Showing papers by "University of Seville published in 1989"
TL;DR: In this article, the ability to determine the actual reaction mechanism (RM) of solid state processes from a single nonisothermal curve was analyzed and discussed, and it was found that the reaction follows the R3 mechanism which is in very good agreement with the results of isothermal experiments.
352 citations
TL;DR: The hypothesis that changes in environmental O2 tension (pO2) could affect the ionic conductances of dissociated type I cells of the carotid body was tested and low pO2 appeared to slow down the activation time course of the K current but deactivation kinetics seemed to be unaltered.
Abstract: The hypothesis that changes in environmental O2 tension (pO2) could affect the ionic conductances of dissociated type I cells of the carotid body was tested. Cells were subjected to whole-cell patch clamp and ionic currents were recorded in a control solution with normal pO2 (pO2 = 150 mmHg) and 3-5 min after exposure to the same solution with a lower pO2. Na and Ca currents were unaffected by lowering pO2 to 10 mmHg, however, in all cells studied (n = 42) exposure to hypoxia produced a reversible reduction of the K current. In 14 cells exposed to a pO2 of 10 mmHg peak K current amplitude decreased to 35 +/- 8% of the control value. The effect of low pO2 was independent of the internal Ca2+ concentration and was observed in the absence of internal exogenous nucleotides. Inhibition of K channel activity by hypoxia is a graded phenomenon and in the range between 70 and 120 mmHg, which includes normal pO2 values in arterial blood, it is directly correlated with pO2 levels. Low pO2 appeared to slow down the activation time course of the K current but deactivation kinetics seemed to be unaltered. Type I cells subjected to current clamp generate large Na- and Ca-dependent action potentials repetitively. Exposure to low pO2 produces a 4-10 mV increase in the action potential amplitude and a faster depolarization rate of pacemaker potentials, which leads to an increase in the firing frequency. Repolarization rate of individual action potentials is, however, unaffected, or slightly increased. The selective inhibition of K channel activity by low pO2 is a phenomenon without precedents in the literature that explains the chemoreceptive properties of type I cells. The nature of the interaction of molecular O2 with the K channel protein is unknown, however, it is argued that a hemoglobin-like O2 sensor, perhaps coupled to a G protein, could be involved.
202 citations
TL;DR: It is shown that the operational transconductance amplifier, as the active element in basic building blocks, can be efficiently used for programmable nonlinear continuous-time function synthesis.
Abstract: It is shown that the operational transconductance amplifier, as the active element in basic building blocks, can be efficiently used for programmable nonlinear continuous-time function synthesis. Two efficient nonlinear function synthesis approaches are presented. The first approach is a rational approximation, and the second is a piecewise-linear approach. Test circuits have been fabricated using a 3- mu m p-well CMOS process. The flexibility of the designed and tested circuits was confirmed. >
164 citations
TL;DR: Metal susceptibility levels of the 238 freshly isolated strains were, in general, very heterogeneous among the four taxonomic groups as well as within the strains included in each group, and the influence of salinity and yeast extract concentrations of the culture medium on the toxicity of the heavy metals tested was studied.
Abstract: The tolerance patterns, expressed as MICs, for 250 moderately halophilic eubacteria to 10 heavy metals were surveyed by using an agar dilution method. The moderate halophiles tested included 12 culture collection strains and fresh isolates representative of Deleya halophila (37 strains), Acinetobacter sp. (24 strains), Flavobacterium sp. (28 strains), and 149 moderately halophilic gram-positive cocci included in the genera Marinococcus, Sporosarcina, Micrococcus, and Staphylococcus. On the basis of the MICs, the collection strains showed, overall, similar responses to silver, cobalt, mercury, nickel, lead, and zinc. All were sensitive to silver, mercury, and zinc and tolerant of lead. The response to arsenate, cadmium, chromium, and copper was very heterogeneous. The metal susceptibility levels of the 238 freshly isolated strains were, in general, very heterogeneous among the four taxonomic groups as well as within the strains included in each group. The highest toxicities were found with mercury, silver, and zinc, while arsenate showed the lowest activity. All these strains were tolerant of nickel, lead, and chromium and sensitive to silver and mercury. Acinetobacter sp. strains were the most heavy-metal tolerant, with the majority of them showing tolerance of eight different metal ions. In contrast, Flavobacterium sp. strains were the most metal sensitive. The influence of salinity and yeast extract concentrations of the culture medium on the toxicity of the heavy metals tested for some representative strains was also studied. Lowering the salinity, in general, led to enhanced sensitivity to cadmium and, in some cases, to cobalt and copper. However, increasing the salinity resulted in only a slight decrease in the cadmium, copper, and nickel toxicities.(ABSTRACT TRUNCATED AT 250 WORDS)
156 citations
TL;DR: Injections of the retrograde tracer, wheat germ agglutinated-horseradish peroxidase were placed in the substantia nigra, in adjoining dopamine-containing cell groups A8 and A10, and in the internal and external parts of the pallidal complex of 20 cats in order to identify the compartmental origins of striatal efferent projections to the pallidum and midbrain.
154 citations
TL;DR: In this paper, the existence of pair fluctuations in rapidly rotating nuclei in connection with the pair gap is reviewed, where the quantities considered are single-particle energies (routhians) and alignments.
Abstract: Empirical evidence for the existence of pair fluctuations in rapidly rotating nuclei in connection with the pair gap is reviewed. The quantities considered are single-particle energies (routhians) and alignments. While the cranked shell model in the presence of static pair correlations provides an accurate description of data at rotational frequencies below the critical frequency corresponding to the collapse of the static pair gap, conspicuous discrepancies are found in the region of and above the pairing phase transition. In particular, a group of excitations is observed displaying lower excitation energies and smaller alignments than those predicted by the cranked shell model. Such excitations can be characterized as behaving as if the correlations induced by the presence of a pairing condensate were not totally obliterated after the "phase transition." A theoretical model, based on the renormalization of the single-particle motion mixed by the coupling to pairing vibrations, is quite successful in explaining the overall trend of the data at rotational frequencies larger than the critical frequency. Smaller alignments and excitation energies are correlated with configurations displaying particle coupling schemes which profit most from fluctuations of the pair gap about its zero equilibrium value. While this model reproduces many of the experimental features, it still overpredicts the alignments by 2-3 units of $\ensuremath{\hbar}$ in the crossing region. Thus other degrees of freedom (both static and dynamic), e.g., deformations, also must play a role at large rotational frequencies.
108 citations
TL;DR: The results indicate that type I cells are excitable and have a variety of ionic conductances, and suggest a possible participation of these conductances in chemoreception.
Abstract: Ionic currents of enzymatically dispersed type I and type II cells of the carotid body have been studied using the whole cell variant of the patch-clamp technique. Type II cells only have a tiny, slowly activating outward potassium cur- rent. By contrast, in every type I chemoreceptor cell studied we found (a) sodium, (b) calcium, and (c) potassium currents. (a) The sodium current has a fast activation time course and an activation threshold at ~-40 mY. At all voltages inactivation follows a single exponential time course. The time constant of inactivation is 0.67 ms at 0 mV. Half steady state inactivation occurs at a membrane potential of ~- 50 mV. (b) The calcium current is almost totally abolished when most of the external calcium is replaced by magnesium. The activation threshold of this cur- rent is at ~-40 mV and at 0 mV it reaches a peak amplitude in 6-8 ms. The calcium current inactivates very slowly and only decreases to 27% of the maximal value at the end of 300-ms pulses to 40 mV. The calcium current was about two times larger when barium ions were used as charge carriers instead of calcium ions. Barium ions also shifted 15-20 mV toward negative voltages the conductance vs. voltage curve. Deactivation kinetics of the calcium current follows a biphasic time course well fitted by the sum of two exponentials. At -80 mV the slow com- ponent has a time constant of 1.3 _+ 0.4 ms whereas the fast component, with an amplitude about 20 times larger than the slow component, has a time constant of 0.16 _+ 0.03 ms. These results suggest that type I cells have predominantly fast deactivating calcium channels. The slow component of the tails may represent the activity of a small population of slowly deactivating calcium channels, although other possibilities are considered. (c) Potassium current seems to be mainly due to the activity of voltage-dependent potassium channels, but a small percentage of calcium-activated channels may also exist. This current activates slowly, reaches a peak amplitude in 5-10 ms, and thereafter slowly inactivates. Inactivation is almost complete in 250-300 ms. The potassium current is reversibly blocked by tetraeth- ylammonium. Under current-clamp conditions type I cells can spontaneously fire large action potentials. These results indicate that type I cells are excitable and
102 citations
TL;DR: The relationship found between G + C-content and codon usage in these genomes correlate with taxonomic distance.
Abstract: The relationship between G + C-content and codon usage in genes of human, mus, rat, bovine and chicken nuclear genomes was investigated. Correlation and lineal regression analyses were carried out on plots that related the frequency of each codon within each synonymous codon group to the G + C-content of the coding sequence as a whole. Under GC pressure, in most of the quartet codon groups there is a preferential choice of the C-ending codon, except in leucine and valine codon groups where the choice of the G-ending codon is preferred. Among ducts, the choice of codons specifying phenylalanine and glutamate shows the strongest dependence on G + C-content. The relationship found between G + C-content and codon usage in these genomes correlate with taxonomic distance.
87 citations
TL;DR: Bacillus halophilus, a new moderately halophilic (optimum growth at 15% salt) species, is described, isolated from rotting wood from the Pacific Ocean.
84 citations
TL;DR: In this paper, the most frequently used kinetic models with respect to the boundary conditions of a rate equation are discussed, where the molar concentration of reactants is frequently replaced by the so-called degree of conversion (a) which is usually defined as 111 ~,=(c,GMGo-G) 0)
82 citations
TL;DR: In this article, the stability of liquid bridges in zero gravity conditions under the influence of an a.c. electric field tangential to the interface is examined, and a static analysis was carried out to find the bifurcation surfaces as a function of the three relevant non-dimensional parameters: Λ, the slenderness or ratio of height to diameter of the cylindrical bridge; β 0, the ratio of dielectric constants of the two fluids used and Ξ, a nondimensional quantity proportional to the applied voltage.
Abstract: The stability of liquid bridges in zero gravity conditions under the influence of an a.c. electric field tangential to the interface is examined in this paper. For the theoretical study, a static analysis was carried out to find the bifurcation surfaces as a function of the three relevant non-dimensional parameters: Λ, the slenderness or ratio of height to diameter of the cylindrical bridge; β0, the ratio of dielectric constants of the two fluids used and Ξ, a non-dimensional quantity proportional to the applied voltage. Stable and unstable regions of Λ−βo−Ξ space were distinguished. Results indicate a strong stabilizing effect for higher values of β0. The experimental study, using silicone and ricinus oil to approximate zero gravity conditions fully confirmed quantitatively the theoretical results.
TL;DR: The interplay of charge diffusion, a hitherto neglected phenomenon, and Coulomb repulsion in the finite-amplitude electroconvection of a layer of insulating liquid subjected to weak unipolar injection is discussed.
Abstract: The interplay of charge diffusion, a hitherto neglected phenomenon, and Coulomb repulsion in the finite-amplitude electroconvection of a layer of insulating liquid subjected to weak unipolar injection is discussed. Analytical considerations and numerical simulations show that there exists a fundamental nondimensional parameter that relates the strength of the Coulomb repulsion to the diffusion coefficient. Unless this parameter is much larger than 1, diffusion must be included. A projection of the two-dimensional charge conservation equation into a one-dimensional space allows us to obtain good estimates of the charge-density distribution for any value of this parameter.
TL;DR: In this paper, a theory of solvent effects on the rate of intramolecular proton transfer (IPT) reactions is presented, where the proton tunnels between two vibrational levels of a double minimum potential.
Abstract: We present a theory of solvent effects on the rate of intramolecular proton‐transfer (IPT) reactions. The proton tunnels between two vibrational levels of a double minimum potential. The proton’s coupling to the solvent is modeled with an oscillator bath, appropriate to reactions where a charge interacts with many solvent molecules. The rate is evaluated by use of the Golden Rule; the perturbation is the level splitting. The IPT rate constant has several limiting expressions, one of which has an activated form. The activation energy is related to the medium reorganization energy, and provides a mechanism to slow the IPT reaction. Since reorganization energies are small in nonpolar and large in polar solvents, the rate is expected to be smaller in the latter class of solvents. Isotopic substitution is predicted to only affect the prefactor of the rate expression. Another regime is obtained for smaller reorganization energies where the solvent dynamics, as described by a dielectric relaxation time, are important. Comparison is made with recent experimental studies of IPT in solution.
TL;DR: The results suggest that ofloxacin could be transported via an amino acid transport system and that the fluorometric assay is a useful method for determining the intracellular penetration of fluoroquinolones, avoiding the use of radiolabeled antimicrobial agents.
Abstract: A fluorometric assay, based on the natural fluorescence of the quinolone nucleus, was used to determine the uptake of ofloxacin by human polymorphonuclear leukocytes. The ratio of cellular concentration to extracellular concentration (C/E) at 20 min and 37 degrees C was 7.2, using an extracellular concentration of 5 micrograms/ml. Uptake was rapid and was not affected by pH (5 to 9), but required elevated environmental temperature and cell viability. The metabolic inhibitors sodium fluoride and sodium cyanide significantly decreased the uptake of ofloxacin. The penetration of ofloxacin was not affected by the presence of glucose or adenosine, but was decreased by L-amino acids (lysine, leucine, and glycine). These results suggest that ofloxacin could be transported via an amino acid transport system and that the fluorometric assay is a useful method for determining the intracellular penetration of fluoroquinolones, avoiding the use of radiolabeled antimicrobial agents.
TL;DR: In this article, a procedure for dynamic stress intensity factor computations using traction singular quarter-point boundary elements is presented, which allows for the study of problems with complex geometry that include one or several cracks.
TL;DR: In this article, a mixture of two benzylic ligands was found to be involved in a fast equilibrium which interchanges the two types of benzyolic ligands, and the synthesis and spectral characterization of the new complexes trans-[Ni(C6H5)X(PMe3)2] (X = Cl, Br).
TL;DR: In this article, an incremental procedure is proposed to deal with the contact problem between deformable bodies with the presence of friction, which is not a problem that can be solved linearly.
Abstract: The contact problem between deformable bodies with the presence of friction is not a problem that can be solved linearly. The uncertainty of the final contact zone and/or the irreversible character of the friction itself are the causes of the nonlinearity. An incremental procedure is proposed to deal with this kind of problem, without restriction in the application of the load. The algorithm has been implemented using as solution tool the Boundary Element Method. The use of discontinuous elements makes the applications of boundary and contact conditions easier.
TL;DR: It is discussed the possible role of mechanical force in converting the dorsoventral tenascin-positive fibrils into the localized pattern of tendon insertions into the proximal parts of the phalanges and an ectodermal role in tendon pattern formation within the mesenchyme.
TL;DR: In this paper, the authors present computational structures based on the theory of fast algorithms for short linear convolutions, which are suitable for the implementation of L-path and L-block digital filters.
Abstract: One of the major problems in the multi-DSP (digital signal processor) implementation of L-path and L-block digital filters is the hardware complexity-throughput rate tradeoff The author presents computational structures based on the theory of fast algorithms for short linear convolutions, which are suitable for the implementation of these types of digital filters He also compares the performance of the structures with two previously published ones The comparison shows that the schemes proposed here are faster and that the complexity-throughput tradeoffs can easily be controlled by the designer >
TL;DR: In this article, the acid-base equilibria of protonation and deprotonation of pyrrole and its benzologs indole and carbazole were reexamined using the Excess Acidity Method (E.A.M.).
TL;DR: The sequence of morphological differentiation of Müller cells in the chick retina was investigated in relation to the differentiation of the retinal neurons using the Golgi method.
Abstract: The sequence of morphological differentiation of Muller cells in the chick retina was investigated in relation to the differentiation of the retinal neurons using the Golgi method. From the beginning of differentiation, the Muller cell develops spurs and lateral processes. Some of these glial processes become transformed into accessory prolongations of the Muller cell. From the 17th or 18th day of incubation, the morphology of the Muller cells is similar to that of the adult retina. On the basis of their inner prolongation, two types of Muller cells were identified. The first type, with diffuse and abundant descending processes, is identical to that described classically. The second type is a cell characterized by sparse and scanty inner ramifications.
This report also describes electron microscopic observations of Muller cells and their enwrapping relationship with the axons of the optic nerve fiber layer.
TL;DR: Three of the new Rhizobium fredii strains isolated by Dowdle and Bohlool (1985) were investigated for their plasmid content, carbon nutritional patterns, salt tolerance and host-range and symbiotic efficiency with eight different legumes of the “cowpea cross-inoculation group”.
01 Jan 1989
TL;DR: Carotenoid production is rarely the main objective of a culture, but colourful products rich in carotenoids are obtained from various plants and algae.
Abstract: Humans,like most other animals, need carotenoids but cannot synthesize them. Our main suppliers are the fruits and vegetables, with lesser, mostly indirect contributions from fungi, algae, and bacteria. Carotenoid production is rarely the main objective of a culture, but colourful products rich in carotenoids are obtained from various plants and algae. The oldest example is saffron (Crocus sativus), still planted in La Mancha, Spain, and elsewhere for the stigmas of its flowers. Many fields of central Mexico become bright orange in the summer with the flowers of cempasuchil (Tagetes tenuifolia, a kind of marigold), whose dried petals are fed to chicken for meat and egg yolk colour. Annatto is extracted from the seeds of a tropical tree, Bixa orellana. The most familiar carotenoid-rich product is probably paprika, a powder made by grinding red peppers (Capsicum annuum).
TL;DR: In this article, the role of chlorine and the thermal pretreatments of the samples in PtRe alloying during the reduction of Pt Al 2 O 3 and PtRe Al O 3 systems has been examined by using the reaction of n -butane hydrogenolysis with the aid of temperature-programmed reduction (TPR) experiments.
TL;DR: In this article, a Boundary Element frequency domain approach that takes into account the dynamic interaction between solid and fluid regions is used to study the seismic response of concrete gravity dams, and results for a particular dam geometry, two different soil profiles, and full and empty reservoir conditions are shown.
Abstract: A Boundary Element frequency domain approach that takes into account the dynamic interaction between solid and fluid regions, which was presented in a separate paper (part I), is used to study the seismic response of concrete gravity dams. Results for a particular dam geometry, two different soil profiles, and full and empty reservoir conditions are shown. The agreement with corresponding published results obtained by other authors using Finite Elements is very good. The BE approach is shown to be capable of modelling a larger variety of soil profiles than any of the previous FE approaches. The effects of several parameters of the model on the seismic response of the dam are studied to show the importance of the joint dam-water-foundation interaction effects and the importance of the correct representation of each one of the three regions involved. Particular attention is paid to the aspects related to the BE modelling of the problem. The use of artificial boundaries, where far-field boundary conditions are prescribed, for cases where the radiation conditions are not satisfied, has been shown to be effective.
TL;DR: During aging, there is a decrease in the activity of the 6-phosphogluconate dehydrogenase enzyme in rat liver, and this could be involved in the loss of its enzyme activity.
TL;DR: The nonlinear Bhatnagar, Gross, and Krook kinetic equation is solved for boundary conditions leading to planar Couette flow and heat transport and in the limit of zero Knudsen number but arbitrary uniformity parameter, an exact ``normal'' solution is obtained.
Abstract: The nonlinear Bhatnagar, Gross, and Krook [Phys. Rev. 94, 511 (1954)] kinetic equation is solved for boundary conditions leading to planar Couette flow and heat transport. In the limit of zero Knudsen number but arbitrary uniformity parameter (shear rate), an exact ``normal'' solution is obtained. The velocity distribution function is illustrated explicitly for states far from equilibrium. At finite Knudsen number, the distribution function is obtained from numerical solution of a set of nonlinear, singular integral equations. Results are presented for a range of values of the Knudsen number and uniformity parameter. The approach to a normal state is studied with a determination of the hydrodynamic profiles, velocity slip, shear viscosity, and a nonlinear Burnett transport coefficient.
TL;DR: A representative of extremely halophilic non-alkaliphilic archaebacterial cocci, recently described by Montero et al., (1988), was studied in detail and a new species Halococcus saccharolyticus sp.
TL;DR: The results indicate that the microtubular systems of Paramecium show marked differences in stability, and the images obtained during the repolymerization by heating suggest that the cortical dikinetids are able to nucleate the micro tubules of the cytoplasmic network.
Abstract: The sensitivity of the microtubular systems to cold and nocodazole treatments as well as the cellular distribution of microtubules containing acetylated a-tubulin have been studied in Paramecium. Our results indicate that the microtubular systems of Paramecium show marked differences in stability. Cold and nocodazole treatments produce the depolymerization of the major part of the cytoplasmic microtubular network while the cortical structures remain stable under treatment. This differential stability of the microtubular systems is associated with the acetylation of the a-tubulin. The use of the antibody 6-11B-1, specific for acetylated α-tubulin, shows that the microtubular systems containing acetylated a-tubulin are the same as those that remain stable after depoly-merizing treatments. Finally, the images obtained during the repolymerization by heating suggest that the cortical dikinetids are able to nucleate the microtubules of the cytoplasmic network.
TL;DR: In this paper, the authors used fuzzy set theory to estimate the net present value of an investment project and developed two models to study the isolated effects of each one of these variables on the net-present value calculations.