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Search Results: 1 - 10 of 130450 matches for " V. Dacal "
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Ab initio calculations of indium arsenide in the wurtzite phase: structural, electronic and optical properties
L. C. O. Dacal,A. Cantarero
Physics , 2013, DOI: 10.1088/2053-1591/1/1/015702
Abstract: Most III-V semiconductors, which acquire the zinc-blende phase as bulk materials, adopt the metastable wurtzite phase when grown in the form of nanowires. These are new semiconductors with new optical properties, in particular, a different electronic band gap when compared with that grown in the zinc-blende phase. The electronic gap of wurtzite InAs at the Gamma-point of the Brillouin zone (E0 gap) has been recently measured, E0 = 0.46 eV at low temperature. The electronic gap at the A point of the Brillouin zone (equivalent to the L point in the zinc-blende structure, E1) has also been obtained recently based on a resonant Raman scattering experiment. In this work, we calculate the band structure of InAs in the zinc-blende and wurtzite phases, using the full potential linearized augmented plane wave method, including spin-orbit interaction. The electronic band gap has been improved through the modified Becke-Johnson exchange-correlation potential. Both the E0 and E1 gaps agree very well with the experiment. From the calculations, a crystal field splitting of 0.122 eV and a spin-orbit splitting of 0.312 eV (the experimental value in zinc-blende InAs is 0.4 eV) has been obtained. Finally, we calculate the dielectric function of InAs in both the zinc-blende and wurtzite phases and a comparative discussion is given.
Effects of an electron gas on the negative trion in semiconductor quantum wells
Luis C. O. Dacal,Jose A. Brum
Physics , 2001, DOI: 10.1016/S1386-9477(01)00485-4
Abstract: We present here the results of calculations of the negative trion binding energy in the presence of an electron gas. The screening of the Coulomb interaction and the Pauli exclusion principle are considered. Our results show a rapid ionization of the negative trion due to the Pauli exclusion principle while the screening is mainly responsible for the weakening of the trion binding energy.
Intrinsic Factors Influencing the Infection by Helminth Parasites in Horses under an Oceanic Climate Area (NW Spain)
I. Francisco,M. Arias,F. J. Corti as,R. Francisco,E. Mochales,V. Dacal,J. L. Suárez,J. Uriarte,P. Morrondo,R. Sánchez-Andrade,P. Díez-Ba os,A. Paz-Silva
Journal of Parasitology Research , 2009, DOI: 10.1155/2009/616173
Abstract: A coprological survey to determine the influence of some intrinsic factors (breed, age, and sex) on the infection by helminth parasites in equine livestock (=418) under an oceanic climate area (NW Spain) was conducted. Faecal samples were individually collected and analyzed by the coprological techniques. The main strongylid genera identified were Trichonema and Cyalocephalus spp (small strongyles) and Strongylus and Triodontophorus (large strongyles). The prevalence of gastrointestinal nematode was 89% (95% CI 86, 92) and 1% cestoda (0, 2). The percentage of horses with strongyloid parasites was 89% (86, 92), 11% (8, 14) for Parascaris, and 3% (1, 5) for Oxyuris. The highest prevalence for ascariosis was observed in the youngest horses (<3 years), for oxyurosis in the >10 years animals, and for strongylosis in the 3–10 years ones. Females were significantly more parasitized than males. A negative correlation between the age and the egg-excretion of ascarids and strongyles was recorded. The autochthonous and the English Pure Blood horses were the most parasitized. We concluded that the infections by helminths, especially the strongyloids, are significantly common in the region, so that greater importance should be given to this situation.
Electric field inversion asymmetry: Rashba and Stark effects for holes in resonant tunneling devices
H. B. de Carvalho,M. J. S. P. Brasil,V. Lopez-Richard,I. Camps,Y. Galvao Gobato,G. E. Marques,L. C. O. Dacal,M. Henini,L. Eaves,G. Hill
Physics , 2006, DOI: 10.1103/PhysRevB.74.041305
Abstract: We report experimental evidence of excitonic spin-splitting, in addition to the conventional Zeeman effect, produced by a combination of the Rashba spin-orbit interaction, Stark shift and charge screening. The electric-field-induced modulation of the spin-splitting are studied during the charging and discharging processes of p-type GaAs/AlAs double barrier resonant tunneling diodes (RTD) under applied bias and magnetic field. The abrupt changes in the photoluminescence, with the applied bias, provide information of the charge accumulation effects on the device.
La dehidroepiandrosterona (DHEA): revisión de su eficacia en el manejo de la disminución de la líbido y de otros síntomas del envejecimiento
Mendivil Dacal,Jesús M.; Borges,Valeria M.;
Actas Urológicas Espa?olas , 2009, DOI: 10.4321/S0210-48062009000400009
Abstract: introduction: the dhea widely used for the control of the symptoms associated with the aging, has been an object of numerous clinical essays with discordant results as for its efficiency. objectives: the present review tries to analyze the existing information by means of a search and systematic review of articles centred on the utilization of the dhea/s for the control of the aging symptoms. material and methods: systematic review of the literature and application of the skills of metaanalisis to value the efficiency of the dhea/s, for it settles down the process of prospective form, 152 articles were checked and 25 were in use for adding only their results. results: since the only (unique) prominent information seems to concern the metabolism of the carbohydrates increasing the efficiency of the insulin. conclusions: the studies do not sustain the usefulness of the dhea for the reduction of the symptoms associated with the aging.
Conductance of three-dimensional cross junctions in the quantum ballistic regime
Dacal, Luis C. O.;Silva, Erasmo A. de Andrada e;
Brazilian Journal of Physics , 2006, DOI: 10.1590/S0103-97332006000300036
Abstract: the influence of dimensionality on the conductance of semiconductor cross junctions is investigated in the effective mass approximation and quantum ballistic regime. our calculations exhibit some similar features for both two- and three-dimensional models, namely the conductance peaks before the fundamental eigenenergy of the quantum wire that represents the sidearms and the zero conductance dip. despite this, we show that, in general, the conductance and the electronic wave function are strongly affected when the third spatial dimension is taken into account. in other words, we prove that two-dimensional models are not suitable for representing this kind of system.
Effects of effective mass discontinuity on the conductance of three-dimensional quantum wires
Dacal, Luis C. O.;Silva, Erasmo A. de Andrada e;
Brazilian Journal of Physics , 2006, DOI: 10.1590/S0103-97332006000600030
Abstract: we calculate the conductance of three-dimensional semiconductor quantum wires considering different effective masses in the contacts and in the channel. we show that, with respect to the case with equal masses in the channel and in the contacts, the amplitude of the conductance oscillations increases if the electron effective mass in the channel is larger and decreases if it is smaller than in the contacts. effects on the density of probability are also shown. these effects of the effective mass discontinuity are explained in terms of kinetic confinement and transmission coefficient modulation.
Síndrome metabólico y sus componentes en pacientes con síndrome de apnea-hipoapnea del sue o Metabolic syndrome and its components in patients with sleep apnea syndrome
M. Tumbeiro,A. Acu?a,M. T. Alves,R. Dacal
Anales del Sistema Sanitario de Navarra , 2011,
Abstract: Fundamento. El síndrome de apnea-hipoapnea del sue o (SAHS) es un factor de riesgo reconocido de patología cardiovascular y la evidencia reciente sugiere que está relacionado con el síndrome metabólico (SM). El objetivo del estudio fue conocer la prevalencia de los componentes individuales del SM y del SM como entidad, en pacientes con sospecha clínica de SAHS, y ver si ambas entidades están en relación con la obesidad central. Material y métodos. Se estudiaron prospectivamente a 486 pacientes consecutivos, 359 hombres (73,9%), con una edad media de 57,3 ± 13,5 a os y un índice de masa corporal (IMC) de 32,1 ± 6,5 kg/m2 con sospecha clínica de SAHS. El SAHS se diagnosticó por registro nocturno. Un Indice de Apnea-Hipoapnea (IAH) > 5 era considerado diagnóstico de SAHS. El SM era diagnosticado siguiendo los criterios de la International Diabetes Federation. Resultados. De los pacientes estudiados 325 (66,9%) eran SAHS de grado moderado-grave. El IAH medio fue de 30,2 ± 23,8. De 456 pacientes (93,8%) teníamos datos para el diagnóstico de SM y su prevalencia fue del 64,7% (295 pacientes). En el análisis multivariante, tanto la edad como el perímetro abdominal se comportaron como predictores de SAHS y de SM (p<0,05). Conclusiones. El SM es más frecuente en pacientes con SAHS, y su prevalencia aumenta con su gravedad. La obesidad central, medida por el perímetro abdominal, resultó ser un factor predictor tanto de SAHS como de SM. Background. Sleep Apnea Syndrome (SAHS) represents a significant risk factor for the development of cardiovascular disease and evidence suggests a relation with Metabolic Syndrome (MS). The aim of this study was to determine the prevalence of individual components of MS and of MS as an entity, in patients with clinical suspicion of SAHS, and their relation to central obesity. Methods. We examined the records of 486 consecutive patients, 359 (73.9%) men, with a mean age of 57.3 ± 13.5 years and a mean body mass index (BMI) of 32.1 ± 6.5 kg/m2), with clinical suspicion of SAHS. SAHS was diagnosed from the nocturnal register. An Apnea-Hipopnea Index (AHI) > 5 was considered SAHS. MS was evaluated according to the diagnostic criteria of the International Diabetes Federation. Results. Three hundred and twenty-five (66.9%) of the entire group were moderate-severe SAHS. The mean of AHI was 30.2 ± 23.8. We had sufficient data available on 456 patients (93.8%) for MS diagnosis and its prevalence was 64.7% (295 patients). Multivariate analysis showed that age and abdominal perimeter were predictors of SAHS and MS (p<0.05). Conclusions. Patien
Síndrome antifosfolipídico primario: características y evolución de una serie de 17 casos
Calvo Romero,J. Ma.; Bureo Dacal,J. C.; Ramos Salado,J. L.; Bureo Dacal,P.; Pérez Miranda,M.;
Anales de Medicina Interna , 2002, DOI: 10.4321/S0212-71992002000500003
Abstract: background: primary antiphospholipid syndrome (aps) is a thrombophilic disorder which is not associated with connective tissue diseases or with other diseases. method: retrospective review of patients diagnosed of primary aps in an internal medicine service between january 1996 and december 2000. results: we identified 17 patients with primary aps. the most common presenting manifestations were deep vein thrombosis (7 cases) and ischemic stroke (3 cases). eleven patients (65%) had vein thrombosis, 4 (24%) arterial thrombosis and no patient had both types of thrombosis. the 15 patients with thrombosis received treatment with indefinite oral anticoagulation (inr between 2.5 and 3.5). there was no recurrence of thrombosis or major hemorrhagic complications after a median follow-up time of 36 months (range 10-52 months). conclusions: the most common presenting manifestation of primary aps is deep vein thrombosis. venous thrombosis is more frequent than arterial thrombosis. the occurrence of both types of thrombosis seems to be exceptional. long-term oral anticoagulation is an effective and safe treatment to prevent the recurrence of thrombosis in patients with primary aps.
Diferencias entre la espondilitis tuberculosa y la espondilitis brucelar
Calvo Romero,J. M.; Ramos Salado,J. L.; García de la Llana,F.; Bureo Dacal,J. C.; Bureo Dacal,P.; Pérez Miranda,M.;
Anales de Medicina Interna , 2001, DOI: 10.4321/S0212-71992001000600005
Abstract: objective: to identify potential differences in the clinical and laboratory characteristics between tuberculous spondylitis (ts) and brucellar spondylitis (bs). patients and methods: retrospective study of patients with ts and bs diagnosed in our hospital between january 1992 and december 1998. results: ts was diagnosed in 17 patients and bs in 10 patients. in our series, a higher delay in the diagnosis (27.9 ± 24.6 vs. 16 ± 5.6 weeks, p= 0,02) was found in ts. there was a higher frequency, but without stadistic significance, of immunosupression, one or several paravertebral or epidural abscesses, spinal cord compression, anemia and an elevated erythrocyte sedimentation rate in ts, and a higher frequency of fever/febricule and residual vertebral pain in bs. lumbar location was the most frequent in both groups (58.8% in ts and 70% in bs). conclusions: it is possible that there were some differences in the clinical and laboratory characteristics between ts and bs which may be an aid in the differential diagnosis of both entities and orient the empirical treatment in these cases without a definitive microbiological diagnosis or while awaiting the diagnostic confirmation.
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