Yang, Chao
2009-07-17
We present a practical approach to calculate the complex band structure of an electrode for quantum transport calculations. This method is designed for plane wave based Hamiltonian with nonlocal pseudopotentials and the auxiliary periodic boundary condition transport calculation approach. Currently there is no direct method to calculate all the evanescent states for a given energy for systems with nonlocal pseudopotentials. On the other hand, in the auxiliary periodic boundary condition transport calculation, there is no need for all the evanescent states at a given energy. The current method fills this niche. The method has been used to study copper and gold nanowires and bulk electrodes.
Exact exchange plane-wave-pseudopotential calculations for slabs.
Engel, Eberhard
2014-05-14
The exact exchange of density functional theory is applied to both free-standing graphene and a Si(111) slab, using the plane-wave pseudopotential (PWPP) approach and a periodic repetition of the supercell containing the slab. It is shown that (i) PWPP calculations with exact exchange for slabs in supercell geometry are basically feasible, (ii) the width of the vacuum required for a decoupling of the slabs is only moderately larger than in the case of the local-density approximation, and (iii) the resulting exchange potential vx shows an extended region, both far outside the surface of the slab and far from the middle of the vacuum region between the slabs, in which vx behaves as -e(2)/z, provided the width of the vacuum is chosen sufficiently large. This last result is corroborated by an analytical analysis of periodically repeated jellium slabs. The intermediate -e(2)/z behavior of vx can be used for an absolute normalization of vx and the total Kohn-Sham potential, which, in turn, allows the determination of the work function.
NASA Astrophysics Data System (ADS)
Pickard, Chris J.; Winkler, Björn; Chen, Roger K.; Payne, M. C.; Lee, M. H.; Lin, J. S.; White, J. A.; Milman, V.; Vanderbilt, David
2000-12-01
We show that plane wave ultrasoft pseudopotential methods readily extend to the calculation of the structural properties of lanthanide and actinide containing compounds. This is demonstrated through a series of calculations performed on UO, UO2, UO3, U3O8, UC2, α-CeC2, CeB6, CeSe, CeO2, NdB6, TmOI, LaBi, LaTiO3, YbO, and elemental Lu.
Pickard; Winkler; Chen; Payne; Lee; Lin; White; Milman; Vanderbilt
2000-12-11
We show that plane wave ultrasoft pseudopotential methods readily extend to the calculation of the structural properties of lanthanide and actinide containing compounds. This is demonstrated through a series of calculations performed on UO, UO2, UO3, U3O8, UC2, alpha-CeC2, CeB6, CeSe, CeO2, NdB6, TmOI, LaBi, LaTiO3, YbO, and elemental Lu.
Plane-wave pseudopotential study of point defects in uranium dioxide
NASA Astrophysics Data System (ADS)
Crocombette, J. P.; Jollet, F.; Nga, L. Thien; Petit, T.
2001-09-01
A study on uranium and oxygen point defects in uranium dioxide using the ab initio plane-wave pseudopotential method in the local density approximation of the density functional theoretical framework is presented. Norm conserving pseudopotentials are used to describe oxygen and uranium atoms. The uranium pseudopotential is specifically described. Its validity is ascertained thanks to a detailed structural study of uranium dioxide and of three phases of metallic uranium (fcc, bcc, and α phase). The free energies of formation of both intrinsic (Frenkel pairs and Schottky defect) and extrinsic (single vacancies or interstitials) defects are calculated. The obtained values form a reliable set of numerical data that are analyzed in the framework of the point defect model which is commonly used to assess defect concentrations in uranium dioxide and their variation with stoichiometry. From the obtained results, the ability of the point defect model to accurately reproduce defect concentrations in uranium dioxide is discussed.
Trail-Needs pseudopotentials in quantum Monte Carlo calculations with plane-wave/blip basis sets
NASA Astrophysics Data System (ADS)
Drummond, N. D.; Trail, J. R.; Needs, R. J.
2016-10-01
We report a systematic analysis of the performance of a widely used set of Dirac-Fock pseudopotentials for quantum Monte Carlo (QMC) calculations. We study each atom in the periodic table from hydrogen (Z =1 ) to mercury (Z =80 ), with the exception of the 4 f elements (57 ≤Z ≤70 ). We demonstrate that ghost states are a potentially serious problem when plane-wave basis sets are used in density functional theory (DFT) orbital-generation calculations, but that this problem can be almost entirely eliminated by choosing the s channel to be local in the DFT calculation; the d channel can then be chosen to be local in subsequent QMC calculations, which generally leads to more accurate results. We investigate the achievable energy variance per electron with different levels of trial wave function and we determine appropriate plane-wave cutoff energies for DFT calculations for each pseudopotential. We demonstrate that the so-called "T-move" scheme in diffusion Monte Carlo is essential for many elements. We investigate the optimal choice of spherical integration rule for pseudopotential projectors in QMC calculations. The information reported here will prove crucial in the planning and execution of QMC projects involving beyond-first-row elements.
Milman, V.; Winkler, B.; White, J.A.; Pickard, C.J.; Payne, M.C.; Akhmatskaya, E.V.; Nobes, R.H.
2000-04-20
Recent developments in density functional theory (DFT) methods applicable to studies of large periodic systems are outlined. During the past three decades, DFT has become an essential part of computational materials science, addressing problems in materials design and processing. The theory allows one to interpret experimental data and to generate property data (such as binding energies of molecules on surfaces) for known materials, and also serves as an aid in the search for and design of novel materials and processes. A number of algorithmic implementations are currently being used, including ultrasoft pseudopotentials, efficient iterative schemes for solving the one-electron DFT equations, and computationally efficient codes for massively parallel computers. The first part of this article provides an overview of plane-wave pseudopotential DFT methods. Their capabilities are subsequently illustrated by examples including the prediction of crystal structures, the study of the compressibility of minerals, and applications to pressure-induced phase transitions. Future theoretical and computational developments are expected to lead to improved accuracy and to treatment of larger systems with a higher computational efficiency.
Three-dimensional plane-wave full-band quantum transport using empirical pseudopotentials
NASA Astrophysics Data System (ADS)
Fang, Jingtian; Vandenberghe, William; Fischetti, Massimo
2015-03-01
We study theoretically the ballistic performance of future sub-5 nm Field-Effect Transistors (FETs) using an atomistic quantum transport formalism based on empirical pseudopotentials, with armchair Graphene NanoRibbons (aGNRs), Silicon NanoWires (SiNWs) and zigzag Carbon NanoTubes (zCNTs) as channel structures. Due to the heavy computational burden from the plane-wave basis set, we restrict our study to ultrasmall devices, characterized by 5 nm channel lengths and 0.7 nm × 0.7 nm cross-sectional areas. Band structure calculations show that aGNRs have an oscillating chirality-dependent band gap. AGNRs with dimer lines N=3p+1 have large band gaps and aGNRFETs show promising device performance in terms of high Ion/Ioff, small drain-induced barrier lowering and limited short channel effects due to their very thin body and associated excellent electrostatics control. N=3p+2 aGNRs have small band gaps and band-to-band tunneling generates a large current at high bias. We also discuss spurious solutions introduced by the envelope function approximation. Device characteristics of SiNWFETs and zCNTFETs are compared to aGNRFETs as well. We acknowledge the support of Nanoelectronics Research Initiatives's (NRI's) Southwest Academy of Nanoelectronics (SWAN).
Propagation of in-plane wave in viscoelastic monolayer graphene via nonlocal strain gradient theory
NASA Astrophysics Data System (ADS)
Xiao, Weiwei; Li, Li; Wang, Meng
2017-06-01
The behaviors of monolayer graphene sheet have attracted increasing attention of many scientists and researchers. In this study, the propagation behaviors of in-plane wave in viscoelastic monolayer graphene are investigated. The constitutive equation and governing equation for in-plane wave propagation is developed by employing Hamilton's principle and nonlocal strain gradient theory. By solving the governing equation of motion, the closed-form dispersion relation between phase velocity and wave number is derived and an asymptotic phase velocity can be acquired. The effects of wave number, material length scale parameter, nonlocal parameter and damping coefficient on in-plane wave propagation behaviors are discussed in the numerical studies. It is found that, when exciting wavelengths or structural dimensions become comparable to the material length scale parameters and nonlocal parameters, the scaling effects on wave propagation behaviors are significant. For nanoscaled graphene sheet, the effects of nonlocal parameter, material length scale parameter and damping coefficient on phase velocity are tiny at low wave numbers while significant at high wave numbers. The phase velocity would increase with the increase of material length scale parameter or the decrease of nonlocal parameter and damping coefficient. Furthermore, results indicate that the asymptotic phase velocity can be increase by increasing material length scale parameter or decreasing nonlocal parameter.
NASA Astrophysics Data System (ADS)
Yaakob, M. K.; Taib, M. F. M.; Lu, L.; Hassan, O. H.; Yahya, M. Z. A.
2015-11-01
The structural, electronic, elastic, and optical properties of BiFeO3 were investigated using the first-principles calculation based on the local density approximation plus U (LDA + U) method in the frame of plane-wave pseudopotential density functional theory. The application of self-interaction corrected LDA + U method improved the accuracy of the calculated properties. Results of structural, electronic, elastic, and optical properties of BiFeO3, calculated using the LDA + U method were in good agreement with other calculation and experimental data; the optimized choice of on-site Coulomb repulsion U was 3 eV for the treatment of strong electronic localized Fe 3d electrons. Based on the calculated band structure and density of states, the on-site Coulomb repulsion U had a significant effect on the hybridized O 2p and Fe 3d states at the valence and the conduction band. Moreover, the elastic stiffness tensor, the longitudinal and shear wave velocities, bulk modulus, Poisson’s ratio, and the Debye temperature were calculated for U = 0, 3, and 6 eV. The elastic stiffness tensor, bulk modulus, sound velocities, and Debye temperature of BiFeO3 consistently decreased with the increase of the U value.
NASA Astrophysics Data System (ADS)
Yao, Yi; Kanai, Yosuke
2017-06-01
We present the implementation and performance of the strongly constrained and appropriately normed, SCAN, meta-GGA exchange-correlation (XC) approximation in the planewave-pseudopotential (PW-PP) formalism using the Troullier-Martins pseudopotential scheme. We studied its performance by applying the PW-PP implementation to several practical applications of interest in condensed matter sciences: (a) crystalline silicon and germanium, (b) martensitic phase transition energetics of phosphorene, and (c) a single water molecule physisorption on a graphene sheet. Given the much-improved accuracy over the GGA functionals and its relatively low computational cost compared to hybrid XC functionals, the SCAN functional is highly promising for various practical applications of density functional theory calculations for condensed matter systems. At same time, the SCAN meta-GGA functional appears to require more careful attention to numerical details. The meta-GGA functional shows more significant dependence on the fast Fourier transform grid, which is used for evaluating the XC potential in real space in the PW-PP formalism, than other more conventional GGA functionals do. Additionally, using pseudopotentials that are generated at a different/lower level of XC approximation could introduce noticeable errors in calculating some properties such as phase transition energetics.
Duan, Xiaofeng F; Burggraf, Larry W; Huang, Lingyu
2013-07-22
To find low energy Si(n)C(n) structures out of hundreds to thousands of isomers we have developed a general method to search for stable isomeric structures that combines Stochastic Potential Surface Search and Pseudopotential Plane-Wave Density Functional Theory Car-Parinello Molecular Dynamics simulated annealing (PSPW-CPMD-SA). We enhanced the Sunders stochastic search method to generate random cluster structures used as seed structures for PSPW-CPMD-SA simulations. This method ensures that each SA simulation samples a different potential surface region to find the regional minimum structure. By iterations of this automated, parallel process on a high performance computer we located hundreds to more than a thousand stable isomers for each Si(n)C(n) cluster. Among these, five to 10 of the lowest energy isomers were further optimized using B3LYP/cc-pVTZ method. We applied this method to Si(n)C(n) (n = 4-12) clusters and found the lowest energy structures, most not previously reported. By analyzing the bonding patterns of low energy structures of each Si(n)C(n) cluster, we observed that carbon segregations tend to form condensed conjugated rings while Si connects to unsaturated bonds at the periphery of the carbon segregation as single atoms or clusters when n is small and when n is large a silicon network spans over the carbon segregation region.
Auxiliary-field quantum Monte Carlo calculations with multiple-projector pseudopotentials
NASA Astrophysics Data System (ADS)
Ma, Fengjie; Zhang, Shiwei; Krakauer, Henry
2017-04-01
We have implemented recently developed multiple-projector pseudopotentials into the plane-wave-based auxiliary-field quantum Monte Carlo (pw-AFQMC) method. Multiple-projector pseudopotentials can yield smaller plane-wave cutoffs while maintaining or improving transferability. This reduces the computational cost of pw-AFQMC, increasing its reach to larger and more complicated systems. We discuss the use of nonlocal pseudopotentials in the separable Kleinman-Bylander form, and the implementation in pw-AFQMC of the multiple-projector optimized norm-conserving pseudopotential ONCVPSP of Hamann. The accuracy of the method is first demonstrated by equation-of-state calculations of the ionic insulator NaCl and more strongly correlated metal Cu. The method is then applied to calibrate the accuracy of density-functional theory (DFT) predictions of the phase stability of recently discovered high temperature and pressure superconducting sulfur hydride systems. We find that DFT results are in good agreement with pw-AFQMC, due to the near cancellation of electron-electron correlation effects between different structures.
Optimization Algorithm for the Generation of ONCV Pseudopotentials
NASA Astrophysics Data System (ADS)
Schlipf, Martin; Gygi, Francois
2015-03-01
We present an optimization algorithm to construct pseudopotentials and use it to generate a set of Optimized Norm-Conserving Vanderbilt (ONCV) pseudopotentials for elements up to Z=83 (Bi) (excluding Lanthanides). We introduce a quality function that assesses the agreement of a pseudopotential calculation with all-electron FLAPW results, and the necessary plane-wave energy cutoff. This quality function allows us to use a Nelder-Mead optimization algorithm on a training set of materials to optimize the input parameters of the pseudopotential construction for most of the periodic table. We control the accuracy of the resulting pseudopotentials on a test set of materials independent of the training set. We find that the automatically constructed pseudopotentials provide a good agreement with the all-electron results obtained using the FLEUR code with a plane-wave energy cutoff of approximately 60 Ry. Supported by DOE/BES Grant DE-SC0008938.
NASA Astrophysics Data System (ADS)
Forgács, Péter; Lukács, Árpád; Romańczukiewicz, Tomasz
2013-12-01
It is shown that in a large class of systems, plane waves act as tractor beams: i.e., an incident plane wave can exert a pulling force on the scatterer. The underlying physical mechanism for the pulling force is due to the sufficiently strong scattering of the incoming wave into another mode carrying more momentum, in which case excess momentum is created behind the scatterer. This tractor beam or negative radiation pressure (NRP) effect, is found to be generic in systems with multiple scattering channels. In a birefringent medium, electromagnetic plane waves incident on a thin plate exert NRP of the same order of magnitude as optical radiation pressure, while in artificial dielectrics (metamaterials), the magnitude of NRP can even be macroscopic. In two dimensions, we study various scattering situations on vortices, and NRP is shown to occur by the scattering of heavy baryons into light leptons off cosmic strings, and by neutron scattering off vortices in the XY model.
Marsh, S.P.
1988-03-08
An explosive plane-wave air lens which enables a spherical wave form to be converted to a planar wave without the need to specially machine or shape explosive materials is described. A disc-shaped impactor having a greater thickness at its center than around its periphery is used to convert the spherical wave into a plane wave. When the wave reaches the impactor, the center of the impactor moves first because the spherical wave reaches the center of the impactor first. The wave strikes the impactor later in time as one moves radially along the impactor. Because the impactor is thinner as one moves radially outward, the velocity of the impactor is greater at the periphery than at the center. An acceptor explosive is positioned so that the impactor strikes the acceptor simultaneously. Consequently, a plane detonation wave is propagated through the acceptor explosive. 4 figs.
Marsh, Stanley P.
1988-01-01
An explosive plane-wave air lens which enables a spherical wave form to be converted to a planar wave without the need to specially machine or shape explosive materials is described. A disc-shaped impactor having a greater thickness at its center than around its periphery is used to convert the spherical wave into a plane wave. When the wave reaches the impactor, the center of the impactor moves first because the spherical wave reaches the center of the impactor first. The wave strikes the impactor later in time as one moves radially along the impactor. Because the impactor is thinner as one moves radially outward, the velocity of the impactor is greater at the periphery than at the center. An acceptor explosive is positioned so that the impactor strikes the acceptor simultaneously. Consequently, a plane detonation wave is propagated through the acceptor explosive.
Marsh, S.P.
1987-03-12
An explosive plane-wave air lens which enables a spherical wave form to be converted to a planar wave without the need to specially machine or shape explosive materials is described. A disc-shaped impactor having a greater thickness at its center than around its periphery is used to convert the spherical wave into a plane wave. When the wave reaches the impactor, the center of the impactor moves first because the spherical wave reaches the center of the impactor first. The wave strikes the impactor later in time as one moves radially along the impactor. Because the impactor is thinner as one moves radially outward, the velocity of the impactor is greater at the periphery than at the center. An acceptor explosive is positioned so that the impactor strikes the acceptor simultaneously. Consequently, a plane detonation wave is propagated through the acceptor explosive. 3 figs., 3 tabs.
NASA Astrophysics Data System (ADS)
Soler, José M.; Williams, Arthur R.
1990-11-01
Results are presented that demonstrate the effectiveness of a calculational method of electronic-structure theory. The method combines the power (tractable basis-set size) and flexibility (transition and first-row elements) of the augmented-plane-wave method with the computational efficiency of the Car-Parrinello method of molecular dynamics and total-energy minimization. Equilibrium geometry and vibrational frequencies in agreement with experiment are presented for Si, to demonstrate agreement with existing methods and for Cu, N2, and H2O to demonstrate the broader applicability of the approach.
Optimization algorithm for the generation of ONCV pseudopotentials
NASA Astrophysics Data System (ADS)
Schlipf, Martin; Gygi, François
2015-11-01
We present an optimization algorithm to construct pseudopotentials and use it to generate a set of Optimized Norm-Conserving Vanderbilt (ONCV) pseudopotentials for elements up to Z = 83 (Bi) (excluding Lanthanides). We introduce a quality function that assesses the agreement of a pseudopotential calculation with all-electron FLAPW results, and the necessary plane-wave energy cutoff. This quality function allows us to use a Nelder-Mead optimization algorithm on a training set of materials to optimize the input parameters of the pseudopotential construction for most of the periodic table. We control the accuracy of the resulting pseudopotentials on a test set of materials independent of the training set. We find that the automatically constructed pseudopotentials
Causal inheritence in plane wave quotients
Hubeny, Veronika E.; Rangamani, Mukund; Ross, Simon F.
2003-11-24
We investigate the appearance of closed timelike curves in quotients of plane waves along spacelike isometries. First we formulate a necessary and sufficient condition for a quotient of a general spacetime to preserve stable causality. We explicitly show that the plane waves are stably causal; in passing, we observe that some pp-waves are not even distinguishing. We then consider the classification of all quotients of the maximally supersymmetric ten-dimensional plane wave under a spacelike isometry, and show that the quotient will lead to closed timelike curves iff the isometry involves a translation along the u direction. The appearance of these closed timelike curves is thus connected to the special properties of the light cones in plane wave spacetimes. We show that all other quotients preserve stable causality.
Double plane wave reverse time migration with plane wave Green's function
NASA Astrophysics Data System (ADS)
Zhao, Z.; Sen, M. K.; Stoffa, P. L.
2015-12-01
Reverse time migration (RTM) is effective in obtaining complex subsurface structures from seismic data. By solving the two-way wave equation, RTM can use entire wavefield for imaging. Although powerful computer are becoming available, the conventional pre-stack shot gather RTM is still computationally expensive. Solving forward and backward wavefield propagation for each source location and shot gather is extremely time consuming, especially for large seismic datasets. We present an efficient, accurate and flexible plane wave RTM in the frequency domain where we utilize a compressed plane wave dataset, known as the double plane wave (DPW) dataset. Provided with densely sampled seismic dataset, shot gathers can be decomposed into source and receiver plane wave components with minimal artifacts. The DPW RTM is derived under the Born approximation and utilizes frequency domain plane wave Green's function for imaging. Time dips in the shot profiles can help to estimate the range of plane wave components present in shot gathers. Therefore, a limited number of plane wave Green's functions are needed for imaging. Plane wave Green's functions can be used for imaging both source and receiver plane waves. Source and receiver reciprocity can be used for imaging plane wave components at no cost and save half of the computation time. As a result, the computational burden for migration is substantially reduced. Plane wave components can be migrated independently to recover specific targets with given dips, and ray parameter common image gathers (CIGs) can be generated after migration directly. The ray parameter CIGs can be used to justify the correctness of velocity models. Subsurface anisotropy effects can also be included in our imaging condition, provided with plane wave Green's functions in the anisotropic media.
Simple Harmonic Motion in Harmonic Plane Waves.
ERIC Educational Resources Information Center
Benumof, Reuben
1980-01-01
Discusses the distribution of kinetic and potential energy in transverse and longitudinal waves and examines the transmission of power and momentum. This discussion is intended to aid in understanding the simple harmonic motion of a particle involved in the propagation of a harmonic mechanical plane wave. (HM)
Simple Harmonic Motion in Harmonic Plane Waves.
ERIC Educational Resources Information Center
Benumof, Reuben
1980-01-01
Discusses the distribution of kinetic and potential energy in transverse and longitudinal waves and examines the transmission of power and momentum. This discussion is intended to aid in understanding the simple harmonic motion of a particle involved in the propagation of a harmonic mechanical plane wave. (HM)
Plane wave reflection at flow intakes
NASA Astrophysics Data System (ADS)
Davies, P. O. A. L.
1987-06-01
A treatment is presented for prediction of the acoustic field associated with an open duct termination whose inflow is at a mean Mach number, and requires a quantitative description of both the acoustic and flow conditions in the vicinity of the open end. This problem is presently simplified by restricting the acoustic field within the duct to plane wave motion, with component wave amplitudes p(+) and p(-), where p(+) is incident at the termination. A 'vena contracta' develops in the pipe just downstream of the intake, leading to a significant mean pressure loss.
Blackfolds, plane waves and minimal surfaces
NASA Astrophysics Data System (ADS)
Armas, Jay; Blau, Matthias
2015-07-01
Minimal surfaces in Euclidean space provide examples of possible non-compact horizon geometries and topologies in asymptotically flat space-time. On the other hand, the existence of limiting surfaces in the space-time provides a simple mechanism for making these configurations compact. Limiting surfaces appear naturally in a given space-time by making minimal surfaces rotate but they are also inherent to plane wave or de Sitter space-times in which case minimal surfaces can be static and compact. We use the blackfold approach in order to scan for possible black hole horizon geometries and topologies in asymptotically flat, plane wave and de Sitter space-times. In the process we uncover several new configurations, such as black helicoids and catenoids, some of which have an asymptotically flat counterpart. In particular, we find that the ultraspinning regime of singly-spinning Myers-Perry black holes, described in terms of the simplest minimal surface (the plane), can be obtained as a limit of a black helicoid, suggesting that these two families of black holes are connected. We also show that minimal surfaces embedded in spheres rather than Euclidean space can be used to construct static compact horizons in asymptotically de Sitter space-times.
Incidence of plane waves upon a fracture
NASA Astrophysics Data System (ADS)
Gu, Boliang; SuáRez-Rivera, R.; Nihei, Kurt T.; Myer, Larry R.
1996-11-01
This paper investigates the details of reflection, transmission, and conversion of plane waves incident upon a fracture at arbitrary angles. The elastic compliance of fractures that is produced by the presence of a planar collection of void spaces and asperities of contact is modeled as a displacement-discontinuity boundary condition between two elastic half-spaces. Closed-form expressions for the transmission and reflection coefficients on a fracture are derived by replacing the boundary conditions for a welded interface by those for a fracture into the standard procedure for plane wave analysis. The closed-form expressions reveal that a single fracture can produce a variety of potentially diagnostic waves such as transmitted waves, reflected waves, converted waves, head waves, and P interface waves and introduce a finite group time delay to all these waves with respect to the incident wave. The amplitude and group time delay of the fracture-induced waves are controlled by the fracture stiffness, wave frequency, and the Poisson's ratio of the medium. The head wave and inhomogeneous P interface waves are generated when an SV wave is incident upon a fracture, at and beyond a critical angle, respectively, which is determined by Snell's law. For some combinations of the fracture stiffness and the Poisson's ratio of the half-spaces, no reflection or transmission of a P wave or an SV wave occurs.
Plane wave gravitons, curvature singularities and string physics
Brooks, R. . Center for Theoretical Physics)
1991-03-21
This paper discusses bounded (compactifying) potentials arising from a conspiracy between plane wave graviton and dilaton condensates. So are string propagation and supersymmetry in spacetimes with curvature singularities.
Force-based optimization of pseudopotentials for non-equilibrium configurations
NASA Astrophysics Data System (ADS)
Brock, Casey N.; Paikoff, Brandon C.; Md Sallih, Muhammad I.; Tackett, Alan R.; Walker, D. Greg
2016-04-01
We have used a multi-objective genetic algorithm to optimize pseudopotentials for force accuracy and computational efficiency. Force accuracy is determined by comparing interatomic forces generated using the pseudopotentials and forces generated using the full-potential linearized augmented-plane wave method. This force-based optimization approach is motivated by applications where interatomic forces are important, including material interfaces, crystal defects, and molecular dynamics. Our method generates Pareto sets of optimized pseudopotentials containing various compromises between accuracy and efficiency. We have tested our method for LiF, Si0.5Ge0.5, and Mo and compared the performance of our pseudopotentials with pseudopotentials available from the ABINIT library. We show that the optimization can generate pseudopotentials with comparable accuracy (in terms of force matching and equation of state) to pseudopotentials in the literature while sometimes significantly improving computational efficiency. For example, we generated pseudopotentials for one system tested that reduced computational work by 71% without loss of accuracy. These results suggest our method can be used to generate pseudopotentials on demand that are tuned for a user's specific application, affording gains in computational efficiency.
Pseudopotentials for quantum Monte Carlo studies of transition metal oxides
Krogel, Jaron T.; Santana Palacio, Juan A.; Reboredo, Fernando A.
2016-02-22
Quantum Monte Carlo (QMC) calculations of transition metal oxides are partially limited by the availability of high-quality pseudopotentials that are both accurate in QMC and compatible with major plane-wave electronic structure codes. We have generated a set of neon-core pseudopotentials with small cutoff radii for the early transition metal elements Sc to Zn within the local density approximation of density functional theory. The pseudopotentials have been directly tested for accuracy within QMC by calculating the first through fourth ionization potentials of the isolated transition metal (M) atoms and the binding curve of each M-O dimer. We find the ionization potentialsmore » to be accurate to 0.16(1) eV, on average, relative to experiment. The equilibrium bond lengths of the dimers are within 0.5(1)% of experimental values, on average, and the binding energies are also typically accurate to 0.18(3) eV. The level of accuracy we find for atoms and dimers is comparable to what has recently been observed for bulk metals and oxides using the same pseudopotentials. Our QMC pseudopotential results compare well with the findings of previous QMC studies and benchmark quantum chemical calculations.« less
Pseudopotentials for quantum Monte Carlo studies of transition metal oxides
Krogel, Jaron T.; Santana Palacio, Juan A.; Reboredo, Fernando A.
2016-02-22
Quantum Monte Carlo (QMC) calculations of transition metal oxides are partially limited by the availability of high-quality pseudopotentials that are both accurate in QMC and compatible with major plane-wave electronic structure codes. We have generated a set of neon-core pseudopotentials with small cutoff radii for the early transition metal elements Sc to Zn within the local density approximation of density functional theory. The pseudopotentials have been directly tested for accuracy within QMC by calculating the first through fourth ionization potentials of the isolated transition metal (M) atoms and the binding curve of each M-O dimer. We find the ionization potentials to be accurate to 0.16(1) eV, on average, relative to experiment. The equilibrium bond lengths of the dimers are within 0.5(1)% of experimental values, on average, and the binding energies are also typically accurate to 0.18(3) eV. The level of accuracy we find for atoms and dimers is comparable to what has recently been observed for bulk metals and oxides using the same pseudopotentials. Our QMC pseudopotential results compare well with the findings of previous QMC studies and benchmark quantum chemical calculations.
NASA Astrophysics Data System (ADS)
Min, Byeong June; Jeong, Hae Kyung; Lee, ChangWoo
2015-08-01
We studied via plane wave pseudopotential total-energy calculations within the local spin density approximation (LSDA) the electronic and the structural properties of amino acids (alanine, glycine, and histidine) attached to graphene oxide (GO) by peptide bonding. The HOMO-LUMO gap, the Hirshfeld charges, and the equilibrium geometrical structures exhibit distinctive variations that depend on the species of the attached amino acid. The GO-amino acid system appears to be a good candidate for a biosensor.
Fast plane wave density functional theory molecular dynamics calculations on multi-GPU machines
Jia, Weile; Fu, Jiyun; Cao, Zongyan; Wang, Long; Chi, Xuebin; Gao, Weiguo; Wang, Lin-Wang
2013-10-15
Plane wave pseudopotential (PWP) density functional theory (DFT) calculation is the most widely used method for material simulations, but its absolute speed stagnated due to the inability to use large scale CPU based computers. By a drastic redesign of the algorithm, and moving all the major computation parts into GPU, we have reached a speed of 12 s per molecular dynamics (MD) step for a 512 atom system using 256 GPU cards. This is about 20 times faster than the CPU version of the code regardless of the number of CPU cores used. Our tests and analysis on different GPU platforms and configurations shed lights on the optimal GPU deployments for PWP-DFT calculations. An 1800 step MD simulation is used to study the liquid phase properties of GaInP.
Pseudopotential study of barium chalcogenides under hydrostatic pressure
NASA Astrophysics Data System (ADS)
Benamrani, A.; Kassali, K.; Bouamama, Kh.
2010-03-01
We present first-principles calculations within the pseudo-potential plane wave method in the local density approximation (LDA) and the generalised gradient approximation so as to study the structural properties of BaX (X=S, Se and Te) in both NaCl and CsCl structures. The elastic, vibrational properties and lattice dynamics are calculated with the LDA and the density functional perturbation theory. The pressure dependence of the structural, vibrational and lattice dynamics has been investigated by varying the volume. A good agreement is obtained between our calculation and the available experimental and theoretical data.
Iterative diagonalization in augmented plane wave based methods in electronic structure calculations
Blaha, P.; Laskowski, R.; Schwarz, K.
2010-01-20
Due to the increased computer power and advanced algorithms, quantum mechanical calculations based on Density Functional Theory are more and more widely used to solve real materials science problems. In this context large nonlinear generalized eigenvalue problems must be solved repeatedly to calculate the electronic ground state of a solid or molecule. Due to the nonlinear nature of this problem, an iterative solution of the eigenvalue problem can be more efficient provided it does not disturb the convergence of the self-consistent-field problem. The blocked Davidson method is one of the widely used and efficient schemes for that purpose, but its performance depends critically on the preconditioning, i.e. the procedure to improve the search space for an accurate solution. For more diagonally dominated problems, which appear typically for plane wave based pseudopotential calculations, the inverse of the diagonal of (H - ES) is used. However, for the more efficient 'augmented plane wave + local-orbitals' basis set this preconditioning is not sufficient due to large off-diagonal terms caused by the local orbitals. We propose a new preconditioner based on the inverse of (H - {lambda}S) and demonstrate its efficiency for real applications using both, a sequential and a parallel implementation of this algorithm into our WIEN2k code.
Colliding plane waves in F(R)=RN gravity
NASA Astrophysics Data System (ADS)
Tahamtan, T.; Halilsoy, M.; Habib Mazharimousavi, S.
2016-10-01
We identify a region of a specific F( R)= R N gravity solution without external sources which is isometric to the spacetime of colliding plane waves (CPW). The analogy renders construction and collision of plane waves in F( R)= R N gravity possible. The geometry of the interaction region is equivalent to the Reissner-Nordström (RN) one, however there is no Einstein-Maxwell (EM) source --this is made possible by using the model of RN gravity and the parameter N>1 creates the source. For N=1, we naturally recover the plane waves (and their collision) in Einstein's theory.
Pseudopotentials from electron density
NASA Astrophysics Data System (ADS)
Nagy, Á.; Andrejkovics, I.
1996-05-01
A method is introduced that allows the construction of pseudopotentials in the density-functional theory. This method is based on a procedure worked out by one of the authors [J. Phys. B 26, 43 (1993); Philos. Mag. B 69, 779 (1994)] for determining Kohn-Sham potentials, one-electron orbitals, and energies from the electron density. The Hartree-Fock densities of Bunge, Barrientos, and Bunge [At. Data Nucl. Data Tables 53, 114 (1993)] are used to obtain the Kohn-Sham potentials of the Li, Na, and K atoms, and then Phillips-Kleinman-type [Phys. Rev. 116, 287 (1959); 118, 1153 (1960)] pseudopotentials are calculated. The arbitrariness of the pseudo-orbital is removed by minimization of the kinetic energy.
Distorted Plane Waves on Manifolds of Nonpositive Curvature
NASA Astrophysics Data System (ADS)
Ingremeau, Maxime
2017-03-01
We will consider the high frequency behaviour of distorted plane waves on manifolds of nonpositive curvature which are Euclidean or hyperbolic near infinity, under the assumption that the curvature is negative close to the trapped set of the geodesic flow and that the topological pressure associated to half the unstable Jacobian is negative. We obtain a precise expression for distorted plane waves in the high frequency limit, similar to the one in Guillarmou and Naud (Am J Math 136:445-479, 2014) in the case of convex co-compact manifolds. In particular, we will show {L_{loc}^∞} bounds on distorted plane waves that are uniform with frequency. We will also show a small-scale equidistribution result for the real part of distorted plane waves, which implies sharp bounds for the volume of their nodal sets.
A new twist on the geometry of gravitational plane waves
NASA Astrophysics Data System (ADS)
Shore, Graham M.
2017-09-01
The geometry of twisted null geodesic congruences in gravitational plane wave spacetimes is explored, with special focus on homogeneous plane waves. The rôle of twist in the relation of the Rosen coordinates adapted to a null congruence with the fundamental Brinkmann coordinates is explained and a generalised form of the Rosen metric describing a gravitational plane wave is derived. The Killing vectors and isometry algebra of homogeneous plane waves (HPWs) are described in both Brinkmann and twisted Rosen form and used to demonstrate the coset space structure of HPWs. The van Vleck-Morette determinant for twisted congruences is evaluated in both Brinkmann and Rosen descriptions. The twisted null congruences of the Ozsváth-Schücking, `anti-Mach' plane wave are investigated in detail. These developments provide the necessary geometric toolkit for future investigations of the rôle of twist in loop effects in quantum field theory in curved spacetime, where gravitational plane waves arise generically as Penrose limits; in string theory, where they are important as string backgrounds; and potentially in the detection of gravitational waves in astronomy.
The Plane-Wave/Super Yang-Mills Duality
Sadri, D
2003-10-14
We present a self-contained review of the Plane-wave/super-Yang-Mills duality, which states that strings on a plane-wave background are dual to a particular large R-charge sector of N=4, D=4 superconformal U(N) gauge theory. This duality is a specification of the usual AdS/CFT correspondence in the ''Penrose limit''. The Penrose limit of AdS{sub 5} S{sup 5} leads to the maximally supersymmetric ten dimensional plane-wave (henceforth the plane-wave) and corresponds to restricting to the large R-charge sector, the BMN sector, of the dual superconformal field theory. After assembling the necessary background knowledge, we state the duality and review some of its supporting evidence. We review the suggestion by 't Hooft that Yang-Mills theories with gauge groups of large rank might be dual to string theories and the realization of this conjecture in the form of the AdS/CFT duality. We discuss plane-waves as exact solutions of supergravity and their appearance as Penrose limits of other backgrounds, then present an overview of string theory on the plane-wave background, discussing the symmetries and spectrum. We then make precise the statement of the proposed duality, classify the BMN operators, and mention some extensions of the proposal. We move on to study the gauge theory side of the duality, studying both quantum and non-planar corrections to correlation functions of BMN operators, and their operator product expansion. The important issue of operator mixing and the resultant need for re-diagonalization is stressed. Finally, we study strings on the plane-wave via light-cone string field theory, and demonstrate agreement on the one-loop correction to the string mass spectrum and the corresponding quantity in the gauge theory. A new presentation of the relevant superalgebra is given.
Aperture domain model image reconstruction (ADMIRE) with plane wave synthesis
NASA Astrophysics Data System (ADS)
Dei, Kazuyuki; Tierney, Jaime; Byram, Brett
2017-03-01
In our previous studies, we demonstrated that our aperture domain model-based clutter suppression algorithm improved image quality of in vivo B-mode data obtained from focused transmit beam sequences. Our approach suppresses off-axis clutter and reverberation and tackles limitations of related algorithms because it preserves RF channel signals and speckle statistics. We call the algorithm aperture domain model image reconstruction (ADMIRE). We previously focused on reverberation suppression, but ADMIRE is also effective at suppressing off-axis clutter. We are interested in how ADMIRE performs on plane wave sequences and the impact of AD- MIRE applied before and after synthetic beamforming of steered plane wave sequences. We employed simulated phantoms using Field II and tissue-mimicking phantoms to evaluate ADMIRE applied to plane wave sequencing. We generated images acquired from plane waves with and without synthetic aperture synthesis and measured contrast and contrast-to-noise ratio (CNR). For simulated cyst images formed from single plane waves, the contrast for delay-and-sum (DAS) and ADMIRE are 15.64 dB and 28.34 dB, respectively, while the CNR are 1.76 dB and 3.90 dB, respectively. Based on these findings, ADMIRE improves plane wave image quality. We also applied ADMIRE to resolution phantoms having a point target at 3 cm depth on-axis, simulating the point spread functions from data obtained from 1 and 75 steered plane waves, along with linear scan at focus of 3 and 4 cm depth. We then examined the outcome of applying ADMIRE before and after synthetic aperture processing. Finally, we applied this to an in vivo carotid artery.
Coded excitation plane wave imaging for shear wave motion detection.
Song, Pengfei; Urban, Matthew W; Manduca, Armando; Greenleaf, James F; Chen, Shigao
2015-07-01
Plane wave imaging has greatly advanced the field of shear wave elastography thanks to its ultrafast imaging frame rate and the large field-of-view (FOV). However, plane wave imaging also has decreased penetration due to lack of transmit focusing, which makes it challenging to use plane waves for shear wave detection in deep tissues and in obese patients. This study investigated the feasibility of implementing coded excitation in plane wave imaging for shear wave detection, with the hypothesis that coded ultrasound signals can provide superior detection penetration and shear wave SNR compared with conventional ultrasound signals. Both phase encoding (Barker code) and frequency encoding (chirp code) methods were studied. A first phantom experiment showed an approximate penetration gain of 2 to 4 cm for the coded pulses. Two subsequent phantom studies showed that all coded pulses outperformed the conventional short imaging pulse by providing superior sensitivity to small motion and robustness to weak ultrasound signals. Finally, an in vivo liver case study on an obese subject (body mass index = 40) demonstrated the feasibility of using the proposed method for in vivo applications, and showed that all coded pulses could provide higher SNR shear wave signals than the conventional short pulse. These findings indicate that by using coded excitation shear wave detection, one can benefit from the ultrafast imaging frame rate and large FOV provided by plane wave imaging while preserving good penetration and shear wave signal quality, which is essential for obtaining robust shear elasticity measurements of tissue.
Liquid Water through Density-Functional Molecular Dynamics: Plane-Wave vs Atomic-Orbital Basis Sets.
Miceli, Giacomo; Hutter, Jürg; Pasquarello, Alfredo
2016-08-09
We determine and compare structural, dynamical, and electronic properties of liquid water at near ambient conditions through density-functional molecular dynamics simulations, when using either plane-wave or atomic-orbital basis sets. In both frameworks, the electronic structure and the atomic forces are self-consistently determined within the same theoretical scheme based on a nonlocal density functional accounting for van der Waals interactions. The overall properties of liquid water achieved within the two frameworks are in excellent agreement with each other. Thus, our study supports that implementations with plane-wave or atomic-orbital basis sets yield equivalent results and can be used indiscriminately in study of liquid water or aqueous solutions.
Simple plane wave implementation for photonic crystal calculations.
Guo, Shangping; Albin, Sacharia
2003-01-27
A simple implementation of plane wave method is presented for modeling photonic crystals with arbitrary shaped 'atoms'. The Fourier transform for a single 'atom' is first calculated either by analytical Fourier transform or numerical FFT, then the shift property is used to obtain the Fourier transform for any arbitrary supercell consisting of a finite number of 'atoms'. To ensure accurate results, generally, two iterating processes including the plane wave iteration and grid resolution iteration must converge. Analysis shows that using analytical Fourier transform when available can improve accuracy and avoid the grid resolution iteration. It converges to the accurate results quickly using a small number of plane waves. Coordinate conversion is used to treat non-orthogonal unit cell with non-regular 'atom' and then is treated by standard numerical FFT. MATLAB source code for the implementation requires about less than 150 statements, and is freely available at http://www.lions.odu.edu/~sguox002.
Adaptive density partitioning technique in the auxiliary plane wave method
NASA Astrophysics Data System (ADS)
Kurashige, Yuki; Nakajima, Takahito; Hirao, Kimihiko
2006-01-01
We have developed the adaptive density partitioning technique (ADPT) in the auxiliary plane wave method, in which a part of the density is expanded to plane waves, for the fast evaluation of Coulomb matrix. Our partitioning is based on the error estimations and allows us to control the accuracy and efficiency. Moreover, we can drastically reduce the core Gaussian products that are left in Gaussian representation (its analytical integrals is the bottleneck in this method). For the taxol molecule with 6-31G** basis, the core Gaussian products accounted only for 5% in submicrohartree error.
Fully converged plane-wave-based self-consistent G W calculations of periodic solids
NASA Astrophysics Data System (ADS)
Cao, Huawei; Yu, Zhongyuan; Lu, Pengfei; Wang, Lin-Wang
2017-01-01
The G W approximation is a well-known method to obtain the quasiparticle and spectral properties of systems ranging from molecules to solids. In practice, G W calculations are often employed with many different approximations and truncations. In this work, we describe the implementation of a fully self-consistent G W approach based on the solution of the Dyson equation using a plane wave basis set. Algorithmic, numerical, and technical details of the self-consistent G W approach are presented. The fully self-consistent G W calculations are performed for GaAs, ZnO, and CdS including semicores in the pseudopotentials. No further approximations and truncations apart from the truncation on the plane wave basis set are made in our implementation of the G W calculation. After adopting a special potential technique, a ˜100 Ry energy cutoff can be used without the loss of accuracy. We found that the self-consistent G W (sc-G W ) significantly overestimates the bulk band gaps, and this overestimation is likely due to the underestimation of the macroscopic dielectric constants. On the other hand, the sc-G W accurately predicts the d -state positions, most likely because the d -state screening does not sensitively depend on the macroscopic dielectric constant. Our work indicates the need to include the high-order vertex term in order for the many-body perturbation theory to accurately predict the semiconductor band gaps. It also sheds some light on why, in some cases, the G0W0 bulk calculation is more accurate than the fully self-consistent G W calculation, because the initial density-functional theory has a better dielectric constant compared to experiments.
Metaphysics of colliding self-gravitating plane waves
Matzner, R.A.; Tipler, F.J.
1984-04-15
We discuss certain global features of colliding plane-wave solutions to Einstein's equations. In particular, we show that the apparently local curvature singularities both in the Khan-Penrose solution and in the Bell-Szekeres solution are actually global. These global singularities are associated with the breakdown of nondegenerate planar symmetry in the characteristic initial data sets.
Metaphysics of colliding self-gravitating plane waves
NASA Astrophysics Data System (ADS)
Matzner, Richard A.; Tipler, Frank J.
1984-04-01
We discuss certain global features of colliding plane-wave solutions to Einstein's equations. In particular, we show that the apparently local curvature singularities both in the Khan-Penrose solution and in the Bell-Szekeres solution are actually global. These global singularities are associated with the breakdown of nondegenerate planar symmetry in the characteristic initial data sets.
An Apparatus for Constructing an Electromagnetic Plane Wave Model
ERIC Educational Resources Information Center
Kneubil, Fabiana Botelho; Loures, Marcus Vinicius Russo; Amado, William
2015-01-01
In this paper we report on an activity aimed at building an electromagnetic wave. This was part of a class on the concept of mass offered to a group of 20 pre-service Brazilian physics teachers. The activity consisted of building a plane wave using an apparatus in which it is possible to fit some rods representing electric and magnetic fields into…
D-branes in Type IIB plane wave background
Lee, Bum-Hoon
2007-01-12
We classify and summarize the intersecting supersymmetric D-branes in the type IIB plane wave background, based on the Green-Schwarz superstring formulation. Many new configurations appears if we turn on the electric or magnetic background fields or boost the D-branes. Applications to the phenomelogical models are left for further study.
An Apparatus for Constructing an Electromagnetic Plane Wave Model
ERIC Educational Resources Information Center
Kneubil, Fabiana Botelho; Loures, Marcus Vinicius Russo; Amado, William
2015-01-01
In this paper we report on an activity aimed at building an electromagnetic wave. This was part of a class on the concept of mass offered to a group of 20 pre-service Brazilian physics teachers. The activity consisted of building a plane wave using an apparatus in which it is possible to fit some rods representing electric and magnetic fields into…
Plane wave (curl; Ω) conforming finite elements for Maxwell's equations
NASA Astrophysics Data System (ADS)
Ledger, P. D.; Morgan, K.; Hassan, O.; Weatherill, N. P.
This paper proposes a discretisation of Maxwell's equations which combines the popular edge elements of Nédélec with expansions of plane waves. The method is applied to simple two dimensional electromagnetic wave propagation and scattering simulations and issues of accuracy and matrix conditioning are investigated.
Structure and magnetism of bulk Fe and Cr: from plane waves to LCAO methods.
Soulairol, R; Fu, Chu-Chun; Barreteau, C
2010-07-28
Magnetic, structural and energetic properties of bulk Fe and Cr were studied using first-principles calculations within density functional theory (DFT). We aimed to identify the dependence of these properties on key approximations of DFT, namely the exchange-correlation functional, the pseudopotential and the basis set. We found a smaller effect of pseudopotentials (PPs) on Fe than on Cr. For instance, the local magnetism of Cr was shown to be particularly sensitive to the potentials representing the core electrons, i.e. projector augmented wave and Vanderbilt ultrasoft PPs predict similar results, whereas standard norm-conserving PPs tend to overestimate the local magnetic moments of Cr in bcc Cr and in dilute bcc FeCr alloys. This drawback is suggested to be closely correlated to the overestimation of Cr solution energy in the latter system. On the other hand, we point out that DFT methods with very reduced localized basis sets (LCAO: linear combination of atomic orbitals) give satisfactory results compared with more robust plane-wave approaches. A minimal-basis representation of '3d' electrons comes to be sufficient to describe non-trivial magnetic phases including spin spirals in both fcc Fe and bcc Cr, as well as the experimental magnetic ground state of bcc Cr showing a spin density wave (SDW) state. In addition, a magnetic 'spd' tight binding model within the Stoner formalism was proposed and validated for Fe and Cr. The respective Stoner parameters were obtained by fitting to DFT data. This efficient semiempirical approach was shown to be accurate enough for studying various collinear and non-collinear phases of bulk Fe and Cr. It also enabled a detailed investigation of different polarization states of SDW in bcc Cr, where the longitudinal state was suggested to be the ground state, consistent with existing experimental data.
Coded Excitation Plane Wave Imaging for Shear Wave Motion Detection
Song, Pengfei; Urban, Matthew W.; Manduca, Armando; Greenleaf, James F.; Chen, Shigao
2015-01-01
Plane wave imaging has greatly advanced the field of shear wave elastography thanks to its ultrafast imaging frame rate and the large field-of-view (FOV). However, plane wave imaging also has decreased penetration due to lack of transmit focusing, which makes it challenging to use plane waves for shear wave detection in deep tissues and in obese patients. This study investigated the feasibility of implementing coded excitation in plane wave imaging for shear wave detection, with the hypothesis that coded ultrasound signals can provide superior detection penetration and shear wave signal-to-noise-ratio (SNR) compared to conventional ultrasound signals. Both phase encoding (Barker code) and frequency encoding (chirp code) methods were studied. A first phantom experiment showed an approximate penetration gain of 2-4 cm for the coded pulses. Two subsequent phantom studies showed that all coded pulses outperformed the conventional short imaging pulse by providing superior sensitivity to small motion and robustness to weak ultrasound signals. Finally, an in vivo liver case study on an obese subject (Body Mass Index = 40) demonstrated the feasibility of using the proposed method for in vivo applications, and showed that all coded pulses could provide higher SNR shear wave signals than the conventional short pulse. These findings indicate that by using coded excitation shear wave detection, one can benefit from the ultrafast imaging frame rate and large FOV provided by plane wave imaging while preserving good penetration and shear wave signal quality, which is essential for obtaining robust shear elasticity measurements of tissue. PMID:26168181
Ab initio Sternheimer-GW method for quasiparticle calculations using plane waves
NASA Astrophysics Data System (ADS)
Lambert, Henry; Giustino, Feliciano
2013-08-01
We report on the extension and implementation of the Sternheimer-GW method introduced by Giustino [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.81.115105 81, 115105 (2010)] to the case of first-principles pseudopotential calculations based on a plane-waves basis. The Sternheimer-GW method consists of calculating the GW self-energy operator without resorting to the standard expansion over unoccupied Kohn-Sham electronic states. The Green's function is calculated by solving linear systems for frequencies along the real axis. The screened Coulomb interaction is calculated for frequencies along the imaginary axis by using the Sternheimer equation. Analytic continuation to the real axis is performed using Padé approximants. The generalized plasmon-pole approximation is avoided by performing explicit calculations at multiple frequencies using Frommer's multishift solver. We demonstrate our methodology by reporting tests on common insulators and semiconductors, including Si, diamond, LiCl, and SiC. Our calculated quasiparticle energies are in agreement with the results of fully converged calculations based on the sum-over-states approach. As the Sternheimer-GW method yields the complete self-energy Σ(r,r',ω) and not only its expectation values on Kohn-Sham states, this work opens the way to nonperturbative GW calculations and to direct calculations of spectral functions for angle-resolved photoemission spectroscopy. As an example of the capabilities of the method we calculate the G0W0 spectral functions of silicon and diamond.
Scattering of a CW plane wave by a pulse
NASA Astrophysics Data System (ADS)
Trivett, D. H.; Rogers, P. H.
1982-05-01
A procedure similar to the CW crossed-beam calculation of Ingard and Pridmore-Brown (1956) is used to calculate the far field scattered sound pressure of a pulse interacting with a plane wave. The scattered sound is found to be at neither the sum nor the difference frequency. It is suggested that this type of interaction is ideal for investigating the scattering of sound by sound, and a numerical solution is used to discuss the general features of the nearfield waveform.
On the propagation of plane waves above an impedance surface
NASA Technical Reports Server (NTRS)
Zhong, F. H.; Vanmoorhem, W. K.
1990-01-01
The propagation of grazing incidence plane waves along a finite impedance boundary is investigated. A solution of the semi-infinite problem, where a harmonic motion, parallel to the boundary, is imposed along a line perpendicular to the boundary, is obtained. This solution consists of quasiplane waves, waves moving parallel to the boundary with amplitude and phase variations perpendicular to the boundary. Several approximations to the full solution are considered.
Plane Waves in a Transparent Isotropic Chiral Medium
NASA Astrophysics Data System (ADS)
Fisanov, V. V.
2015-04-01
A homogeneous isotropic transparent chiral medium supports two normal plane waves with left and right circular polarization and differently valued positive wave numbers. The presence or absence of forward and backward Beltrami waves and their helicity are regulated by the signs of the permittivity and permeability and the strength of the chirality. The ray refractive index is a universal parameter whose sign differentiates the forward and backward waves.
Holography and entropy bounds in the plane wave matrix model
Bousso, Raphael; Mints, Aleksey L.
2006-06-15
As a quantum theory of gravity, matrix theory should provide a realization of the holographic principle, in the sense that a holographic theory should contain one binary degree of freedom per Planck area. We present evidence that Bekenstein's entropy bound, which is related to area differences, is manifest in the plane wave matrix model. If holography is implemented in this way, we predict crossover behavior at strong coupling when the energy exceeds N{sup 2} in units of the mass scale.
Ultrafast vascular strain compounding using plane wave transmission.
Hansen, H H G; Saris, A E C M; Vaka, N R; Nillesen, M M; de Korte, C L
2014-03-03
Deformations of the atherosclerotic vascular wall induced by the pulsating blood can be estimated using ultrasound strain imaging. Because these deformations indirectly provide information on mechanical plaque composition, strain imaging is a promising technique for differentiating between stable and vulnerable atherosclerotic plaques. This paper first explains 1-D radial strain estimation as applied intravascularly in coronary arteries. Next, recent methods for noninvasive vascular strain estimation in a transverse imaging plane are discussed. Finally, a compounding technique that our group recently developed is explained. This technique combines motion estimates of subsequently acquired focused ultrasound images obtained at various insonification angles. However, because the artery moves and deforms during the multi-angle acquisition, errors are introduced when compounding. Recent advances in computational power have enabled plane wave ultrasound acquisition, which allows 100 times faster image acquisition and thus might resolve the motion artifacts. In this paper the performance of strain imaging using plane wave compounding is investigated using simulations of an artery with a vulnerable plaque and experimental data of a two-layered vessel phantom. The results show that plane wave compounding outperforms 0° focused strain imaging. For the simulations, the root mean squared error reduced by 66% and 50% for radial and circumferential strain, respectively. For the experiments, the elastographic signal-to-noise and contrast-to-noise ratio (SNR(e) and CNR(e)) increased with 2.1 dB and 3.7 dB radially, and 5.6 dB and 16.2dB circumferentially. Because of the high frame rate, the plane wave compounding technique can even be further optimized and extended to 3D in future.
Pérez-Jordá, José M
2011-11-28
A series of improvements for the solution of the three-dimensional Schrödinger equation over a method introduced by Gygi [F. Gygi, Europhys. Lett. 19, 617 (1992); F. Gygi, Phys. Rev. B 48, 11692 (1993)] are presented. As in the original Gygi's method, the solution (orbital) is expressed by means of plane waves in adaptive coordinates u, where u is mapped from Cartesian coordinates, u=f(r). The improvements implemented are threefold. First, maps are introduced that allow the application of the method to atoms and molecules without the assistance of the supercell approximation. Second, the electron-nucleus singularities are exactly removed, so that pseudo-potentials are no longer required. Third, the sampling error during integral evaluation is made negligible, which results in a true variational, second-order energy error procedure. The method is tested on the hydrogen atom (ground and excited states) and the H(2)(+) molecule, resulting in milli-Hartree accuracy with a moderate number of plane waves.
Model Pseudopotentials for Color Centers
NASA Astrophysics Data System (ADS)
Gash, P.; Bartram, R. H.; Gryk, T. J.
2010-11-01
The energy-dependent pseudopotentials for electron-excess color centers in ionic crystals adopted by Bartram, Stoneham and Gash (BSG) were determined by a smoothness criterion because the trial wave functions employed are slowly varying on the scale of the ion cores. Energy-independent norm-conserving pseudopotentials were introduced subsequently in the context of molecular-orbital calculations to ensure that the outer parts of valence pseudo-orbitals coincide with those of true valence orbitals. In the present investigation, whole-ion norm-conserving pseudopotentials calculated from numerical wave functions are employed in F-center calculations for comparison with BSG calculations. It is concluded that the smoothness criterion should take precedence in that application.
G W with linearized augmented plane waves extended by high-energy local orbitals
NASA Astrophysics Data System (ADS)
Jiang, Hong; Blaha, Peter
2016-03-01
Many-body perturbation theory in the G W approximation is currently the most accurate and robust first-principles approach to determine the electronic band structure of weakly correlated insulating materials without any empirical input. Recent G W results for ZnO with more careful investigation of the convergence with respect to the number of unoccupied states have led to heated debates regarding the numerical accuracy of previously reported G W results using either pseudopotential plane waves or all-electron linearized augmented plane waves (LAPWs). The latter has been arguably regarded as the most accurate scheme for electronic-structure theory for solids. This work aims to solve the ZnO puzzle via a systematic investigation of the effects of including high-energy local orbitals (HLOs) in the LAPW-based G W calculations of semiconductors. Using ZnO as the prototypical example, it is shown that the inclusion of HLOs has two main effects: it improves the description of high-lying unoccupied states by reducing the linearization errors of the standard LAPW basis, and in addition it provides an efficient way to achieve the completeness in the summation of states in G W calculations. By investigating the convergence of G W band gaps with respect to the number of HLOs for several other typical examples, it was found that the effects of HLOs are highly system-dependent, and in most cases the inclusion of HLOs changes the band gap by less than 0.2 eV. Compared to its effects on the band gap, the consideration of HLOs has even stronger effects on the G W correction to the valence-band maximum, which is of great significance for the G W prediction of the ionization potentials of semiconductors. By considering an extended set of semiconductors with relatively well-established experimental band gaps, it was found that in general using a HLO-enhanced LAPW basis significantly improves the agreement with experiment for both the band gap and the ionization potential, and overall
Stolt's f-k migration for plane wave ultrasound imaging.
Garcia, Damien; Le Tarnec, Louis; Muth, Stéphan; Montagnon, Emmanuel; Porée, Jonathan; Cloutier, Guy
2013-09-01
Ultrafast ultrasound is an emerging modality that offers new perspectives and opportunities in medical imaging. Plane wave imaging (PWI) allows one to attain very high frame rates by transmission of planar ultrasound wave-fronts. As a plane wave reaches a given scatterer, the latter becomes a secondary source emitting upward spherical waves and creating a diffraction hyperbola in the received RF signals. To produce an image of the scatterers, all the hyperbolas must be migrated back to their apexes. To perform beamforming of plane wave echo RFs and return high-quality images at high frame rates, we propose a new migration method carried out in the frequency-wavenumber (f-k) domain. The f-k migration for PWI has been adapted from the Stolt migration for seismic imaging. This migration technique is based on the exploding reflector model (ERM), which consists in assuming that all the scatterers explode in concert and become acoustic sources. The classical ERM model, however, is not appropriate for PWI. We showed that the ERM can be made suitable for PWI by a spatial transformation of the hyperbolic traces present in the RF data. In vitro experiments were performed to outline the advantages of PWI with Stolt's f-k migration over the conventional delay-and-sum (DAS) approach. The Stolt's f-k migration was also compared with the Fourier-based method developed by J.-Y. Lu. Our findings show that multi-angle compounded f-k migrated images are of quality similar to those obtained with a stateof- the-art dynamic focusing mode. This remained true even with a very small number of steering angles, thus ensuring a highly competitive frame rate. In addition, the new FFT-based f-k migration provides comparable or better contrast-to-noise ratio and lateral resolution than the Lu's and DAS migration schemes. Matlab codes for the Stolt's f-k migration for PWI are provided.
Dzubak, Allison L.; Krogel, Jaron T.; Reboredo, Fernando A.
2017-07-10
The necessarily approximate evaluation of non-local pseudopotentials in diffusion Monte Carlo (DMC) introduces localization errors. In this paper, we estimate these errors for two families of non-local pseudopotentials for the first-row transition metal atoms Sc–Zn using an extrapolation scheme and multideterminant wavefunctions. Sensitivities of the error in the DMC energies to the Jastrow factor are used to estimate the quality of two sets of pseudopotentials with respect to locality error reduction. The locality approximation and T-moves scheme are also compared for accuracy of total energies. After estimating the removal of the locality and T-moves errors, we present the range ofmore » fixed-node energies between a single determinant description and a full valence multideterminant complete active space expansion. The results for these pseudopotentials agree with previous findings that the locality approximation is less sensitive to changes in the Jastrow than T-moves yielding more accurate total energies, however not necessarily more accurate energy differences. For both the locality approximation and T-moves, we find decreasing Jastrow sensitivity moving left to right across the series Sc–Zn. The recently generated pseudopotentials of Krogel et al. reduce the magnitude of the locality error compared with the pseudopotentials of Burkatzki et al. by an average estimated 40% using the locality approximation. The estimated locality error is equivalent for both sets of pseudopotentials when T-moves is used. Finally, for the Sc–Zn atomic series with these pseudopotentials, and using up to three-body Jastrow factors, our results suggest that the fixed-node error is dominant over the locality error when a single determinant is used.« less
NASA Astrophysics Data System (ADS)
Dzubak, Allison L.; Krogel, Jaron T.; Reboredo, Fernando A.
2017-07-01
The necessarily approximate evaluation of non-local pseudopotentials in diffusion Monte Carlo (DMC) introduces localization errors. We estimate these errors for two families of non-local pseudopotentials for the first-row transition metal atoms Sc-Zn using an extrapolation scheme and multideterminant wavefunctions. Sensitivities of the error in the DMC energies to the Jastrow factor are used to estimate the quality of two sets of pseudopotentials with respect to locality error reduction. The locality approximation and T-moves scheme are also compared for accuracy of total energies. After estimating the removal of the locality and T-moves errors, we present the range of fixed-node energies between a single determinant description and a full valence multideterminant complete active space expansion. The results for these pseudopotentials agree with previous findings that the locality approximation is less sensitive to changes in the Jastrow than T-moves yielding more accurate total energies, however not necessarily more accurate energy differences. For both the locality approximation and T-moves, we find decreasing Jastrow sensitivity moving left to right across the series Sc-Zn. The recently generated pseudopotentials of Krogel et al. [Phys. Rev. B 93, 075143 (2016)] reduce the magnitude of the locality error compared with the pseudopotentials of Burkatzki et al. [J. Chem. Phys. 129, 164115 (2008)] by an average estimated 40% using the locality approximation. The estimated locality error is equivalent for both sets of pseudopotentials when T-moves is used. For the Sc-Zn atomic series with these pseudopotentials, and using up to three-body Jastrow factors, our results suggest that the fixed-node error is dominant over the locality error when a single determinant is used.
Decoding the matrix: Coincident membranes on the plane wave
Bousso, Raphael; Mints, Aleksey L.
2006-03-15
At the core of nonperturbative theories of quantum gravity lies the holographic encoding of bulk data in large matrices. At present this mapping is poorly understood. The plane wave matrix model provides a laboratory for isolating aspects of this problem in a controlled setting. At large boosts, configurations of concentric membranes become superselection sectors, whose exact spectra are known. From the bulk point of view, one expects product states of individual membranes to be contained within the full spectrum. However, for non-BPS states this inclusion relation is obscured by Gauss law constraints. Its validity rests on nontrivial relations in representation theory, which we identify and verify by explicit computation.
First principles pseudopotential calculations on aluminum and aluminum alloys
Davenport, J.W.; Chetty, N.; Marr, R.B.; Narasimhan, S.; Pasciak, J.E.; Peierls, R.F.; Weinert, M.
1993-12-31
Recent advances in computational techniques have led to the possibility of performing first principles calculations of the energetics of alloy formation on systems involving several hundred atoms. This includes impurity concentrations in the 1% range as well as realistic models of disordered materials (including liquids), vacancies, and grain boundaries. The new techniques involve the use of soft, fully nonlocal pseudopotentials, iterative diagonalization, and parallel computing algorithms. This approach has been pioneered by Car and Parrinello. Here the authors give a review of recent results using parallel and serial algorithms on metallic systems including liquid aluminum and liquid sodium, and also new results on vacancies in aluminum and on aluminum-magnesium alloys.
The implementation of holography in the plane wave matrix model
NASA Astrophysics Data System (ADS)
Mints, Aleksey Leonidovich
It is expected that at the core of nonperturbative theories of quantum gravity, such as M-theory, lies the realization of the holographic principle, in the sense that a holographic theory should contain one binary degree of freedom per Planck area. Present understanding of such theories requires the holographic encoding of bulk data in large matrices. Currently this mapping is poorly understood. The plane wave matrix model provides a laboratory for isolating aspects of this problem in a controlled setting. At large boosts, configurations of concentric membranes become superselection sectors, whose exact spectra are known. From the bulk point of view one expects product states of individual membranes to be contained within the full spectrum. However, for non-BPS states this inclusion relation is obscured by Gauss law constraints. Its validity rests on nontrivial relations in representation theory, which we identify and verify by explicit computation. Beyond the decoding and partial identification of selected states in large matrices, one would like to get a better understanding of the holographic state counting of these degrees of freedom, i.e., entropy. Contrary to the naive expectation of holography realized in terms of the covariant entropy bound, we present evidence that it is the Bekenstein entropy bound, which is related to area differences, that is manifest in the plane wave matrix model. If holography is implemented in this way, we predict crossover behavior at strong coupling when the energy exceeds N2 in units of the mass scale.
Smallwood, C Jay; Larsen, Ross E; Glover, William J; Schwartz, Benjamin J
2006-08-21
Even with modern computers, it is still not possible to solve the Schrodinger equation exactly for systems with more than a handful of electrons. For many systems, the deeply bound core electrons serve merely as placeholders and only a few valence electrons participate in the chemical process of interest. Pseudopotential theory takes advantage of this fact to reduce the dimensionality of a multielectron chemical problem: the Schrodinger equation is solved only for the valence electrons, and the effects of the core electrons are included implicitly via an extra term in the Hamiltonian known as the pseudopotential. Phillips and Kleinman (PK) [Phys. Rev. 116, 287 (1959)]. demonstrated that it is possible to derive a pseudopotential that guarantees that the valence electron wave function is orthogonal to the (implicitly included) core electron wave functions. The PK theory, however, is expensive to implement since the pseudopotential is nonlocal and its computation involves iterative evaluation of the full Hamiltonian. In this paper, we present an analytically exact reformulation of the PK pseudopotential theory. Our reformulation has the advantage that it greatly simplifies the expressions that need to be evaluated during the iterative determination of the pseudopotential, greatly increasing the computational efficiency. We demonstrate our new formalism by calculating the pseudopotential for the 3s valence electron of the Na atom, and in the subsequent paper, we show that pseudopotentials for molecules as complex as tetrahydrofuran can be calculated with our formalism in only a few seconds. Our reformulation also provides a clear geometric interpretation of how the constraint equations in the PK theory, which are required to obtain a unique solution, are themselves sufficient to calculate the pseudopotential.
Inhomogeneous plane waves and cylindrical waves in anisotropic anelastic media
NASA Astrophysics Data System (ADS)
Krebes, E. S.; Le, Lawrence H. T.
1994-12-01
In isotropic anelastic media, the phase velocity of an inhomogeneous plane body wave, which is a function of Q and the degree of inhomogeneity gamma, is significantly less than the corresponding homogeneous wave phase velocity typically only if gamma is very large (unless Q is unusually low). Here we investigate inhomogeneous waves in anisotropic anelastic media, where phase velocities are also functions of the direction of phase propagation theta, and find that (1) the low phase velocities can occur at values of gamma which are substantially less than the isotropic values and that they occur over a limited range of oblique directions theta, and (2) for large positive values of gamma, there are ranges of oblique directions theta in which the inhomogeneous waves cannot propagate at all because there is no physically acceptable solution to the dispersion relation. We show examples of how the waves of case 1 can occur in practice and cause a number of anomalous wave propagation effects. The waves of case 2, though, do not arise in practice (they do not correspond to any points on the horizontal slowness plate). We also show that in the decomposition of a cylindrical wave into plane waves, inhomogeneous plane waves occur whose amplitudes grow in the direction of phase propagation and that this direction is away from the receiver to which they are contributing. The energy in these waves does, however, travel toward the receiver, and their amplitudes decay in the direction of energy propagation. We also show that if the commonly used definition for the quality factor in an isotropic medium, Q = -Re(mu)/Im(mu) where mu is a complex modulus, is applied to an anisotropic anelastic medium in order to study absorption anisotropy, a generally unreliable measure of the anelasticity of inhomogeneous wave propagation in a given arbitrary direction is obtained. The more fundamental definition based on energy loss (i.e., 2pi/Q = Delta E/E) should be used in general, and we present
Gravitational scattering of zero-rest-mass plane waves
NASA Technical Reports Server (NTRS)
De Logi, W. K.; Kovacs, S. J., Jr.
1977-01-01
The Feyman-diagram technique is used to calculate the differential cross sections for the scattering of zero-rest-mass plane waves of spin 0, 1, and 2 by linearized Schwarzschild and Kerr geometries in the long-wavelength weak-field limit. It is found that the polarization of right (or left) circularly polarized electromagnetic waves is unaffected by the scattering process (i.e., helicity is conserved) and that the two helicity (polarization) states of the photon are scattered differently by the Kerr geometry. This coupling between the photon helicity and the angular momentum of the scatterer also leads to a partial polarization of unpolarized incident light. For gravitational waves, on the other hand, there is neither helicity conservation nor helicity-dependent scattering; the angular momentum of the scatterer has no polarizing effect on incident unpolarized gravitational waves.
Augmented-plane-wave calculations on small molecules
Serena, P.A.; Baratoff, A. ); Soler, J.M. )
1993-07-15
We have performed [ital ab] [ital initio] calculations on a wide range of small molecules, demonstrating the accuracy and flexibility of an alternative method for calculating the electronic structure of molecules, solids, and surfaces. It is based on the local-density approximation (LDA) for exchange and correlation and the nonlinear augmented-plane-wave method. Very accurate atomic forces are obtained directly. This allows for implementation of Car-Parrinello-like techniques to determine simultaneously the self-consistent electron wave functions and the equilibrium atomic positions within an iterative scheme. We find excellent agreement with the best existing LDA-based calculations and remarkable agreement with experiment for the equilibrium geometries, vibrational frequencies, and dipole moments of a wide variety of molecules, including strongly bound homopolar and polar molecules, hydrogen-bound and electron-deficient molecules, and weakly bound alkali and noble-metal dimers, although binding energies are overestimated.
Pseudopotential Method for Higher Partial Wave Scattering
Idziaszek, Zbigniew; Calarco, Tommaso
2006-01-13
We present a zero-range pseudopotential applicable for all partial wave interactions between neutral atoms. For p and d waves, we derive effective pseudopotentials, which are useful for problems involving anisotropic external potentials. Finally, we consider two nontrivial applications of the p-wave pseudopotential: we solve analytically the problem of two interacting spin-polarized fermions confined in a harmonic trap, and we analyze the scattering of p-wave interacting particles in a quasi-two-dimensional system.
Acoustic plane wave preferential orientation of metal oxide superconducting materials
Tolt, Thomas L.; Poeppel, Roger B.
1991-01-01
A polycrystalline metal oxide such as YBa.sub.2 Cu.sub.3 O.sub.7-X (where 0
The plain truth about forming a plane wave of neutrons
NASA Astrophysics Data System (ADS)
Wagh, Apoorva G.; Abbas, Sohrab; Treimer, Wolfgang
2011-04-01
We have attained the first sub-arcsecond collimation of a monochromatic neutron beam by diffracting neutrons from a Bragg prism, viz. a single crystal prism operating in the vicinity of Bragg incidence. Analytical as well numerical computations based on the dynamical diffraction theory, led to the optimised collimator configuration of a silicon {1 1 1} Bragg prism for 5.26 Å neutrons. We fabricated a Bragg prism to these specifications, tested and operated it at the double diffractometer setup in Helmholtz Zentrum Berlin to produce a 0.58 arcsec wide monochromatic neutron beam. With a similarly optimised Bragg prism analyser of opposite asymmetry, we recorded a 0.62 arcsec wide virgin rocking curve for this ultra-parallel beam. With this nearly plane-wave neutron beam, we have recorded the first ever USANS spectrum in Q˜10-6 Å-1 range with a hydroxyapatite casein protein sample and demonstrated the instrument capability to characterise agglomerates up to 150 μm in size. The super-collimated monochromatic beam has also enabled us to record the first neutron diffraction pattern from a macroscopic grating of 200 μm period. The transverse coherence length of 175 μm (FWHM) of the ultra-parallel beam derived from the analysis of this pattern, is the greatest achieved to date for Å wavelength neutrons.
NMR Shielding in Metals Using the Augmented Plane Wave Method
2015-01-01
We present calculations of solid state NMR magnetic shielding in metals, which includes both the orbital and the complete spin response of the system in a consistent way. The latter contains an induced spin-polarization of the core states and needs an all-electron self-consistent treatment. In particular, for transition metals, the spin hyperfine field originates not only from the polarization of the valence s-electrons, but the induced magnetic moment of the d-electrons polarizes the core s-states in opposite direction. The method is based on DFT and the augmented plane wave approach as implemented in the WIEN2k code. A comparison between calculated and measured NMR shifts indicates that first-principle calculations can obtain converged results and are more reliable than initially concluded based on previous publications. Nevertheless large k-meshes (up to 2 000 000 k-points in the full Brillouin-zone) and some Fermi-broadening are necessary. Our results show that, in general, both spin and orbital components of the NMR shielding must be evaluated in order to reproduce experimental shifts, because the orbital part cancels the shift of the usually highly ionic reference compound only for simple sp-elements but not for transition metals. This development paves the way for routine NMR calculations of metallic systems. PMID:26322148
Tailored complex 3D vortex lattice structures by perturbed multiples of three-plane waves.
Xavier, Jolly; Vyas, Sunil; Senthilkumaran, Paramasivam; Joseph, Joby
2012-04-20
As three-plane waves are the minimum number required for the formation of vortex-embedded lattice structures by plane wave interference, we present our experimental investigation on the formation of complex 3D photonic vortex lattice structures by a designed superposition of multiples of phase-engineered three-plane waves. The unfolding of the generated complex photonic lattice structures with higher order helical phase is realized by perturbing the superposition of a relatively phase-encoded, axially equidistant multiple of three noncoplanar plane waves. Through a programmable spatial light modulator assisted single step fabrication approach, the unfolded 3D vortex lattice structures are experimentally realized, well matched to our computer simulations. The formation of higher order intertwined helices embedded in these 3D spiraling vortex lattice structures by the superposition of the multiples of phase-engineered three-plane waves interference is also studied.
Del Rio, Beatriz G; Dieterich, Johannes M; Carter, Emily A
2017-08-08
The accuracy of local pseudopotentials (LPSs) is one of two major determinants of the fidelity of orbital-free density functional theory (OFDFT) simulations. We present a global optimization strategy for LPSs that enables OFDFT to reproduce solid and liquid properties obtained from Kohn-Sham DFT. Our optimization strategy can fit arbitrary properties from both solid and liquid phases, so the resulting globally optimized local pseudopotentials (goLPSs) can be used in solid and/or liquid-phase simulations depending on the fitting process. We show three test cases proving that we can (1) improve solid properties compared to our previous bulk-derived local pseudopotential generation scheme; (2) refine predicted liquid and solid properties by adding force matching data; and (3) generate a from-scratch, accurate goLPS from the local channel of a non-local pseudopotential. The proposed scheme therefore serves as a full and improved LPS construction protocol.
Johnston, Jessica C.; Iuliucci, Robbie J.; Facelli, Julio C.; Fitzgerald, George; Mueller, Karl T.
2009-01-01
In order to predict accurately the chemical shift of NMR-active nuclei in solid phase systems, magnetic shielding calculations must be capable of considering the complete lattice structure. Here we assess the accuracy of the density functional theory gauge-including projector augmented wave method, which uses pseudopotentials to approximate the nodal structure of the core electrons, to determine the magnetic properties of crystals by predicting the full chemical-shift tensors of all 13C nuclides in 14 organic single crystals from which experimental tensors have previously been reported. Plane-wave methods use periodic boundary conditions to incorporate the lattice structure, providing a substantial improvement for modeling the chemical shifts in hydrogen-bonded systems. Principal tensor components can now be predicted to an accuracy that approaches the typical experimental uncertainty. Moreover, methods that include the full solid-phase structure enable geometry optimizations to be performed on the input structures prior to calculation of the shielding. Improvement after optimization is noted here even when neutron diffraction data are used for determining the initial structures. After geometry optimization, the isotropic shift can be predicted to within 1 ppm. PMID:19831448
Gozem, Samer; Gunina, Anastasia O.; Ichino, Takatoshi; ...
2015-10-28
The calculation of absolute total cross sections requires accurate wave functions of the photoelectron and of the initial and final states of the system. The essential information contained in the latter two can be condensed into a Dyson orbital. We employ correlated Dyson orbitals and test approximate treatments of the photoelectron wave function, that is, plane and Coulomb waves, by comparing computed and experimental photoionization and photodetachment spectra. We find that in anions, a plane wave treatment of the photoelectron provides a good description of photodetachment spectra. For photoionization of neutral atoms or molecules with one heavy atom, the photoelectronmore » wave function must be treated as a Coulomb wave to account for the interaction of the photoelectron with the +1 charge of the ionized core. For larger molecules, the best agreement with experiment is often achieved by using a Coulomb wave with a partial (effective) charge smaller than unity. This likely derives from the fact that the effective charge at the centroid of the Dyson orbital, which serves as the origin of the spherical wave expansion, is smaller than the total charge of a polyatomic cation. Finally, the results suggest that accurate molecular photoionization cross sections can be computed with a modified central potential model that accounts for the nonspherical charge distribution of the core by adjusting the charge in the center of the expansion.« less
Plane wave discontinuous Galerkin methods for acoustic scattering
NASA Astrophysics Data System (ADS)
Kapita, Shelvean
We apply the Plane Wave Discontinuous Galerkin (PWDG) method to study the direct scattering of acoustic waves from impenetrable obstacles. In the first part of the thesis we consider the full exterior scattering problem with smooth boundaries. This problem is modeled by the Helmholtz equation in the unbounded domain exterior to the scatterer. To compute the scattered field, an artificial boundary is introduced to reduce the infinite domain to a finite computational domain. We then apply Dirichlet-to-Neumann (DtN) and Neumann-to-Dirichlet (NtD) boundary conditions on a circular artificial boundary. By using asymptotic properties of Hankel functions, we are able to prove wavenumber explicit L2-norm error estimates for the DtN-PWDG method on quasi-uniform meshes. Numerical experiments indicate that the accuracy of the PWDG method for the scattering problem is improved by the use of DtN and NtD boundary conditions. The second part of the thesis concerns acoustic scattering from domains with corners. In such domains, quasi-uniform meshes are not efficient so we derive error indicators to drive the selective refinement of the mesh in an adaptive algorithm. We prove a posteriori L2-norm error estimates for the Helmholtz equation with impedance boundary conditions on the artificial boundary. Numerical results demonstrate the efficiency of the proposed indicators. This adaptive strategy is compatible with the DtN and NtD truncation of the infinite domain problem and the combination would significantly improve the accuracy and reliability of PWDG simulations.
NASA Astrophysics Data System (ADS)
Zhu, Wei
This thesis is divided into two parts. The first part, "Supersymmetric Transformation Approach to Pseudopotentials in Condensed Matter Physics", provides a new method to obtain pseudopotentials, The conventional methods of constructing pseudopotentials based on the spirit of Orthogonalized Plane Wave and Augmented Plane Wave, etc. as well as the modern version of the norm-conserving pseudopotentials through density functional theory are first reviewed. Our new supersymmetric approach is aimed at eliminating some of the disadvantages while retaining in full the advantages such as phase equivalence or norm-conserving properties of the pseudopotentials. Vast amounts of numerical computation can be eliminated as compared to the old methods. Details and examples are given. Part two, "Bosonic Superconductivity in Two Dimensions", describes a theory for high Tc superconductivity aimed at the current cuprates superconductors. The current status of the cuprates is first reviewed. A one-band Hubbard model is used to formulate the interaction among the holes doped into the layered compounds. Tightly bound pairs of size ˜ a few lattice spacings are obtained based on the Antiferromagnetic Background Approximation. They are shown to have the dsb{xsp2-ysp2} symmetry. Such boson-like pairs form the basis of charged boson models. After reviewing the properties of an ideal charged bose gas including a perfect Meissner effect for 3D, and a nearly perfect Meissner effect for 2D, we develop a theory for high Tc superconductivity without interlayer coupling as adapted, on the one hand, from Friedberg-Lee's mixed Boson-Fermion model to 2D and, on the other hand, from May's work on two-dimensional ideal charged bosons. In addition to the critical temperature Tsb{May} for transition to a phase exhibiting a near-perfect Meissner effect, a new transition temperature Tsb{c} depending on the finite area of the system and the temperature-dependent coherence length is introduced. The appearance
Plane wave compounding based on a joint transmitting-receiving adaptive beamformer.
Zhao, Jinxin; Wang, Yuanyuan; Zeng, Xing; Yu, Jinhua; Yiu, Billy Y S; Yu, Alfred C H
2015-08-01
Plane wave compounding is a useful mode for ultrasound imaging because it can make a good compromise between imaging quality and frame rate. It is also useful for broad view ultrasound imaging. Traditional coherent plane wave compounding coherently sums the echo data of different steered transmitting waves as the output. The data correlation information of different emissions is not considered. Therefore, some adaptive techniques can be introduced into the compounding procedure. In this paper, we propose a Joint Transmitting-Receiving (JTR) adaptive beamforming scheme for plane wave compounding. Unlike traditional adaptive beamformers, the proposed beamforming scheme is designed for the 2-D data set obtained from multiple plane wave firings. It calculates both the transmitting aperture weights and the receiving aperture weights and then combines them into a 2-D adaptive weight function for compounding. Experiments are conducted on both simulated and phantom data. Results show that the proposed scheme has better performance on both point targets and cysts than the existing plane wave compounding approach. Because of the adaptive process in both apertures for compounding, an improved resolution is observed in both simulation and phantom studies. When the eigenanalysis is introduced, a contrast enhancement is achieved. For the simulated cyst, a contrast ratio (CR) improvement of 48% is achieved compared with the traditional plane wave compounding. For the phantom cyst, this improvement is 213.8%. The proposed scheme also has good robustness against sound velocity errors. Therefore, it is effective in enhancing the coherent plane wave compounding quality.
Plane-wave analysis of solar acoustic-gravity waves: A (slightly) new approach
NASA Technical Reports Server (NTRS)
Bogart, Richard S.; Sa, L. A. D.; Duvall, Thomas L., Jr.; Haber, Deborah A.; Toomre, Juri; Hill, Frank
1995-01-01
The plane-wave decomposition of the acoustic-gravity wave effects observed in the photosphere provides a computationally efficient technique that probes the structure of the upper convective zone and boundary. In this region, the flat sun approximation is considered as being reasonably accurate. A technique to be used for the systematic plane-wave analysis of Michelson Doppler imager data, as part of the solar oscillations investigation, is described. Estimates of sensitivity are presented, and the effects of using different planar mappings are discussed. The technique is compared with previous approaches to the three dimensional plane-wave problem.
Fraunhofer diffraction of the plane wave by a multilevel (quantized) spiral phase plate.
Kotlyar, Victor V; Kovalev, Alexey A
2008-01-15
We obtain an analytical expression in the form of a finite sum of plane waves that describes the paraxial scalar Fraunhofer diffraction of a limited plane wave by a multilevel (quantized) spiral phase plate (SPP) bounded by a polygonal aperture. For several topological charges of the SPP we numerically obtain the minimal number of SPP sectors for which the RMS between the Fraunhofer diffraction patterns for multilevel and continuous SPP does not exceed 2%.
Nazarov, R.; Shulenburger, L.; Hood, Randolph Q.; Morales, M.
2016-03-01
We performed diffusion Monte Carlo (DMC) calculations of the spectroscopic properties of a large set of molecules, assessing the effect of different approximations. In systems containing elements with large atomic numbers, we show that the errors associated with the use of nonlocal mean-field-based pseudopotentials in DMC calculations can be significant and may surpass the fixed-node error. In conclusion, we suggest practical guidelines for reducing these pseudopotential errors, which allow us to obtain DMC-computed spectroscopic parameters of molecules and equation of state properties of solids in excellent agreement with experiment.
Nazarov, Roman; Shulenburger, Luke; Morales, Miguel A.; ...
2016-03-28
Diffusion Monte Carlo (DMC) calculations of the spectroscopic properties of a large set of molecules were performed, assessing the effect of different approximations. In systems containing elements with large atomic numbers, we show that the errors associated with the use of nonlocal mean-field-based pseudopotentials in DMC calculations can be significant and may surpass the fixed-node error. We suggest practical guidelines for reducing these pseudopotential errors, which allow us to obtain DMC-computed spectroscopic parameters of molecules and equation of state properties of solids in excellent agreement with experiment.
NASA Astrophysics Data System (ADS)
Li, Jun; Williamson, Andrew
2005-03-01
Recent experimentsootnotetextY. Wu, et.al., Nature 430, 61 (2004); and references therein invoke Si nanowires as promising materials for nanoscale electronic and optical devices. We carried out electronic structure calculations of silicon chains and nanowires, by using both the full-potential linearized augmented plane wave (FLAPW) methodootnotetextE.Wimmer, H.Krakauer, M.Weinert, AJ Freeman, PRB 24, 864 (1981) and the pseudopotential plane wave method. We studied two sets of H-terminated one nanometer silicon wires, one oriented along (001) and the other along(111); both show direct band gaps, with the (111) oriented wires showing a smaller gap (˜2.1 eV) than (001) (˜2.5 eV). This trend differs from that reported in the literature ootnotetextF. Buda, et.al., PRL 69, 1272 (1992); A. M. Saitta, et.al., PRB 53, 1446 (1996), but it is the same in both our all-electron and well converged pseudopotential calculations. We also found that structural relaxations induce different effects on the band structure of differently oriented wires; the band gap change is nearly 0.2 eV between the ideal and relaxed models for (001) while it is negligible for (111) wires.
NASA Astrophysics Data System (ADS)
Mashhoon, Bahram
2017-05-01
Relativity theory is based on a postulate of locality, which means that the past history of the observer is not directly taken into account. This book argues that the past history should be taken into account. In this way, nonlocality 1R 2i1nr-in the sense of history dependence-is introduced into relativity theory. The deep connection between inertia and gravitation suggests that gravity could be nonlocal, and in nonlocal gravity the fading gravitational memory of past events must then be taken into account. Along this line of thought, a classical nonlocal generalization of Einstein's theory of gravitation has recently been developed. A significant consequence of this theory is that the nonlocal aspect of gravity appears to simulate dark matter. According to nonlocal gravity theory, what astronomers attribute to dark matter should instead be due to the nonlocality of gravitation. Nonlocality dominates on the scale of galaxies and beyond. Memory fades with time; therefore, the nonlocal aspect of gravity becomes weaker as the universe expands. The implications of nonlocal gravity are explored in this book for gravitational lensing, gravitational radiation, the gravitational physics of the Solar System and the internal dynamics of nearby galaxies, as well as clusters of galaxies. This approach is extended to nonlocal Newtonian cosmology, where the attraction of gravity fades with the expansion of the universe. Thus far, scientists have only compared some of the consequences of nonlocal gravity with astronomical observations.
Analysis of a photonic nanojet assuming a focused incident beam instead of a plane wave
NASA Astrophysics Data System (ADS)
Dong, Aotuo; Su, Chin
2014-12-01
The analysis of a photonic nanojet formed by dielectric spheres almost always assumes that the incident field is a plane wave. In this work, using vector spherical harmonics representations, we analyze the case of a more realistic incident field consisting of a focused beam formed by a microscope objective. Also included is the situation in which the sphere is not at the focal plane of the focus beam. We find that the dimension of the nanojet beam waist is less sensitive with respect to the azimuthal angle when compared with the plane wave case. Also, by shifting the particle away from the focal plane, the nanojet beam waist can be positioned outside the particle which otherwise would be inside or at the particle surface. Inherently, no such adjustment is possible with an incident plane wave assumption.
Nonspherical atomic effective pseudopotentials for surface passivation
NASA Astrophysics Data System (ADS)
Karpulevich, Anastasia; Bui, Hanh; Antonov, Denis; Han, Peng; Bester, Gabriel
2016-11-01
We present a method to extract accurate pseudopotentials for surface passivants, within the framework of the atomic effective pseudopotential method. We retain the imaginary part of the pseudopotential in the construction procedure. This imaginary component in reciprocal space translates into a nonspherical component in real space. This asphericity allows to model surface dipoles and their ensuing band offsets. We show that these surface effects need to be taken into account to model electronic properties of quantum dots accurately—which requires to go beyond the spherical potential approximation for the passivant/surface atoms. The good level of transferability, without additional computational costs, is demonstrated for Si, CdSe, and InP nanostructures. The results are directly compared to large-scale density functional theory calculations.
Santarossa, Gianluca; Vargas, Angelo; Iannuzzi, Marcella; Pignedoli, Carlo A; Passerone, Daniele; Baiker, Alfons
2008-12-21
We present a study on structural and electronic properties of bulk platinum and the two surfaces (111) and (100) comparing the Gaussian and plane wave method to standard plane wave schemes, normally employed for density functional theory calculations on metallic systems. The aim of this investigation is the assessment of methods based on the expansion of the Kohn-Sham orbitals into localized basis sets and on the supercell approach, in the description of the metallicity of Pt. Electronic structure calculations performed at Gamma-point only on supercells of different sizes, from 108 up to 864 atoms, are compared to the results obtained for the unit cell of four Pt atoms where the k-point expansion of the wave function over Monkhorst-Pack grids up to (10x10x10) has been employed. The evaluation of the two approaches with respect to bulk properties is done through the calculation of the equilibrium lattice constant, the bulk modulus, and the total and the d-projected density of states. For the Pt(111) and Pt(100) surfaces, we consider the relaxation of the first layers, the surface energies, the work function, the total density of states, as well as the center and filling of the d bands. Our results confirm that the accuracy of two approaches in the description of electronic and structural properties of Pt is equivalent, providing that consistent supercells and k-point meshes are used. Moreover, we estimate the supercell size that can be safely adopted in the Gaussian and plane wave method in order to obtain the same reliability of previous theoretical studies based on well converged plane wave calculations available in literature. The latter studies, in turn, set the level of agreement with experimental data. In particular, we obtain excellent agreement in the evaluation of the density of states for either bulk and surface systems, and our data are also in good agreement with previous works on Pt reported in literature. We conclude that Gaussian and plane wave
Solid explosive plane-wave lenses pressed-to-shape with dies
Olinger, B.
2007-11-01
Solid-explosive plane-wave lenses 1", 2" and 4¼" in diameter have been mass-produced from components pressed-to-shape with aluminum dies. The method used to calculate the contour between the solid plane-wave lens components pressed-to-shape with the dies is explained. The steps taken to press, machine, and assemble the lenses are described. The method of testing the lenses, the results of those tests, and the corrections to the dies are reviewed. The work on the ½", 8", and 12" diameter lenses is also discussed.
Probing the smearing effect by a pointlike graviton in the plane-wave matrix model
Lee, Bum-Hoon; Nam, Siyoung; Shin, Hyeonjoon
2010-08-15
We investigate the interaction between a flat membrane and pointlike graviton in the plane-wave matrix model. The one-loop effective potential in the large-distance limit is computed and is shown to be of r{sup -3} type where r is the distance between two objects. This type of interaction has been interpreted as the one incorporating the smearing effect due to the configuration of a flat membrane in a plane-wave background. Our results support this interpretation and provide more evidence about it.
Population analysis of plane-wave electronic structure calculations of bulk materials
Segall, M.D.; Shah, R.; Pickard, C.J.; Payne, M.C.
1996-12-01
{ital Ab} {ital initio} plane-wave electronic structure calculations are widely used in the study of bulk materials. A technique for the projection of plane-wave states onto a localized basis set is used to calculate atomic charges and bond populations by means of Mulliken analysis. We analyze a number of simple bulk crystals and find correlations of overlap population with covalency of bonding and bond strength, and effective valence charge with ionicity of bonding. Thus, we show that the techniques described in this paper may be usefully applied in the field of solid state physics. {copyright}{ital 1996 The American Physical Society.}
Nonlocality Without Nonlocality
NASA Astrophysics Data System (ADS)
Weinstein, Steven
2009-08-01
Bell’s theorem is purported to demonstrate the impossibility of a local “hidden variable” theory underpinning quantum mechanics. It relies on the well-known assumption of ‘locality’, and also on a little-examined assumption called ‘statistical independence’ ( SI). Violations of this assumption have variously been thought to suggest “backward causation”, a “conspiracy” on the part of nature, or the denial of “free will”. It will be shown here that these are spurious worries, and that denial of SI simply implies nonlocal correlation between spacelike degrees of freedom. Lorentz-invariant theories in which SI does not hold are easily constructed: two are exhibited here. It is conjectured, on this basis, that quantum-mechanical phenomena may be modeled by a local theory after all.
Ultrasound plane-wave imaging with delay multiply and sum beamforming and coherent compounding.
Matrone, Giulia; Savoia, Alessandro S; Caliano, Giosue; Magenes, Giovanni
2016-08-01
Improving the frame rate is an important aspect in medical ultrasound imaging, particularly in 3D/4D cardiac applications. However, an accurate trade-off between the higher frame rate and image contrast and resolution should be performed. Plane-Wave Imaging (PWI) can potentially achieve frame rates in the order of 10 kHz, as it uses a single unfocused plane wave (and thus a single transmit event) to acquire the image of the entire region of interest. The lack of transmit focusing however causes a significant drop of image quality, which can be restored by coherently compounding several tilted plane-wave frames, at the expense of the frame rate. PWI together with the use of a beamforming algorithm able to achieve a higher image contrast resolution, such as the Delay Multiply And Sum (DMAS), could thus allow to improve image quality achieving a high frame rate at the same time. This paper presents the first simulation results obtained by employing DMAS beamforming and PWI with different transmission angles and coherent compounding. The simulated Point Spread Function (PSF) and cyst-phantom images show that DMAS makes it possible to achieve a high image quality with a reduced number of compounded frames compared to standard Delay And Sum (DAS), and hence it can be used to improve the contrast and resolution of plane-wave images still achieving a very high frame rate.
The Relativistic Transformation for an Electromagnetic Plane Wave with General Time Dependence
ERIC Educational Resources Information Center
Smith, Glenn S.
2012-01-01
In special relativity, the transformation between inertial frames for an electromagnetic plane wave is usually derived for the time-harmonic case (the field is a sinusoid of infinite duration), even though all practical waves are of finite duration and may not even contain a dominant sinusoid. This paper presents an alternative derivation in which…
The Relativistic Transformation for an Electromagnetic Plane Wave with General Time Dependence
ERIC Educational Resources Information Center
Smith, Glenn S.
2012-01-01
In special relativity, the transformation between inertial frames for an electromagnetic plane wave is usually derived for the time-harmonic case (the field is a sinusoid of infinite duration), even though all practical waves are of finite duration and may not even contain a dominant sinusoid. This paper presents an alternative derivation in which…
Calculation of atomic forces using the linearized-augmented-plane-wave method
NASA Astrophysics Data System (ADS)
Krimmel, H. G.; Ehmann, J.; Elsässer, C.; Fähnle, M.; Soler, J. M.
1994-09-01
The force formula of Soler and Williams is implemented in the full-potential linearized-augmented-plane-wave program wien93. The feasibility and accuracy of the method is demonstrated by calculations for the H-point phonon in Mo and Li and for the Γ-point phonon in Si and diamond.
Transverse plane wave analysis of short elliptical chamber mufflers: An analytical approach
NASA Astrophysics Data System (ADS)
Mimani, A.; Munjal, M. L.
2011-03-01
Short elliptical chamber mufflers are used often in the modern day automotive exhaust systems. The acoustic analysis of such short chamber mufflers is facilitated by considering a transverse plane wave propagation model along the major axis up to the low frequency limit. The one dimensional differential equation governing the transverse plane wave propagation in such short chambers is solved using the segmentation approaches which are inherently numerical schemes, wherein the transfer matrix relating the upstream state variables to the downstream variables is obtained. Analytical solution of the transverse plane wave model used to analyze such short chambers has not been reported in the literature so far. This present work is thus an attempt to fill up this lacuna, whereby Frobenius solution of the differential equation governing the transverse plane wave propagation is obtained. By taking a sufficient number of terms of the infinite series, an approximate analytical solution so obtained shows good convergence up to about 1300 Hz and also covers most of the range of muffler dimensions used in practice. The transmission loss (TL) performance of the muffler configurations computed by this analytical approach agrees excellently with that computed by the Matrizant approach used earlier by the authors, thereby offering a faster and more elegant alternate method to analyze short elliptical muffler configurations.
NASA Astrophysics Data System (ADS)
Ye, Qian; Jiang, Yikun; Lin, Haoze
2017-03-01
In most textbooks, after discussing the partial transmission and reflection of a plane wave at a planar interface, the power (energy) reflection and transmission coefficients are introduced by calculating the normal-to-interface components of the Poynting vectors for the incident, reflected and transmitted waves, separately. Ambiguity arises among students since, for the Poynting vector to be interpreted as the energy flux density, on the incident (reflected) side, the electric and magnetic fields involved must be the total fields, namely, the sum of incident and reflected fields, instead of the partial fields which are just the incident (reflected) fields. The interpretation of the cross product of partial fields as energy flux has not been obviously justified in most textbooks. Besides, the plane wave is actually an idealisation that is only ever found in textbooks, then what do the reflection and transmission coefficients evaluated for a plane wave really mean for a real beam of limited extent? To provide a clearer physical picture, we exemplify a light beam of finite transverse extent by a fundamental Gaussian beam and simulate its reflection and transmission at a planar interface. Due to its finite transverse extent, we can then insert the incident fields or reflected fields as total fields into the expression of the Poynting vector to evaluate the energy flux and then power reflection and transmission coefficients. We demonstrate that the power reflection and transmission coefficients of a beam of finite extent turn out to be the weighted sum of the corresponding coefficients for all constituent plane wave components that form the beam. The power reflection and transmission coefficients of a single plane wave serve, in turn, as the asymptotes for the corresponding coefficients of a light beam as its width expands infinitely.
From plane waves to local Gaussians for the simulation of correlated periodic systems
NASA Astrophysics Data System (ADS)
Booth, George H.; Tsatsoulis, Theodoros; Chan, Garnet Kin-Lic; Grüneis, Andreas
2016-08-01
We present a simple, robust, and black-box approach to the implementation and use of local, periodic, atom-centered Gaussian basis functions within a plane wave code, in a computationally efficient manner. The procedure outlined is based on the representation of the Gaussians within a finite bandwidth by their underlying plane wave coefficients. The core region is handled within the projected augment wave framework, by pseudizing the Gaussian functions within a cutoff radius around each nucleus, smoothing the functions so that they are faithfully represented by a plane wave basis with only moderate kinetic energy cutoff. To mitigate the effects of the basis set superposition error and incompleteness at the mean-field level introduced by the Gaussian basis, we also propose a hybrid approach, whereby the complete occupied space is first converged within a large plane wave basis, and the Gaussian basis used to construct a complementary virtual space for the application of correlated methods. We demonstrate that these pseudized Gaussians yield compact and systematically improvable spaces with an accuracy comparable to their non-pseudized Gaussian counterparts. A key advantage of the described method is its ability to efficiently capture and describe electronic correlation effects of weakly bound and low-dimensional systems, where plane waves are not sufficiently compact or able to be truncated without unphysical artifacts. We investigate the accuracy of the pseudized Gaussians for the water dimer interaction, neon solid, and water adsorption on a LiH surface, at the level of second-order Møller-Plesset perturbation theory.
Al-Saidi, W A; Krakauer, Henry; Zhang, Shiwei
2007-05-21
The authors present phaseless auxiliary-field (AF) quantum Monte Carlo (QMC) calculations of the ground states of some hydrogen-bonded systems. These systems were selected to test and benchmark different aspects of the new phaseless AF QMC method. They include the transition state of H+H(2) near the equilibrium geometry and in the van der Walls limit, as well as the H(2)O, OH, and H(2)O(2) molecules. Most of these systems present significant challenges for traditional independent-particle electronic structure approaches, and many also have exact results available. The phaseless AF QMC method is used either with a plane wave basis with pseudopotentials or with all-electron Gaussian basis sets. For some systems, calculations are done with both to compare and characterize the performance of AF QMC under different basis sets and different Hubbard-Stratonovich decompositions. Excellent results are obtained using as input single Slater determinant wave functions taken from independent-particle calculations. Comparisons of the Gaussian based AF QMC results with exact full configuration interaction show that the errors from controlling the phase problem with the phaseless approximation are small. At the large basis-size limit, the AF QMC results using both types of basis sets are in good agreement with each other and with experimental values.
Vadali, Ramkumar V; Shi, Yan; Kumar, Sameer; Kale, Laxmikant V; Tuckerman, Mark E; Martyna, Glenn J
2004-12-01
Many systems of great importance in material science, chemistry, solid-state physics, and biophysics require forces generated from an electronic structure calculation, as opposed to an empirically derived force law to describe their properties adequately. The use of such forces as input to Newton's equations of motion forms the basis of the ab initio molecular dynamics method, which is able to treat the dynamics of chemical bond-breaking and -forming events. However, a very large number of electronic structure calculations must be performed to compute an ab initio molecular dynamics trajectory, making the efficiency as well as the accuracy of the electronic structure representation critical issues. One efficient and accurate electronic structure method is the generalized gradient approximation to the Kohn-Sham density functional theory implemented using a plane-wave basis set and atomic pseudopotentials. The marriage of the gradient-corrected density functional approach with molecular dynamics, as pioneered by Car and Parrinello (R. Car and M. Parrinello, Phys Rev Lett 1985, 55, 2471), has been demonstrated to be capable of elucidating the atomic scale structure and dynamics underlying many complex systems at finite temperature. However, despite the relative efficiency of this approach, it has not been possible to obtain parallel scaling of the technique beyond several hundred processors on moderately sized systems using standard approaches. Consequently, the time scales that can be accessed and the degree of phase space sampling are severely limited. To take advantage of next generation computer platforms with thousands of processors such as IBM's BlueGene, a novel scalable parallelization strategy for Car-Parrinello molecular dynamics is developed using the concept of processor virtualization as embodied by the Charm++ parallel programming system. Charm++ allows the diverse elements of a Car-Parrinello molecular dynamics calculation to be interleaved with low
NASA Astrophysics Data System (ADS)
Giaccari, Stefano; Modesto, Leonardo
2017-09-01
We propose an N =1 supersymmetric extension for a class of weakly nonlocal four-dimensional gravitational theories. The construction is done in the superspace where the off-shell supersymmetry is manifest. The tree-level perturbative unitarity is explicitly proved both in superfield formalism and in field components. For the minimal nonlocal supergravity the spectrum is the same as in the local theory and in particular it is ghost free. The supersymmetric extension of the nonlocal Starobinsky theory is found as a straightforward application of the formalism.
Generalized pseudopotentials for higher partial wave scattering.
Stock, René; Silberfarb, Andrew; Bolda, Eric L; Deutsch, Ivan H
2005-01-21
We derive a generalized zero-range pseudopotential applicable to all partial wave solutions to the Schrödinger equation based on a delta-shell potential in the limit that the shell radius approaches zero. This properly models all higher order multipole moments not accounted for with a monopolar delta function at the origin, as used in the familiar Fermi pseudopotential for s-wave scattering. By making the strength of the potential energy dependent, we derive self-consistent solutions for the entire energy spectrum of the realistic potential. We apply this to study two particles in an isotropic harmonic trap, interacting through a central potential, and derive analytic expressions for the energy eigenstates and eigenvalues.
Multiparticle pseudopotentials for multicomponent quantum Hall systems
NASA Astrophysics Data System (ADS)
Davenport, Simon C.; Simon, Steven H.
2012-02-01
The Haldane pseudopotential construction has been an extremely powerful concept in quantum Hall physics—it not only gives a minimal description of the space of Hamiltonians but also suggests special model Hamiltonians (those where certain pseudopotential are set to zero) that may have exactly solvable ground states with interesting properties. The purpose of this paper is to generalize the pseudopotential construction to situations where interactions are N-body and where the particles may have internal degrees of freedom such as spin or valley index. Assuming a rotationally invariant Hamiltonian, the essence of the problem is to obtain a full basis of wave functions for N particles with fixed relative angular momentum L. This basis decomposes into representations of SU(n) with n the number of internal degrees of freedom. We give special attention to the case where the internal degree of freedom has n=2 states, which encompasses the important cases of spin-1/2 particles and quantum Hall bilayers. We also discuss in some detail the cases of spin-1 particles (n=3) and graphene (n=4, including two spin and two valley degrees of freedom).
Density functional calculations of Pd nanoparticles using a plane-wave method.
Viñes, Francesc; Illas, Francesc; Neyman, Konstantin M
2008-09-25
We deal with usage of plane-wave density functional calculations of crystallites formed of 100-200 transition metal atoms to mimic larger experimentally treated particles. A series of model Pd clusters containing up to 225 atoms is chosen as an example. We focused on the description of size-dependent geometric parameters and binding energies of these clusters as compared with previous benchmark calculations; evolution of the particle electronic structure with increasing size has also been addressed. The high performance of the plane-wave calculations for transition-metal nanoparticles has been documented. Implications of this work on broadening opportunities to design and study realistic models of catalytic systems are outlined.
A solution for TM-mode plane waves incident on a two-dimensional inhomogeneity
Lee, K. H.; Morrison, H. F.
1985-07-01
A solution for the electromagnetic fields scattered from a two-dimensional inhomogeneity in a conducting half space has been obtained for an incident TM mode plane wave; the magnetic field is polarized parallel to the strike of the inhomogeneity. The approach has been to determine the scattering currents within the inhomogeneity using an integral equation for the electric fields. This solution is similar in concept to earlier studies of TE mode scattering from two-dimensional inhomogeneities, and it completes the analysis of the scattering of arbitrary plane waves using the integral equation approach. For simple bodies in the earth integral equation solution offers significant computational advantages over alternate finite element or finite difference methods of solution.
Acoustic plane waves incident on an oblique clamped panel in a rectangular duct
NASA Technical Reports Server (NTRS)
Unz, H.; Roskam, J.
1980-01-01
The theory of acoustic plane waves incident on an oblique clamped panel in a rectangular duct was developed from basic theoretical concepts. The coupling theory between the elastic vibrations of the panel (plate) and the oblique incident acoustic plane wave in infinite space was considered in detail, and was used for the oblique clamped panel in the rectangular duct. The partial differential equation which governs the vibrations of the clamped panel (plate) was modified by adding to it stiffness (spring) forces and damping forces. The Transmission Loss coefficient and the Noise Reduction coefficient for oblique incidence were defined and derived in detail. The resonance frequencies excited by the free vibrations of the oblique finite clamped panel (plate) were derived and calculated in detail for the present case.
Comparison of finite source and plane wave scattering from corrugated surfaces
NASA Technical Reports Server (NTRS)
Levine, D. M.
1977-01-01
The choice of a plane wave to represent incident radiation in the analysis of scatter from corrugated surfaces was examined. The physical optics solution obtained for the scattered fields due to an incident plane wave was compared with the solution obtained when the incident radiation is produced by a source of finite size and finite distance from the surface. The two solutions are equivalent if the observer is in the far field of the scatterer and the distance from observer to scatterer is large compared to the radius of curvature at the scatter points, condition not easily satisfied with extended scatterers such as rough surfaces. In general, the two solutions have essential differences such as in the location of the scatter points and the dependence of the scattered fields on the surface properties. The implication of these differences to the definition of a meaningful radar cross section was examined.
In situ technique for measuring the orthogonality of a plane wave to a substrate.
Châteauneuf, Marc; Ayliffe, Michael H; Kirk, Andrew G
2003-05-01
A new compact in situ method of measuring the perpendicularity of a plane wave to a substrate is proposed. Off-axis cylindrical Fresnel lenses are used to focus a portion of the incident plane wave onto target lines. The displacement of the focal line from the targets is determined by the degree of angular misalignment. The proposed design has been incorporated into a 10-mm-thick fused-silica module, which enables us to obtain an alignment precision of better than 0.0083 degrees. This method is designed for use in optical assembly procedures that require an incident collimated beam that is normal to the alignment features. Experimental results are presented.
Well-posedness and generalized plane waves simulations of a 2D mode conversion model
Imbert-Gérard, Lise-Marie
2015-12-15
Certain types of electro-magnetic waves propagating in a plasma can undergo a mode conversion process. In magnetic confinement fusion, this phenomenon is very useful to heat the plasma, since it permits to transfer the heat at or near the plasma center. This work focuses on a mathematical model of wave propagation around the mode conversion region, from both theoretical and numerical points of view. It aims at developing, for a well-posed equation, specific basis functions to study a wave mode conversion process. These basis functions, called generalized plane waves, are intrinsically based on variable coefficients. As such, they are particularly adapted to the mode conversion problem. The design of generalized plane waves for the proposed model is described in detail. Their implementation within a discontinuous Galerkin method then provides numerical simulations of the process. These first 2D simulations for this model agree with qualitative aspects studied in previous works.
A nonperturbative definition of N = 4 Super Yang-Mills by the plane wave matrix model
Shimasaki, Shinji
2008-11-23
We propose a nonperturbative definition of N = 4 Super Yang-Mills(SYM). We realize N = 4 SYM on RxS{sup 3} as the theory around a vacuum of the plane wave matrix model. Our regularization preserves 16 supersymmetries and the gauge symmetry. We perform the one-loop calculation to give evidence that in the continuum limit the superconformal symmetry is restored.
Multiple-scattering corrections in diluted magnetic semiconductors: A plane-wave expansion
NASA Astrophysics Data System (ADS)
Scalbert, D.; Ghazali, A.; Benoit à la Guillaume, C.
1993-12-01
Energy levels of band edges in diluted magnetic semiconductors are calculated in the effective-mass approximation, retaining off-diagonal terms in the exchange interaction and using a plane-wave expansion. This model accounts qualitatively for the observed asymmetry in the splitting of the A exciton in a magnetic field in Cd1-xMnxS for which multiple-scattering corrections are expected to be important.
Generalized plane waves in Poincaré gauge theory of gravity
NASA Astrophysics Data System (ADS)
Blagojević, Milutin; Cvetković, Branislav; Obukhov, Yuri N.
2017-09-01
A family of exact vacuum solutions, representing generalized plane waves propagating on the (anti-)de Sitter background, is constructed in the framework of Poincaré gauge theory. The wave dynamics is defined by the general Lagrangian that includes all parity even and parity odd invariants up to the second order in the gauge field strength. The structure of the solution shows that the wave metric significantly depends on the spacetime torsion.
Theoretical calculation of plane wave speeds for alkali metals under pressure.
NASA Technical Reports Server (NTRS)
Eftis, J.; Macdonald, D. E.; Arkilic, G. M.
1971-01-01
Theoretical calculations of the variation with pressure of small amplitude plane wave speeds are performed for sodium and potassium at zero temperature. The results obtained for wave speeds associated with volume dependent second-order elastic coefficients show better agreement with experimental data than for wave speeds associated with shear dependent coefficients. This result is believed to be due to omission of the band structure correction to the strain energy density.
Castaings; Hosten
2000-03-01
Electrostatic, air-coupled, ultrasonic transducers are used to generate and detect plane waves in viscoelastic, isotropic or anisotropic solid plates. The through-transmitted field is measured and compared to numerical predictions. An inversion scheme is then applied for identifying the values of the complex Cij which are representative of the viscoelasticity properties of the materials. The issue of this work is a contact-free, ultrasonic technique for material characterisation.
Lectures on the plane-wave string/gauge theory duality
NASA Astrophysics Data System (ADS)
Plefka, J. C.
2004-02-01
These lectures give an introduction to the novel duality relating type IIB string theory in a maximally supersymmetric plane-wave background to = 4, d = 4, U(N) super Yang-Mills theory in a particular large N and large R-charge limit due to Berenstein, Maldacena and Nastase. In the first part of these lectures the duality is derived from the AdS/CFT correspondence by taking a Penrose limit of the AdS5 × S5 geometry and studying the corresponding double-scaling limit on the gauge theory side. The resulting free plane-wave superstring is then quantized in light-cone gauge. On the gauge theory side of the correspondence the composite super Yang-Mills operators dual to string excitations are identified, and it is shown how the string spectrum can be mapped to the planar scaling dimensions of these operators. In the second part of these lectures we study the correspondence at the interacting respectively non-planar level. On the gauge theory side it is demonstrated that the large N large R-charge limit in question preserves contributions from Feynman graphs of all genera through the emergence of a new genus counting parameter - in agreement with the string genus expansion for non-zero gs. Effective quantum mechanical tools to compute higher genus contributions to the scaling dimensions of composite operators are developed and explicitly applied in a genus one computation. We then turn to the interacting string theory side and give an elementary introduction into light-cone superstring field theory in a plane-wave background and point out how the genus one prediction from gauge theory can be reproduced. Finally, we summarize the present status of the plane-wave string/gauge theory duality.
Plane Wave Diffraction by a Finite Plate with Impedance Boundary Conditions
Nawaz, Rab; Ayub, Muhammad; Javaid, Akmal
2014-01-01
In this study we have examined a plane wave diffraction problem by a finite plate having different impedance boundaries. The Fourier transforms were used to reduce the governing problem into simultaneous Wiener-Hopf equations which are then solved using the standard Wiener-Hopf procedure. Afterwards the separated and interacted fields were developed asymptotically by using inverse Fourier transform and the modified stationary phase method. Detailed graphical analysis was also made for various physical parameters we were interested in. PMID:24755624
Domain overlap matrices from plane-wave-based methods of electronic structure calculation
NASA Astrophysics Data System (ADS)
Golub, Pavlo; Baranov, Alexey I.
2016-10-01
Plane waves are one of the most popular and efficient basis sets for electronic structure calculations of solids; however, their delocalized nature makes it difficult to employ for them classical orbital-based methods of chemical bonding analysis. The quantum chemical topology approach, introducing chemical concepts via partitioning of real space into chemically meaningful domains, has no difficulties with plane-wave-based basis sets. Many popular tools employed within this approach, for instance delocalization indices, need overlap integrals over these domains—the elements of the so called domain overlap matrices. This article reports an efficient algorithm for evaluation of domain overlap matrix elements for plane-wave-based calculations as well as evaluation of its implementation for one of the most popular projector augmented wave (PAW) methods on the small set of simple and complex solids. The stability of the obtained results with respect to PAW calculation parameters has been investigated, and the comparison of the results with the results from other calculation methods has also been made.
Smoothed half-infinite plane waves: Approaching to their optimum profiles
NASA Astrophysics Data System (ADS)
Sedukhin, Andrey G.
2013-11-01
A concept of homogeneous, smoothed half-infinite plane waves is developed in the framework of a discontinuity-free decomposition of the field of a plane electromagnetic wave diffracted by a perfectly conducting half-infinite screen. It is shown that the entire diffracted field is broken down into the mentioned reflected and transmitted, smoothed half-infinite plane waves and edge quasi-cylindrical waves. In the planes of half-waists, the wavefronts of the smoothed waves are always rigorously plane, whereas their amplitude profiles are odd symmetrical in relation to respective half levels. The smoothed waves possess the phase-conjugate property relative to the planes of their half-waists and, in the first approximation, they are self-similar in the entire space. Also, the amplitude profiles at the half-waists of these waves are well reproduced within certain propagation distances. These and other properties of the smoothed half-infinite plane waves, a procedure for their approximate generation, and two simplest analytic profiles at their half-waists are considered in detail.
Woods, Daniel C; Bolton, J Stuart; Rhoads, Jeffrey F
2015-10-01
The transmission of airborne sound into high-impedance media is of interest in several applications. For example, sonic booms in the atmosphere may impact marine life when incident on the ocean surface, or affect the integrity of existing structures when incident on the ground. Transmission across high impedance-difference interfaces is generally limited by reflection and refraction at the surface, and by the critical angle criterion. However, spatially decaying incident waves, i.e., inhomogeneous or evanescent plane waves, may transmit energy above the critical angle, unlike homogeneous plane waves. The introduction of a decaying component to the incident trace wavenumber creates a nonzero propagating component of the transmitted normal wavenumber, so energy can be transmitted across the interface. A model of evanescent plane waves and their transmission across fluid-fluid and fluid-solid interfaces is developed here. Results are presented for both air-water and air-solid interfaces. The effects of the incident wave parameters (including the frequency, decay rate, and incidence angle) and the interfacial properties are investigated. Conditions for which there is no reflection at the air-solid interface, due to impedance matching between the incident and transmitted waves, are also considered and are found to yield substantial transmission increases over homogeneous incident waves.
Traveling Internal Plane-wave Synthesis (TIPS) for uniform B1 in high field MRI.
Anderson, Adam W
2017-02-01
A new target-field approach to generating uniform radio frequency (RF) fields within the human body for high field MRI is described. The method involves producing a set of external fields which, after interaction with a dielectric object, superimpose to produce a traveling plane wave, exposing all spins to the same RF amplitude (B1) over a cycle of the harmonic field. Conceptually this is similar to conventional RF shimming, but uses a different RF source design, input data, and objective function. The method requires a detailed knowledge of the coupling between exterior field modes, produced by an array of RF sources, and field modes within the body. Given an estimate of the coupling matrix, the linear superposition of external modes that produces a desired internal target field can be determined. The new method is termed Traveling Internal Plane-wave Synthesis (TIPS). A simple design of a coil array is described that can, in principle, generate the required field modes. Simulations demonstrate that radio frequency magnetic fields of nearly uniform (<1% variation) magnitude can be produced within dielectric objects larger than a wavelength in size. If the dielectric medium has non-zero conductivity, traveling waves are attenuated as they traverse the object, but field uniformity within planar slices is preserved. For general 3D imaging, a superposition of plane waves can provide field focusing to balance conductive losses, thereby achieving nearly uniform-magnitude B1+ magnetic fields over a volume of interest.
Local-density-derived semiempirical pseudopotentials
Wang, L.; Zunger, A.
1995-06-15
Transferable screened atomic pseudopotentials were developed 30 years ago in the context of the empirical pseudopotential method (EPM) by adjusting the potential to reproduce observed bulk electronic energies. While extremely useful, such potentials were not constrained to reproduce wave functions and related quantities, nor was there a systematic way to assure transferability to different crystal structures and coordination numbers. Yet, there is a significant contemporary demand for accurate screened pseudopotentials in the context of electronic structure theory of nanostructures, where local-density-approximation (LDA) approaches are both too costly and insufficiently accurate, while effective-mass band approaches are inapplicable when the structures are too small. We can now improve upon the traditional EPM by a two-step process: {ital First}, we invert a set of self-consistently determined screened LDA potentials for a range of bulk crystal structures and unit cell volumes, thus determining spherically symmetric and structurally averaged atomic potentials (SLDA). These potentials reproduce the LDA band structure to better than 0.1 eV, over a range of crystal structures and cell volumes. {ital Second}, we adjust the SLDA to reproduce {ital observed} excitation energies. We find that the adjustment represents a reasonably small perturbation over the SLDA potential, so that the ensuing fitted potential still reproduces a {gt}99.9% overlap with the original LDA pseudowave functions despite the excitation energies being distinctly non-LDA. We apply the method to Si and CdSe in a range of crystal structures, finding excellent agreement with the {ital experimentally} {ital determined} band energies, optical spectra {epsilon}{sub 2}({ital E}), static dielectric constants, deformation potentials, and, at the same time, {ital LDA{minus}quality} wave functions.
Sum, K S; Pan, J
2007-07-01
Distributions of sound pressure and intensity on the surface of a flat impedance strip flush-mounted on a rigid baffle are studied for a grazing incident plane wave. The distributions are obtained by superimposing the unperturbed wave (the specularly reflected wave as if the strip is rigid plus the incident wave) with the radiated wave from the surface vibration of the strip excited by the unperturbed pressure. The radiated pressure interferes with the unperturbed pressure and distorts the propagating plane wave. When the plane wave propagates in the baffle-strip-baffle direction, it encounters discontinuities in acoustical impedance at the baffle-strip and strip-baffle interfaces. The radiated pressure is highest around the baffle-strip interface, but decreases toward the strip-baffle interface where the plane wave distortion reduces accordingly. As the unperturbed and radiated waves have different magnitudes and superimpose out of phase, the surface pressure and intensity increase across the strip in the plane wave propagation direction. Therefore, the surface absorption of the strip is nonzero and nonuniform. This paper provides an understanding of the surface pressure and intensity behaviors of a finite impedance strip for a grazing incident plane wave, and of how the distributed intensity determines the sound absorption coefficient of the strip.
Exact soliton-on-plane-wave solutions for two-component Bose-Einstein condensates.
Li, Lu; Malomed, Boris A; Mihalache, Dumitru; Liu, W M
2006-06-01
By means of the Darboux transformation, we obtain analytical solutions for a soliton set on top of a plane-wave background in coupled Gross-Pitaevskii equations describing a binary Bose-Einstein condensate. We consider basic properties of the solutions with and without the cross interaction [cross phase modulation (XPM)] between the two components of the background. In the absence of the XPM, this solutions maintain properties of one-component condensates, such as the modulation instability (MI); in the presence of the cross interaction, the solutions exhibit different properties, such as restriction of the MI and soliton splitting.
Exact soliton-on-plane-wave solutions for two-component Bose-Einstein condensates
Li Lu; Malomed, Boris A.; Mihalache, Dumitru; Liu, W. M.
2006-06-15
By means of the Darboux transformation, we obtain analytical solutions for a soliton set on top of a plane-wave background in coupled Gross-Pitaevskii equations describing a binary Bose-Einstein condensate. We consider basic properties of the solutions with and without the cross interaction [cross phase modulation (XPM)] between the two components of the background. In the absence of the XPM, this solutions maintain properties of one-component condensates, such as the modulation instability (MI); in the presence of the cross interaction, the solutions exhibit different properties, such as restriction of the MI and soliton splitting.
Plane wave transport method for low symmetry lattices and its application
Srivastava, Manoj K; Wang, Yan; Zhang, Xiaoguang; Nicholson, Don M; Cheng, Hai-Ping
2012-01-01
The existing first-principles plane wave transport method implementation \\cite{,choi-1,qe} has the limitation that it only allows transport directions along lattice vectors perpendicular to the basal plane formed by two other lattice vectors. We generalize the algorithm to low symmetry, nonorthogonal lattices thus allowing solution to problems in which the transport direction is not along any lattice vectors. As an application, we calculate the transmission and reflection coefficients, and determine interface resistance of various grain boundaries in crystalline copper.
NASA Astrophysics Data System (ADS)
Abramov, Arnold; Kostikov, Alexander
2017-03-01
We report the effect of scattering of electromagnetic plane waves by two cylinders on whispering gallery mode (WGM) formation in a cylinder. WGM can occur because of the presence of additional cylinder scatterers at specific location, while WGMs can only form in a single cylinder for specific cylinder radius and/or wavelength values, the matching accuracy required would be much greater than that required in our model for the additional cylinders locations. Analysis of the general solution to the problem showed that the effect can be explained by the interference of waves scattered by additional cylinders and incident on the main cylinder.
Correctability limitations imposed by plane-wave scintillation in multiconjugate adaptive optics.
Lee, Lawton H; Baker, Gary J; Benson, Robert S
2006-10-01
Plane-wave scintillation is shown to impose multiconjugate adaptive optics (MCAO) correctability limitations that are independent of wavefront sensing and reconstruction. Residual phase and log-amplitude variances induced by scintillation in weak turbulence are derived using linear (diffraction-based) diffractive MCAO spatial filters or (diffraction-ignorant) geometric MCAO proportional gains as open-loop control parameters. In the case of Kolmogorov turbulence, expressions involving the Rytov variance and/or weighted C(2)(n) integrals apply. Differences in performance between diffractive MCAO and geometric MCAO resemble chromatic errors. Optimal corrections based on least squares imply irreducible performance limits that are validated by wave-optic simulations.
Electromagnetic plane-wave pulse transmission into a Lorentz half-space.
Cartwright, Natalie A
2011-12-01
The propagation of an electromagnetic plane-wave signal obliquely incident upon a Lorentz half-space is studied analytically. Time-domain asymptotic expressions that increase in accuracy with propagation distance are derived by application of uniform saddle point methods on the Fourier-Laplace integral representation of the transmitted field. The results are shown to be continuous in time and comparable with numerical calculations of the field. Arrival times and angles of refraction are given for prominent transient pulse features and the steady-state signal.
High-frequency plane waves in the ear canal: application of a simple asymptotic theory.
Rabbitt, R D
1988-12-01
An asymptotic theory describing the propagation of plane waves in a variable cross-section ear canal is combined with pressure measurements in order to determine the energy reflection coefficient at the eardrum and the standing wave patterns along the length of the canal. The relative phase of the reflected wave, and the cross-sectional area function of the ear canal, are also determined from the noninvasive pressure measurements. The theory is based on a high-frequency multiscale solution of the one-dimensional horn equation and is shown to agree well with the phase and amplitude of experimental measurements in human replica ear canals.
NASA Astrophysics Data System (ADS)
Fisanov, V. V.
2017-09-01
Analytical expressions for complex values of the wave number, refractive index, and the characteristic wave impedance of homogeneous electromagnetic plane waves propagating in a linear, homogeneous, isotropic medium with losses and gain are derived. Formulas for determining the type of normal wave as a function of the values of the real and imaginary parts of the permittivity and permeability are obtained, and conditions for the appearance of positive and negative refraction at the interface of two isotropic media are indicated. In the approach applied here, the concept of a negative refractive index is not used.
NASA Astrophysics Data System (ADS)
Stotts, S. A.; Knobles, D. P.; Koch, R. A.; Grant, D. E.; Focke, K. C.; Cook, A. J.
2004-03-01
A new, efficient, versatile ray-based model is presented that performs geoacoustic inversions in range-dependent ocean waveguides faster than alternative forward models for which the computation time becomes extremely long, especially for broadband inversions. The water propagation is approximately separated from the seabed interaction using predetermined bathymetry and a possibly range-dependent water sound speed profile. The geometrical optics approximation is used to calculate eigenrays between sources and receivers, including bottom reflecting paths. Modeled broadband pressure fields are obtained by computing the plane wave reflection coefficient at specific angles and frequencies and by then linking this result with the bottom reflected eigenrays. Each perturbation of the seabed requires a recalculation of the plane wave reflection coefficient, but not a recalculation of the eigenrays, resulting in a highly efficient method. Range-independent problems are treated as a limiting case of the approach. The method is first described and then demonstrated with a few simple range-independent theoretical models. The versatility of addressing range-dependence in the bottom seabed is demonstrated with a simulated data set. Finally, the new model is applied to inversion from a measured data set, taken with impulsive sources, for both range-independent and range-dependent continental shelf environments.
Diffraction of a plane wave by a three-dimensional corner
NASA Technical Reports Server (NTRS)
Ting, L.; Kung, F.
1971-01-01
By the superposition of the conical solution for the diffraction of a plane pulse by a three dimensional corner, the solution for a general incident plane wave is constructed. A numerical program is presented for the computation of the pressure distribution on the surface due to an incident plane wave of any wave form and at any incident angle. Numerical examples are presented to show the pressure signature at several points on the surface due to incident wave with a front shock wave, two shock waves in succession, or a compression wave with same peak pressure. The examples show that when the distance of a point on the surface from the edges or the vertex is comparable to the distance for the front pressure raise to reach the maximum, the peak pressure at that point can be much less than that given by a regular reflection, because the diffracted wave front arrives at that point prior to the arrival of the peak incident wave.
Electromagnetic scattering of a polarized plane wave from an ellipsoidal particle in the near field
NASA Astrophysics Data System (ADS)
Chen, Feinan; Li, Jia
2017-06-01
Within the validity of the first-order Born approximation, we study the near-zone evanescent wave properties for a polarized plane wave scattering upon an ellipsoidal particle. Integral expressions are obtained for the three-dimensional electromagnetic field of the near-zone scattered evanescent wave, and the dependences of the scattered intensity distributions on the degree of polarization of the incident wave and the scattering potential profile of the particle are presented. The scattered intensity from the particle can exhibit a focused pattern concentrated around the central scattering region, but the scattered intensity generated from a circularly polarized wave shows a smooth distribution for different scattering angles. Moreover, the scattered intensity also enhances when either the summation index or the effective radius of the particle increases. Our results can be utilized to generate near-field focused scattered patterns that can be tuned flexibly by controlling the degree of the polarization of the plane wave and the scattering potential parameters of the ellipsoidal particle.
Concentration gradient limiter designs for incident plane waves and multiple chromophores
NASA Astrophysics Data System (ADS)
McLean, Daniel G.
1998-10-01
A design method for reverse saturable absorbing (RSA) dye concentration gradient limiters, termed here the Absorption Diffraction Balance (ADB) design method, is used to produce designs for multiple chromophores and is extended to allow incident plane waves. The ADB design method is reviewed for Gaussian beams applied to a constant fluence design and a linear fluence design. These two designs are combined to allow different dyes to be used in different portions of the limiter. It is found that this hybrid design significantly enhances performance under some circumstances. It is also shown to reduce the probability of dye photodegradation. The ADB design method is extended to allow for incident plane waves or a top-hat beam profile. The field at the geometric shadow edge, expressed in terms of Lommel functions, is shown to closely match the Gaussian field when the incident irradiance, power, and second moments are the same. Since the irradiance distribution is not monotonically increasing in the focal region, the required concentration distribution has regions of negative concentration, i.e. gain regions. These designs are useful for initiating numerical nonlinear beam propagation studies.
Plane Wave Imaging for ultrasonic non-destructive testing: Generalization to multimodal imaging.
Le Jeune, Léonard; Robert, Sébastien; Lopez Villaverde, Eduardo; Prada, Claire
2016-01-01
This paper describes a new ultrasonic array imaging method for Non-Destructive Testing (NDT) which is derived from the medical Plane Wave Imaging (PWI) technique. The objective is to perform fast ultrasound imaging with high image quality. The approach is to transmit plane waves at several angles and to record the back-scattered signals with all the array elements. Focusing in receive is then achieved by coherent summations of the signals in every point of a region of interest. The medical PWI is generalized to immersion setups where water acts as a coupling medium and to multimodal (direct, half-skip modes) imaging in order to detect different types of defects (inclusions, porosities, cracks). This method is compared to the Total Focusing Method (TFM) which is the reference imaging technique in NDT. First, the two post-processing algorithms are described. Then experimental results with the array probe either in contact or in immersion are presented. A good agreement between the TFM and the PWI is observed, with three to ten times less transmissions required for the PWI. Copyright © 2015 Elsevier B.V. All rights reserved.
Implementation of linear-scaling plane wave density functional theory on parallel computers
NASA Astrophysics Data System (ADS)
Skylaris, Chris-Kriton; Haynes, Peter D.; Mostofi, Arash A.; Payne, Mike C.
We describe the algorithms we have developed for linear-scaling plane wave density functional calculations on parallel computers as implemented in the onetep program. We outline how onetep achieves plane wave accuracy with a computational cost which increases only linearly with the number of atoms by optimising directly the single-particle density matrix expressed in a psinc basis set. We describe in detail the novel algorithms we have developed for computing with the psinc basis set the quantities needed in the evaluation and optimisation of the total energy within our approach. For our parallel computations we use the general Message Passing Interface (MPI) library of subroutines to exchange data between processors. Accordingly, we have developed efficient schemes for distributing data and computational load to processors in a balanced manner. We describe these schemes in detail and in relation to our algorithms for computations with a psinc basis. Results of tests on different materials show that onetep is an efficient parallel code that should be able to take advantage of a wide range of parallel computer architectures.
Whole body exposure at 2100 MHz induced by plane wave of random incidences in a population
NASA Astrophysics Data System (ADS)
Conil, Emmanuelle; Hadjem, Abdelhamid; El Habachi, Aimad; Wiart, J.
2010-11-01
In this article, the whole body exposure induced by plane wave coming from a random direction of arrival is analyzed at 2100 MHz. This work completes previous studies on the influence of different parameters on the whole body exposure (such as morphology, frequency or usage in near field). The Visible Human phantom has been used to build a surrogate model to predict the whole body exposure depending on the highlighted surface of the phantom and on the direction of arrival of the incident plane wave. For the Visible Human, the error on the whole body averaged Specific Absorption Rate (SAR) is on average 4%. The surrogate model is applied to other 3D anthropomorphic phantoms for a frontal incidence with an averaged error of 10%. The great interest of the surrogate model is the possibility to apply a Monte Carlo process to assess probability distribution function of a population. A recent French anthropometric database of more than 3500 adults is used to build the probability distribution function of the whole body SAR for a random direction of arrival.
Scaled plane-wave Born cross sections for atoms and molecules
NASA Astrophysics Data System (ADS)
Tanaka, H.; Brunger, M. J.; Campbell, L.; Kato, H.; Hoshino, M.; Rau, A. R. P.
2016-04-01
Integral cross sections for optically allowed electronic-state excitations of atoms and molecules by electron impact, by applying scaled plane-wave Born models, are reviewed. Over 40 years ago, Inokuti presented an influential review of charged-particle scattering, based on the theory pioneered by Bethe forty years earlier, which emphasized the importance of reliable cross-section data from low eV energies to high keV energies that are needed in many areas of radiation science with applications to astronomy, plasmas, and medicine. Yet, with a couple of possible exceptions, most computational methods in electron-atom scattering do not, in general, overlap each other's validity range in the region from threshold up to 300 eV and, in particular, in the intermediate region from 30 to 300 eV. This is even more so for electron-molecule scattering. In fact this entire energy range is of great importance and, to bridge the gap between the two regions of low and high energy, scaled plane-wave Born models were developed to provide reliable, comprehensive, and absolute integral cross sections, first for ionization by Kim and Rudd and then extended to optically allowed electronic-state excitation by Kim. These and other scaling models in a broad, general application to electron scattering from atoms and molecules, their theoretical basis, and their results for cross sections along with comparison to experimental measurements are reviewed. Where possible, these data are also compared to results from other computational approaches.
Optimization of exit-plane waves restored from HRTEM through-focal series.
Erni, Rolf; Rossell, Marta D; Nakashima, Philip N H
2010-01-01
Atomic-resolution transmission electron microscopy has largely benefited from the implementation of aberration correctors in the imaging part of the microscope. Though the dominant geometrical axial aberrations can in principle be corrected or suitably adjusted, the impact of higher-order aberrations, which are mainly due to the implementation of non-round electron optical elements, on the imaging process remains unclear. Based on a semi-empirical criterion, we analyze the impact of residual aperture aberrations on the quality of exit-plane waves that are retrieved from through-focal series recorded using an aberration-corrected and monochromated instrument which was operated at 300kV and enabled for an information transfer of approximately 0.05nm. We show that the impact of some of the higher-order aberrations in retrieved exit-plane waves can be balanced by a suitable adjustment of symmetry equivalent lower-order aberrations. We find that proper compensation and correction of 1st and 2nd order aberrations is critical, and that the required accuracy is difficult to achieve. This results in an apparent insensitivity towards residual higher-order aberrations. We also investigate the influence of the detector characteristics on the image contrast. We find that correction for the modulation transfer function results in a contrast gain of up to 40%.
NASA Astrophysics Data System (ADS)
Yong, Peng; Huang, Jianping; Li, Zhenchun; Liao, Wenyuan; Qu, Luping; Li, Qingyang; Liu, Peijun
2016-12-01
In finite difference (FD) method, numerical dispersion is the dominant factor influencing the accuracy of seismic modeling. Various optimized FD schemes for scalar wave modeling have been proposed to reduce grid dispersion, while the optimized time-space domain FD schemes for elastic wave modeling have not been fully investigated yet. In this paper, an optimized FD scheme with Equivalent Staggered Grid (ESG) for elastic modelling has been developed. We start from the constant P- and S-wave speed elastic wave equations and then deduce analytical plane wave solutions in the wavenumber domain with eigenvalue decomposition method. Based on the elastic plane wave solutions, three new time-space domain dispersion relations of ESG elastic modeling are obtained, which are represented by three equations corresponding to P-, S- and converted wave terms in the elastic equations, respectively. By using these new relations, we can study the dispersion errors of different spatial FD terms independently. The dispersion analysis showed that different spatial FD terms have different errors. It is therefore suggested that different FD coefficients to be used to approximate the three spatial derivative terms. In addition, the relative dispersion error in L2-norm is minimized through optimizing FD coefficients using Newton's method. Synthetic examples have demonstrated that this new optimal FD schemes have superior accuracy for elastic wave modeling compared to Taylor-series expansion and optimized space domain FD schemes.
Plane wave solution for elastic wave scattering by a heterogeneous fracture
NASA Astrophysics Data System (ADS)
Nakagawa, Seiji; Nihei, Kurt T.; Myer, Larry R.
2004-06-01
A plane-wave method for computing the three-dimensional scattering of propagating elastic waves by a planar fracture with heterogeneous fracture compliance distribution is presented. This method is based upon the spatial Fourier transform of the seismic displacement-discontinuity (SDD) boundary conditions (also called linear slip interface conditions), and therefore, called the wave-number-domain SDD method (wd-SDD method). The resulting boundary conditions explicitly show the coupling between plane waves with an incident wave number component (specular component) and scattered waves which do not follow Snell's law (nonspecular components) if the fracture is viewed as a planar boundary. For a spatially periodic fracture compliance distribution, these boundary conditions can be cast into a linear system of equations that can be solved for the amplitudes of individual wave modes and wave numbers. We demonstrate the developed technique for a simulated fracture with a stochastic (correlated) surface compliance distribution. Low- and high-frequency solutions of the method are also compared to the predictions by low-order Born series in the weak and strong scattering limit.
Fast solution of elliptic partial differential equations using linear combinations of plane waves
NASA Astrophysics Data System (ADS)
Pérez-Jordá, José M.
2016-02-01
Given an arbitrary elliptic partial differential equation (PDE), a procedure for obtaining its solution is proposed based on the method of Ritz: the solution is written as a linear combination of plane waves and the coefficients are obtained by variational minimization. The PDE to be solved is cast as a system of linear equations A x =b , where the matrix A is not sparse, which prevents the straightforward application of standard iterative methods in order to solve it. This sparseness problem can be circumvented by means of a recursive bisection approach based on the fast Fourier transform, which makes it possible to implement fast versions of some stationary iterative methods (such as Gauss-Seidel) consuming O (N logN ) memory and executing an iteration in O (N log2N ) time, N being the number of plane waves used. In a similar way, fast versions of Krylov subspace methods and multigrid methods can also be implemented. These procedures are tested on Poisson's equation expressed in adaptive coordinates. It is found that the best results are obtained with the GMRES method using a multigrid preconditioner with Gauss-Seidel relaxation steps.
Fast solution of elliptic partial differential equations using linear combinations of plane waves.
Pérez-Jordá, José M
2016-02-01
Given an arbitrary elliptic partial differential equation (PDE), a procedure for obtaining its solution is proposed based on the method of Ritz: the solution is written as a linear combination of plane waves and the coefficients are obtained by variational minimization. The PDE to be solved is cast as a system of linear equations Ax=b, where the matrix A is not sparse, which prevents the straightforward application of standard iterative methods in order to solve it. This sparseness problem can be circumvented by means of a recursive bisection approach based on the fast Fourier transform, which makes it possible to implement fast versions of some stationary iterative methods (such as Gauss-Seidel) consuming O(NlogN) memory and executing an iteration in O(Nlog(2)N) time, N being the number of plane waves used. In a similar way, fast versions of Krylov subspace methods and multigrid methods can also be implemented. These procedures are tested on Poisson's equation expressed in adaptive coordinates. It is found that the best results are obtained with the GMRES method using a multigrid preconditioner with Gauss-Seidel relaxation steps.
NASA Astrophysics Data System (ADS)
Yong, Peng; Huang, Jianping; Li, Zhenchun; Liao, Wenyuan; Qu, Luping; Li, Qingyang; Liu, Peijun
2017-02-01
In finite-difference (FD) method, numerical dispersion is the dominant factor influencing the accuracy of seismic modelling. Various optimized FD schemes for scalar wave modelling have been proposed to reduce grid dispersion, while the optimized time-space domain FD schemes for elastic wave modelling have not been fully investigated yet. In this paper, an optimized FD scheme with Equivalent Staggered Grid (ESG) for elastic modelling has been developed. We start from the constant P- and S-wave speed elastic wave equations and then deduce analytical plane wave solutions in the wavenumber domain with eigenvalue decomposition method. Based on the elastic plane wave solutions, three new time-space domain dispersion relations of ESG elastic modelling are obtained, which are represented by three equations corresponding to P-, S- and converted-wave terms in the elastic equations, respectively. By using these new relations, we can study the dispersion errors of different spatial FD terms independently. The dispersion analysis showed that different spatial FD terms have different errors. It is therefore suggested that different FD coefficients to be used to approximate the three spatial derivative terms. In addition, the relative dispersion error in L2-norm is minimized through optimizing FD coefficients using Newton's method. Synthetic examples have demonstrated that this new optimal FD schemes have superior accuracy for elastic wave modelling compared to Taylor-series expansion and optimized space domain FD schemes.
Plane wave method for elastic wave scattering by a heterogeneous fracture
Nakagawa, Seiji; Nihei, Kurt T.; Myer, Larry R.
2003-02-21
A plane-wave method for computing the three-dimensional scattering of propagating elastic waves by a planar fracture with heterogeneous fracture compliance distribution is presented. This method is based upon the spatial Fourier transform of the seismic displacement-discontinuity (SDD) boundary conditions (also called linear slip interface conditions), and therefore, called the wave-number-domain SDD method (wd-SDD method). The resulting boundary conditions explicitly show the coupling between plane waves with an incident wave number component (specular component) and scattered waves which do not follow Snell's law (nonspecular components) if the fracture is viewed as a planar boundary. For a spatially periodic fracture compliance distribution, these boundary conditions can be cast into a linear system of equations that can be solved for the amplitudes of individual wave modes and wave numbers. We demonstrate the developed technique for a simulated fracture with a stochastic (correlated) surface compliance distribution. Low- and high-frequency solutions of the method are also compared to the predictions by low-order Born series in the weak and strong scattering limit.
Concepts and Tradeoffs in Velocity Estimation With Plane-Wave Contrast-Enhanced Doppler.
Tremblay-Darveau, Charles; Williams, Ross; Sheeran, Paul S; Milot, Laurent; Bruce, Matthew; Burns, Peter N
2016-11-01
While long Doppler ensembles are, in principle, beneficial for velocity estimates, short acoustic pulses must be used in microbubble contrast-enhanced (CE) Doppler to mitigate microbubble destruction. This introduces inherent tradeoffs in velocity estimates with autocorrelators, which are studied here. A model of the autocorrelation function adapted to the microbubble Doppler signal accounting for transit time, the echo frequency uncertainty, and contrast-agent destruction is derived and validated in vitro. It is further demonstrated that a local measurement of the center frequency of the microbubble echo is essential in order to avoid significant bias in velocity estimates arising from the linear and nonlinear frequency-dependent scattering of microbubbles and compensate for the inherent speckle nature of the received echo frequency. For these reasons, broadband Doppler estimators (2-D autocorrelator and Radon projection) are better suited than simpler narrow-band estimators (1-D autocorrelator and 1-D Fourier transform) for CE flow assessment. A case study of perfusion in a VX-2 carcinoma using CE plane-wave Doppler is also shown. We demonstrate that even when considering all uncertainties associated with microbubble-related decorrelation (destruction, pulse bandwidth, transit time, and flow gradient) and the need for real-time imaging, a coefficient of variation of 4% on the axial velocity is achievable with plane-wave imaging.
Rivero, Pablo; Manuel García-Suárez, Víctor; Pereñiguez, David; Utt, Kainen; Yang, Yurong; Bellaiche, Laurent; Park, Kyungwha; Ferrer, Jaime; Barraza-Lopez, Salvador
2015-01-01
We present in this article a pseudopotential (PP) database for DFT calculations in the context of the SIESTA code [1–3]. Comprehensive optimized PPs in two formats (psf files and input files for ATM program) are provided for 20 chemical elements for LDA and GGA exchange-correlation potentials. Our data represents a validated database of PPs for SIESTA DFT calculations. Extensive transferability tests guarantee the usefulness of these PPs. PMID:26217711
Stolt’s f-k migration for plane wave ultrasound imaging
Garcia, Damien; Le Tarnec, Louis; Muth, Stéphan; Montagnon, Emmanuel; Porée, Jonathan; Cloutier, Guy
2013-01-01
Ultrafast ultrasound is an emerging modality that offers new perspectives and opportunities in medical imaging. Plane wave imaging (PWI) allows one to attain very high frame rates by transmission of planar ultrasound wavefronts. As a plane wave reaches a given scatterer, the latter becomes a secondary source emitting upward spherical waves and creating a diffraction hyperbola in the received RF (radio-frequency) signals. To produce an image of the scatterers, all the hyperbolas must be migrated back to their apexes. In order to perform beamforming of plane wave echo RFs and return high-quality images at high frame rates, we propose a new migration method carried out in the frequency-wavenumber (f-k) domain. The f-k migration for PWI has been adapted from the Stolt migration for seismic imaging. This migration technique is based on the exploding reflector model (ERM), which consists in assuming that all the scatterers explode in concert and become acoustic sources. The classical ERM model, however, is not appropriate for PWI. We showed that the ERM can be made suitable for PWI by a spatial transformation of the hyperbolic traces present in the RF data. In vitro experiments were performed to sketch the advantages of PWI with Stolt’s f-k migration over the conventional delay-and-sum (DAS) approach. The Stolt’s f-k migration was also compared with the Fourier-based method developed by J-Y Lu. Our findings show that multi-angle compounded f-k migrated images are of quality similar to those obtained with a state-of-the-art dynamic focusing mode. This remained true even with a very small number of steering angles thus ensuring a highly competitive frame rate. In addition, the new FFT-based f-k migration provides comparable or better contrast-to-noise ratio and lateral resolution than the Lu’s and DAS migration schemes. Matlab codes of the Stolt’s f-k migration for PWI are provided. PMID:24626107
On the scattering of an acoustic plane wave by a soft prolate spheroid
NASA Astrophysics Data System (ADS)
Borromeo, Joseph Michael
This thesis solves the scattering problem in which an acoustic plane wave of propagation number K1 is scattered by a soft prolate spheroid. The interior field of the scatterer is characterized by a propagation number K2, while the field radiated by the scatterer is characterized by the propagation number K3. The three fields and their normal derivatives satisfy boundary conditions at the surface of the scatterer. These boundary conditions involve six complex parameters depending on the propagation numbers. The scattered wave also satisfies the Sommerfeld radiation condition at infinity. Through analytical methods, series representations are constructed for the interior field and scattered field for an arbitrary sphere and a prolate spheroid. In addition, results for the reciprocity relations and Energy theorem are derived. Application to detection of whales and submarines are discussed, as well as classification of fish, squid and zoo plankton. In general Ref[ ] is used for reference and the work is done in three dimensions.
Space-time analogy for partially coherent plane-wave-type pulses.
Lancis, Jesús; Torres-Company, Víctor; Silvestre, Enrique; Andrés, Pedro
2005-11-15
In this Letter we extend the well-known space-time duality to partially coherent wave fields and, as a limit case, to incoherent sources. We show that there is a general analogy between the paraxial diffraction of quasi-monochromatic beams of limited spatial coherence and the temporal distortion of partially coherent plane-wave pulses in parabolic dispersive media. Next, coherence-dependent effects in the propagation of Gaussian Schell-model pulses are retrieved from that of their spatial counterpart, the Gaussian Schell-model beam. Finally, the last result allows us to present a source linewidth analysis in an optical fiber communication system operating around the 1.55 microm wavelength window.
Schwab, Hans-Martin; Beckmann, Martin F.; Schmitz, Georg
2016-01-01
Photoacoustic imaging aims to visualize light absorption properties of biological tissue by receiving a sound wave that is generated inside the observed object as a result of the photoacoustic effect. In clinical applications, the strong light absorption in human skin is a major problem. When high amplitude photoacoustic waves that originate from skin absorption propagate into the tissue, they are reflected back by acoustical scatterers and the reflections contribute to the received signal. The artifacts associated with these reflected waves are referred to as clutter or skin echo and limit the applicability of photoacoustic imaging for medical applications severely. This study seeks to exploit the acoustic tissue information gained by plane wave ultrasound measurements with a linear array in order to correct for reflections in the photoacoustic image. By deriving a theory for clutter waves in k-space and a matching inversion approach, photoacoustic measurements compensated for clutter are shown to be recovered. PMID:27446669
Analysis of near-field Cassegrain reflector - Plane wave versus element-by-element approach
NASA Technical Reports Server (NTRS)
Houshmand, Bijan; Lee, Shung-Wu; Rahmat-Samii, Yahya; Lam, Peter T.
1990-01-01
A near-field Cassegrain reflector (NFCR) is an effective way to magnify a small phased array into a much larger-aperture antenna for limited scan applications. Traditionally the pattern analysis of NFCR is based on a plane wave approach, which simplifies the computation tremendously, but fails to provide design information about the most critical component of the whole antenna system, the feed array. Currently available computers make it possible to calculate the pattern of an NFCR by a more exact element-by-element approach. Each element in the feed array is considered individually, and the diffraction pattern from the subreflector is calculated by the geometrical theory of diffraction (including uniform theories at the shadow boundaries). The field contributions from all elements are superimposed at the curved main reflector surface, and a physical-optics integration is performed to obtain the secondary pattern.
Plane-wave theory of a Michelson laser coupler with a dielectric slab beam splitter
NASA Astrophysics Data System (ADS)
Cooper, Steven J.; Heckenberg, Norman R.
1996-03-01
The plane-wave theory for the transmittance and absorbtance of a perfectly aligned Michelson coupler with a dielectric slab beam splitter is presented. It is shown that the transmittance and absorbtance vary sinusoidally and in quadrature. As a result of this quadrature relationship, the maximum transmittance occurs at a setting of the translatable coupler mirror at which the absorbtance is not at an extremum, and so the curve of output power as a function of coupler setting is asymmetrical with respect to the setting yielding maximum transmittance. Experimental measurements of the output power of a far-infrared HCN laser as a function of the coupler setting confirm this asymmetry, which seems to have been overlooked or ignored in previous studies.
NASA Astrophysics Data System (ADS)
Theobald, Dominik; Egel, Amos; Gomard, Guillaume; Lemmer, Uli
2017-09-01
The computation of light scattering by the superposition T -matrix scheme has been restricted thus far to systems made of particles that are either sparsely distributed or of near-spherical shape. In this work, we extend the range of applicability of the T -matrix method by accounting for the coupling of scattered fields between highly nonspherical particles in close vicinity. This is achieved using an alternative formulation of the translation operator for spherical vector wave functions, based on a plane-wave expansion of the particle's scattered electromagnetic field. The accuracy and versatility of the present approach is demonstrated by simulating arbitrarily oriented and densely packed spheroids, for both dielectric and metallic particles.
NASA Astrophysics Data System (ADS)
Cheng, Qiang; Cui, Tie Jun
2006-12-01
We have investigated the reflection and refraction properties of plane waves incident from free space into a uniaxially anisotropic chiral medium, where the chirality appears only in one direction and the host medium can be either an isotropic dielectric or an anisotropic electric plasma. We show that the reflection and refraction properties are closely related to the dispersion relation of the chiral medium and that negative phase refractions and/or negative group refractions may occur. We further demonstrate that the two eigenwaves within the uniaxially anisotropic chiral medium behave differently with respect to the incident angle, and in some cases only one of them can be supported and transmitted. We have studied the critical angle and Brewster's angle with some special properties. We have also discussed the potential application of the uniaxially anisotropic chiral medium for the polarization beam splitter. Numerical results are given to validate our analysis.
Cheng, Qiang; Cui, Tie Jun
2006-12-01
We have investigated the reflection and refraction properties of plane waves incident from free space into a uniaxially anisotropic chiral medium, where the chirality appears only in one direction and the host medium can be either an isotropic dielectric or an anisotropic electric plasma. We show that the reflection and refraction properties are closely related to the dispersion relation of the chiral medium and that negative phase refractions and/or negative group refractions may occur. We further demonstrate that the two eigenwaves within the uniaxially anisotropic chiral medium behave differently with respect to the incident angle, and in some cases only one of them can be supported and transmitted. We have studied the critical angle and Brewster's angle with some special properties. We have also discussed the potential application of the uniaxially anisotropic chiral medium for the polarization beam splitter. Numerical results are given to validate our analysis.
Nonlinear dynamics and band transport in a superlattice driven by a plane wave
NASA Astrophysics Data System (ADS)
Apostolakis, A.; Awodele, M. K.; Alekseev, K. N.; Kusmartsev, F. V.; Balanov, A. G.
2017-06-01
A quantum particle transport induced in a spatially periodic potential by a propagating plane wave has a number of important implications in a range of topical physical systems. Examples include acoustically driven semiconductor superlattices and cold atoms in an optical crystal. Here we apply a kinetic description of the directed transport in a superlattice beyond standard linear approximation, and utilize exact path-integral solutions of the semiclassical transport equation. We show that the particle drift and average velocities have nonmonotonic dependence on the wave amplitude with several prominent extrema. Such nontrivial kinetic behavior is related to global bifurcations developing with an increase of the wave amplitude. They cause dramatic transformations of the system phase space and lead to changes of the transport regime. We describe different types of phase trajectories contributing to the directed transport and analyze their spectral content.
Schwab, Hans-Martin; Beckmann, Martin F; Schmitz, Georg
2016-04-01
Photoacoustic imaging aims to visualize light absorption properties of biological tissue by receiving a sound wave that is generated inside the observed object as a result of the photoacoustic effect. In clinical applications, the strong light absorption in human skin is a major problem. When high amplitude photoacoustic waves that originate from skin absorption propagate into the tissue, they are reflected back by acoustical scatterers and the reflections contribute to the received signal. The artifacts associated with these reflected waves are referred to as clutter or skin echo and limit the applicability of photoacoustic imaging for medical applications severely. This study seeks to exploit the acoustic tissue information gained by plane wave ultrasound measurements with a linear array in order to correct for reflections in the photoacoustic image. By deriving a theory for clutter waves in k-space and a matching inversion approach, photoacoustic measurements compensated for clutter are shown to be recovered.
LOBSTER: A tool to extract chemical bonding from plane-wave based DFT.
Maintz, Stefan; Deringer, Volker L; Tchougréeff, Andrei L; Dronskowski, Richard
2016-04-30
The computer program LOBSTER (Local Orbital Basis Suite Towards Electronic-Structure Reconstruction) enables chemical-bonding analysis based on periodic plane-wave (PAW) density-functional theory (DFT) output and is applicable to a wide range of first-principles simulations in solid-state and materials chemistry. LOBSTER incorporates analytic projection routines described previously in this very journal [J. Comput. Chem. 2013, 34, 2557] and offers improved functionality. It calculates, among others, atom-projected densities of states (pDOS), projected crystal orbital Hamilton population (pCOHP) curves, and the recently introduced bond-weighted distribution function (BWDF). The software is offered free-of-charge for non-commercial research. © 2016 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.
TM Plane Wave Reflection and Transmission from a One-Dimensional Random Slab
NASA Astrophysics Data System (ADS)
Tamura, Yasuhiko
This paper deals with a TM plane wave reflection and transmission from a one-dimensional random slab with stratified fluctuation by means of the stochastic functional approach. Based on a previous manner [IEICE Trans. Electron. E88-C, 4, pp. 713-720, 2005], an explicit form of the random wavefield is obtained in terms of a Wiener-Hermite expansion with approximate expansion coefficients (Wiener kernels) under small fluctuation. The optical theorem and coherent reflection coefficient are illustrated in figures for several physical parameters. It is then found that the optical theorem by use of the first two or three order Wiener kernels holds with good accuracy and a shift of Brewster's angle appears in the coherent reflection.
Quartic scaling MP2 for solids: A highly parallelized algorithm in the plane wave basis
NASA Astrophysics Data System (ADS)
Schäfer, Tobias; Ramberger, Benjamin; Kresse, Georg
2017-03-01
We present a low-complexity algorithm to calculate the correlation energy of periodic systems in second-order Møller-Plesset (MP2) perturbation theory. In contrast to previous approximation-free MP2 codes, our implementation possesses a quartic scaling, O ( N 4 ) , with respect to the system size N and offers an almost ideal parallelization efficiency. The general issue that the correlation energy converges slowly with the number of basis functions is eased by an internal basis set extrapolation. The key concept to reduce the scaling is to eliminate all summations over virtual orbitals which can be elegantly achieved in the Laplace transformed MP2 formulation using plane wave basis sets and fast Fourier transforms. Analogously, this approach could allow us to calculate second order screened exchange as well as particle-hole ladder diagrams with a similar low complexity. Hence, the presented method can be considered as a step towards systematically improved correlation energies.
PARTICLE DISPLACEMENTS ON THE WALL OF A BOREHOLE FROM INCIDENT PLANE WAVES.
Lee, M.W.
1987-01-01
Particle displacements from incident plane waves at the wall of a fluid-filled borehole are formulated by applying the seismic reciprocity theorem to far-field displacement fields. Such displacement fields are due to point forces acting on a fluid-filled borehole under the assumption of long wavelengths. The displacement fields are analyzed to examine the effect of the borehole on seismic wave propagation, particularly for vertical seismic profiling (VSP) measurements. When the shortest wavelength of interest is approximately 25 times longer than the borehole's diameter, the scattered displacements are proportional to the first power of incident frequency and borehole diameter. When the shortest wavelength of interest is about 40 times longer than the borehole's diameter, borehole effects on VSP measurements using a wall-locking geophone are negligible.
The relativistic transformation for an electromagnetic plane wave with general time dependence
NASA Astrophysics Data System (ADS)
Smith, Glenn S.
2012-03-01
In special relativity, the transformation between inertial frames for an electromagnetic plane wave is usually derived for the time-harmonic case (the field is a sinusoid of infinite duration), even though all practical waves are of finite duration and may not even contain a dominant sinusoid. This paper presents an alternative derivation in which the time dependence of the field is general; for example, it could be a Gaussian pulse in time. The changes that occur on transformation in the quantities that describe the wave are obtained and discussed. These changes include the temporal behaviour, direction of propagation, electromagnetic field, energy, and linear momentum. The derivation uses only elementary principles from special relativity, so it is suitable for an introductory course on the subject or a course on electrodynamics.
Cavity-based linear polarizer immune to the polarization direction of an incident plane wave.
Wang, Jiang; Shen, Zhongxiang; Gao, Xiang; Wu, Wen
2016-01-15
We herein report a linear polarizer based on a 2D array of substrate integrated waveguide cavities, which can convert an arbitrary linearly polarized (LP) incident wave into an outgoing LP wave in a specified polarization direction with constant transmittance. Two orthogonal slots etched on the front surface of the cavity are utilized to couple a wave of arbitrary polarization into the cavity, while another slot on the back side helps to couple the field out along a desired polarization direction. Microwave experiments are performed as a proof of concept. The proposed polarizer exhibits very good performance with stable transmittance as 50% and a polarization extinction ratio over 45 dB. The new polarizer is potentially useful in novel polarization-selective devices that are immune to the polarization direction of an incident plane wave.
NASA Technical Reports Server (NTRS)
Yarrow, Maurice; Vastano, John A.; Lomax, Harvard
1992-01-01
Generic shapes are subjected to pulsed plane waves of arbitrary shape. The resulting scattered electromagnetic fields are determined analytically. These fields are then computed efficiently at field locations for which numerically determined EM fields are required. Of particular interest are the pulsed waveform shapes typically utilized by radar systems. The results can be used to validate the accuracy of finite difference time domain Maxwell's equations solvers. A two-dimensional solver which is second- and fourth-order accurate in space and fourth-order accurate in time is examined. Dielectric media properties are modeled by a ramping technique which simplifies the associated gridding of body shapes. The attributes of the ramping technique are evaluated by comparison with the analytic solutions.
Plane-wave Fresnel diffraction by elliptic apertures: a Fourier-based approach.
Borghi, Riccardo
2014-10-01
A simple theoretical approach to evaluate the scalar wavefield, produced, within paraxial approximation, by the diffraction of monochromatic plane waves impinging on elliptic apertures or obstacles is presented. We find that the diffracted field can be mathematically described in terms of a Fourier series with respect to an angular variable suitably related to the elliptic parametrization of the observation plane. The convergence features of such Fourier series are analyzed, and a priori truncation criterion is also proposed. Two-dimensional maps of the optical intensity diffraction patterns are then numerically generated and compared, at a visual level, with several experimental pictures produced in the past. The last part of this work is devoted to carrying out an analytical investigation of the diffracted field along the ellipse axis. A uniform approximation is derived on applying a method originally developed by Schwarzschild, and an asymptotic estimate, valid in the limit of small eccentricities, is also obtained via the Maggi-Rubinowicz boundary wave theory.
The scattering of obliquely incident plane waves from a corrugated conducting surface
NASA Technical Reports Server (NTRS)
Le Vine, D. M.
1976-01-01
A physical optics solution is presented for the scattering of plane waves from a perfectly conducting corrugated surface in the case of waves incident from an arbitrary direction and for an observer far from the surface. This solution is used to compute the radar cross section of the surface in the case of backscatter from irregular (i.e., stochastic) corrugations. An interesting feature of the solution is the occurrence of singularities in the scattered fields. These singularities appear to be a manifestation of focusing by the surface at its 'stationary' points. Whether or not the singularities occur in the solution depends on the manner in which one restricts the analysis to the far-field.
An efficient algorithm for time propagation as applied to linearized augmented plane wave method
NASA Astrophysics Data System (ADS)
Dewhurst, J. K.; Krieger, K.; Sharma, S.; Gross, E. K. U.
2016-12-01
An algorithm for time propagation of the time-dependent Kohn-Sham equations is presented. The algorithm is based on dividing the Hamiltonian into small time steps and assuming that it is constant over these steps. This allows for the time-propagating Kohn-Sham wave function to be expanded in the instantaneous eigenstates of the Hamiltonian. The method is particularly efficient for basis sets which allow for a full diagonalization of the Hamiltonian matrix. One such basis is the linearized augmented plane waves. In this case we find it is sufficient to perform the evolution as a second-variational step alone, so long as sufficient number of first variational states are used. The algorithm is tested not just for non-magnetic but also for fully non-collinear magnetic systems. We show that even for delicate properties, like the magnetization density, fairly large time-step sizes can be used demonstrating the stability and efficiency of the algorithm.
Ding, Chaoliang; Cai, Yangjian; Zhang, Yongtao; Pan, Liuzhan
2012-06-01
The scattering of a stochastic electromagnetic plane-wave pulse on a deterministic spherical medium is investigated. An analytical formula for the degree of polarization (DOP) of the scattered field in the far zone is derived. Letting pulse duration T(0) → ∞, our formula can be applied to study the scattering of a stationary stochastic electromagnetic light wave. Numerical results show that the DOP of the far zone field is closely determined by the size of the spherical medium when the incident field is a stochastic electromagnetic plane-wave pulse. This is much different from the case when the incident field is a stationary stochastic electromagnetic light wave, where the DOP of the far zone field is independent of the size of the medium. One may obtain the information of the spherical medium by measuring the scattering-induced changes in the DOP of a stochastic electromagnetic plane-wave pulse.
Plane Wave Electromagnetic Reflection and Transmission from a Thin Geologic Layer
NASA Astrophysics Data System (ADS)
Aldridge, D. F.; Weiss, C. J.
2016-12-01
In seismic reflection exploration, a thin geologic layer is defined as one with thickness less than about one-fourth wavelength of an incident plane wave. In this case, distinct reflection arrivals from top and bottom bed boundaries are difficult to recognize. Information regarding layer thickness and material properties is encoded in the amplitude of the composite (reflected and/or transmitted) response. Due to the significantly larger wavelength of an electromagnetic (EM) wave of identical frequency, virtually all geologic layers are considered extremely thin via this definition. This is especially true for a single hydraulic fracture ( 1 cm width) or even a fracture zone ( meters width). In this investigation, we restrict consideration to a normally-incident plane EM wave, and calculate reflection and transmission responses of a uniform-thickness layer embedded between two (possibly dissimilar) homogeneous and isotropic halfspaces. Exact frequency-domain expressions for electric vector E and magnetic vector B are obtained via two equivalent methodologies: 1) summing primaries and all intrabed multiples (the SEIS way), and 2) solving a boundary value problem by imposing wavefield continuity at interfaces (the EM way). Time-domain responses are obtained by inverse numerical Fourier transformation. We predict observable E and B responses, in both reflection and transmission, from layers that are several orders of magnitude smaller than the incident dominant wavelength. Large conductivity or permeability contrast enhances response amplitude, whereas permittivity contrast exerts negligible influence at low frequency. However, responses are relatively insensitive to fixed (parameter × thickness) product, a result that agrees with exact and First Born Approximation scattering theory. An obvious extension involves a non-normal incident plane wave, which offers the intriguing possibility of EM Amplitude vs. Offset (EMAVO) analysis.
NASA Technical Reports Server (NTRS)
Mcaninch, G. L.; Myers, M. K.
1980-01-01
The parabolic approximation for the acoustic equations of motion is applied to the study of the sound field generated by a plane wave at or near grazing incidence to a finite impedance boundary. It is shown how this approximation accounts for effects neglected in the usual plane wave reflection analysis which, at grazing incidence, erroneously predicts complete cancellation of the incident field by the reflected field. Examples are presented which illustrate that the solution obtained by the parabolic approximation contains several of the physical phenomena known to occur in wave propagation near an absorbing boundary.
NASA Technical Reports Server (NTRS)
Mcaninch, G. L.; Myers, M. K.
1980-01-01
The parabolic approximation for the acoustic equations of motion is applied to the study of the sound field generated by a plane wave at or near grazing incidence to a finite impedance boundary. It is shown how this approximation accounts for effects neglected in the usual plane wave reflection analysis which, at grazing incidence, erroneously predicts complete cancellation of the incident field by the reflected field. Examples are presented which illustrate that the solution obtained by the parabolic approximation contains several of the physical phenomena known to occur in wave propagation near an absorbing boundary.
Deser, S; Woodard, R P
2007-09-14
We explore nonlocally modified models of gravity, inspired by quantum loop corrections, as a mechanism for explaining current cosmic acceleration. These theories enjoy two major advantages: they allow a delayed response to cosmic events, here the transition from radiation to matter dominance, and they avoid the usual level of fine-tuning; instead, emulating Dirac's dictum, the required large numbers come from the large time scales involved. Their solar system effects are safely negligible, and they may even prove useful to the black hole information problem.
Generalized pseudopotential theory of d-band metals
Moriarty, J.A.
1983-01-01
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.
NASA Astrophysics Data System (ADS)
Terada, Takahide; Yamanaka, Kazuhiro; Suzuki, Atsuro; Tsubota, Yushi; Wu, Wenjing; Kawabata, Ken-ichi
2017-07-01
Ultrasound computed tomography (USCT) is promising for a non-invasive, painless, operator-independent and quantitative system for breast-cancer screening. Assembly error, production tolerance, and aging-degradation variations of the hardwire components, particularly of plane-wave-based USCT systems, may hamper cost effectiveness, precise imaging, and robust operation. The plane wave is transmitted from a ring-shaped transducer array for receiving the signal at a high signal-to-noise-ratio and fast aperture synthesis. There are four signal-delay components: response delays in the transmitters and receivers and propagation delays depending on the positions of the transducer elements and their directivity. We developed a highly precise calibration method for calibrating these delay components and evaluated it with our prototype plane-wave-based USCT system. Our calibration method was found to be effective in reducing delay errors. Gaps and curves were eliminated from the plane wave, and echo images of wires were sharpened in the entire imaging area.
NASA Astrophysics Data System (ADS)
Zhou, Changguo; Haber, Fred; Jaggard, Dwight L.
1991-02-01
The authors present a deterministic approach to the resolution analysis of the MUSIC algorithm for resolving plane waves contaminated by coherent interference when ensemble average covariance matrices are used. In the analysis, a resolution measure to describe the resolution potential of MUSIC in resolving two plane waves in noise is introduced. A closed-form solution for the resolution measure is given, and the result is compared to the resolution threshold derived by Kaveh and Barabell (1986) when the covariance matrices are estimated from a finite number of snapshots. In the presence of coherent interference, the resolution potential of MUSIC is severely limited, determined mainly by the signal-to-interference ratio (SIR). An approximate expression for the threshold SIR is derived for the cases when SIRs are large and the coherent interference and direct arrivals are well separated in spatial frequency. In these cases, it is shown that the threshold SIR is inversely proportional to the resolution measure, and the spectral estimates at the spatial frequencies of plane wave arrivals are approximately equal to the SIR when the arrivals are resolved. Illustrations are given, using an 11-element uniform array, for the cases of plane wave reflection from an infinite plane and scattering from an infinite conducting circular cylinder.
A projection-free method for representing plane-wave DFT results in an atom-centered basis
Dunnington, Benjamin D.; Schmidt, J. R.
2015-09-14
Plane wave density functional theory (DFT) is a powerful tool for gaining accurate, atomic level insight into bulk and surface structures. Yet, the delocalized nature of the plane wave basis set hinders the application of many powerful post-computation analysis approaches, many of which rely on localized atom-centered basis sets. Traditionally, this gap has been bridged via projection-based techniques from a plane wave to atom-centered basis. We instead propose an alternative projection-free approach utilizing direct calculation of matrix elements of the converged plane wave DFT Hamiltonian in an atom-centered basis. This projection-free approach yields a number of compelling advantages, including strict orthonormality of the resulting bands without artificial band mixing and access to the Hamiltonian matrix elements, while faithfully preserving the underlying DFT band structure. The resulting atomic orbital representation of the Kohn-Sham wavefunction and Hamiltonian provides a gateway to a wide variety of analysis approaches. We demonstrate the utility of the approach for a diverse set of chemical systems and example analysis approaches.
The strain in the array is mainly in the plane (waves below ~1 Hz)
Gomberg, J.; Pavlis, G.; Bodin, P.
1999-01-01
We compare geodetic and single-station methods of measuring dynamic deformations and characterize their causes in the frequency bands 0.5-1.0 Hz and 4.0-8.0 Hz. The geodetic approach utilizes data from small-aperture seismic arrays, applying techniques from geodesy. It requires relatively few assumptions and a priori information. The single-station method uses ground velocities recorded at isolated or single stations and assumes all the deformation is due to plane-wave propagation. It also requires knowledge of the azimuth and horizontal velocity of waves arriving at the recording station. Data employed come from a small-aperture, dense seismic array deployed in Geyokcha, Turkmenistan, and include seismograms recorded by broadband STS2 and short-period L28 sensors. Poor agreement between geodetic and single-station estimates in the 4.0-8.0 Hz passband indicates that the displacement field may vary nonlinearly with distance over distances of ~50 m. STS2 geodetic estimates provide a robust standard in the 0.5-1.0 Hz passband because they appear to be computationally stable and require fewer assumptions than single-station estimates. The agreement between STS2 geodetic estimates and single-station L28 estimates is surprisingly good for the S-wave and early surface waves, suggesting that the single-station analysis should be useful with commonly available data. These results indicate that, in the 0.5 to 1.0 Hz passband, the primary source of dynamic deformation is plane-wave propagation along great-circle source-receiver paths. For later arriving energy, the effects of scattering become important. The local structure beneath the array exerts a strong control on the geometry of the dynamic deformation, implying that it may be difficult to infer source characteristics of modern or paleoearthquakes from indicators of dynamic deformations. However, strong site control also suggests that the dynamic deformations may be predictable, which would be useful for engineering
3D resolution tests of two-plane wave approach using synthetic seismograms
NASA Astrophysics Data System (ADS)
Ceylan, S.; Larmat, C. S.; Sandvol, E. A.
2012-12-01
Two-plane wave tomography (TPWT) is becoming a standard approach to obtain fundamental mode Rayleigh wave phase velocities for a variety of tectonic settings. A recent study by Ceylan et al. (2012) has applied this method to eastern Tibet, using data from INDEPTH-IV and Namche-Barwa seismic experiments. The TPWT assumes that distortion of wavefronts at each station can be expressed as the sum of two plane waves. However, there is currently no robust or complete resolution test for TPWT, to address its limitations such as wavefront healing. In this study, we test the capabilities of TPWT and resolution of INDEPTH-IV seismic experiment, by performing 3D resolution tests using synthetic seismograms. Utilizing SPECFEM3D software, we compute synthetic data sets resolving periods down to ~30 s. We implement a checkerboard upper mantle (for depths between 50 and 650 km) with variable cell sizes, superimposed to PREM as the background model. We then calculate fundamental mode surface wave phase velocities using TPWT for periods between 33-143 seconds, using synthetic seismograms computed from our three dimensional hypothetical model. Assuming a constant Poisson's ratio, we use partial derivatives from Saito (1988) to invert for shear wave velocities. We show that the combination of TPWT and Saito (1988) methods is capable of retrieving anomalies down to depths of ~200 km for Rayleigh waves. Below these depths, we observe evidence of both lateral and vertical smearing. We also find that the traditional method for estimating the resolution of TPWT consistently overestimates phase velocity resolutions. Love waves exhibit adequate resolution down to depths of ~100 km. At depths greater than 100 km, smearing is more evident in SH wave results than those of SV waves. Increased smearing of SH waves is most probably due to propagation characteristics and shallower sensitivity of Love waves. Our results imply that TPWT can be applied to Love waves, making future investigations of
ABINIT: Plane-Wave-Based Density-Functional Theory on High Performance Computers
NASA Astrophysics Data System (ADS)
Torrent, Marc
2014-03-01
For several years, a continuous effort has been produced to adapt electronic structure codes based on Density-Functional Theory to the future computing architectures. Among these codes, ABINIT is based on a plane-wave description of the wave functions which allows to treat systems of any kind. Porting such a code on petascale architectures pose difficulties related to the many-body nature of the DFT equations. To improve the performances of ABINIT - especially for what concerns standard LDA/GGA ground-state and response-function calculations - several strategies have been followed: A full multi-level parallelisation MPI scheme has been implemented, exploiting all possible levels and distributing both computation and memory. It allows to increase the number of distributed processes and could not be achieved without a strong restructuring of the code. The core algorithm used to solve the eigen problem (``Locally Optimal Blocked Congugate Gradient''), a Blocked-Davidson-like algorithm, is based on a distribution of processes combining plane-waves and bands. In addition to the distributed memory parallelization, a full hybrid scheme has been implemented, using standard shared-memory directives (openMP/openACC) or porting some comsuming code sections to Graphics Processing Units (GPU). As no simple performance model exists, the complexity of use has been increased; the code efficiency strongly depends on the distribution of processes among the numerous levels. ABINIT is able to predict the performances of several process distributions and automatically choose the most favourable one. On the other hand, a big effort has been carried out to analyse the performances of the code on petascale architectures, showing which sections of codes have to be improved; they all are related to Matrix Algebra (diagonalisation, orthogonalisation). The different strategies employed to improve the code scalability will be described. They are based on an exploration of new diagonalization
Kawashima, Yukio; Hirao, Kimihiko
2017-03-09
We introduced two methods to correct the singularity in the calculation of long-range Hartree-Fock (HF) exchange for long-range-corrected density functional theory (LC-DFT) calculations in plane-wave basis sets. The first method introduces an auxiliary function to cancel out the singularity. The second method introduces a truncated long-range Coulomb potential, which has no singularity. We assessed the introduced methods using the LC-BLYP functional by applying it to isolated systems of naphthalene and pyridine. We first compared the total energies and the HOMO energies of the singularity-corrected and uncorrected calculations and confirmed that singularity correction is essential for LC-DFT calculations using plane-wave basis sets. The LC-DFT calculation results converged rapidly with respect to the cell size as the other functionals, and their results were in good agreement with the calculated results obtained using Gaussian basis sets. LC-DFT succeeded in obtaining accurate orbital energies and excitation energies. We next applied LC-DFT with singularity correction methods to the electronic structure calculations of the extended systems, Si and SiC. We confirmed that singularity correction is important for calculations of extended systems as well. The calculation results of the valence and conduction bands by LC-BLYP showed good convergence with respect to the number of k points sampled. The introduced methods succeeded in overcoming the singularity problem in HF exchange calculation. We investigated the effect of the singularity correction on the excitation state calculation and found that careful treatment of the singularities is required compared to ground-state calculations. We finally examined the excitonic effect on the band gap of the extended systems. We calculated the excitation energies to the first excited state of the extended systems using a supercell model at the Γ point and found that the excitonic binding energy, supposed to be small for
Nonlocal van der Waals density functional made simple and efficient
NASA Astrophysics Data System (ADS)
Sabatini, Riccardo; Gorni, Tommaso; de Gironcoli, Stefano
2013-01-01
We present a simple revision of the VV10 nonlocal density functional by Vydrov and Van Voorhis [J. Chem. Phys.JCPSA60021-960610.1063/1.3521275 133, 244103 (2010)] for dispersion interactions. Unlike the original functional our modification allows nonlocal correlation energy and its derivatives to be efficiently evaluated in a plane wave framework along the lines pioneered by Román-Pérez and Soler [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.103.096102 103, 096102 (2009)]. Our revised functional maintains the outstanding precision of the original VV10 in noncovalently bound complexes and performs well in representative covalent, ionic, and metallic solids.
Performance bounds for passive sensor arrays operating in a turbulent medium: Plane-wave analysis
NASA Astrophysics Data System (ADS)
Collier, S. L.; Wilson, D. K.
2003-05-01
The performance bounds of a passive acoustic array operating in a turbulent medium with fluctuations described by a von Kármán spectrum are investigated. This treatment considers a single, monochromatic, plane-wave source at near-normal incidence. A line-of-sight propagation path is assumed. The primary interests are in calculating the Cramer-Rao lower bounds of the azimuthal and elevational angles of arrival and in observing how these bounds change with the introduction of additional unknowns, such as the propagation distance, turbulence parameters, and signal-to-noise ratio. In both two and three dimensions, it is found that for large values of the index-of-refraction variance, the Cramer-Rao lower bounds of the angles of arrival increase significantly at large values of the normalized propagation distance. For small values of the index-of-refraction variance and normalized propagation distance, the signal-to-noise ratio is found to be the limiting factor. In the two-dimensional treatment, it is found that the estimate of the angle of arrival will decouple from the estimates of the other parameters with the appropriate choice of array geometry. In three dimensions, again with an appropriate choice of array geometry, the estimates of the azimuth and elevation will decouple from the estimates of the other parameters, but due to the constraints of the model, will remain coupled to one another.
Scaling of plane-wave functions in statistically optimized near-field acoustic holography.
Hald, Jørgen
2014-11-01
Statistically Optimized Near-field Acoustic Holography (SONAH) is a Patch Holography method, meaning that it can be applied in cases where the measurement area covers only part of the source surface. The method performs projections directly in the spatial domain, avoiding the use of spatial discrete Fourier transforms and the associated errors. First, an inverse problem is solved using regularization. For each calculation point a multiplication must then be performed with two transfer vectors--one to get the sound pressure and the other to get the particle velocity. Considering SONAH based on sound pressure measurements, existing derivations consider only pressure reconstruction when setting up the inverse problem, so the evanescent wave amplification associated with the calculation of particle velocity is not taken into account in the regularized solution of the inverse problem. The present paper introduces a scaling of the applied plane wave functions that takes the amplification into account, and it is shown that the previously published virtual source-plane retraction has almost the same effect. The effectiveness of the different solutions is verified through a set of simulated measurements.
Discontinuous Galerkin methods with plane waves for time-harmonic problems
Gabard, Gwenael . E-mail: gabard@soton.ac.uk
2007-08-10
A general framework for discontinuous Galerkin methods in the frequency domain with numerical flux is presented. The main feature of the method is the use of plane waves instead of polynomials to approximate the solution in each element. The method is formulated for a general system of linear hyperbolic equations and is applied to problems of aeroacoustic propagation by solving the two-dimensional linearized Euler equations. It is found that the method requires only a small number of elements per wavelength to obtain accurate solutions and that it is more efficient than high-order DRP schemes. In addition, the conditioning of the method is found to be high but not critical in practice. It is shown that the Ultra-Weak Variational Formulation is in fact a subset of the present discontinuous Galerkin method. A special extension of the method is devised in order to deal with singular solutions generated by point sources like monopoles or dipoles. Aeroacoustic problems with non-uniform flows are also considered and results are presented for the sound radiated from a two-dimensional jet.
The generalized scattering coefficient method for plane wave scattering in layered structures
NASA Astrophysics Data System (ADS)
Liu, Yu; Li, Chao; Wang, Huai-Yu; Zhou, Yun-Song
2017-02-01
The generalized scattering coefficient (GSC) method is pedagogically derived and employed to study the scattering of plane waves in homogeneous and inhomogeneous layered structures. The numerical stabilities and accuracies of this method and other commonly used numerical methods are discussed and compared. For homogeneous layered structures, concise scattering formulas with clear physical interpretations and strong numerical stability are obtained by introducing the GSCs. For inhomogeneous layered structures, three numerical methods are employed: the staircase approximation method, the power series expansion method, and the differential equation based on the GSCs. We investigate the accuracies and convergence behaviors of these methods by comparing their predictions to the exact results. The conclusions are as follows. The staircase approximation method has a slow convergence in spite of its simple and intuitive implementation, and a fine stratification within the inhomogeneous layer is required for obtaining accurate results. The expansion method results are sensitive to the expansion order, and the treatment becomes very complicated for relatively complex configurations, which restricts its applicability. By contrast, the GSC-based differential equation possesses a simple implementation while providing fast and accurate results.
Real-time vector velocity assessment through multigate Doppler and plane waves.
Ricci, Stefano; Bassi, Luca; Tortoli, Piero
2014-02-01
Several ultrasound (US) methods have been recently proposed to produce 2-D velocity vector fields with high temporal and spatial resolution. However, the real-time implementation in US scanners is heavily hampered by the high calculation power required. In this work, we report a real-time vector Doppler imaging method which has been integrated in an open research system. The proposed approach exploits the plane waves transmitted from two sub-arrays of a linear probe to estimate the velocity vectors in 512 sample volumes aligned along the probe axis. The method has been tested for accuracy and reproducibility through simulations and in vitro experiments. Simulations over a 0° to 90° angle range of a 0.5 m/s peak parabolic flow have yielded 0.75° bias and 1.1° standard deviation for direction measurement, and 0.6 cm/s bias with 3.1% coefficient of variation for velocity assessment. In vitro tests have supported the simulation results. Preliminary measurements on the carotid artery of a volunteer have highlighted the real-time system capability of imaging complex flow configurations in an intuitive, easy, and quick way, as shown in a sample supplementary movie. These features have allowed reproducible peak velocity measurements to be obtained, as needed for quantitative investigations on patients.
Plane wave expansion method used to engineer photonic crystal sensors with high efficiency.
Antos, Roman; Vozda, Vojtech; Veis, Martin
2014-02-10
A photonic crystal waveguide (PhC-WG) was reported to be usable as an optical sensor highly sensitive to various material parameters, which can be detected via changes in transmission through the PhC-WG caused by small changes of the refractive index of the medium filling its holes. To monitor these changes accurately, a precise optical model is required, for which the plane wave expansion (PWE) method is convenient. We here demonstrate the revision of the PWE method by employing the complex Fourier factorization approach, which enables the calculation of dispersion diagrams with fast convergence, i.e., with high precision in relatively short time. The PhC-WG is proposed as a line defect in a hexagonal array of cylindrical holes periodically arranged in bulk silicon, filled with a variable medium. The method of monitoring the refractive index changes is based on observing cutoff wavelengths in the PhC-WG dispersion diagrams. The PWE results are also compared with finite-difference time-domain calculations of transmittance carried out on a PhC-WG with finite dimensions.
A plane wave source with minimal harmonic distortion for investigating nonlinear acoustic properties
Lloyd, Christopher W.; Wallace, Kirk D.; Holland, Mark R.; Miller, James G.
2008-01-01
The objective of this investigation is to introduce and validate a practical ultrasound source to be used in the investigation of the nonlinear material properties of liquids and soft tissues studied in vitro. Methods based on the progressive distortion of finite amplitude ultrasonic waves in the low megahertz frequency-range are most easily implemented under the assumption of plane wave propagation. However, achieving an approximately planar ultrasonic field over substantial propagation distances can be challenging. Furthermore, undesired harmonic distortion of the ultrasonic field prior to insonification of the specified region of interest represents another serious limitation. This paper introduces an approach based on the use of the ultrasonic field emanating from a stainless-steel delay line. Both simulation and direct experimental measurement demonstrate that such a field exhibits relatively planar wavefronts to a good approximation (such that a 3 mm diameter receiver would be exposed to no more than 3 dB of loss across its face) and is free from the significant harmonic distortion that would occur in a conventional water path. PMID:17614467
Full waveform inversion of marine reflection data in the plane-wave domain
Minkoff, S.E.; Symes, W.W.
1997-03-01
Full waveform inversion of a p-{tau} marine data set from the Gulf of Mexico provides estimates of the long-wavelength P-wave background velocity, anisotropic seismic source, and three high-frequency elastic parameter reflectivities that explain 70% of the total seismic data and 90% of the data in an interval around the gas sand target. The forward simulator is based on a plane-wave viscoelastic model for P-wave propagation and primary reflections in a layered earth. Differential semblance optimization, a variant of output least-squares inversion, successfully estimates the nonlinear P-wave background velocity and linear reflectivities. Once an accurate velocity is estimated, output least-squares inversion reestimates the reflectivities and an anisotropic seismic source simultaneously. The viscoelastic model predicts the amplitude-versus-angle trend in the data more accurately than does an elastic model. Simultaneous inversion for reflectivities and source explains substantially more of the actual data than does inversion for reflectivities with fixed source from an air-gun modeler. The best reflectivity estimates conform to widely accepted lithologic relationships and closely match the filtered well logs.
Effects of Non-Elevation-Focalized Linear Array Transducer on Ultrasound Plane-Wave Imaging
Wang, Congzhi; Xiao, Yang; Xia, Jingjing; Qiu, Weibao; Zheng, Hairong
2016-01-01
Plane-wave ultrasound imaging (PWUS) has become an important method of ultrasound imaging in recent years as its frame rate has exceeded 10,000 frames per second, allowing ultrasound to be used for two-dimensional shear wave detection and functional brain imaging. However, compared to the traditional focusing and scanning method, PWUS images always suffer from a degradation of lateral resolution and contrast. To improve the image quality of PWUS, many different beamforming algorithms have been proposed and verified. Yet the influence of transducer structure is rarely studied. For this paper, the influence of using an acoustic lens for PWUS was evaluated. Two linear array transducers were fabricated. One was not self-focalized in the elevation direction (non-elevation-focalized transducer, NEFT); the other one was a traditional elevation-focalized transducer (EFT). An initial simulation was conducted to show the influence of elevation focusing. Then the images obtained with NEFT on a standard ultrasound imaging phantom were compared with those obtained with EFT. It was demonstrated that, in a relatively deep region, the contrast of an NEFT image is better than that of an EFT image. These results indicate that a more sophisticated design of ultrasound transducer would further improve the image quality of PWUS. PMID:27845751
Stress formulation in the all-electron full-potential linearized augmented plane wave method
NASA Astrophysics Data System (ADS)
Nagasako, Naoyuki; Oguchi, Tamio
2012-02-01
Stress formulation in the linearlized augmented plane wave (LAPW) method has been proposed in 2002 [1] as an extension of the force formulation in the LAPW method [2]. However, pressure calculations only for Al and Si were reported in Ref.[1] and even now stress calculations have not yet been fully established in the LAPW method. In order to make it possible to efficiently relax lattice shape and atomic positions simultaneously and to precisely evaluate the elastic constants in the LAPW method, we reformulate stress formula in the LAPW method with the Soler-Williams representation [3]. Validity of the formulation is tested by comparing the pressure obtained as the trace of stress tensor with that estimated from total energies for a wide variety of material systems. Results show that pressure is estimated within the accuracy of less than 0.1 GPa. Calculations of the shear elastic constant show that the shear components of the stress tensor are also precisely computed with the present formulation [4].[4pt] [1] T. Thonhauser et al., Solid State Commun. 124, 275 (2002).[0pt] [2] R. Yu et al., Phys. Rev. B 43, 6411 (1991).[0pt] [3] J. M. Soler and A. R. Williams, Phys. Rev. B 40, 1560 (1989).[0pt] [4] N. Nagasako and T. Oguchi, J. Phys. Soc. Jpn. 80, 024701 (2011).
Formulation of the Augmented Plane-Wave and Muffin-Tin Orbital Method
NASA Astrophysics Data System (ADS)
Kotani, Takao; Kino, Hiori; Akai, Hisazumu
2015-03-01
The augmented plane waves and the muffin-tin orbitals method (the PMT method) was proposed by Kotani and van Schilfgaarde in http://dx.doi.org/10.1103/PhysRevB.81.125117, Phys. Rev. B 81, 125117 (2010). It is a mixed basis all-electron full-potential method, which uses two types of augmented waves simultaneously, in addition to the local orbitals. In this paper, this mixed basis method is reformulated on the basis of a new formalism named as the 3-component formalism, which is a mathematically transparent version of the additive augmentation originally proposed by Soler and Williams in http://dx.doi.org/10.1103/PhysRevB.47.6784, Phys. Rev. B 47, 6784 (1993). Atomic forces are easily derived systematically. We discuss some problems in the mixed basis method and ways to manage them. In addition, we compare the method with the PAW method on the same footing. This PMT method is the basis for our new development of the quasiparticle self-consistent GW method in http://dx.doi.org/10.7566/JPSJ.83.094711, J. Phys. Soc. Jpn. 83, 094711 (2014), available as the ecalj package at github.
Plane wave holonomies in quantum gravity. II. A sine wave solution
NASA Astrophysics Data System (ADS)
Neville, Donald E.
2015-08-01
This paper constructs an approximate sinusoidal wave packet solution to the equations of canonical gravity. The theory uses holonomy-flux variables with support on a lattice (LHF =lattice-holonomy flux ). There is an SU(2) holonomy on each edge of the LHF simplex, and the goal is to study the behavior of these holonomies under the influence of a passing gravitational wave. The equations are solved in a small sine approximation: holonomies are expanded in powers of sines and terms beyond sin2 are dropped; also, fields vary slowly from vertex to vertex. The wave is unidirectional and linearly polarized. The Hilbert space is spanned by a set of coherent states tailored to the symmetry of the plane wave case. Fixing the spatial diffeomorphisms is equivalent to fixing the spatial interval between vertices of the loop quantum gravity lattice. This spacing can be chosen such that the eigenvalues of the triad operators are large, as required in the small sine limit, even though the holonomies are not large. Appendices compute the energy of the wave, estimate the lifetime of the coherent state packet, discuss circular polarization and coarse-graining, and determine the behavior of the spinors used in the U(N) SHO realization of LQG.
Zhang, Xiao-Zheng; Thomas, Jean-Hugh; Bi, Chuan-Xing; Pascal, Jean-Claude
2012-10-01
A time-domain plane wave superposition method is proposed to reconstruct nonstationary sound fields. In this method, the sound field is expressed as a superposition of time convolutions between the estimated time-wavenumber spectrum of the sound pressure on a virtual source plane and the time-domain propagation kernel at each wavenumber. By discretizing the time convolutions directly, the reconstruction can be carried out iteratively in the time domain, thus providing the advantage of continuously reconstructing time-dependent pressure signals. In the reconstruction process, the Tikhonov regularization is introduced at each time step to obtain a relevant estimate of the time-wavenumber spectrum on the virtual source plane. Because the double infinite integral of the two-dimensional spatial Fourier transform is discretized directly in the wavenumber domain in the proposed method, it does not need to perform the two-dimensional spatial fast Fourier transform that is generally used in time domain holography and real-time near-field acoustic holography, and therefore it avoids some errors associated with the two-dimensional spatial fast Fourier transform in theory and makes possible to use an irregular microphone array. The feasibility of the proposed method is demonstrated by numerical simulations and an experiment with two speakers.
NASA Astrophysics Data System (ADS)
Hospital-Bravo, Raúl; Sarrate, Josep; Díez, Pedro
2016-05-01
A new 2D numerical model to predict the underwater acoustic propagation is obtained by exploring the potential of the Partition of Unity Method (PUM) enriched with plane waves. The aim of the work is to obtain sound pressure level distributions when multiple operational noise sources are present, in order to assess the acoustic impact over the marine fauna. The model takes advantage of the suitability of the PUM for solving the Helmholtz equation, especially for the practical case of large domains and medium frequencies. The seawater acoustic absorption and the acoustic reflectance of the sea surface and sea bottom are explicitly considered, and perfectly matched layers (PML) are placed at the lateral artificial boundaries to avoid spurious reflexions. The model includes semi-analytical integration rules which are adapted to highly oscillatory integrands with the aim of reducing the computational cost of the integration step. In addition, we develop a novel strategy to mitigate the ill-conditioning of the elemental and global system matrices. Specifically, we compute a low-rank approximation of the local space of solutions, which in turn reduces the number of degrees of freedom, the CPU time and the memory footprint. Numerical examples are presented to illustrate the capabilities of the model and to assess its accuracy.
NASA Astrophysics Data System (ADS)
Hayner, Mark; Hynynen, Kullervo
2001-12-01
Ultrasonic transmission and absorption of oblique plane waves through the human skull are analyzed numerically for frequencies ranging from 1/2 to 1 MHz. These frequencies are optimum for noninvasive ultrasound therapy of brain disorders where numerical predictions of skull transmission are used to set the phase and amplitude of source elements in the phased array focusing system. The idealized model of the skull is a three-layer solid with ivory outer and inner layers and a middle marrow layer. Each layer is modeled as a flat, homogeneous, isotropic, linear solid with effective complex wave speeds to account for focused energy losses due to material damping and scattering. The model is used to predict the amplitude and phase of the transmitted wave and volumetric absorption. Results are reported for three different skull thicknesses: 3 mm, 6 mm, and 9 mm. Thickness resonances are observed in the transmitted wave for 3 mm skulls at all frequencies and for the 6 mm skulls below 0.75 MHz. Otherwise, the transmission is dominated by the direct wave. Skull phase errors due to shear waves are shown to minimally degrade the power at the focus for angles of incidence up to 20° from normal even for low material damping. The location of the peak volumetric absorption occurs either in the outer ivory or middle marrow layer and shown to vary due to wave interference.
NASA Astrophysics Data System (ADS)
Woods, D. C.; Bolton, J. S.; Rhoads, J. F.
2016-09-01
A number of applications, for instance ultrasonic imaging and nondestructive testing, involve the transmission of acoustic energy across fluid-solid interfaces into dissipative solids. However, such transmission is generally hindered by the large impedance mismatch at the interface. In order to address this problem, inhomogeneous plane waves were investigated in this work for the purpose of improving the acoustic energy transmission. To this end, under the assumption of linear hysteretic damping, models for fluid-structure interaction were developed that allow for both homogeneous and inhomogeneous incident waves. For low-loss solids, the results reveal that, at the Rayleigh angle, a unique value of the wave inhomogeneity can be found which minimizes the reflection coefficient, and consequently maximizes the transmission. The results also reveal that with sufficient dissipation levels in the solid material, homogeneous incident waves yield lower reflection values than inhomogeneous waves, due to the large degrees of inhomogeneity inherent in the transmitted waves. Analytical conditions have also been derived which predict the dependence of the optimal incident wave type on the dissipation level and wave speeds in the solid medium. Finally, implications related to the use of acoustic beams of limited spatial extent are discussed.
Including the relativistic kinetic energy in a spline-augmented plane-wave band calculation
Fehrenbach, G.M.; Schmidt, G.
1997-03-01
The first-order relativistic correction to the kinetic energy of an electron, the mass-velocity term, is not bounded from below. It can, therefore, not be used within a variational framework. To overcome this deficiency we developed a method to include the entire relativistic kinetic energy {radical}(p{sup 2}c{sup 2}+m{sub 0}{sup 2}c{sup 4}){minus}m{sub 0}c{sup 2} in a spline-augmented plane-wave band calculation. The first results for silver are quite promising, especially for d and p states: The analysis of the energies of the core states as well as of the valence band structure suggests that the energies of d bands are reproduced within 1 mRy. However, the combination of the relativistic kinetic energy with the Darwin term leads to energies which are too low for s-like valence states by 10 mRy. Therefore, the s and d valence band complex is spread out and the Fermi level is lowered by the same amount as the s states. We expect to overcome these deficiencies in future investigations by using a alternative form of the relativistic potential correction along the lines proposed by Douglas and Kroll. {copyright} {ital 1997} {ital The American Physical Society}
NASA Astrophysics Data System (ADS)
Kurz, Ph.; Förster, F.; Nordström, L.; Bihlmayer, G.; Blügel, S.
2004-01-01
The massively parallelized full-potential linearized augmented plane-wave bulk and film program FLEUR for first-principles calculations in the context of density functional theory was adapted to allow calculations of materials with complex magnetic structures—i.e., with noncollinear spin arrangements and incommensurate spin spirals. The method developed makes no shape approximation to the charge density and works with the continuous vector magnetization density in the interstitial and vacuum region and a collinear magnetization density in the spheres. We give an account of the implementation. Important technical aspects, such as the formulation of a constrained local moment method in a full-potential method that works with a vector magnetization density to deal with specific preselected nonstationary-state spin configurations, the inclusion of the generalized gradient approximation in a noncollinear framework, and the spin-relaxation method are discussed. The significance and validity of different approximations are investigated. We present examples to the various strategies to explore the magnetic ground state, metastable states, and magnetic phase diagrams by relaxation of spin arrangements or by performing calculations for constraint spin configurations to invest the functional dependence of the total energy and magnetic moment with respect to external parameters.
Towards a generalized iso-density continuum model for molecular solvents in plane-wave DFT
NASA Astrophysics Data System (ADS)
Gunceler, Deniz; Arias, T. A.
2017-01-01
Implicit electron-density solvation models offer a computationally efficient solution to the problem of calculating thermodynamic quantities of solvated systems from first-principles quantum mechanics. However, despite much recent interest in such models, to date the applicability of such models in the plane-wave context to non-aqueous solvents has been limited because the determination of the model parameters requires fitting to a large database of experimental solvation energies for each new solvent considered. This work presents a simple approach to quickly find approximations to the non-electrostatic contributions to the solvation energy, allowing for development of new iso-density models for a large class of protic and aprotic solvents from only simple, single-molecule ab initio calculations and readily available bulk thermodynamic data. Finally, to illustrate the capabilities of the resulting theory, we also calculate the surface solvation energies of crystalline LiF in various different non-aqueous solvents, and discuss the observed trends and their relevance to lithium battery technology.
On plane-wave relativistic electrodynamics in plasmas and in vacuum
NASA Astrophysics Data System (ADS)
Fiore, Gaetano
2014-06-01
We revisit the exact microscopic equations (in differential, and equivalent integral form) ruling a relativistic cold plasma after the plane-wave Ansatz, without customary approximations. We show that in the Eulerian description the motion of a very diluted plasma initially at rest and excited by an arbitrary transverse plane electromagnetic travelling-wave has a very simple and explicit dependence on the transverse electromagnetic potential; for a non-zero density plasma the above motion is a good approximation of the real one as long as the back-reaction of the charges on the electromagnetic field can be neglected, i.e. for a time lapse decreasing with the plasma density, and can be used as initial step in an iterative resolution scheme. As one of many possible applications, we use these results to describe how the ponderomotive force of a very intense and short plane laser pulse hitting normally the surface of a plasma boosts the surface electrons into the ion background. In response to this penetration, the electrons are pulled back by the electric force exerted by the ions and the other displaced electrons and may leave the plasma with high energy in the direction opposite to that of propagation of the pulse ‘slingshot effect’ (Fiore G et al 2013 arXiv:1309.1400).
Mukhopadhyay, Partha
2009-12-15
In a previous work (arXiv:0902.3750 [hep-th]) we studied the world-sheet conformal invariance for superstrings in the type IIB R-R plane-wave in semi-light-cone gauge. Here we give further justification to the results found in that work through alternative arguments using dynamical supersymmetries. We show that by using the supersymmetry algebra the same quantum definition of the energy-momentum (EM) tensor can be derived. Furthermore, using certain Jacobi identities we indirectly compute the Virasoro anomaly terms by calculating the second-order supersymmetry variation of the EM tensor. Certain integrated forms of all such terms are shown to vanish. In order to deal with various divergences that appear in such computations we take a point-split definition of the same EM tensor. The final results are shown not to suffer from the ordering ambiguity as noticed in the previous work provided the coincidence limit is taken before sending the regularization parameter to zero at the end of the computation.
NASA Astrophysics Data System (ADS)
Coves, A.; San Blas, A. A.; Gimeno, B.; Andres, Miguel V.; Boria, Vincente E.; Vidal, Antonio M.
2004-04-01
In this paper we analyze the frequency response of one-dimensional periodic dielectric gratings under plane wave excitation using a vectorial modal method in combination with the Generalized Scattering Matrix Technique. A very fast and efficient CAD tool has been developed for the analysis of the scattering of such structures, which allows modifying all the electrical and geometrical parameters, as grating period, thickness, frequency, polarization and angle of incidence. We show that ideal reflection (band-stop) filters with high efficiency can be designed by combining guided-mode resonance effects in periodic dielectric gratings with antireflection effects of thin-film structures, providing a symmetrical line shape with near-zero reflectivity over appreciable frequency bands adjacent to the resonance frequency. A reflection filter example employing common dielectric materials illustrates bandwidth control by grating modulation. Moreover, it is shown that the resonance frequency of the filter can be controlled by the angle of incidence. Finally, it is shown a double-band reflection filter using a structure with two gratings with different periods, with the center frequencies determined by the resonances of the individual single-layer waveguide gratings.
NASA Astrophysics Data System (ADS)
Zunger, Alex
2003-03-01
Semiconductor Quantum Dots that are of sufficient structural quality (good crystallinity, surface passivation, size uniformity) to produce ultra sharp spectroscopic lines worthy of a detailed theoretical effort tend to be rather BIG, containing thousands to million atoms. Yet, in this size regime, the only theoretical methods available are effective-mass based, particle-in-a-box approaches, that neglect multi-band and inter-valley coupling, leading to significant qualitative errors.(A. Zunger,Phys. Stat. Sol. (a) 190), 467 (2002). While LDA-based methods are capable of solving the Single-Particle problem even for ˜1,000 atom dots, the all important many-body problem can be currently addressed only for considerably smaller dots. I will present here a computational alternative which addresses both the single-particle and the Manybody parts of the problem for 10^3 to 10^6 atom dots .The method is applicable both to ``free Standing" (e.g. colloidal) dots of CdSe, InP, InAs and Si, as well as to the strained, ``self-assembled" epitaxial dots of, e.g., InGaAs/GaAs. It is based on a ``Linear Combination of Bulk Bands" (LCBB) approach that expands the dot states in terms of plane wave based (pseudopotential) Bloch states throughout the Brillouin zone. The manybody part is treated via Configuration Interaction. I will illustrate how this method addresses some of the recent striking experimental observations on semiconductor quantum dots:(i) Scaling laws for band gaps and exchange interactions (ii) Rapid Auger transitions in colloidal dots (iii) Coulomb Blocade and Spin Blockade in colloidal dots (iv) Charged Excitons (e.g. Trions) in Self-assembled dots, and (v) excitonic Fine-Structure in self assembled dots.
A Initio Pseudopotentials and Structural Properties of Metals.
NASA Astrophysics Data System (ADS)
Lam, Pui Kwong
The Ab initio pseudopotential method and the density functional approach are employed to study the structural properties of metals. The aim of this study is to gain both a qualitative and quantitative understanding of the connection between the macroscopic structural properties of metals and the microscopic core-valence and valence -valence interactions. Emphasis is placed on metals because relatively simple models can be applied in conjunction with the ab initio method to study trends in the structural properties. This thesis is organized as followed: (1) The analytic behavior of the pseudopotentials are examined in order to get acquainted with their variations across the periodic table. The variations of these potentials are in accord with the chemical trends exhibited by the elements. (2) Detailed calculations and analyses of the various structural properties of Al and Be are presented. These properties include equilibrium lattice constant, bulk modulus, cohesive energy, Poisson ratio, phonon frequencies, elastic constants, and temperature and pressure induced crystal phase transitions. The dependence of these properties on the pseudopotentials are extracted from the ab initio calculations. (3) Simple models which generalize some of these relationships between the structural properties and the pseudopotentials are presented. A preliminary application of the ab initio pseudopotential method to a more complicated system, V(,3)Si, is also discussed.
Tan's distributions and Fermi-Huang pseudopotential in momentum space
NASA Astrophysics Data System (ADS)
Valiente, Manuel
2012-01-01
The long-standing question of finding the momentum representation for the s-wave zero-range interaction in three spatial dimensions is here solved. This is done by expressing a certain distribution, introduced in a formal way in [S. Tan, Ann. Phys. (NY)APNYA60003-491610.1016/j.aop.2008.03.004 323, 2952 (2008)], explicitly. The resulting form of the Fourier-transformed pseudopotential remains very simple. Operator forms for the so-called Tan's selectors, which, together with Fermi-Huang pseudopotential, largely simplify the derivation of Tan's universal relations for the Fermi gas, are here derived and are also very simple. A momentum cutoff version of the pseudopotential is also provided, and with this no apparent contradiction to the notion of integrals in Tan's methods is left. The equivalence, even at the intermediate-step level, between the pseudopotential approach and momentum-space renormalization of the bare Dirac delta interaction is then shown by using the explicit form of the cutoff pseudopotential.
Radiation of de-excited electrons at large times in a strong electromagnetic plane wave
Kazinski, P.O.
2013-12-15
The late time asymptotics of the physical solutions to the Lorentz–Dirac equation in the electromagnetic external fields of simple configurations–the constant homogeneous field, the linearly polarized plane wave (in particular, the constant uniform crossed field), and the circularly polarized plane wave–are found. The solutions to the Landau–Lifshitz equation for the external electromagnetic fields admitting a two-parametric symmetry group, which include as a particular case the above mentioned field configurations, are obtained. Some general properties of the total radiation power of a charged particle are established. In particular, for a circularly polarized wave and constant uniform crossed fields, the total radiation power in the asymptotic regime is independent of the charge and the external field strength, when expressed in terms of the proper-time, and equals a half the rest energy of a charged particle divided by its proper-time. The spectral densities of the radiation power formed on the late time asymptotics are derived for a charged particle moving in the external electromagnetic fields of the simple configurations pointed above. This provides a simple method to verify experimentally that the charged particle has reached the asymptotic regime. -- Highlights: •Late time asymptotics of the solutions to the Lorentz–Dirac equation are studied. •General properties of the total radiation power of electrons are established. •The total radiation power equals a half the rest energy divided by the proper-time. •Spectral densities of radiation formed on the late time asymptotics are derived. •Possible experimental verification of the results is proposed.
Robust angle-independent blood velocity estimation based on dual-angle plane wave imaging.
Fadnes, Solveig; Ekroll, Ingvild Kinn; Nyrnes, Siri Ann; Torp, Hans; Lovstakken, Lasse
2015-10-01
Two-dimensional blood velocity estimation has shown potential to solve the angle-dependency of conventional ultrasound flow imaging. Clutter filtering, however, remains a major challenge for large beam-to-flow angles, leading to signal drop-outs and corrupted velocity estimates. This work presents and evaluates a compounding speckle tracking (ST) algorithm to obtain robust angle-independent 2-D blood velocity estimates for all beam-to-flow angles. A dual-angle plane wave imaging setup with full parallel receive beamforming is utilized to achieve high-frame-rate speckle tracking estimates from two scan angles, which may be compounded to obtain velocity estimates of increased robustness. The acquisition also allows direct comparison with vector Doppler (VD) imaging. Absolute velocity bias and root-mean-square (RMS) error of the compounding ST estimations were investigated using simulations of a rotating flow phantom with low velocities ranging from 0 to 20 cm/s. In a challenging region where the estimates were influenced by clutter filtering, the bias and RMS error for the compounding ST estimates were 11% and 2 cm/s, a significant reduction compared with conventional single-angle ST (22% and 4 cm/s) and VD (36% and 6 cm/s). The method was also tested in vivo for vascular and neonatal cardiac imaging. In a carotid artery bifurcation, the obtained blood velocity estimates showed that the compounded ST method was less influenced by clutter filtering than conventional ST and VD methods. In the cardiac case, it was observed that ST velocity estimation is more affected by low signal-to-noise (SNR) than VD. However, with sufficient SNR the in vivo results indicated that a more robust angle-independent blood velocity estimator is obtained using compounded speckle tracking compared with conventional ST and VD methods.
Fast color flow mode imaging using plane wave excitation and temporal encoding
NASA Astrophysics Data System (ADS)
Udesen, Jesper; Gran, Fredrik; Jensen, Jorgen A.
2005-04-01
In conventional ultrasound color flow mode imaging, a large number (~500) of pulses have to be emitted in order to form a complete velocity map. This lowers the frame-rate and temporal resolution. A method for color flow imaging in which a few (~10) pulses have to be emitted to form a complete velocity image is presented. The method is based on using a plane wave excitation with temporal encoding to compensate for the decreased SNR, resulting from the lack of focusing. The temporal encoding is done with a linear frequency modulated signal. To decrease lateral sidelobes, a Tukey window is used as apodization on the transmitting aperture. The data are beamformed along the direction of the flow, and the velocity is found by 1-D cross correlation of these data. First the method is evaluated in simulations using the Field II program. Secondly, the method is evaluated using the experimental scanner RASMUS and a 7 MHz linear array transducer, which scans a circulating flowrig. The velocity of the blood mimicking fluid in the flowrig is constant and parabolic, and the center of the scanned area is situated at a depth of 40 mm. A CFM image of the blood flow in the flowrig is estimated from two pulse emissions. At the axial center line of the CFM image, the velocity is estimated over the vessel with a mean relative standard deviation of 2.64% and a mean relative bias of 6.91%. At an axial line 5 mm to the right of the center of the CFM image, the velocity is estimated over the vessel with a relative standard deviation of 0.84% and a relative bias of 5.74%. Finally the method is tested on the common carotid artery of a healthy 33-year-old male.
NASA Astrophysics Data System (ADS)
Gauthier, Robert C.; Alzahrani, Mohammed A.; Jafari, Seyed Hamed
2015-02-01
The plane wave expansion (PWM) technique applied to Maxwell's wave equations provides researchers with a supply of information regarding the optical properties of dielectric structures. The technique is well suited for structures that display a linear periodicity. When the focus is directed towards optical resonators and structures that lack linear periodicity the eigen-process can easily exceed computational resources and time constraints. In the case of dielectric structures which display cylindrical or spherical symmetry, a coordinate system specific set of basis functions have been employed to cast Maxwell's wave equations into an eigen-matrix formulation from which the resonator states associated with the dielectric profile can be obtained. As for PWM, the inverse of the dielectric and field components are expanded in the basis functions (Fourier-Fourier-Bessel, FFB, in cylindrical and Fourier- Bessel-Legendre, BLF, in spherical) and orthogonality is employed to form the matrix expressions. The theoretical development details will be presented indicating how certain mathematical complications in the process have been overcome and how the eigen-matrix can be tuned to a specific mode type. The similarities and differences in PWM, FFB and BLF are presented. In the case of structures possessing axial cylindrical symmetry, the inclusion of the z axis component of propagation constant makes the technique applicable to photonic crystal fibers and other waveguide structures. Computational results will be presented for a number of different dielectric geometries including Bragg ring resonators, cylindrical space slot channel waveguides and bottle resonators. Steps to further enhance the computation process will be reported.
Generalized Pseudopotentials for the Anisotropic Fractional Quantum Hall Effect
NASA Astrophysics Data System (ADS)
Yang, Bo; Hu, Zi-Xiang; Lee, Ching Hua; Papić, Z.
2017-04-01
We generalize the notion of Haldane pseudopotentials to anisotropic fractional quantum Hall (FQH) systems that are physically realized, e.g., in tilted magnetic field experiments or anisotropic band structures. This formalism allows us to expand any translation-invariant interaction over a complete basis, and directly reveals the intrinsic metric of incompressible FQH fluids. We show that purely anisotropic pseudopotentials give rise to new types of bound states for small particle clusters in the infinite plane, and can be used as a diagnostic of FQH nematic order. We also demonstrate that generalized pseudopotentials quantify the anisotropic contribution to the effective interaction potential, which can be particularly large in models of fractional Chern insulators.
Relativistic small-core pseudopotentials for actinium, thorium, and protactinium.
Weigand, Anna; Cao, Xiaoyan; Hangele, Tim; Dolg, Michael
2014-04-03
Small-core pseudopotentials for actinium, thorium, and protactinium have been energy-adjusted to multiconfiguration Dirac-Hartree-Fock reference data based on the Dirac-Coulomb-Breit Hamiltonian and the Fermi nucleus model. Corresponding optimized valence basis sets of polarized valence quadruple-ζ quality are presented. Atomic test calculations for the first four ionization potentials show satisfactory results at both the Hartree-Fock and the multireference averaged coupled-pair functional level. Highly correlated Fock-space coupled cluster calculations demonstrate that the new pseudopotentials yield ionization potentials, which are in excellent agreement with corresponding all-electron results and experimental data. The pseudopotentials and basis sets supplement a similar set previously published for uranium.
Contact angles in the pseudopotential lattice Boltzmann modeling of wetting
NASA Astrophysics Data System (ADS)
Li, Qing; Luo, K. H.; Kang, Q. J.; Chen, Q.
2014-11-01
In this paper we investigate the implementation of contact angles in the pseudopotential lattice Boltzmann modeling of wetting at a large density ratio ρL/ρV=500 . The pseudopotential lattice Boltzmann model [X. Shan and H. Chen, Phys. Rev. E 49, 2941 (1994), 10.1103/PhysRevE.49.2941] is a popular mesoscopic model for simulating multiphase flows and interfacial dynamics. In this model the contact angle is usually realized by a fluid-solid interaction. Two widely used fluid-solid interactions, the density-based interaction and the pseudopotential-based interaction, as well as a modified pseudopotential-based interaction formulated in the present paper are numerically investigated and compared in terms of the achievable contact angles, the maximum and the minimum densities, and the spurious currents. It is found that the pseudopotential-based interaction works well for simulating small static (liquid) contact angles θ <90∘ , however, it is unable to reproduce static contact angles close to 180∘. Meanwhile, it is found that the proposed modified pseudopotential-based interaction performs better in light of the maximum and the minimum densities and is overall more suitable for simulating large contact angles θ >90∘ as compared with the two other types of fluid-solid interactions. Furthermore, the spurious currents are found to be enlarged when the fluid-solid interaction force is introduced. Increasing the kinematic viscosity ratio between the vapor and liquid phases is shown to be capable of reducing the spurious currents caused by the fluid-solid interactions.
Contact angles in the pseudopotential lattice Boltzmann modeling of wetting.
Li, Qing; Luo, K H; Kang, Q J; Chen, Q
2014-11-01
In this paper we investigate the implementation of contact angles in the pseudopotential lattice Boltzmann modeling of wetting at a large density ratio ρ_{L}/ρ_{V}=500. The pseudopotential lattice Boltzmann model [X. Shan and H. Chen, Phys. Rev. E 49, 2941 (1994)10.1103/PhysRevE.49.2941] is a popular mesoscopic model for simulating multiphase flows and interfacial dynamics. In this model the contact angle is usually realized by a fluid-solid interaction. Two widely used fluid-solid interactions, the density-based interaction and the pseudopotential-based interaction, as well as a modified pseudopotential-based interaction formulated in the present paper are numerically investigated and compared in terms of the achievable contact angles, the maximum and the minimum densities, and the spurious currents. It is found that the pseudopotential-based interaction works well for simulating small static (liquid) contact angles θ<90^{∘}, however, it is unable to reproduce static contact angles close to 180^{∘}. Meanwhile, it is found that the proposed modified pseudopotential-based interaction performs better in light of the maximum and the minimum densities and is overall more suitable for simulating large contact angles θ>90^{∘} as compared with the two other types of fluid-solid interactions. Furthermore, the spurious currents are found to be enlarged when the fluid-solid interaction force is introduced. Increasing the kinematic viscosity ratio between the vapor and liquid phases is shown to be capable of reducing the spurious currents caused by the fluid-solid interactions.
NASA Astrophysics Data System (ADS)
Li, C. Y.; Lesselier, D.; Zhong, Y.
2015-07-01
The present work aims at building up a full-wave computational model of electromagnetic nondestructive testing of composite materials produced by stacking up dielectric slabs one over the other. In each such dielectric slab, a periodic array of infinite cylindrical fibers is embedded. Electromagnetic scattering of such a multilayered, fiber-based periodic composite is investigated here for an obliquely incident plane wave, the plane of incidence of which differs from the plane orthogonal to the fibers' axes. Full-wave field representations are given first by multipole and plane wave expansions. Mode matching at boundaries between layers then yields the propagating matrices, which are applied to connect reflection and transmission coefficients of the longitudinal field components. Power reflection and transmission coefficients are obtained from time-averaged Poynting vectors. Numerical experiments with comparisons with known results illustrate the accuracy of the model proposed.
NASA Astrophysics Data System (ADS)
King, B.; Hu, H.
2016-12-01
We consider a scalar particle in a background formed by two counterpropagating plane waves. Two cases are studied: (i) dynamics at a magnetic node and (ii) zero initial transverse canonical momentum. The Lorentz and Klein-Gordon equations are solved for these cases and approximations analyzed. For the magnetic-node solution (homogeneous, time-dependent electric field), the modified Volkov wave function which arises from a high-energy approximation is found to be inaccurate for all energies and the solution itself unstable when the photon emission (nonlinear Compton scattering) is included. For the zero initial transverse canonical momentum case, in both quantum and classical cases, forbidden parameter regimes, absent in the plane-wave model, are identified.
NASA Astrophysics Data System (ADS)
Maity, Narottam; Barik, S. P.; Chaudhuri, P. K.
2016-09-01
In this paper, plane wave propagation in a rotating anisotropic material of general nature under the action of a magnetic field of constant magnitude has been investigated. The material is supposed to be porous in nature and contains voids. Following the concept of [Cowin S. C. and Nunziato, J. W. [1983] “Linear elastic materials with voids,” J. Elasticity 13, 125-147.] the governing equations of motion have been written in tensor notation taking account of rotation, magnetic field effect and presence of voids in the medium and the possibility of plane wave propagation has been examined. A number of particular cases have been derived from our general results to match with previously obtained results in this area. Effects of various parameters on the velocity of wave propagation have been presented graphically.
NASA Astrophysics Data System (ADS)
Hu, Min; Wang, Hailong; Gong, Qian; Wang, Shumin
2017-04-01
A comparison is made between the plane wave basis and variational method. Within the framework of effective-mass approximation theory, the variational and plane wave basis method are used to calculate ground state energy and ground state binding energy in low-dimensional nano-structures under the external electric field. Comparing calculation results, the donor binding energies of ground state display the consistent trend, both of them are strongly dependent on the quantum size, impurity position and external electric field. However, the impurity ground state energy calculated using variational method may be larger than the real value and it results in the smaller binding energy for variational method. In addition, the binding energy is more sensitive to the external electric field for the variational method, which can be seen more clearly from Stark shift.
Skigin, Diana C; Depine, Ricardo A
2008-05-01
We show that the problem of scattering of an obliquely incident plane wave by a general-shaped groove engraved on a perfectly conducting plane, which was recently studied by Basha et al. [J. Opt. Soc. Am. A24, 1647 (2007)], was solved 11 years ago using the same formulation. This method was further extended to deal with a finite number of grooves and also with complex apertures including several nonlossy and lossy dielectrics, as well as real metals.
NASA Astrophysics Data System (ADS)
Filk, Thomas
2013-04-01
In this article I investigate several possibilities to define the concept of "temporal non-locality" within the standard framework of quantum theory. In particular, I analyze the notions of "temporally non-local states", "temporally non-local events" and "temporally non-local observables". The idea of temporally non-local events is already inherent in the standard formalism of quantum mechanics, and Basil Hiley recently defined an operator in order to measure the degree of such a temporal non-locality. The concept of temporally non-local states enters as soon as "clock-representing states" are introduced in the context of special and general relativity. It is discussed in which way temporally non-local measurements may find an interesting application for experiments which test temporal versions of Bell inequalities.
Song, Jong-Won; Giorgi, Giacomo; Yamashita, Koichi; Hirao, Kimihiko
2013-06-28
Integrable singularity in the exact exchange calculations in hybrid functionals is an old and well-known problem in plane-wave basis. Recently, we developed a hybrid functional named Gaussian-attenuating Perdew-Burke-Ernzerhof (Gau-PBE), which uses a Gaussian function as a modified Coulomb potential for the exact exchange. We found that the modified Coulomb potential of Gaussian function enables the exact exchange calculation in plane-wave basis to be singularity-free and, as a result, the Gau-PBE functional shows faster energy convergence on k and q grids for the exact exchange calculations. Also, a tight comparison (same k and q meshes) between Gau-PBE and two other hybrid functionals, i.e., PBE0 and HSE06, indicates Gau-PBE functional as the least computational time consuming. The Gau-PBE functional employed in conjunction with a plane wave basis provides bandgaps with higher accuracy than the PBE0 and HSE06 in agreement with bandgaps previously calculated using Gaussian-type-orbitals.
NASA Astrophysics Data System (ADS)
Nguyen, Phuong Hoa; Hofmann, Karl R.; Paasch, Gernot
2002-11-01
In advanced full-band Monte Carlo (MC) models, the Nordheim approximation with a spherical Wigner-Seitz cell for a lattice with two atoms per elementary cell is still common, and in the most detailed work on silicon by Kunikiyo [et al.] [J. Appl. Phys. 74, 297 (1994)], the atomic positions in the cell have been incorrectly introduced in the phonon scattering rates. In this article the correct expressions for the phonon scattering rates based on the screened pseudopotential are formulated for the case of several atoms per unit cell. Furthermore, the simplest wave number dependent approximation is introduced, which contains an average of the cell structure factor and the acoustic and the optical deformation potentials as two parameters to be fitted. While the band structure is determined by the pseudopotential at the reciprocal lattice vectors, the phonon scattering rates are essentially determined by wave numbers below the smallest reciprocal lattice vector. Thus, in the phonon scattering rates, the pseudopotential form factor is modeled by the simple Ashcroft model potential, in contrast to the full band structure, which is calculated using a nonlocal pseudopotential scheme. The parameter in the Ashcroft model potential is determined using a method based on the equilibrium condition. For the screening of the pseudopotential form factor, the Lindhard dielectric function is used. Compared to the Nordheim approximation with a spherical Wigner-Seitz cell, the approximation results in up to 10% lower phonon scattering rates. Examples from a detailed comparison of the influence of the two deformation potentials on the electron and hole drift velocities are presented for Ge and Si at different temperatures. The results are prerequisite for a well-founded choice of the two deformation potentials as fit parameters and they provide an explanation of the differences between the two materials, the origin of the anisotropy of the drift velocities, and the origin of the dent in
NASA Astrophysics Data System (ADS)
Valavanis, A.; Ikonić, Z.; Kelsall, R. W.
2007-05-01
Intervalley mixing between conduction-band states in low-dimensional Si/SiGe heterostructures induces splitting between nominally degenerate energy levels. The symmetric double-valley effective mass approximation and the empirical pseudopotential method are used to find the electronic states in different types of quantum wells. A reasonably good agreement between the two methods is found, with the former being much faster computationally. Aside from being an oscillatory function of well width, the splitting is found to be almost independent of in-plane wave vector, and an increasing function of the magnitude of interface gradient. While the model is defined for symmetric envelope potentials, it is shown to remain reasonably accurate for slightly asymmetric structures such as a double quantum well, making it acceptable for simulation of multilayer intersubband optical devices. Intersubband optical transitions are investigated under both approximations and it is shown that in most cases valley splitting causes linewidth broadening, although under extreme conditions, transition line doublets may result.
A goal-oriented adaptive finite-element approach for plane wave 3-D electromagnetic modelling
NASA Astrophysics Data System (ADS)
Ren, Zhengyong; Kalscheuer, Thomas; Greenhalgh, Stewart; Maurer, Hansruedi
2013-08-01
We have developed a novel goal-oriented adaptive mesh refinement approach for finite-element methods to model plane wave electromagnetic (EM) fields in 3-D earth models based on the electric field differential equation. To handle complicated models of arbitrary conductivity, magnetic permeability and dielectric permittivity involving curved boundaries and surface topography, we employ an unstructured grid approach. The electric field is approximated by linear curl-conforming shape functions which guarantee the divergence-free condition of the electric field within each tetrahedron and continuity of the tangential component of the electric field across the interior boundaries. Based on the non-zero residuals of the approximated electric field and the yet to be satisfied boundary conditions of continuity of both the normal component of the total current density and the tangential component of the magnetic field strength across the interior interfaces, three a-posterior error estimators are proposed as a means to drive the goal-oriented adaptive refinement procedure. The first a-posterior error estimator relies on a combination of the residual of the electric field, the discontinuity of the normal component of the total current density and the discontinuity of the tangential component of the magnetic field strength across the interior faces shared by tetrahedra. The second a-posterior error estimator is expressed in terms of the discontinuity of the normal component of the total current density (conduction plus displacement current). The discontinuity of the tangential component of the magnetic field forms the third a-posterior error estimator. Analytical solutions for magnetotelluric (MT) and radiomagnetotelluric (RMT) fields impinging on a homogeneous half-space model are used to test the performances of the newly developed goal-oriented algorithms using the above three a-posterior error estimators. A trapezoidal topographical model, using normally incident EM waves
Band structure of W and Mo by empirical pseudopotential method
NASA Technical Reports Server (NTRS)
Sridhar, C. G.; Whiting, E. E.
1977-01-01
The empirical pseudopotential method (EPM) is used to calculate the band structure of tungsten and molybdenum. Agreement between the calculated reflectivity, density of states, density of states at the Fermi surface and location of the Fermi surface from this study and experimental measurements and previous calculations is good. Also the charge distribution shows the proper topological distribution of charge for a bcc crystal.
NASA Astrophysics Data System (ADS)
Narayan Vaidya, Arvind; Barbosa da Silva Filho, Pedro
1999-09-01
The Green function for a charged spin- 1/2 particle with anomalous magnetic moment in the presence of a plane-wave external electromagnetic field is calculated and shown to be simply related to the free-particle one.
Wang, Diya; Zong, Yujin; Yang, Xuan; Hu, Hong; Wan, Jinjin; Zhang, Lei; Bouakaz, Ayache; Wan, Mingxi
2016-07-01
The aim of the study described here was to develop an ultrasound contrast plane wave imaging (PWI) method based on pulse-inversion bubble wavelet transform imaging (PIWI) to improve the contrast-to-tissue ratio of contrast images. A pair of inverted "bubble wavelets" with plane waves was constructed according to the modified Herring equation. The original echoes were replaced by the maximum wavelet correlation coefficients obtained from bubble wavelet correlation analysis. The echoes were then summed to distinguish microbubbles from tissues. In in vivo experiments on rabbit kidney, PIWI improved the contrast-to-tissue ratio of contrast images up to 4.5 ± 1.5 dB, compared with that obtained in B-mode (p < 0.05), through use of a pair of inverted plane waves. The disruption rate and infusion time of microbubbles in PIWI-based PWI were then quantified using two perfusion parameters, area under the curve and half transmit time estimated from time-intensity curves, respectively. After time-intensity curves were denoised by detrended fluctuation analysis, the average area under the curve and half transit time of PIWI-based PWI were 55.94% (p < 0.05) and 20.51% (p < 0.05) higher than those of conventional focused imaging, respectively. Because of its high contrast-to-tissue ratio and low disruption of microbubbles, PIWI-based PWI has a long infusion time and is therefore beneficial for transient monitoring and perfusion assessment of microbubbles circulating in vessels. Copyright © 2016 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.
Application of norm-conserving pseudopotentials to intense laser-matter interactions
NASA Astrophysics Data System (ADS)
Tong, Xiao-Min; Wachter, Georg; Sato, Shunsuke A.; Lemell, Christoph; Yabana, Kazuhiro; Burgdörfer, Joachim
2015-10-01
We investigate the applicability of norm-conserving pseudopotentials to intense laser-matter interactions by performing time-dependent density functional theory simulations with an all-electron potential and with norm-conserving pseudopotentials. We find pseudopotentials to be reliable for the simulation of above-threshold ionization over a broad range of laser intensities both for the total ionization probability and the photoelectron energy spectrum. For the simulation of high-order-harmonic generation, pseudopotentials are shown to be applicable for lower-order harmonics in the spectral range in which the one-photon recombination dipole-matrix element can be recovered by the pseudopotential calculation.
NASA Astrophysics Data System (ADS)
Takenaka, H.; Okamoto, T.; Nakamura, T.
2009-12-01
We propose a novel approach for calculating response of three-dimensionally (3D) heterogeneous structure model to an oblique incidence of seismic plane wave with the finite-difference method in the time-domain (FDTD). Computation of seismic response to a plane-wave incidence has many applications of practical interest such as synthesis of teleseismic body waves for source inversion or receiver function analysis, and evaluation of basin effects or local site effects of strong ground motion. However, in most cases of those applications horizontally layered media have been locally employed except recent works based on 2.5D FDTD of Takenaka and Okamoto (1997) which can calculate the 3D response of a 2D heterogeneous model. It has been difficult to calculate the response of a 3D heterogeneous model mainly because of a technical issue. In modeling of seismic wavefields with domain methods such as the FDTD, special manipulation called non-reflecting boundary or absorbing boundary condition is necessary for suppressing the spurious reflections from the boundaries of the computational domain. In 3D modeling some methods are effective for source excitation problems, while for oblique plane-wave incidence problems, as far as we know, almost no method is effective at the side boundaries. Strong artificial reflections from the plane wave at the side boundaries contaminate the computed wavefields. In 2D modeling we could use large computational domain so that the artificial waves arrive at the study area after the all target phases completely pass there. However, in 3D modeling adopting such simple approach is difficult because of its huge requirements of computer memory and CPU time. Here we present a breakthrough to overcome this technical issue. It is a field splitting approach to the discretization of the Floquet transformed elastodynamic equations. This approach was originally introduced by Roden et al. (1998, IEEE TMTT) for implementing periodic boundary conditions into
Plane-wave and common-translation-factor treatments of He sup 2+ +H collisions at high velocities
Errea, L.F. ); Harel, C.; Jouin, H. ); Maidagan, J.M.; Mendez, L. ); Pons, B. ); Riera, A. )
1992-11-01
We complement previous work that showed that the molecular approach, modified with plane-wave translation factors, is able to reproduce the fall of charge-exchange cross sections in He{sup 2+}+H collisions, by presenting the molecular data, and studying the corresponding mechanism. We test the accuracy of simplifications of the method that have been employed in the literature, and that lead to very simple calculations. We show that the common-translation-factor method is also successful at high nuclear velocities, provided that sufficiently excited states are included in the basis; moreover, it yields a simple picture of the mechanism and a description of ionization processes at high velocities.
Definitions of multipartite nonlocality
NASA Astrophysics Data System (ADS)
Bancal, Jean-Daniel; Barrett, Jonathan; Gisin, Nicolas; Pironio, Stefano
2013-07-01
In a multipartite setting, it is possible to distinguish quantum states that are genuinely n-way entangled from those that are separable with respect to some bipartition. Similarly, the nonlocal correlations that can arise from measurements on entangled states can be classified into those that are genuinely n-way nonlocal, and those that are local with respect to some bipartition. Svetlichny introduced an inequality intended as a test for genuine tripartite nonlocality. This work introduces two alternative definitions of n-way nonlocality, which we argue are better motivated both from the point of view of the study of nature, and from the point of view of quantum information theory. We show that these definitions are strictly weaker than Svetlichny's, and introduce a series of suitable Bell-type inequalities for the detection of three-way nonlocality. Numerical evidence suggests that all three-way entangled pure quantum states can produce three-way nonlocal correlations.
The electrical transport properties of liquid Rb using pseudopotential theory
Patel, A. B. Bhatt, N. K. Thakore, B. Y. Jani, A. R.; Vyas, P. R.
2014-04-24
Certain electric transport properties of liquid Rb are reported. The electrical resistivity is calculated by using the self-consistent approximation as suggested by Ferraz and March. The pseudopotential due to Hasegawa et al for full electron-ion interaction, which is valid for all electrons and contains the repulsive delta function due to achieve the necessary s-pseudisation was used for the calculation. Temperature dependence of structure factor is considered through temperature dependent potential parameter in the pair potential. Finally, thermo-electric power and thermal conductivity are obtained. The outcome of the present study is discussed in light of other such results, and confirms the applicability of pseudopotential at very high temperature via temperature dependent pair potential.
Oxley, M.P.; Cosgriff, E.C.; Allen, L.J.
2005-05-27
We show how an effective nonlocality in imaging can lead to the sampling of a spatial region which is not significantly illuminated by an imaging probe. The nonlocality is embodied in the effective nonlocal potential describing inelastic scattering which occurs when coupled channel Schroedinger equations are reduced to a single integro-differential equation. The context in which this prediction will be illustrated is atomic resolution imaging based on energy-loss spectroscopy in scanning transmission electron microscopy.
Oxley, M P; Cosgriff, E C; Allen, L J
2005-05-27
We show how an effective nonlocality in imaging can lead to the sampling of a spatial region which is not significantly illuminated by an imaging probe. The nonlocality is embodied in the effective nonlocal potential describing inelastic scattering which occurs when coupled channel Schrödinger equations are reduced to a single integro-differential equation. The context in which this prediction will be illustrated is atomic resolution imaging based on energy-loss spectroscopy in scanning transmission electron microscopy.
NASA Astrophysics Data System (ADS)
Mashhoon, Bahram
2014-12-01
A brief account of the present status of the recent nonlocal generalization of Einstein's theory of gravitation is presented. The main physical assumptions that underlie this theory are described. We clarify the physical meaning and significance of Weitzenbock's torsion and emphasize its intimate relationship with the gravitational field, characterized by the Riemannian curvature of spacetime. In this theory, nonlocality can simulate dark matter; in fact, in the Newtonian regime, we recover the phenomenological Tohline-Kuhn approach to modified gravity. To account for the observational data regarding dark matter, nonlocality is associated with a characteristic length scale of order 1 kpc. The confrontation of nonlocal gravity with observation is briefly discussed.
Kilcrease, D. P.; Brookes, S.
2013-08-19
The modeling of NLTE plasmas requires the solution of population rate equations to determine the populations of the various atomic levels relevant to a particular problem. The equations require many cross sections for excitation, de-excitation, ionization and recombination. Additionally, a simple and computational fast way to calculate electron collisional excitation cross-sections for ions is by using the plane-wave Born approximation. This is essentially a high-energy approximation and the cross section suffers from the unphysical problem of going to zero near threshold. Various remedies for this problem have been employed with varying degrees of success. We present a correction procedure formore » the Born cross-sections that employs the Elwert–Sommerfeld factor to correct for the use of plane waves instead of Coulomb waves in an attempt to produce a cross-section similar to that from using the more time consuming Coulomb Born approximation. We compare this new approximation with other, often employed correction procedures. Furthermore, we also look at some further modifications to our Born Elwert procedure and its combination with Y.K. Kim's correction of the Coulomb Born approximation for singly charged ions that more accurately approximate convergent close coupling calculations.« less
Chae, Byung Gyu
2014-05-20
We carry out a comparative analysis on a viewing angle change in Fresnel and Fourier holographic images reconstructed by a tilted plane wave. A tilted plane wave illuminating an on-axis hologram generates a diffractive wave carrying the holographic image in a paraxial region of a new diffraction axis. The reconstructed image in the Fresnel hologram is deformed along the new viewing direction, which is well described as Affine transformation. In the Fourier holographic image, the replica of the image is formed without its deformation when the hologram is placed in the front focal plane of the lens, whereas in the case of a hologram that is located at a distance different from a focal length, image deformation arises. This property is investigated through numerical simulation based on a wide-angle diffraction phenomenon. We also perform a similar interpretation for high-order diffraction images appearing in the sampled Fourier hologram and discuss a method for enlarging the viewing angle of the holographic image.
Li, Xiang-Guo; Chu, Iek-Heng; Zhang, X. -G.; Cheng, Hai-Ping
2015-05-28
Electron transport in graphene is along the sheet but junction devices are often made by stacking different sheets together in a “side-contact” geometry which causes the current to flow perpendicular to the sheets within the device. Such geometry presents a challenge to first-principles transport methods. We solve this problem by implementing a plane-wave-based multiple-scattering theory for electron transport. In this study, this implementation improves the computational efficiency over the existing plane-wave transport code, scales better for parallelization over large number of nodes, and does not require the current direction to be along a lattice axis. As a first application, we calculate the tunneling current through a side-contact graphene junction formed by two separate graphene sheets with the edges overlapping each other. We find that transport properties of this junction depend strongly on the AA or AB stacking within the overlapping region as well as the vacuum gap between two graphene sheets. Finally, such transport behaviors are explained in terms of carbon orbital orientation, hybridization, and delocalization as the geometry is varied.
NASA Astrophysics Data System (ADS)
Kilcrease, D. P.; Brookes, S.
2013-12-01
The modeling of NLTE plasmas requires the solution of population rate equations to determine the populations of the various atomic levels relevant to a particular problem. The equations require many cross sections for excitation, de-excitation, ionization and recombination. A simple and computational fast way to calculate electron collisional excitation cross-sections for ions is by using the plane-wave Born approximation. This is essentially a high-energy approximation and the cross section suffers from the unphysical problem of going to zero near threshold. Various remedies for this problem have been employed with varying degrees of success. We present a correction procedure for the Born cross-sections that employs the Elwert-Sommerfeld factor to correct for the use of plane waves instead of Coulomb waves in an attempt to produce a cross-section similar to that from using the more time consuming Coulomb Born approximation. We compare this new approximation with other, often employed correction procedures. We also look at some further modifications to our Born Elwert procedure and its combination with Y.K. Kim's correction of the Coulomb Born approximation for singly charged ions that more accurately approximate convergent close coupling calculations.
Three-dimensional, prestack, plane wave migration of teleseismic P-to-S converted phases: 1. Theory
NASA Astrophysics Data System (ADS)
Poppeliers, Christian; Pavlis, Gary L.
2003-02-01
We present the theoretical foundations for a prestack migration technique to image teleseismic P-to-S converted phases. The method builds on teleseismic P wave deconvolution, pseudostation stacking [, 1999] and on the idea of using a plane wave decomposition for imaging as introduced by [1982]. Deconvolution operators are constructed by pseudostation stacking of the array aligned to the incident P wave arrival times to produce a space-variable deconvolution operator. The resulting data are then muted to remove the deconvolved direct P wave pulse and pseudostation stacked over a grid of feasible slowness vectors. The pseudostation stack interpolates the wave field onto a regular grid along Earth's surface producing a series (one per slowness vector) of uniformly sampled three-dimensional data cubes (two space variables and time). The plane wave components can be propagated downward using a form of approximate ray tracing with a three-dimensional Earth model. This yields a series of distorted cubes topologically equivalent to the original uniformly sampled data cubes. These data volumes are summed as a weighted stack with the weights derived from an integration formula for inverse scattering based on the generalized Radon transform. This allows an image of the subsurface to be constructed on an event by event basis beneath the array. We apply this technique to data from the Lodore array that was deployed in northwestern Colorado. The results suggest the presence of a major lithospheric-scale discontinuity defined by a south dipping boundary.
NASA Astrophysics Data System (ADS)
Nikolaev, A. V.; Lamoen, D.; Partoens, B.
2016-07-01
In order to increase the accuracy of the linearized augmented plane wave (LAPW) method, we present a new approach where the plane wave basis function is augmented by two different atomic radial components constructed at two different linearization energies corresponding to two different electron bands (or energy windows). We demonstrate that this case can be reduced to the standard treatment within the LAPW paradigm where the usual basis set is enriched by the basis functions of the tight binding type, which go to zero with zero derivative at the sphere boundary. We show that the task is closely related with the problem of extended core states which is currently solved by applying the LAPW method with local orbitals (LAPW+LO). In comparison with LAPW+LO, the number of supplemented basis functions in our approach is doubled, which opens up a new channel for the extension of the LAPW and LAPW+LO basis sets. The appearance of new supplemented basis functions absent in the LAPW+LO treatment is closely related with the existence of the u ˙ l -component in the canonical LAPW method. We discuss properties of additional tight binding basis functions and apply the extended basis set for computation of electron energy bands of lanthanum (face and body centered structures) and hexagonal close packed lattice of cadmium. We demonstrate that the new treatment gives lower total energies in comparison with both canonical LAPW and LAPW+LO, with the energy difference more pronounced for intermediate and poor LAPW basis sets.
Kilcrease, D. P.; Brookes, S.
2013-08-19
The modeling of NLTE plasmas requires the solution of population rate equations to determine the populations of the various atomic levels relevant to a particular problem. The equations require many cross sections for excitation, de-excitation, ionization and recombination. Additionally, a simple and computational fast way to calculate electron collisional excitation cross-sections for ions is by using the plane-wave Born approximation. This is essentially a high-energy approximation and the cross section suffers from the unphysical problem of going to zero near threshold. Various remedies for this problem have been employed with varying degrees of success. We present a correction procedure for the Born cross-sections that employs the Elwert–Sommerfeld factor to correct for the use of plane waves instead of Coulomb waves in an attempt to produce a cross-section similar to that from using the more time consuming Coulomb Born approximation. We compare this new approximation with other, often employed correction procedures. Furthermore, we also look at some further modifications to our Born Elwert procedure and its combination with Y.K. Kim's correction of the Coulomb Born approximation for singly charged ions that more accurately approximate convergent close coupling calculations.
NASA Astrophysics Data System (ADS)
Gao, Jing Kun; Qin, Yu Liang; Deng, Bin; Wang, Hong Qiang; Li, Jin; Li, Xiang
2016-04-01
This paper presents two parts of work around terahertz imaging applications. The first part aims at solving the problems occurred with the increasing of the rotation angle. To compensate for the nonlinearity of terahertz radar systems, a calibration signal acquired from a bright target is always used. Generally, this compensation inserts an extra linear phase term in the intermediate frequency (IF) echo signal which is not expected in large-rotation angle imaging applications. We carried out a detailed theoretical analysis on this problem, and a minimum entropy criterion was employed to estimate and compensate for the linear-phase errors. In the second part, the effects of spherical wave on terahertz inverse synthetic aperture imaging are analyzed. Analytic criteria of plane-wave approximation were derived in the cases of different rotation angles. Experimental results of corner reflectors and an aircraft model based on a 330-GHz linear frequency-modulated continuous wave (LFMCW) radar system validated the necessity and effectiveness of the proposed compensation. By comparing the experimental images obtained under plane-wave assumption and spherical-wave correction, it also showed to be highly consistent with the analytic criteria we derived.
Torres, Ana M; Lopez, Jose J; Pueo, Basilio; Cobos, Maximo
2013-04-01
Plane-wave decomposition (PWD) methods using microphone arrays have been shown to be a very useful tool within the applied acoustics community for their multiple applications in room acoustics analysis and synthesis. While many theoretical aspects of PWD have been previously addressed in the literature, the practical advantages of the PWD method to assess the acoustic behavior of real rooms have been barely explored so far. In this paper, the PWD method is employed to analyze the sound field inside a selected set of real rooms having a well-defined purpose. To this end, a circular microphone array is used to capture and process a number of impulse responses at different spatial positions, providing angle-dependent data for both direct and reflected wavefronts. The detection of reflected plane waves is performed by means of image processing techniques applied over the raw array response data and over the PWD data, showing the usefulness of image-processing-based methods for room acoustics analysis.
Zhao, Dan
2011-03-01
Perforated liners with a narrow frequency range are widely used as acoustic dampers to stabilize combustion systems. When the frequency of unstable modes present in the combustion system is within the effective frequency range, the liners can efficiently dissipate acoustic waves. The fraction of the incident waves being absorbed (known as power absorption coefficient) is generally used to characterize the liners damping. To estimate it, plane waves either side of the liners need to be decomposed and characterized. For this, a real-time algorithm is developed. Emphasis is being placed on its ability to online decompose plane waves at multiple mode frequencies. The performance of the algorithm is evaluated first in a numerical model with two unstable modes. It is then experimentally implemented in an acoustically driven pipe system with a lined section attached. The acoustic damping of perforated liners is continuously characterized in real-time. Comparison is then made between the results from the algorithm and those from the short-time fast Fourier transform (FFT)-based techniques, which are typically used in industry. It was found that the real-time algorithm allows faster tracking of the liners damping, even when the forcing frequency was suddenly changed.
Li, Xiang-Guo; Chu, Iek-Heng; Zhang, X. -G.; ...
2015-05-28
Electron transport in graphene is along the sheet but junction devices are often made by stacking different sheets together in a “side-contact” geometry which causes the current to flow perpendicular to the sheets within the device. Such geometry presents a challenge to first-principles transport methods. We solve this problem by implementing a plane-wave-based multiple-scattering theory for electron transport. In this study, this implementation improves the computational efficiency over the existing plane-wave transport code, scales better for parallelization over large number of nodes, and does not require the current direction to be along a lattice axis. As a first application, wemore » calculate the tunneling current through a side-contact graphene junction formed by two separate graphene sheets with the edges overlapping each other. We find that transport properties of this junction depend strongly on the AA or AB stacking within the overlapping region as well as the vacuum gap between two graphene sheets. Finally, such transport behaviors are explained in terms of carbon orbital orientation, hybridization, and delocalization as the geometry is varied.« less
Quantum Nonlocality and Reality
NASA Astrophysics Data System (ADS)
Bell, Mary; Gao, Shan
2016-09-01
Preface; Part I. John Stewart Bell: The Physicist: 1. John Bell: the Irish connection Andrew Whitaker; 2. Recollections of John Bell Michael Nauenberg; 3. John Bell: recollections of a great scientist and a great man Gian-Carlo Ghirardi; Part II. Bell's Theorem: 4. What did Bell really prove? Jean Bricmont; 5. The assumptions of Bell's proof Roderich Tumulka; 6. Bell on Bell's theorem: the changing face of nonlocality Harvey R. Brown and Christopher G. Timpson; 7. Experimental tests of Bell inequalities Marco Genovese; 8. Bell's theorem without inequalities: on the inception and scope of the GHZ theorem Olival Freire, Jr and Osvaldo Pessoa, Jr; 9. Strengthening Bell's theorem: removing the hidden-variable assumption Henry P. Stapp; Part III. Nonlocality: Illusions or Reality?: 10. Is any theory compatible with the quantum predictions necessarily nonlocal? Bernard d'Espagnat; 11. Local causality, probability and explanation Richard A. Healey; 12. Bell inequality and many-worlds interpretation Lev Vaidman; 13. Quantum solipsism and non-locality Travis Norsen; 14. Lessons of Bell's theorem: nonlocality, yes; action at a distance, not necessarily Wayne C. Myrvold; 15. Bell non-locality, Hardy's paradox and hyperplane dependence Gordon N. Fleming; 16. Some thoughts on quantum nonlocality and its apparent incompatibility with relativity Shan Gao; 17. A reasonable thing that just might work Daniel Rohrlich; 18. Weak values and quantum nonlocality Yakir Aharonov and Eliahu Cohen; Part IV. Nonlocal Realistic Theories: 19. Local beables and the foundations of physics Tim Maudlin; 20. John Bell's varying interpretations of quantum mechanics: memories and comments H. Dieter Zeh; 21. Some personal reflections on quantum non-locality and the contributions of John Bell Basil J. Hiley; 22. Bell on Bohm Sheldon Goldstein; 23. Interactions and inequality Philip Pearle; 24. Gravitation and the noise needed in objective reduction models Stephen L. Adler; 25. Towards an objective
Nonlocal teleparallel cosmology.
Bahamonde, Sebastian; Capozziello, Salvatore; Faizal, Mir; Nunes, Rafael C
2017-01-01
Even though it is not possible to differentiate general relativity from teleparallel gravity using classical experiments, it could be possible to discriminate between them by quantum gravitational effects. These effects have motivated the introduction of nonlocal deformations of general relativity, and similar effects are also expected to occur in teleparallel gravity. Here, we study nonlocal deformations of teleparallel gravity along with its cosmological solutions. We observe that nonlocal teleparallel gravity (like nonlocal general relativity) is consistent with the present cosmological data obtained by SNe Ia + BAO + CC + [Formula: see text] observations. Along this track, future experiments probing nonlocal effects could be used to test whether general relativity or teleparallel gravity gives the most consistent picture of gravitational interaction.
Operational Framework for Nonlocality
NASA Astrophysics Data System (ADS)
Gallego, Rodrigo; Würflinger, Lars Erik; Acín, Antonio; Navascués, Miguel
2012-08-01
Because of the importance of entanglement for quantum information purposes, a framework has been developed for its characterization and quantification as a resource based on the following operational principle: entanglement among N parties cannot be created by local operations and classical communication, even when N-1 parties collaborate. More recently, nonlocality has been identified as another resource, alternative to entanglement and necessary for device-independent quantum information protocols. We introduce an operational framework for nonlocality based on a similar principle: nonlocality among N parties cannot be created by local operations and allowed classical communication even when N-1 parties collaborate. We then show that the standard definition of multipartite nonlocality, due to Svetlichny, is inconsistent with this operational approach: according to it, genuine tripartite nonlocality could be created by two collaborating parties. We finally discuss alternative definitions for which consistency is recovered.
Simple way to apply nonlocal van der Waals functionals within all-electron methods
NASA Astrophysics Data System (ADS)
Tran, Fabien; Stelzl, Julia; Koller, David; Ruh, Thomas; Blaha, Peter
2017-08-01
The method based on fast Fourier transforms proposed by G. Román-Pérez and J. M. Soler [Phys. Rev. Lett. 103, 096102 (2009), 10.1103/PhysRevLett.103.096102], which allows for a computationally fast implementation of the nonlocal van der Waals (vdW) functionals, has significantly contributed to making the vdW functionals popular in solid-state physics. However, the Román-Pérez-Soler method relies on a plane-wave expansion of the electron density; therefore it cannot be applied readily to all-electron densities for which an unaffordable number of plane waves would be required for an accurate expansion. In this work, we present the results for the lattice constant and binding energy of solids that were obtained by applying a smoothing procedure to the all-electron density calculated with the linearized augmented plane-wave method. The smoothing procedure has the advantages of being very simple to implement, basis-set independent, and allowing the calculation of the potential. It is also shown that the results agree very well with those from the literature that were obtained with the projector augmented wave method.
NASA Astrophysics Data System (ADS)
Huang, Yong-Sheng; Wang, Nai-Yan; Tang, Xiu-Zhang
2015-05-01
Contrary to the superposition principle, it is well known that photorefraction exists in the vacuum with the presence of a strong static field, a laser field, or a rotational magnetic field. Different from the classical optical crystals, the refractive index also depends on the phase of the strong electromagnetic field. We obtain the phase and direction dependence of the refractive index of a probe wave incident in the strong field of a circular-polarized plane wave by solving the Maxwell equations corrected by the effective Lagrangian. It may provide a valuable theoretical basis to calculate the polarization evolution of waves in the strong electromagnetic circumstances of pulsar or neutron stars. Project supported by the National Basic Research Program of China (Grant No. 2011CB808104) and the National Natural Science Foundation of China (Grant No. 11105233).
NASA Astrophysics Data System (ADS)
Shapoval, Olga V.; Gomez-Diaz, Juan Sebastian; Perruisseau-Carrier, Julien; Mosig, Juan R.; Nosich, Alexander I.
2013-09-01
The plane wave scattering and absorption by finite and infinite gratings of free-space standing infinitely long graphene strips are studied in the THz range. A novel numerical approach, based on graphene surface impedance, hyper-singular integral equations, and the Nystrom method, is proposed. This technique guarantees fast convergence and controlled accuracy of computations. Reflectance, transmittance, and absorbance are carefully studied as a function of graphene and grating parameters, revealing the presence of surface plasmon resonances. Specifically, larger graphene relaxation times increases the number of resonances in the THz range, leading to higher wave transmittance due to the reduced losses; on the other hand an increase of graphene chemical potential up-shifts the frequency of plasmon resonances. It is also shown that a relatively low number of graphene strips (>10) are able to reproduce Rayleigh anomalies. These features make graphene strips good candidates for many applications, including tunable absorbers and frequency selective surfaces.
Colavita, E.; Hacyan, S.
2014-03-15
We analyze the solutions of the Klein–Gordon and Dirac equations describing a charged particle in an electromagnetic plane wave combined with a magnetic field parallel to the direction of propagation of the wave. It is shown that the Klein–Gordon equation admits coherent states as solutions, while the corresponding solutions of the Dirac equation are superpositions of coherent and displaced-number states. Particular attention is paid to the resonant case in which the motion of the particle is unbounded. -- Highlights: •We study a relativistic electron in a particular electromagnetic field configuration. •New exact solutions of the Klein–Gordon and Dirac equations are obtained. •Coherent and displaced number states can describe a relativistic particle.
NASA Astrophysics Data System (ADS)
Fujimori, A.; Minami, F.; Tsuda, N.
1980-10-01
Electronic energy bands have been calculated for CeH2 and CeH3 using the augmented-plane-wave method and have been fitted by the linear-combination-of-atomic-orbitals interpolation scheme. The partial densities of states and the numbers of electrons on atomic orbitals indicate that hydrogen in CeH2 is almost anionlike. When going from CeH2 to CeH3, shallow bonding levels are found to form between the third hydrogen state and conduction electrons of CeH2, other features of CeH2 being little affected by it. Thus the rare-earth dihydrides are regarded as ionic compounds similar to the saline-element dihydrides except for the presence of d-like conduction electrons.
Garcia-Gracia, Hipolito; Gutiérrez-Vega, Julio C
2009-04-01
A detailed analysis of the plane-wave diffraction by a finite-radius circular spiral phase plate (SPP) with integer and fractional topological charge and with variable transmission coefficients inside and outside of the plate edge is presented. We characterize the effect of varying the transmission coefficients and the parameters of the SPP on the propagated field. The vortex structure for integer and fractional phase step of the SPPs with and without phase apodization at the plate edge is also analyzed. The consideration of the interference between the light crossing the SPP and the light that undergoes no phase alteration at the aperture plane reveals new and interesting phenomena associated to this classical problem.
Curved-space trace, chiral, and Einstein anomalies from path integrals, using flat-space plane waves
NASA Astrophysics Data System (ADS)
Ceresole, A.; Pizzochero, P.; van Nieuwenhuizen, P.
1989-03-01
We show that the gravitational trace and chiral anomalies can be computed from the measure by using the same general flat-space methods as used for nongravitational anomalies. No heat-kernel methods, zeta-function regularization, point-splitting techniques, etc., are needed, although they may be used and then simplify the algebra. In particular, we claim that it is not necessary to insert factors of g1/4 which are often added on grounds of covariance, since one-loop anomalies are local objects, while the trace of the Jacobian of the measure is a purely mathematical object which can be evaluated whether or not one has even heard about general relativity. We also show that the trace operation is cyclic by performing two different computations of the Einstein anomaly: once with the regulator in front of the Jacobian and once in the back. In both cases we obtain total derivatives on a plane-wave basis.
Mobile Ultrasound Plane Wave Beamforming on iPhone or iPad using Metal- based GPU Processing
NASA Astrophysics Data System (ADS)
Hewener, Holger J.; Tretbar, Steffen H.
Mobile and cost effective ultrasound devices are being used in point of care scenarios or the drama room. To reduce the costs of such devices we already presented the possibilities of consumer devices like the Apple iPad for full signal processing of raw data for ultrasound image generation. Using technologies like plane wave imaging to generate a full image with only one excitation/reception event the acquisition times and power consumption of ultrasound imaging can be reduced for low power mobile devices based on consumer electronics realizing the transition from FPGA or ASIC based beamforming into more flexible software beamforming. The massive parallel beamforming processing can be done with the Apple framework "Metal" for advanced graphics and general purpose GPU processing for the iOS platform. We were able to integrate the beamforming reconstruction into our mobile ultrasound processing application with imaging rates up to 70 Hz on iPad Air 2 hardware.
Dietrich, F S
2006-09-25
This document is intended to facilitate calculation of inelastic scattering and charge-exchange cross sections in a variety of reaction models, including the plane-wave and distorted-wave approximations and the full coupled-channels treatments. Expressions are given for the coupling potentials between the relevant channels in both coordinate and momentum space. In particular, it is expected that the plane-wave calculations should be useful as a check on the correctness of coupled-channels calculations. The Fourier transform methods used to calculate the plane-wave approximation cross sections are also intended to be used to generate the transition potentials for coupled-channels codes, using a folding model with local effective interactions. Specific expressions are given for calculating transition densities for the folding model in the random phase approximation (RPA).
NASA Astrophysics Data System (ADS)
Kawai, Hiroki; Nagaoka, Tomoaki; Watanabe, Soichi; Saito, Kazuyuki; Takahashi, Masaharu; Ito, Koichi
2010-01-01
This paper presents calculated specific absorption rate (SAR) dosimetry in 4 and 8 week Japanese pregnant-woman models exposed to plane waves over the frequency range of 10 MHz-1.5 GHz. Two types of 2 mm spatial-resolution pregnant-woman models comprised a woman model, which is similar to the average-sized Japanese adult female in height and weight, with a cubic (4 week) embryo or spheroidal (8 week) one. The averaged SAR in the embryos exposed to vertically and horizontally polarized plane waves at four kinds of propagation directions are calculated from 10 MHz to 1.5 GHz. The results indicate that the maximum average SAR in the embryos exposed to plane waves is lower than 0.08 W kg-1 when the incident power density is at the reference level of ICNIRP guideline for general public environment.
Maintz, Stefan; Deringer, Volker L; Tchougréeff, Andrei L; Dronskowski, Richard
2013-11-05
Quantum-chemical computations of solids benefit enormously from numerically efficient plane-wave (PW) basis sets, and together with the projector augmented-wave (PAW) method, the latter have risen to one of the predominant standards in computational solid-state sciences. Despite their advantages, plane waves lack local information, which makes the interpretation of local densities-of-states (DOS) difficult and precludes the direct use of atom-resolved chemical bonding indicators such as the crystal orbital overlap population (COOP) and the crystal orbital Hamilton population (COHP) techniques. Recently, a number of methods have been proposed to overcome this fundamental issue, built around the concept of basis-set projection onto a local auxiliary basis. In this work, we propose a novel computational technique toward this goal by transferring the PW/PAW wavefunctions to a properly chosen local basis using analytically derived expressions. In particular, we describe a general approach to project both PW and PAW eigenstates onto given custom orbitals, which we then exemplify at the hand of contracted multiple-ζ Slater-type orbitals. The validity of the method presented here is illustrated by applications to chemical textbook examples-diamond, gallium arsenide, the transition-metal titanium-as well as nanoscale allotropes of carbon: a nanotube and the C60 fullerene. Remarkably, the analytical approach not only recovers the total and projected electronic DOS with a high degree of confidence, but it also yields a realistic chemical-bonding picture in the framework of the projected COHP method.
Nonlocality from Local Contextuality
NASA Astrophysics Data System (ADS)
Liu, Bi-Heng; Hu, Xiao-Min; Chen, Jiang-Shan; Huang, Yun-Feng; Han, Yong-Jian; Li, Chuan-Feng; Guo, Guang-Can; Cabello, Adán
2016-11-01
We experimentally show that nonlocality can be produced from single-particle contextuality by using two-particle correlations which do not violate any Bell inequality by themselves. This demonstrates that nonlocality can come from an a priori different simpler phenomenon, and connects contextuality and nonlocality, the two critical resources for, respectively, quantum computation and secure communication. From the perspective of quantum information, our experiment constitutes a proof of principle that quantum systems can be used simultaneously for both quantum computation and secure communication.
Nonlocality from Local Contextuality.
Liu, Bi-Heng; Hu, Xiao-Min; Chen, Jiang-Shan; Huang, Yun-Feng; Han, Yong-Jian; Li, Chuan-Feng; Guo, Guang-Can; Cabello, Adán
2016-11-25
We experimentally show that nonlocality can be produced from single-particle contextuality by using two-particle correlations which do not violate any Bell inequality by themselves. This demonstrates that nonlocality can come from an a priori different simpler phenomenon, and connects contextuality and nonlocality, the two critical resources for, respectively, quantum computation and secure communication. From the perspective of quantum information, our experiment constitutes a proof of principle that quantum systems can be used simultaneously for both quantum computation and secure communication.
1983-09-01
developed to handle improperly spaced data., A O’ 4! 44 1 * z WHOI-83-27 1 THE NUMERICAL SYNTHESIS AND INVERSION OF ACOUSTIC FIELDS USING THE HANKEL TRANSFORM...from al-S o G eld q t s . • --. . . . . . --.. ..- , -13 - X z INCIDENT PLANE WAVE /I WATER e BOTTOM /7-7-777 ,U Figure 1.2.1 Incident plane wave...generate the reflected wave iz• (k,x +k’Y -k.1)() The change in sign indicates that the reflected wave is returning in the z direction. The ampli- tude
NASA Astrophysics Data System (ADS)
Anderson, Sean M.; Tancogne-Dejean, Nicolas; Mendoza, Bernardo S.; Véniard, Valérie
2015-02-01
We formulate a theoretical approach of surface second-harmonic generation from semiconductor surfaces based on the length gauge and the electron density operator. Within the independent particle approximation, the nonlinear second-order surface susceptibility tensor χa b c(-2 ω ;ω ,ω ) is calculated, including in one unique formulation (i) the scissors correction, needed to have the correct value of the energy band gap, (ii) the contribution of the nonlocal part of the pseudopotentials, routinely used in ab initio band-structure calculations, and (iii) the derivation for the inclusion of the cut function, used to extract the surface response. The first two contributions are described by spatially nonlocal quantum-mechanical operators and are fully taken into account in the present formulation. As a test case of the approach, we calculate χx x x(-2 ω ;ω ,ω ) for the clean Si (001 )2 ×1 reconstructed surface. The effects of the scissors correction and of the nonlocal part of the pseudopotentials are discussed in surface nonlinear optics. The scissors correction shifts the spectrum to higher energies though the shifting is not rigid and mixes the 1 ω and 2 ω resonances, and has a strong influence in the line shape. The effects of the nonlocal part of the pseudopotentials keeps the same line shape of | χ2×1 x x x(-2 ω ;ω ,ω ) | , but reduces its value by 15%-20%. Therefore the inclusion of the three aforementioned contributions is very important and makes our scheme unprecedented and opens the possibility to study surface second-harmonic generation with more versatility and providing more accurate results.
Multipartite nonlocality distillation
Hsu, Li-Yi; Wu, Keng-Shuo
2010-11-15
The stronger nonlocality than that allowed in quantum theory can provide an advantage in information processing and computation. Since quantum entanglement is distillable, can nonlocality be distilled in the nonsignalling condition? The answer is positive in the bipartite case. In this article the distillability of the multipartite nonlocality is investigated. We propose a distillation protocol solely exploiting xor operations on output bits. The probability-distribution vectors and matrix are introduced to tackle the correlators. It is shown that only the correlators with extreme values can survive the distillation process. As the main result, the amplified nonlocality cannot maximally violate any Bell-type inequality. Accordingly, a distillability criterion in the postquantum region is proposed.
NASA Astrophysics Data System (ADS)
Calcagni, Gianluca; Montobbio, Michele; Nardelli, Giuseppe
2007-12-01
An analytic approach to phenomenological models inspired by cubic string field theory is introduced and applied to some examples. We study a class of actions for a minimally coupled, homogeneous scalar field whose energy density contains infinitely many time derivatives. These nonlocal systems are systematically localized and an algorithm to find cosmological solutions of the dynamical equations is provided. Our formalism is able to define the nonlocal field in regions of the parameter space which are inaccessible by standard methods. Also, problems related to nonlocality are reinterpreted under a novel perspective and naturally overcome. We consider phenomenological models living on a Friedmann-Robertson-Walker background with power-law scale factor, both in four dimensions and on a high-energy braneworld. The quest for solutions unravels general features of nonlocal dynamics indicating several future directions of investigation.
NASA Astrophysics Data System (ADS)
Baboly, Mohammadhosein Ghasemi; Soliman, Yasser; Su, Mehmet F.; Reinke, Charles M.; Leseman, Zayd C.; El-Kady, Ihab
2014-11-01
Plane wave expansion analyses that use the inverse rule to obtain the Fourier coefficients of the elastic tensor instead of the more conventional Laurent's rule, exhibit faster convergence rates for solid-solid phononic crystals. In this work, the band structure convergence of calculations using the inverse rule is investigated and applied to the case of high acoustic impedance contrast solid-solid phononic crystals, previously known for convergence difficulties. Results are contrasted to those obtained with the conventional plane wave expansion method. The inverse rule is found to converge at a much rate for all ranges of impedance contrast, and the ratio between the computational times needed to obtain a convergent band structure for a high-contrast solid-solid phononic crystal with the conventional plane wave expansion method using 1369 reciprocal lattice vectors is as large as 6800:1. This ratio decreases for material sets with lower impedance contrast; however, the inverse rule is still faster for a given error threshold for even the lowest impedance contrast phononic crystals reported in the literature. This convergence enhancement is a major factor in reconsidering the plane wave expansion method as an important tool in obtaining propagating elastic modes in phononic crystals.
NASA Astrophysics Data System (ADS)
Voss, D. E.; Koslover, R. A.; Cremer, C. D.; Silvestro, J.; Miner, L. M.
1990-05-01
The High Power Microwaves (HPM) susceptibility testing often requires irradiating test objects at the highest fluences possible. For aperture antennas, the highest fluences are generally found in the radiating near field region. For valid effects testing, the energy coupled to the object interior must accurately replicate that which would occur in a true weapon environment (plane wave illumination). Some believe that valid testing requires object placement at distances from the aperture exceeding 2 D squared/lambda (D=antenna effective diameter). Many also believe testing at farther away than 2 D squared/lambda guarantees plane wave-like coupling conditions. Neither view is correct. Testing in the reactive field region (less than lambda from the aperture) is generally invalid due to dominance of reactive coupling. For testing in the radiating near field, determination of validity is less trivial. An investigation was performed quantifying deviations from plane wave coupling. The measurements, using an instrumented Maverick missile in an anechoic chamber, and supported by theory, indicate conditions for which testing the Maverick missile accurately simulates plane wave coupling.
NASA Astrophysics Data System (ADS)
Montessori, A.; Prestininzi, P.; La Rocca, M.; Succi, S.
2017-09-01
We present an entropic version of the lattice Boltzmann pseudo-potential approach for the simulation of multiphase flows. The method is shown to correctly simulate the dynamics of impinging droplets on hydrophobic surfaces and head-on and grazing collisions between droplets, at Weber and Reynolds number regimes not accessible to previous pseudo-potential methods at comparable resolution.
NASA Astrophysics Data System (ADS)
Lomakin, Vitaliy; Michielssen, E.
2006-03-01
Phenomena associated with the transmission of transient plane waves through plates perforated by subwavelength holes are studied. Specifically, the time domain transmitted field (TDTF) or transient response of a thin plate (sandwiched in between two dielectric slabs) that is perforated periodically by subwavelength holes and illuminated by a transient plane wave (TPW) is calculated by inverse Fourier transforming the product of the plate' s frequency domain transmission coefficient (FDTC) and the TPWs Fourier transform. The incident TPW comprises smoothed and damped exponentials. The FDTC has pole and branch point (BP) singularities associated with resonant and Rayleigh-Wood anomalies. Special choice of branch cuts associated with the BPs allows choosing the poles on a single Riemann sheet. The TDTF is represented in terms of incident TPW and FDTC pole residues, and branch cut (BC) integrals. The latter are evaluated asymptotically for arbitrary small pole-branch point (BP) separations. The obtained expressions are simplified and interpreted for narrow- and wide-band incident fields, and key characteristics of the transient fields scattered from the above structure are identified. For narrowband fields, only the incident TPW pole contributions are significant and the resulting TDTF is an attenuated and delayed replica of the incident TPW. When the field frequency support is near a FDTC pole, significant positive delays are obtained. When the field frequency support is near a BP, small positive and noticeable negative delays are obtained for large and small pole-BP separation, respectively. For wide-band fields all contributions in the TDTF are significant. The incident TPW pole contributions are significant only for early time. The FDTC pole contributions are the counterparts of frequency domain leaky waves and only are significant for much later time. The BC contributions are the counterparts of frequency domain lateral wave and decay slowly, thereby resulting in
Tests on novel pseudo-potentials generated from diffusion Monte Carlo data.
NASA Astrophysics Data System (ADS)
Reboredo, Fernando; Hood, Randolph; Bajdich, Michal
2012-02-01
Since Dmitri Mendeleev developed a table in 1869 to illustrate recurring ("periodic") trends of the elements, it has been understood that most chemical and physical properties can be described by taking into account the outer most electrons of the atoms. These valence electrons are mainly responsible for the chemical bond. In many ab-initio approaches only valence electrons are taken into account and a pseudopotential is used to mimic the response of the core electrons. Typically an all-electron calculation is used to generate a pseudopotential that is used either within density functional theory or quantum chemistry approaches. In this talk we explain and demonstrate a new method to generate pseudopotentials directly from all-electron many-body diffusion Monte Carlo (DMC) calculations and discuss the results of of the transferability of these pseudopotentials. The advantages of incorporating the exchange and correlation directly from DMC into the pseudopotential are also discussed.
Using pseudopotentials within the interacting quantum atoms approach.
Tiana, Davide; Francisco, E; Blanco, M A; Pendás, A Martín
2009-07-09
A general strategy to extend the interacting quantum atoms (IQA) approach to pseudopotential or effective core potential electronic structure calculations is presented. With the protocol proposed here, the scope of IQA thinking opens to chemical bonding problems in heavy-atom systems, as well as to larger molecules than those presently allowed by computational limitations. We show that, provided that interatomic surfaces are computed from core-reconstructed densities, reasonable results are obtained by integrating reduced density matrices built from the pseudowave functions. Comparison with all-electron results in a few test systems shows that exchange-correlation energies are better reproduced than Coulombic contributions, an effect which is traced to inadequate atomic populations and leakage of the core population into the surrounding quantum atoms.
A generalized nonlocal vector calculus
NASA Astrophysics Data System (ADS)
Alali, Bacim; Liu, Kuo; Gunzburger, Max
2015-10-01
A nonlocal vector calculus was introduced in Du et al. (Math Model Meth Appl Sci 23:493-540, 2013) that has proved useful for the analysis of the peridynamics model of nonlocal mechanics and nonlocal diffusion models. A formulation is developed that provides a more general setting for the nonlocal vector calculus that is independent of particular nonlocal models. It is shown that general nonlocal calculus operators are integral operators with specific integral kernels. General nonlocal calculus properties are developed, including nonlocal integration by parts formula and Green's identities. The nonlocal vector calculus introduced in Du et al. (Math Model Meth Appl Sci 23:493-540, 2013) is shown to be recoverable from the general formulation as a special example. This special nonlocal vector calculus is used to reformulate the peridynamics equation of motion in terms of the nonlocal gradient operator and its adjoint. A new example of nonlocal vector calculus operators is introduced, which shows the potential use of the general formulation for general nonlocal models.
NASA Astrophysics Data System (ADS)
Hovem, Jens M.; Knobles, D. P.
2002-11-01
The paper describes a range-dependent propagation model based on a combination of range-dependent ray tracing and plane-wave bottom responses. The ray-tracing module of the model determines all the eigenrays between any source/receiver pairs and stores the ray histories. The received wave field is then synthesized by adding the contributions of all the eigenrays, taking into account the reflections from the bottom and the surface. The model can treat arbitrarily varying bottom topography and a layered elastic bottom as long as the layers are parallel. In the current version, the bottom is modeled with a sedimentary layer over an elastic half space, but more complicated structures are easily implemented. The new model has been tested against other models on several benchmark problems and also applied in the analysis and modeling of up-slope and down-slope propagation data recorded on a 52-element center-tapered array that was deployed at two locations about 70 miles east of Jacksonville, FL. The paper presents the results of these tests with an assessment of the potential use in connection with geo-acoustic inversion of range-dependent and elastic scenarios. [Work supported by Applied Research Laboratories, The University of Texas.
NASA Astrophysics Data System (ADS)
Usuki, Tsuneo
2013-09-01
The moduli of conventional elastic structural materials are extended to one of the viscoelastic materials through a modification whereby the dynamic moduli converge to the static moduli of elasticity as the fractional order approaches zero. By plotting phase velocity curves and group velocity curves of plane waves and Rayleigh surface wave for a viscoelastic material (polyvinyl chloride foam), the influence of the fractional order of viscoelasticity is examined. The phase and group velocity curves in the high frequency range were derived for longitudinal, transverse, and Rayleigh waves inherent to the viscoelastic material. In addition, the equation for the phase velocity was mathematically derived on the complex plane, too, and graphically illustrated. A phenomenon was found that, at the moment when the fractional order of the time derivative reaches an integer value 1, the curve on the complex plane becomes completely different, exhibiting snap-through behavior. We examined the mechanism of the snap-through mathematically. Numerical calculation examples were solved, and good agreement was confirmed between the numerical calculation and the analytical expression mentioned above. From the results of the numerical example, regularities were derived for the absolute value of the complex phase and group velocities on the complex plane.
NASA Astrophysics Data System (ADS)
Do, V. Nam; Le, H. Anh; Vu, V. Thieu
2017-04-01
We propose a computational approach to combining the plane-wave method and the real-space treatment to describe the periodic variation in the material plane and the decay of wave functions from the material surfaces. The proposed approach is natural for two-dimensional material systems and thus may circumvent some intrinsic limitations involving the artificial replication of material layers in traditional supercell methods. In particular, we show that the proposed method is easy to implement and, especially, computationally effective since low-cost computational algorithms, such as iterative and recursive techniques, can be used to treat matrices with block tridiagonal structure. Using this approach we show first-principles features that supplement the current knowledge of some fundamental issues in bilayer graphene systems, including the coupling between the two graphene layers, the preservation of the σ band of monolayer graphene in the electronic structure of the bilayer system, and the differences in low-energy band structure between the AA- and AB-stacked configurations.
Skaropoulos, N.C.; Ioannidou, M.P.; Chrissoulidis, D.P.
1996-10-01
Understanding the interaction of EM radiation with humans is essential in a number of contemporary applications. Special attention is paid to the absorption of EM energy by the human head, which exhibits a resonant behavior in the frequency band 0.1--3 GHz. The use of handheld transceivers for wireless communications, which operate in close proximity to the head, has raised safety-related questions and questions concerning the effect of the head on the performance of the mobile phone antenna. The induced electromagnetic (EM) field in a layered eccentric spheres structure is determined through a concise analytical formulation based on indirect mode-matching (IMM). The exact analytical solution is applied to a six-layer model of the head. This model allows for eccentricity between the inner and outer sets of concentric spherical layers which simulate brain and skull, respectively. Excitation is provided by a nearby localized source or by an incident plane wave. The numerical application provides information about the total absorbed power, the absorption in each layer, and the spatial distribution of the specific absorption rate (SAR) at frequencies used by cellular phones. The effects of excitation frequency, eccentricity, exposure configuration, and antenna-head separation are investigated.
Gandhi, O.P.; Gu, Y.G.; Chen, J.Y.; Bassen, H.I. )
1992-09-01
The authors have previously reported local, layer-averaged, and whole-body-averaged specific absorption rates and induced currents for a 5,628-cell anatomically based model of a human for plane-wave exposures 20-100 MHz. Using a higher resolution, 45,024-cell model of the human body, calculations have now been extended to 915 MHz using the finite-difference time-domain method. Because of the higher resolution of the model, it has been possible to calculate specific absorption rates for various organs (brain, eyes, heart, lungs, liver, kidneys, and intestines) and for various parts of the body (head, neck, torso, legs, and arms) as a function of frequency in the band 100-915 MHz. Consistent with some of the experimental data in the literature, the highest part-body-averaged specific absorption rate for the head and neck region (as well as for the eyes and brain) occurs at 200 MHz for the isolated condition and at 150 MHz for the grounded condition of the model. Also observed is an increasing specific absorption rate for the eyes for frequencies above 350 MHz due to the superficial nature of power deposition at increasing frequencies.
NASA Technical Reports Server (NTRS)
Raman, Ganesh; Rice, Edward J.; Mankbadi, Reda R.
1988-01-01
The limitations of single frequency plane wave excitation in mixing enhancement are investigated for a circular jet. Measurements made in an 8.8 cm diameter jet are compared with a theoretical model. The measurements are made to quantify mixing at excitation amplitudes up to 2 percent of the jet exit velocity. The initial boundary layer state, the exit mean and fluctuating velocity profiles and spectra are documented for all cases considered. The amplitude of the fundamental wave is recorded along the jet axis for various levels of excitation. As the amplitude of excitation is increased the jet spreading rate is increased, but beyond a saturation amplitude further increases have no effect on the spreading. The experimental results are compared with theoretical estimates. In the theory the flow is split into the mean flow, large scale motions, and fine scale turbulence. Shape assumptions for the mean flow, and fine scale turbulence along with the shape for the large scale motions obtained from a linear stability theory provide the closure. The experimental results compare reasonably well with predictions.
NASA Technical Reports Server (NTRS)
Raman, Ganesh; Rice, Edward J.; Mankbadi, Reda R.
1988-01-01
The limitations of single frequency plane wave excitation in mixing enhancement are investigated for a circular jet. Measurements made in an 8.8 cm diameter jet are compared with a theoretical model. The measurements are made to quantify mixing at excitation amplitudes up to 2 percent of the jet exit velocity. The initial boundary layer state, the exit mean and fluctuating velocity profiles and spectra are documented for all cases considered. The amplitude of the fundamental wave is recorded along the jet axis for various levels of excitation. As the amplitude of excitation is increased the jet spreading rate is increased, but beyond a saturation amplitude further increases have no effect on the spreading. The experimental results are compared with theoretical estimates. In the theory the flow is split into the mean flow, large scale motions, and fine scale turbulence. Shape assumptions for the mean flow, and fine scale turbulence along with the shape for the large scale motions obtained from a linear stability theory provide the closure. The experimental results compare reasonably well with predictions.
Pérez-Jordá, José M
2010-01-14
A new method for solving the Schrödinger equation is proposed, based on the following details. First, a map u=u(r) from Cartesian coordinates r to a new coordinate system u is chosen. Second, the solution (orbital) psi(r) is written in terms of a function U depending on u so that psi(r)=/J(u)/(-1/2)U(u), where /J(u)/ is the Jacobian determinant of the map. Third, U is expressed as a linear combination of plane waves in the u coordinate, U(u)= sum (k)c(k)e(ik x u). Finally, the coefficients c(k) are variationally optimized to obtain the best energy, using a generalization of an algorithm originally developed for the Coulomb potential [J. M. Perez-Jorda, Phys. Rev. B 58, 1230 (1998)]. The method is tested for the radial Schrödinger equation in the hydrogen atom, resulting in micro-Hartree accuracy or better for the energy of ns and np orbitals (with n up to 5) using expansions of moderate length.
Papadakis, Panagiotis I; Piperakis, George S; Kalogerakis, Michael A
2015-02-01
This work studies the reflection coefficient of a plane wave incident on a seafloor consisting of two layers (sediment and substrate), whose interface is linear but not parallel to the water-sediment interface. This is an extension of the well-established and studied reflection coefficient concept for seafloors with parallel layers. Moreover this study introduces the concept of the Coherent Reflection Coefficient (CRC) that extends the usual Rayleigh reflection coefficient definition not only at the water-sediment interface but inside the water column as well. The mathematical formulation of the CRC is derived and its numerical implementation is explained. Based on this implementation a numerical code is developed and incorporated-among other codes-in a user-friendly graphics toolbox that was built to facilitate CRC calculations. Numerical examples for realistic seafloors are presented and the derived results are compared to similar ones for parallel layers, indicating that even for small inclination angles the reflection coefficient difference between parallel and slanted interface layers is substantial, hence cannot be ignored. An imminent application of the extended seafloor model and the CRC introduced in this work is the enhancement of geophysics inversion schemes for the estimation of the seafloor parameters.
NASA Astrophysics Data System (ADS)
Akhlagh Moayed, Alireza; Dang, Shannon; Ramahi, Omar M.; Bizheva, Kostadinka K.
2009-02-01
The early stages of ocular diseases such as Diabetic Retinopathy are manifested by morphological changes in retinal tissue occurring on cellular level. Therefore, a number of ophthalmic diseases can be diagnosed at an early stage by detecting spatial and temporal variations in the scattering profile of retinal tissue. It was recently demonstrated that, OCT can be used to probe the functional response of retinal photoreceptors to external light stimulation [1]-[3]. fUHROCT measures localized differential changes in the retina reflectivity over time resulting from external light stimulation of the retina. Currently the origins of the observed reflectivity changes are not well understood. However, due to the complex nature of retinal physiology using purely experimental approaches in this case is problematic. For example fUHROCT is sensitive to small changes in the refractive index of biological tissue which as demonstrated previously, can result from a number of processes such as membrane hyperpolarization, osmotic swelling, metabolic changes, etc. In this paper, we present a computational model of interaction between photoreceptor cells and optical plane wave based on the Finite Integration Technique (FIT).
Bakker, J F; Paulides, M M; Christ, A; Kuster, N; van Rhoon, G C
2010-06-07
To avoid potentially adverse health effects of electromagnetic fields (EMF), the International Commission on Non-Ionizing Radiation Protection (ICNIRP) has defined EMF reference levels from the basic restrictions on the induced whole-body-averaged specific absorption rate (SAR(wb)) and the peak 10 g spatial-averaged SAR (SAR(10g)). The objective of this study is to assess if the SAR in children remains below the basic restrictions upon exposure at the reference levels. Finite difference time domain (FDTD) modeling was used to calculate the SAR in six children and two adults when exposed to all 12 orthogonal plane wave configurations. A sensitivity study showed an expanded uncertainty of 53% (SAR(wb)) and 58% (SAR(10g)) due to variations in simulation settings and tissue properties. In this study, we found that the basic restriction on the SAR(wb) is occasionally exceeded for children, up to a maximum of 45% in small children. The maximum SAR(10g) values, usually found at body protrusions, remain under the limit for all scenarios studied. Our results are in good agreement with the literature, suggesting that the recommended ICNIRP reference levels may need fine tuning.
Nonlocal chaotic phase synchronization
NASA Astrophysics Data System (ADS)
Zhan, Meng; Zheng, Zhi-Gang; Hu, Gang; Peng, Xi-Hong
2000-09-01
A novel synchronization behavior, nonlocal chaotic phase synchronization, is investigated. For two coupled Rossler oscillators with only one forced by an injected periodic signal, the phase of the unforced oscillator can be locked to the phase of the periodic signal while the forced one is well unlocked by the signal; in a chain of coupled chaotic oscillators with nearest coupling, the phase of an oscillator (or a cluster) can be locked to another nonneighbor one. Moreover, the mechanism underlying the transition to nonlocal synchronization is discussed in detail.
A Class of High Order Nonlocal Operators
NASA Astrophysics Data System (ADS)
Tian, Xiaochuan; Du, Qiang
2016-12-01
We study a class of nonlocal operators that may be seen as high order generalizations of the well known nonlocal diffusion operators. We present properties of the associated nonlocal functionals and nonlocal function spaces including nonlocal versions of Sobolev inequalities such as the nonlocal Poincaré and nonlocal Gagliardo-Nirenberg inequalities. Nonlocal characterizations of high order Sobolev spaces in the spirit of Bourgain-Brezis-Mironescu are provided. Applications of nonlocal calculus of variations to the well-posedness of linear nonlocal models of elastic beams and plates are also considered.
NASA Astrophysics Data System (ADS)
Oberhofer, Harald; Blumberger, Jochen
2010-12-01
We present a plane wave basis set implementation for the calculation of electronic coupling matrix elements of electron transfer reactions within the framework of constrained density functional theory (CDFT). Following the work of Wu and Van Voorhis [J. Chem. Phys. 125, 164105 (2006)], the diabatic wavefunctions are approximated by the Kohn-Sham determinants obtained from CDFT calculations, and the coupling matrix element calculated by an efficient integration scheme. Our results for intermolecular electron transfer in small systems agree very well with high-level ab initio calculations based on generalized Mulliken-Hush theory, and with previous local basis set CDFT calculations. The effect of thermal fluctuations on the coupling matrix element is demonstrated for intramolecular electron transfer in the tetrathiafulvalene-diquinone (Q-TTF-Q-) anion. Sampling the electronic coupling along density functional based molecular dynamics trajectories, we find that thermal fluctuations, in particular the slow bending motion of the molecule, can lead to changes in the instantaneous electron transfer rate by more than an order of magnitude. The thermal average, ( {< {| {H_ab } |^2 } > } )^{1/2} = 6.7 {mH}, is significantly higher than the value obtained for the minimum energy structure, | {H_ab } | = 3.8 {mH}. While CDFT in combination with generalized gradient approximation (GGA) functionals describes the intermolecular electron transfer in the studied systems well, exact exchange is required for Q-TTF-Q- in order to obtain coupling matrix elements in agreement with experiment (3.9 mH). The implementation presented opens up the possibility to compute electronic coupling matrix elements for extended systems where donor, acceptor, and the environment are treated at the quantum mechanical (QM) level.
Tinniswood, A D; Furse, C M; Gandhi, O P
1998-08-01
At certain frequencies, when the human head becomes a resonant structure, the power absorbed by the head and neck, when the body is exposed to a vertically polarized plane wave propagating from front to back, becomes significantly larger than would ordinarily be expected from its shadow cross section. This has possible implications in the study of the biological effects of electromagnetic fields. Additionally the frequencies at which these resonances occur are not readily predicted by simple approximations of the head in isolation. In order to determine these resonant conditions an anatomically based model of the whole human body has been used, with the finite-difference time-domain (FDTD) algorithm to accurately determine field propagation, specific absorption rate (SAR) distributions and power absorption in both the whole body and the head region (head and neck). This paper shows that resonant frequencies can be determined using two methods. The first is by use of the accurate anatomically based model (with heterogeneous tissue properties) and secondly using a model built from parallelepiped sections (for the torso and legs), an ellipsoid for the head and a cylinder for the neck. This approximation to the human body is built from homogeneous tissue the equivalent of two-thirds the conductivity and dielectric constant of that of muscle. An IBM SP-2 supercomputer together with a parallel FDTD code has been used to accommodate the large problem size. We find resonant frequencies for the head and neck at 207 MHz and 193 MHz for the isolated and grounded conditions, with absorption cross sections that are respectively 3.27 and 2.62 times the shadow cross section.
Oberhofer, Harald; Blumberger, Jochen
2010-12-28
We present a plane wave basis set implementation for the calculation of electronic coupling matrix elements of electron transfer reactions within the framework of constrained density functional theory (CDFT). Following the work of Wu and Van Voorhis [J. Chem. Phys. 125, 164105 (2006)], the diabatic wavefunctions are approximated by the Kohn-Sham determinants obtained from CDFT calculations, and the coupling matrix element calculated by an efficient integration scheme. Our results for intermolecular electron transfer in small systems agree very well with high-level ab initio calculations based on generalized Mulliken-Hush theory, and with previous local basis set CDFT calculations. The effect of thermal fluctuations on the coupling matrix element is demonstrated for intramolecular electron transfer in the tetrathiafulvalene-diquinone (Q-TTF-Q(-)) anion. Sampling the electronic coupling along density functional based molecular dynamics trajectories, we find that thermal fluctuations, in particular the slow bending motion of the molecule, can lead to changes in the instantaneous electron transfer rate by more than an order of magnitude. The thermal average, (<|H(ab)|(2)>)(1/2)=6.7 mH, is significantly higher than the value obtained for the minimum energy structure, |H(ab)|=3.8 mH. While CDFT in combination with generalized gradient approximation (GGA) functionals describes the intermolecular electron transfer in the studied systems well, exact exchange is required for Q-TTF-Q(-) in order to obtain coupling matrix elements in agreement with experiment (3.9 mH). The implementation presented opens up the possibility to compute electronic coupling matrix elements for extended systems where donor, acceptor, and the environment are treated at the quantum mechanical (QM) level.
Modified carbon pseudopotential for use in ONIOM calculations of alkyl-substituted metallocenes.
Lewin, John L; Cramer, Christopher J
2008-12-18
Nonrelativistic carbon 1s core pseudopotentials are optimized for substituted cyclopentadienide ring carbons for use in integrated molecular orbital molecular orbital (IMOMO) and integrated molecular orbital molecular mechanics (IMOMM) calculations where the Cp ring substituents are not included in the high-level IMOMO or IMOMM subsystem. Use of the optimized pseudopotential within the IMOMO framework leads to significant improvements in predicted carbonyl stretching frequencies for a series of Cp-ring-methylated zirconocenes compared to using a standard carbon pseudopotential. The technology is less successful in the IMOMM implementation.
ERIC Educational Resources Information Center
Hobson, Art
2012-01-01
Nonlocality arises from the unified "all or nothing" interactions of a spatially extended field quantum such as a photon or an electron. In the double-slit experiment with light, for example, each photon comes through both slits and arrives at the viewing screen as an extended but unified energy bundle or "field quantum." When the photon interacts…
ERIC Educational Resources Information Center
Hobson, Art
2012-01-01
Nonlocality arises from the unified "all or nothing" interactions of a spatially extended field quantum such as a photon or an electron. In the double-slit experiment with light, for example, each photon comes through both slits and arrives at the viewing screen as an extended but unified energy bundle or "field quantum." When the photon interacts…
NASA Astrophysics Data System (ADS)
Filippov, A. I.; Akhmetova, O. V.; Koval‧skii, A. A.
2016-11-01
The filtration-wave process in the central layer of a three-layer anisotropic medium is described as an equivalent plane wave with a modified asymptotic method accurate in the mean. The initial problem is parametrized and broken down into simpler problems for the coefficients of expansion in an asymptotic parameter. The zero expansion coefficient describes the sought plane wave, whereas the first coefficient ensures refinement of the wave-front geometry. The exact solution of the parametrized problem is obtained on the basis of the Fourier sine transformation. The correctness of the developed method is confirmed by comparing the obtained asymptotic solutions and the coefficients of Maclaurin-series expansion of the exact solution of the parametrized problem in a formal parameter.
1983-01-01
r 2) it is not expected that these issues will pose serious problems. It appears that the %7 grid is of fundamental importance in the Hankel... invesion of pressue field data to obtain the parameters of the bottom. In this contwt it is of interest to geophysiciut and others who wih to...RECEIVER HEIGHT COMPENSATION A(k,) Figure V.1.1 The invesion procedure to estimate the plane wave reflection coefficient from the mul field Senerated
Dossou, Kokou B.; Botten, Lindsay C.
2012-08-15
A three-dimensional finite element method (FEM) for the analysis of plane wave diffraction by a bi-periodic slab is described and implemented. A scattering matrix formalism based on the FEM allows the efficient treatment of light reflection and transmission by multilayer bi-periodic structures, and the computation of Bloch modes of three-dimensional arrays. Numerical simulations, which show the accuracy and flexibility of the FEM, are presented.
Singh, Mithun Kuniyil Ajith; Jaeger, Michael; Frenz, Martin; Steenbergen, Wiendelt
2017-04-01
Reflection artifacts caused by acoustic inhomogeneities constitute a major problem in epi-mode biomedical photoacoustic imaging. Photoacoustic transients from the skin and superficial optical absorbers traverse into the tissue and reflect off echogenic structures to generate reflection artifacts. These artifacts cause difficulties in the interpretation of images and reduce contrast and imaging depth. We recently developed a method called PAFUSion (photoacoustic-guided focused ultrasound) to circumvent the problem of reflection artifacts in photoacoustic imaging. We already demonstrated that the photoacoustic signals can be backpropagated using synthetic aperture pulse-echo data for identifying and reducing reflection artifacts in vivo. In this work, we propose an alternative variant of PAFUSion in which synthetic backpropagation of photoacoustic signals is based on multi-angled plane-wave ultrasound measurements. We implemented plane-wave and synthetic aperture PAFUSion in a handheld ultrasound/photoacoustic imaging system and demonstrate reduction of reflection artifacts in phantoms and in vivo measurements on a human finger using both approaches. Our results suggest that, while both approaches are equivalent in terms of artifact reduction efficiency, plane-wave PAFUSion requires less pulse echo acquisitions when the skin absorption is the main cause of reflection artifacts.
Singh, Mithun Kuniyil Ajith; Jaeger, Michael; Frenz, Martin; Steenbergen, Wiendelt
2017-01-01
Reflection artifacts caused by acoustic inhomogeneities constitute a major problem in epi-mode biomedical photoacoustic imaging. Photoacoustic transients from the skin and superficial optical absorbers traverse into the tissue and reflect off echogenic structures to generate reflection artifacts. These artifacts cause difficulties in the interpretation of images and reduce contrast and imaging depth. We recently developed a method called PAFUSion (photoacoustic-guided focused ultrasound) to circumvent the problem of reflection artifacts in photoacoustic imaging. We already demonstrated that the photoacoustic signals can be backpropagated using synthetic aperture pulse-echo data for identifying and reducing reflection artifacts in vivo. In this work, we propose an alternative variant of PAFUSion in which synthetic backpropagation of photoacoustic signals is based on multi-angled plane-wave ultrasound measurements. We implemented plane-wave and synthetic aperture PAFUSion in a handheld ultrasound/photoacoustic imaging system and demonstrate reduction of reflection artifacts in phantoms and in vivo measurements on a human finger using both approaches. Our results suggest that, while both approaches are equivalent in terms of artifact reduction efficiency, plane-wave PAFUSion requires less pulse echo acquisitions when the skin absorption is the main cause of reflection artifacts. PMID:28736669
NASA Astrophysics Data System (ADS)
Shepherd, James J.; Grüneis, Andreas; Booth, George H.; Kresse, Georg; Alavi, Ali
2012-07-01
Using the finite simulation-cell homogeneous electron gas (HEG) as a model, we investigate the convergence of the correlation energy to the complete-basis-set (CBS) limit in methods utilizing plane-wave wave-function expansions. Simple analytic and numerical results from second-order Møller-Plesset theory (MP2) suggest a 1/M decay of the basis-set incompleteness error where M is the number of plane waves used in the calculation, allowing for straightforward extrapolation to the CBS limit. As we shall show, the choice of basis-set truncation when constructing many-electron wave functions is far from obvious, and here we propose several alternatives based on the momentum transfer vector, which greatly improve the rate of convergence. This is demonstrated for a variety of wave-function methods, from MP2 to coupled-cluster doubles theory and the random-phase approximation plus second-order screened exchange. Finite basis-set energies are presented for these methods and compared with exact benchmarks. A transformation can map the orbitals of a general solid state system onto the HEG plane-wave basis and thereby allow application of these methods to more realistic physical problems. We demonstrate this explicitly for solid and molecular lithium hydride.
An analysis of core effects on shape-consistent pseudopotentials.
Fromager, Emmanuel; Maron, Laurent; Teichteil, Christian; Heully, Jean-Louis; Faegri, Knut; Dyall, Ken
2004-11-08
Large core (seven-valence electrons) shape-consistent averaged relativistic pseudopotentials (AREP) including core effects have been derived for the halogen series (Cl,Br,I,At). The influence of core effects on the spin-orbit splitting of the halogen and alkali atoms is clearly demonstrated within an all-electron four-component atomic reference calculation by means of a perturbation analysis. In particular, it is shown that AREPs extracted at the Dirac-Coulomb-Fock level, which already include spin-orbit polarization effects, give excellent results for atomic spectroscopy and equilibrium distances of halogen dimers. We also show that in our approach the core effects, included by configuration interaction using the numerical GRASP code, are transferred to the averaged orbital one-electron energy, defined in a perturbational way. This leads to a modification of the extracted AREPs by core effects, which is illustrated by calculations of the first atomic excited states using these AREPs. These results support the validity of including core effects directly in the AREPs extracted in a shape-consistent scheme. The transferability to the atomic excited states as well as to the molecular case is also verified.
A pseudopotential model for Dirac electrons in graphene with line defects.
Ebert, D; Zhukovsky, V Ch; Stepanov, E A
2014-03-26
We consider electron transport in a planar fermion model containing various types of line defects modeled by δ-function pseudopotentials with different matrix coefficients. After determining the necessary boundary conditions, the transmission probability for electron transport through the defect line is obtained for various types of pseudopotentials. For the schematic model considered, which may describe a graphene structure with different types of linear defects, the valley polarization is obtained.
NASA Technical Reports Server (NTRS)
Bagus, P. S.; Bauschlicher, C. W., Jr.; Nelin, C. J.; Laskowski, B. C.; Seel, M.
1984-01-01
The interaction of CO with Cu5, Ni5, and Al4 are treated as model systems for molecular adsorption on metal surfaces. The effect of the use of pseudopotentials for the metal atoms is studied by considering three types of clusters. In the first case, all of the metal electrons are explicitly included in the wave function; an all electron (AE) treatment. In the second case, the metal atom which directly interacts with the CO is described by AE but the remaining metal atoms include a pseudopotential for their core electrons. Finally, in the third case, all of the metal atoms in the cluster have a pseudopotential treatment for the core electrons. The AE cluster results are taken as reference values for the two pseudopotential treatments. The mixed cluster results are in excellent agreement with those of the all AE clusters; however, the results for the all pseudopotential cluster of Ni5CO or of Cu5CO are qualitatively different. The pseudopotential treatment for all of the metal atoms often leads to results that contain serious errors and it is not a reliable approach.
NASA Astrophysics Data System (ADS)
Chambolle, Antonin; Morini, Massimiliano; Ponsiglione, Marcello
2015-12-01
This paper aims at building a unified framework to deal with a wide class of local and nonlocal translation-invariant geometric flows. We introduce a class of nonlocal generalized mean curvatures and prove the existence and uniqueness for the level set formulation of the corresponding geometric flows. We then introduce a class of generalized perimeters, whose first variation is an admissible generalized curvature. Within this class, we implement a minimizing movements scheme and we prove that it approximates the viscosity solution of the corresponding level set PDE. We also describe several examples and applications. Besides recovering and presenting in a unified way existence, uniqueness, and approximation results for several geometric motions already studied and scattered in the literature, the theory developed in this paper also allows us to establish new results.
Revealing hidden genuine tripartite nonlocality
NASA Astrophysics Data System (ADS)
Paul, Biswajit; Mukherjee, Kaushiki; Sarkar, Debasis
2016-11-01
Nonlocal correlations arising from measurements on tripartite entangled states can be classified into two groups, one genuinely three-way nonlocal and other local with respect to some bipartition. Still, whether a genuinely tripartite entangled quantum state can exhibit genuine three-way nonlocality remains a challenging problem as far as measurement context is concerned. Here we introduce an approach in this regard. We consider three tripartite quantum states, none of which is genuinely three-way nonlocal in a specific Bell scenario (three parties, two measurements per party, two outcomes per measurement), but they can exhibit genuine three-way nonlocality when the initial states are subjected to stochastic local operations and classical communication. So, genuine three-way nonlocality is a resource which can be revealed by using a sequence of measurements.
Acausality in nonlocal gravity theory
NASA Astrophysics Data System (ADS)
Zhang, Ying-li; Koyama, Kazuya; Sasaki, Misao; Zhao, Gong-Bo
2016-03-01
We investigate the nonlocal gravity theory by deriving nonlocal equations of motion using the traditional variation principle in a homogeneous background. We focus on a class of models with a linear nonlocal modification term in the action. It is found that the resulting equations of motion contain the advanced Green's function, implying that there is an acausality problem. As a consequence, a divergence arises in the solutions due to contributions from the future infinity unless the Universe will go back to the radiation dominated era or become the Minkowski spacetime in the future. We also discuss the relation between the original nonlocal equations and its biscalar-tensor representation and identify the auxiliary fields with the corresponding original nonlocal terms. Finally, we show that the acusality problem cannot be avoided by any function of nonlocal terms in the action.
Causality, Nonlocality, and Negative Refraction.
Forcella, Davide; Prada, Claire; Carminati, Rémi
2017-03-31
The importance of spatial nonlocality in the description of negative refraction in electromagnetic materials has been put forward recently. We develop a theory of negative refraction in homogeneous and isotropic media, based on first principles, and that includes nonlocality in its full generality. The theory shows that both dissipation and spatial nonlocality are necessary conditions for the existence of negative refraction. It also provides a sufficient condition in materials with weak spatial nonlocality. These fundamental results should have broad implications in the theoretical and practical analyses of negative refraction of electromagnetic and other kinds of waves.
Burkatzki, M; Filippi, Claudia; Dolg, M
2008-10-28
We extend our recently published set of energy-consistent scalar-relativistic Hartree-Fock pseudopotentials by the 3d-transition metal elements, scandium through zinc. The pseudopotentials do not exhibit a singularity at the nucleus and are therefore suitable for quantum Monte Carlo (QMC) calculations. The pseudopotentials and the accompanying basis sets (VnZ with n=T,Q) are given in standard Gaussian representation and their parameter sets are presented. Coupled cluster, configuration interaction, and QMC studies are carried out for the scandium and titanium atoms and their oxides, demonstrating the good performance of the pseudopotentials. Even though the choice of pseudopotential form is motivated by QMC, these pseudopotentials can also be employed in other quantum chemical approaches.
Marsman, M; Grüneis, A; Paier, J; Kresse, G
2009-05-14
We present an implementation of the canonical formulation of second-order Møller-Plesset (MP2) perturbation theory within the projector-augmented-wave method under periodic boundary conditions using a plane wave basis set. To demonstrate the accuracy of our approach we show that our result for the atomization energy of a LiH molecule at the Hartree-Fock+MP2 level is in excellent agreement with well converged Gaussian-type-orbital calculations. To establish the feasibility of employing MP2 perturbation theory in its canonical form to systems that are periodic in three dimensions we calculated the cohesive energy of bulk LiH.
Saris, Anne; Hansen, Hendrik; Fekkes, Stein; Nillesen, Maartje; Rutten, Marcel; de Korte, Chris
2016-09-07
Conventional color Doppler imaging is limited, since it only provides velocity estimates along the ultrasound beam direction for a restricted field of view at a limited frame rate. High frame rate speckle tracking, using plane wave transmits, has shown potential for 2D blood velocity estimation. However, due to the lack of focusing in transmit, image quality gets reduced, which hampers speckle tracking. Although ultrafast imaging facilitates improved clutter filtering, it still remains a major challenge in blood velocity estimation. Signal drop-outs and poor velocity estimates are still present for high beam-to-flow angles and low blood flow velocities. In this work, ultrafast plane wave imaging was combined with multi-scale speckle tracking to assess the 2D blood velocity vector in a common carotid artery (CCA) flow field. A multi-angled plane wave imaging sequence was used to compare the performance of displacement compounding, coherent compounding and compound speckle tracking. Zero-degree plane wave imaging was also evaluated. The performance of the methods was evaluated before and after clutter filtering for the large range of velocities (0 to 1.5 m/s) that are normally present in a healthy CCA during the cardiac cycle. An extensive simulation study was performed, based on a sophisticated model of the CCA, to investigate and evaluate the performance of the methods at different pulse repetition frequencies and signal-to-noise levels. In vivo data were acquired of a healthy carotid artery bifurcation to support the simulation results. In general, methods utilizing compounding after speckle tracking, i.e., displacement compounding and compound speckle tracking, were least affected by clutter filtering and provided the most robust and accurate estimates for the entire velocity range. Displacement compounding, which uses solely axial information to estimate the velocity vector, provided most accurate velocity estimates, although it required sufficiently high pulse
Saris, Anne E C M; Hansen, Hendrik H G; Fekkes, Stein; Nillesen, Maartje M; Rutten, Marcel C M; de Korte, Chris L
2016-11-01
Conventional color Doppler imaging is limited, since it only provides velocity estimates along the ultrasound beam direction for a restricted field of view at a limited frame rate. High-frame-rate speckle tracking, using plane wave transmits, has shown potential for 2-D blood velocity estimation. However, due to the lack of focusing in transmit, image quality gets reduced, which hampers speckle tracking. Although ultrafast imaging facilitates improved clutter filtering, it still remains a major challenge in blood velocity estimation. Signal dropouts and poor velocity estimates are still present for high beam-to-flow angles and low blood flow velocities. In this paper, ultrafast plane wave imaging was combined with multiscale speckle tracking to assess the 2-D blood velocity vector in a common carotid artery (CCA) flow field. A multiangled plane wave imaging sequence was used to compare the performance of displacement compounding, coherent compounding, and compound speckle tracking. Zero-degree plane wave imaging was also evaluated. The performance of the methods was evaluated before and after clutter filtering for the large range of velocities (0-1.5 m/s) that are normally present in a healthy CCA during the cardiac cycle. An extensive simulation study was performed, based on a sophisticated model of the CCA, to investigate and evaluate the performance of the methods at different pulse repetition frequencies and signal-to-noise levels. In vivo data were acquired of a healthy carotid artery bifurcation to support the simulation results. In general, methods utilizing compounding after speckle tracking, i.e., displacement compounding and compound speckle tracking, were least affected by clutter filtering and provided the most robust and accurate estimates for the entire velocity range. Displacement compounding, which uses solely axial information to estimate the velocity vector, provided most accurate velocity estimates, although it required sufficiently high pulse
Yelkenci, Tanju; Paker, Selcuk
2008-01-01
In this paper, external electric field values that are derived from the largest peak average 10 g SAR (Specific Absorption Rate) results in a realistic human head model are compared with current IEEE and ICNIRP reference levels. The head is illuminated by a plane wave source at seven different frequencies ranging from 500 MHz to 2500 MHz, with five different incident directions and three polarizations. Results reveal that the presence of metallic wire spectacles reduces the external electric field levels in the region above 900 MHz. Comparison of derived electric field values shows that the current IEEE and ICNIRP safety limits provide a conservative estimate.
Dunnington, Benjamin D; Schmidt, J R
2012-06-12
Natural bond orbital (NBO) analysis is a powerful analysis technique capable of generating intuitive chemical representations of otherwise complex quantum mechanical electronic structure results, yielding a localized "Lewis-like" description of bonding and reactivity. We generalize this algorithm to periodic systems, thus expanding the scope of NBO analysis to bulk materials and/or periodic surface models. We employ a projection scheme to further expand the algorithm's applicability to ubiquitous plane-wave density functional theory (PW DFT) calculations. We also present a variety of example applications: examining bulk bonding and surface reconstruction and elucidating fundamental aspects of heterogeneous catalysis-all derived from rigorous underlying PW DFT calculations.
Nonlocal conservation laws for strings
Balachandran, A.P.; Stern, A.
1982-09-15
A finite number of nonlocal conservation laws are found in the Nambu-Goto string model. An infinite number of conserved currents may be obtained by embedding the string in more than 3+1 space-time dimensions. These currents resemble the nonlocal currents found in two-dimensional chiral models.
Rolling Tachyon in Nonlocal Cosmology
Joukovskaya, L.
2007-11-20
Nonlocal cosmological models derived from String Field Theory are considered. A new method for constructing rolling tachyon solutions in the FRW metric in two field configuration is proposed and solutions of the Friedman equations with nonlocal operator are presented. The cosmological properties of these solutions are discussed.
NASA Astrophysics Data System (ADS)
Senno, Gabriel; Bendersky, Ariel; Figueira, Santiago
2016-07-01
The concepts of randomness and non-locality are intimately intertwined outcomes of randomly chosen measurements over entangled systems exhibiting non-local correlations are, if we preclude instantaneous influence between distant measurement choices and outcomes, random. In this paper, we survey some recent advances in the knowledge of the interplay between these two important notions from a quantum information science perspective.
Nonlocal models in continuum mechanics
Johnson, N.L.; Phan-Thien, N.
1993-09-01
The recent appearance of nonlocal methods is examined in the light of traditional continuum mechanics. A comparison of nonlocal approaches in the fields of solid and fluid mechanics reveals that no consistent definition of a nonlocal theory has been used. We suggest a definition based on the violation of the principle of local action in continuum mechanics. From the consideration of the implications of a nonlocal theory based on this definition, we conclude that constitutive relations with nonlocal terms can confuse the traditional separation of the roles between conservation laws and constitutive relations. The diversity of motivations for the nonlocal approaches are presented, resulting primarily from deficiencies in numerical solutions to practical problems. To illustrate these concepts, the history of nonlocal terms in the field of viscoelastic fluids is reviewed. A specific example of a viscoelastic constitutive relation that contains a stress diffusion term is applied to a simple shear flow and found not to be a physical description of any known fluid. We conclude by listing questions that should be asked of nonlocal approaches.
Nonlocal and quasilocal field theories
NASA Astrophysics Data System (ADS)
Tomboulis, E. T.
2015-12-01
We investigate nonlocal field theories, a subject that has attracted some renewed interest in connection with nonlocal gravity models. We study, in particular, scalar theories of interacting delocalized fields, the delocalization being specified by nonlocal integral kernels. We distinguish between strictly nonlocal and quasilocal (compact support) kernels and impose conditions on them to insure UV finiteness and unitarity of amplitudes. We study the classical initial value problem for the partial integro-differential equations of motion in detail. We give rigorous proofs of the existence but accompanying loss of uniqueness of solutions due to the presence of future, as well as past, "delays," a manifestation of acausality. In the quantum theory we derive a generalization of the Bogoliubov causality condition equation for amplitudes, which explicitly exhibits the corrections due to nonlocality. One finds that, remarkably, for quasilocal kernels all acausal effects are confined within the compact support regions. We briefly discuss the extension to other types of fields and prospects of such theories.
The t-matrix resistivity of liquid rare earth metals using pseudopotential
Bhatia, Kamaldeep G.; Bhatt, N. K.; Vyas, P. R.; Gohel, V. B.
2015-06-24
Present theoretical study of liquid metal resistivity of some trivalent (La,Ce,Gd) and divalent (Eu,Yb) rare earth metals using pseudopotential has been carried out employing Ziman’s weak scattering and transition matrix (t-matrix) approaches. Our computed results of liquid metal resistivity using t-matrix approach are better than resistivity computed using Ziman’s approach and are also in excellent agreement with experimental results and other theoretical findings. The present study confirms that for f-shell metals pseudopotential must be determined uniquely and t-matrix approach is more physical in comparison with Ziman’s nearly free electron approach. The present pseudopotential accounts s-p-d hybridization properly. Such success encourages us to study remaining liquid state properties of these metals.
First-principle optimal local pseudopotentials construction via optimized effective potential method
NASA Astrophysics Data System (ADS)
Mi, Wenhui; Zhang, Shoutao; Wang, Yanchao; Ma, Yanming; Miao, Maosheng
2016-04-01
The local pseudopotential (LPP) is an important component of orbital-free density functional theory, a promising large-scale simulation method that can maintain information on a material's electron state. The LPP is usually extracted from solid-state density functional theory calculations, thereby it is difficult to assess its transferability to cases involving very different chemical environments. Here, we reveal a fundamental relation between the first-principles norm-conserving pseudopotential (NCPP) and the LPP. On the basis of this relationship, we demonstrate that the LPP can be constructed optimally from the NCPP for a large number of elements using the optimized effective potential method. Specially, our method provides a unified scheme for constructing and assessing the LPP within the framework of first-principles pseudopotentials. Our practice reveals that the existence of a valid LPP with high transferability may strongly depend on the element.
The t-matrix resistivity of liquid rare earth metals using pseudopotential
NASA Astrophysics Data System (ADS)
Bhatia, Kamaldeep G.; Bhatt, N. K.; Vyas, P. R.; Gohel, V. B.
2015-06-01
Present theoretical study of liquid metal resistivity of some trivalent (La,Ce,Gd) and divalent (Eu,Yb) rare earth metals using pseudopotential has been carried out employing Ziman's weak scattering and transition matrix (t-matrix) approaches. Our computed results of liquid metal resistivity using t-matrix approach are better than resistivity computed using Ziman's approach and are also in excellent agreement with experimental results and other theoretical findings. The present study confirms that for f-shell metals pseudopotential must be determined uniquely and t-matrix approach is more physical in comparison with Ziman's nearly free electron approach. The present pseudopotential accounts s-p-d hybridization properly. Such success encourages us to study remaining liquid state properties of these metals.
Tillmann, K; Thust, A; Urban, K
2004-04-01
With the availability of resolution boosting and delocalization minimizing techniques, for example, spherical aberration correction and exit-plane wave function reconstruction, high-resolution transmission electron microscopy is drawing to a breakthrough with respect to the atomic-scale imaging of common semiconductor materials. In the present study, we apply a combination of these two state-of-the-art techniques to investigate lattice defects in GaAs-based heterostructures at atomic resolution. Focusing on the direct imaging of stacking faults as well as the core structure of edge and partial dislocations, the practical capabilities of both techniques are illustrated. For the first time, we apply the technique of bright-atom contrast imaging at negative spherical aberration together with an appropriate overfocus setting for the investigation of lattice defects in a semiconductor material. For these purposes, the elastic displacements associated with lattice defects in GaAs viewed along the 110 zone axis are measured from experimental images using reciprocal space strain map algorithms. Moreover, we demonstrate the benefits of the retrieval of the exit-plane wave function not only for the elimination of residual imaging artefacts but also for the proper on-line alignment of specimens during operation of the electron microscope--a basic prerequisite to obtain a fair agreement between simulated images and experimental micrographs.
NASA Astrophysics Data System (ADS)
Roberts, O. W.; Li, X.; Jeska, L.
2014-08-01
Recent observations of astrophysical magnetic fields have shown the presence of fluctuations being wave-like (propagating in the plasma frame) and those described as being structure-like (advected by the plasma bulk velocity). Typically with single spacecraft missions it is impossible to differentiate between these two fluctuations, due to the inherent spatio-temporal ambiguity associated with a single point measurement. However missions such as Cluster which contain multiple spacecraft have allowed temporal and spatial changes to be resolved, with techniques such as the k-filtering technique. While this technique does not assume Taylor's hypothesis as is necessary with single spacecraft missions, it does require weak stationarity of the time series, and that the fluctuations can be described by a superposition of plane waves with random phase. In this paper we test whether the method can cope with a synthetic signal which is composed of a combination of non-random phase coherent structures with a mean radius d and a mean separation λ, as well as plane waves with random phase.
NASA Astrophysics Data System (ADS)
Roberts, O. W.; Li, X.; Jeska, L.
2014-12-01
Recent observations of astrophysical magnetic fields have shown the presence of fluctuations being wave-like (propagating in the plasma frame) and those described as being structure-like (advected by the plasma bulk velocity). Typically with single-spacecraft missions it is impossible to differentiate between these two fluctuations, due to the inherent spatio-temporal ambiguity associated with a single point measurement. However missions such as Cluster which contain multiple spacecraft have allowed for temporal and spatial changes to be resolved, using techniques such as k filtering. While this technique does not assume Taylor's hypothesis it requires both weak stationarity of the time series and that the fluctuations can be described by a superposition of plane waves with random phases. In this paper we test whether the method can cope with a synthetic signal which is composed of a combination of non-random-phase coherent structures with a mean radius d and a mean separation λ, as well as plane waves with random phase.
Takahashi, Yukio; Nishino, Yoshinori; Ishikawa, Tetsuya; Tsutsumi, Ryosuke; Kubo, Hideto; Furukawa, Hayato; Mimura, Hidekazu; Matsuyama, Satoshi; Zettsu, Nobuyuki; Matsubara, Eiichiro; Yamauchi, Kazuto
2009-08-01
X-ray waves in the center of the beam waist of nearly diffraction limited focused x-ray beams can be considered to have amplitude and phase that are both almost uniform, i.e., they are x-ray plane waves. Here we report the results of an experimental demonstration of high-resolution diffraction microscopy using the x-ray plane wave of the synchrotron x-ray beam focused using Kirkpatrik-Baez mirrors. A silver nanocube with an edge length of {approx}100 nm is illuminated with the x-ray beam focused to a {approx}1 {mu}m spot at 12 keV. A high-contrast symmetric diffraction pattern of the nanocube is observed in the forward far field. An image of the nanocube is successfully reconstructed by an iterative phasing method and its half-period resolution is 3.0 nm. This method does not only dramatically improve the spatial resolution of x-ray microscopy but also is a key technology for realizing single-pulse diffractive imaging using x-ray free-electron lasers.
Landau parameters for energy density functionals generated by local finite-range pseudopotentials
NASA Astrophysics Data System (ADS)
Idini, A.; Bennaceur, K.; Dobaczewski, J.
2017-06-01
In Landau theory of Fermi liquids, the particle-hole interaction near the Fermi energy in different spin-isospin channels is probed in terms of an expansion over the Legendre polynomials. This provides a useful and efficient way to constrain properties of nuclear energy density functionals in symmetric nuclear matter and finite nuclei. In this study, we present general expressions for Landau parameters corresponding to a two-body central local regularized pseudopotential. We also show results obtained for two recently adjusted NLO and N2LO parametrizations. Such pseudopotentials will be used to determine mean-field and beyond-mean-field properties of paired nuclei across the entire nuclear chart.
Extent of multiparticle quantum nonlocality
Jones, Nick S.; Linden, Noah; Massar, Serge
2005-04-01
It is well known that entangled quantum states are nonlocal: the corrrelations between local measurements carried out on these states cannot be reproduced by local hidden variable models. Svetlichny, followed by others, showed that multipartite quantum states are more nonlocal than bipartite ones in the sense that even some nonlocal classical models with (super-luminal) communication between some of the parties cannot reproduce the quantum correlations. Here we study in detail the kinds of nonlocality present in quantum states. More precisely, we enquire what kinds of classical communication patterns cannot reproduce quantum correlations. By studying the extremal points of the space of all multiparty probability distributions, in which all parties can make one of a pair of measurements each with two possible outcomes, we find a necessary condition for classical nonlocal models to reproduce the statistics of all quantum states. This condition extends and generalizes work of Svetlichny and others in which it was showed that a particular class of classical nonlocal models, the 'separable' models, cannot reproduce the statistics of all multiparticle quantum states. Our condition shows that the nonlocality present in some entangled multiparticle quantum states is much stronger than previously thought. We also study the sufficiency of our condition.
Nonlocal gravity: Conformally flat spacetimes
NASA Astrophysics Data System (ADS)
Bini, Donato; Mashhoon, Bahram
2016-04-01
The field equations of the recent nonlocal generalization of Einstein’s theory of gravitation are presented in a form that is reminiscent of general relativity. The implications of the nonlocal field equations are studied in the case of conformally flat spacetimes. Even in this simple case, the field equations are intractable. Therefore, to gain insight into the nature of these equations, we investigate the structure of nonlocal gravity (NLG) in 2D spacetimes. While any smooth 2D spacetime is conformally flat and satisfies Einstein’s field equations, only a subset containing either a Killing vector or a homothetic Killing vector can satisfy the field equations of NLG.
Nonlocal anomalous Hall effect
NASA Astrophysics Data System (ADS)
Zhang, Shulei; Vignale, Giovanni
Anomalous Hall effect (AHE) is a distinctive transport property of ferromagnetic metals arising from spin orbit coupling (SOC) in concert with spontaneous spin polarization. Nonetheless, recent experiments have shown that the effect also appears in a nonmagnetic metal in contact with a magnetic insulator. The main puzzle lies in the apparent absence of spin polarized electrons in the non-magnetic metal. Here, we theoretically demonstrate that the scattering of electrons from a rough metal-insulator interface is generally spin-dependent, which results in mutual conversion between spin and charge currents flowing in the plane of the layer. It is the current-carrying spin polarized electrons and the spin Hall effect in the bulk of the metal layer that conspire to generate the AH current. This novel AHE differs from the conventional one only in the spatial separation of the SOC and the magnetization, so we name it as nonlocal AHE. In contrast to other previously proposed mechanisms (e.g., spin Hall AHE and magnetic proximity effect (MPE)), the nonlocal AHE appears on the first order of spin Hall angle and does not rely on the induced moments in the metal layer, which make it experimentally detectable by contrasting the AH current directions of two layered structures such as Pt/Cu/YIG and β -Ta/Cu/YIG (with a thin inserted Cu layer to eliminate the MPE). We predict that the directions of the AH currents in these two trilayers would be opposite since the spin Hall angles of Pt and β -Ta are of opposite signs. Work supported by NSF Grants DMR-1406568.
NASA Astrophysics Data System (ADS)
Rakhecha, Shalu; Bhatt, N. K.; Vyas, P. R.; Gohel, V. B.
2016-05-01
In the present communication, we have computed static and dynamic properties (binding energy-E, bulk modulus-B and second moment- <ω2>) as well as first order pressure induced phase transition (FCC-BCC) using local form of pseudopotential for Calcium and Strontium. The form of pseudopotential used for the computation is directly extracted from Generalized Pseudopotential Theory (GPT) which contains three parameters (rc, rd and β). We have suggested a simple method using which pseudopotential is determined by single parameter (β). Our computed results for binding energy and bulk modulii are in excellent agreement with experimental findings and are better than other theoretical results. The present study confirms that s-d hybridization is accounted properly in the presently used pseudopotential and can be extended for the study of lattice mechanical properties of these metals.
NASA Astrophysics Data System (ADS)
Yadav, Jayprakash; Rafique, S. M.; Kumari, Shanti
2009-10-01
In the present paper some superconducting (SC) state parameters of metals Ga, Cd and In have been studied through Harrison's First Principle [HFP] pseudopotential technique using McMillan's formalism. The impact of choosing two different sets of core energy eigenvalues viz. Herman-Skillman and Clementi (or Experimental) has been studied.
Comment on "comparison of the widely used HF pseudo-potentials: MH + (M = Fe, Ru, Os)"
NASA Astrophysics Data System (ADS)
Andrae, Dirk; Dolg, Michael; Stoll, Hermann; Ermler, Walter C.
1994-04-01
It is shown through calculations of the ionization energies of the Fe and Ru atoms that errors attributed to pseudo-potential defects in a recent paper by Leininger [Chem. Phys. Letters 205 (1993) 301] are due, instead, to shortcomings of their valence-interaction treatment.
Norm-conserving pseudopotentials with chemical accuracy compared to all-electron calculations
NASA Astrophysics Data System (ADS)
Willand, Alex; Kvashnin, Yaroslav O.; Genovese, Luigi; Vázquez-Mayagoitia, Álvaro; Deb, Arpan Krishna; Sadeghi, Ali; Deutsch, Thierry; Goedecker, Stefan
2013-03-01
By adding a nonlinear core correction to the well established dual space Gaussian type pseudopotentials for the chemical elements up to the third period, we construct improved pseudopotentials for the Perdew-Burke-Ernzerhof [J. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 77, 3865 (1996), 10.1103/PhysRevLett.77.3865] functional and demonstrate that they exhibit excellent accuracy. Our benchmarks for the G2-1 test set show average atomization energy errors of only half a kcal/mol. The pseudopotentials also remain highly reliable for high pressure phases of crystalline solids. When supplemented by empirical dispersion corrections [S. Grimme, J. Comput. Chem. 27, 1787 (2006), 10.1002/jcc.20495; S. Grimme, J. Antony, S. Ehrlich, and H. Krieg, J. Chem. Phys. 132, 154104 (2010), 10.1063/1.3382344] the average error in the interaction energy between molecules is also about half a kcal/mol. The accuracy that can be obtained by these pseudopotentials in combination with a systematic basis set is well superior to the accuracy that can be obtained by commonly used medium size Gaussian basis sets in all-electron calculations.
NASA Astrophysics Data System (ADS)
Li, Qing; Luo, K. H.
2013-11-01
In this paper, we aim to address an important issue about the pseudopotential lattice Boltzmann (LB) model, which has attracted much attention as a mesoscopic model for simulating interfacial dynamics of complex fluids, but suffers from the problem that the surface tension cannot be tuned independently of the density ratio. In the literature, a multirange potential was devised to adjust the surface tension [Sbragaglia , Phys. Rev. EPLEEE81063-651X10.1103/PhysRevE.75.026702 75, 026702 (2007)]. However, it was recently found that the density ratio of the system will be changed when the multirange potential is employed to adjust the surface tension. An alternative approach is therefore proposed in the present work. The basic strategy is to add a source term to the LB equation so as to tune the surface tension of the pseudopotential LB model. The proposed approach can guarantee that the adjustment of the surface tension does not affect the mechanical stability condition of the pseudopotential LB model, and thus provides a separate control of the surface tension and the density ratio. Meanwhile, it still retains the mesoscopic feature and the computational simplicity of the pseudopotential LB model. Numerical simulations are carried out for stationary droplets, capillary waves, and droplet splashing on a thin liquid film. The numerical results demonstrate that the proposed approach is capable of achieving a tunable surface tension over a very wide range and can keep the density ratio unchanged when adjusting the surface tension.
Complementarity of genuine multipartite Bell nonlocality
NASA Astrophysics Data System (ADS)
Sami, Sasha; Chakrabarty, Indranil; Chaturvedi, Anubhav
2017-08-01
We introduce a feature of no-signaling (Bell) nonlocal theories: namely, when a system of multiple parties manifests genuine nonlocal correlation, then there cannot be arbitrarily high nonlocal correlation among any subset of the parties. We call this feature complementarity of genuine multipartite nonlocality. We use Svetlichny's criterion for genuine multipartite nonlocality and nonlocal games to derive the complementarity relations under no-signaling constraints. We find that the complementarity relations are tightened for the much stricter quantum constraints. We compare this notion with the well-known notion of monogamy of nonlocality. As a consequence, we obtain tighter nontrivial monogamy relations that take into account genuine multipartite nonlocality. Furthermore, we provide numerical evidence showcasing this feature using a bipartite measure and several other well-known tripartite measures of nonlocality.
NASA Astrophysics Data System (ADS)
Zhang, Shen; Wang, Hongwei; Kang, Wei; Zhang, Ping; He, X. T.
2016-04-01
An extended first-principles molecular dynamics (FPMD) method based on Kohn-Sham scheme is proposed to elevate the temperature limit of the FPMD method in the calculation of dense plasmas. The extended method treats the wave functions of high energy electrons as plane waves analytically and thus expands the application of the FPMD method to the region of hot dense plasmas without suffering from the formidable computational costs. In addition, the extended method inherits the high accuracy of the Kohn-Sham scheme and keeps the information of electronic structures. This gives an edge to the extended method in the calculation of mixtures of plasmas composed of heterogeneous ions, high-Z dense plasmas, lowering of ionization potentials, X-ray absorption/emission spectra, and opacities, which are of particular interest to astrophysics, inertial confinement fusion engineering, and laboratory astrophysics.
NASA Technical Reports Server (NTRS)
Lester, H. C.; Posey, J. W.
1976-01-01
A discrete frequency study is made of the influence of source characteristics on the optimal properties of acoustically lined uniform and two section ducts. Two simplified sources, a plane wave and a monopole, are considered in some detail and over a greater frequency range than has been previously studied. Source and termination impedance effects are given limited examination. An example of a turbomachinery source and three associated source variants is also presented. Optimal liner designs based on modal theory approach the Cremer criterion at low frequencies and the geometric acoustics limit at high frequencies. Over an intermediate frequency range, optimal two section liners produced higher transmission losses than did the uniform configurations. Source distribution effects were found to have a significant effect on optimal liner design, but source and termination impedance effects appear to be relatively unimportant.
NASA Technical Reports Server (NTRS)
Unz, H.; Roskam, J.
1979-01-01
The theory of acoustic plane wave normally incident on a clamped panel in a rectangular duct is developed. The coupling theory between the elastic vibrations of the panel (plate) and the acoustic wave propagation in infinite space and in the rectangular duct is considered. The partial differential equation which governs the vibration of the panel (plate) is modified by adding to its stiffness (spring) forces and damping forces, and the fundamental resonance frequency and the attenuation factor are discussed. The noise reduction expression based on the theory is found to agree well with the corresponding experimental data of a sample aluminum panel in the mass controlled region, the damping controlled region, and the stiffness controlled region. All the frequency positions of the upward and downward resonance spikes in the sample experimental data are identified theoretically as resulting from four cross interacting major resonance phenomena: the cavity resonance, the acoustic resonance, the plate resonance, and the wooden back panel resonance.
NASA Astrophysics Data System (ADS)
Ni, Gu-Yan; Yan, Li; Yuan, Nai-Chang
2008-10-01
This paper reports that an analytic method is used to calculate the load responses of the two-wire transmission line excited by a plane-wave directly in the time domain. By the frequency-domain Baum-Liu-Tesche (BLT) equation, the time-domain analytic solutions are obtained and expressed in an infinite geometric series. Moreover, it is shown that there exist only finite nonzero terms in the infinite geometric series if the time variate is at a finite interval. In other word, the time-domain analytic solutions are expanded in a finite geometric series indeed if the time variate is at a finite interval. The computed results are subsequently compared with transient responses obtained by using the frequency-domain BLT equation via a fast Fourier transform, and the agreement is excellent.
Zhang, Shen; Kang, Wei; Wang, Hongwei; Zhang, Ping; He, X. T.
2016-04-15
An extended first-principles molecular dynamics (FPMD) method based on Kohn-Sham scheme is proposed to elevate the temperature limit of the FPMD method in the calculation of dense plasmas. The extended method treats the wave functions of high energy electrons as plane waves analytically and thus expands the application of the FPMD method to the region of hot dense plasmas without suffering from the formidable computational costs. In addition, the extended method inherits the high accuracy of the Kohn-Sham scheme and keeps the information of electronic structures. This gives an edge to the extended method in the calculation of mixtures of plasmas composed of heterogeneous ions, high-Z dense plasmas, lowering of ionization potentials, X-ray absorption/emission spectra, and opacities, which are of particular interest to astrophysics, inertial confinement fusion engineering, and laboratory astrophysics.
Preston, Thomas C; Reid, Jonathan P
2015-06-01
The angular scattering of light from a homogeneous spherical particle in a zeroth-order Bessel beam is calculated using a generalized Lorenz-Mie theory. We investigate the dependence of the angular scattering on the semi-apex angle of the Bessel beam and discuss the major features of the resulting scattering plots. We also compare Bessel beam scattering to plane wave scattering and provide criterion for when the difference between the two cases can be considered negligible. Finally, we discuss a method for characterizing spherical particles using angular light scattering. This work is useful to researchers who are interested in characterizing particles trapped in optical beams using angular dependent light scattering measurements.
Flesch, Martin; Pernot, Mathieu; Provost, Jean; Ferin, Guillaume; Nguyen-Dinh, An; Tanter, Mickael; Deffieux, Thomas
2017-03-01
4D ultrafast ultrasound imaging was recently shown using a 2D matrix (i.e., fully populated) connected to a 1024-channel ultrafast ultrasound scanner. In this study, we investigate the Row-Column Addressing (RCA) matrix approach, which allows a reduction of independent channels from N x N to N + N, with a dedicated beamforming strategy for ultrafast ultrasound imaging based on the coherent compounding of Orthogonal Plane Wave (OPW). OPW is based on coherent compounding of plane wave transmissions in one direction with receive beamforming along the orthogonal direction and its orthogonal companion sequence. Such coherent recombination of complementary orthogonal sequences leads to virtual transmit focusing in both directions which results into a final isotropic Point Spread Function (PSF). In this study, a 32 x 32 2D matrix array probe (1024 channels), centered at 5 MHz was considered. An RCA array, of same footprint with 32 + 32 elements (64 channels), was emulated by summing the elements either along a line or a column in software prior to beamforming. This approach allowed for the direct comparison of the 32 + 32 RCA scheme to the optimal fully sampled 32 x 32 2D matrix configuration, which served as the gold standard. This approach was first studied through PSF simulations and then validated experimentally on a phantom consisting of anechoic cysts and echogenic wires. The Contrast-to-Noise Ratio (CNR) and the lateral resolution of the RCA approach were found to be approximately equal to half (in decibel) and twice the values, respectively, obtained when using the 2D matrix approach. Results in a Doppler phantom and the human humeral artery in vivo confirmed that OPW compound imaging using emulated RCA matrix can achieve a power Doppler with sufficient contrast to recover the vein shape and provides an accurate Doppler spectrum.
NASA Technical Reports Server (NTRS)
Noh, H. M.; Pathak, P. H.
1986-01-01
An approximate but sufficiently accurate high frequency solution which combines the uniform geometrical theory of diffraction (UTD) and the aperture integration (AI) method is developed for analyzing the problem of electromagnetic (EM) plane wave scattering by an open-ended, perfectly-conducting, semi-infinite hollow rectangular waveguide (or duct) with a thin, uniform layer of lossy or absorbing material on its inner wall, and with a planar termination inside. In addition, a high frequency solution for the EM scattering by a two dimensional (2-D), semi-infinite parallel plate waveguide with a absorber coating on the inner walls is also developed as a first step before analyzing the open-ended semi-infinite three dimensional (3-D) rectangular waveguide geometry. The total field scattered by the semi-infinite waveguide consists firstly of the fields scattered from the edges of the aperture at the open-end, and secondly of the fields which are coupled into the waveguide from the open-end and then reflected back from the interior termination to radiate out of the open-end. The first contribution to the scattered field can be found directly via the UTD ray method. The second contribution is found via the AI method which employs rays to describe the fields in the aperture that arrive there after reflecting from the interior termination. It is assumed that the direction of the incident plane wave and the direction of observation lie well inside the forward half space tht exists outside the half space containing the semi-infinite waveguide geometry. Also, the medium exterior to the waveguide is assumed to be free space.
Nonlocal optical response in metallic nanostructures.
Raza, Søren; Bozhevolnyi, Sergey I; Wubs, Martijn; Asger Mortensen, N
2015-05-13
This review provides a broad overview of the studies and effects of nonlocal response in metallic nanostructures. In particular, we thoroughly present the nonlocal hydrodynamic model and the recently introduced generalized nonlocal optical response (GNOR) model. The influence of nonlocal response on plasmonic excitations is studied in key metallic geometries, such as spheres and dimers, and we derive new consequences due to the GNOR model. Finally, we propose several trajectories for future work on nonlocal response, including experimental setups that may unveil further effects of nonlocal response.
Nonlocal Anomalous Hall Effect.
Zhang, Steven S-L; Vignale, Giovanni
2016-04-01
The anomalous Hall (AH) effect is deemed to be a unique transport property of ferromagnetic metals, caused by the concerted action of spin polarization and spin-orbit coupling. Nevertheless, recent experiments have shown that the effect also occurs in a nonmagnetic metal (Pt) in contact with a magnetic insulator [yttrium iron garnet (YIG)], even when precautions are taken to ensure that there is no induced magnetization in the metal. We propose a theory of this effect based on the combined action of spin-dependent scattering from the magnetic interface and the spin-Hall effect in the bulk of the metal. At variance with previous theories, we predict the effect to be of first order in the spin-orbit coupling, just as the conventional anomalous Hall effect-the only difference being the spatial separation of the spin-orbit interaction and the magnetization. For this reason we name this effect the nonlocal anomalous Hall effect and predict that its sign will be determined by the sign of the spin-Hall angle in the metal. The AH conductivity that we calculate from our theory is in order of magnitude agreement with the measured values in Pt/YIG structures.
Bipartite units of nonlocality
Forster, Manuel; Wolf, Stefan
2011-10-15
Imagine a task in which a group of separated players aim to simulate a statistic that violates a Bell inequality. Given measurement choices the players shall announce an output based solely on the results of local operations--which they can discuss before the separation--on shared random data and shared copies of a so-called unit correlation. In the first part of this paper we show that in such a setting the simulation of any bipartite correlation, not containing the possibility of signaling, can be made arbitrarily accurate by increasing the number of shared Popescu-Rohrlich (PR) boxes. This establishes the PR box as a simple asymptotic unit of bipartite nonlocality. In the second part we study whether this property extends to the multipartite case. More generally, we ask if it is possible for separated players to asymptotically reproduce any nonsignaling statistic by local operations on bipartite unit correlations. We find that nonadaptive strategies are limited by a constant accuracy and that arbitrary strategies on n resource correlations make a mistake with a probability greater or equal to c/n, for some constant c.
Nonlocal Anomalous Hall Effect
NASA Astrophysics Data System (ADS)
Zhang, Steven S.-L.; Vignale, Giovanni
2016-04-01
The anomalous Hall (AH) effect is deemed to be a unique transport property of ferromagnetic metals, caused by the concerted action of spin polarization and spin-orbit coupling. Nevertheless, recent experiments have shown that the effect also occurs in a nonmagnetic metal (Pt) in contact with a magnetic insulator [yttrium iron garnet (YIG)], even when precautions are taken to ensure that there is no induced magnetization in the metal. We propose a theory of this effect based on the combined action of spin-dependent scattering from the magnetic interface and the spin-Hall effect in the bulk of the metal. At variance with previous theories, we predict the effect to be of first order in the spin-orbit coupling, just as the conventional anomalous Hall effect—the only difference being the spatial separation of the spin-orbit interaction and the magnetization. For this reason we name this effect the nonlocal anomalous Hall effect and predict that its sign will be determined by the sign of the spin-Hall angle in the metal. The AH conductivity that we calculate from our theory is in order of magnitude agreement with the measured values in Pt /YIG structures.
Nonlocal Intracranial Cavity Extraction
Manjón, José V.; Eskildsen, Simon F.; Coupé, Pierrick; Romero, José E.; Collins, D. Louis; Robles, Montserrat
2014-01-01
Automatic and accurate methods to estimate normalized regional brain volumes from MRI data are valuable tools which may help to obtain an objective diagnosis and followup of many neurological diseases. To estimate such regional brain volumes, the intracranial cavity volume (ICV) is often used for normalization. However, the high variability of brain shape and size due to normal intersubject variability, normal changes occurring over the lifespan, and abnormal changes due to disease makes the ICV estimation problem challenging. In this paper, we present a new approach to perform ICV extraction based on the use of a library of prelabeled brain images to capture the large variability of brain shapes. To this end, an improved nonlocal label fusion scheme based on BEaST technique is proposed to increase the accuracy of the ICV estimation. The proposed method is compared with recent state-of-the-art methods and the results demonstrate an improved performance both in terms of accuracy and reproducibility while maintaining a reduced computational burden. PMID:25328511
Accurate and efficient computation of nonlocal potentials based on Gaussian-sum approximation
NASA Astrophysics Data System (ADS)
Exl, Lukas; Mauser, Norbert J.; Zhang, Yong
2016-12-01
We introduce an accurate and efficient method for the numerical evaluation of nonlocal potentials, including the 3D/2D Coulomb, 2D Poisson and 3D dipole-dipole potentials. Our method is based on a Gaussian-sum approximation of the singular convolution kernel combined with a Taylor expansion of the density. Starting from the convolution formulation of the nonlocal potential, for smooth and fast decaying densities, we make a full use of the Fourier pseudospectral (plane wave) approximation of the density and a separable Gaussian-sum approximation of the kernel in an interval where the singularity (the origin) is excluded. The potential is separated into a regular integral and a near-field singular correction integral. The first is computed with the Fourier pseudospectral method, while the latter is well resolved utilizing a low-order Taylor expansion of the density. Both parts are accelerated by fast Fourier transforms (FFT). The method is accurate (14-16 digits), efficient (O (Nlog N) complexity), low in storage, easily adaptable to other different kernels, applicable for anisotropic densities and highly parallelizable.
Nonlocal Measurements via Quantum Erasure.
Brodutch, Aharon; Cohen, Eliahu
2016-02-19
Nonlocal observables play an important role in quantum theory, from Bell inequalities and various postselection paradoxes to quantum error correction codes. Instantaneous measurement of these observables is known to be a difficult problem, especially when the measurements are projective. The standard von Neumann Hamiltonian used to model projective measurements cannot be implemented directly in a nonlocal scenario and can, in some cases, violate causality. We present a scheme for effectively generating the von Neumann Hamiltonian for nonlocal observables without the need to communicate and adapt. The protocol can be used to perform weak and strong (projective) measurements, as well as measurements at any intermediate strength. It can also be used in practical situations beyond nonlocal measurements. We show how the protocol can be used to probe a version of Hardy's paradox with both weak and strong measurements. The outcomes of these measurements provide a nonintuitive picture of the pre- and postselected system. Our results shed new light on the interplay between quantum measurements, uncertainty, nonlocality, causality, and determinism.
Generating tripartite nonlocality from bipartite resources
NASA Astrophysics Data System (ADS)
Su, Zhaofeng
2017-01-01
Nonlocality is an important resource for quantum information processing. Tripartite nonlocality is more difficult to produce in experiments than bipartite ones. In this paper, we analyze a simple setting to generate tripartite nonlocality from two classes of bipartite resources, namely two-qubit entangled pure states and Werner states. Upper bounds on the tripartite nonlocality, characterized by the maximal violation of Svetlichny inequalities, are given, and the optimal measurements to achieve these bounds are provided.
Cryptographic quantum bound on nonlocality
NASA Astrophysics Data System (ADS)
Ishizaka, Satoshi
2017-02-01
Information causality states that the information obtainable by a receiver cannot be greater than the communication bits from a sender, even if they utilize no-signaling resources. This physical principle successfully explains some boundaries between quantum and postquantum nonlocal correlations, where the obtainable information reaches the maximum limit. We show that no-signaling resources of pure partially entangled states produce randomness (or noise) in the communication bits, and achievement of the maximum limit is impossible, i.e., the information causality principle is insufficient for the full identification of the quantum boundaries already for bipartite settings. The nonlocality inequalities such as so-called the Tsirelson inequality are extended to show how such randomness affects the strength of nonlocal correlations. As a result, a relation followed by most of quantum correlations in the simplest Bell scenario is revealed. The extended inequalities reflect the cryptographic principle such that a completely scrambled message cannot carry information.
Fidelity based measurement induced nonlocality
NASA Astrophysics Data System (ADS)
Muthuganesan, R.; Sankaranarayanan, R.
2017-09-01
In this paper, we propose measurement induced nonlocality (MIN) using a metric based on fidelity to capture global nonlocal effect of a quantum state due to locally invariant projective measurements. This quantity is a remedy for local ancilla problem in the original definition of MIN. We present an analytical expression of the proposed version of MIN for pure bipartite state and 2 × n dimensional mixed state. We also provide an upper bound of the MIN for general mixed state. Finally, we compare this quantity with MINs based on Hilbert-Schmidt norm and skew information for higher dimensional Werner and isotropic states.
Pseudopotential calculations of the structure and harmonic frequencies of HSbO 3 and HAsO 3
NASA Astrophysics Data System (ADS)
Jarrett-Sprague, Stephen A.; Hillier, Ian H.; Burton, Neil A.; Guest, Martyn F.
1990-06-01
The structure and harmonic frequencies of HSbO 3 and HAsO 3 have been predicted using atomic pseudopotentials and have resulted in an assignment of the observed infrared absorptions of the isotomers of HSbO 3.
Magnitude of pseudopotential localization errors in fixed node diffusion quantum Monte Carlo
NASA Astrophysics Data System (ADS)
Krogel, Jaron T.; Kent, P. R. C.
2017-06-01
Growth in computational resources has lead to the application of real space diffusion quantum Monte Carlo to increasingly heavy elements. Although generally assumed to be small, we find that when using standard techniques, the pseudopotential localization error can be large, on the order of an electron volt for an isolated cerium atom. We formally show that the localization error can be reduced to zero with improvements to the Jastrow factor alone, and we define a metric of Jastrow sensitivity that may be useful in the design of pseudopotentials. We employ an extrapolation scheme to extract the bare fixed node energy and estimate the localization error in both the locality approximation and the T-moves schemes for the Ce atom in charge states 3+ and 4+. The locality approximation exhibits the lowest Jastrow sensitivity and generally smaller localization errors than T-moves although the locality approximation energy approaches the localization free limit from above/below for the 3+/4+ charge state. We find that energy minimized Jastrow factors including three-body electron-electron-ion terms are the most effective at reducing the localization error for both the locality approximation and T-moves for the case of the Ce atom. Less complex or variance minimized Jastrows are generally less effective. Our results suggest that further improvements to Jastrow factors and trial wavefunction forms may be needed to reduce localization errors to chemical accuracy when medium core pseudopotentials are applied to heavy elements such as Ce.
NASA Astrophysics Data System (ADS)
Hangele, Tim; Dolg, Michael
2013-01-01
Relativistic energy-consistent pseudopotentials modelling the Dirac-Coulomb-Breit Hamiltonian with a finite nucleus model for the superheavy elements with nuclear charges 111-118 were calibrated in atomic and molecular calculations against fully relativistic all-electron reference data. Various choices for the adjustment of the f-potentials were investigated and an improved parametrization is recommended. Using the resulting pseudopotentials relativistic all-electron reference data can be reproduced at the self-consistent field level with average absolute (relative) errors of 0.0030 Å (0.15%) for bond lengths and 2.79 N m-1 (1.26%) for force constants for 24 diatomic test molecules, i.e., neutral or singly charged monohydrides, monofluorides, and monochlorides with closed-shell electronic structure. At the second-order Møller-Plesset perturbation theory level the corresponding average deviations are 0.0033 Å (0.15%) for bond lengths and 2.86 N m-1 (1.40%) for force constants. Corresponding improved f-potentials were also derived for the pseudopotentials modelling in addition the leading contributions from quantum electrodynamics.
Khajepor, Sorush; Wen, John; Chen, Baixin
2015-02-01
Pseudopotential lattice Boltzmann (LB) models have been recognized as efficient numerical tools to simulate complex fluid systems, including those at thermodynamic equilibrium states and with phase transitions. However, when the equation of state (EOS) of real fluids is implemented, the existing pseudopotential LB models suffer from thermodynamic inconsistency. This study presents a multipseudopotential interparticle interaction (MPI) scheme, which is fully consistent with thermodynamics and applicable to engineering applications. In this framework, multiple pseudopotentials are employed to represent dominant interaction potentials at different extents of the mean free path of particles. By simulating van der Waals and Carnahan-Starling fluids, it is demonstrated that the MPI scheme can correctly simulate the physical nature of two-phase systems on the lattice including the continuum predictions of liquid-vapor coexistence states and the sound speeds in liquid and vapor phases. It is also shown that the lattice interactions of the MPI scheme represent underlying molecular interactions as they vary in a broad range from strong short-distance repulsions to weak long-distance attractions during phase transitions. Consequently, the MPI is proved to be a reliable LB scheme as it avoids generating unphysical potentials in implementing the EOSs of real fluids and limiting the spurious velocities at the interface of two-phase systems. Additionally, a straightforward procedure is suggested and discussed to preset the MPI system with the two-phase properties of a selected fluid.
NASA Astrophysics Data System (ADS)
Matsushima, S.; Sanchez-Sesma, F. J.; Kawase, H.
2010-12-01
In this work we explore the application of diffuse field concepts to analyze strong motion records at a site in which site effects can be described using a one dimensional (1D) model. For this case we derived a corollary of Claerbout (1968) result for 1D layered medium. We found that the imaginary part of Green function at the free surface is proportional to the square of the absolute value of the corresponding transfer function for a plane, vertically incident wave with unit amplitude. Average strong ground motion in a "sufficiently" flat layered site will be statistically equivalent. We may conceive the illumination as produced by incident plane waves. They represent the most important part of earthquake ground motions. Their associated motions, being multiple scattered, are formed of waves that sample significant portions of the considered area. This is a distinctive feature of earthquake motions, for which the excited domain is large, basically from the source to the receiver. For a set of incoming plane waves (of P, SV, and SH types) with varying azimuths and incidence angles we assume that the ground motion will be spatially homogeneous in a statistical sense. In other words, the average of normalized ground motion spectral densities will depend only on depth. Therefore, we can apply a 1D description of wave propagation for a diffuse (average) field of ground motions. To prove the above hypothesis for H/V ratios of earthquake ground motions, we first show a comparison of averaged synthetics of 1D underground structures with a corresponding simple theoretical prediction from 1D transfer functions. After summing up a few hundreds of synthetics with different angles of incidences, azimuths, and polarizations, we can obtain identical H/V ratios that the simple theory of diffuse field predicts. Then we show several examples of H/V ratios for actual seismic motions observed in Japan. We found that the earthquake H/V ratios are quite stable (and converging rapidly
NASA Astrophysics Data System (ADS)
Flesch, M.; Pernot, M.; Provost, J.; Ferin, G.; Nguyen-Dinh, A.; Tanter, M.; Deffieux, T.
2017-06-01
4D ultrafast ultrasound imaging was recently shown using a 2D matrix (i.e. fully populated) connected to a 1024-channel ultrafast ultrasound scanner. In this study, we investigate the row-column addressing (RCA) matrix approach, which allows a reduction of independent channels from N × N to N + N, with a dedicated beamforming strategy for ultrafast ultrasound imaging based on the coherent compounding of orthogonal plane wave (OPW). OPW is based on coherent compounding of plane wave transmissions in one direction with receive beamforming along the orthogonal direction and its orthogonal companion sequence. Such coherent recombination of complementary orthogonal sequences leads to the virtual transmit focusing in both directions which results into a final isotropic point spread function (PSF). In this study, a 32 × 32 2D matrix array probe (1024 channels), centered at 5 MHz was considered. An RCA array, of same footprint with 32 + 32 elements (64 channels), was emulated by summing the elements either along a line or a column in software prior to beamforming. This approach allowed for the direct comparison of the 32 + 32 RCA scheme to the optimal fully sampled 32 × 32 2D matrix configuration, which served as the gold standard. This approach was first studied through PSF simulations and then validated experimentally on a phantom consisting of anechoic cysts and echogenic wires. The contrast-to-noise ratio and the lateral resolution of the RCA approach were found to be approximately equal to half (in decibel) and twice the values, respectively, obtained when using the 2D matrix approach. Results in a Doppler phantom and the human humeral artery in vivo confirmed that ultrafast Doppler imaging can be achieved with reduced performances when compared against the equivalent 2D matrix. Volumetric anatomic Doppler rendering and voxel-based pulsed Doppler quantification are presented as well. OPW compound imaging
Learning Non-Local Dependencies
ERIC Educational Resources Information Center
Kuhn, Gustav; Dienes, Zoltan
2008-01-01
This paper addresses the nature of the temporary storage buffer used in implicit or statistical learning. Kuhn and Dienes [Kuhn, G., & Dienes, Z. (2005). Implicit learning of nonlocal musical rules: implicitly learning more than chunks. "Journal of Experimental Psychology-Learning Memory and Cognition," 31(6) 1417-1432] showed that people could…
Nonlocal Equations with Measure Data
NASA Astrophysics Data System (ADS)
Kuusi, Tuomo; Mingione, Giuseppe; Sire, Yannick
2015-08-01
We develop an existence, regularity and potential theory for nonlinear integrodifferential equations involving measure data. The nonlocal elliptic operators considered are possibly degenerate and cover the case of the fractional p-Laplacean operator with measurable coefficients. We introduce a natural function class where we solve the Dirichlet problem, and prove basic and optimal nonlinear Wolff potential estimates for solutions. These are the exact analogs of the results valid in the case of local quasilinear degenerate equations established by Boccardo and Gallouët (J Funct Anal 87:149-169, 1989, Partial Differ Equ 17:641-655, 1992) and Kilpeläinen and Malý (Ann Scuola Norm Sup Pisa Cl Sci (IV) 19:591-613, 1992, Acta Math 172:137-161, 1994). As a consequence, we establish a number of results that can be considered as basic building blocks for a nonlocal, nonlinear potential theory: fine properties of solutions, Calderón-Zygmund estimates, continuity and boundedness criteria are established via Wolff potentials. A main tool is the introduction of a global excess functional that allows us to prove a nonlocal analog of the classical theory due to Campanato (Ann Mat Pura Appl (IV) 69:321-381, 1965). Our results cover the case of linear nonlocal equations with measurable coefficients, and the one of the fractional Laplacean, and are new already in such cases.
Nonlocal response of hyperbolic metasurfaces.
Correas-Serrano, D; Gomez-Diaz, J S; Tymchenko, M; Alù, A
2015-11-16
We analyze and model the nonlocal response of ultrathin hyperbolic metasurfaces (HMTSs) by applying an effective medium approach. We show that the intrinsic spatial dispersion in the materials employed to realize the metasurfaces imposes a wavenumber cutoff on the hyperbolic isofrequency contour, inversely proportional to the Fermi velocity, and we compare it with the cutoff arising from the structure granularity. In the particular case of HTMSs implemented by an array of graphene nanostrips, we find that graphene nonlocality can become the dominant mechanism that closes the hyperbolic contour - imposing a wavenumber cutoff at around 300k(0) - in realistic configurations with periodicity L<π/(300k(0)), thus providing a practical design rule to implement HMTSs at THz and infrared frequencies. In contrast, more common plasmonic materials, such as noble metals, operate at much higher frequencies, and therefore their intrinsic nonlocal response is mainly relevant in hyperbolic metasurfaces and metamaterials with periodicity below a few nm, being very weak in practical scenarios. In addition, we investigate how spatial dispersion affects the spontaneous emission rate of emitters located close to HMTSs. Our results establish an upper bound set by nonlocality to the maximum field confinement and light-matter interactions achievable in practical HMTSs, and may find application in the practical development of hyperlenses, sensors and on-chip networks.
Quantum nonlocality does not exist.
Tipler, Frank J
2014-08-05
Quantum nonlocality is shown to be an artifact of the Copenhagen interpretation, in which each observed quantity has exactly one value at any instant. In reality, all physical systems obey quantum mechanics, which obeys no such rule. Locality is restored if observed and observer are both assumed to obey quantum mechanics, as in the many-worlds interpretation (MWI). Using the MWI, I show that the quantum side of Bell's inequality, generally believed nonlocal, is really due to a series of three measurements (not two as in the standard, oversimplified analysis), all three of which have only local effects. Thus, experiments confirming "nonlocality" are actually confirming the MWI. The mistaken interpretation of nonlocality experiments depends crucially on a question-begging version of the Born interpretation, which makes sense only in "collapse" versions of quantum theory, about the meaning of the modulus of the wave function, so I use the interpretation based on the MWI, namely that the wave function is a world density amplitude, not a probability amplitude. This view allows the Born interpretation to be derived directly from the Schrödinger equation, by applying the Schrödinger equation to both the observed and the observer.
Learning Non-Local Dependencies
ERIC Educational Resources Information Center
Kuhn, Gustav; Dienes, Zoltan
2008-01-01
This paper addresses the nature of the temporary storage buffer used in implicit or statistical learning. Kuhn and Dienes [Kuhn, G., & Dienes, Z. (2005). Implicit learning of nonlocal musical rules: implicitly learning more than chunks. "Journal of Experimental Psychology-Learning Memory and Cognition," 31(6) 1417-1432] showed that people could…
Leow, Chee Hau; Bazigou, Eleni; Eckersley, Robert J; Yu, Alfred C H; Weinberg, Peter D; Tang, Meng-Xing
2015-11-01
Ultrasound imaging is the most widely used method for visualising and quantifying blood flow in medical practice, but existing techniques have various limitations in terms of imaging sensitivity, field of view, flow angle dependence, and imaging depth. In this study, we developed an ultrasound imaging velocimetry approach capable of visualising and quantifying dynamic flow, by combining high-frame-rate plane wave ultrasound imaging, microbubble contrast agents, pulse inversion contrast imaging and speckle image tracking algorithms. The system was initially evaluated in vitro on both straight and carotid-mimicking vessels with steady and pulsatile flows and in vivo in the rabbit aorta. Colour and spectral Doppler measurements were also made. Initial flow mapping results were compared with theoretical prediction and reference Doppler measurements and indicate the potential of the new system as a highly sensitive, accurate, angle-independent and full field-of-view velocity mapping tool capable of tracking and quantifying fast and dynamic flows. Copyright © 2015 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.
Fang, Changming; Li, Wun-Fan; Koster, Rik S; Klimeš, Jiří; van Blaaderen, Alfons; van Huis, Marijn A
2015-01-07
Knowledge about the intrinsic electronic properties of water is imperative for understanding the behaviour of aqueous solutions that are used throughout biology, chemistry, physics, and industry. The calculation of the electronic band gap of liquids is challenging, because the most accurate ab initio approaches can be applied only to small numbers of atoms, while large numbers of atoms are required for having configurations that are representative of a liquid. Here we show that a high-accuracy value for the electronic band gap of water can be obtained by combining beyond-DFT methods and statistical time-averaging. Liquid water is simulated at 300 K using a plane-wave density functional theory molecular dynamics (PW-DFT-MD) simulation and a van der Waals density functional (optB88-vdW). After applying a self-consistent GW correction the band gap of liquid water at 300 K is calculated as 7.3 eV, in good agreement with recent experimental observations in the literature (6.9 eV). For simulations of phase transformations and chemical reactions in water or aqueous solutions whereby an accurate description of the electronic structure is required, we suggest to use these advanced GW corrections in combination with the statistical analysis of quantum mechanical MD simulations.
NASA Technical Reports Server (NTRS)
Kattawar, G. W.
1980-01-01
The multipole expansion obtained by Morita et al. (1968) of the Gaussian laser beam used to levitate an aerosol particle in order that its complete phase matrix may be measured is compared with that of Tsai and Pogorzelski (1975) in order to demonstrate the effect of the incorrect expansion used by Morita. Errors incurred by the use of an equation in which one side satisfies the scalar wave equation while the other side does not and can be reduced to a plane wave amplitude are calculated as functions of the inverse of the wave number times the beam waist, the wave number times the radial spherical coordinate and the angular spherical coordinate. Errors on the order of a few percent, considered undetectable are obtained in the squared-field amplitudes due to the expansion, however, they are found to become significant (several tens of percent) when the angle is zero. It is concluded that the expansion of Morita should only be used in the regions where the spherical angle is less than 0.01 and its product with the wave number and the radial spherical coordinate is less than unity.
NASA Astrophysics Data System (ADS)
Zhao, Jing; Zhao, Li-Ming
2012-05-01
In this paper, the second-harmonic generation (SHG) in a one-dimensional nonlinear crystal that is embedded in air is investigated. Previously, the identical configuration was studied in Li Z. Y. et al., Phys. Rev. B, 60 (1999) 10644, without the use of the slowly varying amplitude approximation (SVAA), but by adopting the infinite plane-wave approximation (PWA), despite the fact that this approximation is not quite applicable to such a system. We calculate the SHG conversion efficiency without a PWA, and compare the results with those from the quoted reference. The investigation reveals that conversion efficiencies of SHG as calculated by the two methods appear to exhibit significant differences, and that the SHG may be modulated by the field of a fundamental wave (FW). The ratio between SHG conversion efficiencies as produced by the two methods shows a periodic variation, and this oscillatory behavior is fully consistent with the variation in transmittance of the FW. Quasi-phase matching (QPM) is also studied, and we find that the location of the peak for SHG conversion efficiency deviates from Δd=0, which differs from the conventional QPM results.
Rivero, Pablo; Loschen, Christoph; Moreira, Ibério De P R; Illas, Francesc
2009-11-15
This work explores the performance of periodic plane wave density functional theory calculations with an on-site Coulomb correction to the standard LDA and GGA exchange-correlation potential--commonly used to describe strongly correlated solids--in describing the magnetic coupling constant of a series of molecular compounds representative of dinuclear Cu complexes and of organic diradicals. The resulting LDA+U or GGA+U formalisms, lead to results comparable to experiment and to those obtained by means of standard hybrid functionals provided that the value of the U parameter is adequately chosen. Hence, these methods offer an alternative efficient computational scheme to correct LDA and GGA approaches to adequately describe the electronic structure and magnetic coupling in large molecular magnetic systems, although at the expenses of introducing an empirical (U) parameter. For all investigated copper dinuclear systems, the LDA+U and GGA+U approaches lead to an improvement in the description of magnetic properties over the original LDA and GGA schemes with an accuracy similar to that arising from the hybrid B3LYP functional, by increasing the on-site Coulomb repulsion with a moderate U value. Nevertheless, the introduction of an arbitrary U value in the 0-10 eV range most often provides the correct ground-state spin distribution and the correct sign of the magnetic coupling constant.
Bandura, A V; Sofo, J O; Kubicki, J D
2006-04-27
Plane-wave density functional theory (DFT-PW) calculations were performed on bulk SnO2 (cassiterite) and the (100), (110), (001), and (101) surfaces with and without H2O present. A classical interatomic force field has been developed to describe bulk SnO2 and SnO2-H2O surface interactions. Periodic density functional theory calculations using the program VASP (Kresse et al., 1996) and molecular cluster calculations using Gaussian 03 (Frisch et al., 2003) were used to derive the parametrization of the force field. The program GULP (Gale, 1997) was used to optimize parameters to reproduce experimental and ab initio results. The experimental crystal structure and elastic constants of SnO2 are reproduced reasonably well with the force field. Furthermore, surface atom relaxations and structures of adsorbed H2O molecules agree well between the ab initio and force field predictions. H2O addition above that required to form a monolayer results in consistent structures between the DFT-PW and classical force field results as well.
NASA Astrophysics Data System (ADS)
Dixit, Anant; Ángyán, János G.; Rocca, Dario
2016-09-01
A new formalism was recently proposed to improve random phase approximation (RPA) correlation energies by including approximate exchange effects [B. Mussard et al., J. Chem. Theory Comput. 12, 2191 (2016)]. Within this framework, by keeping only the electron-hole contributions to the exchange kernel, two approximations can be obtained: An adiabatic connection analog of the second order screened exchange (AC-SOSEX) and an approximate electron-hole time-dependent Hartree-Fock (eh-TDHF). Here we show how this formalism is suitable for an efficient implementation within the plane-wave basis set. The response functions involved in the AC-SOSEX and eh-TDHF equations can indeed be compactly represented by an auxiliary basis set obtained from the diagonalization of an approximate dielectric matrix. Additionally, the explicit calculation of unoccupied states can be avoided by using density functional perturbation theory techniques and the matrix elements of dynamical response functions can be efficiently computed by applying the Lanczos algorithm. As shown by several applications to reaction energies and weakly bound dimers, the inclusion of the electron-hole kernel significantly improves the accuracy of ground-state correlation energies with respect to RPA and semi-local functionals.
Niedermayr, Florian; Leitgeb, Norbert; Siegl, Werner
2012-05-31
Because of a lack of thermal models, to date, limitation of exposure to an electromagnetic field (EMF) has been based on restricting intracorporal specific absorption rates. To allow convenient compliance checks, reference field values have been defined. If they are met, compliance with basic restrictions is assumed. This article demonstrates that this assumption is not valid in every case. It has therefore been investigated as to whether the biological goal of limiting tissue heating is still met, in particular with regard to children. The thermal solver applied is based on the bioheat equation, with implemented additional improvements that allow consideration of blood flow and metabolic rate as a function of local tissue temperature rise and, in addition, adapt the blood temperature relative to the absorbed power. As a further improvement, heat exchange at the tissue/air boundary has been modeled, with radiation, convection, and sweating considered as well. The mathematical equations describing these additional thermoregulatory mechanisms were taken from the literature and unified in the thermoregulatory model used for this study. For the investigated case of plane wave exposure, the results confirm the violation of the basic restrictions in five of the six models when exposed to reference EMF levels. However, using thermal modeling, it was possible to demonstrate that heating remained within the biological tolerances. In particular, temperature elevation of the body core temperature remained <0.014°C and the local peak temperature did not exceed 1°C.
Kotlyar, Victor V; Kovalev, Alexey A; Skidanov, Roman V; Moiseev, Oleg Yu; Soifer, Victor A
2007-07-01
We derive what we believe to be new analytical relations to describe the Fraunhofer diffraction of the finite-radius plane wave by a helical axicon (HA) and a spiral phase plate (SPP). The solutions are deduced in the form of a series of the Bessel functions for the HA and a finite sum of the Bessel functions for the SPP. The solution for the HA changes to that for the SPP if the axicon parameter is set equal to zero. We also derive what we believe to be new analytical relations to describe the Fresnel and Fraunhofer diffraction of the Gaussian beam by a HA are derived. The solutions are deduced in the form of a series of the hypergeometric functions. We have fabricated by photolithography a binary diffractive optical element (a HA with number n=10) able to produce in the focal plane of a spherical lens an optical vortex, which was then used to perform rotation of several polystyrene beads of diameter 5 microm.
Zhang, Tian; Chen, Lin; Wang, Bing; Li, Xun
2015-06-09
We investigate optical field enhancement for a wide mid-infrared range, originating from the excitation of graphene plasmons, by introducing a graded dielectric grating of varying period underneath a graphene monolayer. Excitation of the plasmonic mode can be achieved by illuminating a normal-incidence plane wave on the gratings due to guided-mode resonance. The gratings of varying period enable the excitation of the plasmonic mode with a very high field enhancement factor (to the order of magnitude of 1000) within a wide spectral band, which leads to the frequency-dependent spatially separated localization of the infrared spectrum modes. We also demonstrate that the excitation position of the plasmonic mode can be freely tuned by varying the thickness of the interlayer as well as the chemical potential of the graphene monolayer. This structure enables the design of two-dimensional plasmonic photonic circuits and metamaterials targeted towards numerous potential applications including optoelectronic detectors, light-harvest devices, on-chip optical interconnects, biosensors, and light-matter interactions.
NASA Astrophysics Data System (ADS)
Zhang, Tian; Chen, Lin; Wang, Bing; Li, Xun
2015-06-01
We investigate optical field enhancement for a wide mid-infrared range, originating from the excitation of graphene plasmons, by introducing a graded dielectric grating of varying period underneath a graphene monolayer. Excitation of the plasmonic mode can be achieved by illuminating a normal-incidence plane wave on the gratings due to guided-mode resonance. The gratings of varying period enable the excitation of the plasmonic mode with a very high field enhancement factor (to the order of magnitude of 1000) within a wide spectral band, which leads to the frequency-dependent spatially separated localization of the infrared spectrum modes. We also demonstrate that the excitation position of the plasmonic mode can be freely tuned by varying the thickness of the interlayer as well as the chemical potential of the graphene monolayer. This structure enables the design of two-dimensional plasmonic photonic circuits and metamaterials targeted towards numerous potential applications including optoelectronic detectors, light-harvest devices, on-chip optical interconnects, biosensors, and light-matter interactions.
NASA Astrophysics Data System (ADS)
Bluegel, Stefan
2005-03-01
In order to calculate on the basis of the single particle picture as provided by the density-functional theory (DFT), the spin-dependent tunneling through barriers and interfaces of materials with increasing chemical and structural complexity, an extention of the full-potential linearized augmented plane- wave method (FLAPW) as realized in the FLEUR code is introduced. The volume in which the electrons scatter is sandwiched between two semi-infinite leads. The leads and the scattering volume are described by an embedding Green function formalism. Different scenarios of electron transport such as sequential and coherent tunneling is formulated and will be compared. Several applications will be presented. The method is used to understand the spin-polarized scanning tunneling microscope. For a three- layer heterosystem SrRuO3/SrTiO3/SrRuO3, the effect of different orbital characters of the states at the Fermi level on the tunneling conductance was investigated. The main focus is on the Fe/MgO/Fe system for which we show that very small changes at the interface can have drastic effects on the conductance.
NASA Astrophysics Data System (ADS)
Wagner, L. S.; Forsyth, D. W.; Fouch, M. J.; James, D. E.
2009-12-01
The High Lava Plains (HLP) of eastern Oregon represent an unusual track of bimodal volcanism extending from the southeastern-most corner of the state to its current position beneath the Newberry Volcano on the eastern margin of the Cascades. The silicic volcanism is time progressive along this track, beginning some 15 Ma near the Owyhee plateau and then trending to the north east. The timing and location of the start of the HLP coincides with that of the initial volcanism associated with the Yellowstone/Snake River Plain track (YSRP). While the YSRP has often been interpreted as the classic intra-continental hot spot track, the HLP, which trends almost normal to absolute plate motion, is harder to explain. This study uses the 100+ stations associated with the HLP seismic deployment together with another ~100 Earthscope Transportable Array stations (TA) to perform a high resolution inversion for Rayleigh wave phase velocities using the 2-plane-wave methodology of Forsyth and Li (2004). Because of the comparatively small grid spacing of this study, we are able to discern much finer scale structures than studies looking at the entire western U.S. with only TA stations. Preliminary results indicate very low velocities across the study area, especially at upper mantle depths. Especially low velocities are seen beneath the Owyhee plateau and along both the HLP and YSRP tracks. Final details about the exact geometries of these features will help constrain possible scenarios for the formation of the HLP volcanic sequence.
Magnitude of pseudopotential localization errors in fixed node diffusion quantum Monte Carlo
Krogel, Jaron T.; Kent, P. R. C.
2017-06-22
Growth in computational resources has lead to the application of real space diffusion quantum Monte Carlo to increasingly heavy elements. Although generally assumed to be small, we find that when using standard techniques, the pseudopotential localization error can be large, on the order of an electron volt for an isolated cerium atom. We formally show that the localization error can be reduced to zero with improvements to the Jastrow factor alone, and we define a metric of Jastrow sensitivity that may be useful in the design of pseudopotentials. We employ an extrapolation scheme to extract the bare fixed node energymore » and estimate the localization error in both the locality approximation and the T-moves schemes for the Ce atom in charge states 3+/4+. The locality approximation exhibits the lowest Jastrow sensitivity and generally smaller localization errors than T-moves although the locality approximation energy approaches the localization free limit from above/below for the 3+/4+ charge state. We find that energy minimized Jastrow factors including three-body electron-electron-ion terms are the most effective at reducing the localization error for both the locality approximation and T-moves for the case of the Ce atom. Less complex or variance minimized Jastrows are generally less effective. Finally, our results suggest that further improvements to Jastrow factors and trial wavefunction forms may be needed to reduce localization errors to chemical accuracy when medium core pseudopotentials are applied to heavy elements such as Ce.« less
Third-order analysis of pseudopotential lattice Boltzmann model for multiphase flow
NASA Astrophysics Data System (ADS)
Huang, Rongzong; Wu, Huiying
2016-12-01
In this work, a third-order Chapman-Enskog analysis of the multiple-relaxation-time (MRT) pseudopotential lattice Boltzmann (LB) model for multiphase flow is performed for the first time. The leading terms on the interaction force, consisting of an anisotropic and an isotropic term, are successfully identified in the third-order macroscopic equation recovered by the lattice Boltzmann equation (LBE), and then new mathematical insights into the pseudopotential LB model are provided. For the third-order anisotropic term, numerical tests show that it can cause the stationary droplet to become out-of-round, which suggests the isotropic property of the LBE needs to be seriously considered in the pseudopotential LB model. By adopting the classical equilibrium moment or setting the so-called "magic" parameter to 1/12, the anisotropic term can be eliminated, which is found from the present third-order analysis and also validated numerically. As for the third-order isotropic term, when and only when it is considered, accurate continuum form pressure tensor can be definitely obtained, by which the predicted coexistence densities always agree well with the numerical results. Compared with this continuum form pressure tensor, the classical discrete form pressure tensor is accurate only when the isotropic term is a specific one. At last, in the framework of the present third-order analysis, a consistent scheme for third-order additional term is proposed, which can be used to independently adjust the coexistence densities and surface tension. Numerical tests are subsequently carried out to validate the present scheme.
Chaudhury, Kunal N; Singer, Amit
2012-11-01
In this letter, we note that the denoising performance of Non-Local Means (NLM) can be improved at large noise levels by replacing the mean by the Euclidean median. We call this new denoising algorithm the Non-Local Euclidean Medians (NLEM). At the heart of NLEM is the observation that the median is more robust to outliers than the mean. In particular, we provide a simple geometric insight that explains why NLEM performs better than NLM in the vicinity of edges, particularly at large noise levels. NLEM can be efficiently implemented using iteratively reweighted least squares, and its computational complexity is comparable to that of NLM. We provide some preliminary results to study the proposed algorithm and to compare it with NLM.
Activation of nonlocal quantum resources.
Navascués, Miguel; Vértesi, Tamás
2011-02-11
We find two two-qubit bipartite states ρ1, ρ2 such that arbitrarily many copies of one or the other cannot exhibit nonlocal correlations in a two-setting-two-outcome Bell scenario. However, the bipartite state ρ1 ⊗ ρ2 violates the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality [J. F. Clauser, M. A. Horne, A. Shimony, and R. A. Holt, Phys. Rev. Lett. 23, 880 (1969).] by an amount of 2.023. We also identify a CHSH-local state ρ such that ρ⊗2 is CHSH inequality-violating. The tools employed can be easily adapted to find instances of nonlocality activation in arbitrary Bell scenarios.
Nonlocality and conflicting interest games.
Pappa, Anna; Kumar, Niraj; Lawson, Thomas; Santha, Miklos; Zhang, Shengyu; Diamanti, Eleni; Kerenidis, Iordanis
2015-01-16
Nonlocality enables two parties to win specific games with probabilities strictly higher than allowed by any classical theory. Nevertheless, all known such examples consider games where the two parties have a common interest, since they jointly win or lose the game. The main question we ask here is whether the nonlocal feature of quantum mechanics can offer an advantage in a scenario where the two parties have conflicting interests. We answer this in the affirmative by presenting a simple conflicting interest game, where quantum strategies outperform classical ones. Moreover, we show that our game has a fair quantum equilibrium with higher payoffs for both players than in any fair classical equilibrium. Finally, we play the game using a commercial entangled photon source and demonstrate experimentally the quantum advantage.
Certifying nonlocality from separable marginals
NASA Astrophysics Data System (ADS)
Vértesi, Tamás; Laskowski, Wiesław; Pál, Károly F.
2014-01-01
Imagine three parties, Alice, Bob, and Charlie, who share a state of three qubits such that all two-party reduced states A-B, A-C, and B-C are separable. Suppose that they have information only about these marginals but not about the global state. According to recent results, there exists an example for a set of three separable two-party reduced states that is only compatible with an entangled global state. In this paper, we show a stronger result by exhibiting separable two-party reduced states A-B, A-C, and B-C, such that any global state compatible with these marginals is nonlocal. Hence, we obtain that nonlocality of multipartite states can be certified from information only about separable marginals.
Del Ben, Mauro Hutter, Jürg; VandeVondele, Joost
2015-09-14
The forces acting on the atoms as well as the stress tensor are crucial ingredients for calculating the structural and dynamical properties of systems in the condensed phase. Here, these derivatives of the total energy are evaluated for the second-order Møller-Plesset perturbation energy (MP2) in the framework of the resolution of identity Gaussian and plane waves method, in a way that is fully consistent with how the total energy is computed. This consistency is non-trivial, given the different ways employed to compute Coulomb, exchange, and canonical four center integrals, and allows, for example, for energy conserving dynamics in various ensembles. Based on this formalism, a massively parallel algorithm has been developed for finite and extended system. The designed parallel algorithm displays, with respect to the system size, cubic, quartic, and quintic requirements, respectively, for the memory, communication, and computation. All these requirements are reduced with an increasing number of processes, and the measured performance shows excellent parallel scalability and efficiency up to thousands of nodes. Additionally, the computationally more demanding quintic scaling steps can be accelerated by employing graphics processing units (GPU’s) showing, for large systems, a gain of almost a factor two compared to the standard central processing unit-only case. In this way, the evaluation of the derivatives of the RI-MP2 energy can be performed within a few minutes for systems containing hundreds of atoms and thousands of basis functions. With good time to solution, the implementation thus opens the possibility to perform molecular dynamics (MD) simulations in various ensembles (microcanonical ensemble and isobaric-isothermal ensemble) at the MP2 level of theory. Geometry optimization, full cell relaxation, and energy conserving MD simulations have been performed for a variety of molecular crystals including NH{sub 3}, CO{sub 2}, formic acid, and benzene.
NASA Astrophysics Data System (ADS)
Del Ben, Mauro; Hutter, Jürg; VandeVondele, Joost
2015-09-01
The forces acting on the atoms as well as the stress tensor are crucial ingredients for calculating the structural and dynamical properties of systems in the condensed phase. Here, these derivatives of the total energy are evaluated for the second-order Møller-Plesset perturbation energy (MP2) in the framework of the resolution of identity Gaussian and plane waves method, in a way that is fully consistent with how the total energy is computed. This consistency is non-trivial, given the different ways employed to compute Coulomb, exchange, and canonical four center integrals, and allows, for example, for energy conserving dynamics in various ensembles. Based on this formalism, a massively parallel algorithm has been developed for finite and extended system. The designed parallel algorithm displays, with respect to the system size, cubic, quartic, and quintic requirements, respectively, for the memory, communication, and computation. All these requirements are reduced with an increasing number of processes, and the measured performance shows excellent parallel scalability and efficiency up to thousands of nodes. Additionally, the computationally more demanding quintic scaling steps can be accelerated by employing graphics processing units (GPU's) showing, for large systems, a gain of almost a factor two compared to the standard central processing unit-only case. In this way, the evaluation of the derivatives of the RI-MP2 energy can be performed within a few minutes for systems containing hundreds of atoms and thousands of basis functions. With good time to solution, the implementation thus opens the possibility to perform molecular dynamics (MD) simulations in various ensembles (microcanonical ensemble and isobaric-isothermal ensemble) at the MP2 level of theory. Geometry optimization, full cell relaxation, and energy conserving MD simulations have been performed for a variety of molecular crystals including NH3, CO2, formic acid, and benzene.
NASA Astrophysics Data System (ADS)
Mokrousov, Y.; Bihlmayer, G.; Blügel, S.
2005-07-01
We present an implementation of the full-potential linearized augmented plane-wave (FLAPW) method for carrying out ab initio calculations of the ground state electronic properties of (magnetic) metallic nanowires and nanotubes based on the density-functional theory (DFT). The method is truly one-dimensional, uses explicitly a wire geometry and is realized as an extension of the FLEUR code. It includes a wide variety of chiral symmetries known for tubular and other one-dimensional systems. A comparative study shows that in this geometry computations are considerably faster than the widely used supercell approach. The method was applied to some typical model structures explored in the field of nanospintronics: the gold nanowire Au(6,0), the free-standing Fe monowire, and the hybrid structure Fe@Au(6,0). Their atomic structures are determined by total energy minimization and force calculations. We calculated the magnetic properties including the magnetocrystalline anisotropy energies, the band structures, and densities of states in these systems using the local density approximation (LDA) and the generalized gradient approximation (GGA) to the DFT. The results agree nicely with the data available in the literature. We found that Fe wires are ferromagnetic and are prone to a Peierls dimerization. The Fe filled gold nanotube shows a large negative spin polarization at the Fermi level, which makes this structure a possible candidate for spin-dependent transport applications in the field of spintronics. The Au tube encasing the Fe wire changes the magnetization direction of the Fe wire and increases the magnetocrystalline anisotropy energy by an order of magnitude.
Simulating contrast inversion in atomic force microscopy imaging with real-space pseudopotentials
NASA Astrophysics Data System (ADS)
Lee, Alex J.; Sakai, Yuki; Chelikowsky, James R.
2017-02-01
Atomic force microscopy (AFM) measurements have reported contrast inversions for systems such as Cu2N and graphene that can hamper image interpretation and characterization. Here, we apply a simulation method based on ab initio real-space pseudopotentials to gain an understanding of the tip-sample interactions that influence the inversion. We find that chemically reactive tips induce an attractive binding force that results in the contrast inversion. We find that the inversion is tip height dependent and not observed when using less reactive CO-functionalized tips.
Band structure calculation of GaSe-based nanostructures using empirical pseudopotential method
NASA Astrophysics Data System (ADS)
Osadchy, A. V.; Volotovskiy, S. G.; Obraztsova, E. D.; Savin, V. V.; Golovashkin, D. L.
2016-08-01
In this paper we present the results of band structure computer simulation of GaSe- based nanostructures using the empirical pseudopotential method. Calculations were performed using a specially developed software that allows performing simulations using cluster computing. Application of this method significantly reduces the demands on computing resources compared to traditional approaches based on ab-initio techniques and provides receiving the adequate comparable results. The use of cluster computing allows to obtain information for structures that require an explicit account of a significant number of atoms, such as quantum dots and quantum pillars.
Márkus, Attila; Házi, Gábor
2011-04-01
An extension of the pseudopotential lattice Boltzmann method is introduced to simulate heat transfer problems involving phase transition. Using this model, evaporation through a plane interface and two-phase Poiseuille flow were simulated and the macroscopic jump conditions were utilized to evaluate the accuracy of the method. We have found that the simulation results are in very good agreement with the analytical solutions as far as we take into account the extent of the interface during the evaluation. Using the same model heterogeneous boiling was simulated taking into account the geometry of a cavity and the important features of the boiling process could be observed in the simulation results.
Boundary fluxes for nonlocal diffusion
NASA Astrophysics Data System (ADS)
Cortazar, Carmen; Elgueta, Manuel; Rossi, Julio D.; Wolanski, Noemi
We study a nonlocal diffusion operator in a bounded smooth domain prescribing the flux through the boundary. This problem may be seen as a generalization of the usual Neumann problem for the heat equation. First, we prove existence, uniqueness and a comparison principle. Next, we study the behavior of solutions for some prescribed boundary data including blowing up ones. Finally, we look at a nonlinear flux boundary condition.
Temporal nonlocality in bistable perception
NASA Astrophysics Data System (ADS)
Atmanspacher, Harald; Filk, Thomas
2012-12-01
A novel conceptual framework for theoretical psychology is presented and illustrated for the example of bistable perception. A basic formal feature of this framework is the non-commutativity of operations acting on mental states. A corresponding model for the bistable perception of ambiguous stimuli, the Necker-Zeno model, is sketched and some empirical evidence for it so far is described. It is discussed how a temporal nonlocality of mental states, predicted by the model, can be understood and tested.
Nonlocal distillation based on multisetting Bell inequality
NASA Astrophysics Data System (ADS)
Ye, Xiang-Jun; Deng, Dong-Ling; Chen, Jing-Ling
2012-12-01
Inspired by the recent works of Foster [Phys. Rev. Lett.0031-900710.1103/PhysRevLett.102.120401 102, 120401 (2009)] and Brunner [Phys. Rev. Lett.0031-900710.1103/PhysRevLett.102.160403 102, 160403 (2009)], we present a nonlocality distillation protocol for two three-level (qutrit) systems in the framework of generalized nonsignaling theories. Our protocol is based on a three-setting Bell inequality. It works efficiently for a specific class of three-input-three-output nonlocal boxes. In the asymptotic limit, all these nonlocal boxes can be distilled to the maximally nonlocal box defined by the inequality and nonsignaling constraints. Then we introduce a contracting protocol that reduces these boxes to the so-called “correlated nonlocal boxes.” As a result, our three-input-three-output nonlocal boxes also make communication complexity trivial and appear very unlikely to exist in nature.
Quantum nonlocality does not exist
Tipler, Frank J.
2014-01-01
Quantum nonlocality is shown to be an artifact of the Copenhagen interpretation, in which each observed quantity has exactly one value at any instant. In reality, all physical systems obey quantum mechanics, which obeys no such rule. Locality is restored if observed and observer are both assumed to obey quantum mechanics, as in the many-worlds interpretation (MWI). Using the MWI, I show that the quantum side of Bell’s inequality, generally believed nonlocal, is really due to a series of three measurements (not two as in the standard, oversimplified analysis), all three of which have only local effects. Thus, experiments confirming “nonlocality” are actually confirming the MWI. The mistaken interpretation of nonlocality experiments depends crucially on a question-begging version of the Born interpretation, which makes sense only in “collapse” versions of quantum theory, about the meaning of the modulus of the wave function, so I use the interpretation based on the MWI, namely that the wave function is a world density amplitude, not a probability amplitude. This view allows the Born interpretation to be derived directly from the Schrödinger equation, by applying the Schrödinger equation to both the observed and the observer. PMID:25015084
Detrimental nonlocality in luminescence measurements
NASA Astrophysics Data System (ADS)
Pluska, Mariusz; Czerwinski, Andrzej
2017-08-01
Luminescence studies are used to investigate the local properties of various light-emitting materials. A critical issue of these studies is presented that the signals often lack all advantages of luminescence-studies of high locality, and may originate from an extended spatial region of even a few millimeters in size or the whole sample, i.e., places other than intended for investigation. This is a key problem for research and development in photonics. Due to this nonlocality, information indicating defects, irregularities, nonuniformities and inhomogeneities is lost. The issue refers to typical structures with a strong built-in electric field. Such fields exist intentionally in most photonic structures and occur unintentionally in many other materials investigated by applied physics. We reveal [using test samples prepared with focused ion beam (FIB) on an AlGaAs/GaAs laser heterostructure with an InGaAs quantum well (QW)] that nonlocality increases at low temperatures. This is contrary to the widely expected outcome, as low-temperature luminescence measurements are usually assumed to be free from disturbances. We explain many effects observed due to nonlocality in luminescence studies and prove that separation of the investigated area by focused ion beam milling is a practical solution enabling truly local luminescence measurements. All conclusions drawn using the example of cathodoluminescence are useful for other luminescence techniques.
Frustrated Brownian Motion of Nonlocal Solitary Waves
Folli, V.; Conti, C.
2010-05-14
We investigate the evolution of solitary waves in a nonlocal medium in the presence of disorder. By using a perturbational approach, we show that an increasing degree of nonlocality may largely hamper the Brownian motion of self-trapped wave packets. The result is valid for any kind of nonlocality and in the presence of nonparaxial effects. Analytical predictions are compared with numerical simulations based on stochastic partial differential equations.
Origin of Dynamical Quantum Non-locality
NASA Astrophysics Data System (ADS)
Pachon, Cesar E.; Pachon, Leonardo A.
2014-03-01
Non-locality is one of the hallmarks of quantum mechanics and is responsible for paradigmatic features such as entanglement and the Aharonov-Bohm effect. Non-locality comes in two ``flavours'': a kinematic non-locality- arising from the structure of the Hilbert space- and a dynamical non-locality- arising from the quantum equations of motion-. Kinematic non-locality is unable to induce any change in the probability distributions, so that the ``action-at-a-distance'' cannot manifest. Conversely, dynamical non-locality does create explicit changes in probability, though in a ``causality-preserving'' manner. The origin of non-locality of quantum measurements and its relations to the fundamental postulates of quantum mechanics, such as the uncertainty principle, have been only recently elucidated. Here we trace the origin of dynamical non-locality to the superposition principle. This relation allows us to establish and identify how the uncertainty and the superposition principles determine the non-local character of the outcome of a quantum measurement. Being based on group theoretical and path integral formulations, our formulation admits immediate generalizations and extensions to to, e.g., quantum field theory. This work was supported by the Departamento Administrativo de Ciencia, Tecnologia e Innovacion -COLCIENCIAS- of Colombia under the grant number 111556934912.
Unified criteria for multipartite quantum nonlocality
Cavalcanti, E. G.; He, Q. Y.; Reid, M. D.; Wiseman, H. M.
2011-09-15
Wiseman and co-workers [H. M. Wiseman, S. J. Jones, and A. C. Doherty, Phys. Rev. Lett. 98, 140402, (2007)] proposed a distinction among the nonlocality classes of Bell's nonlocality, Einstein-Podolsky-Rosen (EPR) paradox or steering, and entanglement based on whether or not an overseer trusts each party in a bipartite scenario where they are asked to demonstrate entanglement. Here we extend that concept to the multipartite case and derive inequalities that progressively test for those classes of nonlocality, with different thresholds for each level. This framework includes the three classes of nonlocality above in special cases and introduces a family of others.
Nonlocality and entanglement in the XY model
Batle, J.; Casas, M.
2010-12-15
Nonlocality and quantum entanglement constitute two special features of quantum systems of paramount importance in quantum-information theory (QIT). Essentially regarded as identical or equivalent for many years, they constitute different concepts. Describing nonlocality by means of the maximal violation of two Bell inequalities, we study both entanglement and nonlocality for two and three spins in the XY model. Our results shed light on the description of nonlocality and the possible information-theoretic task limitations of entanglement in an infinite quantum system.
NASA Astrophysics Data System (ADS)
Bretonnet, J. L.; Regnaut, C.
1985-04-01
We present the results of calculations of the static structure factor S(q) of liquid Al and Ga at the melting point. These calculations were motivated because many simple liquid metals exhibit structure anomalies taking the form of a shoulder on the main peak or even an asymmetry in the peak itself, while other liquid metals are correctly predicted by the standard models of liquid structure. Al and Ga have similar valence, electronic density, and size of their ionic radius; therefore, their pair potentials are somewhat similar. Despite this, their structure factors display most of the differences that can be observed among the variety of liquid metals. Starting from the Shaw optimized model potential [Phys. Rev. 174, 769 (1968)], a pair potential is constructed. A comparative examination of the electron-gas response function of Vashishta and Singwi [Phys. Rev. B 6, 875 (1972)] and of Ichimaru and Utsumi [Phys. Rev. B 24, 7385 (1981)] is carried out. Different depletion hole distributions are also used and full nonlocality is taken into account through effective masses. So S(q) is calculated by means of the optimized random-phase approximation. Particular attention is also devoted to the low-q region. By comparison with Monte Carlo computation, we show the limitation of various thermodynamic perturbation methods, such as the random-phase approximation or the soft-sphere model. The study of S(q) provides a stringent test of the model potential, where the electron-ion pseudopotential and the local-field correction are of prime importance, but where effective masses and depletion hole distribution may also have a role to play.
Kassab, E.; Seiti, K.; Allavena, M.
1988-11-17
SCF ab initio calculations at the 6-31G level have been used to investigate the structure of several aggregates simulating some of the proton donor sites within faujasite-type zeolites. The Si(OH)/sub 4/, H/sub 3/SiOHAlH/sub 3/, and (OH)/sub 3/SiOHAl(OH)/sub 3/ clusters have been successively examined. Deprotonation energies and charge distribution are determined at a higher level by using a 6-31G basis set augmented with polarization and diffuse functions. The results are compared with values obtained by using pseudopotential methods. The small differences between the two sets of results demonstrate that comparable accuracy should be expected from both procedures. Finally, deprotonation energies of (OH)/sub 3/T/sub 1/OHT/sub 2/(OH)/sub 3/ aggregates (T/sub 1/, T/sub 2/ = AlSi, BSi, GaSi; AlGe, BGe, GaGe) are calculated by using pseudopotential methods and compared with the results given by the semiempirical MNDO method. In some cases ab initio SCF calculations were also performed. The results confirm that the inclusion of boron atom lowers the acidity as already demonstrated by experimental investigation. The effects due to the inclusion of Ga are discussed and compared to available experimental data.
Analysis of force treatment in the pseudopotential lattice Boltzmann equation method
NASA Astrophysics Data System (ADS)
Zheng, Lin; Zhai, Qinglan; Zheng, Song
2017-04-01
In this paper, different force treatments are analyzed in detail for a pseudopotential lattice Boltzmann equation (LBE), and the contribution of third-order error terms to pressure tensor with a force scheme is analyzed by a higher-order Chapman-Enskog expansion technique. From the theoretical analysis, the performance of the original force treatment of Shan-Chen (SC), Ladd, Guo et al., and the exact difference method (EDM) are ɛLadd<ɛGuo<ɛEDM≤ɛSC with the relaxation time τ ≥1 , while ɛLadd<ɛGuo<ɛSC<ɛEDM with τ <1 ; here ɛ is a parameter related to the mechanical stability and the subscripts are the corresponding force scheme. To be consistent with the thermodynamic theory, a force term is introduced to modify the coefficients in the pressure tensor. Some numerical simulations are conducted to show that the predictions of modified force treatment of the pseudopotential LBE are all in good agreement with the analytical solution and other predictions.
A pseudopotential approach to the superconducting state properties of metallic glass ?
NASA Astrophysics Data System (ADS)
Sharma, Ritu; Sharma, K. S.
1997-08-01
The superconducting state properties of the metallic glass 0953-2048/10/8/005/img2 have been investigated in the BCS - Eliashberg - McMillan framework by extending this theory to the binary metal glasses. Pseudo ions with average properties have been considered to replace both types of ions in the system. Values of the superconducting state parameters, namely electron - phonon coupling strength 0953-2048/10/8/005/img3, Coloumb pseudopotential 0953-2048/10/8/005/img4, transition temperature 0953-2048/10/8/005/img5, isotope effect exponent 0953-2048/10/8/005/img6 and interaction strength 0953-2048/10/8/005/img7 have been worked out using Ashcroft's potential and the linear potential due to Sharma and Kachhava along with six different forms of dielectric screening. The form factors directly obtained from the screened pseudopotential of Veljkovic and Slavic have also been used to explicitly observe the effect of the dielectric screening on 0953-2048/10/8/005/img8 and 0953-2048/10/8/005/img9 through 0953-2048/10/8/005/img10. The results obtained established the presence of a superconducting phase in 0953-2048/10/8/005/img2 glass.
Self-consistent pseudopotentials in the thermodynamic limit. II. The state-dependent one-body field
NASA Astrophysics Data System (ADS)
Hernández, E. S.; Plastino, A.; Szybisz, L.
1980-07-01
We explore the concept of the pseudopotential, introduced in a previous paper, within the context of the exact boundary condition for a system of fermions interacting through a pair-wise, hard-core potential, in the thermodynamic limit. We discuss several Ansätze for the Lagrange multipliers that allow the inclusion of the boundary conditions into the variational principle. It is found that under a given Ansatz, a dynamical, microscopic interpretation of the pseudopotential can be put forward. A comparison between this situation and the coherent approximation induced by the use of the correlation function is also presented. NUCLEAR STRUCTURE Hard-core interactions, boundary condition, variational principle constrained Hartree-Fock problem; Ansatz, structure of the pseudopotential, state dependence.
Peterson, Kirk A.; Figgen, Detlev; Goll, Erich; Stoll, Hermann; Dolg, Michael F.
2003-12-01
Series of correlation consistent basis sets have been developed for the post-d group 16-18 elements in conjunction with small-core relativistic pseudopotentials (PPs) of the energy-consistent variety. The latter were adjusted to multiconfiguration Dirac-Hartree-Fock data based on the Dirac-Coulomb-Breit Hamiltonian. The outer-core (n-1)spd shells are explicitly treated together with the nsp valence shell with these PPs. The accompanying cc-pVnZ-PP and aug-cc-pVnZ-PP basis sets range in size from DZ to 5Z quality and yield systematic convergence of both Hartree-Fock and correlated total energies. In addition to the calculation of atomic electron affinities and dipole polarizabilities of the rare gas atoms, numerous molecular benchmark calculations (HBr, HI, HAt, Br2, I2, At2, SiSe, SiTe, SiPo, KrH+, XeH+, and RnH+) are also reported at the coupled cluster level of theory. For the purposes of comparison, all-electron calculations using the Douglas-Kroll-Hess Hamiltonian have also been carried out for the halogen-containing molecules using basis sets of 5Z quality.
NASA Astrophysics Data System (ADS)
Leclaire, Sébastien; Parmigiani, Andrea; Chopard, Bastien; Latt, Jonas
In this paper, a lattice Boltzmann color-gradient method is compared with a multi-component pseudo-potential lattice Boltzmann model for two test problems: a droplet deformation in a shear flow and a rising bubble subject to buoyancy forces. With the help of these two problems, the behavior of the two models is compared in situations of competing viscous, capillary and gravity forces. It is found that both models are able to generate relevant scientific results. However, while the color-gradient model is more complex than the pseudo-potential approach, numerical experiments show that it is also more powerful and suffers fewer limitations.
Levashov, P R; Sin'ko, G V; Smirnov, N A; Minakov, D V; Shemyakin, O P; Khishchenko, K V
2010-12-22
In the present work, we compare the thermal contribution of electrons to thermodynamic functions of metals in different models at high densities and electron temperatures. One of the theoretical approaches, the full-potential linear-muffin-tin-orbital method, treats all electrons in the framework of density functional theory (DFT). The other approach, VASP, uses projector-augmented-wave pseudopotentials for the core electrons and considers the valent electrons also in the context of DFT. We analyze the limitations of the pseudopotential approach and compare the DFT results with a finite-temperature Thomas-Fermi model and two semiempirical equations of state.
NASA Astrophysics Data System (ADS)
Levashov, P. R.; Sin'ko, G. V.; Smirnov, N. A.; Minakov, D. V.; Shemyakin, O. P.; Khishchenko, K. V.
2010-12-01
In the present work, we compare the thermal contribution of electrons to thermodynamic functions of metals in different models at high densities and electron temperatures. One of the theoretical approaches, the full-potential linear-muffin-tin-orbital method, treats all electrons in the framework of density functional theory (DFT). The other approach, VASP, uses projector-augmented-wave pseudopotentials for the core electrons and considers the valent electrons also in the context of DFT. We analyze the limitations of the pseudopotential approach and compare the DFT results with a finite-temperature Thomas-Fermi model and two semiempirical equations of state.
NASA Astrophysics Data System (ADS)
Zheng, X. H.; Walmsley, D. G.
2017-01-01
Applying the Heine-Abarenkov pseudopotential to aluminium and lead in both the superconducting and normal states, Carbotte and coworkers have set a challenging standard befitting the status of the classic BCS superconductor theory. Upholding the same standard and equipped with the technique of numerical inversion, we have extracted alternative pseudopotentials from experimental data with minimal prejudgement that might cloud the physics. The two potentials are broadly consistent in the superconducting state but distinctly different in the normal state. This is an urgent issue requiring confirmation or refutation in the context of the current search for high temperature conventional superconductivity.
Plasma instabilities observed in the E region over Arecibo and a proposed nonlocal theory
NASA Astrophysics Data System (ADS)
Rosado-Román, José M.; Swartz, Wesley E.; Farley, Donald T.
2004-11-01
We describe simultaneous radar observations made with the Cornell University Portable Radar Interferometer (CUPRI) at 50 MHz and the Arecibo incoherent scatter radar (ISR) at 430 MHz during the El Coquí campaign of 1992 in Puerto Rico. The goal was to study the plasma instabilities that cause coherent radar backscatter from the E region at mid-latitudes. The common volume data reveal that the coherent CUPRI echoes come from sporadic-E layers that exhibit no obvious gravity wave modulation but possess high densities and sharp gradients. The echoes with positive (negative) Doppler shifts, i.e. eastward (westward) plasma wave phase velocities, come from the top (bottom) of the layer, in agreement with simple local equatorial gradient-drift instability theory, even though this theory is not valid at mid-latitudes, where nonlocal shorting effects along magnetic field lines play a crucial role. We have developed a nonlocal theory that takes these effects into account. Our theory, which is discussed in detail in a companion paper, does not invoke any unusual layer geometry, in contrast to the ideas proposed in several papers in recent years. The unstable eigenmodes are a sum of plane waves with k-vectors having a small component parallel to the geomagnetic field, such that the modes are confined primarily to either the top or bottom of the layer, depending on the driving electric field. The direction of these k-vectors deviates from normal to the magnetic field by at most a few tenths of a degree. The k-vectors are also approximately aligned with the E×B drift. While both the density and potential fluctuations peak in amplitude on the unstable side of the layer, the density peak is closer to the maximum of the layer than is the potential peak. We do not in this paper deal with the "quasi-periodic" or QP nature of the radar echoes that is sometimes, but certainly not always, seen.
Nonlocal problems in thin domains
NASA Astrophysics Data System (ADS)
Pereira, Marcone C.; Rossi, Julio D.
2017-08-01
In this paper we consider nonlocal problems in thin domains. First, we deal with a nonlocal Neumann problem, that is, we study the behavior of the solutions to f (x) =∫Ω1×Ω2Jɛ (x - y) (uɛ (y) -uɛ (x)) dy with Jɛ (z) = J (z1 , ɛz2) and Ω =Ω1 ×Ω2 ⊂RN =R N1 ×R N2 a bounded domain. We find that there is a limit problem, that is, we show that uɛ →u0 as ɛ → 0 in Ω and this limit function verifies ∫Ω2 f (x1 ,x2) dx2 = |Ω2 |∫Ω1 J (x1 -y1 , 0) (U0 (y1) -U0 (x1)) dy1, with U0 (x1) =∫Ω2u0 (x1 ,x2) dx2. In addition, we deal with a double limit when we add to this model a rescale in the kernel with a parameter that controls the size of the support of J. We show that this double limit exhibits some interesting features. We also study a nonlocal Dirichlet problem f (x) =∫RNJɛ (x - y) (uɛ (y) -uɛ (x)) dy, x ∈ Ω, with uɛ (x) ≡ 0, x ∈RN ∖ Ω, and deal with similar issues. In this case the limit as ɛ → 0 is u0 = 0 and the double limit problem commutes and also gives v ≡ 0 at the end.
A nonlocal inhomogeneous dispersal process
NASA Astrophysics Data System (ADS)
Cortázar, C.; Coville, J.; Elgueta, M.; Martínez, S.
This article in devoted to the study of the nonlocal dispersal equation u(x,t)=∫R J({x-y}/{g(y)}){u(y,t)}/{g(y)} dy-u(x,t) in R×[0,∞), and its stationary counterpart. We prove global existence for the initial value problem, and under suitable hypothesis on g and J, we prove that positive bounded stationary solutions exist. We also analyze the asymptotic behavior of the finite mass solutions as t→∞, showing that they converge locally to zero.
Multipole vector solitons in nonlocal nonlinear media.
Kartashov, Yaroslav V; Torner, Lluis; Vysloukh, Victor A; Mihalache, Dumitru
2006-05-15
We show that multipole solitons can be made stable via vectorial coupling in bulk nonlocal nonlinear media. Such vector solitons are composed of mutually incoherent nodeless and multipole components jointly inducing a nonlinear refractive index profile. We found that stabilization of the otherwise highly unstable multipoles occurs below certain maximum energy flow. Such a threshold is determined by the nonlocality degree.
Complete band gaps including non-local effects occur only in the relaxed micromorphic model
NASA Astrophysics Data System (ADS)
Madeo, Angela; Neff, Patrizio; d'Agostino, Marco Valerio; Barbagallo, Gabriele
2016-11-01
In this paper, we substantiate the claim implicitly made in previous works that the relaxed micromorphic model is the only linear, isotropic, reversibly elastic, nonlocal generalized continuum model able to describe complete band-gaps on a phenomenological level. To this end, we recapitulate the response of the standard Mindlin-Eringen micromorphic model with the full micro-distortion gradient ∇P, the relaxed micromorphic model depending only on the Curl P of the micro-distortion P, and a variant of the standard micromorphic model, in which the curvature depends only on the divergence Div P of the micro distortion. The Div-model has size-effects, but the dispersion analysis for plane waves shows the incapability of that model to even produce a partial band gap. Combining the curvature to depend quadratically on Div P and Curl P shows that such a model is similar to the standard Mindlin-Eringen model, which can eventually show only a partial band gap.
Nonlocal Galileons and self-acceleration
NASA Astrophysics Data System (ADS)
Gabadadze, Gregory; Yu, Siqing
2017-05-01
A certain class of nonlocal theories eliminates an arbitrary cosmological constant (CC) from a universe that can be perceived as our world. Dark energy then cannot be explained by a CC; it could however be due to massive gravity. We calculate the new corrections, which originate from the nonlocal terms that eliminate the CC, to the decoupling limit Lagrangian of massive gravity. The new nonlocal terms also have internal field space Galilean symmetry and are referred here as ;nonlocal Galileons.; We then study a self-accelerated solution and show that the new nonlocal terms change the perturbative stability analysis. In particular, small fluctuations are now stable and non-superluminal for some simple parameter choices, whereas for the same choices the pure massive gravity fluctuations are unstable. We also study stable spherically symmetric solutions on this background.
Nonlocal thermal transport in solar flares
NASA Technical Reports Server (NTRS)
Karpen, Judith T.; Devore, C. Richard
1987-01-01
A flaring solar atmosphere is modeled assuming classical thermal transport, locally limited thermal transport, and nonlocal thermal transport. The classical, local, and nonlocal expressions for the heat flux yield significantly different temperature, density, and velocity profiles throughout the rise phase of the flare. Evaporation of chromospheric material begins earlier in the nonlocal case than in the classical or local calculations, but reaches much lower upward velocities. Much higher coronal temperatures are achieved in the nonlocal calculations owing to the combined effects of delocalization and flux limiting. The peak velocity and momentum are roughly the same in all three cases. A more impulsive energy release influences the evolution of the nonlocal model more than the classical and locally limited cases.
Hyperbolic metamaterial lens with hydrodynamic nonlocal response.
Yan, Wei; Mortensen, N Asger; Wubs, Martijn
2013-06-17
We investigate the effects of hydrodynamic nonlocal response in hyperbolic metamaterials (HMMs), focusing on the experimentally realizable parameter regime where unit cells are much smaller than an optical wavelength but much larger than the wavelengths of the longitudinal pressure waves of the free-electron plasma in the metal constituents. We derive the nonlocal corrections to the effective material parameters analytically, and illustrate the noticeable nonlocal effects on the dispersion curves numerically. As an application, we find that the focusing characteristics of a HMM lens in the local-response approximation and in the hydrodynamic Drude model can differ considerably. In particular, the optimal frequency for imaging in the nonlocal theory is blueshifted with respect to that in the local theory. Thus, to detect whether nonlocal response is at work in a hyperbolic metamaterial, we propose to measure the near-field distribution of a hyperbolic metamaterial lens.
Pseudopotential-based study of electron transport in low-dimensionality nanostructures
NASA Astrophysics Data System (ADS)
Fischetti, Massimo
2013-03-01
Pseudopotentials- empirical and ab initio - are now being more commonly used to study not only the atomic and electronic structure of nanometer-scale systems, but also their electronic transport properties. Here we shall give a bird-eye view of the use of density functional theory (DFT) to calibrate empirical pseudopotentials (EPs), of EPs to calculate efficiently the electronic structure of low-dimensionality systems, the most significant electronic scattering processes, and to study semiclassical and quantum electronic transport. Low-dimensionality systems considered here include thin semiconductor layers, graphene, graphene- and silicane-nanoribbons, and silicon nanowires. Regarding graphene, the high electron mobility measured in suspended graphene sheets (~ 200,000 cm2/Vs) is the result of a relatively weak carrier-phonon and the strong dielectric-screening property. However, in practical applications graphene is likely to be supported by an insulating substrate, top-gated, and possibly used in the form of narrow armchair-edge nanoribbons (aGNRs) in order to open a gap. We will discuss several scattering processes which may affect the electron transport properties in these situations. First, we shall present results of the calculation of the intrinsic electron-phonon scattering rates in suspended graphene using empirical pseudopotentials and the rigid-ion approximation, resulting in an electron mobility consistent with the experimental results. We shall then discuss the role of interfacial coupled substrate optical-phonon/graphene-plasmons in depressing the electron mobility in graphene supported by several insulators (SiO2, HfO2, Al2O3, and h-BN). We shall also discuss the role of Coulomb scattering with charged defects/impurities in gated graphene sheets and the role of the metal gate in screening this interaction. Finally, we shall review the strong effect of line edge roughness (LER) on electron transport and localization in narrow aGNRs resulting from the
Percolation transitions with nonlocal constraint.
Shim, Pyoung-Seop; Lee, Hyun Keun; Noh, Jae Dong
2012-09-01
We investigate percolation transitions in a nonlocal network model numerically. In this model, each node has an exclusive partner and a link is forbidden between two nodes whose r-neighbors share any exclusive pair. The r-neighbor of a node x is defined as a set of at most N(r) neighbors of x, where N is the total number of nodes. The parameter r controls the strength of a nonlocal effect. The system is found to undergo a percolation transition belonging to the mean-field universality class for r<1/2. On the other hand, for r>1/2, the system undergoes a peculiar phase transition from a nonpercolating phase to a quasicritical phase where the largest cluster size G scales as G~N(α) with α=0.74(1). In the marginal case with r=1/2, the model displays a percolation transition that does not belong to the mean-field universality class.
Excited calculations of large scale multiwalled nanotubes using real-space pseudopotential methods
NASA Astrophysics Data System (ADS)
Lena, Charles; Chelikowsky, James; Deslippe, Jack; Saad, Yousef; Yang, Chao; Louie, Steven G.
2015-03-01
One method for calculating excited states is the GW method. The GW method has many computational requirements. One of the bottlenecks is the calculation of numerous empty states. Within density functional theory, we use a real-space pseudopotential method (PARSEC) to calculate these empty states for multiwalled nanotubes. We illustrate the use of these empty states for calculating excited states using the GW method (BerkeleyGW). We demonstrate why using real-space density functional theory is advantageous for calculating empty states. Support provided by the SciDAC program, Department of Energy, Office of Science, Advanced Scientific Computing Research and Basic Energy Sciences. Grant Numbers DE-SC0008877 (Austin) and DE-FG02-12ER4 (Berkeley)
Scalable real space pseudopotential-density functional codes for materials applications
NASA Astrophysics Data System (ADS)
Chelikowsky, James R.; Lena, Charles; Schofield, Grady; Saad, Yousef; Deslippe, Jack; Yang, Chao
2015-03-01
Real-space pseudopotential density functional theory has proven to be an efficient method for computing the properties of matter in many different states and geometries, including liquids, wires, slabs and clusters with and without spin polarization. Fully self-consistent solutions have been routinely obtained for systems with thousands of atoms. However, there are still systems where quantum mechanical accuracy is desired, but scalability proves to be a hindrance, such as large biological molecules or complex interfaces. We will present an overview of our work on new algorithms, which offer improved scalability by implementing another layer of parallelism, and by optimizing communication and memory management. Support provided by the SciDAC program, Department of Energy, Office of Science, Advanced Scientific Computing Research and Basic Energy Sciences. Grant Numbers DE-SC0008877 (Austin) and DE-FG02-12ER4 (Berkeley).
NASA Astrophysics Data System (ADS)
Sakurai, Masahiro; Souto-Casares, Jaime; Chelikowsky, James R.
2016-07-01
We examine the structural stability and magnetization for nickel clusters containing up to 500 atoms by performing first-principles calculations based on pseudopotential in real space computed within density-functional theory. After structural relaxation, Ni clusters in this size range favor either an fcc structure, which is a crystal structure in bulk, or an icosahedral structure, which is expected for small clusters. The calculated total magnetic moments per atom of energetically stable clusters agree well with experiment, wherein the moments decrease nonmonotonically toward the bulk value as the cluster size increases. We analyze the spatial distribution of the local magnetic moment, which explains why the magnetic moments of Ni clusters are enhanced compared to their bulk value.
The neglected nonlocal effects of deforestation
NASA Astrophysics Data System (ADS)
Winckler, Johannes; Reick, Christian; Pongratz, Julia
2017-04-01
Deforestation changes surface temperature locally via biogeophysical effects by changing the water, energy and momentum balance. Adding to these locally induced changes (local effects), deforestation at a given location can cause changes in temperature elsewhere (nonlocal effects). Most previous studies have not considered local and nonlocal effects separately, but investigated the total (local plus nonlocal) effects, for which global deforestation was found to cause a global mean cooling. Recent modeling and observational studies focused on the isolated local effects: The local effects are relevant for local living conditions, and they can be obtained from in-situ and satellite observations. Observational studies suggest that the local effects of potential deforestation cause a warming when averaged globally. This contrast between local warming and total cooling indicates that the nonlocal effects of deforestation are causing a cooling and thus counteract the local effects. It is still unclear how the nonlocal effects depend on the spatial scale of deforestation, and whether they still compensate the local warming in a more realistic spatial distribution of deforestation. To investigate this, we use a fully coupled climate model and separate local and nonlocal effects of deforestation in three steps: Starting from a forest world, we simulate deforestation in one out of four grid boxes using a regular spatial pattern and increase the number of deforestation grid boxes step-wise up to three out of four boxes in subsequent simulations. To compare these idealized spatial distributions of deforestation to a more realistic case, we separate local and nonlocal effects in a simulation where deforestation is applied in regions where it occurred historically. We find that the nonlocal effects scale nearly linearly with the number of deforested grid boxes, and the spatial distribution of the nonlocal effects is similar for the regular spatial distribution of deforestation
Hu, Anguang; Chan, Nora W C; Dunlap, Brett I
2017-08-21
The computation of s-type Gaussian pseudopotential matrix elements involving low powers of the distance from the pseudopotential center using Gaussian orbitals can be reduced to familiar integrals. They may be directly expressed as either simple three-center overlap integrals for even powers of the radial distance from the pseudopotential center or related to the three-center nuclear integrals of a Gaussian charge distribution for odd powers. Orbital angular momentum about each atom is added to these integrals by solid-harmonic differentiation with respect to its center. The solid-harmonic addition theorem allows all the integrals to be factored into products of invariant one-dimensional integrals involving the Gaussian exponents and angular factors that contain the azimuthal quantum numbers but are independent of all Gaussian exponents. Precomputing the angular factors allow looping over all Gaussian exponents about the three centers. The fact that solid harmonics are eigenstates of angular momentum removes the singularities seen in previous treatments of pseudopotential matrix elements.
NASA Astrophysics Data System (ADS)
Hu, Anguang; Chan, Nora W. C.; Dunlap, Brett I.
2017-08-01
The computation of s-type Gaussian pseudopotential matrix elements involving low powers of the distance from the pseudopotential center using Gaussian orbitals can be reduced to familiar integrals. They may be directly expressed as either simple three-center overlap integrals for even powers of the radial distance from the pseudopotential center or related to the three-center nuclear integrals of a Gaussian charge distribution for odd powers. Orbital angular momentum about each atom is added to these integrals by solid-harmonic differentiation with respect to its center. The solid-harmonic addition theorem allows all the integrals to be factored into products of invariant one-dimensional integrals involving the Gaussian exponents and angular factors that contain the azimuthal quantum numbers but are independent of all Gaussian exponents. Precomputing the angular factors allow looping over all Gaussian exponents about the three centers. The fact that solid harmonics are eigenstates of angular momentum removes the singularities seen in previous treatments of pseudopotential matrix elements.
Piquini, P.; Zunger, A.; Magri, R.
2008-01-01
The band edges and band gaps of (InAs){sub n}/(GaSb){sub m} (n,m=1,20) superlattices have been theoretically studied through the plane-wave empirical pseudopotential method for different situations: (i) different substrates, GaSb and InAs; (ii) different point group symmetries, C{sub 2v} and D{sub 2d}; and (iii) different growth directions, (001) and (110). We find that (a) the band gaps for the (001) C{sub 2v} superlattices on a GaSb substrate exhibit a nonmonotonic behavior as a function of the GaSb barrier thickness when the number of (InAs){sub n} layers exceed n=5; (b) substrate effects: compared with the GaSb substrate, the different strain field generated by the InAs substrate leads to a larger variation of the band gaps for the (001) C{sub 2v} superlattices as a function of the InAs well thickness; (c) effect of the type of interfacial bonds: the In-Sb bonds at the interfaces of the (001) D{sub 2d} superlattices partially pin the band edge states, reducing the influence of the confinement effects on electrons and holes, and lowering the band gaps as compared to the (001) C{sub 2v} case. The valence band maximum of the (001) D{sub 2d} superlattices with Ga-As bonds at the interfaces are shifted down, increasing the band gaps as compared to the (001) C{sub 2v} case; (d) effect of layer orientation: the presence of In-Sb bonds at both interfaces of the (110) superlattices pin the band edge states and reduces the band gaps, as compared to the (001) C{sub 2v} case. An anticrossing between the electron and hole levels in the (110) superlattices, for thin GaSb and thick InAs layers, leads to an increase of the band gaps, as a function of the InAs thickness; (e) superlattices vs random alloys: the comparison between the band edges and band gaps of the superlattices on a GaSb substrate and those for random alloys, lattice matched to a GaSb substrate, as a function of the In composition, shows that the random alloys present almost always higher band gaps and give a
Hirata, Akimasa; Laakso, Ilkka; Oizumi, Takuya; Hanatani, Ryuto; Chan, Kwok Hung; Wiart, Joe
2013-02-21
According to the international safety guidelines/standard, the whole-body-averaged specific absorption rate (Poljak et al 2003 IEEE Trans. Electromagn. Compat. 45 141-5) and the peak spatial average SAR are used as metrics for human protection from whole-body and localized exposures, respectively. The IEEE standard (IEEE 2006 IEEE C95.1) indicates that the upper boundary frequency, over which the whole-body-averaged SAR is deemed to be the basic restriction, has been reduced from 6 to 3 GHz, because radio-wave energy is absorbed around the body surface when the frequency is increased. However, no quantitative discussion has been provided to support this description especially from the standpoint of temperature elevation. It is of interest to investigate the maximum temperature elevation in addition to the core temperature even for a whole-body exposure. In the present study, using anatomically based human models, we computed the SAR and the temperature elevation for a plane-wave exposure from 30 MHz to 6 GHz, taking into account the thermoregulatory response. As the primary result, we found that the ratio of the core temperature elevation to the whole-body-averaged SAR is almost frequency independent for frequencies below a few gigahertz; the ratio decreases above this frequency. At frequencies higher than a few gigahertz, core temperature elevation for the same whole-body averaged SAR becomes lower due to heat convection from the skin to air. This lower core temperature elevation is attributable to skin temperature elevation caused by the power absorption around the body surface. Then, core temperature elevation even for whole-body averaged SAR of 4 W kg(-1) with the duration of 1 h was at most 0.8 °C, which is smaller than a threshold considered in the safety guidelines/standard. Further, the peak 10 g averaged SAR is correlated with the maximum body temperature elevations without extremities and pinna over the frequencies considered. These findings
NASA Astrophysics Data System (ADS)
Goodman, M. L.
2008-12-01
Analytic solutions of an MHD model that includes an anisotropic, inhomogeneous electrical conductivity tensor containing Hall, Pedersen, and Spitzer conductivities are used to compute resistive heating rates as a function of height z from the photosphere to the lower corona due to dissipation of driven, linear, non- plane waves. The background state of the atmosphere is assumed to be an FAL atmosphere. This state is linearly perturbed by a harmonic perturbation of frequency ν. The height dependence of the perturbation in the presence of the inhomogeneous background state is determined by solving the MHD equations given the harmonic, horizontal, driving magnetic field Bx1 at the photosphere, the constant vertical magnetic field Bz, and the magnetic field strength Bcond(z) that enters the electrical conductivity tensor. The variation of the heating rates per unit volume and mass with ν, Bx1, and Bcond(0) are determined. The heating rates are found to be ∝ Bcond(0)2 Bx12, and to increase with ν. The Pedersen resistivity is ∝ Bcond(0)2. It is several orders of magnitude greater than the Spitzer resistivity in the chromosphere, and determines the rate of heating by Pedersen current dissipation in the chromosphere. The Pedersen current is essentially a proton current in the chromosphere. The onset of Pedersen current dissipation rates large enough to balance the net radiative loss from the chromosphere occurs near the height of the FAL temperature minimum, and is triggered by the product of the electron and proton magnetizations first exceeding unity. The magnetizations and heating rate increase rapidly with height beginning near the temperature minimum. For the special case of Bz = 200 G, Bx1=140 G, and 400 ≤ Bcond(0) ≤ 1500 G the driver frequency for which the period averaged chromospheric heating flux FCh = 5 × 106 ergs-cm-2-sec-1 has the corresponding range of 91 ≥ ν ≥ 25 mHz. Larger magnetic field strengths correspond to lower frequencies for a
Quantum Nonlocal Boxes Exhibit Stronger Distillability
NASA Astrophysics Data System (ADS)
Høyer, Peter; Rashid, Jibran
2013-06-01
The hypothetical nonlocal box (NLB) proposed by Popescu and Rohrlich allows two spatially separated parties, Alice and Bob, to exhibit stronger than quantum correlations. If the generated correlations are weak, they can sometimes be distilled into a stronger correlation by repeated applications of the NLB. Motivated by the limited distillability of NLBs, we initiate here a study of the distillation of correlations for nonlocal boxes that output quantum states rather than classical bits (qNLBs). We propose a new protocol for distillation and show that it asymptotically distills a class of correlated quantum nonlocal boxes to the value (1)/(2)(3√ {3}+1) ≈ 3.098076, whereas in contrast, the optimal non-adaptive parity protocol for classical nonlocal boxes asymptotically distills only to the value 3.0. We show that our protocol is an optimal non-adaptive protocol for 1, 2 and 3 qNLB copies by constructing a matching dual solution for the associated primal semidefinite program (SDP). We conclude that qNLBs are a stronger resource for nonlocality than NLBs. The main premise that develops from this conclusion is that the NLB model is not the strongest resource to investigate the fundamental principles that limit quantum nonlocality. As such, our work provides strong motivation to reconsider the status quo of the principles that are known to limit nonlocal correlations under the framework of qNLBs rather than NLBs.
Effects of d-electrons in pseudopotential screened-exchange density functional calculations
NASA Astrophysics Data System (ADS)
Lee, Byounghak; Wang, Lin-Wang; Canning, Andrew
2008-06-01
We report a theoretical study on the role of shallow d states in the screened-exchange local density approximation (sX-LDA) band structure of binary semiconductor systems. We found that inaccurate pseudo-wave functions can lead to (1) an overestimation of the screened-exchange interaction between the localized d states and the delocalized higher energy s and p states, and (2) an underestimation of the screened-exchange interaction between the d states. The resulting sX-LDA band structures have substantially smaller band gaps compared with experiments. We correct the pseudo-wave functions of d states by including the semicore s and p states of the same shell in the valence states. The correction of pseudo-wave functions yields band gaps and d-state binding energies in good agreement with experiments and the full potential linearized augmented plane wave sX-LDA calculations. Compared with the quasiparticle GW method, our sX-LDA results shows not only similar quality on the band gaps but also much better d-state binding energies. Combined with its capability of ground-state structure calculation, the sX-LDA is expected to be a valuable theoretical tool for the II-VI and III-V (especially the III-N) bulk semiconductors and nanostructure studies.
Effects of d-electrons in pseudopotential screened-exchange density functional calculations
Lee, Byounghak; Canning, Andrew; Wang, Lin-Wang
2007-09-12
We report a theoretical study on the role of shallow d states in the screened-exchange local density approximation (sX-LDA) band structure of binary semiconductor systems.We found that inaccurate pseudo-wavefunctions can lead to 1) an overestimation of the screened-exchange interaction betweenthe localized d states and the delocalized higher energy s and p states and 2) an underestimation of the screened-exchange interaction between the d states. The resulting sX-LDA band structures have substantially smaller band gaps compared with experiments. We correct the pseudo-wavefunctions of d states by including the semicore s and p states of the same shell in the valence states. The correction of pseudo-wavefunctions yields band gaps and d state binding energies in good agreement with experiments and the full potential linearized augmented plane wave sX-LDA calculations. Compared with the quasi-particle GW method, our sX-LDA results shows not only similar quality on the band gaps but also much better d state binding energies. Combined with its capability of ground state structure calculation, the sX-LDA is expected to be a valuable theoretical tool for the II-VI and III-V (especially the III-N) bulk semiconductors and nanostructure studies.
Nonlocal effects and countermeasures in cascading failures.
Witthaut, Dirk; Timme, Marc
2015-09-01
We study the propagation of cascading failures in complex supply networks with a focus on nonlocal effects occurring far away from the initial failure. It is shown that a high clustering and a small average path length of a network generally suppress nonlocal overloads. These properties are typical for many real-world networks, often called small-world networks, such that cascades propagate mostly locally in these networks. Furthermore, we analyze the spatial aspects of countermeasures based on the intentional removal of additional edges. Nonlocal actions are generally required in networks that have a low redundancy and are thus especially vulnerable to cascades.
Local renormalizable gauge theories from nonlocal operators
Capri, M.A.L. Lemes, V.E.R. Sobreiro, R.F. Sorella, S.P. Thibes, R.
2008-03-15
The possibility that nonlocal operators might be added to the Yang-Mills action is investigated. We point out that there exists a class of nonlocal operators which lead to renormalizable gauge theories. These operators turn out to be localizable by means of the introduction of auxiliary fields. The renormalizability is thus ensured by the symmetry content exhibited by the resulting local theory. The example of the nonlocal operator Tr{integral}A{sub {mu}}1/(D{sup 2}) A{sub {mu}} is analyzed in detail. A few remarks on the possible role that these operators might have for confining theories are outlined.
Bell-type inequalities for nonlocal resources
NASA Astrophysics Data System (ADS)
Brunner, Nicolas; Scarani, Valerio; Gisin, Nicolas
2006-11-01
We present bipartite Bell-type inequalities which allow the two partners to use some nonlocal resource. Such inequalities can only be violated if the parties use a resource which is more nonlocal than the one permitted by the inequality. We introduce a family of N-input nonlocal machines, which are generalizations of the well-known PR (Popescu-Rohrlich) box. Then we construct Bell-type inequalities that cannot be violated by strategies that use one of these new machines. Finally we discuss implications for the simulation of quantum states.
Nonlocal study of ultimate plasmon hybridization.
Raza, Søren; Wubs, Martijn; Bozhevolnyi, Sergey I; Mortensen, N Asger
2015-03-01
Within our recently proposed generalized nonlocal optical response (GNOR) model, where nonlocal response is included by taking into account both convective and diffusive currents of the conduction electrons, we revisit the fundamental problem of an optically excited plasmonic dimer. We consider the transition from separated dimers via touching dimers to finally overlapping dimers. In particular, we focus on the touching case, showing a fundamental limit on the hybridization of the bonding plasmon modes due to nonlocality. Using transformation optics, we determine a simple analytical equation for the resonance energies.
Non-locality of experimental qutrit pairs
NASA Astrophysics Data System (ADS)
Bernhard, C.; Bessire, B.; Montina, A.; Pfaffhauser, M.; Stefanov, A.; Wolf, S.
2014-10-01
The insight due to John Bell that the joint behavior of individually measured entangled quantum systems cannot be explained by shared information remains a mystery to this day. We describe an experiment, and its analysis, displaying non-locality of entangled qutrit pairs. The non-locality of such systems, as compared to qubit pairs, is of particular interest since it potentially opens the door for tests of bipartite non-local behavior independent of probabilistic Bell inequalities, but of deterministic nature. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘50 years of Bell’s theorem’.
On a nonlocal model of image segmentation
NASA Astrophysics Data System (ADS)
Gajewski, Herbert; Gärtner, Klaus
2005-07-01
We understand an image as binary grey ‘alloy’ of a black and a white component and use a nonlocal phase separation model to describe image segmentation. The model consists in a degenerate nonlinear parabolic equation with a nonlocal drift term additionally to the familiar Perona-Malik model. We formulate conditions for the model parameters to guarantee global existence of a unique solution that tends exponentially in time to a unique steady state. This steady state is solution of a nonlocal nonlinear elliptic boundary value problem and allows a variational characterization. Numerical examples demonstrate the properties of the model.
Cusp Formation for a Nonlocal Evolution Equation
NASA Astrophysics Data System (ADS)
Hoang, Vu; Radosz, Maria
2017-02-01
Córdoba et al. (Ann Math 162(3):1377-1389, 2005) introduced a nonlocal active scalar equation as a one-dimensional analogue of the surface-quasigeostrophic equation. It has been conjectured, based on numerical evidence, that the solution forms a cusp-like singularity in finite time. Up until now, no active scalar with nonlocal flux is known for which cusp formation has been rigorously shown. In this paper, we introduce and study a nonlocal active scalar, inspired by the Córdoba-Córdoba-Fontelos equation, and prove that either a cusp- or needle-like singularity forms in finite time.
Local, nonlocal quantumness and information theoretic measures
NASA Astrophysics Data System (ADS)
Agrawal, Pankaj; Sazim, Sk; Chakrabarty, Indranil; Pati, Arun K.
2016-08-01
It has been suggested that there may exist quantum correlations that go beyond entanglement. The existence of such correlations can be revealed by information theoretic quantities such as quantum discord, but not by the conventional measures of entanglement. We argue that a state displays quantumness, that can be of local and nonlocal origin. Information theoretic measures not only characterize the nonlocal quantumness, but also the local quantumness, such as the “local superposition”. This can be a reason, why such measures are nonzero, when there is no entanglement. We consider a generalized version of the Werner state to demonstrate the interplay of local quantumness, nonlocal quantumness and classical mixedness of a state.
Experimental test of nonlocal causality
Ringbauer, Martin; Giarmatzi, Christina; Chaves, Rafael; Costa, Fabio; White, Andrew G.; Fedrizzi, Alessandro
2016-01-01
Explaining observations in terms of causes and effects is central to empirical science. However, correlations between entangled quantum particles seem to defy such an explanation. This implies that some of the fundamental assumptions of causal explanations have to give way. We consider a relaxation of one of these assumptions, Bell’s local causality, by allowing outcome dependence: a direct causal influence between the outcomes of measurements of remote parties. We use interventional data from a photonic experiment to bound the strength of this causal influence in a two-party Bell scenario, and observational data from a Bell-type inequality test for the considered models. Our results demonstrate the incompatibility of quantum mechanics with a broad class of nonlocal causal models, which includes Bell-local models as a special case. Recovering a classical causal picture of quantum correlations thus requires an even more radical modification of our classical notion of cause and effect. PMID:27532045
Experimental test of nonlocal causality.
Ringbauer, Martin; Giarmatzi, Christina; Chaves, Rafael; Costa, Fabio; White, Andrew G; Fedrizzi, Alessandro
2016-08-01
Explaining observations in terms of causes and effects is central to empirical science. However, correlations between entangled quantum particles seem to defy such an explanation. This implies that some of the fundamental assumptions of causal explanations have to give way. We consider a relaxation of one of these assumptions, Bell's local causality, by allowing outcome dependence: a direct causal influence between the outcomes of measurements of remote parties. We use interventional data from a photonic experiment to bound the strength of this causal influence in a two-party Bell scenario, and observational data from a Bell-type inequality test for the considered models. Our results demonstrate the incompatibility of quantum mechanics with a broad class of nonlocal causal models, which includes Bell-local models as a special case. Recovering a classical causal picture of quantum correlations thus requires an even more radical modification of our classical notion of cause and effect.
Nonlocal quantum gravity: A review
NASA Astrophysics Data System (ADS)
Modesto, Leonardo; Rachwał, Lesław
We hereby review a class of quantum gravitational theories based on weakly nonlocal analytic classical actions. The most general action is characterized by two nonpolynomial entire functions (form-factors) in terms quadratic in curvature. The form-factors avert the presence of poltergeists, that plague any local higher derivative theory of gravity and improve the high-energy behavior of loop amplitudes. For pedagogical purposes, it is proved that the theory is super-renormalizable in any dimension, i.e. only one-loop divergences survive, and is asymptotically free. Furthermore, due to dimensional reasons, in odd dimensions, there are no counterterms for pure gravity and the theory turns out to be finite. Moreover, we show that it is always possible to choose the additional terms in the action (higher in curvature) in such a way to make the full theory UV-finite and therefore, scale-invariant in quantum realm, also in even dimension.
Film edge nonlocal spin valves.
McCallum, Andrew T; Johnson, Mark
2009-06-01
Spintronics is a new paradigm for integrated digital electronics. Recently established as a niche for nonvolatile magnetic random access memory (MRAM), it offers new functionality while demonstrating low-power and high-speed performance. However, to reach high density spintronic technology must make a transition to the nanometer scale. Prototype devices are presently made using a planar geometry and have an area determined by the lithographic feature size, currently about 100 nm. Here we present a new nonplanar geometry in which one lateral dimension is given by a film thickness, on the order of 10 nm. With this new approach, cell sizes can shrink by an order of magnitude. The geometry is demonstrated with a nonlocal spin valve, where we study devices with an injector/detector separation much less than the spin diffusion length.
Nonlocal advantage of quantum coherence
NASA Astrophysics Data System (ADS)
Mondal, Debasis; Pramanik, Tanumoy; Pati, Arun Kumar
2017-01-01
A bipartite state is said to be steerable if and only if it does not have a single-system description, i.e., the bipartite state cannot be explained by a local hidden state model. Several steering inequalities have been derived using different local uncertainty relations to verify the ability to control the state of one subsystem by the other party. Here, we derive complementarity relations between coherences measured on mutually unbiased bases using various coherence measures such as the l1-norm, relative entropy, and skew information. Using these relations, we derive conditions under which a nonlocal advantage of quantum coherence can be achieved and the state is steerable. We show that not all steerable states can achieve such an advantage.
Experimental many-pairs nonlocality
NASA Astrophysics Data System (ADS)
Poh, Hou Shun; Cerè, Alessandro; Bancal, Jean-Daniel; Cai, Yu; Sangouard, Nicolas; Scarani, Valerio; Kurtsiefer, Christian
2017-08-01
Collective measurements on large quantum systems together with a majority voting strategy can lead to a violation of the Clauser-Horne-Shimony-Holt Bell inequality. In the presence of many entangled pairs, this violation decreases quickly with the number of pairs and vanishes for some critical pair number that is a function of the noise present in the system. Here we show that a different binning strategy can lead to a more substantial Bell violation when the noise is sufficiently small. Given the relation between the critical pair number and the source noise, we then present an experiment where the critical pair number is used to quantify the quality of a high visibility photon pair source. Our results demonstrate nonlocal correlations using collective measurements operating on clusters of more than 40 photon pairs.
Entanglement and quantum nonlocality demystified
NASA Astrophysics Data System (ADS)
Kupczynski, Marian
2012-12-01
Quantum nonlocality is presented often as the most remarkable and inexplicable phenomenon known to modern science. It has been known already for a long time that the probabilistic models used to prove Bell and Clauser-Horn-Shimony-Holt inequalities (BI-CHSH) for spin polarization correlation experiments (SPCE) are incompatible with the experimental protocols of SPCE. In particular these models use the same common probability space, joint probability distributions and/or conditional independence to describe coincidence experiments in incompatible experimental settings. Strangely enough these results are not known or simply neglected. This is why we will once again reanalyze Bell locality assumptions and show that they have nothing to do with the notion of Einsteinian locality therefore their violation should not be called quantum nonlocality but rather quantum non-Kolmogorovness or quantum contextuality. Moreover if local variables describing the measuring instruments are correctly taken into account then BI-CHSH can no longer be proven and one can easily construct non-signaling probabilistic models able to reproduce the predictions of QT. The violation of BI-CHSH is considered usually as a proof that a quantum state is entangled. Since BI-CHSH are violated also in some experiments from outside the domain of quantum physics therefore the entanglement is not exclusively a quantum phenomenon. In order to further demystify these notions we show that one can prepare two macroscopic systems in such a way that simple realizable local experiments on these systems violate BI. In view of these arguments the further testing of BI-CHSH inequalities in search for the loopholes does not seem to be necessary.
Family of nonlocal bound entangled states
NASA Astrophysics Data System (ADS)
Yu, Sixia; Oh, C. H.
2017-03-01
Bound entanglement, being entangled yet not distillable, is essential to our understanding of the relations between nonlocality and entanglement besides its applications in certain quantum information tasks. Recently, bound entangled states that violate a Bell inequality have been constructed for a two-qutrit system, disproving a conjecture by Peres that bound entanglement is local. Here we construct this kind of nonlocal bound entangled state for all finite dimensions larger than two, making possible their experimental demonstration in most general systems. We propose a Bell inequality, based on a Hardy-type argument for nonlocality, and a steering inequality to identify their nonlocality. We also provide a family of entanglement witnesses to detect their entanglement beyond the Bell inequality and the steering inequality.
Plasmonic nanostructures: local versus nonlocal response
NASA Astrophysics Data System (ADS)
Toscano, Giuseppe; Wubs, Martijn; Xiao, Sanshui; Yan, Min; Öztürk, Z. Fatih; Jauho, Antti-Pekka; Mortensen, N. A.
2010-08-01
We study the importance of taking the nonlocal optical response of metals into account for accurate determination of optical properties of nanoplasmonic structures. Here we focus on the computational physics aspects of this problem, and in particular we report on the nonlocal-response package that we wrote for state-of the art numerical software, enabling us to take into account the nonlocal material response of metals for any arbitrarily shaped nanoplasmonic structures, without much numerical overhead as compared to the standard local response. Our method is a frequency-domain method, and hence it is sensitive to possible narrow resonances that may arise due to strong electronic quantum confinement in the metal. This feature allows us to accurately determine which geometries are strongly affected by nonlocal response, for example regarding applications based on electric field enhancement properties for which metal nanostructures are widely used.
Symmetric states: Their nonlocality and entanglement
Wang, Zizhu; Markham, Damian
2014-12-04
The nonlocality of permutation symmetric states of qubits is shown via an extension of the Hardy paradox and the extension of the associated inequality. This is achieved by using the Majorana representation, which is also a powerful tool in the study of entanglement properties of symmetric states. Through the Majorana representation, different nonlocal properties can be linked to different entanglement properties of a state, which is useful in determining the usefulness of different states in different quantum information processing tasks.
Experimental falsification of Leggett's nonlocal variable model.
Branciard, Cyril; Ling, Alexander; Gisin, Nicolas; Kurtsiefer, Christian; Lamas-Linares, Antia; Scarani, Valerio
2007-11-23
Bell's theorem guarantees that no model based on local variables can reproduce quantum correlations. Also, some models based on nonlocal variables, if subject to apparently "reasonable" constraints, may fail to reproduce quantum physics. In this Letter, we introduce a family of inequalities, which use a finite number of measurement settings, and which therefore allow testing Leggett's nonlocal model versus quantum physics. Our experimental data falsify Leggett's model and are in agreement with quantum predictions.
Palatini formulation of non-local gravity
NASA Astrophysics Data System (ADS)
Briscese, F.; Pucheu, M. L.
We derive the dynamical equations for a non-local gravity model in the Palatini formalism and we discuss some of the properties of this model. We have show that, in some specific case, the vacuum solutions of general relativity are also vacuum solutions of the non-local model, so we conclude that, at least in this case, the singularities of Einstein’s gravity are not removed.
Chaotic Orbits for Systems of Nonlocal Equations
NASA Astrophysics Data System (ADS)
Dipierro, Serena; Patrizi, Stefania; Valdinoci, Enrico
2017-01-01
We consider a system of nonlocal equations driven by a perturbed periodic potential. We construct multibump solutions that connect one integer point to another one in a prescribed way. In particular, heteroclinic, homoclinic and chaotic trajectories are constructed. This is the first attempt to consider a nonlocal version of this type of dynamical systems in a variational setting and the first result regarding symbolic dynamics in a fractional framework.
Robust non-local median filter
NASA Astrophysics Data System (ADS)
Matsuoka, Jyohei; Koga, Takanori; Suetake, Noriaki; Uchino, Eiji
2017-04-01
This paper describes a novel image filter with superior performance on detail-preserving removal of random-valued impulse noise superimposed on natural gray-scale images. The non-local means filter is in the limelight as a way of Gaussian noise removal with superior performance on detail preservation. By referring the fundamental concept of the non-local means, we had proposed a non-local median filter as a specialized way for random-valued impulse noise removal so far. In the non-local processing, the output of a filter is calculated from pixels in blocks which are similar to the block centered at a pixel of interest. As a result, aggressive noise removal is conducted without destroying the detailed structures in an original image. However, the performance of non-local processing decreases enormously in the case of high noise occurrence probability. A cause of this problem is that the superimposed noise disturbs accurate calculation of the similarity between the blocks. To cope with this problem, we propose an improved non-local median filter which is robust to the high level of corruption by introducing a new similarity measure considering possibility of being the original signal. The effectiveness and validity of the proposed method are verified in a series of experiments using natural gray-scale images.
Robust non-local median filter
NASA Astrophysics Data System (ADS)
Matsuoka, Jyohei; Koga, Takanori; Suetake, Noriaki; Uchino, Eiji
2017-01-01
This paper describes a novel image filter with superior performance on detail-preserving removal of random-valued impulse noise superimposed on natural gray-scale images. The non-local means filter is in the limelight as a way of Gaussian noise removal with superior performance on detail preservation. By referring the fundamental concept of the non-local means, we had proposed a non-local median filter as a specialized way for random-valued impulse noise removal so far. In the non-local processing, the output of a filter is calculated from pixels in blocks which are similar to the block centered at a pixel of interest. As a result, aggressive noise removal is conducted without destroying the detailed structures in an original image. However, the performance of non-local processing decreases enormously in the case of high noise occurrence probability. A cause of this problem is that the superimposed noise disturbs accurate calculation of the similarity between the blocks. To cope with this problem, we propose an improved non-local median filter which is robust to the high level of corruption by introducing a new similarity measure considering possibility of being the original signal. The effectiveness and validity of the proposed method are verified in a series of experiments using natural gray-scale images.
Effects of nonlocality on transfer reactions
NASA Astrophysics Data System (ADS)
Titus, Luke
Nuclear reactions play a key role in the study of nuclei away from stability. Single-nucleon transfer reactions involving deuterons provide an exceptional tool to study the single-particle structure of nuclei. Theoretically, these reactions are attractive as they can be cast into a three-body problem composed of a neutron, proton, and the target nucleus. Optical potentials are a common ingredient in reactions studies. Traditionally, nucleon-nucleus optical potentials are made local for convenience. The effects of nonlocal potentials have historically been included approximately by applying a correction factor to the solution of the corresponding equation for the local equivalent interaction. This is usually referred to as the Perey correction factor. In this thesis, we have systematically investigated the effects of nonlocality on (p,d) and (d,p) transfer reactions, and the validity of the Perey correction factor. We implemented a method to solve the single channel nonlocal equation for both bound and scattering states. We also developed an improved formalism for nonlocal interactions that includes deuteron breakup in transfer reactions. This new formalism, the nonlocal adiabatic distorted wave approximation, was used to study the effects of including nonlocality consistently in ( d,p) transfer reactions. For the (p,d) transfer reactions, we solved the nonlocal scattering and bound state equations using the Perey-Buck type interaction, and compared to local equivalent calculations. Using the distorted wave Born approximation we construct the T-matrix for (p,d) transfer on 17O, 41Ca, 49Ca, 127 Sn, 133Sn, and 209Pb at 20 and 50 MeV. Additionally we studied (p,d) reactions on 40Ca using the the nonlocal dispersive optical model. We have also included nonlocality consistently into the adiabatic distorted wave approximation and have investigated the effects of nonlocality on on (d,p) transfer reactions for deuterons impinged on 16O, 40Ca, 48Ca, 126Sn, 132Sn, 208Pb at 10
Kunkri, Samir; Choudhary, Sujit K.; Ahanj, Ali; Joag, Pramod
2006-02-15
Here we deal with a nonlocality argument proposed by Cabello, which is more general than Hardy's nonlocality argument, but still maximally entangled states do not respond. However, for most of the other entangled states, maximum probability of success of this argument is more than that of the Hardy's argument.
NASA Astrophysics Data System (ADS)
Kunkri, Samir; Choudhary, Sujit K.; Ahanj, Ali; Joag, Pramod
2006-02-01
Here we deal with a nonlocality argument proposed by Cabello, which is more general than Hardy’s nonlocality argument, but still maximally entangled states do not respond. However, for most of the other entangled states, maximum probability of success of this argument is more than that of the Hardy’s argument.
NASA Astrophysics Data System (ADS)
Kumar, Priyank; Bhatt, N. K.; Vyas, P. R.; Gohel, V. B.
2017-07-01
In the present communication, the ion motional contribution (F_{ion}) to the total Helmholtz free energy has been accounted for by using mean field potential (MFP) approximation. The MFP is constructed using the local pseudopotential for divalent ytterbium and trivalent cerium. Further, MFP is used to evaluate static as well as temperature-dependent thermodynamic properties of these metals up to their melting temperature. Computed results are compared with experimental findings as well as results obtained by applying other theoretical methods. Present conjunction scheme with its computational simplicity, physical transparency and transferability of local pseudopotential explains the role of pressure-induced interband transfer of electrons which is crucial in the determination of thermodynamic properties of complex metals like lanthanides.
NASA Astrophysics Data System (ADS)
Nault, Zachary; Cancio, Antonio
2013-03-01
Much recent development in DFT has focused on improving GGAs. Two schemes are second order GGA (SOGGA) and the APBE which builds the GGA from atomic systems and not the HEG. Both of these have been tested within an all electron (AE) environment, providing the most accurate results. The focus of many simulations, however, is on large systems using pseudopotentials (PsP's). Are these PsP calculations, which rely on functionals tested in an AE environment, accurately reproducing the AE ground state properties? If not, can the deficiencies be identified? To assess this, we use the PsP generator APE, using the functional library libXC which works with the PsP package ABINIT and the AE package Elk. We generate standard Troullier-Martin PsP's based on common and new XC functionals (LDA, PBE, PBEsol, APBE, SOGGA) and test their performance in 13 solids (Na, Li, Al, C, Si, GaAs, NaCl, LiF, LiCl, Cu, Pd, Rh, and Ag). We measure how well three ground state properties (lattice constant, bulk modulus, and cohesive energy) are calculated with PsP's as compared to the corresponding AE calculations.
White, W.T. III
1985-11-04
We have studied two-photon absorption in solids theoretically and experimentally. We have shown that it is possible to use accurate band structure techniques to compute two-photon absorption spectra within 15% of measured values in a wide band-gap material, ZnS. The empirical pseudopotential technique that we used is significantly more accurate than previous models of two-photon absorption in zinc blende materials, including present tunneling theories (which are essentially parabolic-band results in disguise) and the nonparabolic-band formalism of Pidgeon et al. and Weiler. The agreement between our predictions and previous measurements allowed us to use ZnS as a reference material in order to validate a technique for measuring two-photon absorption that was previously untried in solids, pulsed dual-beam thermal lensing. With the validated technique, we examined nonlinear absorption in one other crystal (rutile) and in several glasses, including silicates, borosilicates, and one phosphate glass. Initially, we believed that the absorption edges of all the materials were comparable; however, subsequent evidence suggested that the effective band-gap energies of the glasses were above the energy of two photons in our measurement. Therefore, we attribute the nonlinear absorption that we observed in glasses to impurities or defects. The measured nonlinear absorption coefficients were of the order of a few cm/TW in the glasses and of the order of 10 cm/GW in the crystals, four orders of magnitude higher than in glasses. 292 refs.
Cuadrado, R; Cerdá, J I
2012-02-29
We present an efficient implementation of the spin-orbit coupling within the density functional theory based SIESTA code (2002 J. Phys.: Condens. Matter 14 2745) using the fully relativistic and totally separable pseudopotential formalism of Hemstreet et al (1993 Phys. Rev. B 47 4238). First, we obtain the spin-orbit splittings for several systems ranging from isolated atoms to bulk metals and semiconductors as well as the Au(111) surface state. Next, and after extensive tests on the accuracy of the formalism, we also demonstrate its capability to yield reliable values for the magnetic anisotropy energy in magnetic systems. In particular, we focus on the L1(0) binary alloys and on two large molecules: Mn(6)O(2)(H -sao)(6)(O(2)CH)(2)(CH(3)OH)(4) and Co(4)(hmp)(4)(CH(3)OH)(4)Cl(4). In all cases our calculated anisotropies are in good agreement with those obtained with full-potential methods, despite the latter being, in general, computationally more demanding.
Atomistic Pseudopotential Calculations of Thickness-Fluctuation GaAs Quantum Dots
Luo, J. W.; Bester, G.; Zunger, A.
2009-03-01
We calculate the electronic and optical properties of thickness-fluctuation quantum dots of different sizes and elongations using an atomistic empirical pseudopotential approach and configuration interaction. The carriers are confined by a monolayer fluctuation in the thickness of a GaAs/Al{sub 0.3}Ga{sub 0.7}As quantum well with a nominal thickness between 10 and 20 monolayers. For 10 monolayer thickness, we find several confined electron and hole levels of dominant heavy-hole character penetrating deep into the barrier (out of plane) and far beyond the physical dimension of the monolayer step (in-plane). The spatial extent of the states is strongly affected by the random-alloy fluctuations of the barrier, pushing the states toward Ga-rich regions of the interface. The similarity in the spatial extent of the electron and hole states leads to strong oscillator strength and a rich optical spectrum. The exciton as well as biexciton and trions (positive and negative) all show several lines in absorption despite the very shallow confinement potential given in these structures. The effects of correlations is drastic on the optical spectrum with the creation of highly correlated states that deviate strongly from the uncorrelated results.
Contact angle adjustment in equation-of-state-based pseudopotential model.
Hu, Anjie; Li, Longjian; Uddin, Rizwan; Liu, Dong
2016-05-01
The single component pseudopotential lattice Boltzmann model has been widely applied in multiphase simulation due to its simplicity and stability. In many studies, it has been claimed that this model can be stable for density ratios larger than 1000. However, the application of the model is still limited to small density ratios when the contact angle is considered. The reason is that the original contact angle adjustment method influences the stability of the model. Moreover, simulation results in the present work show that, by applying the original contact angle adjustment method, the density distribution near the wall is artificially changed, and the contact angle is dependent on the surface tension. Hence, it is very inconvenient to apply this method with a fixed contact angle, and the accuracy of the model cannot be guaranteed. To solve these problems, a contact angle adjustment method based on the geometry analysis is proposed and numerically compared with the original method. Simulation results show that, with our contact angle adjustment method, the stability of the model is highly improved when the density ratio is relatively large, and it is independent of the surface tension.
Scalable real space pseudopotential density functional codes for materials in the exascale regime
NASA Astrophysics Data System (ADS)
Lena, Charles; Chelikowsky, James; Schofield, Grady; Biller, Ariel; Kronik, Leeor; Saad, Yousef; Deslippe, Jack
Real-space pseudopotential density functional theory has proven to be an efficient method for computing the properties of matter in many different states and geometries, including liquids, wires, slabs, and clusters with and without spin polarization. Fully self-consistent solutions using this approach have been routinely obtained for systems with thousands of atoms. Yet, there are many systems of notable larger sizes where quantum mechanical accuracy is desired, but scalability proves to be a hindrance. Such systems include large biological molecules, complex nanostructures, or mismatched interfaces. We will present an overview of our new massively parallel algorithms, which offer improved scalability in preparation for exascale supercomputing. We will illustrate these algorithms by considering the electronic structure of a Si nanocrystal exceeding 104 atoms. Support provided by the SciDAC program, Department of Energy, Office of Science, Advanced Scientific Computing Research and Basic Energy Sciences. Grant Numbers DE-SC0008877 (Austin) and DE-FG02-12ER4 (Berkeley).
Contact angle adjustment in equation-of-state-based pseudopotential model
NASA Astrophysics Data System (ADS)
Hu, Anjie; Li, Longjian; Uddin, Rizwan; Liu, Dong
2016-05-01
The single component pseudopotential lattice Boltzmann model has been widely applied in multiphase simulation due to its simplicity and stability. In many studies, it has been claimed that this model can be stable for density ratios larger than 1000. However, the application of the model is still limited to small density ratios when the contact angle is considered. The reason is that the original contact angle adjustment method influences the stability of the model. Moreover, simulation results in the present work show that, by applying the original contact angle adjustment method, the density distribution near the wall is artificially changed, and the contact angle is dependent on the surface tension. Hence, it is very inconvenient to apply this method with a fixed contact angle, and the accuracy of the model cannot be guaranteed. To solve these problems, a contact angle adjustment method based on the geometry analysis is proposed and numerically compared with the original method. Simulation results show that, with our contact angle adjustment method, the stability of the model is highly improved when the density ratio is relatively large, and it is independent of the surface tension.
Pseudo-Potentials in Dense and He-like Hot temperature Plasmas
NASA Astrophysics Data System (ADS)
Deutsch, Claude; Rahal, Hamid
2012-10-01
Extending our former derivations in dense and high temperature plasmas of hydrogenic effective interactions mimiking the Heisenberg uncertainty principle [1,2], we worked out in a canonical ensemble, effective interactions in He-like plasmas where an orbital 1s electron remains strongly tighted to the He-like ions. The plasma electrons are then taken into account through appropriate Slater sums obtained in the most economical hydrogenic extension of the He-like bound and scattered states with angular orbital momentum l<3. Ground states are described by a multi-parametric HF approximation [3]. We thus obtain Diffraction-corrected electron-ion pseudo-potentials taking into account of a polarizable and nonpointlike ion core. Very large enhancements and discrepancies are obtained when they are contrasted to their H-like homologs with ion charge Z=2,10 and 92. These results are of obvious significance for He-like warm dense matter plasmas.Ionization is also considered.[4pt] [1] C. Deutsch, Phys. Lett. A60, 317 (1977)[4pt] [2] C. Deutsch, Y. Furutani and M.M. Gombert, Phys. Rep. 69,86 (1981)[0pt] [3] E. Clementi and C. Roetti, Atomic Data and Nucl. Data Tables, 14,177(1974)
Relativistic Pseudopotential Followed by Restoration Method for Studying Heavy-Atom Systems
NASA Astrophysics Data System (ADS)
Petrov, Alexander; Skripnikov, Leonid; Mosyagin, Nikolay; Titov, Anatoly
2012-06-01
Precise all-electron four-component treatment of molecules with heavy elements is yet rather consuming. In turn, the relativistic pseudopotential (RPP) method is the most straightforward way now to study efficiently ``valence'' (optic, electric, chemical etc.) properties of rather complicated systems. However, the valence molecular spinors are usually smoothed in atomic cores. Therefore, direct calculation of electronic densities near heavy nuclei within the RPP approach is impossible. In the report, an approach based on the RPP method and one-center core-restoration technique [1] developed by the authors for such studies is discussed. It efficiency is illustrated in benchmark to-date calculations of magnetic-dipole and electric quadrupole hyperfine-structure constants, as well as the space parity (P) and time-reversal symmetry (T) nonconservation effects in polar heavy-atom molecules, including HfF^+, WC, PbF^+, PbO, YbF, ThO and some other candidates which are studied now as promising molecules for the experimental search of the electron electric dipole moment (eEDM). [4pt] [1] A.V.Titov, N.S.Mosyagin, A.N.Petrov, T.A.Isaev, D.DeMille, Progr. Theor. Chem. Phys., 15B, 253 (2006).
Optical scheme for simulating post-quantum nonlocality distillation.
Chu, Wen-Jing; Yang, Ming; Pan, Guo-Zhu; Yang, Qing; Cao, Zhuo-Liang
2016-11-28
An optical scheme for simulating nonlocality distillation is proposed in post-quantum regime. The nonlocal boxes are simulated by measurements on appropriately pre- and post-selected polarization entangled photon pairs, i.e. post-quantum nonlocality is simulated by exploiting fair-sampling loophole in a Bell test. Mod 2 addition on the outputs of two nonlocal boxes combined with pre- and post-selection operations constitutes the key operation of simulating nonlocality distillation. This scheme provides a possible tool for the experimental study on the nonlocality in post-quantum regime and the exact physical principle precisely distinguishing physically realizable correlations from nonphysical ones.
NASA Astrophysics Data System (ADS)
Yang, Yun-Qing; Chen, Yong
2011-01-01
Based on the method developed by Nucci, the pseudopotentials, Lax pairs and the singularity manifold equations of the generalized fifth-order KdV equation are derived. By choosing different coefficient, the corresponding results and the Bäcklund transformations can be obtained on three conditioners which include Caudrey—Dodd—Gibbon—Sawada—Kotera equation, the Lax equation and the Kaup-kupershmidt equation.
Nonlocal electrodynamics in Weyl semimetals
NASA Astrophysics Data System (ADS)
Rosenstein, B.; Kao, H. C.; Lewkowicz, M.
2017-02-01
Recently synthesized three-dimensional materials with Dirac spectrum exhibit peculiar electric transport qualitatively different from its two-dimensional analog, graphene. By neglecting impurity scattering, the real part of the conductivity is strongly frequency dependent, while the imaginary part is nonzero unlike in undoped, clean graphene. The Coulomb interaction between electrons is unscreened as in a dielectric and hence is long range. We demonstrate that the interaction correction renders the electrodynamics nonlocal on a mesoscopic scale. The longitudinal conductivity σL and the transverse conductivity σT are different in the long-wavelength limit and consequently the standard local Ohm's law description does not apply. This leads to several remarkable effects in optical response. The p -polarized light generates in these materials bulk plasmons as well as the transversal waves. At a specific frequency the two modes coincide, a phenomenon impossible in a local medium. For any frequency there is a Brewster angle where total absorption occurs, turning the Weyl semimetals opaque. The effect of the surface, including the Fermi arcs, is discussed.
NASA Astrophysics Data System (ADS)
Thompson, Ian
2010-11-01
In all direct reactions to probe the structure of exotic nuclei at FRIB, optical potentials will be needed in the entrance and exit channels. At high energies Glauber approximations may be useful, but a low energies (5 to 20 MeV/nucleon) other approaches are required. Recent work of the UNEDF project [1] has shown that reaction cross sections at these energies can be accounted for by calculating all inelastic and transfer channels reachable by one particle-hole transitions from the elastic channel. In this model space, we may also calculate the two-step dynamic polarization potential (DPP) that adds to the bare folded potential to form the complex optical potential. Our calculations of the DPP, however, show that its non-localities are very significant, as well as the partial-wave dependence of both its real and imaginary components. The Perey factors (the wave function ratio to that from an equivalent local potential) are more than 20% different from unity, especially for partial waves inside grazing. These factors combine to suggest a reexamination of the validity of local and L-independent fitted optical potentials, especially for capture reactions that are dominated by low partial waves. Prepared by LLNL under Contract DE-AC52-07NA27344. [1] G.P.A. Nobre, F.S. Dietrich, J.E. Escher, I.J. Thompson, M. Dupuis, J. Terasaki and J. Engel, submitted to Phys. Rev. Letts., 2010.
NASA Astrophysics Data System (ADS)
Çakan, Aslı; Sevik, Cem; Bulutay, Ceyhun
2016-03-01
The properties of a semiconductor are drastically modified when the crystal point group symmetry is broken under an arbitrary strain. We investigate the family of semiconductors consisting of GaAs, GaSb, InAs and InSb, considering their electronic band structure and deformation potentials subject to various strains based on hybrid density functional theory. Guided by these first-principles results, we develop strain-compliant local pseudopotentials for use in the empirical pseudopotential method (EPM). We demonstrate that the newly proposed empirical pseudopotentials perform well close to band edges and under anisotropic crystal deformations. Using the EPM, we explore the heavy hole-light hole mixing characteristics under different stress directions, which may be useful in manipulating their transport properties and optical selection rules. The very low 5 Ry cutoff targeted in the generated pseudopotentials paves the way for large-scale EPM-based electronic structure computations involving these lattice mismatched constituents.
Maximally nonlocal theories cannot be maximally random.
de la Torre, Gonzalo; Hoban, Matty J; Dhara, Chirag; Prettico, Giuseppe; Acín, Antonio
2015-04-24
Correlations that violate a Bell inequality are said to be nonlocal; i.e., they do not admit a local and deterministic explanation. Great effort has been devoted to study how the amount of nonlocality (as measured by a Bell inequality violation) serves to quantify the amount of randomness present in observed correlations. In this work we reverse this research program and ask what do the randomness certification capabilities of a theory tell us about the nonlocality of that theory. We find that, contrary to initial intuition, maximal randomness certification cannot occur in maximally nonlocal theories. We go on and show that quantum theory, in contrast, permits certification of maximal randomness in all dichotomic scenarios. We hence pose the question of whether quantum theory is optimal for randomness; i.e., is it the most nonlocal theory that allows maximal randomness certification? We answer this question in the negative by identifying a larger-than-quantum set of correlations capable of this feat. Not only are these results relevant to understanding quantum mechanics' fundamental features, but also put fundamental restrictions on device-independent protocols based on the no-signaling principle.
NASA Astrophysics Data System (ADS)
Bester, Gabriel
2006-03-01
The optical spectrum and the charging energies of semiconductor quantum dots have been recently measured with high accuracy. Both of these experimental techniques probe many-body states that are not directly described by independent particle theories such as the density functional theory. On the other hand, quasi- particle theories that can in principle address the problem, such as GW, are computationally too demanding for the study of nanostructures (as opposed to clusters) where many thousands of atoms are involved. One way to approach this problem is to use the effective mass approximation or the k.p method and choose a confinement potential that reproduces a few known experimental facts (e.g. the splitting between confined levels). These methods can provide a good initial guess but were shown to be too crude to enable a quantitative comparision with recent experiments. We therefore adopt a bottom-up atomistic approach where instead of starting from a simplified approach, such as effective mass, and progressively increase the complexity by adding parameters, we start from the accurate atomistic description (LDA or GW) and work ourselves up using a few well controlled approximations.I will first present the method, namely (i) the scheme that is used to derive the empirical pseudopotentials including the piezoelectric effect, (ii) the choices that have to be made for the basis used to expand the wave functions, (iii) the inclusion of corelations through Bethe-Salpeter-like treatment. I will then present recent applications of the theory to calculate the fine-structure [1] of excitons and charged excitons, the charging spectra of holes [2] and the degree or entanglement stored in a quantum dot molecule [3].[1] G. Bester, S.V. Nair, A. Zunger, prb 67, 161306 (2003). [2] L. He, G. Bester, A. Zunger, PRL (in press). [3] G. Bester, J. Shumway, A. Zunger, PRL 93, 047401 (2004)
NASA Astrophysics Data System (ADS)
Titov, Anatoly V.; Petrov, Alexander N.; Skripnikov, Leonid V.; Mosyagin, Nikolai S.
2011-06-01
The relativistic pseudopotential (RPP) calculations of valence (spectroscopic, chemical etc.) properties of molecules are very efficient because the modern two-component RPP methods allows one to treat very accurately the correlation and relativistic effects for the valence electrons of a molecule and to reduce dramatically the computational cost. The valence molecular spinors are usually smoothed in atomic cores and, as a result, direct calculation of electronic densities near heavy nuclei within such approach directly is impossible. Precise calculations of such properties, as hyperfine constants and other magnetic properties, parity nonconservation effects, which are described by the operators heavily concentrated in atomic cores, usually require very accurate accounting for both relativistic and correlation effects. Electronic structure should be well evaluated in both valence and atomic core regions. However, precise all-electron four-component treatment of molecules with heavy elements is yet rather consuming. In the report, an alternative approach based on the RPP method and one-center core-restoration technique [1] developed by the authors for such studies is discussed. Its efficiency is illustrated in benchmark to-date calculations of magnetic-dipole and electric quadrupole hyperfine-structure constants, as well as the space parity (P) and time-reversal symmetry (T) nonconservation effects in polar heavy-atom molecules, including HfF^+, PtH^+, ThO and WC, which are studied now as promising candidates for the experimental search of the electron electric dipole moment (eEDM). [1] A.V.Titov, N.S.Mosyagin, A.N.Petrov, T.A.Isaev, D.DeMille, Progr. Theor. Chem. Phys., 15B, 253 (2006).
Covariant nonlocal chiral quark models with separable interactions
Dumm, D. Gomez; Grunfeld, A. G.; Scoccola, N. N.
2006-09-01
We present a comparative analysis of chiral quark models which include nonlocal covariant four-fermion couplings. We consider two alternative ways of introducing the nonlocality, as well as various shapes for the momentum-dependent form factors governing the effective interactions. In all cases we study the behavior of model parameters and analyze numerical results for constituent quark masses and quark propagator poles. Advantages of these covariant nonlocal schemes over instantaneous nonlocal schemes and the standard NJL model are pointed out.
Tuning quantum nonlocal effects in graphene plasmonics
NASA Astrophysics Data System (ADS)
Lundeberg, Mark B.; Gao, Yuanda; Asgari, Reza; Tan, Cheng; Van Duppen, Ben; Autore, Marta; Alonso-González, Pablo; Woessner, Achim; Watanabe, Kenji; Taniguchi, Takashi; Hillenbrand, Rainer; Hone, James; Polini, Marco; Koppens, Frank H. L.
2017-07-01
The response of electron systems to electrodynamic fields that change rapidly in space is endowed by unique features, including an exquisite spatial nonlocality. This can reveal much about the materials’ electronic structure that is invisible in standard probes that use gradually varying fields. Here, we use graphene plasmons, propagating at extremely slow velocities close to the electron Fermi velocity, to probe the nonlocal response of the graphene electron liquid. The near-field imaging experiments reveal a parameter-free match with the full quantum description of the massless Dirac electron gas, which involves three types of nonlocal quantum effects: single-particle velocity matching, interaction-enhanced Fermi velocity, and interaction-reduced compressibility. Our experimental approach can determine the full spatiotemporal response of an electron system.
Transfer reaction code with nonlocal interactions
NASA Astrophysics Data System (ADS)
Titus, L. J.; Ross, A.; Nunes, F. M.
2016-10-01
We present a suite of codes (NLAT for nonlocal adiabatic transfer) to calculate the transfer cross section for single-nucleon transfer reactions, (d , N) or (N , d) , including nonlocal nucleon-target interactions, within the adiabatic distorted wave approximation. For this purpose, we implement an iterative method for solving the second order nonlocal differential equation, for both scattering and bound states. The final observables that can be obtained with NLAT are differential angular distributions for the cross sections of A(d , N) B or B(N , d) A. Details on the implementation of the T-matrix to obtain the final cross sections within the adiabatic distorted wave approximation method are also provided. This code is suitable to be applied for deuteron induced reactions in the range of Ed =10-70 MeV, and provides cross sections with 4% accuracy.
Transfer reaction code with nonlocal interactions
Titus, L. J.; Ross, A.; Nunes, F. M.
2016-07-14
Here, we present a suite of codes (NLAT for nonlocal adiabatic transfer) to calculate the transfer cross section for single-nucleon transfer reactions, (d,N) or (N,d), including nonlocal nucleon-target interactions, within the adiabatic distorted wave approximation. For this purpose, we implement an iterative method for solving the second order nonlocal differential equation, for both scattering and bound states. The final observables that can be obtained with NLAT are dif- ferential angular distributions for the cross sections of A(d,N)B or B(N,d)A. Details on the implementation of the T-matrix to obtain the final cross sections within the adiabatic distorted wave approximation method are also provided. This code is suitable to be applied for deuteron induced reactions in the range of E_{d} = 10–70 MeV, and provides cross sections with 4% accuracy.
Tuning quantum nonlocal effects in graphene plasmonics.
Lundeberg, Mark B; Gao, Yuanda; Asgari, Reza; Tan, Cheng; Van Duppen, Ben; Autore, Marta; Alonso-González, Pablo; Woessner, Achim; Watanabe, Kenji; Taniguchi, Takashi; Hillenbrand, Rainer; Hone, James; Polini, Marco; Koppens, Frank H L
2017-07-14
The response of electron systems to electrodynamic fields that change rapidly in space is endowed by unique features, including an exquisite spatial nonlocality. This can reveal much about the materials' electronic structure that is invisible in standard probes that use gradually varying fields. Here, we use graphene plasmons, propagating at extremely slow velocities close to the electron Fermi velocity, to probe the nonlocal response of the graphene electron liquid. The near-field imaging experiments reveal a parameter-free match with the full quantum description of the massless Dirac electron gas, which involves three types of nonlocal quantum effects: single-particle velocity matching, interaction-enhanced Fermi velocity, and interaction-reduced compressibility. Our experimental approach can determine the full spatiotemporal response of an electron system. Copyright © 2017, American Association for the Advancement of Science.
Black hole information, unitarity, and nonlocality
Giddings, Steven B.
2006-11-15
The black hole information paradox apparently indicates the need for a fundamentally new ingredient in physics. The leading contender is nonlocality. Possible mechanisms for the nonlocality needed to restore unitarity to black hole evolution are investigated. Suggestions that such dynamics arise from ultra-Planckian modes in Hawking's derivation are investigated and found not to be relevant, in a picture using smooth slices spanning the exterior and interior of the horizon. However, no simultaneous description of modes that have fallen into the black hole and outgoing Hawking modes can be given without appearance of a large kinematic invariant, or other dependence on ultra-Planckian physics. This indicates that a reliable argument for information loss has not been constructed, and that strong gravitational dynamics is important. Such dynamics has been argued to be fundamentally nonlocal in extreme situations, such as those required to investigate the fate of information.
Hardy's criterion of nonlocality for mixed states
Ghirardi, GianCarlo; Marinatto, Luca
2006-03-15
We generalize Hardy's proof of nonlocality to the case of bipartite mixed statistical operators, and we exhibit a necessary condition which has to be satisfied by any given mixed state {sigma} in order that a local and realistic hidden variable model exists which accounts for the quantum mechanical predictions implied by {sigma}. Failure of this condition will imply both the impossibility of any local explanation of certain joint probability distributions in terms of hidden variables and the nonseparability of the considered mixed statistical operator. Our result can be also used to determine the maximum amount of noise, arising from imperfect experimental implementations of the original Hardy's proof of nonlocality, in presence of which it is still possible to put into evidence the nonlocal features of certain mixed states.
Effectively nonlocal metric-affine gravity
NASA Astrophysics Data System (ADS)
Golovnev, Alexey; Koivisto, Tomi; Sandstad, Marit
2016-03-01
In metric-affine theories of gravity such as the C-theories, the spacetime connection is associated to a metric that is nontrivially related to the physical metric. In this article, such theories are rewritten in terms of a single metric, and it is shown that they can be recast as effectively nonlocal gravity. With some assumptions, known ghost-free theories with nonsingular and cosmologically interesting properties may be recovered. Relations between different formulations are analyzed at both perturbative and nonperturbative levels, taking carefully into account subtleties with boundary conditions in the presence of integral operators in the action, and equivalences between theories related by nonlocal redefinitions of the fields are verified at the level of equations of motion. This suggests a possible geometrical interpretation of nonlocal gravity as an emergent property of non-Riemannian spacetime structure.
Nonlocal Markovian models for image denoising
NASA Astrophysics Data System (ADS)
Salvadeo, Denis H. P.; Mascarenhas, Nelson D. A.; Levada, Alexandre L. M.
2016-01-01
Currently, the state-of-the art methods for image denoising are patch-based approaches. Redundant information present in nonlocal regions (patches) of the image is considered for better image modeling, resulting in an improved quality of filtering. In this respect, nonlocal Markov random field (MRF) models are proposed by redefining the energy functions of classical MRF models to adopt a nonlocal approach. With the new energy functions, the pairwise pixel interaction is weighted according to the similarities between the patches corresponding to each pair. Also, a maximum pseudolikelihood estimation of the spatial dependency parameter (β) for these models is presented here. For evaluating this proposal, these models are used as an a priori model in a maximum a posteriori estimation to denoise additive white Gaussian noise in images. Finally, results display a notable improvement in both quantitative and qualitative terms in comparison with the local MRFs.
Towards an emerging understanding of non-locality phenomena and non-local transport
NASA Astrophysics Data System (ADS)
Ida, K.; Shi, Z.; Sun, H. J.; Inagaki, S.; Kamiya, K.; Rice, J. E.; Tamura, N.; Diamond, P. H.; Dif-Pradalier, G.; Zou, X. L.; Itoh, K.; Sugita, S.; Gürcan, O. D.; Estrada, T.; Hidalgo, C.; Hahm, T. S.; Field, A.; Ding, X. T.; Sakamoto, Y.; Oldenbürger, S.; Yoshinuma, M.; Kobayashi, T.; Jiang, M.; Hahn, S. H.; Jeon, Y. M.; Hong, S. H.; Kosuga, Y.; Dong, J.; Itoh, S.-I.
2015-01-01
In this paper, recent progress on experimental analysis and theoretical models for non-local transport (non-Fickian fluxes in real space) is reviewed. The non-locality in the heat and momentum transport observed in the plasma, the departures from linear flux-gradient proportionality, and externally triggered non-local transport phenomena are described in both L-mode and improved-mode plasmas. Ongoing evaluation of ‘fast front’ and ‘intrinsically non-local’ models, and their success in comparisons with experimental data, are discussed
Non-locality Sudden Death in Tripartite Systems
Jaeger, Gregg; Ann, Kevin
2009-03-10
Bell non-locality sudden death is the disappearance of non-local properties in finite times under local phase noise, which decoheres states only in the infinite-time limit. We consider the relationship between decoherence, disentanglement, and Bell non-locality sudden death in bipartite and tripartite systems in specific large classes of state preparation.
NASA Astrophysics Data System (ADS)
Rosado-Roman, J. M.; Farley, D. T.; Swartz, W. E.; Seyler, C. E.
2001-05-01
Common volume observations with the Cornell University Portable Radar Interferometer (CUPRI) coherent scatter radar and the Arecibo Observatory incoherent scatter radar (AO-ISR) obtained during the NASA El Coquí campaign of 1992, are used to study the causes of coherent radar backscatter at mid-latitudes. The common volume data reveal that coherent scatter echoes are obtained from sporadic E (Es) layers that exhibit little or no gravity wave altitude modulation and possess high densities and sharp gradients. The echoes are associated with larger than typical F-region south-perpendicular electric fields. The echoes appear to come from the linearly unstable side of the Es layers even though the usual local linear theory is invalid at mid-latitudes. Non-local shorting effects along magnetic field lines play a crucial role at mid-latitudes, and we have developed a theory that takes this into account. The unstable eigen modes are a sum of plane waves with k vectors varying vertically about pure perpendicular propagation by a few degrees (allowing for the spatial localization of the modes on the top or bottom of the layer). The k vectors are also approximately aligned with the E x B drift. While both density and potential modes peak in amplitude on the unstable side of the layer, the density mode peaks closer to the maximum of the layer than does the potential mode. The separation and shape of the modes is determined by the profile of the vertical scale length, Lz = Ne / (d)/(dz) Ne; convergent growing solutions are found when the scale length profile exhibits a deep local minimum (steep gradient). We used a narrow Gaussian layer superimposed on a constant background density. Perhaps surprisingly, the constant background is essential for the numerical calculations. It can be small but not zero.
Reversed rainbow with a nonlocal metamaterial
Morgado, Tiago A. Marcos, João S.; Silveirinha, Mário G.; Costa, João T.; Costa, Jorge R.; Fernandes, Carlos A.
2014-12-29
One of the intriguing potentials of metamaterials is the possibility to realize a nonlocal electromagnetic reaction, such that the effective medium response at a given point is fundamentally entangled with the macroscopic field distribution at long distances. Here, it is experimentally and numerically verified that a microwave nonlocal metamaterial formed by crossed metallic wires enables a low-loss broadband anomalous material response such that the refractive index decreases with frequency. Notably, it is shown that an electromagnetic beam refracted by our metamaterial prism creates a reversed microwave rainbow.
Experimental nonlocal and surreal Bohmian trajectories.
Mahler, Dylan H; Rozema, Lee; Fisher, Kent; Vermeyden, Lydia; Resch, Kevin J; Wiseman, Howard M; Steinberg, Aephraim
2016-02-01
Weak measurement allows one to empirically determine a set of average trajectories for an ensemble of quantum particles. However, when two particles are entangled, the trajectories of the first particle can depend nonlocally on the position of the second particle. Moreover, the theory describing these trajectories, called Bohmian mechanics, predicts trajectories that were at first deemed "surreal" when the second particle is used to probe the position of the first particle. We entangle two photons and determine a set of Bohmian trajectories for one of them using weak measurements and postselection. We show that the trajectories seem surreal only if one ignores their manifest nonlocality.
Experimental nonlocal and surreal Bohmian trajectories
Mahler, Dylan H.; Rozema, Lee; Fisher, Kent; Vermeyden, Lydia; Resch, Kevin J.; Wiseman, Howard M.; Steinberg, Aephraim
2016-01-01
Weak measurement allows one to empirically determine a set of average trajectories for an ensemble of quantum particles. However, when two particles are entangled, the trajectories of the first particle can depend nonlocally on the position of the second particle. Moreover, the theory describing these trajectories, called Bohmian mechanics, predicts trajectories that were at first deemed “surreal” when the second particle is used to probe the position of the first particle. We entangle two photons and determine a set of Bohmian trajectories for one of them using weak measurements and postselection. We show that the trajectories seem surreal only if one ignores their manifest nonlocality. PMID:26989784
Compressive Sensing via Nonlocal Smoothed Rank Function
Fan, Ya-Ru; Liu, Jun; Zhao, Xi-Le
2016-01-01
Compressive sensing (CS) theory asserts that we can reconstruct signals and images with only a small number of samples or measurements. Recent works exploiting the nonlocal similarity have led to better results in various CS studies. To better exploit the nonlocal similarity, in this paper, we propose a non-convex smoothed rank function based model for CS image reconstruction. We also propose an efficient alternating minimization method to solve the proposed model, which reduces a difficult and coupled problem to two tractable subproblems. Experimental results have shown that the proposed method performs better than several existing state-of-the-art CS methods for image reconstruction. PMID:27583683
Observational viability and stability of nonlocal cosmology
Deser, S.; Woodard, R.P. E-mail: woodard@phys.ufl.edu
2013-11-01
We show that the nonlocal gravity models, proposed to explain current cosmic acceleration without dark energy, pass two essential tests: first, they can be defined so as not to alter the, observationally correct, general relativity predictions for gravitationally bound systems. Second, they are stable, ghost-free, with no additional excitations beyond those of general relativity. In this they differ from their, ghostful, localized versions. The systems' initial value constraints are the same as in general relativity, and our nonlocal modifications never convert the original gravitons into ghosts.
Compressive Sensing via Nonlocal Smoothed Rank Function.
Fan, Ya-Ru; Huang, Ting-Zhu; Liu, Jun; Zhao, Xi-Le
2016-01-01
Compressive sensing (CS) theory asserts that we can reconstruct signals and images with only a small number of samples or measurements. Recent works exploiting the nonlocal similarity have led to better results in various CS studies. To better exploit the nonlocal similarity, in this paper, we propose a non-convex smoothed rank function based model for CS image reconstruction. We also propose an efficient alternating minimization method to solve the proposed model, which reduces a difficult and coupled problem to two tractable subproblems. Experimental results have shown that the proposed method performs better than several existing state-of-the-art CS methods for image reconstruction.
Breather solitons in highly nonlocal media
NASA Astrophysics Data System (ADS)
Alberucci, Alessandro; Jisha, Chandroth P.; Assanto, Gaetano
2016-12-01
We investigate the breathing of optical spatial solitons in highly nonlocal media. We use a generalization of the Ehrenfest theorem (1990 Am. J. Phys. 58 742) leading to a fourth-order ordinary differential equation, the latter ruling the beam width evolution in propagation. In actual highly nonlocal materials, the original accessible soliton model by Snyder and Mitchell (1997 Science 276 1538) cannot accurately describe the dynamics of self-confined beams: the transverse size oscillations have a period which not only depends on power, but also on the initial width. Modeling the nonlinear response by a Poisson equation driven by the beam intensity we verify the theoretical results against numerical simulations.
Spatial optical solitons in highly nonlocal media
NASA Astrophysics Data System (ADS)
Alberucci, Alessandro; Jisha, Chandroth P.; Smyth, Noel F.; Assanto, Gaetano
2015-01-01
We theoretically investigate the propagation of bright spatial solitary waves in highly nonlocal media possessing radial symmetry in a three-dimensional cylindrical geometry. Focusing on a thermal nonlinearity, modeled by a Poisson equation, we show how the profile of the light-induced waveguide strongly depends on the extension of the nonlinear medium in the propagation direction as compared to the beamwidth. We demonstrate that self-trapped beams undergo oscillations in size, either periodically or aperiodically, depending on the input waist and power. The—usually neglected—role of the longitudinal nonlocality as well as the detrimental effect of absorptive losses are addressed.
Nonlocal Coulomb drag in Weyl semimetals
NASA Astrophysics Data System (ADS)
Baum, Yuval; Stern, Ady
2017-02-01
Nonlocality is one of the most striking signatures of the topological nature of Weyl semimetals. We propose to probe the nonlocality in these materials via a measurement of a magnetic-field-dependent Coulomb drag between two sheets of graphene which are separated by a three-dimensional slab of Weyl semimetal. We predict a mechanism of Coulomb drag, based on cyclotron orbits that are split between opposite surfaces of the semimetal. In the absence of impurity scattering between different Weyl nodes, this mechanism does not decay with the thickness of the semimetal.