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1

Behavior of molecules on interstellar grains - Application of the Langevin equation and iterative extended Hueckel  

Science.gov (United States)

The Langevin equation was used to explore an adsorbate desorption mechanism. Calculations were performed using iterative extended Hueckel on a silica model site with various small adsorbates, e.g., H, CH, OH, NO, CO. It was found that barriers to free traversal from one site to another are substantial (about 3-10 eV). A bootstrap desorption mechanism for some molecules in the process of forming at a site also became apparent from the calculations. The desorption mechanisms appear to be somewhat balanced by a counterforce - the attraction of sites for the newly desorbed molecule. The order of attraction to a silica grain site for the diatomic molecules considered was OH greater than CH greater than CO greater than NO, when these entities were sufficiently distant. The nature of the silica grain and that of the 'cold' desorption mechanism, when considered together, suggest that the abundance of very small grains might be less common than anticipated.

Aronowitz, S.; Chang, S.

1980-01-01

2

Theoretical calculation of band structure and superconductivity under pressure  

International Nuclear Information System (INIS)

We present a brief review of a theoretical calculation of band structure and superconducting transition temperature (Tc) in the high pressure phases of 5B group elements such as phosphorus (P), arsenic (As). We also report the calculations done on the transition metal zirconium (Zr) in the high pressure bcc phase and transition metal carbide NbC. The effect of pressure on the band structure is obtained by means of the linear muffin-tin orbital method. The superconducting transition temperature (Tc) is calculated using either McMillan or Allen-Dyne's formula. The calculated values of Tc are compared with the available experimental data. (author). 29 refs., 6 tabs

1993-01-01

3

Hueckel model for metal clusters: Ground states and low energy isomers  

Energy Technology Data Exchange (ETDEWEB)

Hueckel model with one [ital s]-electron per atom is used to study the geometries and electronic structures of clusters of 9 to 22 atoms. Two different optimization schemes for obtaining the ground states are used; (i) minimization of an approximate Hueckel ground state energy starting from a random geometry and (ii) simulated annealing. Both methods give similar and new ground state geometries for clusters with 10 to 14 atoms. All clusters with more than 10 atoms will be distorted if the bond distance is allowed to vary [plus minus]5.5%. The ground states of clusters with atoms 10, 11, 12, and 14 are found to have the [ital N]=9 cluster as the basic building block, whereas the [ital N]=13 cluster is a distorted cuboctahedron. As a general trend, the deformation of clusters increases from atom number 8 to 14 and shrinks again from 15 to 20 atoms, in accordance with jellium model results.

Yoshida, A. (Niels Bohr Institute, Blegdamsvej 17, DK-2100 Copenhagen (Denmark) Department of Physics, University of Virginia, Charlottesville, Virginia 22901 (United States)); Dossing, T. (Niels Bohr Institute, Blegdamsvej 17, DK-2100 Copenhagen (Denmark) Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)); Manninen, M. (Niels Bohr Institute, Blegdamsvej 17, DK-2100 Copenhagen (Denmark) Department of Physics, University of Jyvaeskylae, P.O. Box 35, FIN-40351 Jyvaeskylae (Finland))

1994-08-15

4

Neutrino flux calculations for the AGS narrow band beam  

International Nuclear Information System (INIS)

Presented are results of calculations of nu/sub ?/ fluxes in the AGS neutrino beam with the new dichromatic horn. The wide band beam nu/sub ?/, as well as the nu/sub e/ backgrounds, are discussed. The nu/sub e//nu/sub ?/ ratio is about 8 x 10-3. The possible sources and magnitudes of uncertainties are discussed. Finally, the calculated fluxes are compared with beam measurements

1987-02-05

5

First-principles electronic-band calculations on organic conductors  

Directory of Open Access Journals (Sweden)

Full Text Available Predicting electronic-band structures is a key issue in understanding the properties of materials or in materials design. In this review article, application examples of first-principles calculations, which are not based on adjustable empirical parameters, to study electronic structures of organic conductors are described.

Shoji Ishibashi

2009-01-01

6

Elementary energy bands in band structure calculations of some wide-bandgap crystals  

Energy Technology Data Exchange (ETDEWEB)

Semiconducting Tl{sub 3}AsS{sub 4} crystal was chosen as an example to show that its valence band is composed of the elementary energy bands. Their topology and symmetry obtained in the empty-lattice approximation is confirmed by ab initio band structure calculations. It was shown that these elementary energy bands correspond to the Wyckoff position c in a unit cell. Earlier predictions that the largest electron density distribution is focused in the vicinity of this position, similarly to the case of YAlO{sub 3} and SbSI crystals, is confirmed. A conclusion on the common topology and symmetry of the elementary energy bands in electronic and phonon spectra is presented. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Sznajder, M. [Institute of Physics, University of Rzeszow, Rejtana 16a, 35-310 Rzeszow (Poland); Bercha, D.M. [Institute of Physics, University of Rzeszow, Rejtana 16a, 35-310 Rzeszow (Poland); Institute of Physics and Chemistry of Solid State, Uzhgorod National University, 54 Voloshin Str. 88000 Uzhgorod (Ukraine); Rushchanskii, K.Z. [Institute of Physics and Chemistry of Solid State, Uzhgorod National University, 54 Voloshin Str. 88000 Uzhgorod (Ukraine)

2004-01-01

7

Nonlocal pseudopotentials in complex band-structure and photoemission calculations  

Energy Technology Data Exchange (ETDEWEB)

Based on a recently proposed localization procedure, a nonlocal pseudopotential scheme is derived to calculate potential coefficients V{sub {rvec G}{rvec G}{sup {prime}}}({rvec k}) which can be decomposed into terms, each being quadratic in {rvec k} and multiplied by a function of ({rvec G}{minus}{rvec G}{sup {prime}}), thus making them applicable to some important cases where local potential coefficients are required. Electronic structure calculations for semiconductors are in agreement with well-known semiempirical local pseudopotential band structures, as shown for GaAs. Nevertheless, the potential may significantly deviate from the semiempirical results. In order to test wave functions and transition probabilities, we prove the success of the procedure in a more troublesome case, i.e., applying it to a transition-metal compound as the experimentally well-investigated layered crystal TiSe{sub 2}, which up to now was not treated with a pseudopotential. Photoemission spectra within the one-step model are presented using Pendry`s method of complex band-structure calculation. The latter formalism had to be slightly generalized for the quasilocal properties of the potential. The agreement of the spectra with experimental data shows this method to be a reliable and practical tool to use nonlocal pseudopotentials for conduction-band wave functions of electron spectroscopies. {copyright} {ital 1997} {ital The American Physical Society}

Boedicker, A.; Schattke, W. [Institut fuer Theoretische Physik, Leibnizstrae 15, D-24118 Kiel (Germany)

1997-02-01

8

Nonlocal pseudopotentials in complex band-structure and photoemission calculations  

International Nuclear Information System (INIS)

Based on a recently proposed localization procedure, a nonlocal pseudopotential scheme is derived to calculate potential coefficients Vrvec Grvec G'(rvec k) which can be decomposed into terms, each being quadratic in rvec k and multiplied by a function of (rvec G-rvec G'), thus making them applicable to some important cases where local potential coefficients are required. Electronic structure calculations for semiconductors are in agreement with well-known semiempirical local pseudopotential band structures, as shown for GaAs. Nevertheless, the potential may significantly deviate from the semiempirical results. In order to test wave functions and transition probabilities, we prove the success of the procedure in a more troublesome case, i.e., applying it to a transition-metal compound as the experimentally well-investigated layered crystal TiSe2, which up to now was not treated with a pseudopotential. Photoemission spectra within the one-step model are presented using Pendry's method of complex band-structure calculation. The latter formalism had to be slightly generalized for the quasilocal properties of the potential. The agreement of the spectra with experimental data shows this method to be a reliable and practical tool to use nonlocal pseudopotentials for conduction-band wave functions of electron spectroscopies. copyright 1997 The American Physical Society

1997-02-01

9

Hueckel versus Moebius aromaticity: The particle in a cylinder versus a Moebius strip  

International Nuclear Information System (INIS)

The one-particle-constrained-to-a-Moebius-strip model is studied quantum mechanically. The results are used to account for the chemical concept of Moebius aromaticity. In addition, the one-particle-in-a-cylinder model is used to explain the Hueckel aromaticity. Using the principles of quantum mechanics and applying the appropriate boundary conditions, the 4N + 2 and 4N electrons aromaticity rules are confirmed for these two types of aromaticity. A numerical technique for obtaining an exact solution of the Schroedinger equation of the Moebius model is also suggested.

2010-12-01

10

Perturbation expansion of the ground-state energy for the one-dimensional cyclic Hubbard system in the Hueckel limit  

International Nuclear Information System (INIS)

The perturbation expansion coefficients for the ground-state energy of the half-filled one-dimensional Hubbard model with N = 4? + 2, (? = 1,2,...) sites and satisfying cyclic boundary conditions were calculated in the Hueckel limit (U/? ? 0), where ? designates the one-electron hopping or resonance integral, and U, the two-electron on-site Coulomb integral. This was achieved by solving-order by order-the Lieb-Wu equations, a system of transcendental equations that determines the set of quasi-momenta (ki) and spin variable ?? for this model. The exact values for these quantities were found for the N = 6 member ring up to the 20th order in terms of the coupling constant B = U/2?, as well as numerically for 10 ? N ? 50, and the N = 6 Lieb-Wu system was reduced to a system of sextic algebraic equations. These results are compared with those of the infinite system derived analytically by Misurkin and Ovchinnikov. It is further shown how the results of this article can be used for the interpolation by the root of a polynomial. It is demonstrated that a polynomial of relatively small degree provides a very good approximation for the energy in the intermediate coupling region. 20 refs., 3 tabs

1995-03-05

11

Emission bands of phosphorus and calculation of band structure of rare earth phosphides  

International Nuclear Information System (INIS)

The method of x-ray emission spectroscopy has been used to investigate the electronic structure of monophosphides of rare-earth metals (REM). The fluorescence K bands of phosphorus have been obtained in LaP, PrP, SmP, GdP, TbP, DyP, HoP, ErP, TmP, YbP, and LuP and also the Lsub(2,3) bands of phosphorus in ErP, TmP, YbP, and LuP. Using the Green function technique involving the muffin-tin potential, the energy spectrum for ErP has been calculated in the single-electron approximation. The hystogram of electronic state distribution N(E) is compared with the experimental K and Lsub(2,3) bands of phosphorus in ErP. The agreement between the main details of N(E) and that of x-ray spectra allows to state that the model used provides a good description of the electron density distribution in crystals of REM monophosphides. In accordance with the character of the N(E) distribution the compounds under study are classified as semimetals or semiconductors with a very narrow forbidden band

1977-01-01

12

Photonic band-structure calculations using the boundary element method  

Science.gov (United States)

A boundary element method is developed for calculating the photon modes of periodic structures whose unit cells consist of piecewise homogeneous dielectric materials of arbitrary shapes. Green's function techniques are used to derive integral equations for these structures. These equations involve integrals over the boundaries between the regions, which are discretized and solved numerically. Thus the full set of Maxwell's equations with boundary conditions in d independent variables is changed into an integral equation in d-1 variables. We calculate the mode frequencies and field patterns for wave vectors throughout the Brillouin zone, thus allowing the determination of photonic band gaps. We show that this method generally provides improved calculational efficiency as compared to alternative approaches, and that it is more effective in treating high-frequency modes. Previously we have discussed this approach for electronic states in nanostructuresfootnote P. A. Knipp and T. L. Reinecke, Phys. Rev. B 54, 1880 (1996). and for photonic modes in waveguides. Here we extend this technique for photonic modes in periodic structures. Illustrative examples are given here for several two-dimensional systems.

Knipp, P. A.; Reinecke, T. L.

1997-03-01

13

Electronic band structure calculations of bismuth-antimony nanowires  

Science.gov (United States)

Alloys of bismuth and antimony received initial interest due to their unmatched low-temperature thermoelectric performance, and have drawn more recent attention as the first 3D topological insulators. One-dimensional bismuth-antimony (BiSb) nanowires display interesting quantum confinement effects, and are expected to exhibit even better thermoelectric properties than bulk BiSb. Due to the small, anisotropic carrier effective masses, the electronic properties of BiSb nanowires show great sensitivity to nanowire diameter, crystalline orientation, and alloy composition. We develop a theoretical model for calculating the band structure of BiSb nanowires. For a given crystalline orientation, BiSb nanowires can be in the semimetallic, direct semiconducting, or indirect semiconducting phase, depending on nanowire diameter and alloy composition. These ``phase diagrams'' turn out to be remarkably similar among the different orientations, which is surprising in light of the anisotropy of the bulk BiSb Fermi surface. We predict a novel direct semiconducting phase for nanowires with diameter less than ˜15 nm, over a narrow composition range. We also find that, in contrast to the bulk and thin film BiSb cases, a gapless state with Dirac dispersion cannot be realized in BiSb nanowires.

Levin, Andrei; Dresselhaus, Mildred

2012-02-01

14

Energy band calculation of amorphous indium tin oxide films on polyethylene terephthalate substrate with indirect transition  

International Nuclear Information System (INIS)

Amorphous indium tin oxide films were grown on a polyethylene terephthalate substrate by RF-magnetron sputtering. The energy band, which contained not only the width of the optical band but also detailed information about the Fermi level (Ef) and mobility edge (Ec'), was calculated according to the theory of amorphous semiconductors with the experimental parameters of transmittance and electrical conductivity. Furthermore, the calculated energy band can be used to effectively explain both the variation of electrical conductivity and the weak absorption at the wavelength range of 750-800 nm in our experiment. An indirect transition was also clearly observed in our samples during the calculation of the optical energy band.

2009-01-21

15

IBM-2 calculation of band mixing in {sup 132}Ba  

Energy Technology Data Exchange (ETDEWEB)

The band crossing in {sup 132}Ba has been investigated by using the interacting boson model. A broken neutron pair has been coupled to a collective boson core. The boson-fermion interaction hamiltonian contains terms which can transform a boson into a pair of quasiparticles and vice versa. The parameters were partly determined by fitting the collective states of {sup 132,134}Ba and the yrast states of {sup 131}Ba. The energy backbending has been satisfactorily reproduced. Good agreement of the electromagnetic moments has been reached. The structure of the wave functions has been discussed. (author)

Gelberg, A.; Otsuka, T. [Tokyo Univ., Dept. of Physics, Tokyo (Japan); Yoshida, N. [Kansai Univ., Faculty of Informatics, Takatsuki, Osaka (Japan); Arima, A. [House of Councilors, Tokyo (Japan); Gade, A.; Dewald, A; Brentano, P. von [Institut fuer Kernphysik der Universitaet zu Koeln, Koeln (Germany)

2000-07-01

16

Metal-ceramic adhesion: Synthesis of aluminum and chromium mixed metal oxides and extended Hueckel modeling of metal-metal oxide interfaces  

Energy Technology Data Exchange (ETDEWEB)

Methods of chemical synthesis and theoretical calculation was used to form new materials that have improved adhesion of a thin metal film to a ceramic. Two goals of this investigation were to develop new synthesis of metal-ceramic couples with improved adhesion between the two components and a fundamental understanding of the chemical factors that affect adhesion. Extended Hueckel calculations were performed on a series of Pt- and NiPt-NiO metal-ceramic couples to examine bonding. The calculations showed an 5 fold increase in adhesion energy in NiPt-NiO over Pt-NiO. Bonding across the interface is found to decrease with increased electron donation as interfacially antibonding orbitals are filled. The synthesis of (Al[sub 1[minus]x]Cr[sub x])[sub 2]O[sub 3] mixed metal oxide powders and coatings by sol-gel methodology utilizing three chromium precursors is reported. Thus, Al[Cr(CO)[sub 3]C[sub 5]H[sub 5

Boorse, R.S.

1993-01-01

17

Energy bands in graphene: Comparison between the tight-binding model and ab initio calculations  

Science.gov (United States)

We compare the classification of the electron bands in graphene, obtained by group theory algebra in the framework of a tight-binding model (TBM), with that calculated in a density-functional-theory (DFT) framework. Identification in the DFT band structure of all eight energy bands (four valence and four conduction bands) corresponding to the TBM-derived energy bands is performed and the corresponding analysis is presented. The four occupied (three ?-like and one ?-like) and three unoccupied (two ?-like and one ?-like) bands given by the DFT closely correspond to those predicted by the TBM, both by their symmetry and their dispersion law. However, the two lowest lying at the ?-point unoccupied bands (one of them of a ?-like type and the other of a ?-like one), are not of the TBM type. According to both their symmetry and the electron density these bands are plane waves orthogonal to the TBM valence bands; dispersion of these states can be determined unambiguously up to the Brillouin zone borders. On the other hand, the fourth unoccupied band given by the TBM can be identified among those given by the DFT band calculations; it is situated rather high with respect to energy. The interaction of this band with the free-electron states is so strong that it exists only in part of the k space.

Kogan, E.; Nazarov, V. U.; Silkin, V. M.; Kaveh, M.

2014-04-01

18

First-principle band calculation of ruthenium for various phases  

CERN Document Server

The total energies and the magnetic moments of Ru for HCP, BCC, FCC, BCT structures were calculated by using a first-principle full-potential linearized augmented plane-wave (FLAPW) method based on the generalized gradient approximation (GGA). HCP has the lowest energy among the structures calculated, which agrees with the experimental result that HCP is the equilibrium phase of Ru. The total energy of BCT Ru has the local minimum at c/a=sq root 2 (FCC) with a=5.13 au, c=7.25 au and c/a=0.83 with a=6.15 au, c=5.11 au. It is pointed out that these phases are possibly metastable. The BCC structure, which corresponds to BCT with a=c=5.78 au, is unstable because it is at a saddle point of the total energy. BCT Ru of c/a<1 has a magnetic moment at the stable volume.

Watanabe, S; Kai, T; Shiiki, K

2000-01-01

19

Calculation of band offsets at the CdS/SnS heterojunction  

Energy Technology Data Exchange (ETDEWEB)

SnS is a promising material for heterojunction solar cells, but the energy band alignment is not known for SnS-based heterojunctions. In this study, the energy band offset at the CdS/SnS heterojunction is calculated using the first principle, density-functional, pseudopotential method. A procedure analogous to that used in the core-level photoemission spectroscopy is adopted to calculate the band offset. The 4d core-level difference between Cd and Sn was estimated from the energy calculation of a superstructure consisting of zincblende CdS and rock-salt or zincblende SnS. The calculated valence-band offset is 0.1 eV when the rock-salt SnS is assumed and 0.84 eV when the zincblende SnS is assumed. (author)

Ichimura, Masaya [Department of Engineering Physics, Electronics and Mechanics, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555 (Japan)

2009-03-15

20

Energy band calculation of amorphous indium tin oxide films on polyethylene terephthalate substrate with indirect transition  

Energy Technology Data Exchange (ETDEWEB)

Amorphous indium tin oxide films were grown on a polyethylene terephthalate substrate by RF-magnetron sputtering. The energy band, which contained not only the width of the optical band but also detailed information about the Fermi level (E{sub f}) and mobility edge (E{sub c}'), was calculated according to the theory of amorphous semiconductors with the experimental parameters of transmittance and electrical conductivity. Furthermore, the calculated energy band can be used to effectively explain both the variation of electrical conductivity and the weak absorption at the wavelength range of 750-800 nm in our experiment. An indirect transition was also clearly observed in our samples during the calculation of the optical energy band.

Yin Xuesong; Tang Wu; Weng Xiaolong; Deng Longjiang, E-mail: tang@uestc.edu.c [State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054 (China)

2009-01-21

 
 
 
 
21

Calculations of ? and ?? band B(E2) transition probabilities within Triaxial Projected Shell Model  

International Nuclear Information System (INIS)

The Triaxial Projected Shell Model (TPSM) provides a unified microscopic description of rotational and multi-phonon vibrational states. We applied the TPSM model with its new capability to calculate B(E2) [1] values in the rare-earth region. The energies of the double-phonon states are reproduced. The calculated B(E2) values agree within an order of magnitude with the experimental ones. The calculations point to the identification of the new K=4+ band in 162Dy as a possible ??-band

2002-11-06

22

Band structure derived properties of HfO2 from first principles calculations  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electronic band structures and optical properties of cubic, tetragonal, and monoclinic phases of HfO2 are calculated using the first-principles linear augmented plane-wave method, within the density functional theory and generalized gradient approximation, and taking into account full-relativistic contributions. From the band structures, the electron- and hole-effective masses were obtained. Relativistic effects play an important role, which is reflected in the effective...

Garcia, Joelson Cott; Lino, A. T.; Scolfaro, L. M. R.; Leite, J. R.; Freire, V. N.; Farias, G. A.; Silva Jr, E. F. Da

2012-01-01

23

Band structure calculations of Cu(In1-xGax)Se2  

International Nuclear Information System (INIS)

First principles density calculations of the band structure, and density of states of the Cu(In1-xGax)Se2 in the chalcopyrite type structure have been carried out using the density functional theory. The relationship between the band gap and chemical composition in the structure is discussed. The effective masses of the electrons and holes in the different composition crystals are reported.

2010-10-25

24

Study of ZrCl by self-consistent band calculation  

Energy Technology Data Exchange (ETDEWEB)

A nonrelativistic self-consistent electronic band structure calculation has been performed on zirconium monochloride using the KKR method. The exchange potential was approximated by the X..cap alpha.. method. The compound contains homoatomic layers in the sequence Cl--Zr--Zr--Cl and has the characteristics of a graphite-like two-dimensional metal. A substantial charge transfer is found toward the metallic layers and away from the loosely bonded halogen layer. There is also significant admixture of Zr-d character within the filled Cl-3p bands. The total density of states is in good agreement with the valence band photoemission results.

Marchiando, J.F.

1979-07-01

25

Calculation of Energy Band Diagram of a Photoelectrochemical Water Splitting Cell  

CERN Document Server

A physical model is presented for a semiconductor electrode of a photoelectrochemical (PEC) cell, accounting for the potential drop in the Helmholtz layer. Hence both band edge pinning and unpinning are naturally included in our description. The model is based on the continuity equations for charge carriers and direct charge transfer from the energy bands to the electrolyte. A quantitative calculation of the position of the energy bands and the variation of the quasi-Fermi levels in the semiconductor with respect to the water reduction and oxidation potentials is presented. Calculated current-voltage curves are compared with established analytical models and measurement. Our model calculations are suitable to enhance understanding and improve properties of semiconductors for photoelectrochemical water splitting.

Cendula, P; Gimenez, S; Schmid, M; Bisquert, J; Graetzel, M; Schumacher, J O

2014-01-01

26

Dielectric band structure of crystals: General properties, and calculations for silicon  

International Nuclear Information System (INIS)

We shift the dielectric band structure method, orginially proposed by Baldereschi and Tosatti for the description of microscopic electronic screening in crystals. Some general properties are examined first, including the requirements of causality and stability. The specific test case of silicon is then considered. Dielectric bands are calculated, according to several different prescriptions for the construction of the dielectric matrix. It is shown that the results allow a very direct appraisal of the screening properties of the system, as well as of the quality of the dielectric model adopted. The electronic charge displacement induced by ?sub(25') and X_3 phonon-like displacements of the atoms is also calculated and compared with the results of existent full self-consistent calculations. Conclusions are drawn on the relative accuracies of the dielectric band structures. (author)

1981-01-01

27

Debye-Hueckel solution for steady electro-osmotic flow of a micropolar fluid in a cylindrical microcapillary  

CERN Document Server

Analytic expressions for the speed, flux, microrotation, stress, and couple stress in a micropolar fluid exhibiting steady, symmetric and one-dimensional electro-osmotic flow in a uniform cylindrical microcapillary were derived under the constraint of the Debye-Hueckel approximation, which is applicable when the cross-sectional radius of the microcapillary exceeds the Debye length, provided that the zeta potential is sufficiently small in magnitude. As the aciculate particles in a micropolar fluid can rotate without translation, micropolarity influences fluid speed, fluid flux, and one of the two non-zero components of the stress tensor. The axial speed in a micropolar fluid intensifies as the radius increases. The stress tensor is confined to the region near the wall of the microcapillary but the couple stress tensor is uniform across the cross-section.

Siddiqui, Abuzar A

2011-01-01

28

Electron momentum distribution in vanadium: Compton scattering measurements and band-structure calculation  

International Nuclear Information System (INIS)

The [100], [110], and [111] Compton profiles and reciprocal form factors have been derived from Compton scattering measurements made with 60-keV "2"4"1Am ? rays on single-crystal samples of vanadium. The same quantities have also been obtained theoretically on the basis of a self-consistent linear-muffin-tin-orbital band-structure calculation, using the local-density approximation for the exchange-correlation potential. An r-space procedure was adopted to calculate the reciprocal form factor B(r) directly from the wave functions. The experimental and theoretical results are compared with previous 412-keV Compton scattering measurements and other band-structure calculations. All calculations overestimate the Compton profile anisotropies at low momenta

1986-01-15

29

Volume and surface photoemission from tungsten. I. Calculation of band structure and emission spectra  

DEFF Research Database (Denmark)

The electronic energy-band structure of tungsten has been calculated by means of the relativistic-augmented-plane-wave method. A series of mutually related potentials are constructed by varying the electronic configuration and the amount of Slater exchange included. The best band structure is obtained from an ad hoc potential based on a Dirac-Slater atomic calculation for the ground-state configuration and with full Slater exchange in the atomic as well as in the crystal potential. The selection of this best potential is justified by comparing the calculated band structure to Fermi-surface experiments and to optical-reflectance measurements up to 5-eV photon energy. The temperature and strain responses in the band structure are estimated from band calculations with four different lattice constants. The band structure was determined in the entire Brillouin zone and is applied to a calculation of photoemission spectra from W single crystals. The nondirect as well as the direct models for bulk photoemission processes are investigated. The emission from the three low-index surfaces (100), (110), and (111) exhibits strong dependence on direction and acceptance cone. According to the present band model there should essentially be no emission normal to the (110) face for photon energies between 9.4 and 10.6 eV. Experimental observation of emission in this gap, however, implies effects not included in the simple bulk models. In particular, effects arising from surface emission have been considered, i.e., emission of those electrons which are excited in a single-step process from initial states near the surface to final states outside the crystal. The electrons that are emitted from the surface in directions perpendicular to the crystal planes carry information on the one-dimensional surface density of states. The present work includes a crude estimate of this surface density of states, which is derived from the bulk band structure by narrowing the d bands according to an effective number of neighbors per surface atom. Estimates of surface relaxation effects are also included.

1974-01-01

30

Electronegativity calculation of bulk modulus and band gap of ternary ZnO-based alloys  

International Nuclear Information System (INIS)

In this work, the bulk moduli and band gaps of MxZn1?xO (M = Be, Mg, Ca, Cd) alloys in the whole composition range were quantitatively calculated by using the electronegativity-related models for bulk modulus and band gap, respectively. We found that the change trends of bulk modulus and band gap with an increase of M concentration x are same for BexZn1?xO and CdxZn1?xO, while the change trends are reverse for MgxZn1?xO and CaxZn1?xO. It was revealed that the bulk modulus is related to the valence electron density of atoms whereas the band gap is strongly influenced by the detailed chemical bonding behaviors of constituent atoms. The current work provides us a useful guide to compositionally design advanced alloy materials with both good mechanical and optoelectronic properties.

2012-10-01

31

Carbon K -shell near-edge structure: Multiple scattering and band-theory calculations  

Energy Technology Data Exchange (ETDEWEB)

The carbon {ital K}-shell near-edge absorption fine structure of both diamond and graphite has been calculated by the multiple-scattering method and by a single-particle self-consistent pseudo-atomic-orbital band-theory method. We compare the results of these two calculations with experiment, and show that they both give agreement with the experimental near-edge structure.

Weng, X.; Rez, P. (Center for Solid State Science, Arizona State University, Tempe, Arizona 85287-1704 (US) Department of Physics, Arizona State University, Tempe, Arizona 85287-1504); Ma, H. (Center for Solid State Science, Arizona State University, Tempe, Arizona 85287-1704 Department of Chemistry, Arizona State University, Tempe, Arizona 85287-1604)

1989-08-15

32

XPS valence band spectra and theoretical calculations for investigations on thiogermanate and thiosilicate glasses  

International Nuclear Information System (INIS)

This paper reports on investigations of thiogermanate and thiosilicate crystals and glasses by means of XPS valence band spectra and theoretical calculations (FLAPW method). The calculations were achieved on three crystallized phases GeS2, Na2GeS3 and SiS2 and valence band spectra (visualization of the occupied electronic density of states) were precisely interpreted through modulated density of states and charge density maps. This information was used to go further in the structural investigations of some thiogermanate and thiosilicate glasses. In sodium thiogermanates, an increase in Ge-Ge bonds was revealed as the modifier content (Na2S) increases. In thiosilicates, the evolution of the valence spectra according to the nature of the alkaline atoms (Li, Na) has been interpreted as changes in the local connectivity of units (edge or corner sharing tetrahedra). This study exhibits the potentialities of valence band spectra to provide information on glassy systems

2006-04-21

33

SUBBAND STATES IN INVERSION LAYERS FROM SINGLE AND MULTIPLE BAND CALCULATIONS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Selfconsistent subband calculations for inversion layers on InSb and HgCdTe are performed using a single (2x2) and a multiple band (8x8) model. We obtain subband separations and Fermi energies that are independent of the models.

Malcher, F.; Ziegler, A.; Ro?ssler, U.; Lommer, G.

1987-01-01

34

Band structure calculations for dilute nitride quantum wells under compressive or tensile strain  

International Nuclear Information System (INIS)

We have calculated the band structure of InGaAsN/GaAs(N)/GaAs compressively strained quantum wells (QW) emitting at 1.3 ?m using the band anticrossing model and an eight-band kp Hamiltonian. The calculated interband optical transition energies have been compared to the experimental ones deduced from photocurrent, photoluminescence and excitation of photoluminescence spectroscopy experiments and measured laser characteristics extracted from the recent literature. Because of the high compressive strain in the QW, strain-compensated structures may be required in order to grow stable multiple QWs; in view of this we have studied the band structure of InGaAsN/GaAsP/GaAs QWs emitting at 1.3 ?m. Dilute nitride structures also offer the possibility of growing tensile strained QW lasers on InP substrate emitting in the 1.55 ?m emission wavelength range. In order to evaluate the potentialities of such structures we have determined the band characteristics of InGaAsN/InGaAsP/InP heterostructures with a TM polarized fundamental transition

2004-08-11

35

Calculation of isotopic profile during band displacement on ion exchange resins  

International Nuclear Information System (INIS)

A method has been developed to calculate the isotopic profile during band displacement on ion exchange resins using computer simulation. Persoz had utilized this technique earlier for calculating the isotopic profile during band displacement as well as frontal analysis. The present report deals with a simplification of the method used by Persoz by reducing the number of variables and making certain approximations where the separation factor is not far from unity. Calculations were made for the typical case of boron isotope separation. The results obtained by the modified method were found to be in very good agreement with those obtained by using an exact equation, at the same time requiring conside--rably less computer time. (author)

1981-01-01

36

Hartree-Fock and Hartree-Fock-Bogolyubov calculations of superdeformed bands  

Energy Technology Data Exchange (ETDEWEB)

Some original features are presented of the cranked mean-field derived with the Skyrme effective interaction. Results obtained with this method which concerns the questions raised by the existence of identical SD bands in the {sup 192}Hg region are discussed. In order to include pairing effects, one must replace cranked Hartree-Fock (HF) equations by cranked Hartree-Fock-Bogolyubov (HFB) equations. It is shown that a mean-field calculation can generate identical rotational bands in nuclei differing by one or two nucleons in either the Dy or the Hg regions. (K.A.) 27 refs., 5 figs., 1 tab.

Flocard, H.; Gall, B. [Paris-11 Univ., 91 - Orsay (France). Inst. de Physique Nucleaire; Chen, B.Q. [California Inst. of Tech., Pasadena, CA (United States). W.K. Kellogg Radiation Lab.; Dobaczewski, J. [Warsaw Univ. (Poland). Inst. Fizyki Teoretycznej; Heenen, P.H. [Universite Libre de Bruxelles (Belgium); Weiss, M.S. [Lawrence Livermore National Lab., CA (United States); Bonche, P.

1992-12-07

37

Hartree-Fock and Hartree-Fock-Bogolyubov calculations of superdeformed bands  

International Nuclear Information System (INIS)

Some original features are presented of the cranked mean-field derived with the Skyrme effective interaction. Results obtained with this method which concerns the questions raised by the existence of identical SD bands in the 192Hg region are discussed. In order to include pairing effects, one must replace cranked Hartree-Fock (HF) equations by cranked Hartree-Fock-Bogolyubov (HFB) equations. It is shown that a mean-field calculation can generate identical rotational bands in nuclei differing by one or two nucleons in either the Dy or the Hg regions. (K.A.) 27 refs., 5 figs., 1 tab

1992-10-26

38

Precision photonic band structure calculation of Abrikosov periodic lattice in type-II superconductors  

CERN Document Server

We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-II superconductors forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and obtaining the band structure from the permittivity, which depends on the above parameters and the frequency. This is while the characteristics of such crystals highly vary with an externally applied static normal magnetic field, leading to nonlinear behavior of the band structure, which also has nonlinear dependence on the temperature. The similar analysis for every arbitrary lattice structure is also possible to be developed by this approach as presented in this work. We also present some examples and discuss the results.

Kokabi, Alireza; Khorasani, Sina; Fardmanesh, Mehdi

2011-01-01

39

Precision photonic band structure calculation of Abrikosov periodic lattice in type-II superconductors  

International Nuclear Information System (INIS)

We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-II superconductors forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and obtaining the band structure from the permittivity, which depends on the above parameters and the frequency. This is while the characteristics of such crystals highly vary with an externally applied static normal magnetic field, leading to nonlinear behavior of the band structure, which also has nonlinear dependence on the temperature. The similar analysis for every arbitrary lattice structure is also possible to be developed by this approach as presented in this work. We also present some examples and discuss the results

2007-09-01

40

CdSe/CdTe interface band gaps and band offsets calculated using spin–orbit and self-energy corrections  

International Nuclear Information System (INIS)

We performed ab initio calculations of the electronic structures of bulk CdSe and CdTe, and their interface band alignments on the CdSe in-plane lattice parameters. For this, we employed the LDA-1/2 self-energy correction scheme to obtain corrected band gaps and band offsets. Our calculations include the spin–orbit effects for the bulk cases, which have shown to be of importance for the equilibrium systems and are possibly degraded in these strained semiconductors. Therefore, the SO showed reduced importance for the band alignment of this particular system. Moreover, the electronic structure calculated along the transition region across the CdSe/CdTe interface shows an interesting non-monotonic variation of the band gap in the range 0.8–1.8 eV, which may enhance the absorption of light for corresponding frequencies at the interface between these two materials in photovoltaic applications.

2012-09-20

 
 
 
 
41

Photonic band calculation in the form of $k(\\omega)$ including evanescent waves  

CERN Multimedia

We give a general method to calculate photonic band structure in the form of wave number $k$ as a function of frequency $\\omega$, which is required whenever we want to calculate signal intensity related with photonic band structure. This method is based on the fact that the elements of the coefficient matrix for the plane wave expansion of the Maxwell equations contain wave number up to the second order, which allows us to rewrite the original eigenvalue equation for $\\omega^2$ into that for wave number. This method is much better, especially for complex wave numbers, than the transfer matrix method of Pendry, which gives the eigenvalues in the form of exp$[ikd]$ . As a simplest example, we show a comparison of $\\omega(k)$ and $k(\\omega)$ for a model of intersecting square rods.

Cho, K; Bamba, M; Cho, Kikuo; Ushida, Jun; Bamba, Motoaki

2003-01-01

42

Tight binding electronic band structure calculation of achiral boron nitride single wall nanotubes  

International Nuclear Information System (INIS)

In this paper we report the Tight-Binding method, for the electronic structure calculations of achiral single wall Boron Nitride nanotubes. We have used the contribution of ? electron only to define the electronic band structure for the solid. The Zone-folding method is used for the Brillouin Zone definition. Calculation of tight binding model parameters is done by fitting them to available experimental results of two-dimensional hexagonal monolayers of Boron Nitride. It has been found that all the boron nitride nanotubes (both zigzag and armchair) are constant gap semiconductors with a band gap of 5.27eV. All zigzag BNNTs are found to be direct gap semiconductors while all armchair nanotubes are indirect gap semiconductors. (author)

2006-12-26

43

Efficient calculation of inelastic vibration signals in electron transport: Beyond the wide-band approximation  

DEFF Research Database (Denmark)

We extend the simple and efficient lowest order expansion (LOE) for inelastic electron tunneling spectroscopy (IETS) to include variations in the electronic structure on the scale of the vibration energies. This enables first-principles calculations of IETS line shapes for molecular junctions close to resonances and band edges. We demonstrate how this is relevant for the interpretation of experimental IETS using both a simple model and first-principles simulations.

Lu, Jing Tao; Christensen, Rasmus Bjerregaard

2014-01-01

44

Rigid muffin-tin calculations of superconducting parameters in d- and f-band metals  

International Nuclear Information System (INIS)

We present a brief review of calculations of superconducting parameters within the widely used rigid muffin-tin (RMT) approximation. The systems which are discussed are the Group V bcc transitional elements, transition-metal carbides and nitrides. Nb-based A15 compounds, hydrides and f-band metals. Where experimental information on ?_2(?)F(?) is available, we compare the first frequency moment, which is independent of the lattice vibrational spectrum, directly with the theoretical calculation to assess the accuracy of the RMT ansatz. The ability of the RMT approach to predict trends correctly is also surveyed. (orig.)

1982-06-30

45

Proper Generalized Decomposition applied to linear acoustic: A new tool for broad band calculation  

Science.gov (United States)

The calculation of the acoustic response of systems in frequency bands is becoming increasingly important in simulation-based engineering design. This is particularly true in medium-frequency bands, where the response is very sensitive to the frequency. Some standard techniques for addressing these problems present a frequency dependent formulation and may involve fixed-frequency calculations at many different frequencies. In this paper, we propose a new technique which combines the Variational Theory of Complex Rays (VTCR) with Proper Generalized Decomposition (PGD) and does not require the resolution of acoustic problems at many frequencies. In this approach, the VTCR is used to find an approximate solution of a medium-frequency acoustic problem using only a few degrees of freedom (DOFs). Then, PGD is used to find a representation of the approximate solution which is separated between two variables, the wave propagation direction and the frequency. A relevant numerical example is used to present the strategy and illustrate its applicability for frequency band calculations.

Barbarulo, Andrea; Ladevèze, Pierre; Riou, Hervé; Kovalevsky, Louis

2014-05-01

46

Electronegativity calculation of bulk modulus and band gap of ternary ZnO-based alloys  

Energy Technology Data Exchange (ETDEWEB)

In this work, the bulk moduli and band gaps of M{sub x}Zn{sub 1?x}O (M = Be, Mg, Ca, Cd) alloys in the whole composition range were quantitatively calculated by using the electronegativity-related models for bulk modulus and band gap, respectively. We found that the change trends of bulk modulus and band gap with an increase of M concentration x are same for Be{sub x}Zn{sub 1?x}O and Cd{sub x}Zn{sub 1?x}O, while the change trends are reverse for Mg{sub x}Zn{sub 1?x}O and Ca{sub x}Zn{sub 1?x}O. It was revealed that the bulk modulus is related to the valence electron density of atoms whereas the band gap is strongly influenced by the detailed chemical bonding behaviors of constituent atoms. The current work provides us a useful guide to compositionally design advanced alloy materials with both good mechanical and optoelectronic properties.

Li, Keyan; Kang, Congying [State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024 (China); Xue, Dongfeng, E-mail: dongfeng@ciac.jl.cn [State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024 (China); State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China)

2012-10-15

47

XPS valence band spectra and theoretical calculations for investigations on thiogermanate and thiosilicate glasses  

Energy Technology Data Exchange (ETDEWEB)

This paper reports on investigations of thiogermanate and thiosilicate crystals and glasses by means of XPS valence band spectra and theoretical calculations (FLAPW method). The calculations were achieved on three crystallized phases GeS{sub 2}, Na{sub 2}GeS{sub 3} and SiS{sub 2} and valence band spectra (visualization of the occupied electronic density of states) were precisely interpreted through modulated density of states and charge density maps. This information was used to go further in the structural investigations of some thiogermanate and thiosilicate glasses. In sodium thiogermanates, an increase in Ge-Ge bonds was revealed as the modifier content (Na{sub 2}S) increases. In thiosilicates, the evolution of the valence spectra according to the nature of the alkaline atoms (Li, Na) has been interpreted as changes in the local connectivity of units (edge or corner sharing tetrahedra). This study exhibits the potentialities of valence band spectra to provide information on glassy systems.

Foix, D. [Laboratoire de Chimie Theorique et Physicochimie Moleculaire, CNRS UMR 5624, LPCM/Helioparc PAU Pyrenees, 2 Avenue du President Angot, 64053 PAU Cedex 9 (France); Martinez, H. [Laboratoire de Chimie Theorique et Physicochimie Moleculaire, CNRS UMR 5624, LPCM/Helioparc PAU Pyrenees, 2 Avenue du President Angot, 64053 PAU Cedex 9 (France)], E-mail: herve.martinez@univ-pau.fr; Pradel, A. [Laboratoire de Physicochimie de la Matiere Condensee, UMR 5617, CC 3 Universite Montpellier II, 34095 Montpellier Cedex 5 (France); Ribes, M. [Laboratoire de Physicochimie de la Matiere Condensee, UMR 5617, CC 3 Universite Montpellier II, 34095 Montpellier Cedex 5 (France); Gonbeau, D. [Laboratoire de Chimie Theorique et Physicochimie Moleculaire, CNRS UMR 5624, LPCM/Helioparc PAU Pyrenees, 2 Avenue du President Angot, 64053 PAU Cedex 9 (France)], E-mail: danielle.gonbeau@univ-pau.fr

2006-04-21

48

Semiempirical method for calculating structure and band gap of semiconducting polymers  

International Nuclear Information System (INIS)

A semiempirical method that yields accurate band gaps and atomic positions in sp2-hybridized, organic, semiconducting polymers has been obtained. This method is a tight-binding calculation where most of the parameters are determined via an ab initio local density approximation method leaving only ?-? interactions to be adjusted empirically. Once fitted for one or two systems, the method can be applied to other similar systems without further adjustment. Accurate results have been demonstrated for a number of semiconducting polymers that contain C, S, N, and H. (c) 1999 American Institute of Physics

1999-12-08

49

Fast distributed phononic band-structure calculations through a GPU accelerated mixed-variational formulation  

CERN Document Server

In this paper we present a Graphical Processing Unit accelerated mixed variational formulation for fast phononic band-structure calculation of arbitrarily complex unit cells and report speed gains of a hundred fold over unoptimized serial cpu computations. To the author's knowledge this is the first application of gpu computing to a non-FE/FDTD bandstructure algorithm. The formulation is presented in a form which is applicable to 1-, 2-, and 3-D cases. However, in this paper we concentrate on optimizing the formulation within the paradigm of gpu computing, presenting results for 2-D unit cells. We describe the application of the formulation with a long term view towards highly efficient and massively distributed band-structure algorithms suitable for tackling optimization and inverse problems. We report that the accurate band-structure evaluation over the boundary of the Irreducible Brillouin Zone (IBZ) for the first 18 phononic branches of a complex 2-D unit cell (with 1132 different phases) can be achieved ...

Srivastava, Ankit

2013-01-01

50

From Metal Cluster to Metal Nanowire: A Topological Analysis of Electron Density and Band Structure Calculation  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract:We investigate a theoretical model of molecular metalwire constructed from linear polynuclear metal complexes. In particular we study the linear Crn metal complex and Cr molecular metalwire. The electron density distributions of the model nanowire and the linear Crn metal complexes, with n = 3, 5, and 7, are calculated by employing CRYSTAL98 package with topological analysis. The preliminary results indicate that the bonding types between any two neighboring Cr are all the same, namely the polarized open-shell interaction. The pattern of electron density distribution in metal complexes resembles that of the model Cr nanowire as the number of metal ions increases. The conductivity of the model Cr nanowire is also tested by performing the band structure calculation.

Yu Wang

2002-01-01

51

Band structure and optical properties of antimony-sulfobromide: density functional calculation  

Science.gov (United States)

The electronic structure, linear, and non-linear optical properties of ferroelectric-semiconductor SbSBr are investigated in the non-polar (paraelectric) and polar (ferroelectric) phase, using the density functional methods in the generalized gradient approximation. The electronic band structure obtained shows that SbSBr has an indirect forbidden gap of 2.16 and 2.21 eV in the paraelectric and ferroelectric phase, respectively. The linear photon-energy dependent dielectric functions and some optical functions, such as absorption and extinction coefficients, refractive index, energy-loss function, reflectivity, and optical conductivity in both phases and photon-energy dependent second-order susceptibilities in the ferroelectric phase are calculated. Moreover, some important optical parameters, such as the effective number of valence electrons and the effective optical dielectric constant, are calculated in both phases.

Akkus, Harun; Mamedov, Amirullah M.; Kazempour, Ali; Akbarzadeh, Hadi

2008-03-01

52

Fundamental characteristics of a new Hg3TeCl4 crystal obtained by means of the elementary energy bands concept based on AB INITIO band structure calculations  

International Nuclear Information System (INIS)

Ab initio band structure calculations of the orthorhombic Hg3TeCl4 crystals of the symmetry D2h15 were performed and the topology of its valence band was analyzed in the framework of the elementary energy bands concepts. The effective masses of charge carriers were estimated. It was demonstrated that the anisotropy of the effective mass tensor components does not coincide with the mechanical one of the Hg3TeCl4 crystal. A possible reason of this fact was proposed.

2009-01-01

53

Exact-exchange based quasiparticle energy calculations for the band gap, effective masses and deformation potentials of ScN  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The band gaps, longitudinal and transverse effective masses, and deformation potentials of ScN in the rock-salt structure have been calculated employing G0W0-quasiparticle calculations using exact-exchange Kohn-Sham density functional theory one-particle wavefunctions and energies as input. Our quasiparticle gaps support recent experimental observations that ScN has a much lower indirect band gap than previously thought. The results are analyzed in terms of the influence of ...

Qteish, Abdallah; Rinke, Patrick; Scheffler, Matthias; Neugebauer, Joerg

2006-01-01

54

Camel-back band-induced power factor enhancement of thermoelectric lead-tellurium from Boltzmann transport calculations  

Science.gov (United States)

Band structures of PbTe can be abnormally bended via dual-doping on both the cationic and anionic sites to form camel-back multivalley energy band structures near the band edge. As a result, additional carrier pockets and strong intervalley scattering of carriers are introduced. Boltzmann transport calculations indicate that their contradictory effects yield remarkably enhanced power factor due to the improved thermopower and almost unchanged electrical conductivity in low temperature and high carrier concentration ranges. These findings prove dual-doping-induced band bending as an effective approach to improve the thermoelectric properties of PbTe and other similar materials.

Wang, X. G.; Wang, L.; Liu, J.; Peng, L. M.

2014-03-01

55

First-Principles Band Calculations on Electronic Structures of Ag-Doped Rutile and Anatase TiO2  

International Nuclear Information System (INIS)

The electronic structures of Ag-doped rutile and anatase TiO2 are studied by first-principles band calculations based on density functional theory with the full-potential linearized-augmented-plane-wave method. New occupied bands are found between the band gaps of both Ag-doped rutile and anatase TiO2. The formation of these new bands can be explained mainly by their orbitals of Ag 4d states mixed with Ti 3d states and are supposed to contribute to their visible light absorption. (condensed matter: electronicstructure, electrical, magnetic, and opticalproperties)

2009-07-01

56

The use of bulk states to accelerate the band edge state calculation of a semiconductor quantum dot  

International Nuclear Information System (INIS)

We present a new technique to accelerate the convergence of the folded spectrum method in empirical pseudopotential band edge state calculations for colloidal quantum dots. We use bulk band states of the materials constituent of the quantum dot to construct initial vectors and a preconditioner. We apply these to accelerate the convergence of the folded spectrum method for the interior states at the top of the valence and the bottom of the conduction band. For large CdSe quantum dots, the number of iteration steps until convergence decreases by about a factor of 4 compared to previous calculations

2007-05-01

57

Linear combination of bulk bands method for large-scale electronic structure calculations on strained nanostructures  

International Nuclear Information System (INIS)

A open-quotes strained linear combination of bulk bandsclose quotes method is introduced for calculating the single-particle electronic states of strained, million-atom nanostructure systems, within an empirical pseudopotential Hamiltonian. This method expands the wave functions of a nanostructure (superlattice, wire, and dot) as linear combinations of bulk Bloch states of the constituent materials, over band indices n and wave vectors k. This allows one to use physical intuition in selecting the n and k that are most relevant for a given problem. This constitutes a useful approximation over the open-quotes direct diagonalizationclose quotes approach where the basis is complete (individual plane waves) but unintuitive. It also constitutes a dramatic improvement upon the k·p approach, where the continuum model Hamiltonian is used, losing the atomistic details of the system. For a pyramidal InAs quantum dot embedded in GaAs, we find electronic eigenenergies that are within 20 meV of the exact direct diagonalization calculation, while the speed of the current method is 100 endash 1000 times faster. The sublinear scaling of the current method with the size of the system enables one to calculate the atomistic electronic states of a million-atom system on a personal computer in about 10 h. Sufficient detail is provided in the formalism, so that the method can be promptly implemented. copyright 1999 The American Physical Society

1999-06-01

58

Band calculations of the GPA high-pressure effects on the heavy lanthanide metals  

International Nuclear Information System (INIS)

Jackson's group and Mito's group have performed the systematic studies for the GPa high-pressure effects on the magnetic properties of the heavy lanthanide elements. They found that the Curie temperatures decrease linearly with increasing pressure and the magnetic signals disappear at around 9.0 GPa for Gd, 7.5 GPa for Tb, 7.4 GPa for Dy and 11.0 GPa for Ho. With the Anderson's point of view, the results of our band calculation conclude that some part of the decreasing of the bulk magnetization of Gd by pressure is caused by the narrowing of the bandwidth of itinerant s, d hybridized conduction electrons and the broadening of the bandwidth of localized f-orbital electrons

2007-03-01

59

On optimizing Jacobi–Davidson method for calculating eigenvalues in low dimensional structures using eight band k · p model  

International Nuclear Information System (INIS)

The paper presents two ways of improving the Jacobi–Davidson method for calculating the eigenvalues and eigenvectors described by eight-band k · p model for quantum dots and other low dimensional structures. First, the method is extended by the application of time reversal symmetry operator. This extension allows efficient calculations of the twofold degeneracy present in the multiband k · p model and other interior eigenvalues. Second, the preconditioner for the indefinite matrix which comes from the discretization of the eight band k · p Hamiltonian is presented. The construction of this preconditioner is based on physical considerations about energy band structure in the k · p model. On the basis of two real examples, it is shown that the preconditioner can significantly shorten the time needed to calculate the interior eigenvalues, despite the fact that the memory usage of the preconditioner and Hamiltionian is comparable. Finally, some technical details for implementing the eight band k · p Hamiltonian and the eigensolver are provided

2013-09-15

60

Ab-initio calculations of the Optical band-gap of TiO2 thin films  

CERN Multimedia

Titanium dioxide has been extensively studied in recent decades for its important photocatalytic application in environmental purification. The search for a method to narrow the optical band-gap of TiO2 plays a key role for enhancing its photocatalytic application. The optical band gap of epitaxial rutile and anatase TiO2 thin films deposited by helicon magnetron sputtering on sapphire and on SrTiO3 substrates was correlated to the lattice constants estimated from HRTEM images and SAED. The optical band-gap of 3.03 eV for bulk-rutile increased for the thin films to 3.37 on sapphire. The band gap of 3.20 eV for bulk-anatase increases to 3.51 on SrTiO3. In order to interpret the optical band gap expansion for both phases, ab-initio calculations were performed using the Vienna ab-initio software. The calculations for rutile as well anatase show an almost linear increase of the band gap width with decreasing volume or increasing lattice constant a. The calculated band gap fits well with the experimental values. T...

Wunderlich, W; Tanemura, M; Tanemura, S; Jin, P; Kaneko, K; Terai, A; Nabatova-Gabin, N; Belkada, R; Wunderlich, Wilfried; Miao, Lei; Tanemura, Masaki; Tanemura, Sakae; Jin, Ping; Kaneko, Kenji; Terai, Asuka; Nabatova-Gabin, Nataliya; Belkada, Rachid

2004-01-01

 
 
 
 
61

Biaxial strain effects on the electronic band structure of wurtzite InxGa1-xN alloys using first-principles calculations  

Science.gov (United States)

Numerical simulation based on first-principles calculations is applied to study the energy band structural characteristics and the band-gap properties of wurtzite InGaN. The results show that the direct band gap, the band gap bowing parameter, the width of valence band, and the width of top valence band increase with compressive strain and decrease with tensile strain. The biaxial strain effect on the indirect band gap is little. In general, there is a larger band gap bowing parameter and larger strain-induced band gap bowing variation in Ga-rich alloys. In addition, the direct band gap, the indirect band gap, the width of valence band, and the width of top valence band decrease with increase of indium composition. Wurtzite InGaN remains the characteristic of a direct band gap material under biaxial stress.

Liou, Bo-Ting; Wu, Bang-Yenn; Kuo, Yen-Kuang

2012-02-01

62

Relativistic band-structure calculations for CeTIn sub 5 (T=Ir and Co) and analysis of the energy bands by using tight-binding method  

CERN Document Server

In order to investigate electronic properties of recently discovered heavy fermion superconductors CeTIn sub 5 (T=Ir and Co), we employ the relativistic linear augmented-plane-wave (RLAPW) method to clarify the energy band structures and Fermi surfaces of those materials. The obtained energy bands mainly due to the large hybridization between Ce 4 f and In 5 p states well reproduce the Fermi surfaces consistent with the de Haas-van Alphen experimental results. However, when we attempt to understand magnetism and superconductively in CeTIn sub 5 from the microscopic viewpoint, the energy bands obtained in the RLAPW method are too complicated to analyze the system by further including electron correlations. Thus, it is necessary to prepare a more simplified model, keeping correctly the essential characters of the energy bands obtained in the band-structure calculation. For the purpose, we construct a tight-binding model for CeTIn sub 5 by including f-f and p-p hoppings as well as f-p hybridization, which are ex...

Maehira, T; Ueda, K; Hasegawa, A

2003-01-01

63

Individual differences in brain dynamics: important implications for the calculation of event-related band power.  

Science.gov (United States)

Measures of event-related band power such as event-related desynchronization (ERD) are conventionally analyzed within fixed frequency bands, although it is known that EEG frequency varies as a function of a variety of factors. The question of how to determine these frequency bands for ERD analyses is discussed and a new method is proposed. The rationale of this new method is to adjust the frequency bands to the individual alpha frequency (IAF) for each subject and to determine the bandwidth for the alpha and theta bands as a percentage of IAF. As an example, if IAF equals 12 Hz, the widths of the alpha and theta bands are larger as compared to a subject with an IAF of, e.g., only 8 Hz. The results of an oddball paradigm show that the proposed method is superior to methods that are based on fixed frequencies and fixed bandwidths. PMID:9742677

Doppelmayr, M; Klimesch, W; Pachinger, T; Ripper, B

1998-07-01

64

Band structure of the solid state - interpretation of the nature of the chemical bond in some transition metal compounds in terms of energy band structure calculations  

International Nuclear Information System (INIS)

The nature of chemical binding for some transition metal compounds (ScN, ScO, TiC, TiN, Tio, VC, VN, VO) with NaCl structure is discussed in terms of energy band structure calculations. The discussion is based on the wave functions and energy eigenvalues, as calculated by the 'Quasi self sonsistent APW method' as well as on the energy eigen values and eigen vectors resulting from the Slater-Koster LCAO-Tight binding interpolation scheme. The LCAO-TB l-like partial density of states can be used to analyse the valence bands. This analysis shows, that the deepest valence band has predominantly s-character. The following bands, which can be derived in essence from the atomic 2p states of the of the non metal are characterized not only by the partial p-like density of states but also by a substantial contribution from the d-like partial density of states, which is decreasing going from a particular Carbide to the corresponding Oxide. For the valence bands, which can be associated with the atomic 3d states of the metal, the density of states exhibits besides the partial d-density of states small contributions from the partial p-like density of states. The decomposition of the d-like partial density of states into an esub(g)-like and a tsub(2g)-like contribution is discussed. By analyzing the APW crystal wave functions the partial l-like charges inside each atomic sphere can be obtained. If the APW total charges within the atomic spheres are compared with the charges of a hypothetical crystal, which correspond to a superposition of the charge densities of the neutral atoms, a transfer of electrons from the metal to the non-metal sphere is found for all compounds under investigation. (orig.)

1975-11-01

65

Band gap calculations of the semiconductor BNxP1?x using modified Becke–Johnson approximation  

International Nuclear Information System (INIS)

Highlights: ? The Modified Becke–Johnson scheme gives a very accurate band gap. ? We have shown the invalidity of Vegard’s linear rule for BNxP1?x. ? The band gap changes with alloy concentration are important in band gap engineering. - Abstract: In this work, the electronic properties of BN, BP and BNxP1?x compounds have been investigated by means of first-principles density-functional total-energy calculation using the all-electron full potential linear augmented plane-wave method (FP-LAPW). The (FP-LAPW) method was used within the density functional theory (DFT) along with the Engel–Vosko and Becke–Johnson exchange correlation potential. The energy bands along high symmetry directions, the density of states and bowing distributions are calculated. The results have been discussed in terms of previously existing experimental and theoretical data, and comparisons with similar compounds have been made. Analysis of band structure suggests direct and pseudo-direct band gaps for both compounds.

2013-01-05

66

Ab-initio calculation of the valence-band offset at strained GaAs/InAs (001) heterojunction.  

Science.gov (United States)

We present a self consistent pseudopotential calculation of the valence band offset (VBO) at GaAs/InAs (001) strained heterojunction, which is chosen as an example of the isovalent polar with common-anion lattice mismatched heterojunctions. The effects of...

N. Tit M. Peressi S. Baroni

1993-01-01

67

Application of the new LDA+GTB method for the band structure calculation of n-type cuprates  

International Nuclear Information System (INIS)

A novel hybrid scheme is proposed and applied for band structure calculations of undoped n-type cuprate Nd2CuO4. The ab initio LDA calculation is used to obtain single electron and Coulomb parameters of the multiband Hubbard-type model. In strong correlation regime the electronic structure within this model is calculated by the generalized tight-binding (GTB) method, that combines the exact diagonalization of the model Hamiltonian for a small cluster with perturbation treatment of the intercluster hopping and interactions. For Nd2CuO4, this scheme results in charge transfer insulator with value of the gap and band dispersion in agreement to the experimental data

2006-05-01

68

Relativistic Band-Structure Calculations for CeTIn$_5$(T=Ir and Co)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In order to investigate electronic properties of recently discovered heavy fermion superconductors CeTIn$_5$ (T=Ir and Co), we employ the relativistic linear augmented-plane-wave (RLAPW) method to clarify the energy band structures and Fermi surfaces of those materials. The obtained energy bands mainly due to the large hybridization between Ce $4f$ and In 5$p$ states well reproduce the Fermi surfaces consistent with the de Haas-van Alphen experimental results. However, when ...

Maehira, T.; Hotta, T.; Ueda, K.; Hasegawa, A.

2002-01-01

69

Band structure and effective mass calculations for III-V compound semiconductors using hybrid functionals and optimized local potentials  

International Nuclear Information System (INIS)

The band structures of III-V semiconductors (InP, InAs, InSb, GaAs, and GaSb) are calculated using the HSE06 hybrid functional, GW, and local potentials optimized for the description of band gaps. We show that the inclusion of a quarter of the exact HF exchange allows to predict accurate direct band gaps for InP, InAs, and InSb, i.e., 1.48, 0.42, 0.28 eV, in good agreement with recent experiments, i.e., 1.42, 0.42, 0.24 eV, respectively. The calculated effective masses and Luttinger parameters are also in reasonable agreement with experiment, although a tendency towards underestimation is observed with increasing anion mass. In order to find more efficient methods than hybrid functionals, the modified Becke-Johnson exchange potential is also employed to calculate the effective masses. The agreement of the effective masses with experiment is comparable to the one obtained with the HSE06 hybrid functional. Therefore, this opens a way to model band structures of much large systems than possible using hybrid functionals.

2010-03-21

70

Calculation of electron orbital for the design of the X-band LINAC  

International Nuclear Information System (INIS)

The X-band linear accelerator, which can generate such a short pulse as 100fs, is under design at the Nuclear Engineering Research Laboratory, the University of Tokyo. The design study of the X-band linac is carried out by using PARMELA and SUPERFISH. Then it is found that 600 ps (tail-to-tail) emission from a thermionic gun can be bunched to about 1 ps (FWHM) at the end of the 2nd accelerating tube and 80% of the initial charge is transmitted. (author)

1995-10-01

71

Does the band gap calculated from the photocurrent of Schottky devices lead to erroneous results? Analysis for CdTe  

International Nuclear Information System (INIS)

In recent years there has been an increased interest in flexible, lightweight photovoltaic modules based on thin metallic substrates. This paper reports some optoelectronic properties of electrodeposited CdTe thin films grown onto lightweight stainless steel (SS) foils. The optoelectronic properties were investigated with Schottky barriers of Au/CdTe/SS structure. The influence of the built-in potential of the Schottky junction on the bulk and the interface recombination of the photo-generated minority carriers is explained with the existing models. The voltage-dependent collection functions influence the photocurrent of the devices in both short- and long-wavelength regions of the spectrum. It is observed that in the photovoltaic mode the contribution due to the collection functions depends on the open-circuit voltage of the device. Au/CdTe Schottky devices, having higher open-circuit voltage, exhibit a better response in the long wavelength region. This is due to the efficient collection of the carriers generated in the bulk of the film and in such devices the contribution from the bulk collection function is higher. The enhancement in the bulk collection function causes a shift in the response of the device to higher wavelengths giving lower values for the calculated band gap. Due to this dependence of the long wavelength response on the open-circuit voltage of the devices, the band gap calculated from the photocurrent of different Schottky devices gives different values for the band gap of the material. Thus the method of calculating the band gap from the photocurrent of Schottky devices can lead to erroneous conclusions regarding the band gap of the material. (author)

2000-07-07

72

Symmetry Aspects of the Band Structure and Motion Equations Applied in Calculating the Cyclotron Frequency of Electrons in Metals  

Directory of Open Access Journals (Sweden)

Full Text Available Cyclotron frequency of a crystal electron is, in general, not an easily accessible parameter. Nevertheless, its calculation can be simplified when the symmetry properties of the band structure and those of the motion equations in the magnetic field are simultaneously taken into account. In effect, a combined symmetry of the electron Hamiltonian and that of the Lorentz equation provide us with a non-linear oscillator problem of high symmetry. In the next step, the kinetic energy of the oscillator can be separated from the whole of electron energy and applied in a new kind of calculation of the cyclotron frequency which is much more simple than before. In consequence, a detailed approach to the electron circulation, also in more complex band structures, becomes a relatively easy task. For different crystal lattices of cubic symmetry taken as examples the cyclotron frequency of the present and a former method are compared numerically giving the same results.

Stanislaw Olszewski

2011-08-01

73

Theoretical calculation of spectrum of M band for Ni-like Au ion using the model of unresolved transition array  

International Nuclear Information System (INIS)

Unresolved transition array model is applied to calculate the characteristic parameters of eight transition arrays consisted in the spectrum of Ni-like Au(Au51+), i.e., mean wave number, full width at half maximum, total strength, number of line. The eight transition arrays are superposed according to their total strength with a Gaussian curve, agreement with experiment is generally excellent and makes measurement with high space and time resolution of M band spectrum for Au possible

1998-05-01

74

Theory of composite-band Wannier states and order-N electronic-structure calculations  

Digital Repository Infrastructure Vision for European Research (DRIVER)

From the order-N electronic-structure formulation, a Hamiltonian is derived, of which lowest eigen state is the generalized or composite-band Wannier state. This Hamiltonian maps the locality of the Wannier state to that of a virtual impurity state and to a perturbation from a bonding orbital. These theories are demonstrated in the diamond-structure solids, where the Wannier states are constructed by a practical order-N algorithm with the Hamiltonian. The results give a prot...

Hoshi, Takeo; Fujiwara, Takeo

1999-01-01

75

Electron momentum density and band structure calculations of {alpha}- and {beta}-GeTe  

Energy Technology Data Exchange (ETDEWEB)

We have measured isotropic experimental Compton profile of {alpha}-GeTe by employing high energy (662 keV) {gamma}-radiation from a {sup 137}Cs isotope. To compare our experiment, we have also computed energy bands, density of states, electron momentum densities and Compton profiles of {alpha}- and {beta}-phases of GeTe using the linear combination of atomic orbitals method. The electron momentum density is found to play a major role in understanding the topology of bands in the vicinity of the Fermi level. It is seen that the density functional theory (DFT) with generalised gradient approximation is relatively in better agreement with the experiment than the local density approximation and hybrid Hartree-Fock/DFT. - Highlights: > Compton profile of {alpha}-GeTe using a 20 Ci {sup 137}Cs Compton spectrometer. > Compared experimental Compton data with density functional theory. > Reported energy bands and density of states of {alpha}- and {beta}-GeTe. > EVED profiles analysed to check the covalent character.

Vadkhiya, Laxman [Department of Physics, University College of Science, M.L. Sukhadia University, Udaipur 313001, Rajasthan (India); Arora, Gunjan [Department of Physics, Techno India NJR Institute of Technology, Udaipur 313002, Rajasthan (India); Rathor, Ashish [Department of Physics, University College of Science, M.L. Sukhadia University, Udaipur 313001, Rajasthan (India); Ahuja, B.L., E-mail: blahuja@yahoo.com [Department of Physics, University College of Science, M.L. Sukhadia University, Udaipur 313001, Rajasthan (India)

2011-12-15

76

A method for calculating wide band electromagnetic interference from power line corona  

International Nuclear Information System (INIS)

An algorithm for calculating electromagnetic interference from power line corona for a range of frequencies from 100 kHz to 30 MHz is demonstrated. It can be used for calculations at any distance or direction from the line. The algorithm incorporates an existing generation function which has been optimized by comparison to long term electromagnetic interference measurements

1995-07-01

77

N-doping induced band-gap reduction in III-V semiconductors: First-principles calculations  

Energy Technology Data Exchange (ETDEWEB)

Nitrogen doping often induces the band-gap reduction for III-V semiconductors. To understand its origin and feature, the chemical trend of reduction is studied by the first-principles calculation with comparing the cases of various III-V compounds. We found that III-V semiconductors are categorized al least into two groups; the large band-gap reduction occurs for InP, InAs, InSb, GaAs, and GaSb, while there is little reduction and appears a deep level of nitrogen in the band gap for AlAs, AlP, AlSb, and GaP. It is shown that such difference reflects the order of energy positions of host cation s-orbital and the nitrogen 3s-orbital states. Reflecting orbital hybridization originated from such difference, calculated optical spectra show different features near absorption edges (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Ishikawa, Masato [Semiconductor Headquarters, Yokogawa Electric Corporation, 4-1-55 Koyama, Sagamihara, Kanagawa 229-1207 (Japan); Nakayama, Takashi [Department of Physics, Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522 (Japan)

2011-02-15

78

Hartree-Fock and Hartree-Fock-Bogoliubov calculations of superdeformed bands  

International Nuclear Information System (INIS)

I present some original features of the cranked mean-field derived with the Skyrme effective interaction. Then I discuss results obtained with this method which concern the questions raised by the existence of identical SD bands in the 192Hg region. In order to include pairing effects, one must replace cranked HF equations by cranked HFB. I describe the method we are presently using and our first results. In the last section, based on the comparison of our results whith data, I extrapolate the most promising lines of work which should help improve our understanding of nuclear spectroscopy in terms of effective interactions. (orig.)

1993-05-31

79

Hartree-Fock and Hartree-Fock-Bogoliubov calculations of superdeformed bands  

Energy Technology Data Exchange (ETDEWEB)

I present some original features of the cranked mean-field derived with the Skyrme effective interaction. Then I discuss results obtained with this method which concern the questions raised by the existence of identical SD bands in the [sup 192]Hg region. In order to include pairing effects, one must replace cranked HF equations by cranked HFB. I describe the method we are presently using and our first results. In the last section, based on the comparison of our results whith data, I extrapolate the most promising lines of work which should help improve our understanding of nuclear spectroscopy in terms of effective interactions. (orig.)

Flocard, H. (Div. de Physique Theorique, I.P.N., 91 - Orsay (France)); Chen, B.Q. (W.K. Kellog Radiation Lab., California Inst. of Tech., Pasadena, CA (United States)); Gall, B. (Div. de Physique Theorique, I.P.N., 91 - Orsay (France)); Bonche, P. (SPhT, C.E. Saclay, 91 - Gif sur Yvette (France)); Dobaczewski, J. (Inst. of Theoretical Physics, Warsaw Univ. (Poland)); Heenen, P.H. (Service de Physique Nucleaire Theorique, Bruxelles (Belgium)); Weiss, M.S. (Physics Dept., Lawrence Livermore National Lab., CA (United States))

1993-05-31

80

ACCELERATING STRUCTURE: Physical calculation for an X-band hybrid dielectric-iris-loaded accelerator  

Science.gov (United States)

A small, high performance X-band hybrid dielectric-iris-loaded travelling-wave linac with the length of 1.47 m and the maximum accelerating gradient of 45 MV/m has been designed. The beam energy of 33 MeV, the energy spread of 0.5%, the beam emittance of about 5.7 ?mm · mrad and the capture efficiency of 40% are reached by adjusting the sizes of the accelerating cavities and the phase velocity. The attenuation per unit length of structure, the shunt impedance Rs, the quality factor Q, the group velocity and the phase velocity are also presented.

He, Xiao-Dong; Wu, Cong-Feng; Feng, Guang-Yao; Dong, Sai; Pei, Yuan-Ji

2009-06-01

 
 
 
 
81

Magnetism and superconductivity in C15 compounds from self-consistent band calculations  

Science.gov (United States)

All-atom-all-electron self-consistent semirelativistic linear muffin-tin orbital energy-band studies are reported for TiBe2, ZrZn2 (at ambient and high pressures), the high-Tc superconductor ZrV2, and the ultralow-Tc superconductor YAl2. Total and partial (by atom type and l values) density of states, Stoner-like parameters, electron-phonon coupling parameter ? and superconducting transition temperatures Tc (determined within the rigid muffin-tin approximation and McMillan's strong coupling theory with and without paramagnon contributions), and their behavior under applied pressure are used to discuss the origin of their observed magnetism and/or superconductivity. From an analysis of the results, we suggest possible high-Tc superconductivity at high pressure for ZrZn2, and its unlikely occurrence for TiBe2 unless dominant soft phonon modes exist.

Jarlborg, T.; Freeman, A. J.

1980-09-01

82

Communication: electronic band gaps of semiconducting zig-zag carbon nanotubes from many-body perturbation theory calculations.  

Science.gov (United States)

Electronic band gaps for optically allowed transitions are calculated for a series of semiconducting single-walled zig-zag carbon nanotubes of increasing diameter within the many-body perturbation theory GW method. The dependence of the evaluated gaps with respect to tube diameters is then compared with those found from previous experimental data for optical gaps combined with theoretical estimations of exciton binding energies. We find that our GW gaps confirm the behavior inferred from experiment. The relationship between the electronic gap and the diameter extrapolated from the GW values is also in excellent agreement with a direct measurement recently performed through scanning tunneling spectroscopy. PMID:22583270

Umari, P; Petrenko, O; Taioli, S; De Souza, M M

2012-05-14

83

Sulfur-doping of rutile-titanium dioxide by ion implantation: Photocurrent spectroscopy and first-principles band calculation studies  

International Nuclear Information System (INIS)

Sulfur (S)-doped titanium dioxide (TiO2) was synthesized by ion implantation and subsequent thermal annealing. The S ions were implanted into the single crystals of rutile TiO2 at a fluence of 8x1015 ions/cm2. According to the results of Rutherford backscattering spectroscopy and ion channeling analysis, the irradiation damage recovered by annealing at 600 deg. C in air. In the annealed crystal, the S atoms occupied oxygen sites for form Ti-S bonds, as confirmed by x-ray photoelectron spectroscopy. Compared to the pure TiO2, a photocurrent was observed in the lower-energy regions for the S-doped TiO2. Based on the theoretical analyses by the first-principles band calculations using the full potential linearized augmented plane-wave methods within the generalized gradient approximation, the mixing of the S 3p states with the valence band (VB) was found to contribute to the increasing width of the VB. This leads to the band gap narrowing in the S-doped TiO2. Therefore, the photon-to-carrier conversion was induced during irradiation by visible light above 420 nm (<2.9 eV)

2003-05-01

84

A modified band approach for the accurate calculation of online photolysis rates in stratospheric-tropospheric Chemical Transport Models  

Directory of Open Access Journals (Sweden)

Full Text Available Here we present an efficient and accurate method for the online calculation of photolysis rates relevant to both the stratosphere and troposphere for use in global Chemistry Transport Models and General Circulation Models. The method is a modified version of the band model introduced by Landgraf and Crutzen (1998 which has been updated to improve the performance of the approach for solar zenith angles >72° without the use of any implicit parameterisations. For this purpose, additional sets of band parameters have been defined for instances where the incident angle of the light beam is between 72–93°, in conjunction with a scaling component for the far UV region of the spectrum (?=178.6–202.0 nm. For incident angles between 85–93° we introduce a modification for pseudo-sphericity that improves the accuracy of the 2-stream approximation. We show that this modified version of the Practical Improved Flux Method (PIFM is accurate for angles <93° by comparing the resulting height resolved actinic fluxes with a recently developed full spherical reference model. We also show that the modified band method is more accurate than the original, with errors generally being less than ±10% throughout the atmospheric column for a diverse range of chemical species. Moreover, we perform certain sensitivity studies that indicate it is robust and performs well over a wide range of conditions relevant to the atmosphere.

J. E. Williams

2006-01-01

85

Field modulation in bilayer graphene band structure  

Energy Technology Data Exchange (ETDEWEB)

Using an external electric field, one can modulate the band gap of Bernal stacked bilayer graphene by breaking the A-B-tilde symmetry. We analyze strain effects on the bilayer graphene using the extended Hueckel theory and find that reduced interlayer distance results in higher band gap modulation, as expected. Furthermore, above about 2.5 A interlayer distance, the band gap is direct, follows a convex relation with the electric field and saturates to a value determined by the interlayer distance. However, below about 2.5 A, the band gap is indirect, the trend becomes concave and a threshold electric field is observed, which also depends on the stacking distance. (fast track communication)

Raza, Hassan; Kan, Edwin C [School of Electrical and Computer Engineering, Cornell University, Ithaca, NY 14853 (United States)], E-mail: hr89@cornell.edu

2009-03-11

86

Coupled-cluster calculations of the lowest 0-0 bands of the electronic excitation spectrum of naphthalene.  

Science.gov (United States)

Approximate singles and doubles coupled-cluster (CC2) calculations have been carried out for the 0-0 bands of the 1Ag? 1B3u and 1Ag? 1B2u transitions of naphthalene. The vertical excitation energies calculated for the 16 lowest excited singlet states have also been calculated using a sequence of large basis sets. The CC2 excitation energies extrapolated to the basis-set limit are in rather good agreement with values recently calculated at the multiconfiguration second-order perturbation theory (CASPT2) and at the singles, doubles and approximate triples (CC3) levels. Best values for the vertical excitation energies and the 0-0 transition energies have been obtained by adding higher-order correlation contributions to the basis-set extrapolated CC2 energies. For some of the states, the best estimated vertical excitation energies in this work deviate up to 0.3 eV from the previously best estimated energies, because larger basis sets have been employed in this study. The calculations of the 0-0 transitions show the importance of considering vibrational effects when aiming at reliable comparisons of calculated and measured excitation energies for assessing the accuracy of employed computational methods. Calculations at the density functional theory (DFT) level using Becke's three-parameter functional (B3LYP) yield less accurate excitation energies. At the B3LYP level, the two lowest states appear in reverse order with a deviation of 0.50 eV from experiment for the 0-0 transition energy of the 1B3u state. PMID:24406689

Fliegl, Heike; Sundholm, Dage

2014-06-01

87

Metal-ceramic interface adhesion: Band structure calculations on Pt-NiO couples  

Energy Technology Data Exchange (ETDEWEB)

A problem of critical technological importance and fundamental scientific interest in materials science and materials engineering is that of adhesion between metals and ceramics. metal-ceramic adhesion is important to such industrial areas as microelectronics, catalysts, protective coatings for metals and metal-ceramic composite materials. Under certain annealing conditions Pt-NiO couples form NiPt intermetallic layers at the interface. It has been suggested that an observed 4-fold increase in the ultimate shear strength of the interface upon inclusion of a 1-nm-thick NiPt interlayer is caused by metal-oxygen bonding at the interface. Extended Huckel calculations, within the tight-binding formalism, have been performed on a series of Pt- and NiPt-NiO metal-ceramic couples to elucidate the nature of the bonding at these interfaces. the calculations showed an approximately 5-fold increase in adhesion energy in NiPt-NiO over Pt-NiO. This attributed to the more efficient electron donating capability of nickel compared to that of platinum. Bonding across the interface is found to decrease with increased electron donation as interfacially antibonding orbitals are filled. Theoretical reasons for the eventual mechanical failure in the oxide component are adduced. 25 refs., 7 figs., 3 tabs.

Boorse, R.S.; Burlitch, J.M.; Hoffmann, R.; Alemany, P. (Cornell Univ., Ithaca, NY (United States))

1993-04-01

88

Unified calculations of the optical band positions and EPR g factors for NaCrS2 crystal  

Science.gov (United States)

Six optical band positions and EPR g factors g, g? for the trigonal Cr3+ octahedral clusters in NaCrS2 crystal are calculated together through the complete diagonalization (of energy matrix) method based on the two-spin–orbit-parameter model, where besides the contribution due to the spin–orbit parameter of central dn ion in the conventional crystal-field theory, the contribution due to the spin–orbit parameter of ligand ion via the covalence effect is also considered. In the calculations, the crystal-field parameters Bkl are obtained from the superposition model with the structural data of Cr3+ octahedral clusters in NaCrS2 crystal measured exactly by the X-ray diffraction method. The calculated optical and EPR spectral data are in a reasonable agreement with the observed values. So, the reliability of the superposition model in the studies of crystal-field parameters for dn ions in crystals is confirmed, and the complete diagonalization (of energy matrix) method based on the two-spin–orbit-model is effective in the unified calculations of optical and EPR spectral data for dn ions in crystals.

Mei, Yang; Zheng, Wen-Chen; Zhang, Lin

2014-06-01

89

Inelastic plasmon and inter-band electron-scattering potentials for Si from dielectric matrix calculations  

International Nuclear Information System (INIS)

Inelastic scattering of electrons in a crystalline environment may be represented by a complex non-hermitian potential. Completed generalised expressions for this inelastic electron scattering potential matrix, including virtual inelastic scattering, are derived for outer-shell electron and plasmon excitations. The relationship between these expressions and the general anisotropic dielectric response matrix of the solid is discussed. These generalised expressions necessarily include the off-diagonal terms representing effects due to departure from translational invariance in the interaction. Results are presented for the diagonal back structure dependent inelastic and virtual inelastic scattering potentials for Si, from a calculation of the inverse dielectric matrix in the random phase approximation. Good agreement is found with experiment as a function of incident energies from 10 eV to 100 keV. Anisotropy effects and hence the interaction de localisation represented by the off-diagonal scattering potential terms, are found to be significant below 1 keV. 38 refs., 2 figs

1994-01-01

90

Calculations of intersection cross-slip activation energies in fcc metals using nudged elastic band method  

Energy Technology Data Exchange (ETDEWEB)

The nudged elastic band (NEB) method is used to evaluate activation energies for dislocation intersection cross-slip in face-centered cubic (fcc) nickel and copper, to extend our prior work which used an approximate method. In this work we also extend the study by including Hirth locks (HL) in addition to Lomer-Cottrell locks and glide locks (GL). Using atomistic (molecular statics) simulations with embedded atom potentials we evaluated the activation barrier for a dislocation to transform from fully residing on the glide plane to fully residing on the cross-slip plane when intersecting a 120{sup o} forest dislocation in both Ni and Cu. The initial separation between the screw and the intersecting dislocation on the (1 1 1) glide plane is varied to find a minimum in the activation energy. The NEB method gives energies that are {approx}10% lower than those reported in our prior work. It is estimated that the activation energies for cross-slip from the fully glide plane state to the partially cross-slipped state at the 120{sup o} intersection forming GL in Ni and Cu are {approx}0.47 and {approx}0.65 eV, respectively, and from the fully cross-slip plane state to the partially cross-slipped state forming LC are {approx}0.68 and {approx}0.67 eV. The activation energies for cross-slip from the fully glide plane state to the partially cross-slipped state at the 120{sup o} intersection forming HL in Ni and Cu are estimated to be {approx}0.09 and {approx}0.31 eV, respectively. These values are a factor of 3-20 lower than the activation energy for bulk cross-slip in Ni and, a factor of 2-6 lower than the activation energy for cross-slip in Cu estimated by Friedel-Escaig analysis. These results suggest that cross-slip should nucleate preferentially at selected screw dislocation intersections in fcc materials and the activation energies for such mechanisms are also a function of stacking fault energy.

Rao, S.I., E-mail: satish.rao@wpafb.af.mil [UES Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432-1894 (United States); Dimiduk, D.M. [Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/MLLM, Wright-Patterson AFB, OH 45433-7817 (United States); Parthasarathy, T.A. [UES Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432-1894 (United States); El-Awady, J. [Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218 (United States); Woodward, C.; Uchic, M.D. [Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/MLLM, Wright-Patterson AFB, OH 45433-7817 (United States)

2011-11-15

91

Calculation of the radiation exchange in a closed chamber by the method of radiation bands in comparison to the method of the average radiation parameter  

Energy Technology Data Exchange (ETDEWEB)

Two methods for calculating the radiation exchange within a closed chamber with isothermic material, i.e. the classical method of the average emission capacity and the method of the black radiation bands, are compared and approximate auxiliary equations are developed for both methods. The calculation results of the methods investigated differ by approx. 30 to 80 %. The measurements which have been carried out confirm the greater accurracy of the radiation bands method.

Szargut, J.; Wandrasz, J.

1978-08-01

92

IOS and ECS line coupling calculation for the CO-He system - Influence on the vibration-rotation band shapes  

Science.gov (United States)

Line coupling coefficients resulting from rotational excitation of CO perturbed by He are computed within the infinite order sudden approximation (IOSA) and within the energy corrected sudden approximation (ECSA). The influence of this line coupling on the 1-0 CO-He vibration-rotation band shape is then computed for the case of weakly overlapping lines in the 292-78 K temperature range. The IOS and ECS results differ only at 78 K by a weak amount at high frequencies. Comparison with an additive superposition of Lorentzian lines shows strong modifications in the troughs between the lines. These calculated modifications are in excellent quantitative agreement with recent experimental data for all the temperatures considered. The applicability of previous approaches to CO-He system, based on either the strong collision model or exponential energy gap law, is also discussed.

Boissoles, J.; Boulet, C.; Robert, D.; Green, S.

1987-01-01

93

A postprocessing method based on high-resolution spectral estimation for FDTD calculation of phononic band structures  

Energy Technology Data Exchange (ETDEWEB)

If the energy bands of a phononic crystal are calculated by the finite difference time domain (FDTD) method combined with the fast Fourier transform (FFT), good estimation of the eigenfrequencies can only be ensured by the postprocessing of sufficiently long time series generated by a large number of FDTD iterations. In this paper, a postprocessing method based on the high-resolution spectral estimation via the Yule-Walker method is proposed to overcome this difficulty. Numerical simulation results for three-dimensional acoustic and two-dimensional elastic systems show that, compared with the classic FFT-based postprocessing method, the proposed method can give much better estimation of the eigenfrequencies when the FDTD is run with relatively few iterations.

Su Xiaoxing, E-mail: xxsu@bjtu.edu.c [School of Electronic and Information Engineering, Beijing Jiaotong University, Beijing 100044 (China); Li Jianbao; Wang Yuesheng [Institute of Engineering Mechanics, Beijing Jiaotong University, Beijing 100044 (China)

2010-05-15

94

First-principles calculation of band offsets, optical bowings, and defects in CdS, CdSe, CdTe, and their alloys  

International Nuclear Information System (INIS)

Using first principles band structure theory we have calculated (i) the alloy bowing coefficients, (ii) the alloy mixing enthalpies, and (iii) the interfacial valence band offsets for three Cd-based (CdS, CdSe, CdTe) compounds. We have also calculated defect formation energies and defect transition energy levels of Cd vacancy VCd and CuCd substitutional defect in CdS and CdTe, as well as the isovalent defect TeS in CdS. The calculated results are compared with available experimental data. (c) 2000 American Institute of Physics

2000-02-01

95

Calculation of the X-Ray emission K and L 2,3 bands of metallic magnesium and aluminum with allowance for multielectron effects  

Science.gov (United States)

A procedure is proposed to calculate the shape of the characteristic X-ray emission bands of metals with allowance for multielectron effects. The effects of the dynamic screening of a core vacancy by conduction electrons and the Auger effect in the valence band are taken into account. The dynamic screening of a core vacancy, which is known to be called the MND (Mahan-Nozeieres-De Dominics) effect, is taken into account by an ab initio band calculation of crystals using the PAW (projected augmented waves) method. The Auger effect is taken into account by a semiempirical method using the approximation of a quadratic dependence of the level width in the valence band on the difference between the level energy and the Fermi energy. The proposed calculation procedure is used to describe the X-ray emission K and L 2,3 bands of metallic magnesium and aluminum crystals. The calculated spectra agree well with the experimental bands both near the Fermi level and in the low-energy part of the spectra in all cases.

Ovcharenko, R. E.; Tupitsyn, I. I.; Savinov, E. P.; Voloshina, E. N.; Dedkov, Yu. S.; Shulakov, A. S.

2014-01-01

96

Comparison between Fermi-Dirac and Boltzmann Methods for Band-bending Calculations of Si/CaF2/Au Hot Electron Emitter  

Science.gov (United States)

Fermic-Dirac statistics is used to calculate the band bending at the semiconductor surface of n-Si/CaF2/Au hot electron emitter. Due to the need for the application of a relatively large positive voltage and an ultra-thin insulator layer in the scanning hot electron microscopy (SHEM) experiment for this emitter, the Fermi level can cross the conduction band bottom at the semiconductor surface. A partial region of the space charge at the semiconductor surface will be in the state of degeneracy and the Boltzmann statistics will be invalid even for the non-degenerate substrate. The calculated results of band bending from the Boltzmann approximation and Fermi-Dirac statistics are compared for different doping densities and different insulator thicknesses. At the same time, the effect of band bending obtained by the two methods on the transmission probability of electrons through the insulator has also been discussed.

Zhang, Bingyang; Ikeda, Yoshihiro; KazuhitoFuruya, KazuhitoFuruya; Kikegawa, Nobutaka

1999-04-01

97

First-principles band-structure calculations and X-ray photoelectron spectroscopy studies of the electronic structure of TlPb2Cl5  

International Nuclear Information System (INIS)

Highlights: • Electronic structure of TlPb2Cl5 is calculated by the FP-LAPW method. • The valence band is dominated by contributions of Cl 3p states. • Contributions of Pb 6p* states dominate at the bottom of the conduction band. • The FP-LAPW data allow concluding that TlPb2Cl5 is an indirect-gap material. • XPS core-level and valence-band spectra of polycrystalline TlPb2Cl5 are measured. -- Abstract: We report on first-principles calculations of total and partial densities of states of atoms constituting TlPb2Cl5 using the full potential linearized augmented plane wave (FP-LAPW) method. The calculations reveal that the valence band of TlPb2Cl5 is dominated by contributions of the Cl 3p-like states, which contribute mainly at the top of the valence band with also significant contributions throughout the whole valence-band region. In addition, the bottom of the conduction band of TlPb2Cl5 is composed mainly of contributions of the unoccupied Pb 6p-like states. Our FP-LAPW data indicate that the TlPb2Cl5 compound is an indirect-gap material with band gap of 3.42 eV. The X-ray photoelectron core-level and valence-band spectra for pristine and Ar+ ion-irradiated surfaces of a TlPb2Cl5 polycrystalline sample were measured. The measurements reveal high chemical stability and confirm experimentally the low hygroscopicity of TlPb2Cl5 surface

2014-01-05

98

First-principles band-structure calculations and X-ray photoelectron spectroscopy studies of the electronic structure of TlPb{sub 2}Cl{sub 5}  

Energy Technology Data Exchange (ETDEWEB)

Highlights: • Electronic structure of TlPb{sub 2}Cl{sub 5} is calculated by the FP-LAPW method. • The valence band is dominated by contributions of Cl 3p states. • Contributions of Pb 6p{sup *} states dominate at the bottom of the conduction band. • The FP-LAPW data allow concluding that TlPb{sub 2}Cl{sub 5} is an indirect-gap material. • XPS core-level and valence-band spectra of polycrystalline TlPb{sub 2}Cl{sub 5} are measured. -- Abstract: We report on first-principles calculations of total and partial densities of states of atoms constituting TlPb{sub 2}Cl{sub 5} using the full potential linearized augmented plane wave (FP-LAPW) method. The calculations reveal that the valence band of TlPb{sub 2}Cl{sub 5} is dominated by contributions of the Cl 3p-like states, which contribute mainly at the top of the valence band with also significant contributions throughout the whole valence-band region. In addition, the bottom of the conduction band of TlPb{sub 2}Cl{sub 5} is composed mainly of contributions of the unoccupied Pb 6p-like states. Our FP-LAPW data indicate that the TlPb{sub 2}Cl{sub 5} compound is an indirect-gap material with band gap of 3.42 eV. The X-ray photoelectron core-level and valence-band spectra for pristine and Ar{sup +} ion-irradiated surfaces of a TlPb{sub 2}Cl{sub 5} polycrystalline sample were measured. The measurements reveal high chemical stability and confirm experimentally the low hygroscopicity of TlPb{sub 2}Cl{sub 5} surface.

Khyzhun, O.Y., E-mail: khyzhun@ipms.kiev.ua [Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, Kyiv 03142 (Ukraine); Bekenev, V.L.; Denysyuk, N.M. [Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, Kyiv 03142 (Ukraine); Parasyuk, O.V. [Department of Inorganic and Physical Chemistry, Eastern European National University, 13 Voli Avenue, Lutsk 43025 (Ukraine); Fedorchuk, A.O. [Department of Inorganic and Organic Chemistry, Lviv National University of Veterinary Medicine and Biotechnologies, Pekarska St., 50, 79010 Lviv (Ukraine)

2014-01-05

99

Calculation of the band structure of GdCo_2, GdRh_2 e GdIr_2 by the APW method  

International Nuclear Information System (INIS)

The band structure of GdCo_2, GdRh_2, GdIr_2 has been calculated by the APW method. A histogram of the density of states is presented for each compound. The bands are transition-metal-like, with s-d hybridization near the Fermi level. The 5d character near the Fermi level increases as one goes from Co to Ir

1974-01-01

100

Band structure calculations of CuAlO2, CuGaO2, CuInO2, and CuCrO2 by screened exchange  

Science.gov (United States)

We report density functional theory band structure calculations on the transparent conducting oxides CuAlO2, CuGaO2, CuInO2, and CuCrO2. The use of the hybrid functional screened-exchange local density approximation (sX-LDA) leads to considerably improved electronic properties compared to standard LDA and generalized gradient approximation (GGA) approaches. We show that the resulting electronic band gaps compare well with experimental values and previous quasiparticle calculations, and show the correct trends with respect to the atomic number of the cation (Al, Ga, In). The resulting energetic depths of Cu d and O p levels and the valence-band widths are considerable improvements compared to LDA and GGA and are in good agreement with available x-ray photoelectron spectroscopy data. Lastly, we show the calculated imaginary part of the dielectric function for all four systems.

Gillen, Roland; Robertson, John

2011-07-01

 
 
 
 
101

Comments on "Band gap and band parameters of InN and GaN from quasiparticle energy calculations based on exact-exchange density-functional theory" [Appl. Phys. Lett. 89, 161919 (2006)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An oversight of some previous density functional calculations of the band gaps of wurtzite and cubic InN and of wurtzite GaN by Rinke et al. [Appl. Phys. Lett. 89,161919, 2006] led to an inaccurate and misleading statement relative to limitations of density functional theory (DFT) for the description of electronic properties of these materials. These comments address this statement. In particular, they show that some local density approximation (LDA) calculations have correc...

Bagayoko, D.; Franklin, L.; Zhao, G. L.

2011-01-01

102

Augmented Fourier components method for constructing the crystal potential in self-consistent band-structure calculations  

Science.gov (United States)

We describe a method to perform self-consistent band structure calculations. This combination of the extended linear augmented plane wave (ELAPW)-kp method with a plane-wave basis set offers a scheme to construct the crystal potential alternative to the well-known full-potential linear augmented plane wave (FLAPW) technique. We propose a representation of the crystal density that is free from unphysical computational parameters specific to the representation of the wave functions. The valence density is divided into two parts, one of which is expanded in a Fourier series and the other one is localized within small spheres surrounding the nuclei. It is shown that to a good approximation the latter part can be represented by its Y00 component. The quality of the representation is controlled by the number of Fourier components of the density, and the computational effort can be balanced with the desired accuracy. By construction the density is smooth everywhere in the unit cell. The technique of constructing the potential, the augmented Fourier components method (AFC), is described. The properties of the method are demonstrated using the cubic semiconductors Si, SiC, GaAs, BaTiO3, KNbO3, KTaO3, and metallic 1T chalcogenides TiS2 and TiSe2 as examples. The self-consistent density-of-states curves are presented. With the AFC ELAPW-kp method optical properties of TiSe2 are calculated; complex dielectric function and reflectivity are in good agreement with experimental results.

Krasovskii, E. E.; Starrost, F.; Schattke, W.

1999-04-01

103

Integral Intensities of Absorption Bands of Silicon Tetrafluoride in the Gas Phase and Cryogenic Solutions: Experiment and Calculation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The spectral characteristics of the SiF4 molecule in the range 3100700 cm1, including the absorption range of the band 3, are studied in the gas phase at P = 0.47 bar and in solutions in liquefied Ar and Kr. In the cryogenic solutions, the relative intensities of the vibrational bands, including the bands of the isotopically substituted molecules, are determined. The absorption coefficients of the combination bands 23, 3 + 1, 3 + 4, and 34 are measured in the solution in Kr. In the gas phase ...

2005-01-01

104

Band gap calculations of the semiconductor BN{sub x}P{sub 1-x} using modified Becke-Johnson approximation  

Energy Technology Data Exchange (ETDEWEB)

Highlights: Black-Right-Pointing-Pointer The Modified Becke-Johnson scheme gives a very accurate band gap. Black-Right-Pointing-Pointer We have shown the invalidity of Vegard's linear rule for BN{sub x}P{sub 1-x}. Black-Right-Pointing-Pointer The band gap changes with alloy concentration are important in band gap engineering. - Abstract: In this work, the electronic properties of BN, BP and BN{sub x}P{sub 1-x} compounds have been investigated by means of first-principles density-functional total-energy calculation using the all-electron full potential linear augmented plane-wave method (FP-LAPW). The (FP-LAPW) method was used within the density functional theory (DFT) along with the Engel-Vosko and Becke-Johnson exchange correlation potential. The energy bands along high symmetry directions, the density of states and bowing distributions are calculated. The results have been discussed in terms of previously existing experimental and theoretical data, and comparisons with similar compounds have been made. Analysis of band structure suggests direct and pseudo-direct band gaps for both compounds.

Benkraouda, M. [Department of Physics, United Arab Emirates University, Al-Ain, P.O. Box 17551 (United Arab Emirates); Amrane, N., E-mail: namrane@uaeu.ac.ae [Department of Physics, United Arab Emirates University, Al-Ain, P.O. Box 17551 (United Arab Emirates)

2013-01-05

105

Nudged elastic band calculation of minimal energy paths for the conformational change of a GG non-canonical pair.  

Science.gov (United States)

The nudged elastic band (NEB) technique has been implemented in AMBER to calculate low-energy paths for conformational changes. A novel simulated annealing protocol that does not require an initial hypothesis for the path is used to sample low-energy paths. This was used to study the conformational change of an RNA cis Watson-Crick/Hoogsteen GG non-canonical pair, with one G syn around the glycosidic bond and the other anti. A previous solution structure, determined by NMR-constrained modeling, demonstrated that the GG pairs change from (syn)G-(anti)G to (anti)G-(syn)G in the context of duplex r(GCAGGCGUGC) on the millisecond timescale. The set of low-energy paths found by NEB show that each G flips independently around the glycosidic bond, with the anti G flipping to syn first. Guanine bases flip without opening adjacent base-pairs by protruding into the major groove, accommodated by a transient change by the ribose to C2'-exo sugar pucker. Hydrogen bonds between bases and the backbone, which lower the energetic barrier to flipping, are observed along the path. The results show the plasticity of RNA base-pairs in helices, which is important for biological processes, including mismatch repair, protein recognition, and translation. The modeling of the GG conformational change also demonstrates that NEB can be used to discover non-trivial paths for macromolecules and therefore NEB can be used as an exploratory method for predicting putative conformational change paths. PMID:16487974

Mathews, David H; Case, David A

2006-04-14

106

Calculation of the Energy-Band Structure of the Kronig-Penney Model Using the Nearly-Free and Tightly-Bound-Electron Approximations  

Science.gov (United States)

Calculates the energy-band structure of noninteracting electrons in a one-dimensional crystal using exact and approximate methods for a rectangular-well atomic potential. A comparison of the two solutions as a function of potential-well depth and ratio of lattice spacing to well width is presented. (Author/GA)

Wetsel, Grover C., Jr.

1978-01-01

107

Band structure of MoS_2, MoSe_2, and alpha-MoTe_2 Angle-resolved photoelectron spectroscopy and ab-initio calculations  

CERN Document Server

In this work the complete valence-band structure of the molybdenum dichalcogenides MoS_2, MoSe_2, and alpha-MoTe_2 is presented and discussed in comparison. The valence bands have been studied using both angle-resolved photoelectron spectroscopy (ARPES) with synchrotron radiation, as well as, ab-initio band-structure calculations. The ARPES measurements have been carried out in the constant-final-state (CFS) mode. The results of the calculations show in general very good agreement with the experimentally determined valence-band structures allowing for a clear identification of the observed features. The dispersion of the valence bands as a function of the perpendicular component k_perp of the wave vector reveals a decreasing three-dimensional character from MoS_2 to alpha-MoTe_2 which is attributed to an increasing interlayer distance in the three compounds. The effect of this k_perp dispersion on the determination of the exact dispersion of the individual states as a function of k_parallel is discussed. By p...

Böker, T; Müller, A; Janowitz, C; Manzke, R; Voss, D; Krüger, P; Mazur, A I; Pollmann, J; Boeker, Th.

2001-01-01

108

Theoretical calculations of the optical band positions and spin-Hamiltonian parameters for Cr3+ ions in Y2Ti2O7 crystal  

Science.gov (United States)

The optical band positions and spin-Hamiltonian parameters (g factors g?g? and zero-field splitting D) for the trigonal Cr3+ centers in Y2Ti2O7 crystal are calculated from the complete diagonalization (of energy matrix) method based on the two-spin-orbit-parameter model. In the calculations, the contributions to spectral data from both the spin-orbit parameter of central dn ion and that of ligand ion are considered and the crystal field parameters used are estimated from the superposition model. The calculated results are in reasonable agreement with the experimental values. The defect structures of Cr3+ center is suggested.

Yang, Mei; Yu-Guang, Yang; Wen-Chen, Zheng

2012-09-01

109

Band-structure calculations of noble-gas and alkali halide solids using accurate Kohn-Sham potentials with self-interaction correction  

Energy Technology Data Exchange (ETDEWEB)

The optimized-effective-potential (OEP) method and a method developed recently by Krieger, Li, and Iafrate (KLI) are applied to the band-structure calculations of noble-gas and alkali halide solids employing the self-interaction-corrected (SIC) local-spin-density (LSD) approximation for the exchange-correlation energy functional. The resulting band gaps from both calculations are found to be in fair agreement with the experimental values. The discrepancies are typically within a few percent with results that are nearly the same as those of previously published orbital-dependent multipotential SIC calculations, whereas the LSD results underestimate the band gaps by as much as 40%. As in the LSD---and it is believed to be the case even for the exact Kohn-Sham potential---both the OEP and KLI predict valence-band widths which are narrower than those of experiment. In all cases, the KLI method yields essentially the same results as the OEP.

Li, Y.; Krieger, J.B. (Department of Physics, Brooklyn College, City University of New York, Brooklyn, New York 11210 (United States)); Norman, M.R. (Material Sciences Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)); Iafrate, G.J. (U.S. Army Research Office, Research Triangle Park, North Carolina 27709-2211 (United States))

1991-11-15

110

First-principles calculation of the band gap of AlxGa1¡-xN and InxGa1¡-xN  

Directory of Open Access Journals (Sweden)

Full Text Available Ab-initio calculations of the band gap variation of AlxGa1¡xN and InxGa1¡xN ternary compounds were carried out using the Full-Potential Linearized Augmented Plane Waves (FLAPW method, within the Density Functional Theory (DFT. These nitrides were modeled in their wurtzite structure using the supercell method, for concentrations x = 0, 0.25, 0.50, 0.75 and 1.0. To optimize the cell parameters of the binary compounds we used the PBE96 (Perdew et al., Phys. Rev. Lett. 77 (1996 3865 exchange correlation functional. For the band structure calculations, we used both PBE96 and EV93 (Engel et al., Phys. Rev. B 47 (1993 13164 exchange correlation functionals. We considered experimental and calculated (with PBE96 lattice parameters to work out the electronic properties. We found that the fundamental gap is direct in all compounds. The calculation with EV93 functional gives a better band gap estimation for binary nitrides. The bowing parameter was also estimated obtaining the values b = 0.74 eV for AlxGa1¡xN and b = 2.12 eV for InxGa1¡xN.

Armando Reyes-Serrato

2008-01-01

111

First-principles calculation of the band offset at BaO/BaTiO$_3$ and SrO/SrTiO$_3$ interfaces  

CERN Document Server

We report first-principles density-functional pseudopotential calculations on the atomic structures, electronic properties, and band offsets of BaO/BaTiO$_3$ and SrO/SrTiO$_3$ nanosized heterojunctions grown on top of a silicon substrate. The density of states at the junction does not reveal any electronic induced interface states. A dominant perovskite character is found at the interface layer. The tunability of the band offset with the strain conditions imposed by the substrate is studied. Using previously reported theoretical data available for Si/SrO, Si/BaO and BaTiO$_{3}$/SrRuO$_{3}$ interfaces we extrapolate a value for the band alignments along the whole gate stacks of technological interest: Si/SrO/SrTiO$_3$ and Si/BaO/BaTiO$_3$/SrRuO$_3$ heterostructures.

Junquera, J; Ordejón, P; Ghosez, P; Junquera, Javier; Zimmer, Magali; Ordejon, Pablo; Ghosez, Philippe

2002-01-01

112

Band gap and band parameters of InN and GaN from quasiparticle energy calculations based on exact-exchange density-functional theory  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have studied the electronic structure of InN and GaN employing G0W0 calculations based on exact-exchange density-functional theory. For InN our approach predicts a gap of 0.7 eV. Taking the Burnstein-Moss effect into account, the increase of the apparent quasiparticle gap with increasing electron concentration is in good agreement with the observed blue shift of the experimental optical absorption edge. Moreover, the concentration dependence of the effective mass, which r...

Rinke, Patrick; Qteish, Abdallah; Winkelnkemper, Momme; Bimberg, Dieter; Neugebauer, Joerg; Scheffler, Matthias

2006-01-01

113

Valence Band Density of States of Cu3Si Studied by Soft X-Ray Emission Spectroscopy and a First-Principle Molecular Orbital Calculation  

Science.gov (United States)

A systematic study of the valence band structure of Cu3Si has been performed by soft X-ray emission spectroscopy and a first-principle molecular orbital calculation using the discrete-variational (DV)-X? cluster model. The existence of Cu 4s, 4p states in the valence band and their important contributions to the valence band as that of Cu 3d are indicated together with previously reported ones. The high-binding energy peak in the Si L2,3 emission spectrum is considered to originate mainly from the Si-Si 3s bonding state but also have a certain contribution of Si 3s bonding state with Cu 4s, 4p. On the other hand, the low-binding energy peaks in the Si L2,3 emission band are attributed to both the antibonding states of Si 3s and the bonding states of Si 3d with Cu 4s, 4p and Cu 3d. The bonding states of Si 3s with Cu 4s, 4p and Cu 3d are expected to exist in the lower part of the valence band for ?\\prime-Cu3Si on the basis of the theoretical calculations. As for Si p states, the high-binding energy peak and the low-binding energy peak in the Si K? emission spectrum should be attributed to the Si 3p bonding state and antibonding state with Cu 3d and Cu 4s, 4p, respectively, according to the theoretical calculations. A comparison is made between experimental spectra and theoretical density of states.

An, Zhenlian; Kamezawa, Chihiro; Hirai, Masaaki; Kusaka, Masahiko; Iwami, Motohiro

2002-12-01

114

UV-ray photoelectron and ab initio band calculation studies on electronic structures of Cr- or Nb-ion implanted titanium dioxide  

International Nuclear Information System (INIS)

The electronic structure of TiO2 doped with Cr or Nb by ion implantation is investigated by UPS and ab initio band calculations. Rutile TiO2 was implanted with 150 keV Cr or Nb ions and subsequently annealed in an air, and the recovery of radiation damage and substitution of implanted metals for Ti atoms was confirmed. UPS spectra for both of these oxides revealed a signal corresponding to the electron-occupied level in the band gap. For Cr-doped TiO2, this signal appeared close to the edge of the valence band (VB), while Nb-doped TiO2 exhibited a small signal far from the VB edge. According to band calculations, the midgap levels of Cr- and Nb-doped TiO2 consist of the electronic states localized in the Cr t2g orbital and delocalized over the Ti t2g and Nb t2g orbitals, respectively. Consequently, the electronic character of both of these oxides is determined by the energy of the t2g states of Ti and the dopant

2003-05-01

115

Precise band structure and Fermi-surface calculation for YBa2Cu3O7: Importance of three-dimensional dispersion  

International Nuclear Information System (INIS)

With the appearance of angle-resolved photoemission data allowing the identification and measurement of the Fermi surface of the high-Tc cuprate superconductors, it is important to have precise local-density calculations with which to compare. We present well-converged local-density predictions of the band structure and Fermi surface of YBa2Cu3O7, giving special attention to the position of the flat Cu-O chain-derived bands and the effect of the buckling of the Cu-O chain that is predicted by total-energy calculations and that has been inferred by an x-ray-scattering study. We emphasize the c-axis dispersion that will lead to apparent broadening of the Fermi surface in experiments interpreted in terms of a two-dimensional electronic structure

1990-11-01

116

The electronic band parameters calculated by the Kronig-Penney method for Cd1-xZnxS quantum dot superlattices  

International Nuclear Information System (INIS)

This work reports on a theoretical study of superlattices based on Cd1-xZnxS quantum dots embedded in an insulating material. We show, in particular, how this system can be assumed to a series of flattened cylindrical quantum dots with a finite barrier height at the boundary. In this paper, are also reviewed the approximations needed to calculate the band edges of the Cd1-xZnxS superlattices with use of the Kronig-Penney model. The electronic states and the electron effective masses of both ?1- and ?2-minibands have been computed as a function of zinc composition for different inter-quantum dot separations. As is found, the CdS system is appropriate to give rise a superlattice behavior for conduction electrons in a relatively large range of inter-sheet separations. An attempt to explain the electron band parameters calculated will be presented.

2009-05-12

117

Electronic band structure calculations on thin films of the L21 full Heusler alloys X2YSi (X, Y = Mn, Fe, and Co): Toward spintronic materials  

International Nuclear Information System (INIS)

To design half-metallic materials in thin film form for spintronic devices, the electronic structures of full Heusler alloys (Mn2FeSi, Fe2MnSi, Fe2FeSi, Fe2CoSi, and Co2FeSi) with an L21 structure have been investigated using density functional theory calculations with Gaussian-type functions in a periodic boundary condition. Considering the metal composition, layer thickness, and orbital symmetries, a 5-layered Co2FeSi thin film, whose surface consists of a Si layer, was found to have stable half-metallic nature with a band gap of ca. 0.6 eV in the minority spin state. Using the group theory, the difference between electronic structures in bulk and thin film conditions was discussed. - Highlights: ? Electronic band structure calculations of L21 full Heusler alloy thin films. ? Spintronic materials. ? Electronic properties dependency on layer thickness.

2012-05-31

118

Quasiparticle self-consistent GW calculations for PbS, PbSe, and PbTe: Band structure and pressure coefficients  

DEFF Research Database (Denmark)

The electronic band structures of PbS, PbSe, and PbTe in the rocksalt structure are calculated with the quasiparticle self-consistent GW (QSGW) approach with spin-orbit coupling included. The semiconducting gaps and their deformation potentials as well as the effective masses are obtained. The GW approximation provides a correct description of the electronic structure around the gap, in contrast to the local-density approximation, which leads to inverted gaps in the lead chalcogenides. The QSGW calculations are in good quantitative agreement with experimental values of the gaps and masses. At moderate hole doping a complex filamental Fermi-surface structure develops with ensuing large density of states. The pressure-induced gap closure leads to linear (Dirac-type) band dispersions around the L point.

Svane, Axel; Christensen, Niels Egede

2010-01-01

119

Electronic structure and optical absorption bands of the U center in alkaline earth fluorides calculated by the SCF-MSX? method  

International Nuclear Information System (INIS)

The self-consistent-field multiple-scattering method in the X? approximation is used to calculate the electronic structure and the optical transition energies of the U center in CaF_2, SrF_2 and BaF_2. The very good agreement obtained between the experimental and theoretical results concerning the optical bands indicates that the scheme used is convenient to treat this type of defect

1976-03-01

120

Electronic structure of SrPt{sub 4}Ge{sub 1}2: a study by soft x-ray photoelectron spectroscopy and band structure calculations  

Energy Technology Data Exchange (ETDEWEB)

We present a comparative study of the electronic structure of the superconducting skutterudite SrPt{sub 4}Ge{sub 12} by means of soft X-ray photoelectron spectroscopy and full potential band structure calculations. Excellent agreement between the measured and the calculated valence spectra is observed, confirming the picture of rather localized, low lying Pt 5d states compared to Pt metal. This implicates that the states at the Fermi level stem predominantly from Ge 4p electrons. An analysis of the chemical bonding in SrPt{sub 4}Ge{sub 12} based on the electron localizability indicator is given.

Gegner, Jan; Regesch, David; Fujiwara, Hidenori; Haupricht, Tim; Tjeng, Liu Hao [II. Physikalisches Institut, Universitaet Koeln (Germany); Rosner, Helge; Schnelle, Walter; Gumeniuk, Roman; Leithe-Jasper, Andreas; Ormeci, Alim; Grin, Juri [Max-Planck-Institut fuer Chemische Physik Fester Stoffe, Dresden (Germany); Hsieh, H.H. [Chung Cheng Institute of Technology, National Defense University, Taoyuan (China); Lin, H.J.; Chen, C.T. [National Synchrotron Radiation Research Center (NSRRC), Hsinchu (China)

2009-07-01

 
 
 
 
121

Electronic structure of SrPt4Ge12: a study by soft x-ray photoelectron spectroscopy and band structure calculations  

International Nuclear Information System (INIS)

We present a comparative study of the electronic structure of the superconducting skutterudite SrPt4Ge12 by means of soft X-ray photoelectron spectroscopy and full potential band structure calculations. Excellent agreement between the measured and the calculated valence spectra is observed, confirming the picture of rather localized, low lying Pt 5d states compared to Pt metal. This implicates that the states at the Fermi level stem predominantly from Ge 4p electrons. An analysis of the chemical bonding in SrPt4Ge12 based on the electron localizability indicator is given.

2009-03-22

122

LDA + GTB (generalized tight-binding) method for the electronic structure calculations of strongly correlated electron systems: Application for the band structure calculations of p-type cuprates  

International Nuclear Information System (INIS)

Mean-field theory of the non-superconducting phase of the high-Tc cuprates is formulated within the effective t-t'-t''-J model with three-site correlated hoppings. This model with the ab initio calculated parameters results from the LDA + GTB method. The static spin and kinematical correlation functions beyond Hubbard I approximation are calculated self-consistently taking into account hoppings to the first, the second, and the third neighboring sites, as well as the three-site correlated hoppings. The obtained Fermi surface evolves from hole-pockets at low-doping to large hole-type Fermi surface at higher doping concentrations. Calculated doping dependence of the nodal Fermi velocity, the effective mass and the chemical potential shift are in good agreement with experimental data

2007-09-01

123

Measurements and calculations of ethylene line-broadening by argon in the ?7 band at room temperature  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract Argon broadening coefficients are measured for 32 vibrotational lines in the ?7 band of ethylene at room temperature using a tunable diode-laser spectrometer. These lines with 3? J ? 19, 0? Ka ? 4, 2 ? Kc ? 19 in the P, Q and R branches are located in the spectral range 919-1023 cm-1. The fitting of experimental line shapes with Rautian profile provides the collisional widths slightly larger t...

2008-01-01

124

Energy band structure calculations of Ga{sub x}In{sub 1?x}P alloys under the influence of temperature and pressure  

Energy Technology Data Exchange (ETDEWEB)

Highlights: •Effect of temperature of Ga{sub x}In{sub 1?x}P alloy was calculated. •Effect of hydrostatic pressure of Ga{sub x}In{sub 1?x}P alloy was calculated. •Refractive index and high frequency dielectric constant were studied. •Good agreement between our results and published data was obtained. -- Abstract: This work is concerned with the dependence of the electronic energy band structures for Ga{sub x}In{sub 1?x}P alloys on temperature and pressure. The calculations are based on local empirical pseudo-potential method (EPM) coupled with the virtual crystal approximation (VCA) which incorporates compositional disorder as an effective potential. The direct and indirect energy band gaps of the considered alloys have been determined over entire composition parameter, x from 0 to 1, temperature from T = 0 K to 500 K and pressure from P=0Kbar to 120 Kbar. In addition, the refractive index and dielectric constant of the considered alloys under the effect of composition, temperature and pressure have also been studied. The ternary alloys Ga{sub x}In{sub 1?x}P is bordered by two binary compounds GaP and InP which have been studied recently by our group. Comparison of the calculated results with the experimental and published data showed good agreement.

Degheidy, Abdel Razik; Elwakil, Sayed Abdel Aty; Elkenany, Elkenany Brens, E-mail: kena@mans.edu.eg

2013-10-15

125

Finite difference time domain calculation of three-dimensional phononic band structures using a postprocessing method based on the filter diagonalization  

International Nuclear Information System (INIS)

If the band structure of a three-dimensional (3D) phononic crystal (PNC) is calculated by using the finite difference time domain (FDTD) method combined with the fast Fourier transform (FFT)-based postprocessing method, good results can only be ensured by a sufficiently large number of FDTD iterations. On a common computer platform, the total computation time will be very long. To overcome this difficulty, an excellent harmonic inversion algorithm called the filter diagonalization method (FDM) can be used in the postprocessing to reduce the number of FDTD iterations. However, the low efficiency of the FDM, which occurs when a relatively long time series is given, does not necessarily ensure an effective reduction of the total computation time. In this paper, a postprocessing method based on the FDM is proposed. The main procedure of the method is designed considering the aim to make the time spent on the method itself far less than the corresponding time spent on the FDTD iterations. To this end, the FDTD time series is preprocessed to be shortened significantly before the FDM frequency extraction. The preprocessing procedure is performed with the filter and decimation operations, which are widely used in narrow-band signal processing. Numerical results for a typical 3D solid PNC system show that the proposed postprocessing method can be used to effectively reduce the total computation time of the FDTD calculation of 3D phononic band structures.

2011-10-01

126

Finite difference time domain calculation of three-dimensional phononic band structures using a postprocessing method based on the filter diagonalization  

Energy Technology Data Exchange (ETDEWEB)

If the band structure of a three-dimensional (3D) phononic crystal (PNC) is calculated by using the finite difference time domain (FDTD) method combined with the fast Fourier transform (FFT)-based postprocessing method, good results can only be ensured by a sufficiently large number of FDTD iterations. On a common computer platform, the total computation time will be very long. To overcome this difficulty, an excellent harmonic inversion algorithm called the filter diagonalization method (FDM) can be used in the postprocessing to reduce the number of FDTD iterations. However, the low efficiency of the FDM, which occurs when a relatively long time series is given, does not necessarily ensure an effective reduction of the total computation time. In this paper, a postprocessing method based on the FDM is proposed. The main procedure of the method is designed considering the aim to make the time spent on the method itself far less than the corresponding time spent on the FDTD iterations. To this end, the FDTD time series is preprocessed to be shortened significantly before the FDM frequency extraction. The preprocessing procedure is performed with the filter and decimation operations, which are widely used in narrow-band signal processing. Numerical results for a typical 3D solid PNC system show that the proposed postprocessing method can be used to effectively reduce the total computation time of the FDTD calculation of 3D phononic band structures.

Su Xiaoxing [School of Electronic and Information Engineering, Beijing Jiaotong University, Beijing 100044 (China); Ma Tianxue; Wang Yuesheng, E-mail: xxsu@bjtu.edu.cn [Institute of Engineering Mechanics, Beijing Jiaotong University, Beijing 100044 (China)

2011-10-15

127

GaMnAs: Position of Mn-d levels and majority spin band gap predicted from GGA-1/2 calculations  

Science.gov (United States)

Among all magnetic semiconductors, GaMnAs seems to be the most important one. In this work, we present accurate first-principles calculations of GaMnAs within the GGA-1/2 approach: We concentrate our efforts in obtaining the position of the peak of Mn-d levels in the valence band and also the majority spin band gap. For the position of the Mn-d peak, we find a value of 3.3 eV below the Fermi level, in good agreement with the most recent experimental results of 3.5 and 3.7 eV. An analytical expression that fits the calculated Eg(x) for majority spin is derived in order to provide ready access to the band gap for the composition range from 0 to 0.25. We found a value of 3.9 eV for the gap bowing parameter. The results agree well with the most recent experimental data.

Pelá, R. R.; Marques, M.; Ferreira, L. G.; Furthmüller, J.; Teles, L. K.

2012-05-01

128

Rotational bands in 235U comparison with rotor-plus-quasiparticle calculations using H.F. orbitals  

International Nuclear Information System (INIS)

235U was Coulomb excited with 84Kr beams of 370 and 450 Mev. Observed energy levels are tabulated. Then the spectrum of 235U was determined from self-consistent calculations of the neighboring even-even core nuclei 234U and 236U within a rotor-plus-quasi-particle approach. The calculations reproduced the trends of the experimental low-energy spectrum quite well; this fact confirms the rotational nature of 235U. 1 figure, 2 tables

1979-10-01

129

The Uncertainties of the Calculated Optical Basicity from the Optical Band Gap and the Refractive Index for Some Oxide Glass Systems  

Directory of Open Access Journals (Sweden)

Full Text Available In this study, the uncertainties of the optical basicity calculation based on the optical band gap and the refractive index for two glass systems (K2O-Nb2O5-TeO2, B2O3-Na2O-TeO2, have been estimated. The results benefits are very important in the determination of the optical basicity of binary and ternary glass systems. It has been established that as in the binary glass systems, there is a general trend of increasing the oxide ion polarizability with decreasing the oxide optical band gap and increasing the refractive index of the glass samples. Also it has been found that the uncertainty of the optical basicity estimation is around ±5 to ±15%. Some tables have been reported to help us predict the method used to determine the optical basicity for a glass system accurately.

El-Sayed Mostafa

2005-01-01

130

Local ab initio methods for calculating optical band gaps in periodic systems. I. Periodic density fitted local configuration interaction singles method for polymers.  

Science.gov (United States)

We present a density fitted local configuration interaction singles (CIS) method for calculating optical band gaps in 1D-periodic systems. The method is based on the Davidson diagonalization procedure, carried out in the reciprocal space. The one-electron part of the matrix-vector products is also evaluated in the reciprocal space, where the diagonality of the Fock matrix can be exploited. The contraction of the CIS vectors with the two electron integrals is performed in the direct space in the basis of localized occupied (Wannier) and virtual (projected atomic) orbitals. The direct space approach allows to utilize the sparsity of the integrals due to the local representation and locality of the exciton. The density fitting approximation employed for the two electron integrals reduces the nominal scaling with unit cell size to O(N(4)). Test calculations on a series of prototypical systems demonstrate that the method in its present stage can be used to calculate the excitonic band gaps of polymers with up to a few dozens of atoms in the cell. The computational cost depends on the locality of the exciton, but even relatively delocalized excitons occurring in the polybiphenyl in the parallel orientation, can be routinely treated with this method. PMID:21384944

Lorenz, Marco; Usvyat, Denis; Schütz, Martin

2011-03-01

131

On the importance of constrained atomic relaxations in the Nudged Elastic Band calculations of the Peierls barriers of dislocations  

CERN Document Server

We demonstrate that the straightforward application of the Nudged Elastic Band (NEB) method does not determine the correct Peierls barrier of 1/2 screw dislocations in BCC metals. Although this method guarantees that the states (images) of the system are distributed uniformly along the minimum energy path, it does not imply that the dislocation positions are distributed uniformly along this path. In fact, clustering of dislocation positions near potential minima occurs which leads to an overestimate of both the slope of the Peierls barrier and the Peierls stress. We propose a modification in which the NEB method is applied only to a small number of degrees of freedom that determine the position of the dislocation, while all other coordinates of atoms are relaxed by molecular statics as in any atomistic study. This modified NEB method with relaxations gives the Peierls barrier that increases smoothly with the dislocation position and the corresponding Peierls stress agrees well with that evaluated by the direc...

Gröger, R

2011-01-01

132

Semiclassical calculations of half-widths and line shifts for transitions in the 30012?00001 and 30013?00001 bands of CO2. III: Self collisions  

International Nuclear Information System (INIS)

This paper is the third in a series devoted to accurate semi-empirical calculations of pressure-broadened half-widths, pressure-induced line shifts, and the temperature dependence of the half-widths of carbon dioxide. In this work complex Robert-Bonamy (CRB) calculations were made for transitions in two of the Fermi-tetrad bands for self-collisions, i.e. the CO2-CO2 system. The intermolecular potential (IP) was adjusted to match measurements of the half-width, its temperature dependence, and the line shift. It is shown that small changes in the parameters describing the IP lead to noticeable changes in the line shape parameters and that it is possible to find a set of IP parameters, which, when used in the CRB formalism, yield half-widths, their temperature dependence, and line shifts in excellent agreement with measurement. This work demonstrates that this agreement can be obtained if the atom-atom potential is expanded to high order and rank (here 20 4 4), the real and imaginary (S1 and Im(S2)) components are retained, and the determination of the trajectories is made by solving Hamilton's equations. It was found that the temperature dependence of the half-width is sensitive to the range of temperatures used in the fit and that the vibrational dependence of the line shape parameters for these two bands is very small. Databases of the half-width, its temperature dependence, and the line shift for the atmospheres of Venus (296-700 K fit range for the temperature exponents of the half-widths) and Mars (125-296 K fit range for the temperature exponents of the half-widths) are provided. The calculations are compared with the measured data for the bands under study.

2012-08-01

133

Photolysis rate coefficients in the upper atmosphere: Effect of line by line calculations of the O2 absorption cross section in the Schumann-Runge bands  

International Nuclear Information System (INIS)

A line by line (LBL) method to calculate highly resolved O2 absorption cross sections in the Schumann-Runge (SR) bands region was developed and integrated in the widely used Tropospheric Ultraviolet Visible (TUV) model to calculate accurate photolysis rate coefficients (J values) in the upper atmosphere at both small and large solar zenith angles (SZA). In order to obtain the O2 cross section between 49,000 and 57,000cm-1, an algorithm which considers the position, strength, and half width of each spectral line was used. Every transition was calculated by using the HIgh-resolution TRANsmission molecular absorption database (HITRAN) and a Voigt profile. The temperature dependence of both the strength and the half widths was considered within the range of temperatures characteristic of the US standard atmosphere, although the results show a very good agreement also at 79K. The cross section calculation was carried out on a 0.5cm-1 grid and the contributions from all the lines lying at +/-500cm-1 were considered for every wavelength. Both the SR and the Herzberg continuums were included. By coupling the LBL method to the TUV model, full radiative transfer calculations that compute J values including Rayleigh scattering at high altitudes and large SZA can now be done. Thus, the J values calculations were performed for altitudes from 0 to 120km and for SZA up to 89o. The results show, in the JO2 case, differences of more than +/-10% (e.g. at 96km and 30o) when compared against the last version of the TUV model (4.4), which uses the Koppers and Murtagh parameterization for the O2 cross section. Consequently, the J values of species with cross sections overlapping the SR band region show variable differences at lower altitudes. Although many species have been analyzed, the results for only four of them (O2, N2O, HNO3, CFC12) are presented. Due to the fact that the HNO3 absorption cross section extends up to 350nm this molecule was used to verify the consistency of the new TUV-LBL at lower altitudes. Thus, it shows differences up to 5.7% at 21km but 0% in the troposphere. Because of the more accurate consideration of the Rayleigh scattering the distribution of the actinic flux in its direct and diffuse components (in the SR bands wavelength interval) is also modified

2007-03-01

134

Photolysis rate coefficients in the upper atmosphere: Effect of line by line calculations of the O{sub 2} absorption cross section in the Schumann-Runge bands  

Energy Technology Data Exchange (ETDEWEB)

A line by line (LBL) method to calculate highly resolved O{sub 2} absorption cross sections in the Schumann-Runge (SR) bands region was developed and integrated in the widely used Tropospheric Ultraviolet Visible (TUV) model to calculate accurate photolysis rate coefficients (J values) in the upper atmosphere at both small and large solar zenith angles (SZA). In order to obtain the O{sub 2} cross section between 49,000 and 57,000cm{sup -1}, an algorithm which considers the position, strength, and half width of each spectral line was used. Every transition was calculated by using the HIgh-resolution TRANsmission molecular absorption database (HITRAN) and a Voigt profile. The temperature dependence of both the strength and the half widths was considered within the range of temperatures characteristic of the US standard atmosphere, although the results show a very good agreement also at 79K. The cross section calculation was carried out on a 0.5cm{sup -1} grid and the contributions from all the lines lying at +/-500cm{sup -1} were considered for every wavelength. Both the SR and the Herzberg continuums were included. By coupling the LBL method to the TUV model, full radiative transfer calculations that compute J values including Rayleigh scattering at high altitudes and large SZA can now be done. Thus, the J values calculations were performed for altitudes from 0 to 120km and for SZA up to 89{sup o}. The results show, in the J{sub O{sub 2}} case, differences of more than +/-10% (e.g. at 96km and 30{sup o}) when compared against the last version of the TUV model (4.4), which uses the Koppers and Murtagh parameterization for the O{sub 2} cross section. Consequently, the J values of species with cross sections overlapping the SR band region show variable differences at lower altitudes. Although many species have been analyzed, the results for only four of them (O{sub 2}, N{sub 2}O, HNO{sub 3}, CFC12) are presented. Due to the fact that the HNO{sub 3} absorption cross section extends up to 350nm this molecule was used to verify the consistency of the new TUV-LBL at lower altitudes. Thus, it shows differences up to 5.7% at 21km but 0% in the troposphere. Because of the more accurate consideration of the Rayleigh scattering the distribution of the actinic flux in its direct and diffuse components (in the SR bands wavelength interval) is also modified.

Fernandez, Rafael P. [INFIQC, Centro Laser de Ciencias Moleculares, Departamento de Fisico Quimica, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, 5000, Cordoba (Argentina); Palancar, Gustavo G. [INFIQC, Centro Laser de Ciencias Moleculares, Departamento de Fisico Quimica, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, 5000, Cordoba (Argentina)]. E-mail: palancar@fcq.unc.edu.ar; Madronich, Sasha [Atmospheric Chemistry Division, National Center for Atmospheric Research, 1850 Table mesa Drive, Boulder, CO, 80303 (United States); Toselli, Beatriz M. [INFIQC, Centro Laser de Ciencias Moleculares, Departamento de Fisico Quimica, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, 5000, Cordoba (Argentina)]. E-mail: tosellib@fcq.unc.edu.ar

2007-03-15

135

Calculation of band offsets in Cd1-xXxTe alloys, X = Zn, Mg, Hg and Mn and magnetic effects in CdMnTe  

International Nuclear Information System (INIS)

Highlights: ? The conduction and valence band offsets of the pseudo-morphically strained Cd1-xXxTe layer on relaxed Cd1-yXyTe substrate, are investigated for X = Zn, Mg, Hg and Mn in the entire range 0 ? x,y ? 1. ? For Cd1-xMnxTe diluted magnetic semiconductors, the exchange interactions are determined in the order to take into account magnetic effect. ? The conduction and valence band offsets of Cd1-xMnxTe/CdTe interface are calculated in the whole range of Mn composition x and for magnetic field values equal to 0 and 5 T. - Abstract: Due to the large variety of properties offered by the telluride binaries CdTe, ZnTe, MgTe, HgTe and MnTe as well as their mixed ternary alloys, an accurate knowledge of their electronic band parameters is crucial. These materials have been extensively studied but, some points bearing on several properties have never previously reported or are still not clear. In this paper, we report results on the conduction and valence band offsets of the pseudo-morphically strained Cd1-xXxTe layer on relaxed Cd1-yXyTe substrate, X = Zn, Hg, Mg and Mn. Based on the Van Der Walle model, calculations have been performed for the all range of material and substrate 0 ? x,y ? 1. These discontinuities have not yet calculated for X = Mg, Mn or Hg in the all range 0 ? x,y ? 1. For the CdMnTe diluted magnetic semiconductor which we focus more interest due to its considerable current interest for applications, calculations have been done without and with correction taking into account magnetic effect of magnesium ions Mn2+. It is found that the introduction of only a few percent of Mn into CdTe provides a unique opportunity to combine two important fields in physics, semiconductivity and magnetism. We can take advantage both of possibility of applications in solid-state lasers and exceptional magnetic properties offered by this magnetic diluted semiconductor. This study presents important quantities that are required to model quantum structures and offers a fast and inexpensive way to check device designs and processes.

2011-07-21

136

The Uncertainties of the Calculated Optical Basicity from the Optical Band Gap and the Refractive Index for Some Oxide Glass Systems  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this study, the uncertainties of the optical basicity calculation based on the optical band gap and the refractive index for two glass systems (K2O-Nb2O5-TeO2, B2O3-Na2O-TeO2), have been estimated. The results benefits are very important in the determination of the optical basicity of binary and ternary glass systems. It has been established that as in the binary glass systems, there is a general trend ...

El-Sayed Mostafa

2005-01-01

137

First-principles calculation of the band gap of AlxGa1¡-xN and InxGa1¡-xN  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Ab-initio calculations of the band gap variation of AlxGa1¡xN and InxGa1¡xN ternary compounds were carried out using the Full-Potential Linearized Augmented Plane Waves (FLAPW) method, within the Density Functional Theory (DFT). These nitrides were modeled in their wurtzite structure using the supercell method, for concentrations x = 0, 0.25, 0.50, 0.75 and 1.0. To optimize the cell parameters of the binary compounds we used the PBE96 (Perdew et al., Phys. Rev. Lett. 77 (1996) 3865) exchang...

2008-01-01

138

The density of states and band gap of liquid water by sequential Monte Carlo/Quantum mechanics calculations  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english Electronic properties of liquid water were investigated by sequential Monte Carlo/Quantum mechanics calculations. The density of states (DOS) and HOMO-LUMO gap (E G) of liquid water have been determined by Hartree-Fock and Density Functional Theory (DFT) calculations. The quantum mechanical calculat [...] ions were carried out over uncorrelated supermolecular structures generated by the Monte Carlo simulations. The DFT calculations were performed with a modified B3LYP exchange-correlation functional proposed by Abu-Awwad and Politzer which was parametrized to reproduce valence orbital energies in agreement with experimental ionization potentials of the water molecule. We have analyzed the dependence of the DOS and HOMO-LUMO gap on the number of water molecules and on surface effects. Our prediction for E G is 6:5 ± 0:5 eV in good agreement with a recent experimental prediction of 6.9 eV.

P. Cabral do, Couto; R. C., Guedes; B. J. Costa, Cabral.

139

Stability and band gaps of InGaAs, BGaAs, and BInGaAs alloys: Density-functional supercell calculations  

International Nuclear Information System (INIS)

The influence of arrangement and content of substituents (B, In) in BGaAs, InGaAs, and BInGaAs alloys on the stabilities and band gaps is investigated using density-functional supercell calculations. The stability of ternary alloys decreases from InGaAs over BGaAs to GaAsN. Typical substituent structures show the following stability order: isolated substituents - [110] chains - clusters - twisted [111] chains - (200/211) arrangements (most stable). This is valid for both the In- and B-poor as well as the In- and B-rich alloys. From the fact that grown InGaAs provides a different gap than the most stable arrangement one can conclude that other structures (isolated indium atoms or InmAs clusters) are formed during the growth. Simultaneous substitutions (BInGaAs) of larger (In) and smaller (B) atoms prefer arrangements in larger distances (220) for isovalent boron substitution and in In-B bonds for antisite boron substitution. The high degree boron antisite substitution induces partially occupied acceptor bands which lead to a strong reduction of the band gap in comparison to the isovalent substitution. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2007-06-01

140

A modified band approach for the accurate calculation of on-line photolysis rates in stratospheric-tropospheric Chemical Transport Models  

Directory of Open Access Journals (Sweden)

Full Text Available Here we present an efficient and accurate method for the online calculation of photolysis rates relevant to both the stratosphere and troposphere for use in global Chemistry Transport Models. The method is a modified version of the band model introduced by Landgraf and Crutzen (1998 which has been updated to improve the performance of the approach for solar zenith angles >75° without the use of any implicit parameterisations. For this purpose, additional sets of band parameters have been defined for instances where the incident angle of the light beam is between 75–93°, in conjunction with a scaling component for the far UV region of the spectrum (?=176.6–202.0 nm. For incident angles between 85–93° we introduce a modification for pseudo-sphericity that improves the accuracy of the 2-stream approximation. We show that this modified version of PIFM is accurate for angles <93° by comparing the resulting height resolved actinic fluxes with a recently developed full spherical reference model. We also show that the modified band method is more accurate than the original, with errors generally being ±10% throughout the atmospheric column for a diverse range of chemical species. Moreover, we perform certain sensitivity studies that indicate it is robust and performs well over a wide range of conditions relevant to the atmosphere.

J. E. Williams

2006-05-01

 
 
 
 
141

Surface rumples and band gap reductions of cubic BaZrO3 (001) surface studied by means of first-principles calculations  

International Nuclear Information System (INIS)

Electronic properties of the (001) surface of cubic BaZrO3 with BaO and ZrO2 terminations have been studied using first-principles calculations. Surface structure, partial density of states, band structure and surface energy have been obtained. We find that the largest relaxation appears in the first layer of atoms, and the relaxation of the BaO-terminated surface is larger than that of the ZrO2-terminated surface. The surface rumpling of the BaO-terminated surface is also larger than that of the ZrO2-terminated surface. Results of surface energy calculations reveal that the BaZrO3 surface is likely to be more stable than the PbZrO3 surface

2008-01-01

142

Thomas-Fermi-Dirac calculations of valence band states in two p-type delta-doped ZnSe quantum wells  

Energy Technology Data Exchange (ETDEWEB)

We present the hole sub-band structure study in two p-type {delta}-doped ZnSe QW's. An analytical expression for the Hartree-Fock potential is obtained following the lines of the Thomas-Fermi-Dirac (TFD) approximation. We have analyzed the dependence of the hole energy levels to the impurity density and the interlayer distance between wells. The exchange effects are also included in the present survey. We find that many body effects cannot be ignored because these are really important in the calculation at least in the low concentration regime. We have obtained an energy difference between the top of the valence band and the ground energy of the heavy hole ladder of meV in good agreement with the experimental reports (eV) available. We calculate the mobility ratio between double {delta}-doped QW's and simple {delta}-doped QW based on a phenomenological formula. We find the optimum interlayer distance between wells for maximum mobility for three impurity concentrations, which can be of great importance for technological applications. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Rodriguez-Vargas, I.; Gaggero-Sager, L.M.; Martinez-Orozco, J.C. [Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa 62210 Cuernavaca, Morelos (Mexico)

2005-04-01

143

The electronic band parameters calculated by the Kronig-Penney method for Cd{sub 1-x}Zn{sub x}S quantum dot superlattices  

Energy Technology Data Exchange (ETDEWEB)

This work reports on a theoretical study of superlattices based on Cd{sub 1-x}Zn{sub x}S quantum dots embedded in an insulating material. We show, in particular, how this system can be assumed to a series of flattened cylindrical quantum dots with a finite barrier height at the boundary. In this paper, are also reviewed the approximations needed to calculate the band edges of the Cd{sub 1-x}Zn{sub x}S superlattices with use of the Kronig-Penney model. The electronic states and the electron effective masses of both {gamma}{sub 1}- and {gamma}{sub 2}-minibands have been computed as a function of zinc composition for different inter-quantum dot separations. As is found, the CdS system is appropriate to give rise a superlattice behavior for conduction electrons in a relatively large range of inter-sheet separations. An attempt to explain the electron band parameters calculated will be presented.

Sakly, A. [Unite de Physique Quantique, Faculte des Sciences, Avenue de l' Environnement, 5000 Monastir (Tunisia); Safta, N. [Laboratoire de Physique des Semi-conducteurs et des Composants Electroniques, Faculte des Sciences, Avenue de l' environnement, 5000 Monastir (Tunisia)], E-mail: saftanabil@yahoo.fr; Mejri, H. [Unite de Recherche de Mathematiques Appliquees et Physique Mathematiques, Ecole Preparatoire aux Academies Militaires, Avenue Marechal Tito, 4029 Sousse (Tunisia); Lamine, A. Ben [Unite de Physique Quantique, Faculte des Sciences, Avenue de l' Environnement, 5000 Monastir (Tunisia)

2009-05-12

144

Full-band structure calculations of optical injection in semiconductors: Investigations of one-color, two-color, and pump-probe scenarios  

Science.gov (United States)

Carrier, spin, charge current, and spin current injection by one- and two-color optical schemes are investigated within 30-band k ? p theory. Parameters of the band model are optimized to give full-Brillouin zone band structures for GaAs and Ge that give accurate Gamma-point effective masses and gyromagnetic factors and give access to the L valley, and to the E1 and E1 + Delta1 critical points in the linear optical absorption. Calculations of one- and two-photon carrier and spin injection and two-color current injection are performed for excitation energies in the range of 0--4 eV in GaAs and 0--3.5 eV in Ge. Significant spin and spin current injection occurs with 30% spin polarization in GaAs and Ge at photon energy matching the E1 critical point. Further, the anisotropy and disparity of the current injection between parallel and perpendicular linearly-polarized beam configurations are calculated. For light propagating along a crystal axis, anisotropic contributions in coherent current control and two-photon spin injection give rise to normal current components and in-plane spin components. In Ge, contributions from the holes to spin, electrical current, and spin current injection are investigated. Optical orientation results in 83% spin-polarized holes at the band edge. The effects of carrier dynamics in Ge are treated within a rate-equation model. The detection of spin dynamics in a pump-probe setup is considered, and the Fermi-factor approach is justified for electrons but not for holes. Carrier and current injection are further investigated in single-layer and bilayer graphene within the tight-binding model. In single-layer graphene, the linear-circular dichroism in two-photon absorption yields an absorption coefficient that is twice as large for circularly polarized light compared to linearly polarized light. Coherent current injection is largest for co-circularly polarized beams and zero for cross-circularly polarized beams. For linearly polarized beams, the magnitude of the injected current is independent of beam polarizations. In contrast, the injected current in bilayer graphene shows disparity between parallel and perpendicular configurations of the beams. The resulting angular dependence of the current is a macroscopic, measurable consequence of interlayer coupling in the bilayer.

Robinson, Michael

145

Density-functional band-structure calculations for La-, Y-, and Sc-filled CoP3-based skutterudite structures  

International Nuclear Information System (INIS)

The crystal structure, thermodynamic stability, and electronic structure of La-, Y-, and Sc-filled CoP3 are predicted from density-functional band-structure calculations. The size of the cubic voids in the skutterudite structure is changed much less than the difference in size between the different filling atoms, and we expect that the larger rattling amplitude of the smaller Sc and Y atoms may decrease the lattice thermal conductivity of Sc- and Y-filled structures significantly compared to La-filled structures. The solubility of La, Y, and Sc in CoP3 is calculated to be around 5, 3-6 %, and below 1% at 0 K, respectively. Based on similar systems, this is expected to increase considerably if Fe is substituted for Co. Fe substitution is also expected to compensate the increased charge carrier concentration of the filled structures that is seen in the calculated electron density of states. In conclusion, Sc- or Y-filled (FeCo)P3 skutterudite structures are promising materials for thermoelectric applications

2004-11-15

146

Combining GW calculations with exact-exchange density-functional theory: An analysis of valence-band photoemission for compound semiconductors  

CERN Multimedia

We report quasiparticle-energy calculations of the electronic bandstructure as measured by valence-band photoemission for selected II-VI compounds and group-III-nitrides. By applying GW as perturbation to the ground state of the fictitious, non-interacting Kohn-Sham electrons of density-functional theory (DFT) we systematically study the electronic structure of zinc-blende GaN, ZnO, ZnS and CdS. Special emphasis is put on analysing the role played by the cation semicore d-electrons that are explicitly included as valence electrons in our pseudopotential approach. Unlike in the majority of previous GW studies, which are almost exlusively based on ground state calculations in the local-density approximation (LDA), we combine GW with exact-exchange DFT calculations in the optimised-effective potential approach (OEPx). This is a much more elaborate and computationally expensive approach. However, we show that applying the OEPx approach leads to an improved description of the d-electron hybridisation compared to t...

Rinke, P; Neugebauer, J; Freysoldt, C; Scheffler, M; Rinke, Patrick; Qteish, Abdallah; Neugebauer, Joerg; Freysoldt, Christoph; Scheffler, Matthias

2005-01-01

147

Absorption intensities of rovibronic transitions in the A-band of 16O2: Analysis and calculation of magnetic dipole and electric quadrupole contributions  

Science.gov (United States)

The recently measured magnetic dipole (M1) absorption intensities of rovibronic transitions in the A-band (b?g+1-X?g-3, 030 band) of 16O2 are theoretically analyzed employing a model in which the b?g+1:X?g-3 mutual perturbations are treated to a sufficient degree of accuracy. Effects of rotational perturbations became manifest in the data analysis and rovibronic correction parameters are needed to reconcile theory and experiment. At a subtle level there is evidence of Herman-Wallis (HW) type effect arising from vibration-rotation interaction in the b and X states. The functional form for the HW correction factor is arrived at from first principles. The final calculations reproduce the measured intensities to fraction of a percent, well within the measurement accuracy. The present analysis leads to the value <=0.02679(4) ?B for the M1 transition moment, and the spontaneous emission rate (Einstein-A coefficient) ?0,0=0.0874 s-1. For the sake of completeness, the electric quadrupole (E2) contribution to the observed intensities is also quantitatively assessed.

Balasubramanian, T. K.; Mishra, Adya P.; Kshirsagar, R. J.

2014-01-01

148

RPC Calculations for K-forbidden Transitions in 183W, Evidence for Large Inertial Parameter Connected with High-lying Rotational Bands  

International Nuclear Information System (INIS)

Recent measurements have shown that the transitions deexciting the 453 keV 7/2- level in 183W to the K = 1/2- and 3/2- bands are strongly retarded. The data for B(M1) and B(E2) are analyzed in terms of the RPC model (rotation + particle motion + coupling). With the ?K = 1 (Coriolis) coupling, the K-forbidden M1-transitions proceed via admixtures of high-lying 5/2- bands. A reasonable and unambiguous fit to the data is obtained by varying the strength of the coupling. Allowing for various uncertainties and corrections, one finds that the inertial parameter (the inverse of the coupling constant, i. e. 2J(2?)2/(?)2 may have values between roughly 1 and 3 times the rigid rotator value of 2J(2?)2/(?)2, thus being unexpectedly large. Calculations with the ?K=2 coupling were also performed and turn out not to give better agreement with experiment

1967-01-01

149

Spectra calculations in central and wing regions of CO2 IR bands between 10 and 20 ?m. II. Atmospheric solar occultation spectra  

International Nuclear Information System (INIS)

The theoretical approach based on the Energy Corrected Sudden Approximation presented in the previous companion paper is used in order to account for line-mixing effects in infrared bands of CO2. Its performance, which was demonstrated using laboratory spectra is confirmed here by considering atmospheric transmission in the 10-14 ?m region. Comparisons are made between forward calculations of atmospheric transmission spectra and values measured using two different solar occultation experiments based on high resolution Fourier transform instruments. The results demonstrate that neglecting line-mixing and using a Voigt model can lead to a very large overestimation of absorption that may extend over more than 300 cm-1 in the wing of the CO2 ?2 band. They also demonstrate the capability of our model to represent accurately the absorption in the entire region for a variety of atmospheric paths. Among positive consequences of the quality of the model, the possibility of retrieving amounts of (heavy) trace gases with weak and broad absorption features is demonstrated

2005-01-01

150

Spectra calculations in central and wing regions of CO{sub 2} IR bands between 10 and 20 {mu}m. II. Atmospheric solar occultation spectra  

Energy Technology Data Exchange (ETDEWEB)

The theoretical approach based on the Energy Corrected Sudden Approximation presented in the previous companion paper is used in order to account for line-mixing effects in infrared bands of CO{sub 2}. Its performance, which was demonstrated using laboratory spectra is confirmed here by considering atmospheric transmission in the 10-14 {mu}m region. Comparisons are made between forward calculations of atmospheric transmission spectra and values measured using two different solar occultation experiments based on high resolution Fourier transform instruments. The results demonstrate that neglecting line-mixing and using a Voigt model can lead to a very large overestimation of absorption that may extend over more than 300 cm{sup -1} in the wing of the CO{sub 2} {nu}{sub 2} band. They also demonstrate the capability of our model to represent accurately the absorption in the entire region for a variety of atmospheric paths. Among positive consequences of the quality of the model, the possibility of retrieving amounts of (heavy) trace gases with weak and broad absorption features is demonstrated.

Niro, F.; Hase, F.; Camy-Peyret, C.; Payan, S.; Hartmann, J.-M. E-mail: jean-michel.hartmann@ppm.u-psud.fr

2005-01-01

151

An improvement of the filter diagonalization-based post-processing method applied to finite difference time domain calculations of three-dimensional phononic band structures  

International Nuclear Information System (INIS)

When three-dimensional (3D) phononic band structures are calculated by using the finite difference time domain (FDTD) method with a relatively small number of iterations, the results can be effectively improved by post-processing the FDTD time series (FDTD-TS) based on the filter diagonalization method (FDM), instead of the classical fast Fourier transform. In this paper, we propose a way to further improve the performance of the FDM-based post-processing method by introducing a relatively large number of observing points to record the FDTD-TS. To this end, the existing scheme of FDTD-TS preprocessing is modified. With the new preprocessing scheme, the processing efficiency of a single FDTD-TS can be improved significantly, and thus the entire post-processing method can have sufficiently high efficiency even when a relatively large number of observing points are used. The feasibility of the proposed method for improvement is verified by the numerical results.

2012-10-01

152

Optimization of the Jastrow factor using the random-phase approximation and a similarity-transformed Hamiltonian: Application to band-structure calculation for some semiconductors and insulators  

Science.gov (United States)

Based on the random-phase approximation and the transcorrelated (TC) method, we optimize the Jastrow factor together with one-electron orbitals in the Slater determinant in the correlated wave function with a new scheme for periodic systems. The TC method is one of the promising wave function theories for first-principles electronic structure calculation, where the many-body wave function is approximated as a product of a Slater determinant and a Jastrow factor, and the Hamiltonian is similarity-transformed by the Jastrow factor. Using this similarity-transformed Hamiltonian, we can optimize the one-electron orbitals without evaluating 3N-dimensional integrations for the N-electron system. In contrast, optimization of the Jastrow factor within the framework of the TC method is computationally much more expensive and has not been performed for solid-state calculations before. In this study, we also benefit from the similarity-transformation in optimizing the Jastrow factor. Our optimization scheme is tested in applications to some solids from narrow-gap semiconductors to wide-gap insulators, and it is verified that the band gap of a wide-gap insulator and the lattice constants of some solids are improved by this optimization with reasonable computational cost.

Ochi, Masayuki; Sodeyama, Keitaro; Tsuneyuki, Shinji

2014-02-01

153

The application of the Modified Band Approach for the calculation of on-line photodissociation rate constants in TM5: implications for oxidative capacity  

Directory of Open Access Journals (Sweden)

Full Text Available A flexible and explicit on-line parameterization for the calculation of tropospheric photodissociation rate constants (J-values has been integrated into the global Chemistry Transport Model TM5. Here we provide a comprehensive description of this Modified Band Approach (MBA including details of the optimization procedure employed, the methodology applied for calculating actinic fluxes, the photochemical reaction data used for each chemical species and the parameterizations adopted for improving the description of scattering and absorption by clouds and aerosols. The resulting J-values change markedly throughout the troposphere when compared to the offline approach used to date, with significant increases in the boundary layer and upper troposphere. Conversely, for the middle troposphere a reduction in the actinic flux results in a decrease in J-values. Integrating effects shows that application of the MBA introduces seasonal dependent differences in important trace gas oxidants. Tropospheric ozone changes by ±5% in the seasonal mean mixing ratios throughout the troposphere, which induces changes of ±15% in tropospheric OH. In part this is due to an increase in the re-cycling efficiency of nitrogen oxides. The overall increase in northern hemispheric tropospheric ozone strengthens the oxidizing capacity of the troposphere significantly and reduces the lifetime of CO and CH4 by ~5% and ~4%, respectively. Changes in the tropospheric CO burden, however, are limited to a few percent due to competing effects. Comparing the distribution of tropospheric ozone in the boundary layer and middle troposphere against observations in Europe shows there are improvements in the model performance during boreal winter in the Northern Hemisphere near regions affected by high nitrogen oxide emissions. Monthly mean total columns of nitrogen dioxide and formaldehyde also compare more favorably against OMI and SCIAMACHY total column observations.

J. E. Williams

2011-09-01

154

The application of the Modified Band Approach for the calculation of on-line photodissociation rate constants in TM5: implications for oxidative capacity  

Directory of Open Access Journals (Sweden)

Full Text Available A flexible and explicit on-line parameterization for the calculation of tropospheric photodissociation rate constants (J-values has been integrated into the global Chemistry Transport Model TM5. Here we provide a comprehensive description of this Modified Band Approach (MBA including details of the optimization procedure employed, the methodology applied for calculating actinic fluxes, the photochemical reaction data used for each chemical species, the aerosol climatology which is adopted and the parameterizations adopted for improving the description of scattering and absorption by clouds. The resulting J-values change markedly throughout the troposphere when compared to the offline approach used to date, with significant increases in the boundary layer and upper troposphere. Conversely, for the middle troposphere a reduction in the actinic flux results in a decrease in J-values. Integrating effects shows that application of the MBA introduces seasonal dependent differences in important trace gas oxidants. Tropospheric ozone (O3 changes by ±10% in the seasonal mean mixing ratios throughout the troposphere, especially over land. These changes and the perturbations in the photolysis rate of O3 induce changes of ±15% in tropospheric OH. In part this is due to an increase in the re-cycling efficiency of nitrogen oxides. The overall increase in northern hemispheric tropospheric ozone strengthens the oxidizing capacity of the troposphere significantly and reduces the lifetime of CO and CH4 by ~5 % and ~4%, respectively. Changes in the tropospheric CO burden, however, are limited to a few percent due to competing effects. Comparing the distribution of tropospheric ozone in the boundary layer and middle troposphere against observations in Europe shows there are improvements in the model performance during boreal winter in the Northern Hemisphere near regions affected by high nitrogen oxide emissions. Monthly mean total columns of nitrogen dioxide and formaldehyde also compare more favorably against OMI and SCIAMACHY total column observations.

J. E. Williams

2012-01-01

155

Photodissociation of water. II. Wave packet calculations for the photofragmentation of H2O and D2O in the B~ band  

Science.gov (United States)

A complete three-dimensional quantum mechanical description of the photodissociation of water in the B~ band, starting from its rotational ground state, is presented. In order to include B~-X~ vibronic coupling and the B~-A~ Renner-Teller coupling, diabatic electronic states have been constructed from adiabatic electronic states and matrix elements of the electronic angular momentum operators, following the procedure developed by A. J. Dobbyn and P. J. Knowles [Mol. Phys. 91, 1107 (1997)], using the ab initio results discussed in the preceding paper. The dynamics is studied using wave packet methods, and the evolution of the time-dependent wave function is discussed in detail. Results for the H2O and D2O absorption spectra, OH(A)/OH(X) and OD(A)/OD(X) branching ratios, and rovibrational distributions of the OH and OD fragments are presented and compared with available experimental data. The present theoretical results agree at least qualitatively with the experiments. The calculations show that the absorption spectrum and the product state distributions are strongly influenced by long-lived resonances on the adiabatic B~ state. It is also shown that molecular rotation plays an important role in the photofragmentation process, due to both the Renner-Teller B~-X~ mixing, and the strong effect of out-of-plane molecular rotations (K>0) on the dynamics at near linear HOH and HHO geometries.

van Harrevelt, Rob; van Hemert, Marc C.

2000-04-01

156

Spectra calculations in central and wing regions of CO2 IR bands between 10 and 20 ?m. I: model and laboratory measurements  

International Nuclear Information System (INIS)

Temperature (200-300 K) and pressure (70-200 atm) dependent laboratory measurements of infrared transmission by CO2-N2 mixtures have been made. From these experiments the absorption coefficient is reconstructed, over a range of several orders of magnitude, between 600 and 1000 cm-1. The elevated densities used in the experiments (up to 200 atm) magnify the contribution of the wings of the ?2 band lines. In order to analyze the spectra, a theoretical model based on the energy corrected sudden approximation is proposed which accounts for line-mixing effects within the impact approximation. This approach uses the model and associated parameters built previously to model Q branches (JQSRT 1999;61:153) but extends it by now including all P, Q, and R lines. No adjustable parameters are used and fundamental properties of the collisional relaxation operator are verified by using a renormalization procedure. Comparisons between measured and calculated spectra confirm that neglecting line-mixing (Lorentzian model) leads to an overestimation of absorption by up to three orders of magnitude in the far wings. On the other hand, the proposed approach leads to satisfactory results both in regions dominated by contributions of local lines and in the wing: measured spectra are correctly modeled over a range where absorption varies by more than four orders of magnitude. The largest discrepancies, which appear about 150 cm-1 from the ?2 center, can be due to finite duration of collisions effects or to uncertainties in the experimental determination of very weak absorption

2004-11-01

157

Measurements and Theoretical Calculations of N2-broadening and N2-shift Coefficients in the v2 band of CH3D  

Science.gov (United States)

In this paper, we report measured Lorentz N2-broadening and N2-induced pressure-shift coefficients of CH3D in the v2 fundamental band using a multispectrum fitting technique. These measurements were made by analyzing 11 laboratory absorption spectra recorded at 0.0056 cm(exp -1) resolution using the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak, Arizona. The spectra were obtained using two absorption cells with path lengths of 10.2 and 25 cm. The total sample pressures ranged from 0.98 to 402.25 Torr with CH3D volume mixing ratios of 0.01 in nitrogen. We have been able to determine the N2 pressure- broadening coefficients of 368 v2 transitions with quantum numbers as high as J"= 20 and K = 16, where K" = K' equivalent to K (for a parallel band). The measured N2-broadening coefficients range from 0.0248 to 0.0742 cm(exp -1) atm(exp -1) at 296 K. All the measured pressure-shifts are negative. The reported N2-induced pressure-shift coefficients vary from about 0.0003 to 0.0094 cm(exp -1) atm(exp -1). We have examined the dependence of the measured broadening and shift parameters on the J", and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = -J", J", and J" + 1 in the (sup Q)P-, (sup Q)Q-, and (sup Q)R-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.7%. The N2-broadening and pressureshift coefficients were calculated on the basis of a semiclassical model of interacting linear molecules performed by considering in addition to the electrostatic contributions the atom atom Lennard-Jones potential. The theoretical results of the broadening coefficients are in good overall agreement with the experimental data (8.7%). The N2-pressure shifts whose vibrational contribution is derived from parameters fitted in the (sup Q)Q-branch of self-induced shifts of CH3D, are also in reasonable agreement with the scattered experimental data (20% in most cases).

Predoi-Cross, A.; Hambrook, Kyle; Brawley-Tremblay, Marco; Bouanich, J. P.; Smith, Mary Ann H.

2006-01-01

158

First-principles calculations of band-gap properties of zinc-blende BxGa1-xN and BxGa1-xNyAs1-y alloys  

Science.gov (United States)

We present first-principles calculations of the band-gap properties of the zinc-blende BN, GaN and BxGa1-xN alloys. By 16-atom supercells to model a random alloy, the direct band-gap (?15v-?1c) bowing of 5.0 eV is obtained for BxGa1-xN alloys in the range of 0~37.5%, and the bowing parameter increases by 0.043eV/%B with boron (B) composition increasing. In addition, our calculated results show that 0.8eV (1550nm) direct transition band-gap energy of BxGa1-xNyAs1-y lattice matches to Si can be theoretically obtained while boron (B) composition is 4% and nitrogen (N) composition is 16%.

Lv, Kun-He; Wang, Qi; Yan, Ying-Ce; Guo, Xin; Huang, Yong-Qing; Ren, Xiao-Min

2011-11-01

159

Crystallographic and magnetic structure of SrCoO2.5 brownmillerite: Neutron study coupled with band-structure calculations  

Science.gov (United States)

A study of the crystallographic and magnetic structure of SrCoO2.5 with a brownmillerite-type structure has been carried out from neutron powder-diffraction (NPD) measurements at temperatures ranging from 10 to 623 K, across the Néel temperature (TN=537K) of this antiferromagnetic oxide. The study has been complemented with differential scanning calorimeter (DSC), dc susceptibility and magnetization measurements. Although the refinement of the crystal structure from NPD data is possible in the orthorhombic Pnma and Ima2 space groups, the support of ab-initio band-structure calculations has allowed us to select, without ambiguity, the Ima2 space group as the ground state for SrCoO2.5 brownmillerite. In Ima2 the crystallographic structure of SrCoO2.5 is described as layers of corner-sharing Co1O6 octahedra alternating along the a axis with layers of vertex-sharing Co2O4 tetrahedra, conforming chains running along the [0 0 1] direction. The magnetic structure below TN=537K is G -type with the magnetic moments directed along the c axis. This magnetic arrangement is stable from TN down to 10 K. At T=10K , the magnetic moment values for Co1 and Co2 atoms are 3.12(13)?B and 2.88(14)?B , respectively, compatible with a Co2+? state, where ? stands for a ligand hole. The magnetic susceptibility curves show, below 200 K, a divergence of zero-field cooling and field cooling curves, displaying broad maxima which are interpreted as due to the presence of ferromagnetic clusters embedded into an antiferromagnetic matrix. These inhomogeneities are inherent to the synthesis process, by quenching microcrystalline samples of SrCoO3-x composition from high temperature, where cubic, ferromagnetic perovskites have been identified by diffraction methods.

Muñoz, A.; de La Calle, C.; Alonso, J. A.; Botta, P. M.; Pardo, V.; Baldomir, D.; Rivas, J.

2008-08-01

160

Spectra calculations in central and wing regions of CO{sub 2} IR bands between 10 and 20 {mu}m. I: model and laboratory measurements  

Energy Technology Data Exchange (ETDEWEB)

Temperature (200-300 K) and pressure (70-200 atm) dependent laboratory measurements of infrared transmission by CO{sub 2}-N{sub 2} mixtures have been made. From these experiments the absorption coefficient is reconstructed, over a range of several orders of magnitude, between 600 and 1000 cm{sup -1}. The elevated densities used in the experiments (up to 200 atm) magnify the contribution of the wings of the {nu}{sub 2} band lines. In order to analyze the spectra, a theoretical model based on the energy corrected sudden approximation is proposed which accounts for line-mixing effects within the impact approximation. This approach uses the model and associated parameters built previously to model Q branches (JQSRT 1999;61:153) but extends it by now including all P, Q, and R lines. No adjustable parameters are used and fundamental properties of the collisional relaxation operator are verified by using a renormalization procedure. Comparisons between measured and calculated spectra confirm that neglecting line-mixing (Lorentzian model) leads to an overestimation of absorption by up to three orders of magnitude in the far wings. On the other hand, the proposed approach leads to satisfactory results both in regions dominated by contributions of local lines and in the wing: measured spectra are correctly modeled over a range where absorption varies by more than four orders of magnitude. The largest discrepancies, which appear about 150 cm{sup -1} from the {nu}{sub 2} center, can be due to finite duration of collisions effects or to uncertainties in the experimental determination of very weak absorption.

Niro, F.; Boulet, C.; Hartmann, J.-M. E-mail: jean-michel.hartmann@ppm.u-psud.fr

2004-11-01

 
 
 
 
161

Calculation of equilibria at elevated temperatures using the MINTEQ geochemical code  

Energy Technology Data Exchange (ETDEWEB)

Coefficients and equations for calculating mineral hydrolysis constants, solubility products and formation constants for 60 minerals and 57 aqueous species in the 13 component thermodynamic system K/sub 2/O-Na/sub 2/O-CaO-MgO-FeO-Al/sub 2/O/sub 3/-SiO/sub 2/-CO/sub 2/-H/sub 2/O-HF-HCl-H/sub 2/S-H/sub 2/SO/sub 4/ are presented in a format suitable for inclusion in the MINTEQ computer code. The temperature functions presented for minerals are based on the MINTEQ data base at 25/degree/C and the integration of analytical heat capacity power functions. This approach ensures that the temperature functions join smoothly with the low-temperature data base. A new subroutine, DEBYE, was added to MINTEQ that is used to calculate the theoretical Debye-Hueckel parameters A and B as a function of temperature. In addition, this subroutine also calculates a universal value of the extended Debye-Hueckel parameter, b/sub i/, as a function of temperature. The coefficients and equations provide the capability to use MINTEQ to more accurately calculate water/rock equilibrium for temperatures of up to 250/degree/C, and in dilute, low-sulfate, near neutral groundwaters to 300/degree/C. 52 refs., 1 fig., 6 tabs.

Smith, R.W.

1988-12-01

162

Calculations of electronic structure, elastic properties for YxGa1?xN and band offsets of YxGa1?xN/ScyGa1?yN heterointerfaces  

International Nuclear Information System (INIS)

Using the pseudopotential scheme under the virtual crystal approximation combined with the Harrison bond-orbital model, we report a theoretical investigation of the electronic and elastic properties of YxGa1?xN ternary alloys in the zinc-blende structure. Besides, band offsets calculations for pseudomorphically strained YxGa1?xN/ScyGa1?yN interfaces have been performed on the basis of the model solid theory. Our results agree generally well with the available experimental and previously published theoretical data. The composition dependence of the selected features of YxGa1?xN such as energy band gaps, effective masses, elastic constants, bulk modulus, shear modulus, internal strain parameter, and valence and conduction band offsets has been examined. To the author's best knowledge, there had been no reported work on these properties for the material under load

2008-09-01

163

Particular relative positions of low energy levels in the h/sub 11/2/ band structure of /sup 119/Xe experiment and IBFA calculations  

CERN Document Server

The level ordering of the lowest members in the h/sub 11/2/ band structure of /sup 119/Xe is discussed and compared with those of xenon isotopes and isotones. A description is given in terms of the interacting boson fermion model. (5 refs).

Gizon, J; Crawford, J; Cunningham, M A; Gizon, A

1981-01-01

164

Ultrawide Band Electromagnetic Pulses  

International Science & Technology Center (ISTC)

Development of New Calculation-Theoretical and Metrologic Approaches in Technology of Ultrawide Band Electromagnetic Pulses, Elaboration and Investigation of Standard Field-Forming Systems of Subnanosecond Pulse Field

165

Band gap bowing of binary alloys: Experimental results compared to theoretical tight-binding supercell calculations for Cd{sub x}Zn{sub 1-x}Se  

Energy Technology Data Exchange (ETDEWEB)

Compound semiconductor alloys of the type A{sub x}B{sub 1-x}C find widespread applications as their electronic bulk band gap varies continuously with x, and therefore a tayloring of the energy gap is possible by variation of the concentration. We model the electronic properties of such semiconductor alloys by a multiband sp{sup 3} tight-binding model on a finite ensemble of supercells and determine the band gap of the alloy. This treatment allows for an intrinsic reproduction of band bowing effects as a function of the concentration x and is exact in the alloy-induced disorder. In the present talk, we concentrate on bulk Cd{sub x}Zn{sub 1-x}Se as a well-defined model system and give a careful analysis on the proper choice of the basis set and supercell size, as well as on the necessary number of realizations. The results are compared to experimental results obtained from ellipsometric measurements of Cd{sub x}Zn{sub 1-x}Se layers prepared by molecular beam epitaxy (MBE) and photoluminescence (PL) measurements on Cd{sub x}Zn{sub 1-x}Se nanowires reported in the literature.

Mourad, Daniel; Czycholl, Gerd [Institut fuer Theoretische Physik, Universitaet Bremen (Germany); Kruse, Carsten; Klembt, Sebastian; Retzlaff, Reiner; Hommel, Detlef [Institut fuer Festkoerperphysik, Universitaet Bremen (Germany); Gartner, Mariuca; Anastasescu, Mihai [Institute fuer Physikalische Chemie ' ' Ilie Murgulescu' ' , Rumaenische Akademie (Romania)

2011-07-01

166

Band gap bowing of binary alloys: Experimental results compared to theoretical tight-binding supercell calculations for CdxZn1-xSe  

International Nuclear Information System (INIS)

Compound semiconductor alloys of the type AxB1-xC find widespread applications as their electronic bulk band gap varies continuously with x, and therefore a tayloring of the energy gap is possible by variation of the concentration. We model the electronic properties of such semiconductor alloys by a multiband sp3 tight-binding model on a finite ensemble of supercells and determine the band gap of the alloy. This treatment allows for an intrinsic reproduction of band bowing effects as a function of the concentration x and is exact in the alloy-induced disorder. In the present talk, we concentrate on bulk CdxZn1-xSe as a well-defined model system and give a careful analysis on the proper choice of the basis set and supercell size, as well as on the necessary number of realizations. The results are compared to experimental results obtained from ellipsometric measurements of CdxZn1-xSe layers prepared by molecular beam epitaxy (MBE) and photoluminescence (PL) measurements on CdxZn1-xSe nanowires reported in the literature.

2011-03-13

167

Band gap bowing of binary alloys: Experimental results compared to theoretical tight-binding supercell calculations for CdZnSe  

CERN Document Server

Compound semiconductor alloys of the type ABC find widespread applications as their electronic bulk band gap varies continuously with x, and therefore a tayloring of the energy gap is possible by variation of the concentration. We model the electronic properties of such semiconductor alloys by a multiband tight-binding model on a finite ensemble of supercells and determine the band gap of the alloy. This treatment allows for an intrinsic reproduction of band bowing effects as a function of the concentration x and is exact in the alloy-induced disorder. In the present paper, we concentrate on bulk CdZnSe as a well-defined model system and give a careful analysis on the proper choice of the basis set and supercell size, as well as on the necessary number of realizations. The results are compared to experimental results obtained from ellipsometric measurements of CdZnSe layers prepared by molecular beam epitaxy (MBE) and photoluminescence (PL) measurements on catalytically grown CdZnSe nanowires reported in the ...

Mourad, Daniel; Klembt, Sebastian; Retzlaff, Reiner; Gartner, Mariuca; Anastasescu, Mihai; Hommel, Detlef; Czycholl, Gerd

2010-01-01

168

First-principles calculations of the phase diagrams and band gaps in CuInSe2-CuGaSe2 and CuInSe2-CuAlSe2 pseudobinary systems  

Science.gov (United States)

The phase diagrams and band gaps in CuInSe2-CuGaSe2 (CIS-CGS) and CuInSe2-CuAlSe2 (CIS-CAS) pseudobinary systems are determined using a combination of first-principles calculations based on a hybrid Hartree-Fock density functional approach, cluster expansion, and Monte Carlo simulations. The CIS-CGS and CIS-CAS systems show phase-separation critical temperatures of 420 and 460 K, respectively. For both CuIn1-xGaxSe2 (CIGS) and CuIn1-xAlxSe2 (CIAS) alloys, the dependence of the band gaps on the temperature before quench is suggested to be small through the analysis of atomic configurational effects. The band gaps are generally close to those at the ideal disorder state and exhibit nearly quadratic composition dependences, i.e., band bowing. Composition-dependent bowing behavior is identified for CIAS, with a stronger bowing in a higher CAS composition range.

Kumagai, Yu; Soda, Yoshito; Oba, Fumiyasu; Seko, Atsuto; Tanaka, Isao

2012-01-01

169

Ab Initio factorized LCAO calculations of the electronic band structure of ZnSe, ZnS, and the (ZnSe)1(ZnS)1 strained-layer superlattice  

International Nuclear Information System (INIS)

The authors report on the results of electronic band structure calculations of bulk ZnSe, bulk ZnS and the (ZnSe)1(ZnS)1, strained-layer superlattice (SLS) using the ab initio factorized linear combination of atomic orbitals method. The bulk calculations were done using the standard primitive nonrectangular 2-atom zinc blende unit cell, while the SLS calculation was done using a primitive tetragonal 4-atom unit cell modeled from the CuAu I structure. The analytic fit to the SLS crystalline potential was determined by using the nonlinear coefficients from the bulk fits. The CPU time saved by factorizing the energy matrix integrals and using a rectangular unit cell is discussed

1992-03-14

170

Spectra calculations in central and wing regions of CO2 IR bands between 10 and 20 ?m. III: atmospheric emission spectra  

International Nuclear Information System (INIS)

A theoretical model for the prediction of CO2 absorption in both central and wing regions of infrared absorption bands was presented in the companion paper I. It correctly accounts for line-mixing effects and was validated by comparisons with laboratory spectra in the 600-1000 cm-1 region. This quality was confirmed using atmospheric transmissions measured by solar occultation experiments in the second paper. The present work completes these studies by now considering atmospheric emission in the 10-20 ?m range. Comparisons are made between computed atmospheric radiances and measurements obtained using four different Fourier transform experiments collecting spectra for nadir, up-looking, as well as limb (from balloon and satellite) geometries. Our results confirm that using a Voigt model can lead to very large errors that affect the spectrum more than 300 cm-1 away from the center of the CO2 ?2 band. They also demonstrate the capability of our model to represent accurately the radiances in the entire region for a variety of atmospheric paths. This success opens interesting perspectives for the sounding of pressure and temperature profiles, particularly at low altitudes. Another benefit of the quality of the model should be an increased accuracy in the retrieval of atmospheric state parameters from broad features in the measured spectra (clouds, aerosols, heavy trace gases)

2005-01-01

171

Spectra calculations in central and wing regions of CO{sub 2} IR bands between 10 and 20 {mu}m. III: atmospheric emission spectra  

Energy Technology Data Exchange (ETDEWEB)

A theoretical model for the prediction of CO{sub 2} absorption in both central and wing regions of infrared absorption bands was presented in the companion paper I. It correctly accounts for line-mixing effects and was validated by comparisons with laboratory spectra in the 600-1000 cm{sup -1} region. This quality was confirmed using atmospheric transmissions measured by solar occultation experiments in the second paper. The present work completes these studies by now considering atmospheric emission in the 10-20 {mu}m range. Comparisons are made between computed atmospheric radiances and measurements obtained using four different Fourier transform experiments collecting spectra for nadir, up-looking, as well as limb (from balloon and satellite) geometries. Our results confirm that using a Voigt model can lead to very large errors that affect the spectrum more than 300 cm{sup -1} away from the center of the CO{sub 2} {nu}{sub 2} band. They also demonstrate the capability of our model to represent accurately the radiances in the entire region for a variety of atmospheric paths. This success opens interesting perspectives for the sounding of pressure and temperature profiles, particularly at low altitudes. Another benefit of the quality of the model should be an increased accuracy in the retrieval of atmospheric state parameters from broad features in the measured spectra (clouds, aerosols, heavy trace gases)

Niro, F.; Clarmann, T. von; Jucks, K.; Hartmann, J.-M. E-mail: jean-michel.hartmann@ppm.u-psud.fr

2005-01-01

172

Real-structure effects: Band gaps of Mg_xZn_{1-x}O, Cd_xZn_{1-x}O, and n-type ZnO from ab-initio calculations  

Energy Technology Data Exchange (ETDEWEB)

Many-body perturbation theory is applied to compute the quasiparticle electronic structures and the optical-absorption spectra (including excitonic effects) for several transparent conducting oxides. We discuss HSE+G{sub 0}W{sub 0} results for band structures, fundamental band gaps, and effective electron masses of MgO, ZnO, CdO, SnO{sub 2}, SnO, In{sub 2}O{sub 3}, and SiO{sub 2}. The Bethe-Salpeter equation is solved to account for excitonic effects in the calculation of the frequency-dependent absorption coefficients. We show that the HSE+G{sub 0}W{sub 0} approach and the solution of the Bethe-Salpeter equation are very well-suited to describe the electronic structure and the optical properties of various transparent conducting oxides in good agreement with experiment.

Schleife, A; Bechstedt, F

2012-02-15

173

Standardization of methods of calculating the weighting functions on the basis of the parameters of the fine structure of the absorption bands of atmospheric gases  

Science.gov (United States)

Point 7 of a list of works conducted by the USSR in accordance with the Joint Soviet-American Research Program on improving methods of heat probes from satellites is discussed. Numerous calculations of transmission functions, along with tables are enclosed.

1978-01-01

174

Ab initio calculation of band edges modified by (001) biaxial strain in group IIIA-VA and group IIB-VIA semiconductors: Application to quasiparticle energy levels of strained InAs/InP quantum dot  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Results of first-principles full potential calculations of absolute position of valence and conduction energy bands as a function of (001) biaxial strain are reported for group IIIA-VA (InAs, GaAs, InP) and group IIB-VIA (CdTe, ZnTe) semiconductors. Our computational procedure is based on the Kohn-Sham form of density functional theory (KS DFT), local spin density approximation (LSDA), variational treatment of spin-orbital coupling, and augmented plane wave plus local orbitals method (APW + l...

Kadantsev, Eugene S.; Zielinski, Michal; Korkusinski, Marek; Hawrylak, Pawel

2010-01-01

175

Second-order advantage obtained from standard addition first-order instrumental data and multivariate curve resolution-alternating least squares. Calculation of the feasible bands of results.  

Science.gov (United States)

In order to achieve the second-order advantage, second-order data per sample is usually required, e.g., kinetic-spectrophotometric data. In this study, instead of monitoring the time evolution of spectra (and collecting the kinetic-spectrophotometric data) replicate spectra are used to build a virtual second order data. This data matrix (replicate mode×?) is rank deficient. Augmentation of these data with standard addition data [or standard sample(s)] will break the rank deficiency, making the quantification of the analyte of interest possible. The MCR-ALS algorithm was applied for the resolution and quantitation of the analyte in both simulated and experimental data sets. In order to evaluate the rotational ambiguity in the retrieved solutions, the MCR-BANDS algorithm was employed. It has been shown that the reliability of the quantitative results significantly depends on the amount of spectral overlap in the spectral region of occurrence of the compound of interest and the remaining constituent(s). PMID:24370937

Mohseni, Naimeh; Bahram, Morteza; Olivieri, Alejandro C

2014-03-25

176

Strongly coupled bands as 'effectively' decoupled bands  

International Nuclear Information System (INIS)

We present experimental evidence which suggests that almost all the strongly coupled bands in the rare-earth region may also be treated as ''effectively'' decoupled bands. In contrast to the usual decoupled bands, the strongly coupled bands seem to arise from a system where a particle carrying an ''effective'' angular momentum j' is aligned to an even-even core having an ''effective'' rotational angular momentum R' which is not necessarily zero for the band head but may even have R'=2 or, 4 or, 6... etc. We attempt to explain these observations in a simple physical picture wherein Jsub(R), the projection of j, the particle angular momentum, on the rotation axis, is taken as the effectively aligned spin of the last particle. Preliminary results from schematic bandmixing calculations for hsub(9/2) and fsub(5/2) orbitals with the Fermi energy lying near the high K single particle levels indeed reveal the existence of ''effectively'' decoupled bands which seem to agree with this physical picture. (orig.)

1984-05-01

177

Electronic band structure calculations on thin films of the L2{sub 1} full Heusler alloys X{sub 2}YSi (X, Y = Mn, Fe, and Co): Toward spintronic materials  

Energy Technology Data Exchange (ETDEWEB)

To design half-metallic materials in thin film form for spintronic devices, the electronic structures of full Heusler alloys (Mn{sub 2}FeSi, Fe{sub 2}MnSi, Fe{sub 2}FeSi, Fe{sub 2}CoSi, and Co{sub 2}FeSi) with an L2{sub 1} structure have been investigated using density functional theory calculations with Gaussian-type functions in a periodic boundary condition. Considering the metal composition, layer thickness, and orbital symmetries, a 5-layered Co{sub 2}FeSi thin film, whose surface consists of a Si layer, was found to have stable half-metallic nature with a band gap of ca. 0.6 eV in the minority spin state. Using the group theory, the difference between electronic structures in bulk and thin film conditions was discussed. - Highlights: Black-Right-Pointing-Pointer Electronic band structure calculations of L2{sub 1} full Heusler alloy thin films. Black-Right-Pointing-Pointer Spintronic materials. Black-Right-Pointing-Pointer Electronic properties dependency on layer thickness.

Mori, Hirotoshi, E-mail: mori.hirotoshi@ocha.ac.jp [Division of Advanced Sciences, Ocha-dai Academic Production, Ochanomizu University, 2-1-1 Ohtsuka, Bunkyo-ku, Tokyo 112-8610 (Japan); Odahara, Yosuke; Shigyo, Daisuke; Yoshitake, Tsuyoshi; Miyoshi, Eisaku [Graduate School of Engineering Sciences, Kyushu University, 6-1 Kasuga park, Kasuga, 816-8580 (Japan)

2012-05-31

178

Theoretical calculations of the optical band positions and zero-field splitting 2D for Cr{sup 3+} ions in fluoride garnet Na{sub 3}Li{sub 3}In{sub 2}F{sub 12}  

Energy Technology Data Exchange (ETDEWEB)

Five optical band positions and one EPR zero-field splitting 2D for Cr{sup 3+} ions at the trigonally-distorted octahedral In{sup 3+} site in fluoride garnet Na{sub 3}Li{sub 3}In{sub 2}F{sub 12} are calculated together from the complete diagonalization (of energy matrix) method based on the two-spin–orbit-parameter model, where the contributions from both the spin–orbit parameters of central d{sup n} ion and ligand ion are contained. The calculated results are in reasonable agreement with the experimental values. The calculations show that similar to the bonding length (i. e., metal-ligand distance) R, the bonding angle ? (between the direction of R and C{sub 3} axis) is different from the corresponding one in the host crystal Na{sub 3}Li{sub 3}In{sub 2}F{sub 12} because of the size mismatching substitution. It appears that the complete diagonalization (of energy matrix) method based on the two-spin–orbit-parameter model is effective in the unified calculation of optical spectra and EPR zero-field splitting for d{sup 3} ions in crystals.

Mei, Yang [School of Physics and Electronic Engineering, Mianyang Normal University, Mianyang 621000 (China); Research Center of Laser Fusion, CAEP, Mianyang 621900 (China); Zheng, Wen-Chen, E-mail: zhengwc1@163.com [Department of Material Science, Sichuan University, Chengdu 610064 (China); Zhang, Lin [Research Center of Laser Fusion, CAEP, Mianyang 621900 (China)

2013-12-15

179

Theoretical calculations of the optical band positions and zero-field splitting 2D for Cr3+ ions in fluoride garnet Na3Li3In2F12  

International Nuclear Information System (INIS)

Five optical band positions and one EPR zero-field splitting 2D for Cr3+ ions at the trigonally-distorted octahedral In3+ site in fluoride garnet Na3Li3In2F12 are calculated together from the complete diagonalization (of energy matrix) method based on the two-spin–orbit-parameter model, where the contributions from both the spin–orbit parameters of central dn ion and ligand ion are contained. The calculated results are in reasonable agreement with the experimental values. The calculations show that similar to the bonding length (i. e., metal-ligand distance) R, the bonding angle ? (between the direction of R and C3 axis) is different from the corresponding one in the host crystal Na3Li3In2F12 because of the size mismatching substitution. It appears that the complete diagonalization (of energy matrix) method based on the two-spin–orbit-parameter model is effective in the unified calculation of optical spectra and EPR zero-field splitting for d3 ions in crystals

2013-12-15

180

Thomas-Fermi-Dirac calculations of valence band states of double p-type d-doped quantum wells in Si  

Energy Technology Data Exchange (ETDEWEB)

We present the hole subband structure calculation in double {delta}-doped (DDD) quantum wells in Si. We have used an analytical expression for the Hartree-Fock potential previously obtained within the lines of the Thomas-Fermi-Dirac (TFD) approximation. We have analysed the hole levels as a function of the interlayer distance as well as for different densities of impurities. It is found a difference of 60 Aa in the degeneration distance of the system with and without exchange effects in the low impurity density regime (p{sub 2D}=1 x 10{sup 12} cm{sup -2}), while in the high impurity density such difference is about 5 Aa. We also present the mobility ratio between DDD and simple {delta}-doped (SDD) quantum wells. We have found the interlayer distance for the maximum mobility for the whole range of impurities. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Rodriguez-Vargas, I.; Gaggero-Sager, L.M. [Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, 62210 Cuernavaca, Morelos (Mexico)

2005-08-01

 
 
 
 
181

Electronic properties of cubic TaCxN1-x: A comparative study using self-consistent cluster and ab initio band-structure calculations and X-ray spectroscopy  

International Nuclear Information System (INIS)

To investigate the influence of substitution of carbon atoms for nitrogen atoms in the cubic TaCxN1-x carbonitrides, total and partial densities of states were calculated for TaC, TaC0.5N0.5 and TaN compounds (NaCl structure) using the self-consistent cluster (with the FEFF8 code) and ab initio band-structure augmented plane wave + local orbitals (APW + LO) methods. In the present work a rather good agreement of the theoretical FEFF8 and APW + LO data for electronic properties of the TaCxN1-x system under consideration was obtained. The results indicate that a strong hybridization of the Ta 5d- and C(N) 2p-like states is characteristic for the valence band of the TaCxN1-x carbonitrides. When going from TaC to TaN through the TaC0.5N0.5 carbonitride, the main maxima of curves representing total and partial Ta 5d densities of states shift in the direction opposite to the position of the Fermi level. In the above sequence of compounds, an increase of occupation of the near-Fermi sub-band formed by contributions of Ta 5d(t2g) states has been detected. The theoretical FEFF8 and APW + LO results for the electronic structure of the TaCxN1-x carbonitrides were found to be in excellent agreement with the experimental data derived in the present work employing X-ray photoelectron, emission and absorption spectroscopy methods for cubic TaC0.98, TaC0.52N0.49 and TaN0.97 compounds

2009-03-20

182

Energy Band Gaps and Optical Spectra of Pure and Zn-, Se-, and Rare Earth-Doped III-V Semiconductors from All-Electron Non-Local Screened Exchange Density Functional Calculations  

Science.gov (United States)

The accurate calculation of energy band gaps in semiconductors remains a challenge, especially when dopants such as rare earth elements are considered. Based on the work of Massidda et al. (S. Massidda, A. Continenza, M. Posternak, and A. Baldereschi, Phys. Rev. B 55), 13494 (1997), we have implemented the non-local screened exchange (sX-LDA) approach (D. M. Bylander and L. Kleinman, Phys. Rev. B 41), 7868 (1990); A. Seidl, A. Görling, P. Vogl, J. A. Majewski, and M. Levy, Phys. Rev. B 53, 3764 (1996) within the all-electron FLAPW method (H. J. F. Jansen and A. J. Freeman, Phys. Rev. B 30), 561 (1984). Good values for band gaps have been achieved for pure semiconductors including Si, Ge, GaAs, InP, InAs, and InSb. Thus, this approach forms a sound basis for the description of the electronic structures and optical spectra of doped systems. Results will be presented for GaAs and InAs doped with Zn, Se, and Ce.

Geller, Clint B.; Wolf, Walter; Wimmer, Erich; Mannstadt, Wolfgang

1998-03-01

183

ELECTRONIC BAND STRUCTURE OF THE ORDERED Zn0.5Cd0.5Se ALLOY CALCULATED BY THE SEMI-EMPIRICAL TIGHT-BINDING METHOD CONSIDERING SECOND-NEAREST NEIGHBOR  

Directory of Open Access Journals (Sweden)

Full Text Available Usually, semiconductor ternary alloys are studied via a pseudo-binary approach in which the semiconductoris described like a crystalline array were the cation/anion sub-lattice consist of a random distribution of thecationic/anionic atoms. However, in the case of reported III-V and II-VI artificial structures, in which anordering of either the cations or the anions of the respective fcc sub-lattice is involved, a pseudo-binaryapproach can no longer be employed, an atomistic point of view, which takes into account the localstructure, must be used to study the electronic and optical properties of these artificial semiconductoralloys. In particular, the ordered Zn0.5Cd0.5Se alloy has to be described as a crystal with the simple-tetragonalBravais lattice with a composition equal to the zincblende random ternary alloy. The change of symmetryproperties of the tetragonal alloy, in relation to the cubic alloy, results mainly in two effects: i reduction ofthe banned gap, and ii crystal field cleavage of the valence band maximum. In this work, the electronicband structure of the ordered Zn0.5Cd0.5Se alloy is calculated using a second nearest neighbor semi-empiricaltight binding method. Also, it is compared with the electronic band structure obtained by FP-LAPW (fullpotentiallinearized augmented-plane wave method.

Juan Carlos Salcedo-Reyes

2008-09-01

184

Valence band electronic structure of Nd{sub 1?x}Y{sub x}MnO{sub 3} using X-ray absorption, photoemission and GGA + U calculations  

Energy Technology Data Exchange (ETDEWEB)

Highlights: •Decrease in the occupancy of Mn 3d orbitals with doping. •Greater splitting of the e{sub g} orbitals due to the increased Jahn–Teller distortion with doping. •Decrease in O 2p–Mn 3d charge transfer character with doping. •Increase in charge transfer energy and band gap with doping. •Calculations hint a subtle change from a charge transfer to Mott–Hubbard type insulator with doping. -- Abstract: The electronic structures of Nd{sub 1?x}Y{sub x}MnO{sub 3} (x = 0–0.5) were studied using X-ray absorption near-edge structure (XANES) at the Mn L{sub 3,2}- and O K-edge along with valence-band photoemission spectroscopy (VB-PES). The systematic increase in white-line intensity of the Mn L{sub 3,2}-edge with doping, suggests a decrease in the occupancy of Mn 3d orbitals. The O K-edge XANES shows a depletion of unoccupied states above the Fermi energy. The changes in the O K-edge spectra due to doping reflects an increase in the Jahn–Teller distortion. The VB-PES shows broadening of the features associated with Mn 3d and O 2p hybridized states and the shift of these features to a slightly higher binding energy in agreement with our GGA + U calculations. The system shows a net shift of the occupied and unoccupied states away from the Fermi energy with doping. The shift in theoretical site-projected density of states of x = 0.5 composition with respect to x = 0 suggest a subtle change from a charge transfer to Mott–Hubbard type insulator.

Balasubramanian, Padmanabhan, E-mail: padmanabhan@iopb.res.in [Department of Physics, Tamkang University, Tamsui 251, Taiwan (China); Institute of Physics, Bhubaneshwar 751005 (India); Nair, Harikrishnan S. [J?lich Center for Neutron Sciences, Forschungszentrum J?lich, Outstation at FRM II, LichtenberGstr. 1, Garching 85747 (Germany); Tsai, H.M. [Department of Physics, Tamkang University, Tamsui 251, Taiwan (China); National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan (China); Bhattacharjee, S. [Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala (Sweden); Liu, M.T. [Department of Physics, Tamkang University, Tamsui 251, Taiwan (China); Yadav, Ruchika [Department of Physics, Indian Institute of Science, C.V. Raman Avenue, Bangalore 560012 (India); Chiou, J.W. [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Lin, H.J.; Pi, T.W. [National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan (China); Tsai, M.H. [Department of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan (China); Elizabeth, Suja [Department of Physics, Indian Institute of Science, C.V. Raman Avenue, Bangalore 560012 (India); Pao, C.W.; Wang, B.Y.; Chuang, C.H.; Pong, W.F. [Department of Physics, Tamkang University, Tamsui 251, Taiwan (China)

2013-08-15

185

Room-temperature Broadening and Pressure-shift Coefficients in the nu(exp 2) Band of CH3D-O2: Measurements and Semi-classical Calculations  

Science.gov (United States)

We report measured Lorentz O2-broadening and O2-induced pressure-shift coefficients of CH3D in the nu(exp 2) fundamental band. Using a multispectrum fitting technique we have analyzed 11 laboratory absorption spectra recorded at 0.011 cm(exp 1) resolution using the McMath-Pierce Fourier transform spectrometer, Kitt Peak, Arizona. Two absorption cells with path lengths of 10.2 and 25 cm were used to record the spectra. The total sample pressures ranged from 0.98 to 339.85 Torr with CH3D volume mixing ratios of 0.012 in oxygen. We report measurements for O2 pressure-broadening coefficients of 320 nu(exp 2) transitions with quantum numbers as high as J0(sup w) = 17 and K = 14, where K(sup w) = K' is equivalent to K (for a parallel band). The measured O2-broadening coefficients range from 0.0153 to 0.0645 cm(exp -1) atm(exp -1) at 296 K. All the measured pressure-shifts are negative. The reported O2-induced pressure-shift coefficients vary from about -0.0017 to -0.0068 cm(exp -1) atm(exp -1). We have examined the dependence of the measured broadening and shift parameters on the J(sup W), and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = -J(sup W), J(sup W), and J(sup w) + 1 in the QP-, QQ-, and QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.4%. The O2-broadening and pressure shift coefficients were calculated on the basis of a semiclassical model of interacting linear molecules performed by considering in addition to the electrostatic contributions the atom-atom Lennard-Jones potential. The theoretical results of the broadening coefficients are generally larger than the experimental data. Using for the trajectory model an isotropic Lennard-Jones potential derived from molecular parameters instead of the spherical average of the atom-atom model, a better agreement is obtained with these data, especially for |m| <= 12 values (11.3% for the first calculation and 8.1% for the second calculation). The O2-pressure shifts whose vibrational contribution are either derived from parameters fitted in the QQ-branch of selfinduced shifts of CH3D or those obtained from pressure shifts induced by Xe in the nu(sup 3) band of CH3D are in reasonable agreement with the scattered experimental data (17.0% for the first calculation and 18.7% for the second calculation).

Predoi-Cross, Adriana; Hambrook, Kyle; Brawley-Tremblay, Shannon; Bouanich, Jean-Pierre; Devi, V. Malathy; Smith, Mary Ann H.

2006-01-01

186

Propagation of Adiabatic Shear Bands  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The dynamic propagation of a shear band is assessed in mode II. A layer of finite thickness is subjected to siinple shearing. The band propagates in the shear direction under steady state conditions. A variational approach is developed to calculate the shear band velocity and the length of the process zone. We analyse the roles of inertia, of loading conditions and of material properties such as yield stress, strain (or thermal) softening, strain hardening, strain rate sensitivity. The effect...

Mercier, S.; Molinari, A.

1997-01-01

187

Rotational bands in 107Cd  

Science.gov (United States)

High-spin states in 107Cd were populated by the reaction 94Zr( 17O, 4n) at 80 MeV and their decay was studied by ?-spectroscopic methods using the NORDBALL multi-detector array. The experiment included ?-ray yields, ?-coincidences and ?-ray angular correlation measurements. Rotational bands were observed up to spin {39}/{2} and ( {51}/{2}+) in the negative- and positive-parity bands, respectively. Calculations of total routhian surfaces and quasi-particle routhians have been performed and are used for assigning quasiparticle configurations to the bands. In the g{7}/{2} neutron band, a h{11}/{2} neutron alignment is observed. A large signature spliting is expected in the ? g{7}/{2} band before the band crossing. For the band built on a single ? h{11}/{2} quasiparticle, an alignment of either g{7}/{2}or h{11}/{2} neutrons is proposed. Shape change effects are discussed.

Jerrestam, Dan; Lidén, F.; Gizon, J.; Hildingsson, L.; Klamra, W.; Wyss, R.; Barnéod, D.; Kownacki, J.; Lindblad, Th.; Nyberg, J.

1992-08-01

188

Rotational bands in 107Cd  

International Nuclear Information System (INIS)

High-spin states in 107Cd were populated by the reaction 94Zr(17O, 4n) at 80 MeV and their decay was studied by ?-spectroscopic methods using the NORDBALL multi-detector array. The experiment included ?-ray yields, ??-coincidences and ?-ray angular correlation measurements. Rotational bands were observed up to spin 39-/2 and (51+/2) in the negative- and positive-parity bands, respectively. Calculations of total routhian surfaces and quasi-particle routhians have been performed and are used for assigning quasiparticle configurations to the bands. In the g7/2 neutron band, a h11/2 neutron alignment is observed. A large signature splitting is expected in the ?g7/2 band before the band crossing. For the band built on a single ?h11/2 quasiparticle, an alignment of either g7/2 or h11/2 neutrons is proposed. Shape change effects are discussed. (orig.)

1992-08-17

189

Band Together!  

Science.gov (United States)

After nearly a decade as band director at St. James High School in St. James, Missouri, Derek Limback knows that the key to building a successful program is putting the program itself above everything else. Limback strives to augment not only his students' musical prowess, but also their leadership skills. Key to his philosophy is instilling a…

Olson, Cathy Applefeld

2011-01-01

190

Chemically induced compaction bands in geomaterials  

Science.gov (United States)

Compaction bands play an important role in oil production and may provide useful information on various geological processes. Various mechanisms can be involved at different scales: the micro scale (e.g. the grain scale), the meso scale (e.g. the Representative Element Volume) and the macro scale (e.g. the structure). Moreover, hydro-chemo-mechanical couplings might play an important role in triggering instabilities in the form of compaction bands. Compaction bands can be seen as an instability of the underneath mathematical problem leading to localization of deformation [1,2,3]. Here we explore the conditions of compaction banding in quartz-based geomaterials by considering the effect of chemical dissolution and precipitation [4,5]. In due course of the loading process grain crushing affects the residual strength, the porosity and the permeability of the material. Moreover, at the micro-level, grain crushing results in an increase of the grain specific surface, which accelerates the dissolution [6]. Consequently, the silica is removed more rapidly from the grain skeleton and the overall mechanical properties are degraded due to chemical factors. The proposed model accounts for these phenomena. In particular, the diffusion of the diluted in the water silica is considered through the mass balance equation of the porous medium. The reduction of the mechanical strength of the material is described through a macroscopic failure criterion with chemical softening. The grain size reduction is related to the total energy input [7]. A grain size and porosity dependent permeability law is adopted. These degradation mechanisms are coupled with the dissolution/precipitation reaction kinetics. The obtained hydro-chemo-mechanical model is used to investigate the conditions, the material parameters and the chemical factors inducing compaction bands formation. References [1] J.W. Rudnicki, and J.R. Rice. "Conditions for the Localization of Deformation in Pressure-sensitive Dilatant Materials." Journal of the Mechanics and Physics of Solids 23.6 (1975): 371-394. [2] I. Vardoulakis and J. Sulem: Bifurcation analysis in geomechanics. Blackie. 1995. [3] J.W. Rudnicki, "Conditions for Compaction and Shear Bands in a Transversely Isotropic Material." International Journal of Solids and Structures 39.13-14 (2002): 3741-3756. [4] L.-B. Hu and T. Hueckel. "Coupled Chemo-mechanics of Intergranular Contact: Toward a Three-scale Model." Computers and Geotechnics 34.4 (2007): 306-327. [5] R. Nova, R. Castellanza, and C. Tamagnini. "A Constitutive Model for Bonded Geomaterials Subject to Mechanical And/or Chemical Degradation." International Journal for Numerical and Analytical Methods in Geomechanics 27.9 (2003): 705-732. [6] J.D. Rimstidt and H.L. Barnes. "The Kinetics of Silica-water Reactions." Geochimica et Cosmochimica Acta 44.11 (1980): 1683-1699. [7] P.V. Lade, J.A. Yamamuro and P.A. Bopp "Significance of Particle Crushing in Granular Materials." Journal of Geotechnical Engineering, 122.4 (1996): 309-316.

Stefanou, Ioannis; Sulem, Jean

2013-04-01

191

Quasirelativistic band structure of bismuth telluride  

International Nuclear Information System (INIS)

The band structure of bismuth telluride belonging to the group of the Asub(2)Ssup(5)BsUb(3)-type crystals with the Dsub(3d)sup(5) symmetry is under consideration. The Bi2Te3 band structure was calculated using the Pauli equation pseudopotential method. Calculation results are presented for the Brillouin zone symmetric points. The energy bands are classified according to their symmetry. The evailable basic parameters of the bismuth telluride band structure are compared with the result of other paper. Analysis of the calculated band structure shows that there is some difference of the band behaviour in the direction perpendicular to quintet (GITAL, KA, XU) layers that of bands lying in the quintet plane (other Brillouin zone directions). In the first case the energy band dispersion is well below than that in the second case. This fact conforms with a lower current carrier mobility in the direction perpendicular to the layers, as compared to other crystal directions

1985-09-01

192

Calculation of attenuation by rain using the DAH model and diameter of antennas for the Ka Band in Mexico; Calculo de atenuacion por lluvia usando el modelo DAH y diametro de antena para Banda Ka en Mexico  

Energy Technology Data Exchange (ETDEWEB)

In the last years, the peak in the demand of satellite communication service has caused the saturation in the use of the frequencies corresponding to the band, Cand Ku. Due to this, the engineers have looked for viable alternatives, in order to satisfy the current requisition, as well as the future demand, for which a considerable increment is expected. One of these alternatives is the use of the Ka Band (20Hz/30Hz), that is why the importance of studying the propagation effects that are experienced at these frequencies, especially the attenuation effect by rain, as in this case, where it is significant. The present article has the purpose to describe the use of the Modelo DAH (whose authors are Asoka Dissanayake, Jeremy Allnutt and Fatim Haidara), mixed with the global maps of distribution of rain by Crane, for the calculation of the attenuation by rain in satellite communication systems operated in the Ka Band. Besides, antenna diameters for the systems of communications in Ka Band in different locations of the Mexican Republic, using for it the attenuation margins for rain obtained through the Modelo DAH, and using as references the characteristics of the ANIK F2 satellite and a terrestrial station VSAT, are proposed. [Spanish] En los ultimos anos, el auge en la demanda de servicios de comunicacion por satelite ha provocado la saturacion en los uso de la frecuencia correspondientes a las bandas C y Ku. Debido a esta razon, se han buscado alternativas viables para poder satisfacer la demanda actual, asi como la demanda futura, para la cual se espera un incremento considerable. Una de estas alternativas es el uso de Banda Ka (20Hz/30Hz), de ahi la importancia del estudio sobre los efectos de programacion que se experimentan a esta frecuencia, en especial, el efecto de atencion por lluvias, ya que sen este caso resulta ser significativa. El presente articulo tiene como finalidad describir el uso del Modelo DAH (cuyos autores son Asoka Dissanayake, Jeremy Allnutt y Fatim Haidara), combinado con los mapas globales de distribucion de lluvia de Crane, para el calculo de la atencion por lluvia en sistema de comunicacion por satelite que operen en la Banda Ka. Ademas, se proponen diametros de antena para los sistemas de comunicaciones en Banda Ka en diferentes localidades de la Republica Mexicana, empleando para ello, los margenes de atencion por lluvia obtenidos a trav del Modelo DAH, y usando como referencia las caracteristicas del satelite de comunicaciones ANIK F2 y de una estacion terrena VSAT.Se muestra una fig. de la atenuacion por lluvia a 27.5 gHz y de los diametros de antena para banda Ka en Mexico. Se da una tabla de la atenuacion por lluvia a 29.5 GHz y a 20.2 GHz.

Landeros-Ayala, S.; Neri-Vela, R; Cruz-Sanchez, H.; Hernandez-Bautista, H. [Universidad Nacional Autonoma de Mexico, Mexico, D.F. (Mexico)

2002-03-01

193

Band crossing in 170Os  

International Nuclear Information System (INIS)

Excited states in the neutron-deficient nucleus 170Os were identified up to spin (24+) in the yrast band and to spin (23-) in the lowest negative-parity band. Deformation systematics implied by the 2+ state energies for the very light osmium isotopes are compared with theory. Band-crossing frequencies, alignments and alignment gains are compared with cranked shell model calculations. Deformation changes are required to obtain detailed agreement. A three-band mixing approach is invoked to explain the low spin yrast anomaly in 172Os and to reproduce the yrast band in 170Os. The excitation energy of the postulated intruder band in 1700s and 172Os is deduced

1988-01-01

194

Candidate chiral bands in 198Tl  

International Nuclear Information System (INIS)

High-spin states in 198Tl were studied using the 197Au(?, 3n) reaction. The level scheme was considerably extended including two new bands and several non-yrast levels. One of the new bands is possibly a chiral partner to the yrast ?h9/2 x ?i13/2-1 band. Two-quasiparticle-plus-triaxial-rotor model calculations suggest an aplanar orientation of the total angular momenta for these bands, thus supporting possible chirality. (orig.)

2010-07-01

195

Energy Bands of Hexagonal NiS.  

Science.gov (United States)

Energy bands are calculated for hexagonal NiS using lattice constants and crystal potential appropriate to the metallic phase. Group theoretic results for s, p, and d bands in the NiAs structure are obtained, and the calculation is performed using a first...

J. L. Fry J. M. Tyler

1970-01-01

196

Nonzero Quadrupole Moments of Candidate Tetrahedral Bands  

International Nuclear Information System (INIS)

Negative-parity bands in the vicinity of 156Gd and 160Yb have been suggested as candidates for the rotation of tetrahedral nuclei. We report the observation of the odd and even-spin members of the lowest energy negative-parity bands in 160Yb and 154Gd. The properties of these bands are similar to the proposed tetrahedral band of 156Gd and its even-spin partner. Band-mixing calculations are performed and absolute and relative quadrupole moments deduced for 160Yb and 154Gd. The values are inconsistent with zero, as required for tetrahedral shape, and the bands are interpreted as octupole vibrational bands. The failure to observe the in-band E2 transitions of the bands at low spins can be understood using the measured B(E1) and B(E2) values.

2010-01-15

197

Nonzero quadrupole moments of candidate tetrahedral bands.  

Science.gov (United States)

Negative-parity bands in the vicinity of 156Gd and 160Yb have been suggested as candidates for the rotation of tetrahedral nuclei. We report the observation of the odd and even-spin members of the lowest energy negative-parity bands in 160Yb and 154Gd. The properties of these bands are similar to the proposed tetrahedral band of 156Gd and its even-spin partner. Band-mixing calculations are performed and absolute and relative quadrupole moments deduced for 160Yb and 154Gd. The values are inconsistent with zero, as required for tetrahedral shape, and the bands are interpreted as octupole vibrational bands. The failure to observe the in-band E2 transitions of the bands at low spins can be understood using the measured B(E1) and B(E2) values. PMID:20366588

Bark, R A; Sharpey-Schafer, J F; Maliage, S M; Madiba, T E; Komati, F S; Lawrie, E A; Lawrie, J J; Lindsay, R; Maine, P; Mullins, S M; Murray, S H T; Ncapayi, N J; Ramashidza, T M; Smit, F D; Vymers, P

2010-01-15

198

Band structures in 129Cs  

International Nuclear Information System (INIS)

The 122Sn(11B,4n) fusion-evaporation reaction at Elab=60 MeV was used to populate excited states in 129Cs, and the deexcitations were investigated using in-beam ?-ray spectroscopic techniques. The level scheme of 129Cs is established up to ?8 MeV excitation energy and 47/2 h spin. The observed band structures are interpreted for their configurations in the framework of cranking model calculations and systematic of the neighboring 55Cs isotopes. A negative-parity ?I=1 coupled band has been assigned the ?h11/2 x ?(h11/2)2 configuration as solution of the tilted-axis cranking, which coexists with the ?h11/2 yrast band resulting from the principal-axis cranking. A new band has been identified as a ?-vibrational band built on the ?h11/2 orbital. A pair of strongly coupled positive-parity bands exhibiting similar features have been assigned different unpaired three-quasiparticle configurations involving the ?h11/2 x ?h11/2 component. The previously identified unfavored signature partners of the ?d5/2 and ?g7/2 bands are reassigned as ? vibrations of the core coupled to the ?g7/2 single-particle configuration, and the favored signature of the ?d5/2 band, respectively.

2009-04-01

199

Rotational bands of the 160Gd nuclei  

International Nuclear Information System (INIS)

Fast neutron beam measurement of 160Gd gamma radiation spectra in the (n, n'?) inelastic scattering reaction was performed. 324 lines are observed. 260 lines of those are observed for the first time. Experimental ratios of the reduced probabilities of E1, E2 transitions are presented. Energy values of rotational band levels have been calculated according to several models: the Resamr-Grayner rotational-vibrational model, the Bogh-Mottelson rotational band mixing model, the Arima-Jaxello interacting boson model. Good agreement with experiment has been obtained in the rotational band mixing and rotational vibrational models. Deviations of calculated level energy values from experimental don't exceed several keV. The calculations according to the interacting boson model witihin the limit of SU(3) dynamic symmetry have shown satisfactory agreement for ground and ?-bands however a ?-band and a band with Ksup(?)=4+ were reproduced with a larger deviation

1985-05-01

200

Investigation of chiral bands in 106Ag  

International Nuclear Information System (INIS)

Dipole bands in 106Ag have been studied with the ?-detector array AFRODITE at iThemba LABS, South Africa. A 96Zr(14N,4n)106Ag reaction at a beam energy of 71 MeV has been used. The three previously known negative-parity bands in 106Ag have been extended. Bands 1 and 2 were proposed to be chiral partner bands. However, in view of the present results, bands 2 and 3 seem to be better candidates for chiral partner bands since their staggering parameters, B(M1)/B(E2) ratios, kinematic moments of inertia and quasiparticle alignments agree much better than those of bands 1 and 2. Triaxial relativistic mean field (RMF) and particle-rotor model (PRM) calculations support this interpretation. In the potential energy surface of 106Ag, obtained in RMF calculations, two minima have been found in the ?2-? plane. Based on PRM calculations using the deformation parameters of the two minima and a ?h11/2 x ?g-19/2 particle-hole configuration, bands 2 and 3 may represent partners with chiral vibration at ??12degree. Band 1, located in the other minimum, may be a magnetic dipole band or the partner of a second pair of chiral bands.

2010-03-15

 
 
 
 
201

Study of band structure of neutron-rich Pr isotopes  

Science.gov (United States)

The newly established bands in 151,153Pr are studied by using projected shell model approach. The calculated level scheme is in good agreement with the experimental data and the reflection-symmetric-quasi-particle rotor model. The present calculations predict proton g9/2, K = 9/2 band as the lowest positive parity band in both the nuclei.

Ram, Daya; Krishan, Gopal; Devi, Rani; Khosa, S. K.

2013-04-01

202

Modeling of optical gain in GaInNAs quantum wells by using 8-band and 10-band models  

Science.gov (United States)

We analyzed two approaches to calculate band structure and optical gain in GaInNAs/GaAs quantum well structures based on 10-band and 8-band kp models. The obtained results are discussed in the context of importance of conduction band nonparabolicity. We also briefly report on the influence of hydrostatic pressure on optical gain in this system.

Gladysiewicz, M.; Wartak, M. S.

2014-03-01

203

Proportion of recovered goose and brant bands that are reported  

Science.gov (United States)

A few more than one-third of the goose and brant bands recovered by hunters were reported to the Bird Banding Laboratory (a rate of 0.361) during the 1962-64 hunting seasons. We calculated this band-reporting rate by comparing the estimated number of goose and brant bands recovered by hunters, based on a mail questionnaire survey, with the number of bands actually reported to the Bird Banding Laboratory. This band-reporting rate is probably representative only of the 1962-65 period. It is likely that, in earlier years, a greater proportion (perhaps about 0.60) of recovered goose and brant bands were reported.

Martinson, R.K.; McCann, J.A.

1966-01-01

204

Amniotic constriction bands  

Science.gov (United States)

Pseudo-ainhum; Streeter's dysplasia; Amniotic band sequence; Amniotic band syndrome ... Amniotic constriction bands are caused by damage to a part of the placenta called the amnion. The placenta carries blood to ...

205

Congenital Constriction Band Syndrome  

Directory of Open Access Journals (Sweden)

Full Text Available Congenital constriction bands are anomalous bands that encircle a digit or an extremity. Congenitalconstriction band syndrome is rare condition and is mostly associated with other musculoskeletaldisorders.We report such a rare experience.

Rajesh Gupta, Fareed Malik, Rishabh Gupta, M.A.Basit, Dara Singh

2008-04-01

206

Band structure of superlattice with ?-like potential  

International Nuclear Information System (INIS)

Band structure of superlattice with ?-like potential has been calculated taking into account interaction of carriers of different kinds. Superlattices of semiconductors with degenerated valence band and zero-gap semiconductors have been considered. For the latter semimetal-semiconductor transition has been obtained. (author). 8 refs, 1 fig

1993-01-01

207

Superdeformed bands in {sup 145}Gd  

Energy Technology Data Exchange (ETDEWEB)

The dynamic moments of inertia of the superdeformed bands in {sup 145}Gd have been analysed in the framework of cranked Woods-Saxon-Strutinski model. Special attention was given for the observed in experiment band crossing region. The calculated moments of inertia describe fairly well the measured data. 4 refs, 2 figs.

Rzaca-Urban, T. [Warsaw Univ., Inst. of Experimental Physics, Warsaw (Poland); Lieder, R.M.; Utzelmann, S.; Gast, W.; Jaeger, H.M. [Forschungszentrum Juelich GmbH, Inst. fuer Kernphysik, Juelich (Germany); Georgiev, A. [Forschungszentrum Juelich GmbH, Inst. fuer Kernphysik, Juelich (Germany)]|[Bulgarian Academy of Sciences, Sofia (Bulgaria); Bazacco, D.; Lunardi, S.; Menegazzo, R.; Rossi-Alvarez, C. [Istituto Nazionale di Fisica Nucleare, Padua (Italy); Angelis, G. de.; Napoli, D.R.; Vedovato, G. [Istituto Nazionale di Fisica Nucleare, Legnaro (Italy); Wyss, R. [Royal Inst. of Technology, Dept. of Plasma Physics, Stockholm (Sweden)

1996-12-31

208

Band Structure and Effective Masses of ZnMgO  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We analyze the influence of the Mg concentration on several important properties of the band structure of ZnMgO alloys in wurtzite structure using ab initio calculations. For this purpose, the band structure for finite concentrations is defined in terms of the Bloch spectral density, which can be calculated within the coherent potential approximation. We investigate the concentration dependence of the band gap and the crystal-field splitting of the valence bands. The effecti...

Franz, Christian; Giar, Marcel; Heinemann, Markus; Czerner, Michael; Heiliger, Christian

2013-01-01

209

Come Join the Band  

Science.gov (United States)

A growing number of students in Blue Springs, Missouri, are joining the band, drawn by a band director who emphasizes caring and inclusiveness. In the four years since Melissia Goff arrived at Blue Springs High School, the school's extensive band program has swelled. The marching band alone has gone from 100 to 185 participants. Also under Goff's…

Olson, Cathy Applefeld

2011-01-01

210

Band head spin and moment of inertia for super deformed rotational bands using the VMI model  

International Nuclear Information System (INIS)

Nearly all the super-deformed bands (SD) have been observed with hanging transitions, as a result only the ?-ray energies are known with no firm spin parity assignments. Knowledge of the spin-parities is very crucial for their configuration assignments and for complete theoretical understanding of the SD bands. The VMI model has been applied to calculate the lowest spin (and hence the K-value) and also the gamma energies for the SD bands. The calculated band head spin is compared with other theoretical estimates available in the literature

2013-12-01

211

Highly deformed band structure in 57Co  

International Nuclear Information System (INIS)

Rotational bands have been found in 57Co using the 28Si(32S,3p) reaction at 130 MeV. The bands, extending the mass 60 region of large deformation down to Z=27, are signature-partner sequences. Their quadrupole moments are similar to those of bands in the neighboring nuclei. The features of the new bands are described by Skyrme Hartree-Fock calculations favoring a configuration assignment with one neutron and one proton excited in the respective 1g9/2 intruder orbital. An attempt to describe the magnetic (M1) properties of the signature-partner structure is also presented

2002-03-01

212

Band structure of boron doped carbon nanotubes  

CERN Document Server

We present {\\it ab initio} and self-consistent tight-binding calculations on the band structure of single wall semiconducting carbon nanotubes with high degrees (up to 25 %) of boron substitution. Besides a lowering of the Fermi energy into the valence band, a regular, periodic distribution of the p-dopants leads to the formation of a dispersive ``acceptor''-like band in the band gap of the undoped tube. This comes from the superposition of acceptor levels at the boron atoms with the delocalized carbon $\\pi$-orbitals. Irregular (random) boron-doping leads to a high concentration of hybrids of acceptor and unoccupied carbon states above the Fermi edge.

Wirtz, L; Wirtz, Ludger; Rubio, Angel

2003-01-01

213

Wide band 140 GHz TWTA  

Science.gov (United States)

A single section low gain 140 GHz 200 watt travelling wave tube has been designed. The design uses the biperiodic ladder circuit of the 140 GHz extended interaction klystron amplifier developed on a previous Laboratory Command (LABCOM) contract. Circuit properties were obtained using X band models and the length of circuit needed for 20dB small signal gain was calculated as 0.9 inches (2.3 cm). Using X band models also, the required circuit to waveguide transitions were developed with voltage standing wave ratios of less than 1.3:1 within the operating band 137.5 to 142.5 GHz. The first experimental tube is expected to be tested in October 1992.

1992-07-01

214

Multiple band structures in 68Ge  

International Nuclear Information System (INIS)

Low- and high-spin states of 68Ge are investigated through in-beam ?-ray spectroscopy via the 58Ni(12C,2p), 63Cu(7Li,2n), and 52Cr(19F,p2n) reactions. A surprising richness of collective bands is observed in 68Ge including three even parity bands built on 8+ levels, the lower two of which are assigned as rotational aligned bands built on both proton and neutron (g/sub 9/2/)2 configurations, and three odd parity bands built on ? and ? configurations that include the g/sub 9/2/ orbit. Details of the multiple bands and other levels observed in 68Ge are presented. Rotation-aligned model calculations and interacting boson model calculations for 68Ge are also described

1981-01-01

215

Band structure in 77,79Sr  

International Nuclear Information System (INIS)

We have investigated the structure of the collective bands in 77,79Sr within our deformed configuration mixing (DCM) shell model based on Hartree-Fock states. In our model, the single particle orbits 1p3/2, 0f5/2, 1p1/2 and 0g9/2 are taken as the configuration space with 56Ni as the core. A modified Kuo interaction for this basis space is used in our calculation. The different levels are classified into collective bands on the basis of the B(E2) values among them. The calculated collective bands and the B(E2) values are compared with available experimental data. Our calculation is able to reproduce the identical bands observed in 77Sr, 78Sr and 78Rb. (author)

1997-04-01

216

Competition between triaxial bands and highly deformed intruder bands around 180Os  

International Nuclear Information System (INIS)

Angular momentum alignment processes in nuclei around 180Os are discussed within the deformed shell model using the Woods-Saxon potential and the monopole pairing interaction. The crossings between bands of different structures are analysed and predictions are made for the possible observation of highly deformed intruder bands. Predictions of Q0 moments are presented for the highly deformed bands and tables of calculated deformations for 178-183Os are given. (orig.)

1990-05-07

217

Diet after gastric banding  

Science.gov (United States)

... off part of your stomach with an adjustable band. After surgery you will eat less food, and ... foods with texture together with protein helps gastric band patients stay satisfied longer. This includes things like ...

218

Band structure analysis of the conduction-band mass anisotropy in 6H and 4H SiC  

CERN Document Server

The band structures of 6H and 4H SiC calculated by means of the FP-LMTO method are used to determine the effective mass tensors for their conduction-band minima. The results are shown to be consistent with recent optically detected cyclotron resonance measurements and predict an unusual band filling dependence for 6H-SiC.

Lambrecht, W R L; Lambrecht, Walter R. L.; Segall, Benjamin

1995-01-01

219

Super deformed bands in A 180 mass region  

International Nuclear Information System (INIS)

In this work a re-investigation of deformed bands in the mass region A?180, was carried out, making use of the available experimental data of both W and Os even-even isotopes. Discussing the back bending phenomenon in all isotopes understudy, and searching for a second back bending, to declare the presence of the so-called tilted super band. Band crossing was also discussed and the average moment of inertia was calculated. At last the hint of Makito about tilted band was also declared in the frame work of rotational band. Also the staggering of gamma vibrational band was also discussed

2005-04-01

220

Yrast Band in 122I and Band Termination  

International Nuclear Information System (INIS)

High spin states of the odd-odd nucleus 122I have been investigated via the fusion-evaporation reaction 116Cd(11B, 5n) at a beam energy of 68 MeV. The yrast band is extended up to I? = (29+). The band termination at I? = (22+) reported in previous studies is confirmed and interpreted as arising from a shape change from collective prolate to noncollective oblate according to Total-Routhian-Surface (TRS) calculations. In addition, the I?=(29+) state is assigned to the [?h11/2(?g7/2)2]23/2-[(?h11/2)3(?d5/2)2]35/2- configuration corresponding to the full alignment of all valance nucleons outside the semi-closed shell.

2012-05-01

 
 
 
 
221

Band structure of FeBO3: Implications for tailoring the band gap of nanoparticles  

Science.gov (United States)

The energy band structure of a transparent, green, room-temperature ferromagnetic FeBO3 has been calculated using density functional theory within the generalized gradient approximation (GGA) and the GGA+U approach. The electronic structure of FeBO3 is predicted to be antiferromagnetic and insulating, both in perfect agreement with available experiments. The predicted band structure, in particular, the shapes of the valence and conduction band edges, provides great insights into tailoring the optical band gap of FeBO3 nanoparticles: for the particle size close to 3 nm, the visible spectral region extends from green up to blue due to quantum confinement.

Shang, Shunli; Wang, Yi; Liu, Zi-Kui; Yang, Chia-En; Yin, Shizhuo

2007-12-01

222

Modelling of Wide-Band-Gap Semiconductor Alloys.  

Science.gov (United States)

The grant studies the band gap bowing and miscibility in wide-band-gap nitride alloy systems by means of first principles LMTO calculations. Calculations were completed for Al(x)B(1-x)N and In(x)Ga(1-x)N ordered structures and disordered alloys using a cl...

W. R. Lambrecht

1995-01-01

223

CHEMEOS: A New Chemical-Picture-Based Model for Plasma Equation-of-State Calculations  

International Nuclear Information System (INIS)

We present the results of a new plasma equation-of-state (EOS) model currently under development at the Atomic and Optical Theory Group (T-4) in Los Alamos. This model is based on the chemical picture of the plasma and uses the free-energy-minimization technique and the occupation-probability formalism. The model is constructed as a combination of ideal and non-ideal contributions to the total Helmholtz free energy of the plasma including the effects of plasma microfields, strong coupling, and the hard-sphere description of the finite sizes of atomic species with bound electrons. These types of models have been recognized as a convenient and computationally inexpensive tool for modeling of local-thermal-equilibrium (LTE) plasmas for a broad range of temperatures and densities, We calculate the thermodynamic characteristics of the plasma (such as pressure and internal energy), and populations and occupation probabilities of atomic bound states. In addition to a smooth truncation of partition functions necessary for extracting ion populations from the system of Saha-type equations, the occupation probabilities can also be used for the merging of Rydberg line series into their associated bound-free edges.In the low-density, high-temperature regimes the plasma effects are adequately described by the Debye-Hueckel model and its corresponding contribution to the total Helmholtz free energy of the plasma. In strongly-coupled plasmas, however, the Debye-Hueckel approximation is no longer appropriate. In order to extend the validity of our EOS model to strongly-coupled plasmas while maintaining the analytic nature of our model, we adopt fits to the plasma free energy based on hypernetted-chain and Monte Carlo simulations. Our results for hydrogen are compared to other theoretical models. Hydrogen has been selected as a test-case on which improvements in EOS physics are benchmarked before analogous upgrades are included for any element in the EOS part of the new Los Alamos opacity code ATOMIC

2004-10-20

224

Direct band gap wurtzite gallium phosphide nanowires.  

Science.gov (United States)

The main challenge for light-emitting diodes is to increase the efficiency in the green part of the spectrum. Gallium phosphide (GaP) with the normal cubic crystal structure has an indirect band gap, which severely limits the green emission efficiency. Band structure calculations have predicted a direct band gap for wurtzite GaP. Here, we report the fabrication of GaP nanowires with pure hexagonal crystal structure and demonstrate the direct nature of the band gap. We observe strong photoluminescence at a wavelength of 594 nm with short lifetime, typical for a direct band gap. Furthermore, by incorporation of aluminum or arsenic in the GaP nanowires, the emitted wavelength is tuned across an important range of the visible light spectrum (555-690 nm). This approach of crystal structure engineering enables new pathways to tailor materials properties enhancing the functionality. PMID:23464761

Assali, S; Zardo, I; Plissard, S; Kriegner, D; Verheijen, M A; Bauer, G; Meijerink, A; Belabbes, A; Bechstedt, F; Haverkort, J E M; Bakkers, E P A M

2013-04-10

225

Bulk band gaps in divalent hexaborides  

Energy Technology Data Exchange (ETDEWEB)

Complementary angle-resolved photoemission and bulk-sensitive k-resolved resonant inelastic x-ray scattering of divalent hexaborides reveal a >1 eV X-point gap between the valence and conduction bands, in contradiction to the band overlap assumed in several models of their novel ferromagnetism. This semiconducting gap implies that carriers detected in transport measurements arise from defects, and the measured location of the bulk Fermi level at the bottom of the conduction band implicates boron vacancies as the origin of the excess electrons. The measured band structure and X-point gap in CaB6 additionally provide a stringent test case for proper inclusion of many-body effects in quasi-particle band calculations.

Denlinger, Jonathan; Clack, Jules A.; Allen, James W.; Gweon, Gey-Hong; Poirier, Derek M.; Olson, Cliff G.; Sarrao, John L.; Bianchi, Andrea D.; Fisk, Zachary

2002-08-01

226

Gravity Calculator  

Science.gov (United States)

The gravity calculator calculates the gravitational force between two masses. Also included is a visualization of the typical measurement of gravitational force (weight) in different environments (stationary and free fall).

Brendan Cannell, Ronnie Johnson, The Shodor Education Foundation, Inc.

227

Multiple band structures in 191Hg  

International Nuclear Information System (INIS)

The level structure of the nucleus 191Hg has been considerably extended from previous studies by using the 160Gd(36S, 5n) reaction in conjunction with an array of Compton-suppressed germanium detectors. A series of 13 different level sequences has been established in addition to three superdeformed bands. A majority of the band structures can be understood in cranked shell model calculations assuming on oblate collective nuclear shape. There is some evidence for the onset of triaxiality. Finally, two bands of single-particle character have been found. They are interpreted as being associated with a prolate non-collective shape (?=-120deg). (orig.)

1992-01-01

228

Wide Band to ''Double Band'' upgrade  

International Nuclear Information System (INIS)

The Wide Band beam currently uses electrons obtained from secondary photon conversions to produce the photon beam incident on the experimental targets. By transporting the positrons produced in these conversions as well as the electrons it is possible to almost double the number of photons delivered to the experiments per primary beam proton. 11 figs

1988-01-01

229

Band Structure and Electrical Conductivity in Semiconductors  

Science.gov (United States)

In this experiment, we will, 1. understand how conductivity in semiconductors depends on carrier concentration and mobility, and how these depend on temperature, 2. distinguish between intrinsic and extrinsic temperature regimes and identify the applicable temperature range from an examination of measured data, 3. appreciate and utilize the advantages of the four-probe resistance measurement technique, 4. calculate the energy band gap for doped Si and pure Ge, 5. calculate the temperature dependent coefficient of the majority carriers, 6. through experimental realizations, appreciate a physical understanding of the band gap structure of semiconductors.

Khalid, Asma; Anwar, Muhammad S.; Zia, Wasif

2012-07-08

230

Band structure of CdTe-ZnTe superlattice  

International Nuclear Information System (INIS)

We perform an empirical tight-binding band structure calculation for the superlattice CdTe-ZnTe. We examine the effect of strain and valence band offset on it. We find that the 6% lattice mismatch causes strain to play an important role. The trend of the superlattice band gap for all widths considered is to decrease as the valence band offset increases. We have found two interface states not reported before. This is our main result. They lie in energy about 100 meV above the valence band edge. Since this energy is about equal to the difference between our calculated superlattice band gap and the value reported experimentally, we claim that optical absorption is measuring the transitions from these interface states to the conduction band. New more detailed experiments could settle this interesting problem. (author). 8 refs, 2 figs, 2 tabs

1988-01-01

231

Chiral bands in 105Rh  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english The 105Rh nucleus has been studied by in-beam gamma spectroscopy with the heavy-ion fusion-evaporation reaction 100Mo(11B, 02ngamma) at 43 MeV. A rich variety of structures was observed at high and low spin, using gamma - gamma - t and gamma - gamma - particle coincidences a [...] nd directional correlation ratios. Four magnetic dipole bands have also been observed at high spin. Two of them are nearly degenerate in excitation energy and could be chiral partners, as predicted by Tilted Axis Cranking calculations.

J.A., Alcántara-Núñez; J.R.B., Oliveira; E.W., Cybulska; N.H., Medina; M.N., Rao; R.V., Ribas; M.A., Rizzutto; W.A., Seale; F., Falla-Sotelo; K.T., Wiedemann; V.I., Dimitrov; S., Frauendorf.

232

Investigation of chiral bands in {sup 106}Ag  

Energy Technology Data Exchange (ETDEWEB)

Dipole bands in {sup 106}Ag have been studied with the {gamma}-detector array AFRODITE at iThemba LABS, South Africa. A {sup 96}Zr({sup 14}N,4n){sup 106}Ag reaction at a beam energy of 71 MeV has been used. The three previously known negative-parity bands in {sup 106}Ag have been extended. Bands 1 and 2 were proposed to be chiral partner bands. However, in view of the present results, bands 2 and 3 seem to be better candidates for chiral partner bands since their staggering parameters, B(M1)/B(E2) ratios, kinematic moments of inertia and quasiparticle alignments agree much better than those of bands 1 and 2. Triaxial relativistic mean field (RMF) and particle-rotor model (PRM) calculations support this interpretation. In the potential energy surface of {sup 106}Ag, obtained in RMF calculations, two minima have been found in the {beta}{sub 2}-{gamma} plane. Based on PRM calculations using the deformation parameters of the two minima and a {nu}h{sub 11/2} x {pi}g{sup -1}{sub 9/2} particle-hole configuration, bands 2 and 3 may represent partners with chiral vibration at {gamma}{approx}12degree. Band 1, located in the other minimum, may be a magnetic dipole band or the partner of a second pair of chiral bands.

Lieder, Evgenia [Themba LABS, Somerset West (South Africa); FhG, INT, Euskirchen (Germany); Lieder, Rainer; Bark, Rob; Lawrie, Elena; Lawrie, Kobus; Ntshangase, Sifiso; Mullins, Simon; Papka, Paul; Kheswa, Ntombi [Themba LABS, Somerset West (South Africa); Meng, Jie [PhS, PKU, Beijing (China); PhS, BUAA, Beijing (China); Qi, Bin [SDU, Weihai (China); Zhang, Shuangquan; Li, Zhipan [PhS, PKU, Beijing (China)

2010-07-01

233

Singing with the Band  

Science.gov (United States)

Usually band, orchestra, and choir directors work independently. However, the authors--one a choral director, the other a band director--have learned that making music together makes friends. Not only can ensemble directors get along, but joint concerts may be just the way to help students see how music can reach the heart. Combined instrumental…

Altman, Timothy Meyer; Wright, Gary K.

2012-01-01

234

Stretch Band Exercise Program  

Science.gov (United States)

This article discusses how to use stretch bands for improving total body fitness and quality of life. A stretch band exercise program offers a versatile and inexpensive option to motivate participants to exercise. The authors suggest practical exercises that can be used in physical education to improve or maintain muscular strength and endurance,…

Skirka, Nicholas; Hume, Donald

2007-01-01

235

Rubber Band Science  

Science.gov (United States)

Not only are rubber bands great for binding objects together, but they can be used in a simple science experiment that involves predicting, problem solving, measuring, graphing, and experimenting. In this article, the author describes how rubber bands can be used to teach the force of mass.

Cowens, John

2005-01-01

236

Progressive Band Selection  

Science.gov (United States)

Progressive band selection (PBS) reduces spectral redundancy without significant loss of information, thereby reducing hyperspectral image data volume and processing time. Used onboard a spacecraft, it can also reduce image downlink time. PBS prioritizes an image's spectral bands according to priority scores that measure their significance to a specific application. Then it uses one of three methods to select an appropriate number of the most useful bands. Key challenges for PBS include selecting an appropriate criterion to generate band priority scores, and determining how many bands should be retained in the reduced image. The image's Virtual Dimensionality (VD), once computed, is a reasonable estimate of the latter. We describe the major design details of PBS and test PBS in a land classification experiment.

Fisher, Kevin; Chang, Chein-I

2009-01-01

237

LHC Bellows Impedance Calculations  

CERN Multimedia

To compensate for thermal expansion the LHC ring has to accommodate about 2500 bellows which, together with beam position monitors, are the main contributors to the LHC broad-band impedance budget. In order to reduce this impedance to an acceptable value the bellows have to be shielded. In this paper we compare different designs proposed for the bellows and calculate their transverse and longitudinal wakefields and impedances. Owing to the 3D geometry of the bellows, the code MAFIA was used for the wakefield calculations; when possible the MAFIA results were compared to those obtained with ABCI. The results presented in this paper indicate that the latest bellows design, in which shielding is provided by sprung fingers which can slide along the beam screen, has impedances smaller tha those previously estimated according to a rather conservative scaling of SSC calculations and LEP measurements. Several failure modes, such as missing fingers and imperfect RF contact, have also been studied.

Dyachkov, M

1997-01-01

238

Magnetism in disjoint/non-disjoint composite bands  

Energy Technology Data Exchange (ETDEWEB)

Graphical abstract: Non-bonding degenerate systems with disjoint/non-disjoint composite bands are suggested. Regardless of the disjoint bands, these systems are predicted to be ferromagnetic due to non-trivial exchange interactions in the non-disjoint bands. Highlights: Black-Right-Pointing-Pointer Non-bonding systems with disjoint/non-disjoint composite bands are suggested. Black-Right-Pointing-Pointer Regardless of the disjoint bands, these systems are predicted to be ferromagnetic. Black-Right-Pointing-Pointer Organic ferromagnets based on the composite bands are suggested. Black-Right-Pointing-Pointer Wannier analysis and DFT calculations supported the ferromagnetic interactions. - Abstract: Non-bonding degenerate systems with disjoint/non-disjoint composite bands are suggested. In these systems, one of the non-bonding bands is disjoint, and another is non-disjoint type. Whereas the Wannier functions in the former bands span no common atoms, the Wannier functions in the latter bands span common atoms. Regardless of the disjoint bands, these systems are predicted to be ferromagnetic due to non-trivial exchange interactions in the non-disjoint bands. The ferromagnetic interactions are supported by DFT calculations.

Hatanaka, Masashi, E-mail: mhatanaka@xug.biglobe.ne.jp [Department of Green and Sustainable Chemistry, School of Engineering, Tokyo Denki University, 2-2 Kanda Nishiki-cho, Chiyoda-ku, Tokyo 101-8457 (Japan)

2012-01-02

239

Relativistic energy bands of zinc by the RKKRZ method  

International Nuclear Information System (INIS)

A first principle calculation of the relativistic band structure of zinc, a divalent hcp metal, by the relativistic KKRZ method in conjunction with the relativistic quantum defect method is reported. Usinq the energy band data the density of states and the optical absorption spectrum are also obtained. The results show that Zn is a free electron like metal with the conduction band minimum lying above the 3d band. Even though this feature contradicts the finding of Juras et al in their nonrelativistic calculation by the Green's function method, the present results are consistent with other theoretical investigation. The most important aspects of this relativistic calculation are the lifting of the degeneracy at the symmetry point K and raising of the third and the fourth bands at the symmetry point L of the Brillouin zone. These facts, though change the shape of the Fermi surface, and the optical spectrum in comparison with the nonrelativistic calculations, are in good agreement with experimental results. (author)

1980-08-01

240

Band termination in 123I  

International Nuclear Information System (INIS)

High-spin states in the nucleus 123I were populated by the 110Pd(16O, p4n) reaction at 75 MeV. ?-ray energies, intensities, ?-? coincidences, and directional correlation ratios were measured. The rotational band built on the ?h11/2 single-particle state was extended to spin I=35/2-; at higher spin the level spacings and the feeding pattern were found to become irregular, indicating a sudden change of structure. The 39/2- state and a higher-lying 43/2- level were interpreted as aligned oblate states, in line with the systematics of the lighter odd-A iodine isotopes. Total Routhian surface calculations were performed and were found to support the occurrence of a band termination. Higher-lying levels that feed the h11/2 band were identified, reaching spin I?47/2 and an excitation energy of about 9 MeV. copyright 1997 The American Physical Society

1997-09-01

 
 
 
 
241

Collective band structure in "6"6Zn  

International Nuclear Information System (INIS)

The collective nature of states in "6"6Zn has been studied by carrying out a deformed configuration mixing shell model calculation in 1psub(3/2)0fsub(5/2)1psub(1/2)0gsub(9/2) model space. An effective interaction obtained for this space by Kuo has been used. The collective structure for 2 positive-parity bands and 5 negative-parity bands is identified. A qualitative understanding of the backbending at the J = 6"+ state in the yrast positive-parity band is given in terms of the band crossing of the ground-state band and the more deformed excited band arising from 2p2h excitation to the gsub(9/2) orbit. Several high-spin members of the observed bands as well as in-band E2 transition strengths have been predicted. (orig.)

1981-11-30

242

Band structure of UO/sub 2/: an angle resolved and resonant photoemission study  

Energy Technology Data Exchange (ETDEWEB)

A detailed study of angle resolved photoemission of UO/sub 2/ <100> in the normal emission configuration is presented. The results are compared to a semirelativistic LAPW band calculation with the actual calculated empty bands used in the data reduction. Excellent agreement is found with calculations both for filled states as well as critical points in the empty states with no adjustment of bands. f-p hybridization is found at the leading edge of the valence band and not at the bottom of the valence band. p-d hybridization is found throughout the valence bands.

Arko, A.J.; Koelling, D.D.; Boring, A.M.; Ellis, W.P.; Cox, L.E.

1985-10-01

243

Electronic band structure of transparent conductor. Nb-doped anatase TiO2  

International Nuclear Information System (INIS)

We have investigated electronic band structure of a transparent conducting oxide, Nb-doped anatase TiO2 (TNO), by means of first-principles band calculations and photoemission measurements. The band calculations revealed that Nb 4d orbitals are strongly hybridized with Ti 3d ones to form a d-nature condition band, without impurity states in the in-gap region, resulting in high carrier density exceeding 1021 cm-3 and excellent optical transparency in the visible region. Furthermore, we confirmed that the results of valence band and core-level photoemission measurements are consistent with prediction by the present band calculations. (author)

2008-11-01

244

Tremor bands sweep Cascadia  

Science.gov (United States)

In the last few years, the spatiotemporal distribution of non-volcanic tremor (NVT) activity has been watched with intense curiosity in Cascadia, Japan, and San Andreas Fault. During an episodic tremor and slip (ETS) event in the Cascadia Subduction Zone (CSZ), the dominant tremor migration pattern is characterized by along-strike marching of tremor at a rate of 10 km/day. Spatiotemporal evolution gives critical clues on the physical mechanism of NVT, and the evolving state of stress in the fault. However, tremor migration, its variations over different time-scales, and its underlying physics remain poorly understood. We recorded the May 2008 ETS event in Cascadia with a dense small-aperture seismic array, and beamformed to detect and locate tremor with unparalleled resolution [Ghosh et al., GRL, 2009]. The beams reveal that tremor occurs in elongated bands that extend ~50 km in the direction parallel to the convergence of CSZ and only 10-15 km in the along-strike direction. This is in contrast to the wider blobs of tremor locations seen using a conventional envelope cross-correlation method. The peak activities of the tremor bands are well separated in space and time. Each band remains active for a good part of a day, and fades away while the adjacent band is slowly peaking up. During the 2008 ETS event, these convergence-parallel tremor bands swept the Cascadia megathrust from SE to NW in the region most clearly imaged by our array, producing the long-term tremor migration. Embedded within the bands lie long streaks of tremor that show steady and rapid migration on time-scales of several minutes to an hour at velocities of several tens of km/hr. These tremor streaks also propagate mostly convergence-parallel, along a particular band, both up- and down-dip. The elongated shape of the tremor bands may cause by the tendency of the tremor streaks to align parallel to the direction of subduction. We propose that each tremor band is the result of failure of a section of the megathrust with slow slip. The sweeping bands may indicate progressive stress transfer on the subduction fault. One band releases stress from a section of the fault, and loads the adjacent region, which promotes failure and activates the next band. The physical mechanism causing the streaks, however, is not clear. The velocity of migration within the tremor streaks may suggests fluid pressure waves advancing along the linear corrugated weak features on the fault.

Ghosh, A.; Vidale, J. E.; Sweet, J. R.; Creager, K. C.; Wech, A.; Houston, H.

2009-12-01

245

MEMS Calculator  

Science.gov (United States)

SRD 166 MEMS Calculator (Web, free access)   This MEMS Calculator determines the following thin film properties from data taken with an optical interferometer or comparable instrument: a) residual strain from fixed-fixed beams, b) strain gradient from cantilevers, c) step heights or thicknesses from step-height test structures, and d) in-plane lengths or deflections. Then, residual stress and stress gradient calculations can be made after an optical vibrometer or comparable instrument is used to obtain Young's modulus from resonating cantilevers or fixed-fixed beams. In addition, wafer bond strength is determined from micro-chevron test structures using a material test machine.

246

The surface band structure of W(112)  

International Nuclear Information System (INIS)

Both the experimental and theoretical band structure of the W(112) surface are presented, with the theoretical band structure calculated by the film-LAPW (linearized augmented plane waves) method. The results permit one to compare the W(112) and Mo(112) band structures and illuminate the similarities. It is found that for the W(112) surface the main photoemission features combine contributions from both the surface and bulk, as has been previously noted for Mo(112). The main differences between the electronic structures of the furrowed W(112) and Mo(112) surfaces are seen in the width of occupied bands. The differences are attributed to the extent of localization of valence 4d and 5s electrons in Mo and 5d and 6s electrons in W. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2004-03-01

247

Exact-exchange-based quasiparticle calculations  

International Nuclear Information System (INIS)

One-particle wave functions and energies from Kohn-Sham calculations with the exact local Kohn-Sham exchange and the local density approximation (LDA) correlation potential [EXX(c)] are used as input for quasiparticle calculations in the GW approximation (GWA) for eight semiconductors. Quasiparticle corrections to EXX(c) band gaps are small when EXX(c) band gaps are close to experiment. In the case of diamond, quasiparticle calculations are essential to remedy a 0.7 eV underestimate of the experimental band gap within EXX(c). The accuracy of EXX(c)-based GWA calculations for the determination of band gaps is as good as the accuracy of LDA-based GWA calculations. For the lowest valence band width a qualitatively different behavior is observed for medium- and wide-gap materials. The valence band width of medium- (wide-) gap materials is reduced (increased) in EXX(c) compared to the LDA. Quasiparticle corrections lead to a further reduction (increase). As a consequence, EXX(c)-based quasiparticle calculations give valence band widths that are generally 1-2 eV smaller (larger) than experiment for medium- (wide-) gap materials. (c) 2000 The American Physical Society

2000-09-15

248

Rotational bands in [sup 107]Cd  

Energy Technology Data Exchange (ETDEWEB)

High-spin states in [sup 107]Cd were populated by the reaction [sup 94]Zr([sup 17]O, 4n) at 80 MeV and their decay was studied by [gamma]-spectroscopic methods using the NORDBALL multi-detector array. The experiment included [gamma]-ray yields, [gamma][gamma]-coincidences and [gamma]-ray angular correlation measurements. Rotational bands were observed up to spin 39-/2 and (51+/2) in the negative- and positive-parity bands, respectively. Calculations of total routhian surfaces and quasi-particle routhians have been performed and are used for assigning quasiparticle configurations to the bands. In the g[sub 7/2] neutron band, a h[sub 11/2] neutron alignment is observed. A large signature splitting is expected in the [nu]g[sub 7/2] band before the band crossing. For the band built on a single [nu]h[sub 11/2] quasiparticle, an alignment of either g[sub 7/2] or h[sub 11/2] neutrons is proposed. Shape change effects are discussed. (orig.).

Jerrestam, D. (Uppsala Univ., Nykoeping (Sweden) Niels Bohr Inst., Roskilde (Denmark)); Liden, F. (Physics Dept., Schuster Lab., Manchester Univ. (United Kingdom)); Gizon, J.; Barneoud, D. (Inst. des Sciences Nucleaires, Joseph Fourier Univ., 38 - Grenoble (France)); Hildingsson, L.; Klamra, W.; Lindblad, T. (Manne Siegbahn Inst. of Physics, Stockholm (Sweden)); Wyss, R. (Manne Siegbahn Inst. of Physics, Stockholm (Sweden) Royal Inst. of Tech., Physics Dept., Stockholm (Sweden)); Kownacki, J. (Inst. of Experimental Physics, Warsaw Univ. (Poland)); Nyberg, J. (Niels Bohr Inst., Roskilde (Denmark))

1992-08-17

249

Is the rigid-band model valid for Mosub(c)Nbsub(1-c) alloys  

International Nuclear Information System (INIS)

The electronic structure of disordered Nb-Mo alloys has been calculated using the CPA for a muffin-tin potential model of the alloy potential. The bonding part of the alloy 'band' structure is rigid-band-like. In the antibonding bands there are significant non-rigid-band effects. (author)

1977-08-19

250

Band Gap Engineering of Crystal Materials: Band Gap Estimation of Semiconductors via Electronegativity  

Science.gov (United States)

We have developed empirical equations to quantitatively calculate the band gap values of binary ANB8-N and ternary ABC2 chalcopyrite semiconductors from the general viewpoint of chemical bonding processes upon electronegativity (EN). It is found that the band gap of crystal materials is essentially determined by the binding energy of chemical bonds to the bonding electrons, which can be effectively described by the average attractive abilities of two bonded atoms to their valence electrons and the delocalization degree of the valence electrons. The calculated band gap values of a large number of compounds can agree well with the available experimental data. This work provides us an efficient approach to quantitatively predict the band gap values of inorganic crystal materials on the basis of fundamental atom parameters such as EN, atomic radius, etc.

Li, Keyan; Li, Yanju; Xue, Dongfeng

2012-06-01

251

Level density calculation for deformed nuclei  

International Nuclear Information System (INIS)

Level densities for the rare earth and actinide nuclei have been calculated using a modified version of the Ericson formalism. The assumption was made, that K (the projection of J on the symmetry axis of the nucleus) is a good quantum number in the compound nucleus. Individual level densities for the different (K,J) values of the compound nucleus formed by low energy neutron interactions were calculated. The results show good agreement with the interpretation of recent results obtained on U-235 in this laboratory. Using the above calculations it is also possible to infer from the measured level densities the locations of the band heads of different K bands in the compound nucleus. The results also indicate that the K bands responsible for the level densities exclude the ground state rotational band. Levels built on the higher lying ? and ? vibrational bands and their composites are sufficient in number to explain the observed level densities. 4 tables

1975-10-01

252

New results on the superdeformed {sup 196}Pb nucleus: The decay of the excited bands to the yrast band  

Energy Technology Data Exchange (ETDEWEB)

The study of the superdeformed (SD) {sup 196}Pb nucleus has been revisited using the EUROGAM phase 2 spectrometer. In addition to the known yrast and two lowest excited SD bands, a third excited SD band has been seen. All of the three excited bands were found to decay to the yrast SD band through, presumably, E1 transitions, allowing relative spin and excitation energy assignments. Comparisons with calculations using the random-phase approximation suggest that all three excited bands can be interpreted as octupole vibrational structures.

Bouneau, S.; Azaiez, F.; Duprat, J. [IPN, Orsay (France)] [and others

1996-12-31

253

SPI Calculator  

Digital Repository Infrastructure Vision for European Research (DRIVER)

[EN] *Objectives: The program calculates time series of the Standardised Precipitation Index (SPEI). *Technical Characteristics: The program is executed from the Windows console. From an input data file containing monthly time series of cumulative precipitation, the program computes the SPI accumulated at the time interval specified by the user, and generates a new data file with the SPI time series. It is easy to create a batch script for automating the calculation of the SPI ov...

Begueri?a, Santiago; Vicente Serrano, Sergio M.

2009-01-01

254

XPS band emission and density of states of CoAl  

International Nuclear Information System (INIS)

An investigation of the electronic structure of an ordered equimolar CoAl alloy is discussed on the basis of a recently calculated self-consistent band structure and a measured XPS valence band spectrum. The valence band and core lines of CoAl by XPS are reported for the first time. Experimental and calculated values of the spectra have been compared

1981-11-01

255

Supersymmetry and Identical Bands  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Supersymmetry as applied to identical bands is discussed. A review of the work of the Koeln-Dubna group on this topic is given and examples in 171,172Yb, 173,174Hf, and 195,194Pt are discussed. The role of pseudo-spin in the supersymmetry is investigated. A recent precision lifetime measurement for identical bands in 171,172Yb is discussed.

Von Brentano, P.

2003-01-01

256

Intermediate band solar cells  

Science.gov (United States)

Intermediate band (IB)solar cells aim to exploit the energy of below bandgap energy photons in solar cells. They are based in a material that, in addition to the conventional conduction and valence bands, have an electronic band (named intermediate band) located inside the bandgap and separated from the conduction and valence band by a null density of states. The theoretical limiting efficiency of these cells is equivalent to that of a triple junction solar cell (63.2% at maximum concentration) but requiring a single material instead. Several approaches are being followed worldwide to take to practice this concept. They can be classified into ``bulk'' or ``quantum dot'' approaches. In the ``bulk'' approach, the IB emerges from the insertion of impurities that can be incorporated inside the semiconductor at high densities (beyond the Mott's transition) without forming clusters and that typically would produce deep centers at low densities. Examples experimentally pursued worldwide under this approach are the following material systems: Si:Ti, InGaN:Mn, ZnTe:O and Cu(InGa)S2:Ti. In the ``quantum dot'' approach, the IB arises from the quantum confinement of the electrons usually in the conduction band. This system has allowed in the past to demonstrate some of the principles of operation of the IB solar cells on the basis mainly of the InAs/GaAs system. This system, however, is not optimum for IB solar cell operation and the challenge is now to find a feasible combination of materials that allow both to introduce the confined energy level at the appropriate position as well as to do it at the time the number of additional energy levels introduced between the intermediate band and the conduction band is minimized.

Marti, Antonio

2010-03-01

257

Microscopic analysis of the valence band and impurity band theories of (Ga,Mn)As  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We analyze microscopically the valence and impurity band models of ferromagnetic (Ga,Mn)As. We find that the tight-binding Anderson approach with conventional parameterization and the full potential LDA+U calculations give a very similar picture of states near the Fermi energy which reside in an exchange-split sp-d hybridized valence band with dominant orbital character of the host semiconductor; this microscopic spectral character is consistent with the physical premise of ...

Masek, J.; Maca, F.; Kudrnovsky, J.; Makarovsky, O.; Eaves, L.; Campion, R. P.; Edmonds, K. W.; Rushforth, A. W.; Foxon, C. T.; Gallagher, B. L.; Novak, V.; Sinova, Jairo; Jungwirth, T.

2010-01-01

258

Investigation of lifetimes in dipole bands of 141Eu  

International Nuclear Information System (INIS)

Lifetimes have been measured for dipole bands in 141Eu using DSAM. The deduced B(M1) and B(E2) values as well as B(M1)/B(E2) ratios are compared with calculations in the framework of the TAC (Tilted Axis Cranking) and SPAC (Shears mechanism with Principal Axis Cranking) models. The dipole bands can be interpreted as magnetic rotational bands. (orig.)

2004-07-01

259

Investigation of lifetimes in the dipole band of 139Sm  

International Nuclear Information System (INIS)

Lifetimes have been measured for a dipole band in 139Sm using DSAM. The deduced B(M1) and B(E2) values as well as B(M1)/B(E2) ratios are compared with calculations in the framework of the TAC (Tilted Axis Cranking) and SPAC (Shears mechanism with Principal Axis Cranking) models. The dipole band in 139Sm can be considered as a magnetic rotational band with a prolate or triaxial nuclear deformation. (orig.)

2008-09-01

260

Investigation of lifetimes in dipole bands of 142Gd  

International Nuclear Information System (INIS)

Lifetimes have been measured for dipole bands in 142Gd using DSAM. The deduced B(M1) and B(E2) values as well as B(M1)/B(E2) ratios are compared with calculations in the framework of the TAC (Tilted Axis Cranking) and SPAC (shears mechanism with Principal Axis Cranking) models. The dipole bands DB1 to DB4 can be interpreted as magnetic rotational bands. (orig.)

2005-02-01

 
 
 
 
261

Study of magnetic rotational bands in 139Pm nucleus  

International Nuclear Information System (INIS)

High-spin states in 139Pm have been studied via the 116Cd(27Al, 4n) heavy-ion fusion-evaporation reaction. The ?-? coincidences were measured with 12 HpGe detectors. Based on ?-? coincidence relationships and previously known levels in 139Pm, two ?I=1 negative-parity bands have been established. From the systematic comparison with the neighbouring nuclei and semi-classical effective interaction model (SPAC) calculations, the two bands were suggested as magnetic rotational bands. (authors)

2012-03-01

262

Collective bands in 106Ag and 107Ag  

Science.gov (United States)

The nuclei 106Ag and 107Ag have been studied using 80 MeV 17O ions impinging on 94Zr. The ?- rays were detected with the NORDBALL array and light charged particles with a charged-particle detector system. Rotational bands have been established using ?-ray yields, ?? coincidences and angular correlation information. Calculations of spin diabatic surfaces have been done and are used for assigning quasiparticle configurations to the bands. Deformation effects are observed in almost all bands.

Jerrestam, Dan; Klamra, W.; Gizon, J.; Lidén, F.; Hildingsson, L.; Kownacki, J.; Lindblad, Th.; Nyberg, J.

1994-09-01

263

Band structures and shape coexistence in {sup 187}Pt  

Energy Technology Data Exchange (ETDEWEB)

High-spin states in {sup 187}Pt have been studied by means of {gamma}-ray spectroscopy techniques. Known bands have been significantly extended and new bands have been found. The band structures are discussed in the framework of the cranking model and negative-parity states are compared with calculations performed with a semi-microscopic axial-rotor plus one-quasiparticle coupling model. Shape coexistence is observed from low excitation energy. (orig.)

Hojman, D. [Comision Nacional de Energia Atomica, Departamento de Fisica, Buenos Aires (Argentina); CONICET, Buenos Aires (Argentina); Cardona, M.A. [Comision Nacional de Energia Atomica, Departamento de Fisica, Buenos Aires (Argentina); CONICET, Buenos Aires (Argentina); Universidad Nacional de San Martin, Buenos Aires (Argentina); Roussiere, B.; Sauvage, J. [IN2P3/CNRS/Universite Paris-Sud, Institut de Physique Nucleaire, Orsay (France); Riley, M.A.; Tabor, S.L.; Hoffman, C.R.; Aguilar, A.; Cluff, W.T.; Hinners, T.; Lagergren, K.; Lee, S.; Perry, M.; Pipidis, A.; Tripathi, V. [Florida State University, Department of Physics, Tallahassee, Florida (United States)

2012-06-15

264

Band structures and shape coexistence in 187Pt  

International Nuclear Information System (INIS)

High-spin states in 187Pt have been studied by means of ?-ray spectroscopy techniques. Known bands have been significantly extended and new bands have been found. The band structures are discussed in the framework of the cranking model and negative-parity states are compared with calculations performed with a semi-microscopic axial-rotor plus one-quasiparticle coupling model. Shape coexistence is observed from low excitation energy. (orig.)

2012-06-01

265

A Holographic Model of Two-Band Superconductor  

CERN Document Server

We construct a holographic two-band superconductor model with interband Josephson coupling. We investigate the effects the Josephson coupling has on the superconducting condensates and the critical temperature for their formation numerically, as well as analytically where possible. We calculate the AC conductivity and find it qualitatively similar to the single band superconductor. We investigate the nodal structure of our holographic two-band superconductor from the low temperature behavior of the thermal conductivity and find it nodeless.

Wen, Wen-Yu; Wu, Shang-Yu

2013-01-01

266

On the Raman light scattering in two-band superconductors  

Science.gov (United States)

The Raman light scattering in a superconductor has been theoretically investigated at T=0 on the base of the two-band model taking into account the fluctuations of phases of order parameters and scalar potential. The imaginary part of the Raman response function has been calculated. The resulting Raman intensity contains three terms: the sum of contributions of each of two bands and fluctuational contribution due to inter-band transitions of Cooper pairs.

Kon, L. Z.; Ciobanu, I. P.; Digor, D. F.

1996-02-01

267

Optical band-gap determination of nanostructured WO3 film  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The optical band-gap energy of a nanostructured tungsten trioxide film is determined using the photoacoustic spectroscopy method under continuous light excitation. The mechanism of the photoacoustic signal generation is discussed. The band-gap energy is also computed by other methods. The absorption coefficient as well as the band-gap energy of three different crystal structures of tungsten trioxide is calculated by a first-principles Green's function approach using the projector augmented wa...

Gonzalez-borrero, P. P.; Sato, F.; Medina, A. N.; Baesso, M. L.; Bento, A. C.; Baldissera, G.; Persson, C.; Niklasson, Gunnar A.; Granqvist, Claes Go?ran; Da Silva, A. Ferreira

2010-01-01

268

Continuity chords of bands and band structure of semiconducting compounds with TlSe-type structure  

International Nuclear Information System (INIS)

All the simple band representations of the space group D/sub 4h//sup 18/ are constructed. Using the concept of band representation and continuity chord, developed by Zak, it is shown that for semiconducting compounds with TlSe-type structure it is possible to extract some useful information about the character of localization of basic functions, belonging to the same band, i.e. in fact about the nature of the chemical bond responsible for the observed band structure. In particular, from the comparison with a calculated band structure of the ternary semiconducting compounds with TlSe-type structure, it is shown that the lower four valence bands correspond to s-states of chalcogen atoms. Two following valence bands correspond to s-states of three-valent cations. Then, a large group of ten valence bands is produced by p/sub z/-states of chalcogen atoms and p/sub x/-, p/sub y/-, p/sub z/-states of three-valent cations. (author)

1985-09-01

269

Inflation Calculator  

Science.gov (United States)

This simple inflation calculator uses the Consumer Price Index to adjust any given amount of money, from 1800 to 1998. Creator S. Morgan Friedman uses data from the Historical Statistics of the United States for statistics predating 1975 and the annual Statistics Abstracts of the United States for data from 1975 to 1998. Links to other online inflation information are also included.

Friedman, S. M.

270

Photonic band structure and omnidirectional band gap in anisotropic superlattice  

International Nuclear Information System (INIS)

We investigate theoretically the photonic band structure of one-dimensional superlattice (SL) composed of alternating anisotropic layers with their principal axis oriented at arbitrary directions. The dispersion relation of order two is calculated analytically by using the 4 x 4 matrix method which is based on boundary conditions of the electric and magnetic fields at each interface. It is shown that such structures can exhibit coupled electromagnetic modes between transverse magnetic TM and transverse electric TE modes, and dispersion curves that do not exist in superlattices composed only of isotropic layers. For a given value of the wave vector kparallel (parallel to the layers), the dispersion curves (frequency ?) versus kB (where kB is the Bloch wave vector of the periodic system along the axis of the superlattice) is illustrated. Specific applications of these results are given for the case of biaxial superlattice. With an appropriate choice of the superlattice parameters, we show that it is possible to realise, for these coupled electromagnetic waves, an absolute (or omnidirectional) band gap of width depending on the anisotropic parameters of the media forming the SL. (author)

2004-01-01

271

Exploring the origin of degenerate doublet bands in $^{106}$Ag  

CERN Document Server

The electromagnetic transition probabilities of the excited levels for the two nearly degenerate bands of $^{106}$Ag have been measured using the Doppler Shift Attenuation Method. A comparison with the calculated values using triaxial projected shell model approach indicates that these bands originate from two different quasi-particle configurations but constructed from the same mean-field deformation.

Rather, N; Chattopadhyay, S; Roy, S; Rajbanshi, S; Gowsami, A; Bhat, G H; Sheikh, J A; Palit, R; Pal, S; Saha, S; Sethi, J; Biswas, S; Singh, P; Jain, H C

2013-01-01

272

Nontrivial topological states on a Möbius band  

Science.gov (United States)

In the field of topological insulators, the topological properties of quantum states in samples with simple geometries, such as a cylinder or a ribbon, have been classified and understood during the past decade. Here we extend these studies to a Möbius band and argue that its lack of orientability prevents a smooth global definition of parity-odd quantities such as pseudovectors. In particular, the Chern number, the topological invariant for the quantum Hall effect, lies in this class. The definition of spin on the Möbius band translates into the idea of the orientable double cover, an analogy used to explain the possibility of having the quantum spin Hall effect on the Möbius band. We also provide symmetry arguments to show the possible lattice structures and Hamiltonian terms for which topological states may exist in a Möbius band, and we locate our systems in the classification of topological states. Then, we propose a method to calculate Möbius dispersions from those of the cylinder, and we show the results for a honeycomb and a kagome Möbius band with different types of edge termination. Although the quantum spin Hall effect may occur in these systems when intrinsic spin-orbit coupling is present, the quantum Hall effect is more intricate and requires the presence of a domain wall in the sample. We propose an experimental setup which could allow for the realization of the elusive quantum Hall effect in a Möbius band.

Beugeling, W.; Quelle, A.; Morais Smith, C.

2014-06-01

273

Rotational bands in {sup 238}U  

Energy Technology Data Exchange (ETDEWEB)

A thick foil of {sup 238}U was bombarded with {sup 209}Bi beams at 1130 and 1330 MeV, delivered by the TASCC facility at Chalk River Laboratories. Gamma-ray spectroscopy of states populated in multiple Coulomb excitation was performed with the 8{pi} spectrometer, an instrument comprising 20 Compton-suppressed HPGe detectors and 71 BGO ball elements. The event trigger required that 3 BGO elements and 2 HPGe detectors fire in coincidence. The experiment achieved a high degree of sensitivity, the weakest rotational band observed had about 0.16% intensity of the ground state rotational band. Several bands were observed to high spin for the first time, including the {gamma}-vibrational band (spin 27{sup +}) and the octupole bands with K=0 (spin 31{sup -}), K=1 (spin 28{sup -}) and K=2 (spin 25{sup -}). Results for positive and negative parity vibrational bands are compared with cranked RPA calculations. Although this theory can explain some features of the data, many puzzling aspects remain to be explored. (orig.).

Ward, D. [Atomic Energy of Canada Ltd., Chalk River, ON (Canada). Chalk River Nuclear Labs.; Andrews, H.R. [Atomic Energy of Canada Ltd., Chalk River, ON (Canada). Chalk River Nuclear Labs.; Ball, G.C. [Atomic Energy of Canada Ltd., Chalk River, ON (Canada). Chalk River Nuclear Labs.; Galindo-Uribarri, A. [Atomic Energy of Canada Ltd., Chalk River, ON (Canada). Chalk River Nuclear Labs.; Janzen, V.P. [Atomic Energy of Canada Ltd., Chalk River, ON (Canada). Chalk River Nuclear Labs.; Nakatsukasa, T. [Atomic Energy of Canada Ltd., Chalk River, ON (Canada). Chalk River Nuclear Labs.; Radford, D.C. [Atomic Energy of Canada Ltd., Chalk River, ON (Canada). Chalk River Nuclear Labs.; Drake, T.E. [Toronto Univ., Toronto, Ont. (Canada). Phys. Dept.; DeGraaf, J. [Toronto Univ., Toronto, Ont. (Canada). Phys. Dept.; Pilotte, S. [Universite Louis Pasteur, 67037 Strasbourg, Cedex (France); Shimizu, Y.R. [Department of Physics, Kyushu University, Fukuoka (Japan)

1996-04-01

274

Interacting Excited Rotational Bands  

CERN Document Server

The role of the rotating mean field and residual interactions is discussed on the basis of recent experimental interaction matrix elements and distribution of level distances. Based on a careful identification of the rotational bands in four rare-earth nuclei, carried out earlier, most of the interactions are found to be generated by a two-body residual interaction. Some hindrance is observed with respect to changes in the K quantum number. Level distance distributions address in a more general way the question of the independence of excitations within rotational states. Both types of experimental information, band interactions and level distances, are in general accordance with mean field bands interacting with a standard surface--delta interaction.

Døssing, T; Hagemann, G B; Harsmann, A; Toermanen, S; Oedegard, S; Matsuo, M; Vigezzi, E; Broglia, R A

1999-01-01

275

More than thirty bands in {sup 177}Re  

Energy Technology Data Exchange (ETDEWEB)

The level scheme of {sup 177}Re has been extended extensively, with fragments of more than thirty bands, characterised by a given signature, observed. Alignments at low frequency in one-quasiparticle bands are interpreted as deformation effects and compared with the predictions of cranking calculations. The previously assigned one-quasiparticle {pi}i{sub 13/2} band is shown to be a mixture of three-quasiparticle and vibrational character. The non-observation of the one-quasiparticle {pi}i{sub 13/2} band is explained as being due to crossings of its s-band by competing bands. A number of high-K bands are also reported, including five- and seven-quasiparticle bands. Configuration assignments for these bands are aided by comparing experimental g{sub K} values with ``effective`` g{sub K} values, calculated with a semi-classical expression taking Coriolis mixing into account. The population of the yrast band was observed to oscillate with every four units of spin. (orig.).

Bark, R.A. [Niels Bohr Inst., Copenhagen (Denmark); Hagemann, G.B. [Niels Bohr Inst., Copenhagen (Denmark); Herskind, B. [Niels Bohr Inst., Copenhagen (Denmark); Jensen, H.J. [Niels Bohr Inst., Copenhagen (Denmark); Korten, W. [Niels Bohr Inst., Copenhagen (Denmark); Wrzesinski, J. [Niels Bohr Inst., Copenhagen (Denmark); Carlsson, H. [Department of Physics, University of Lund, S-223 62 Lund (Sweden); Bergstroem, M. [Department of Physics, University of Lund, S-223 62 Lund (Sweden); Brockstedt, A. [Department of Physics, University of Lund, S-223 62 Lund (Sweden); Nordlund, A. [Department of Physics, University of Lund, S-223 62 Lund (Sweden); Ryde, H. [Department of Physics, University of Lund, S-223 62 Lund (Sweden); Bosetti, P. [Department of Physics, University of Milano, Milan (Italy); Leoni, S. [Department of Physics, University of Milano, Milan (Italy); Ingebretsen, F. [Department of Physics, University of Oslo, Oslo (Norway); Tjoem, P.O. [Department of Physics, University of Oslo, Oslo (Norway)

1995-08-21

276

More than thirty bands in "1"7"7Re  

International Nuclear Information System (INIS)

The level scheme of "1"7"7Re has been extended extensively, with fragments of more than thirty bands, characterised by a given signature, observed. Alignments at low frequency in one-quasiparticle bands are interpreted as deformation effects and compared with the predictions of cranking calculations. The previously assigned one-quasiparticle ?i_1_3_/_2 band is shown to be a mixture of three-quasiparticle and vibrational character. The non-observation of the one-quasiparticle ?i_1_3_/_2 band is explained as being due to crossings of its s-band by competing bands. A number of high-K bands are also reported, including five- and seven-quasiparticle bands. Configuration assignments for these bands are aided by comparing experimental g_K values with ''effective'' g_K values, calculated with a semi-classical expression taking Coriolis mixing into account. The population of the yrast band was observed to oscillate with every four units of spin. (orig.)

1995-08-21

277

Plane-Wave-Gaussian Energy-Band Study of Nb.  

Science.gov (United States)

The numerical accuracy of the plane-wave-Gaussian (PWG) mixed-basis method of calculating crystalline energy bands is displayed for Nb. Atomic studies involving the Gaussian basis and crystalline studies involving the PWG mixed basis are systematically de...

R. N. Euwema

1971-01-01

278

Green function approach to interface states in band inverted junctions  

CERN Document Server

We calculate interface states in semiconductor heterostructures with band inversion using a Green function approach and the so called {\\em point interaction potentials}. Effects of external fields can be included in a straightforward fashion.

Domínguez-Adame, F

1994-01-01

279

Unfolding first-principles band structures.  

Science.gov (United States)

A general method is presented to unfold band structures of first-principles supercell calculations with proper spectral weight, allowing easier visualization of the electronic structure and the degree of broken translational symmetry. The resulting unfolded band structures contain additional rich information from the Kohn-Sham orbitals, and absorb the structure factor that makes them ideal for a direct comparison with angle resolved photoemission spectroscopy experiments. With negligible computational expense via the use of Wannier functions, this simple method has great practical value in the studies of a wide range of materials containing impurities, vacancies, lattice distortions, or spontaneous long-range orders. PMID:20867120

Ku, Wei; Berlijn, Tom; Lee, Chi-Cheng

2010-05-28

280

Electronic band structure of helical iodine chains  

Energy Technology Data Exchange (ETDEWEB)

The electronic band structure of helical iodine chains was calculated within the empirical tight binding approach. The screw symmetry of the system was used to reduce the size of the problem to a single atom with four atomic orbitals. The overlap parameters were fitted to reproduce the DFT results for a linear iodine chain. The obtained results for helical chains have shown the energy band splitting due to the overlap between p orbitals introduced by the structure twisting. The splitting magnitude depends on the pitch of the helix. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Rybkovskiy, Dmitry [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, 38 Vavilov street, 119991 Moscow (Russian Federation); Moscow State Institute of Radio Engineering, Electronics and Automation (Technical University), 78 Vernadskogo Prospect, 119454 Moscow (Russian Federation); Osadchy, Alexander; Obraztsova, Elena [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, 38 Vavilov street, 119991 Moscow (Russian Federation)

2012-12-15

 
 
 
 
281

Ultra wide band antennas  

CERN Document Server

Ultra Wide Band Technology (UWB) has reached a level of maturity that allows us to offer wireless links with either high or low data rates. These wireless links are frequently associated with a location capability for which ultimate accuracy varies with the inverse of the frequency bandwidth. Using time or frequency domain waveforms, they are currently the subject of international standards facilitating their commercial implementation. Drawing up a complete state of the art, Ultra Wide Band Antennas is aimed at students, engineers and researchers and presents a summary of internationally recog

Begaud, Xavier

2013-01-01

282

Band structure of the spectra of Hamiltonians of regular polynucleotide duplexes  

Science.gov (United States)

We calculate the band structure of the spectra of Hamiltonians of regular DNA duplexes and show that in single-stranded periodic polynucleotides whose period is determined by the number m of nucleotides in an elementary cell, the spectrum consists of m nonintersecting energy bands. In DNA duplexes, the number of energy bands is equal to 2m, and the bands can intersect. Discrete energy levels can be present in forbidden bands in the case of (semi)bounded chains or duplexes.

Lakhno, V. D.; Sultanov, V. B.

2013-09-01

283

Calculator thermometer  

International Nuclear Information System (INIS)

An inexpensive substitution for calibrated thermocouples, linearizing electronics, and the NBS thermocouple tables is obtained through the use of a hand-held calculator. Automatic offset corrections and interpolations to an output temperature are possible in a one button operation beginning with voltmeter EMF. The inverse operation is also given. Appropriate constants have been found for the Cu-constantan, iron-constantan, and chromel-alumel thermocouples

1979-01-01

284

Burnout calculation  

International Nuclear Information System (INIS)

Reviewed is the effect of heat flux of different system parameters on critical density in order to give an initial view on the value of several parameters. A thorough analysis of different equations is carried out to calculate burnout is steam-water flows in uniformly heated tubes, annular, and rectangular channels and rod bundles. Effect of heat flux density distribution and flux twisting on burnout and storage determination according to burnout are commended

1980-01-01

285

SPEI Calculator  

Digital Repository Infrastructure Vision for European Research (DRIVER)

[EN] *Objectives: The program calculates time series of the Standardised Precipitation-Evapotransporation Index (SPEI). *Technical Characteristics: The program is executed from the Windows console. From an input data file containing monthly time series of precipitation and mean temperature, plus the geographic coordinates of the observatory, the program computes the SPEI accumulated at the time interval specified by the user, and generates a new data file with the SPEI time serie...

Begueri?a, Santiago; Vicente Serrano, Sergio M.

2009-01-01

286

Band Structure of New ReFeAsO Superconductors  

Directory of Open Access Journals (Sweden)

Full Text Available We investigate the band structure of Fe-based superconductors using the first-principle method of density-functional theory. We calculated the band structure and the density of states at the Fermi level for ReFeAsO (Re = Sm, Er superconductors. Our calculations indicate that the maximum critical superconducting transition temperature Tc will be observed for compounds with Sm and Er at 55 and 46 K, respectively.

Hyun-Tak Kim

2013-05-01

287

Observation of Multiple Chiral Doublet Bands in $^{133}$Ce  

CERN Document Server

Two distinct sets of chiral-partner bands have been identified in the nucleus $^{133}$Ce. They constitute a multiple chiral doublet (M$\\chi$D), a phenomenon predicted by relativistic mean field (RMF) calculations and observed experimentally here for the first time. The properties of these chiral bands are in good agreement with results of calculations based on a combination of the constrained triaxial RMF theory and the particle-rotor model.

Ayangeakaa, A D; Anthony, M D; Frauendorf, S; Matta, J T; Nayak, B K; Patel, D; Chen, Q B; Zhang, S Q; Zhao, P W; Qi, B; Meng, J; Janssens, R V F; Carpenter, M P; Chiara, C J; Kondev, F G; Lauritsen, T; Seweryniak, D; Zhu, S; Ghugre, S S; Palit, R

2013-01-01

288

DUAL BAND MONOPOLE ANTENNA DESIGN  

Directory of Open Access Journals (Sweden)

Full Text Available The WLAN and Bluetooth applications become popular in mobile devices, integrating GSM and ISM bands operation in one compact antenna, can reduce the size of mobile devices. Recently, lot many investigations are carried out in designing a dual band antennas with operating frequencies in GSM band and in ISM band for mobile devices. Printed monopoles are under this investigation. In this paper, dual-band printed monopoles are presented to operate at GSM band i.e. 900 MHz and ISM band i.e. 2.4 GHz. We intend to observe the antenna characteristics on the network analyzer and verify the theoretical results with the practical ones.

P. Jithu

2013-06-01

289

Rubber Band Car  

Science.gov (United States)

In this design challenge activity, learners build a car that can travel at least four feet using rubber band power and use the design process to debug problems. Learners can follow up this activity with the "Motorized Car" and "Customized Car" activities in the Leader Notes guide.

Wgbh

2010-01-01

290

A Holographic Flat Band  

CERN Multimedia

We describe a novel implementation of non-relativistic fermions in AdS/CFT by imposing Lorentz violating boundary conditions for a Dirac spinor in AdS4. The dual boundary theory is scale invariant and exhibits a number of interesting properties, including a dispersionless flat band of gapless excitations.

Laia, João N

2011-01-01

291

Rubber Band newton Scale  

Science.gov (United States)

In this activity, learners make a simple spring-like scale using a rubber band instead of a spring, and calibrate the scale in newtons (N). Learners will gain an understanding of and familiarity with the newton as a unit of force, and use the scale to weigh common objects.

Rathjen, Don

2009-01-01

292

Strain-Induced Band Profile of Stacked InAs/GaAs Quantum Dots  

Directory of Open Access Journals (Sweden)

Full Text Available The strain distribution and band profile in triply stacked InAs/GaAs quantum dots with dot spacing of 0.0 - 6.0 nm was calculated. The continuum elasticity theory for strain distribution and 8-band k.p theory for band structure was used. The use of the k.p method to calculate band structure with and without including the effects of strain is reported. The calculated results show the importance of strain effect on the confinement potential of the band structure for triply stacked InAs/GaAs quantum dots.doi:10.14456/WJST.2014.18

Worasak SUKKABOT

2014-02-01

293

Band structures of rare gas solids within the GW approximation  

CERN Document Server

Band structures for solid rare gases (Ne, Ar) have been calculated using the GW approximation. All electron and pseudopotential ab initio calculations were performed using Gaussian orbital basis sets and the dependence of particle-hole gaps and electron affinities on basis set and treatment of core electrons is investigated. All electron GW calculations have a smaller particle-hole gap than pseudopotential GW calculations by up to 0.2 eV. Quasiparticle electron and hole excitation energies, valence band widths and electron affinities are generally in very good agreement with those derived from optical absorption and photoemission measurements.

Galamic-Mulaomerovic, S

2004-01-01

294

The behaviour of the moment of inertia curve in a recrossing of the ground state band and the super band in "1"5"8Er  

International Nuclear Information System (INIS)

The recrossing of the ground state band with the super band as an explanation for the second anomaly in "1"5"8Er is examined in terms of the moment of inertia. A two band mixing calculation does not reproduce the experimenal moment of inertia curve

1978-01-01

295

Linear methods in band theory  

DEFF Research Database (Denmark)

Two approximate methods for solving the band-structure problem in an efficient and physically transparent way are presented and discussed in detail. The variational principle for the one-electron Hamiltonian is used in both schemes, and the trial functions are linear combinations of energy-independent augmented plane waves (APW) and muffin-tin orbitals (MTO), respectively. The secular equations are therefore eigenvalue equations, linear in energy. The trial functions are defined with respect to a muffin-tin (MT) potential and the energy bands depend on the potential in the spheres through potential parameters which describe the energy dependence of the logarithmic derivatives. Inside the spheres, the energy-independent APW is that linear combination of an exact solution, at the arbitrary but fixed energy Eν, and its energy derivative which matches continuously and differentiably onto the plane-wave part in the interstitial region. The energies obtained with the linear-APW method for the MT potential have errors of order (E-Ev)4. Similarly, the energy-independent MTO is that linear combination which matches onto that solution of the Laplace equation in the interstitial region which is regular at infinity. The energies obtained with the linear-MTO method have additional errors of order (E-Vmtz)2, arising from the interstitial region where the potential is Vmtz. The linear-APW (LAPW) method combines desirable features of the APW and OPW methods; it can treat d bands, the energy dependence of its pseudopotential is linear and, owing to the smoothness of the energy-independent APW at the spheres, non-MT contributions to the potential are included principally through their Fourier components. The linear-MTO (LMTO) method is particularly suited for closely packed structures and it combines desirable features of Korringa-Kohn-Rostoker, linear-combination-of-atomic-orbitals, and cellular methods; the secular matrix is linear in energy, the overlap integrals factorize as potential parameters and structure constants, the latter are canonical in the sense that they neither depend on the energy nor the cell volume and they specify the boundary conditions on a single MT or atomic sphere in the most convenient way. This method is very well suited for self-consistent calculations. The empty-lattice test is applied to the linear-MTO method and the free-electron energy bands are accurately reproduced. Finally, it is shown how relativistic effects may be included in both the LAPW and LMTO methods.

1975-01-01

296

Effect of size of silica microspheres on photonic band gap  

Science.gov (United States)

In present work photonic crystals of different size of silica microspheres have been fabricated. The optical properties of these developed photonic crystals have been studied using UV-visible spectroscopy. UV-visible spectroscopy shows that they have photonic band gap that can be tuned in visible and infrared regime by changing the size of silica microspheres. The photonic band gap structures of these photonic crystals have been calculated using MIT photonic band gap package. It also reveals that with the increase in size of silica microspheres the photonic band gap shifts to lower energy region.

Dhiman, N.; Sharma, A.; Singh, B. P.; Gathania, A. K.

2014-04-01

297

Gutzwiller theory of band magnetism in LaOFeAs  

International Nuclear Information System (INIS)

For the iron pnictide LaOFeAs we investigate multi-band Hubbard models which are assumed to capture the relevant physics. In our calculations, we employ the Gutzwiller variational theory which is a genuine many particle approach. We will present results both on the paramagnetic and antiferromagnetic phases of our model systems. These results show that a five band-model is not adequate to capture the relevant physics in LaOFeAs. However, our results for the eight band-model which includes the arsenic 4p bands reproduce the experimental data, especially the small magnetic moment, for a broad parameter regime.

2012-03-25

298

Configurations of superdeformed bands in 193Pb  

International Nuclear Information System (INIS)

The six superdeformed bands in 193Pb have been studied with the EUROGAM 2 ?-ray spectrometer using the 168Er(30Si,5n)193Pb reaction. The results are discussed in terms of cranked-Hartree-Fock-Bogolioubov-Lipkin-Nogami calculations. From the at sign FF (2) moment of inertia behavior as function of the rotational frequency and the M1 and E2 decay competition of the superdeformed states, the bands are interpreted as three pairs of signature partners based on quasineutron excitations. Dipole transitions linking two signature partner superdeformed bands have been observed and, for the first time in lead isotopes, the branching ratio B(M1)/B(E2)=0.15±0.04 ?2N/e2b2 has been extracted. copyright 1996 The American Physical Society

1996-06-01

299

MRO Ka-Band Demonstration  

Science.gov (United States)

This viewgraph presentation reviews the Mars Reconnaissance Orbiter use of the Ka-band. Due to lack of spectrum at X-band (8.41 GHz) NASA is switching to Ka-band (32 GHz) for its Deep Space Missions. This is 50 MHz bandwidth at X-band vs. 500 MHz at Ka-band. Weather events cause a greater degradation for the Ka-band link. Therefore, the Ka-band needs to be operated in a different manner than the X-band. The Ka-band achieves a maximum average capacity at a lower weather reliability than X-band (80 to 90% for Ka-band vs. 95% for X-band). Studies have been done to suggest different methods of operation for Ka-band. The Mars Reconnaissance Orbiter (MRO) will allow us to evaluate the proposed methods of operations for the Ka-band The MRO is the first spacecraft to have a fully functioning independent Ka-band downlink stream.

Shambayati, Shervin

2006-01-01

300

Two dimensional rotational band searching technique  

Energy Technology Data Exchange (ETDEWEB)

A method for searching for rotational band structures in multidimensional data sets will be discussed. By ordering {gamma}-ray transition energies E{sub 3} > E{sub 2} > E{sub 1}, and plotting E{sub 3} - E{sub 2} vs. E{sub 2} - E{sub 1}, one produces a characteristic spot pattern that depends upon the dynamic moment-of-inertia of the nucleus. We have developed a simple model to calculate such spot patterns using the rotational model equation: E(I) = AI(I+ 1)+BI{sup 2}(I+ 1){sup 2} +CI{sup 3}(I+1){sup 3}+.... Calculated patterns for superdeformed bands using two parameters (A, B) and three parameters (A, B, C) will be shown and compared to experimental data for {sup 193}Pb and {sup 194}Pb. The calculated pattern is compared to the experimental pattern by generating a {open_quotes}figure-of-merit{close_quotes}, X{sup 2} = {Sigma}{sub ij} (I{sub Cij}-I{sub xij}){sup 2}/N, where I{sub c} is the calculated intensity in channel ij, I{sub x} is the experimental intensity in that channel, and N is the total number of channels (for normalization). Searches for new bands can be performed by generating gated E{sub 3} - E{sub 2} vs. E{sub 2} - E{sub 1} experimental spectra, calculating spot patterns for reasonable ranges of A, B and C parameters, and finally calculating X{sup 2} for all calculated patterns for all experimental spectra and investigating the promising X{sup 2} values.

Stoyer, M.A.; Henry, E.A.; Becker, J.A.; Brinkman, M.J.; Farris, L.P.; Hughes, J.R. [Lawrence Livermore National Laboratory, CA (United States)

1993-10-01

 
 
 
 
301

Band gap and band discontinuities at crystalline Pr2O3/Si(001) heterojunctions  

Science.gov (United States)

We report the experimental results on the band alignment of Pr2O3 films on Si(001) as prepared by molecular beam epitaxy. Using x-ray photoelectron spectroscopy, we obtain a valence band offset at the Pr2O3/Si(001) interface of (1.1+/-0.2) eV. High field tunneling was used to extract the conduction band offset of (0.5-1.5) eV. Thus, the Pr2O3/Si(001) interface band alignment is symmetric, desired for applying such materials in both n- and p-type devices. The band gap of bulk Pr2O3 should be between 2.5 and 3.9 eV. Using scanning tunneling spectroscopy, we find a surface-state band gap of about 3.2 eV for monolayer coverage. In agreement with recent pseudopotential calculations, the electron masses in the oxide appear to be very large. This effect, together with the suitable band offsets lead to the unusually low leakage currents recently measured.

Osten, H. J.; Liu, J. P.; Müssig, H. J.

2002-01-01

302

Reliability calculations  

International Nuclear Information System (INIS)

Risk and reliability analysis is increasingly being used in evaluations of plant safety and plant reliability. The analysis can be performed either during the design process or during the operation time, with the purpose to improve the safety or the reliability. Due to plant complexity and safety and availability requirements, sophisticated tools, which are flexible and efficient, are needed. Such tools have been developed in the last 20 years and they have to be continuously refined to meet the growing requirements. Two different areas of application were analysed. In structural reliability probabilistic approaches have been introduced in some cases for the calculation of the reliability of structures or components. A new computer program has been developed based upon numerical integration in several variables. In systems reliability Monte Carlo simulation programs are used especially in analysis of very complex systems. In order to increase the applicability of the programs variance reduction techniques can be applied to speed up the calculation process. Variance reduction techniques have been studied and procedures for implementation of importance sampling are suggested. (author)

1986-01-01

303

Configuration assignment to ground state rotational band of 184Au  

International Nuclear Information System (INIS)

Recently, the rotational level scheme of 184Au has been investigated by means of in-beam ? -ray spectroscopy techniques. On the basis of a comparison of the measured and calculated B(M1)/B(E2) ratios, Li et al. suggested a highly mixed character for the ground state two quasiparticle (2qp) rotational band of 184Au. In this paper, the configuration assignment to ground state band of 184Au is revisited in terms of Two Quasi-Particle Rotor Model (TQPRM) calculations. Our results further strengthen the earlier proposed configuration assignments to this band

2013-12-01

304

Correlated band structure of 3d2 vanadates  

International Nuclear Information System (INIS)

We study the correlated band structure and the momentum-resolved spectra for 3d2 vanadates, like La O3 and YVO3, using a combination of a first-principles technique and dynamical mean-field theory with a Monte Carlo impurity solver. The self-energy for the effective 3d bands is calculated using maximum-entropy spectral analysis of the Monte Carlo results and a self-consistent procedure. We use this self-energy to calculate the full momentum-resolved spectrum and the correlated band structure, which we compare to available spectroscopy experimental results. We also discuss the effects of the lattice distortions and chemistry

2008-02-25

305

Small Quadrupole Deformation for the Dipole Bands in 112In  

CERN Multimedia

High spin states in $^{112}$In were investigated using $^{100}$Mo($^{16}$O, p3n) reaction at 80 MeV. The excited level have been observed up to 5.6 MeV excitation energy and spin $\\sim$ 20$\\hbar$ with the level scheme showing three dipole bands. The polarization and lifetime measurements were carried out for the dipole bands. Tilted axis cranking model calculations were performed for different quasi-particle configurations of this doubly odd nucleus. Comparison of the calculations of the model with the B(M1) transition strengths of the positive and negative parity bands firmly established their configurations.

Trivedi, T; Sethi, J; Saha, S; Kumar, S; Naik, Z; Parkar, V V; Naidu, B S; Deo, A Y; Raghav, A; Joshi, P K; Jain, H C; Sihotra, S; Mehta, D; Jain, A K; Choudhury, D; Negi, D; Roy, S; Chattopadhyay, S; Singh, A K; Singh, P; Biswas, D C; Bhowmik, R K; Muralithar, S; Singh, R P; Kumar, R; Rani, K

2012-01-01

306

Structure of positive-parity yrast band in sup 8 sup 0 Br 27.50.+e; 21.10.Re; 21.10.Tg; NUCLEAR REACTION 76 Ge( 7 Li, 3n); Enriched targets; E = 32 MeV; Measured E gamma,I gamma,gamma-gamma-t; DCO ratios; Doppler shifts; 80 Br; Deduced levels; J pi; (E2); band structure; Comparison with cranked-shell model calculations  

CERN Document Server

The states of the positive-parity yrast band in sup 8 sup 0 Br have been investigated using the sup 7 sup 6 Ge( sup 7 Li, 3n gamma ) reaction at a beam energy of 32 MeV. The band has been extended up to 4450 keV with a spin of (14 sup + ). Unambiguous spin assignments are made for states up to 2944.0 keV and gamma -ray multipole mixing ratios are determined for several DELTA J=1 transitions. Lifetimes studies for the 10 sup + , 11 sup + and 12 sup + states provide an estimate of the quadrupole deformation in this band. Cranking model analysis of the experimental data reveals a signature inversion at a spin of 12 Planck constant and a probable neutron alignment at Planck constant omega approx 0.7 MeV. The results are discussed within the framework of the systematics of similar bands in the lighter Br isotopes and the cranked-shell model. In addition, a new positive-parity and two negative-parity sequences have been identified.

Ray, I; Bhattacharya, S; Saha-Sarkar, M; Muralithar, S; Singh, R P; Bhowmik, R K

2000-01-01

307

Symmetrical band-pass loudspeaker systems  

Science.gov (United States)

Loudspeaker systems are analyzed in a doctoral dissertation. The dissertation concerns loudspeaker systems, which are known as subwoofers or band-pass loudspeaker systems. Their advantages include: high- quality sound reproduction in the low-frequency range, small dimensions, small nonlinear distortions and the fact that they can be placed anywhere in a room or car. Band-pass loudspeaker systems are used widely in the so- called Home Theatre as well as to provide sound in cinema, theatre, concert, discotheque, opera, operetta, philharmonic and amphitheater halls, at open-air concerts, and so on. Various designs are mass-produced by a large number of manufacturers. The study covers an analysis of band-pass loudspeaker systems to which the frequency transformation, i.e. the reactance transformation, has been applied. Since this is a symmetrical transformation, amplitude frequency responses of the studied band-pass systems are also symmetrical (logarithmic scale of a frequency). As a result, the high-pass loudspeaker system design method, known as the Thiele-Small, Benson analysis, can be employed. The investigations include the formulation of band-pass system equations (fourth, sixth and eighth-order polynomials) and the subsequent derivation of relations for the calculation of system parameters. The obtained results enable the calculation of optimum designs for prescribed alignments, e.g. (Chebyshev) equal-ripple, (Butterworth) maximally flat, or quasi-maximally flat (QB). The analysis covers fourth, sixth and eighth-order symmetrical systems. Eighth-order systems have been divided into three kinds according to three ways of physical realization. The doctoral dissertation includes band-pass loudspeaker systems, which can be designed with active or passive filters or without the filter. Designed systems consist of a loudspeaker whose front of a diaphragm is loaded with a Helmholtz resonator, i.e. an enclosure with a vent, which radiates sound outwards. The back is loaded with a closed-box or the Helmholtz resonator.

Matusiak, Grzegorz Piotr

2001-12-01

308

Rubber Band Recoil  

Digital Repository Infrastructure Vision for European Research (DRIVER)

When an initially stretched rubber band is suddenly released at one end, an axial-stress front propagating at the celerity of sound separates a free and a stretched domain of the elastic material. As soon as it reaches the clamped end, the front rebounds and a compression front propagates backward. When the length of the compressed area exceeds Euler critical length, a dynamic buckling instability develops. The rebound is analysed using Saint-Venant's theory of impacts and we use a dynamical ...

2007-01-01

309

Susceptibilities for first principles band structures  

Science.gov (United States)

We present a parallel implementation of a new method for calculating the unenhanced susceptibility proposed by us recently. Our implementation uses the first principles LMTO band structure within the tight binding approach as input to calculate the joint density of states. The susceptibility is then obtained by integrating over the product of the joint density of states and a Lindhard function. Our program, which has a simple friendly user interface, runs on the PC with a quadputer board, a Meiko Surface running CSTools powered either by T800 or i860 compute boards and the Intel iPSC/860 hypercube in Daresbury. Our method incorporates the troublesome matrix elements naturally and our results on Pd and Ni show that the decrease in ?( q) as we go away from the Brillouin zone centre is due mainly to the matrix elements rather than to the band energies.

Crockford, D. J.; Yeung, W.

1993-04-01

310

Graphene Nano ribbon Conductance Model in Parabolic Band Structure  

International Nuclear Information System (INIS)

Many experimental measurements have been done on GNR conductance. In this paper, analytical model of GNR conductance is presented. Moreover, comparison with published data which illustrates good agreement between them is studied. Conductance of GNR as a one-dimensional device channel with parabolic band structures near the charge neutrality point is improved. Based on quantum confinement effect, the conductance of GNR in parabolic part of the band structure, also the temperature-dependent conductance which displays minimum conductance near the charge neutrality point are calculated. Graphene nano ribbon (GNR) with parabolic band structure near the minimum band energy terminates Fermi-Dirac integral base method on band structure study. While band structure is parabola, semiconducting GNRs conductance is a function of Fermi-Dirac integral which is based on Maxwell approximation in nondegenerate limit especially for a long channel

2010-01-01

311

Graphene Nanoribbon Conductance Model in Parabolic Band Structure  

Directory of Open Access Journals (Sweden)

Full Text Available Many experimental measurements have been done on GNR conductance. In this paper, analytical model of GNR conductance is presented. Moreover, comparison with published data which illustrates good agreement between them is studied. Conductance of GNR as a one-dimensional device channel with parabolic band structures near the charge neutrality point is improved. Based on quantum confinement effect, the conductance of GNR in parabolic part of the band structure, also the temperature-dependent conductance which displays minimum conductance near the charge neutrality point are calculated. Graphene nanoribbon (GNR with parabolic band structure near the minimum band energy terminates Fermi-Dirac integral base method on band structure study. While band structure is parabola, semiconducting GNRs conductance is a function of Fermi-Dirac integral which is based on Maxwell approximation in nondegenerate limit especially for a long channel.

Mohammad Taghi Ahmadi

2010-01-01

312

Cluster structure and deformed bands in the 38Ar nucleus  

International Nuclear Information System (INIS)

The structure of the 38Ar nucleus is investigated by the 34S+? orthogonality condition model (OCM). The energy spectra, electromagnetic transitions and ? spectroscopic factors are calculated. The excited states can be grouped into several bands according to the leading configurations of their wave functions, and the structures of the bands are discussed. The first excited K?=0+ band is found to be predominantly 34S+? cluster states. It is also shown that the observed energies and E2 transitions of the band are well reproduced by the model. The existence of a negative-parity doublet band of the band is also predicted. The strength of the ?-cluster states is shown to be spread over several levels due to mixing of shell-model states and various ?-cluster states

2013-06-17

313

Search for positive parity bands in 117Xe  

International Nuclear Information System (INIS)

Excited states of 117Xe were populated via the reaction 28Si+92Mo at 100-120MeV. More than 40 new ?-transitions and three new positive parity bands have been observed by means of in-beam ?-ray spectroscopy. The previously known ?h11/2 bands were confirmed, and the ?g7/2 favored band was extended up to 47/2+ in which two bandcrossings have been observed at h?=0.33 and 0.44MeV, respectively. The band structures have been discussed by means of TRS and CSM calculations. A newly observed rotational band consisting of five ?-transitions has been considered as the ?h11/2 band of 117Cs. ((orig.))

1995-02-06

314

Band theory of the intermetallic compound UGe3  

International Nuclear Information System (INIS)

The one-electron energy band structure for UGe3, which has attracted interest as a typical spin-fluctuation system, is calculated by an APW method with the LSD approximation exchange potential. Relativistic effects are taken into account. The 5f electrons hybridise with the Ge 4p electrons considerably and form bands which spread over about 0.2 Ryd. The Fermi level lies at a sharp peak in the density of states. The Fermi surface, the extremal cross-sectional area and the cyclotron mass are calculated carefully. The Fermi surface consists of two closed hole sheets centred at R in the eighth and ninth bands, and a lens-like electron pocket at M and a hollow-ball-like electron sheet centred at R in the tenth band. There exists no open orbit. These calculated results account well for experimental results for the de Haas-van Alphen effect and the magnetoresistance. (author)

1984-01-01

315

CMB Broad-Band Power Spectrum Estimation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The natural outcome of theoretical calculations of microwave background anisotropy is the angular power spectrum ${\\cal C}_\\ell$ as a function of multipole number $\\ell$. Experimental ${\\cal C}_\\ell$'s are needed for direct comparison. Estimation procedures using statistics linear in the pixel amplitudes as well as the conventional but less useful quadratic combinations are described. For most current experiments, a single broad-band power amplitude is all that one can get w...

Bond, J. Richard

1994-01-01

316

Bandgaps and band bowing in semiconductor alloys  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The bandgap and band bowing parameter of semiconductor alloys are calculated with a fast and realistic approach. The method is a dielectric scaling approximation that is based on a scissor approximation. It adds an energy shift to the bandgap provided by the local density approximation (LDA) of the density functional theory (DFT). The energy shift consists of a material-independent constant weighted by the inverse of the high-frequency dielectric constant. The salient featur...

Sandu, Titus; Iftimie, Radu I.

2010-01-01

317

Colourful calculations  

International Nuclear Information System (INIS)

The formidable computational power of lattice QCD is finally allowing researchers to make solid predictions about the force that binds quarks inside protons and neutrons, describes Christine Davies. Understanding how the universe works at the most fundamental scale is often likened to peeling away the layers of an onion. The outermost layer of the onion represents atoms, and we have known about these for a century or so. The next layer of structure, which was revealed by Rutherford in 1911, is the atomic nucleus - a much smaller object that contains almost all of the atomic mass. Some 20 years after that discovery, physicists realized that the nucleus is composed of more fundamental objects called protons and neutrons. However, peeling back the next layer of the onion has turned out to be much more of a challenge. It is now universally accepted that protons and neutrons are made up of fractionally charged particles called quarks: two 'up' quarks and a 'down' quark in a proton, and two downs and an up in a neutron. There are six types of quarks in total, but none of them has ever been observed as a free particle. Smashing protons together at enormous energies in particle accelerators, for instance, reveals not single quarks but yet more particles made of quarks. Such particles are called hadrons, and there are hundreds of them: some are 'baryons', which contain three quarks, while the rest are 'mesons' made up of quark-antiquark pairs. It might therefore seem, as indeed it did to particle physicists in the 1960s, that the core of the onion is forever hidden. The only way we can understand the properties of quarks is to compare experimental measurements of hadrons with calculations based on quantum chromodynamics or QCD: the theory of the 'strong force' that binds quarks together. Despite being around for over 30 years, however, the equations of QCD have proved eye-wateringly difficult to solve. Indeed, to the immense frustration of particle physicists, it has been impossible to calculate properties of hadrons with an accuracy of better than 10%. In the December issue of Physics World, Christine Davies shows how a the technique 'lattice QCD' is allowing these equations to be solved much more accurately by representing space-time as a 4D lattice - which, she says, could reveal what the final layer of the onion looks like. (U.K.)

2006-12-01

318

Population of rotational bands in superheavy nuclei  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Using the statistical approach, we study the population of ground-state rotational bands of superheavy nuclei produced in the fusion-evaporation reactions 208Pb(48Ca, 2n)254No, 206Pb(48Ca, 2n)252No, and 204Hg(48Ca, 2n)250Fm. We calculate relative intensities of E2-transitions between the rotational states and entry spin distributions of the residual nuclei, evaporation residue cross sections, and excitation functions for these reactions. Fermi-gas model is used for the calculation of level de...

Zubov A.S.; Sargsyan V.V.; Adamian G.G.; Antonenko N.V.

2012-01-01

319

New Kronig-Penney equation emphasizing the band edge conditions  

International Nuclear Information System (INIS)

The Kronig-Penney problem is a textbook example for discussing band dispersions and band gap formation in periodic layered media. For example, in photonic crystals, the behaviour of bands next to the band edges is important for further discussions of such effects as inhibited light emission, slow light and negative index of refraction. However, the standard Kronig-Penney equation does not explicitly state the band edge conditions. This paper derives a new solution for the Kronig-Penney problem that explicitly displays the band edge conditions as well as contains all other essential physics of band formation. Therefore, the present exposition should show the student that the band edge conditions are not simply special cases of the familiar Kronig-Penney equation but, instead, are an integral part of the band theory. For the computationally minded student, the new equation is particularly convenient for calculating the positions of closely spaced band edges. The present results can be taught alongside the Kronig-Penney equation in advanced undergraduate or beginning graduate quantum mechanics, solid state theory and photonics courses dealing with wave propagation through periodic layered media

2008-05-01

320

New Kronig-Penney equation emphasizing the band edge conditions  

Energy Technology Data Exchange (ETDEWEB)

The Kronig-Penney problem is a textbook example for discussing band dispersions and band gap formation in periodic layered media. For example, in photonic crystals, the behaviour of bands next to the band edges is important for further discussions of such effects as inhibited light emission, slow light and negative index of refraction. However, the standard Kronig-Penney equation does not explicitly state the band edge conditions. This paper derives a new solution for the Kronig-Penney problem that explicitly displays the band edge conditions as well as contains all other essential physics of band formation. Therefore, the present exposition should show the student that the band edge conditions are not simply special cases of the familiar Kronig-Penney equation but, instead, are an integral part of the band theory. For the computationally minded student, the new equation is particularly convenient for calculating the positions of closely spaced band edges. The present results can be taught alongside the Kronig-Penney equation in advanced undergraduate or beginning graduate quantum mechanics, solid state theory and photonics courses dealing with wave propagation through periodic layered media.

Szmulowicz, Frank [University of Dayton Research Institute, 300 College Park Ave., Dayton, OH 45469-0072 (United States)], E-mail: Frank.Szmulowicz@wpafb.af.mil

2008-05-15

 
 
 
 
321

New Kronig Penney equation emphasizing the band edge conditions  

Science.gov (United States)

The Kronig-Penney problem is a textbook example for discussing band dispersions and band gap formation in periodic layered media. For example, in photonic crystals, the behaviour of bands next to the band edges is important for further discussions of such effects as inhibited light emission, slow light and negative index of refraction. However, the standard Kronig-Penney equation does not explicitly state the band edge conditions. This paper derives a new solution for the Kronig-Penney problem that explicitly displays the band edge conditions as well as contains all other essential physics of band formation. Therefore, the present exposition should show the student that the band edge conditions are not simply special cases of the familiar Kronig-Penney equation but, instead, are an integral part of the band theory. For the computationally minded student, the new equation is particularly convenient for calculating the positions of closely spaced band edges. The present results can be taught alongside the Kronig-Penney equation in advanced undergraduate or beginning graduate quantum mechanics, solid state theory and photonics courses dealing with wave propagation through periodic layered media.

Szmulowicz, Frank

2008-05-01

322

Band structures of defective graphenes  

Energy Technology Data Exchange (ETDEWEB)

Band structures of defective graphenes are analyzed by crystal orbital method. In laterally slipped faults, there appear {sigma} bands consisting of weakly interacted dangling bonds. The peculiar {sigma} bands cross with frontier {pi} bands, and the resultant double occupation leads to the disappearance of ferromagnetic interactions. On the other hand, in longitudinally slipped faults, there are no crossings of the {sigma} bands within the frontier levels, and the ferromagnetic interactions result from polycarbene-type spin alignment. - Research Highlights: Band structures in defective graphenes are analyzed. Lateral slipping in graphenes quenches the ferromagnetic interactions. In the lateral slipping modes, {sigma} bands cross with {pi} frontier bands and reduce the magnetism. Longitudinal slipping in graphenes causes carbene-type ferromagnetic interactions.

Hatanaka, Masashi, E-mail: mhatanaka@xug.biglobe.ne.j [Department of Green and Sustainable Chemistry, School of Engineering, Tokyo Denki University, 2-2 Kanda Nishiki-cho, Chiyoda-ku, Tokyo 101-8457 (Japan)

2011-03-15

323

Remote Sensing Interactive: Band Combination  

Science.gov (United States)

Band Combination is one of a number of interactive tools being developed to illustrate basic remote sensing concepts. Here, the user is able to experiment with RGB bands on three different image modes: MODIS, ASTER and LANDSAT.

324

Hofstadter butterflies for flat bands  

CERN Document Server

Hofstadter's diagram, or the energy spectrum against the magnetic field in tight-binding systems, is obtained for the models having flat (dispersionless) one-electron band(s) that have originally been proposed for itinerant spin ferromagnetism. Magnetic fields preserve those flat bands that arise from a topological reason, while dispersions emerge in a singular manner for the flat bands arising from interference, implying an anomalous orbital magnetism.

Aoki, H; Matsumura, H; Aoki, Hideo; Ando, Masato; Matsumura, Hajime

1996-01-01

325

Semiconductors bonds and bands  

CERN Document Server

As we settle into this second decade of the twenty-first century, it is evident that the advances in micro-electronics have truly revolutionized our day-to-day lifestyle. The technology is built upon semiconductors, materials in which the band gap has been engineered for special values suitable to the particular application. This book, written specifically for a one semester course for graduate students, provides a thorough understanding of the key solid state physics of semiconductors. It describes how quantum mechanics gives semiconductors unique properties that enabled the micro-electronics revolution, and sustain the ever-growing importance of this revolution.

Ferry, David K

2013-01-01

326

UV Huggins Bands of Ozone.  

Science.gov (United States)

A recent analysis on the Huggins bands of ozone deduced the symmetry type of the upper electronic state of this band system. Their analysis, however, depends critically on the vibrational quantum number assignment of a band having an od v3' number. Becaus...

D. H. Katayama

1987-01-01

327

Spectral electron momentum density calculation in graphite  

International Nuclear Information System (INIS)

The linear muffin-tin orbital method has been used to calculate energy-momentum distribution of valence electrons in graphite along major symmetry directions and as the spherical average over the irreducible wedge of the Brillouin zone. These data bridge the gap between existing band structure calculations and emerging electron momentum spectroscopy of solids. The calculation has been validated by comparison to the most accurate experimental data on the highly oriented laser annealed carbon films. 14 refs., 1 tab., 4 figs

1995-01-01

328

Spectral electron momentum density calculation in graphite  

Energy Technology Data Exchange (ETDEWEB)

The linear muffin-tin orbital method has been used to calculate energy-momentum distribution of valence electrons in graphite along major symmetry directions and as the spherical average over the irreducible wedge of the Brillouin zone. These data bridge the gap between existing band structure calculations and emerging electron momentum spectroscopy of solids. The calculation has been validated by comparison to the most accurate experimental data on the highly oriented laser annealed carbon films. 14 refs., 1 tab., 4 figs.

Kheifets, A.S.; Vos, M.

1995-02-01

329

Calculation of Gilbert damping in ferromagnetic ?lms  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The Gilbert damping constant in the phenomenological Landau-Lifshitz-Gilbert equation which describes the dynamics of magnetization, is calculated for Fe, Co and Ni bulk ferromagnets, Co ?lms and Co/Pd bilayers within a nine-band tight-binding model with spin-orbit coupling included. The calculational effciency is remarkably improved by introducing ?nite temperature into the electronic occupation factors and subsequent summation over the Matsubara frequencies. The calculated dependence of...

Barati E.; Cinal M.; Edwards D. M.; Umerski A.

2013-01-01

330

Investigation of Dipole Bands in the 142Gd region with EUROBALL  

International Nuclear Information System (INIS)

Lifetimes have been measured for dipole bands in 142Gd and 141Eu. The resulting B(M1) and B(E2) values are compared with calculations in the framework of the TAC (Tilted Axis Cranking) and SPAC (Shears mechanism with Principal Axis Cranking) models. The dipole bands can be interpreted as magnetic rotational bands with a significant contribution of collectivity

2004-02-27

331

A narrow conduction band in YBa2Cu3O7 - ?  

International Nuclear Information System (INIS)

LDA band-structure calculations of YBa2Cu3O7 - ? show wide bands (of several eV) spanning Ef. The authors discuss how experiments especially transport measurements, contradict this and indicate the presence of a narrow conduction band (about a tenth of an eV wide)

1989-07-23

332

Rotational bands in 170Yb observed following (?,xn) reactions  

International Nuclear Information System (INIS)

At least seven side bands, with Ksup(?) = (0+), (1-), (2+), (3-), 4-, 6-, and 7-, have been identified in 170Yb up to high spin, using ?-ray techniques following (?,2n) and (?,4n) reactions. Backbending in the positive-parity yrast band is confirmed, and candidates for low-spin members of the S-band are found. The negative-parity yrast band has behaviour characteristic of both strong coupling and decoupling. These properties, together with those in the other negative-parity side bands, are interpreted as arising from Coriolis effects on the quasiparticle configurations, and the experimental results are compared with a two-quasiparticle-plus-rotor calculation. Evidence of ?K = 2 mixing is found in the K = (3) side band. The relationship between the moments of inertia of the positive-parity and negative-parity yrast bands in the N = 100 isotones is discussed in the framework of a simple empirical model, giving insight into the presence or absence of backbending. The negative-parity yrast bands in the N = 100 isotones are compared. Their significant differences are qualitatively reproduced in two-quasiparticle-plus-rotor calculations. (orig.)

1981-07-20

333

Tuning two-dimensional band structure of Cu(111) surface-state electrons that interplay with artificial supramolecular architectures  

Science.gov (United States)

We report on the modulation of two-dimensional (2D) bands of Cu(111) surface-state electrons by three isostructural supramolecular honeycomb architectures with different periodicity or constituent molecules. Using Fourier-transformed scanning tunneling spectroscopy and model calculations, we resolved the 2D band structures and found that the intrinsic surface-state band is split into discrete bands. The band characteristics including band gap, band bottom, and bandwidth are controlled by the network unit cell size and the nature of the molecule-surface interaction. In particular, Dirac cones emerge where the second and third bands meet at the K points of the Brillouin zone of the supramolecular lattice.

Wang, Shiyong; Wang, Weihua; Tan, Liang Z.; Li, Xing Guang; Shi, Zilang; Kuang, Guowen; Liu, Pei Nian; Louie, Steven G.; Lin, Nian

2013-12-01

334

A Multi-band Wavelet Watermarking Scheme  

Directory of Open Access Journals (Sweden)

Full Text Available This paper presents a new multi-band wavelet watermarking scheme. Compared with conventional watermarking schemes implemented in two-band wavelet domain, by incorporating the principal component analysis (PCA technique the proposed blind watermarking in the multi-band wavelet domain can achieve higher perceptual transparency and stronger robustness. Specifically, the developed watermarking scheme can successfully resist common signal processing such as JPEG compression with quality factor as low as 15, and some geometric distortions such as cropping (cropped by 50\\%. In addition, the proposed multi-band wavelet based watermarking scheme can be parameterized, thus resulting in more security. That is, an attacker may not be able to detect the embedded watermark if the attacker does not know the parameter. Different from many other watermarking schemes, in which the watermark detection threshold is chosen empirically, the false positive rate of the proposed watermarking scheme can be calculated analytically so that watermark detection threshold can be chosen based solely on the targeted false positive.

Xiangui Kang

2008-03-01

335

Band structures of rare earth metals  

International Nuclear Information System (INIS)

Recent magnetic, optical and neutron scattering experiments made possible by the availability of high purity samples are providing increasingly detailed information about the electronic structure of the rare earth metals. The first calculations for the paramagnetics state of these fascinating metals have long served as a valuable heuristic model for understanding many earlier experimental results. It is expected that more accurate calculations for the magnetic ground state will be equally valuable in fostering the traditionally fruitful interaction between theory and experiment. Such calculations present a formidable challenge since they require a relativistic approach to spin polarization and a suitable treatment of the highly localized 4f-shell. The calculations can be guided by comparison with precise experimental results and by self-consistent calculations for non-magnetic metals with similar electronic structures. In this paper we review the present status of band structure calculations for the rare earth metals, and give details of a self-consistent, relativistic, ferromagneitc calculation for gadolinium

1978-09-07

336

Study of One-Quasiproton Bands of 129La Using the Projected Shell Model  

International Nuclear Information System (INIS)

The projected shell model is applied to the nucleus 129La. The results of theoretical calculations about the one-quasiproton bands are compared with experimental data, the agreement with the yrast ?h11/2 band and ?g7/2 band is satisfactory. We also assign the ?g7/2x[?h11l/2]2 configuration with an oblate shape for one of bands in 129La. (author)

2001-01-01

337

Lone conduction band in Cu2ZnSnSe4  

Science.gov (United States)

We present experimental proof for a narrow first conduction band in Cu2ZnSnSe4 semiconductor films as it has been predicted by theoretical calculations. The optical absorption characteristics of Cu2ZnSnSe4 thin films are analyzed by optical transmission spectroscopy. The experimental data show strong evidence for three absorption edges, as expected from theory, involving the valence band and two conduction bands, which are separated by a second band gap.

Gütay, Levent; Redinger, Alex; Djemour, Rabie; Siebentritt, Susanne

2012-03-01

338

Diffuse interstellar bands  

International Nuclear Information System (INIS)

The paper presents a review of the observational investigations of the diffuse interstellar bands (DIBs) which, despite being the object of considerable research, remain unidentified since 1921. The review is focused on the most recent investigations done with the aid of solid-state detectors which make it possible to obtain high S/N spectra. It is shown that DIBs may be divided into three (or more) families probably caused by different agents. The observed profiles are usually altered by Doppler splitting when reddened stars are observed through several clouds. Also, single clouds may differ considerably in their optical properties. The paper presents intrinsic (i.e., originating in single clouds) high-resolution profiles of several DIBs. These profiles are not dependent on the structure of the interstellar medium toward the observed objects. 39 references

339

Diffuse interstellar bands  

Energy Technology Data Exchange (ETDEWEB)

The paper presents a review of the observational investigations of the diffuse interstellar bands (DIBs) which, despite being the object of considerable research, remain unidentified since 1921. The review is focused on the most recent investigations done with the aid of solid-state detectors which make it possible to obtain high S/N spectra. It is shown that DIBs may be divided into three (or more) families probably caused by different agents. The observed profiles are usually altered by Doppler splitting when reddened stars are observed through several clouds. Also, single clouds may differ considerably in their optical properties. The paper presents intrinsic (i.e., originating in single clouds) high-resolution profiles of several DIBs. These profiles are not dependent on the structure of the interstellar medium toward the observed objects. 39 references.

Krelowski, J.

1988-08-01

340

Wide band ENDOR spectrometer  

International Nuclear Information System (INIS)

The construction of an ENDOR spectrometer operating from 0,5 to 75 MHz within a single band, with ore Klystron and homodine detection, and no fundamental changes on the electron spin resonance spectrometer was described. The ENDOR signal can be detected both by amplitude modulation of the frequency field, or direct detection of the ESR output, which is taken to a signal analyser. The signal-to-noise ratio is raised by averaging rather than filtering avoiding the use of long time constants, providing natural line widths. The experimental apparatus and the spectra obtained are described. A discussion, relating the ENDOR line amplitudes with the experimental conditions is done and ENDOR mechanism, in which there is a relevant presence of cross relaxation is proposed

1973-01-01

 
 
 
 
341

Self-consistent, relativistic, ferromagnetic band structure of gadolinium  

International Nuclear Information System (INIS)

An initial self-consistent calculation of the ground state magnetic band structure of gadolinium is described. A linearized APW method was used which included all single particle relativistic effects except spin-orbit coupling. The spin polarized potential was obtained in the muffin-tin form using the local spin density approximation for exchange and correlation. The most striking and unorthodox aspect of the results is the position of the 4f spin-down ''bands'' which are required to float just on top of the Fermi level in order to obtain convergence. If the 4f states (l = 3 resonance) are removed from the occupied region of the conduction bands the magnetic moment is approximately .75 ?/sub B//atom; however, as the 4f spin-down states are allowed to find their own position they hybridize with the conduction bands at the Fermi level and the moment becomes smaller. Means of improving the calculation are discussed

1977-08-18

342

Band gap bowing and band offsets in relaxed and strained Si1-xGex alloys by employing a new nonlinear interpolation scheme  

Science.gov (United States)

We present nonlocal empirical pseudopotential calculations for SiGe alloys employing a novel nonlinear interpolation scheme. Our interpolation scheme is able to correctly model for the first time the band gap bowing observed in relaxed SiGe alloys. The valence-band-edge and conduction-band-edge energies in relaxed Si1-xGex for arbitrary x, which are difficult to obtain by experimental techniques, have been evaluated using pseudopotential calculations. We have also calculated the band energies of pseudomorphic [100]-strained Si1-xGex alloys grown over unstrained Si1-yGey substrates. The energy gaps, valence and conduction band offsets, effective masses, and strain induced splittings in pseudomorphic SiGe layers are calculated for the whole range of alloy compositions x and y.

Sant, Saurabh; Lodha, Saurabh; Ganguly, Udayan; Mahapatra, Souvik; Heinz, Frederik O.; Smith, Lee; Moroz, Victor; Ganguly, Swaroop

2013-01-01

343

Band crossing in the superdeformed bands in {sup 145}Gd  

Energy Technology Data Exchange (ETDEWEB)

Gamma-rays emitted from {sup 145}Gd excited in the heavy ion reaction of {sup 36}S with the {sup 114}Cd target at energy of 182 MeV have been investigated. Two new superdeformed bands have been established, consisting of 18 and 17 transitions. The first excited superdeformed band shows two subsequent band crossing at rotational frequency of about 0.4 and 0.68 MeV. 2 figs, 2 refs.

Rzaca-Urban, T. [Warsaw Univ., Inst. of Experimental Physics, Warsaw (Poland); Lieder, R.M.; Utzelmann, S. [Forschungszentrum Juelich GmbH, Inst. fuer Kernphysik, Juelich (Germany)

1995-12-31

344

Multiphonon ?-vibrational bands in the ?-soft nucleus 138Nd  

Science.gov (United States)

The low spin states of 138Nd have been reinvestigated via the 124Te(19F,4n1p) reaction at a beam energy of 103 MeV. The quasi-one-phonon ?-vibrational band based on the 1013.7 keV level has been expanded and the quasi-two-phonon ?-vibrational band built on the 1842.7 keV level has been proposed. A systematic comparison supports our assignments for multiphonon ?-vibrational bands in 138Nd. The characteristics of ? softness in 138Nd have been discussed. Triaxial projected shell model calculations can well describe the rotational feature of the bands, but they fail to reproduce simultaneously the bandhead energies of the two ?-vibrational bands if a fixed triaxial deformation is assumed.

Li, H. J.; Xiao, Z. G.; Zhu, S. J.; Yeoh, E. Y.; Liu, Y. X.; Sun, Y.; Zhang, Z.; Wang, R. S.; Yi, H.; Yan, W. H.; Xu, Q.; Wu, X. G.; He, C. Y.; Zheng, Y.; Li, G. S.; Li, C. B.; Li, H. W.; Liu, J. J.; Hu, S. P.; Wang, J. L.; Yao, S. H.

2013-05-01

345

Flat band electrons and interactions in rhombohedral trilayer graphene  

Science.gov (United States)

Multilayer graphene systems with a rhombohedral stacking order harbor nearly flat bands in their single-particle spectrum. We propose ansatz states to describe the surface-localized states of flat band electrons. The absence of kinetic dispersion near the Fermi level leaves the interaction as a dominate mechanism to govern the low-energy physics of a low-density electron system. We build up an effective lattice model in two interacting low-energy bands, where the full terms of the Coulomb interaction, including those long-range and off-diagonal parts, have been considered. The interaction matrix coefficients in the many-body Hamiltonian model are directly calculated for a trilayer system using orthonormal Wannier basis. We then present a flat band projection to yield an interaction-only lattice model for flat band electrons. We find that this limited model might energetically favor a ferromagnetic quantum crystal under certain conditions.

Wang, Hao; Gao, Jin-Hua; Zhang, Fu-Chun

2013-04-01

346

Band Population Measurements in a Purely Optical Dark Lattice  

CERN Multimedia

We create a dark optical lattice structure using a blue detuned laser field coupling an atomic ground state of total angular momentum F simultaneously to two excited states with angular momenta F and F-1, or F and F+1. The atoms are trapped at locations of purely circular polarization. The cooling process efficiently accumulates almost half of the atomic population in the lowest energy band which is only weakly coupled to the light field. The populations of the two lowest energy bands reaches 70%. Kinetic energies on the order of the recoil energy are obtained by adiabatically reducing the optical potential. The band populations are directly mapped on free particle momentum intervals by this adiabatic release. In an experiment with subrecoil momentum resolution we measure the band populations and find good absolute agreement with the theoretically calculated steady state band populations.

Sander, F; Hänsch, T W; Stecher, H; Ritsch, H; Sander, Frank; Esslinger, Tilman; Hansch, Theodor W.; Stecher, Herwig; Ritsch, Helmut

1996-01-01

347

M-Band Graphic Equalizer  

Directory of Open Access Journals (Sweden)

Full Text Available This paper deals with the concept of filter banks. Filter banks are a group of band-pass filters connected in parallel. Each parallel connection forms a channel for different frequency-bands present in the input signal. The output of the filter bank is formed by merging these channels. The main theme behind the use of filter banksis to boost or attenuate different individual bands of frequencies present in a signal, without affecting other bands. There are several ways of realizing an filter bank and one such way is the Cosine Modulated filter bank. Instead of designing band-pass filters for different bands, the cosine modulated filter banks, modulates a lowpass filter. In simple words, it simply shifts the pass band of the low pass filter towards higher frequencies, and there by covering the entire band of frequencies of the input signal. Filter banks have many applications in the field of signal processing. Perhaps one of the biggest applications is Graphic Equalizer, where in, the user can‘graphically’ modify different bands. The design and implementation of a filter bank as M-Band Graphic Equalizer is covered in this paper.

Dr. P. Mallikarjuna Rao

2011-08-01

348

Band gap modulation of a carbon nanotube by hydrogen functionalization  

International Nuclear Information System (INIS)

We have investigated a modification of electronic structures of a carbon nanotube by hydrogen functionalization. Carbon nanotubes were exposed to atomic hydrogen which was generated by a hot tungsten filament in the vacuum chamber. Current-voltage characteristics clearly showed a band gap widening after hydrogenation. This was explained by an enhancement of sp3 hybridization with hydrogen chemisorption on the tube wall. Our density functional calculations also predicted a strong chemisorption with pi electron modulation and the band gap widening upon hydrogenation

2003-02-01

349

Systematic description of superdeformed bands in the Mass-190 region  

Energy Technology Data Exchange (ETDEWEB)

Superdeformed bands for the mass-190 region are described by the Projected Shell Model. Even-even, odd mass and odd-odd nuclei are equally well described. Good agreement with available data for all isotopes studied is obtained. Our,calculation of electromagnetic properties and pairing correlations provides an understanding of the observed gradual increase of dynamical moments of inertia with angular momentum observed in many bands in this mass region.

Sun, Y.; Guidry, M. [Oak Ridge National Lab., TN (United States)][Tennessee Univ., Knoxville, TN (United States). Dept. of Physics and Astronomy; Zhang, J. [Tennessee Univ., Knoxville, TN (United States). Dept. of Physics and Astronomy

1996-12-31

350

Systematic description of superdeformed bands in the Mass-190 region  

International Nuclear Information System (INIS)

Superdeformed bands for the mass-190 region are described by the Projected Shell Model. Even-even, odd mass and odd-odd nuclei are equally well described. Good agreement with available data for all isotopes studied is obtained. Our,calculation of electromagnetic properties and pairing correlations provides an understanding of the observed gradual increase of dynamical moments of inertia with angular momentum observed in many bands in this mass region

1996-07-22

351

Systematic description of superdeformed bands in the mass-190 region  

Energy Technology Data Exchange (ETDEWEB)

Superdeformed bands for the mass-190 region are described by the Projected Shell Model. Even-even, odd mass and odd-odd nuclei are equally well described. Good agreement with available data for all isotopes studied is obtained. The authors calculation of electromagnetic properties and pairing correlations provides an understanding of the observed gradual increase of dynamical moments of inertia with angular momentum observed in many bands in this mass region.

Sun, Yang; Guidry, M. [Oak Ridge National Lab., TN (United States)]|[Univ. of Tennessee, Knoxville, TN (United States); Zhang, Jing-ye [Univ. of Tennessee, Knoxville, TN (United States)

1996-12-31

352

Rotational effect on electromagnetic transitions after band-crossing  

International Nuclear Information System (INIS)

The signature-dependence of B(M1)-values and dynamical quadrupole moments Q(1) and Q(2) after the band-crossing are investigated by meams of the extended particle-rotor model. The calculated values are in qualitative agreement with the measrued data. It was noted that in 159Tm the ?-value is quite different before and after the band-crossing

1990-01-01

353

Shear banding and interfacial instability in planar Poiseuille flow  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Motivated by the need for a theoretical study in a planar geometry that can easily be implemented experimentally, we study the pressure driven Poiseuille flow of a shear banding fluid. After discussing the "basic states" predicted by a one dimensional calculation that assumes a flat interface between the bands, we proceed to demonstrate such an interface to be unstable with respect to the growth of undulations along it. We give results for the growth rate and wavevector of t...

Fielding, Suzanne M.; Wilson, Helen J.

2009-01-01

354

In-band and inter-band B(E2) values within the Triaxial Projected Shell Model  

International Nuclear Information System (INIS)

The Triaxial Projected Shell Model (TPSM) has been successful in providing a microscopic description of the energies of multi-phonon vibrational bands in deformed nuclei. We report here on an extension of the TPSM to allow, for the first time, calculations of B(E2) values connecting ?- and ??-vibrational bands and the ground-state band. The method is applied to 166,168Er. It is shown that most of the existing B(E2) data can be reproduced rather well, thus strongly supporting the classification of these states as ?-vibrational states. However, significant differences between the data and the calculation are seen in those B(E2) values which involve odd-spin states of the ?-band. Understanding these discrepancies requires accurate experimental measurements and perhaps further improvements of the TPSM. (orig.)

2002-12-01

355

In-Band and Inter-Band B(E2) Values within the Triaxial Projected Shell Model  

CERN Document Server

The Triaxial Projected Shell Model (TPSM) has been successful in providing a microscopic description of the energies of multi-phonon vibrational bands in deformed nuclei. We report here on an extension of the TPSM to allow, for the first time, calculations of B(E2) values connecting gamma- and gamma-gamma-vibrational bands and the ground state band. The method is applied to 166,168Er. It is shown that most of the existing B(E2) data can be reproduced rather well, thus strongly supporting the classification of these states as gamma-vibrational states. However, significant differences between the data and the calculation are seen in those B(E2) values which involve odd-spin states of the gamma-band. Understanding these discrepancies requires accurate experimental measurements and perhaps further improvements of the TPSM.

Boutachkov, P; Sun, Y; Sheikh-Javid, A; Frauendorf, S

2002-01-01

356

High-spin intruder band in $^{107}$In  

CERN Document Server

High-spin states in the neutron deficient nucleus $^{107}$In were studied via the $^{58}$Ni($^{52}$Cr, 3p) reaction. In-beam $\\gamma$ rays were measured using the JUROGAM detector array. A rotational cascade consisting of ten $\\gamma$-ray transitions which decays to the 19/2$^{+}$ level at 2.002 MeV was observed. The band exhibits the features typical for smooth terminating bands which also appear in rotational bands of heavier nuclei in the A$\\sim$100 region. The results are compared with Total Routhian Surface and Cranked Nilsson-Strutinsky calculations.

Ideguchi, E; Ganio?lu, E; Hadinia, B; Lagergren, K; Bäck, T; Johnson, A; Wyss, R; Eeckhaudt, S; Grahn, T; Greenlees, P; Julin, R; Juutinen, S; Kettunen, H; Leino, M; Leppanen, A -P; Nieminen, P; Nyman, M; Pakarinen, J; Rahkila, P; Scholey, C; Uusitalo, J; Joss, D T; Paul, E S; Wiseman, D R; Wadsworth, R; Afanasjev, A V; Ragnarsson, I

2010-01-01

357

Gutzwiller theory of band magnetism in LaOFeAs.  

Science.gov (United States)

We use the Gutzwiller variational theory to calculate the ground-state phase diagram and quasiparticle bands of LaOFeAs. The Fe3d-As4p Wannier-orbital basis obtained from density-functional theory defines the band part of our eight-band Hubbard model. The full atomic interaction between the electrons in the iron orbitals is parametrized by the Hubbard interaction U and an average Hund's-rule interaction J. We reproduce the experimentally observed small ordered magnetic moment over a large region of (U,J) parameter space. The magnetically ordered phase is a stripe spin-density wave of quasiparticles. PMID:22400768

Schickling, Tobias; Gebhard, Florian; Bünemann, Jörg; Boeri, Lilia; Andersen, Ole K; Weber, Werner

2012-01-20

358

Band offsets for pseudomorphic InP/GaAs  

International Nuclear Information System (INIS)

Recently determined band-edge hydrostatic deformation potentials are used to predict heterojunction band offsets for the pseudomorphic GaAs-InP system. The calculations include GaAs/InP, InP/GaAs, and strained-layer GaAs-InP superlattices for both [100] and [111] oriented epitaxial growth. The offsets are type II for the unstrained case. The large hydrostatic contributions to the stress-induced band offsets can convert the offsets to type I. This conversion is especially apparent for growth in the [111] direction because of the small Poisson ratio for biaxial stress in the (111) plane

1989-01-16

359

Collective bands in [sup 106]Ag and [sup 107]Ag  

Energy Technology Data Exchange (ETDEWEB)

The nuclei [sup 106]Ag and [sup 107]Ag have been studied using 80 MeV [sup 17]O ions impinging on [sup 94]Zr. The [gamma]-rays were detected with the NORDBALL array and light charged particles with a charged-particle detector system. Rotational bands have been established using [gamma]-ray yields, [gamma][gamma] coincidences and angular correlation information. Calculations of spin diabatic surfaces have been done and are used for assigning quasiparticle configurations to the bands. Deformation effects are observed in almost all bands. ((orig.))

Jerrestam, Dan (Department of Neutron Research, Uppsala University, Studsvik, S-611 82 Nykoeping (Sweden)); Klamra, W. (Manne Siegbahn Institute of Physics, Frescativ. 24, S-10405 Stockholm (Sweden)); Gizon, J. (Institut des Sciences Nucleaires, IN2P3-CNRS/Universite Joseph Fourier, 53 avenue des Martyrs, F-38026 Grenoble cedex (France)); Liden, F. (Manne Siegbahn Institute of Physics, Frescativ. 24, S-10405 Stockholm (Sweden)); Hildingsson, L. (Manne Siegbahn Institute of Physics, Frescativ. 24, S-10405 Stockholm (Sweden)); Kownacki, J. (Institute of Experimental Physics, University of Warsaw, Warsaw (Poland)); Lindblad, T. (Manne Siegbahn Institute of Physics, Frescativ. 24, S-10405 Stockholm (Sweden)); Nyberg, J. (The Niels Bohr Institute, Risoe, DK-4000 Roskilde (Denmark))

1994-09-26

360

Band-gap narrowing in ordered and disordered semiconductor alloys  

International Nuclear Information System (INIS)

Either spontaneous or artificial ordering of semiconductor alloys into CuAu-like, chalcopyrite, or CuPt-like structures is predicted to be accompanied by a reduction in the direct band gaps relative to the average over the binaries. In this letter calculated results are presented for seven III-V and II-VI alloys. We identify the mechanism for this band-gap narrowing as band folding followed by repulsion between the folded states. The latter is coupled by the non-zinc-blende component of the superlattice potential. The same physical mechanism (but to a different extent) is responsible for gap bowing in disordered alloys

1990-02-12

 
 
 
 
361

Progress on energy band structure studies of wide-band-gap semiconductors in NSRL  

International Nuclear Information System (INIS)

In this paper, authors report the progress on energy band structure studies of wide-band-gap semiconductors in NSRL. The energy band structure of ZnO and its native point defects have been calculated by using FP-LMTO method for the first time. Authors confirmed theoretically that Zn is the main factor to induce the native n-type conductivity in ZnO, which effects on the spectral properties of ZnO are also discussed. The energy band dispersion of both bulk and surface states on wurtzite (GaN(0001) has been studied by using synchrotron radiation angle resolved photo-electron spectroscopy (SRARPES). A theoretical calculation of the atomic and electronic structure of ?-SiC(110) surface is also presented by using FPLAPW method for the first time. The results show that the surface is characterized by a top-layer bond-length-contracting rotation relaxation and the surface relaxation induces the change from metallic to semiconducting characterization

2003-06-01

362

Band structure and hole scattering in p-PbTe  

International Nuclear Information System (INIS)

Mobility (u), thermoemf (?), and temperature dependences of the Hall constant (R) in p-PbTe were calculated. While calculating considered has been the effect of the free electron mass contribution to the density mass of states at the band bottom and to the effective width of the forbidden band in the framework of the Cane type model, which leads to the absence of a ''mirror property'' of conductivity and valency bands. It is shown that, while taking into account the temperature dependence of the Hall factor, the appearance of maximum on R(T) curves may be explained only with due account of the contribution from interband scattering. Taking account of acoustic and optical mechanisms of scattering, it becomes possible to explain satisfactorily the temperature and concentration dependences of u, the temperature dependences of R and concentration dependences of ? up to concentrations of about 1020 cm-3 at heavy band parameters of msub(h)=1msub(e), ?0.18 eV. Qualitative considerations of the shape of isoenergetic surfaces of a heavy band were undertaken to explain the concentration dependences of b=usub(h)/usub(l) and causes of deviation of experimental and calculated values of ?. It is shown that the above surfaces have a complicated structure, and the heavy band may be substantially nonparabolic

1979-03-01

363

Band alignment of SnS/Zn(O,S) heterojunctions in SnS thin film solar cells  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Band alignment is critical to the performance of heterojunction thin film solar cells. In this letter, we report band alignment studies of SnS/Zn(O,S) heterojunctions with various compositions of Zn(O,S). Valence band offsets (VBOs) are measured by femtosecond laser pump/probe ultraviolet photoelectron spectroscopy (fs-UPS) from which conduction band offsets (CBOs) are calculated by combining with band gaps obtained by optical transmission/reflection measurements. The SnS/Zn(O,S) heterojuncti...

Sun, Leizhi; Haight, Richard; Sinsermsuksakul, Prasert; Bok Kim, Sang; Park, Helen Hejin; Gordon, Roy Gerald

2013-01-01

364

Band structures of ZnTe:O alloys with isolated oxygen and with clustered oxygen impurities  

Energy Technology Data Exchange (ETDEWEB)

Highlights: • Band structures of ZnTe:O alloy highly depends on the status of oxygen. • Clustered oxygen lowers the bandgap while isolated oxygen increases the bandgap. • The solar adsorption efficiency of ZnTe:O can be improved by oxygen clustering. -- Abstract: First-principles calculations reveal that band structures of ZnTe:O alloys highly depend on the configuration of oxygen in the alloy. For alloys with isolated oxygen, the calculated band structure shows the formation of intermediate states between valence and conduction band and the shift of conduction band to higher energy level. It expands the gap between valence and conduction band. For alloys with clustered oxygen, the formation of intermediate band is still observed, while the gap between valence and conduction band is decreased. For alloys with oxygen impurities adjacent to Zn vacancy, the band structure only shows the decrease of the gap between valence and conduction band without the formation of any intermediate band. These results suggest the critical role of Zn–O bonding in determining the energy level of the impurity states. On the basis of our results, a possible band engineering approach is suggested in order to improve the performance of ZnTe:O alloy as intermediate band solar adsorbent.

Ling, Chen, E-mail: chen.ling@tema.toyota.com; Zhou, Li Qin; Banerjee, Debasish; Jia, Hongfei

2014-01-25

365

Band structures of ZnTe:O alloys with isolated oxygen and with clustered oxygen impurities  

International Nuclear Information System (INIS)

Highlights: • Band structures of ZnTe:O alloy highly depends on the status of oxygen. • Clustered oxygen lowers the bandgap while isolated oxygen increases the bandgap. • The solar adsorption efficiency of ZnTe:O can be improved by oxygen clustering. -- Abstract: First-principles calculations reveal that band structures of ZnTe:O alloys highly depend on the configuration of oxygen in the alloy. For alloys with isolated oxygen, the calculated band structure shows the formation of intermediate states between valence and conduction band and the shift of conduction band to higher energy level. It expands the gap between valence and conduction band. For alloys with clustered oxygen, the formation of intermediate band is still observed, while the gap between valence and conduction band is decreased. For alloys with oxygen impurities adjacent to Zn vacancy, the band structure only shows the decrease of the gap between valence and conduction band without the formation of any intermediate band. These results suggest the critical role of Zn–O bonding in determining the energy level of the impurity states. On the basis of our results, a possible band engineering approach is suggested in order to improve the performance of ZnTe:O alloy as intermediate band solar adsorbent

2014-01-25

366

Estimating Band-to-Band Misregistrations in Multivariate Imagery.  

Science.gov (United States)

In this paper, we use simulations and some theory to show that many of the standard techniques used to estimate band-to-band misregistrations in multivariate imagery are biased. These biases, although typically small, become important because they are muc...

M. Berman A. A. Green L. Bischof S. J. Davies M. D. Craig

1992-01-01

367

Garage Band or GarageBand[R]? Remixing Musical Futures  

Science.gov (United States)

In this paper, I suggest that it is perhaps time to consider the pedagogy of popular music in more extensive terms than conventional rock band practices have to offer. One direction in which this might lead is the expansion of the informal pedagogy based on a "garage band" model to encompass various modes of digital artistry wherever this artistry…

Vakeva, Lauri

2010-01-01

368

Photonic band structure  

International Nuclear Information System (INIS)

We learned how to create 3-dimensionally periodic dielectric structures which are to photon waves, as semiconductor crystals are to electron waves. That is, these photonic crystals have a photonic bandgap, a band of frequencies in which electromagnetic waves are forbidden, irrespective of propagation direction in space. Photonic bandgaps provide for spontaneous emission inhibition and allow for a new class of electromagnetic micro-cavities. If the perfect 3-dimensional periodicity is broken by a local defect, then local electromagnetic modes can occur within the forbidden bandgap. The addition of extra dielectric material locally, inside the photonic crystal, produces open-quotes donorclose quotes modes. Conversely, the local removal of dielectric material from the photonic crystal produces open-quotes acceptorclose quotes modes. Therefore, it will now be possible to make high-Q electromagnetic cavities of volume approx-lt 1 cubic wavelength, for short wavelengths at which metallic cavities are useless. These new dielectric micro-resonators can cover the range all the way from millimeter waves, down to ultraviolet wavelengths

1993-05-01

369

Spectra of {gamma} rays feeding superdeformed bands  

Energy Technology Data Exchange (ETDEWEB)

The spectrum of {gamma}rays coincident with SD transitions contains the transitions which populate the SD band. This spectrum can provide information on the feeding mechanism and on the properties (moment of inertia, collectivity) of excited SD states. We used a model we developed to explain the feeding of SD bands, to calculate the spectrum of feeding {gamma}rays. The Monte Carlo simulations take into account the trigger conditions present in our Eurogam experiment. Both experimental and theoretical spectra contain a statistical component and a broad E2 peak (from transitions occurring between excited states in the SD well). There is good resemblance between the measured and calculated spectra although the calculated multiplicity of an E2 bump is low by {approximately}30%. Work is continuing to improve the quality of the fits, which will result in a better understanding of excited SD states. In addition, a model for the last steps, which cool the {gamma} cascade into the SD yrast line, needs to be developed. A strong M1/E2 low-energy component, which we believe is responsible for this cooling, was observed.

Lauritsen, T.; Khoo, T.L.; Henry, R.G. [and others

1995-08-01

370

Diffusion Quantum Monte Carlo Calculations of Excited States of Silicon  

CERN Multimedia

The band structure of silicon is calculated at the Gamma, X, and L wave vectors using diffusion quantum Monte Carlo methods. Excited states are formed by promoting an electron from the valence band into the conduction band. We obtain good agreement with experiment for states around the gap region and demonstrate that the method works equally well for direct and indirect excitations, and that one can calculate many excited states at each wave vector. This work establishes the fixed-node DMC approach as an accurate method for calculating the energies of low lying excitations in solids.

Williamson, A J; Needs, R J; Rajagopal, G; Hood, Randolph Q.

1998-01-01

371

Improving hyperspectral band selection by constructing an estimated reference map  

Science.gov (United States)

We investigate band selection for hyperspectral image classification. Mutual information (MI) measures the statistical dependence between two random variables. By modeling the reference map as one of the two random variables, MI can, therefore, be used to select the bands that are more useful for image classification. A new method is proposed to estimate the MI using an optimally constructed reference map, reducing reliance on ground-truth information. To reduce the interferences from noise and clutters, the reference map is constructed by averaging a subset of spectral bands that are chosen with the best capability to approximate the ground truth. To automatically find these bands, we develop a searching strategy consisting of differentiable MI, gradient ascending algorithm, and random-start optimization. Experiments on AVIRIS 92AV3C dataset and Pavia University scene dataset show that the proposed method outperformed the benchmark methods. In AVIRIS 92AV3C dataset, up to 55% of bands can be removed without significant loss of classification accuracy, compared to the 40% from that using the reference map accompanied with the dataset. Meanwhile, its performance is much more robust to accuracy degradation when bands are cut off beyond 60%, revealing a better agreement in the MI calculation. In Pavia University scene dataset, using 45 bands achieved 86.18% classification accuracy, which is only 1.5% lower than that using all the 103 bands.

Guo, Baofeng; Damper, Robert I.; Gunn, Steve R.; Nelson, James D. B.

2014-01-01

372

Comparison of RESRAD with hand calculations  

International Nuclear Information System (INIS)

This report is a continuation of an earlier comparison done with two other computer programs, GENII and PATHRAE. The dose calculations by the two programs were compared with each other and with hand calculations. These band calculations have now been compared with RESRAD Version 5.41 to examine the use of standard models and parameters in this computer program. The hand calculations disclosed a significant computational error in RESRAD. The Pu-241 ingestion doses are five orders of magnitude too small. In addition, the external doses from some nuclides differ greatly from expected values. Both of these deficiencies have been corrected in later versions of RESRAD

1995-12-12

373

Calculated threshold current of GaAs quantum well lasers  

Energy Technology Data Exchange (ETDEWEB)

A model calculation of the threshold current of a laser in a quantum well structure is presented. The band-to-band radiative recombination rate is calculated using a constant density of states and the k-selection rule. This calculation shows that the threshold current of a GaAs single quantum well laser has low-temperature sensitivity (T/sub 0/approx.330 K for T>300 K). The calculated threshold current of a 200-A-wide GaAs single quantum well laser is approx.550 A/cm/sup 2/. The results of the calculation are compared with experimental results.

Dutta, N.K.

1982-11-01

374

Single Band Helical Antenna in Axial Mode  

Directory of Open Access Journals (Sweden)

Full Text Available Helical antennas have been widely used in a various useful applications, due to their low weight and low profile conformability, easy and cheap realization.Radiation properties of this antenna are examined both theoretically and experimentally. In this paper, an attempt has been made to investigate new helical antenna structure for Applications. CST MWS Software is used for the simulation and design calculations of the helical antennas. The axial ratio, return loss, VSWR, Directivity, gain, radiation pattern is evaluated. Using CST MWS simulation software proposed antenna is designed/simulated and optimized. The antenna exhibits a single band from 0 GHz to 3 GHz for GPS and several satellite applications

Parminder Singh

2012-11-01

375

Rotational and vibrational bands in 108Pd  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english The 108Pd nucleus has been studied with the 100Mo(11B, p2ngamma) reaction at 43 MeV incident energy. gamma -gamma - t, gamma -gamma - charged particle coincidences and directional correlation ratios were measured using the gamma spectrometer formed by four Compton suppressed HPGe detectors and a 4pi [...] charged-particle ancillary detector system. The struture of the bands was interpreted within the framework of the cranked shell model and total Routhian calculations.

J.A., Alcántara-Núñez; J.R.B., Oliveira; E.W., Cybulska; N.H., Medina; M.N., Rao; R.V., Ribas; M.A., Rizzutto; W.A., Seale; F., Falla-Sotelo.

376

Magnetic and Cohesive Properties from Cononical Bands  

DEFF Research Database (Denmark)

The atomic volumes, the bulk moduli, the magnetizations, the gain susceptibilities and the derivatives of these quantities with respect to pressure have been obtained from first principles for Fe, Ni, Rh, Pd, Ir and Pt at 0K using canonical band theory and the local spin-density approximation for exchange and correlation. The agreement with experiment is surprisingly good. For Fe the calculated ferromagnetic contribution to the pressure is nearly large enough to account for the relative softness and large volume in the BCC phase and it creates an instability in the FCC phase.

Poulsen, U. K.

1976-01-01

377

A theoretical approach to the design of reduced band gap noncorrosive electrodes for photoelectrochemical solar cells  

International Nuclear Information System (INIS)

Preliminary results from our charge self-consistent LCAO band structure (CSCBS) calculations with Bloch sums as the basis reveal that a noncorrosive reduced band gap electrode for photoelectrochemical solar cells may be produced from a (1:1) mixture of ?-PbO2 and TiO2 (both rutile). The band gaps for the constituents (?-PbO2 and TiO2) and the 1:1 mixture are calculated and a detailed characterization of the valence and the conduction bands is undertaken to offer a possible mechanism for the reduction of the band gap of the mixture. The band gap for the perovskite PbTiO3 is also calculated to offer a guideline for selecting from the competing pathways to the fabrication of noncorrosive photoelectrochemical electrodes

1990-03-17

378

Pressure induced band gap opening of AlH{sub 3}  

Energy Technology Data Exchange (ETDEWEB)

Pressure-induced band gap opening (PIBGO) of AlH{sub 3} with a Pm3{sup ¯}n structure is verified by using first-principles calculations. With increasing pressure, the semimetallic band structures change to the indirect band gap semiconducting band structure at about 300 GPa. The key points of this phenomenon are (1) the moderately large difference of electronegativity between aluminium and hydrogen and (2) the orthogonality between the 3s states and 2s states of Al. We have been confirmed that the structure is stable up to and including 500 GPa resulting from the structural relaxation and phonon calculations. The band gap is more accurately confirmed by GW calculations than done by DFT-GGA ones. The band gap may open at about 200 GPa. This phenomenon may be verified by means of a leading-edge experimental technique.

Geshi, Masaaki, E-mail: geshi@insd.osaka-u.ac.jp [Institute for NanoScience Design (INSD), Osaka University 1-3 Machikaneyama, Toyonaka, Osaka 560-8531 (Japan); Fukazawa, Taro [Graduate School of Engineering Science, Osaka University 1-3 Machikaneyama, Toyonaka, Osaka 560-8531 (Japan)

2013-02-15

379

Paleomagnetic dating of liesegang bands  

Energy Technology Data Exchange (ETDEWEB)

Paleomagnetic analysis, in conjunction with petrographic studies, was used to date the formation of hematite liesegang bands in the Ordovician Upper Arbuckle Group in southern Oklahoma. The hematite bands form symmetrical patterns on both sides of calcite-filled fractures in dolomite beds. The bands decrease in abundance and become more diffuse away from the fractures. Dedolomite is common near the fractures. Samples from distinctly banded dolomite near the fractures contain a relatively strong chemical remanent magnetization (CRM) with a southeasterly declination and shallow inclination. Samples farther from the fractures that are less distinctly banded or have no bands contain a weaker and less table CRM. Petrographic evidence and stable demagnetization to 600/sup 0/C indicate that the CRM resides in hematite. Samples were collected from both flanks of the Arbuckle Anticline (late Pennsylvanian folding), and a fold test demonstrates that the CRM is post-folding. The pole position for the CRM corresponds to the Early Permian (approx. 280 Ma) part of the Apparent Polar Wander Path for stable North America. These results suggest that the liesegang bands formed in the Early Permian, probably by rhythmic precipitation of hematite from fluids that moved out from the fractures. The fluids also apparently caused dedolomitization and precipitation of calcite in intercrystalline pore spaces. These fluids were probably the source of iron for the bands, although iron released from dedolimitization of ferroan dolomite may have been a local source.

Cochran, K.A.; Elmore, R.

1985-01-01

380

The Moral Ends of Band  

Science.gov (United States)

This article provides a theoretical framework through which to reimagine and revitalize contemporary music education practices, using the large ensemble paradigm called "band" as the primary unit of analysis. Literature suggests that band places too much emphasis on teacher control and external measures of validation. Critics propose replacing…

Allsup, Randall Everett

2012-01-01

 
 
 
 
381

Level density calculation for deformed nuclei. [Modified Ericson formalism  

Energy Technology Data Exchange (ETDEWEB)

Level densities for the rare earth and actinide nuclei have been calculated using a modified version of the Ericson formalism. The assumption was made, that K (the projection of J on the symmetry axis of the nucleus) is a good quantum number in the compound nucleus. Individual level densities for the different (K,J) values of the compound nucleus formed by low energy neutron interactions were calculated. The results show good agreement with the interpretation of recent results obtained on U-235 in this laboratory. Using the above calculations it is also possible to infer from the measured level densities the locations of the band heads of different K bands in the compound nucleus. The results also indicate that the K bands responsible for the level densities exclude the ground state rotational band. Levels built on the higher lying ..beta.. and ..gamma.. vibrational bands and their composites are sufficient in number to explain the observed level densities. 4 tables. (auth)

Felvinci, J.P.; Cacuci, D.; Melkonian, E.

1975-10-01

382

Superdeformed band in 130Ce  

International Nuclear Information System (INIS)

An open-quotes identicalclose quotes superdeformed (SD) band has been discovered in the nucleus 130Ce. This band has transition energies which are identical to the half-way points between the energies in the yrast SD band of 131Ce to a mean degeneracy of 0.4%. The discovery of this band completes the chain of SD Ce isotopes from 129Ce to 133Ce. However, at 0.5% of the reaction channel, it is populated with an intensity which is an order of magnitude smaller than neighboring SD bands. The valence neutron configuration is assigned as ?61 with a hole in either the [523]7/2- or [411]1/2+ Nilsson orbitals. copyright 1996 The American Physical Society

1997-01-01

383

Dual-band infrared camera  

Science.gov (United States)

Every year, numerous accidents happen on European roads due to bad visibility (fog, night, heavy rain). Similarly, the dramatic aviation accidents of year 2001 in Milan and Zurich have reminded us that aviation safety is equally affected by reduced visibility. A dual-band thermal imager was developed in order to raise human situation awareness under conditions of reduced visibility especially in the automotive and aeronautical context but also for all transportation or surveillance tasks. The chosen wavelength bands are the Short Wave Infrared SWIR and the Long Wave Infrared LWIR band which are less obscured by reduced visibility conditions than the visible band. Furthermore, our field tests clearly show that the two different spectral bands very often contain complementary information. Pyramidal fusion is used to integrate complementary and redundant features of the multi-spectral images into a fused image which can be displayed on a monitor to provide more and better information for the driver or pilot.

Vogel, H.; Schlemmer, H.

2005-10-01

384

Electronic transport and magnetic properties of a new nickel antimonide telluride, Ni2SbTe2  

International Nuclear Information System (INIS)

The mixed anion compound, Ni2SbTe2, has been prepared from the elements in a potassium iodide flux. The crystal structure is solved in the hexagonal space group P63/mmc (no. 194) with lattice parameters a=b=3.9030(9) A and c=15.634(3) A. Sb and Te occupy crystallographically distinct anion sites within the crystal structure. The Seebeck coefficient, electrical resistivity, and magnetic susceptibility have been measured for the title compound, and shows typical metallic behavior. Extended Hueckel band structure calculations also predict metallic behavior in bands dominated by Ni and Te orbital contributions

2004-03-10

385

The Band-Gap and TRUE Band-Gap in Nominally Metallic Carbon Nanotubes: the Tight-Binding Study on Corrugation Effect  

Science.gov (United States)

In this paper, the band-gap and true band-gap are analyzed for the corrugated structures of various types of single wall carbon nanotubes (SWCNTs) within the tight binding approximation. We show that corrugation, combined with curvature effect, yields naturally the true small band-gap in all SWCNTs with small radius. The more stable corrugated structures of SWCNTs are backed by the abinitio total energy calculations for nominally metallic armchair SWCNTs.

Lu, Hongxia; Wu, Jianbao; Wang, Jizhen; Shi, Shaocong; Zhang, Weiyi

2014-03-01

386

Compact Dual Band Microstrip Antenna for Ku-Band Application  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A new design of dual band compact microstrip antenna is proposed for Ku-band applications. Dual band is achieved using three pairs of thin slits from the sides of a rectangular patch and feeding with a microstrip feedline. The antenna has a compact structure and the total size is 9.50 by 10 by 0.254 mm. The result shows that the return loss of -23.83 dB is achieved at the first resonant frequency of 12.54 GHz and -14.04 dB is obtained at the second resonant frequency of 14.15 GHz. The antenna...

Islam, M. T.; Misran, N.; Mobashsher, A. T.

2010-01-01

387

Theoretical studies on band structure and optical properties of 3C-SiC by FPLAPW  

International Nuclear Information System (INIS)

The band structure and optical properties of 3C-SiC are studied by using a full potential linearized augmented plane waves (FPLAPW) method. The imaginary and real parts of the dielectric function have been obtained from the band structure calculation. The critical point structure of the dielectric function is analyzed to identify the optical transition. The refractive index, extinction coefficient and reflectivity have been calculated from obtained dielectric function. The calculated results are in agreement with the experiments

2005-06-01

388

Franck–Condon factors and observed band strength distribution in the vibrational structure of the Ag2 D-X band system  

Directory of Open Access Journals (Sweden)

Full Text Available TPotential curves for the X1Sg+ and D1Su+ states of three diatomic silver isotopomers, 107Ag2, 107Ag109Ag and 109Ag2, were determined from the best available molecular constants by the Rydberg–Klein–Rees method. From these potentials, Franck–Condon factors and band-origin wavenumbers were computed, and the reliability of the obtained values was verified by comparison with the observed band strength distribution and the measured band origin po¬sitions in a previously recorded D-X spectrum. The ratios of the Franck–Con¬don factors to those of corresponding isotopic bands were found to be very close to unity, revealing only a very small isotopic effect on the Franck–Condon factors of Ag2 D-X bands. The isotopic shifts of the calculated band origins agree well with previously measured displacements of band heads.

ANKICA ANTI?-JOVANOVI?

2010-05-01

389

The Importance of Static Correlation in the Band Structure of High Temperature Superconductors  

CERN Document Server

Recently we presented a new band structure for La(2-x)Sr(x)CuO(4) and other high temperature superconductors in which a second narrow band was seen to cross the primary band at the Fermi level. The existence of this second Fermi level band is in complete disagreement with the commonly accepted LDA band structure. Yet it provided a crucial piece of physics which led to an explanation for superconductivity and other unusual phenomena in these materials. In this work we present details as to the nature of the failure of conventional methods in deriving the band structure of the cuprates. In particular, we use a number of chemical analogues to describe the problem of static correlation in the band structure calculations and show how this can be corrected with the predictable outcome of a Fermi level band crossing.

Perry, J K

1999-01-01

390

The study of energy bands in neutron-deficient 123,125Ce nuclei  

Science.gov (United States)

Theoretical investigation of energy bands of 123,125Ce is performed by applying the projected shell model approach. The present calculation is viewed to reproduce the known experimental data of these nuclei, qualitatively. Not only this, the configurations of diverse bands are also obtained by an analysis of the band diagrams. The low-lying states of the bands are seen to arise from one quasiparticle configuration whereas the high-spin states arise from multi-quasiparticle configurations. The signature partner band of negative parity band is predicted in 123Ce. The ground state bands and relative energies of some bands with respect to them are predicted in 123,125Ce that can be helpful for future experiments.

Kumar, Rawan; Devi, Rani; Khosa, S. K.

2013-06-01

391

Modeling charged defects inside density functional theory band gaps  

Science.gov (United States)

Density functional theory (DFT) has emerged as an important tool to probe microscopic behavior in materials. The fundamental band gap defines the energy scale for charge transition energy levels of point defects in ionic and covalent materials. The eigenvalue gap between occupied and unoccupied states in conventional DFT, the Kohn–Sham gap, is often half or less of the experimental band gap, seemingly precluding quantitative studies of charged defects. Applying explicit and rigorous control of charge boundary conditions in supercells, we find that calculations of defect energy levels derived from total energy differences give accurate predictions of charge transition energy levels in Si and GaAs, unhampered by a band gap problem. The GaAs system provides a good theoretical laboratory for investigating band gap effects in defect level calculations: depending on the functional and pseudopotential, the Kohn–Sham gap can be as large as 1.1 eV or as small as 0.1 eV. We find that the effective defect band gap, the computed range in defect levels, is mostly insensitive to the Kohn–Sham gap, demonstrating it is often possible to use conventional DFT for quantitative studies of defect chemistry governing interesting materials behavior in semiconductors and oxides despite a band gap problem.

Schultz, Peter A.; Edwards, Arthur H.

2014-05-01

392

Population of rotational bands in superheavy nuclei  

Directory of Open Access Journals (Sweden)

Full Text Available Using the statistical approach, we study the population of ground-state rotational bands of superheavy nuclei produced in the fusion-evaporation reactions 208Pb(48Ca, 2n254No, 206Pb(48Ca, 2n252No, and 204Hg(48Ca, 2n250Fm. We calculate relative intensities of E2-transitions between the rotational states and entry spin distributions of the residual nuclei, evaporation residue cross sections, and excitation functions for these reactions. Fermi-gas model is used for the calculation of level density, and damping of shell effects both with excitation energy and angular momentum is taking into account. The results are in a good agreement with the experiment data.

Antonenko N.V.

2012-02-01

393

Population of rotational bands in superheavy nuclei  

Science.gov (United States)

Using the statistical approach, we study the population of ground-state rotational bands of superheavy nuclei produced in the fusion-evaporation reactions 208Pb(48Ca, 2n)254No, 206Pb(48Ca, 2n)252No, and 204Hg(48Ca, 2n)250Fm. We calculate relative intensities of E2-transitions between the rotational states and entry spin distributions of the residual nuclei, evaporation residue cross sections, and excitation functions for these reactions. Fermi-gas model is used for the calculation of level density, and damping of shell effects both with excitation energy and angular momentum is taking into account. The results are in a good agreement with the experiment data.

Zubov, A. S.; Sargsyan, V. V.; Adamian, G. G.; Antonenko, N. V.

2012-02-01

394

Pseudopotential band structure of indium nitride  

International Nuclear Information System (INIS)

The band structure, density of states and the imaginary part of the dielectric function have been calculated for indium nitride by a pseudopotential method. Comparison with published reflectance data permits the identification of principal optical transitions at the GAMMA,M,K, and H symmetry points and we have been able to correct previous transition assignments. The calculated long-wavelength refractive index of 2.88 +- 0.5 compares well with experiment. The material has a direct energy gap at the zone center and the spherically symmetric extrema are well described by scalar effective masses of 0.17m0, 0.5m0 (holes), and 0.12m0 (electrons)

1986-01-15

395

Band crossings at very high spins  

International Nuclear Information System (INIS)

A formalism to calculate very high spin states is described in which it is possible not only to calculate yrast energies, but also excited bands. Backbends due to configuration changes are clearly apparent and many configurations can be followed outside the region where they are yrast. The present results can be considered in relation to experiment where the relevant data is available mainly in the form of so-called #betta# - #betta# correlation plots. In the case of 166Yb, such comparisons suggest that the stripes at high transition energies in the correlation plots can be understood as backbends caused either by strongly aligned orbitals crossing the Fermi-surface or changes in deformation. (U.K.)

1982-04-08

396

Relativistic and Non-Relativistic Mean Field Investigation of the Superdeformed Bands in 62Zn  

Science.gov (United States)

Following the first discovery of the superdeformed (SD) band in the A ~ 60 mass region, we calculate several low-lying SD bands in 62Zn using the relativistic mean field and Skyrme-Hartree-Fock models. Both models can reproduce the experimental moment of inertia very well, but we find that the calculated band, which corresponds to the experimentally observed band, does not become the lowest one. This trend is common among all the parameter sets which are widely used in RMF and SHF studies, and it seems to be connected with the fact that the position of the g9/2 level is not reproduced in 56Ni.

Madokoro, H.; Matsuzaki, M.

1999-05-01

397

Information retrieval from wide-band meteorological data - An example  

Science.gov (United States)

The methods proposed by Smith and Adelfang (1981) and Smith et al. (1982) are used to calculate probabilities over rectangles and sectors of the gust magnitude-gust length plane; probabilities over the same regions are also calculated from the observed distributions and a comparison is also presented to demonstrate the accuracy of the statistical model. These and other statistical results are calculated from samples of Jimsphere wind profiles at Cape Canaveral. The results are presented for a variety of wavelength bands, altitudes, and seasons. It is shown that wind perturbations observed in Jimsphere wind profiles in various wavelength bands can be analyzed by using digital filters. The relationship between gust magnitude and gust length is modeled with the bivariate gamma distribution. It is pointed out that application of the model to calculate probabilities over specific areas of the gust magnitude-gust length plane can be useful in aerospace design.

Adelfang, S. I.; Smith, O. E.

1983-01-01

398

Tunable band gap in few-layer graphene by surface adsorption  

Digital Repository Infrastructure Vision for European Research (DRIVER)

There is a tunable band gap in ABC-stacked few-layer graphene (FLG) via applying a vertical electric field, but the operation of FLG-based field effect transistor (FET) requires two gates to create a band gap and tune channel's conductance individually. Using first principle calculations, we propose an alternative scheme to open a band gap in ABC-stacked FLG namely via single-side adsorption. The band gap is generally proportional to the charge transfer density. The capability to open a band ...

Quhe, Ruge; Ma, Jianhua; Zeng, Zesheng; Tang, Kechao; Zheng, Jiaxin; Wang, Yangyang; Ni, Zeyuan; Wang, Lu; Gao, Zhengxiang; Shi, Junjie; Lu, Jing

2013-01-01

399

Band crossing in Shears band of $^{108}$Cd  

CERN Document Server

The level lifetimes have been measured for a Shears band of $^{108}$Cd which exhibits bandcrossing. The observed level energies and B(M1) rates have been successfully described by a semi-classical geometric model based on shear mechanism. In this geometric model, the bandcrossing in Shears band has been described as the reopening of the angle between the blades of a shear.

Roy, Santosh; Pal, S; Chattopadhyay, S; Bhattacharya, S; Goswami, A; Jain, H C; Joshi, P K; Bhowmik, R K; Kumar, R; Muralithar, S; Singh, R P; Madhavan, N; Rao, P V Madhusudhana

2010-01-01

400

A comparative study of semiempirical bond dissociation energy calculations  

Energy Technology Data Exchange (ETDEWEB)

Anderson's modified version of the extended Hueckel molecular orbital method and the MNDO and AM1 methods of Dewar are used to study bond cleavage in molecular fragments of interest in coal liquefaction. Geometric conformations, molecular orbital coefficients for the HOMO's and LUMO's, and bond dissociation energies are computed and compared for the three methods. Qualitative agreement with experiment for bond cleavage is observed for the three methods for the neutral molecule. However the ASED-MO method appears to best describe the bond cleavage in the presence of an electron-accepting catalyst.

Ades, H.F.; Companion, A.L.; Subbaswamy, K.R. (Univ. of Kentucky, Lexington (United States))

1991-08-22

 
 
 
 
401

Multiple triaxial bands and abnormal signature inversion in As3374  

Science.gov (United States)

Excited states of the odd–odd nucleus 74As have been investigated via heavy ion fusion evaporation reaction Zn70(Li7,3n)As74 at beam energy of 30 MeV. The properties of the positive- and the negative- parity bands can be interpreted in terms of the Cranked Nilsson–Strutinsky (CNS) model calculations which show that the observed bands are built on the triaxial deformed shape. The inversion of the favored and unfavored signature branches observed in the positive-parity bands presents at high spins rather than normal signature inversion occurs at low spins. This phenomenon may be explained as the origin of unpaired band crossing in a highly rotating triaxial nucleus.

Hu, Shi-Peng; Ma, Hai-Liang; Cao, Xue-Peng; Wu, Xiao-Guang; Zhang, Huan-Qiao; Hua, Hui; Sun, Jun-Jie; Sun, Hui-Bin; He, Chuang-Ye; Zheng, Yun; Li, Guang-Sheng; Li, Cong-Bo; Yao, Shun-He; Yu, Bei-Bei; Wang, Jin-Long; Li, Hong-We; Wu, Yi-Heng; Liu, Jia-Jian; Luo, Peng-Wei; Xu, Chuan; Cheng, Yi-Yuan

2014-05-01

402

Shape coexistence and band crossings in 174Pt  

International Nuclear Information System (INIS)

High-spin states in 174Pt were populated via the 92Mo(84Sr,2p) and 92Mo(84Sr,2p2n) reactions. The ground-state band has been extended from I=14 to 24 (tentatively 26) and a new side band is observed up to a spin of 21 (tentatively 23). A low-frequency crossing is observed in the latter band at a rotational frequency that is similar to that seen in the ground-state band. The first and second i13/2 neutron alignments are also observed in 174Pt. Surprisingly, these crossings occur at approximately the same frequency. Total Routhian surface and cranked shell model calculations are used in an attempt to understand this behavior

2004-07-01

403

Electronic structure of periodic curved surfaces -- topological band structure  

CERN Document Server

Electronic band structure for electrons bound on periodic minimal surfaces is differential-geometrically formulated and numerically calculated. We focus on minimal surfaces because they are not only mathematically elegant (with the surface characterized completely in terms of "navels") but represent the topology of real systems such as zeolites and negative-curvature fullerene. The band structure turns out to be primarily determined by the topology of the surface, i.e., how the wavefunction interferes on a multiply-connected surface, so that the bands are little affected by the way in which we confine the electrons on the surface (thin-slab limit or zero thickness from the outset). Another curiosity is that different minimal surfaces connected by the Bonnet transformation (such as Schwarz's P- and D-surfaces) possess one-to-one correspondence in their band energies at Brillouin zone boundaries.

Aoki, H; Takeda, D; Morise, H

2001-01-01

404

Formal Verification of Air Traffic Conflict Prevention Bands Algorithms  

Science.gov (United States)

In air traffic management, a pairwise conflict is a predicted loss of separation between two aircraft, referred to as the ownship and the intruder. A conflict prevention bands system computes ranges of maneuvers for the ownship that characterize regions in the airspace that are either conflict-free or 'don't go' zones that the ownship has to avoid. Conflict prevention bands are surprisingly difficult to define and analyze. Errors in the calculation of prevention bands may result in incorrect separation assurance information being displayed to pilots or air traffic controllers. This paper presents provably correct 3-dimensional prevention bands algorithms for ranges of track angle; ground speed, and vertical speed maneuvers. The algorithms have been mechanically verified in the Prototype Verification System (PVS). The verification presented in this paper extends in a non-trivial way that of previously published 2-dimensional algorithms.

Narkawicz, Anthony J.; Munoz, Cesar A.; Dowek, Gilles

2010-01-01

405

Infrared radiation parameterizations for the minor CO2 bands and for several CFC bands in the window region  

Science.gov (United States)

Fast and accurate parameterizations have been developed for the transmission functions of the CO2 9.4- and 10.4-micron bands, as well as the CFC-11, CFC-12, and CFC-22 bands located in the 8-12-micron region. The parameterizations are based on line-by-line calculations of transmission functions for the CO2 bands and on high spectral resolution laboratory measurements of the absorption coefficients for the CFC bands. Also developed are the parameterizations for the H2O transmission functions for the corresponding spectral bands. Compared to the high-resolution calculations, fluxes at the tropopause computed with the parameterizations are accurate to within 10 percent when overlapping of gas absorptions within a band is taken into account. For individual gas absorption, the accuracy is of order 0-2 percent. The climatic effects of these trace gases have been studied using a zonally averaged multilayer energy balance model, which includes seasonal cycles and a simplified deep ocean. With the trace gas abundances taken to follow the Intergovernmental Panel on Climate Change Low Emissions 'B' scenario, the transient response of the surface temperature is simulated for the period 1900-2060.

Kratz, David P.; Chou, Ming-Dah; Yan, Michael M.-H.

1993-01-01

406

Flexural wave propagation in beams with periodically attached vibration absorbers: Band-gap behavior and band formation mechanisms  

Science.gov (United States)

This paper is concerned with flexural wave propagation and vibration transmission in beams with periodically attached vibration absorbers. Such periodic systems feature unique wave filtering characteristics that can find applications in the control of wave propagation in flexural beam structures. The study is performed by using an exact analytical approach based on a combination of the spectral element method and periodic structure theory. Both infinite and finite periodic structures are considered. An explicit expression is provided for the calculation of propagation constants and thus the complex band structures, and it is further developed to examine the effects of various system parameters on the band-gap behavior, including the position, width and wave attenuation performance of all the band gaps. The band formation mechanisms of such periodic systems are explained via both derivations and physical models, yielding explicit equations to enable the prediction of all the band edge frequencies in an exact manner without the need to calculate propagation constants. Based on these equations, explicit formulas are further derived to determine the conditions for the transition and near-coupling between local resonance and Bragg scattering, each being a unique band-gap opening mechanism.

Xiao, Yong; Wen, Jihong; Yu, Dianlong; Wen, Xisen

2013-02-01

407

Performance Analysis of IIR Digital Band Stop Filter  

Directory of Open Access Journals (Sweden)

Full Text Available IIR Band-stop filter is recursive in nature i.e. the present output sample depends on the past input sample, past output samples and the present input samples. If the past and present inputs and output are varied the resulting present output will be changed. The Band-stop filter rejects one band of frequency and allows all other frequency band to pass. In this paper, the performance analysis of Band-stop filter is done using the Modified Analog-to-Digital Mapping technique and simulated in Matlab7. The response of the filter can be modified by changing the value of the components. The coefficients that are essentially required to design a IIR Digital Band-stop filter, are also calculated using the above mentioned algorithm and finally the magnitude response and the stability of the filter are determined using Matlab7 with satisfying results. The pole-zero plot of a system, filter in this case, determines the stability of the predesigned IIR Band-stop filter.

Subhadeep Chakraborty, Abhirup Patra

2013-05-01

408

Surface electron band structure and VLEED reflectivity for Al(111)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The 2D layer Green function scattering method is used to calculate the energy of surface states and resonances at Gamma-bar for Al(111) for both below and above the vacuum level. The surface barrier potential is represented by an empirical form. The above vacuum level surface electron band structure for this surface has not been calculated before and it is important in understanding many surface phenomena. The geometric structure of the Al(111) surface is known from intensit...

Read, M. N.

2008-01-01

409

The transverse wakefield calculated by double circuit model  

CERN Document Server

X-band accelerator for multi-bunches has been a new way to produce high luminosity and energy efficiency bunches. As the smaller size and multi-bunches, the wakefield is more severe in X-band accelerator, unless some means of strongly suppressing of the transverse wakefield is adopted in the design of the accelerating structure. To calculate the transverse wakefield of the structure, wakefield calculated through the double circuit model has been demonstrated and its application in the structure designed.

Bin, Yang Xiong

2014-01-01

410

Electronic structure calculations on nitride semiconductors and their alloys  

International Nuclear Information System (INIS)

Calculations of the electronic properties of AIN, GaN, InN and their alloys are presented. Initial calculations are performed using the first principles pseudopotential method to obtain accurate lattice constants. Further calculations then investigate bonding in the nitrides through population analysis and density of state calculations. The empirical pseudopotential method is also used in this work. Pseudopotentials for each of the nitrides are constructed using a functional form that allows strained material and alloys to be studied. The conventional k.p valence band parameters for both zincblende and wurtzite are obtained from the empirical band structure using two different methods. A Monte-Carlo fitting of the k.p band structure to the pseudopotential data (or an effective mass method for the zincblende structure) is used to produce one set. Another set is obtained directly from the momentum matrix elements and energy eigenvalues at the centre of the Brillouin zone. Both methods of calculating k.p parameters produce band structure in excellent agreement with the original empirical band calculations near the centre of the Brillouin zone. The advantage of the direct method is that it produces consistent sets of parameters, and can be used in studies involving a series of alloy compositions. Further empirical pseudopotential method calculations are then performed for alloys of the nitrides. In particular, the variation of the band gap with alloy composition is investigated, and good agreement with theory and experiment is found. The direct method is used to obtain k.p parameters for the alloys, and is contrasted with the fitting approach. The behaviour of the nitrides under strain is also studied. In particular. valence band offsets for nitride heterojunctions are calculated, and a strong forward- backward asymmetry in the band offset is found, in good agreement with other results in the literature. (author)

2000-01-01

411

Correlated band structure of 3d{sup 2} vanadates  

Energy Technology Data Exchange (ETDEWEB)

We study the correlated band structure and the momentum-resolved spectra for 3d{sup 2} vanadates, like La O{sub 3} and YVO{sub 3}, using a combination of a first-principles technique and dynamical mean-field theory with a Monte Carlo impurity solver. The self-energy for the effective 3d bands is calculated using maximum-entropy spectral analysis of the Monte Carlo results and a self-consistent procedure. We use this self-energy to calculate the full momentum-resolved spectrum and the correlated band structure, which we compare to available spectroscopy experimental results. We also discuss the effects of the lattice distortions and chemistry.

Heilmann, David; Pavarini, Eva [Institut fuer Festkoerperforschung, Forschungszentrum Juelich (Germany)

2008-07-01

412

Band Edge Energies and Band Gaps of Quaternary GaInAsSb Alloys  

Science.gov (United States)

Quaternary alloys without a common atom such as (Ga,In)-(As,Sb) pose a difficult combinatorially design problem in that there are many different atomic configurations even when the system is constrained to be lattice-matched on a substrate. Using an atomistic pseudopotential approach we have calculated the band edge energies of this quaternary random alloys as a function of Ga/In (x) and As/Sb (y) compositions assuming lattice-matching to either GaSb or InAs. The alloy is represented by a large supercell with random atomic occupations and atomic positions relaxed via the atomistic VFF functional. We find upwards bowing for both the conduction and valence band edge energies. On GaSb, the transition from staggered to broken-gap lineup is found to occur at x = 0.81 and y = 0.92, while on InAs it occurs at x = 0.59 and y = 0.62. We show that at the usual growth temperatures this quaternary alloy is not random but tends to exhibit an increased number of Ga-Sb and In-As bonds and a reduced number of In-Sb and Ga-As bonds. This effect brings the calculated band gaps in better agreement with experimental data. T. Magri, A. Zunger, H. Kroemer, JAP 98, 043701 (2005)

Magri, Rita; Zunger, Alex; Kroemer, Herbert

2007-03-01

413

Traditional banding of chromosomes for cytogenetic analysis.  

Science.gov (United States)

Traditional banding of metaphase chromosomes allows identification of individual chromosomes and detection of gross chromosomal anomalies and abnormal chromosome structures. Giemsa (G) banding is the older and more familiar nonfluorescent technique that produces characteristic banding patterns. DAPI , a fluorescent DNA stain, produces banding patterns similar to those of G-banding and is much simpler to perform. PMID:18228454

Bayani, Jane; Squire, Jeremy A

2004-09-01

414

Conductive Bands Diminish Electrostatic Discharges  

Science.gov (United States)

Electrostatic discharges on surfaces covered with electrically insulating paints reduced by connecting edges of painted surfaces to electrical grounds with band of conductive material. Prevents charge build up on paint which eventually arcs to conductive surface, damaging structures and equipment.

Leung, Philip L.; Whittlesey, Albert

1992-01-01

415

Population and properties of superdeformed bands in A ~ 150 region  

Science.gov (United States)

The production of superdeformed nuclei, treated as cluster configurations in the A ~ 150 region is described in the framework of statistical approach and the dinuclear system concept. The competition of particle emission from the dinuclear system and quasifission is taken into account. The calculated nuclear characteristics of the superdeformed band in 152Dy are close to the experimental values.

Zubov, A. S.; Sargsyan, V. V.; Adamian, G. G.; Antonenko, N. V.

2013-04-01

416

Systematic description of superdeformed bands in the Mass-190 region.  

Science.gov (United States)

Superdeformed bands for the mass-190 region are described by the Projected Shell Model. Even-even, odd mass and odd-odd nuclei are equally well described. Good agreement with available data for all isotopes studied is obtained. Our,calculation of electrom...

Y. Sun M. Guidry J. Zhang

1996-01-01

417

Two-band model and MgB$_2$ superconductivity  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A simple two-band model with interband scattering of intraband pairs is applied to MgB$_2$ superconductivity. An adjustable parameters set is chosen. The calculated $T_c$ vs doping, isotope exponent and the heat capacity jump are in qualitative agreement with the observations.

Kristoffel, N.; O?rd, T.

2001-01-01

418

A study of higher-band dipole wakefields in X-band accelerating structures for the G/NLC  

CERN Document Server

The X-band linacs for the GLC/NLC (Global Linear Collider/Next Linear Collider) have evolved from the DDS (Damped Detuned Structure) series [1,2]. The present series of accelerating structures are each 60 cm in length and incorporate both damping and detuning of the dipole modes which comprise the wakefield. In order to adequately damp the wakefield the dipole frequencies of adjacent structures are interleaved. The properties of the first dipole band have been extensively studied. However, limited analysis has been done on the higher order dipole bands. Here, we calculate the contribution of the higher order bands of the interleaved structures to the wakefield using a mode matching computer code [3]. Beam dynamics issues are also studied by tracking the beam through the complete linac using the particle beam tracking code LIAR [4].

Jones, R M

2004-01-01

419

Narrow-Band Microwave Filters  

Directory of Open Access Journals (Sweden)

Full Text Available Original design of the narrow-band compact filters based on the high-quality waveguide-dielectric resonator with anisotropic materials has been presented in this work. Designed filters satisfy the contradictory requirements: they provide the narrow frequency band (0.05 ÷ 0.1 % of the main frequency f0 and the low initial losses ?0 ? 1 dB.

A.V. Strizhachenko

2010-01-01

420

Supermatrix Representations of Semigroup Bands  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Various semigroups of noninvertible supermatrices of the special (antitriangle) shape having nilpotent Berezinian which appear in supersymmetric theories are defined and investigated. A subset of them continuously represents left and right zero semigroups and rectangular bands. The ideal properties of higher order rectangular band analogs and the ``wreath'' version of them are studied in detail. We introduce the ``fine'' equivalence relations leading to ``multidimesional'' e...

Duplij, Steven

1996-01-01

 
 
 
 
421

Quasiparticle band structures and lifetimes in noble metals using Gaussian orbital basis sets  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present the calculations of quasiparticle bandstructures and lifetimes for noble metals Cu and Ag within the GW approximation based on localized Gaussian orbital basis sets. For Cu, both the calculated positions of the d bands and the width of the d bands are within 0.1 eV compared to the experimental results. For Ag, partial core correction should be included in the pseudopotential to get reliable positions of the d bands. The calculated lifetimes agree with the experiment in the energy r...

Silkin, Viatcheslav M.; Chulkov, Eugene V.

2010-01-01

422

Multiple-scattering approach to band theory. II. Fast band theory  

International Nuclear Information System (INIS)

The multiple-scattering equations are used to derive a set of band-theory equations that are called the pivoted-multiple-scattering (PMS) equations. The PMS equations are as legitimate a basis for band-theory calculation as the Korringa-Kohn-Rostoker (KKR) equations that are also derived from the multiple-scattering theory. The primary usefulness of the PMS equations is that an approximate expression can be derived from them that gives all the eigenvalues for one k with a single-matrix diagonalization. This expression has the form of a quadratic eigenvalue equation. The usefulness and accuracy of this quadratic KKR formalism is demonstrated by a number of numerical studies

1982-08-15

423

Very Wide Band Absorption of Sunlight Spectra using Titanium Dioxide Particles with Distributed Band Gap  

Directory of Open Access Journals (Sweden)

Full Text Available In this report we proposed an alternative approach to improve the absorption of solar radiation by titanium dioxide (TiO2 particles. We did not dope pure TiO2 with appropriate elements, but we just searched for low-grade (technical grade TiO2 in the market. We assumed low grade TiO2s are those containing dopant atoms of different concentrations and of different elements. By inspecting the UV-Vis spectra of the samples we finally found TiO2 that absorbs nearly all visible spectra (from less than 200 nm to more than 800 nm. By assuming the powder consisted of distributed band gaps, we proposed a simple method for calculating the band gap distribution. We also used the TiO2 for making a prototype of solar cell and for a photocatalys to decompose organic pollutants in water, both are under sunlight illumination.

Mikrajuddin Abdullah

2010-02-01

424

Dosimetry of narrow band UVB treatments  

International Nuclear Information System (INIS)

Full text: For many years psoriasis has been treated with broad band UVB lamps. These lamps have a bell shaped spectrum which peaks at 305 nm and extends from 280 nm to 350 nm. However research with monochromatic UV radiation has shown that wavelengths between 300 nm and 320 nm are the most efficacious for clearing psoriasis while wavelengths below 305 nm are most effective for producing the undesirable side effect of erythema (sunburn). In response to these findings Philips developed a narrow band UVB tube in which a large fraction of the output was confined to a narrow peak (bandwidth 2.5 nm) situated at 311 nm. Christchurch Hospital replaced broad band UVB with narrow band treatments in August 1995 and as this required UV exposures to be substantially increased new protocols had to be developed. Three aspects needed to be addressed. These were translating the dose from broad band to narrow band for current patients, determining the initial dose for new patients and developing a formula for increasing subsequent exposures to both types of patient. To translate doses the spectral irradiance (?W/cm2/nm) that would fall on the patient was measured in both the old broad band and the new narrow band treatment units and from this UV doses were calculated. All doses were expressed in mJ/cm2 of unweighted UV over the range 250 nm to 400 nm. The erythemal effectiveness of the two units were compared by using the CIE 1987 curve to express doses in terms of the equivalent exposure of monochromatic 297 nm radiation. It was found that an exposure of 3.96 mJ/cm2 from the broad band FS40 tubes and 12.79 mJ/cm2 from the narrow band TL/01 tubes were both equivalent to 1.00 mJ/cm2 of monochromatic 297 nm radiation so when transferring patients all broad band doses needed to be increased by a factor of 3.2. Before transferring any patients this factor was confirmed by conducting two minimal erythema dose (MED) tests on a normal subject, one in each unit. For new patients a narrow band treatment schedule has been developed which is based on the patient' s MED. Before commencing treatments the patient is given an MED test using untanned skin on the inner surface of the forearm. The initial dose is 70% of the MED and each subsequent exposure is increased by a constant increment, namely 21.4% of the initial dose. This progression continues until the dose reaches three times the MED at which time it is held constant. Treatments are given twice per week up to a maximum of 30 treatments or until the psoriasis clears. If mild erythema occurs the next treatment is held at the previous dose while for more severe erythema it is missed entirely. This schedule is similar to the one in use at The Royal Victoria Infirmary, Newcastle upon Tyne, but with two minor exceptions. In Newcastle the increments are larger (on average 45% of the initial dose) but they only occur once a week. The transfer from broad band to narrow band was accomplished successfully without any incidence of erythema. After four months experience the 31 patients who were currently following the MED based protocol were reviewed. The lowest MED measured was 500 mJ/cm2 while the highest (three in number) exceeded 1110 mJ/cm2. Eleven of the patients exhibited erythema at some point in their treatment but it was only necessary to reduce the dose increment in one case. Of the remaining 20 patients, 13 who showed poor clearing of their psoriasis were placed on a dose schedules in which the dose increments were increased by between 20 % to 33%. In view of the fact almost equal numbers of patients received too large or too small a dose the schedule can be considered to be a good compromise

1996-10-21

425

Predictions for Localized Compaction Bands  

Science.gov (United States)

Compaction bands are narrow, planar zones of localized pure compressive deformation (without shear) that form perpendicular to the direction of the maximum compressive stress. They have been observed in porous sandstones in the laboratory under conditions for which uniform (non-localized) compression is also a possible mode of deformation and in the field. Because the porosity and permeability in the bands is less than in the surrounding material, formation of these bands in reservoirs and aquifers can dramatically alter the character of the fluid flow. Olsson (\\textit{JGR}, 1999) has pointed out that conditions for the occurrence of compaction bands can be derived by the same approach used by Rudnicki and Rice (\\textit{J. Mech. Phys. Solids}, 1975) to predict the onset of shear bands: determining the conditions on the constitutive parameters for which localized deformation is an alternative to uniform deformation. This procedure is applied to the predict the onset of compaction bands in the axisymmetric compression test for a transversely isotropic material (with the isotropy axis coinciding with the specimen axis) described by a linear relation between stress-rates and strain-rates. Compaction bands are first predicted to occur when E=-(9/2)r? K, where E is the tangent modulus (slope of stress vs. strain curve), ? is the negative of the ratio of increments of lateral to axial deformation (at constant confining stress), r is the ratio of axial to lateral stress increments causing zero axial deformation and K is a modulus relating increments of lateral stress and strain. In axisymmetric compression experiments, compaction bands are typically observed on relatively flat portions of the stress-strain curve indicating that E? 0. Some experimental evidence suggests that the deformation is nearly uniaxial, ? ? 0 but the non-uniform deformation makes precise measurements difficult. Shear bands (sometimes at low angles to the specimen axis) are frequently observed in conjunction with or in the absence of compaction bands. The predictions of both depend sensitively on the constitutive formulation and, in materials modeled by both a shear yield surface and a ''cap'', on the intersection of the two surfaces.