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Sample records for hueckel band calculations

  1. Thermodynamics of electrolytes. 12. Dielectric properties of water and Debye--Hueckel parameters to 3500C and 1 kbar

    International Nuclear Information System (INIS)

    In preparation for work with aqueous electrolytes at above saturation pressures and at temperatures to 3500C, an equation was developed for the representation of the dielectric constant of water over this range. With this equation and an equation of state for water, the Debye--Hueckel limiting law parameters for osmotic and activity coefficients, enthalpies, heat capacities, volumes, compressibilities, and expansibilities were calculated and are presented. 5 figures, 4 tables

  2. InN{x}As{1-x} band gap energy and band bowing coefficient calculation

    Science.gov (United States)

    Sentosa, D.; Tang, X.; Chua, S. J.

    2007-12-01

    The band gap energies of zinc-blende InN{x}As{1-x} alloy as a function of its nitrogen composition have been calculated using the density functional theory. The results agree well with those obtained from experimental results. The minimum band gap energy of InN{x}As{1-x} alloy obtained is 70 meV at its N composition of 0.45. The band gap bowing coefficient of InN{x}As{1-x} alloy is obtained from the curve fitting of the simulated band gap energy versus the nitrogen composition, x. The band gap bowing coefficient of zinc-blende InN{x}As{1-x} alloy is found to be 2.072 ± 0.236 eV. The energy band gap for InN is also correctly predicted from this calculation.

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

    Science.gov (United States)

    Sznajder, M.; Bercha, D. M.; Rushchanskii, K. Z.

    2004-01-01

    Semiconducting Tl3AsS4 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 YAlO3 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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

    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.)

  5. The calculation of band gap energy in zinc oxide films

    Science.gov (United States)

    Arif, Ali; Belahssen, Okba; Gareh, Salim; Benramache, Said

    2015-01-01

    We investigated the optical properties of undoped zinc oxide thin films as the n-type semiconductor; the thin films were deposited at different precursor molarities by ultrasonic spray and spray pyrolysis techniques. The thin films were deposited at different substrate temperatures ranging between 200 and 500 °C. In this paper, we present a new approach to control the optical gap energy of ZnO thin films by concentration of the ZnO solution and substrate temperatures from experimental data, which were published in international journals. The model proposed to calculate the band gap energy with the Urbach energy was investigated. The relation between the experimental data and theoretical calculation suggests that the band gap energies are predominantly estimated by the Urbach energies, film transparency, and concentration of the ZnO solution and substrate temperatures. The measurements by these proposal models are in qualitative agreements with the experimental data; the correlation coefficient values were varied in the range 0.96–0.99999, indicating high quality representation of data based on Equation (2), so that the relative errors of all calculation are smaller than 4%. Thus, one can suppose that the undoped ZnO thin films are chemically purer and have many fewer defects and less disorder owing to an almost complete chemical decomposition and contained higher optical band gap energy.

  6. Band gap calculations with Becke-Johnson exchange potential

    International Nuclear Information System (INIS)

    Recently, a simple analytical form for the exchange potential was proposed by Becke and Johnson. This potential, which depends on the kinetic-energy density, was shown to reproduce very well the shape of the exact exchange potential (obtained with the optimized effective potential method) for atoms. Calculations on solids show that the Becke-Johnson potential leads to a better description of band gaps of semiconductors and insulators with respect to the standard local density and Perdew-Burke-Ernzerhof approximations for the exchange-correlation potential. Comparison is also made with the values obtained with the Engel-Vosko exchange potential which was also developed using the exact exchange potential

  7. Rigorous study of the mean field approximation of Debye and Hueckel for Coulomb systems

    International Nuclear Information System (INIS)

    The statistical mechanics of a classical charge symmetric Coulomb system is studied in three dimensions in the limit that the plasma parameter (the inverse temperature divided by the Debye length) goes to zero. To make the system stable, a short range interaction, e.g., hard cores is included. This short range interaction is allowed to go to zero as the plasma parameter goes to zero. Debye and Hueckel used a mean field approximation to give a nonrigorous study of Coulomb systems in his limit. For a system with no external charge distribution, it is shown that the pressure, density, and correlation functions are asymptotic to their Debye-Hueckel approximations. These approximations consist of the ideal gas term plus a term of one lower order in the plasma parameter. The main tools are the Sine-Gordon transformation, the Mayer expansion, and some new correlation inequalities. The sine-Gordon transformation and the Mayer expansion are used to express the observables as functional integrals with respect to a Gaussian measure. The correlation inequalities help control these functional integrals

  8. Elementary energy bands in ab initio calculations of the YAlO3 and SbSI crystal band structure

    Science.gov (United States)

    Bercha, D. M.; Rushchanskii, K. Z.; Sznajder, M.; Matkovskii, A.; Potera, P.

    2002-11-01

    The local density approximation has been implemented to determine the band structure of orthorhombic crystals YAlO3 (YAP) and SbSI. The topology of the valence band structures was analyzed. It has been demonstrated that Zak's elementary energy bands in the band structure are distinguishable on the basis of the empty-lattice approximation. The calculated electron density distribution of YAP and SbSI crystals is related to particular Wyckoff positions. Moreover, there is a direct correspondence between the obtained elementary energy bands and the aforementioned Wyckoff positions characterized by electron density distribution.

  9. Optical properties of novel intermediate band indium thiospinel materials by quantum mechanical calculations

    OpenAIRE

    Wahnón Benarroch, Perla; Aguilera Bonet, Irene; Palacios Clemente, Pablo; Sánchez Noriega, Kefrén; Conesa, Jose Carlos

    2009-01-01

    In this work we present quantum mechanic calculations using the Density Functional Theory for several transition metal substituted octahedral thiospinels derivatives of the In2S3 and MgIn2S4 compounds. The calculations predict that these materials will have a partially filled band inside the band-gap of the aforementioned semiconductors and due to that can be proposed as a novel class of high efficiency photovoltaic materials for intermediate band solar cells. The new band enables absorption ...

  10. Self-consistent Hartree energy band calculation for manganese oxide (MnO)

    International Nuclear Information System (INIS)

    A self-consistent Hartree energy band calculation was done for the MnO crystal using the linear combination of atomic orbitals (LCAO) method. Gaussian type atomic orbitals were used in the LCAO method. This calculation was done for paramagnetic MnO with the NaCl lattice structure. The results show that the energy bands around the Fermi level of MnO are unusually flat, meaning that the electrons in this region are strongly localized. Therefore short range correlation was added to the results of this band calculation. The short range correlation effects were added by calculating atomic type corrections to the original band structure. The results of this correlation calculation show that a large amount of energy is required to excite an electron from the Mn 3d band. Therefore the lowest excitation (the one that requires the least energy) is an excitation from the top of the O 2p band to the Fermi level. This yields a fundamental band gap of 4.8 eV which is in good agreement with optical absorption experiments. This fundamental band gap of 4.8 eV implies that MnO is an insulator, in agreement with conductivity experiments. The Hartree results for the valence bands of MnO agree very well with the results of photoemission experiments. In comparison to the photoemission data, the results of the self-consistent Hartree calculation are an order of magnitude better than the results of the only other band calculation for MnO. Comparison with band calculations for other transitiowith band calculations for other transition metal oxides (other than MnO) imply that with a good self-consistent Hartree energy band calculation for MnO can be superior

  11. Measurements and calculations of two-dimensional band gap structure composed of narrowly slit tubes

    Science.gov (United States)

    Cui, Zhan You; Chen, Tian Ning; Wu, Jiu Hui; Chen, Hua Ling; Zhang, Bo

    2008-10-01

    In this letter, large band gap properties of a two-dimensional stop band gap system composed of steel tubes are reported, which are embedded with periodic narrow slits in each half of the annular tube. The band gap with finite thickness samples is experimentally investigated and theoretically calculated. The results show that without enlarging the lattice constant, the starting frequency of the band gap is reduced, and using the periodic narrow slits with multiwidth can enlarge the stop band of this system due to the multicavity resonance.

  12. Calculation of the energy band structures in semiconductors by RAPW method

    International Nuclear Information System (INIS)

    To calculate the energy band structures in semiconductors using the relativistic augmented plane wave method, atomic potential and charge density are needed, which are calculated by self-consistent method. Wave function for one electron is determined by solving the Dirac equation with the Hartree-Fock equation based on the slater's exchange potential. The results of calculation for Cu+1 are given. (Author)

  13. The use of Wannier function in the calculations of band structure of covalent crystals

    International Nuclear Information System (INIS)

    A variational procedure has been used to build up Wannier functions to study the energy bands of diamond, silicon and ?-tin. For the case of silicon the Wannier function, density of charge and band structure are calculated self-consistently and a simple method in a non-self-consistent way has been used to compute the band structure of diamond, silicon and ?-tin. The method seems to be effective to describe the electronic properties of covalent crystals. (author)

  14. Comparison between experiment and calculated band structures for DyN and SmN

    OpenAIRE

    Preston, A. R. H.; Granville, S.; Housden, D. H.; Ludbrook, B.; Ruck, B. J.; Trodahl, H. J.; Bittar, A.; Williams, G. V. M.; Downes, J. E.; Demasi, A.; Zhang, Y.; Smith, K. E.; Lambrecht, W. R. L.

    2007-01-01

    We investigate the electronic band structure of two of the rare-earth nitrides, DyN and SmN. Resistivity measurements imply that both materials have a semiconducting ground state, and both show resistivity anomalies coinciding with the magnetic transition, despite the different magnetic states in DyN and SmN. X-ray absorption and emission measurements are in excellent agreement with LSDA+U calculations, although for SmN the calculations predict a zero band gap.

  15. The Study of Band Structure of Graphite Intercalation Compound Containing Sodium Calculated Using Density Functional Theory

    Science.gov (United States)

    Nazrul Rosli, Ahmad; Fatimah Wahab, Izzati; Zabidi, Noriza Ahmad; Abu Kassim, Hasan

    2015-06-01

    Sodium intercalation in graphite (GIC-Na) was investigated by the first principle calculation. The structure of GIC-Na was calculated using density functional theory (DFT) with the aid of CASTEP module of Material Studio. The exchange correlation functional has been treat by local density approximation (LDA) and generalized gradient approximation (GGA). It was shown that, unlike potassium GIC and lithium GIC, the band gap of GIC-Na was not induced and has same value of band gap with bulk graphite.

  16. Emergence of rotational bands in ab initio no-core configuration interaction calculations

    CERN Document Server

    Caprio, M A; Vary, J P; Smith, R

    2015-01-01

    Rotational bands have been observed to emerge in ab initio no-core configuration interaction (NCCI) calculations for p-shell nuclei, as evidenced by rotational patterns for excitation energies, electromagnetic moments, and electromagnetic transitions. We investigate the ab initio emergence of nuclear rotation in the Be isotopes, focusing on 9Be for illustration, and make use of basis extrapolation methods to obtain ab initio predictions of rotational band parameters for comparison with experiment. We find robust signatures for rotational motion, which reproduce both qualitative and quantitative features of the experimentally observed bands.

  17. 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 X3 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)

  18. Comparison Between Experiment and Calculated Band Structures for DyN and SmN

    Energy Technology Data Exchange (ETDEWEB)

    Preston,A.; Granville, S.; Housden, D.; Ludbrook, B.; Ruck, B.; Trodahl, H.; Bittar, A.; Williams, G.; Downes, J.; et al

    2007-01-01

    We investigate the electronic band structure of two of the rare-earth nitrides, DyN and SmN. Resistivity measurements imply that both materials have a semiconducting ground state, and both show resistivity anomalies coinciding with the magnetic transition, despite the different magnetic states in DyN and SmN. X-ray absorption and emission measurements are in excellent agreement with densities of states obtained from LSDA+U calculations, although for SmN the calculations predict a zero band gap.

  19. Band-structure calculations for the 3d transition metal oxides in GW

    Science.gov (United States)

    Lany, Stephan

    2013-02-01

    Many-body GW calculations have emerged as a standard for the prediction of band gaps, band structures, and optical properties for main-group semiconductors and insulators, but it is not well established how predictive the GW method is in general for transition metal (TM) compounds. Surveying the series of 3d oxides within a typical GW approach using the random-phase approximation reveals mixed results, including cases where the calculated band gap is either too small or too large, depending on the oxidation states of the TM (e.g., FeO/Fe2O3, Cu2O/CuO). The problem appears to originate mostly from a too high average d-orbital energy, whereas the splitting between occupied and unoccupied d symmetries seems to be reasonably accurate. It is shown that augmenting the GW self-energy by an attractive (negative) and occupation-independent on-site potential for the TM d orbitals with a single parameter per TM cation can reconcile the band gaps for different oxide stoichiometries and TM oxidation states. In Cu2O, which is considered here in more detail, standard GW based on wave functions from initial density or hybrid functional calculations yields an unphysical prediction with an incorrect ordering of the conduction bands, even when the magnitude of the band gap is in apparent agreement with experiment. The correct band ordering is restored either by applying the d-state potential or by iterating the wave functions to self-consistency, which both have the effect of lowering the Cu-d orbital energy. While it remains to be determined which improvements over standard GW implementations are needed to achieve an accurate ab initio description for a wide range of transition metal compounds, the application of the empirical on-site potential serves to mitigate the problems specifically related to d states in GW calculations.

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

    DEFF Research Database (Denmark)

    Christensen, N. Egede; Feuerbacher, B.

    1974-01-01

    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.

  1. Tunnelling through a semiconducting spacer: complex band predictions vs. thin film calculations

    OpenAIRE

    Peralta-ramos, J.; Milano, J.; Llois, A. M.

    2008-01-01

    Using a simple tight-binding model, we compare the limitations of the tunnelling predictions coming out of the complex band structure of a semiconductor with the output of thin film calculations done for the same semiconducting spacer but considering it to be of finite width, and sandwiched by metallic electrodes. The comparison is made as a function of spacer width and interfacial roughness.

  2. 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)

  3. Band gap engineering of early transition-metal-doped anatase TiO?: first principles calculations.

    Science.gov (United States)

    Li, C; Zhao, Y F; Gong, Y Y; Wang, T; Sun, C Q

    2014-10-21

    The thermal stability and electronic structures of anatase TiO2 doped with early transition metals (TM) (group III-B = Sc, Y and La; group IV-B = Zr and Hf; group V-B = V, Nb and Ta) have been studied using first principles calculations. It was found that all doped systems are thermodynamically stable, and their band gaps were reduced by 1-1.3 eV compared to pure TiO2. Doping with transition metals affects the strength of the hybrid orbital of TM-O bonding, and the band gap increases approximately linearly with the MP value of TM-O bonding. PMID:25183457

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

    Energy Technology Data Exchange (ETDEWEB)

    Ribeiro, M. [Centro de Pesquisas Avancadas Wernher von Braun, Av. Alice de Castro P.N. Mattosinho 301, CEP 13098-392 Campinas, SP (Brazil); Ferreira, L.G. [Departamento de Fisica dos Materiais e Mecanica, Instituto de Fisica, Universidade de Sao Paulo, 05315-970 Sao Paulo, SP (Brazil); Fonseca, L.R.C. [Center for Semiconductor Components, State University of Campinas, R. Pandia Calogeras 90, 13083-870 Campinas, SP (Brazil); Ramprasad, R. [Department of Chemical, Materials and Biomolecular Engineering, Institute of Materials Science, University of Connecticut, 97 North Eagleville Road, Storrs, CT 06269 (United States)

    2012-09-20

    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.

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

    CERN Document Server

    Siddiqui, Abuzar A

    2011-01-01

    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.

  6. Numerical extraction of de Haas - van Alphen frequencies from calculated band energies

    CERN Document Server

    Rourke, P M C

    2008-01-01

    A new algorithm for extracting de Haas - van Alphen frequencies, effective masses, and electronic density of states contributions from calculated band energies is presented. The algorithm creates an interpolated k-space "super cell", which is broken into slices perpendicular to the desired magnetic field direction. Fermi surface orbits are located within each slice, and de Haas - van Alphen frequencies, effective masses and density of states contributions are calculated. Orbits are then matched across slices, and extremal orbits determined. This technique has been successful in locating extremal orbits not previously noticed in the complicated topology of existing UPt3 band-structure data; these new orbits agree with experimental de Haas - van Alphen measurements on this material, and solidify the case for a fully-itinerant model of UPt3.

  7. Numerical extraction of de Haas-van Alphen frequencies from calculated band energies

    Science.gov (United States)

    Rourke, P. M. C.; Julian, S. R.

    2012-02-01

    A new algorithm for extracting de Haas-van Alphen frequencies and effective masses from calculated band energies is presented. The algorithm creates an interpolated k-space "super cell," which is broken into slices perpendicular to the desired magnetic field direction. Fermi surface orbits are located within each slice, and de Haas-van Alphen frequencies and effective masses are calculated. Orbits are then matched across slices, and extremal orbits determined. This technique has been successful in locating extremal orbits not previously noticed in the complicated topology of existing UPt 3 band-structure data; these new orbits agree with experimental de Haas-van Alphen measurements on this material, and solidify the case for a fully-itinerant model of UPt 3.

  8. 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)

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

    DEFF Research Database (Denmark)

    Lu, Jing Tao; Christensen, Rasmus Bjerregaard

    2014-01-01

    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.

  10. Angle-resolved photoemission and quasiparticle calculation of ZnO: The need for d band shift in oxide semiconductors

    Science.gov (United States)

    Lim, Linda Y.; Lany, Stephan; Chang, Young Jun; Rotenberg, Eli; Zunger, Alex; Toney, Michael F.

    2012-12-01

    ZnO is a prototypical semiconductor with occupied d10 bands that interact with the anion p states and is thus challenging for electronic structure theories. Within the context of these theories, incomplete cancellation of the self-interaction energy results in a Zn d band that is too high in energy, resulting in upwards repulsion of the valence band maximum (VBM) states, and an unphysical reduction of the band gap. Methods such as GW should significantly reduce the self-interaction error, and in order to evaluate such calculations, we measured high-resolution and resonant angle-resolved photoemission spectroscopy (ARPES) and compared these to several electronic structure calculations. We find that, in a standard GW calculation, the d bands remain too high in energy by more than 1 eV irrespective of the Hamiltonian used for generating the input wave functions, causing a slight underestimation of the band gap due to the p-d repulsion. We show that a good agreement with the ARPES data over the full valence band spectrum is obtained, when the Zn-d band energy is shifted down by applying an on-site potential Vd for Zn-d states during the GW calculations to match the measured d band position. The magnitude of the GW quasiparticle energy shift relative to the initial density functional calculation is of importance for the prediction of charged defect formation energies, band-offsets, and ionization potentials.

  11. Model calculation of N2 Vegard-Kaplan band emissions in Martian dayglow

    CERN Document Server

    Jain, Sonal Kumar

    2011-01-01

    A model for N2 Vegard-Kaplan (VK) band (A^3Sigma_u^+ - X^1Sigma_g^+) emissions in Martian dayglow has been developed to explain the recent observations made by the Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars (SPICAM) ultraviolet spectrograph aboard Mars Express. Steady state photoelectron fluxes and volume excitation rates have been calculated using the analytical yield spectra technique. Since interstate cascading is important for triplet states of N2, the population of any given level of N2 triplet states is calculated under statistical equilibrium considering direct excitation, cascading, and quenching effects. Relative population of all vibrational levels of each triplet state is calculated in the model. Line of sight intensities and height-integrated overhead intensities have been calculated for VK, first positive (B^3Pi_g - A^3Sigma_u^+), second positive (C^3Pi_u - B^3Pi_g), and Wu-Benesch (W^3Delta_u - B^3Pi_g) bands of N2. A reduction in the N2 density by a factor of 3 ...

  12. Accurate band gaps of semiconductors and insulators from Quantum Monte Carlo calculations

    Science.gov (United States)

    Nazarov, Roman; Hood, Randolph; Morales, Miguel

    2015-03-01

    Ab initio calculations are useful tools in developing materials with targeted band gaps for semiconductor industry. Unfortunately, the main workhorse of ab initio calculations - density functional theory (DFT) in local density approximation (LDA) or generalized gradient approximation (GGA) underestimates band gaps. Several approaches have been proposed starting from empirical corrections to more elaborate exchange-correlation functionals to deal with this problem. But none of these work well for the entire range of semiconductors and insulators. Deficiencies of DFT as a mean field method can be overcome using many-body techniques. Quantum Monte Carlo (QMC) methods can obtain a nearly exact numerical solutions of both total energies and spectral properties. Diffusion Monte Carlo (DMC), the most widely used QMC method, has been shown to provide gold standard results for different material properties, including spectroscopic constants of dimers and clusters, equation of state for solids, accurate descriptions of defects in metals and insulators. To test DMC's accuracy in a wider range of semiconductors and insulators we have computed band gaps of several semiconductors and insulators. We show that DMC can provide superior agreement with experiment compared with more traditional DFT approaches including high level exchange-correlation functionals (e.g. HSE).

  13. Compton profiles and band structure calculations of CdS and CdTe

    International Nuclear Information System (INIS)

    In this paper we present the isotropic Compton profiles of zinc-blende CdS and CdTe measured at an intermediate resolution of 0.39 a.u. using our 20 Ci 137Cs Compton spectrometer. The electronic band structure calculations for both the zinc-blende structure compounds and also wurtzite CdS have been undertaken using various schemes of ab-initio linear combination of atomic orbitals calculations implemented in CRYSTAL03 code. The band structure and Mulliken's populations are reported using density functional scheme. In case of wurtzite CdS, our theoretical anisotropies in directional Compton profiles are compared with available experimental data. In case of both the zinc-blende compounds, the isotropic experimental profiles are found to be in better agreement with the present Hartree-Fock calculations. A study of the equal-valence-electron-density experimental profiles of zinc-blende CdS and CdTe shows that the CdS is more ionic than CdTe. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. Accounting for many-body correlation effects in the calculation of the valence band photoelectron emission spectra of ferromagnets

    International Nuclear Information System (INIS)

    The influence of dynamical correlation effects on the valence band photoelectron emission of ferromagnetic Fe, Co and Ni has been investigated. Angle-resolved as well as angle-integrated valence band photoelectron emission spectra were calculated on the basis of the one-particle Green's function, which was obtained by using the fully relativistic Korringa-Kohn-Rostoker method. The correlation effects have been included in terms of the electronic self-energy which was calculated self-consistently within Dynamical Mean-Field Theory (DMFT). In addition a theoretical approach to calculate high-energy angle-resolved valence band photoelectron emission spectra is presented

  15. Slave-boson calculation of the Landau parameters of the one-band Hubbard model

    Science.gov (United States)

    Li, Tiecheng; Bénard, Pierre

    1994-12-01

    We present a microscopic slave-boson calculation of the three Landau parameters Fs0, Fa0, and Fs1 of the Hubbard model for any strength of the interaction U and any filling ?=1-n. The Landau parameter Fa1 is then obtained by using the s-p approximation on the forward-scattering sum rule for the Landau parameters. General analytic expressions are given for the four Landau parameters and related observables. Simple asymptotic expressions for these quantities in four interesting regimes on the U,? manifold are presented. We also show the results of numerical calculations of these quantities for the full range of U and ? for a system with a flat density of states, which are then compared with the experimental results for normal 3He. We find good agreement with the experimentally deduced Landau parameters for both the half-filled-band model and the ?-dependent model at reasonable values of U and ?.

  16. Emergence of rotational bands in ab initio no-core configuration interaction calculations of the Be isotopes

    CERN Document Server

    Maris, P; Vary, J P

    2014-01-01

    The emergence of rotational bands is observed in no-core configuration interaction (NCCI) calculations for the Be isotopes (7<=A<=12), as evidenced by rotational patterns for excitation energies, electromagnetic moments, and electromagnetic transitions. Yrast and low-lying excited bands are found. The results indicate well-developed rotational structure in NCCI calculations, using the JISP16 realistic nucleon-nucleon interaction within finite, computationally-accessible configuration spaces.

  17. 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

  18. Quantum Debye-Hueckel theory and the possible plasma phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Baker, G. Jr.

    1998-09-03

    In this paper the author first sketches the calculation of the pressure of a neutral, ion-electron gas as an expansion in powers of the electron charge, e, by means of the Matsubara, finite-temperature, many-body, perturbation theory. He then goes on to derive the Debye-H{umlt u} term and other equations to support his contentions. His results support but do not prove the existence of a phase transition.

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

    CERN Document Server

    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

    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...

  20. Assessment of the re-ordered wide band model for non-grey radiative transfer calculations in 3D enclosures

    International Nuclear Information System (INIS)

    The objective of the present study is to evaluate variations of the re-ordered wide band model for non-grey radiative transfer calculations in 3D enclosures using the discrete ordinates method. First, the performance of various angular and spatial discretisation schemes of the discrete ordinates method is investigated. Then, several formulations, averaging procedures, and scaling methods of the re-ordered wide band model are tested, and the results are validated against those of a statistical narrow band model. The grey gases formulation using three optimised absorption coefficient is found to be the most efficient method

  1. Photon path length distributions for cloudy skies – oxygen A-Band measurements and model calculations

    Directory of Open Access Journals (Sweden)

    O. Funk

    Full Text Available This paper addresses the statistics underlying cloudy sky radiative transfer (RT by inspection of the distribution of the path lengths of solar photons. Recent studies indicate that this approach is promising, since it might reveal characteristics about the diffusion process underlying atmospheric radiative transfer (Pfeilsticker, 1999. Moreover, it uses an observable that is directly related to the atmospheric absorption and, therefore, of climatic relevance. However, these studies are based largely on the accuracy of the measurement of the photon path length distribution (PPD. This paper presents a refined analysis method based on high resolution spectroscopy of the oxygen A-band. The method is validated by Monte Carlo simulation atmospheric spectra. Additionally, a new method to measure the effective optical thickness of cloud layers, based on fitting the measured differential transmissions with a 1-dimensional (discrete ordinate RT model, is presented. These methods are applied to measurements conducted during the cloud radar inter-comparison campaign CLARE’98, which supplied detailed cloud structure information, required for the further analysis. For some exemplary cases, measured path length distributions and optical thicknesses are presented and backed by detailed RT model calculations. For all cases, reasonable PPDs can be retrieved and the effects of the vertical cloud structure are found. The inferred cloud optical thicknesses are in agreement with liquid water path measurements.

    Key words. Meteorology and atmospheric dynamics (radiative processes; instruments and techniques

  2. 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.

  3. Tight-binding calculations of the band structure and total energies of the various phases of magnesium

    Science.gov (United States)

    Gotsis, H. J.; Papaconstantopoulos, D. A.; Mehl, M. J.

    2002-04-01

    Tight-binding calculations for Mg in a variety of crystal structures are reported using the nonorthogonal tight-binding model with parameters selected to fit accurately first-principles results. These parameters correctly predict hcp to be the stable crystal structure. We have calculated electronic properties (band structure and density of states), elastic constants, phonon frequencies at high-symmetry points, surface energies, surface electronic structure, stacking fault energies, the energy of a small cubic cluster, and finally, dynamical properties. We find good agreement with previous calculations and experiment.

  4. Electronic structure and optical properties of Cs2HgI4: Experimental study and band-structure DFT calculations

    Science.gov (United States)

    Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Shkumat, P. N.; Myronchuk, G. L.; Khvyshchun, M.; Fedorchuk, A. O.; Parasyuk, O. V.; Khyzhun, O. Y.

    2015-04-01

    High-quality single crystal of cesium mercury tetraiodide, Cs2HgI4, has been synthesized by the vertical Bridgman-Stockbarger method and its crystal structure has been refined. In addition, electronic structure and optical properties of Cs2HgI4 have been studied. For the crystal under study, X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces have been measured. The present X-ray photoelectron spectroscopy (XPS) results indicate that the Cs2HgI4 single crystal surface is very sensitive with respect to Ar+ ion-irradiation. In particular, Ar+ bombardment of the single crystal surface alters the elemental stoichiometry of the Cs2HgI4 surface. To elucidate peculiarities of the energy distribution of the electronic states within the valence-band and conduction-band regions of the Cs2HgI4 compound, we have performed first-principles band-structure calculations based on density functional theory (DFT) as incorporated in the WIEN2k package. Total and partial densities of states for Cs2HgI4 have been calculated. The DFT calculations reveal that the I p states make the major contributions in the upper portion of the valence band, while the Hg d, Cs p and I s states are the dominant contributors in its lower portion. Temperature dependence of the light absorption coefficient and specific electrical conductivity has been explored for Cs2HgI4 in the temperature range of 77-300 K. Main optical characteristics of the Cs2HgI4 compound have been elucidated by the first-principles calculations.

  5. Improved cache performance in Monte Carlo transport calculations using energy banding

    Science.gov (United States)

    Siegel, A.; Smith, K.; Felker, K.; Romano, P.; Forget, B.; Beckman, P.

    2014-04-01

    We present an energy banding algorithm for Monte Carlo (MC) neutral particle transport simulations which depend on large cross section lookup tables. In MC codes, read-only cross section data tables are accessed frequently, exhibit poor locality, and are typically too much large to fit in fast memory. Thus, performance is often limited by long latencies to RAM, or by off-node communication latencies when the data footprint is very large and must be decomposed on a distributed memory machine. The proposed energy banding algorithm allows maximal temporal reuse of data in band sizes that can flexibly accommodate different architectural features. The energy banding algorithm is general and has a number of benefits compared to the traditional approach. In the present analysis we explore its potential to achieve improvements in time-to-solution on modern cache-based architectures.

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

    International Nuclear Information System (INIS)

    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. - Highlights: • Six optical band positions and g factors g||, g? of NaCrS2 are calculated together. • Calculation is using the complete diagonalization (of energy matrix) method. • The diagonalization method is based on the two-spin–orbit-parameter model. • Reliability of superposition model in the studies of CF parameters is confirmed

  7. Ab initio calculation of natural band offsets of all group IV, II-VI and III-V semiconductors

    Science.gov (United States)

    Wei, Su-Huai; Walsh, Aron; Li, Yong-Hua; Gong, Xingao

    2010-03-01

    The natural band offset between semiconductors is one of the most fundamental properties in materials physics. It is a necessary quantity to assess charge transport and quantum confinement, and is of particular relevance to the design of optoelectronic devices which feature an interface between two or more materials. However, in the past, the natural band offset calculations were based on the assumption that certain reference levels (core levels, average Coulomb potentials, etc.) have zero absolute deformation potential, and thus align between the bulk and heterostructures. In this study [1], using an all-electron band structure approach, we have systematically calculated the natural band offsets between all group IV, III-V and II-VI semiconductor compounds, taking into account the deformation potential of the core states. This revised approach removes assumptions regarding the deformation potential of the reference levels, and offers a more reliable prediction of the `natural' unstrained offsets. Comparison is made to experimental work, where a noticeable improvement is found compared to previous methodologies. [1] Y.-H. Li et al., Appl. Phys. Lett. 94, 212109 (2009).

  8. Systematic Two-band Model Calculations of the GMR Effect with Metallic and Nonmetallic Spacers and with Impurities

    CERN Document Server

    Gebele, O; Krey, U; Krompiewski, S

    1999-01-01

    By an accurate Green's function method we calculate resistances and the corresponding Giant Magneto-Resistance effects (GMR) of two metallic ferromagnetic films separated by different spacers, metallic and non-metallic ones, in a simplified model on a sc lattice, in CPP and CIP geometries (i.e. current perpendicular or parallel to the planes), without impurities, or with interface- or bulk impurities. The electronic structure of the systems is approximated by two hybridized orbitals per atom, to mimic s-bands and d-bands and their hybridization. We show that such calculations usually give rough estimates only, but of the correct order of magnitude; in particular, the predictions on the impurity effects depend strongly on the model parameters. One of our main results is the prediction of huge CPP-GMR effects for {\\it non-metallic} spacers in the ballistic limit.

  9. Band-gap bowing calculation of Si xSn 1- x alloy

    Science.gov (United States)

    Ferhat, M.; Zaoui, A.

    2001-04-01

    Using ab initio pseudopotential method within the local density approximation we have investigated the electronic properties of Si xSn 1- x semiconducting alloy. The bowing parameter of the band-gap energy variation with alloy concentration is found to be large. We also analyzed its origin in terms of chemical and structural effects.

  10. Constrained Nudged Elastic Band calculation of the Peierls barrier with atomic relaxations.

    Czech Academy of Sciences Publication Activity Database

    Gröger, Roman; Vitek, V.

    2012-01-01

    Ro?. 20, ?. 3 (2012), 035019. ISSN 0965-0393 R&D Projects: GA ?R GAP204/10/0255; GA MŠk(CZ) ED1.1.00/02.0068 Institutional research plan: CEZ:AV0Z20410507 Keywords : dislocation * Peierls barrier * Nudged Elastic Band Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.932, year: 2012

  11. A Formulation for the Static Permittivity of Water and Steam at Temperatures from 238 K to 873 K at Pressures up to 1200 MPa, Including Derivatives and Debye Hueckel Coefficients

    International Nuclear Information System (INIS)

    A new formulation is presented of the static relative permittivity or dielectric constant of water and steam, including supercooled and supercritical states. The range is from 238 K to 873 K, at pressures up to 1200 MPa. The formulation is based on the ITS-90 temperature scale. It correlates a selected set of data from a recently published collection of all experimental data. The set includes new data in the liquid water and the steam regions that have not been part of earlier correlations. The physical basis for the formulation is the so-called g-factor in the form proposed by Harris and Alder. An empirical 12-parameter form for the g-factor as a function of the independent variables temperature and density is used. For the conversion of experimental pressures to densities, the newest formulation of the equation of state of water on the ITS-90, prepared by Wagner and Pruss, has been used. All experimental data are compared with the formulation. The reliability of the new formulation is assessed in all subregions. Comparisons with previous formulations are presented. Auxiliary dielectric-constant formulations as functions of temperature are included for the saturated vapor and liquid states. The pressure and temperature derivatives of the dielectric constant and the Debye endash Hueckel limiting-law slopes are calculated, their reliability is estimated, and they are compared with experimentally derived values and with previous correlations. All equations are given in correlations. All equations are given in this paper, along with short tables. An implementation of this formulation for the dielectric constant is available on disk [A. H. Harvey, A. P. Peskin, and S. A. Klein, NIST/ASME Steam Properties, NIST Standard Reference Database 10, Version 2.1, Standard Reference Data Program, NIST, Gaithersburg, MD (1997)]. copyright 1997 American Institute of Physics and American Chemical Society

  12. Calculation of the Hartree-Fock band structure in solid rare gases and ionic compounds - Application to the optical transitions

    International Nuclear Information System (INIS)

    The well-known 'augmented plane waves' method, for the calculation of electronic states in crystals, is first reviewed. A modification of this method in the case of insulators is then described, which treats exchange in the exact Hartree-Fock formulation, without use of the common free-electron approximation. The band structure of several rare gases (Ne, Ar) and ionic compounds (LiF, NaF, KF, LiCl, NaCl, KCl) has been calculated and discussed. The main point is the strong influence of correlation effects which must be taken into account before comparison between calculated and measured optical transitions. Such an improvement is obtained by including a local polarization potential in the one-electron Hamiltonian, leading to a good agreement of the theoretical transitions with the experimental ones. (author)

  13. Band-gap bowing coefficients in large size-mismatched II-VI alloys: first-principles calculations

    Science.gov (United States)

    Moon, Chang-Youn; Wei, Su-Huai; Zhu, Y. Z.; Chen, G. D.

    2006-12-01

    Band-gap bowing coefficients in large size-mismatched II-VI alloys MIIX1-xVIOx with MII=Zn and Cd, and XVI=S , Se, and Te in the zinc-blende structure are calculated using first-principles methods. We show that in these systems, the bowing coefficients are large and composition dependent. The bowing coefficients increase as the size and chemical mismatch between the constituents increase. The bowing coefficients for the Zn alloys are larger than the corresponding Cd alloys, but smaller than the corresponding III-V alloys. We show that these results can be explained by the size and atomic eigenvalue differences between the constituents and the resulting band offsets and isovalent defect levels in these systems. Our results are compared with recent experimental data.

  14. 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)

  15. High-pressure 155Gd Moessbauer experiments on Gd intermetallic compounds compared with first-principles band-structure calculations

    International Nuclear Information System (INIS)

    High-pressure 155Gd Moessbauer measurements on Gd metal, GdCo5, GdRu2Si2, and Gd2Co17N3 were performed at 4.2 K. The maximum pressures reached were about 18 GPa. The resulting volume reductions of 20 30% were determined using high-pressure x-ray diffraction. The pressure dependence of the electric-field gradients and hyperfine fields obtained for the first three systems was compared with predictions from first-principles band-structure calculations. Significant changes of the hyperfine parameters are observed, especially for elemental Gd metal. With increasing pressure, an increase of the electron density at the Gd nuclei is found in all compounds. The values of the hyperfine field initially increase with pressure. For Gd metal the induced structural phase transitions result in large changes in the electric-field gradient at the nucleus (Vzz). The intermetallic compounds show no structural phase transitions and relatively small changes in Vzz. The combination of experiment and calculations indicates that the transition-metal magnetic moments decrease at high pressure. Although for zero pressure predictions of the electric-field gradient and the hyperfine fields, based on the calculations, are quite accurate, the calculated pressure dependence of the hyperfine parameters for Gd, GdCo5, and GdRu2Si2 does not in all cases lead to a satisfact does not in all cases lead to a satisfactory agreement with experiment. The application of pressures therefore may give additional stimulus for the improvement of the theoretical description of band structures and hyperfine parameters. copyright 1997 The American Physical Society

  16. Ab-initio calculation of band structure and linear optical properties of SbSI in para- and ferroelectric phases

    Science.gov (United States)

    Akkus, Harun; Mamedov, Amirullah

    2007-03-01

    An ab-initio pseudopotential calculation has been performed by using density functional methods within the local density approximation (LDA) to investigate the band structure and optical properties of the ferroelectric-semiconductor SbSI in the para- and ferroelectric phases. It has been shown that SbSI has an indirect gap in both phases (1.45 eV and 1.49 eV in the para- and ferroelectric phases respectively) and that the smallest direct gap is at the S point of the Brillouin zone (1.56 eV and 1.58 eV in the para- and ferroelectric phases respectively). Furthermore, it is shown that first-order phase transition, from the paraelectric phase to the ferroelectric phase (the transiton temperature is about 22 °C), does not change the nature of the band gap. Moreover, the linear frequency dependent dielectric function, including self-energy effects, has been calculated along the c-polar axis in the para- and ferroelectric phases.

  17. The role of high-level calculations in the assignment of the Q-band spectra of chlorophyll

    International Nuclear Information System (INIS)

    We recently established a novel assignment of the visible absorption spectrum of chlorophyll-a that sees the two components Qx and Qy of the low-energy Q band as being intrinsically mixed by non-adiabatic coupling. This ended 50 years debate as to the nature of the Q bands, with prior discussion poised only in the language of the Born-Oppenheimer and Condon approximations. The new assignment presents significant ramifications for exciton transport and quantum coherence effects in photosystems. Results from state of the art electronic structure calculations have always been used to justify assignments, but quantitative inaccuracies and systematic failures have historically limited usefulness. We examine the role of CAM-B3LYP time-dependent density-functional theory (TD-DFT) and Symmetry Adapted Cluster-Configuration Interaction (SAC-CI) calculations in first showing that all previous assignments were untenable, in justifying the new assignment, in making some extraordinary predictions that were vindicated by the new assignment, and in then identifying small but significant anomalies in the extensive experimental data record

  18. The role of high-level calculations in the assignment of the Q-band spectra of chlorophyll

    Energy Technology Data Exchange (ETDEWEB)

    Reimers, Jeffrey R. [School of Physics and Materials Science, The University of Technology, Sydney NSW (Australia); Cai, Zheng-Li [School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane QLD4001 (Australia); Kobayashi, Rika [Australian National University Supercomputer Facility, Mills Rd, Canberra, ACT 0200 (Australia); Rätsep, Margus [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia); Freiberg, Arvi [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia and Institute of Molecular and Cell Biology, University of Tartu, Riia 23, 51010 Tartu (Estonia); Krausz, Elmars [Research School of Chemistry, The Australian National University, Canberra 2601 (Australia)

    2014-10-06

    We recently established a novel assignment of the visible absorption spectrum of chlorophyll-a that sees the two components Q{sub x} and Q{sub y} of the low-energy Q band as being intrinsically mixed by non-adiabatic coupling. This ended 50 years debate as to the nature of the Q bands, with prior discussion poised only in the language of the Born-Oppenheimer and Condon approximations. The new assignment presents significant ramifications for exciton transport and quantum coherence effects in photosystems. Results from state of the art electronic structure calculations have always been used to justify assignments, but quantitative inaccuracies and systematic failures have historically limited usefulness. We examine the role of CAM-B3LYP time-dependent density-functional theory (TD-DFT) and Symmetry Adapted Cluster-Configuration Interaction (SAC-CI) calculations in first showing that all previous assignments were untenable, in justifying the new assignment, in making some extraordinary predictions that were vindicated by the new assignment, and in then identifying small but significant anomalies in the extensive experimental data record.

  19. Constrained nudged elastic band calculation of the Peierls barrier with atomic relaxations

    International Nuclear Information System (INIS)

    We demonstrate that the straightforward application of the nudged elastic band (NEB) method does not determine the correct Peierls barrier of 1/2?1 1 1? 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 direct application of stress in the atomistic modeling of the dislocation glide. (paper)

  20. 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

  1. Band structure engineering of monolayer MoS2 on h-BN: first-principles calculations

    International Nuclear Information System (INIS)

    We have carried out first-principles calculations and theoretical analysis to explore the structural and electronic properties of MoS2/n-h-BN heterostructures consisting of monolayer MoS2 on top of h-BN substrates with one to five layers. We find that the MoS2/n-h-BN heterostructures show indirect bandgap features with both of CBM (in the K point) and VBM (in the ? point) localized on the monolayer MoS2. Difference charge density and surface bands indicate there is no obvious charge exchange in the heterostructure systems. We show that the changes from a direct bandgap in monolayer free-stranding MoS2 to an indirect bandgap in MoS2/n-h-BN heterostructure is induced by the strain. Moreover, we find that the bandgaps of MoS2/n-h-BN heterostructures decrease with increasing number of h-BN layers, which is proposed to result from the different strain distributions in MoS2 due to the varieties of lattice mismatch rates between MoS2 and h-BN layers. Our results suggest that the MoS2/n-h-BN heterostructure could serve as a prototypical example for band structure engineering of 2D crystals with atomic layer precision. (paper)

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

    Science.gov (United States)

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

    1987-01-01

    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.

  3. Angular momentum projected multi-cranked configuration mixing for reliable calculation of high-spin rotational bands

    CERN Document Server

    Shimada, Mitsuhiro; Shimizu, Yoshifumi R

    2015-01-01

    By employing the angular momentum projection technique we propose a method to reliably calculate the quantum spectrum of nuclear collective rotation. The method utilizes several cranked mean-field states with different rotational frequencies and they are superposed in the sense of the configuration mixing or the generator coordinate method, after performing the projection; the idea was originally suggested by Peierls-Thouless in 1962. It is found that the spectrum as a result of the configuration mixing does not essentially depend on chosen sets of cranking frequencies if the number of mean-field states utilized in the mixing is larger than a certain small value. We apply this method to three examples employing the Gogny D1S effective interaction and show that it is useful to study high-spin rotational bands by means of the angular momentum projection method.

  4. 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)

    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

    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.

  5. 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

  6. State-to-state rotational phase coherence effect on the vibration-rotation band shape - An accurate quantum calculation for CO-He

    Science.gov (United States)

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

    1989-01-01

    Accurate coupled state calculations of line coupling are performed for infrared lines of carbon monoxide perturbed by helium. Such calculations lead to both real and imaginary line couplings. For the first time, the effect of this imaginary line couplings, connected with state-to-state rotational phase coherences, on infrared band shape, is analyzed. An extension of detailed balance principle to the complex plane is suggested from the present computed off-diagonal cross sections. This allows us to understand the physical mechanism underlying the weak effect of phase coherences on CO-He infrared band shape.

  7. A plane-wave expansion method based on the effective medium theory for calculating the band structure of a two-dimensional photonic crystal

    International Nuclear Information System (INIS)

    A plane-wave expansion method based on the effective medium theory for calculating the band structure of a two-dimensional photonic crystal is presented. Compared to two other plane-wave expansion methods, the present method has a faster convergence and advantage to calculate the band structure for complicated structures. Using the present fast method, a photonic crystal with a large complete bandgap ??=0.1111(2?c/a) (a is the lattice constant) is found. The designed photonic crystal is formed by a triangular array of elliptic air holes in GaAs medium

  8. Electronic bands and excited states of III-V semiconductor polytypes with screened-exchange density functional calculations

    International Nuclear Information System (INIS)

    The electronic band structures and excited states of III-V semiconductors such as GaP, AlP, AlAs, and AlSb for various polytypes are determined employing the screened-exchange density functional calculations implemented in the full-potential linearized augmented plane-wave methods. We demonstrate that GaP and AlSb in the wurtzite (WZ) structure have direct gap while III-V semiconductors in the zinc blende, 4H, and 6H structures considered in this study exhibit an indirect gap. Furthermore, we find that inclusion of Al atoms less than 17% and 83% in the hexagonal AlxGa1?xP and AlxGa1?xAs alloys, respectively, leads to a direct transition with a gap energy of ?2.3 eV. The feasibility of III-V semiconductors with a direct gap in WZ structure offers a possible crystal structure engineering to tune the optical properties of semiconductor materials

  9. Electronic bands and excited states of III-V semiconductor polytypes with screened-exchange density functional calculations

    Energy Technology Data Exchange (ETDEWEB)

    Akiyama, Toru; Nakamura, Kohji; Ito, Tomonori [Department of Physics Engineering, Mie University, 1577 Kurima-Machiya, Tsu 514-8507 (Japan); Freeman, Arthur J. [Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208 (United States)

    2014-03-31

    The electronic band structures and excited states of III-V semiconductors such as GaP, AlP, AlAs, and AlSb for various polytypes are determined employing the screened-exchange density functional calculations implemented in the full-potential linearized augmented plane-wave methods. We demonstrate that GaP and AlSb in the wurtzite (WZ) structure have direct gap while III-V semiconductors in the zinc blende, 4H, and 6H structures considered in this study exhibit an indirect gap. Furthermore, we find that inclusion of Al atoms less than 17% and 83% in the hexagonal Al{sub x}Ga{sub 1?x}P and Al{sub x}Ga{sub 1?x}As alloys, respectively, leads to a direct transition with a gap energy of ?2.3 eV. The feasibility of III-V semiconductors with a direct gap in WZ structure offers a possible crystal structure engineering to tune the optical properties of semiconductor materials.

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

    OpenAIRE

    Williams, J. E.; Strunk, A.; Huijnen, V.; Weele, M.

    2011-01-01

    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...

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

    CERN Document Server

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

    2001-01-01

    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...

  12. Experimental study and calculations of nitric oxide absorption in the ?(0,0) and ?(1,0) bands for strong temperature conditions

    International Nuclear Information System (INIS)

    Absorption spectra of nitric oxide in the ?(0,0) and ?(1,0) bands have been measured for hard temperature conditions up to 1700 K in order to validate a model for the simulation of these two bands. The good agreement between experiments and calculations (relative errors of 2-5% for the ?(0,0) band and 10-15% for the ?(1,0) band) consolidates the two important assumptions concerning the intermediate Hund's case between (a) and (b) for the X2? state of the ?(0,0) and ?(1,0) absorption bands and the use of collisional broadening parameters of ?(0,0) to simulate the ?(1,0) band. Using this simulation, a study of the Beer-Lambert law behavior at high temperature has been carried out. With the instrument resolution used for these experiments, it was shown that a correction of the Beer-Lambert law is necessary. To apply this technique for the measurements of NO concentrations inside the combustion chamber of an optical SI engine, a new formulation of the Beer-Lambert law has been introduced, since the modified form proposed in the literature is no longer applicable in the total column range of interest

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

    International Nuclear Information System (INIS)

    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

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

    Directory of Open Access Journals (Sweden)

    Roberto N\\u00FA\\u00F1ez-Gonz\\u00E1lez

    2008-01-01

    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.

  15. Dependence of band gap bowing of epitaxial InxGa1-xN on composition, strain and ordering effects by first-principles calculations

    International Nuclear Information System (INIS)

    The band gap of InxGa1-xN alloys does not only depend on the In composition, but also on the strain state and the ordering of In atoms. We performed a theoretical study to disentangle the different effects. According to our results, the band gaps of InxGa1-xN alloys show parabolic behavior in compressive regions and linear dependence in the tensile regions. We further find a universal bowing behavior in InxGa1-xN alloys for the whole In content range under constant relative strain. Inhomogeneous In distributions lead to a narrower band gap, but are energetically unfavorable. Based on the calculated results, an interpolating form for the band gap as a function of ordering, biaxial strain and chemical content for InxGa1-xN alloys is suggested. Our results provide guidance to determine the band gaps of InxGa1-xN alloys under real experiment conditions.

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

    DEFF Research Database (Denmark)

    Svane, Axel; Christensen, Niels Egede

    2010-01-01

    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.

  17. Experimental line broadening and line shift coefficients of the acetylene ? 1 + ? 3 band pressurized by hydrogen and deuterium and comparison with calculations

    Science.gov (United States)

    Thibault, F.; Fuller, E. P.; Grabow, K. A.; Hardwick, J. L.; Marcus, C. I.; Marston, D.; Robertson, L. A.; Senning, E. N.; Stoffel, M. C.; Wiser, R. S.

    2009-07-01

    Theoretical and experimental values have been determined for the pressure broadening of the ? 1 + ? 3 band of acetylene by hydrogen and deuterium at 195 K, and experimental values of the pressure shifts have been determined. Theoretical values have been calculated on the basis of a recent potential energy surface using the close coupling scheme. We discuss the detailed contribution of the various rotational angular momenta of the perturbing gas and the ortho and para contribution to the total pressure broadening cross-sections. We give routes to circumvent the computational cost of such calculations. Experimental values have been measured using a tunable diode laser spectrometer assuming a Voigt line shape. These pressure broadening parameters are compared with measurements performed recently at room temperature and with present measurements performed at 195 K in the ? 1 + ? 3 band of acetylene. A satisfactory agreement is obtained with the present results and available ones at 295 K.

  18. Rain Rate-Radar Reflectivity Relationship for Drop Size Distribution and Rain Attenuation Calculation of Ku Band Signals

    OpenAIRE

    Govardhani.Immadi; Kotamraju, Sarat K.; Habibulla Khan; Venkata Narayana, M.

    2014-01-01

    With the increased demand for long distance Tele communication day by day, satellite communication system was developed. Satellite communications utilize L, C, Ku and Ka bands of frequency to fulfil all the requirements. Utilization of higher frequencies causes severe attenuation due to rain. Rain attenuation is noticeable for frequencies above 10ghz. Amount of attenuation depends on whether the operating wave length is comparable with rain drop diameter or not. In this paper the main focus i...

  19. 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)

    El-Sayed Mostafa

    2005-01-01

    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.

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

    Science.gov (United States)

    Lamouroux, Julien; Gamache, Robert R.; Laraia, Anne L.; Hartmann, Jean-Michel; Boulet, Christian

    2012-08-01

    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.

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

    Scientific Electronic Library Online (English)

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

    2004-03-01

    Full Text Available 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.

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

    CERN Document Server

    Gröger, R

    2011-01-01

    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...

  3. Rain Rate-Radar Reflectivity Relationship for Drop Size Distribution and Rain Attenuation Calculation of Ku Band Signals

    Directory of Open Access Journals (Sweden)

    Govardhani.Immadi

    2014-05-01

    Full Text Available With the increased demand for long distance Tele communication day by day, satellite communication system was developed. Satellite communications utilize L, C, Ku and Ka bands of frequency to fulfil all the requirements. Utilization of higher frequencies causes severe attenuation due to rain. Rain attenuation is noticeable for frequencies above 10ghz. Amount of attenuation depends on whether the operating wave length is comparable with rain drop diameter or not. In this paper the main focus is on drop size distribution using empirical methods, especially Marshall and Palmer distributions. Empirical methods deal with power law relation between the rain rate(mm/h and radar reflectivity(dBz. Finally it is discussed about the rain rate variation, radar reflectivity, drop size distribution, that is made for two rain events at K L University, Vijayawada on 4th September 2013 and on 18 th August 2013.

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

    CERN Document Server

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

    2005-01-01

    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...

  5. 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

  6. Valence bands of the Cu-III-VI2 chalcopyrites studied by photoemission spectra, X-ray emission spectra, and electronic structure calculations

    International Nuclear Information System (INIS)

    Ultraviolet and X-ray excited photoemission spectra and Cu K?5 X-ray emission spectra are used to measure the valence band density of states in CuGaTe2 and CuInTe2. In both compounds the density of states exhibits five structures which are ascribed to Cu 3d-Te 5p hybridized states, Ga 4s/In 5s-Te 5p bonding states, and Te 5s states. The valence band density of states of all Ga- and In-containing Cu-III-VI2 is calculated in an atomic orbital basis with the noble metal d states explicitly included. The agreement between theory and experiment is good for CuGaTe2 and except the In 5s-VI p bonding states also for the Cu-In-VI2 chalcopyrites. Larger discrepancies between theory and experiment are found for CuGaS2 and CuGaSe2. (author)

  7. Effects of Strain and Quantum Confinement in Optically Pumped Nuclear Magnetic Resonance in GaAs: Interpretation Guided by Spin-Dependent Band Structure Calculations

    Science.gov (United States)

    Bowers, Clifford; Wood, Ryan; Dipta, Saha; Tokarski, John; McCarthy, Lauren; Sanders, Gary; Stanton, Christopher; McGill, Stephen; Reyes, Arneil; Kuhns, Phil; Reno, John

    2015-03-01

    A combined experimental-theoretical study of optically pumped NMR (OPNMR) has been performed in a GaAs/Al0.1Ga0.9As quantum well film epoxy bonded to a Si substrate with thermally induced biaxial strain. The photon energy dependence of the Ga OPNMR signal was recorded at magnetic fields of 4.9 and 9.4 T at a temperature of 4.8-5.4 K. The data were compared to the nuclear spin polarization calculated from the differential absorption to spin-up and spin-down states of the electron conduction band using a modified Pidgeon Brown model. Comparison of theory with experiment facilitated the assignment of features in the OPNMR energy dependence to specific interband Landau level transitions. The results provide insight into how effects of strain and quantum confinement are manifested in optical nuclear polarization in semiconductors.

  8. First-principles calculation of the band gap of Al xGa1-xN and In xGa1-x N

    Scientific Electronic Library Online (English)

    Roberto, Núñez-González; Armando, Reyes-Serrato; Alvaro, Posada-Amarillas; Donald H, Galván.

    2008-11-01

    Full Text Available En este trabajo se realizaron cálculos de primeros principios de la variación del ancho de banda prohibido en los compuestos ternarios Al xGa1-xN e In xGa1-x N, utilizando el Método Linealizado de Ondas Planas Aumentadas con Potencial Completo (FLAPW), dentro del marco de la Teoría del Funcional de [...] la Densidad (DFT). Los nitruros fueron modelados en una estructura tipo wurzita utilizando el método de supercelda, y considerando las concentraciones x = 0, 0.25, 0.50, 0.75 y 1.0. Para la optimización de los parámetros de red se utilizó el potencial de correlación-intercambio PBE96 (Perdew et al., Phys. Rev. Lett. 77 (1996) 3865). Para el cálculo de la estructura de bandas de energía se utilizaron los funcionales PBE96 y EV93 (Engel et al., Phys. Rev. B 47 (1993) 13164). Se consideraron parámetros de red experimentales y calculados (con PBE96) para los cálculos de las propiedades electrónicas. Nuestros cálculos indican que la banda prohibida fundamental es directa en estos compuestos. Los cálculos con el funcional EV93 dan como resultado una mejor estimación de los anchos de las bandas prohibidas de los compuestos binarios. Calculamos el parámetro de curvatura, obteniendo los valores b = 0.74 eV para Al xGa1-xN y b = 2.12 eV para In xGa1-x N. Abstract in english Ab-initio calculations of the band gap variation of Al xGa1-xN and In xGa1-x N 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 su [...] percell 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 Al xGa1-xN and b = 2.12 eV for In xGa1-x N.

  9. 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)

    J. E. Williams

    2011-09-01

    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.

  10. 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)

    J. E. Williams

    2012-01-01

    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.

  11. Cathode catalysts for fuel cell development: A theoretical study based on band structure calculations for tungsten nitride and cobalt tungsten nitrides

    International Nuclear Information System (INIS)

    Band structure calculations were performed for tungsten nitride, cobalt tungsten nitrides, and platinum slabs. The major requirements for the development of a superior cathode catalyst are: (1) that the Fermi level of the cathode catalyst is close to the energy level of the lowest unoccupied molecular orbital of O2, the lowest unoccupied atomic orbital of an oxygen atom, and the lowest unoccupied atomic orbital of a hydrogen atom so that they can readily interact with one another; and (2) that the cathode catalysts have smaller ?E value which represent the difference between the Fermi level and the peak position of the density of states of the Op orbital of O2 adsorbed on the catalyst. The active site structures of cobalt tungsten nitrides for activation of the oxygen reduction reaction were found to have the surface structure of Co-O-Co, which lowered the unoccupied orbital of the oxygen atom to approximately that of the Fermi level. However, this structure concomitantly lowered the Fermi level, which resulted in an increase in ?E. Consequently, the optimal cathode catalyst regarding the surface conformation contains a Co-O-Co structure that is dispersed on the surface of the cobalt tungsten nitride. The cobalt tungsten oxynitride exhibited a catalytic activity for the oxygen reduction reaction. A linear dependence is observed between the ?E and the oxygen reduction reaction offset potentials of the tungsten nitride, cobalt tungsteof the tungsten nitride, cobalt tungsten nitride, cobalt tungsten oxynitride, and platinum.

  12. Semiclassical calculations of half-widths and line shifts for transitions in the 30012?00001 and 30013?00001 bands of CO2 II: Collisions with O2 and air

    Science.gov (United States)

    Lamouroux, Julien; Gamache, Robert R.; Laraia, Anne L.; Hartmann, Jean-Michel; Boulet, Christian

    2012-07-01

    The complex Robert-Bonamy (CRB) formalism was used to calculate the half-width, its temperature dependence, and the line shift for CO2 for transitions in the 30012?00001 and 30013?00001 bands with O2 as the perturbing gas. The calculations were done for rotational quantum numbers from J=0 to J=120 with no ad hoc scaling of the line shape equations. The intermolecular potential parameters are adjusted on accurate experimental measurements of the half-widths, its temperature dependence, and the pressure-induced line shifts so that a single intermolecular potential reproduces all three parameters. Using the results of this work and previous results for N2-broadening, air-broadening line shape parameters were also determined. The comparison of the CRB calculations with the experimental data available in the literature for the three line shape coefficients demonstrates the quality of the present calculations for the both bands under study.

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

    OpenAIRE

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

    2010-01-01

    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 a...

  14. Calculation of equilibria at elevated temperatures using the MINTEQ geochemical code

    Energy Technology Data Exchange (ETDEWEB)

    Smith, R.W.

    1988-12-01

    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.

  15. Gastric Banding

    Science.gov (United States)

    ... two FDA approved gastric banding devices on the market designed to treat obesity: Lap-Band Gastric Banding ... moving of the gastric band from its original position, requiring another surgery to reposition it erosion of ...

  16. Dependence of band gap bowing of epitaxial In{sub x}Ga{sub 1-x}N on composition, strain and ordering effects by first-principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Cui, Ying; Lee, Sangheon; Leyson, Gerard; Freysoldt, Christoph; Neugebauer, Joerg [Max-Planck-Institut fuer Eisenforschung, Max-Planck-Str. 1, 40627 Duesseldorf (Germany)

    2013-07-01

    The band gap of In{sub x}Ga{sub 1-x}N alloys does not only depend on the In composition, but also on the strain state and the ordering of In atoms. We performed a theoretical study to disentangle the different effects. According to our results, the band gaps of In{sub x}Ga{sub 1-x}N alloys show parabolic behavior in compressive regions and linear dependence in the tensile regions. We further find a universal bowing behavior in In{sub x}Ga{sub 1-x}N alloys for the whole In content range under constant relative strain. Inhomogeneous In distributions lead to a narrower band gap, but are energetically unfavorable. Based on the calculated results, an interpolating form for the band gap as a function of ordering, biaxial strain and chemical content for In{sub x}Ga{sub 1-x}N alloys is suggested. Our results provide guidance to determine the band gaps of In{sub x}Ga{sub 1-x}N alloys under real experiment conditions.

  17. Magnetic rotation (MR) band crossing in N=78 odd-Z nuclei: Tilted axis cranking (TAC) calculations to explore the role of nucleons

    Science.gov (United States)

    Kumar, Suresh

    2014-08-01

    Magnetic Rotation (MR) band crossing is studied systematically in N=78 isotones (La, Pr, Pm and Eu) using Tilted Axis Cranking (TAC) model. The observables such as I(¯h) vs ¯h?, excitation energy E(MeV) vs spin I(¯h), and the B(M1)/B(E2) vs I(¯h) were considered to pinpoint MR crossing in these nuclei. The results of tilted axis cranking were compared with these experimental observables. The B(M1) and B(E2) values were also reported and used to understand the crossing behaviour of these MR bands. The systematic evolution of this phenomenon in N=78 odd-Z istotones leads to understand the role of nucleons in MR band crossing.

  18. 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

  19. Field theoretic calculation of the surface tension for a model electrolyte system

    International Nuclear Information System (INIS)

    We carry out the calculation of the surface tension for a model electrolyte to first order in a cumulant expansion about a free-field theory equivalent to the Debye-Hueckel approximation. In contrast with previous calculations, the surface tension is calculated directly without recourse to integrating thermodynamic relations. The system considered is a monovalent electrolyte with a region at the interface, of width h, from which the ionic species are excluded. In the case where the external dielectric constant ?0 is smaller than the electrolyte solution's dielectric constant ? we show that the calculation at this order can be fully regularized. In the case where h is taken to be zero the Onsager-Samaras limiting law for the excess surface tension of dilute electrolyte solutions is recovered, with corrections coming from a nonzero value of ?0/?

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

    CERN Document Server

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

    2010-01-01

    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 ...

  1. 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.

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

    Science.gov (United States)

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

    2010-10-01

    Compound semiconductor alloys of the type AxB1-xC find widespread applications as their electronic bulk band gap varies continuously with x , and therefore a tailoring of the energy gap is possible by variation in 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 paper, 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 and photoluminescence measurements on catalytically grown CdxZn1-xSe nanowires reported in the literature.

  3. 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)

    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

    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.

  4. 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)

    Schleife, A; Bechstedt, F

    2012-02-15

    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.

  5. 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)

  6. Electronic structure and phase stability of oxide semiconductors: Performance of dielectric-dependent hybrid functional DFT, benchmarked against G W band structure calculations and experiments

    Science.gov (United States)

    Gerosa, Matteo; Bottani, Carlo Enrico; Caramella, Lucia; Onida, Giovanni; Di Valentin, Cristiana; Pacchioni, Gianfranco

    2015-04-01

    We investigate band gaps, equilibrium structures, and phase stabilities of several bulk polymorphs of wide-gap oxide semiconductors ZnO, TiO2,ZrO2, and WO3. We are particularly concerned with assessing the performance of hybrid functionals built with the fraction of Hartree-Fock exact exchange obtained from the computed electronic dielectric constant of the material. We provide comparison with more standard density-functional theory and GW methods. We finally analyze the chemical reduction of TiO2 into Ti2O3 , involving a change in oxide stoichiometry. We show that the dielectric-dependent hybrid functional is generally good at reproducing both ground-state (lattice constants, phase stability sequences, and reaction energies) and excited-state (photoemission gaps) properties within a single, fully ab initio framework.

  7. Calculation of the magnetic field in the banding block model of the booster in the High Energy Physics Institute (IFVE), taking into account electrotechnical steel anisotropy

    International Nuclear Information System (INIS)

    In the paper the technique and results of the magnetic field calculation in the bending block model of IFVE booster taking into account the magnetoanisotropic steel features, as a working material, are presented. Two versions of steel rolling direction orientation relative to the mean plane of the operating magnet gap are considered. It is shown, that transverse orientation provides better field homogeneity

  8. Photonic band gap materials

    Science.gov (United States)

    Cassagne, D.

    Photonic band gap materials Photonic band gap materials are periodic dielectric structures that control the propagation of electromagnetic waves. We describe the plane wave method, which allows to calculate the band structures of photonic crystals. By symmetry analysis and a perturbative approach, we predict the appearance of the low energy photonic band gaps of hexagonal structures. We propose new two-dimensional structures called graphite and boron nitride. Using a transfer matrix method, we calculate the transmission of the graphite structure and we show the crucial role of the coupling with external modes. We study the appearance of allowed modes in the photonic band gap by the introduction of localized defects in the periodicity. Finally, we discuss the properties of opals formed by self-organized silica microspheres, which are very promising for the fabrication of three-dimensional photonic crystals. Les matériaux à bandes interdites photoniques sont des structures diélectriques périodiques qui contrôlent la propagation des ondes électromagnétiques. Nous décrivons la méthode des ondes planes qui permet de calculer les structures de bandes des cristaux photoniques. Par une analyse de la symétrie et une approche perturbative, nous précisons les conditions d'existence des bandes interdites de basse énergie. Nous proposons de nouvelles structures bidimensionnelles appelées graphite et nitrure de bore. Grâce à une méthode de matrices de transfert, nous calculons la transmission de la structure graphite et nous mettons en évidence le rôle fondamental du couplage avec les modes extérieurs. Nous étudions l'apparition de modes permis dans la bande interdite grâce à l'introduction de défauts dans la périodicité. Enfin, nous discutons les propriétés des opales constituées de micro-billes de silice auto-organisées, qui sont très prometteuses pour la fabrication de cristaux photoniques tridimensionnels.

  9. Band Interaction between Chiral Doublet Bands

    International Nuclear Information System (INIS)

    Band interaction between the chiral doublet bands based on ?h11/2 vh?111/2 configuration is investigated in the particle rotor model with different triaxial deformation ?. The variation of chiral partner states with ? values is understood qualitatively based on the basic picture of two interaction levels, which is confirmed further by the calculated overlap integral of wave functions at different ? values. It is found that the interaction strengths of chiral partner states are obviously different for odd spins and even ones. (nuclear physics)

  10. Electronic structure of Cu1-xNixRh2S4 and CuRh2Se4: Band-structure calculations, x-ray photoemission, and fluorescence measurements

    International Nuclear Information System (INIS)

    The electronic structure of spinel-type Cu1-xNixRh2S4 (x=0.0, 0.1, 0.3, 0.5, 1.0) and CuRh2Se4 compounds has been studied by means of x-ray photoelectron (XPS) and fluorescent spectroscopy. Cu L3, Ni L3, S L2,3, and Se M2,3 x-ray emission spectra (XES) were measured near thresholds at Beamline 8.0 of the Lawrence Berkeley Laboratory's Advanced Light Source. XES measurements of the constituent atoms of these compounds, reduced to the same binding energy scale, are found to be in excellent agreement with XPS valence bands. The calculated XES spectra which include dipole matrix elements show that the partial density of states reproduce experimental spectra quite well. States near the Fermi level (EF) have strong Rh d and S(Se) p character in all compounds. In NiRh2S4 the Ni 3d states contribute strongly at EF, whereas in both Cu compounds the Cu 3d bands are only ?1 eV wide and centered ?2.5 eV below EF, leaving very little 3d character at EF. The density of states at the Fermi level is less in NiRh2S4 than in CuRh2S4. This difference may contribute to the observed decrease, as a function of Ni concentration, in the superconducting transition temperature in Cu1-xNixRh2S4. The density of states of the ordered. The density of states of the ordered alloy Cu0.5Ni0.5Rh2S4 shows behavior that is more ''split-band''-like than ''rigid-band''-like. (c) 2000 The American Physical Society

  11. Electronic band structure and optical properties of titanium oxyphosphates Li0.50Co0.25TiO(PO4) single crystals: An ab-initio calculations

    International Nuclear Information System (INIS)

    From the refined atomic positions obtained by Belmal et al. (2004) using X-ray diffraction for Li0.50Co0.25TiO(PO4), we have performed a structural optimization by minimizing the forces acting on the atoms keeping the lattice parameters fixed at the experimental values. With this relaxed (optimized) geometry we have performed a comprehensive theoretical study of electronic properties and dispersion of the linear optical susceptibilities using the full potential linear augmented plane wave (FP-LAPW) method. The generalized gradient approximation (GGA) exchange-correlation potential was applied. In addition, the Engel-Vosko generalized gradient approximation (EVGGA) was used for comparison with GGA because it is known that EVGGA approach yields better band splitting compared to the GGA. We have calculated the band structure, and the total and partial densities of states. The electron charge densities and the bonding properties were analyzed and discussed. The complex dielectric optical susceptibilities were discussed in detail. - Graphical abstract: It is shown that P is tetrahedrally coordinated by four O ions. Highlights: ? Comprehensive theoretical study of electronic and optical properties was performed. ? Using X-ray diffraction data we have performed a structural optimization. ? The electron charge densities and the bonding properties were analyzed and discussed. ? Fermi surface was analyzed since it is useful for predictind since it is useful for predicting thermal, magnetic, and optical properties. ? The density of states at EF and the electronic specific heat coefficient were calculated.

  12. 12-band $\\textbf{k}\\cdot\\textbf{p}$ model for dilute bismide alloys of (In)GaAs derived from supercell calculations

    OpenAIRE

    Broderick, Christopher A.; Usman, Muhammad; O Reilly, Eoin P.

    2013-01-01

    Incorporation of bismuth (Bi) in dilute quantities in (In)GaAs has been shown to lead to unique electronic properties that can in principle be exploited for the design of high efficiency telecomm lasers. This motivates the development of simple models of the electronic structure of these dilute bismide alloys, which can be used to evaluate their potential as a candidate material system for optical applications. Here, we begin by using detailed calculations based on an $sp^{3...

  13. Accurate collision-induced line-coupling parameters for the fundamental band of CO in He - Close coupling and coupled states scattering calculations

    Science.gov (United States)

    Green, Sheldon; Boissoles, J.; Boulet, C.

    1988-01-01

    The first accurate theoretical values for off-diagonal (i.e., line-coupling) pressure-broadening cross sections are presented. Calculations were done for CO perturbed by He at thermal collision energies using an accurate ab initio potential energy surface. Converged close coupling, i.e., numerically exact values, were obtained for coupling to the R(0) and R(2) lines. These were used to test the coupled states (CS) and infinite order sudden (IOS) approximate scattering methods. CS was found to be of quantitative accuracy (a few percent) and has been used to obtain coupling values for lines to R(10). IOS values are less accurate, but, owing to their simplicity, may nonetheless prove useful as has been recently demonstrated.

  14. 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)

    Juan Carlos Salcedo-Reyes

    2008-09-01

    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.

  15. Semiclassical calculations of half-widths and line shifts for transitions in the 30012?00001 and 30013?00001 bands of CO2, I: Collisions with N2

    Science.gov (United States)

    Gamache, Robert R.; Lamouroux, Julien; Laraia, Anne L.; Hartmann, Jean-Michel; Boulet, Christian

    2012-07-01

    Calculations of the half-width, its temperature dependence, and the line shift are made for the rotational states J=0-120 for two of the Fermi-tetrad bands (30012?00001 and 30013?00001) of CO2 perturbed by N2. The calculations employ the semi-classical complex Robert-Bonamy method with no ad hoc scaling, J-dependent or otherwise, and an intermolecular potential (IP) comprised of an electrostatic part, an atom-atom part, and an isotropic London dispersion part. The averaging over the impact parameter b and relative speed v are explicitly carried out. Many interesting features about CO2 as the radiating molecule are elucidated. Effects of the trajectory model, the order of the expansion of the atom-atom component of the potential, and the inclusion of the imaginary terms are studied. It is shown that the results are very sensitive to the intermolecular potential. The final IP parameters give results that demonstrate excellent agreement with measurement for the three line shape parameters studied in this work.

  16. Chemically induced compaction bands in geomaterials

    Science.gov (United States)

    Stefanou, Ioannis; Sulem, Jean

    2013-04-01

    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.

  17. 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)

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

    2002-03-01

    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.

  18. 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.)

  19. Band structure of boron doped carbon nanotubes

    OpenAIRE

    Wirtz, Ludger; Rubio Secades, A?ngel

    2003-01-01

    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...

  20. 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.

  1. 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.

  2. System and method for progressive band selection for hyperspectral images

    Science.gov (United States)

    Fisher, Kevin (Inventor)

    2013-01-01

    Disclosed herein are systems, methods, and non-transitory computer-readable storage media for progressive band selection for hyperspectral images. A system having module configured to control a processor to practice the method calculates a virtual dimensionality of a hyperspectral image having multiple bands to determine a quantity Q of how many bands are needed for a threshold level of information, ranks each band based on a statistical measure, selects Q bands from the multiple bands to generate a subset of bands based on the virtual dimensionality, and generates a reduced image based on the subset of bands. This approach can create reduced datasets of full hyperspectral images tailored for individual applications. The system uses a metric specific to a target application to rank the image bands, and then selects the most useful bands. The number of bands selected can be specified manually or calculated from the hyperspectral image's virtual dimensionality.

  3. BAND GAP VARIATION OF GALLIUM SELENIDE UNDER HIGH PRESSURE

    OpenAIRE

    Gauthier, Mélanie; Polian, A.; Besson, J

    1984-01-01

    Taking into account the lamellar structure of GaSe, we reproduce its complex band gap variation under pressure. The model joint with recent band structure calculation fits very well with experimental data.

  4. A simple theoretical approach to calculate the electrical conductivity of nonideal copper plasma

    International Nuclear Information System (INIS)

    A simple theoretical approach to calculate the electrical conductivity of partially ionized nonideal copper plasma is introduced. The densities of plasma species are calculated, to machine accuracy, including electronic excitation and allowing for high ionization states up to the atomic number of the element. Depression of ionization energies is taken into account using an interpolation formula that is valid over a wide range of densities. The formula yields the results of the Debye-Hueckel and the ion-sphere models at the limiting boundaries of low and high densities, respectively. The nonideal Coulomb logarithm is represented by an analytic wide-range formula supplemented by a specially tailored cutoff parameter. Effects of excluding excited and high ionization states on the calculation of ionization equilibrium and electrical conductivity of copper are investigated and assessed. Computational results of the electrical conductivity are compared with results from other theoretical models and available experimental measurements and showed reasonable agreement. A discussion about the choice of the ion-sphere radius is included and concerns about thermodynamic inconsistency when using the modified nonideal Saha equations are discussed and cleared

  5. Candidate chiral bands in {sup 198}Tl

    Energy Technology Data Exchange (ETDEWEB)

    Lawrie, E.A.; Lawrie, J.J.; Bark, R.A.; Mullins, S.M.; Murray, S.H.T. [Themba LABS, Somerset West (South Africa); Vymers, P.A.; Maliage, S.M.; Masiteng, P.L.; Ramashidzha, T.M.; Sharpey-Schafer, J.F.; Shirinda, O. [Themba LABS, Somerset West (South Africa); University of the Western Cape, Bellville (South Africa); Vieu, Ch.; Schueck, C. [CNRS - IN2P3, Centre de Spectrometrie Nucleaire et de Spectrometrie de Masse, Orsay (France); Lindsay, R. [University of the Western Cape, Bellville (South Africa); Mabala, G.K. [Themba LABS, Somerset West (South Africa); University of Cape Town, Department of Physics, Rondebosch (South Africa); Ragnarsson, I. [Lund University, Division of Mathematical Physics, LHT, Lund (Sweden)

    2010-07-15

    High-spin states in {sup 198}Tl were studied using the {sup 197}Au({alpha}, 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 {pi}h{sub 9/2} x {nu}i{sub 13/2}{sup -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.)

  6. Band structure of boron doped carbon nanotubes

    CERN Document Server

    Wirtz, L; Wirtz, Ludger; Rubio, Angel

    2003-01-01

    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.

  7. Band Structures of Plasmonic Polarons

    Science.gov (United States)

    Caruso, Fabio; Lambert, Henry; Giustino, Feliciano

    2015-03-01

    In angle-resolved photoemission spectroscopy (ARPES), the acceleration of a photo-electron upon photon absorption may trigger shake-up excitations in the sample, leading to the emission of phonons, electron-hole pairs, and plasmons, the latter being collective charge-density fluctuations. Using state-of-the-art many-body calculations based on the `GW plus cumulant' approach, we show that electron-plasmon interactions induce plasmonic polaron bands in group IV transition metal dichalcogenide monolayers (MoS2, MoSe2, WS2, WSe2). We find that the energy vs. momentum dispersion relations of these plasmonic structures closely follow the standard valence bands, although they appear broadened and blueshifted by the plasmon energy. Based on our results we identify general criteria for observing plasmonic polaron bands in the angle-resolved photoelectron spectra of solids.

  8. Computational optical band gap bowing of III-V semiconductors alloys

    Science.gov (United States)

    Ferhat, M.

    2004-08-01

    A phenomenological model is described for the calculations of the optical band bowing of III-V semiconductor alloys. The optical band gap bowing is shown to account successfully for theoretical calculations and the experimental data.

  9. Electron relaxation in the conduction band of wide-band-gap oxides

    Science.gov (United States)

    Daguzan, Ph.; Martin, P.; Guizard, S.; Petite, G.

    1995-12-01

    Using quantum kinetic equations with memory we calculate the time-dependent distribution function of an electron gas injected suddenly in the conduction band of a wide-band-gap insulator. A comparison is made with the semiclassical Boltzmann equation approach. We show that due to the large electron-phonon coupling occurring in such materials a quantum approach is needed.

  10. Spectral band selection for classification of soil organic matter content

    Science.gov (United States)

    Henderson, Tracey L.; Szilagyi, Andrea; Baumgardner, Marion F.; Chen, Chih-Chien Thomas; Landgrebe, David A.

    1989-01-01

    This paper describes the spectral-band-selection (SBS) algorithm of Chen and Landgrebe (1987, 1988, and 1989) and uses the algorithm to classify the organic matter content in the earth's surface soil. The effectiveness of the algorithm was evaluated comparing the results of classification of the soil organic matter using SBS bands with those obtained using Landsat MSS bands and TM bands, showing that the algorithm was successful in finding important spectral bands for classification of organic matter content. Using the calculated bands, the probabilities of correct classification for climate-stratified data were found to range from 0.910 to 0.980.

  11. Photonic band gap materials

    International Nuclear Information System (INIS)

    An overview of the theoretical and experimental efforts in obtaining a photonic band gap, a frequency band in three-dimensional dielectric structures in which electromagnetic waves are forbidden, is presented

  12. Rubber Band Racers

    Science.gov (United States)

    IEEE

    2013-08-30

    In this activity, learners explore the design of rubber band powered cars. Learners work in teams of "engineers" to design and build their own rubber band cars out of everyday items. They test their rubber band cars, evaluate their results, and present to the group.

  13. Band offsets in heterojunctions between cubic perovskite oxides

    OpenAIRE

    Lebedev, Alexander I.

    2014-01-01

    The band offsets for nine heterojunctions between titanates, zirconates, and niobates with the cubic perovskite structure were calculated from first principles. The effect of strain in contacting oxides on their energy structure, many-body corrections to the position of the band edges (calculated in the GW approximation), and the splitting of the conduction band resulting from spin-orbit interaction were consistently taken into account. It was shown that the neglect of the m...

  14. Multiple triaxial bands in 138Nd

    Science.gov (United States)

    Petrache, C. M.; Ragnarsson, I.; Ma, Hai-Liang; Leguillon, R.; Zerrouki, T.; Bazzacco, D.; Lunardi, S.

    2015-02-01

    High-spin states in 138Nd were investigated by using the 48Ca+94Zr reaction and ? -ray coincidences were acquired with the GASP spectrometer. A rich level scheme was developed including 14 new bands of quadrupole transitions at very high spins. Linking transitions connecting 11 high-spin bands to low-energy states have been observed. Calculations based on the cranked Nilsson-Strutinsky formalism have been used to assign configurations to the observed bands. The main result of these calculations is that all 14 bands exhibit a stable triaxial deformation up to the highest observed spins, giving strong support to the existence of a triaxial minimum with normal deformation and positive asymmetry parameter in nuclei with a few holes in the N =82 shell closure.

  15. Mesoscale Banded Precipitation

    Science.gov (United States)

    2014-09-14

    Precipitation frequently falls and accumulates in discrete bands with accumulations that vary markedly over short distances. This module examines several mechanisms that result in mesoscale banded precipitation, focusing primarily on processes at work in midlatitude cyclones. The module starts with a review of the Norwegian and conveyor belt cyclone models. Then several banding processes are examined in detail, including deformation/frontogenesis, the Trowal (Trough of Warm Air Aloft), frontal merger, CSI/slantwise convection, and melting/evaporation-induced circulations. The module concludes with discussions of the representation of banded precipitation by NWP models and the detection of banded precipitation with satellite sensors.

  16. Electronic Band Structure and Sub-band-gap Absorption of Nitrogen Hyperdoped Silicon.

    Science.gov (United States)

    Zhu, Zhen; Shao, Hezhu; Dong, Xiao; Li, Ning; Ning, Bo-Yuan; Ning, Xi-Jing; Zhao, Li; Zhuang, Jun

    2015-01-01

    We investigated the atomic geometry, electronic band structure, and optical absorption of nitrogen hyperdoped silicon based on first-principles calculations. The results show that all the paired nitrogen defects we studied do not introduce intermediate band, while most of single nitrogen defects can introduce intermediate band in the gap. Considering the stability of the single defects and the rapid resolidification following the laser melting process in our sample preparation method, we conclude that the substitutional nitrogen defect, whose fraction was tiny and could be neglected before, should have considerable fraction in the hyperdoped silicon and results in the visible sub-band-gap absorption as observed in the experiment. Furthermore, our calculations show that the substitutional nitrogen defect has good stability, which could be one of the reasons why the sub-band-gap absorptance remains almost unchanged after annealing. PMID:26012369

  17. Decay out of a Superdeformed Band

    OpenAIRE

    Gu, J. Z.; Weidenmueller, H. A.

    1999-01-01

    Using a statistical model for the normally deformed states and for their coupling to a member of the superdeformed band, we calculate the ensemble average and the fluctuations of the intensity for decay out of the superdeformed band and of the intraband decay intensity. We show that both intensities depend on two dimensionless variables: The ratio $\\Gamma^{\\downarrow}/\\Gamma_S$ and the ratio $\\Gamma_N/d$. Here, $\\Gamma^{\\downarrow}$ is the spreading width for the mixing of t...

  18. Electrically Tunable Band Gap in Silicene

    OpenAIRE

    Drummond, Neil; Zolyomi, Viktor; Falko, Vladimir

    2011-01-01

    We report calculations of the electronic structure of silicene and the stability of its weakly buckled honeycomb lattice in an external electric field oriented perpendicular to the monolayer of Si atoms. We find that the electric field produces a tunable band gap in the Dirac-type electronic spectrum, the gap being suppressed by a factor of about eight by the high polarizability of the system. At low electric fields, the interplay between this tunable band gap, which is spec...

  19. Band structures in 99Rh

    International Nuclear Information System (INIS)

    Excited states in the 99Rh nucleus were populated using the fusion-evaporation reaction 75As(28Si,2p2n) at Elab=120 MeV and the de-excitations were investigated through in-beam ?-ray spectroscopic techniques using the INGA spectrometer consisting of 18 clover detectors. The observed band structures are discussed in the framework of tilted axis cranking shell-model calculations. Level structures at low energies are identified as resulting from the rotational bands based on the ?p1/2 and ?g9/2 configurations. The ?I = 1 coupled bands are observed at higher excitation energies and have been interpreted as based on the ?g9/2??g7/2??d5/2, ?p1/2??h11/2??d5/2 and ?g9/2??h11/2??g7/2 configurations. Calculations based on cranked Nilsson–Strutinsky (CNS) formalism have been performed to interpret the favoured states with I? = (41/2?, 43/2?) and (51/2?, 53/2?) as maximal spin aligned states built on the valence space ?(d5/2g7/2)15/2,17/23(h11/2)11/21 configuration combined with the fully-aligned ?(g9/2)25/25 configuration and the ?(g9/2)15/25 configuration with one anti-aligned g9/2 proton, respectively. (paper)

  20. Band structure of honeycomb photonic crystal slabs

    OpenAIRE

    Weng, Tai-i; Guo, G. Y.

    2006-01-01

    Two-dimensional (2D) honeycomb photonic crystals with cylinders and connecting walls have the potential to have a large full band gap. In experiments, 2D photonic crystals do not have an infinite height, and therefore, we investigate the effects of the thickness of the walls, the height of the slabs and the type of the substrates on the photonic bands and gap maps of 2D honeycomb photonic crystal slabs. The band structures are calculated by the plane wave expansion method an...

  1. Declination Calculator

    National Oceanic and Atmospheric Administration, Department of Commerce — Declination is calculated using the current International Geomagnetic Reference Field (IGRF) model. Declination is calculated using the current World Magnetic Model...

  2. Bolus calculators.

    Science.gov (United States)

    Schmidt, Signe; Nørgaard, Kirsten

    2014-09-01

    Matching meal insulin to carbohydrate intake, blood glucose, and activity level is recommended in type 1 diabetes management. Calculating an appropriate insulin bolus size several times per day is, however, challenging and resource demanding. Accordingly, there is a need for bolus calculators to support patients in insulin treatment decisions. Currently, bolus calculators are available integrated in insulin pumps, as stand-alone devices and in the form of software applications that can be downloaded to, for example, smartphones. Functionality and complexity of bolus calculators vary greatly, and the few handfuls of published bolus calculator studies are heterogeneous with regard to study design, intervention, duration, and outcome measures. Furthermore, many factors unrelated to the specific device affect outcomes from bolus calculator use and therefore bolus calculator study comparisons should be conducted cautiously. Despite these reservations, there seems to be increasing evidence that bolus calculators may improve glycemic control and treatment satisfaction in patients who use the devices actively and as intended. PMID:24876436

  3. Investigation of chiral bands in {sup 106}Ag

    Energy Technology Data Exchange (ETDEWEB)

    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

    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.

  4. Flat bands in the Weaire–Thorpe model and silicene

    Science.gov (United States)

    Hatsugai, Y.; Shiraishi, K.; Aoki, H.

    2015-02-01

    In order to analytically capture and identify peculiarities in the electronic structure of silicene, the Weaire–Thorpe (WT) model, a standard model for treating three-dimensional (3D) silicon, is applied to silicene with a buckled 2D structure. In the original WT model for four hybridized sp3 orbitals on each atom along with inter-atom hopping, the band structure can be systematically examined in 3D, where flat (dispersionless) bands exist as well. For examining silicene, here we re-formulate the WT model in terms of the overlapping molecular-orbital (MO) method which enables us to describe flat bands away from the electron–hole symmetric point. The overlapping MO formalism indeed enables us to reveal an important difference: while in 3D the dipersive bands with cones are sandwiched by doubly-degenerate flat bands, in 2D the dipersive bands with cones are sandwiched by triply-degenerate and non-degenerate (nearly) flat bands, which is consistent with the original band calculation by Takeda and Shiraishi. Thus there emerges a picture for why the whole band structure of silicene comprises a pair of dispersive bands with Dirac cones with each of the bands touching a nearly flat (narrow) band at ?. We can also recognize that, for band engineering, the bonds perpendicular to the atomic plane are crucial, and that ferromagnetism or structural instabilities are expected if we can shift the chemical potential close to the flat bands.

  5. Chiral bands in 105Rh

    Scientific Electronic Library Online (English)

    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.

    2004-09-01

    Full Text Available 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.

  6. Two-Photon Absorption in Size-Quantized Semiconductors with Degenerated Valence Band

    OpenAIRE

    Ismailov, T. G.

    2000-01-01

    Two photon absorption in size-quantized films of semiconductors with degenerated band structures are investigated. The carrier energy spectrum and wavefunctions in the bands are calculated using two-band Kane model with spin taken into accont. Two-photon absorption coefficients for different polarizations of incident radiations are calculated. The strong dependence of two-photon absorption on polarizations are stated.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-12-31

    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.

  8. 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

  9. Band gap of a topological insulator nanotube

    International Nuclear Information System (INIS)

    We study the electronic structure of a topological insulator Bi2Te3 cylindrical nanotube. The energy spectrum was calculated in the framework of the kp theory near the ? point of the surface Brilloiun zone. A band gap size dependence of the topological insulator nanotube was studied. A comparative analysis of the topological insulator direct band gap of Bi2Te3 and Bi2Se3 nanowires as a function of radius was performed. Due to a high surface-to-volume ratio, a variation in the ratio of the nanotube external radius to internal radius provides a 50-fold decrease in the topological insulator band gap compared to the respective bulk value. The size dependence of the topological insulator nanotube band gap is much stronger than that for the topological insulator nanowires. (authors)

  10. 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.

  11. Origin of the unusually large band-gap bowing and the breakdown of the band-edge distribution rule in the SnxGe1-x alloys

    Science.gov (United States)

    Yin, Wan-Jian; Gong, Xin-Gao; Wei, Su-Huai

    2008-10-01

    The unusual nonlinear behaviors of the band gaps in SnxGe1-x alloys are investigated using first-principles calculations. We show that the large bowing of the direct band gap is induced by the disordering effect. Moreover, we calculated individual contribution of the band-edge states and found that the bowing of the conduction band edge is much larger than the bowing of the valence band edge, although the natural valence-band offset between Ge and Sn is larger than the natural conduction-band offset. The breakdown of the band-edge distribution rule is explained by the large lattice mismatch between Ge and Sn and the large deformation potential of the band-edge states.

  12. Martindale Calculators

    Science.gov (United States)

    Martindale Calculators is a Web-based tool collection that contains over 19,000 online calculators created by over "3,450" very "creative" individuals, businesses and â??tax supported entities world wide.â? The collection is organized by the following topics: mathematics; statistics; science A-Z; chemistry; physics, astrophysics and astronomy; engineering A-Z; and electrical engineering, computer engineering, & computer science. Each section includes a wealth of websites to explore, all related to mathematical calculations, mostly course materials and articles. Another section lists online calculators relevant for various industries, such as aviation, cosmetics, insurance, and library science. The list is organized alphabetically and creatively stretches the meaning of â??calculatorâ? to include such things as name translators and databases on animal breeds.

  13. Analytical results for random band matrices with preferential basis

    CERN Document Server

    Frahm, K M

    1995-01-01

    Using the supersymmetry method we analytically calculate the local density of states, the localiztion length, the generalized inverse participation ratios, and the distribution function of eigenvector components for the superposition of a random band matrix with a strongly fluctuating diagonal matrix. In this way we extend previously known results for ordinary band matrices to the class of random band matrices with preferential basis. Our analytical results are in good agreement with (but more general than) recent numerical findings by Jacquod and Shepelyansky.

  14. Band-gap bowing, band offsets, and electron affinity for InGaN alloys: A DFT study.

    Science.gov (United States)

    Moses, Poul; van de Walle, Chris

    2009-03-01

    InGaN alloys are successfully being used in optical, electronic, and photovoltaic devices; a novel application is for photochemical water splitting. In order to further improve InGaN-based devices a detailed understanding of the materials properties as a function of alloy composition is needed. To obtain such insight we have investigated the band bowing and absolute band positions of InGaN alloys using density functional theory. The HSE exchange correlation functional has been used in order to accurately calculate the electronic band structure [1]. Detailed surface calculations have been performed that, combined with bulk calculations for alloys, yield information about the positions of valence and conduction bands on an absolute energy scale. We will discuss bowing effects, band offsets, and electron affinities in light of the application of InGaN alloys for photochemical hydrogen production. [1] J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 118, 8207 (2003)

  15. Decay of superdeformed bands

    International Nuclear Information System (INIS)

    One of the major challenges in the study of superdeformation is to directly connect the large number of superdeformed bands now known to the yrast states. In this way, excitation energies, spins and parities can be assigned to the levels in the second well which is essential to establish the collective and single-particle components of these bands. This paper will review some of the progress which has been made to understand the decay of superdeformed bands using the new arrays including the measurement of the total decay spectrum and the establishment of direct one-step decays from the superdeformed band to the yrast line in 194Hg. 42 refs., 5 figs

  16. Laparoscopic gastric banding

    Science.gov (United States)

    ... Gastric band may slip partly out of place Gastritis (inflamed stomach lining), heartburn , or stomach ulcers Infection ... You may be asked to stop taking aspirin, ibuprofen (Advil, Motrin), vitamin E, warfarin (Coumadin), and any ...

  17. Electronic band structure of CdF2

    International Nuclear Information System (INIS)

    Energy distribution curves (EDC) of electrons photoemitted (h?1 = 21.22 eV and h?2 = 40.8 eV) from the valence band (F-2p) and the Cd 4d band of a CdF2 crystal are measured and the valence and conduction band structures are calculated using the local empirical pseudopotential method (EPM). Comparison of the measured and calculated data show that the three main maxima measured in the valence band correspond well to the maxima in X5, L3, and X5 obtained in the calculated histogram of the valence band density of states. The influence of the final-state structure on the position of peaks in the valence band is not observed on EDCs obtained for both, h?1 and h?2 photoemission exciting energies. For Cd 4d band the wide splitting of 1.46 eV is obtained only for h?1 = 21.22 eV while it is not obtained on EDC for h?2 = 40.8 eV. This Cd 4d band splitting may be caused by the influence of the final density-of-states maximum obtained in conduction band in X1-point. The results obtained are compared with reflectivity data available in the literature. (author)

  18. EO-1 Hyperion and ALI bands simulation to Landat 7 ETM+ bands and comparison

    Science.gov (United States)

    Nikolakopoulos, Konstantinos G.; Skianis, Georgios Aim.; Vaiopoulos, Dimitrios A.

    2007-10-01

    Numerous satellite sensor systems have been launched during the last twenty years and satellite data are increasingly being used in regional or global vegetation monitoring. The observation of global vegetation from multiple satellites requires much effort to ensure continuity and compatibility due to differences in sensor characteristics and product generation algorithms. More recently the launch of hyperspectral sensor like Hyperion make the compatibility problem even more difficult as the very narrow hyperspectral bands need to be simulated to the broader multispectral bands before proceed to any further comparison. In this study we tried to compare multispectral (Landsat ETM + and EO-1 Advanced Land Imager) data with hyperspectral (Hyperion) data for the vegetation cover mapping of Milos Island. All the data were collected the same day within one-minute time. As a result the atmospheric conditions were exactly the same and that make the data ideal for comparison. The performance of the EO-1 Hyperion imaging spectrometer with the Advanced Land Imager (ALI) and the Landsat 7 ETM+ sensor was compared using a method that aggregated portions of the Hyperion 10 nm bands to simulate the broader multispectral bands of ALI and ETM+. The general process was to calculate a weighted sum of the Hyperion bands that covered each Landsat band. The weights used in the sum were derived, by comparing the spectral response of the hyperspectral bands with the respective multispectral band. The Normalized Difference Vegetation Index was used for the comparison of the three data sets and the results are presented in this study.

  19. Supersymmetry and Identical Bands

    OpenAIRE

    Von Brentano, P.

    2003-01-01

    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.

  20. Study of positive parity bands in 137Pr

    International Nuclear Information System (INIS)

    In this paper the analysis and interpretation of the positive parity states in 137Pr have been reported. The detailed interpretation with configuration assignments and the calculations for the bands will be reported

  1. Braille Calculator

    Directory of Open Access Journals (Sweden)

    Yoshit V. Gidh

    2013-02-01

    Full Text Available A thorough grounding in mathematics enhances educational and occupational opportunities for all people, whether sighted or visually impaired. In day-to-day routines, a practical understanding of mathematics allows a person to function more successfully and independently.? Access to, and doing mathematics, is one of the biggest obstacles for blind students in school and at the university. Our Braille Calculator will present new approaches to offering blind students better access to math, to provide new tools for doing math. In this report, the basic problems and solutions to the problem are discussed as a means of laying the groundwork for our Braille Calculator. Many aspects and concepts of mathematics are visual and spatial in nature. Students who are blind or visually impaired, and their teachers, now have standards which are closely aligned with those used for sighted students. Braille mathematics standards are essential to ensure that functionally blind students become literate in mathematics. However for complex engineering and statistical calculations even sighted students have to depend on Calculator. So we came up with an idea of Braille Calculator

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

    OpenAIRE

    Worasak SUKKABOT

    2014-01-01

    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 qua...

  3. Band structure of DyN and SmN

    CERN Document Server

    Preston, A R H; Housden, D H; Ludbrook, B; Ruck, B J; Trodahl, H J; Bittar, A; Williams, G V M; Downes, J E; Smith, K E; Lambrecht, W R L

    2007-01-01

    We investigate the electronic band structure of two of the rare-earth nitrides, DyN and SmN. Resistivity measurements imply that both materials have a semiconducting ground state, and both show resistivity anomalies coinciding with the magnetic transition, despite the different magnetic states in DyN and SmN. X-ray absorption and emission measurements are in excellent agreement with LSDA+U calculations, although for SmN the calculations predict a zero band gap.

  4. Electron currents associated with an auroral band

    International Nuclear Information System (INIS)

    Measurements of electron pitch angle distributions and energy spectra over a broad auroral band were used to calculate net electric current carried by auroral electrons in the vicinity of the band. The particle energy spectrometers were carried by a Nike-Tomahawk rocket launched from Poker Flat, Alaska, at 0722 UT on February 25, 1972. Data are presented which indicate the existence of upward field-aligned currents of electrons in the energy range 0.5-20 keV. The spatial relationship of these currents to visual structure of the auroral arc and the characteristics of the electrons carrying the currents are discussed

  5. Characterization of superdeformed bands in 62Zn

    International Nuclear Information System (INIS)

    Combined data from four fusion-evaporation reaction experiments were utilized to investigate deformed and superdeformed structures in 3062Zn32. Combination of the Gammasphere ?-ray spectrometer and ancillary particle detection systems allowed for the connection of rotational bands to well-known, low-lying excited states in 62Zn, as well as spectroscopy of discrete high-spin states reaching excitation energies of Ex=42.5 MeV. Four well- or superdeformed bands in 62Zn are characterized and described by means of cranked Nilsson-Strutinsky calculations.

  6. The behaviour of the moment of inertia curve in a recrossing of the ground state band and the super band in 158Er

    International Nuclear Information System (INIS)

    The recrossing of the ground state band with the super band as an explanation for the second anomaly in 158Er is examined in terms of the moment of inertia. A two band mixing calculation does not reproduce the experimenal moment of inertia curve

  7. 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)

  8. Inflation Calculator

    Science.gov (United States)

    Friedman, S. Morgan.

    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.

  9. Tunable and sizable band gap in silicene by surface adsorption

    OpenAIRE

    Quhe, Ruge; Fei, Ruixiang; Liu, Qihang; Zheng, Jiaxin; Li, Hong; Xu, Chengyong; Ni, Zeyuan; Wang, Yangyang; Yu, Dapeng; Gao, Zhengxiang; Lu, Jing

    2012-01-01

    Opening a sizable band gap without degrading its high carrier mobility is as vital for silicene as for graphene to its application as a high-performance field effect transistor (FET). Our density functional theory calculations predict that a band gap is opened in silicene by single-side adsorption of alkali atom as a result of sublattice or bond symmetry breaking. The band gap size is controllable by changing the adsorption coverage, with an impressive maximum band gap up to 0.50?eV. The ab...

  10. Synthesizing folded band chaos.

    Science.gov (United States)

    Corron, Ned J; Hayes, Scott T; Pethel, Shawn D; Blakely, Jonathan N

    2007-04-01

    A randomly driven linear filter that synthesizes Lorenz-like, reverse-time chaos is shown also to produce Rössler-like folded band wave forms when driven using a different encoding of the random source. The relationship between the topological entropy of the random source, dissipation in the linear filter, and the positive Lyapunov exponent for the reverse-time wave form is exposed. The two drive encodings are viewed as grammar restrictions on a more general encoding that produces a chaotic superset encompassing both the Lorenz butterfly and Rössler folded band paradigms of nonlinear dynamics. PMID:17500950

  11. Ultra wide band antennas

    CERN Document Server

    Begaud, Xavier

    2013-01-01

    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

  12. Calculation Software

    Science.gov (United States)

    1994-01-01

    MathSoft Plus 5.0 is a calculation software package for electrical engineers and computer scientists who need advanced math functionality. It incorporates SmartMath, an expert system that determines a strategy for solving difficult mathematical problems. SmartMath was the result of the integration into Mathcad of CLIPS, a NASA-developed shell for creating expert systems. By using CLIPS, MathSoft, Inc. was able to save the time and money involved in writing the original program.

  13. Braille Calculator

    OpenAIRE

    Gidh, Yoshit V.; Latey, Mahesh S.; Arpita Roy, Kunal Shah; Savita Ingle

    2013-01-01

    A thorough grounding in mathematics enhances educational and occupational opportunities for all people, whether sighted or visually impaired. In day-to-day routines, a practical understanding of mathematics allows a person to function more successfully and independently.? Access to, and doing mathematics, is one of the biggest obstacles for blind students in school and at the university. Our Braille Calculator will present new approaches to offering blind students better access to math, to ...

  14. 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

  15. An innovative band-to-band tunneling analytical model and implications in compact modeling of tunneling-based devices

    Science.gov (United States)

    De Michielis, L.; Da?tekin, N.; Biswas, A.; Lattanzio, L.; Selmi, L.; Luisier, M.; Riel, H.; Ionescu, A. M.

    2013-09-01

    In this paper, an analytical band-to-band tunneling model is proposed, validated by means of drift-diffusion simulation and comparison with experimental data, implemented in Verilog-A, and finally proven with SPICE simulator through simulation of circuits featuring tunneling diodes. The p-n junction current calculation starts from a non-local Band-to-Band tunneling theory including the electron-phonon interaction and therefore it is particularly suited for indirect semiconductor materials such as silicon- or germanium-based interband tunneling devices.

  16. DUAL BAND MONOPOLE ANTENNA DESIGN

    OpenAIRE

    P. Jithu; Paul, A; V. Pithadia; R. Misquitta; U. P. Khot

    2013-01-01

    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 GH...

  17. DUAL BAND MONOPOLE ANTENNA DESIGN

    Directory of Open Access Journals (Sweden)

    P. Jithu

    2013-06-01

    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.

  18. Colloidal Nanoparticles for Intermediate Band Solar Cells

    Science.gov (United States)

    Voros, Marton; Galli, Giulia; Zimanyi, Gergely

    2015-03-01

    The Intermediate Band (IB) solar cell concept is a promising idea to transcend the Shockley-Queisser limit. Using the results of first principles calculations, we proposed that colloidal nanoparticles (CNPs) are a viable and efficient platform for the implementation of the IB solar cell concept. We focused on CdSe and we showed that intragap states present in the isolated dots with reconstructed surfaces combine to form an IB in arrays of NPs, which is well separated from the valence and conduction band edges. We also showed that in solution such IB may be electron doped using, e.g. decamethylcobaltocene, thus activating an IB-induced absorption process. Our results, together with the recent report of a nearly 9% efficient CNP solar cell indicate that colloidal nanoparticle intermediate band solar cells are a promising platform to overcome the Shockley-Queisser limit. The Intermediate Band (IB) solar cell concept is a promising idea to transcend the Shockley-Queisser limit. Using the results of first principles calculations, we proposed that colloidal nanoparticles (CNPs) are a viable and efficient platform for the implementation of the IB solar cell concept. We focused on CdSe and we showed that intragap states present in the isolated dots with reconstructed surfaces combine to form an IB in arrays of NPs, which is well separated from the valence and conduction band edges. We also showed that in solution such IB may be electron doped using, e.g. decamethylcobaltocene, thus activating an IB-induced absorption process. Our results, together with the recent report of a nearly 9% efficient CNP solar cell indicate that colloidal nanoparticle intermediate band solar cells are a promising platform to overcome the Shockley-Queisser limit. Work supported by NSF Solar Collaborative under DMR-1035468 and the Center for Advanced Solar Photophysics, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences.

  19. Symmetrical band-pass loudspeaker systems

    Science.gov (United States)

    Matusiak, Grzegorz Piotr

    2001-12-01

    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.

  20. Graphene Nanoribbon Conductance Model in Parabolic Band Structure

    Directory of Open Access Journals (Sweden)

    Mohammad Taghi Ahmadi

    2010-01-01

    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.

  1. Edge configurational effect on band gaps in graphene nanoribbons

    Science.gov (United States)

    Deepika, Kumar, T. J. Dhilip; Shukla, Alok; Kumar, Rakesh

    2015-03-01

    In this article, we put forward a resolution to the prolonged ambiguity in energy band gaps between theory and experiments of fabricated graphene nanoribbons (GNRs). Band structure calculations using density functional theory are performed on oxygen-passivated GNR supercells of customized edge configurations without disturbing the inherent s p2 hybridization of carbon atoms. Direct band gaps are observed for both zigzag and armchair GNRs, consistent with the experimental reports. In addition, we provide an explanation of the experimentally observed scattered band gap values of GNRs as a function of width in a crystallographic orientation on the basis of edge configurations. We conclude that edge configurations of GNRs significantly contribute to band gap formation in addition to its width for a given crystallographic orientation and will play a crucial role in band gap engineering of GNRs for future research on fabrication of nanoelectronic devices.

  2. Elucidating the stop bands of structurally colored systems through recursion

    CERN Document Server

    Amir, Ariel

    2012-01-01

    Interference phenomena are the source of some of the spectacular colors of animals and plants in nature. In some of these systems, the physical structure consists of an ordered array of layers with alternating high and low refractive indices. This periodicity leads to an optical band structure that is analogous to the electronic band structure encountered in semiconductor physics; namely, specific bands of wavelengths (the stop bands) are perfectly reflected. Here, we present a minimal model for optical band structure in a periodic multilayer and solve it using recursion relations. We present experimental data for various beetles, whose optical structure resembles the proposed model. The stop bands emerge in the limit of an infinite number of layers by finding the fixed point of the recursive relations. In order for these to converge, an infinitesimal amount of absorption needs to be present, reminiscent of the regularization procedures commonly used in physics calculations. Thus, using only the phenomenon of...

  3. Fractal Property of Band Branching in Fibonacci Mesoscopic Rings

    Science.gov (United States)

    Wen-Jeng Hsueh,; Ren-Zheng Qiu,; Chih-Wei Wu,

    2010-06-01

    We present the branching rules of the energy spectrum for a one-dimensional Fibonacci array of AB rings with an arbitrary generation based on the band map diagram. A band edge equation with the recursive scheme is used in calculating the band map to avoid numerical instability. We find that the energy spectrum for the Fibonacci AB rings with an arbitrary generation can be divided to several regions, each of which has a similar pattern. As the generation order is greater than two, the characteristics of the subbands branching in each region, including the zero transmission lines, the enveloped group bands, the major subgaps, convergence of the group bands and major subgaps for a higher generation, and number of splitting subbands in each group band for an arbitrary generation, have been proposed in the study. Moreover, electron localization in the major subgaps of the Fibonacci rings is demonstrated by the transmission spectra.

  4. Analysis and machine mapping of the distribution of band recoveries

    Science.gov (United States)

    Cowardin, L.M.

    1977-01-01

    A method of calculating distance and bearing from banding site to recovery location based on the solution of a spherical triangle is presented. X and Y distances on an ordinate grid were applied to computer plotting of recoveries on a map. The advantages and disadvantages of tables of recoveries by State or degree block, axial lines, and distance of recovery from banding site for presentation and comparison of the spatial distribution of band recoveries are discussed. A special web-shaped partition formed by concentric circles about the point of banding and great circles at 30-degree intervals through the point of banding has certain advantages over other methods. Comparison of distributions by means of a X? contingency test is illustrated. The statistic V = X?/N can be used as a measure of difference between two distributions of band recoveries and its possible use is illustrated as a measure of the degree of migrational homing.

  5. 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)

  6. Rubber Band Racer

    Science.gov (United States)

    Watsonville Environmental Science Workshop

    2011-01-01

    In this activity, learners construct speedy vehicles made out of paper plates and powered by twisted rubber bands. This toy is an excellent demonstration of potential and kinetic energy and how things move. This project can also be used to help learners understand Newton's Laws of Motion and friction. Activity guide has detailed step-by-step instructions, illustrations, and focus questions.

  7. Rubber Band Thermodynamics

    Science.gov (United States)

    2012-04-09

    In this demonstration, learners explore the thermal properties of rubber. Learners investigate whether a rubber band contracts or expands when heated. Learners discover that when rubber is heated it behaves differently than most familiar materials. Most materials expand when they are heated, but rubber contracts.

  8. Rubber Band Boat

    Science.gov (United States)

    Watsonville Environmental Science Workshop

    2011-01-01

    In this activity, learners build styrofoam boats powered by twisted rubber bands. Use this activity to introduce learners to potential energy, kinetic energy, Newton's Laws of Motion, rotational motion, and density. Note: a drill is required for this activity, and is not included in the cost of materials.

  9. Rubber Band Car

    Science.gov (United States)

    WGBH

    2010-01-01

    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.

  10. The Rubber Band Problem

    Science.gov (United States)

    A simple experimental apparatus made of rubber band and books is used by student teams challenged with demonstrating the concepts of friction, force, and inertia. This resource is from PUMAS - Practical Uses of Math and Science - a collection of brief examples created by scientists and engineers showing how math and science topics taught in K-12 classes have real world applications.

  11. Rubber Band newton Scale

    Science.gov (United States)

    Don Rathjen

    2009-01-01

    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.

  12. Calculator calculus

    CERN Document Server

    McCarty, George

    1982-01-01

    How THIS BOOK DIFFERS This book is about the calculus. What distinguishes it, however, from other books is that it uses the pocket calculator to illustrate the theory. A computation that requires hours of labor when done by hand with tables is quite inappropriate as an example or exercise in a beginning calculus course. But that same computation can become a delicate illustration of the theory when the student does it in seconds on his calculator. t Furthermore, the student's own personal involvement and easy accomplishment give hi~ reassurance and en­ couragement. The machine is like a microscope, and its magnification is a hundred millionfold. We shall be interested in limits, and no stage of numerical approximation proves anything about the limit. However, the derivative of fex) = 67.SgX, for instance, acquires real meaning when a student first appreciates its values as numbers, as limits of 10 100 1000 t A quick example is 1.1 , 1.01 , 1.001 , •••• Another example is t = 0.1, 0.01, in the functio...

  13. 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)

  14. Origin of the unusually large band gap bowing and the breakdown of the band-edge distribution rule in the SnxGe1-x alloys

    Science.gov (United States)

    Yin, Wan-Jian; Gong, Xin-Gao; Wei, Su-Huai

    2009-03-01

    Most semiconductor alloy AxB1-x has a non-linear dependence of its band gap Eg(x) as a function of the alloy composition x, and the variation is usually described by a parabolic function Eg(x) = xEg^A + (1-x)Eg^B - bgx(1-x), where Eg^A and Eg^B are the band gaps of A and B at their respective equilibrium lattice constants and bg is the so-called bowing parameter. The conventional band-edge distribution of bg is usually described by the equation bVBM(CBM) = ?EVBM(CBM)/?Egbg , where ?EVBM(CBM) and ?EVBM(CBM) are VBM and CBM natural band offsets. Using first-principles calculations, we investigate the unusual nonlinear behaviors of the band gaps in SnxGe1-x alloys. We show that the large bowing of the direct band gap is induced by the disordering effect. Moreover, we calculated individual contribution of the band edge states and find that the bowing of the conduction band edge is much larger than the bowing of the valence band edge, although the natural valence band offset between Ge and Sn is larger than the natural conduction band offset. The breakdown of the band-edge distribution rule is explained by the large lattice mismatch between Ge and Sn and the large deformation potential of the band edge states.

  15. Rotational and vibrational bands in 108Pd

    Scientific Electronic Library Online (English)

    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.

    2004-09-01

    Full Text Available 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.

  16. Population of rotational bands in superheavy nuclei

    OpenAIRE

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

    2012-01-01

    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...

  17. Ab Initio Calculations of Oxosulfatovanadates

    DEFF Research Database (Denmark)

    FrØberg, Torben; Johansen, Helge

    1996-01-01

    Restricted Hartree-Fock and multi-configurational self-consistent-field calculations together with secondorder perturbation theory have been used to study the geometry, the electron density, and the electronicspectrum of (VO2SO4)-. A bidentate sulphate attachment to vanadium was found to be stable with anO-V-O angle of 72.5 degrees . The calculated spectrum shows bands in reasonable agreement with anexperimental spectrum which has been attributed to (VO2SO4)-. The geometry and the electron density fortwo binuclear vanadium complexes proposed as intermediates in the vanadium catalyzed SO2 oxidationhave further been studied.

  18. Structures calculation

    International Nuclear Information System (INIS)

    Structures calculation is a research and applications field in permanent evolution thanks to the development of more and more performing computer tools for the modeling and the numerical simulation of complex structures taking into account the behaviour of more and more sophisticated materials. The aim of the Computational Structural Mechanics Association (CSMA) is to develop technical and scientific exchanges between industrial and research partners. This colloquium, organized every 2 years comprises 4 general conferences and 125 communications. Five papers were selected for INIS. Three of them deal with the dynamical modeling of the vibrational behaviour of reactor core components (fuel assemblies and control rod clusters), one concerns the load resistance of multi-perforated metal structures like steam generator tube plates or turbine blades, and the last paper concerns the humidity stability of composite materials used in particle detectors. (J.S.)

  19. AMNIOTIC BAND SYNDROME

    Directory of Open Access Journals (Sweden)

    Jovana ?or?evi?

    2009-04-01

    Full Text Available Amniotic band syndrome (ABS is a set of congenital malformations attributed to amniotic bands that entangle fetal parts during intrauterine life, which results in a broad spectrum of anatomic disturbances - ranging from minor constriction rings and lymphedema of the digits to complex, bizarre multiple congenital anomalies incompatible with life. ABS is not very often, but should be considered in every newborn with congenital anomalies, especially defects of extremities and/or body walls. ABS can be diagnosed prenatally by ultrasound; otherwise, the defects are seen after birth. Child's karyotyping is of great importance, in order to avoid misdiagnosis and incorrect information of recurrence risk. A team of specialists should be included in the treatment and follow-up of children with ABS, according to individual needs of every single patient.The aim of this paper is to point out diagnostic and therapeutic approaches in newborns with ABS trough the report of two cases.

  20. Bandcrossing of magnetic rotation bands in 137Pr

    International Nuclear Information System (INIS)

    The odd mass nucleus 137Pr has been studied to high spins in order to investigate the magnetic rotation phenomenon in mass 130 region using the 122Sn(19F,4n)137Pr reaction at a beam energy of 80 MeV. A known ?I=1 band has been extended to J?=47/2- with the addition of three new transitions. Directional Correlation of Oriented Nuclei (DCO) ratios and linear polarization measurements have been performed to assign the multipolarities of gamma transitions and the spins and parities of the energy levels in this band, now established as the M1 band. The combination of M1 transitions along with cross over E2 transitions have been observed in this band for the first time. The experimentally deduced B(M1)/B(E2) ratios show a decrease with increasing spin after band-crossing suggesting magnetic rotation. TAC calculations for the 3qp: ?h11/2 x ?(h11/2)-2 configuration reproduce the experimental observations in the lower spin part of the ?I=1 band and the 5qp: ?h11/2(g7/2)2 x ?(h11/2)-2 configuration reproduces the ?I=1 band at higher spins; the crossing of the bands based on the two configuration leads to a back-bending also. Theoretical calculations also support a magnetic rotation nature for both the configurations

  1. 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.

  2. Computational optical band gap bowing of III-V semiconductors alloys

    Energy Technology Data Exchange (ETDEWEB)

    Ferhat, M. [Departement de Physique, Universite des Sciences et de la Technologie d' Oran (USTO), Oran (Algeria)

    2004-08-01

    A phenomenological model is described for the calculations of the optical band bowing of III-V semiconductor alloys. The optical band gap bowing is shown to account successfully for theoretical calculations and the experimental data. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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

    Science.gov (United States)

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

    2013-01-01

    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.

  4. Semiconductors bonds and bands

    CERN Document Server

    Ferry, David K

    2013-01-01

    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.

  5. Rotational bands and shape changes in 105Rh

    International Nuclear Information System (INIS)

    The 105Rh nucleus has been studied by in-beam ? spectroscopy with the heavy-ion fusion-evaporation reaction 100Mo(11B, ?2n?) at 39 MeV. Gamma-gamma-t coincidences and directional correlation ratios were measured. Four rotational bands have been identified with similar characteristics to those in other A?100 odd-proton nuclei. The positive-parity yrast band based on the ?g9/2 configuration and the negative-parity ?p1/2 band, showing large signature splittings, exhibit band crossings at the frequencies of 0.38 MeV and 0.48 MeV, respectively. Experimental Routhians and alignments as well as B(M1)/B(E2) ratios were extracted. The structure of the bands was interpreted within the framework of the cranked shell model and total Routhian surface calculations. copyright 1997 The American Physical Society

  6. Tunable and sizable band gap in silicene by surface adsorption

    Science.gov (United States)

    Quhe, Ruge; Fei, Ruixiang; Liu, Qihang; Zheng, Jiaxin; Li, Hong; Xu, Chengyong; Ni, Zeyuan; Wang, Yangyang; Yu, Dapeng; Gao, Zhengxiang; Lu, Jing

    2012-01-01

    Opening a sizable band gap without degrading its high carrier mobility is as vital for silicene as for graphene to its application as a high-performance field effect transistor (FET). Our density functional theory calculations predict that a band gap is opened in silicene by single-side adsorption of alkali atom as a result of sublattice or bond symmetry breaking. The band gap size is controllable by changing the adsorption coverage, with an impressive maximum band gap up to 0.50?eV. The ab initio quantum transport simulation of a bottom-gated FET based on a sodium-covered silicene reveals a transport gap, which is consistent with the band gap, and the resulting on/off current ratio is up to 108. Therefore, a way is paved for silicene as the channel of a high-performance FET. PMID:23152944

  7. A Multi-band Wavelet Watermarking Scheme

    Directory of Open Access Journals (Sweden)

    Xiangui Kang

    2008-03-01

    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.

  8. Electronic band structure and photoemission: A review and projection

    International Nuclear Information System (INIS)

    A brief review of electronic-structure calculations in solids, as a means of interpreting photoemission spectra, is presented. The calculations are, in general, of three types: ordinary one-electron-like band structures, which apply to bulk solids and are the basis of all other calculations; surface modified calculations, which take into account, self-consistently if at all possible, the presence of a vacuum-solid interface and of the electronic modifications caused thereby; and many-body calculations, which go beyond average-field approximations and consider dynamic rearrangement effects caused by electron-electron correlations during the photoemission process. 44 refs

  9. 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

  10. Conduction band energy levels in superlattices with complex unit cells

    International Nuclear Information System (INIS)

    The conduction band energy levels and wavefunctions in a number of superlattices with more than two layers per unit cell have been calculated using an effective mass model. Many of these structures exhibit energy levels which can be modeled as resulting from a conventional superlattice with a modified bulk conduction band minimum in the effective wells. These structures should be useful for extending the size of the superlattice periods in strained-layer superlattices

  11. Flat-band ferromagnetism in quantum dot superlattices

    OpenAIRE

    Tamura, Hiroyuki; SHIRAISHI, KENJI; Kimura, Takashi; Takayanagi, Hideaki

    2001-01-01

    Possibility of flat-band ferromagnetism in quantum dot arrays is theoretically discussed. By using a quantum dot as a building block, quantum dot superlattices are possible. We consider dot arrays on Lieb and kagome lattices known to exhibit flat band ferromagnetism. By performing an exact diagonalization of the Hubbard Hamiltonian, we calculate the energy difference between the ferromagnetic ground state and the paramagnetic excited state, and discuss the stability of the f...

  12. Systematic description of superdeformed bands in the mass-190 region

    Energy Technology Data Exchange (ETDEWEB)

    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

    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.

  13. Strain modulated band gap of edge passivated armchair graphene nanoribbons

    CERN Document Server

    Peng, Xihong

    2011-01-01

    First principles calculations were performed to study strain effects on band gap of armchair graphene nanoribbons (AGNRs)with different edge passivation, including H, O, and OH group. The band gap of the H-passivated AGNRs shows a nearly periodic zigzag variation under strain. For O and OH passivation, the zigzag patterns are significantly shifted by a modified quantum confinement due to the edges. In addition, the band gap of the O-passivated AGNRs experiences a direct-to-indirect transition with sufficient tensile strain (~5%). The indirect gap reduces to zero with further increased strain.

  14. Transition temperature of two-band superconductors with Anderson impurities

    International Nuclear Information System (INIS)

    The influence of impurities on the superconducting transition temperature of two-band superconductors containing Anderson impurities is investigated. It is found that the concentration-dependent transition temperature shows typical departures from the formula for a single-band superconductor. These departures occur because of the interband scattering of conduction electrons on impurities. The calculations reveal clearly that in the presence of impurities the effective pairing interaction becomes coupling-parameter dependent, giving rise to a new pair-weakening mechanism. Analytic results for T/sub c/ on the basis of this simple two-band model are presented

  15. 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

  16. Multiple triaxial bands and abnormal signature inversion in As3374

    OpenAIRE

    Hu, Shi-PengChina Institute of Atomic Energy, Beijing 102413, China; Ma, Hai-Liang(China Institute of Atomic Energy, Beijing 102413, China); Cao, Xue-Peng(China Institute of Atomic Energy, Beijing 102413, China); Wu, Xiao-Guang(China Institute of Atomic Energy, Beijing 102413, China); Zhang, Huan-Qiao(China Institute of Atomic Energy, Beijing 102413, China); Hua, Hui; Sun, Jun-Jie(School of Physics, State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China); Sun, Hui-Bin(College of Physics Science and Technology, Shenzhen University, Shenzhen 518060, China); He, Chuang-Ye; Zheng, Yun; Li, Guang-Sheng(China Institute of Atomic Energy, Beijing 102413, China); Li, Cong-Bo(China Institute of Atomic Energy, Beijing 102413, China); Yao, Shun-He(China Institute of Atomic Energy, Beijing 102413, China); Yu, Bei-Bei(China Institute of Atomic Energy, Beijing 102413, China); Wang, Jin-Long

    2014-01-01

    Excited states of the odd–odd nucleus 74 As 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 hi...

  17. A new construction algorithm of narrow-band function for artificial history simulation method based on narrow-band superposition

    International Nuclear Information System (INIS)

    In this paper, a new type of narrow-band function is proposed for the artificial history simulation method based on narrow-band superposition, which aims to meet the needs of both fitting of the target response spectrum and envelop of the power spectral density. The new narrow-band function is based on the normal distribution function and trigonometric functions. Its band width can be controlled and it decays rapidly on both sides. While the target response spectrum is fitted by superimposing the new narrow-band time history, the power spectral density is enveloped by modifying the Fourier amplitude spectrum locally. The numerical example demonstrates that not only the artificial time history generated by this algorithm reaches high matching precision to the target response spectrum, but also the corresponding calculated power spectrum envelopes the target power spectrum. (authors)

  18. Bulk band structure of Bi2Te3

    DEFF Research Database (Denmark)

    Michiardi, Matteo; Aguilera, Irene

    2014-01-01

    The bulk band structure of Bi2Te3 has been determined by angle-resolved photoemission spectroscopy and compared to first-principles calculations. We have performed calculations using the local density approximation (LDA) of density functional theory and the one-shot GW approximation within the all-electron full-potential linearized augmented-plane-wave (FLAPW) formalism, fully taking into account spin-orbit coupling. Quasiparticle effects produce significant changes in the band structure of Bi2Te3 when compared to LDA. Experimental and calculated results are compared in the spectral regions where distinct differences between the LDA and GW results are present. Overall a superior agreement with GW is found, highlighting the importance of many-body effects in the band structure of this family of topological insulators.

  19. Double crossing of the ground rotational band and super band

    International Nuclear Information System (INIS)

    We suggest that the crossing of the ground rotational band by a second rotational-aligned band may in fact be a double crossing. From extrapolations of the rotational energy formula, we show that one could expect such a second crossing around I approx. = 30 in 158Er. This provides an alternative explanation in terms of a double band crossing for the second discontinuity recently observed in the moment of inertia about I = 28 in 158Er

  20. M-Band Graphic Equalizer

    Directory of Open Access Journals (Sweden)

    Dr. P. Mallikarjuna Rao

    2011-08-01

    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.

  1. Himmelsmechanik. Band III: Gravitationstheorie.

    Science.gov (United States)

    Schneider, M.

    This book is the third in a now four volume set (for the first volume see 55.003.023, the second see 58.003.013). Der dritte Band des Lehrbuchs über Himmelsmechanik behandelt deren Formulierung auf der Grundlage der Einsteinschen Gravitationstheorie. Dargestellt werden zunächst die Strukturen der Minkowskischen Raumzeit und ihre Folgen für die Orts- und Zeitmessung. Anschließend werden die Einsteinsche Raumzeit durch eine konstruktive Axiomatik begründet und die Einsteinschen Feldgleichungen aufgestellt. Ausführlich werden das Schwarzschild-Problem, lineare und nach-Newtonsche Näherungen der Feld- und Bewegungsgleichungen behandelt. Daran schließt sich an die Behandlung der Ausbreitung elektromagnetischer Wellen und eine Theorie der Bezugssysteme in der Einsteinschen Raumzeit. Breiten Raum nimmt die Darstellung des relativistischen Zwei- und N-Körper-Problems, die Spin-Bahn-Kopplung, die relativistische Theorie von Rotation und Figur von Körpern ein.

  2. Peculiarities of band structure in bivalent rare earth monosulfides

    International Nuclear Information System (INIS)

    Total and local partial densities of states in rare-earth (SmS, EuS, YbS) monosulfides were calculated by the Green function method. Calculational results are compared with the x-ray and x-ray electron spectroscopy data. It is established that in YbS and EuS in comparison with SmS a band of metal f-states moves away from the conductivity band bottom thus increasing the energy-gap width. It is concluded with provision for value of charge transfer between sulfur and REE atoms that chemical bond in REE monosulfides is not purely ionic

  3. Description of the candidate chiral doublet bands in 98Tc

    International Nuclear Information System (INIS)

    The candidate chiral doublet bands in 98Tc with configuration ?g9/2 ? ?h11/2 are studied theoretically for the first time via the triaxial particle rotor model. The main properties of the doublet bands including the energy spectra and electromagnetic transitions are calculated for different triaxiality parameter ?, and the data in 98Tc can be well described by the calculations with ? = 38°. Based on the analysis of angular momentum components, it is found that the chiral rotational geometry in 98Tc deviates from the ideal chiral picture. (authors)

  4. Spectra of {gamma} rays feeding superdeformed bands

    Energy Technology Data Exchange (ETDEWEB)

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

    1995-08-01

    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.

  5. Multi-band quantum ratchets

    OpenAIRE

    Grifoni, M.; Ferreira, M. S.; Peguiron, J.; Majer, J. B.

    2002-01-01

    We investigate directed motion in non-adiabatically rocked ratchet systems sustaining few bands below the barrier. Upon restricting the dynamics to the lowest M bands, the total system-plus-bath Hamiltonian is mapped onto a discrete tight-binding model containing all the information both on the intra- and inter-well tunneling motion. A closed form for the current in the incoherent tunneling regime is obtained. In effective single-band ratchets, no current rectification occur...

  6. Development of Wide Band Feeds

    Science.gov (United States)

    Ujihara, H.; Ichikawa, R.

    2012-12-01

    Wide Band feeds are being developed at NICT, NAOJ, and some universities in Japan for VLBI2010, SKA, and MARBLE. SKA, the Square Kilometre Array, will comprise thousands of radio telescopes with square kilometer aperture size for radio astronomy. MARBLE consists of small portable VLBI stations developed at NICT and GSI in Japan. They all need wide band feeds with a greater than 1:10 frequency ratio. Thus we have been studying wide band feeds with dual linear polarization for these applications.

  7. Characterization of band structure for transverse acoustic phonons in Fibonacci superlattices by a bandedge formalism

    International Nuclear Information System (INIS)

    We present a divergence-free method to determine the characteristics of band structures and projected band structures of transverse acoustic phonons in Fibonacci superlattices. A set of bandedge equations is formulated to solve the band structures for the phonon instead of using the traditional dispersion relation. Numerical calculations show band structures calculated by the present method for the Fibonacci superlattice without numerical instability, which may occur in traditional methods. Based on the present formalism, the band structure for the acoustic phonons has been characterized by closure points and the projected bandgaps of the forbidden bands. The projected bandgaps are determined by the projected band structure, which is characterized by the cross points of the projected bandedges. We observed that the band structure and projected band structure and their characteristics were quite different for different generation orders and the basic layers for the Fibonacci superlattice. In this study, concise rules to determine these characteristics of the band structure and the projected band structure, including the number and the location of closure points of forbidden bands and those of projected bandgaps, in Fibonacci superlattices with arbitrary generation order and basic layers are proposed.

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

    International Nuclear Information System (INIS)

    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

  9. Obtaining an intermediate band photovoltaic material through the Bi insertion in CdTe

    OpenAIRE

    Seminóvski Pérez, Yohanna; Palacios Clemente, Pablo; Wahnón Benarroch, Perla

    2013-01-01

    Defect interaction can take place in CdTe under Te and Bi rich conditions. We demonstrate in this work through first principles calculations, that this phenomenon allows a Jahn Teller distortion to form an isolated half-filled intermediate band in the host semiconductor band-gap. This delocalized energy band supports the experimental deep level reported in the host band-gap of CdTe at a low bismuth concentration. Furthermore, the calculated optical absorption of CdTe:Bi in this work shows a s...

  10. Quasiparticle band structures and thermoelectric transport properties of p-type SnSe

    OpenAIRE

    Shi, Guangsha; Kioupakis, Emmanouil

    2014-01-01

    We used density functional and many-body perturbation theory to calculate the quasiparticle band structures and electronic transport parameters of p-type SnSe both for the low-temperature Pnma and high-temperature Cmcm phases. The Pnma phase has an indirect band gap of 0.829 eV while the Cmcm has a direct band gap of 0.464 eV. Both phases exhibit multiple local band extrema within an energy range comparable to the thermal energy of carriers from the global extrema. We calcul...

  11. Single Band Helical Antenna in Axial Mode

    Directory of Open Access Journals (Sweden)

    Parminder Singh

    2012-11-01

    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

  12. Comparison between ab initio energy band structures of various chlorinated polyethylene derivatives

    Science.gov (United States)

    Assad Abdel-Raouf, Mohamed

    1989-09-01

    The band structures of various chlorinated polyethylene derivatives are calculated using an ab initio self-consisten field (SCF) linear combination of atomic orbitals (LCAO) technique. The results illustrate that the conduction band is shifted steadily towards lower energies as the number of chlorine atoms in the unit cell increases, and the gap between valence and conduction bands is decreased monotonically. The possibility of n-doping is explored. The comparison between the band structures of the chlorinated polymers and that of polytrifluorochloroethylene shows that the latter possesses a lower-lying conduction band and is, therefore, more adequate for doping.

  13. The transverse wakefield calculated by double circuit model

    CERN Document Server

    Bin, Yang Xiong

    2014-01-01

    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.

  14. A well-deformed band in 134 Pr

    International Nuclear Information System (INIS)

    Available as short communication only. The high spin band structures in the odd-odd nucleus 134 Pr have been investigated via the 110 Pd (28 Si, p 3 n) reaction at a beam energy of 130 MeV. The beam was provided by the Tandem XTU accelerator in Legnaro. Gamma rays were detected with the GA.SP. detector array. About 400 million events consisting of triple and higher fold coincidences have been recorded, from which ?-? coincidence matrices have been constructed. Multipolarities were determined from DCO ratios. Previous results have been confirmed and extended, and, in addition, a well-deformed band has been observed. The transitions in this band were found to have the same multipolarity (assumed stretched quadrupole). This band strongly resembles the high j well-deformed intruder bands known in 134'136 Pm. We have also identified the transitions which de-excite this band (whose intensity in the lowest transitions is about 10% of the channel population) towards the normally deformed states. It is tempting to assign to this band a configuration ?h11/2 x ?i13/2 with the proton in the favoured signature, which leads to even spin values and negative parity. On the other hand, this band behaves like the one observed in 134 Pm, where the ?h11/2 x ? h9/2 configuration have been assigned. Preliminary CSM calculations seem to favour the later configuration. Total routhian surfr configuration. Total routhian surfaces provide a deformation ??0.2 for the normally deformed bands and ??0.3 for the well-deformed band. (Author) 1 Fig., 2 Refs

  15. Information retrieval from wide-band meteorological data - An example

    Science.gov (United States)

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

    1983-01-01

    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.

  16. Observation of the microstructure in the adiabatic shear band of 7075 aluminum alloy

    International Nuclear Information System (INIS)

    A considerable amount of adiabatic shear bands (ASBs) were obtained by means of the thick-walled cylinder (TWC) external explosive collapse technique. Two types of shear bands with different morphologies are distinguished on the cross-section of the tube, which are called deformed band and transformed band, respectively. Cracks are confirmed to develop from the transformed bands rather than the deformed band. Transmission electron microscopy (TEM) investigation indicates that ultrafine grains, with average size less than 100 nm, are produced at the center of the transformed band. At the edge of the transformed band the grains are elongated in the shearing direction. The grains in the matrix are two orders of magnitude larger than those in the transformed band. The precipitation within the shear band and the matrix is quite different. Calculation estimates that the temperature in the shear band exceeds the recrystallization temperature of the 7075 aluminum alloy. It is proposed that dynamic recrystallization occurs in the transformed band and produces the ultrafine grains. Microhardness test results show that the transformed band is much 'harder' than the matrix.

  17. New low-energy levels calculation for 155Eu

    Scientific Electronic Library Online (English)

    F. A., Genezini; C. B., Zamboni; J., Mesa; M. T. F. da, Cruz.

    2005-09-01

    Full Text Available We have revisited the low-energy calculation of odd Z 155Eu in the frame of a semi-microscopic formalism as a support for the interpretation of the experimental results for the multipole mixing ratios of some electromagnetic transitions. The deformation parameters were obtained through a macroscopic [...] -microscopic method, and the proton single particle levels, calculated with realistic Woods-Saxon potential were used as input in a quasi-particle calculation of the first few rotational band heads in the Lipkin-Nogami BCS aproximation. A better agreement is found between the experimental and calculated band heads if compared with previous evaluations and RIPL recommended values.

  18. Macroscopic optical response and photonic bands

    CERN Document Server

    Perez-Huerta, J S; Mendoza, Bernardo S; Mochan, W Luis

    2012-01-01

    We develop a formalism for the calculation of the macroscopic dielectric response of composite systems made of particles of one material embedded periodically within a matrix of another material, each of which is characterized by a well defined dielectric function. The nature of these dielectric functions is arbitrary, and could correspond to dielectric or conducting, transparent or opaque, absorptive and dispersive materials. The geometry of the particles and the Bravais lattice of the composite are also arbitrary. Our formalism goes beyond the longwavelenght approximation as it fully incorporates retardation effects. We test our formalism through the study the propagation of electromagnetic waves in 2D photonic crystals made of periodic arrays of cylindrical holes in a dispersionless dielectric host. Our macroscopic theory yields a spatially dispersive macroscopic response which allows the calculation of the full photonic band structure of the system, as well as the characterization of its normal modes, upo...

  19. Population of rotational bands in superheavy nuclei

    Directory of Open Access Journals (Sweden)

    Antonenko N.V.

    2012-02-01

    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.

  20. Electronic structure of periodic curved surfaces -- topological band structure

    CERN Document Server

    Aoki, H; Takeda, D; Morise, H

    2001-01-01

    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.

  1. Band structure in the doubly magic nucleus 56Ni

    International Nuclear Information System (INIS)

    Band structures near yrast lines of the Z=N doubly magic nucleus 56Ni are investigated with the configuration-dependent cranked Nilsson-Strutinsky approach. The observed deformed bands are confirmed as highly deformed and their properties are explained theoretically. The calculated transition quadrupole moments Qt, ?1.7 eb at low spin as well as the kinematic and dynamic moments of inertia J(1) and J(2) for configurations of interest are found to be generally in good agreement with the observed results. Two terminating states at 20+ and 29- for the two observed bands and other terminations in 56Ni are also predicted. It is found that the configuration-dependent cranked Nilsson-Strutinsky approach is better in the description of nuclear properties and band structures at high spin than other models. (author)

  2. Multiple triaxial bands and abnormal signature inversion in 7433As

    International Nuclear Information System (INIS)

    Excited states of the odd–odd nucleus 74As have been investigated via heavy ion fusion evaporation reaction 70Zn(7Li,3n)74As 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.

  3. Band gap engineering strategy via polarization rotation in perovskite ferroelectrics

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Fenggong, E-mail: fenggong@sas.upenn.edu; Grinberg, Ilya; Rappe, Andrew M., E-mail: rappe@sas.upenn.edu [The Makineni Theoretical Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104–6323 (United States)

    2014-04-14

    We propose a strategy to engineer the band gaps of perovskite oxide ferroelectrics, supported by first principles calculations. We find that the band gaps of perovskites can be substantially reduced by as much as 1.2?eV through local rhombohedral-to-tetragonal structural transition. Furthermore, the strong polarization of the rhombohedral perovskite is largely preserved by its tetragonal counterpart. The B-cation off-center displacements and the resulting enhancement of the antibonding character in the conduction band give rise to the wider band gaps of the rhombohedral perovskites. The correlation between the structure, polarization orientation, and electronic structure lays a good foundation for understanding the physics of more complex perovskite solid solutions and provides a route for the design of photovoltaic perovskite ferroelectrics.

  4. Formal Verification of Air Traffic Conflict Prevention Bands Algorithms

    Science.gov (United States)

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

    2010-01-01

    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.

  5. Lasing at the band edges of plasmonic lattices

    CERN Document Server

    Schokker, A Hinke

    2014-01-01

    We report room temperature lasing in two-dimensional diffractive lattices of silver and gold plasmon particle arrays embedded in a dye-doped polymer that acts both as waveguide and gain medium. As compared to conventional dielectric distributed feedback lasers, a central question is how the underlying band structure from which lasing emerges is modified by both the much stronger scattering and the disadvantageous loss of metal. We use spectrally resolved back-focal plane imaging to measure the wavelength- and angle dependence of emission below and above threshold, thereby mapping the band structure. We find that for silver particles, the band structure is strongly modified compared to dielectric reference DFB lasers, since the strong scattering gives large stop gaps. In contrast, gold particles scatter weakly and absorb strongly, so that thresholds are higher, but the band structure is not strongly modified. The experimental findings are supported by finite element and fourier modal method calculations of the...

  6. Band gap engineering strategy via polarization rotation in perovskite ferroelectrics

    International Nuclear Information System (INIS)

    We propose a strategy to engineer the band gaps of perovskite oxide ferroelectrics, supported by first principles calculations. We find that the band gaps of perovskites can be substantially reduced by as much as 1.2?eV through local rhombohedral-to-tetragonal structural transition. Furthermore, the strong polarization of the rhombohedral perovskite is largely preserved by its tetragonal counterpart. The B-cation off-center displacements and the resulting enhancement of the antibonding character in the conduction band give rise to the wider band gaps of the rhombohedral perovskites. The correlation between the structure, polarization orientation, and electronic structure lays a good foundation for understanding the physics of more complex perovskite solid solutions and provides a route for the design of photovoltaic perovskite ferroelectrics

  7. Band structures and transmission spectra of piezoelectric superlattices

    Science.gov (United States)

    Zhang, Weiyi; Liu, Zhenxing; Wang, Zhenlin

    2005-05-01

    The polaritonlike excitations in piezoelectric-modulated superlattices are studied systematically by combining the plane wave expansion method and transfer matrix method; these two complementary methods yield the full band structures of the system and mode-coupling information with the external incident waves. Both the band structures and transmission spectra are calculated and analyzed for superlattices made of LiNbO3 , and the polaritonlike band gap (divided by midgap frequency) of 19% is found in the computed transmission spectra of electromagnetic wave. Furthermore, our study shows that the transmission spectra depend sensitively on the sample thickness and the well defined polaritonlike band gap takes shape only when the number of periods exceeds 10 000. Our results offer a natural explanation as to why previous experiments failed to observe the gap in a sample with 250 periods.

  8. Band offsets in c-Si/Si-XII heterojunctions

    Science.gov (United States)

    Mustafa, Jamal I.; Malone, Brad D.; Cohen, Marvin L.; Louie, Steven G.

    2014-08-01

    Silicon has a rich phase diagram with a multitude of phases existing over a wide range of pressures and temperatures, in addition to the common cubic silicon (c-Si) phase. One such phase, Si-XII, was first observed less than 2 decades ago in diamond anvil experiments, and more recently as a product of nanoindentation. In some of these latter experiments, I-V measurements were performed to characterize the c-Si/Si-XII interface that results when Si-XII is formed in cubic silicon substrates. In this paper we describe calculations of the band offsets in c-Si/Si-XII heterojunctions. We find that the heterojunction is of Type I and that the band offsets are estimated to be ?Ev=0.3 eV and ?Ec=0.5 eV for the valence bands and conduction bands, respectively.

  9. Compact Dual Band Microstrip Antenna for Ku-Band Application

    OpenAIRE

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

    2010-01-01

    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...

  10. Band mixing in 29Si and 29P

    International Nuclear Information System (INIS)

    The experimental data of the 28Si(?, t)29P and 28Si(?, 3He)29Si reactions at 45 MeV have been analysed in terms of full finite-range coupled-channels calculations. In the calculations, the reaction paths, direct and two step via the inelastic states of the initial and final nuclei have been treated in terms of the finite-range transfer theory. The spectroscopic amplitudes connecting the deformed initial and final nuclei in both the reactions are obtained from Nilsson's model. The data of both the reactions, populating the 1/2+, 3/2+ and 5/2+ states in the K? = 1/2+ band and the 3/2+ and 5/2+ states in the K? = 3/2+ band, are best described by about 20% mixing of between the two bands. The effects of normal Woods-Saxon (WS), squared WS and molecular type of ?-nucleus potentials are also discussed

  11. Band mixing in 29Si and 29P

    Science.gov (United States)

    Hossain, S.; Abdullah, M. N. A.; Das, S. K.; Uddin, M. A.; Basak, A. K.; Gupta, H. M. Sen; Thompson, I. J.; Malik, F. B.

    2005-05-01

    The experimental data of the 28Si(?, t)29P and 28Si(?, 3He)29Si reactions at 45 MeV have been analysed in terms of full finite-range coupled-channels calculations. In the calculations, the reaction paths, direct and two step via the inelastic states of the initial and final nuclei have been treated in terms of the finite-range transfer theory. The spectroscopic amplitudes connecting the deformed initial and final nuclei in both the reactions are obtained from Nilsson's model. The data of both the reactions, populating the 1/2+, 3/2+ and 5/2+ states in the K? = 1/2+ band and the 3/2+ and 5/2+ states in the K? = 3/2+ band, are best described by about 20% mixing of between the two bands. The effects of normal Woods-Saxon (WS), squared WS and molecular type of ?-nucleus potentials are also discussed.

  12. Band Structure and Quantum Confined Stark Effect in InN/GaN superlattices

    DEFF Research Database (Denmark)

    Gorczyca, I.; Suski, T.

    2012-01-01

    InN/GaN superlattices offer an important way of band gap engineering in the blue-green range of the spectrum. This approach represents a more controlled method than the band gap tuning in quantum well systems by application of InGaN alloys. The electronic structures of short-period wurtzite InN/GaN(0001) superlattices are investigated, and the variation of the band gap with the thicknesses of the well and the barrier is discussed. Superlattices of the form mInN/nGaN with n ? m are simulated using band structure calculations in the Local Density Approximation with a semiempirical correction for the gap error. The calculated band gap shows a strong decrease with the thickness (m) of the InN well. In superlattices containing a single layer of InN (m = 1) the band gap increases weakly with the GaN barrier thickness n, reaching a saturation value around 2 eV. In superlattices with n = m and n > 5 the band gap closes and the systems become “metallic”. These effects are related to the existence of the built-in electric fields that strongly influence valence- and conduction-band profiles and thus determine effective band gap and emission energies of the superlattices. Varying the widths of the quantum wells and barriers one may tune band gaps over a wide spectral range, which provides flexibility in band gap engineering.

  13. Graphical comparison of calculated internal conversion coefficients

    International Nuclear Information System (INIS)

    Calculated values of the coefficients of internal conversion of gamma rays in the K shell and L1, L2, L3 subshells from published tabulations by Band and Trzhaskovskaya and by Roesel et al. at Data Nucl. Data Tables, 21, 92-514(1978) are compared with values obtained by computer interpolation among tabulated values of Hager and Seltzer Nucl. Data, A4, 1-235(1968). In some cases, agreement among the three calculations is remarkably good, and differences are generally less than 5%. In a few cases, there are differences as large as 20 to 50%, corresponding to the threshold effect described by Roesel et al. The Z-dependent resonance minimum described by Roesel et al. is also observed in the comparison of E1-E4 conversion in the L1 subshell. In several cases (notably M1-M4 conversion in the K shell and L1 subshell), the Band and Roesel calculations show dramatically different dependence on gamma energy and atomic number. For Z = 100, the Band calculation for E4 conversion in the L3 subshell shows irregular behavior at energies below the K-shell binding energy. A few high-quality measurements of internal conversion coefficients (+-5%) would help greatly to establish a basis for choice among the theoretical calculations. 32 figures

  14. Population and properties of superdeformed bands in A ? 150 region

    International Nuclear Information System (INIS)

    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.

  15. MAGNETIC BAND STRUCTURE OF CrO2

    OpenAIRE

    Ka?mper, K.; Schmitt, W.; Gu?ntherodt, G.; Gambino, R.; Ruf, R.

    1988-01-01

    Spin-resolved photoemission of polycrystalline CrO2 films shows 3d states with a nearly + 100 % spin polarization about 2 eV below the Fermi level (EF). Extremely low intensity is observed near EF. Our findings are in contrast to recent band structure calculations, predicting CrO2 to be a half-metallic ferromagnet.

  16. First-principles study of Cu2ZnSnS4 and the related band offsets for photovoltaic applications

    International Nuclear Information System (INIS)

    First-principles calculations of the band offsets between Cu2ZnSnS4 (CZTS) and XS (X = Cd, Zn) are performed. While the interface dipole contribution for the band offsets is calculated using the Perdew-Burke-Ernzerhof functional, the Heyd-Scuseria-Ernzerhof hybrid functional is employed to introduce the quasiparticle corrections to the band offsets. The calculated conduction band offset between CZTS and CdS is 0.2 eV, validating CdS for the buffer layer of the CZTS solar cell. The small conduction band offset stems from the band gap narrowing of CdS under the interface strain caused by the lattice misfit with CZTS. A large valence band offset over 0.9 eV between CZTS and ZnS indicates that precipitated ZnS is regarded as an inactive insulator phase in CZTS absorbers.

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

    CERN Document Server

    Jones, R M

    2004-01-01

    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].

  18. P-band focus problem

    Science.gov (United States)

    Mansfield, Arthur W.; Rais, Houra

    1997-06-01

    For the problem of finding downed aircraft in forested areas, the NASA Search and Rescue Project has developed a system based on using fully polarimetric L-Band and P-Band synthetic aperture radar (SAR). Because of the resolution of the sensor and the size of the target, single-look imagery must be used. The problem of focusing the SAR imagery is a difficult one, especially at P-Band. An approach has been implemented with considerable success, based on a variant of the phase gradient autofocus algorithm, which provides the higher-order-than- quadratic phase correction needed.

  19. MANIFESTATION OF DEFORMATION EFFECT IN BAND SPECTRA IN CRYSTALS WITH INHOMOGENEOUS BONDING

    OpenAIRE

    Bercha, D. M.; Rushchanskii, K. Z.; Slipukhina, I. V.; Bercha, I. V.

    2003-01-01

    The effect of the shear strains on the energy spectrum of the strongly anisotropic SbSI crystal has been investigated by group-theoretical method in combination with the Pikus method of invariants. The first-principles local density approximation has been implemented to determine the band structure of the crystal. Ab initio calculations of the band structure have shown an exact localization of twofold degenerate maximum of the valence band in the T point. It turned out that the shear strains ...

  20. Study of Band Structure of Two-Dimensional Anisotropic Honeycomb Photonic Crystals

    Science.gov (United States)

    Sedghi, A.; Soufiani, A. Rounaghi

    2013-10-01

    Using the plane wave expansion method, we have calculated, for both E and H polarizations, the band structure of 2D anisotropic photonic crystals with honeycomb lattice composed of anisotropic tellurium (Te) rods embedded in air background. The two rods in the unit cell are chosen square and circular in shape. Here, from a practical point of view, in order to obtain maximum band gaps, we have also studied the band structure as a function of size of rods.

  1. Electronic Band Dispersion of Graphene Nanoribbons via Fourier-Transformed Scanning Tunneling Spectroscopy

    OpenAIRE

    So?de, Hajo; Talirz, Leopold; Gro?ning, Oliver; Pignedoli, Carlo Antonio; Berger, Reinhard; Feng, Xinliang; Mu?llen, Klaus; Fasel, Roman; Ruffieux, Pascal

    2014-01-01

    Atomically precise armchair graphene nanoribbons of width $N=7$ (7-AGNRs) are investigated by scanning tunneling spectroscopy (STS) on Au(111). The analysis of energy-dependent standing wave patterns of finite length ribbons allows, by Fourier transformation, the direct extraction of the dispersion relation of frontier electronic states. Aided by density functional theory calculations, we assign the states to the valence band, the conduction band and the next empty band of 7...

  2. Nonequilibrium Green's function formulation of intersubband absorption for nonparabolic single-band effective mass Hamiltonian

    Science.gov (United States)

    Kolek, Andrzej

    2015-05-01

    The formulas are derived that enable calculations of intersubband absorption coefficient within nonequilibrium Green's function method applied to a single-band effective-mass Hamiltonian with the energy dependent effective mass. The derivation provides also the formulas for the virtual valence band components of the two-band Green's functions which can be used for more exact estimation of the density of states and electrons and more reliable treatment of electronic transport in unipolar n-type heterostructure semiconductor devices.

  3. Comparing C- and L-band SAR images for sea ice motion estimation

    Science.gov (United States)

    Lehtiranta, J.; Siiriä, S.; Karvonen, J.

    2015-02-01

    Pairs of consecutive C-band synthetic-aperture radar (SAR) images are routinely used for sea ice motion estimation. The L-band radar has a fundamentally different character, as its longer wavelength penetrates deeper into sea ice. L-band SAR provides information on the seasonal sea ice inner structure in addition to the surface roughness that dominates C-band images. This is especially useful in the Baltic Sea, which lacks multiyear ice and icebergs, known to be confusing targets for L-band sea ice classification. In this work, L-band SAR images are investigated for sea ice motion estimation using the well-established maximal cross-correlation (MCC) approach. This work provides the first comparison of L-band and C-band SAR images for the purpose of motion estimation. The cross-correlation calculations are hardware accelerated using new OpenCL-based source code, which is made available through the author's web site. It is found that L-band images are preferable for motion estimation over C-band images. It is also shown that motion estimation is possible between a C-band and an L-band image using the maximal cross-correlation technique.

  4. X-ray aided permeability computations inside compaction bands in sandstones

    Science.gov (United States)

    Andrade, J.; Lenoir, N.; Sun, W.; Rudnicki, J. W.

    2009-12-01

    This work presents preliminary data on permeability calculations using 3D X-ray tomography images taken inside and outside compaction bands. Aztec sandstone samples are taken from the Valley of Fire in Nevada and are scanned using the synchrotron APS facility at Argonne National Laboratory. The 3D microstructures inside and outside the compaction bands, formed in situ, are then used to perform lattice Boltzmann computations to estimate the components of permeability in different principal directions. We show that i) the permeability component in the direction perpendicular to the compaction band is reduced by orders of magnitude in the presence of a compaction band, ii) inside the compaction band, there is a strong anisotropy manifested by the permeability tensor, and iii) the Kozeny-Carman relation does a pretty good job at estimating the permeability outside of the compaction band, but fails to estimate the reduction in permeability in the presence of compaction bands.

  5. Band structure from random interactions

    OpenAIRE

    Bijker, R.; Frank, A.

    1999-01-01

    The anharmonic vibrator and rotor regions in nuclei are investigated in the framework of the interacting boson model using an ensemble of random one- and two-body interactions. We find a predominance of L(P)=0(+) ground states, as well as strong evidence for the occurrence of both vibrational and rotational band structures. This remarkable result suggests that such band structures represent a far more general (robust) property of the collective model space than is generally ...

  6. Dipole Bands in 196Hg

    International Nuclear Information System (INIS)

    High spin states in 196Hg have been populated in the 198Pt(?,6n) reaction at 65 MeV and the level scheme has been extended. A new dipole band has been observed and a previously observed dipole has been confirmed. Excitation energies, spins and parities of these bands were determined from DCO ratio and linear polarization measurements. Possible quasiparticle excitations responsible for these structures are discussed.

  7. Band structure from random interactions

    CERN Document Server

    Bijker, R

    2000-01-01

    The anharmonic vibrator and rotor regions in nuclei are investigated in the framework of the interacting boson model using an ensemble of random one- and two-body interactions. We find a predominance of L(P)=0(+) ground states, as well as strong evidence for the occurrence of both vibrational and rotational band structures. This remarkable result suggests that such band structures represent a far more general (robust) property of the collective model space than is generally thought.

  8. 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 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

  9. All-electron Exact Exchange Treatment of Semiconductors: Effect of Core-valence Interaction on Band-gap and $d$-band Position

    CERN Document Server

    Sharma, S; Ambrosch-Draxl, C

    2005-01-01

    Exact exchange (EXX) Kohn-Sham calculations within an all-electron full-potential method are performed on a range of semiconductors and insulators (Ge, GaAs, CdS, Si, ZnS, C, BN, Ne, Ar, Kr and Xe). We find that the band-gaps are not as close to experiment as those obtained from previous pseudopotential EXX calculations. Full-potential band-gaps are also not significantly better for $sp$ semiconductors than for insulators, as had been found for pseudopotentials. The locations of $d$-band states, determined using the full-potential EXX method, are in excellent agreement with experiment, irrespective of whether these states are core, semi-core or valence. We conclude that the inclusion of the core-valence interaction is necessary for accurate determination of EXX Kohn-Sham band structures, indicating a possible deficiency in pseudopotential calculations.

  10. Model for minority-carrier band-gap states in semiconductors

    International Nuclear Information System (INIS)

    A variational calculation is presented for the energies of electrons and holes which interact with a random distribution of donor impurities in a semiconductor. At high density, smaller band-gap narrowing is predicted for a random distribution than for an ordered one. A new model is presented for the minority-carrier states in the band gap

  11. Dilatational band formation in bone.

    Science.gov (United States)

    Poundarik, Atharva A; Diab, Tamim; Sroga, Grazyna E; Ural, Ani; Boskey, Adele L; Gundberg, Caren M; Vashishth, Deepak

    2012-11-20

    Toughening in hierarchically structured materials like bone arises from the arrangement of constituent material elements and their interactions. Unlike microcracking, which entails micrometer-level separation, there is no known evidence of fracture at the level of bone's nanostructure. Here, we show that the initiation of fracture occurs in bone at the nanometer scale by dilatational bands. Through fatigue and indentation tests and laser confocal, scanning electron, and atomic force microscopies on human and bovine bone specimens, we established that dilatational bands of the order of 100 nm form as ellipsoidal voids in between fused mineral aggregates and two adjacent proteins, osteocalcin (OC) and osteopontin (OPN). Laser microdissection and ELISA of bone microdamage support our claim that OC and OPN colocalize with dilatational bands. Fracture tests on bones from OC and/or OPN knockout mice (OC(-/-), OPN(-/-), OC-OPN(-/-;-/-)) confirm that these two proteins regulate dilatational band formation and bone matrix toughness. On the basis of these observations, we propose molecular deformation and fracture mechanics models, illustrating the role of OC and OPN in dilatational band formation, and predict that the nanometer scale of tissue organization, associated with dilatational bands, affects fracture at higher scales and determines fracture toughness of bone. PMID:23129653

  12. Probing Time-Odd and Tensor Terms of The Skyrme Functional in Superdeformed Bands

    International Nuclear Information System (INIS)

    We briefly discuss Hartree Fock Bogoliubov (HFB) plus self consistent cranking calculations for the superdeformed band in 194Hg, using the full Skyrme energy density functional including tensor terms in the p-h channel.

  13. Positron band structures of GaAs and CdTe

    International Nuclear Information System (INIS)

    The problem of positron and structure in a periodic lattice is similar to its electron counterpart. GaAs and CdTe positron band structures are calculated, a comparison between the electron and positron energies is discussed. (author)

  14. Thermal emissivity for finite three-dimensional photonic band gap crystals

    OpenAIRE

    Stimpson, Andrew J.; Dowling, Jonathan P

    2002-01-01

    We discuss the results of computer model for the thermal emissivity of a three-dimensional photonic band gap (PBG) crystal, specifically an inverted opal structure. The thermal emittance for a range of frequencies and angles is calculated.

  15. Band alignment of semiconductors from density-functional theory and many-body perturbation theory

    Science.gov (United States)

    Hinuma, Yoyo; Grüneis, Andreas; Kresse, Georg; Oba, Fumiyasu

    2014-10-01

    The band lineup, or alignment, of semiconductors is investigated via first-principles calculations based on density functional theory (DFT) and many-body perturbation theory (MBPT). Twenty-one semiconductors including C, Si, and Ge in the diamond structure, BN, AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb, ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe in the zinc-blende structure, and GaN and ZnO in the wurtzite structure are considered in view of their fundamental and technological importance. Band alignments are determined using the valence and conduction band offsets from heterointerface calculations, the ionization potential (IP) and electron affinity (EA) from surface calculations, and the valence band maximum and conduction band minimum relative to the branch point energy, or charge neutrality level, from bulk calculations. The performance of various approximations to DFT and MBPT, namely the Perdew-Burke-Ernzerhof (PBE) semilocal functional, the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, and the GW approximation with and without vertex corrections in the screened Coulomb interaction, is assessed using the GW?1 approximation as a reference, where first-order vertex corrections are included in the self-energy. The experimental IPs, EAs, and band offsets are well reproduced by GW?1 for most of the semiconductor surfaces and heterointerfaces considered in this study. The PBE and HSE functionals show sizable errors in the IPs and EAs, in particular for group II-VI semiconductors with wide band gaps, but are much better in the prediction of relative band positions or band offsets due to error cancellation. The performance of the GW approximation is almost on par with GW?1 as far as relative band positions are concerned. The band alignments based on average interfacial band offsets for all pairs of 17 semiconductors and branch point energies agree with explicitly calculated interfacial band offsets with small mean absolute errors of both ˜0.1eV, indicating a good overall transitivity of the band offsets. The alignment based on IPs from selected nonpolar surfaces performs comparably well in the prediction of band offsets at most of the considered interfaces. The maximum errors are, however, as large as 0.3, 0.4, and 0.7 eV for the alignments based on the average band offsets, branch point energies, and IPs, respectively. This margin of error should be taken into account when performing materials screening using these alignments.

  16. Calculation of Gilbert damping in ferromagnetic ?lms

    Directory of Open Access Journals (Sweden)

    Edwards D. M.

    2013-01-01

    Full Text Available 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 Gilbert damping constant on scattering rate for bulk Fe, Co and Ni is in good agreement with the results of previous ab initio calculations. Calculations are reported for ferromagnetic Co metallic ?lms and Co/Pd bilayers. The dependence of the Gilbert damping constant on Co ?lm thickness, for various scattering rates, is studied and compared with recent experiments.

  17. Vibrational Spectra and Quantum Calculations of Ethylbenzene

    Science.gov (United States)

    Wang, Jian; Qiu, Xue-jun; Wang, Yan-mei; Zhang, Song; Zhang, Bing

    2012-10-01

    Normal vibrations of ethylbenzene in the first excited state have been studied using resonant two-photon ionization spectroscopy. The band origin of ethylbenzene of S1?S0 transition appeared at 37586 cm-1. A vibrational spectrum of 2000 cm-1 above the band origin in the first excited state has been obtained. Several chain torsions and normal vibrations are obtained in the spectrum. The energies of the first excited state are calculated by the time-dependent density function theory and configuration interaction singles (CIS) methods with various basis sets. The optimized structures and vibrational frequencies of the S0 and S1 states are calculated using Hartree-Fock and CIS methods with 6-311++G(2d,2p) basis set. The calculated geometric structures in the S0 and S1 states are gauche conformations that the symmetric plane of ethyl group is perpendicular to the ring plane. All the observed spectral bands have been successfully assigned with the help of our calculations.

  18. Search for superdeformed bands in {sup 154}Dy

    Energy Technology Data Exchange (ETDEWEB)

    Nisius, D.; Janssens, R.V.F.; Khoo, T.L. [and others

    1995-08-01

    The island of superdeformation in the vicinity of the doubly magic {sup 152}Dy yrast superdeformed (SD) band is thought to be well understood in the framework of cranked mean field calculations. In particular, the calculations suggested that in {sup 154}Dy there should be no yrast or near yrast SD minimum in the 40-60 h spin range, where SD bands in this mass region are thought to be {sup 153}Dy nucleus, it is populated. However, with the presence of five SD bands in the neighboring necessary to ascertain if the addition of one single neutron diminishes the importance of shell effects to the extent that superdeformation can no longer be sustained. In an experiment utilizing the increased resolving power of the early implementation phase of Gammasphere, the reaction {sup 122}Sn({sup 36}S,4n) at 165 MeV was employed to populate high spin states in {sup 154}Dy. In a four-day run with 36 detectors, over one billion triple and higher fold coincidence events were recorded. One new SD band was identified and was assigned to {sup 154}Dy. From comparisons with the Im{sup (2)} moments of inertia of the SD bands in {sup 152}Dy and {sup 153}Dy, a configuration based on (514)9/2{sup 2} neutrons coupled to the {sup 152}Dy SD core was proposed. One unexpected and as yet unexplained feature of this new SD band is that the transition energies are almost identical to those of an excited SD band in {sup 153}Dy. It is also worth noting that the feeding of the yrast states is similar to that achieved by the deexcitation from the ensemble of all entry states in the reaction. This observation emphasizes the statistical nature of the decay-out process. A paper reporting these results was accepted for publication.

  19. Band gap modulation of functionalized metal-organic frameworks.

    Science.gov (United States)

    Musho, Terence; Li, Jiangtan; Wu, Nianqiang

    2014-11-21

    Metal-organic frameworks (MOFs) have been envisioned as alternatives to planar metallic catalysts for solar-to-fuel conversion. This is a direct result of their porous structure and the ability to tailor their optical absorption properties. This study investigates the band gap modulation of Zr-UiO-66 MOFs from both the computational and experimental points of view for three linker designs that include benzenedicarboxylate (BDC), BDC-NO2, and BDC-NH2. Emphasis in this study was aimed at understanding the influence of the bonding between the aromatic ring and the functional group. A ground state density functional theory (DFT) calculation was carried out to investigate the projected density of states and the origins of the modulation. A time-dependent density functional theory (TDDFT) calculation of the hydrogen terminated linkers confirmed the modulation and accounted for the electron charge transfer providing comparable optical band gap predictions to experimental results. Computational results confirmed the hybridization of the carbon-nitrogen bond in conjunction with the donor state resulting from the NH2 functionalization. The NO2 functionalization resulted in an acceptor configuration with marginal modification to the valence band maximum. The largest modulation was BDC-NH2 with a band gap of 2.75 eV, followed by BDC-NO2 with a band gap of 2.93 eV and BDC with a band gap of 3.76 eV. The electron effective mass was predicted from the band structure to be 8.9 me for all MOF designs. PMID:25269595

  20. Spins of superdeformed band in {sup 192}Hg

    Energy Technology Data Exchange (ETDEWEB)

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

    1995-08-01

    Determination of the spins of SD states is the most important challenge in the study of superdeformation. Knowledge of the spin will provide crucial information on SD bands, in particular on the fascinating phenomenon of bands with identical energies and moments of inertia. Angular distribution coefficients of the {gamma}rays decaying out of the {sup 192}Hg SD band were determined using Eurogam data. These coefficients, as well as the spectral shape and multiplicity of the spectrum, are compared with the results of calculations, thereby providing a check on these calculations. From the measured decay multiplicity and the calculated average spin removed per photon (0.3 h), we deduce the average spin {bar I}{sub decay} removed by the {gamma} rays connecting SD and normal states. The spin I{sub SD} of the SD band from which the decay occurs is given by I{sub SD} = {bar I} decay + {bar I} ND, where {bar I} ND is the average spin removed by the normal yrast states. The state from which the major decay out of the SD band occurs is found to have spin 9.5 {plus_minus} 0.8 h. Since angular momentum is (quantized), this leads to a spin assignment of 9 or 10 h. The latter value is favored since the yrast band in the SD well must have only even spin values. This constitutes the first deduction of spin from data in the mass 150 and 190 regions. The spin of 10 h agrees with the spin which is inferred from a model, using the observed moment of inertia (Im){sup (2)}{omega}.

  1. A novel design UWB antenna having band notch characteristics

    Science.gov (United States)

    Gour, Ajay S.; Mathur, Dhirendra

    2013-01-01

    A Novel Design using two feed structure for Ultra Wide Band Antenna with band notch characteristics is being presented in this paper. The simulated antenna so designed have a compact small physical size of 16 mm (L) × 20 mm (W) × 1.6 mm (h) of the overall design with the patch size as 11.86 mm (L) × 8.96 mm (W). The antenna is designed to simulate at 10 GHz. The substrate used is Duroid™ with a relative permittivity of (?r=2.2) and the return loss so measured is calculated below -10 dB for the range 3.1-19.53 GHz with band notching in the frequency band 5.1-5.8 GHz (i.e. WLAN). To achieve such UWB antenna with band notch, the three concepts used are introduced, the first one is using two feeding structure, the second one is using steps at the bottom of the patch, introducing steps at the bottom centre of the patch for band notching. The final impedance bandwidth so measured is 145 % which is a very high bandwidth so obtained. The optimized antenna designed can be used in any of the wireless device for UWB applications.

  2. An algebraic approach to scattering and band structure problems

    International Nuclear Information System (INIS)

    It is shown that both bound and scattering states of a class of potentials are related to the unitary representations of certain groups. For such systems the scattering matrix can be calculated in a completely algebraic way through the use of the Euclidean group to describe asymptotic behaviour. The band structures associated with a family of periodic potentials can also be obtained from the group theory. These results suggest that an algebraic approach to scattering and band structure problems similar to that applied to bound states is possible

  3. C-Band LINAC for a race track microtron

    OpenAIRE

    Carrillo Barrera, David Manuel

    2010-01-01

    The general aim of this thesis is to do the radiofrequency (RF) design of a 2 MeV C-Band linac for a RTM, the mechanical design and thermo mechanical calculations and to follow the machining procedure. Afterwards, a test bench has to be designed so the RF cold measurements may be carried out. In addition, the process of brazing of accelerating cavities will be studied. The novelty of this thesis arises from the fact that C-band linac was never used before in RTM. Specific of...

  4. The nature of the electronic band gap in lanthanide oxides

    OpenAIRE

    Gillen, Roland; Clark, Stewart J.; Robertson, John

    2012-01-01

    Accurate electronic structures of the technologically important lanthanide/rare earth sesquioxides (Ln2O3, with Ln=La,...,Lu) and CeO2 have been calculated using hybrid density functionals HSE03, HSE06 and screened-exchange (sX-LDA). We find that these density functional methods describe the strongly correlated Ln f-electrons as well as the recent G0W0@LDA+U results, generally yielding the correct band gaps and trends across the Ln-period. For HSE, the band gap between O 2p ...

  5. Correlation Effects in Auger CVV Spectra from Partially Filled Bands

    Science.gov (United States)

    Cini, Michele

    1992-01-01

    Auger Line Shape Analysis from solids with open bands has been made considerable progress in recent years. Calculations on Graphite and Pd were encouraging, and new developements in the formalism look promising. However, it must be recognized that the current theory remains much more phenomenological and less predictive and reliable than it is for closed bands. In some sense, the comparison with experiments is more succcesful than our real understanding deserves. This is hardly surprising, in view of the much more fundamental character of the problems involved. An attempt will be made to assess the present state of the theory and foreshadow the directions of future research.

  6. Band theory of the linear magnetostriction for ferromagnetic transition metals

    International Nuclear Information System (INIS)

    It is shown that for ferromagnetic transition metals with cubic symmetry the change of one-electron state occupation numbers, caused by the influence of the spin-orbit interaction and lattice deformation on initially double degenerate electronic bands which intersect the Fermi level, may be considered as the mechanism of linear magnetostriction. Expressions for magnetostriction constants for the [100] and [111] directions are calculated. The crude estimation for Ni shows that the proposed mechanism gives the correct result for the [111] direction. In the last case, other details of the electronic band structure must be taken into account. (author)

  7. Semiempirical calculations of the electronic structure in ionic crystals

    International Nuclear Information System (INIS)

    Calculations of the electronic structure in ionic crystals with and without defects were performed using the standard molecular orbit CNDO/INDO program for molecular calculation but some important modifications and parameters optimization have been adopted to be suited to the ionic crystal condition. The calculated results, such as the width of valence bands and band gap, ground levels of perfect ionic crystals and F colour center in LIF, are listed and compared with previous results in our knowledge. (author). 11 refs, 1 fig., 3 tabs

  8. Magnetic Field Calculator

    National Oceanic and Atmospheric Administration, Department of Commerce — The Magnetic Field Calculator will calculate the total magnetic field, including components (declination, inclination, horizontal intensity, northerly intensity,...

  9. Yrast and excited highly deformed bands in 134 Nd

    International Nuclear Information System (INIS)

    Available as short communication only. The states of 134 Nd were populated in the reaction 110 Pd (28 Si, 4 n) at a beam energy of 130 MeV. The beam was provided by the Tandem XTU Accelerator in Legnaro and the ?-rays were detected with the GA.SP. spectrometer. For this experiment there are installed 31 Ge+AC detectors and the events consisted of triple and higher fold coincidence data. The most intense channels in these reactions are 134 Nd (4 n), 133 Nd (5 n), 134 Pr (p 3 n), 133 Pr (p 4 n), 131 Ce (?3 n). The 4 n channel was selected by proper gates on the total energy and multiplicity. These data revealed two bands of 12 and 11 transitions, respectively, having a level spacing of about 70 MeV (typical for the highly deformed bands in the A=130 mass region). ?-? coincidence matrices were constructed by gating on uncontaminated lines of these bands. By gating again on the members of the bands in these matrices, double gated spectra were obtained which attribute without doubt these structures to 134 Nd. The better resolution of GA.SP. array allowed us to separate the yrast highly deformed band of 134 Nd from that of the 131 Ce although transitions in the lower part of these bands are nearly equal. The ?-ray energies of the yrast highly deformed band in 134 Nd are close within at most 6 keV to those in 135 Nd revealing a tse in 135 Nd revealing a twinning effect as the one observed in the A=150 mass region. Interpretation of these bands in terms of CSM calculations is in progress. (Author) 1 Fig

  10. Distillation Calculations with a Programmable Calculator.

    Science.gov (United States)

    Walker, Charles A.; Halpern, Bret L.

    1983-01-01

    Describes a three-step approach for teaching multicomponent distillation to undergraduates, emphasizing patterns of distribution as an aid to understanding the separation processes. Indicates that the second step can be carried out by programmable calculators. (A more complete set of programs for additional calculations is available from the…

  11. MANIFESTATION OF DEFORMATION EFFECT IN BAND SPECTRA IN CRYSTALS WITH INHOMOGENEOUS BONDING

    Directory of Open Access Journals (Sweden)

    D.M.Bercha

    2003-01-01

    Full Text Available The effect of the shear strains on the energy spectrum of the strongly anisotropic SbSI crystal has been investigated by group-theoretical method in combination with the Pikus method of invariants. The first-principles local density approximation has been implemented to determine the band structure of the crystal. Ab initio calculations of the band structure have shown an exact localization of twofold degenerate maximum of the valence band in the T point. It turned out that the shear strains result in the band topology changes in the vicinity of the T point and the k-linear term appears in the corresponding dispersion law.

  12. Systematic search of candidate chiral bands in odd-odd 122-132Cs isotopes

    International Nuclear Information System (INIS)

    Two nearly degenerate candidate chiral bands have been observed in odd-odd 122-132Cs isotopes. These bands are built on the ?h11/2 (direct x)?h11/2 configuration. Systematic analyses associated with the partner bands are presented. The degree of energy degeneracy, the energy staggering parameter S(I), the B(M1)/B(E2) ratios and the TRS calculations have been deduced for these doublet bands. Systematic comparisons indicate that the odd-odd 126, 128,130Cs isotopes have stable chiral structure at higher spin range. (authors)

  13. Discrete Linking Transitions For A Superdeformed Band In The A ? 80 Region

    International Nuclear Information System (INIS)

    The yrast superdeformed (SD) band in 84Zr has been linked to states of normal deformation (ND) by three single-step ? decays. The spins and parity of the SD band were determined through angular distributions of two of these links. The properties of this band and its decay to ND states are compared with linked SD bands in other mass regions. SD intensity profiles, calculated SD-ND potential barriers, and results of a statistical-decay analysis suggest there is significant SD-ND mixing involved

  14. Identicity in high-K three quasiparticle rotational bands: a theoretical approach

    International Nuclear Information System (INIS)

    The systematics are studied for the identical band phenomenon in high-K three quasiparticle rotational bands. The identical rotational bands based on the same bandhead spin are analyzed on the basis of similarities in ?-ray energies, dynamic moment of inertia and kinematic moment of inertia in particular, which is a function of deformation degrees of freedom, pairing strengths and Nilsson orbitals in nuclei. It is established that a combined effect of all these parameters decides the identicity of the moment of inertia in high-K three quasiparticle rotational bands as the systematics are backed by the Tilted Axis Cranking model calculations. (paper)

  15. Gyrotropic band gap optical sensors

    Science.gov (United States)

    Dissanayake, Neluka K.; Levy, Miguel; Jalali, Amir A.; Fratello, V. J.

    2010-05-01

    Faraday-effect-active photonic band gap structures fabricated in iron garnet films are shown to provide a platform for optical sensing based on refractive index detection. Strong near-band gap-edge polarization rotations serve as a sensitive probe to cover-index changes in birefringent magneto-optic waveguides. A wide index range from air to n =1.6 is explored. Device sensitivity is found to improve with cover index increase. Theoretical analysis of Bloch modes polarization state shows large near stop-band edge rotations and strong sensitivity to cover index. The combined effects of geometrical waveguide birefringence and Faraday rotation contribute to the strength of the sensor response.

  16. Modification of Casimir Forces Due to Band Gaps in Periodic Structures

    Science.gov (United States)

    Villarreal, C.; Esquivel-Sirvent, R.; Cocoletzi, G. H.

    The Casimir force between inhomogeneous slabs that exhibit a band-like structure is calculated. The slabs are made of basic unit cells each made of two layers of different materials. As the number of unit cells increases the Casimir force between the slabs changes, since the reflectivity develops a band-like structure characterized by frequency regions of high reflectivity. This is also evident in the difference of the local density of states between free and boundary distorted vacuum, that becomes maximum at frequencies corresponding to the band gaps. The calculations are restricted to vacuum modes with wave vectors perpendicular to the slabs.

  17. Algorithm for extraction of quantum oscillation orbits from band structure data

    Science.gov (United States)

    Rourke, Patrick; Julian, Stephen

    2008-03-01

    In determining the Fermi surface of a material, quantum oscillation measurements are often compared to band structure calculations. Each oscillation frequency corresponds to an electron (or hole) orbit on the Fermi surface, perpendicular to the applied magnetic field; only orbits enclosing areas that are locally extremal are detected. To facilitate comparisons between theory and experiment, we have developed an algorithm, ``SKEAF,'' which finds extremal orbits in band structure calculations and determines quantum oscillation frequencies, effective masses and band specific heat contributions. Our code uses a k-space supercell approach, and can successfully locate geometrically-complicated orbits. Example results will be presented for the heavy fermion material UPt3.

  18. Tunable Band Gap and Conductivity Type of ZnSe/Si Core-Shell Nanowire Heterostructures

    OpenAIRE

    Yijie Zeng; Huaizhong Xing; Yanbian Fang; Yan Huang; Aijiang Lu; Xiaoshuang Chen

    2014-01-01

    The electronic properties of zincblende ZnSe/Si core-shell nanowires (NWs) with a diameter of 1.1–2.8 nm are calculated by means of the first principle calculation. Band gaps of both ZnSe-core/Si-shell and Si-core/ZnSe-shell NWs are much smaller than those of pure ZnSe or Si NWs. Band alignment analysis reveals that the small band gaps of ZnSe/Si core-shell NWs are caused by the interface state. Fixing the ZnSe core size and enlarging the Si shell would turn the NWs from intrinsic to p-type...

  19. Large band gap bowing of InxGa1-xN alloys

    Science.gov (United States)

    McCluskey, M. D.; Van de Walle, C. G.; Master, C. P.; Romano, L. T.; Johnson, N. M.

    1998-05-01

    Band gap measurements have been performed on strained InxGa1-xN epilayers with x?0.12. The experimental data indicate that the bowing of the band gap is much larger than commonly assumed. We have performed first-principles calculations for the band gap as a function of alloy composition and find that the bowing is strongly composition dependent. At x=0.125 the calculated bowing parameter is b=3.5 eV, in good agreement with the experimental values.

  20. Crossing of shears bands in 196Pb

    International Nuclear Information System (INIS)

    High-spin states in 196Pb have been populated using the reaction 170Er(30Si, 4n). The previously observed shear bands in this nucleus have been extended and some of their transitions have been reordered. They now form regular bands with band crossings. One of the bands splits into two pathways at high spin. (orig.)

  1. Dual-Band Tunable Recursive Active Filter

    OpenAIRE

    Segovia Vargas, Daniel; Garci?a Pe?rez, Oscar Alberto; Gonza?lez Posadas, Vicente; Aznar Ballesta, Francisco

    2011-01-01

    This letter presents a novel recursive active filter topology that provides dual-band performance, with independent tuning capability in both bands. The dual-band operation is achieved by using two independent feedback lines. Additionally, linear phase shifters based on left-handed cells are included in these two branches in order to tune the center frequency of both pass bands.

  2. Shape Coexistence and Band Termination in Doubly Magic Nucleus 40Ca

    International Nuclear Information System (INIS)

    Shape coexistence and band structure near yrast line of the Z = N doubly magic nucleus 40Ca have been investigated by the configuration-dependent cranked Nilsson-Strutinsky approach. The observed normal deformed and superdeformed bands are explained and the terminating states are confirmed by the calculations. The transition quadrupole moment Qt of the calculated superdeformed band is in good agreement with the observed one at high spin. There is shape coexistence within the same configuration. Possible normal deformed and superdeformed bands with rotation around the intermediate axis in several interesting configurations of 40Ca are discussed. Possible favored superdeformed band terminations in 38Ca and 38Ar are predicted. The experimental results in 38Ar are discussed simply.

  3. Low Loss Plastic Terahertz Photonic Band-Gap Fibres

    International Nuclear Information System (INIS)

    We report a numerical investigation on terahertz wave propagation in plastic photonic band-gap fibres which are characterized by a 19-unit-cell air core and hexagonal air holes with rounded corners in cladding. Using the finite element method, the leakage loss and absorption loss are calculated and the transmission properties are analysed. The lowest loss of 0.268 dB/m is obtained. Numerical results show that the fibres could liberate the constraints of background materials beyond the transparency region in terahertz wave band, and efficiently minimize the effect of absorption by background materials, which present great advantage of plastic photonic band-gap fibres in long distance terahertz delivery. (fundamental areas of phenomenology(including applications))

  4. Automated effective band structures for defective and mismatched supercells.

    Science.gov (United States)

    Brommer, Peter; Quigley, David

    2014-12-01

    In plane-wave density functional theory codes, defects and incommensurate structures are usually represented in supercells. However, interpretation of E versus k band structures is most effective within the primitive cell, where comparison to ideal structures and spectroscopy experiments are most natural. Popescu and Zunger recently described a method to derive effective band structures (EBS) from supercell calculations in the context of random alloys. In this paper, we present bs_sc2pc, an implementation of this method in the CASTEP code, which generates an EBS using the structural data of the supercell and the underlying primitive cell with symmetry considerations handled automatically. We demonstrate the functionality of our implementation in three test cases illustrating the efficacy of this scheme for capturing the effect of vacancies, substitutions and lattice mismatch on effective primitive cell band structures. PMID:25388668

  5. Search for excited superdeformed bands in {sup 151}Dy

    Energy Technology Data Exchange (ETDEWEB)

    Nisius, D.; Janssens, R.V.F.; Crowell, B. [and others

    1995-08-01

    Following the first report of superdeformed (SD) bands with identical transition energies in the pairs ({sup 151}Tb*,{sup 152}Dy), ({sup 150}Gd*, {sup 151}Tb) and ({sup 153}Dy*, {sup 152}Dy) (where * denotes an excited SD band), it was proposed by Nazarewicz et al. that the observations could be understood in a strong-coupling approach if pseudo SU(3) symmetry were invoked. In this model there are three limiting values of the decoupling parameter; i.e. a = 0, {plus_minus}1. In the first two cases mentioned above the pairs of bands have nearly identical transition energies and are interpreted as proton excitations involving the [200]1/2 pseudospin orbital coupled to the {sup 152}Dy core, for which the value of the decoupling parameter is calculated to be a =+1.

  6. Electrical conductivity for the strongly correlated and hybridized Hubbard band

    International Nuclear Information System (INIS)

    The magnetic and electrical transport properties of strongly correlated Hubbard model (f-band) hybridizing with non-correlated conduction band (c-band) was studied. The many-body model Hamiltonian was treated within the modified alloy analogy scheme and the resulting one-body problem was solved with the use of coherent potential approximation. Within Kubo-Greenwood formalism the dc electrical conductivity for bcc magnetic system was calculated and its variation with temperature and number of electrons was examined for different values of the Coulomb and hybridization (V) coupling constants. We found that the effect of strong correlations and hybridization on the conductivity is similar to that produced by the scattering due to the s-f interaction (spin disorder resistivity). (author)

  7. Collective band properties in actinide nuclei well deformed

    International Nuclear Information System (INIS)

    In actinides, proton i13/2 orbitals and neutron j15/2 orbitals are both near Fermi surface. At a great rotation speed, driving and Coriolis forces change the surface forces, in particular, they lower pairing forces inside the nucleus. The use of Coulomb excitation with the help of heavy and very heavy projectiles such as 32S, 84Kr, 142Nd, 208Pb at 232Th together with the most recent techniques of spectroscopy allowed to populate yrast bands of 230Th, 232Th, 235U and 237Np nuclei up to high spin states and together the even-even nuclei states in different collective bands. Experimental results have been analyzed in the frame of the different current models. The low spin states of rotational bands have been reproduced in a previous calculation using the nucleon-nucleon effective interaction of Skyrme III

  8. Residual stress dependant anisotropic band gap of various (hkl) oriented BaI2 films

    Science.gov (United States)

    Kumar, Pradeep; Gulia, Vikash; Vedeshwar, Agnikumar G.

    2013-11-01

    The thermally evaporated layer structured BaI2 grows in various completely preferred (hkl) film orientations with different growth parameters like film thickness, deposition rate, substrate temperature, etc. which were characterized by structural, morphological, and optical absorption measurements. Structural analysis reveals the strain in the films and the optical absorption shows a direct type band gap. The varying band gaps of these films were found to scale linearly with their strain. The elastic moduli and other constants were also calculated using Density Functional Theory (DFT) formalism implemented in WIEN2K code for converting the strain into residual stress. Films of different six (hkl) orientations show stress free anisotropic band gaps (2.48-3.43 eV) and both positive and negative pressure coefficients. The negative and positive pressure coefficients of band gap are attributed to the strain in I-I (or Ba-Ba or both) and Ba-I distances along [hkl], respectively. The calculated band gaps are also compared with those experimentally determined. The average pressure coefficient of band gap of all six orientations (-0.071 eV/GPa) found to be significantly higher than that calculated (-0.047 eV/GPa) by volumetric pressure dependence. Various these issues have been discussed with consistent arguments. The electron effective mass me*=0.66m0 and the hole effective mass mh*=0.53m0 have been determined from the calculated band structure.

  9. Residual stress dependant anisotropic band gap of various (hkl) oriented BaI2 films

    International Nuclear Information System (INIS)

    The thermally evaporated layer structured BaI2 grows in various completely preferred (hkl) film orientations with different growth parameters like film thickness, deposition rate, substrate temperature, etc. which were characterized by structural, morphological, and optical absorption measurements. Structural analysis reveals the strain in the films and the optical absorption shows a direct type band gap. The varying band gaps of these films were found to scale linearly with their strain. The elastic moduli and other constants were also calculated using Density Functional Theory (DFT) formalism implemented in WIEN2K code for converting the strain into residual stress. Films of different six (hkl) orientations show stress free anisotropic band gaps (2.48–3.43?eV) and both positive and negative pressure coefficients. The negative and positive pressure coefficients of band gap are attributed to the strain in I-I (or Ba-Ba or both) and Ba-I distances along [hkl], respectively. The calculated band gaps are also compared with those experimentally determined. The average pressure coefficient of band gap of all six orientations (?0.071?eV/GPa) found to be significantly higher than that calculated (?0.047?eV/GPa) by volumetric pressure dependence. Various these issues have been discussed with consistent arguments. The electron effective mass me*=0.66m0 and the hole effective mass mh*=0.53m0 have been determined from the calculated band structure

  10. Nuclear structure calculations in vanadium isotopes

    International Nuclear Information System (INIS)

    Nuclear structure calculations for the low-lying states in even-N isotopes sup(47, 49, 51)V and odd-N isotopes sup(48, 50)V are performed in the framework of Hartree-Fock projection formalism. All the nucleous outside 40Ca core are explicitly treated in the pf-shell configuration space by employing a realistic nucleon-nucleon interaction. The energy levels, static electromagnetic moments and the electromagnetic transition probabilities are evaluated from band-mixing calculations wherein the lowest four energetically close intrinsic states of the nuclei are taken into account. The theoretical results are in fair agreement with the experimental data. (author)

  11. Hyperspectral band depth analysis for a better estimation of grass biomass ( Cenchrus ciliaris) measured under controlled laboratory conditions

    Science.gov (United States)

    Mutanga, Onisimo; Skidmore, Andrew K.

    2004-05-01

    Remote sensing of grass quantity is important for providing information about the productivity and functioning of rangelands. Existing indices used to estimate grass quantity, such as normalized difference vegetation index (NDVI) are of limited value due to the saturation problem, especially in dense vegetation with 100% leaf area cover. Therefore, there is need to explore new techniques to resolve the saturation problem. In this study we tested the utility of band depth analysis to estimate grass quantity in dense vegetation. Band depth indices calculated from continuum-removed spectra of Cenchrus ciliaris grass, measured at canopy level in the visible spectral domain (550-750 nm) were used to estimate biomass. Band depth analysis results were compared to two narrow band NDVIs calculated using near-infrared and red bands. Results indicate that, the band depth analysis methodology could estimate quantity with a high coefficient of determination of 0.81, 0.83, 0.86 and 0.85 for band depth (BD), band depth ratio (BDR), normalized band depth index (NBDI) and band depth normalized to area (BNA), respectively. Narrow band NDVIs yielded lower correlations (0.31 and 0.32 for NDVI 1 and NDVI 2, respectively). Thus, band depth can estimate quantity in densely vegetated areas where NDVI values reach an asymptote.

  12. Linear magnetostriction near Curie temperature: Analytical calculations

    International Nuclear Information System (INIS)

    Analytical calculations have been performed of the linear magnetostriction ?s in a t2g model band system. The Hamiltonian includes spin-orbit coupling, strain-dependent crystal field, orbital, and spin Zeeman energies. The model density of states is assumed to be six Lorenztian functions. We have calculated a ratio of a magnetostrictive critical index to the magnetic critical index ?=?ln(?s)/?ln(?)=?/?, where ? is the Stoner gap, ?=?ln(?s)/?ln(?), ?=?ln(?)/?ln(?), and ? is the reduced temperature. Information on many-body magnetic effects is assumed to be carried in the index ?; for a given ?, the coefficient ? is calculated within the Stoner model of a degenerate band. Results are obtained for different numbers of electrons in the model band. Qualitative agreement with experimental data is obtained, in particular, for amorphous alloys with small magnetostriction, based on Co and Ni. For these alloys, both experimental and theoretical results are higher than the commonly accepted value of 2.0, which was derived for insulators within the Callen theory. copyright 1997 American Institute of Physics

  13. Band structure of fcc-C60 solid state crystal study

    Directory of Open Access Journals (Sweden)

    S Javanbakht

    2009-09-01

    Full Text Available We studied the architecture of the C60 cluster to drive its atomic positions which can be seen at room temperature. We then used the obtained carbon positions as a basis set for the fcc structure to construct the fcc-C60 compound. Self consistent calculations were performed based on the density functional theory (DFT utilizing the accurate WIEN2K code to solve the single-particle Kohen-Sham equation within the augmented plane waves plus local orbital (APW+lo method. The cohesive energy has been found to be 1.537 eV for the fcc-C60 . The calculated small cohesive energy that results from the weak Van der Waals-London interactions among a C60 cluster with its nearest neighbors is in good agreement with experiment. The electron densities of states (DOSs were calculated for a C60 macromolecule as well as the fcc-C60 compound and the results were compared with each other. The band gap from DOS calculations has been found to be 0.7 eV. Band structures were also calculated within the generalized gradient approximation (GGA. The band structure calculation results in 1.04 eV for the direct band gap. Two kinds of ? and ? bonds were determined in the band structure. Our results are in good agreement with experiment and pseudopotential calculations.

  14. Understanding intermediate-band solar cells

    OpenAIRE

    Luque Lo?pez, Antonio; Marti? Vega, Antonio; Stanley, Colin

    2012-01-01

    The intermediate-band solar cell is designed to provide a large photogenerated current while maintaining a high output voltage. To make this possible, these cells incorporate an energy band that is partially filled with electrons within the forbidden bandgap of a semiconductor. Photons with insufficient energy to pump electrons from the valence band to the conduction band can use this intermediate band as a stepping stone to generate an electron-hole pair. Nanostructured materials and certain...

  15. Theory of Band Warping and its Effects on Thermoelectronic Transport Properties

    CERN Document Server

    Mecholsky, Nicholas A; Pegg, Ian L; Fornari, Marco

    2014-01-01

    Optical and transport properties of materials depend heavily upon features of electronic band structures in proximity to energy extrema in the Brillouin zone (BZ). Such features are generally described in terms of multi-dimensional quadratic expansions and corresponding definitions of effective masses. Multi-dimensional expansions, however, are permissible only under strict conditions that are typically violated by degenerate bands and even some non-degenerate bands. Suggestive terms such as "band warping" or "corrugated energy surfaces" have been used to refer to such situations and ad hoc methods have been developed to treat them. While numerical calculations may reflect such features, a complete theory of band warping has not been developed. We develop a generally applicable theory, based on radial expansions, and a corresponding definition of angular effective mass. Our theory also accounts for effects of band non-parabolicity and anisotropy, which hitherto have not been precisely distinguished from, if n...

  16. Band Structure and Fermi Surface of Cu2Sb by the LMTO Method

    DEFF Research Database (Denmark)

    Jan, J. P.; Skriver, Hans Lomholt

    1977-01-01

    The linear muffin-tin orbital (LMTO) method of bandstructure calculation has been applied to the simple tetragonal compound Cu2Sb. The d bands of Cu lie substantially below the Fermi level, and the Fermi surface is a recognizable distortion of the free-electron model. The Fermi surface has sheets in four bands. The first and second bands contain closed sheets, degenerate along a plane in the absence of spin-orbit splitting. The third band contains a multiply-connected sheet. The fourth band consists of undulating columns, degenerate along a plane with the third band in the absence of spin-orbit splitting, and of another closed sheet. Earlier de Haas-van Alphen results are explained semiquantitatively by the model, which also accounts for open orbits seen in high-field magnetoresistance experiments.

  17. Predicted photonic band gaps in diamond-lattice crystals built from silicon truncated tetrahedrons

    CERN Document Server

    Woldering, Léon A; Elwenspoek, Miko C

    2011-01-01

    Recently, a silicon micromachining method to produce tetrahedral silicon particles was discovered. In this report, we determine the optical properties of diamond-lattice photonic crystals when assembled from such particles. The optical properties are found using band structure calculations. We show that crystal structures built from such silicon tetrahedra are expected to display small stop gaps. Wide photonic band gaps appear when truncated tetrahedral particles are used to build the photonic crystals. With such truncated tetrahedral particles, a band gap with a width of 23.6% can be achieved, which is more than twice as wide compared to band gaps in self-assembled diamond-lattices of hard-spheres. The width of the band gap is insensitive to small deviations from the optimal amount of truncation. This works paves the way to a new class of silicon diamond-lattice band gap crystals that can be obtained through self-assembly.

  18. Band Structure and Optical Properties of Ordered AuCu3

    DEFF Research Database (Denmark)

    Skriver, Hans Lomholt; Lengkeek, H. P.

    1979-01-01

    The optical spectra of ordered AuCu3 have been measured at low temperatures by a direct ellipsometric technique. We find several structural elements above the absorption edge as well as in the infrared. The measured spectra are interpreted in terms of the interband absorption calculated from an ab initio band structure obtained by the relativistic linear muffin-tin orbitals method. The band calculation reveals that ordered AuCu3 has distinct copper and gold d bands positioned in and hybridizing with an s band common to copper and gold. The calculated state density is found to be in good agreement with experiment. The Fermi surface is presented and is found to originate mainly in copper 4s and 4p states.

  19. Band Anticrossing in Highly Mismatched Compound Semiconductor Alloys

    Science.gov (United States)

    Yu, Kin Man; Wu, J.; Walukiewicz, W.; Ager, J. W.; Haller, E. E.; Miotkowski, I.; Su, Ching-Hua; Curreri, Peter A. (Technical Monitor)

    2001-01-01

    Compound semiconductor alloys in which metallic anions are partially replaced with more electronegative isoelectronic atoms have recently attracted significant attention. Group IIIN(sub x)V(sub 1-x) alloys with a small amount of the electronegative N substituting more metallic column V elements has been the most extensively studied class of such Highly Mismatched Alloys (HMAs). We have shown that many of the unusual properties of the IIIN(sub x)V(sub 1-x) alloys can be well explained by the Band Anticrossing (BAC) model that describes the electronic structure in terms of an interaction between highly localized levels of substitutional N and the extended states of the host semiconductor matrix. Most recently the BAC model has been also used to explain similar modifications of the electronic band structure observed in Te-rich ZnS(sub x)Te(sub 1-x) and ZnSe(sub y)Te(sub 1-y) alloys. To date studies of HMAs have been limited to materials with relatively small concentrations of highly electronegative atoms. Here we report investigations of the electronic structure of ZnSe(sub y)Te(sub 1-y) alloys in the entire composition range, y between 0 and 1. The samples used in this study are bulk ZnSe(sub y)Te(sub 1-y) crystals grown by either a modified Bridgman method or by physical vapor transport. Photomodulated reflection (PR) spectroscopy was used to measure the composition dependence of optical transitions from the valence band edge and from the spin-orbit split off band to the conduction band. The pressure dependence of the band gap was measured using optical absorption in a diamond anvil cell. We find that the energy of the spin-orbit split off valence band edge does not depend on composition and is located at about 3 eV below the conduction band edge of ZnSe. On the Te-rich side the pressure and the composition dependence of the optical transitions are well explained by the BAC model which describes the downward shift of the conduction band edge in terms of the interaction between localized Se states and the conduction band. On the other hand we show that the large band gap reduction observed on the Se-rich side of the alloy system is a result of an interaction between the localized Te level and the valence bands. This interaction leads to the formation of a Te-like valence band edge that strongly interacts with the light hole valence band. Calculations based on a modified k(sup dot)p model account for the reduction of the band gap and the large increase of the spin-orbit splitting observed in Se-rich ZnSe(sub y)Te(sub 1-y) alloys. We will also discuss the importance of these new results for understanding of the electronic structure and band offsets in other highly mismatched alloy systems.

  20. Metaphyseal bands in osteogenesis imperfecta

    Directory of Open Access Journals (Sweden)

    Suresh S

    2010-01-01

    Full Text Available An increasing number of patients with osteogenesis imperfecta are undergoing pamidronate therapy to prevent the incidence of fragility fractures. The authors herein report a child aged 3 years who received five cycles of pamidronate, resulting in metaphyseal bands, known as "zebra lines."

  1. Metaphyseal bands in osteogenesis imperfecta

    OpenAIRE

    Suresh S; Thomas John

    2010-01-01

    An increasing number of patients with osteogenesis imperfecta are undergoing pamidronate therapy to prevent the incidence of fragility fractures. The authors herein report a child aged 3 years who received five cycles of pamidronate, resulting in metaphyseal bands, known as "zebra lines."

  2. Band structure and nuclear dynamics

    International Nuclear Information System (INIS)

    The relation between the Variable Moment of Inertia model and the Interacting Boson Model are discussed from a phenomenological viewpoint. New results on ground state mean-square radii in nuclei far from stability are reported, and a discussion of band structure extending to high angular momentum states and methods of extracting information on the underlying dynamics is given

  3. Polarizability calculations on water, hydrogen, oxygen, and carbon dioxide

    Science.gov (United States)

    Nir, S.; Adams, S.; Rein, R.

    1973-01-01

    A semiclassical model of damped oscillators is used as a basis for the calculation of the dispersion of the refractive index, polarizability, and dielectric permeability in water, hydrogen, and oxygen in liquid and gaseous states, and in gaseous carbon dioxide. The absorption coefficient and the imaginary part of the refractive index are also calculated at corresponding wavelengths. A good agreement is obtained between the observed and calculated values of refractive indices, and between those of absorption coefficients in the region of absorption bands. The calculated values of oscillator strengths and damping factors are also discussed. The value of the polarizability of liquid water was about 2.8 times that of previous calculations.

  4. Electronic band structure of the ordered Zn0.5Cd0.5Se alloy calculated by the semi-empirical tight-binding method considering second-nearest neighbor / Estructura electrónica de bandas de la aleación ordenada de Zn0.5Cd0.5Se calculada por el método semi-empírico de enlace fuerte teniendo en cuenta interacción a segundos vecinos

    Scientific Electronic Library Online (English)

    Juan Carlos, Salcedo-Reyes.

    2008-07-01

    Full Text Available Aunque la descripción de las aleaciones ternarias semiconductoras se hace tradicionalmente asumiendo la aproximación de compuesto pseudo-binario. Para el caso de aleaciones artificiales de compuestos II-VI y III-V, en las cuales se ha reportado un ordenamiento inducido por el crecimiento, una aproxi [...] mación de este tipo no es aplicable, de modo que, con el fin de hacer una descripción adecuada de las propiedades ópticas y electrónicas de dichas aleaciones artificiales, se debe asumir una descripción atomística que tenga en cuenta la estructura local. En particular, para la aleación ordenada de Zn0.5Cd0.5Se, el cambio de simetría implica que se debe usar una estructura tetragonal simple, dando lugar, principalmente, a dos efectos: i) disminución de la brecha prohibida del material y ii) un desdoblamiento en el máximo de la banda de valencia. En este trabajo se calcula la estructura de bandas de la aleación ordenada de Zn0.5Cd0.5Se usando la aproximación semi-empírica de enlace fuerte teniendo en cuenta interacción a segundos vecinos y se compara con la estructura de bandas obtenida por el método FP-LAPW (full-potential linearized augmentedplane wave). Se obtiene una buena concordancia de las principales características entre las estructuras de bandas calculadas por el método semi-empírico y el método ab initio. Abstract in english Usually, semiconductor ternary alloys are studied via a pseudo-binary approach in which the semiconductor is described like a crystalline array were the cation/anion sub-lattice consist of a random distribution of the cationic/anionic atoms. However, in the case of reported III-V and II-VI artificia [...] l structures, in which an ordering of either the cations or the anions of the respective fcc sub-lattice is involved, a pseudo-binary approach can no longer be employed, an atomistic point of view, which takes into account the local structure, must be used to study the electronic and optical properties of these artificial semiconductor alloys. In particular, the ordered Zn0.5Cd0.5Se alloy has to be described as a crystal with the simple-tetragonal Bravais lattice with a composition equal to the zincblende random ternary alloy. The change of symmetry properties of the tetragonal alloy, in relation to the cubic alloy, results mainly in two effects: i) reduction of the banned gap, and ii) crystal field cleavage of the valence band maximum. In this work, the electronic band structure of the ordered Zn0.5Cd0.5Se alloy is calculated using a second nearest neighbor semi-empirical tight binding method. Also, it is compared with the electronic band structure obtained by FP-LAPW (fullpotential linearized augmented-plane wave) method.

  5. Photovoltaic properties of low band gap ferroelectric perovskite oxides

    Science.gov (United States)

    Huang, Xin; Paudel, Tula; Dong, Shuai; Tsymbal, Evgeny

    2015-03-01

    Low band gap ferroelectric perovskite oxides are promising for photovoltaic applications due to their high absorption in the visible optical spectrum and a possibility of having large open circuit voltage. Additionally, an intrinsic electric field present in these materials provides a bias for electron-hole separation without requiring p-n junctions as in conventional solar cells. High quality thin films of these compounds can be grown with atomic layer precision allowing control over surface and defect properties. Initial screening based on the electronic band gap and the energy dependent absorption coefficient calculated within density functional theory shows that hexagonal rare-earth manganites and ferrites are promising as photovoltaic absorbers. As a model, we consider hexagonal TbMnO3. This compound has almost ideal band gap of about 1.4 eV, very high ferroelectric Curie temperature, and can be grown epitaxially. Additionally hexagonal TbMnO3 offers possibility of coherent structure with transparent conductor ZnO. We find that the absorption is sufficiently high and dominated by interband transitions between the Mn d-bands. We will present the theoretically calculated photovoltaic efficiency of hexagonal TbMnO3 and explore other ferroelectric perovskite oxides.

  6. Band structure of CdTe under high pressure

    International Nuclear Information System (INIS)

    The band structures and density of states of cadmium telluride (CdTe) under various pressures ranging from normal to 4.5 Mbar are obtained. The electronic band structure at normal pressure of CdTe (ZnS structure) is analyzed and the direct band gap value is found to be 1.654 eV. CdTe becomes metal and superconductor under high pressure but before that it undergoes structural phase transition from ZnS phase to NaCl phase. The equilibrium lattice constant, bulk modulus and the phase transition pressure at which the compounds undergo structural phase transition from ZnS to NaCl are predicted from the total energy calculations. The density of states at the Fermi level (N(EF)) gets enhanced after metallization, which leads to the superconductivity in CdTe. In our calculation, the metallization pressure (PM = 1.935 Mbar) and the corresponding reduced volume ((V/V0)M = 0.458) are estimated. Metallization occurs via direct closing of band gap at ? point. (author)

  7. High spin band structure of 3885Sr47

    Science.gov (United States)

    Kumar, S.; Kumar, Naveen; Mandal, S.; Pancholi, S. C.; Srivastava, P. C.; Jain, A. K.; Palit, R.; Saha, S.; Sethi, J.; Naidu, B. S.; Donthi, R.; Joshi, P. K.; Trivedi, T.; Muralithar, S.; Singh, R. P.; Kumar, R.; Dhal, A.; Bhowmik, R. K.

    2014-08-01

    High spin states in the Sr85 nucleus were populated in the reaction Ge76(13C,4n) at a beam energy of 45 MeV. The ?-? and ?-?-? coincidence measurements have been utilized to establish the level scheme of Sr85 up to I?=35/2-. Nearly 50 new ? rays and about 25 new levels were identified and most of the previously known levels confirmed. The spin-parity assignment of the levels was made by using the directional correlations of the oriented nuclei ratios and polarization asymmetry measurements. The shell-model calculations have been performed by using two recent interactions, JUN45 and jj44b, for a detailed comparison between theoretical results and the experimental data obtained in the present work. The shell-model results are in good agreements with the experimental data and are able to explain the various features such as the odd-even staggering well. Tilted axis cranking calculations were also performed to understand the magnetic rotation (MR) phenomenon at higher spins. One of the positive-parity ?I =1 bands has been assigned a three-quasiparticle (3qp) configuration, which appears to behave like a MR band. A negative-parity band populated up to I?=35/2- was also assigned a 3qp configuration at low spin and a five-quasiparticle configuration at high spin; however, it does not exhibit the expected MR features, in contrast to a similar band in the Kr83 nucleus.

  8. Table of superdeformed nuclear bands and fission isomers

    Energy Technology Data Exchange (ETDEWEB)

    Firestone, R.B. [Lawrence Berkeley Lab., CA (United States); Singh, B. [McMaster Univ., Hamilton, ON (Canada)

    1994-06-01

    A minimum in the second potential well of deformed nuclei was predicted and the associated shell gaps are illustrated in the harmonic oscillator potential shell energy surface calculations shown in this report. A strong superdeformed minimum in {sup 152}Dy was predicted for {beta}{sub 2}-0.65. Subsequently, a discrete set of {gamma}-ray transitions in {sup 152}DY was observed and, assigned to the predicted superdeformed band. Extensive research at several laboratories has since focused on searching for other mass regions of large deformation. A new generation of {gamma}-ray detector arrays is already producing a wealth of information about the mechanisms for feeding and deexciting superdeformed bands. These bands have been found in three distinct regions near A=l30, 150, and 190. This research extends upon previous work in the actinide region near A=240 where fission isomers were identified and also associated with the second potential well. Quadrupole moment measurements for selected cases in each mass region are consistent with assigning the bands to excitations in the second local minimum. As part of our committment to maintain nuclear structure data as current as possible in the Evaluated Nuclear Structure Reference File (ENSDF) and the Table of Isotopes, we have updated the information on superdeformed nuclear bands. As of April 1994, we have complied data from 86 superdeformed bands and 46 fission isomers identified in 73 nuclides for this report. For each nuclide there is a complete level table listing both normal and superdeformed band assignments; level energy, spin, parity, half-life, magneto moments, decay branchings; and the energies, final levels, relative intensities, multipolarities, and mixing ratios for transitions deexciting each level. Mass excess, decay energies, and proton and neutron separation energies are also provided from the evaluation of Audi and Wapstra.

  9. Table of superdeformed nuclear bands and fission isomers

    International Nuclear Information System (INIS)

    A minimum in the second potential well of deformed nuclei was predicted and the associated shell gaps are illustrated in the harmonic oscillator potential shell energy surface calculations shown in this report. A strong superdeformed minimum in 152Dy was predicted for ?2-0.65. Subsequently, a discrete set of ?-ray transitions in 152DY was observed and, assigned to the predicted superdeformed band. Extensive research at several laboratories has since focused on searching for other mass regions of large deformation. A new generation of ?-ray detector arrays is already producing a wealth of information about the mechanisms for feeding and deexciting superdeformed bands. These bands have been found in three distinct regions near A=l30, 150, and 190. This research extends upon previous work in the actinide region near A=240 where fission isomers were identified and also associated with the second potential well. Quadrupole moment measurements for selected cases in each mass region are consistent with assigning the bands to excitations in the second local minimum. As part of our committment to maintain nuclear structure data as current as possible in the Evaluated Nuclear Structure Reference File (ENSDF) and the Table of Isotopes, we have updated the information on superdeformed nuclear bands. As of April 1994, we have complied data from 86 superdeformed bands and 46 fission isomers identified in 73 nuclides for this report. For each nuclide there is a complete level table listing both normal and superdeformed band assignments; level energy, spin, parity, half-life, magneto moments, decay branchings; and the energies, final levels, relative intensities, multipolarities, and mixing ratios for transitions deexciting each level. Mass excess, decay energies, and proton and neutron separation energies are also provided from the evaluation of Audi and Wapstra

  10. Monolayer semiconducting transition metal dichalcogenide alloys: Stability and band bowing

    Science.gov (United States)

    Kang, Jun; Tongay, Sefaattin; Li, Jingbo; Wu, Junqiao

    2013-04-01

    The stability and band bowing effects of two-dimensional transition metal dichalcogenide alloys MX2(1-x)X'2x (M = Mo, W, and X, X' = S, Se, Te) are investigated by employing the cluster expansion method and the special quasi-random structure approach. It is shown that for (S, Se) alloys, there exist stable ordered alloy structures with concentration x equal to 1/3, 1/2, and 2/3, which can be explained by the small lattice mismatch between the constituents and a large additional charge exchange, while no ordered configuration exists for (Se, Te) and (S, Te) alloys at 0 K. The calculated phase diagrams indicate that complete miscibility in the alloys can be achieved at moderate temperatures. The bowing in lattice constant for the alloys is quite small, while the bowing in band gap, and more so in band edge positions, is much more significant. By decomposing the formation of alloy into multiple steps, it is found that the band bowing is the joint effect of volume deformation, chemical difference, and a low-dimensionality enhanced structure relaxation. The direct band gaps in these alloys continuously tunable from 1.8 eV to 1.0 eV, along with the moderate miscibility temperatures, make them good candidates for two-dimensional optoelectronics.

  11. Strain sensitivity of band gaps of Sn-containing semiconductors

    DEFF Research Database (Denmark)

    Li, Hong; Castelli, Ivano Eligio

    2015-01-01

    Tuning of band gaps of semiconductors is a way to optimize materials for applications within photovoltaics or as photocatalysts. One way to achieve this is through applying strain to the materials. We investigate the effect of strain on a range of Sn-containing semiconductors using density functional theory and many-body perturbation theory calculations. We find that the band gaps of bulk Sn oxides with SnO6 octahedra are highly sensitive to volumetric strain. By applying a small isotropic strain of 2% (-2%), a decrease (increase) of band gaps as large as 0.8 to 1.0 eV are obtained. We attribute the ultrahigh strain sensitivity to the pure Sn s-state character of the conduction-band edges. Other Sn-containing compounds may show both increasing and decreasing gaps under tensile strain and we show that the behavior can be understood by analyzing the role of the Sn s states in both the valence and the conduction bands.

  12. On-orbit calibration performance of MODIS TDI bands

    Science.gov (United States)

    Chu, Mike; Sun, Junqiang; Angal, Amit; Chen, Hongda; Geng, Xu; Choi, Taeyoung; Xiong, Xiaoxiang (Jack)

    2013-09-01

    Bands 13 (667 nm) and 14 (678 nm) of the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra and Aqua satellites are built with a time delay and integration (TDI) circuit and a high-low dual-gain setting intended for the monitoring of the ocean environment. An important on-orbit performance issue for the high-gain output of Terra Band 14 and Aqua Band 13 and 14 is that these three bands saturate during standard on-orbit calibrations using the onboard solar diffuser (SD). Consequently, their calibration procedure requires a derivation different from other reflective solar bands (RSB). A high-low scaling-ratio approach is employed for these bands to obtain the high-gain coefficients via the low-gain output 13L and 14L through a calculated constant ratio derived from other sources. Currently, earth view (EV) scenes over the North Atlantic Ocean are used as the primary sources. As it also has been observed that the response versus scan-angle (RVS) exhibits noticeable changes with time for RSB, a time-dependent RVS calibration algorithm has been implemented based on the SD and lunar calibration results. This paper reviews the electronic design and operation of Band 13 and 14, discusses the SD calibration and the saturation issue of the high-gain output, and the time-dependent RVS algorithms. Long-term performance of the calibration coefficient and RVS are presented. The long-term trend shows that the gain-change for Terra MODIS Band 13 and 14, for both high- and lowgain bands, is significant at 6% and 23%, but is more modest for Aqua MODIS Band 13 and 14 at 6% and 2%. The gain ratios 13H/13L and 14H/14L are very stable at the level of 0.01% for both MODIS instruments. The long-term gain difference due to RVS effect is up to 3% for Terra MODIS and about 2% and below for Aqua MODIS.

  13. ''Shears bands'' in Pb nuclei - a new nuclear structure effect

    International Nuclear Information System (INIS)

    In nuclei in the mass region around A = 190-200 a large number of regular dipole sequences have recently been found. In these bands the gain in angular momentum may not be created by collective rotation as is usual for more deformed nuclei, but stems from aligning the proton and neutron spins in the direction of the total spin axis. Calculations within the framework of the tilted axis cranking model reproduce the available experimental data and support the alignment picture. (orig.)

  14. Generalized pseudopotential theory of d-band metals

    International Nuclear Information System (INIS)

    The generalized pseudopotential theory (GPT) of metals is reviewed with emphasis on recent developments. This theory, which attempts to rigorously extend to d-band metals the spirit of conventional simple-metal pseudopotential perturbation theory, has now been optimized and fully integrated with the Kohn-Sham local-density-functional formalism, allowing for systematic first-principles calculations. Recent work on the problems of cohesion, lattice dynamics, structural phase stability, pressure- and temperature-induced phase transitions, and melting is discussed

  15. Itinerant Flat-Band Magnetism in Hydrogenated Carbon Nanotubes

    OpenAIRE

    Yang, Xiaoping; Wu, Gang

    2010-01-01

    We investigate the electronic and magnetic properties of hydrogenated carbon nanotubes using ab initio spin-polarized calculations within both the local density approximation (LDA) and the generalized gradient approximation (GGA). We find that the combination of charge transfer and carbon network distortion makes the spin-polarized flat-band appear in the tube's energy gap. Various spin-dependent ground state properties are predicted with the changes of the radii, the chiral...

  16. Controlling Band Gap in Silicene Monolayer Using External Electric Field

    OpenAIRE

    Chinnathambi, Kamal

    2012-01-01

    We study the geometric and electronic structures of silicene monolayer using density functional theory based calculations. The electronic structures of silicene show that it is a semi-metal and the charge carriers in silicene behave like massless Dirac-Fermions since it possesses linear dispersion around Dirac point. Our results show that the band gap in silicene monolayer can be opened up at Fermi level due to an external electric field by breaking the inversion symmetry. T...

  17. Strong Band Hybridization between Silicene and Ag(111)Substrate

    OpenAIRE

    Yuan, Yakun; Quhe, Ruge; Zheng, Jiaxin; Wang, Yangyang; Ni, Zeyuan; Shi, Junjie; Lu, Jing

    2013-01-01

    By using first-principles calculations, we systematically investigated several observed phases of silicene on Ag(111) substrates and their electronic structures. We find that the original Dirac cone of silicene is about 1.5-1.7 eV deeply below the Fermi level and severely destroyed by the band hybridization between silicene and Ag in all the examined phases. Thus, silicene synthesized on Ag(111) substrates could not preserve its excellent electronic property and new method i...

  18. Periodic Anderson model with electron-phonon correlated conduction band

    OpenAIRE

    Zhang, Peng; Reis, Peter; Tam, Ka-Ming; Jarrell, Mark; Moreno, Juana; Assaad, Fakher; McMahan, Andy

    2012-01-01

    This paper reports dynamical mean field calculations for the periodic Anderson model in which the conduction band is coupled to phonons. Motivated in part by recent attention to the role of phonons in the $\\gamma$-$\\alpha$ transition in Ce, this model yields a rich and unexpected phase diagram which is of intrinsic interest. Specifically, above a critical value of the electron-phonon interaction, a first order transition with two coexisting phases develops in the temperature...

  19. Research reactor calculations

    International Nuclear Information System (INIS)

    Basic principles and physical models for practical research reactor calculations are presented using widely available computer codes. Core and fuel management calculations of plate-type and TRIGA reactors are considered. (author)

  20. Superposition of Waves Calculator

    Science.gov (United States)

    David Joiner

    The Superposition of Waves Calculators show the result of adding two or more waves of the form y = A * cos ( k * x + phi ) or y = A * cos ( k * x + phi - omega * t ). The calculation of wave packets is also included.

  1. Personal Finance Calculations.

    Science.gov (United States)

    Argo, Mark

    1982-01-01

    Contains explanations and examples of mathematical calculations for a secondary level course on personal finance. How to calculate total monetary cost of an item, monthly payments, different types of interest, annual percentage rates, and unit pricing is explained. (RM)

  2. Heterogeneous Calculation of ?

    International Nuclear Information System (INIS)

    A heterogeneous method of calculating the fast fission factor given by Naudet has been applied to the Carlvik - Pershagen definition of ?. An exact calculation of the collision probabilities is included in the programme developed for the Ferranti - Mercury computer

  3. Deformation bands in porous sandstones their microstructure and petrophysical properties

    Energy Technology Data Exchange (ETDEWEB)

    Torabi, Anita

    2007-12-15

    Deformation bands are commonly thin tabular zones of crushed or reorganized grains that form in highly porous rocks and sediments. Unlike a fault, typically the slip is negligible in deformation bands. In this dissertation the microstructure and petrophysical properties of deformation bands have been investigated through microscopy and numerical analysis of experimental and natural examples. The experimental work consists of a series of ring-shear experiments performed on porous sand at 5 and 20 MPa normal stresses and followed by microscopic examination of thin sections from the sheared samples. The results of the ring-shear experiments and comparison of them to natural deformation bands reveals that burial depth (level of normal stress in the experiments) and the amount of shear displacement during deformation are the two significant factors influencing the mode in which grains break and the type of shear zone that forms. Two end-member types of experimental shear zones were identified: (a) Shear zones with diffuse boundaries, which formed at low levels of normal stress and/or shear displacement; and (b) Shear zones with sharp boundaries, which formed at higher levels of normal stress and/or shear displacement. Our interpretation is that with increasing burial depth (approximately more than one kilometer, simulated in the experiments by higher levels of normal stress), the predominant mode of grain fracturing changes from flaking to splitting; which facilitates the formation of sharp-boundary shear zones. This change to grain splitting increases the power law dimension of the grain size distribution (D is about 1.5 in sharp boundary shear zones). Based on our observations, initial grain size has no influence in the deformation behavior of the sand at 5 MPa normal stresses. A new type of cataclastic deformation band is described through outcrop and microscopic studies; here termed a 'slipped deformation band'. Whereas previously reported cataclastic deformation bands are characterized by strain hardening, these new bands feature a central slip surface, which indicates late strain softening. They lack the characteristic compaction envelop, and are typified by higher porosity and lower permeability than previously-described cataclastic deformation bands. Intense background fracturing of the host rock and significant initial porosity are considered to be important in creating these newly-discovered deformation bands. In a related study, we investigate, for millimeter- wide deformation bands, the scale limitation inherent in laboratory measurements of porosity and permeability. The scale limitations imposed by the deformation band relative to the physical sample size motivated us to develop a new method for determining porosity and permeability based on image processing. While plug measurements measure the effective permeability across a 25.4 mm (1 inch) long sample, which includes both host rock and deformation band, the method presented here provides a means to estimate porosity and permeability of deformation band on microscale. This method utilizes low-order (one- and two orders) spatial correlation functions to analyze high-resolution, high-magnification backscatter images, to estimate the porosity and specific surface area of the pore-grain interface in the deformed sandstones. Further, this work demonstrates the use of a modified version of the Kozeny-Carmen relation to calculate permeability by using porosity and specific surface area obtained through the image processing. The result shows that permeability difference between the band and the host rock is up to four orders of magnitude. Moreover, the porosities and permeabilities estimated from image processing are lower than those obtained from their plug measurements; hence the traditional laboratory measurements have been overestimating permeability because of the previously-unrecognized scale problem. In addition, the image processing results clearly show that, as a result of microstructural variation, both porosity and permeability vary along the leng

  4. Population of rotational bands in superheavy nuclei

    International Nuclear Information System (INIS)

    The spectroscopy of superheavy elements (SHE) is very important for the modern nuclear physics. Comparing the structure predictions of different theoretical models with the experimental data, one can find out their applicability in the region of SHE. This can be very useful for the determination of the next proton magic number beyond Z = 82. Using the statistical approach, we study the population of rotational bands in super-heavy nuclei produced in fusion-evaporation reactions. The reactions 208Pb(48Ca, 2n)254No, 206Pb(48Ca, 2n)252No, and 204Hg(48Ca, 2n)250Fm are considered. The population cross section of state L+ depends on survival of the compound nucleus against fission. The calculated relative intensities of E2-transitions at different spins, which can be compared with the experimental values, are defined by these partial population cross sections. Fermi-gas model is used for the calculation of level densities, and damping of shell effects with excitation energy and angular momentum is taking into account. For more accurate description of the capture process near the Coulomb barrier we use the quantum diffusion approach based on the formalism of reduced density matrix. Taking the same set of parameters, we also describe the excitation functions for these reactions. The results are in a good agreement with the experiment data. Using the parameter of damping of shell effects with angular momentum, we can estimate the moment of inertia of the nucleus at the saddle point

  5. EO-1 Hyperion and ALI bands simulation to Landat 7 ETM+ bands for mineral mapping in Milos Island

    Science.gov (United States)

    Nikolakopoulos, Konstantinos G.; Tsombos, Panagiotis I.; Skianis, George Aim.; Vaiopoulos, Dimitrios A.

    2008-10-01

    During the last two decades, airborne hyperspectral sensors such as the AVIRIS or DAIS have been proved very useful but quite expensive tool for the detection and mapping of earth surface minerals. On November 2000 the launch of the Earth Observing 1 (EO-1) satellite, which included Hyperion, the first spaceborne imaging spectrometer, provided a new low cost tool in remote sensing research. This study evaluates hyperspectral data from Hyperion, as well as multispectral data from the EO-1 Advanced Land Imager (ALI) and the Landsat 7 ETM+ for mineral mapping in Milos Island. The three sensors examined in this study have similar spatial resolution, totally different spectral resolution and radiometric quality characteristics. All the data were collected the same day within one-minute time. As a result the atmospheric conditions were exactly the same and that make the data ideal for comparison. The performance of the EO-1 Hyperion imaging spectrometer with the Advanced Land Imager (ALI) and the Landsat 7 ETM+ sensor was compared using a method that aggregated portions of the Hyperion 10 nm bands to simulate the broader multispectral bands of ALI and ETM+. The general process was to calculate a weighted sum of the Hyperion bands that covered each Landsat band. The weights used in the sum were derived, by comparing the spectral response of the hyperspectral bands with the respective multispectral band. Different band ratios like the TM3/TM1 sensitive on the iron oxide detection, or different combinations sensitive on mineral (TM5/7, TM5/4, TM3/1) or hydrothermal anomalies (TM5/7, TM3/1, TM4/3) detection were used for the comparison of the three data sets and the results are presented in this study.

  6. Physics of cuprates with the two-band Hubbard model - The validity of the one-band Hubbard model

    CERN Document Server

    MacRidin, A; Jarrell, M; Sawatzky, G A; Maier, Th.

    2004-01-01

    We calculate the properties of the two-band Hubbard model using the Dynamical Cluster Approximation. The phase diagram resembles the generic phase diagram of the cuprates, showing a strong asymmetry with respect to electron and hole doped regimes, in agreement with experiment. Asymmetric features are also seen in one-particle spectral functions and in the charge, spin and d-wave pairing susceptibility functions. We address the possible reduction of the two-band model to a low-energy single-band one, as it was suggested by Zhang and Rice. Comparing the two-band Hubbard model properties with the single-band Hubbard model ones, we have found similar low-energy physics provided that the next-nearest-neighbor hopping term t' has a significant value ($t'/t \\approx 0.3$). The parameter t' is the main culprit for the electron-hole asymmetry. However, a significant value of t' cannot be provided in a strict Zhang and Rice picture where the extra holes added into the system bind to the existing Cu holes forming local s...

  7. Band gaps in InN/GaN superlattices: Nonpolar and polar growth directions

    International Nuclear Information System (INIS)

    The electronic structures of nonpolar short-period InN/GaN superlattices (SLs) grown in the wurtzite a- and m-directions have been calculated and compared to previous calculations for polar superlattices (grown in the c-direction). The variation of the band gaps with the composition (m, n) of the mInN/nGaN unit cells of the superlattices was examined. The band structures were obtained by self-consistent calculations based on the local density approximation to the density functional theory using the Linear-Muffin-Tin-Orbital method with a semi-empirical correction for the band gaps. The calculated band gaps and their pressure coefficients for nonpolar superlattices are similar to those calculated for bulk InGaN alloys with an equivalent In/Ga concentration ratio. This is very different from what has been found in polar superlattices where the band gaps are much smaller and vanish when the number m of InN layers in the unit cell exceeds three. A strong internal electric field is responsible for this behavior of polar structures. Experimental photoluminescence data for polar SLs agree very well with gaps calculated for the nonpolar structures. It is suggested that this is caused by screening of the electric field in the polar structures by carriers originating from unintentional defects

  8. Mechanism of photonic band gap, optical properties, tuning and applications

    International Nuclear Information System (INIS)

    Mechanism of occurrence of Photonic Band Gap (PBG) is presented for 3-D structure using close packed face centered cubic lattice. Concepts and our work, specifically optical properties of 3-D photonic crystal, relative width, filling fraction, effective refractive index, alternative mechanism of photonic band gap scattering strength and dielectric contrast, effect of fluctuations and minimum refractive index contrast, are reported. The temperature tuning and anisotropy of nematic and ferroelectric liquid crystal infiltrated opal for different phase transitions are given. Effective dielectric constant with filling fraction using Maxwell Garnet theory (MG), multiple modified Maxwell Garnet (MMMG) and Effective Medium theory (EM) and results are compared with experiment to understand the occurrence of PBG. Our calculations of Lamb shifts including fluctuations are given and compared with those of literature values. We have also done band structure calculations including anisotropy and compared isotropic characteristic of liquid crystal. A possibility of lowest refractive index contrast useful for the fabrication of PBG is given. Our calculations for relative width as a function of refractive index contrast are reported and comparisons with existing theoretical and experimental optimal values are briefed. Applications of photonic crystals are summarized. The investigations conducted on PBG materials and reported here may pave the way for understanding the challenges in the field of PBG. (author)

  9. Signature Splitting in 7/2 [633]v band of 175Hf

    Directory of Open Access Journals (Sweden)

    Singh Jagjit

    2014-03-01

    Full Text Available In this paper, we present an explanation of signature splitting observed in the one quasiparticle rotational band (7/2[633]? of 175Hf in terms of one particle plus rotor model (PRM calculations. The role of angular momentum dependence of the inertia parameter and rotational correction term appearing in Coriolis mixing calculations to explain signature effects is discussed.

  10. Research on identical bands of superdeformed nuclei

    International Nuclear Information System (INIS)

    The recent development of superdeformed identical bands are briefly reviewed. Some typical superdeformed bands are analyzed by the formula of Bohr-Mottelson's I(I + 1) expansion. The results show that the dynamic moments of inertia J(2) of so-called two identical bands are very similar, but kinetic moments of inertia J(1) and band head moments of inertia J0 are not equal. Signature partner bands are almost identical. Their J0, J(1), J(2) are almost identical respectively. Bohr-Mottelson Model is still one model which successfully explains the formation of identical bands

  11. Rotational bands in 115Sb

    International Nuclear Information System (INIS)

    High-spin states of 115Sb were studied by in-beam ?-ray spectroscopy using the 89Y (29Si, 2pn) fusionevaporation reaction at a beam energy of 108 MeV. The experiments included ?-? coincidence and directional correlation of oriented nuclei (DCO) ratio measurements using six BGO Compton suppressed Ge detectors. An intruder ?J=2 rotational band has been identified for the first time and it is interpreted as the h11/2 proton coupled to a two particle-two hole (2p-2h) deformed state of the 114Sn core. A ?J=1 rotational band based on the 2p-1h, ?{g27/2xg-19/2}, configuration has been extended to the 29/2+ state at an excitation energy of 5241 keV. (orig.)

  12. Dilatational band formation in bone

    OpenAIRE

    Poundarik, Atharva A.; Diab, Tamim; Sroga, Grazyna E.; Ural, Ani; Boskey, Adele L.; Gundberg, Caren M.; Vashishth, Deepak

    2012-01-01

    Toughening in hierarchically structured materials like bone arises from the arrangement of constituent material elements and their interactions. Unlike microcracking, which entails micrometer-level separation, there is no known evidence of fracture at the level of bone’s nanostructure. Here, we show that the initiation of fracture occurs in bone at the nanometer scale by dilatational bands. Through fatigue and indentation tests and laser confocal, scanning electron, and atomic force microsc...

  13. Ka-Band Mobile Experiments

    Science.gov (United States)

    Abbe, B. S.; Jedrey, T. C.; Agan, M. J.

    1994-01-01

    The National Aeronautics and Space Administration (NASA) through the Jet Propulsion Laboratory (JPL) has been involved in the development of mobile satcom technologies for more that ten years. The initial work was performed at L-band (1.5-1.6 GHz), and included system studies and analysis, subsystem and full terminal development, and culminated in numerous field experiments and demonstrations under the Mobile Satellite Experiments (MSAT-X) program.

  14. Transistorized wide band pulse amplifier

    International Nuclear Information System (INIS)

    A simple wide band amplifier is described below, having a stability better than 10/00 deg-1 centigrade, a current gain of 103, bandwidth of 30 MHz, and a signal to noise current ratio of about 100. This amplifier has been studied to answer the necessity of a fast transistor head amplifier for nuclear detectors, having in mind pile up and overloading problems. (author)

  15. Crossing of large multi-quasiparticle magnetic rotation bands in $^{198}$Bi

    CERN Document Server

    Pai, H; Bhattacharya, S; Bhattacharya, C; Bhattacharyya, S; Bhattacharjee, T; Basu, S K; Kundu, S; Ghosh, T K; Banerjee, K; Rana, T K; Meena, J K; Bhowmik, R K; Singh, R P; Muralithar, S; Chanda, S; Garg, R; Maheshwari, B; Jain, A K

    2014-01-01

    High-spin states in the doubly-odd $^{198}$Bi nucleus have been studied by using the $^{185,187}$Re($^{16}$O, xn) reactions at the beam energy of 112.5 MeV. $\\gamma-\\gamma$ coincidence were measured by using the INGA array with 15 Compton suppressed clover HPGe detectors. The observed levels have been assigned definite spin-parity. The high spin structure is grouped into three bands (B1, B2 and B3), of which two (B1 and B2) exhibit the properties of magnetic rotation (MR). Tilted axis cranking calculations were carried out to explain the MR bands having large multi-quasiparticle configurations. The calculated results explain the bands B1 and B2 very nicely, confirming the shears mechanism and suggest a crossing of two MR bands in both the cases. The crossing is from 6-qp to 8-qp in band B1 and from 4-qp to 6-qp in band B2, a very rare finding. A semiclassical model has also been used to obtain the particle-hole interaction strengths for the bands B1 and B2, below the band crossing.

  16. Entropic bands in quantum scattering

    International Nuclear Information System (INIS)

    In this paper we report the results on the investigation of some fundamental physical questions concerning entropic bounds, once the basic experimental information is fixed and used as constraints in the variational procedure. The optimal entropic upper bounds are proved by using Lagrange multipliers method and Tsallis-like entropies for quantum scattering of spinless particles. Hence, the problem is to find an upper bounds (for the lower bound see our earlier paper) for each Tsallis-like scattering entropy S?(q) (? ? ? , L, ?L, and q in R) when the elastic integrated cross section ? el and the forward differential cross section d?/d?, are fixed. The results are expressed in terms of the optimal entropies obtained from the principle of minimum distance in the space of states. To summarize, we conclude that by proving the optimal entropic upper bound as well as by extending the lower bounds, we introduced a new concept in quantum physics, namely the entropic bands. This new concept was experimentally illustrated using 49 sets of phase shifts of pion-nucleus scatterings. So, the first experimental tests of these entropic bands are presented for both, extensive (q=1) and nonextensive (q=0.75 and q=1.50) cases. Some results about the entropic bands in quantum physics are also presented in a recent paper published in Phys.Rev. E. (authors)

  17. Study of chiral bands by nucleon pair model

    International Nuclear Information System (INIS)

    Chiral band has its origin in the two combinations of spins which are generated when angular momentum of deformed nuclear core (even-even) and two angular momenta carried by one neutron and one proton are combined, and that cannot be rotationally transformed. Existence of two band pair nearly degenerated has been predicted corresponding to right-handed and left-handed band systems. Numbers of experimental results suggesting the pair have been recently reported in the region of odd-odd nuclei near the mass number 130. In this paper, results of analyses based on nucleon pair model, which is perfectly microscopic theory conserving both rotational symmetry and particle number, are reported on some candidates nuclei. SD pair model used here describes nuclear states by combining plural collective motion nucleon pairs which have either 0(S) or 2(D) angular momentum. Energy levels of Xe-132, Xe-131, Cs-133 and Cs-132 are calculated using five orbits both for neutrons and protons, and adopting pair correlation plus quadrupole-quadrupole interaction Hamiltonian. Low excitation levels are satisfactorily reproduced in the Xe-132 even-even nucleus. The wavering character of quasi band is also reproduced. For odd nuclei, Xe-131 and Cs-133, the experimental relation between even parity states and odd parity states are not reproduced successfully. For odd-odd nucleus Cs-132, alignment of valence nucleons and then changes of core angular momentum are found. It is concluded from this ctum are found. It is concluded from this calculation that the angular momentum of core, that of one neutron and that of one proton do not become mutually perpendicular. It is also concluded that the two bands cannot be separated as right-handed and left-handed ones. (S. Funahashi)

  18. Bosonic condensation in a flat energy band

    CERN Document Server

    Baboux, F; Jacqmin, T; Biondi, M; Lemaître, A; Gratiet, L Le; Sagnes, I; Schmidt, S; Türeci, H E; Amo, A; Bloch, J

    2015-01-01

    Flat bands are non-dispersive energy bands made of fully degenerate quantum states. Such bands are expected to support emergent phenomena with extraordinary spatial and temporal structures, as they strongly enhance the effect of any perturbation induced by disorder, dissipation or interactions. However, flat bands usually appear at energies above the ground state, preventing their study in systems in thermodynamic equilibrium. Here we use cavity polaritons to circumvent this issue. We engineer a flat band in a frustrated lattice of micro-pillar optical cavities. By taking advantage of the non-hermiticity of our system, we achieve for the first time bosonic condensation in a flat band. This allows revealing the peculiar effect of disorder in such band: The condensate fragments into highly localized modes, reflecting the elementary eigenstates produced by geometric frustration. This non-hermitian engineering of a bosonic flat band condensate offers a novel approach to studying coherent phases of light and matte...

  19. Valence band structure and density of states effective mass model of biaxial tensile strained silicon based on k · p theory

    Science.gov (United States)

    Kuang, Qian-Wei; Liu, Hong-Xia; Wang, Shu-Long; Qin, Shan-Shan; Wang, Zhi-Lin

    2011-12-01

    After constructing a stress and strain model, the valence bands of in-plane biaxial tensile strained Si is calculated by k · p method. In the paper we calculate the accurate anisotropy valance bands and the splitting energy between light and heavy hole bands. The results show that the valance bands are highly distorted, and the anisotropy is more obvious. To obtain the density of states (DOS) effective mass, which is a very important parameter for device modeling, a DOS effective mass model of biaxial tensile strained Si is constructed based on the valance band calculation. This model can be directly used in the device model of metal—oxide semiconductor field effect transistor (MOSFET). It also a provides valuable reference for biaxial tensile strained silicon MOSFET design.

  20. Core calculations of JMTR

    Energy Technology Data Exchange (ETDEWEB)

    Nagao, Yoshiharu [Japan Atomic Energy Research Inst., Oarai, Ibaraki (Japan). Oarai Research Establishment

    1998-03-01

    In material testing reactors like the JMTR (Japan Material Testing Reactor) of 50 MW in Japan Atomic Energy Research Institute, the neutron flux and neutron energy spectra of irradiated samples show complex distributions. It is necessary to assess the neutron flux and neutron energy spectra of an irradiation field by carrying out the nuclear calculation of the core for every operation cycle. In order to advance core calculation, in the JMTR, the application of MCNP to the assessment of core reactivity and neutron flux and spectra has been investigated. In this study, in order to reduce the time for calculation and variance, the comparison of the results of the calculations by the use of K code and fixed source and the use of Weight Window were investigated. As to the calculation method, the modeling of the total JMTR core, the conditions for calculation and the adopted variance reduction technique are explained. The results of calculation are shown. Significant difference was not observed in the results of neutron flux calculations according to the difference of the modeling of fuel region in the calculations by K code and fixed source. The method of assessing the results of neutron flux calculation is described. (K.I.)

  1. Calculating strain in 3D DEM simulations

    Science.gov (United States)

    O'Sullivan, C.; Butlanska, J.; Cheung, G.

    2010-06-01

    Particulate DEM allows us to simulate and evaluate in detail the evolution of localizations in particulate material, whether bonded/cemented or unbonded. DEM simulations generate a wealth of particle scale data including particle displacements, velocities and contact forces. Traditionally in geomechanics we understand material response based upon a continuum mechanics framework that considers stress and strain. There is little debate as to how to calculate stress from DEM simulation results, however there is no consensus on how to calculate strain. Most of the methods proposed in the literature to calculate strain have considered the overall response of an assembly of grains, rather than the local in homogeneities that are associated with shear band evolution. This paper outlines the challenges associated with quantifying strain based upon DEM simulation results and demonstrates that a local wavelet based homogenization approach as proposed by may have advantages over triangulation based linear interpolation.

  2. Calculating strain in 3D DEM simulations

    International Nuclear Information System (INIS)

    Particulate DEM allows us to simulate and evaluate in detail the evolution of localizations in particulate material, whether bonded/cemented or unbonded. DEM simulations generate a wealth of particle scale data including particle displacements, velocities and contact forces. Traditionally in geomechanics we understand material response based upon a continuum mechanics framework that considers stress and strain. There is little debate as to how to calculate stress from DEM simulation results, however there is no consensus on how to calculate strain. Most of the methods proposed in the literature to calculate strain have considered the overall response of an assembly of grains, rather than the local in homogeneities that are associated with shear band evolution. This paper outlines the challenges associated with quantifying strain based upon DEM simulation results and demonstrates that a local wavelet based homogenization approach as proposed by may have advantages over triangulation based linear interpolation.

  3. The laparoscopic banded gastric bypass – operation technique

    Directory of Open Access Journals (Sweden)

    Simon Küsters

    2010-03-01

    Full Text Available The banded Roux-en-Y gastric bypass can be used as a primary or revisionary bariatric procedure. This article describesthe operation technique including materials, size and placement of the banding and gives an overview con cerningevolution and indications of the operation. A video of a primary banded Roux-en-Y gastric bypass is presented.

  4. Wavelength influence in sub-pixel temperature retrieval using the dual-band technique

    Directory of Open Access Journals (Sweden)

    M. F. Buongiorno

    2006-06-01

    Full Text Available The thermal model proposed by Crisp and Baloga (1990 for active lava flows considers thermal flux as a function of the fractional area of two thermally distinct radiant surfaces. In this model, the larger surface area corresponds to the cooler crust of the flow and the other, much smaller to fractures in the crust. These cracks temperature is much higher than the crust one and approaches the temperature of the molten or plastic interior flow. The dual-band method needs two distinct SWIR (short wave infrared bands to formulate a two equations system from the simultaneous solution of the Planck equation in each band. The system solutions consist in the crust temperature and the fractional area of the hot component. The dual band technique originally builds on data acquired by sensors (such as Landsat TM with two SWIR bands only. The use of hyperspectral imaging spectrometers allows us to test the dual-band technique using different wavelengths in the SWIR range of the spectrum. DAIS 7915 is equipped with 40 bands into the range 1.54-2.49 nm which represent potential input in dual band calculation. This study aims to compare results derived by inserting assorted couples of wavelengths into the equation system. The analysis of these data provides useful information on dual-band technique accuracy.

  5. Comparing C- and L-band SAR images for sea ice motion estimation

    Directory of Open Access Journals (Sweden)

    J. Lehtiranta

    2014-05-01

    Full Text Available Pairs of consecutive C-band SAR images are routinely used for sea ice motion estimation. In addition to the surface roughness L-band SAR imagery provides information of the seasonal sea ice inner structure, which is especially useful in the Baltic Sea lacking multiyear ice and icebergs. In this work, L-band SAR images are investigated for sea ice motion estimation using the well-established maximal cross-correlation approach. This work provides the first comparison of L-band and C-band SAR images for the purpose of motion estimation. The cross-correlation calculations are hardware accelerated using new OpenCL-based source code, which is made available through the author's web site. It is found that L-band images are preferable for motion estimation over C-band images. It is also shown that motion estimation is possible between a C-band and an L-band image using the maximal cross-correlation technique.

  6. Electron and hole states in quantum-dot quantum wells within a spherical 8-band model

    CERN Document Server

    Pokatilov, E P; Fomin, V M; Devreese, J T

    2001-01-01

    In order to study heterostructures composed both of materials with strongly different parameters and of materials with narrow band gaps, we have developed an approach, which combines the spherical 8-band effective-mass Hamiltonian and the Burt's envelope function representation. Using this method, electron and hole states are calculated in CdS/HgS/CdS/H_2O and CdTe/HgTe/CdTe/H_2O quantum-dot quantum-well heterostructures. Radial components of the wave functions of the lowest S and P electron and hole states in typical quantum-dot quantum wells (QDQWs) are presented as a function of radius. The 6-band-hole components of the radial wave functions of an electron in the 8-band model have amplitudes comparable with the amplitude of the corresponding 2-band-electron component. This is a consequence of the coupling between the conduction and valence bands, which gives a strong nonparabolicity of the conduction band. At the same time, the 2-band-electron component of the radial wave functions of a hole in the 8-band ...

  7. Rotational bands in 152Sm observed following the (?,2n?) reaction

    International Nuclear Information System (INIS)

    The level structure of 152Sm has been studied with various spectroscopic techniques using the (?,2n?) reaction. Seven rotational bands were identified up to spin values of 9 to 14h, viz. the ground-state band, the ?- and ?-bands, and four negative-parity bands (NPB's). In the ?-band a beginning of backbending or upbending was observed at I approx. equal to 14 h/2?. Two of the NPB's are based upon collective states; the lowest can be interpreted as an aligned octupole band, the other one shows two-quasiparticle characteristics at high spin. The properties of the other NPB's are consistent with Ksup(?) = 5- and Ksup(?) = 7- two-quasiparticle configurations of the bandheads. At high spin these bands are strongly mixed. Excitation energies for all bands with a collective bandhead, as well as B(E1) and B(E2) branching ratios and (for the ?-band) X(E0/E2) ratios, were compared with IBA calculations. (orig.)

  8. Theory of Auger electron and appearance-potential spectroscopy from solids with partially filled valence bands: Effects of valence-band-core interaction

    Science.gov (United States)

    Potthoff, M.; Braun, J.; Borstel, G.; Nolting, W.

    1993-05-01

    CVV Auger electron and appearance-potential spectra of solids are well known to exhibit strong satellite features depending on the ratio of on-site Coulomb interaction among the valence-band electrons U and the width of the free Bloch band W. We present a theory that additionally includes the effects of the Coulomb interaction between the valence-band electrons and the core electrons Uc. The spectra are influenced by the screening of the core hole in the initial state for Auger electron spectroscopy (AES), the sudden response of the valence-band electrons after the destruction of the core hole and, for appearance-potential spectroscopy (APS), by the scattering at the core hole in the final state. These effects become important especially for systems with partially filled energy bands. For APS, however, the Uc interaction already yields nontrivial effects for the limiting case of a completely empty valence band. The localized core hole implies a breakdown of translational symmetry in the distribution of the valence-band electrons, which renders the calculation more difficult. But, extending the theory to finite temperatures, we will show that the translational symmetry may be reestablished in a formal way. Both the AES and APS intensities are directly related to a proper three-particle spectral density that exactly reflects the crystal periodicity. Within the framework of the single-band Hubbard model, which is extended to include the Uc interaction, we calculate the three-particle spectral density in a generalized ladder approximation. The Uc interaction is treated by means of perturbation theory. We develop the theory for the zeroth- and first-order contributions and look at the interesting limiting cases of a completely filled and empty valence band.

  9. Franck-Condon factors and r-centroids for the B-X bands of 10B18O and 11B18O molecules

    Directory of Open Access Journals (Sweden)

    VOJISLAV BOJOVIC

    2005-05-01

    Full Text Available Frank–Condon factors and r-centroids have been calculated for the B2S+ –X2S+ bands of the 10B18O and 11B18O isotopic molecules assuming that both the B and X states follow a Morse potential curve. The calculated q n'n" values are compared with observed band intensities and the relationship between the r-centroids and the band positions has been determined and is discussed.

  10. Self-consistent Green's function method for dilute nitride conduction band structure

    International Nuclear Information System (INIS)

    We present a self-consistent Green's function (SCGF) approach for the Anderson many-impurity model to calculate the band dispersion and density of states near the conduction band edge in GaNxAs1?x dilute nitride alloys. Two different models of the N states have been studied to investigate the band structure of these materials: (1) the two-band model, which assumes all N states have the same energy, EN; (2) a model which includes a full distribution of N states obtained by allowing for direct interaction between N sites. The density of states, projected onto extended and localised states, calculated by the SCGF two-band model, are in excellent agreement with those previously obtained in supercell calculations and reveal a gap in the density of states just above EN, in contrast with the results of previous non-self-consistent Green's function calculations. However, including the full distribution of N states in a SCGF calculation removes this gap, in agreement with experiment. (paper)

  11. Anomalous band-gap bowing of AlN(1-x)Px alloy

    OpenAIRE

    M. J. Winiarski; Polak, M.; Scharoch, P.

    2014-01-01

    Electronic structure of zinc blende AlN(1-x)$Px alloy has been calculated from first principles. Structural optimisation has been performed within the framework of LDA and the band-gaps calculated with the modified Becke-Jonson (MBJLDA) method. Two approaches have been examined: the virtual crystal approximation (VCA) and the supercell-based calculations (SC). The composition dependence of the lattice parameter obtained from the SC obeys Vegard's law whereas the volume optim...

  12. TRIGLAV, Research Reactor Calculations

    International Nuclear Information System (INIS)

    1 - Description of program or function: A computer program for reactor calculations of mixed cores in TRIGA Mark II research reactor. It can be applied for fuel element burn-up calculations, for power and flux distributions calculations and for reactivity predictions. 2 - Methods: Program is based on four group time independent diffusion equation in two dimensional cylindrical (r, theta) geometry. Diffusion equation is solved using finite differences method with iteration of fission density

  13. Recent developments in high-spin calculations in atomic nuclei

    International Nuclear Information System (INIS)

    A brief introduction to the recent achievements in the high-spin domain in nuclear physics is given. Results of the calculations in highly developed rotational bands in deformed nuclei, as well as the calculations in the structure of the yrast isomers are presented. The calculations fail in two aspects: local minima in the yrast line are not confirmed experimentally, the overall slope of the yrast line in 152Dy is considerably overestimated. The calculations of the yrast line with new Woods-Saxon parameters are now in progress. The parameters are chosen to reproduce the large gap in the levels at proton number Z=64. (M.H.)

  14. Electronics Environmental Benefits Calculator

    U.S. Environmental Protection Agency — The Electronics Environmental Benefits Calculator (EEBC) was developed to assist organizations in estimating the environmental benefits of greening their purchase,...

  15. Electrical installation calculations basic

    CERN Document Server

    Kitcher, Christopher

    2013-01-01

    All the essential calculations required for basic electrical installation workThe Electrical Installation Calculations series has proved an invaluable reference for over forty years, for both apprentices and professional electrical installation engineers alike. The book provides a step-by-step guide to the successful application of electrical installation calculations required in day-to-day electrical engineering practice. A step-by-step guide to everyday calculations used on the job An essential aid to the City & Guilds certificates at Levels 2 and 3Fo

  16. Magnetic Field Grid Calculator

    National Oceanic and Atmospheric Administration, Department of Commerce — The Magnetic Field Properties Calculator will computes the estimated values of Earth's magnetic field(declination, inclination, vertical component, northerly...

  17. Waste Package Lifting Calculation

    International Nuclear Information System (INIS)

    The objective of this calculation is to evaluate the structural response of the waste package during the horizontal and vertical lifting operations in order to support the waste package lifting feature design. The scope of this calculation includes the evaluation of the 21 PWR UCF (pressurized water reactor uncanistered fuel) waste package, naval waste package, 5 DHLW/DOE SNF (defense high-level waste/Department of Energy spent nuclear fuel)--short waste package, and 44 BWR (boiling water reactor) UCF waste package. Procedure AP-3.12Q, Revision 0, ICN 0, calculations, is used to develop and document this calculation

  18. An alternative tool to explain Hooke’s Law and the principle of Dynamometer: The rubber band

    Directory of Open Access Journals (Sweden)

    Gül Ünal Çoban

    2011-03-01

    Full Text Available In this experiment, behaviors of the elastic materials when exerted a force were interpreted through the graphs wherethe elasticity coefficient of the rubber band was calculated. At the same time, the reason for using an elastic materialinside the dynamometer and the limits of elasticity were discussed by two different demonstrations conducted withrubber band.

  19. An alternative tool to explain Hooke’s Law and the principle of Dynamometer: The rubber band

    OpenAIRE

    Gül Ünal Çoban; Serap Kaya ?engören; Seda Korkubilmez

    2011-01-01

    In this experiment, behaviors of the elastic materials when exerted a force were interpreted through the graphs wherethe elasticity coefficient of the rubber band was calculated. At the same time, the reason for using an elastic materialinside the dynamometer and the limits of elasticity were discussed by two different demonstrations conducted withrubber band.

  20. Band gap bowing and electron localization of GaxIn1-xN

    Science.gov (United States)

    Lee, Byounghak; Wang, Lin Wang

    2006-11-01

    The band gap bowing and the electron localization of GaxIn1-xN are calculated using both the local density approximation (LDA) and screened-exchange local density functional (sX-LDA) methods. The calculated sX-LDA band gaps are in good agreement with the experimentally observed values, with errors of -0.26 and 0.09eV for bulk GaN and InN, respectively. The LDA band gap errors are 1.33 and 0.81eV for GaN and InN, in order. In contrast to the gap itself, the band gap bowing parameter is found to be very similar in sX-LDA and LDA. We identify the localization of hole states in GaxIn1-xN alloys along In-N-In chains. The predicted localization is stronger in sX-LDA.

  1. Superdeformed bands in 80-83Sr, 82-84Y, 83,84Zr: Transition quadrupole moments, moments of inertia, and configuration assignments

    International Nuclear Information System (INIS)

    Multiple superdeformed bands in the nuclei 80-83Sr, 82-84Y, and 83,84Zr have been studied in a backed-target experiment, using the Gammasphere and the Microball 4? detector arrays. For 15 bands in these nuclei, average transition quadrupole moments have been measured with high accuracy, using the Doppler-shift attenuation method. Among these are the newly observed superdeformed bands in 83,84Y, which are 'isospectral' with the bands in 82,83 Sr. These 'isospectral' bands have nearly identical transition quadrupole moments. Two of the bands in 81Sr interact and cross transitions between them are observed. The present measurements place stringent conditions on configuration assignments for the bands obtained from two types of mean-field calculations, leading to a consistent understanding of the mass ?80 superdeformed bands. The assignments for different bands arise from one or more nucleons occupying the N0=5h11/2 intruder orbital

  2. S-Band Antenna Array

    OpenAIRE

    Dalevi, Mathias

    2010-01-01

    This report presents concepts for a planar active electronically scanned antenna(AESA). The goal of the project was to devlop a low-weight, low profile, thin, S-band antenna with wide-scan angle capabilities. In the final concept the service aspects of the T/R-modules was also taken into acount in order to allow easy and fast replacements of these components. The antenna was designed and optimised using the commercial software Ansoft HFSS. A prototype of the antenna was constructed and later ...

  3. Detailed Study of the TE band structure of two dimensional metallic photonic crystals with square symmetry

    Science.gov (United States)

    Sedghi, Aliasghar; Valiaghaie, Soma; Soufiani, Ahad Rounaghi

    2014-10-01

    By virtue of the efficiency of the Dirichlet-to-Neumann map method, we have calculated, for H-polarization (TE mode), the band structure of 2D photonic crystals with a square lattice composed of metallic rods embedded in an air background. The rod in the unit cell is chosen to be circular in shape. Here, from a practical point of view, in order to obtain maximum band gaps, we have studied the band structure as a function of the size of the rods. We have also studied the flat bands appearing in the band structures and have shown that for frequencies around the surface plasmon frequency, the modes are highly localized at the interface between the metallic rods and the air background.

  4. Fe-substituted indium thiospinels: New intermediate band semiconductors with better absorption of solar energy

    Science.gov (United States)

    Chen, Ping; Chen, Haijie; Qin, Mingsheng; Yang, Chongyin; Zhao, Wei; Liu, Yufeng; Zhang, Wenqing; Huang, Fuqiang

    2013-06-01

    The indium thiospinels In2S3 and MgIn2S4 are promising host for the intermediated band (IB) photovoltaic materials due to their ideal band gap value. Here, the optical properties and electronic structure of Fe-doped In2S3 and MgIn2S4 have been investigated. All the Fe-substituted semiconductors exhibit two additional absorption bands at about 0.7 and 1.25 eV, respectively. The results of first-principles calculations revealed that the Fe substituted at the octahedral In site would introduce a partially filled IB into the band gap. Thanks to the formation of IB, the Fe-substituted semiconductors have the ability to absorb the photons with energies below the band gap. With the wide-spectrum absorption of solar energy, these materials possess potential applications in photovoltaic domain.

  5. Unified description of perturbation theory and band center anomaly in one-dimensional Anderson localization

    International Nuclear Information System (INIS)

    We calculated numerically the localization length of one-dimensional Anderson model with diagonal disorder. For weak disorder, we showed that the localization length changes continuously as the energy changes from the band center to the boundary of the anomalous region near the band edge. We found that all the localization lengths for different disorder strengths and different energies collapse onto a single curve, which can be fitted by a simple equation. Thus the description of the perturbation theory and the band center anomaly were unified into this equation. -- Highlights: ? We study the band center anomaly of one-dimensional Anderson localization. ? We study numerically the Lyapunov exponent through a parametrization method of the transfer matrix. ? We give a unified equation to describe the band center anomaly and perturbation theory.

  6. Band alignment between GaN and ZrO2 formed by atomic layer deposition

    International Nuclear Information System (INIS)

    The band alignment between Ga-face GaN and atomic-layer-deposited ZrO2 was investigated using X-ray photoelectron spectroscopy (XPS). The dependence of Ga 3d and Zr 3d core-level positions on the take-off angles indicated upward band bending at GaN surface and potential gradient in ZrO2 layer. Based on angle-resolved XPS measurements combined with numerical calculations, valence band discontinuity ?EV of 1?±?0.2?eV and conduction band discontinuity ?EC of 1.2?±?0.2?eV at ZrO2/GaN interface were determined by taking GaN surface band bending and potential gradient in ZrO2 layer into account.

  7. Band alignment between GaN and ZrO2 formed by atomic layer deposition

    Science.gov (United States)

    Ye, Gang; Wang, Hong; Arulkumaran, Subramaniam; Ng, Geok Ing; Li, Yang; Liu, Zhi Hong; Ang, Kian Siong

    2014-07-01

    The band alignment between Ga-face GaN and atomic-layer-deposited ZrO2 was investigated using X-ray photoelectron spectroscopy (XPS). The dependence of Ga 3d and Zr 3d core-level positions on the take-off angles indicated upward band bending at GaN surface and potential gradient in ZrO2 layer. Based on angle-resolved XPS measurements combined with numerical calculations, valence band discontinuity ?EV of 1 ± 0.2 eV and conduction band discontinuity ?EC of 1.2 ± 0.2 eV at ZrO2/GaN interface were determined by taking GaN surface band bending and potential gradient in ZrO2 layer into account.

  8. Straddling to staggered band gap transition and optics of double-walled carbon nanotubes

    Science.gov (United States)

    Kutana, Alex; Artyukhov, Vasilii I.; Yakobson, Boris I.

    2015-03-01

    Single-walled carbon nanotubes have outstanding optical properties that show pronounced dependence on their helicity. Techniques for helicity separation or selective growth enabled extensive studies of their optics. However, in double-walled nanotubes (DWNT) the inner wall helicity is hard to control. Only recently effective techniques for DWNT sorting and helicity assignment were developed, and experiments on helicity-controlled DWNT reveal remarkable new optical effects. Here we study the effect of breaking of ? band symmetry by wall curvature, creating a potential difference between the inside and outside of a nanotube. In DWNT, this intrinsic flexoelectric voltage, V ~ 1 / R , shifts the bands of the inner wall, and above a certain threshold the voltage exceeds the band offset (~ 1 /R2), marking the transition from conventional straddling to staggered band structure, where frontier electronic bands are localized on different walls. This has dramatic optical implications which we study using density functional theory and many-body GW +BSE calculations.

  9. Band Alignment for Ambipolar-Doping of SnxZn1-xTe Alloys

    International Nuclear Information System (INIS)

    Using the first-principles band-structure method and a special quasirandom structure (SQS) approach, we have systematically calculated the alloy bowing coefficients and the nature band offsets of SnxZn1-xTe alloys. We show that the bowing coefficients and band gaps of these alloys are sensitively composition dependent. Due to wave functions full overlapping and delocalization of the Sn outermost p orbits and Zn s orbits, the coupling between these states is very strong, resulting in a significant downshift of conduction band edge with the increase of the Sn concentration x, While the valence band edge keeps almost unchanged compared with that of the binary ZnTe, thus improving the possibility for ambipolar-doping. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  10. Study of the satellite bands of RbCs molecule in the near UV

    International Nuclear Information System (INIS)

    By comparing high-resolution absorption spectra of Rb and Cs vapor with Rb–Cs vapor mixture spectrum we were able to identify several satellite bands of RbCs molecule at 362.2 nm, 372.5 nm and 390.7 nm. These bands represent lower Rydberg states of the RbCs molecule which may be further studied at ultracold conditions. - Highlights: • Comparison of high-resolution absorption spectra of Rb, Cs and RbCs vapor mixture. • Satellite bands of RbCs molecule at 362.2 nm, 372.5 nm and 390.7 nm. • Avoided crossings of potential curves at long-range inter-atomic region. • The observed satellite bands may be observed in the mixed Rb–Cs MOT. • The satellite bands can be used for comparison with ab initio RbCs calculations

  11. The Effects of Band Director Leadership Style and Student Leadership Ability on Band Festival Ratings

    Science.gov (United States)

    Davison, P. Dru

    2007-01-01

    This study examined the relationship between band director leadership styles and the strength of student leadership within the bands. This study also examined the differences between leadership styles, student leadership strength, and band festival ratings (marching and concert). Subjects (N = 42) were band directors from Texas and Arkansas who…

  12. Shear bands in aluminium-lithium alloys

    International Nuclear Information System (INIS)

    The formation of shear bands in Al-Li alloys in cold rolling and their influence on mechanical properties of rolled and heat treated sheets are under consideration. It is shown that shear bands as well as the network of recrystallized grains along previous bands are undesirable structural constituents in aluminum alloy sheets as they decrease processing and operational properties of alloys. In further metal forming the localization of strain is observed along shear bands or zones of recrystallized grains. To avoid failure due to shear band formation it is recommended to roll alloys in as-annealed state and properly regulate reduction degree

  13. Self-Shielding at the X-Point in the CO E(1)-X(0) Band of CO

    Science.gov (United States)

    Lyons, J. R.; Boney, E.; Marcus, R. A.

    2008-03-01

    Photochemical calculations for one band of CO demonstrate that self-shielding can occur for X-point conditions, but the magnitude of the resulting isotope anomaly is significantly reduced compared to self-shielding at lower temperatures.

  14. SMART and SMARTI: visible and IR atmospheric radiative-transfer libraries optimized for wide-band applications

    Science.gov (United States)

    Ross, Vincent; Dion, Denis

    2011-05-01

    A new C++ library for radiative transfer calculations in the visible and infrared bands which uses MODTRAN as a primary source for atmospheric optical parameters has been developed at Defense R&D Canada, Valcartier (DRDC Valcartier). The main benefit of the library is its capability to perform fast wide spectral band calculations with an appreciably high accuracy. Coherent calculations on wide bands are made possible by using a modified version of the correlated-k theory. The main features of the library are discussed, and comparisons with conventional spectral MODTRAN 4 calculations are presented. It is shown that the library is capable of producing band results that are usually within 5% of MODTRAN 4 with computation times that are thousands of times faster.

  15. First principle calculation of elastic and thermodynamic properties of stishovite

    International Nuclear Information System (INIS)

    Using ab initio plane-wave pseudo-potential density functional theory method, the elastic constants and band structures of stishovite were calculated. The calculated elastic constants under ambient conditions agree well with previous experimental and theoretical data. C13, C33, C44, and C66 increase nearly linearly with pressure while C11 and C12 show irregularly changes with pressure over 20 GPa. The shear modulus (C11-C12)/2 was observed to decrease drastically between 40 GPa and 50 GPa, indicating acoustic mode softening in consistency with the phase transition to CaCl2-type structure around 50 GPa. The calculated band structures show no obvious difference at 0 and 80 GPa, being consistent with the high incompressibility of stishovite. With a quasi-harmonic Debye model, thermodynamic properties of stishovite were also calculated and the results are in good agreement with available experimental data. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  16. Excited states and terminating bands in 123,124I

    International Nuclear Information System (INIS)

    High spin states in 123,124I were populated via the 116Cd(11B,xn) reaction at 38 MeV bombarding energy and via the 110Pd(18O,pxn) reaction at 75 MeV energy. ?-ray energies, intensities, ?? coincidences and DCO ratios were measured with the GASP spectrometer. The level schemes were extended considerably. Band terminations were observed in both nuclei. In 123I the rotational band, which is 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 structure change. The (39/2)- state and the higher-lying (43/2)- level were interpreted as aligned oblate states. In 124I a decoupled band was found to terminate in the same spin region. Total Routhian surface calculations were performed which support the occurrence of a band termination. (author)

  17. Radiofrequency signal affects alpha band in resting electroencephalogram.

    Science.gov (United States)

    Ghosn, Rania; Yahia-Cherif, Lydia; Hugueville, Laurent; Ducorps, Antoine; Lemaréchal, Jean-Didier; Thuróczy, György; de Seze, René; Selmaoui, Brahim

    2015-04-01

    The aim of the present work was to investigate the effects of the radiofrequency (RF) electromagnetic fields (EMFs) on human resting EEG with a control of some parameters that are known to affect alpha band, such as electrode impedance, salivary cortisol, and caffeine. Eyes-open and eyes-closed resting EEG data were recorded in 26 healthy young subjects under two conditions: sham exposure and real exposure in double-blind, counterbalanced, crossover design. Spectral power of EEG rhythms was calculated for the alpha band (8-12 Hz). Saliva samples were collected before and after the study. Salivary cortisol and caffeine were assessed by ELISA and HPLC, respectively. The electrode impedance was recorded at the beginning of each run. Compared with the sham session, the exposure session showed a statistically significant (P < 0.0001) decrease of the alpha band spectral power during closed-eyes condition. This effect persisted in the postexposure session (P < 0.0001). No significant changes were detected in electrode impedance, salivary cortisol, and caffeine in the sham session compared with the exposure one. These results suggest that GSM-EMFs of a mobile phone affect the alpha band within spectral power of resting human EEG. PMID:25695646

  18. Lasing at the band edges of plasmonic lattices

    Science.gov (United States)

    Schokker, A. Hinke; Koenderink, A. Femius

    2014-10-01

    We report room-temperature lasing in two-dimensional diffractive lattices of silver and gold plasmon particle arrays embedded in a dye-doped polymer that acts both as waveguide and gain medium. As compared to conventional dielectric distributed feedback (DFB) lasers, a central question is how the underlying band structure from which lasing emerges is modified by both the much stronger scattering and the disadvantageous loss of metal. We use spectrally resolved back-focal plane imaging to measure the wavelength and angle dependence of emission below and above threshold, thereby mapping the band structure. We find that, for silver particles, the band structure is strongly modified compared to dielectric reference DFB lasers since the strong scattering gives large stop gaps. In contrast, gold particles scatter weakly and absorb strongly, so that thresholds are higher, but the band structure is not strongly modified. The experimental findings are supported by finite element and Fourier modal method calculations of the single-particle scattering strength and lattice extinction.

  19. Novel band structures in silicene on monolayer zinc sulfide substrate

    Science.gov (United States)

    Li, Sheng-shi; Zhang, Chang-wen; Yan, Shi-shen; Hu, Shu-jun; Ji, Wei-xiao; Wang, Pei-ji; Li, Ping

    2014-10-01

    Opening a sizable band gap in the zero-gap silicene without lowering the carrier mobility is a key issue for its application in nanoelectronics. Based on ?rst-principles calculations, we find that the interaction energies are in the range of -0.09?0.3?eV?per Si atom, indicating a weak interaction between silicene and ZnS monolayer and the ABZn stacking is the most stable pattern. The band gap of silicene can be effectively tuned ranging from 0.025 to 1.05?eV in silicene and ZnS heterobilayer (Si/ZnS HBL). An unexpected indirect-direct band gap crossover is also observed in HBLs, dependent on the stacking pattern, interlayer spacing and external strain effects on silicene. Interestingly, the characteristics of Dirac cone with a nearly linear band dispersion relation of silicene can be preserved in the ABS pattern which is a metastable state, accompanied by a small electron effective mass and thus the carrier mobility is expected not to degrade much. These provide a possible way to design effective FETs out of silicene on a ZnS monolayer.

  20. Investigation of the Band Gap in Co3O4

    Science.gov (United States)

    Sholte, Mark; Lin, Chungwei; Kormondy, Kristy; Nunley, Timothy; Posadas, Agham; Zollner, Stefan; Demkov, Alexander

    2015-03-01

    Co3O4 is a strongly correlated oxide with a spinel structure and G-type antiferromagnetic order at temperatures below 40 K. It is a widely studied material owing to its applications in gas sensing, spintronics, batteries, and catalysis. The strong correlation and magnetism make it a difficult material to model from first principles. Density functional theory calculations require the use of a Hubbard U to correctly model its magnetic behavior. The band gap is sensitive to the choice of U allowing one to tailor the gap to a wide range of values. This often provides a phenomenological approach to determining U, but in the case of Co3O4 there is no experimental consensus on the actual value of the band gap. We utilize an alternate approach by matching the theoretical valence band structure to the actual valence band data obtained via x-ray photoemission spectroscopy. This generated set of U values is used to compute an absorption spectrum, which is in good agreement with ellipsometry results.

  1. Novel band structures in silicene on monolayer zinc sulfide substrate.

    Science.gov (United States)

    Li, Sheng-shi; Zhang, Chang-wen; Yan, Shi-shen; Hu, Shu-jun; Ji, Wei-xiao; Wang, Pei-ji; Li, Ping

    2014-10-01

    Opening a sizable band gap in the zero-gap silicene without lowering the carrier mobility is a key issue for its application in nanoelectronics. Based on ?rst-principles calculations, we find that the interaction energies are in the range of -0.09?0.3?eV?per Si atom, indicating a weak interaction between silicene and ZnS monolayer and the ABZn stacking is the most stable pattern. The band gap of silicene can be effectively tuned ranging from 0.025 to 1.05?eV in silicene and ZnS heterobilayer (Si/ZnS HBL). An unexpected indirect-direct band gap crossover is also observed in HBLs, dependent on the stacking pattern, interlayer spacing and external strain effects on silicene. Interestingly, the characteristics of Dirac cone with a nearly linear band dispersion relation of silicene can be preserved in the ABS pattern which is a metastable state, accompanied by a small electron effective mass and thus the carrier mobility is expected not to degrade much. These provide a possible way to design effective FETs out of silicene on a ZnS monolayer. PMID:25158645

  2. Unified description of perturbation theory and band center anomaly in one-dimensional Anderson localization

    OpenAIRE

    Kang, Kai; Qin, Shaojing; Wang, Chuilin

    2010-01-01

    We calculated numerically the localization length of one-dimensional Anderson model with diagonal disorder. For weak disorder, we showed that the localization length changes continuously as the energy changes from the band center to the boundary of the anomalous region near the band edge. We found that all the localization lengths for different disorder strengths and different energies collapse onto a single curve, which can be fitted by a simple equation. Thus the descripti...

  3. Theory of valence-band and core-level photoemission from plutonium dioxide

    OpenAIRE

    Kolorenc, Jindrich; Kozub, Agnieszka L.; Shick, Alexander B.

    2014-01-01

    The correlated-band theory implemented as a combination of the local-density approximation with the dynamical mean-field theory is applied to PuO2. An insulating electronic structure, consistent with the experimental valence-band photoemission spectra, is obtained. The calculations yield a nonmagnetic ground state that is characterized by a noninteger filling of the plutonium 5f shell. The noninteger filling as well as the satellites appearing in the 4f core-level photoemiss...

  4. Information on the band structure of ferromagnetic Ni from ?SR-Knight shift measurements

    International Nuclear Information System (INIS)

    The authors present results on the temperature dependence of the Knight shift of the hyperfine field at a positive muon in ferromagnetic Nickel and show that the results allow a determination of the Stoner gap, that is the gap between the top of the majority d-band and the Fermi energy. The consistency of the analysis supports the SWS-model but the obtained value for the Stoner gap is far below the predictions of most ferromagnetic band structure calculations. (Auth.)

  5. PWR core design calculations

    International Nuclear Information System (INIS)

    Functional description of the programme package Cord-2 for PWR core design calculations is presented. Programme package is briefly described. Use of the package and calculational procedures for typical core design problems are treated. Comparison of main results with experimental values is presented as part of the verification process. (author)

  6. Atmospheric Stability Calculator

    Science.gov (United States)

    The Shodor Education Foundation, Inc.

    This calculator calculates the type of stability, given the observed (or environmental) lapse rate. We can compare this lapse rate for any given day to the "standard" dry and moist lapse rates shown in the table below. Based on a comparison of these values, we can determine how stable the atmosphere might be.

  7. Statistical Tables Calculator

    Science.gov (United States)

    Dinov, Ivo

    This page, created by Ino Dinov of the University of California, Berkeley, provides distribution calculators for the binomial, normal, Student's T, Chi-square, and Fisher's F distributions. Users set the parameters and enter either the probability or the test statistic and the calculators return the missing value. This is a simple, yet effective, statistical tool for instructors and students.

  8. Band mixing in {sup 29}Si and {sup 29}P

    Energy Technology Data Exchange (ETDEWEB)

    Hossain, S [Department of Physics, University of Rajshahi, Rajshahi 6205 (Bangladesh); Abdullah, M N A [Department of Physics, University of Rajshahi, Rajshahi 6205 (Bangladesh); Das, S K [Department of Physics, Shahjalal University of Science and Technology, Sylhet (Bangladesh); Uddin, M A [Department of Physics, University of Rajshahi, Rajshahi 6205 (Bangladesh); Basak, A K [Department of Physics, University of Rajshahi, Rajshahi 6205 (Bangladesh); Gupta, H M Sen [Department of Physics, University of Dhaka, Dhaka (Bangladesh); Thompson, I J [Department of Physics, University of Surrey, Guildford GU2 7XH (United Kingdom); Malik, F B [Department of Physics, Southern Illinois University, Carbondale, IL 62901 (United States)

    2005-05-01

    The experimental data of the {sup 28}Si({alpha}, t){sup 29}P and {sup 28}Si({alpha}, {sup 3}He){sup 29}Si reactions at 45 MeV have been analysed in terms of full finite-range coupled-channels calculations. In the calculations, the reaction paths, direct and two step via the inelastic states of the initial and final nuclei have been treated in terms of the finite-range transfer theory. The spectroscopic amplitudes connecting the deformed initial and final nuclei in both the reactions are obtained from Nilsson's model. The data of both the reactions, populating the 1/2{sup +}, 3/2{sup +} and 5/2{sup +} states in the K{sup {pi}} = 1/2{sup +} band and the 3/2{sup +} and 5/2{sup +} states in the K{sup {pi}} = 3/2{sup +} band, are best described by about 20% mixing of between the two bands. The effects of normal Woods-Saxon (WS), squared WS and molecular type of {alpha}-nucleus potentials are also discussed.

  9. Electron correlations in narrow energy bands: modified polar model approach

    Directory of Open Access Journals (Sweden)

    L. Didukh

    2008-09-01

    Full Text Available The electron correlations in narrow energy bands are examined within the framework of the modified form of polar model. This model permits to analyze the effect of strong Coulomb correlation, inter-atomic exchange and correlated hopping of electrons and explain some peculiarities of the properties of narrow-band materials, namely the metal-insulator transition with an increase of temperature, nonlinear concentration dependence of Curie temperature and peculiarities of transport properties of electronic subsystem. Using a variant of generalized Hartree-Fock approximation, the single-electron Green's function and quasi-particle energy spectrum of the model are calculated. Metal-insulator transition with the change of temperature is investigated in a system with correlated hopping. Processes of ferromagnetic ordering stabilization in the system with various forms of electronic DOS are studied. The static conductivity and effective spin-dependent masses of current carriers are calculated as a function of electron concentration at various DOS forms. The correlated hopping is shown to cause the electron-hole asymmetry of transport and ferromagnetic properties of narrow band materials.

  10. Understanding intermediate-band solar cells

    Science.gov (United States)

    Luque, Antonio; Martí, Antonio; Stanley, Colin

    2012-03-01

    The intermediate-band solar cell is designed to provide a large photogenerated current while maintaining a high output voltage. To make this possible, these cells incorporate an energy band that is partially filled with electrons within the forbidden bandgap of a semiconductor. Photons with insufficient energy to pump electrons from the valence band to the conduction band can use this intermediate band as a stepping stone to generate an electron-hole pair. Nanostructured materials and certain alloys have been employed in the practical implementation of intermediate-band solar cells, although challenges still remain for realizing practical devices. Here we offer our present understanding of intermediate-band solar cells, as well as a review of the different approaches pursed for their practical implementation. We also discuss how best to resolve the remaining technical issues.

  11. Arto New String Calculator

    Science.gov (United States)

    Wikla, Arto

    Designed by a senior lecturer at the Department of Computer Science at the University of Helsinki in Finland, this website is a stand-alone Pascal program for string calculations. The idea came to him while visiting a French lute maker friend and the site has been continually updated since the original program was conceived. The calculator is useful only for calculating the tensions and diameters of strings made of homogenous material, thus wound strings, catlines and other such strings are excluded. The calculator is designed with lute instruments in mind but can be used for any stringed instrument: harpsichord, harp, guitar and pianos. The site provides easy to follow instructions and a glossary of the terms. Java 1.4 or 1.5 must be enabled to use this calculator.

  12. Le classique en bande dessinée

    Directory of Open Access Journals (Sweden)

    Frank-Michel Gorgeard

    2011-07-01

    Full Text Available Quelles sont les grandes œuvres de la bande dessinée, celles qui font son histoire, ses « classiques » ? Sont-ils bien ceux que l’on croit ? On s’efforce ici de répondre à cette question en confrontant les discours et les pratiques des auteurs, de la critique et des éditeurs. La notion de classique, particulièrement polysémique, apparaît d’autant plus brouillée que les producteurs font rarement référence au travail de leurs pairs en raison notamment de l’incapacité supposée ou réelle du public à les comprendre. Elle-même s’explique par l’état du champ, en cours d’autonomisation : en l’absence d’un arbitre faisant autorité et qui serait l’école, la notion de « classsique » se retrouve au cœur d’une lutte entre deux pôles antagonistes. Alors qu’une partie de la critique et des éditeurs célèbre des « classiques » qui sont autant de bandes dessinées conventionelles, établissant ainsi une « confusion du langage », d’autres, qui affirment des positions artistiques exigeantes, rejettent le mot de classique mais identifient des maîtres, reconnaissent des précurseurs, prospectent du côté de l’avant-garde.

  13. Band-gap bowing, band offsets, and electron affinities for AlN, GaN, InN and InGaN: A DFT study

    Science.gov (United States)

    Moses, Poul Georg; van de Walle, Chris G.; Miao, Maosheng

    2009-11-01

    AlN, GaN, and InN and their alloys are successfully being used in optical, electronic, and photovoltaic devices; a novel application is for photochemical water splitting. In order to further improve nitride-based devices a detailed understanding of the materials properties as a function of alloy composition is needed. To obtain such insight we have investigated the band gap and absolute band positions of AlN, GaN, InN and InGaN using density functional theory. The HSE exchange correlation functional has been used in order to accurately calculate the electronic band structure [1]. Detailed surface calculations have been performed that, combined with bulk calculations for alloys, yield information about the positions of valence and conduction bands on an absolute energy scale. We will discuss bowing effects, band offsets, and electron affinities in light of the application for photochemical hydrogen production. [4pt] [1] J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 118, 8207 (2003)

  14. Band-gap structures of surface-plasmon polaritons in a subwavelength metal slit filled with periodic dielectrics

    International Nuclear Information System (INIS)

    We propose a combination structure which consists of a subwavelength metal slit filled periodically with two different dielectrics to modulate slit plasmon polaritons (slit-PPs). The transmission spectra are simulated by the finite-difference time-domain method and the photonic band gaps are observed. The theoretical formula to calculate the band-gap structures is deduced and the calculation results agree satisfactorily with simulated results. This structure can be termed as slit-PP crystal.

  15. A 100 MHz 4 channels Narrow-band Chebyshev Filter for LTE Application

    Directory of Open Access Journals (Sweden)

    Othman A.R.

    2014-12-01

    Full Text Available This paper presents the design of a 100 MHz bandwidth with suitable for 4 channels narrow-band using Chebyshev filter at 5.75 GHz frequency. The design development includes calculation, simulation, measurement and testing. The simulation has been simulated using Ansoft Designer software to determine the bandwidth and the insertion loss, |S21|. The band-pass filter design used Duriod 5880 TLY-5A-0200-CH/CH microstrip substrate parameters and lumped components with Chebyshev passive filter topology. The design is useful for applications in multi-channel narrow-band of wireless communication systems for front-end receiver architecture design.

  16. Flexible single pump hybrid fiber amplifier for the S+C bands

    Science.gov (United States)

    Rocha, A. M.; Nogueira, R. N.

    2014-06-01

    This work proposes optical amplification in the S+C bands using a hybrid optical fiber amplifier (HFA) that uses a single wavelength pump. Its configuration is based on an erbium doped amplifier (EDFA) to provide gain over the C band and a distributed Raman fiber amplifier (RFA) to attain gain over the S band. Moreover, the proposed amplifier uses standard commercially available fibers. The HFA was numerically characterized and its optimal configuration was calculated using optimization procedures based on genetic algorithms. A flexible HFA configuration was achieved allowing a span length up to 100 km.

  17. ?-Ray Spectroscopy at the Limits: First Observation of Rotational Bands in 255Lr

    International Nuclear Information System (INIS)

    The rotational band structure of 255Lr has been investigated using advanced in-beam ?-ray spectroscopic techniques. To date, 255Lr is the heaviest nucleus to be studied in this manner. One rotational band has been unambiguously observed and strong evidence for a second rotational structure was found. The structures are tentatively assigned to be based on the 1/2-[521] and 7/2-[514] Nilsson states, consistent with assignments from recently obtained ? decay data. The experimental rotational band dynamic moment of inertia is used to test self-consistent mean-field calculations using the Skyrme SLy4 interaction and a density-dependent pairing force.

  18. Thermal genesis of the bottom of main electron's energy band in a flat nanofilm

    International Nuclear Information System (INIS)

    By the example of a plane nanoheterosystem ?-HgS/?-CdS, the shift of the electron's band bottom as a function of both the film thickness and the temperature is numerically calculated. It is shown that, as the temperature grows, the electron-phonon interaction in the processes of absorption and emission leads to a shift of the band bottom to the region of lower energies. The mechanisms of the increase in the shift with the temperature in films with various thickness, as well as the reasons for different shift rates of the electron's band bottom with increase in the temperature, are established

  19. Band inversion mechanism in topological insulators: A guideline for materials design

    KAUST Repository

    Zhu, Zhiyong

    2012-06-01

    Alteration of the topological order by band inversion is a key ingredient of a topologically nontrivial material. Using first-principles calculations for HgTe, PtScBi, and Bi2Se3, we argue that it is not accurate to ascribe the band inversion to the spin-orbit coupling. Instead, scalar relativistic effects and/or lattice distortions are found to be essential. Therefore, the search for topologically nontrivial materials should focus on band shifts due to these mechanisms rather than spin-orbit coupling. We propose an effective scheme to search for new topological insulators.

  20. Application of Hyperspectral Band Elimiation Technique to PVT Images of Composite Structures

    Directory of Open Access Journals (Sweden)

    Mahmoud Zaki Iskandarani

    2012-10-01

    Full Text Available A new approach to NDT of composite structures using Band Elimination of the analyzed image index by Hyperspectral image analysis approach is presented and discussed. The matrix Band Elimination technique allows the monitoring and analysis of a components structure based on Filtering of bands and correlation between sequentially pulsed thermal images and their indices. The technique produces several matrices resulting from frame deviation and pixel redistribution calculations for intelligent classification and property prediction. The obtained results proved the technique to be capable of identifying damaged components with ability to model various types of damage under different conditions.

  1. Tunable Band Gap and Conductivity Type of ZnSe/Si Core-Shell Nanowire Heterostructures

    Directory of Open Access Journals (Sweden)

    Yijie Zeng

    2014-10-01

    Full Text Available The electronic properties of zincblende ZnSe/Si core-shell nanowires (NWs with a diameter of 1.1–2.8 nm are calculated by means of the first principle calculation. Band gaps of both ZnSe-core/Si-shell and Si-core/ZnSe-shell NWs are much smaller than those of pure ZnSe or Si NWs. Band alignment analysis reveals that the small band gaps of ZnSe/Si core-shell NWs are caused by the interface state. Fixing the ZnSe core size and enlarging the Si shell would turn the NWs from intrinsic to p-type, then to metallic. However, Fixing the Si core and enlarging the ZnSe shell would not change the band gap significantly. The partial charge distribution diagram shows that the conduction band maximum (CBM is confined in Si, while the valence band maximum (VBM is mainly distributed around the interface. Our findings also show that the band gap and conductivity type of ZnSe/Si core-shell NWs can be tuned by the concentration and diameter of the core-shell material, respectively.

  2. Band offsets and optical bowings of chalcopyrites and Zn-based II-VI alloys

    International Nuclear Information System (INIS)

    Using first-principles band-structure theory we have systematically calculated the (i) alloy bowing coefficients, (ii) alloy mixing enthalpies, and (iii) interfacial valence- and conduction-band offsets for three mixed-anion (CuInX2, X=S, Se, Te) and three mixed-cation (CuMSe2, M=Al, Ga, In) chalcopyrite systems. The random chalcopyrite alloys are represented by special quasirandom structures (SQS). The calculated bowing coefficients are in good agreement with the most recent experimental data for stoichiometric alloys. Results for the mixing enthalpies and the band offsets are provided as predictions to be tested experimentally. Comparing our calculated bowing and band offsets for the mixed-anion chalcopyrite alloys with those of the corresponding Zn chalcogenide alloys (ZnX, X=S, Se, Te), we find that the larger p-d coupling in chalcopyrite alloys reduces their band offsets and optical bowing. Bowing parameters for ordered, Zn-based II-VI alloys in the CuAu, CuPt, and chalcopyrite structures are presented: we find that ordered Zn2SeTe has bowing coefficients of 1.44 and 3.15 eV in the CuAu and CuPt structures, while the random ZnSexTe1-x alloy has a bowing of 1.14 eV. The band alignment between CuInSe2 and CuInSe2-derived ordered vacancy compounds are also presented

  3. Anomalous band-gap bowing of AlN1?xPx alloy

    International Nuclear Information System (INIS)

    Highlights: •Structural and electronic properties of AlN1?xPx from first principles. •The supercell and the virtual crystall approximation methods applied and compared. •Anomalously high band-gap bowing found. •Similarities of band-gap behavior to that in BN1?xPx noticed. •Performance of MBJLDA with the pseudopotential approach discussed. -- Abstract: Electronic structure of zinc blende AlN1?xPx alloy has been calculated from first principles. Structural optimization has been performed within the framework of LDA and the band-gaps calculated with the modified Becke–Jonson (MBJLDA) method. Two approaches have been examined: the virtual crystal approximation (VCA) and the supercell-based calculations (SC). The composition dependence of the lattice parameter obtained from the SC obeys Vegard’s law whereas the volume optimization in the VCA leads to an anomalous bowing of the lattice constant. A strong correlation between the band-gaps and the structural parameter in the VCA method has been observed. On the other hand, in the SC method the supercell size and atoms arrangement (clustered vs. uniform) appear to have a great influence on the computed band-gaps. In particular, an anomalously big band-gap bowing has been found in the case of a clustered configuration with relaxed geometry. Based on the performed tests and obtained results some general features of MBJLDA are discussed and its performance for similar systems predicted

  4. Rotational band structure in 132La

    International Nuclear Information System (INIS)

    '3'2La was studied using on-line gamma-spectroscopy through the reactions '124,126Te(11,10B, 3, 4n)132La. The excitation function was obtained with 10B(Elab=41.4; 45.4 and 48 MeV) in order to identify 132La gamma-transitions. Gamma-gamma coincidences and angular distributions were performed for the 126Te(10B, 4n)132La reaction. From the experimental results a rotational band with strongest M1 transitions and less intense 'cross-overs' E2 transitions was constructed. Using the methods of Bengtsson and Frauendorf the alignment (ix) and the Routhian (e') as a function of the angular velocity (?) were also obtained from the experimental data. It was observed a constant alignment up to ??0.4 MeV, and a signature-splitting ?e'=25keV. Preliminary triaxial Cranking-Shell Model calculations indicate that a ?=-8deg deformation is consistent with the signature-splitting value of 25 keV experimentally observed. (Author)

  5. Band description of materials with localizing orbitals

    International Nuclear Information System (INIS)

    Density functional theory is a form of many-body theory which maps the problem onto an equivalent single particle-like system by limiting to the ground state (or some limited ensemble). So it should be surprising that this ground state theory could have any relevance whatsoever to the excitation properties of a material - and yet it does when used carefully. However, the most interesting materials involve active orbitals which are at least partially localized in space and this has profound effects both on the ground state and the excitation spectrum. My long term interest is in Ce and actinide compounds such that the popular concerns are mixed valence, heavy fermions, and the various forms of magnetic transitions. Band structure calculations can give a great deal of information concerning the mechanisms and degree of the localization as shown by examples using the Ce and U Ll2 structured materials and the Ce cubic Laves phase materials. There are some difficulties due to an incomplete knowledge of the functionals involved which causes an underestimate of the local character. This is illustrated and discussed

  6. ?2 + ?4 band of 12CF4

    International Nuclear Information System (INIS)

    From a high-resolution diode laser spectrum of cooled 12CF4, line assignments in ?2 + ?4 at 1066.4 cm-1 have been made for tetrahedral subspecies to J = 20, and in many cases to higher J. Spectroscopic constants have been obtained from a least-squares fit of the Hamiltonian, and the relative intensities of the assigned lines have been calculated. The ground- and excited-state rotational constants, Coriolis constant, and splitting of the F1 and F2 vibrational substates have the values B0 = 0.191688 +- 0.000020 cm-1, B = 0.191442 +- 0.000020 cm-1, zeta4 = 0.3605 +- 0.0002, ? = 0.5757 +- 0.0017 cm-1. The C-F bond length in the ground vibrational state is thus r0 = 1.31752 +- 0.00007A. The analysis of a combination band such as this provides a method of obtaining ground-state spectroscopic constants of spherical-top molecules directly from the infrared spectrum, without the necessity of measuring weak forbidden transitions. The assignments allow accurate predictions of the frequencies emitted by the CO2-pumped CF4 laser

  7. Energy spectrum of second valence band in PbSnTe solid solutions

    International Nuclear Information System (INIS)

    PbTe, PbSnTe solid solutions have a complex structure of valence band. Energy spectrum of the second valence band was calculated, effective masses and g factor were determined in the paper. P model was used in calculations. Electron spectrum in this model is constructed using metal spectrum of praphase -a hypothetic crystal with a simple cubic lattice and half-filled P bands, appeared from orbitales. It is shown that in Pbsub(1-x)Snsub(x)Te solid solutions energy gap and effective mass depend slightly on composition. P model parameters calculated in the approximation of a virtual crystal for composition x=0.2 give effective masses m2*=0.2 m0, m2*=0.04 m0

  8. G0W0 band structure of CdWO4

    International Nuclear Information System (INIS)

    The full quasiparticle band structure of CdWO4 is calculated within the single-shot GW (G0W0) approximation using maximally localized Wannier functions, which allows one to assess the validity of the commonly used scissor operator. Calculations are performed using the Godby–Needs plasmon pole model and the accurate contour deformation technique. It is shown that while the two methods yield identical band gap energies, the low-lying states are given inaccurately by the plasmon pole model. We report a band gap energy of 4.94 eV, including spin–orbit interaction at the DFT–LDA (density functional theory–local density approximation) level. Quasiparticle renormalization in CdWO4 is shown to be correlated with localization distance. Electron and hole effective masses are calculated at the DFT and G0W0 levels. (paper)

  9. CALCULATION OF THE CIRCULAR POLARIZATION OF QUANTUM WELL PHOTOLUMINESCENCE

    OpenAIRE

    A. Twardowski; Hermann, C.

    1987-01-01

    We present the first calculation of Al1-xGaxAs/GaAs quantum wells photoluminescence polarization under circularly polarized excitation, taking into account the complex structure of theQW valence band. A careful analysis of the published excitation spectra on the Al1-xGaxAs/GaAs system stresses the importance of excitonic effects and electron spin relaxation.

  10. PWR core design calculations

    International Nuclear Information System (INIS)

    This text treats the calculational tools, i.e. computer programs for core design calculations. Computer codes for solving stationary problems will be presented, based on a multi-group diffusion theory. There is a large variety of such codes. They use different geometrical models and methods of solution. For the author's purposes it is only important to see their main and common feature which have influence on practical core design calculations and not to go into details about their structure. It is not his intention to select or recommend the best computer codes for practical application because the decision depends on too many uncertain parameters such as: scope of the design problems, computer size and background knowledge of the user. Computer codes to which reference will be made in the following text may be considered typical but not necessarily the best of their type. The text also treats calculations of PWR operational properties: critical boron concentration, reactivity coefficients, control rod worths, etc. Attention is paid more to the explanation of physical phenomena behind the calculational procedures than to calculations themselves. It is shown that calculational procedures may base upon different approaches, they can be more analytically or more empirically oriented, but they always have to reflect the same physical reality

  11. The APOGEE Spectral Line List for H band Spectroscopy

    CERN Document Server

    Shetrone, Matthew; Lawler, James; Prieto, Carlos Allende; Johnson, Jennifer A; Smith, Verne; Cunha, Katia; Holtzman, Jon; Perez, Ana Garcia; Meszaros, Szabolcs; Sobeck, Jennifer; Zamora, Olga; Garcia-Hernandez, Anibal; Souto, Diogo; Chojnowski, Drew; Koesterke, Lars; Majewski, Steven

    2015-01-01

    We present the $H$ band spectral line lists adopted by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). The APOGEE line lists comprise astrophysical, theoretical, and laboratory sources from the literature, as well as newly evaluated astrophysical oscillator strengths and damping parameters. We discuss the construction of the APOGEE line list, which is one of the critical inputs for the APOGEE Stellar Parameters and Chemical Abundances Pipeline (ASPCAP), and present three different versions that have been used at various stages of the project. The methodology for the newly calculated astrophysical line lists is reviewed. The largest of these three line lists contains 134457 molecular and atomic transitions. In addition to the format adopted to store the data, the line lists are available in MOOG, Synspec and Turbospectrum formats. We also present a list of $H$ band spectral features that are either poorly represented or completely missing in our line list. This list is based on the average...

  12. Nature of the electronic band gap in lanthanide oxides

    Science.gov (United States)

    Gillen, Roland; Clark, Stewart J.; Robertson, John

    2013-03-01

    Accurate electronic structures of the technologically important lanthanide/rare-earth sesquioxides (Ln2O3, with Ln=La,⋯,Lu) and CeO2 have been calculated using hybrid density functionals HSE03, HSE06, and screened exchange (sX-LDA). We find that these density functional methods describe the strongly correlated Ln f electrons as well as the recent G0W0@LDA+U results, generally yielding the correct band gaps and trends across the Ln period. For HSE, the band gap between O 2p states and lanthanide 5d states is nearly independent of the lanthanide, while the minimum gap varies as filled or empty Ln 4f states come into this gap. sX-LDA predicts the unoccupied 4f levels at higher energies, which leads to a better agreement with experiments for Sm2O3, Eu2O3, and Yb2O3.

  13. Shell-model operator for K-band splitting

    International Nuclear Information System (INIS)

    A microscopic shell-model operator that generates K-band splitting is introduced. An analytic matrix representation for this K2 operator is given in angular momentum projected states of the SU(3) contains SO(3) group reduction. The K2 operator can also be used to resolve multiple occurrences of L-values in SU(3) representations, that is, it provides for a resolution of the SU(3) contains SO(3) state labelling problem. Results for the leading SU(3) representations of 24Mg and 168Er, with (?, ?) = (8, 4) and (30, 8) respectively, are presented to show that K2 is very nearly diagonal in an angular momentum projected SU(3)containsSO(3) basis. An analysis of K-band splitting for 24Mg and 168Er is used to demonstrate the utility of the theory for carrying out shell-model calculations. (orig.)

  14. Band gap bowing in quaternary nitride semiconducting alloys

    DEFF Research Database (Denmark)

    Gorczyka, Isabela; Suski, T.

    2011-01-01

    Structural properties of InxGayAl1?x?yN alloys are derived from total-energy minimization within the local-density approximation (LDA). The electronic properties are studied by band structure calculations including a semiempirical correction for the “LDA gap error.” The effects of varying the composition and atomic arrangements are examined using a supercell geometry. An analytical expression for the band gap is derived for the entire range of compositions. The range of (x, y) values for which InxGayAl1?x?yN is lattice matched to GaN, and the ensuing energy gaps, are given. This range of available gaps becomes smaller when In atoms form clusters. Comparison to experimental data is made.

  15. Band gap bowing in quaternary nitride semiconducting alloys

    Science.gov (United States)

    Gorczyca, I.; Suski, T.; Christensen, N. E.; Svane, A.

    2011-06-01

    Structural properties of InxGayAl1-x-yN alloys are derived from total-energy minimization within the local-density approximation (LDA). The electronic properties are studied by band structure calculations including a semiempirical correction for the "LDA gap error." The effects of varying the composition and atomic arrangements are examined using a supercell geometry. An analytical expression for the band gap is derived for the entire range of compositions. The range of (x, y) values for which InxGayAl1-x-yN is lattice matched to GaN, and the ensuing energy gaps, are given. This range of available gaps becomes smaller when In atoms form clusters. Comparison to experimental data is made.

  16. Band gap tunability of magneto-elastic phononic crystal

    Science.gov (United States)

    Bou Matar, O.; Robillard, J. F.; Vasseur, J. O.; Hladky-Hennion, A.-C.; Deymier, P. A.; Pernod, P.; Preobrazhensky, V.

    2012-03-01

    The possibility of control and tuning of the band structures of phononic crystals offered by the introduction of an active magnetoelastic material and the application of an external magnetic field is studied. Two means to obtain large elastic properties variations in magnetoelastic material are considered: Giant magnetostriction and spin reorientation transition effects. A plane wave expansion method is used to calculate the band structures. The magnetoelastic coupling is taken into account through the consideration of an equivalent piezomagnetic material model with elastic, piezomagnetic, and magnetic permeability tensors varying as a function of the amplitude and orientation of the applied magnetic field. Results of contactless tunability of the absolute bandgap are presented for a two-dimensional phononic crystal constituted of Terfenol-D square rod embedded in an epoxy matrix.

  17. Radioactive cloud dose calculations

    International Nuclear Information System (INIS)

    Radiological dosage principles, as well as methods for calculating external and internal dose rates, following dispersion and deposition of radioactive materials in the atmosphere are described. Emphasis has been placed on analytical solutions that are appropriate for hand calculations. In addition, the methods for calculating dose rates from ingestion are discussed. A brief description of several computer programs are included for information on radionuclides. There has been no attempt to be comprehensive, and only a sampling of programs has been selected to illustrate the variety available

  18. Photonic band structures of quadrangular multiconnected networks

    Science.gov (United States)

    Song, Huan-Huan; Yang, Xiang-Bo

    2010-07-01

    By means of the network equation and generalized dimensionless Floquet-Bloch theorem, this paper investigates the properties of the band number and width for quadrangular multiconnected networks (QMNs) with a different number of connected waveguide segments (NCWSs) and various matching ratio of waveguide length (MRWL). It is found that all photonic bands are wide bands when the MRWL is integer. If the integer attribute of MRWL is broken, narrow bands will be created from the wide band near the centre of band structure. For two-segment-connected networks and three-segment-connected networks, it obtains a series of formulae of the band number and width. On the other hand, it proposes a so-called concept of two-segment-connected quantum subsystem and uses it to discuss the complexity of the band structures of QMNs. Based on these formulae, one can dominate the number, width and position of photonic bands within designed frequencies by adjusting the NCWS and MRWL. There would be potential applications for designing optical switches, optical narrow-band filters, dense wavelength-division-multiplexing devices and other correlative waveguide network devices.

  19. A simplified method for the computation of correlation effects on the band structure of semiconductors

    CERN Document Server

    Birkenheuer, U; Stoll, H; Birkenheuer, Uwe; Fulde, Peter; Stoll, Hermann

    2005-01-01

    We present a simplified computational scheme in order to calculate the effects of electron correlations on the energy bands of diamond and silicon. By adopting a quasiparticle picture we compute first the relaxation and polarization effects around an electron set into a conduction band Wannier orbital. This is done by allowing the valence orbitals to relax within a self-consistent field (SCF) calculation. The diagonal matrix element of the Hamiltonian leads to a shift of the center of gravity of the conduction band while the off-diagonal matrix elements result in a small reduction of the conduction-electron band width. This calculation is supplemented by the computation of the loss of ground state correlations due to the blocked Wannier orbital into which the added electron has been placed. The same procedure applies to the removal of an electron, i.e., to the valence bands. But the latter have been calculated previously in some detail and previous results are used in order to estimate the energy gap in the t...

  20. Band Structure and Fermi-Surface Properties of Ordered beta-Brass

    DEFF Research Database (Denmark)

    Skriver, Hans Lomholt; Christensen, N. E.

    1973-01-01

    The band structure of ordered ?-brass (??-CuZn) has been calculated throughout the Brillouin zone by the augmented-plane-wave method. The present band model differs from previous calculations with respect to the position and width of the Cu 3d band. The derived dielectric function ?2(?) and the photoemission spectra agree well with experiments. We find that the main absorption edge as observed in the ?2 trace has contributions from conduction-band transitions as well as transitions from the Cu d states. The comparison to photoemission results indicates that the calculated Cu d bands are too narrow, but that their position relative to the Fermi level is correct. The derived Fermi-surface model allows a detailed interpretation of the de Hass-van Alphen (dHvA) data. The present model has no open orbit along for B?? ?110?. This agrees with dHvA as well as magnetoresistance measurements. Four new extremal cross sections have been found and related to previously unexplained dHvA frequencies. In general, the Fermi-surface dimensions agree extremely well with dHvA measurements, and the ratios between the experimental and the calculated cyclotron masses vary between 1.18 and 1.43.

  1. In-clustering induced anomalousbehavior of band gap in InAlN and InGaN

    DEFF Research Database (Denmark)

    Gorczyca, I.; Suski, T.

    2010-01-01

    Electronic band structure calculations of In containing ternary nitride alloys are presented showing a strong modification of the band gap, EG and its pressure coefficient, dEG/dp, as a function of In-content. Two different arrangements of In atoms are considered: uniform and clustered. It is shown that Indium clustering is the additional, large factor leading to the unusual bowings of the band gaps and their pressure coefficients. The theoretical results are compared with experimental data on variations of EG with In content. In the analysis of observed phenomena we point out the particular role of the uppermost valence band.

  2. Giant Rashba-type splitting in molybdenum-driven bands of MoS2/Bi (111 ) heterostructure

    Science.gov (United States)

    Lee, Kyuhwan; Yun, Won Seok; Lee, J. D.

    2015-03-01

    We investigate the electronic band structure of the MoS2/Bi (111 ) heterostructure, for which the supercell calculation is performed due to the lattice mismatch between two structures but the effective primitive cell is recovered by using the band unfolding technique. It is found that the strong molybdenum-bismuth band hybridization together with a generation of the interfacial dipole field induces the giant Rashba-type splitting accompanying the proper spin topology in molybdenum-driven bands at the ? point. Similar splittings are also found in the heterostructure with other transition-metal dichalcogenides, i.e., with MoSe2,WS2, and WSe2.

  3. Systematics of energy differences as signs of intruder bands and parameter independent tests of interacting boson models for octupole states

    International Nuclear Information System (INIS)

    The systematics of differences of levels of ground-state ?1 and ?1 bands in medium and heavy nuclei are shown to be smooth, even in cases in which the corresponding band heads show irregular behaviour. Deviations from these smooth systematics are shown to be signs of the presence of intruder bands, for which a new criterion is found. The systematics of differences of levels of octupole bands are used as parameter independent tests for the versions of the interacting boson model suitable for the description of octupole deformations as well as octupole vibrations. Examples of the usefulness of the present systematics in testing the predictions of various microscopic calculations are given. (author)

  4. Crossing points in the electronic band structure of vanadium oxide

    Directory of Open Access Journals (Sweden)

    Keshav N. Shrivastava

    2010-03-01

    Full Text Available The electronic band structures of several models of vanadium oxide are calculated. In the models 1-3, every vanadium atom is connected to 4 oxygen atoms and every oxygen atom is connected to 4 vanadium atoms. In model 1, a=b=c 2.3574 Å; in model 2, a= 4.7148 Å, b= 2.3574 Å and c= 2.3574 Å; and in model 3, a= 4.7148 Å, b= 2.3574 Å and c= 4.7148 Å. In the models 4-6, every vanadium atom is connected to 4 oxygen atoms and every oxygen atom is connected to 2 vanadium atoms. In model 4, a=b= 4.551 Å and c= 2.851 Å; in model 5, a=b=c= 3.468 Å; and in model 6, a=b=c= 3.171 Å. We have searched for a crossing point in the band structure of all the models. In model 1 there is a point at which five bands appear to meet but the gap is 7.3 meV. In model 2 there is a crossing point between G and F points and there is a point between F and Q with the gap ? 3.6608 meV. In model 3, the gap is very small, ~ 10-5 eV. In model 4, the gap is 5.25 meV. In model 5, the gap between Z and G points is 2.035 meV, and in model 6 the gap at Z point is 4.3175 meV. The crossing point in model 2 looks like one line is bent so that the supersymmetry is broken. When pseudopotentials are replaced by a full band calculation, the crossing point changes into a gap of 2.72 x 10-4 eV.

  5. Band gaps in jagged and straight graphene nanoribbons tunable by an external electric field

    Science.gov (United States)

    Saroka, V. A.; Batrakov, K. G.; Demin, V. A.; Chernozatonskii, L. A.

    2015-04-01

    Band gap control by an external field is useful in various optical, infrared and THz applications. However, widely tunable band gaps are still not practical due to a variety of reasons. Using the orthogonal tight-binding method for ?-electrons, we have investigated the effect of the external electric field on a subclass of monolayer chevron-type graphene nanoribbons that can be referred to as jagged graphene nanoribbons. A classification of these ribbons was proposed and band gaps for applied fields up to the SiO2 breakdown strength (1 V nm?1) were calculated. According to the tight-binding model, band gap opening (or closing) takes place for some types of jagged graphene nanoribbons in the external electric field that lies on the plane of the structure and perpendicular to its longitudinal axis. Tunability of the band gap up to 0.6 eV is attainable for narrow ribbons. In the case of jagged ribbons with armchair edges larger jags forming a chevron pattern of the ribbon enhance the controllability of the band gap. For jagged ribbons with zigzag and armchair edges regions of linear and quadratic dependence of the band gap on the external electric field can be found that are useful in devices with controllable modulation of the band gap.

  6. Photonic band gap of superconductor-medium structure: Two-dimensional triangular lattice

    International Nuclear Information System (INIS)

    Highlights: • Plane wave expansion is generalized to superconductor-medium periodic structure. • A wider band gap appears than that in conventional photonic crystals. • Part of original energy levels are rearranged upon consideration of the superconductivity. • Band gap width decreases monotonically with penetration length, but not with the filling factor. • Band gaps can be partially shut down or opened by adjusting filling factor. - Abstract: Based on London theory a general form of wave equation is formulated for both dielectric medium and superconductor. Using the wave equation and applying plane wave expansion, we have numerically calculated the band structures and density of states of a photonic crystal, whose intersection is constructed by a two-dimensional triangular lattice of superconductor padding in dielectric medium. Results indicate a wider band gap in the superconductor-medium photonic crystal than that in conventional photonic crystals. And part of original energy levels are found to be rearranged upon consideration of the superconductivity. The dependence of band gap on penetration length and filling factor is also discussed. Band gap width decreases monotonically with the penetration length, but not with the filling factor. Band gaps can be partially shut down or opened by adjusting filling factor

  7. High spin yrast and non yrast bands in 176 Os, 178 Os and 180 Os

    International Nuclear Information System (INIS)

    High spin yrast and non-yrast states have been identified in 176Os, 178Os and 180Os using (16O,xn) reactions, and ?-ray techniques. Band crossing anomalies are observed in each of the positive parity yrast bands. The magnitude of these anomalies decreases with decreasing neutron number, an effect attributed to the change in the moment of inertia of the ground state rotational bands. A 23 ns isomer is identified at 1930 keV in 180Os. The configuration of this isomer is discussed on the basis of the properties of its rotational band. Negative parity, odd and even spin, sideband sequences are observed in each isotope. Their relationship to rotation aligned octupole and 2-quasiparticle bands is discussed from their excitation energies, band spacings, and decay properties. Detailed calculations for Coriolis mixed bands are carried out for the likely 2-quasiproton and 2-quasineutron configurations. An anomaly observed at spin 17 in the odd-spin negative parity sequence in 180Os is attributed to a band crossing with a four quasiparticle configuration

  8. Soft-rotator model analysis of collective band structures of even-even actinide nuclei

    International Nuclear Information System (INIS)

    Positive-parity collective band structures of low-lying levels in even-even actinide nuclei were analyzed based on an extension of the Davydov-Chaban soft rotator model, which accounts for the rotation and ?-and ?-vibrations of even-even nuclei with non-axial quadrupole deformation. The parameters to reproduce the 4-bands, i.e., the ground-state rotational band, the K?2 band, and the n?=1 and n?=1 bands, were obtained, and their systematic trends were deduced. Based on this result the unassigned band having a sequence of 0+, 2+, 4+, ···, which is observed in many actinide nuclei, was assigned likely to be the n?=1 band. The systematic trends of the parameters found in this work could be a guide to estimate the collective band structure of nuclei for which such data are poorly known. The correct assignment of collective levels was found to be important for the calculation of neutron inelastic scattering cross sections. (author)

  9. Validation of reactor calculations

    International Nuclear Information System (INIS)

    The purpose of this presentation is to describe the methods and procedures for systematic verification of reactor calculations. Some important benchmark test cases are presented for power and research reactor codes. (author)

  10. Hydrogen Solution Calculator

    Science.gov (United States)

    David Joiner

    This calculator prints the closed form solution of the hydrogen wave function for given energy states. In addition, closed form expressions for the Associated Legendre Functions and Laguerre Polynomials (radial solution of hydrogen wave function) are included.

  11. Handout on shielding calculation

    International Nuclear Information System (INIS)

    In order to avoid the difficulties of the radioprotection supervisors in the tasks related to shielding calculations, is presented in this paper the basic concepts of shielding theory. It also includes exercises and examples. (author)

  12. Design of Folded Multilayer Microstrip Tri-Band Hairpin Band Pass Filter

    Directory of Open Access Journals (Sweden)

    K. Vidhya

    2013-07-01

    Full Text Available This study presents a novel approach for realizing miniaturized multi layer folded tri band micro-strip band pass filter for Wireless Local Area Network (WLAN and Worldwide interoperatability for Microwave Access (WiMAX applications. The proposed filter consists of a pair of folded hairpin stepped impedance resonators and pair of open loop resonators to achieve tri-band performance. The size of the folded micro-strip tri-band filter is reduced by nearly 60% due to the structural folding arrangement of SIR compared with conventional multilayer triband filter. The folded hairpin resonator helps to reduce the size of the filter. The stepped impedance resonators are designed to operate at the first and third pass bands and the open loop resonators at the second pass band. The design methodology of the tri-band band pass filter was presented. The simulated results of proposed tri-band filter were compared with the conventional one and tabulated.

  13. Reactor lattice transport calculations

    International Nuclear Information System (INIS)

    The present lecture is a continuation of the lecture on Introduction to the Neutron Transport Phenomena. It comprises three aspects of lattice calculations. First the idea of a reactor lattice is introduced. Then the main definitions used in reactor lattice analysis are given, and finally two basic methods applied for solution of the transport equations are defined. Several remarks on secondary results from lattice transport calculations are added. (author)

  14. Calculating a Biodiversity Index

    Science.gov (United States)

    In this Biodiversity Counts activity, students learn how scientists calculate a biodiversity index using a page from the phone book as their data source. The printable five-page PDF handout includes a series of inquiry-based questions to get students thinking about what they already know about biodiversity and how living and non-living things are connected, step-by-step directions for calculating a biodiversity index, and a worksheet that includes brainstorming questions and areas for recording answers.

  15. Calculation of seismic loads

    International Nuclear Information System (INIS)

    The report gives two examples for the practical treatment of seismic loads: 1) To determine the least favourable seismic load function for a selected site, cooperation with geologists and geophysicists is required, 2) engineers are required for the mechanical-mathematical design of a vibrating support construction and the calculation of the vibrations due to seismic forces. Examples are the calculation of a pipeline system and the behaviour of a PWR containment. (GL)

  16. Polarization propagator calculations

    International Nuclear Information System (INIS)

    The latest theoretical developments of the polarization propagator method are discussed. This propagator is the double-time Green's function which describes the propagation of a density disturbance through an interacting system. The application of the method in calculations of excitation properties of atomic, molecular and metallic systems are outlined with examples of calculations of electronic spectra, radiative lifetimes of excited states, second order optical and magnetic properties and ground state correlation energies. (C.F.)

  17. Current interruption transients calculation

    CERN Document Server

    Peelo, David F

    2014-01-01

    Provides an original, detailed and practical description of current interruption transients, origins, and the circuits involved, and how they can be calculated Current Interruption Transients Calculationis a comprehensive resource for the understanding, calculation and analysis of the transient recovery voltages (TRVs) and related re-ignition or re-striking transients associated with fault current interruption and the switching of inductive and capacitive load currents in circuits. This book provides an original, detailed and practical description of current interruption transients, origins,

  18. Coexistence of spherical states with deformed and superdeformed bands in doubly magic 40-Ca; A shell model challenge

    CERN Document Server

    Caurier, E; Nowacki, F; Poves, A

    2007-01-01

    Large scale shell model calculations, with dimensions reaching 10**9, are carried out to describe the recently observed deformed (ND) and superdeformed (SD) bands based on the first and second excited 0+ states of 40-Ca at 3.35-MeV and 5.21-MeV respectively. A valence space comprising two major oscillator shells, sd and pf, can accommodate most of the relevant degrees of freedom of this problem. The ND band is dominated by configurations with four particles promoted to the pf-shell (4p-4h in short). The SD band by 8p-8h configurations. The ground state of 40-Ca is strongly correlated, but the closed shell still amounts to 65%. The energies of the bands are very well reproduced by the calculations. The out-band transitions connecting the SD band with other states are very small and depend on the details of the mixing among the different np-nh configurations, in spite of that, the calculation describes them reasonably. For the in-band transition probabilities along the SD band, we predict a fairly constant tran...

  19. SbSI Based Photonic Crystal Superlattices: Band Structure and Optics

    Science.gov (United States)

    S?msek, Sevket; Koc, Husnu; Palaz, Selam?; Oltulu, Oral; Mamedov, Am?rullah M.; Ozbay, Ekmel

    2015-03-01

    In this work, we present an investigation of the optical properties and band structure calculations for the photonic crystal structures (PCs) based on one-dimensional (1D)-photonic crystal. Here we use 1D SbSI based layers in air background. We have theoretically calculated the photonic band structure and optical properties of SbSI based PC superlattices. In our simulation, we employed the finite-difference time domain (FDTD) technique and the plane wave expansion method (PWE), which implies the solution of Maxwell equations with centered finite-difference expressions for the space and time derivatives.

  20. Theoretical study of positive-parity doublet bands in 124Cs

    International Nuclear Information System (INIS)

    Positive-parity doublet bands in the odd-odd nucleus 124Cs have been studied by using the two quasiparticles plus a triaxial rotor model. The energy spectra and electromagnetic properties are calculated and compared with the available experimental results. Good agreement is obtained in the present calculation. The chiral geometry and its evolution with angular momentum for doublet bands in 124Cs is also exhibited and discussed based on the analysis of the expectation values and the probability distributions of the angular momentum.

  1. Band gap control via tuning of inversion degree in CdIn$_2$S$_4$ spinel

    CERN Document Server

    Seminóvski, Yohanna; Wahnón, Perla; Grau-Crespo, Ricardo

    2012-01-01

    Based on theoretical arguments we propose a possible route for controlling the band-gap in the promising photovoltaic material CdIn$_2$S$_4$. Our \\textit{ab initio} calculations show that the experimental degree of inversion in this spinel (fraction of tetrahedral sites occupied by In) corresponds approximately to the equilibrium value given by the minimum of the theoretical inversion free energy at a typical synthesis temperature. Modification of this temperature, or of the cooling rate after synthesis, is then expected to change the inversion degree, which in turn sensitively tunes the electronic band-gap of the solid, as shown here by accurate screened hybrid functional calculations.

  2. Band crossing in the O(6) symmetry region around A=130

    International Nuclear Information System (INIS)

    The band crossing in 128,132Ba has been studied by using the model in which two neutrons and two protons have been coupled to a proton-neutron boson model core. The properties of the isomeric 10+ state in 132Ba have been well described. The most striking features of 128Ba are the three-band mixing and the fact that both 10+ and 12+ states are mixed. Lifetimes in the yrast cascade and E2 branching ratios have been calculated. The calculation is in satisfactory agreement with the experimental data. (author)

  3. DSN 100-meter X and S band microwave antenna design and performance

    Science.gov (United States)

    Williams, W. F.

    1978-01-01

    The RF performance is studied for large reflector antenna systems (100 meters) when using the high efficiency dual shaped reflector approach. An altered phase was considered so that the scattered field from a shaped surface could be used in the JPL efficiency program. A new dual band (X-S) microwave feed horn was used in the shaping calculations. A great many shaping calculations were made for various horn sizes and locations and final RF efficiencies are reported. A conclusion is reached that when using the new dual band horn, shaping should probably be performed using the pattern of the lower frequency

  4. Intruder bands in Z = 51 nuclei

    International Nuclear Information System (INIS)

    Recent investigations of h11/2 proton intruder bands in odd 51Sb nuclei are reported. In addition to experiments performed at SUNY Stony Brook and Chalk River, data from Early Implementation of GAMMASPHERE (analysis in progress) are presented. In particular, the nuclei 109Sb and 111Sb are discussed. Rotational bands based on the ?h11/2 orbital coupled to a 2p2h deformed state of the 50Sn core have been observed. These bands have been observed to high spin, and in the case of 109Sb to a rotational frequency of 1.4 MeV, the highest frequency observed in a heavy nucleus. The dynamic moments of inertia in these bands decrease slowly with frequency, suggesting a gradual band termination. The systematics of such bands in 109-119Sb will be discussed

  5. Filters for dual band infrared imagers

    Science.gov (United States)

    Rahmlow, Thomas D., Jr.; Lazo-Wasem, Jeanne E.; Wilkinson, Scott; Tinker, Flemming

    2009-05-01

    Dual band infrared imagers require a similar set of filters as are needed by single band infrared imagers but with the added requirement of high transmission in the mid and far infrared. The design of discrete layer filters with optimized dual band transmission is investigated for three types of filters. These are a visible-infrared beamsplitter, a long wavelength edge filter and a dual bandpass cold filter. These designs illustrate the role that harmonic reflection bands can play in the design of dual band filters. The visible reflection beamsplitter design does not have harmonics in the infrared but requires additional layers to reduce reflection at mid and long wavelengths. The long wavelength edge filter requires suppression of the second and third harmonics while the sensor band pass cold filter can use harmonics to advantage. Design techniques are discussed and the results of an initial set of fabrication runs are presented to assess the sensitivity of example designs to manufacturing errors.

  6. Band edge singularities and density of states in YTaO4 and YNbO4

    International Nuclear Information System (INIS)

    We study the structural and electronic properties of YTaO4 and YNbO4 by means of accurate first-principle total energy calculations. The calculations are based on density functional theory (DFT). The total energy, electronic band structure, and density of states are calculated via the full potential linear-augmented plane wave approach, as implemented in the WIEN2K code, within the framework of DFT. The results show that the valence bands of tantalate and niobate systems are from O 2p states. Conduction bands are divided into two parts. The lower conduction band is mainly composed of Ta 5d or Nb 4d states and the upper conduction bands involve contribution mainly from Y 4d states of YTaO4 or YNbO4. The efficient band gaps in yttrium tantalate and niobate are determined about 4.8 and 4.1 eV, respectively. The agreement between the calculations and the experimental data is excellent. The efficient band gap and a simple model illustrating excitation and emission process in considered host lattices are discussed. (authors)

  7. An automated search algorithm for superdeformed bands

    International Nuclear Information System (INIS)

    An algorithm is presented which searches ?-ray coincidences of arbitrarily high fold for the regular sequences of transitions which characterize the decay of superdeformed rotational bands. The algorithm was used to analyze data gathered by the EUROGAM multi-detector array. It successfully located all but one of the known superdeformed bands in 149Gd found by conventional methods and, in addition, found at least one new band as well. ((orig.))

  8. Banded vegetation: biological productivity and resilience

    Science.gov (United States)

    Yizhaq, Hezi; Gilad, Erez; Meron, Ehud

    2005-10-01

    Vegetation band patterns on hill slopes are studied using a mathematical model. The model applies to drylands, where the limiting resource is water, and takes into account positive feedback effects between biomass and water. Multiple band patterns coexisting in wide precipitation ranges are found. For given precipitation and slope conditions band patterns with higher wavenumbers are more biologically productive. High-wavenumber patterns, however, are less resilient to environmental changes.

  9. Efficient Spectrum Utilization of Uhf Broadcast Band

    OpenAIRE

    Shi, Lei

    2014-01-01

    The UHF band between 470-790 MHz, currently occupied by digital ter- restrial TV (DTT) distribution in Europe, is widely regarded as a premium spectrum band for providing mobile coverage. With the exponential increase in wireless data traffic in recent years, there has been growing interests in gaining access to this spectrum band for wireless broadband services. The secondary access in TV White Space is considered as one cost-effective way to reuse the spectrum unoccupied by the primary DTT ...

  10. Coherent band pathways between knots and links

    CERN Document Server

    Buck, Dorothy

    2014-01-01

    We categorise coherent band (aka nullification) pathways between knots and 2-component links. Additionally, we characterise the minimal coherent band pathways (with intermediates) between any two knots or 2-component links with small crossing number. We demonstrate these band surgeries for knots and links with small crossing number. We apply these results to place lower bounds on the minimum number of recombinant events separating DNA configurations, restrict the recombination pathways and determine chirality and/or orientation of the resulting recombinant DNA molecules.

  11. Rotational bands and chirality in 194Tl

    Science.gov (United States)

    Masiteng, P. L.; Lawrie, E. A.; Ramashidzha, T. M.; Lawrie, J. J.; Bark, R. A.; Lindsay, R.; Komati, F.; Kau, J.; Maine, P.; Maliage, S. M.; Matamba, I.; Mullins, S. M.; Murray, S. H. T.; Mutshena, K. P.; Pasternak, A. A.; Roux, D. G.; Sharpey-Schafer, J. F.; Shirinda, O.; Vymers, P. A.

    2014-07-01

    The high-spin states in 194Tl were studied using the 181Ta(18O, 5n) reaction and the AFRODITE -ray spectrometer at iThemba LABS. The level scheme of 194Tl was considerably extended with several new bands. Three negative-parity 4-quasiparticle bands were observed and associated with configurations. Two of these form a candidate chiral pair with excellent near-degeneracy. In addition two new positive-parity bands were found.

  12. The population and decay of superdeformed bands

    International Nuclear Information System (INIS)

    The population of superdeformed bands is studied with a simple model, where two type of states (normal-deformed and superdeformed) are separated by an energy barrier, and decay via collective E2 or statistical E1 transitions. The strong E2 rates in the superdeformed bands and the different level density of the two type of states can explain the general behavior of the population of these bands as a function of spin. (author)

  13. Band structure in classical field theory

    OpenAIRE

    Salem, Michael; Vachaspati, Tanmay

    2002-01-01

    Stability and instability bands in classical mechanics are well-studied in connection with systems such as described by the Mathieu equation. We examine whether such band structure can arise in classical field theory in the context of an embedded kink in 1+1 dimensions. The static embedded kink is unstable to perturbations but we show that if the kink is dynamic it can exhibit stability in certain parameter bands. Our results are relevant for estimating the lifetimes of vari...

  14. On the persistence of adiabatic shear bands

    OpenAIRE

    Bassim M.N.; Boakye-Yiadom S.; Al-Ameeri S.

    2012-01-01

    It is generally agreed that the initiation and development of adiabatic shear bands (ASBs) are manifestations of damage in metallic materials subjected to high strain rates and large strains as those due to impact in a Hopkinson Bar system. Models for evolution of these bands have been described in the literature. One question that has not received attention is how persistent these bands are and whether their presence and effect can be reversed or eliminated by using a process of thermal (hea...

  15. Identical Bands and ?I=2 Staggering in Superdeformed Nuclei in A~150 Mass Region Using Three Parameters Rotational Model

    Directory of Open Access Journals (Sweden)

    Khalaf A. M.

    2012-10-01

    Full Text Available By using a computer simulated search program, the experimental gamma transition energies for superdeformed rotational bands (SDRB’s in A ? 150 region are fitted to proposed three-parameters model. The model parameters and the spin of the bandhead were obtained for the selected ten SDRB’s namely: 150Gd (yrast and excited SD bands, 151Tb (yrast and excited SD bands, 152Dy (yrast SD bands, 148Gd (SD-1,SD-6, 149Gd(SD-1,153Dy (SD-1 and 148Eu (SD-1. The Kinematic J(1 and dynamic J(2 moments of inertia are studied as a function of the rotational frequency ~?. From the calculated results, we notic that the excited SD bands have identical energies to their Z+1 neighbours for the twinned SD bands in N=86 nuclei. Also the analysis done allows us to confirm ?I = 2 staggering in the yrast SD bands of 148Gd,149Gd,153Dy, and 148Eu andin the excited SD bands of 148Gd, by performing a staggering parameter analysis. For each band, we calculated the deviation of the gamma ray energies from smooth reference representing the finite difference approximation to the fourth derivative of the gamma ray transition energies at a given spin.

  16. Residual stress dependant anisotropic band gap of various (hkl) oriented BaI{sub 2} films

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Pradeep; Gulia, Vikash; Vedeshwar, Agnikumar G., E-mail: agni@physics.du.ac.in, E-mail: agvedeshwar@gmail.com [Thin Film Laboratory, Department of Physics and Astrophysics, University of Delhi, Delhi-110007 (India)

    2013-11-21

    The thermally evaporated layer structured BaI{sub 2} grows in various completely preferred (hkl) film orientations with different growth parameters like film thickness, deposition rate, substrate temperature, etc. which were characterized by structural, morphological, and optical absorption measurements. Structural analysis reveals the strain in the films and the optical absorption shows a direct type band gap. The varying band gaps of these films were found to scale linearly with their strain. The elastic moduli and other constants were also calculated using Density Functional Theory (DFT) formalism implemented in WIEN2K code for converting the strain into residual stress. Films of different six (hkl) orientations show stress free anisotropic band gaps (2.48–3.43?eV) and both positive and negative pressure coefficients. The negative and positive pressure coefficients of band gap are attributed to the strain in I-I (or Ba-Ba or both) and Ba-I distances along [hkl], respectively. The calculated band gaps are also compared with those experimentally determined. The average pressure coefficient of band gap of all six orientations (?0.071?eV/GPa) found to be significantly higher than that calculated (?0.047?eV/GPa) by volumetric pressure dependence. Various these issues have been discussed with consistent arguments. The electron effective mass m{sub e}{sup *}=0.66m{sub 0} and the hole effective mass m{sub h}{sup *}=0.53m{sub 0} have been determined from the calculated band structure.

  17. A hybrid variational-perturbation calculation of the ro-vibrational spectrum of nitric acid

    CERN Document Server

    Pavlyuchko, A I; Tennyson, Jonathan

    2014-01-01

    Rotation-vibration spectra of the nitric acid molecule, HNO\\3, are calculated for wavenumbers up to 7000~\\cm. Calculations are performed using a Hamiltonian expressed in internal curvilinear vibrational coordinates solved using a hybrid variational-perturbation method. An initial potential energy surface (PES) and dipole moment function (DMF) are calculated {\\it ab initio} at the CCSD(T)/aug-cc-pVQZ level of theory. Parameters of the PES and DMF are varied to minimize differences between the calculated and experimental transition frequencies and intensities. The average, absolute deviation between calculated and experimental values is 0.2~\\cm\\ for frequencies in the fundamental bands and 0.4~\\cm\\ for those in the first overtone and lowest combination bands. For the intensities, the calculated and experimental values differ by 0.3\\% and 40\\% for the fundamentals and overtones, respectively. The optimized PES and DMF are used to calculate the room-temperature ro-vibrational spectrum. These calculation reproduce...

  18. Study of negative-parity high-spin bands in 102Ru

    International Nuclear Information System (INIS)

    Complete text of publication follows. Several nuclear structure phenomena related to triaxiality have been pointed out in the region of transitional nuclei near A ? 100 below the tin isotope chain. The occurrence of signature inversion has been reported in 98,100-103Rh isotopes and recently, chiral twin bands have been found in 104,105,106Rh nuclei. More recently, the rigid or ?-soft type of triaxiality in 102Ru has been examined through an analysis of the excitation energies in the low-spin quasi-? band. In the present work we report on extension of the band structure of 102Ru. High-spin states in the nucleus 102Ru were investigated via the 96Zr(13C,?3n) reaction at beam energies of 51 and 58 MeV with the Euroball IV ?-ray spectrometer and the Diamant charged particle array. The already known negative-parity bands (bands 2 and 3 in Fig. 1) were extended up to Ex ?11 and ?9 MeV with I? = (23-) and (20-), respectively. In addition, two new negative-parity bands were observed shown as bands 4 and 5 in Fig. 1. The deduced high-spin structure has been compared with Woods-Saxon TRS calculations. On the basis of the comparison of measured and calculated Routhians, aligned angular momenta and M1/E2 branching ratios ?h11/2(g7/2, d5/2) configurations are suggested for all the negative-parity bands. The obtained re-parity bands. The obtained results have been presented in Ref. (author)

  19. Structure of superdeformed bands in 195Hg

    International Nuclear Information System (INIS)

    Four new superdeformed bands have been observed with the Gammasphere array and have been assigned to the 195Hg nucleus. Two of the bands are interpreted as signature partners most likely based on Nosc=6 neutron quasiparticles coupled to a superdeformed core, while the other two appear to be based on a j15/2 intruder orbital. These four bands do not exhibit a simple, open-quotes identical bandsclose quotes relationship to other superdeformed bands in this mass region. copyright 1997 The American Physical Society

  20. Possible chiral bands in 194Tl

    Science.gov (United States)

    Masiteng, P. L.; Lawrie, E. A.; Ramashidzha, T. M.; Lawrie, J. J.; Bark, R. A.; Kau, J.; Komati, F.; Lindsay, R.; Maliage, S. M.; Matamba, I.; Mullins, S. M.; Mutshena, P.; Murray, S. H. T.; Sharpey-Schafer, J. F.; Vymers, P. A.; Zhang, Y.

    2011-10-01

    High spin states in 194Tl, excited through the 181Ta(18O,5n) fusion evaporation reaction, were studied using the AFRODITE array at iThemba LABS. Candidate chiral bands built on the ?h9/2??i13/21 configuration were found. Furthermore these bands were observed through a band crossing caused by the excitation of a ?i13/2 pair. Above the band crossing the excitation energies remain close, suggesting that chirality may persist for the four quasiparticle configuration too.

  1. Possible chiral bands in 194Tl

    International Nuclear Information System (INIS)

    High spin states in 194Tl, excited through the 181Ta(18O,5n) fusion evaporation reaction, were studied using the AFRODITE array at iThemba LABS. Candidate chiral bands built on the ?h9/2 x ?i13/21 configuration were found. Furthermore these bands were observed through a band crossing caused by the excitation of a ?i13/2 pair. Above the band crossing the excitation energies remain close, suggesting that chirality may persist for the four quasiparticle configuration too.

  2. UWB Band Pass Filter with WLAN notch

    OpenAIRE

    Kumar, Harish; Bhardwaj, Vibhor Kumar; M D, Upadhayay

    2012-01-01

    In this paper, UWB technology operating in broad frequency range of 3.1-10.6 GHz has shown great achievement for high- speed wireless communications. to satisfy the UWB system requirements, a band pass filter with a broad pass band width, low insertion loss, and high stop-band suppression. UWB band-pass filter (BPF) with wireless local area network (WLAN) notch at 5.8 GHz and 3-dB fractional bandwidth of 108% using a microstrip structure is presented. Initially a two transmission pole UWB ban...

  3. Uncertainty calculations made easier

    International Nuclear Information System (INIS)

    The results are presented of a neutron cross section sensitivity/uncertainty analysis performed in a complicated 2D model of the NET shielding blanket design inside the ITER torus design, surrounded by the cryostat/biological shield as planned for ITER. The calculations were performed with a code system developed at ECN Petten, with which sensitivity/uncertainty calculations become relatively simple. In order to check the deterministic neutron transport calculations (performed with DORT), calculations were also performed with the Monte Carlo code MCNP. Care was taken to model the 2.0 cm wide gaps between two blanket segments, as the neutron flux behind the vacuum vessel is largely determined by neutrons streaming through these gaps. The resulting neutron flux spectra are in excellent agreement up to the end of the cryostat. It is noted, that at this position the attenuation of the neutron flux is about 1 l orders of magnitude. The uncertainty in the energy integrated flux at the beginning of the vacuum vessel and at the beginning of the cryostat was determined in the calculations. The uncertainty appears to be strongly dependent on the exact geometry: if the gaps are filled with stainless steel, the neutron spectrum changes strongly, which results in an uncertainty of 70% in the energy integrated flux at the beginning of the cryostat in the no-gap-geometry, compared to an uncertainty of only 5% in the gap-geometry. Therefore, it is essential to take into account the exact geometry in sensitivity/uncertainty calculations. Furthermore, this study shows that an improvement of the covariance data is urgently needed in order to obtain reliable estimates of the uncertainties in response parameters in neutron transport calculations. (orig./GL)

  4. Band structure of surface barrier states and resonances

    International Nuclear Information System (INIS)

    Full text: G. Binnig and H. Rohrer, Nobel Prize Winners for the invention of the Scanning Tunneling Microscope, write in the opening sentence of one of their papers, co-authored with others : 'One of the fundamental problems in surface physics is obtaining knowledge of the electron-metal-surface interaction potential.' Although it is known that the surface barrier has an 'image' asymptotic form and saturates or weakens closer to the crystal surface, the position of the image tail, momentum dependence of the barrier height and saturation closer to the surface have not been agreed upon by different workers and techniques to this day. Ab initio calculations using the density functional approximation produce locations for the position of the image tail which differ by ?50% depending on whether the exiting or incoming electron is considered part of the crystal or a classical charge interacting with the electron gas. Very low energy electron diffraction (VLEED), k-resolved inverse photoemission spectroscopy (KRIPES) and 2-photon photoemission spectroscopy (2PPE) are sensitive to the barrier but analyses to date have not yielded consistent conclusions. In this work we have used our plane-wave scattering method to calculate the barrier energy band structure for Cu (001) over the whole SBZ to compare with experimental results from KRIPES and 2PPE data as well as the calculation of Smith et al. This calculation used a parameterized nearly-free-electron function to represent tly-free-electron function to represent the substrate scattering and could only produce states not resonances which occur outside of bulk band gaps and above the barrier height. As well, no inelastic scattering could be included. We show that inelastic scattering, surface restructuring and an extended data-base must be included for definitive conclusions about details of the barrier. Also, our calculation shows above-barrier resonances are strong and should be measured by experimentalists to extract the momentum dependent saturation and height of the barrier

  5. Narrow-band guided-mode resonance filters: Theory and experiments

    Science.gov (United States)

    Thurman, Samuel Trent

    For more than ten years now, there has been much interest in developing guided-mode resonance (GMR) filters for optical narrow-band filtering applications. Here, analytic methods for simultaneous control over a filter's line shape symmetry, side-band levels, pass-band width, and pass-band shape are studied. Symmetry and side-band levels are managed by an improved version of the so-called thin-film method of Wang and Magnusson [Opt. Lett. 19, 919--921 (1994)]. Inadequacies of the original method are related to an unjustified long-wavelength approximation in calculating the effective-index of a grating. Improved results are obtained by using a more accurate effective-index model or rigorous techniques with the thin-film method. Pole-zero analysis is used to derive symmetry conditions and approximate expressions for the side-band levels of a GMR filter. Results of the pole-zero analysis provide a convenient means of evaluating filter performance and reinforce the principles of the thin-film method. Additional control over pass-band width is achieved by incorporating techniques for adjusting the loss of the resonant mode into the thin-film method. Several factors that limit the minimum obtainable pass-band width are discussed. Two methods that provide additional control over pass-band shape are presented. The first involves stacking GMR filters on top of one another such that reflections from each filter interfere to produce a more rectangular pass-band, while the second is to design a filter with two closely spaced resonances that overlap. Filters based on the second technique are designed using pole-zero analysis conditions a maximally-flat pass-band. Experimental results are presented for two GMR filters that demonstrate simultaneous control over symmetry, side-band levels, and pass-band width. Both filters exhibit line shapes that are fairly symmetric on a logarithmic scale and centered about lambda = 1550 nm. The first has a spectral width of 1.87 nm and -20 dB side-bands, while the second has a spectral width of 0.43 nm and -25 dB side-bands. Differences between experimental and expected values are attributed to scattering losses.

  6. Isolated flat bands and spin-1 conical bands in two-dimensional lattices

    Science.gov (United States)

    Green, Dmitry; Santos, Luiz; Chamon, Claudio

    2010-08-01

    Dispersionless bands, such as Landau levels, serve as a good starting point for obtaining interesting correlated states when interactions are added. With this motivation in mind, we study a variety of dispersionless (“flat”) band structures that arise in tight-binding Hamiltonians defined on hexagonal and kagome lattices with staggered fluxes. The flat bands and their neighboring dispersing bands have several notable features: (a) flat bands can be isolated from other bands by breaking time-reversal symmetry, allowing for an extensive degeneracy when these bands are partially filled; (b) an isolated flat band corresponds to a critical point between regimes where the band is electron-like or hole-like, with an anomalous Hall conductance that changes sign across the transition; (c) when the gap between a flat band and two neighboring bands closes, the system is described by a single spin-1 conical-like spectrum, extending to higher angular momentum the spin-1/2 Dirac-like spectra in topological insulators and graphene; (d) some configurations of parameters admit two isolated parallel flat bands, raising the possibility of exotic “heavy excitons”; and (e) we find that the Chern number of the flat bands, in all instances that we study here, is zero.

  7. ?h11/2 intruder and ?g9/2-1 strongly coupled bands in 115Sb

    International Nuclear Information System (INIS)

    High spin states have been populated in 115Sb with the reaction 100Mo(19F,4n)115Sb at a beam energy of 82 MeV. Two intruder rotational bands (?I=2) extending to spins 43/2- and 51/2- have been observed. The extracted relative B(E2) value supports the nearly diabatic nature of these two bands. The transition energies in these two bands are nearly similar and the bands have a relative spin alignment of 4? at low frequencies. The bands have been interpreted to be based on the ?h11/2 orbital coupled to the deformed 2p-2h states of the 114Sn core. Possible quasiparticle configurations for the excited negative parity band are discussed and it is suggested that this band is based on aligned h11/2 neutrons, the yrare extension of which is observed diabatically down to very low spin values. Two strongly coupled (?I=1) rotational bands involving the (?g9/2)-1 configuration have been observed, of which the known strongly coupled band has been extended from 23/2+ to 37/2+ in spin and the extracted B(M1;I?I-1)/B(E2;I?I-2) values for this band are compared with the Doenau-Frauendorf formula. Alignment features due to the h11/2 neutrons in the observed bands are compared with the core nucleus 114Sn and cranked shell model calculations. Equilibrium deformations for a range of odd Sb isotopes have been calculatedSb isotopes have been calculated with various intrinsic proton configurations. copyright 1996 The American Physical Society

  8. Effects of strain, d-band filling, and oxidation state on the bulk electronic structure of cubic 3d perovskites.

    Science.gov (United States)

    Akhade, Sneha A; Kitchin, John R

    2011-09-14

    The properties of the d-band structure of the transition metal atom in cubic LaBO(3) and SrBO(3) perovskites (where B = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) and their dependence on strain, d-band filling, and oxidation state were investigated using density functional theory calculations and atom-projected density of states. The strain dependence of the d-band width is shown to depend systematically on the size of the B atom. We show that the transition metal d-band width and center are linearly correlated with each other in agreement with a rectangular band model. A simple matrix element formalism based on the solid state table can readily predict the strain dependence of the d-band width. PMID:21932913

  9. Wannier-like functions and tight-binding parametrization for the manganese bands in CaMnO sub 3

    CERN Document Server

    Saha-Dasgupta, T

    2003-01-01

    We study the electronic band structure of CaMnO sub 3 , in order to understand the origin of the dispersion of the Mn(e sub g) bands, which is in contrast with the predicted dispersionless bands within the Anderson-Hasegawa double-exchange model with infinite Hund's-rule coupling. A downfolding technique within the newly developed muffin-tin orbital-based method is used to analyse the density-functional band structure obtained in the local spin density approximation. The finite Hund's coupling parameter in realistic situations allows the same-spin bands on the two manganese sublattices to mix producing a large dispersion. The calculated Wannier functions for the Mn(e sub g) bands also show large oxygen character at sites further away from nearest oxygen sites causing long-ranged Mn-Mn hopping processes.

  10. Internal radiation dose calculation

    International Nuclear Information System (INIS)

    A method of internal absorbed dose calculation recommended by the Medical Internal Radiation Dose (MIRD) Committee is presented in this paper along with the recent results. The absorbed dose in MIRD method is expressed as a function of the following factors, the quantity of the radionuclides irradiating tissues, the energy released by the radionuclides, and the fraction of energy released by the radionuclides absorbed in the tissues. The dose absorbed into a specific target organ from a specific source organ can be calculated, provided that the mass of the target and the cumulative activity in the source are known. The calculation of the absorbed fractions in the monoenergetic sources uniformely distributed in the various organs of a heteregeneous phantom was performed by Snyder et al. using the Monte Carlo technique. The cummulative activity in a source organ is to be found from the medical or biological data, while the remaining terms can be obtained by physical and anatomical data. A quantity S, which corresponds to the absorbed dose per unit cumulative activity, was introduced to calculate the average dose. Various examples of dose calculation are introduced. (Kato, T.)

  11. ''Shears bands'' in 199Pb and 200Pb

    International Nuclear Information System (INIS)

    High-spin states in 199Pb and 200Pb have been investigated by in-beam ?-ray spectroscopy using several different reactions. In addition to an extension of the spherical level scheme, eight (possibly ten) regular sequences of dipole transitions are found. They are built on oblate proton 2p2h states that are coupled to neutron i13/2 excitations. The experimental results are compared to tilted-axis cranking calculations. A new way of generating regular bands is suggested, that combines collective rotation with a continuous and simultaneous reorientation of neutron and proton spins into the direction of the total angular momentum. ((orig.))

  12. Design of Low Band Gap Double Perovskites from First Principles

    OpenAIRE

    Berger, Robert F.; Neaton, Jeffrey B.

    2012-01-01

    Using density functional theory (DFT)-based calculations, we propose a family of metastable, as-yet unmade V5+ and Cr6+ double perovskite compounds with low band gaps spanning much of the visible region of the solar spectrum. Through analysis of a related set of measured optical gaps of d0 ABO3 perovskites and A2B'BO6 double perovskites, an ad hoc procedure is developed to correct DFT and many-body perturbation theory gaps, bringing them into quantitative agreement with expe...

  13. Shape coexistence and strongly coupled bands in 118Sb

    International Nuclear Information System (INIS)

    Excited states of 118Sb were populated via the 116Cd(7Li,5n)118Sb fusion-evaporation reaction at a beam energy of 50 MeV. The previously known level scheme has been considerably extended, and about 36 new transitions were added into the level scheme of 118Sb. One new rotational band has been identified, and assigned the ?g9/2-1 x ?g7/2 configuration. The configuration-fixed constrained triaxial relativistic mean-field approaches and the particle-rotor model calculations are employed for analysis of the level structure of 118Sb.

  14. Tuning of X-band traveling-wave accelerating structures

    International Nuclear Information System (INIS)

    This paper derives and explains the full procedure used to tune an X-band traveling-wave accelerating structure from the “bead-pull” measurement data. The local reflection of each cell caused by frequency detuning is calculated from the measured field profile deduced from the reflection from a dielectric perturbation (so-called “bead”) and is corrected by monitoring the input reflection coefficient. The structure output matching is made by tuning the last two cells to cancel the reflected wave. This method also gives the relationship of the reflection and frequency detuning, making it possible to evaluate the dimensional tolerances achieved in manufacture

  15. Electronic band structure and intermolecular interaction in substituted thiophene polymorphs

    International Nuclear Information System (INIS)

    Total energy calculations based on a density-functional tight-binding scheme have been performed on polymorphic modifications of various thiophene crystals. The electronic band structures exhibit a quasi-one-dimensional interaction in the triclinic crystals, while the monoclinic modifications show no dispersion over the whole Brillouin zone. The main interaction mechanism can be described as a d-? wave function overlap between sulfur and carbon. The strong intermolecular interaction may induce an interchain excitation, responsible for the different optical properties of the polymorphs

  16. Band width and multiple-angle valence-state mapping of diamond

    Energy Technology Data Exchange (ETDEWEB)

    Jimenez, I.; Terminello, L.J.; Sutherland, D.G.J. [Lawrence Berkeley National Lab., CA (United States)] [and others

    1997-04-01

    The band width may be considered the single most important parameter characterizing the electronic structure of a solid. The ratio of band width and Coulomb repulsion determines how correlated or delocalized an electron system is. Some of the most interesting solids straddle the boundary between localized and delocalized, e.g. the high-temperature superconductors. The bulk of the band calculations available today is based on local density functional (DF) theory. Even though the Kohn-Sham eigenvalues from that theory do not represent the outcome of a band-mapping experiment, they are remarkably similar to the bands mapped via photoemission. Strictly speaking, one should use an excited state calculation that takes the solid`s many-body screening response to the hole created in photoemission into account. Diamond is a useful prototype semiconductor because of its low atomic number and large band width, which has made it a long-time favorite for testing band theory. Yet, the two experimental values of the band width of diamond have error bars of {+-}1 eV and differ by 3.2 eV. To obtain an accurate valence band width for diamond, the authors use a band-mapping method that collects momentum distributions instead of the usual energy distributions. This method has undergone extensive experimental and theoretical tests in determining the band width of lithium fluoride. An efficient, imaging photoelectron spectrometer is coupled with a state-of-the-art undulator beam line at the Advanced Light Source to allow collection of a large number of data sets. Since it takes only a few seconds to take a picture of the photoelectrons emitted into a 84{degrees} cone, the authors can use photon energies as high as 350 eV where the cross section for photoemission from the valence band is already quite low, but the emitted photoelectrons behave free-electron-like. This make its much easier to locate the origin of the inter-band transitions in momentum space.

  17. Calculated hyperfine fields of light interstitials in Fe

    International Nuclear Information System (INIS)

    Super-cell band structure calculations with the Korringa-Kohn-Rostoker method in the framework of the local-spin-density approximation are performed on ferromagnetic iron with typical elements (B, C and N) at the octahedral interstitial sites for the purpose of studying hyperfine fields of light interstitials. Lattice relaxations around the interstitial atoms are allowed in these calculations. Calculated hyperfine fields of these interstitial impurities are in better agreement with experimental values than the results obtained previously for unrelaxed lattices, showing that the inclusion of the lattice relaxation is crucial in these systems. (orig.)

  18. Geogebra: Calculation of Centroid

    Directory of Open Access Journals (Sweden)

    Qamil Kllogjeri

    2012-09-01

    Full Text Available Our paper is result of the research done in a special direction for solving problems of physics by using GeoGebra programme: calculation of centroid. Lots of simulations of physical phenomena from the class of Mechanics can be performed and computational problems can be solved with GeoGebra. GeoGebra offers many commands and one of them is the command “centroid” to calculate the coordinates of the centroid of a polygon but, we have created a new tool to calculate the coordinates of the centroid of a plane region bounded by curves. Our work is part of the passionate work of many GeoGebra users which will result with a very rich fund of GeoGebra virtual tools, examples and experiences that will be worldwidely available for many teachers and practioners.

  19. Glauber amplitude calculation method

    International Nuclear Information System (INIS)

    In the framework of eikonal approach the problem of calculating cross section of the composed system quasielastic scattering is considered. The one-particle densities of the system as well as the constituent elastic scattering amplitude are given by Gaussian functions. The calculation algorithm of these cross sections based on using diagram, representation of Glauber expansion terms is proposed. By this algorithm after having integrated the multidimensional Gaussian functions by any coordinate of constituent system a concept of a scattering diagram was used. It enables one to execute reducing of similar members of Glauber series

  20. Confidence Calculation with AMV+

    Energy Technology Data Exchange (ETDEWEB)

    Fossum, A.F.

    1999-02-19

    The iterative advanced mean value algorithm (AMV+), introduced nearly ten years ago, is now widely used as a cost-effective probabilistic structural analysis tool when the use of sampling methods is cost prohibitive (Wu et al., 1990). The need to establish confidence bounds on calculated probabilities arises because of the presence of uncertainties in measured means and variances of input random variables. In this paper an algorithm is proposed that makes use of the AMV+ procedure and analytically derived probability sensitivities to determine confidence bounds on calculated probabilities.