Showing papers by "University of Seville published in 1990"

Nonlinear switched capacitor 'neural' networks for optimization problems

Abstract: A systematic approach is presented for the design of analog neural nonlinear programming solvers using switched-capacitor (SC) integrated circuit techniques. The method is based on formulating a dynamic gradient system whose state evolves in time toward the solution point of the corresponding programming problem. A neuron cell for the linear and the quadratic problem suitable for monolithic implementation is introduced. The design of this neuron and its corresponding synapses using SC techniques is considered in detail. An SC circuit architecture based on a reduced set of basic building blocks with high modularity is presented. Simulation results using a mixed-mode simulator (DIANA) and experimental results from breadboard prototypes are included, illustrating the validity of the proposed techniques. >

On the design of voltage-controlled sinusoidal oscillators using OTAs

Abstract: A unified systematic approach to the design of voltage-controlled oscillators using only operational transconductance amplifiers (OTAs) and capacitors is discussed. Two classical oscillator models, i.e. quadrature and bandpass-based, are employed to generate several oscillator structures. They are very appropriate for silicon monolithic implementations. The resulting oscillation frequencies are proportional to the transconductance of the OTA, and this makes the structures well-suited for building voltage controlled oscillators (VCOs). Amplitude stabilization circuits using both automatic gain control (AGC) mechanisms and limitation schemes are presented. The circuits are compatible with the transconductance amplifier capacitor oscillator (TACO). Experimental results from bipolar breadboard and CMOS IC prototypes showing the potential of OTA-based oscillators for high-frequency VCO operation are included. >

A CMOS Implementation of Fitzhugh-Nagumo Neuron Model

Abstract: A CMOS circuit is proposed that emulates FitzHugh-Nagumo's differential equations using OTAs, diode connected MOSFETs and capacitors. These equations model the fundamental behavior of biological neuron cells. Fitz-Hugh-Nagumo's model is characterized by two threshold values. If the input to the neuron is between the two thresholds the output yields a sequence of firing pulses, if the input is outside this range, no output is observed. The resulting circuit due to the (voltage) programmability of the OTA allows one to easily vary parameters. Thus a large family of solutions can be obtained including the Van der Pol's equation. Experimental results from a CMOS prototype are given that show the suitability of the technique used, and their potential for biological CMOS system emulation.

Liquid-vapour coexistence of the gay-berne fluid by gibbs-ensemble simulation

Abstract: The Gibbs-ensemble Monte Carlo simulation method is used to predict the liquid-vapour coexistence of a fluid whose molecules interact with a cut and shifted Gay-Berne pair potential with elongation κ = 3 and well-depth ratio κ′ = 5. From these simulation results we estimate the temperature, density and pressure at the critical point to be kT c/eo = 0·489 ± 0·005, ρcσ3 o = 0·096 ± 0·004, p cσ3 o/eo = 0·0138 ± 0·0014. We also present evidence of the existence of the vapour-isotropic-liquid-solid triple point. Comparison with the density-functional approximation shows that this theoretical method predicts coexistence and critical temperatures that are too low.

High‐Temperature Creep of Yttria‐Stabilized Zirconia Single Crystals

Abstract: Creep of 9.4-mol%-Y2O3-stabilized cubic ZrO2 has been studied between 1300° and 1550°C. Conventional power-law creep (stress exponent n∼ 4.5) is found at the higher temperatures, with an activation energy (∼6 eV) corresponding to cation diffusion. Transition to a different creep mechanism occurs at the lower temperatures, as indicated by higher values of the stress exponent (n∼ 7) and an activation energy (∼7.5 eV) higher than that for cation self-diffusion. The lower-temperature behavior is caused by a competition between cross-slip-controlled and recovery-controlled creep. Consideration of all the creep and diffusion data now available suggests that the rate-controlling high-temperature mass transport in Y2O3-stabilized ZrO2 can be described by D= 10−3 exp(-5.0 eV/kT) m2·s−1.

Magma mixing in the subvolcanic environment: petrology of the Gerena interaction zone near Seville, Spain

Abstract: The mechanisms by which felsic and mafic magmas interact and approach a uniform hybrid composition through the processes of mingling and mixing have been studied in a high-level subvolcanic setting in the Spanish Hercynian at Gerena, near Seville. The compositions involved are calc-alkaline and the situation is one of tonalite-quartz diorite synplutonic dykes injected into a granitic magma chamber. The resulting hybrids include dykes, pillows and globules of tonalite with chilled margins which are variously disrupted and homogenised with the host granite. The present investigation is based on field and petrographic observations of hybridization textures, the identification of different stages in the crystallisation history of the tonalite through mineral textures, and the characterization of mineral compositions at these various stages. Proportions of the end-member magmas involved were obtained by major-oxide mixing models and tested satisfactorily with trace elements. A mechanistic model is presented to account for these observations which involves the early quenching of the tonalite when it was emplaced into the granite magma chamber. After high temperature crystallization had occurred the two magmas attained thermal equilibrium and disruption of the tonalite in the high energy regime of this subvolcanic complex resulted in dispersion of fragments and crystals through the granite giving rise to hybrid granodiorite compositions. It is argued that such high-energy flow conditions are a necessary requirement for effective hybridization in this environment in contrast to most large-scale magma chamber settings where mixing is driven by thermal and buoyancy contrasts.

On the effects of solvent and intermolecular fluctuations in proton transfer reactions

Abstract: We present a theory of proton transfer reactions which incorporate the modulation of the proton’s potential surface by intermolecular vibrations and the effect of coupling to solvent degrees of freedom. The proton tunnels between states corresponding to it being localized in the wells of a double minimum potential. The resulting tunnel splitting depends on the intermolecular separation. The solvent response to the proton’s charge is modeled as that of a damped oscillator, allowing the introduction of friction effects in the solvent dynamics. The rate of transfer is evaluated by perturbation theory in the level splitting. We find that typically the intermolecular and solvent contributions enhance the rate relative to the values obtained in their absence. This effect is evident at low temperature where friction can enhance the rate by increasing opportunity for solvent tunneling. At high temperature the intermolecular motion enhances the rate by sampling over a distribution of tunnel splittings.

Fine needle aspiration in myxoid tumors of the soft tissues.

Abstract: Myxoid tumors of soft tissues constitute a histogenetically heterogeneous group of lesions, both benign and malignant, that show an overproduction of mucopolysaccharide substances. A correlative fine needle aspiration (FNA) cytologic and histologic study was performed on 16 such cases (3 intramuscular myxomas, 2 lipoblastomas, 6 myxoid liposarcomas, 4 myxoid malignant fibrous histocytomas [MFHs] and 1 extraskeletal myxoid chondrosarcoma), with electron microscopic examination of the aspirate in 4 cases. FNA of all tumors produced a gelatinous material. Smears from all but one of the tumors had a granular myxoid background substance that stained blue to blue-red with the Diff-Quik stain; the exception was the extraskeletal myxoid chondrosarcoma, whose smears stained intensely blue-red to red. On light microscopy, only lipomatous tumors had distinctive cells with diagnostic value: the lipoblasts. Although the arrangement of lipoblasts in lipoblastomas differed somewhat from that found in myxoid liposarcomas, clinical data were important for making a definitive diagnosis. Intramuscular myxomas generally showed a low cellularity composed of fibroblastlike cells with no cytologic atypia. Myxoid MFHs were composed of fibroblastlike cells and macrophagelike cells; the elongated cells with slight-to-moderate nuclear atypia predominated in tumors of low-grade malignancy, while polygonal or round cells with one or more nuclei and marked nuclear atypia predominated in high-grade tumors. Although extraskeletal myxoid chondrosarcoma was mainly differentiated from low-grade myxoid MFH by its metachromatic matrix, ultrastructural studies showed the distinctive distended cisternae with microtubular aggregates in the extraskeletal myxoid chondrosarcoma, thus contributing to the definitive diagnosis.

Asymptotic exponential stability of stochastic partial differential equations with delay

Abstract: Sufficient conditions for pathwise asymptotic exponential stability of the solution of the stochastic PDE with delay d x t = Ax tdt + B(xp(t)) dwt are given. The assumptions on the operators A and B are essentially the same as in the case without delay. In addition, our deduction also shows an alternative proof for some of the results in this case. In fact, the crucial difference is that we do not use the operator P employed by Haussmann and Ichikawa.

Purification and properties of glutamine synthetases from the cyanobacteria Synechocystis sp. strain PCC 6803 and Calothrix sp. strain PCC 7601.

Abstract: Glutamine synthetases (GSs) from two cyanobacteria, one unicellular (Synechocystis sp. strain PCC 6803) and the other filamentous (Calothrix sp. strain PCC 7601 [Fremyella diplosiphon]), were purified to homogeneity. The biosynthetic activities of both enzymes were strongly inhibited by ADP, indicating that the energy charge of the cell might regulate the GS activity. Both cyanobacteria exhibited an ammonium-mediated repression of GS synthesis. In addition, the Synechocystis sp. showed an inactivation of GS promoted by ammonium that had not been demonstrated previously in cyanobacteria.

Behavior of accessory abducens and abducens motoneurons during eye retraction and rotation in the alert cat.

Abstract: 1. The activity of both accessory abducens (Acc Abd) and abducens (Abd) motoneurons (Mns) was recorded in the alert cat during eye retraction and rotational eye movements. Cats were fitted with two scleral coils, one measured rotational eye movements directly and the other retraction by distinguishing the translational component. 2. Acc Abd and Abd Mns were identified following antidromic activation from electrical stimulation of the ipsilateral VIth nerve. 3. In response to corneal air puffs, bursts of spikes were produced in all (n = 30) Acc Abd Mns. The burst began 7.2 +/- 1.2 (SD) ms after onset of the air puff and 8.9 +/- 1.9 ms before eye retraction. 4. Acc Abd Mns were silent throughout all types of rotational eye movements, and tonic activity was not observed during intervals without air-puff stimulation. 5. In contrast, all (n = 50) identified Abd Mns exhibited a burst and/or pause in activity preceding and during horizontal saccades as well as a tonic activity proportional to eye position. 6. Only 10% of Abd Mns fired a weak burst of spikes in response to air-puff stimulation. 7. We conclude that Acc Abd Mns are exclusively involved in eye retraction in the cat and that only a few Abd Mns have an eye-retraction signal added to their eye position and velocity signals. Thus any rotational eye-movement response described in retractor bulbi muscle must result from innervation by Mns located in the Abd and/or the oculomotor nuclei. 8. The organization of the prenuclear circuitry and species variation are discussed in view of the nictiating membrane extension response measured in associative learning.

Microgranular enclaves as indicators of hybridization processes in granitoid rocks, Hercynian Belt, Spain

Abstract: Many Hercynian granitoids of calc-alkaline composition are characterized by the presence of microgranular enclaves of tonalite to diorite composition. Though some differences in size, shape, and relative abundance of the enclaves are observed between deep-seated, high-level, and subvolcanic plutons, there are considerable similarities in texture, grain size, and composition. In magma interaction zones where basic and silicic magmas mingled, enclaves were generated from the disruption, by convective flow, of synplutonic dykes of basic, fractionated, perhaps hybrid, magmas. Many enclaves can be interpreted as non-consolidated portions of basic magma in thermal equilibrium with the host granitoid. Under such condition, enclaves are easily disaggregated and mixed with the host granitoid, contributing to the hybridization of the latter. The process implies the development of special textures in both enclave and host granitoid, and may be tested by chemical variations and correlations, suggesting that the presence of enclaves, with these particular textures and compositions, may imply that a form of hybridization was involved in the genesis of the host granitoids.

Compressive Creep of SiC‐Whisker‐Reinforced Al2O3

Abstract: Compressive creep of SiC-whisker-reinforced Al{sub 2}O{sub 3} composites (0. 5. 15. and 25 wt% SiC) was measured in the temperature range of 1300{degrees} to 1500{degrees}C in air and argon. The creep resistance increased with increasing whisker concentration. The results indicate that the whiskers degraded in air, increasing strain rates compared to those in argon. Stress exponents between 1.0 and 2.0 and an activation energy of 620 {plus minus} 100 kJ/mol were measured. Transmission electron microscopy observations indicate that cavitation was minimal and that the deformed composites had the same dislocation structure as did the as-received samples.

Parents' Ideas About the Development and Education of Their Children. Answers to Some Questions

Abstract: The ideas of parents concerning the development, upbringing, and education of their children have become a subject that has produced a lot of work in developmental research in recent years. However, there still remain grey areas and contradictions which need to be further clarified. While trying to steer clear of the fragmentary nature of research done in this area, this paper analyses a wide-ranging set of ideas of differing content. An attempt is then made to find elements that help characterise the overall pattern of these ideas. The study also tries to clarify the amount of weight that should be given to each of the determining variables that go to make up parents' ideas (educational background, professional status, rural or urban residence, previous experience as parents), while at the same time analysing the degree of concurrence, or lack of it, existing within the married couple. Three classes of parents are seen to exist (traditional, modern, and paradoxical) and the educational background is seen...

Uptake and intracellular activity of an optically active ofloxacin isomer in human neutrophils and tissue culture cells.

Abstract: The penetration of an optically active ofloxacin isomer [(-)-ofloxacin] into human neutrophils and different tissue culture cells (HEp-2, McCoy, MDCK, and Vero) was studied and compared with that of ofloxacin by a fluorometric assay. The cellular-to-extracellular-concentration ratios (C/E) of (-)-ofloxacin were always higher than 6, significantly greater than those of ofloxacin at extracellular concentrations of 5 and 10 mg/liter. The penetration of (-)-ofloxacin and ofloxacin was doubled when neutrophils were stimulated by phorbol myristate acetate but not affected after ingestion of opsonized Staphylococcus aureus. The C/E ratios of (-)-ofloxacin and ofloxacin for different tissue culture epithelial cells and fibroblasts were lower than those of neutrophils but still higher than 2. Both compounds produced a significant reduction in viable intraphagocytic S. aureus during 3 h of exposure to antimicrobial agents. We conclude that (-)-ofloxacin appears to reach higher intracellular concentrations than ofloxacin, remaining active inside the neutrophils.

Glycogenolytic effect of pancreastatin in the rat.

Abstract: Pancreastatin is a novel 49-amino acid peptide with a C-terminal glycine amide. The peptide was isolated from porcine pancreatic extracts and shows a structural similarity to chromogranin A. The effect of synthetic porcine pancreastatin on blood glucose levels and hepatic glycogen content was investigated in rats in vivo. Pancreastatin (300 pmol/kg) produced a time-dependent decrease in glycogen content of liver and a slight hyperglycemia. Basal plasma insulin and glucagon levels were not modified by pancreastatin. We suggest that pancreastatin could play a biological role in the glucose metabolism through a glycogenolytic effect.

Implementation of the fast decoupled load flow on a vector computer

Abstract: The authors present a method which improves the application of supercomputer technology to power systems problems. The approach explored compensates for the short vectors that occur in power systems calculations by modifying the technique used for partitioning a matrix. The concept of indistinguishable nodes is extended to the factorization path graph and is employed in the partition of a matrix with no fill-ins. The general idea is to increase the size of the vectors without increasing the number of operations. The authors demonstrate the performance of the proposed method by incorporating it into a fast decoupled load flow program running on a CRAY X/MP-48 supercomputer. Significant improvements over results using conventional computers were obtained. With the more than 22 MFLOPS (million floating-point operations per second) for the entire process using standard FORTRAN language. Claims are substantiated by experiments using test data from several configurations of actual power systems. >

Estimating microbial biomass nitrogen using the fumigation-incubation and fumigation-extraction methods in a warm-temperate forest soil

Abstract: Microbial biomass-N was measured in the top 60 cm of acid soils on a forested slope using the fumigation-incubation and fumigation-extraction methods. Average microbial biomass-N was 54.4 and 68.5 g N m−2, respectively. Statistical differences between methods and depths were detected, but not between sites along the slope. Estimates of microbial biomass-N measured by the two methods were correlated only in samples taken from 0–20 cm (r = 0.77, P < 0.01). With both methods microbial biomass-N decreased rapidly with depth following a multiplicative model. Organic carbon showed a significant curvilinear relationship with microbial biomass-N measured in the 0–20 cm by the fumigation extraction method (r = 0.81, P < 0.001) and by fumigation-incubation (r = 0.72, P < 0.001). In a multiple linear regression with organic C, the pH of the samples improved the relationship with fumigation extraction values (multiple r = 0.82, P < 0.001) and with fumigation-incubation values (multiple r = 0.79. P < 0.001). but pll only explained 4.9 and 5.2% of the variance. When only the 0.20 cm samples are considered, only organic C explained a significant portion of the variance in the distribution of microbial biomass. The N in microbial biomass accounted for 3.3 and 2.6% of the total N in the soil when using the fumigation extraction and the fumigation incubation techniques, respectively. The results obtained using the easier fumigation extraction procedure seem more reliable and predictable by environmental factors than those obtained by fumigation incubation.

Identification and cloning of nodulation genes and host specificity determinants of the broad host-range Rhizobium leguminosarum biovar phaseoli strain CIAT899.

Abstract: Summary Rhizobium Ieguminosarum biovar phaseoli type II strain CIAT899 nodulates a wide range of hosts: Phaseolus vulgaris (beans), Leucaena esculenta (leucaena) and Macroptilium atropurpureum (siratro). A nodulation region from the symbiotic plasmid has been isolated and characterized. This region, which is contained in the overlapping cosmid clones pCV38 and pCV117, is able to induce nodutes in beans, leucaena and siratro roots when introduced in strains cured for the symbiotic plasmid, pSym. In addition, this cloned region extends the host range of Rhizobium meliloti and R. leguminosarum biovar (bv.) trifolii wild-type strains to nodulate beans. Analysis of constructed subclones indicates that a 6.4 kb Hin dlll fragment contains the essential genes required for nodule induction on all three hosts. Rhizobium leguminosarum bv. phaseoli type I strain CE3 nodulates only beans. However, CE3 transconjugants harbouring plasmid pCV3802 (which hybridized to a nodD heterologous probe), were capable of eliciting nodules on leucaena and siratro roots. Our results suggest that the CIAT899 DNA region hybridizing with the R. meliloti nodD detector is involved in the extension of host specificity to promote nodule formation in P. vulgaris, L. esculenta and M. atropurpureum.

Response of Dams to Earthquakes Including Effects of Sediments

Abstract: Using a technique based on the boundary element method, results are obtained for two‐dimensional dam‐water‐sediments‐foundation systems subjected to ground motion. Both deep‐stratum and half‐space idealizations of the foundation are considered. The results confirm the findings of previous investigations with respect to dam‐water and dam‐foundation interactions. However, they are in contrast with some of the results of an earlier study obtained using the so‐called “wave reflection coefficient” approach when considering dam‐water‐foundation systems. Specifically, in the case of a half‐space foundation and a full reservoir, the “wave reflection coefficient” approach leads to substantial underestimation (approximately 24% for the system considered) of the peak value of the crest horizontal acceleration due to time‐harmonic horizontal ground motion. Apparently, this is due to the excessive damping introduced into the dam‐water‐foundation system by the absorbing boundary condition imposed on the bottom of the r...

High temperature mechanical behavior of porous open-cell Al2O3

Abstract: Crushing strength and fracture toughness values have been determined for open-cell Al 2 O 3 of density less than 30% of the theoretical density for temperatures up to 1500°C. Room temperature crushing strengths as a function of relative density were found to obey approximately a model for mechanical properties based on bending of individual struts within a cell. Fracture toughness values showed some deviation from the model, which was attributed to the presence of closed cells and microstructural inhomogeneities. Strength and toughness increased at about 900–1100°C but declined above 1200°C. Compressive creep of the open-cell Al 2 O 3 has been measured for temperatures of 1200–1500°C. Creep occured by diffusional flow for strain rates between 10 −8 and 10 −6 s −1 for stresses in the range 20–100 kPa. The activation energy for steady state creep was 504 kJ mol −1 , which is typical for creep of dense Al 2 O 3 . The onset of tertiary creep was associated with the formation of creep cracks in the struts subjected to bending.