4,964 research outputs found
Quantum Multibaker Maps: Extreme Quantum Regime
We introduce a family of models for quantum mechanical, one-dimensional
random walks, called quantum multibaker maps (QMB). These are Weyl
quantizations of the classical multibaker models previously considered by
Gaspard, Tasaki and others. Depending on the properties of the phases
parametrizing the quantization, we consider only two classes of the QMB maps:
uniform and random. Uniform QMB maps are characterized by phases which are the
same in every unit cell of the multibaker chain. Random QMB maps have phases
that vary randomly from unit cell to unit cell. The eigenstates in the former
case are extended while in the latter they are localized. In the uniform case
and for large , analytic solutions can be obtained for the time
dependent quantum states for periodic chains and for open chains with absorbing
boundary conditions. Steady state solutions and the properties of the
relaxation to a steady state for a uniform QMB chain in contact with
``particle'' reservoirs can also be described analytically. The analytical
results are consistent with, and confirmed by, results obtained from numerical
methods. We report here results for the deep quantum regime (large ) of
the uniform QMB, as well as some results for the random QMB. We leave the
moderate and small results as well as further consideration of the
other versions of the QMB for further publications.Comment: 17 pages, referee's and editor's comments addresse
Obtenção de luteína, violaxantina e B-caroteno a partir de espinafre (Spinacea oleracea LINNEU).
Effect of a Voltage Probe on the Phase-Coherent Conductance of a Ballistic Chaotic Cavity
The effect of an invasive voltage probe on the phase-coherent conduction
through a ballistic chaotic cavity is investigated by random-matrix theory. The
entire distribution P(G) of the conductance G is computed for the case that the
cavity is coupled to source and drain by two point contacts with a quantized
conductance of 2 e^2/h, both in the presence (beta = 1) and absence (beta = 2)
of time-reversal symmetry. The loss of phase-coherence induced by the voltage
probe causes a crossover from P(G) ~ G^(-1 + beta/2) to a Gaussian centered at
G = e^2/h with a beta-dependent width. ***Submitted to Physical Review B.***Comment: 9 pages, REVTeX-3.0, 4 postscript figures appended as self-extracting
archive, INLO-PUB-941020
Obtaining zeaxanthin and violaxanthin standards for high performance liquid chromatography from solanum pseudocapsicum and capsicum annuum.
A bright impulsive solar burst detected at 30 THz
Ground- and space-based observations of solar flares from radio wavelengths
to gamma-rays have produced considerable insights but raised several unsolved
controversies. The last unexplored wavelength frontier for solar flares is in
the range of submillimeter and infrared wavelengths. Here we report the
detection of an intense impulsive burst at 30 THz using a new imaging system.
The 30 THz emission exhibited remarkable time coincidence with peaks observed
at microwave, mm/submm, visible, EUV and hard X-ray wavelengths. The emission
location coincides with a very weak white-light feature, and is consistent with
heating below the temperature minimum in the atmosphere. However, there are
problems in attributing the heating to accelerated electrons. The peak 30 THz
flux is several times larger than the usual microwave peak near 9 GHz,
attributed to non-thermal electrons in the corona. The 30 THz emission could be
consistent with an optically thick spectrum increasing from low to high
frequencies. It might be part of the same spectral component found at sub-THz
frequencies whose nature remains mysterious. Further observations at these
wavelengths will provide a new window for flare studies.Comment: 9 pages, 11 figures, accepted by Astrophysical Journal, March 23,
201
Land evaluation combined with climatic risk estimate for corn using geographic information system
O objetivo deste trabalho foi determinar a aptidão agrícola das terras para cultura do milho em sistema de produção tecnificado, a partir de dados extraídos de levantamento de solos em escala 1:50.000 e da estimativa do risco climático, usando um sistema de informações geográficas. A área de estudo foi a bacia hidrográfica do rio Jardim, no Distrito Federal. Utilizou-se um modelo de balanço hídrico para simular o risco climático para a cultura do milho (Zea mays L.), considerando nove datas de plantio. Foram definidos valores quantitativos para cada um das propriedades condicionadoras da produtividade do milho em áreas de cerrado e, por meio de algoritmos de lógica booleana estabelecidos com base em critérios definidos em tabelas-guia previamente elaboradas, foram realizados cruzamentos consecutivos que permitiram a elaboração de mapas de aptidão agrícola das terras para a cultura do milho, com cinco classes, que evidenciaram a variação temporal da aptidão. Constatou-se que 66,5 % da área total não apresentou limitações físicas, 96% das terras foram restritas em fertilidade e o período de menor risco climático foi de 11 a 20/10.The objective of this work was to propose a methodology for land evaluation based on planting information, soil data extracted from a soil survey in a scale 1:50,000, and estimate of climatic risk, using a geographic information system (GIS). The reference area was the Jardim watershed, in the Federal District (Brazil). A water balance model was used to simulate the climatic risk for the corn crop (Zea mays L.), at nine different planting dates. Quantitative values for corn productivity parameters were defined for the cerrado region. Using algorithms of Boolean logic, established by a previously elaborated guide, serial crossings were accomplished allowing the elaboration of agricultural suitability maps of the lands for corn production, with five classes. The results showed a land instability variation, with time. It was verified that 66.5 % of the total area did not present physical limitations, 96 % of the lands had their soil fertility restricted and the period of least climatic risk was October 11-20
Immunoexpression Of Cd95 In Chronic Gastritis And Gastric Mucosa-associated Lymphomas.
CD95 (Fas/APO-1)-mediated apoptosis plays an important role in immunological regulation and is related to the pathogenesis of autoimmune diseases. Immunoexpression of CD95 has been reported to frequently occur in low grade non-Hodgkin lymphomas, especially of post-germinal center histogenesis, among which those originating in mucosa-associated lymphoid tissue (MALT lymphomas). However, there is no report comparing in situ immunoexpression of this marker in lymphomas and the hyperplastic lymphoid reaction (chronic gastritis) related to Helicobacter pylori infection. The purpose of the present research was to compare the intensity of lymphoid CD95 immunoexpression in 15 cases of H. pylori-related chronic gastritis and 15 gastric MALT lymphomas. CD95 (anti-CD95) was detected by an immunoperoxidase technique in paraffin sections using the catalyzed amplification system. Graduation of reaction intensity (percentage of CD95-positive cells) was semiquantitative, from 1+ to 4+. Nine cases of chronic gastritis were 4+, five 2+ and one 1+. Three lymphomas were 4+, three 3+, four 2+, four 1+, and one was negative. Although 14 of 15 lymphomas were positive for CD95, the intensity of the reaction was significantly weaker compared to that obtained with gastric tissue for patients with gastritis (P = 0.03). The difference in CD95 immunoexpression does not seem to be useful as an isolated criterion in the differential diagnosis between chronic gastritis and MALT lymphomas since there was overlapping of immunostaining patterns. However, it suggests the possibility of a pathogenetic role of this apoptosis-regulating protein in MALT lymphomas.371397-40
Método cromatográfico alternativo para análise de açúcares em alimentos com menor impacto ambiental.
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