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Search Results: 1 - 10 of 4714 matches for " Salvador Godoy "
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A Basis for Causal Scattering Waves, Relativistic Diffraction in Time Functions  [PDF]
Salvador Godoy, Karen Villa
Journal of Modern Physics (JMP) , 2016, DOI: 10.4236/jmp.2016.710107
Abstract: Relativistic diffraction in time wave functions can be used as a basis for causal scattering waves. We derive such exact wave function for a beam of Dirac and Klein-Gordon particles. The transient Dirac spinors are expressed in terms of integral defined functions which are the relativistic equivalent of the Fresnel integrals. When plotted versus time the exact relativistic densities show transient oscillations which resemble a diffraction pattern. The Dirac and Klein-Gordon time oscillations look different, hence relativistic diffraction in time depends strongly on the particle spin.
Theory of Conductivity in Semiconducting Single-Wall Carbon Nanotubes  [PDF]
Shigeji Fujita, Salvador Godoy, Akira Suzuki
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.310191
Abstract: The conduction of a single-wall carbon nanotube depends on the pitch. If there are an integral number of carbon hexagons per pitch, then the system is periodic along the tube axis and allows “holes” (not “electrons”) to move inside the tube. This case accounts for a semiconducting behavior with the activation energy of the order of around 3 meV. There is a distribution of the activation energy since the pitch and the circumference can vary. Otherwise nanotubes show metallic behaviors (significantly higher conductivity). “Electrons” and “holes” can move in the graphene wall (two dimensions). The conduction in the wall is the same as in graphene if the finiteness of the circumference is disregarded. Cooper pairs formed by the phonon exchange attraction moving in the wall is shown to generate a temperature-independent conduction at low temperature (3 - 20 K).
Quantum statistical model for superconducting phase in graphene and nanotubes
Shigeji Fujita,Rohit Singh,Salvador Godoy,Kei Ito
Physics , 2009,
Abstract: A quantum statistical theory is presented, supporting a superconducting state of an ultrahigh critical temperature (1275 K) in the multiwalled nanotubes reported by Zhao and Beeli [Phys. Rev. B 77, 245433 (2008)].
On the metal-insulator-transition in vanadium dioxide
Shigeji Fujita,Azita Jovaini,Salvador Godoy,Akira Suzuki
Physics , 2012, DOI: 10.1016/j.physleta.2012.08.027
Abstract: Vanadium dioxide (VO$_2$) undergoes a metal-insulator transition (MIT) at 340 K with the structural change between tetragonal and monoclinic crystals as the temperature is lowered. The conductivity $\sigma$ drops at MIT by four orders of magnitude. The low-temperature monoclinic phase is known to have a lower ground-state energy. The existence of a $k$-vector ${\boldsymbol k}$ is prerequisite for the conduction since the ${\boldsymbol k}$ appears in the semiclassical equation of motion for the conduction electron (wave packet). Each wave packet is, by assumption, composed of the plane waves proceeding in the ${\boldsymbol k}$ direction perpendicular to the plane. The tetragonal (VO$_2$)$_3$ unit cells are periodic along the crystal's $x$-, $y$-, and z-axes, and hence there are three-dimensional $k$-vectors. The periodicity using the non-orthogonal bases does not legitimize the electron dynamics in solids. There are one-dimensional ${\boldsymbol k}$ along the c-axis for a monoclinic crystal. We believe this decrease in the dimensionality of the $k$-vectors is the cause of the conductivity drop. Triclinic and trigonal (rhombohedral) crystals have no $k$-vectors, and hence they must be insulators. The majority carriers in graphite are "electrons", which is shown by using an orthogonal unit cell for the hexagonal lattice.
Eficiencia en la producción y distribución de biomasa en variedades precoces de algodón
Arturo Gaytu00E1n Mascorro,Arturo Palomo Gil,Salvador Godoy Avila
Revista fitotecnia mexicana , 2001,
An Alternative View to the Cause of Market Failures: A Dynamic Approach  [PDF]
Salvador Contreras
Theoretical Economics Letters (TEL) , 2014, DOI: 10.4236/tel.2014.47069

This paper presents an alternative view to the cause and size of market failures. The work here suggest that the size of the market failure is not man made per se but rather given a full set of initial conditions it is endogenous to the dynamical forces at play. It is shown that the level and variance of market failures is tied to the location of the steady state (i.e. level of development). The paper finds that only changes to the location of the steady state produces changes to the potential level of the market failure. This paper adds to the increasing body of literature the notion that institutional change is not a sufficient condition to sustained economic development.

Rendimiento, componentes del rendimiento y calidad de fibra del algodón en relación con la dosis de nitrógeno y la densidad poblacional
Arturo Palomo Gil,Arturo Gaytu00E1n Mascorro,Salvador Godoy u00C1vila
Revista fitotecnia mexicana , 2003,
Abstract: Las variedades mexicanas de algodón (Gossypium hirsutum L.) son más precoces y de menor tama o vegetativa que las variedades extranjeras tradicionalmente sembradas. Por su estructura, las variedades mexicanas ocupan menos espacio por lo que es posible que, para mostrar su potencial productivo, requieran de una mayor densidad poblacional y de una dosis de fertilización nitrogenada diferente a las requeridas por las variedades tardías. En este trabajo se evaluó la respuesta de la variedad Laguna 89 a dosis de fertilización nitrogenada y a densidades de población. En el sistema de producción de surcos estrechos (distancia de 0.70 m entre surcos), en 1997 y 1998 se probaron seis dosis de N: 0, 40, 80, 120 (testigo comercial), 160 y 200 kg ha-1, y cuatro densidades: 70 000 (testigo comercial), 82 500, 95 000 y 108 000 plantas/ha. Se midió el rendimiento de algodón en hueso y pluma, la precocidad de la primera cosecha, los componentes del rendimiento y la calidad de fibra. Se detectaron diferencias entre a os en las variables evaluadas, pero no hubo interacción de a o con dosis de N o densidad de plantas. No hubo efectos significativos de la dosis de N o de la densidad poblacional, ni de sus interacciones en el rendimiento y precocidad, pero si en el porcentaje de fibra , que fueron mayores con las dosis de N de 0, 40, 120 y 160 kg ha-1. Con dosis altas de N aumentó el índice de semilla y la resistencia de la fibra. A medida que aumentó la densidad poblacional disminuyó el rendimiento por planta y el número de capullos por planta. La densidad de plantas no afectó la longitud de la fibra, pero sí la resistencia y la finura; la fibra más resistente se obtuvo con densidades de 82 500 y 95 000 plantas/ha, y en las densidades altas la fibra fue más gruesa.
Introducing Engineering Students to Historical/Cultural Perspectives through Story-Centered On-Line Learning  [PDF]
Luis A Godoy
Creative Education (CE) , 2011, DOI: 10.4236/ce.2011.22009
Abstract: Several authors argued that history of science should be an integral part of science education; however, there are many obstacles to carry out an implementation within this approach, including that lecturers normally lack a necessary historical background (a situation that is largely aggravated in engineering faculties), and the impossi- bility of including new courses or credits in an already tight curriculum. The development of on-line modules that engineering students can work outside their normal schedule of classes, introducing historical/cultural per- spectives, is presented in this paper. E-learning and knowledge management strategies are used in the context of science education at undergraduate and graduate levels. The approach is based on learning-by-doing in a virtual environment, and specifically presents story-centered activities, in which the student is faced with a problem and plays the role of an expert to provide a solution to the case. The specific case considered develops in the form of a controversy concerning the origin of the studies of column buckling. Two sets of information are available for navigation in the module: specific information that the student can explore (containing historical material di- rectly connected to the case provided), and more general information (providing the historical/cultural context to the problem). A first application has been made with civil engineering students, who had to write a two-page white paper as a consequence of their work on the problem. The interest generated in the participating students and the positive evaluation of their experience seems to indicate that this type of activity can serve to enhance traditional engineering lectures by incorporating a historical dimension. The present web-based approach could be extended to tackle similar conflicts in fields for which there is ample documentation available in the literature or in other historical episodes which may lead to rich discussions.
A Unified Methodology to Evaluate Supervised and Non-Supervised Classification Algorithms
Godoy Calderón, Salvador;Martínez Trinidad, José Francisco;Lazo-Cortes, Manuel S;Díaz de León Santiago, Juan Luis;
Computación y Sistemas , 2006,
Abstract: there is presently no unified methodology that allows the evaluation of supervised or non-supervised classification algorithms. supervised problems are evaluated through quality functions while non-supervised problems are evaluated through several structural indexes. in both cases a lot of useful information remains hidden or is not considered by the evaluation method, such as the quality of the sample or the structural change generated by the classification algorithm. this work proposes a unified methodology that can be used to evaluate both type of classification problems. this new methodology yields a larger amount of information to the evaluator regarding the quality of the initial sample, when it exists, and regarding the change produced by the classification algorithm in the case of non-supervised classification problems. it also offers the added possibility of making comparative evaluations with different algorithms.
Respuesta del algodón cv. Cian precoz 3 al espaciamiento entre surcos y densidad poblacional. I. Rendimiento, precocidad y calidad de fibra: (con 8 cuadros)
Gaytán-Mascorro,Arturo; Palomo-Gil,Arturo; Reta-Sánchez,David G; Godoy-ávila,Salvador; García-Casta?eda,Enrique A;
Phyton (Buenos Aires) , 2004,
Abstract: ultra-narrow rows system and high plant densities, are an alternative to diminish the high cotton production costs, and to increase cotton crop yields. the objective of this work was to learn about the performance of an early cotton variety (cian precoz 3) to ultra-narrow rows and high plant densities cotton production system. four row distances were evaluated, they were; a single rows 50 cm apart, a single row 76 cm apart, two plant hills 30 cm apart sown on 90 cm beds, and three plants hills 30 cm apart sown on 140 cm beds. plant densities studied were 8, 12, 15, and 20 plants m-2. seed and lint cotton yields, yield components, earliness, cover crop close, leaf area index (lai), and fiber quality were measured. there was no cotton yield response to row distances or plant densities. fifty cm rows matured the 85% of bolls one week earlier, crop cover closed 10 daysearlier, and developed less lai, than the 76 cm rows (check). crop cover close, lai and yield components were not affected by plant densities. all treatments showed high fiber quality. benefits of planting cotton in ultra-narrow rows are a short crop cycle and low machinery use.
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