Search results for " GAP"
showing 10 items of 811 documents
EFFECTS OF DATA GAP ON THE CAPABILITY TO DETECT TREND IN HYDROCLIMATOLOGICAL TIME SERIES
2012
In the last decades the growing concerns about the existence of global climatic changes push many researchers to use different trend test in order to identify whether monotonic trends exist in hydroclimatological time series such as temperature, precipitation, and streamflow. Unfortunately, these time series often suffer from missing data values mainly due to malfunctioning of gauge for specific time periods. Starting from this premise, the main target of our work is to investigate the effect of data gap in a time series on the results provided by the most used trend test: the nonparametric Mann–Kendall statistical test. Firstly, different synthetic time series characterized by different si…
Probing the electronic states of high-TMR off-stoichiometric Co2MnSi thin films by hard x-ray photoelectron spectroscopy
2014
The tunnel magnetoresistance ratio (TMR) of fully epitaxial magnetic tunnel junctions with an off-stoichiometric Co${}_{2}$MnSi Heusler alloy has been shown to exhibit a systematic dependence on Mn content, reaching 1135% at 4.2 K for Co${}_{2}$Mn${}_{1.29}$Si. In this paper, we explain the behavior of the observed TMR ratio using ab initio calculations and hard x-ray photoelectron spectroscopy (HAXPES). For the Mn-deficient samples, we show that the the drop of the TMR is caused by Co antisite atoms, which impose extra states into the minority-spin band gap. On the other hand, Mn-excess composition shows nearly half-metallic behavior. This result can be intuitively understood since both Co…
Los canecillos de la Capilla del Cementerio de San Juan del Hospital de Valencia
2020
In the medieval cemetery of the Historic Site of San Juan del Hospital of Valencia is housed a small funeral chapel founded in the late thirteenth century by the knight Arnau de Romaní. Along its cornice there are a series of heads of animals and humans that are one of the few sculptural vestiges inserted into the Romanesque iconographic tradition that are preserved in the city. So far they have not aroused the interest of specialists and no one has dedicated a detailed study to these curious and interesting images located in the marginal spaces of such a beautiful building. This article aims to complete this gap addressing the study of the corbels of the small temple, projecting a thematic…
Electronic and optical properties of CeO 2 from first principles calculations
2016
International audience; First-principles calculations of the electronic structure of CeO2 nanoparticles (NPs) were performed to investigate published experimental data obtained by different spectroscopies. The main features of the valence and conduction bands have been analyzed from the total and partial density of states. Several functionals were applied to interpret and quantify the optical properties, including the dielectric function, extinction coefficient and refractive index. It is found that the on-site hybrid functional B3PW91 modelled most suitably the band gap region of CeO2 NPs and consequently gave a more accurate band gap value. It also agreed very well with the experimental v…
A Theoretical Study on the Low-Lying Excited States of 2,2′:5′,2′′-Terthiophene and 2,2′:5′,2′′:5′′,2′′′-Quaterthiophene
2005
The nature and properties of the low-lying singlet and triplet valence excited states of 2,2':5',2-terthiophene (terthiophene) and 2,2':5',2:5,2'-quictterthiophene (tetrdthiophene) are discussed on the basis of high-level ab initio. computations. The spectrascopic features determined experimentally for short α-oligothiophenes are rationalised on theoretical grounds. Special attention is devoted to the nonradiative decay process through intersystem crossing (ISC) from the singlet to the triplet manifold, which is known to be relatively less efficient in tetrathiophene. Along the geometry relaxation of the S 1 state of terthiophene, the S' 1 and T 2 states become degenerate, which leads. to a…
VEH electronic structure of Si60
1993
Abstract We present a valence effective Hamiltonian (VEH) theoretical investigation on the electronic structure of Si60. The VEH one-electron energy level distribution calculated for Si60 is used to predict the ionization potential (7.86 eV), electron affinity (6.62 eV) and HOMO-LUMO energy gap (1.24 eV) of Si60. We also report the first allowed electronic transitions of Si60. The results are compared with other theoretical levels and with those calculated for C60.
Pressure Dependence of the Band Gaps and Charge Densities in Si
1994
The empirical local and nonlocal pseudopotentials of Si which can describe the electronic energy structure over a wide energy range of more than 20 eV from the bottom of the valence band is determined for different pressures. The nonlocality of the potential is described by the Gaussian model. The predictions for the linear and quadratic pressure coefficients are consistent with the experiment. The valence charge densities of Si under high pressure are studied. The forbidden X-ray factor F(222) is very stable under pressure and changes by less than 3% under volume changes of the order of 5%.
First-principles calculations of surfaceHcenters inBaF2
2010
H center, a hole trapped at an interstitial anion site, placed on the 111 surface of Barium fluoride BaF2 has been studied by using density functional theory DFT with hybrid exchange potentials, namely, DFT-B3PW. Two different configurations of surface H center are investigated carefully. Both surface H-center systems have strong relaxations because of the surface effect. In the configuration that the interstitial fluorine atom is within the surface, named case 1 in this paper, the unpaired electron is almost equally distributed onto the two atoms of the H center, which is quite different from the bulk H-center case. The other configuration with one of the F atoms of the H center located ab…
Electronic properties of poly(pyrrylene vinylenes): a theoretical approach
1993
Abstract We present a theoretical investigation of the electronic properties of poly(pyrrylene vinylene) and its methyl and methoxy derivatives by using the valence effective Hamiltonian (VEH) method. Theoretical calculations predict that the electronic properties of poly(pyrrylene vinylene) remain almost unaffected upon methyl substitution, while a noticeable lowering of ∼0.4 eV is obtained for the ionization potential and energy gap upon methoxy substitution. The VEH trends are in quantitative agreement with experimental data reported for poly(thienylene vinylene) derivatives.
Ground state properties of SmB6
2002
Abstract We have studied the ground state properties of the intermediate valence narrow-gap semiconductor SmB 6 by means of point-contact (PC) spectroscopy and specific heat measurements. The density of states derived from PC tunneling spectra could be decomposed into two energy-dependent parts with E g =21 meV and E d =4.5 meV wide gaps, and a finite residual density of states at the Fermi level. The specific heat of SmB 6 is enhanced below about 2 K, more pronounced for the sample with less impurities. This behavior can be attributed to the formation of a coherent state within the residual density of states in the energy gap.