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Search Results: 1 - 10 of 603096 matches for " Luis A. Díaz-Alejo "
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Effects of the Addition of Ortho- and Para-NH2 Substituted Tetraphenylporphyrins on the Structure of Nylon 66
Luis A. Díaz-Alejo,E. Carmina Menchaca-Campos,J. Uruchurtu Chavarín,R. Sosa-Fonseca,Miguel A. García-Sánchez
International Journal of Polymer Science , 2013, DOI: 10.1155/2013/323854
Abstract: The synthetic tetrapyrrole macrocycles, such as porphyrins (H2P) and phthalocyanines (H2Pc), exhibit interesting physicochemical properties suitable to be used in modern technology. For many applications, those species should be trapped or fixed inside graphite, hydrotalcites, silica, TiO2, or polymers. Methodologies for the optimization of the properties of porphyrins, trapped or fixed inside polymers, have been barely developed. Our research works in the development of methodologies for the optimization of incorporation and display of properties of tetrapyrrole macrocycles inside inorganic, polymeric, or hybrid networks. This paper shows some results about the effect of the spatial disposition of the amine (–NH2) groups attached on the periphery of substituted tetraphenylporphyrins, on the Nylon 66 structure and on the display of the physicochemical properties of the trapped macrocycles. Nylon 66 was synthesized from adipoyl chloride and hexamethylenediamine in presence of tetraphenylporphyrins substituted with –NH2 groups localized at the ortho- or para-positions of the phenyls. Cobalt complexes formation was used to quantify the amount of porphyrins in the polymer fibers. Characterization results show that the spatial position of amine groups of the porphyrins has important structural and textural effect on the Nylon 66 fibers and on the fluorescence of the porphyrins integrated into the fibers. 1. Introduction Porphyrins are tetrapyrrole macrocyclic compounds playing a transcendental role in nature as one of the principal components of molecules such as (i) chlorophyll, (ii) the heme group in blood and cytochromes and (iii) cyanocobalamin (Vitamin B12) [1–3]. Formally, porphyrins are modified or substituted aromatic tetrapyrrole macrocyclic compounds derived from porphin (Figure 1), which consists of four pyrrole rings bonded through methine (=CH) bridges in order to form a planar and highly conjugated macrocycle. In the free bases of porphyrins, the two pyrrolic hydrogens can be substituted by a cation, and the remaining two nitrogens tend to easily coordinate with a metal nucleus as to form a stable metalloporphyrin. Synthetic porphyrinic complexes, involving practically all metallic elements of the periodic table, have been synthesized already [2–4]. The central space of porphyrins can only accommodate ions having an atomic radius smaller than 0.201?nm [2–4]; thus, causing that in the porphyrinic complexes containing the larger ions, the metallic element must be located outside of the molecular plane. Similar to the size of the cation, the
Laser-Induced Breakdown Spectroscopy (LIBS) Applied in the Differentiation of Arabica and Robusta Coffee  [PDF]
Abigail María Díaz Guerrero, Luis Vidal Ponce Cabrera, Teresa Flores Reyes, Rogelio Ortega Izaguirre
Optics and Photonics Journal (OPJ) , 2017, DOI: 10.4236/opj.2017.710018
Abstract: Coffee is one of the most consumed and commercialized crops in the world, which is why there is a potential risk to find arabica coffee (an expensive variety) adulterated with robusta coffee (a cheaper variety). The currently used technique for certifying coffee, High Performance Liquid Chromatography (HPLC), requires the sample to be subjected to a chemical treatment prior to analysis; in addition, the equipment is bulky and can not be moved easily. Laser Induced Breakdown Spectroscopy (LIBS) is a technique which does not require that samples be subjected to a chemical pretreatment, and equipment is small and portable, this can save valuable time in coffee trading. The purpose of this research was to demonstrate that LIBS can be applied to solve various problems related with the coffee authentication. Green coffee pills with different concentrations of arabica and robusta varieties were analyzed by LIBS, the results were used in the construction of calibration curves for the detection of the degree of simulated adulteration in coffee. It was found that the relative intensities of Ca (392.4 nm), Sr (407.1 nm), N (500.5 nm) and Na (588.7 nm), as well as the intensity ratios of Ca II (392.4 nm)/N I (500.5 nm), Sr I (407.1 nm)/N I (500.5 nm)and N I (500.5 nm)/Na I (588.7 nm) can be used for this purpose. It is concluded that the differentiation of coffee and the detection of its adulteration is possible with the use of LIBS. Further, with the use of an Artificial Neural Network (ANN) of type Multilayer Perceptron, it was possible to correctly classify the spectra of arabica and robusta roasted coffee.
Transmisión de pulsos luminosos ultracortos que inciden oblicuamente sobre un medio absorbente y/o dispersivo
H. Ramírez Díaz,M.M. Méndez Otero,E.A. Martí Paname?o,C.A. Alejo Armenta
Revista mexicana de física , 2004,
Abstract: Se estudia la transmisi′on, a trav′es de un medio material, de pulsos ′opticos polarizados linealmente, los cuales inciden oblicuamente desde el vac′ o. La geometr′ a analizada considera que el campo el′ectrico tiene componentes paralela y perpendicular al plano de incidencia. Se encuentran expresiones anal′ ticas para los campos el′ectrico y magn′etico dentro del medio material; la forma funcional de dichas expresiones permite relacionar las partes imaginaria y real del vector de onda, tanto con la p′erdida de la amplitud espectral del pulso como con su direcci′on de propagaci′on. Se encuentra una relaci′on integral generalizada para el vector de Poynting, en el dominio del tiempo, la cual es v′alida para medios dispersivos y absorbentes.
A Check List to Reduce Misuse of Primary Cesarean Sections in Women with a Single Fetus in Cephalic Position  [PDF]
Catalina Acu?a Pradilla, Delgzar Raúl Gómez Pereira, Luis Alfonso Díaz-Martínez
Health (Health) , 2017, DOI: 10.4236/health.2017.98090
Abstract: Background: Avoiding primary C-section is the safest and most effective way of decreasing C-section rates. We analyzed circumstances and decisions made among pregnant women without history of C-section and cephalic single fetus (group B), who ended up having a Cesarean birth, to identify opportunities that may optimize the decisions about delivery. Methodology: We evaluated the clinical histories of pregnant women from group B who completed their pregnancies in the Hospital Universitario de Santander (Bucaramanga, Colombia) during 2013. We evaluated the decision moments from admission until birth, including the registry of the reasons for having a C-section, compliance of all the criteria to support the decision and its appropriateness, and how adequate were the procedures done during the induction or augmentation of labor. Results: We evaluated 1320 histories; 666 (55.7%) ended by C-Section. In 59.8% of the histories, we identified at least one decision that could have been addressed differently to optimize the delivery type and, potentially, avoid ending in a Cesarean birth. The most frequent opportunities arise due to a lack of clarity in the record of the reason for performing the C-section (70.1%), and inadequate use of labor induction in the patients that had to end their gestation (38.5%). Conclusion: In the Hospital Universitario de Santander during 2013, despite observing a meaningful subregistry of the indication to perform a C-section, we found that in one out of every two patients there are opportunities of improvement in the registry and attention to reduce the high incidence of C-sections in the institution. This analysis allowed us to create a checklist to fill out before making the final decision of performing a Cesarean birth.
Valorization of Solid Waste Recovery in an Institution of Higher Education  [PDF]
Nora E. Munguía, ángela M. Díaz, Luis E. Velazquez, Rafael Perez, Javier Esquer, David S. Zepeda
Green and Sustainable Chemistry (GSC) , 2018, DOI: 10.4236/gsc.2018.82013
Abstract: One of the biggest challenges for organizations, cities and countries is waste management. Currently, 1.3 million tons of solid wastes are generated in the cities and by 2025 it is estimated that this volume will increase up to 2.2 billion tons. Considering this, it is clear that strategies for the reduction of waste generation are needed. In order to achieve this arduous and critic task changes in education, culture and public policy are required and one of the strategies that emerge as one of the most effective is the “zero waste” programs. This paper shows the foundation of a zero waste program based on previous and successful experiences in institutions of higher education. It presents the characterization and quantification of waste, as well as the valorization of it and potential environmental and economic benefits of the implementation of this kind of programs in higher education institutions. Results show that reduction and valorization of waste generation is possible in academic sectors while other outcomes emerge, such as the generation of human capital for the implementation of this kind of programs in different sectors of society and, in that way, contribute in the transition towards sustainable development.
Competencias y organización en Venezuela de los servicios de salud y seguridad en el trabajo
Luis Eduardo,Díaz; A?ez Castillo,María Alejandra;
Gaceta Laboral , 2009,
Abstract: the principal objective of this study is to explain competences and organization for the health and job security services in venezuela in the light of the great challenges implied in fulfilling the ends for which they were created, given the shortages, ambiguities and difficulties in setting up and operating these services. the study is of a documentary, descriptive type, starting with the observation and analysis of national and international bodies of law in order to extract comparative experiences regarding their application and practical viability. results show the complexity of their organization--multidisciplinary and obligatory for the employer-- parallel to a significant accumulation of unavoidable competences in terms of planning and organizing work to guarantee worker safety and health, being a kind of physiological organ for the company that rationalizes individual work and the social factors that influence it. finally, some recommendations are formulated in terms of the need to educate and raise awareness for the social actors regarding the importance of a culture of security that passes through the elaboration of a national prevention program to display other, more specific points in another study.
Competencias y organización en Venezuela de los servicios de salud y seguridad en el trabajo Competences and organization for health and job security services in Venezuela
Díaz Luis Eduardo,María Alejandra A?ez Castillo
Gaceta Laboral , 2009,
Abstract: El objetivo principal de esta investigación es explicar las competencias y organización de los Servicios de Salud y Seguridad del Trabajo en Venezuela, en virtud de los grandes retos que implica el cumplimiento de la finalidad para la cual fueron creados, dadas las carencias, ambigüedades y dificultades para la constitución y funcionamiento de dichos servicios. Se trata de una investigación de tipo documental y descriptiva partiendo de la observación y análisis de cuerpos normativos nacionales e internacionales, a los fines de extraer la experiencia comparada en torno a su aplicación y viabilidad práctica. Como resultado de ello, se evidencia la complejidad de su organización, multidisciplinaria y obligatoria por parte del empleador, paralelamente a un cúmulo significativo de competencias ineludibles en cuanto a la planificación y organización del trabajo, para garantizar la seguridad y salud laboral, siendo una especie de órgano fisiológico de la empresa que, racionaliza el trabajo individual y los factores sociales que influyen en él. Se formularon finalmente algunas recomendaciones en cuanto a la necesidad de educar y concientizar a los actores sociales en torno a la importancia de una cultura de seguridad que pasa por la elaboración de un programa nacional de prevención para desplegar en otra investigación otras más específicas. The principal objective of this study is to explain competences and organization for the Health and Job Security Services in Venezuela in the light of the great challenges implied in fulfilling the ends for which they were created, given the shortages, ambiguities and difficulties in setting up and operating these services. The study is of a documentary, descriptive type, starting with the observation and analysis of national and international bodies of law in order to extract comparative experiences regarding their application and practical viability. Results show the complexity of their organization--multidisciplinary and obligatory for the employer-- parallel to a significant accumulation of unavoidable competences in terms of planning and organizing work to guarantee worker safety and health, being a kind of physiological organ for the company that rationalizes individual work and the social factors that influence it. Finally, some recommendations are formulated in terms of the need to educate and raise awareness for the social actors regarding the importance of a culture of security that passes through the elaboration of a national prevention program to display other, more specific points in another study.
Relaciones entre la nota de egreso de los titulados universitarios y su inserción laboral Relationships between University graduates' marks and their labour outcomes.
Luis A. García,Carlos E. Díaz
European Journal of Education and Psychology , 2009,
Abstract: Son muchos los factores que están involucrados en la toma de decisiones de los egresados universitarios a la hora de construir su propio itinerario formativo y laboral, siendo la nota de egreso un elemento a considerar. En el presente trabajo se aborda el posible papel de este aspecto como mediador en dicho proceso, analizando las relaciones que presenta dicha variable con la participación en programas de formación de postgrado y la dilación en la incorporación al mercado de trabajo. La población de estudio está compuesta por 15.360 egresados universitarios que finalizaron su titulación en la Universidad de La Laguna entre los a os 2002 y 2007. Los resultados obtenidos indican que, generalmente, los egresados con que participan en programas de formación de postgrado y quienes invierten más tiempo en incorporarse al mercado de trabajo han obtenido mejores calificaciones académicas. En este sentido, algunas titulaciones de Ciencias de la Salud como Medicina o Fisioterapia se comportan en sentido inverso, pudiendo deberse esto a los mecanismos específicos de incorporación de candidatos con los que cuenta el sistema sanitario. Palabras clave: Inserción laboral, expediente académico, formación de postgrado. There are many different factors involved on university graduates’ decision making about their own careers after graduation, being university grades a main element to be considered. University grades’ hypothetical role as mediator on this process and relationships between this variable, invested time to obtain a job and involvement on postgraduate programs are analyzed on this study. Researched population consists of 15.360 graduates who finished their degrees between 2002 and 2007 in La Laguna’s University. Data shows graduates who are involved on postgraduate programs and those who invest more time to obtain a job usually had better grades. However, results are different on some health degrees such as Medicine or Physiotherapy, probably because Health Services have their own recruitment procedures. Key words: Labour outcomes, european space for higher education.
Enfisema bulloso bilateral gigante por déficit de alfa1-antitripsina
Leal Mursulí,Armando; Ramos Díaz,Nélida; Castellanos González,Juan Antonio; Adefna Pérez,Radamés I.; Riano Arencibia,Miguel A.; González Alejo,Antonio J.;
Revista Cubana de Cirug?-a , 2009,
Abstract: the case of a female patient aged 48 with a giant bilateral bullous emphysema and low levels of alpha1-antitripsine determined at the labcel laboratory of ?dr. miguel enríquez?. faculty of medical sciences was reported. the definition of alpha1-antitrypsin is the result of a genetical defect and approximately 75 % of the adults with a severe lack of this protein develop an emphysema that often begins before the 40 years of age. in order to discuss the results of the complementary tests, the treatment and evolution of this patient, we present this paper for considering it important for the medicosurgical practice.
Cuerpo extra?o intrapulmonar: presentación de un caso y revisión de la literatura
Leal Mursulí,Armando; Castellanos González,Juan Antonio; Ramos Díaz,Nélida; Adefna Pérez,Radamés I.; Riano Arencibia,Miguel A; Gonzalez Alejo,Antonio J;
Revista Cubana de Cirug?-a , 2009,
Abstract: the case of a 58-year-old female patient that was admitted in ?dr. miguel enríquez? university hospital due to a picture of respiratory difficulty with a non-satisfactory evolution was presented. after the hematological, imaging and functional complementary tests, an intrapulmonary foreign body was diagnosed. she was operated on, and a small nail was found in the inferior lobule of the left lung. due to its uncommon localization in this type of accident and to the difficulty of the clinical suspicion and, consequently, of its treatment, this case was presented to show the most important clinical, surgical and pathological aspects.
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