21,490 research outputs found
SU(1,1) Coherent States For Position-Dependent Mass Singular Oscillators
The Schroedinger equation for position-dependent mass singular oscillators is
solved by means of the factorization method and point transformations. These
systems share their spectrum with the conventional singular oscillator. Ladder
operators are constructed to close the su(1,1) Lie algebra and the involved
point transformations are shown to preserve the structure of the
Barut-Girardello and Perelomov coherent states.Comment: 11 pages, 5 figures. This shortened version (includes new references)
has been adapted for its publication in International Journal of Theoretical
Physic
Vacuum-UV spectroscopy of interstellar ice analogs. II. Absorption cross-sections of nonpolar ice molecules
Dust grains in cold circumstellar regions and dark-cloud interiors at 10-20 K
are covered by ice mantles. A nonthermal desorption mechanism is invoked to
explain the presence of gas-phase molecules in these environments, such as the
photodesorption induced by irradiation of ice due to secondary ultraviolet
photons. To quantify the effects of ice photoprocessing, an estimate of the
photon absorption in ice mantles is required. In a recent work, we reported the
vacuum-ultraviolet (VUV) absorption cross sections of nonpolar molecules in the
solid phase. The aim was to estimate the VUV-absorption cross sections of
nonpolar molecular ice components, including CH4, CO2, N2, and O2. The column
densities of the ice samples deposited at 8 K were measured in situ by infrared
spectroscopy in transmittance. VUV spectra of the ice samples were collected in
the 120-160 nm (10.33-7.74 eV) range using a commercial microwave-discharged
hydrogen flow lamp. We found that, as expected, solid N2 has the lowest
VUV-absorption cross section, which about three orders of magnitude lower than
that of other species such as O2, which is also homonuclear. Methane (CH4) ice
presents a high absorption near Ly-alpha (121.6 nm) and does not absorb below
148 nm. Estimating the ice absorption cross sections is essential for models of
ice photoprocessing and allows estimating the ice photodesorption rates as the
number of photodesorbed molecules per absorbed photon in the ice.Comment: 9 pages, 6 figures, 7 table
Diversidade genética de cultivares de uva para processamento no Vale do São Francisco.
Os objetivos deste trabalho foram avaliar o comportamento agronômico, quantificar a variabilidade e estimar as distâncias genéticas de 66 acessos de videira destinadas a elaboração de vinhos, presente no Banco de Germoplasma de Videira da EMBRAPA Semi-Árido, em Juazeiro, BA, por meio da caracterização de descritores fenotípicos de variação contínua e discreta. As técnicas multivariadas utilizadas, componentes principais, método de otimização de Tocher, e projeção gráfica das distâncias, foram eficientes no agrupamento dos genótipos mais similares, de acordo com as suas características fenotípicas. Não houve concordância na formação dos grupos pelo método de otimização de Tocher, quando foram avaliadas características morfo-agronômicas de variação contínua e discreta. A utilização de variáveis discretas permitiu a separação de Vitis vinifera e híbridos em grupos distintos. Correlações significativas positivas foram observadas entre peso, comprimento e largura de cachos, bem como, correlação negativa entre acidez total titulável e relação SST/ATT. 84,12% da variação total presente nos dados originais foi explicada pelos primeiros quatro componentes principais. Os resultados obtidos demonstram que existe pequena variabilidade entre os acessos de uvas para vinho no Banco de Germoplasma da Embrapa Semi-Árido
Results in Kalb-Ramond field localization and resonances on deformed branes
We make an analysis about several aspects of localization of the Kalb-Ramond
gauge field in a specific four dimensional AdS membrane embedded in a five
dimensional space-time. The membrane is generated from a deformation of the
potential and belongs to a new class of defect solutions. In
this context we find resonance structures in the analysis of massive modes. The
study of deformed defects is important because they contain internal structures
and these may have implications to the way the background space-time is
constructed and the way its curvature behaves. The main objective here is to
observe the contributions of the deformation procedure to the resonances and
the well known field localization methods.Comment: 6 pages, 7 figures, Latex with EPL macr
Pressure induced enhancement of ferroelectricity in multiferroic MnO(=Tb,Dy, and Ho)
Measurements of ferroelectric polarization and dielectric constant were done
on MnO (=Tb, Dy, and Ho) with applied hydrostatic pressures of up
to 18 kbar. At ambient pressure, distinctive anomalies were observed in the
temperature profile of both physical properties at critical temperatures
marking the onset of long range AFM order (T), ferroelectricity
(T) as well as at temperatures when anomalous changes in the
polarization, dielectric constant and spin wave commensurability have been
previously reported. In particular, the step in the dielectric constant at low
temperatures (T), associated with both a drop in the ferroelectric
polarization and an incommensurate magnetic structure, was shown to be suddenly
quenched upon passing an -dependent critical pressure. This was shown to
correlate with the stabilization of the high ferroelectric polarization state
which is coincident with the commensurate magnetic structure. The observation
is suggested to be due to a pressure induced phase transition into a
commensurate magnetic structure as exemplified by the pressure-temperature
(-) phase diagrams constructed in this work. The - phase diagrams
are determined for all three compounds.Comment: 8 pages, 6 figures, submitted for review in Phys. Rev.
- …