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Search Results: 1 - 10 of 170325 matches for " H.;Alves "
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Ab initio Calculations of the Vibrational Modes of MnAs and Ga1-xMnxAs
H. W. Leite Alves
Physics , 2006, DOI: 10.1063/1.2729814
Abstract: In this work, we present our theoretical results for the equation of state and the phonon dispersions of MnAs, as well as the Mn concentration dependence of both the lattice parameter and the phonon frequencies of the cubic GaMnAs alloys. The results are in good agreement with the experimental results whenever this comparison is possible. Based on the obtained results, the lattice constants and the phonon frequencies of the alloys do not obey the Vegard rule.
Orion Revisited - I. The massive cluster in front of the Orion Nebula Cluster
J. Alves,H. Bouy
Physics , 2012, DOI: 10.1051/0004-6361/201220119
Abstract: The aim of this work is to characterize the stellar population between Earth and the Orion A molecular cloud where the well known star formation benchmark Orion Nebula Cluster (ONC) is embedded. We use the denser regions the Orion A cloud to block optical background light, effectively isolating the stellar population in front of it. We then use a multi-wavelength observational approach to characterize the cloud's foreground stellar population. We find that there is a rich stellar population in front of the Orion A cloud, from B-stars to M-stars, with a distinct 1) spatial distribution, 2) luminosity function, and 3) velocity dispersion from the reddened population inside the Orion A cloud. The spatial distribution of this population peaks strongly around NGC 1980 (iota Ori) and is, in all likelihood, the extended stellar content of this poorly studied cluster. We infer an age of ~4-5 Myr for NGC 1980 and estimate a cluster population of the order of 2000 stars, which makes it one of the most massive clusters in the entire Orion complex. What is currently taken in the literature as the ONC is then a mix of several intrinsically different populations, namely: 1) the youngest population, including the Trapezium cluster and ongoing star formation in the dense gas inside the nebula, 2) the foreground population, dominated by the NGC 1980 cluster, and 3) the poorly constrained population of foreground and background Galactic field stars. Our results support a scenario where the ONC and L1641N are not directly associated with NGC 1980, i.e., they are not the same population emerging from its parental cloud, but are instead distinct overlapping populations. This result calls for a revision of most of the observables in the benchmark ONC region (e.g., ages, age spread, cluster size, mass function, disk frequency, etc.). (abridged)
Melhoramento do cafeeiro: XIV - Competi??o de variedades comerciais em Monte Alegre do Sul
Antunes Filho, H.;Alves, S.;
Bragantia , 1960, DOI: 10.1590/S0006-87051960000100007
Abstract: in 1949 on experiment was started in the northwestern region of s. paulo to compare the behovior in this area of the best new stra.ns of coffee that hod been selected previously in campinas. this trial was made with the following commercial varieties: nacional, amarelo de botucatu, bourbon vermelho. bourbon amarelo, mundo novo, caturra vermelho, caturra amarelo, laurina, maragogipe a. d., and semperflorens. an incomplete block design was used with fifteen blocks of four treatments. a single plot consisted of ten coffee holes, with three seedlings per hole. protection against erosion was built around each hole. the first commercial yield was obtained in 1952. the data on the total yields, expressed in kilograms of ripe fruit, in the years 1952 to 1956, are presented in table 1. the analysis revealed that the mundo novo coffee yielded more than all other varieties. the yields of bourbon amarelo, bourbon vermelho, and calurra vermelho did not differ significantly. the varieties nacional and amarelo de botucatu produced less than the mundo novo, bourbon amarelo, bourbon vermelho and caturra amarelo (table 2). the data presented in table i also indicate that the yield of the varieties with yellow fruit is greater than the corresponding ones with red fruit, as follows; the bourbon amarelo produced more fruits than the bourbon vermelho, caturra amarelo more than caturra vermelho, and amarelo de botucatu more than the nacional variety. the difference in yield was not significant and may be due to a pleiotropic effect of the xanthocarp allele. an analysis was also undertaken with the yield expressed in kg of clean coffee and the observed results are almost of the same order, when compared to the yield expressed in kg of ripe fruits (table 3). the relation of the weight of ripe fruits to clean coffee was determined every year from samples taken from the total yield of every plot. only the laurina variety and mundo novo coffee gave poor outturn (table 4). the mundo novo strain
Observa es sobre A Tradu o de Textos Matemáticos Cuneiformes
Carlos H. B. Gon?alves
Bolema: Boletim de Educa??o Matemática , 2011,
Abstract: Neste trabalho, tratamos de certos problemas de tradu o próprios dos textos cuneiformes em geral e mais especificamente dos textos cuneiformes matemáticos. Analisamos esses problemas a partir de três pontos de vista. Inicialmente, consideramos as media es intelectuais pelas quais passa um texto cuneiforme até sua tradu o. Em segundo lugar, tratamos das particularidades da conceitua o matemática cuneiforme, isto é, das diferen as em rela o à matemática de nosso tempo. Por fim, abordamos aspectos das línguas originais dos textos cuneiformes que ainda est o em discuss o pelo campo. Como conclus o, sugerimos que os resultados dessa análise s o relevantes n o somente para o processo de tradu o, mas também para a leitura de tradu es de textos matemáticos cuneiformes. Palavras-chave: Textos Cuneiformes. Matemática. Período Babil nio Antigo. Tradu o. Acádio. Remarks about The Translation of Mathematical Cuneiform Texts Abstract In this work, I deal with certain problems of translation that belong to cuneiform texts in general and more specifically to mathematical cuneiform texts. I analyse these problems from three points of view. Initially, I consider the intellectual mediations a cuneiform text undergoes until its translation. Next, I deal with the particularities of the concepts of the cuneiform mathematics, that is to say, its differences in relation to the mathematics of our time. Lastly, I treat aspects of the original languages of cuneiform texts that are still under discussion by the field. As a conclusion, I suggest that the results of this analysis are relevant not only to the translation process, but also to the reading of translations of mathematical cuneiform texts. Keywords: Cuneiform texts. Mathematics. Old Babylonian Period. Translation. Akkadian.
Band-like transport and trapping in TMTSF Single Crystal Transistors
H. Xie,H. Alves,A. F. Morpurgo
Physics , 2009,
Abstract: We perform a combined experimental and theoretical study of tetramethyltetraselenafulvalene (TMTSF) single-crystal field-effect transistors, whose electrical characteristics exhibit clear signatures of the intrinsic transport properties of the material. We introduce a simple, well-defined model based on physical parameters and we successfully reproduce quantitatively the device properties as a function of temperature and carrier density. The analysis allows its internal consistency to be checked, and enables the reliable extraction of the density and characteristic energy of shallow and deep traps in the material. Our findings indicate that shallow traps originate from electrostatic potential fluctuations generated by charges fixed in the deep traps.
Morphology and Thermal Properties of Core-Shell PVA/PLA Ultrafine Fibers Produced by Coaxial Electrospinning  [PDF]
Raquel P. Gon?alves, Flavia F. F. da Silva, Paulo H. S. Picciani, Marcos L. Dias
Materials Sciences and Applications (MSA) , 2015, DOI: 10.4236/msa.2015.62022
Abstract: Coaxial electrospinning process was used to produce biodegradable membranes made of coreshell fibers of a poly(lactic acid) (PLA) shell and a poly(vinyl alcohol) (PVA) core. Scanning electron microscopy analyses of these structures showed that the PLA shell can present certain porosity depending on the process condition. FTIR-ATR and contact angle measurements also suggested imprisonment of the PVA core within the PLA shell. This type of structure was also confirmed by means of transmissions electron microscopy. The morphology of these fibers was dependent on the flow rate of both core and shell solutions, and homogeneous and smooth surface was only attained when the flow rate of the external PLA solution was 4 times the flow rate of the internal PVA solution. The increase in the PLA solution flow rate increases the diameter of the core-shell fiber which reaches up to 1.7 μm. Nevertheless, fibers with smaller average diameter could also be produced (200 nm). These core-shell fibers presented improved hydrophilicity as compared with monolithic PLA fibers.
Sombreamento arbóreo e orienta??o de instala??es avícolas
Alves, Sulivan P.;Rodrigues, Edmundo H. V.;
Engenharia Agrícola , 2004, DOI: 10.1590/S0100-69162004000200001
Abstract: this present paper deals with the contribution of tree shading to reduction radiation heat load in poultry houses. typically dimensioned facilities, east-west and north-south-oriented, located at the southern latitudes of 0; 10; 20 and 30 degrees were considered. sheltering efficiency was expressed as an index in function of space and time. such index (isg) takes into account the shading effect of trees in and out the facility. use of tree shading was more efficient in the north and northeast regions of brazil, where the solar irradiation is higher than south and southeast regions. the east-west as well for the north-south orientations of the facilities the same was observed. an index of isg of 25% was observed in the northeast region for east-west oriented facilities, while a value of isg = 33% was observed for the north-south orientation. for all the latitudes shading effects were more efficient in the north-south orientation. the southeast index was isg = 21% for the east-west and isg = 32% for the north-south orientation.
Kinetic Monte Carlo simulation of the nitridation of the GaAs (100) surfaces
Castro, A. P.;Alves, H. W. Leite;
Brazilian Journal of Physics , 2006, DOI: 10.1590/S0103-97332006000300019
Abstract: we present, our preliminary results of a systematic theoretical study of the adsorption of n over as-terminated gaas (100) (2×1) surfaces. we analyzed the changes in the bond-lengths, bond-angles and the energetics involved before and after deposition. our results show that the n-atoms will prefer the unoccupied sites of the surface, close to the as dimer. the presence of n pushes the as dimer out of the surface, leading to the anion exchange between n and as atoms. based on our results, we discussed the kinetics of the n islands formation during epitaxial growth of the iii-nitrides.
Structural and electronic properties of the SiC (100) surfaces
Soares, J. S.;Alves, H. W. Leite;
Brazilian Journal of Physics , 2006, DOI: 10.1590/S0103-97332006000300017
Abstract: in this work, we present our preliminary ab initio results for the structural and electronic properties of both si- and c-terminated sic (100) surfaces in (2×1) and c(2×2) reconstruction patterns. based on our results, we found that the si-terminated surfaces are dominated by weak bonded si-dimers, which are stabilized only at si-rich conditions, leading to (3×2) or more complex reconstruction patterns, as verified experimentally. also, our results show that the c-terminated surfaces is characterized by strong triply-bonded c-dimers, in a c(2×2) reconstruction pattern, which consists of c2 pairs over si bridge sites, in agreement with experimental results.
Ab initio determination of the (100) surfaces phonon dispersions of the SiC
Soares, J. S.;Alves, H. W. Leite;
Brazilian Journal of Physics , 2006, DOI: 10.1590/S0103-97332006000300018
Abstract: in this work, we presented our preliminary ab initio results for the vibrational modes and the phonon frequencies of the sic (100) surfaces. our results are in good agreement with the available experimental data whenever this comparison is possible. for the accepted models of the c-terminated surfaces in the c(2×2) reconstruction, while in the bridge-dimer model there is an acetylene-like vibrational a1 mode at 2031 cm-1, which is infrared active, in the staggered-dimer model, there is a füchs-kliewer (fk) mode at 1328 cm-1, which is experimentally detected. for si-terminated surfaces in the p(2×1) reconstruction, instead, no fk was obtained, in contradiction with the hreels experimental results for the si-terminated surfaces, but they are in consonance with the fact that this surface should be described by a (3×2) or more complex models.
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