841 research outputs found
The self-consistent quantum-electrostatic problem in strongly non-linear regime
The self-consistent quantum-electrostatic (also known as
Poisson-Schr\"odinger) problem is notoriously difficult in situations where the
density of states varies rapidly with energy. At low temperatures, these
fluctuations make the problem highly non-linear which renders iterative schemes
deeply unstable. We present a stable algorithm that provides a solution to this
problem with controlled accuracy. The technique is intrinsically convergent
including in highly non-linear regimes. We illustrate our approach with (i) a
calculation of the compressible and incompressible stripes in the integer
quantum Hall regime and (ii) a calculation of the differential conductance of a
quantum point contact geometry. Our technique provides a viable route for the
predictive modeling of the transport properties of quantum nanoelectronics
devices.Comment: 28 pages. 14 figures. Added solution to a potential failure mode of
the algorith
How do edge states position themselves in a quantum Hall graphene pn junction?
Recent experiments have shown that electronic Mach-Zehnder interferometers of
unprecedented fidelities could be built using a graphene pn junction in the
quantum Hall regime. In these junctions, two different edge states
corresponding to two different valley configurations are spatially separated
and form the two arms of the interferometer. The observed separation, of
several tens of nanometers, has been found to be abnormally high and thus
associated to unrealistic values of the exchange interaction. In this work, we
show that, although the separation is due to exchange interaction, its actual
value is entirely governed by the sample geometry and independent of the value
of the exchange splitting. Our analysis follows the lines of the classical work
of Chklovski-Shklovskii- Glazman on electrostatically induced edge state
reconstruction and includes quantitative numerical calculations in the
experimental geometries.Comment: 4 pages, 4 figure
Detecção de sinais de mudanças climáticas para algumas localidades do sertão do Pajeú - PE.
São duas as principais maneiras nas quais os efeitos do aquecimento global sobre o ciclo hidrológico nos trópicos pode afetar significativamente a demanda hÃdrica para culturas: O aumento da temperatura promovendo aumento da evapotranspiração, aumento da deficiência hÃdrica e o aumento dos perÃodos de estiagem. Há indicações de aumento da temperatura do ar e da duração dos veranicos sobre o Sertão de Pernambuco. Estudos recentes sobre o aquecimento global indicam que as mudanças climáticas poderão afetar a produção nacional e aumento das áreas de risco na Região Nordeste do Brasil (NEB). Nesse contexto, as análises das variações da duração e freqüência dos perÃodos de veranicos, bem como, a ocorrência de chuvas intensas, servirão como base para a detecção dos efeitos do aquecimento global em mudanças climáticas locais e seus impactos na agricultura da Região. Os resultados encontrados mostram que aumento dos dias secos, do tamanho médio dos veranicos e dos máximos veranicos. Os resultados das análises das freqüências de ocorrência de chuvas intensas, também, mostraram que, na microrregião do Pajeú, as precipitações extremas estão aumento.CBA 2009
Visible spectroscopy of the new ESO Large Program on trans-Neptunian objects and Centaurs: final results
A second large programme (LP) for the physical studies of TNOs and Centaurs,
started at ESO Cerro Paranal on October 2006 to obtain high-quality data, has
recently been concluded. In this paper we present the spectra of these pristine
bodies obtained in the visible range during the last two semesters of the LP.
We investigate the spectral behaviour of the TNOs and Centaurs observed, and we
analyse the spectral slopes distribution of the full data set coming from this
LP and from the literature. We computed the spectral slope for each observed
object, and searched for possible weak absorption features. A statistical
analysis was performed on a total sample of 73 TNOs and Centaurs to look for
possible correlations between dynamical classes, orbital parameters, and
spectral gradient. We obtained new spectra for 28 bodies, 15 of which were
observed for the first time. All the new presented spectra are featureless,
including 2003 AZ84, for which a faint and broad absorption band possibly
attributed to hydrated silicates on its surface has been reported. The data
confirm a wide variety of spectral behaviours, with neutral--grey to very red
gradients. An analysis of the spectral slopes available from this LP and in the
literature for a total sample of 73 Centaurs and TNOs shows that there is a
lack of very red objects in the classical population. We present the results of
the statistical analysis of the spectral slope distribution versus orbital
parameters. In particular, we confirm a strong anticorrelation between spectral
slope and orbital inclination for the classical population. A strong
correlation is also found between the spectral slope and orbital eccentricity
for resonant TNOs, with objects having higher spectral slope values with
increasing eccentricity.Comment: 11 pages, 9 figure
Fertilidade do solo e manejo da adubação NPK para alta produtividade de milho no Brasil Central.
bitstream/item/77755/1/circ-181.pd
FotossÃntese de cajueiro-anão precoce submetido ao estresse salino.
bitstream/CNPAT/7829/1/pd_6.pd
Parasitóides (Hymenoptera) de Anastrepha spp. obtidos em frutos coletados na zona urbana de Santana, AP.
A Mouse Model of Metabolic Syndrome: Insulin Resistance, Fatty Liver and Non-Alcoholic Fatty Pancreas Disease (NAFPD) in C57BL/6 Mice Fed a High Fat Diet
Diet-induced obesity in C57BL/6 mice triggers common features of human metabolic syndrome (MetS). The purpose is to assess the suitability of a diet-induced obesity model for investigating non-alcoholic fatty pancreatic disease (NAFPD), fatty liver and insulin resistance. Adult C57BL/6 mice were fed either high-fat chow (HFC, 60% fat) or standard chow (SC, 10% fat) during a 16-week period. We evaluated in both groups: hepatopancreatic injuries, pancreatic islets size, alpha and beta-cell immunodensities, intraperitoneal insulin tolerance test (IPITT) and oral glucose tolerance test (OGTT). The HFC mice displayed greater mass gain (p<0.0001) and total visceral fat pads (p<0.001). OGTT showed impairment of glucose clearance in HFC mice (p<0.0001). IPITT revealed insulin resistance in HFC mice (p<0.0001). The HFC mice showed larger pancreatic islet size and significantly greater alpha and beta-cell immunodensities than SC mice. Pancreas and liver from HFC were heavier and contained higher fat concentration. In conclusion, C57BL/6 mice fed a high-fat diet develop features of NAFPD. Insulin resistance and ectopic accumulation of hepatic fat are well known to occur in MetS. Additionally, the importance of fat accumulation in the pancreas has been recently highlighted. Therefore, this model could help to elucidate target organ alterations associated with metabolic syndrome
Transneptunian objects and Centaurs from light curves
We analyze a vast light curve database by obtaining mean rotational
properties of the entire sample, determining the spin frequency distribution
and comparing those data with a simple model based on hydrostatic equilibrium.
For the rotation periods, the mean value obtained is 6.95 h for the whole
sample, 6.88 h for the Trans-neptunian objects (TNOs) alone and 6.75 h for the
Centaurs. From Maxwellian fits to the rotational frequencies distribution the
mean rotation rates are 7.35 h for the entire sample, 7.71 h for the TNOs alone
and 8.95 h for the Centaurs. These results are obtained by taking into account
the criteria of considering a single-peak light curve for objects with
amplitudes lower than 0.15 mag and a double-peak light curve for objects with
variability >0.15mag. The best Maxwellian fits were obtained with the threshold
between 0.10 and 0.15mag. The mean light-curve amplitude for the entire sample
is 0.26 mag, 0.25mag for TNOs only, and 0.26mag for the Centaurs. The amplitude
versus Hv correlation clearly indicates that the smaller (and collisionally
evolved) objects are more elongated than the bigger ones. From the model
results, it appears that hydrostatic equilibrium can explain the statistical
results of almost the entire sample, which means hydrostatic equilibrium is
probably reached by almost all TNOs in the H range [-1,7]. This implies that
for plausible albedos of 0.04 to 0.20, objects with diameters from 300km to
even 100km would likely be in equilibrium. Thus, the great majority of objects
would qualify as being dwarf planets because they would meet the hydrostatic
equilibrium condition. The best model density corresponds to 1100 kg/m3.Comment: 21 pages, 8 figures. Astronomy & Astrophysics, in pres
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