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Search Results: 1 - 10 of 45778 matches for " Juan Manuel Navarrete "
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Consolidation of Ancient Raw Materials Using a Reversible, Elastic, Soft Polymer  [PDF]
Juan Manuel Navarrete, Gustavo Leonardo Martínez
Advances in Materials Physics and Chemistry (AMPC) , 2012, DOI: 10.4236/ampc.2012.21006
Abstract: Aging of ancient raw materials usually finish with disintegration, which starts on surface of walls to progress toward the inside mass of a huge variety of mineral compounds. This is particularly harmful when antique buildings keep mural paintings, which suffers destruction before the wall itself. Same case appears on sculptures and monuments, whose surfaces are often attacked by living organisms which start a deterioration process previous to complete disintegration. The main factor to produce these unwanted effects is humidity, either rain for materials exposed to open air, or underground humidity going up by capillarity of minerals, in this case represented by porosity of associated salts forming the material. This paper describes a method to measure easily the relative porosity of diverse raw materials at laboratory level, by using a radioactive labeled solution, and also a procedure to reduce their porosity of those minerals. The efficiency of this procedure is measured in the same way, and so the results obtained at laboratory level have encouraged its use at real scale, where it has been quite successful for a number of materials in a limited span of five years.
Production of Carbon Nanotubes and Hydrogen Catalyzed with Ni/MCM-41 Catalysts  [PDF]
Zhiqi Wang, Juan Navarrete
Green and Sustainable Chemistry (GSC) , 2012, DOI: 10.4236/gsc.2012.23014
Abstract: Methane catalytic decomposition (MCD) over Ni/MCM-41 catalysts was tested in a microreactor to simultaneously produce hydrogen and carbon nanotubes (CNTs). The methane conversion reached 30% to 47% at a moderate temperature range from 400°C to 600°C and the catalytic activity of the catalysts remains stable during 500 min steam on time. CNTs were chiefly formed through tip-growth mode, due to the weak interaction between the metallic Ni and the support. Most of the Ni particles are located on the tip of the produced CNTs, which avoids rapid deactivation of the catalyst resulted from carbon encapsulation. Large Ni particles usually lead to the formation of CNTs with big diameter. During the reaction, the shape of Ni particles changed from pseudo-sphere to diamond-like. All the CNTs consist of multiple layer walls and are curved in certain degree.
Keggin Structure and Surface Acidity of 12-Phosphotungstic Acid Grafted Zr-MCM-48 Mesoporous Molecular Sieves  [PDF]
Zhiqi Wang, Juan Navarrete
World Journal of Nano Science and Engineering (WJNSE) , 2012, DOI: 10.4236/wjnse.2012.23017
Abstract: A zirconium modified MCM-48 mesoporous material was synthesized by surfactant-templated method. Surface grafting Zr-MCM-48 with tungstophosphoric acid led to a great enhancement of both the number of the Br?nsted acid sites and acidity strength in comparison with the bare support. At 100°C, the 30 wt% H3PW12O40/Zr-MCM-48 contained 174 μmol/g Br?nsted acid sites which were 14.5 times greater than that of Zr-MCM-48. The Keggin structure of the grafted heteropolyacid was rather stable after calcination at 400°C for 2 h, approximately 93.3% of Keggin structure in the dispersed heteropolyacid were remained without destruction but slightly distorted in some degree, as evidenced by FTIR characterization and 31P NMR-MAS analysis. This H3PW12O40/Zr-MCM-48 solid with three dimensional mesoporous system, large surface area and very strong Br?nsted acidity will be a promising catalyst for acid catalytic reactions.
Evaluación de parámetros plaquetarios en trombocitosis pediátrica
Salazar,Lizbeth; Navarrete,Marta; Jiménez,Rafael; Carrillo,Juan Manuel; Barrantes,Max; Valverde,Berta; Mora,Luis;
Revista Costarricense de Ciencias Médicas , 1999,
Abstract: the high amount of platelets has important implications in diagnosis and treatment of the patients. in the present study, lt could be proven the utility of the index mpv, (mean platelet volume) and the pdw (variation in platelet size distribution) in the platelet diseases. we found 45% pediatric patients with reactive thrombocytemia alterations in the vpm, in the pdw or in both, in comparison with the values that were obtained in the control group. they present platelets with smaller size and with more heterogeneity lt is important to consider these available parameters at the moment, in order to heip in the differential diagnosis of thrombocytosis at the first line.
Abordaje epidemiológico de un brote de trastorno conversivo epidémico en adolescentes
Susana Navarrete Navarro,Carlos Riebeling Navarro,Juan Manuel Mejía Arangure,Arnulfo Nava Zavala
Salud mental , 2006,
Abstract: Introducción En la bibliografía mundial existen informes sobre la existencia de brotes del trastorno conversivo epidémico, la mayoría de los cuales se relaciona con personal que labora en fábricas, generalmente bajo condiciones de estrés o presión. Los objetivos de este estudio fueron: encontrar el origen o causa del brote en la población afectada, identificar el mecanismo de transmisión del evento, y determinar los factores de riesgo asociados al mismo. Material y métodos La investigación incluyó: 1) un censo y la búsqueda activa de los alumnos afectados, 2) la realización de un estudio de casos y controles para identificar factores de riesgo asociados al problema mencionado, 3) toma de muestras de alimentos y bebidas, para su estudio microbiológico y toxicológico, 4) investigación en SEDESOL sobre el grado de contaminación atmosférica. Resultados Se identificaron 455 alumnos en el turno matutino. Se detectó un total de 52 casos acordes con la definición operacional, lo cual correspondió a una tasa de ataque de 11.4%; 27 mujeres y 25 hombres. Se entrevistó a todos ellos y se detectó que la frecuencia de síntomas entre los alumnos fue como sigue: desmayo 100%, cefalea 88%, parestesias 56%, dificultad para la movilización de alguna extremidad 35%, ardor de ojos 27%, ardor de nariz 10%, dolor abdominal 3% y vómito 3%. La tasa de ataque fue significativamente más alta en las ni as menores de 15 a os (91%) que en las de mayor edad (9%). El género femenino presentó 7 veces mayor riesgo de ser caso y, en relación a la edad, las menores de 15 a os tuvieron 4 veces mayor probabilidad de ser casos (p< 0.05). La tasa de ataque por ubicación de los alumnos dentro del plantel fue: planta baja 22.4%, primer piso 7.1% y segundo piso 4.1%. Un 60% de los casos se encontró en dos grupos escolares (1oB y 2oA), estos se encontraban en la planta baja durante el desarrollo del suceso. El pertenecer a alguno de estos dos grupos representó 7 veces más riesgo de ser caso (p<0.05). La bebida X que en un inicio fue se alada como la culpable del brote, durante el análisis estadístico mostró una razón de momios menor a uno (factor de protección y no de riesgo). Ninguno de los alimentos examinados resultó positivo en las pruebas de detección de agentes tóxicos y microbiológicos. Discusión Las pruebas estadísticas que se realizaron, mostraron que el número atribuible de casos que se explicaría mediante los diferentes riesgos calculados, es muy bajo en relación con el número total de casos. Para complementar estos resultados se realizó un análisis multivariante en aquellas variables
Isobars Separation (137Cs-137mBa-137Ba) from Marine Sediments, in Order to Evaluate Directly Their Radioactive Contamination by Mass Spectrometry  [PDF]
Karla Fernández, Juan Manuel Navarrete, Miguel Angel Zú?iga, Ernesto Hernández
World Journal of Nuclear Science and Technology (WJNST) , 2020, DOI: 10.4236/wjnst.2020.101004
Abstract: Marine sediments contamination by fission product 137Cs-137mBa is a fact since the period 1945-65, when plus than two thousand atomic explosion tests were performed mainly in the southern seas, earth region with minor population density. However, marine flows have produced dissemination of this radioactive pair through the sea bottom all over the world, at different levels, because the sea movement and natural decaying of radioactive pair: parent 137Cs (t1/2 = 30.17 years) and daughter 137mBa (t1/2 = 2.55 minutes). Radioactive detection of these contaminants, compared as percentage with that of natural 40K (t1/2 = 1.28 × 109 years, 0.0118% of elementary K) leads to radiation contamination factor (RCF), as one possible unit to measure the radioactive contamination intensity in different regions, as well to determine if there is some other possible source of this contaminant, for example water cooling from power nuclear reactors when it is discharged at sea. However, radioactive detection always implies an unavoidable statistical variation, which makes more difficult to appreciate the changes as function of time and region. But at beginning of this century, mass spectrometry has got impressive advances, which makes it much more precise and sensible than radioactive detection [1]. This paper attempts to measure with other units the radioactive contamination: 137Cs atoms number per gram of sample, instead radioactivity, which could be more direct and with minor standard deviation that radioactive detection, solving at same time the isobars separation: 137Cs versus 137mBa plus elementary 137Ba (11.23% of Ba element).
Aplicación de la imagen multiespectral al estudio y conservación del arte rupestre postpaleolítico
Vicent Garcia, Juan Manuel,Montero Ruíz, Ignacio,Rodríguez Alcalde, ángel L.,Martínez Navarrete, M. Isabel
Trabajos de Prehistoria , 1996,
Abstract: Rock art deteriorates because of both environmental factors and visitor erosion which affect its conservation and, therefore, its study. Graphic recording carried out in the past is sometimes the only recorded evidence for what once existed. However, the graphic record also presents problems of preservation on the long-term, a problem particularly highlighted on modern color photographic materials. In this paper we deal with new approaches to solve this problem. We illustrate our work with the photographic collection about Levantine rock art, which belongs to the CSIC, and is held in the Department of Prehistory of Centro de Estudios Históricos. Two methods are highlighted: the use of the new Kodak Photo CD system, and the multiband Digital Imaging analysis. El deterioro que padece el arte rupestre tanto por factores ambientales como antrópicos ata e a su conservación e investigación en el futuro. La documentación gráfica, en algunos casos el único vestigio disponible, se ve limitada también por problemas de conservación a largo plazo, en especial cuando se trata de fotografía en color. En este trabajo se plantean nuevas líneas de investigación para solventar estos problemas a partir de una investigación en curso en el Departamento de Prehistoria del Centro de Estudios Históricos (CSIC). Se trata de la conversión del importante archivo fotográfico del Corpus de Pintura Rupestre Levantina a formatos digitales (Kodak Photo CD) y la aplicación del tratamiento digital de imagen multiespectral a la investigación de estas manifestaciones artísticas.
Exposición laboral a mycobacterium bovis multirresistente en un hospital de Zaragoza
Solano Bernad,Víctor Manuel; Hernández Navarrete,María Jesús; Martín Sánchez,Juan Ignacio; Martínez Sánchez,Elena Vanessa; Arribas Llorente,José Luis;
Revista Espa?ola de Salud Pública , 2003, DOI: 10.1590/S1135-57272003000200003
Abstract: background: those working in a hospital environment are exposed to different occupational risks, although more specifically biological ones. one of the major risks is that of exposure by airborne transmission, more specifically, tuberculosis. this study is aimed at providing a description and analysis of the results of the implementation of an evaluation and surveillance protocol following occupational exposure to multiresistant mycobacterium bovis (mrmb). method: a male patient was diagnosed with mrmb infection at the miguel servet hospital in zaragoza in 1999 following ten days without respiratory isolation. during this period, he came into contact with 167 employees from different hospital departments. a surveillance and contact control protocol was prepared based on: completing a survey and undergoing an initial mantoux (if the employee had previously tested negative for tuberculin), followed three months later by a chest x-ray and then a two-year clinical follow-up (check-ups every three months) for those having tested positive for tuberculin and no administering of chemoprophylaxis even though signs of infection were to have been found. results: information was gathered on 160 employees (96%). a total of 94 employees (59%) had previously undergone a mantoux, seven (7) having had tuberculosis. it was necessary for a follow-up to be conducted on sixty-one (61) employees who tested positive (29 previously positive and 32 detected in the initial mantoux). no employee who had tested negative on an initial mantoux tested positive on repeated testing three months later nor showed any symptoms indicative of transmission during the follow-up period. some variables, such as age or working in the infectious disease unit were related, on a statistically significant basis, to follow-up being required. conclusions: the risk of occupational transmission following contact with mrmb might be similar to m. tuberculosis, although further experience would be required in order to
Citogenética y citoquímica de pacientes con leucemia en dos hospitales neotropicales
Solís,María Virginia; Alvarado,María de los Angeles; Ruiz,Edward; Carrillo,Juan Manuel; Navarrete,Marta; Sánchez,German; Jiménez,Elías;
Revista de Biología Tropical , 2000,
Abstract: a cytogenetic and/or cytochemical study was performed in 166 individuals with leukemia or related disorders, in two major costa rican hospitals. in those patients treated at an adult?s hospital (14 years old and over), acute leukemias represented 66% of all cases. in that hospital the most frequent types of disorders were, in decreasing order: anll (m1), all, cml (all of them showed the ph chromosome) and mds. in the cases from a childrens? hospital (<14 years old) acute leukemias were 98%. among them the order of frequency was: all (70%): all-1(84%), all-2(16%) and anll (27%): m5am3m4m5b. in all 85% were type b and occurred mostly in women while 15% of them were type t and more frequent in males. there was 5.6% infant leukemia, which presented a similar number of acute lymphoids and myeloids. the cytogenetic pattern was similar among costa rica and other tropical and temperate countries.
Environmental impact of copper mining and metallurgy during the Bronze Age at Kargaly (Orenburg region, Russia)
Vicent García, Juan Manuel,Martínez Navarrete, M.a Isabel,López Sáez, José Antonio,de Zavala Morencos, Ignacio
Trabajos de Prehistoria , 2010,
Abstract: Kargaly (Orenburg, Russia) is a copper-producing region in which two main phases of mining activity have taken place: the 4th-2nd millennia BC and the 18th-20th centuries AD. This article is a comparative study on the impact of those mining episodes in the distribution of the forest resources in the region, aimed to estimate the scale of prehistoric mining and metallurgical works. For that purpose two paleopalinological sequences obtained from natural deposits located in Kargaly are analysed by inferential Statistics and Multivariate Methods. The results are compared both with a regional sampling of recent pollen rain supported by an analytical model of the present day landscape, and with the anthracological data coming from the Late Bronze Age settlement of Gorny 1. Analysis confirm the large scale of the prehistoric mining impact on the forest cover from the beginnings, as well as the strong effect of husbandry once mining works ended. These results allow us to dismiss a climatic change as main explanation for the detected diachronic variability in the palinological record. They also prove the viability of the proposed approach as a means of integrating the paleoenvironmental disciplines in Landscape Archaeology. Kargaly (región de Orenburgo, Rusia) es una región cuprífera explotada entre los milenios IV y II cal BC y los siglos XVIII y XX d.C. El objetivo del artículo es estudiar comparativamente el impacto de estos episodios mineros en la distribución de los recursos forestales de la región, para aproximar la escala de las operaciones minero-metalúrgicas prehistóricas. Para ello se analizan con métodos estadísticos inferenciales y multivariantes dos secuencias paleopalinológicas procedentes de depósitos naturales de la región y se comparan con un muestreo regional de la lluvia polínica reciente apoyado por un modelo analítico del paisaje actual y con los datos antracológicos procedentes del asentamiento del Bronce Final Gorny 1. Los análisis confirman la gran escala del impacto de la minería prehistórica en la cubierta forestal desde sus inicios, pero también los efectos de las prácticas pastoriles en las fases posteriores al final de la misma. Estos resultados permiten descartar el cambio climático como principal explicación de la variabilidad diacrónica en el registro palinológico, y confirman la viabilidad del enfoque propuesto como medio de integrar las disciplinas paleoambientales en la Arqueología del Paisaje.
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