20,794 research outputs found
Exotic looped trajectories via quantum marking
We provide an analytical and theoretical study of exotic looped trajectories
(ELTs) in a double-slit interferometer with quantum marking. We use an excited
Rydberg-like atom and which-way detectors such as superconducting cavities,
just as in the Scully-Englert-Walther interferometer. We indicate appropriate
conditions on the atomic beam or superconducting cavities so that we determine
an interference pattern and fringe visibility exclusive from the ELTs. We
quantitatively describe our results for Rubidium atoms and propose this
framework as an alternative scheme to the double-slit experiment modified to
interfere only these exotic trajectories.Comment: 10 pages, 5 figure
Catálogo de recursos em informação agropecuária na internet: desenvolvimento de website.
O presente trabalho sintetiza o processo de desenvolvimento do site do Catálogo de Recursos em Informação Agropecuária (CRIA) na internet. Enfoques relativos ao design do site, organização e armazenamento da informação são descritos. O site CRIA pretende contribuir para a qualificação, a dissemincação e o acesso a recursos de infofrmação demandada, pelos diversos segmentos do agronegócio, utilizando a rede internet como infra-estrutura de comunicação.bitstream/item/76670/1/CNPTIA-COM.TEC.-2-99.pd
The silicon stable isotope distribution along the GEOVIDE section (GEOTRACES GA-01) of the North Atlantic Ocean
The stable isotope composition of dissolved silicon in seawater (δ30SiDSi) was examined at 10 stations along the GEOVIDE section (GEOTRACES GA-01), spanning the North Atlantic Ocean (40–60∘ N) and Labrador Sea. Variations in δ30SiDSi below 500 m were closely tied to the distribution of water masses. Higher δ30SiDSi values are associated with intermediate and deep water masses of northern Atlantic or Arctic Ocean origin, whilst lower δ30SiDSi values are associated with DSi-rich waters sourced ultimately from the Southern Ocean. Correspondingly, the lowest δ30SiDSi values were observed in the deep and abyssal eastern North Atlantic, where dense southern-sourced waters dominate. The extent to which the spreading of water masses influences the δ30SiDSi distribution is marked clearly by Labrador Sea Water (LSW), whose high δ30SiDSi signature is visible not only within its region of formation within the Labrador and Irminger seas, but also throughout the mid-depth western and eastern North Atlantic Ocean. Both δ30SiDSi and hydrographic parameters document the circulation of LSW into the eastern North Atlantic, where it overlies southern-sourced Lower Deep Water. The GEOVIDE δ30SiDSi distribution thus provides a clear view of the direct interaction between subpolar/polar water masses of northern and southern origin, and allow examination of the extent to which these far-field signals influence the local δ30SiDSi distribution
Modified Bethe-Weizsacker mass formula with isotonic shift and new driplines
Nuclear masses are calculated using the modified Bethe-Weizsacker mass
formula in which the isotonic shifts have been incorporated. The results are
compared with the improved liquid drop model with isotonic shift. Mass excesses
predicted by this method compares well with the microscopic-macroscopic model
while being much more simple. The neutron and proton drip lines have been
predicted using this modified Bethe-Weizsacker mass formula with isotonic
shifts.Comment: 9 pages including 2 figure
COMPARATIVE STUDY OF DIFFERENT MODELS FOR CALCULATION OF DNI
For prospecting or design of Concentrating Solar Power (CSP) systems it is necessary to know the distribution of the Direct Normal Irradiance (DNI) of the region. However, due to the recurring operational problems of measuring instruments, the use of mathematical models estimating the local DNI can be a very useful tool. The objective of this work is to construct a mathematical model that is used in the calculation of the DNI using experimental data provided by the Laboratory of Tropical Environmental Variables (LAVAT/INPE). This model was compared with other mathematical models already present in the literature. The consideration of clean-sky was used, that is, the effects of cloudiness, among others, were neglected
Spectral and Fermi surface properties from Wannier interpolation
We present an efficient first-principles approach for calculating Fermi
surface averages and spectral properties of solids, and use it to compute the
low-field Hall coefficient of several cubic metals and the magnetic circular
dichroism of iron. The first step is to perform a conventional first-principles
calculation and store the low-lying Bloch functions evaluated on a uniform grid
of k-points in the Brillouin zone. We then map those states onto a set of
maximally-localized Wannier functions, and evaluate the matrix elements of the
Hamiltonian and the other needed operators between the Wannier orbitals, thus
setting up an ``exact tight-binding model.'' In this compact representation the
k-space quantities are evaluated inexpensively using a generalized
Slater-Koster interpolation. Because of the strong localization of the Wannier
orbitals in real space, the smoothness and accuracy of the k-space
interpolation increases rapidly with the number of grid points originally used
to construct the Wannier functions. This allows k-space integrals to be
performed with ab-initio accuracy at low cost. In the Wannier representation,
band gradients, effective masses, and other k-derivatives needed for transport
and optical coefficients can be evaluated analytically, producing numerically
stable results even at band crossings and near weak avoided crossings.Comment: 12 pages, 7 figure
Low temperature structural effects in the (TMTSF)PF and AsF Bechgaard salts
We present a detailed low-temperature investigation of the statics and
dynamics of the anions and methyl groups in the organic conductors
(TMTSF)PF and (TMTSF)AsF (TMTSF :
tetramethyl-tetraselenafulvalene). The 4 K neutron scattering structure
refinement of the fully deuterated (TMTSF)PF-D12 salt allows locating
precisely the methyl groups at 4 K. This structure is compared to the one of
the fully hydrogenated (TMTSF)PF-H12 salt previously determined at the
same temperature. Surprisingly it is found that deuteration corresponds to the
application of a negative pressure of 5 x 10 MPa to the H12 salt. Accurate
measurements of the Bragg intensity show anomalous thermal variations at low
temperature both in the deuterated PF and AsF salts. Two different
thermal behaviors have been distinguished. Low-Bragg-angle measurements reflect
the presence of low-frequency modes at characteristic energies {\theta} =
8.3 K and {\theta} = 6.7 K for the PF-D12 and AsF-D12 salts,
respectively. These modes correspond to the low-temperature methyl group
motion. Large-Bragg-angle measurements evidence an unexpected structural change
around 55 K which probably corresponds to the linkage of the anions to the
methyl groups via the formation of F...D-CD2 bonds observed in the 4 K
structural refinement. Finally we show that the thermal expansion coefficient
of (TMTSF)PF is dominated by the librational motion of the PF
units. We quantitatively analyze the low-temperature variation of the lattice
expansion via the contribution of Einstein oscillators, which allows us to
determine for the first time the characteristic frequency of the PF6
librations: {\theta} = 50 K and {\theta} = 76 K for the PF-D12 and
PF-H12 salts, respectively
Estrutura genética populacional de bacurizeiros na região Meio-Norte do Brasil.
A região Meio-Norte caracteriza-se pela sua biodiversidade, com destaque para espécies frutíferas nativas, como, por exemplo, o bacurizeiro, cujos frutos são apreciados na alimentação pelas populações locais. A fragmentação e/ou desmatamento que ocorre nessa área causa danos para populações de plantas, afetando a estrutura genética destas. Assim esse estudo verificou a estruturação genética em cinco populações de bacurizeiro dos Estados do Maranhão e Piauí por meio de marcadores entre simples sequências repetidas (ISSR) e da análise de variância molecular. Da diversidade genética total, 28,88% foi dividido entre as populações e 77,16% dentro das populações, portanto há estruturação significativa entre as populações
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