341 research outputs found
Transition from Diffusive to Localized Regimes in Surface Corrugated Optical Waveguides
Exact calculations of the transmittance of surface corrugated optical
waveguides are presented. The elastic scattering of diffuse light or other
electromagnetic waves from a rough surface induces a diffusive transport along
the waveguide axis. As the length of the corrugated part of the waveguide
increases, a transition from the diffusive to the localized regime is observed.
This involves an analogy with electron conduction in nanowires, and hence, a
concept analogous to that of ``resistance'' can be introduced. We show an
oscillatory behavior of both the elastic mean free path and the localization
length versus the wavelength.Comment: 3 pages, REVTEX, 3 PS figure
A class of colliding waves in metric-affine gravity, nonmetricity and torsion shock waves
By using our recent generalization of the colliding waves concept to
metric-affine gravity theories, and also our generalization of the advanced and
retarded time coordinate representation in terms of Jacobi functions, we find a
general class of colliding wave solutions with fourth degree polynomials in
metric-affine gravity. We show that our general approach contains the standard
second degree polynomials colliding wave solutions as a particular case.Comment: 13 pages, latex, to appear in J.Math.Phy
Microstructure and secondary phases in coevaporated CuInS2 films: Dependence on growth temperature and chemical composition
The microstructure of CuInS2-(CIS2) polycrystalline films deposited onto Mo-coated glass has been analyzed by Raman scattering, Auger electron spectroscopy (AES), transmission electron microscopy, and x-ray diffraction techniques. Samples were obtained by a coevaporation procedure that allows different Cu-to-In composition ratios (from Cu-rich to Cu-poor films). Films were grown at different temperatures between 370 and 520-°C. The combination of micro-Raman and AES techniques onto Ar+-sputtered samples has allowed us to identify the main secondary phases from Cu-poor films such as CuIn5S8 (at the central region of the layer) and MoS2 (at the CIS2/Mo interface). For Cu-rich films, secondary phases are CuS at the surface of as-grown layers and MoS2 at the CIS2/Mo interface. The lower intensity of the MoS2 modes from the Raman spectra measured at these samples suggests excess Cu to inhibit MoS2 interface formation. Decreasing the temperature of deposition to 420-°C leads to an inhibition in observing these secondary phases. This inhibition is also accompanied by a significant broadening and blueshift of the main A1 Raman mode from CIS2, as well as by an increase in the contribution of an additional mode at about 305 cm-1. The experimental data suggest that these effects are related to a decrease in structural quality of the CIS2 films obtained under low-temperature deposition conditions, which are likely connected to the inhibition in the measured spectra of secondary-phase vibrational modes
Multisymplectic Geometry and Multisymplectic Preissman Scheme for the KP Equation
The multisymplectic structure of the KP equation is obtained directly from
the variational principal. Using the covariant De Donder-Weyl Hamilton function
theories, we reformulate the KP equation to the multisymplectic form which
proposed by Bridges. From the multisymplectic equation, we can derive a
multisymplectic numerical scheme of the KP equation which can be simplified to
multisymplectic forty-five points scheme.Comment: 17 papges, 8 figure
Luminescence study of thermal treated and laser irradiated Bi_12GeO_20 and Bi_12SiO_20 crystals
Changes on the defect structure of Bi12GeO20 (BGO) and Bi12SiO20 (BSO) crystals induced by thermal treatments and laser irradiation have been studied by means of cathodoluminescence in the scanning electron microscope. The results have been compared to those previously reported for untreated and electron irradiated samples and recombination mechanisms responsible for some of the observed luminescence bands are discussed. Annealing of EGO samples causes the appearance of a new luminescence band at about 390 nm. The centers responsible for this band decorate the deformation slip bands in quenched EGO as observed in the cathodoluminescence images. The emission observed in BSO in the same spectral range is quenched during the annealing treatment. The annealing induced reduction of Bi ions to metallic Bi appears to be related to the quenching of a band at 640 nm observed in untreated samples
Current density maps, magnetizability, and nuclear magnetic shielding tensors of bis-heteropentalenes. II. Furo-furan Isomers
Magnetic susceptibility and nuclear magnetic shielding at the nuclei of bis-heteropentalenes formed by two furan units ([2,3-b], [3,2-b], [3,4-b], and [3,4-c] isomers) have been computed by several approximated techniques and a large Gaussian basis set to achieve near Hartree–Fock estimates. Ab initio models of the ring currents induced by a magnetic field normal to the molecular plane were obtained for the three isomeric systems of higher symmetry, showing that the π electrons give rise to intense diamagnetic circulation. The π currents are responsible for enhanced magnetic anisotropy and strong out-of-plane proton deshielding. The theoretical findings are used to build up a “diatropicity matrix” for two fused five-membered heterocyclic [email protected] ; [email protected]
Sensitivity plots for WIMP direct detection using the annual modulation signature
Annual modulation due to the Earth's motion around the Sun is a well known
signature of the expected WIMP signal induced in a solid state underground
detector. In the present letter we discuss the prospects of this technique on
statistical grounds, introducing annual-modulation sensitivity plots for the
WIMP-nucleon scalar cross section for different materials and experimental
conditions. The highest sensitivity to modulation is found in the WIMP mass
interval 10 GeV< m_W < 130 GeV, the actual upper limit depending from the
choice of the astrophysical parameters, while the lowest values of the
explorable WIMP-nucleon elastic cross-sections fall in most cases within one
order of magnitude of the sensitivities of present direct detection WIMP
searches.Comment: 24 pages, ReVTeX, 9 figures, submitted to Astroparticle Physic
Higher order corrections to primordial spectra from cosmological inflation
We calculate power spectra of cosmological perturbations at high accuracy for
two classes of inflation models. We classify the models according to the
behaviour of the Hubble distance during inflation. Our approximation works if
the Hubble distance can be approximated either to be a constant or to grow
linearly with cosmic time. Many popular inflationary models can be described in
this way, e.g., chaotic inflation with a monomial potential, power-law
inflation and inflation at a maximum. Our scheme of approximation does not rely
on a slow-roll expansion. Thus we can make accurate predictions for some of the
models with large slow-roll parameters.Comment: 13 pages, 1 figure; section on consistency relations of inflation
added; accepted by Physics Letters
Nasca Lines: A Mystery wrapped in an Enigma
We analyze the geometrical structure of the astonishing Nasca geoglyphs in
terms of their fractal dimension with the idea of dating these manifestations
of human cultural engagements in relation to one another. Our findings suggest
that the first delineated images consist of straight, parallel lines and that
having sophisticated their abilities, Nasca artist moved on to the design of
more complex structures.Comment: 6 pages, 1 color figure and 2 graphs. To appear in Chao
Role of toxin activation on binding and pore formation activity of the Bacillus thuringiensis Cry3 toxins in membranes of Leptinotarsa decemlineata (Say)
AbstractBinding and pore formation constitute key steps in the mode of action of Bacillus thuringiensis δ-endotoxins.In this work, we present a comparative analysis of toxin-binding capacities of proteolytically processed Cry3A, Cry3B and Cry3C toxins to brush border membranes (BBMV) of the Colorado potato beetle Leptinotarsa decemlineata (CPB), a major potato coleopteran-insect pest. Competition experiments showed that the three Cry3 proteolytically activated toxins share a common binding site. Also heterologous competition experiments showed that Cry3Aa and Cry3Ca toxins have an extra binding site that is not shared with Cry3Ba toxin. The pore formation activity of the three different Cry3 toxins is analysed. High pore-formation activities were observed in Cry3 toxins obtained by proteolytical activation with CPB BBMV in contrast to toxins activated with either trypsin or chymotrypsin proteases. The pore-formation activity correlated with the formation of soluble oligomeric structures. Our data support that, similarly to the Cry1A toxins, the Cry3 oligomer is formed after receptor binding and before membrane insertion, forming a pre-pore structure that is insertion-competent
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