6,613 research outputs found
Melting temperature of screened Wigner crystal on helium films by molecular dynamics
Using molecular dynamics (MD) simulation, we have calculated the melting
temperature of two-dimensional electron systems on \AA-\AA helium
films supported by substrates of dielectric constants
at areal densities varying from cm to cm. Our results are in good agreement with the available
theoretical and experimental results.Comment: 4 pages and 4 figure
Spin-polarized transport in ferromagnetic multilayered semiconductor nanostructures
The occurrence of inhomogeneous spin-density distribution in multilayered
ferromagnetic diluted magnetic semiconductor nanostructures leads to strong
dependence of the spin-polarized transport properties on these systems. The
spin-dependent mobility, conductivity and resistivity in
(Ga,Mn)As/GaAs,(Ga,Mn)N/GaN, and (Si,Mn)/Si multilayers are calculated as a
function of temperature, scaled by the average magnetization of the diluted
magnetic semiconductor layers. An increase of the resistivity near the
transition temperature is obtained. We observed that the spin-polarized
transport properties changes strongly among the three materials.Comment: 3 pages, 4 figure
Porta-enxertos para laranjeiras-doces (Citrus sinensis (L.) OSB.), em Rio Branco, Acre.
O objetivo deste trabalho foi de avaliar o comportamento de sete cultivares de laranjeiras-doces: 'Baia 101', 'Baianinha IAC 79', 'Monte Parnaso', 'Pêra D6', 'Natal 112', 'Valência 27' e 'Aquiri', sobre diferentes porta-enxertos: limão 'Cravo', tangerinas 'Cleópatra' e 'Sunki' e citrange 'Carrizo', nas condições edafoclimáticas de Rio Branco, Acre. O delineamento experimental foi em parcelas subdivididas, com as cultivares nas parcelas, os porta-enxertos nas subparcelas e os quatro anos de avaliação como repetições. As laranjeiras 'Pêra D6', 'Natal 112' e 'Valência 27' apresentaram tendências de maior produção quando enxertadas sobre o limão 'Cravo', e a laranja 'Aquiri' quando enxertada sobre citrange 'Carrizo'. Em relação aos demais porta-enxertos, o limão 'Cravo' mostrou tendências de induzir maior produção/volume de copa e peso médio do fruto, e menor teor de sólidos solúveis totais e acidez total. As laranjas do grupo Baia ('Baia 101', 'Baianinha IAC 79' e 'Monte Parnaso') produziram frutos com baixa percentagem de suco; não são recomendadas para plantio em Rio Branco, AC. Com base nos resultados obtidos, recomendam-se os porta-enxertos citrange 'Carrizo', tangerina 'Cleópatra' e limão 'Cravo' para a laranja 'Aquiri', e o porta-enxerto limão 'Cravo' para as laranjas 'Pêra D6', 'Natal 112' e 'Valência 27'
Phase selective growth of Cu12Sb4S13 and Cu3SbS4 thin films by chalcogenization of simultaneous sputtered metal precursors
In this work, it is presented a procedure to grow single phase Cu12Sb4S13 and Cu3SbS4 thin films consisting on the annealing of simultaneously sputtered metal precursors fllowed by a annealing treatment in a sulphur atmosphere. The selection of the ternary phase which is intended to grow is performed by adjusting the sulfur evaporation temperature in chalcogenization process. It is
shown that for a sulphur evaporation temperature of 140 ◦C the predominant phase is Cu12Sb4S13 and for 180 ◦C the predominant phase is Cu3SbS4. In order to ensure precursor composition homogeneity, the Cu-Sb metallic precursors are deposited simultaneously by rf magnetron sputtering using adjustable segmented targets. The morphological characterization of the films was made
by scanning electron microscopy and the composition was analysed by energy dispersive spectroscopy. The structural analysis and phase identification were performed by X-ray diffraction and Raman scattering. The optical properties were studied through spectrophotometry on films deposited directly on bare glass.publishe
Fatores abióticos envolvidos na tolerância de trigo à geada.
O objetivo deste trabalho foi avaliar a influência da aclimatação, da intensidade de geada e da disponibilidade hídrica sobre os danos causados pela geada em trigo. Os experimentos foram conduzidos em telados, com trigo cultivado em vasos. A aclimatação e a incidência de geada foram simuladas em câmaras de crescimento. Os fatores abióticos avaliados foram: regimes de aclimatação (com e sem); gradiente de temperatura (2, -2, -4 e -7°C); e variação de disponibilidade hídrica no solo, antes da geada (9, 6, 3 e 1 dia sem irrigação). Todos os fatores foram avaliados no afilhamento, alongamento e espigamento das cultivares: BR-18 Terena, mais tolerante à geada; e BRS 194, menos tolerante. As variáveis avaliadas foram: grau de queima de folhas, sete dias após a geada; massa de matéria seca total; e massa de grãos. A aclimatação do trigo, antes da geada, diminuiu os danos provocados antes do espigamento, e resultou em menor queima de folhas e maior rendimento de grãos. A temperatura de -7°C, no espigamento, resultou em falha na produção de grãos de ambas as cultivares; e os prejuízos com geada foram menores nas plantas com nove dias sem irrigação. As condições anteriores à ocorrência de geada têm influência sobre os danos provocados por ela
Spray drift and pest control from aerial applications on soybeans.
Abstract: Pesticide drift is an issue in modern farming, mainly for crops under constant spraying as soybeans. This study aimed at assessing drift and pest control for aerial applications in soybean crops. Hydraulic nozzles and rotary atomizers, regulated to a wide spectrum of droplet sizes, sprayed thiamethoxam plus lambda-cyhalothrin using an agricultural aircraft Ipanema 202A at volume rate of 20 L ha?1. Treatments consisted of testing two devices: a rotary cage atomizer (Micronair AU 5000) with blade angles of 65° for larger droplets, and with angle of 55° for smaller ones; and a set of adjustable nozzles (Stol model) with deflector angle of 90° for smaller droplets, and with angle of 30° for larger ones. Drift was evaluated through quantification of active ingredient, by means of liquid chromatography, on nylon strings set 20, 40, 80, 160 and 320 m downwind from the applied area. Control efficiency was measured by counting caterpillars and stinkbugs found five days after spray. Rotary atomizers produced lesser drift compared to adjustable nozzles at the designed setting. Furthermore, drift can be reduced through a suitable regulation of the devices, keeping an effective pest control
Pattern formation and coexistence domains for a nonlocal population dynamics
In this communication we propose a most general equation to study pattern
formation for one-species population and their limit domains in systems of
length L. To accomplish this we include non-locality in the growth and
competition terms where the integral kernels are now depend on characteristic
length parameters alpha and beta. Therefore, we derived a parameter space
(alpha,beta) where it is possible to analyze a coexistence curve
alpha*=alpha*(\beta) which delimits domains for the existence (or not) of
pattern formation in population dynamics systems. We show that this curve has
an analogy with coexistence curve in classical thermodynamics and critical
phenomena physics. We have successfully compared this model with experimental
data for diffusion of Escherichia coli populations
Three Dimensional de Sitter Gravity and the Correspondence
Certain aspects of three dimensional asymptotically de Sitter spaces are
studied, with emphasis on the mapping between gravity observables and the
representation of the conformal symmetry of the boundary. In particular, we
show that non-real conformal weights for the boundary theory correspond to
space-times that have non-zero angular momentum. Some miscellaneous results on
the role of the holonomies and isometry groups are also presented.Comment: 10 pages, 1 figure, uses epsf. Added references and a discussion on
the (dis)similarities with previous work
Relationship between the morphogenesis of Italian ryegrass cv. 'BRS Ponteio' with forage and seed production.
This study aims to verify, accurate and precisely, the responses of Italian ryegrass 'BRS Ponteio' cultivar to different frequencies of defoliation for forage production and especially for seed production. For this purpose, a randomized block design experiment with four replications was conducted. Four frequencies of defoliation were applied (zero, one, two, and three) based on the thermal sum, evaluating the rate of leaf appearance (LAR), phyllochron (P), leaf expansion rate (LER), leaf senescence rate (LSR), stems expansion rate (SER), tillering rate (TR), leaf life span (LL), forage production, proportion of leaf blades, stems plus sheaths, senescent material, and inflorescences, as well as seed production. Second defoliation noticeably altered the morphogenic plant responses, reduced expansion rates and leaf appearance, increased rates of tillering and stems expansion. This phenotypic maintained a high seed production and provided a harvest of forage mass 100% higher than the collected mass in the first cutting. Third defoliation led to an increase of 100% of the harvested forage mass; however, it caused drastic and negative changes in the morphogenic characteristics and seed yielding
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