1,167 research outputs found
Quantum dot as a spin-current diode: A master-equation approach
We report a study of spin dependent transport in a system composed of a
quantum dot coupled to a normal metal lead and a ferromagnetic lead (NM-QD-FM).
We use the master equation approach to calculate the spin-resolved currents in
the presence of an external bias and an intra-dot Coulomb interaction. We find
that for a range of positive external biases (current flow from the normal
metal to the ferromagnet) the current polarization
is suppressed to
zero, while for the corresponding negative biases (current flow from the
ferromagnet to the normal metal) attains a relative maximum value. The
system thus operates as a rectifier for spin--current polarization. This effect
follows from an interplay between Coulomb interaction and nonequilibrium spin
accumulation in the dot. In the parameter range considered, we also show that
the above results can be obtained via nonequilibrium Green functions within a
Hartree-Fock type approximation.Comment: 7 two-column pages, 5 figures. v2 (published): title changed, some
added text to Sec. II and Appendix and some minor changes to the figure
Contraintes a lâadoption de la methode de lâhygiene sanitaire des vergers pour la lutte contre les mouches nuisibles aux fruits (Diptera, Tephritidae) par les producteurs de mangues et dâagrumes au Benin
No AbstractMots-clĂ©s: BĂ©nin, hygiĂšne sanitaire des vergers, mouches de fruits, producteurs de mangues et dâagrumesÂ
Effects of the Energy Error Distribution of Fluorescence Telescopes on the UHECR energy spectrum
The measurement of the ultra high energy cosmic ray (UHECR) spectrum is
strongly affected by uncertainties on the reconstructed energy. The
determination of the presence or absence of the GZK cutoff and its position in
the energy spectrum depends not only on high statistics but also on the shape
of the energy error distribution. Here we determine the energy error
distribution for fluorescence telescopes, based on a Monte Carlo simulation.
The HiRes and Auger fluorescence telescopes are simulated in detail. We analyze
the UHECR spectrum convolved with this energy error distribution. We compare
this spectrum with one convolved with a lognormal error distribution as well as
with a Gaussian error distribution. We show that the energy error distribution
for fluorescence detectors can not be represented by these known distributions.
We conclude that the convolved energy spectrum will be smeared but not enough
to affect the GZK cutoff detection. This conclusion stands for both HiRes and
Auger fluorescence telescopes. This result differs from the effect of the
energy error distribution obtained with ground detectors and reinforces the
importance of the fluorescence energy measurement. We also investigate the
effect of possible fluorescence yield measurement errors in the energy
spectrum.Comment: 24 pages, 11 figure
A student-centered approach for developing active learning: the construction of physical models as a teaching tool in medical physiology
BACKGROUND: Teaching physiology, a complex and constantly evolving subject, is not a simple task. A considerable body of knowledge about cognitive processes and teaching and learning methods has accumulated over the years, helping teachers to determine the most efficient way to teach, and highlighting student's active participation as a means to improve learning outcomes. In this context, this paper describes and qualitatively analyzes an experience of a student-centered teaching-learning methodology based on the construction of physiological-physical models, focusing on their possible application in the practice of teaching physiology. METHODS: After having Physiology classes and revising the literature, students, divided in small groups, built physiological-physical models predominantly using low-cost materials, for studying different topics in Physiology. Groups were followed by monitors and guided by teachers during the whole process, finally presenting the results in a Symposium on Integrative Physiology. RESULTS: Along the proposed activities, students were capable of efficiently creating physiological-physical models (118 in total) highly representative of different physiological processes. The implementation of the proposal indicated that students successfully achieved active learning and meaningful learning in Physiology while addressing multiple learning styles. CONCLUSION: The proposed method has proved to be an attractive, accessible and relatively simple approach to facilitate the physiology teaching-learning process, while facing difficulties imposed by recent requirements, especially those relating to the use of experimental animals and professional training guidelines. Finally, students' active participation in the production of knowledge may result in a holistic education, and possibly, better professional practices
Bone Characteristics Of Broiler Chickens Fed Diets Supplemented With Solanum Glaucophyllum
The aim of this study was to assess the characteristics of the tibiotarsus of male broilers at 21 and 35 days of age. The percentages of collagenous proteins (CP), non-collagenous proteins (NCP), ash, and minerals (calcium, phosphorus, potassium and sodium), as well as weight of dried and defatted tibiotarsus in natura were determined. A total of 648 CobbÂź male broilers were used in a random block design study with 6 treatments, 6 replicates, and 18 birds per experimental unit. The treatments consisted of diet supplementation with 0.0, 0.5, 1.0, 1.5, 2.0, and 2.5 ÎŒg of active Vitamin D3 per kg of feed. The birds were weighed at 21 and 35 days of age and one bird per repetition with the mean weight of the experimental unit was slaughtered to collect the tibiotarsus. The organic and mineral composition of the bone was affected by the addition of active Vitamin D3 to the feed. Our results indicate that a dose of up to 1.50 ÎŒg of 1,25(OH)2D3/kg of feed is ideal for male broilers between 8 and 35 days of age.37138139
Stochastic reaction-diffusion modeling of calcium dynamics in 3D-dendritic spines of purkinje cells
Calcium (Ca(2+)) is a second messenger assumed to control changes in synaptic strength in the form of both long-term depression (LTD) and long-term potentiation (LTP) at Purkinje cell dendritic spine synapses via inositol trisphosphate (IP(3)) induced Ca(2+) release. These Ca(2+) transients happen in response to stimuli from parallel fibers (PF) from granule cells and climbing fibers (CF) from the inferior olivary nucleus. These events occur at low numbers of free Ca(2+) requiring stochastic single particle methods when modeling them. We use the stochastic particle simulation program MCell to simulate Ca(2+) transients within a three-dimensional Purkinje cell dendritic spine. The model spine includes the endoplasmic reticulum (ER), several Ca(2+) transporters, and endogenous buffer molecules. Our simulations successfully reproduce properties of Ca(2+) transients in different dynamical situations. We test two different models of the IP(3) receptor (IP3R). The model with non-linear concentration response of binding of activating Ca(2+) reproduces experimental results better than the model with linear response due to the filtering of noise. Our results also suggest that Ca(2+) dependent inhibition of the IP3R needs to be slow in order to reproduce experimental results. Simulations suggest the experimentally observed optimal timing window of CF stimuli to arise from the relative timing of CF influx of Ca(2+) and IP(3) production sensitizing IP3R for Ca(2+) induced Ca(2+) release. We also model Ataxia, a loss of fine motor control assumed to be the result of malfunctioning information transmission at the granule to Purkinje cell synapse, resulting in a decrease or loss of Ca2+ transients. Finally, we propose possible ways of recovering Ca(2+) transients under Ataxia
Ergonomic evaluation of workload by milk production â a bibliometric analysis
Introduction and Objective
The purpose of this study was to select in a structured manner the relevant articles with scientific recognition, and simultaneously identify the characteristics of these publications that may scientifically enrich the theme in a portfolio of papers. The theme involves ergonomics in milk production as a criterion for evaluating and improving organizational performance in the milking sector.
Material and Methods
The study used ProKnow-C as a theoretical instrument for intervention.
Results
The main results show: i) a bibliographic portfolio of 18 items aligned with the view adopted by researchers which served as a theoretical framework for this research; ii) The article entitled âWrist positions and movements as possible risk factors during machine milkingâ, by Marianne StĂ„l, Gert-Ă
ke Hansson and Ulrich Moritz in 1999 and published in the Journal of Applied Ergonomics presented the highest scientific recognition, iii) the authors highlighted in the bibliographic portfolio or in its references researching the subject are Gert-Ă
ke Hansson, Marianne StÄl and Stefan Pinzke, and iv) the International Journal of Industrial Ergonomics shows the highest number of scientific articles in the bibliographic portfolio.
Conclusions
The studies selected using the methodology indicate research in ergonomics focused on the production of milk in rural areas, specifically in the milking sector, are generally related to the health and safety of the workers
FATORES AMBIENTAIS QUE INFLUENCIAM O PESO Ă DESMAMA, ANO E SOBREANO EM BOVINOS DA RAĂA NELORE MOCHA, NO SUDOESTE DE MATO GROSSO DO SUL - BRASIL
Animals of the race Nelore hornless (mocha = sem cornos) in regime of pastures in
the three territorial units of the Southwest region of Mato Grosso do Sul, Brazil, in the period of 27
years, were analyzed with the objective of evaluating the environmental and genetic effects on the
weight of these animals. Relative data to 21,919 observations of weights at the weaning (W205), at
the year (W365) and at 18-month (W550) have been considered. Analyses were accomplished by
the method of the minimum squares, to verify the influence of some environmental factors. The
statistical model included the fixed effects of year and month from birth, sex, area and the covariable
of age of the cow to the childbirth (lineal and quadratic). The observed average of the weight to the
205 days of 9,256 observations was of 181,30 ± 23,29 kg, for weight to the 365 days with average
of 7,786 observations was of 244,51 ± 35,49 kg and for the weight to the 550 days of 4,877
observations was of 327,54 ± 47,80 kg. The effects of them were half significant (PAnimais da raça Nelore Mocha, criados em regime de pastagens, na região sudoeste
do estado de Mato Grosso do Sul, no perĂodo de 27 anos, permitiu a confecção de um banco de
dados com 21.919 observaçÔes de pesos a desmama (P205), ao ano (P365) e ao sobreano (P550).
Estas foram analisadas pelo mĂ©todo dos quadrados mĂnimos, para verificar a influĂȘncia dos fatores
ambientais sobre as mesmas. O modelo estatĂstico incluiu os efeitos fixos de ano e mĂȘs de nascimento
do bezerro, sexo, região e a covariåvel de idade da vaca ao parto (linear e quadråtico). A média
observada do peso aos 205 dias de 9.256 observaçÔes foi de 181,30 ± 23,29 kg, para peso aos
365 dias, de 7.786 animais, a média foi 244,51 ± 35,49 kg e para o peso aos 550 dias, 4.877
observaçÔes a média do peso foi de 327,54 ± 47,80 kg. Os efeitos foram significativos (
Future environmental and agricultural impacts of Brazil's Forest Code
The role of improving the enforcement of Brazil's Forest Code in reducing deforestation in the Amazon has been highlighted in many studies. However, in a context of strong political pressure for loosening environmental protections, the future impacts of a nationwide implementation of the Forest Code on both environment and agriculture remain poorly understood. Here, we present a spatially explicit assessment of Brazil's 2012 Forest Code through the year 2050; specifically, we use a partial equilibrium economic model that provides a globally consistent national modeling framework with detailed representation of the agricultural sector and spatially explicit land-use change. We test for the combined or isolated impacts of the different measures of the Forest Code, including deforestation control and obligatory forest restoration with or without environmental reserve quotas. Our results show that, if rigorously enforced, the Forest Code could prevent a net loss of 53.4 million hectares (Mha) of forest and native vegetation by 2050, 43.1 Mha (81%) of which are in the Amazon alone. The control of illegal deforestation promotes the largest environmental benefits, but the obligatory restoration of illegally deforested areas creates 12.9 Mha of new forested area. Environmental reserve quotas further protect 5.8 Mha of undisturbed natural vegetation. Compared to a scenario without the Forest Code, by 2050, cropland area is only reduced by 4% and the cattle herd by 8%. Our results show that compliance with the Forest Code requires an increase in cattle productivity of 56% over four decades, with a combination of a higher use of supplements and an adoption of semi-intensive pasture management. We estimate that the enforcement of the Forest Code could contribute up to 1.03 PgCO<sub>2</sub>e to the ambitious GHG emissions reduction target set by Brazil for 2030
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