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Search Results: 1 - 10 of 605605 matches for " Juan A. Díaz-Celaya "
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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.
Predicting the onset and persistence of episodes of depression in primary health care. The predictD-Spain study: Methodology
Juan Bellón, Berta Moreno-Küstner, Francisco Torres-González, Carmen Montón-Franco, María GildeGómez-Barragán, Marta Sánchez-Celaya, Miguel Díaz-Barreiros, Catalina Vicens, Juan de Dios Luna, Jorge A Cervilla, Blanca Gutierrez, María Martínez-Ca?avate, Bárbara Oliván-Blázquez, Ana Vázquez-Medrano, María Sánchez-Artiaga, Sebastia March, Emma Motrico, Victor Ruiz-García, Paulette Brangier-Wainberg, María del Mar Mu?oz-García, Irwin Nazareth, Michael King, the predictD group
BMC Public Health , 2008, DOI: 10.1186/1471-2458-8-256
Abstract: This is a prospective cohort study. A systematic random sample of general practice attendees aged 18 to 75 has been recruited in seven Spanish provinces. Depression is being measured with the CIDI at baseline, and at 6, 12, 24 and 36 months. A set of individual, environmental, genetic, professional and organizational risk factors are to be assessed at each follow-up point. In a separate reliability study, a proportional random sample of 401 participants completed the test-retest (251 researcher-administered and 150 self-administered) between October 2005 and February 2006. We have also checked 118,398 items for data entry from a random sample of 480 patients stratified by province.All items and questionnaires had good test-retest reliability for both methods of administration, except for the use of recreational drugs over the previous six months. Cronbach's alphas were good and their factorial analyses coherent for the three scales evaluated (social support from family and friends, dissatisfaction with paid work, and dissatisfaction with unpaid work). There were 191 (0.16%) data entry errors.The items and questionnaires were reliable and data quality control was excellent. When we eventually obtain our risk index for the onset and persistence of depression, we will be able to determine the individual risk of each patient evaluated in primary health care.In 2001 depression was the third leading cause of disease burden in high-income countries [1]. In 2004 the total annual cost of depression in Europe was estimated to be 118 billion euros, or 253 euros per inhabitant [2]. The prevalence of major depression is about 7% in the community [3] and 14% in general practice attendees [4]. Relapse is frequent up to 10 years after the first presentation [5] and residual disability is common [6].The prevalence of depression is determined by exposure to risk factors that precipitate or maintain episodes of depression. With few exceptions, the prevalence and incidence of depressiv
Origin and SEM analysis of aerosols in the high mountain of Tenerife (Canary Islands)  [PDF]
Juan D. Delgado, Omaira E. García, Ana M. Díaz, Juan P. Díaz, Francisco J. Expósito, Emilio Cuevas, Xavier Querol, Andrés Alastuey, Sonia Castillo
Natural Science (NS) , 2010, DOI: 10.4236/ns.2010.210139
Abstract: Focusing on aerosolized matter of relevance to respiratory health, a major public health issue worldwide, we studied mineral and biological aerosol (bioaerosol) composition (TSP and PM2.5) and geographical origins during dust intrusions in the Canary Islands. Seven days’ back- ward trajectories were assessed daily during March 2004 with the ends of back trajectories being the sampling station of Iza?a (high moun- tain, 2360 m a.s.l. at the Ca?adas del Teide National Park, Tenerife island), a free troposphere site allowing characterization of dust with low influence of other pollutant sources. Scanning electron microscopy (SEM) was used to survey major types of airborne particles in the dust plumes. Control, non-intrusion conditions correspond to Atlantic oceanic middle troposphere (OMT) air masses. Of the 14 samples taken, 1 corresponded to a control (clear atmosphere conditions), and the remaining 13 to dust intrusions, with the following sources: African Dust; EAM: mixture of Europe, Africa and Oceanic; MaA: maritime aerosols. Of the air masses, 79% were directly transported to the islands from Africa, and an increase of African dust events was detected when comparing with a 52-year previous data sequence. Quartz microcristals and aggregates of quartz and platy clay were the dominant minerals identified, with marine salt and gypsum also present. Freshwater diatom tests (from two Aulacoseira species) represented the most important biogenic aerosols, although fungi and pollen were also detected. The diverse and complex mixture of respirable particles in large quantities in airborne dust, especially from nearby Sahara and from the Sahelian region, is of maximum interest for air- way pathology in the Canaries, including the highly visited highlands in Tenerife.
Alternativa de mecanismo de traducción de lenguajes mediante análisis de símbolos de sincronización: T_Gsig
Carlos A. Tavera,Juan F. Díaz
Ingeniería y Desarrollo , 2009,
Abstract: En este artículo se propone un mecanismo de traducción que transforma un programa visual especificado sintácticamente en forma textual, hacia un código de un lenguaje textual. Fundamentalmente, el mecanismo consiste en tomar la especificación de un constructor simple o compuesto, eliminar la información visual mediante análisis de símbolos de sincronización, y transformarlo en un programa equivalente en lenguaje textual. Inicialmente, en el artículo se presenta de manera formal el mecanismo de traducción, luego, se muestran las plantillas para su implementación, y al final, se presentan los resultados de la traducción a través de reglas.
GEOMORFOLOGíA Y FORMACIONES ARRECIFALES RECIENTES DE ISLA FUERTE Y BAJO BUSHNELL, PLATAFORMA CONTINENTAL DEL CARIBE COLOMBIANO
Díaz,Juan M.; Sánchez,Juan A.; Díaz-Pulido,Guillermo;
Boletín de Investigaciones Marinas y Costeras - INVEMAR , 1996,
Abstract: based on field surveys and interpretation of aerial photography and echosounder profiles, a general description of the geomorphological features and a characterization of the coralline structures of two reefal areas off the southern-central colombian caribbean coast, isla fuerte and bajo bushnell, are presented. isla fuerte is a partially emerged holocenic reef-complex. the insular shelf occupies an area of about 13 km2 and, besides a highstanding island, it has diverse geomorphological features such as a seaward fringing barrier reef, a peripherical reef-belt at the outer shelf margin, and shallow patch reefs, as well as large seagrass meadows on its leeward side. on the other hand, bushnell is a dome-shaped coral bank, about 1300 m in diameter, with a minimum depth of 12 m, located near the shelf-edge. despite the bottom communities being relatively homogeneous and their boundaries are ill-defined, at least four ecological bottom units could be distinguished at bushnell on the basis of the presence/dominance of conspicuous sessile organisms. the zone of greater living coral coverage corresponds to the shallowest, seaward part of the shoal. a list of coral species observed in both areas is included. like other coral banks and islands off the central part of the colombian caribbean coast, the origin of these high-reliefs on the continental shelf seems to be related to diapiric and tectonic activity, and subsequent colonization by hermatipic organisms since holocene times.
MOLUSCOS Y SU TAXOCENOSIS EN LOS FONDOS SOMEROS DEL SECTOR SUR DE LA PLATAFORMA CONTINENTAL DEL CARIBE COLOMBIANO
García-Valencia,Carolina; Díaz,Juan Manuel;
Boletín de Investigaciones Marinas y Costeras - INVEMAR , 2000,
Abstract: during a baseline survey of the shallow bottoms (10-50 m) of the southern continental shelf of the colombian caribbean, a total of 35 molluscan species belonging to 24 families was collected. three main molluscan bottom assemblages were recognized according to species composition and abundance, whose distribution seems likely to be controlled rather by depth than by sediment features. twenty four of the species were not recorded before from this area of the colombian caribbean.
DETECCIóN Y AISLAMIENTO ROBUSTO DE FALLAS MEDIANTE OBSERVADORES CON ENTRADAS DESCONOCIDAS
ANZUREZ MARíN,JUAN; PITALúA DíAZ,NUN;
DYNA , 2009,
Abstract: a technique for design of unknown inputs observers is presented, applied to the solution of fault detection problem. the proposed technique is mainly based on observation of error signals known as residuals, which are obtained by taking away actual input from estimated input. in an unknown inputs observer the state estimation error vector approaches zero asymptotically, regardless the presence of the unknown inputs or perturbations in the system. diagnosis algorithm was satisfactorily tested in a hydraulic liquid level system in simulation as well as real time.
ETHANOL PRODUCTION FROM PAPER SLUDGE USING KLUYVEROMYCES MARXIANUS
MADRID,LINA MARíA; QUINTERO DíAZ,JUAN CARLOS;
DYNA , 2011,
Abstract: recycled paper sludge is a promising raw material for ethanol production. in this study, we first evaluated the effects of ethanol concentration, solids load, and cellulose crystallinity on the enzymatic hydrolysis of cellulose to produce reducing sugars. we then evaluated the production of ethanol by either saccharification and simultaneous fermentation (ssf) or separated hydrolysis and fermentation (shf) using the yeast kluyveromyces marxianus atcc 36907. we found that cellulose hydrolysis decreased as ethanol concentrations increased; at 40 g/l ethanol, the reducing sugar production was decreased by 79 %. hydrolysis also decreased as solids load increased; at 9 % of solids, the cellulose conversion was 76 % of the stoichiometric production. the ethanol yield and cellulose conversion rate were higher with ssf as opposed to shf processes at 72 h of treatment.
Limitantes físicos y bióticos de la regeneración arbórea en matorrales sucesionales de la Isla Grande de Chiloé, Chile
DíAZ,MARíA F; ARMESTO,JUAN J;
Revista chilena de historia natural , 2007, DOI: 10.4067/S0716-078X2007000100002
Abstract: successional shrublands created by clearcutting and burning of forests are frequent in chiloé island and surrounding mainland in southern chile. these areas are characterized by seasonally waterlogged soils, and vegetation dominated by sedges, ferns and shrubs, such as baccharis patagonica, with thick carpets of sphagnum moss occupying the spaces between shrubs. tree regeneration in these sites was shown to be sparse or completely lacking (< 0.3 seedlings m-2) compared with 7.2 seedlings m-2 in adjacent forests. colonization of shade-intolerant, pioneer trees may be reduced underneath baccharis due to crown shading and on top of sphagnum cushions, because of unfavorable conditions for tree establishment, including low ph and soil water saturation. we evaluated differences in germination rates among pioneer tree species grown in an experimental soil moisture gradient. seed germination percentage was low for drimys winteri and nothofagus nitida unrelated to humidity conditions but differed between substrates (moss vs. soil). embothrium had higher germination and survivorship when growing on sphagnum cushions. we also monitored seedling survival of two pioneer tree species (embothrium coccineum and drimys winteri) transplanted directly under baccharis shrubs, in open areas, or on moss patches. even though survivorship of embothrium and drimys under baccharis was < 40 %, in one of the study sites, there were no differences between treatments. waterlogged soils would constraint tree regeneration on successional shrublands due to a lack of elevated substrates. however, the presence of sphagnum cushions favors embothrium establishment, and thus may facilitate restoration of these sites
Estado de la resistencia a insecticidas en cepas de terreno de la especie Blattella germanica (Dictyoptera: Blattellidae) procedentes del municipio Pinar del Río
Díaz,Cristina; Enríquez,Dagoberto; Bisset,Juan A.;
Revista Cubana de Medicina Tropical , 2003,
Abstract: a study of the levels of resistance to 10 insecticides: 4 organophosphate compounds (malathion, clorpirifos, methyl-pyrimifos and diazinon), 2 carbamates (propoxur and bendiocarb) and 4 pyrethroids (cypermethrin, deltamethrin, lamda-cyhalothrin and cyfluthrin) was conducted in 5 strains of blatella germanica (linnaeus, 1767) collected in the field of pinar del río. high levels of resistance to bediocarb, cypermethrin and deltamethrin insecticides; low level of resistance to diazinon; from moderate to high resistance to methyl-pyrimifos, as well as susceptibility to one insecticide in each study group: clorpirifos (organophosphate), propoxur (carbamate) and cyfluthrin (pyrethroid); were detected. only a strain presented low resistance to malathion (inicio carlos manuel) and to lambda-cyhalothrin (consejo celso maragoto). cypermethrin-deltamethrin cross resistance was evidenced. it did not affect the susceptibility to lambda-cyalothrin and cyfluthrin.
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