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Search Results: 1 - 10 of 229921 matches for " Alfredo R. Vilchis-Nestor "
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Facile Solventless Synthesis of a Nylon-6,6/Silver Nanoparticles Composite and Its XPS Study
Raúl A. Morales-Luckie,Víctor Sánchez-Mendieta,Oscar Olea-Mejia,Alfredo R. Vilchis-Nestor,Gustavo López-Téllez,Víctor Varela-Guerrero,L. Huerta,Jesús Arenas-Alatorre
International Journal of Polymer Science , 2013, DOI: 10.1155/2013/235850
Abstract: Silver nanoparticles were synthesized and supported on thin nylon membranes by means of a simple method of impregnation and chemical reduction of Ag ions at ambient conditions. Particles of less than 10?nm were obtained using this methodology, in which the nylon fibers behave as constrained nanoreactors. Pores on nylon fibres along with oxygen and nitrogen from amide moieties in nylon provide effective sites for in situ reduction of silver ions and for the formation and stabilization of Ag nanoparticles. Transmission electron microscopy (TEM) analysis showed that silver nanoparticles are well dispersed throughout the nylon fibers. Furthermore, an interaction between nitrogen of amides moieties of nylon-6,6 and silver nanoparticles has been found by X-ray photoelectron spectroscopy (XPS). 1. Introduction Research on the synthesis of mesoporous materials containing nanoparticles represents a fast-developing area of nanoscience and nanotechnology. This interest is stimulated by several possible application areas of these materials including catalytic [1], magnetic [2], and optoelectronic [3, 4]. Metal nanoparticles dispersed in polymeric matrixes have recently been the subject of intense study aiming to develop nanocomposite films [5–8]. General approaches for the synthesis and support of nanoparticles inside porous materials include impregnation [9] and deposition-precipitation [10]. A drawback of this nanocomposites is the difficulty to disperse nanoparticles in most systems [11]; hence one potential advantage of such metal/polymer systems is that the size and distribution of dispersed metal nanoparticles can be readily controlled based on the properties of the host polymer [12, 13]. Silver particles with a narrow size distribution have been produced upon reversible chemical transformation between metallic and oxide states in a titania matrix [14] and in a mesoporous silica which was grafted with hydrophobic –Si(CH3)3 groups at the pore surface [15]. Nylon is an electron-rich and polar synthetic polymer (polyamide) usually made from the monomers adipoyl chloride and hexamethylene diamine to form a linear molecular chain (Figure 1). Synthetic nylon membranes have a porous structure [16] and are composed of microfibrils that are interconnected forming a three-dimensional network. Such morphological features provide a unique reaction vessel for synthesizing and supporting metal nanoparticles, allowing enhanced access of guest molecules to catalytic centres, compared with nonporous films. Figure 1: Characteristic synthesis of nylon-6,6 fibers. In this work,
SERS Properties of Different Sized and Shaped Gold Nanoparticles Biosynthesized under Different Environmental Conditions by Neurospora crassa Extract
Katrin Quester, Miguel Avalos-Borja, Alfredo Rafael Vilchis-Nestor, Marco Antonio Camacho-López, Ernestina Castro-Longoria
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0077486
Abstract: Surface-enhanced Raman scattering (SERS) is a surface-sensitive technique that enhances Raman scattering by molecules adsorbed on rough metal surfaces. It is known that metal nanoparticles, especially gold and silver nanoparticles, exhibit great SERS properties, which make them very attractive for the development of biosensors and biocatalysts. On the other hand, the development of ecofriendly methods for the synthesis of metallic nanostructures has become the focus of research in several countries, and many microorganisms and plants have already been used to biosynthesize metallic nanostructures. However, the majority of these are pathogenic to plants or humans. Here, we report gold nanoparticles with good SERS properties, biosynthesized by Neurospora crassa extract under different environmental conditions, increasing Raman signals up to 40 times using methylene blue as a target molecule. Incubation of tetrachloroauric acid solution with the fungal extract at 60°C and a pH value of a) 3, b) 5.5, and c) 10 resulted in the formation of gold nanoparticles of a) different shapes like triangles, hexagons, pentagons etc. in a broad size range of about 10-200 nm, b) mostly quasi-spheres with some different shapes in a main size range of 6-23 nm, and c) only quasi-spheres of 3-12 nm. Analyses included TEM, HRTEM, and EDS in order to corroborate the shape and the elemental character of the gold nanoparticles, respectively. The results presented here show that these ‘green’ synthesized gold nanoparticles might have potential applicability in the field of biological sensing.
Responsabilidad Social en la formación profesional en Ciencias Económicas
Marcelo Claudio Périssé,Carlos Alfredo Ferrari,Juan Andrés Roger,Nestor Andrés Bursesi
Técnica Administrativa , 2009,
Abstract: En el marco del rol activo de la Universidad en su relación con las empresas y con la comunidad toda; y aplicando al ámbito de la educación superior de las Ciencias Económicas el concepto de Responsabilidad Social, a partir de la necesidad de inculcar a los estudiantes la conducta ética en forma transversal en toda la carrera universitaria, el presente trabajo intenta desarrollar la noción de Responsabilidad Social Universitaria, sobre la base del dise o de un modelo metodológico transdisciplinar que sirva a un proceso de ense anza-aprendizaje aplicable en la formación de los futuros graduados en Ciencias Económicas.
Subsurface structure of the Tecocomulco sub-basin (northeastern Mexico basin), and its relationship to regional
J. O. Campos-Enríquez,D. R. Alatriste-Vilchis,R. Huizar-álvarez,R. Marines-Campos
Geofísica internacional , 2003,
Abstract: Gravity, magnetics, DC resistivity, VLF profiles, geologic mapping, and analysis of regional lineaments in the Tecocomulco sub-basin of the northeastern Mexico Basin were carried out. To the south, the structure is of the half-graben type. To the north, the basin gets wider. Three NW-SE faults bound the half-graben to the E while only one delimits it to the W. Faults delimiting the half-graben, as well as several cinder cones and the neighboring ranges delimiting the basin, have a NE-SW orientation. The half-graben structure is due to tilting towards the NW of regional shallow crustal blocks. A chain of cinder cones interrupts the southward surficial drainage towards the neighboring Apan Basin, but we infer a communication at depth between these two sub-basins through a narrow graben. The faults in the Tecocomulco basin might still be active, as inferred by low-level seismic activity. DC resistivity helped to characterize the stratigraphic sequence of the volcano-sedimentary infill. The Acoculco caldera is not a piston-like caldera but a collapsed graben caldera. The Chichicuautla caldera has been downfaulted to the south by a NW-SE fault. The gravity signature of the southern half of this caldera is masked by the presence of a structural high, or by mafic bodies.
Prebuckling enhancement of beams and plates under uncertain loadings and arbitrary initial imperfections
Faria, Alfredo R. de;
Journal of the Brazilian Society of Mechanical Sciences and Engineering , 2007, DOI: 10.1590/S1678-58782007000400007
Abstract: crooked beams and plates with arbitrary initial geometric imperfections are optimized in order to improve their prebuckling response in the presence of uncertain loadings. a novel optimization approach is presented to simultaneously handle the two types of uncertainties: arbitrary initial imperfection patterns and arbitrary loadings. a remarkable improvement in the prebuckling response of optimal designs is achieved by reducing the level of prebuckling displacements measured in some appropriate norm, irrespective of the uncertain imperfection pattern or loading. two different norms are proposed, each one applicable to the beam or to the plate problem. the definitions of appropriate norms allow for the use of a minimax optimization approach that can consider the arbitrariness of both geometric imperfections and loadings. it is shown that the minimax procedure leads to optimum structural designs, in terms of optimal stiffness distribution, that are at the same time insensitive to perturbations in the loading space and to the pattern of initial imperfections in structure.
Palabras-n en contextos no negativos
Alfredo R. Amaiz
Lexis , 2002,
El suministro de sulfathiazol en ni os tuberculosos
Revista chilena de pediatría , 1947,
La globalización, el discurso económico y las diferencias culturales
Alfredo Rébori
Revista Theomai , 2003,
Abstract: The intent of this essay is to discuss about the phenomenon called Globalization , its impact on different culture values over which it interacts, and the role that values play on the theoretical development of Economy as a scientific discipline. One trigger for the writing of this paper, if not the first, is the perception coming from divers discourses politics, other social sciences, journalistic, religious, and from the own economic sciences- about the existence of one economic statement surrounding the Globalization phenomenon; in which man changes his role of subject of economic activity and non economic one, into a consumption object motivated by an increasing materialistic behavior, and where humanistic values have no more place. Paper mentioned a prosperous ideas stream to better understand the economic problem and its solutions , going ahead of the field study, trying to build a shared vision including different dimensions as values, technology, market and institutions.
Alfredo Villavicencio Ríos
Derecho PUCP , 2013,
Alfredo Villavicencio Ríos
Derecho PUCP , 2012,
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