Showing papers by "University of Seville published in 1987"
TL;DR: In this paper, Bilby, Cottrell and Swinden applied the crack model to simulate the blocking of the plastic zone at the grain boundary and to obtain the stress concentration ahead of the crack as it approaches the barrier.
Abstract: The behaviour of short cracks approaching growth barriers (eg grain boundaries) is considered The crack model of Bilby, Cottrell and Swinden is applied to simulate the blocking of the plastic zone at the grain boundary and to obtain the stress concentration ahead of the crack as it approaches the barrier The idea of the Hall-Petch type relationship that the transmission of slip across grain boundaries needs the previous achievement of a critical stress has been used By making the crack growth rate proportional to the plastic displacement at the root of the crack the deceleration behaviour of short cracks and the existence of non-propagating cracks may be explained The fatigue limit is related to the stress below which a crack growing in a single grain is unable to promote slip in the neighbouring grain The different behaviour in the so-called long crack period has been rationalized in terms of the plastic zone exceeding the grain size For this case, and in the grain completely included within the plastic zone, the Hall-Petch analysis must be applied Hence the maximum back-stress sustained by this grain cannot exceed the yield stress After this point the Bilby et al model is used with uy as a friction stress (ie the Dugdale model) Finally use is made of Fracture Mechanics to correlate the results in the long crack phase
112 citations
TL;DR: In this article, the functioning of an electrostatic precipitator in the light of previous studies on various regimes of electroconvection in both parallel and divergent electric fields is examined.
Abstract: The functioning of an electrostatic precipitator in the light of previous studies on various regimes of electroconvection in both parallel and divergent electric fields is examined. Coupling between velocity and charge density fluctuations for both ions and charged particles is discussed. It is shown that for a certain diameter range of the particles, their nondimensional mobility parameter takes values similar to those characterizing ions in liquids. An experimental simulation using insulating liquids is proposed.
103 citations
TL;DR: The results bring out similarities between the carotenoid biosynthetic pathways of Gibberella and Phycomyces, and significant differences in their respective regulations.
Abstract: The orange pigment neurosporaxanthin colours the mycelia of wild Gibberella fujijuori (Fusarium monifliforme) grown in the light, but is barely detectable in the dark. We have isolated carotenoid mutants from conidia exposed to N-methyl-N′-nitro-N-nitroso-guanidine and other mutagens. Specific blocks in the pathway are represented by white mutants accumulating phytoene and red mutants accumulating torulene; there are also mutants without carotenoids or with complex carotenoid mixtures. Regulatory mutants overproduce neurosporaxanthin, both in the light and in the dark. Other mutants contain considerable neurosporaxanthin in the dark, but less than in the light. The results bring out similarities between the carotenoid biosynthetic pathways of Gibberella and Phycomyces, and significant differences in their respective regulations.
83 citations
TL;DR: In this paper, it was shown that the activation energy of a solid state transformation fitting a Johnson-Melh-Avrami (JMA) kinetic can be determined from the Kissinger's method, even if ERT is smaller than 5.
74 citations
01 Aug 1987
TL;DR: In this paper, a special-purpose analog computer made of switched-capacitor circuits is presented for analyzing chaos and bifurcation phenomena in nonlinear discrete dynamical systems modeled by discrete maps.
Abstract: A special-purpose analog computer made of switched-capacitor circuits is presented for analyzing chaos and bifurcation phenomena in nonlinear discrete dynamical systems modeled by discrete maps x n + 1 = f(x n ) Experimental results are given for four switched-capacitor circuits described by well-known discrete maps; namely, the logistic map, the piecewise-linear unimodal (one-hump) map, the Henon map, and the Lozi map.
73 citations
TL;DR: Different patterns of metal susceptibility were found for all the halobacteria tested, and there was a uniform susceptibility to mercury and silver, and all strains tested were multiply metal tolerant.
Abstract: Sixty-eight halobacteria, including both culture collection strains and fresh isolates from widely differing geographical areas, were tested for susceptibility to arsenate, cadmium, chromium, cobalt, copper, lead, mercury, nickel, silver, and zinc ions by an agar dilution technique. The culture collection strains showed different susceptibilities, clustering into five groups. Halobacterium mediterranei and Halobacterium volcanii were the most metal tolerant, whereas Haloarcula californiae and Haloarcula sinaiiensis had the highest susceptibilities of the culture collection strains. Different patterns of metal susceptibility were found for all the halobacteria tested, and there was a uniform susceptibility to mercury and silver. All strains tested were multiply metal tolerant.
62 citations
TL;DR: The findings show that the sagittal and transverse diameters are clearly different, as well as the total area of the foramen magnum, these parameters being larger in male skulls than in female.
Abstract: The sagittal and transverse diameters of the foramen magnum were examined in 100 human skulls (74 male, 26 female). The results were statistically analyzed and compared with those obtained by other authors. Our findings show that the sagittal and transverse diameters are clearly different, as well as the total area of the foramen magnum, these parameters being larger in male skulls than in female.
62 citations
TL;DR: In this paper, a nonlinear Fokker-Planck equation is derived to describe the cooperative behavior of general stochastic systems interacting via mean-field couplings, in the limit of an infinite number of such systems.
Abstract: A nonlinear Fokker-Planck equation is derived to describe the cooperative behavior of general stochastic systems interacting via mean-field couplings, in the limit of an infinite number of such systems. Disordered systems are also considered. In the weak-noise limit; a general result yields the possibility of having bifurcations from stationary solutions of the nonlinear Fokker-Planck equation into stable time-dependent solutions. The latter are interpreted as non-equilibrium probability distributions (states), and the bifurcations to them as nonequilibrium phase transitions. In the thermodynamic limit, results for three models are given for illustrative purposes. A model of self-synchronization of nonlinear oscillators presents a Hopf bifurcation to a time-periodic probability density, which can be analyzed for any value of the noise. The effects of disorder are illustrated by a simplified version of the Sompolinsky-Zippelius model of spin-glasses. Finally, results for the Fukuyama-Lee-Fisher model of charge-density waves are given. A singular perturbation analysis shows that the depinning transition is a bifurcation problem modified by the disorder noise due to impurities. Far from the bifurcation point, the CDW is either pinned or free, obeying (to leading order) the Gruner-Zawadowki-Chaikin equation. Near the bifurcation, the disorder noise drastically modifies the pattern, giving a quenched average of the CDW current which is constant. Critical exponents are found to depend on the noise, and they are larger than Fisher's values for the two probability distributions considered.
59 citations
TL;DR: In this paper, the passivation effect created by a reaction product other than sulfur is neutralized to some extent by introducing metal sulfides such as HgS, As2S3, SnS and CoS, so that the metal sulfide nuclei deposited on the passivating layer restore the initial reactivity between the solid and the leaching solution.
54 citations
TL;DR: Results suggest that insulin activates the pentose phosphate cycle through the activation of fatty acid synthesis, which is regulated by the activation or inhibition of different NADPH-consuming pathways.
50 citations
TL;DR: Rifapentine and rifampin showed the highest activity against intracellular staphylococci in both peritoneal macrophages and polymorphonuclear leukocytes, and teicoplanin, which achieved high cellular levels with both types of phagocytes, failed to produce a significant reduction in viable intraphagocyticStaphylitis epidermidis.
Abstract: Rifapentine uptake by human peritoneal macrophages and polymorphonuclear leukocytes was evaluated and its activity against intracellular Staphylococcus aureus and Staphylococcus epidermidis in both types of phagocytes was compared to that of rifampin, teicoplanin and clindamycin. Uptake of radiolabeled rifapentine by peritoneal macrophages (intracellular/extracellular ratio 61.4 +/- 5.8) and polymorphonuclear leukocytes (intracellular/extracellular ratio 87.6 +/- 3.9) was significantly higher than that of teicoplanin (intracellular/extracellular ratio 40.8 +/- 3.6 and 52.3 +/- 3.2 respectively) and clindamycin (intracellular/extracellular ratio 6.9 +/- 0.4 and 8.3 +/- 0.5 respectively). Rifapentine and rifampin showed the highest activity against intracellular staphylococci in both peritoneal macrophages and polymorphonuclear leukocytes. Clindamycin also showed efficient intracellular activity. In contrast, teicoplanin, which achieved high cellular levels with both types of phagocytes, failed to produce a significant reduction in viable intraphagocytic Staphylococcus epidermidis. On the basis of these findings it is suggested that rifapentine may play a future role in the treatment of certain types of staphylococcal infection.
TL;DR: The hepatotoxicity of atrazine was investigated by studying clinical parameters related to hepatic function and by electron microscopy, and revealed hepatocytic proliferation and degeneration of smooth endoplasmic reticulum, lipid accumulation and alteration of bile canaliculi proportional to dose and duration of treatment.
Abstract: The hepatotoxicity of atrazine was investigated by studying clinical parameters related to hepatic function and by electron microscopy. Three groups to male albino rats (Wistar strain) received 100, 200 and 400 mg of atrazine/per kg of body weight/per day, for 14 days. One group received 600 mg atrazine/per kg of body weight/per day, for 7 days. At termination of dosing, the animals were sacrificed and blood was drawn for the determination of serum total lipids, glucose, alanine aminotransferase (ALT) and alkaline phosphatase (SAP). A dose dependent decrease in serum glucose concentration was observed in all the groups. In contrast, a dose relate increase in total serum lipids, was apparent at all dose levels studied. Activity of serum ALT and SAP increased approximately 60% and 200% respectively in rats given 600 mg atrazine/kg bw for 7 days. The liver was examined grossly and microscopically. Electron microscopy disclosed no changes in the hepatocytes of rats treated with the low dose (100 mg/kg bw). At high doses, electron microscopy revealed hepatocytic proliferation and degeneration of smooth endoplasmic reticulum, lipid accumulation and alteration of bile canaliculi proportional to dose and duration of treatment.
TL;DR: A highly ethanol-tolerant Saccharomyces wine strain is able, after growth in the presence of ethanol, to efficiently improve the ethanol tolerance of its membrane, while a less-tolerance laboratory strain is unable to adapt its membrane to ethanol.
Abstract: A highly ethanol-tolerant Saccharomyces wine strain is able, after growth in the presence of ethanol, to efficiently improve the ethanol tolerance of its membrane. A less-tolerant Saccharomyces laboratory strain, however, is unable to adapt its membrane to ethanol. Furthermore, after growth in the presence of ethanol, the membrane of the latter strain becomes increasingly sensitive, although this is a reversible process. Reversion to a higher tolerance occurs only after the addition of an energy source and does not take place in the presence of cycloheximide.
TL;DR: The irreversible momentum and heat fluxes are found to be nonanalytic functions of the velocity gradients, indicating that the Chapman-Enskog expansion does not converge for this state.
Abstract: Explicit expressions for the heat and momentum transport are given for a gas in a stationary state with temperature and velocity gradients. The results are obtained from a formally exact analysis of the normal solution to the Bhatnagar-Gross-Krook model for the nonlinear Boltzmann equation, and are not restricted to small gradients. The irreversible momentum and heat fluxes are found to be nonanalytic functions of the velocity gradients, indicating that the Chapman-Enskog expansion does not converge for this state. However, these fluxes are analytic in the temperature gradients; in particular, the heat flux is simply proportional to the temperature gradient so that Fourier's law applies even for large gradients. The space dependence of the thermodynamic and velocity fields is determined as a function of the interaction potential, and the results for Maxwell molecules and hard spheres are compared.
TL;DR: The well-known heterogeneity of adult amacrine cells seems to be preluded by differences in neuroblastic migratory patterns, suggesting the existence of at least two different subsets of amacine cell precursors.
Abstract: The migration of amacrine neuroblasts toward the prospective amacrine cell layer in the chick embryo retina has been studied, in Golgi-stained sections, between days 5 and 9 of embryogenesis. Two distinct populations of presumptive amacrine neuroblasts have been identified on the basis of their shape and migratory behavior. One population (smooth amacrine neuroblasts) display smooth, monopolar or bipolar contours, moving freely across the retina without major changes in the original postmitotic shape, and give processes only after reaching the primitive inner plexiform layer. The second population (multipodial amacrine neuroblasts) includes multipolar neuroblasts with abundant filiform and/or lamelliform processes sprouting in various directions; these highly plastic cells begin modifying their shapes at the time of release from the ventricular lining and continue to do so as they move toward their definitive location. Thus, the well-known heterogeneity of adult amacrine cells seems to be preluded by differences in neuroblastic migratory patterns, suggesting the existence of at least two different subsets of amacrine cell precursors.
TL;DR: In this paper, transfer chemical potentials have been derived from appropriate solubility measurements for several iron(II)-and iron(III)-diimine-cyanide complexes into aqueous methanol.
Abstract: The solvatochromic behaviour of several complexes [Fe(LL)2(CN)2] with LL=Schiff base diimine has been established in a series of non-aqueous solvents, as has that of two analogues containing diazabutadiene ligands. Transfer chemical potentials have been derived from appropriate solubility measurements for several iron(II)-and iron(III)-diimine-cyanide complexes into aqueous methanol, and for [Fe(bipy)2(CN)2] into several binary aqueous solvent series. The usefulness of solvatochromic shifts and transfer chemical potentials as indicators of selective solvation is discussed. Kinetics of oxidation of catechol and of 4-t-butyl catechol by [Fe(bipy)(CN)4]− in aqueous solution are described.
01 Jan 1987
TL;DR: In the case of plants growing in natural ecosystems, only a few estimates have been made for chaparral and tundra species (Miller and Stoner 1979; Merino et al. 1982) as mentioned in this paper.
Abstract: The costs in terms of respired photosynthate involved in growing and maintaining leaves is an important consideration for understanding the overall carbon balance of plants. Estimates of these costs have been made for a number of crop species (Penning de Vries 1975; Hunt and Loomis 1979). In the case of plants growing in natural ecosystems, only a few estimates have been made for chaparral and tundra species (Miller and Stoner 1979; Merino et al. 1982).
TL;DR: In this paper, a population of identical nonlinear oscillators, subject to random forces and coupled via a mean-field interaction, is studied in the thermodynamic limit, and the model presents a nonequilibrium phase transition from a stationary to a time-periodic probability density.
Abstract: A population of identical nonlinear oscillators, subject to random forces and coupled via a mean-field interaction, is studied in the thermodynamic limit. The model presents a nonequilibrium phase transition from a stationary to a time-periodic probability density. Below the transition line, the population of oscillators is in a quiescent state with order parameter equal to zero. Above the transition line, there is a state of collective rhythmicity characterized by a time-periodic behavior of the order parameter and all moments of the probability distribution. The information entropy of the ensemble is a constant both below and above the critical line. Analytical and numerical analyses of the model are provided.
TL;DR: Results suggest that the Rhizobium leguminosarum biovar trifolii symbiotic plasmid pRtr5a harbours the symbiotic determinants for nodulation on H. coronarium.
Abstract: The Rhizobium leguminosarum biovar trifolii symbiotic plasmid pRtr5a was transferred to the Rhizobium sp. (Hedysarum coronarium) strain RB16. Transconjugants carrying pRtr5a ineffectively nodulated Trifolium repens, T. pratense and T. alexandrinum and were unable to nodulate H. coronarium plants. Agarose gel electrophoresis of transconjugants showed that all had lost an indigenous plasmid (230 Md). These results suggest that this plasmid harbours the symbiotic determinants for nodulation on H. coronarium.
TL;DR: The cyst wall of Paraurostyla weissei consists of four morphologically distinct layers and shows an ultrastructure and composition similar to that of the previously described kinetosome-resorbing cysts, and its cytoplasm displays characteristics of “urostylid-type” cysts.
Abstract: The cyst wall of Paraurostyla weissei consists of four morphologically distinct layers. It shows an ultrastructure and composition similar to that of the previously described kinetosome-resorbing cysts, and its cytoplasm displays characteristics of “urostylid-type” cysts. Therefore it is possible to consider it a “transition ciliate” between Stichotrichina and Sporadotrichina.
TL;DR: Although a fairly high number of genes were involved at the various tolerance levels of the wine and laboratory strains, different genes limited growth at different ethanol concentrations indicating that ethanol inhibition is the result of the inhibition of different cellular functions with increasing ethanol concentrations.
Abstract: The genetic basis of ethanol tolerance was investigated in homothallic and heterothallic ethanol-tolerant wine yeasts. All strains were diploid or nearly diploid and able to sporulate. Some possessed recessive lethal alleles. Their meiotic segregation with regard to ethanol tolerance indicates that recessive alleles able to decrease ethanol tolerance were present in the heterozygosis state in the parental wine strains. The number of genes able to spontaneously mutate to alleles of ethanol sensitivity were greater than these found in auxotrophic phenotypes. In homothallic strains segregation in the second generation has to be explained by the simultaneous presence of aneuploidy and ethanol-sensitive alleles. In non-isogenic strains, genes involved in ethanol tolerance had complementary functions. Although a fairly high number of genes were involved at the various tolerance levels of the wine and laboratory strains, different genes limited growth at different ethanol concentrations indicating that ethanol inhibition is the result of the inhibition of different cellular functions with increasing ethanol concentrations.
TL;DR: In this article, the damping width of the giant dipole resonance (GDR) built on the ground state and on excited states of 90 Zr, which is spherical at zero spin and temperature, and 164 Er which is deformed.
TL;DR: The hypothesis that patients with aneuploid differentiated carcinoma represent a higher risk group and are probably more prone to developing anaplastic carcinoma is supported.
Abstract: Fifteen cases of anaplastic thyroid carcinoma, including eight cases with a differentiated component, were studied by DNA analysis. All areas of anaplastic carcinoma showed an aneuploid DNA content. The eight cases of anaplastic carcinoma with differentiated component (two follicular carcinomas, two papillary carcinomas, one Hurthle cell carcinoma and three poorly differentiated carcinomas) exhibited aneuploid DNA content in the differentiated area of the tumour. Karyometric parameters allowed a fairly clear separation between giant cell, spindle cell and differentiated components. The results support the hypothesis that patients with aneuploid differentiated carcinoma represent a higher risk group and are probably more prone to developing anaplastic carcinoma.
TL;DR: In this paper, it has been shown that this transformation obeys the Avrami-Erofeev law with an exponent n = 2 and an activation energy close to 84 ± 3 kJ mol−1.
TL;DR: A hyperbolic relationship between plasma thyroxine concentrations and phosphofructokinase-1 activity was found and this relationship could account for the decrease in carbohydrate metabolism in heart from hypothyroid rats.
Abstract: Experimental hypothyroidism was induced in rats by the administration of NaClO4. Hearts from normal and hypothyroid rats were homogenized, and the extracts were assayed for phosphofructokinase-1 and phosphofructokinase-2 activity and fructose 2,6-bisphosphate concentrations. Hypothyroidism was associated with a drastic loss of phosphofructokinase-1 activity. A hyperbolic relationship between plasma thyroxine concentrations and phosphofructokinase-1 activity was found. As treatment with NaClO4 progressed, the decrease in blood thyroxine was faster than the decrease in enzyme activity. After prolonged hypothyroidism (a decrease in thyroxine of more than 10-fold), a 4-fold decrease in phosphofructokinase-1 activity was observed. In this metabolic condition 2-fold decreases in phosphofructokinase-2 activity and in fructose 2,6-bisphosphate were observed. A similar decrease in phosphofructokinase-1 activity in a partially purified preparation was found. The addition of L-thyroxine in the diet had little effect on phosphofructokinase-1 activity. However, exposure of minced pieces of hearts of hypothyroid rats to tri-iodothyronine for 5 h resulted in a clear increase in phosphofructokinase-1 activity, which was partially prevented by the simultaneous addition of cycloheximide. These results could account for the decrease in carbohydrate metabolism in heart from hypothyroid rats.
TL;DR: Strain S442, a new mutant of the fungus Phycomyces blakesleeanus, has a greenish colour and a distinct green fluorescence under long-UV light and genetic analysis shows that the new mutation occurs at gene carB, whose protein product catalyses the four dehydrogenations of phytoene to lycopene via phy tofluene, ζ-carotene, and neurosporene.
TL;DR: L -Cyteine and l -Methionine are effective inhibitors of the OASSase activity, which is also inhibited by hydroxylamine and p-hydroxymercuribenzoate (pHMB).
TL;DR: Both the high-hopper and the wild-type element proved to undergo secondary transpositions, albeit at different frequencies, and several types of mutants induced by either of these elements are described.
Abstract: The tetracycline-resistant transposon Tn10 and its “high-hopper” derivative Tn10HH104 were introduced into the Azotobacter vinelandii genome using suicide conjugative plasmids derived from pRK2013. Several types of mutants induced by either of these elements are described. Nif- mutants (deficient in nitrogen fixation) were easily isolated, whereas the isolation of other mutant types (auxotrophs, sugar non-users) required special selection conditions. The characterization of the mutations as transposon insertions was often complicated and sometimes required a combination of genetic and physical tests. A common source of complication, the existence of double inserts, was found among the mutants induced by Tn10HH104 but not among those induced by Tn10. Both the high-hopper and the wild-type element proved to undergo secondary transpositions, albeit at different frequencies. Another type of complication, the existence of heterozygotes, occurred because of the high level of redundancy of the A. vinelandii genome.