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991.
F. Sanchez-Bajo Isidro Cachadiña Juan de Dios Solier Fernando Guiberteau Francisco L. Cumbrera 《Journal of the American Ceramic Society》1997,80(1):232-236
The precise microstructural characterization of the yttriapartially stabilized zirconia (Y-PSZ) system by means of X-ray diffractometry (XRD) experiments faces a serious challenge: the discrimination beween the cubic, c , and pseudocubic, t', phases. We show how the confusion between the two phases goes beyond a simple qualitative problem, because the relative abundances for all the present polymorphs can be substantially modified. This is particularly true for the amount of transformable tetragonal phase, which is of paramount importance for the design of zirconia-based tough ceramics. Similarly, we show that a conclusive discrimination between c and I' phases is possible on the basis of XRD experiments by a careful application of the Rietveld method and by emphasizing some subtle details around the angular domain close to the {200} planes. The procedure is applied to samples of Y-PSZ (4.7 mol%). 相似文献
992.
M. Isabel Gil Cristina García-Viguera Peter Bridle Francisco A. Tomás-Barberán 《European Food Research and Technology》1995,200(4):278-281
A simple technique for the routine capillary electrophoretic analysis of phenolic compounds in red wines from different Spanish regions, is described. Separation was achieved using a fused-silica capillary column with a borate buffer at pH 9.5, and UV detection at 280 nm. The compounds identified were: (-)-epicatechin, (+)-catechin, (-)-epigallocatechin, syringic acid, vanillic acid, gallic acid, 3,4 dihydroxybenzoic acid, p-coumaric acid, caffeic acid and the hydroxycinnamic tartaric acid esterscis- andtrans-coumamyl tartaric acid andcis-caffeoyl tartaric acid. Different wines showed very similar electrophoretic profiles, but significant quantitative differences were observed. 相似文献
993.
María Elisa Marín‐Zamora Francisco Rojas‐Melgarejo Francisco García‐Cnovas Pedro Antonio García‐Ruiz 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(12):1356-1364
Mushroom tyrosinase was immobilized by adsorption onto the totally cinnamoylated derivative of D ‐sorbitol. The polymerization and cross‐linking of the derivative initially obtained was achieved by irradiation in the ultraviolet region, where this prepolymer shows maximum sensitivity. Immobilization of tyrosinase on this support involves a process of physical adsorption and intense hydrophobic interactions between the cinnamoyl groups of the support and related groups of the enzyme. The pH value, enzyme concentration and immobilization time were all important parameters affecting immobilization efficiency; also, enzyme immobilization efficiency correlated well with the tyrosinase isoelectric point. The immobilized enzyme showed an optimum measuring pH of 3.5 and greater activity at acid and neutral pH values than the soluble enzyme. The optimal reaction temperature was 35 °C and the temperature profile was broader than that of the free enzyme or of the enzyme immobilized on other supports. The apparent Michaelis constant of mushroom tyrosinase immobilized on the SOTCN derivative acting on 4‐tert‐butylcatechol (TBC) was 0.40 ± 0.02 mmol dm?3, which was lower than for the soluble enzyme, suggesting that the affinity of this enzyme for this substrate was greater when immobilized than when in solution. Immobilization stabilized the enzyme and made it less susceptible to activity loss during storage at pH values in the range 4–5.5, and the suicide inactivation of the immobilized tyrosinase was null or negligible in a reaction medium with 4‐tert‐butylcatechol at a concentration of 0.4 mmol dm?3. The results show that cinnamic carbohydrate esters of D ‐sorbitol are an appropriate support for tyrosinase immobilization and could be of use for several tyrosinase applications. Copyright © 2005 Society of Chemical Industry 相似文献
994.
Manuel Mazo Francisco J. Rodríguez José L. Lázaro Jesús Ureña Juan C. García Enrique Santiso Pedro Revenga J. Jesús García 《Autonomous Robots》1995,2(3):203-224
This paper describes a wheelchair for physically disabled people developed within the UMIDAM Project. A dependent-user recognition voice system and ultrasonic and infrared sensor systems has been integrated in this wheelchair. In this way we have obtained a wheelchair which can be driven with using voice commands and with the possibility of avoiding obstacles and downstairs or hole detection. The wheelchair has also been developed to allow autonomous driving (for example, following walls). The project, in which two prototypes have been produced, has been carried out totally in the Electronics Department of the University of Alcalá (Spain). It has been financed by the ONCE. Electronic system configuration, a sensor system, a mechanical model, control (low level control, control by voice commands), voice recognition and autonomous control are considered. The results of the experiments carried out on the two prototypes are also given. 相似文献
995.
996.
Alberto Domínguez Francisco J Deive M Angeles Sanromn María A Longo 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(11):1166-1170
The production of extracellular lipase in submerged cultures of Yarrowia lipolytica CECT 1240 has been investigated. Several compounds have been added to the culture medium, in order to assess their efficiency as inducers of lipase production. First, the effect of triglycerides (olive oil, sunflower oil, tributyrin) and fatty acids (oleic acid) has been studied. The highest activity level was obtained with sunflower oil (58 U cm?3), followed by olive oil (49 U cm?3). The cultures with tributyrin and oleic acid attained similar activities (33 U cm?3). Then, several surfactants (Tween 80, Triton X‐100, gum arabic, polyethylene glycol 200) were added to the cultures with sunflower oil, in an attempt to increase the levels of extracellular lipase activity. The obtained activities were slightly lower than those achieved without surfactants. The assay of a wide range of surfactant concentrations in the case of PEG‐200 (with which the highest activity levels had been attained) did not improve the results. This strain secreted lipase concentrations two‐fold higher and showed significantly different behaviour towards the presence of surfactants in the culture medium, compared with other wild‐type Yarrowia lipolytica strains. Copyright © 2003 Society of Chemical Industry 相似文献
997.
Miguel A. Alvarez-Merino Francisco Carrasco-Marí n Carlos Moreno-Castilla 《Applied catalysis. B, Environmental》1997,13(3-4):229-240
Adsorption of SO2 under dynamic conditions from an SO2-air mixture at 298 and 573 K on alkaline-oxide-containing activated carbons has been studied. The adsorption capacity of these samples at 298 K was, in general, lower than that in the original activated carbons and mainly governed by their microporosity accessible to benzene. However, at 573 K, the alkaline-oxide-containing activated carbons adsorbed a greater amount of SO2 than the original activated carbon, following the order Na ≥ K > Rb. At both adsorption temperatures, part of the SO2 adsorbed formed H2SO4 and Me2SO4, where Me = Na, K or Rb. When the SO2 adsorption was carried out at 573 K, this gas fixed additional oxygen complexes that evolved as CO2 under heating up to 873 K in He flow, probably by reaction of SO2 with carbon surface atoms of a basic nature that are not able to chemisorb oxygen from the air at the same conditions. 相似文献
998.
Multilayered multiconductor transmission lines with polygonal cross-section-perfect conductors are analyzed under a quasi-TEM approach. According to a model previously proposed by the authors, each polygonal cross-section conductor is modeled as a set of zero-thickness strips. The substrates can be lossy, and present possible gyromagnetic (longitudinal magnetization) characteristics as well as dielectric anisotropic properties. The method of moments of Galerkin is applied in the spectral domain to analyze the model structure. Special attention has been paid to the fast and accurate computation of spectral integrals. Thus, the possible symmetries of the Galerkin matrix are emphasized and recurrence formulas to compute the tail integrals have been developed. © 1994 John Wiley & Sons, Inc. 相似文献
999.
Javier Guevara Francisco Parisi Ana Maria Llois Mariana Weissmann 《Computational Materials Science》1998,10(1-4):440-443
We calculate the electronic structure of 3d transition-metal clusters with a model Hamiltonian that takes into account electron spillover at the cluster surface and uses bulk parameter values for the interactions. We perform calculations for fcc and bcc clusters of up to 260 atoms making use of symmetry properties. We obtain magnetic moments per shell and ionization potentials for Ni, Co, and Fe clusters starting from an spd-bulk parametrization. 相似文献
1000.
Rosario Zamora José L. Navarro Francisco J. Hidalgo 《Journal of the American Oil Chemists' Society》1994,71(4):361-364
Unsaponifiable matter from 19 olive and olive pomace oils were studied by high-resolution13C nuclear magnetic resonance spectroscopy. Their spectra showed characteristic peaks that corresponded to molecular substructures
rather than the individual constituents present in the unsaponifiable matter. The presence of squalene and other hydrocarbons,
sterols and triterpenic alcohols, in addition to other groups of minor compounds, were observed. Based on the analysis of
these spectra, it was possible to distinguish among different grades of olive oils by using stepwise discriminant analysis.
This direct method of analysis is suggested to be used in artificial neural networks to define oil identity and quality. 相似文献