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Search Results: 1 - 10 of 6478 matches for " Flores Alvarado "
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Helmholtz Theorems, Gauge Transformations, General Covariance and the Empirical Meaning of Gauge Conditions  [PDF]
Andrew Chubykalo, Augusto Espinoza, Rolando Alvarado Flores
Journal of Modern Physics (JMP) , 2016, DOI: 10.4236/jmp.2016.79092
Abstract: It is well known that the use of Helmholtz decomposition theorem for static vector fields \"\", when applied to the time dependent vector fields?\"\", \"\"which represent the electromagnetic field, allows us to obtain instantaneous-like solutions all along . For this reason, some people thought (see e.g. [1] and references therein) that the Helmholtz theorem cannot be applied to time dependent vector fields and some modification is wanted in order to get the retarded solutions. However, the use of the Helmholtz theorem for static vector fields is correct even for time dependent vector fields (see, e.g. [2]), so a relation between the solutions was required, in such a way that a retarded solution can be transformed in an instantaneous one, and conversely. On this paper we want to suggest, following most of the time the mathematical formalism of Woodside in [3], that: 1) there are many Helmholtz decompositions, all equally consistent, 2) each one is naturally related to a space-time structure, 3) when we use the Helmholtz decomposition for the electromagnetic potentials it is equivalent to a gauge transformation, 4) there is a natural methodological criterion for choosing the gauge according to the structure postulated for a global space-time, 5) the Helmholtz decomposition is the manifestation at the level of the fields that a gauge is involved. So, when we relate the retarded solution to the instantaneous one what we do is to change the gauge and the space-time. And, if the Helmholtz decompositions are related to a space-time structure, and are equivalent to gauge transformations, each gauge transformation is natural for a specific space-time. In this way, a Helmholtz decomposition for Euclidean space is equivalent to the Coulomb gauge and a Helmholtz decomposition for the Minkowski space is equivalent to the Lorenz gauge. This leads us to consider that the theories defined by different gauges may be mathematically equivalent, because they can be related by means of a gauge transformation, but they are not empirically equivalent, because they have quite different observational consequences due to the different space-time structure involved.
Observaciones sobre la no linealidad
Rolando Alvarado Flores
Ciencia Ergo Sum , 2001,
Abstract: Se estudia el papel que juega el análisis no lineal de los sistemas físicos como un nuevo instrumento cognitivo que puede ser usado en física así como en otras áreas de investigación. Para ello, se parte de reconstruir la noción de ?paradigma? de modo tal que pueda ser utilizada como unidad de análisis, y de una teoría de la referencia que elimina los designadores rígidos como inútiles en la práctica científica.
DNA Barcodes in Fig Cultivars (Ficus carica L.) Using ITS Regions of Ribosomal DNA, the psbA-trnH Spacer and the matK Coding Sequence  [PDF]
Carlos Castro, Alejandro Hernandez, Luis Alvarado, Dora Flores
American Journal of Plant Sciences (AJPS) , 2015, DOI: 10.4236/ajps.2015.61011
Abstract: Molecular markers provide a useful method for genotype characterization and allow a high precision determination of the genetic relationship between cultivars and varieties. A system based on DNA sequences—which is known as DNA barcoding—will choose one or several standard loci which can be sequenced and compared to differentiate between species. In this research, the ITS, matK, and trnH-psbA sequences were evaluated for the molecular identification of seven F. carica genotypes, generating complete sequences for the first two loci, but unable to produce bidirectional sequences by using the trnH-psbA sequence. The ITS sequence presented the highest variation rates, while the phylogeny constructed with the matK sequence obtained the highest percentage of solved monophyletic groups. Through Pearson’s correlation analysis, it was possible to determine the existence of a significant correlation between the ITS region and psbA-trnH, and the matK and psbA-trnH sequences, but not between ITS and matK. The phylogenies constructed with the ITS + matK barcodes and ITS + matK + psbA-trnH presented the highest percentage for resolution. However, considering the cost efficiency and the facilitated recovery by using PCR, the matK + ITS combination is recommended.
Effect of Using Two Different Types of Carbon Nanotubes for Blackberry (Rubus adenotrichos) in Vitro Plant Rooting, Growth and Histology  [PDF]
Dora Flores, Randall Chacón, Luis Alvarado, Alexander Schmidt, Carlos Alvarado, Juan Chaves
American Journal of Plant Sciences (AJPS) , 2014, DOI: 10.4236/ajps.2014.524367
Abstract: Nanoparticles are able to interact with biomolecules, creating functional nanosystems for transportation within in vivo cells, and leading to the study of their potential applications in the field of plant biotechnology. Therefore, the aim of this research was to determine the growth and rooting effect of functionalized (SWCNTs-COOH) and non-functionalized nanoparticles with iron residue inner particles (SWCNTs-Fe) in blackberry (Rubus adenotrichos) in vitro plants. Two types of SWCNTs were used, both of them characterized in a solid sample through Raman spectroscopy (λ = 532 nm) showing differences in the G band between SWCNT + Fe and SWCNT + COOH. The in vitro plants (approximately 15 mm length) were inoculated in a rooting medium. Six treatments were established: 4, 8, 12 μg/ml for each type of SWCNTs and a control without nanotubes. The assessed variables consisted of the average number of days for root emergence, average number of roots per plant, average root length per plant and the average stem length. This study determined that, in general, the SWCNTs-COOH promoted the growth of the in vitro plants under this assay, when compared to the SWCNTs-Fe trials. The lowest SWCNTs-COOH dose evidenced the best results for the assessed variables. Additionally, the histological analysis also evidenced that the plants treated with SWCNTs-COOH nanotubes (4 μg/ml) increased their cellular metabolism when compared to the control group.
An Algebraic Characterization of singular quasi-bi-Hamiltonian systems
Rolando Alvarado Flores,Maximo A. Aguero Granados
Physics , 2002,
Abstract: In this paper we prove an algebraic criterion which characterizes singular quasi-bi-hamiltonian structures constructed on the lines of a general, simple, new formal procedure proposed by the authors. This procedure shows that for the definition of a quasi-bi-hamiltonian system the requirement of non-singular Poisson tensors, contained in the original definition by Brouzet et al., is not essential. Besides, it is incidentally shown that one method of constructing Poisson tensors available in the literature is a particular case of ours. We present 2 examples.
A Critical Approach to Total and Partial Derivatives
Andrew E. Chubykalo,Rolando Alvarado Flores
Physics , 2002,
Abstract: In this brief note we critically examine the process of partial and of total differentiation, showing some of the problems that arise when we relate both concepts. A way to solve all the problems is proposed.
Errores médicos
Alvarado-Guevara,Ana Teresa; Flores-Sandí,Grettchen;
Acta Médica Costarricense , 2009,
Abstract: a medical error is a fault that occurs during the delivery of health care that has caused damage to the patient. it could be related to the organization and implementation of the medical service, through multiple and complex mechanisms. none of the medical areas is exempt of them. the legal analysis of diagnostic errors is difficult because many times they are inevitable. however, as soon as their possible causes-cognitive errors, system errors and no fault errors-are analyzed, it is possible to establish strategies to minimize them. the most important approach to a medical or diagnostic error is to confront it with reliability and clarity.
Percepciones y supuestos sobre la ense?anza de la ciencia: Las concepciones de los investigadores universitarios
Alvarado Rodríguez, María Eugenia;Flores-Camacho, Fernando;
Perfiles educativos , 2010,
Abstract: this article presents the results of a study that involves researchers in several scientific areas at the universidad nacional autónoma de méxico (national autonomous university of mexico) with regard to their conceptions about teaching science at the university. it is part of a wider study about the origin and the development of the conceptions about science that prevail amongst the researchers in sciences. it offers a short overview about the educational research on teaching sciences and afterwards presents the ideas expressed by several researchers about teaching and learning sciences, such as ideas and views about the teachers training and updating, the lack of connection between teaching and research, the infrastructure and economic problems and other obstacles for teaching sciences. in the central part of this work the authors show the kind of ideas shown by the researchers about teaching sciences and they propose a critical and comparative analysis of such ideas and conceptions. they also show the problems that underlie naive conceptions about the teaching and learning processes and they emphasize some of the implications around the difficulties in improving scientific education at the university.
Percepciones y supuestos sobre la ense anza de la ciencia. Las concepciones de los investigadores universitarios
María Eugenia Alvarado Rodríguez,Fernando Flores-Camacho
Perfiles educativos , 2010,
Abstract: Se presentan resultados de un estudio con investigadores de diversas áreas científicas de la UNAM en relación a sus concepciones sobre la ense anza de la ciencia en el marco universitario. El texto forma parte de un estudio sobre el origen y desarrollo de las concepciones de ciencia que prevalecen entre los investigadores en ciencias. Se aborda un breve panorama en relación a la investigación educativa en la ense anza de las ciencias para, posteriormente, presentar las ideas expresadas por diversos investigadores en torno a la ense anza de la ciencia y del aprendizaje, como son: ideas y perspectivas en formación y actualización docente, desvinculación docencia investigación, infraestructura y problemas de índole económica, y obstáculos para la ense anza de la ciencia. En el desarrollo del trabajo se muestra el tipo de ideas que tienen los investigadores en torno a la ense anza de la ciencia y se hace un análisis crítico y comparativo de tales ideas y concepciones. Se muestran los problemas que subyacen a concepciones ingenuas sobre los procesos de ense anza y aprendizaje y se anotan algunas implicaciones en torno a las dificultades de mejorar la educación científica en la universidad.
Síndrome de Cimitarra: a propósito de dos casos recientes
Alejandra Flores Badilla,Alcibey Alvarado González,Carlos Mas Romero
Revista Costarricense de Cardiología , 2002,
Abstract:
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