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Search Results: 1 - 10 of 594322 matches for " J. M. Crespo "
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Mineral phosphate solubilization activity of gluconacetobacter diazotrophicus under P-limitation and plant root environment  [PDF]
J. M. Crespo, J. L. Boiardi, M. F. Luna
Agricultural Sciences (AS) , 2011, DOI: 10.4236/as.2011.21003
Abstract: The ability to solubilize insoluble inorganic pho- sphate compounds by Gluconacetobacter diazotrophicus was studied using different cul-ture approaches. Qualitative plate assays using tricalcium phosphate as the sole P-source showed that G. diazotrophicus produced solu-bilization only when aldoses were used as the C-source. Extracellular aldose oxidation via a pyrroloquinoline quinone-linked glucose dehy-drogenase (PQQ-GDH) is the main pathway for glucose metabolism in G. diazotrophicus. In batch cultures with 5 g l-1 of hydroxyapatite as the P-source and glucose as the C-source, more than 98% of insoluble P was solubilized. No solubilization was observed neither using glyc-erol nor culturing a PQQ-GDH mutant of G. di-azotrophicus. Solubilizaton was not affected by adding 100 mmol l-1 of MES buffer. Continuous cultures of G. diazotrophicus showed significant activities of PQQ-GDH either under C or P limi-tation. An intense acidification in the root envi-ronment of tomato and wheat seedlings inocu-lated with a G. diazotrophicus PAL5 was ob-served. Seedlings inoculated with a PQQ-GDH mutant strain of G. diazotrophicus showed no acidification. Our results suggest that G. di-azotrophicus is an excellent candidate to be used as biofertilizer because in addition to the already described plant growth-promoting abili-ties of this organism, it shows a significant mineral phosphate solubilization capacity.
Variational approach for walking solitons in birefringent fibres
N. J. Rodriguez-Fernandez,J. M. Soto-Crespo
Physics , 2002, DOI: 10.1080/09500349808231741
Abstract: We use the variational method to obtain approximate analytical expressions for the stationary pulselike solutions in birefringent fibers when differences in both phase velocities and group velocities between the two components and rapidly oscillating terms are taken into account. After checking the validity of the approximation we study how the soliton pulse shape depends on its velocity and nonlinear propagation constant. By numerically solving the propagation equation we have found that most of these stationary solutions are stable.
Recycling of the Granite Quarries and Municipal Incinerator Wastes for the Processing of New Materials as Porcelainized Stoneware
Hernández-Crespo, M. S.,Rincón, J. Ma.
Materiales de Construccion , 2000,
Abstract: In the 1980s started in the ceramic sector the material conception of porcelainized stoneware, a product with versatile and modern characteristics similar to those of the natural stone, depicting improved properties to the marble and granite. Porcelanized stoneware is a compact ceramic material, very hard and homogeneous, generally not fully vitreous (unglazed) in its surface, obtained by fast firing from compositions enriched in kaolinite, which contain a large quantity of fluxes. The raw materials for body are a mixture that contains an adequate relationship of kaolinitic clays, feldspars and quartz. Such material is characterized by its low or almost zero porosity, being adequated to sustain heavy and high traffic intensity for uses in and outside of buildings with wide range of aspects, desings and colors. By considering the chemistry and mineralogical composition of the granite and incinerator wastes, this paper describes their use in the processing of construction materials, specifically, in a new type of stoneware flooring and covering materials. According to the most of the physical and mechanical properties here determined, these "Modified Porcelainized Stoneware" (MPS) materials are close to the conventional porcelainized stoneware and glass ceramics products. Hacia la década de los a os 80 se inicia en el sector cerámico la concepción del gres porcelánico, material de características modernas y versátiles semejantes a las de la piedra natural, pero que incluso supera en utilidad y prestaciones al mármol y al granito. El gres porcelánico es un material cerámico compacto, muy duro y homogéneo, no vidriado en su superficie, obtenido por cocción rápida de composiciones ricas en caolinita y una gran cantidad de fundentes; es decir, de una mezcla cerámica que contiene una relación adecuada de arcillas de tipo caolinítico, feldespatos y cuarzo. Dicho material se caracteriza por su baja o casi nula porosidad; es ideal para soportar tráfico pesado y alto tránsito, para usos en interiores y exteriores, con una variedad muy extensa de aspectos dise os y colores. En razón de la composición química y mineralógica de los residuos de granito y de incineradoras de residuos sólidos urbanos (RSU) se planteó determinar su aprovechamiento en la obtención de materiales de construcción, específicamente, en revestimientos y pavimentos de gres porcelánico. Los resultados han revelado la viabilidad de estos residuos en cuanto a su aprovechamiento en la obtención de nuevos materiales tipo gres porcelánico ó "Gres Porcelánico Modificado" (GPM). De acuerdo con algunas d
Nitric oxide decreases intestinal haemorrhagic lesions in rat anaphylaxis independently of mast cell activation
J. Carvalho Tavares,A. Moreno,M. Sánchez Crespo
Mediators of Inflammation , 1997, DOI: 10.1080/09629359791893
Análisis de componentes de material frágil por medio de métodos numéricos
Rubio, M. D.,Crespo, C. J.,Jakel, R.,Dietz, P.
Revista de Metalurgia , 1998,
Abstract: Some materials are fragile due to the great number of microcraks produced during their conformation processes, for example ceramics. That is the reason why, along these years different design criteria have been proposed to calculate these fragile materials, specially ceramics, based in probabilistic theories. A program to calculate ceramic components with these criteria has been developed in the I.M.W. (Clausthal, Germany). This program works as a subprocessor of the finite element program MARC, and can analyse the probability of survival of a component with three general criteria and with fracture mechanics criteria (eleven when calculating volume components and six for surface ones). Those criteria have been implemented also to calculate the probability of survival with applied loads during time intervals and to calculate security factors. Los materiales frágiles deben sus características al elevado número de microgrietas producidas en su conformación. Es por ello por lo que han ido apareciendo una serie de criterios de cálculo específicos para estos materiales que se basan en cálculos de tipo probabilista y en las propiedades del material definidas por Weibull. En el I.M.W. (Clausthal, Alemania) se ha desarrollado un programa de cálculo de resistencia de piezas de estos materiales, por ejemplo cerámicas, que trabaja como subprocesador de un programa de elementos finitos, MARC, de forma que permite analizar la probabilidad de vida de las piezas según tres criterios generales y criterios de mecánica de fractura (once para elementos de volumen y seis para elementos de superficie). Asimismo, el programa permite calcular la probabilidad de fallo, según estos criterios en el caso de que se realicen cálculos con carga aplicada durante intervalos de tiempo, y realizar cálculos de factores de seguridad con los que se ha dise ado la pieza.
Effects of core degrees of freedom in the low energy $^7$Be$(p,γ)^8$B reaction
F. M. Nunes,R. Crespo,I. J. Thompson
Physics , 1997,
Abstract: Quadrupole and octupole couplings to all bound states of $^7$Be are included in describing the capture reaction $^7$Be$(p,\gamma)^8$B. We verify, contrary to what we had initially stated, that the energy behaviour of the Astrophysical S-factor in the energy range of interest is not significantly sensitive to the core couplings in the g.s. (g.s.) of $^8$B although its overall magnitude is shifted. We find there is some sensitivity to the various deformation models when introducing the nuclear interaction for calculating the scattering states. The various deformation models predict quite different contributions to the quadrupole and magnetic moments but in order to compare with the data the quadrupole and magnetic moment of $^7$Be need to be measured.
Cascaded Nondegenerate Four-Wave Mixing Technique for High-Power Single-Cycle Pulse Synthesis in the Visible and Ultraviolet Ranges
Rosa Weigand,J. T. Mendonca,Helder M. Crespo
Physics , 2009, DOI: 10.1103/PhysRevA.79.063838
Abstract: We present a new technique to synthesize high-power single-cycle pulses in the visible and ultraviolet ranges by coherent superposition of a multiband octave-spanning spectrum obtained by highly-nondegenerate cascaded four-wave mixing of femtosecond pulses in bulk isotropic nonresonant media. The generation of coherent spectra spanning over two octaves in bandwidth is experimentally demonstrated using a thin fused silica slide. Full characterization of the intervening multicolored fields using frequency-resolved optical gating, where multiple cascaded orders have been measured simultaneously for the first time, supports the possibility of direct synthesis of near-single-cycle 2.2 fs visible-UV pulses without recurring to complex amplitude or phase control, which should enable many applications in science and technology.
How unique is the Asymptotic Normalisation Coefficient (ANC) method?
J. C. Fernandes,R. Crespo,F. M. Nunes
Physics , 2000, DOI: 10.1103/PhysRevC.61.064616
Abstract: The asymptotic normalisation coefficients (ANC) for the vertex $^{10}$B $\to$ $^9$Be + p is deduced from a set of different proton transfer reactions at different energies. This set should ensure the peripheral character of the reaction and availability of data for the elastic channels. The problems associated with the characteristics of the data and the analysis are discussed. For a subgroup of the set of available data, the uniqueness property of the extracted ANC is fulfilled. However, more measurements are needed before a definite conclusion can be drawn.
Continuum effects in reactions involving weakly bound nuclei
A. M. Moro,R. Crespo,F. Nunes,I. J. Thompson
Physics , 2003, DOI: 10.1016/S0375-9474(03)01407-6
Abstract: The relevance of the continuum effects in transfer reactions is discussed in conection with the determination of observables of astrophysical interest. In particular, we examine the validity of the Distorted Wave Born Approximation (DWBA) as a tool to extract the astrophysical \emph{(S_{17}(0))} factor. For this purpose, we present calculations for the reaction (^{14})N((^{7} )Be,(^{8})B)(^{13})C comparing the DWBA method with the more sophysticated CDCC-Born approximation
(^{8})B breakup in elastic and transfer reactions
A. M. Moro,R. Crespo,F. Nunes,I. J. Thompson
Physics , 2002, DOI: 10.1103/PhysRevC.66.024612
Abstract: We have studied the transfer reaction $^{14}$N($^7$Be,$^8$B)$^{13}$C at (\mathrm{E}_{\mathrm{lab}}=84) MeV, paying special attention to the effects of the coupling to the continuum in the exit channel. Using the Continuum Discretized Coupled Channels (CDCC) formalism, we find that these effects are important for the description of the elastic scattering observables. However, for the transfer process, differences between the predictions of the differential cross section within the Distorted Wave Born Approximation (DWBA) and the CDCC-Born approximation (CDCC-BA) are found to be negligible. This result supports the use of the DWBA method as a reliable tool to extract the $S_{17}(0)$ factor in this case.
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