pathologists evaluated a number of designated architectural features to assign grades to 41 cases of well- to moderately differentiated adenocarcinoma, and their opinions were compared. The consensus opinion was obtained and evaluated against objective measurements of glandular architecture that were obtained by morphometric techniques. The observers agreed on gland size, gland uniformity, and the number of glands per field in only 49%, 31%, and 39% of cases, respectively. There were significant differences in the Gleason grades assigned by observers. Paired matching of individual Gleason grades showed agreement among observers in 44% (18 of 41), 56% (23 of 41), and 75% (31 of 41) of cases, respectively. This level of interobserver disagreement occurred even though cases with predominant patterns were selected carefully and those with variable patterns were excluded. A direct relationship appears to exist between increasing Gleason grade and increasing glandular variability, and there is an inverse relationship between Gleason grade, gland lumen area, and the number of glandular nuclei, as assessed by a group of pathologists.
TL;DR: The first report of (8Z)-fusarin C as a natural product is reported, isolated from cultures of Gibberella fujikuroi and determined by spectroscopy.
TL;DR: It is concluded that although non-mucoid strains of P. aeruginosa initially colonise plastic surfaces better than mucoids strains, mucoid strain strains also persist on these surfaces.
Abstract: Summary. The adherence of six non-mucoid and three mucoid strains of Pseudomonas aeruginosa to polyvinyl chloride (PVC), polyurethane (PU) and siliconised latex (SL) was evaluated by a radiometric method and scanning electronmicroscopy. Initially greater numbers of mucoid than non-mucoid strains adhered to all three materials. Hydrophobic non-mucoid strains adhered more efficiently than hydrophilic strains. Numbers of adherent non-mucoid P. aeruginosa cells increased with time, reaching a peak, which was different for each strain, at 1–4h for PU, 4 h–2 days for SL and 2–3 days for PVC; thereafter a gradual decrease was observed, maximal and final values of adherence being higher with PVC and SL than with PU. Adherence of mucoid strains increased with time in 3–5 days, until a stready state was reached. We conclude that although non-mucoid strains of P. aeruginosa initially colonise plastic surfaces better than mucoid strains, mucoid strains also persist on these surfaces.
Journal Article•
TL;DR: It is proposed that the age-related increase in the efficacy of GABA-enhancement of [3H]flunitrazepam binding could be correlated with the rise in the proportion of type I benzodiazepine receptor in 24-month-old hippocampal membranes.
Abstract: We have characterized the pharmacologic properties of the gamma-aminobutyric acid (GABAA)/benzodiazepine receptor complex in hippocampal membranes from 3-month- and 24-month-old Wistar rats. No major changes were found in [3H]flunitrazepam or [3H]muscimol binding parameters. Neither the dissociation constant(s) nor the Bmax for either ligand seemed to be modified during aging in hippocampus. Furthermore, the allosteric interaction between the barbiturates binding site and the GABA binding site, determined by pentobarbital stimulation of [3H] muscimol binding, remained unaltered. However, there was a significant increase with aging in the efficacy of the GABA-enhancement of [3H]flunitrazepam binding. On the other hand, we have also detected a significant increase in the proportion of type I benzodiazepine receptor in 24-month-old hippocampal membranes. We propose that the age-related increase in the efficacy of GABA-enhancement of [3H]flunitrazepam binding could be correlated with the increase in the proportion of type I benzodiazepine receptor. Based on these results it is tempting to speculate that the age-dependent modifications on the GABAA/benzodiazepine receptor might reflect an age-dependent neuronal degeneration of the hippocampus or the hippocampal formation.
TL;DR: In this paper, the photochemical activity of undoped and iron-doped TiO2 particles was studied by laser flash photolysis, where a short duration laser pulse was used to produce electron-hole pairs; methyl viologen was employed as electron scavenger.
Abstract: The photochemical activity of undoped and iron-doped TiO2 particles was studied by laser flash photolysis. A short duration laser pulse was used to produce electron-hole pairs; methyl viologen was employed as electron scavenger. The presence of small amounts of iron ions (less than 0.5%) in TiO2 matrices is beneficial to the photoreduction of methyl viologen (MV2+); by contrast, an increase in the amount of iron doping in TiO2 samples (from 0.5% to 5%) sharply reduces the MV+ yield to a value similar to that when pure TiO2 is used. The implications of these results to charge transfer photoreactions, such as dinitrogen reduction to ammonia, are discussed.
TL;DR: This investigation examined the extent to which the activity of a prostaglandin in the anterior hypothalamic, preoptic area of the rat plays a role in the intense fever induced by macrophage inflammatory protein-1 (MIP-1) applied directly to this anatomical region.
Abstract: This investigation examined the extent to which the activity of a prostaglandin (PG) in the anterior hypothalamic, preoptic area (AH/POA) of the rat plays a role in the intense fever induced by macrophage inflammatory protein-1 (MIP-1) applied directly to this anatomical region. For the microinjection of both a PG synthesis inhibitor, indomethacin, and MIP-1 into sites within the AH/POA, guide cannulae were implanted chronically just above this pyrogen-reactive region. Postoperatively, the body temperature (Tb) of each rat was monitored in the unrestrained condition by means of a colonic thermistor probe. MIP-1 microinjected into the AH/POA in a 0.5-microliter volume evoked a biphasic fever when given in a dose of 5.6 picograms (pg) and a monophasic fever in a dose of 28 pg. The latency of the febrile response was ordinarily 15 min with an asymptote of 1.5 degrees C reached ordinarily within 2.0-2.5 h. When the cytokine-reactive site in the AH/POA was pretreated with indomethacin microinjected in an efficacious dose of 0.5 microgram, the MIP-1 fever evoked by 5.6 pg was not inhibited. Further, pretreatment of AH/POA sites with indomethacin prior to the higher 28-pg dose of MIP-1 delayed the febrile response but did not block it. As a systemic control, indomethacin also was administered intraperitoneally in a dose of 5.0 mg/kg, again 15 min prior to the microinjection of MIP-1 into the AH/POA. In this case, indomethacin only partially attenuated but did not block the fever evoked by either dose of MIP-1.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: A new screening procedure was used to isolate 14 gib mutants of Gibberella fujikuroi with modifications in the production of gibberellins with modifications of carotenoid biosynthesis, finding that alpha-Picoline, an inhibitor of lycopene cyclase in G. fujkuroi, inhibits gib berellin biosynthesis.
Abstract: A new screening procedure was used to isolate 14 gib mutants of Gibberella fujikuroi with modifications in the production of gibberellins. The production of carotenoids and gibberellins was investigated in the gib mutants and in representative car mutants with various modifications of carotenoid biosynthesis. The determinations of gibberellins were carried out with a simplified fluorescence method. One of the mutants lacked both gibberellins and carotenoids. In many mutants the two pathways compensated each other: an increase in the production of one group of compounds was accompanied by a decrease in the production of the other. Under certain conditions the compensation was quantitative when the output of the two pathways was measured in moles of the common precursor, geranylgeranyl pyrophosphate. α-Picoline, an inhibitor of lycopene cyclase in G. fujikuroi, inhibits gibberellin biosynthesis. Other agents that affect the accumulation of carotenoids have no noticeable effect on the accumulation of gibberellins; such is the case with diphenylamine and β-ionone, two inhibitors of phytoene dehydrogenation, and visible light, which stimulates carotenogenesis.
TL;DR: In this paper, the Boundary Element Method is employed as a numerical tool, being particularly suitable for contact problems, and the particular characteristics of this kind of problem relevant to the design of an efficient solution procedure are discussed.
TL;DR: In this article, diisopropylethylamine or pyridine was used to convert diicetone-D-glucose to its (S)- or (R)-methanesulfinates 1 and 2 in 90 and 87% yield by treatment with methylsulfinyl chloride in the presence of diisOPL.