Search results for "BAND"
showing 10 items of 2610 documents
Topological Devil's staircase in atomic two-leg ladders
2019
Abstract We show that a hierarchy of topological phases in one dimension—a topological Devil’s staircase—can emerge at fractional filling fractions in interacting systems, whose single-particle band structure describes a topological or a crystalline topological insulator. Focusing on a specific example in the BDI class, we present a field-theoretical argument based on bosonization that indicates how the system, as a function of the filling fraction, hosts a series of density waves. Subsequently, based on a numerical investigation of the low-lying energy spectrum, Wilczek–Zee phases, and entanglement spectra, we show that they are symmetry protected topological phases. In sharp contrast to t…
Effects of Carbon-sp3 Bridging on the Electronic Properties of Oligothiophenes
1999
Abstract The electronic properties of rigidified, carbon sp 3 -bridged bithiophenes and terthiophenes have been investigated using density functional theory calculations, sp 3 Bridging has no effect on the bandgap other than that associated to the planarization of the system. Rigidification significantly improves the ability of oligothiophenes as electron donors but diminishes their electron accepting capacity. Grafting of substituents at the sp 3 bridging carbon slightly modifies the electronic properties.
L-Band Vegetation optical depth and effective scattering albedo estimation from SMAP
2017
Abstract Over land the vegetation canopy affects the microwave brightness temperature by emission, scattering and attenuation of surface soil emission. Attenuation, as represented by vegetation optical depth (VOD), is a potentially useful ecological indicator. The NASA Soil Moisture Active Passive (SMAP) mission carries significant potential for VOD estimates because of its radio frequency interference mitigation efforts and because the L-band signal penetrates deeper into the vegetation canopy than the higher frequency bands used for many previous VOD retrievals. In this study, we apply the multi-temporal dual-channel retrieval algorithm (MT-DCA) to derive global VOD, soil moisture, and ef…
Roughness and vegetation parameterizations at L-band for soil moisture retrievals over a vineyard field
2015
Abstract The capability of L-band radiometry to monitor surface soil moisture (SM) at global scale has been analyzed in numerous studies, mostly in the framework of the ESA SMOS and NASA SMAP missions. To retrieve SM from L-band radiometric observations, two significant effects have to be accounted for, namely soil roughness and vegetation optical depth. In this study, soil roughness effects on retrieved SM values were evaluated using brightness temperatures acquired by the L-band ELBARA-II radiometer, over a vineyard field at the Valencia Anchor Station (VAS) site during the year 2013. Different combinations of the values of the model parameters used to account for soil roughness effects (…
A generalized soil-adjusted vegetation index
2002
Operational monitoring of vegetative cover by remote sensing currently involves the utilisation of vegetation indices (VIs), most of them being functions of the reflectance in red (R) and near-infrared (NIR) spectral bands. A generalized soil-adjusted vegetation index (GESAVI), theoretically based on a simple vegetation canopy model, is introduced. It is defined in terms of the soil line parameters (A and B) as: GESAVI=(NIRBRA)/(R+Z), where Z is related to the red reflectance at the cross point between the soil line and vegetation isolines. As Z is a soil adjustment coefficient, this new index can be considered as belonging to the SAVI family. In order to analyze the GESAVI sensitivity to s…
Nonlinear pressure dependence of the direct band gap in adamantine ordered-vacancy compounds
2010
A strong nonlinear pressure dependence of the optical absorption edge has been measured in defect chalcopyrites CdGa{sub 2}Se{sub 4} and HgGa{sub 2}Se{sub 4}. The behavior is due to the nonlinear pressure dependence of the direct band-gap energy in these compounds as confirmed by ab initio calculations. Our calculations for CdGa{sub 2}Se{sub 4}, HgGa{sub 2}Se{sub 4} and monoclinic {beta}-Ga{sub 2}Se{sub 3} provide evidence that the nonlinear pressure dependence of the direct band-gap energy is a general feature of adamantine ordered-vacancy compounds irrespective of their composition and crystalline structure. The nonlinear behavior is due to a conduction band anticrossing at the {Gamma} po…
Phoxonic Hybrid Superlattice
2015
We studied experimentally and theoretically the direction-dependent elastic and electromagnetic wave propagation in a supported film of hybrid PMMA (poly[methyl-methacrylate])-TiO2 superlattice (SL). In the direction normal to the layers, this one-dimensional periodic structure opens propagation band gaps for both hypersonic (GHz) phonons and near-UV photons. The high mismatch of elastic and optical impedance results in a large dual phoxonic band gap. The presence of defects inherent to the spin-coating fabrication technique is sensitively manifested in the band gap region. Utilizing Brillouin light scattering, phonon propagation along the layers was observed to be distinctly different from…
Personalized multimedia touristic services for hybrid broadcast/broadband mobile receivers
2010
This paper presents the topology of a multimedia tourism service that targets mobile devices equipped with broadband and either multicast or broadcast access capabilities. Multicast / Broadcast access is used to handle the delivery of multimedia data to many simultaneous users in the service area. The solution adopted is based on existing standards for mobile TV services, but introducing features that enable the provision of generic multimedia services on top of mobile hybrid broadband and broadcast networks. Furthermore, this paper shows how to use standardized interfaces originally defined for interactive mobile TV broadcasting to build personalized mobile multimedia services that do not …
Scanning electron microscopy characterization of ZnSe single crystals grown by solid-phase recrystallization
2000
ZnSe single crystals were grown from n-type microcrystalline boules by a Solid Phase Recrystallization (SPR) method. The recrystallizations were performed under different atmospheres, Ar or Se, and pressures to investigate the influence of growth conditions on the structural features of the resulting crystals. The samples were mechanically and mechano-chemically polished in a bromine methanol solution and, then, etched in HCl for a short time, before characterization. The homogeneity and the nature of defects in the crystals were studied by Cathodoluminescence (CL) in the scanning electron microscope (SEM). CL measurements show the existence of slip bands in the recrystallized samples, like…
A first-principles DFT study of UN bulk and (001) surface: comparative LCAO and PW calculations.
2008
LCAO and PW DFT calculations of the lattice constant, bulk modulus, cohesive energy, charge distribu- tion, band structure, and DOS for UN single crystal are analyzed. It is demonstrated that a choice of the uranium atom relativistic effective core potentials considerably affects the band structure and magnetic structure at low tem- peratures. All calculations indicate mixed metallic-covalent chemical bonding in UN crystal with U5f states near the Fermi level. On the basis of the experience accumulated in UN bulk simulations, we compare the atomic and elec- tronic structure as well as the formation energy for UN(001) surface calculated on slabs of different thickness using both DFT approach…