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Search Results: 1 - 10 of 436013 matches for " J. D. Correa "
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Eliminación de Bandas Calientes en Reformador de Gas Natural
Correa,D.J.;
Información tecnológica , 2004, DOI: 10.4067/S0718-07642004000300015
Abstract: the purpose of this study was to find the causes of formation of hot bands due to coke deposition in a natural gas reformer which caused the unit to go out of service, resulting in higher production costs. a literature study was made to determine the variables which affected the incidence of this problem, and to produce an index which quantified the formation of coke, named obstruction index. the impact of different variables was systematically analyzed and these variables were related to the evolution of the obstruction index, always taking into account the information from the industrial plant studied. all hypotheses were discarded except that relating to the presence of light hydrocarbons. it was determined that the problem of the hot bands did not originate within the reforming unit, but rather upstream of the process in the desulfurization unit
Eliminación de Bandas Calientes en Reformador de Gas Natural Elimination of Hot Bands in a Natural Gas Reformer
D.J. Correa
Información Tecnológica , 2004,
Abstract: El objetivo de este trabajo fue encontrar las causas de la formación de bandas calientes por deposición de coque en un reformador de gas natural, que provoca la salida de servicio de la unidad y mayores costos de producción. Se recurrió a la literatura para determinar las variables que tienen incidencia en esta problemática y se creó un trazador que cuantifica la formación de coque, denominado índice de Obstrucción. Se analizó sistemáticamente el impacto de las distintas variables y se relacionaron con la evolución del índice de Obstrucción, siempre tomando información de la propia planta industrial. Descartando todas las hipótesis, excepto la presencia de hidrocarburos livianos, se determinó que el problema de las bandas calientes no se origina en el propio horno de reforma, sino aguas arriba del proceso, en el desulfurador The purpose of this study was to find the causes of formation of hot bands due to coke deposition in a natural gas reformer which caused the unit to go out of service, resulting in higher production costs. A literature study was made to determine the variables which affected the incidence of this problem, and to produce an index which quantified the formation of coke, named Obstruction Index. The impact of different variables was systematically analyzed and these variables were related to the evolution of the Obstruction Index, always taking into account the information from the industrial plant studied. All hypotheses were discarded except that relating to the presence of light hydrocarbons. It was determined that the problem of the hot bands did not originate within the reforming unit, but rather upstream of the process in the desulfurization unit
Ab-initio analysis of superstructures revealed by STM on bilayer graphene
E. Cisternas,J. D. Correa
Physics , 2012, DOI: 10.1016/j.chemphys.2012.09.021
Abstract: In this work we performed density functional theory calculations for a twisted bilayer graphene (BLG). Several conmensurable rotation angles were analyzed and for each one a constant height mode STM image was obtained. These STM images, calculated under the Tersoff-Hamman theory, reproduce the main features experimentally observed, paticularly superstructures and giant corrugations. In this way we confirm that STM characterization of twisted BLG can produce superstructures whose tunneling current intensity maxima occur over regions with $AA$ stacking. Additionally we give new evidence in favour of an electronic origin for the superstructures instead another physical grounds.
Noncovalent functionalization of carbon nanotubes and graphene with tetraphenylporphyrins: Stability and optical properties from ab-initio calculations
Walter Orellana,J. D. Correa
Physics , 2015, DOI: 10.1007/s10853-014-8650-0
Abstract: The stability, electronic and optical properties of single-walled carbon nanotubes (CNTs) and graphene noncovalently functionalized with free-base tetraphenylporphyrin (TPP) molecules is addressed by density functional theory calculations, including corrections to dispersive interactions. We study the TPP physisorption on 42 CNT species, particularly those with chiral indices ($n$,$m$), where $5 \leq n \leq 12$ and $0\leq m\leq n$. Our results show a quite strong $\pi$-$\pi$ interaction between TPP and the CNT surface, with binding energies ranging from 1.1 to 1.8 eV, where higher energies can be associated with increasing CNT diameters. We also find that the TPP optical absorptions would not be affected by the CNT diameter or chirality. Results for the TPP physisorption on graphene show a remarkable stability with binding energy of 3.2 eV, inducing a small redshift on the $\pi$-stacked TPP absorption bands. The strong graphene-TPP interaction also induces a charge transfer from TPP to graphene, indicating a $n$-type doping mechanism without compromising the graphene structure.
Farmacovigilancia de los Agonistas Adrenérgicos en pacientes de la unidad de cuidados intensivos del hospital "Dr. Miguel Pérez Carre?o"
Magaldi,L; Alvis,J; Correa,D;
Archivos Venezolanos de Farmacología y Terapéutica , 2004,
Abstract: a descriptive study was made in 84 patients to determined adverse drugs reactions (dar) during the iv treatment with some of the following adrenergic agonists: norepinephrine (0,5m/kg/min), epinephrine (0.1m/kg/min), dopamine (3m/kg/min.) and dobutamine (5m/kg/min). the yellow card of cevifare was used as the instrument for registry of the dar. dar were analyzed by its type, severity and causality. 83.33% of the patients had dar, being most frequent: tachycardia (47,61%), pallor (23,80%), hypertension (11,90%) and arrhythmias (7,14%). all the dar were type a, mild 50%, moderate 40% and serious 10%. 100% of dar analyzed were proved. although the adrenergic agonists turned out to be safe, the epinephrine has the risk of producing distal necrosis, thus the nursing role in practicing pharmacovigilance is to prevent or to diminish the possibility of appearance of dar in the patients under her care.
Farmacovigilancia de los Agonistas Adrenérgicos en pacientes de la unidad de cuidados intensivos del hospital "Dr. Miguel Pérez Carre o"
L Magaldi,J Alvis,D Correa
Archivos Venezolanos de Farmacología y Terapéutica , 2004,
Abstract: Se realizó un estudio de tipo prospectivo descriptivo en 84 pacientes en quienes se determinaron las reacciones adversas (RAM′s) tras la administración IV de alguno de los siguientes agonistas adrenérgicos: noradrenalina (0,5 my/kg/min.), adrenalina (0,1my/kg/min), dopamina (3my/kg/min.) y dobutamina (5my/kg/min.). Se utilizó como instrumento de registro de las RAM′s la Hoja Amarilla de CEVIFARE. Se procedió a la identificación de las RAM′s por su tipo, severidad y causalidad. El 83,33% de los pacientes presentaron RAM′s, siendo las más frecuentes: taquicardia (47,61%), palidez (23,80%), hipertensión (11,90%) y arritmias (7,14%). Todas las RAM′s fueron del tipo A, el 50% leves, 40% moderadas y 10% graves. El 100% de las RAM′s analizadas fueron probadas. Aunque los agonistas adrenérgicos estudiados resultaron ser seguros, la adrenalina tiene el riesgo de producir necrosis tisular distal, por lo cual el papel de la Enfermera(o) que practica la farmacovigilancia es prevenir o disminuir la posibilidad de aparición de RAM′s en los pacientes a su cuidado. A descriptive study was made in 84 patients to determined adverse drugs reactions (DAR) during the IV treatment with some of the following adrenergic agonists: norepinephrine (0,5mu/kg/min), epinephrine (0.1mu/kg/min), dopamine (3mu/kg/min.) and dobutamine (5mu/kg/min). The Yellow Card of CEVIFARE was used as the instrument for registry of the DAR. DAR were analyzed by its type, severity and causality. 83.33% of the patients had DAR, being most frequent: tachycardia (47,61%), pallor (23,80%), hypertension (11,90%) and arrhythmias (7,14%). All the DAR were type A, mild 50%, moderate 40% and serious 10%. 100% of DAR analyzed were proved. Although the adrenergic agonists turned out to be safe, the epinephrine has the risk of producing distal necrosis, thus the Nursing role in practicing pharmacovigilance is to prevent or to diminish the possibility of appearance of DAR in the patients under her care.
Binding energy and photoionization cross-section in GaAs quantum well-wires and quantum dots: magnetic field and hydrostatic pressure effects
Correa, J. D.;Porras-Montenegro, N.;Duque, C. A.;
Brazilian Journal of Physics , 2006, DOI: 10.1590/S0103-97332006000300041
Abstract: using a variational procedure for a hydrogenic donor-impurity we have investigated the influence of an axial magnetic field and hydrostatic pressure in the binding energy and the impurity-related photoionization cross-section in 1d and 0d gaas low dimensional systems. our results are given as a function of the radius, the impurity position, the polarization of the photon, the applied magnetic field, the normalized photon energy, and the hydrostatic pressure. in order to describe the g-x mixing in the ga1-xalxas layer, we use a phenomenological procedure to describe the variation of the potential barrier that confines the carriers in the gaas layer. our results agree with previous theoretical investigations in the limit of atmospheric pressure. we found that the binding energy and the photoionization cross-section depend on the size of the structures, the potential well height, the hydrostatic pressure, and the magnetic field.
Characterization of light-cured dental composites prepared from Bis-GMA/TEEDGDMA and Bis-GMA/MPS mistures
Y. Veranes,D. Correa,J. M. Martin,R. Krael
Latin American applied research , 2006,
Abstract: The aim of this study was to prepare light-cured dental composites and to evaluate their physical, chemical and mechanical properties. Experimental composites were prepared from 2, 2 bis [4-(2-hidroxy 3-metacriloxypropoxi) phenyl] propane (Bis-GMA), tetraethyleneglycol dimethacrylate (TEEGDMA), 3-methacryloxypropyl trimethoxysilane (MPS) and a hybrid filler consisting of quartz and colloidal silica particles (Aerosil 90). The initiation system was based on the pair Camphorquinone (CQ) / N, N dimethylaminoethylmethacrylate (DMAEMA). The experimental composites and a commercial dental composite used as reference (Charisma ) were submitted to determinations of depth of cure, water absorption and solubility, compressive and diametral tensile strengths, and elastic modulus, according to the indications of the ISO standards. The experimental resins presented adequate values for most of the analyzed properties, except for compressive strengths. In the Bis-GMA/ MPS/quartz-aerosil composite a better integration between filler and matrix was observed. The Bis-GMA/TEEGDMA/quartz-aerosil composite showed the best performance in regards to depth of cure, solubility in water, diametral tensile strength and elastic modulus. The properties of this composite were better than those of the commercial reference material, except for compressive strength.
Moiré patterns on STM images of graphite from surface and subsurface rotated layer
M. Flores,E. Cisternas,J. D. Correa,P. Vargas
Physics , 2012, DOI: 10.1016/j.chemphys.2013.06.022
Abstract: We have observed with STM moir\'e patterns corresponding to the rotation of one graphene layer on HOPG surface. The moir\'e patterns were characterized by rotation angle and extension in the plane. Additionally, by identifying border domains and defects we can discriminate between moir\'e patterns due to rotation on the surface or subsurface layer. For a better understanding of moir\'e patterns formation we have studied by first principles an array of three graphene layers where the top or the middle layer appears rotated around the stacking axis. We compare the experimental and theoretical results and we show the strong influence of rotations both in surface and subsurface layers for moir\'e patterns formation in corresponding STM images.
Comparison Between Aqueous and Nonaqueous AOT-Heptane Reverse Micelles Using Acridine Orange as Molecular Probe
R. D. Falcone,N. M. Correa,M. A. Biasutti,J. J. Silber
Molecules , 2000, DOI: 10.3390/50300553
Abstract: Aqueous and nonaqueous AOT/n-heptane reverse micelles where characterized by UV-Visible and fluorescence spectroscopy of AO. The study shows the presence of the dimer in aqueous reverse micelles which is not present in the nonaqueous systems. It seems that there is a conversion of the dimer to monomer in the aqueous reverse micelles at high AOT concentration. In the nonaqueous systems, there is only partition of the monomer. The apparent constants of these processes were calculated.
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