Showing papers by "Polytechnic University of Valencia published in 1991"
TL;DR: In this article, the influence of these parameters on the nucleation and crystal growth rates and on the chemical composition of the final crystalline material is discussed, as well as their influence on the growth rate of zeolite Beta.
143 citations
TL;DR: In this article, strong base catalysts have been prepared by substituting a part of the Mg z+ located at the borders of the channels of the sepiolite with alkaline ions.
135 citations
01 Jun 1991
TL;DR: Second generation multicomputers use wormhole routing, allowing a very low channel set-up time and drastically reducing the dependency between network latency and internode distance.
Abstract: Second generation multicomputers use wormhole routing, allowing a very low channel set-up time and drastically reducing the dependency between network latency and internode distance. Deadlock-free routing strategies have been developed, allowing the implementation of fast hardware routers that reduce the communication bottleneck. Also, adaptive routing algorithms with deadlock-avoidance or deadlock-recovery techniques have been proposed for some topologies, being very effective and outperforming static strategies.
103 citations
TL;DR: Using deuterated para-xylene as a reactant, this article found that more than 20% of the meta- and ortho-xylenes, obtained when using a HY zeolite as catalyst, are formed via a bimolecular mechanism.
85 citations
TL;DR: The results showed that isolates of different species were able to produce aflatoxins B1, B2, G1, and G2, sterigmatocystin, ochratoxin A, patulin, citrinin, penicillic acid, zearalenone, and griseofulvin.
Abstract: A survey was carried out to obtain data on the occurrence of mycotoxins and the mycotoxin-producing potential of fungi isolated from nuts (almonds, peanuts, hazelnuts, pistachio nuts) and sunflower seeds in Spain. Thin-layer chromatography was used to separate the toxins. Aflatoxins were detected in one sample of almonds (95 ppb aflatoxin B1 and 15 ppb aflaxtoxin B2) and in one sample of peanuts at a level below 10 ppb of aflatoxin B1. 100% of samples showed variable incidence of fungal contamination. The predominant fungi present in samples were Penicillium spp, Aspergillus niger, A. flavus, A. glaucus and Rhizopus spp. The results showed that isolates of different species were able to produce aflatoxins B1, B2, G1, and G2, sterigmatocystin, ochratoxin A, patulin, citrinin, penicillic acid, zearalenone, and griseofulvin.
80 citations
TL;DR: The characteristics of this proteinase were similar to pepsin and identical to those displayed by a previously described tomato 37-kilodalton aspartyl proteinase active against tomato PR proteins, suggesting that these extracellular proteases could play a role in a conserved mechanism for PR protein turnover in plants.
Abstract: Tobacco (Nicotiana tabacum L.) leaves were found to contain an extracellular proteinase that endoproteolytically cleaves tobacco pathogenesis-related (PR) proteins. This proteinase was partially purified from tobacco leaves and characterized as an aspartyl proteinase with a pH optimum around pH 3 and a molecular mass of 36,000 to 40,000 daltons. In vitro, the enzyme cleaved purified tobacco and tomato PR proteins into discrete fragments. The characteristics of this proteinase were similar to pepsin and identical to those displayed by a previously described tomato 37-kilodalton aspartyl proteinase active against tomato PR proteins (I Rodrigo, P Vera, V Conejero [1989] Eur J Biochem 184: 663-669), suggesting that these extracellular proteases could play a role in a conserved mechanism for PR protein turnover in plants.
79 citations
TL;DR: In this article, the isomerization and disproportionation of m-xylene has been performed over zeolite β samples with Si/Al ratios in the range from 11 to 42.
70 citations
TL;DR: In this article, a theory is proposed in order to interpret the data in a unique theoretical framework, based on the existence in amorphous polymers of quasipunctual defects whose concentration decreases during structural relaxation, and the occurrence of hierarchical correlation effects conditioning molecular mobility.
Abstract: Structural relaxation of glassy poly(methyl methacrylate) (PMMA) was studied with several techniques: differential scanning calorimetry (DSC), volumetry by thermomechanical analysis (TMA) and mechanical spectroscopy. A theory is proposed in order to interpret the data in a unique theoretical framework. This theory is developed on the basis of two main physical assumptions: (i) the existence in amorphous polymers of quasipunctual defects whose concentration decreases during structural relaxation, and (ii) the occurrence of hierarchical correlation effects conditioning molecular mobility. As a first approximation a self-consistent semiquantitative description of the results is obtained, i. e., the experimental results obtained for the different quantities on PMMA can be accounted for employing always the same set of model parameters. However, it seems that a significant difference exists between the relaxation times associated with the different experimental techniques.
59 citations
TL;DR: Tomato P23 is the previously described NP24 protein found to be associated to osmotic stress in tomato, and the possible role of pathogenesis-related P23 protein as a component of a general mechanism of response of the plant is discussed.
Abstract: P23, a 23 kDa pathogenesis-related (PR) protein, was purified from citrus exocortis viroid (CEVd)-infected tomato leaves. Partial amino acid sequencing of this protein including the N-terminal and nine additional tryptic fragments covering about 50% of its primary structure revealed extensive homologies to the members of the family of plant thaumatin-like proteins. Sequence alignment revealed that tomato P23 is the previously described NP24 protein found to be associated to osmotic stress in tomato. In view of this fact the possible role of pathogenesis-related P23 protein as a component of a general mechanism of response of the plant is discussed.
57 citations
TL;DR: In this article, the central manifold method was applied to the BWR dynamical system to reduce the dimension of the state space and obtained a reduced two dimensional one which contains all the information about the bifurcation.
56 citations
TL;DR: In this article, the effects of salinity on growth, ion content, water relationships, and chlorophyll and proline levels were measured on one-year-old 'Verna' and 'Fino' lemon (Citrus limon [L] Burm.
Abstract: Effects of salinity on growth, ion content, water relationships, and chlorophyll and proline levels were measured on one‐year‐old ‘Verna’ and ‘Fino’ lemon (Citrus limon [L] Burm. F.) scions budded to either Sour orange (C. aurantium L.) or macrophylla (C. macrophylla Wester) rootstock. Trees were grown in nutrient solutions containing 2 (control), 40, or 80 mol m‐3 NaCl for 75 days. Growth of all combinations was reduced by salinity, but this effect was greater for both scions budded on macrophylla. Leaf chloride and sodium concentrations were lower in both scions budded on Sour orange. Leaf salt concentration was scion dependent. Leaves of ‘Fino’ lemon had higher levels of both chloride and sodium than did leaves of ‘Verna’ lemon, regardless of the rootstock considered. Despite an accumulation of chloride and sodium in the leaves of salinized trees, leaf water potential and leaf water content increased above the control level. However, stomatal conductance declined in all rootstock/scion combina...
TL;DR: In this article, the Beckmann rearrangement of cyclohexanone oxime (1) was carried out in the liquid phase in the presence of a series of acid zeolites (HY-20, HY-50, HYD, and HZSM-5) at different reaction temperatures.
TL;DR: While parent compounds showed very little or no phototoxicity, the most toxic photoproducts were systematically the benzylic alcohols, which showed lytic activity to erythrocytes and cytotoxicity to cultured fibroblasts, which partly explain the in vivo photot toxicity of this family of drugs.
22 Apr 1991
TL;DR: Adaptive routing algorithms withdeadlock-avoidance or deadlock-recovery techniques have been proposed for some topologies, being very effective and outperforming static strategies.
Abstract: Second generation multicomputers use wormhole routing, drastically reducing the dependency between network latency and internode distance. Deadlock-free routing strategies have been developed, allowing the implementation of fast hardware routers. Also, adaptive routing algorithms with deadlock-avoidance or deadlock-recovery techniques have been proposed for some topologies, being very effective and outperforming static strategies.
TL;DR: In this paper, the behaviour of the Cr(III)/Cr(II) redox reactions and the hydrogen evolution on gold graphite electrodes has been studied with the aim of increasing the efficiency of an Fe/Cr redox flow battery.
TL;DR: The development of viroid-like symptoms, the production of associated pathogenesis-related proteins, and the rise in protease activity induced by silver nitrate, were all suppressed by exogenous application of putrescine.
Abstract: The levels of polyamines in leaves of Gynura aurantiaca DC and tomato, Lycopersicon esculentum Mill. cv Rutgers, infected with citrus exocortis viroid (CEVd) or treated with silver nitrate or ethephon (2-chloroethylphosphonic acid) were measured by HPLC in relation to development of symptoms. Previously it had been demonstrated that treatment of G. aurantiaca plants with silver nitrate or ethephon closely mimicked the effects of viroid infection in the plants. In the studies reported here, a marked decrease in putrescine level was observed in plants infected by CEVd or treated with silver ions or ethephon. There was no significant change in either spermidine or spermine levels. Treatment of G. aurantiaca plants with specific inhibitors of ethylene biosynthesis (aminoethoxyvinylglycine, Co2+) or ethylene action (norbornadiene) prevented the decrease of putrescine associated with silver nitrate treatment and had no effect on spermidine or spermine levels. The development of viroid-like symptoms, the production of associated pathogenesis-related proteins, and the rise in protease activity induced by silver nitrate, were all suppressed by exogenous application of putrescine. The decreased level of putrescine as an ethylene-mediated step in the transduction of the viroid and silver or ethephon signaling is discussed.
TL;DR: In this paper, the physical changes occurring during the so-called "boixet" step of the manufacturing process of Xixona turron have been studied and an attempt has been made to explain the role of major turron components in this change by using rheological measurements and particle-size analysis techniques.
TL;DR: In this paper, dielectric measurements on a family of poly(mono-nalkyl itaconates) have been performed and two relaxation peaks have been observed within the temperature range studied.
01 Jan 1991
TL;DR: The application to the Segura River Basin in Spain demonstrates the usefulness of the Aquatool programs when dealing with complex systems as tools to obtain design and management guidelines and realtime aids to decision making.
Abstract: Aquatool, a computer-assisted support system for water resources research and management, is presented. The system includes three main modules: 1) a module for water resources schemes optimization, 2) a module for the simulation of the management of water resources systems, including the conjunctive use of surface and groundwater, and 3) a module for groundwater model preprocessing designed to include distributed aquifer submodels in the simulation model. Interactive graphic input data interfaces and postprocessors facilitate the entering of schemes and data as well as the analysis of results. The application to the Segura River Basin in Spain demonstrates the usefulness of the programs when dealing with complex systems as tools to obtain design and management guidelines and realtime aids to decision making.
TL;DR: The concept of rectangular co-solution of a polynomial matrix equation is introduced which permit us to obtain a description of the general solution of systems of higher order differential equations with constant coefficients in a way analogous to the scalar case.
TL;DR: In this paper, the dynamic mechanical relaxation spectra of a series of composites with a matrix of poly(ethyl methacrylate) reinforced with continuous Kevlar fibers were analyzed.
Abstract: The dynamic mechanical relaxation spectra of a series of composites with a matrix of poly(ethyl methacrylate) reinforced with continuous Kevlar fibers present several characteristics that have been proposed in the literature regarding polymer composites as a proof of the existence of an interphase between the polymeric matrix and the filler with mechanical properties different from both: The α-relaxation, associated with the glass transition of the matrix, is shifted in the temperature axis, and a peak appears in the tan δ vs. temperature plot, which was not present either in the matrix or in the fiber relaxation spectra. Nevertheless, a simple block model which does not include the existence of such an interphase is able to reproduce not only the dependence of the loss tangent and storage modulus with the fiber content, but also the shift of the α-relaxation and the presence of the new α′ peak in the composites.
TL;DR: In this paper, the generality of any finite-element model is studied, and the authors present a 3D model for failure analysis of concrete structures, which they call fully triaxial and brittle in nature.
TL;DR: In this article, a flow-injection method was developed for the enzymatic determination of glycerol in wines using a reactor containing immobilized glycerokinase and glycerols-3′-phosphate oxidase.
Abstract: A flow-injection method was developed for the enzymatic determination of glycerol in wines using a reactor containing immobilized glycerokinase and glycerol-3′-phosphate oxidase. Hydrogen peroxide from the reaction was monitored by chemiluminescence after reaction with an alkaline reagent containing luminol and hexacyanoferrate (III). Calibration curves were linear between 25 mg/L and 250 mg/L of glycerol for injected volume 29 μL. The method gave satisfactory results compared with a gas-chromatographic method. No sample pre-treatment was necessary and a sampling frequency of 30/hr could be achieved.
TL;DR: In this paper, the condensation of benzaldehyde with ethyl cyanoacetate, ethyl malonate and ethyl acetoacetate was carried out with high rates and selectivity promoted by lithium-, sodium, potassium-, and caesium-exchanged X and Y zeolites and on sodium-Germanium substituted faujasite.
Abstract: The condensation of benzaldehyde with ethyl cyanoacetate, ethyl malonate and ethyl acetoacetate were carried out with high rates and selectivity promoted by lithium-, sodium, potassium-, and caesium-exchanged X and Y zeolites and on sodium-Germanium substituted faujasite. The 2-nitrobenzaldehyde, 3-nitrobenzaldehyde, 2-trifluoromethylbenzaldehyde and 2,4-dichlorobenzaldehyde were condensed with ethyl acetoacetate to obtain precursors in the production of dihydropyridine derivatives in the presence of these base catalysts operating in a batch reactor at moderate temperatures. The most active zeolites are more active than pyridine, and less active than piperidine, showing basic sites with pKb
TL;DR: In this paper, the influence of the gel composition on the nature and chemical composition of the crystalline phases obtained is discussed and the ion exchange properties and the i.r. and Raman spectra show that zeolite Phi is an offretite-related material and probably a new member of the ABC-6 family.
TL;DR: In this paper, a calorimetric study of poly(mono-n-alkyl itaconates) containing 8, 10, 12 and 14 carbon atoms in the side chain was performed.
Abstract: A calorimetric study of poly(mono-n-alkyl itaconates) containing 8, 10, 12 and 14 carbon atoms in the side chain was performed. No glass transition temperature (Tg) was observed in the temperature range 213-263 K, but a melting process was observed for the dodecyl and tetradecyl derivatives, which was attributed to crystalline order in the long side chains.
TL;DR: Wheat samples from Spanish flour factories were screened for patulin and patulin-producing moulds and stationary dark cultures were found to be more efficient that shaken or fermentation cultures in YES medium and the influence of other incubation conditions in the yield was investigated.
Abstract: Sixty-four wheat samples from Spanish flour factories were screened for patulin and patulin-producing moulds. None of them was found to contain any patulin, whereas samples experimentally contaminated with this toxin proved it to be highly unstable. On the other hand, Penicillium griseofulvum was the only in vitro patulin-producing species found (19 samples). Mould growth in the samples was investigated by using yeast-sucrose medium (YES) and high-performance liquid chromatography (HPLC) to measure the amounts of toxin produced during 40 day's incubation at 20 and 28°C. The highest yield rate of patulin was obtained between the 20th and 30th day of incubation; such a rate, however, was very low throughout the vigorous growth phase, during the first 20 days of incubation. The more appropriate temperature for incubation and patulin production was 28 °C. We also investigated the influence of other incubation conditions in the yield and found stationary dark cultures to be more efficient that shaken or fermentation cultures in YES medium. The best patulin yield achieved was 11.9 mg in the culture broth and 6.3 mg in the mycelium from 100 ml of medium.
TL;DR: The use of a very strong base catalyst can be disadvantageous because it can also catalyze other, non desired, more demanding reactions, with the corresponding decrease in selectivity to the desired product.
Abstract: There are a series of reactions such as isomerization, alkylation, dimerization of olefins, condensation, etc, which are catalyzed by bases. Solid base catalysts are competitive with respect to solid acid catalyst for carrying out reactions which can be catalyzed by either acids or bases. Solid bases can successfuly catalyze transformations of organic substrates containing heteroatoms, such as N, O, and S. Solid acids, which can also catalyze these reactions, often are poisoned by those substrates. Moreover, in some cases, such as olefin and alkyne isomerizations, it is possible by using bases to achieve stereochemical control. This has impulsed researches to look for very strong solid base catalysts, i.e., superbasic solids, such as supported alkaline metals. These, while active at moderate temperatures, present a major drawback derived from their relatively low stability and frequent catalyst regenerations. However, there are a significant number of interesting reactions which can also be catalyzed by bases with medium strength. In this case, the use of a very strong base catalyst can be disadvantageous because it can also catalyze other, non desired, more demanding reactions, with the corresponding decrease in selectivity to the desired product. Furthermore, in some processes, it can become more critical to adequately control the acid-base pairs than to achieve a very strong type of basic sites.
TL;DR: In this article, the critical micelle concentration (CMC) values of the Hyamine 2389 surfactant, an alkyl (C9C15) benzyltrimethylammonium chloride, are determined.