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Search Results: 1 - 10 of 28823 matches for " Fernando Alvarez-Ramirez "
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New Approaches to the Computer Simulation of Amorphous Alloys: A Review
Ariel A. Valladares,Juan A. Díaz-Celaya,Jonathan Galván-Colín,Luis M. Mejía-Mendoza,José A. Reyes-Retana,Renela M. Valladares,Alexander Valladares,Fernando Alvarez-Ramirez,Dongdong Qu,Jun Shen
Materials , 2011, DOI: 10.3390/ma4040716
Abstract: In this work we review our new methods to computer generate amorphous atomic topologies of several binary alloys: SiH, SiN, CN; binary systems based on group IV elements like SiC; the GeSe 2 chalcogenide; aluminum-based systems: AlN and AlSi, and the CuZr amorphous alloy. We use an ab initio approach based on density functionals and computationally thermally-randomized periodically-continued cells with at least 108 atoms. The computational thermal process to generate the amorphous alloys is the undermelt-quench approach, or one of its variants, that consists in linearly heating the samples to just below their melting (or liquidus) temperatures, and then linearly cooling them afterwards. These processes are carried out from initial crystalline conditions using short and long time steps. We find that a step four-times the default time step is adequate for most of the simulations. Radial distribution functions (partial and total) are calculated and compared whenever possible with experimental results, and the agreement is very good. For some materials we report studies of the effect of the topological disorder on their electronic and vibrational densities of states and on their optical properties.
Non-integrability of some few body problems in two degrees of freedom
Primitivo Acosta-Humanez,Martha Alvarez-Ramirez,Joaquin Delgado
Physics , 2008,
Abstract: The basic theory of Differential Galois and in particular Morales--Ramis theory is reviewed with focus in analyzing the non--integrability of various problems of few bodies in Celestial Mechanics. The main theoretical tools are: Morales--Ramis theorem, the algebrization method of Acosta--Bl\'azquez and Kovacic's algorithm. Morales--Ramis states that if Hamiltonian system has an additional meromorphic integral in involution in a neighborhood of a specific solution, then the differential Galois group of the normal variational equations is abelian. The algebrization method permits under general conditions to recast the variational equation in a form suitable for its analysis by means of Kovacic's algorithm. We apply these tools to various examples of few body problems in Celestial Mechanics: (a) the elliptic restricted three body in the plane with collision of the primaries; (b) a general Hamiltonian system of two degrees of freedom with homogeneous potential of degree -1; here we perform McGehee's blow up and obtain the normal variational equation in the form of an hypergeometric equation. We recover Yoshida's criterion for non--integrability. Then we contrast two methods to compute the Galois group: the well known, based in the Schwartz--Kimura table, and the lesser based in Kovacic's algorithm. We apply these methodology to three problems: the rectangular four body problem, the anisotropic Kepler problem and two uncoupled Kepler problems in the line; the last two depend on a mass parameter, but while in the anisotropic problem it is integrable for only two values of the parameter, the two uncoupled Kepler problems is completely integrable for all values of the masses.
Mejora en el control en cascada para reactores tubulares
Hernández-Martínez, E.;Urrea, R.;Alvarez-Ramirez, J.;
Revista mexicana de ingeniería química , 2008,
Abstract: tubular reactors are difficult to operate due the intricate coupling between transport processes, nonlinear chemical kinetics, and their distributed nature. however, due to numerous industrial applications for chemical tubular reactors, the problem of monitoring and controlling them effectively is of great safety and economical importance. in this work, we introduce a new cascade control scheme based on three-temperature measurement distributed along the axial position of the tubular reactor with respect to a weighted average temperature (wav). the control configuration exploits the information provided by two additional temperatures sensor located at the feed and the output of the tubular reactor. the configuration with wav improves the behavior of the control scheme by enhancing the disturbance and parameter's uncertainty. numerical simulations are used to illustrate and compare the control performance.
Experimental Evaluation of the Concentration Zone Widths in Cane Sugar Crystallization using Data and Image Acquisition
O. Velazquez-Camilo,E. Bolanos-Reynoso,L. Lopez-Zamora,J. Alvarez-Ramirez
Lecture Notes in Engineering and Computer Science , 2010,
Abstract:
BREAKDOWN OF SCALING PROPERTIES IN ABNORMAL HEART RATE VARIABILITY
Rodríguez, E.,De Luca,Meraz, M.,Alvarez-Ramirez, J.
Journal of applied research and technology , 2006,
Abstract: The heart rate variability (HRV) of subjects with normal sinus rhythm (NSR) and subjects with congestive heart failure(CHF) is compared by using a structure function borrowed from turbulence studies. Firstly, it is shown that the HRV ofsubjects with NSR displays a power law scaling property, which indicates the presence of structured heartbeat controlmechanisms. Secondly, it is found that such a scaling property is partially lost for subjects with CHF. The absence ofscaling properties is associated to the presence of uncorrelated (i.e., noise-like) heart rate variations. In order to gaininsights on the source of the scaling property, the HRV is analyzed from a systemic (i.e., feedback control) viewpoint inthe frequency domain. It is found that the HRV of subjects with NSR is governed by a stable adaptive control mechanismpresumably located in the autonomic nervous system. In the case of subjects with CHF, the results show that thisregulation mechanism is partially or totally absent, which is interpreted as the cause of the breakdown of the scalinglaw property.
DEPRESSIVE SYMPTOMS IN ADOLESCENT WOMEN: PREVALENCE AND INTERPERSONAL ASSOCIATED FACTORS
Fernando Ramirez
Revista Peruana de Epidemiologia , 2010,
Abstract: Objectives: To estimate the prevalence of depressive symptoms in teenagers senior students from a public college and to identify interpersonal relationship factors associated with it. Methods: Cross-sectional study. The sample was 176 students (15 to 19 years), the instrument consisted of two parts, the first one collected demographic data and the second one was the Reynolds Adolescent Depression Scale (RADS). We used SPSS.15.0, we calculated descriptive statistics such as frequency distributions and percentages; in order to assess the association of variables selected, chi-square was used and a logistic regression model was performed. Results: Of all students 28 (15.9%) were 15 years old, 125 (71.0%) were 16 and 23 (13.1%) 17. The prevalence of depression was 29.5%. Bivariate analysis of depression with sociodemographic characteristics showed that age, overtime study outside the classroom, history of sexual violence and school violence were statistically associated (p <0.05). In the logistic regression, history of school aggression (adjusted OR 4.5, IC95%: 2.0 -10.1), having 16 years (adjusted OR 3.6, IC95%: 1.4-9.1) and history of sexual assault (adjusted OR 2.6, 95% CI: 1.1-7.0) were associated to the presence of depressive symptoms in the adolescence. Conclusions: History of school aggression and history of sexual aggression are interpersonal relationship factors associated with a higher risk of depressive symptoms in a teenager. Early identification of these risk factors will help reduce the impact of this disease in the family, society and the academic performance; it would also contribute to the reduction of the suicide risk, substance abuse, and persistence of depressive disorders in adulthood.
Nanomedicine: Application Areas and Development Prospects
Houria Boulaiz,Pablo J. Alvarez,Alberto Ramirez,Juan A. Marchal,Jose Prados,Fernando Rodríguez-Serrano,Macarena Perán,Consolación Melguizo,Antonia Aranega
International Journal of Molecular Sciences , 2011, DOI: 10.3390/ijms12053303
Abstract: Nanotechnology, along with related concepts such as nanomaterials, nanostructures and nanoparticles, has become a priority area for scientific research and technological development. Nanotechnology, i.e., the creation and utilization of materials and devices at nanometer scale, already has multiple applications in electronics and other fields. However, the greatest expectations are for its application in biotechnology and health, with the direct impact these could have on the quality of health in future societies. The emerging discipline of nanomedicine brings nanotechnology and medicine together in order to develop novel therapies and improve existing treatments. In nanomedicine, atoms and molecules are manipulated to produce nanostructures of the same size as biomolecules for interaction with human cells. This procedure offers a range of new solutions for diagnoses and “smart” treatments by stimulating the body’s own repair mechanisms. It will enhance the early diagnosis and treatment of diseases such as cancer, diabetes, Alzheimer’s, Parkinson’s and cardiovascular diseases. Preventive medicine may then become a reality.
MINERíA DE DATOS BASADA EN LóGICA DIFUSA PARA LA INTERPRETACIóN DE CONSULTAS VAGAS DEPENDIENTES DEL CONTEXTO LINGüíSTICO
CLAUDIA JIMENEZ RAMIREZ,HERNáN ALVAREZ ZAPATA
DYNA , 2012,
Abstract: En este artículo se presenta un método propuesto para que un sistema flexible de consulta-respuesta a bases de datos pueda hallar, de manera autónoma y dinámicamente, la semántica de las condiciones vagas de las consultas, explorando los datos disponibles en la base de datos y usando lógica difusa. La máquina de inferencia del sistema, según el contexto lingüístico delimitado por cada consulta, elige un modelo de conjunto difuso entre los modelos predefinidos para diferentes patrones sintácticos con los que puede encajar el texto de una consulta vaga y considerando diferentes niveles de granularidad en la categorización de los objetos. Se estima el valor de los parámetros del conjunto difuso que representa una etiqueta lingüística, usando un método no supervisado y no paramétrico en el proceso de discriminación; evitando así, la intervención de expertos. Con esto se logra que los sistemas no sólo sean adaptables, sino confiables gracias a la validez de sus respuestas.
Etiology and Management of Hemorrhagic Complications of Portal Hypertension in Children
Alejandro Costaguta,Fernando Alvarez
International Journal of Hepatology , 2012, DOI: 10.1155/2012/879163
Abstract: Portal hypertension in children represents a particular diagnostic and management challenge for several reasons: (1) treatment outcomes should be evaluated in relationship with a long-life expectancy, (2) pediatric patients with portal hypertension constitute an heterogeneous population, both in terms of individual characteristics and diversity of liver diseases; making comparison between treatment outcomes very difficult, (3) application of techniques and procedures developed in adult patients (v.gr. TIPS) face size limitations in small children, and (4) absence of data from well-controlled trials in children forces pediatric specialists to adapt results obtained from adult cohorts suffering from diseases such as HCV and alcoholic cirrhosis. Despite those limitations, substantial progress in the treatment of children with portal hypertension has been achieved in recent years, with better outcomes and survival. Two main factors influence our therapeutic decision: age of the patient and etiology of the liver disease. Therefore, diagnosis and treatment of complications of portal hypertension in children need to be described taking such factors into consideration. This paper summarizes current knowledge and expert opinion.
Determinantes del éxito gerencial
Fernando Toro Alvarez
Revista Latinoamericana de Psicología , 1996,
Abstract: Este estudio se realizó con el propósito de identificar diversas condiciones personales determinantes del éxito de 120 gerentes de sucursales de una organización del sector financiero. Se partió del concepto de Lawler ID acerca de que el desempe o laboral se encuentra determinado y regulado por los conocimientos, las habilidades y la motivación para el trabajo. Se formularon tres indicadores objetivos de éxito: colocación, captación y rentabilidad de la oficina. Como variables independientes se midieron los conocimientos específicos para el cargo, habilidades intelectuales relevantes, factores motivacionales y factores de personalidad. Se realizaron análisis de varianza, de significación de diferencias y de regresión múltiple. Los resultados mostraron que los conocimientos institucionales, una motivación de poder algo más baja, el interés por la promoción, parmia y mucha tensión érgica explicaban el 26% del éxito gerencial.
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