Статті в журналах: "Local Density Shadow Wave Function"

1

REATTO, L., and D. E. GALLI. "WHAT IS A ROTON?" International Journal of Modern Physics B 13, no. 05n06 (March 10, 1999): 607–16. http://dx.doi.org/10.1142/s0217979299000497.

Повний текст джерела

Анотація:

Many models of a roton in superfluid 4 He have been proposed over the years but no general consensus has been reached yet on the nature of such excitation. We present a number of new results relating to this question. We have developed an accurate representation of the wave function of such excitation which is based on a shadow function. This allows to treat the short range backflow effects in a non perturbative way. The theory gives results in quantitative agreement with experiment. Starting from such eigenstates of momentum we build wave–packets and study local quantities like density, momentum and vorticity. No model agrees with our results for the excitations in the roton minimum region because we find that the excitations have in a varying degree characters of single particle, of non quantized smoke ring and of collective excitation. We have also considered 4 He in two dimensions and we find similar results. In 2D we have studied also maxon and high frequency phonon wave–packets.

Стилі APA, Harvard, Vancouver, ISO та ін.

2

REATTO, L., M. ROSSI, and D. E. GALLI. "BOSE–EINSTEIN CONDENSATION IN BULK AND CONFINED SOLID HELIUM." International Journal of Modern Physics B 20, no. 30n31 (December 20, 2006): 5081–92. http://dx.doi.org/10.1142/s0217979206036120.

Повний текст джерела

Анотація:

We address the question if the ground state of solid 4 He has the number of lattice sites equal to the number of atoms (commensurate state) or if it is different (incommensurate state). We point out that energy computation from simulation as performed by now cannot be used to decide this question and that the presently best variational wave function, a shadow wave function, gives an incommensurate state. We have extended the calculation of the one–body density matrix ρ1 to the exact Shadow Path Integral Ground State method. Calculation of ρ1 at ρ = 0.031 Å-3 shows that Vacancy–Interstitial pair processes are present also in the exact computation but the simulated system size is too small to infer the presence of off–diagonal long range order. Variational simulations of 4 He confined in a narrow cylindrical pore are also discussed.

Стилі APA, Harvard, Vancouver, ISO та ін.

3

Nguyen-Truong, Hieu T., Tan-Tien Pham, Nam H. Vu, Dang H. Ngo, and Hung M. Le. "Energy-loss Function for Lead." Communications in Physics 27, no. 1 (May 17, 2017): 65. http://dx.doi.org/10.15625/0868-3166/27/1/9201.

Повний текст джерела

Анотація:

We study the energy-loss function for lead in the framework of the time-dependent density functional theory, using the full-potential linearized augmented plane-wave plus local orbitals method. The ab initio calculations are performed in the adiabatic local density approximation. The comparison between the obtained energy-loss function for zero momentum transfer with those from reflection electron energy loss spectroscopy measurements and from first-principles calculations shows good agreement.

Стилі APA, Harvard, Vancouver, ISO та ін.

4

FALCÓN, CLAUDIO, and STÉPHAN FAUVE. "LOCAL DYNAMICS OF DEFECTS IN PARAMETRICALLY EXCITED WAVES." International Journal of Bifurcation and Chaos 19, no. 10 (October 2009): 3553–59. http://dx.doi.org/10.1142/s0218127409024992.

Повний текст джерела

Анотація:

We present an experimental study on the local dynamics of parametrically excited waves at an air–water interface when defects are present in the wave pattern. The probability density function (PDF) of the local wave amplitude displays an exponential part for values close to the average amplitude and decreases sharply to zero for large amplitudes. The power spectral density (PSD) of the local amplitude fluctuations shows a power-law behavior over one decade which we relate to a regime of defect-mediated turbulence.

Стилі APA, Harvard, Vancouver, ISO та ін.

5

Onwuagba, B. N. "Localization of the 4f wave-function in cesium." Canadian Journal of Physics 74, no. 9-10 (September 1, 1996): 565–67. http://dx.doi.org/10.1139/p96-083.

Повний текст джерела

Анотація:

The local spin density approximation is used in the study of the localization of the 4f wave function in cesium, by superimposing the radial part of the kinetic-energy term on the self-consistent field potential VSCF(r). The results obtained show a collapsed 4f wave function in Cs+, but not in neutral Cs, which compares favourably with the previous findings and provide good insight into the understanding of the collapsed 4f wave function in cesium.

Стилі APA, Harvard, Vancouver, ISO та ін.

6

Ran, Lingkun, and Shouting Gao. "A Three-Dimensional Wave-Activity Relation for Pseudomomentum." Journal of the Atmospheric Sciences 64, no. 6 (June 2007): 2126–34. http://dx.doi.org/10.1175/jas3931.1.

Повний текст джерела

Анотація:

A three-dimensional, nonhydrostatic local wave-activity relation for pseudomomentum is derived from the nonhydrostatic primitive equations in Cartesian coordinates by using an extension of the momentum–Casimir method. The stationary and zonally symmetric basic states are chosen and a Casimir function, which is the single-valued function of potential vorticity and potential temperature, is introduced in the derivation. The wave-activity density and wave-activity flux of the local wave-activity relation for pseudomomentum are expressed entirely in terms of Eulerian quantities so that they are easily calculated with atmospheric data and do not require the knowledge of particle placements. Constructed in the ageostrophic and nonhydrostatic dynamical framework, the local wave-activity relation for pseudomomentum is applicable to diagnosing the evolution and propagation of mesoscale weather systems.

Стилі APA, Harvard, Vancouver, ISO та ін.

7

MODANESE, GIOVANNI. "LOCAL CONTRIBUTION OF A QUANTUM CONDENSATE TO THE VACUUM ENERGY DENSITY." Modern Physics Letters A 18, no. 10 (March 28, 2003): 683–90. http://dx.doi.org/10.1142/s0217732303009812.

Повний текст джерела

Анотація:

We evaluate the local contribution gμνL of coherent matter with Lagrangian density L to the vacuum energy density. Focusing on the case of superconductors obeying the Ginzburg–Landau equation, we express the relativistic invariant density L in terms of low-energy quantities containing the pairs density. We discuss under which physical conditions the sign of the local contribution of the collective wave function to the vacuum energy density is positive or negative. Effects of this kind can play an important role in bringing the local changes in the amplitude of gravitational vacuum fluctuations — a phenomenon reminiscent of the Casimir effect in QED.

Стилі APA, Harvard, Vancouver, ISO та ін.

8

Mestel, L., and K. Subramanian. "Galactic Dynamos and Density Wave Theory." Symposium - International Astronomical Union 140 (1990): 135. http://dx.doi.org/10.1017/s0074180900189764.

Повний текст джерела

Анотація:

A steady density wave in the stellar background of a disk–like galaxy is supposed to force a spiral shock wave in the interstellar gas. The jump in vorticity across the shock leads to a locally enhanced helicity, and so to an α–effect which is steady but azimuth–dependent in the frame rotating with the angular velocity ω of the density wave. This is simulated by the adoption of the form for the local dynamo growth rate arising when the standard kinematic dynamo equation is treated by the thin–disk approximation (Ruzmaikin et al 1988). The global magnetic field is proportional to the function Q satisfying where η is the turbulent resistivity (for simplicity assumed uniform) and is the laminar angular velocity of the gas in the inertial frame. We look for solutions of the form where is a global eigen-value, and the non-vanishing of couples all odd or all the even m-values. Anticipating that the strong differential rotation will ensure that in the modes with the largest growth-rate the higher-m parts are weak, the equations are truncated, leaving just a pair in q1, q-1, to describe a basically bisymmetric (m = 1) mode. Approximate treatment by the WKBJ technique suggests that a corotating growing mode (with Γ real and positive) will differ significantly from zero over the range between the points where Numerical solutions have been found for a set of illustrative parameters with corotation occurring at 6.67 kpc, and the turbulence parameters close to those in the M51 mode studied by Ruzmaikin et al which extends over = 1 kpc. Three growing corotating modes were found, the fastest extending for ~ 3 kpc, the other two for over 4 kpc. The first two grow 2-3 times faster, the third somewhat slower, than the M51 mode.

Стилі APA, Harvard, Vancouver, ISO та ін.

9

Naim, Carmelo, and Claudio Amovilli. "Extraction of a One-Particle Reduced Density Matrix from a Quantum Monte Carlo Electronic Density: A New Tool for Studying Nondynamic Correlation." Computation 9, no. 12 (December 9, 2021): 135. http://dx.doi.org/10.3390/computation9120135.

Повний текст джерела

Анотація:

In this work, we present a method to build a first order reduced density matrix (1-RDM) of a molecule from variational Quantum Monte Carlo (VMC) computations by means of a given correlated mapping wave function. Such a wave function is modeled on a Generalized Valence Bond plus Complete Active Space Configuration Interaction form and fits at best the density resulting from the Slater-Jastrow wave function of VMC. The accuracy of the method proposed has been proved by comparing the resulting kinetic energy with the corresponding VMC value. This 1-RDM is used to analyze the amount of correlation eventually captured in Kohn-Sham calculations performed in an unrestricted approach (UKS-DFT) and with different energy functionals. We performed test calculations on a selected set of molecules that show a significant multireference character. In this analysis, we compared both local and global indicators of nondynamic and dynamic correlation. Moreover, following the natural orbital decomposition of the 1-RDM, we also compared the effective temperatures of the corresponding Fermi-like distributions. Although there is a general agreement between UKS-DFT and VMC, we found the best match with the functional LC-BLYP.

Стилі APA, Harvard, Vancouver, ISO та ін.

10

Gomes, André Severo Pereira, Christoph R. Jacob, and Lucas Visscher. "Calculation of local excitations in large systems by embedding wave-function theory in density-functional theory." Physical Chemistry Chemical Physics 10, no. 35 (2008): 5353. http://dx.doi.org/10.1039/b805739g.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

11

Hallo, Miroslav, Walter Imperatori, Francesco Panzera, and Donat Fäh. "Joint multizonal transdimensional Bayesian inversion of surface wave dispersion and ellipticity curves for local near-surface imaging." Geophysical Journal International 226, no. 1 (March 26, 2021): 627–59. http://dx.doi.org/10.1093/gji/ggab116.

Повний текст джерела

Анотація:

Summary Physical properties of near-surface soil and rock layers play a fundamental role in the seismic site effects analysis, being an essential element of seismic hazard assessment. Site-specific mechanical properties (i.e. shear- and compressional-wave velocities and mass density) can be inferred from surface wave dispersion and horizontal-to-vertical or ellipticity data by non-linear inversion techniques. Nevertheless, results typically exhibit significant inherent non-uniqueness as different models may fit the data equally well. Standard optimization inversion techniques minimize data misfit, resulting in a single representative model, rejecting other models providing similar misfit values. An alternative inversion technique can be formulated in the Bayesian framework, where the posterior probability density on the model space is inferred. This paper introduces an inversion approach of surface wave dispersion and ellipticity data based on a novel multizonal transdimensional Bayesian formulation. In particular, we parametrize 1-D layered velocity models by the varying number of Voronoi nuclei, allowing us to treat the number of layers as an unknown parameter of the inverse problem. The chosen parametrization leads to the transdimensional formulation of the model space, sampled by a reversible jump Markov chain Monte Carlo algorithm to provide an ensemble of random samples following the posterior probability density of model parameters. The used type of the sampling algorithm controls a model complexity (i.e. the number of layers) self-adaptively based on the measured data's information content. The method novelty lies in the parsimonious selection of sampling models and in the multizonal formulation of prior assumptions on model parameters, the latter allows including additional site-specific constraints in the inversion. These assumptions may be based on, e.g. stratigraphic logs, standard penetration tests, known water table, and bedrock depth. The multizonal formulation fully preserves the validity of the transdimensional one, as demonstrated analytically. The resultant ensemble of model samples is a discrete approximation of the posterior probability density function of model parameters and associated properties (e.g. VS30, quarter-wavelength average velocity profile and theoretical SH-wave amplification function). Although the ultimate result is the posterior probability density function, some representative models are selected according to data fit and maximum of the posterior probability density function. We first validate our inversion approach based on synthetic tests and then apply it to field data acquired from the active seismic survey and single-station measurements of ambient vibrations at the SENGL seismic station site in central Switzerland.

Стилі APA, Harvard, Vancouver, ISO та ін.

12

Baroni, Cosetta, Giacomo Gori, Maria Luisa Chiofalo, and Andrea Trombettoni. "Effect of Inter-Well Interactions on Non-Linear Beam Splitters for Matter-Wave Interferometers." Condensed Matter 5, no. 2 (April 21, 2020): 31. http://dx.doi.org/10.3390/condmat5020031.

Повний текст джерела

Анотація:

We study the non-linear beam splitter in matter-wave interferometers using ultracold quantum gases in a double-well configuration in presence of non-local interactions inducing inter-well density-density coupling, as they can be realized, e.g., with dipolar gases. We explore this effect after considering different input states, in the form of either coherent, or Twin-Fock, or NOON states. We first review the non-interacting limit and the case in which only the local interaction is present, including the study of sensitivity near the self-trapping threshold. Then, we consider the two-mode model in the presence of inter-well interactions and consider the scaling of the sensitivity as a function of the non-local coupling strength. Our analysis clearly shows that non-local interactions can compensate the degradation of the sensitivity induced by local interactions, so that they may be used to restore optimal sensitivity.

Стилі APA, Harvard, Vancouver, ISO та ін.

13

GALLI, D. E., and L. REATTO. "BOSE–EINSTEIN CONDENSATION AND EXCITATIONS IN SOLID 4He WITH VACANCIES." International Journal of Modern Physics B 17, no. 28 (November 10, 2003): 5243–53. http://dx.doi.org/10.1142/s0217979203020387.

Повний текст джерела

Анотація:

We have studied the ground state and excited state properties of solid 4 He on the basis of the variational shadow wave function technique (SWF), which allows for relaxation and delocalisation of vacancies. We have found that a finite concentration of vacancies, if present, induces Bose-Einstein condensation (BEC) of the atoms at density close to the T=0 K melting where vacancies are delocalised. No BEC is present in a perfect crystal or in a defected solid at higher densities. We have extended this technique to study longitudinal phonons in solid 4 He and to study the vacancy excitation at a finite momentum; we have been able to compute for the first time the vacancy excitation spectrum in solid 4 He at density close to melting. Our results give a band width of about 8 K.

Стилі APA, Harvard, Vancouver, ISO та ін.

14

Shi, Rui, and Hajime Tanaka. "Distinct signature of local tetrahedral ordering in the scattering function of covalent liquids and glasses." Science Advances 5, no. 3 (March 2019): eaav3194. http://dx.doi.org/10.1126/sciadv.aav3194.

Повний текст джерела

Анотація:

Tetrahedral amorphous materials such as SiO2, GeO2, Si, Ge, C, and chalcogenides are extremely important in nature and technology. It is known that covalent bonding favors local tetrahedral order in these materials. However, how to extract information on this structural order from the scattering function has remained elusive. By analyzing the structure of simulated SiO2 and experimental data of various tetrahedral materials, we show that the lowest wave number peak, known as the first sharp diffraction peak (FSDP), and a few higher wave number ones in the scattering functions come from the characteristic density waves of a single tetrahedral unit. FSDP is thus a direct measure of the tetrahedrality. This finding opens the door for long-awaited experimental access to the characterization of disordered amorphous structures.

Стилі APA, Harvard, Vancouver, ISO та ін.

15

Liu, Wei, Francis P. Bretherton, Zhengyu Liu, Leslie Smith, Hao Lu, and Christopher J. Rutland. "Breaking of Progressive Internal Gravity Waves: Convective Instability and Shear Instability*." Journal of Physical Oceanography 40, no. 10 (October 1, 2010): 2243–63. http://dx.doi.org/10.1175/2010jpo4432.1.

Повний текст джерела

Анотація:

Abstract The breaking of a monochromatic two-dimensional internal gravity wave is studied using a newly developed spectral/pseudospectral model. The model features vertical nonperiodic boundary conditions that ensure a realistic simulation of wave breaking during the wave propagation. Isopycnal overturning is induced at a local wave steepness of sc = 0.75–0.79, which is below the conventional threshold of s = 1. Isopycnal overturning is a sufficient condition for subsequent wave breaking by convective instability. When s = sc, little primary wave energy is being transferred to high-mode harmonics. Beyond s = 1, high-mode harmonics grow rapidly. Primary wave energy is more efficiently transferred by waves of lower frequency. A local gradient Richardson number is defined as Ri = −(g/ρ0)(dρ/dz)/ζ2 to isolate convective instability (Ri ≤ 0) and wave-induced shear instability (0 < Ri < 0.25), where dρ/dz is the local vertical density gradient and ζ is the horizontal vorticity. Consistent with linear wave theory, the probability density function (PDF) for occurrence of convective instability has a maximum at wave phase ϕ = π/2, where the wave-induced density perturbations to the background stratification are the greatest, whereas the wave-induced shear instability has maxima around ϕ = 0 (wave trough) and ϕ = π (wave crest). Nonlinearities in the wave-induced flow broaden the phase span in PDFs of both instabilities. Diapycnal mixing in numerical simulations may be compared with that in realistic oceanic flows in terms of the Cox number. In the numerical simulations, the Cox numbers increase from 1.5 (s = 0.78) to 21.5 (s = 1.1), and the latter is in the lower range of reported values for the ocean.

Стилі APA, Harvard, Vancouver, ISO та ін.

16

Philip, Sharon S., Anushika Athauda, Yosuke Goto, Yoshikazu Mizuguchi, and Despina Louca. "Out-of-Plane Sulfur Distortions in the Bi4O4S3 Superconductor." Condensed Matter 6, no. 4 (November 26, 2021): 48. http://dx.doi.org/10.3390/condmat6040048.

Повний текст джерела

Анотація:

The local atomic structure of the non-magnetic layered superconductor Bi4O4S3 was investigated using neutron diffraction and pair density function (PDF) analysis. Although on average, the crystal structure is well ordered, evidence for local, out–of–plane sulfur distortions is provided, which may act as a conduit for charge transfer from the SO4 blocks into the superconducting BiS2 planes. In contrast with LaO1−xFxBiS2, no sulfur distortions were detected in the planes, which indicates that charge density wave fluctuations are not supported in Bi4O4S3.

Стилі APA, Harvard, Vancouver, ISO та ін.

17

Gidopoulos, Nikitas I., and E. K. U. Gross. "Electronic non-adiabatic states: towards a density functional theory beyond the Born–Oppenheimer approximation." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 372, no. 2011 (March 13, 2014): 20130059. http://dx.doi.org/10.1098/rsta.2013.0059.

Повний текст джерела

Анотація:

A novel treatment of non-adiabatic couplings is proposed. The derivation is based on a theorem by Hunter stating that the wave function of the complete system of electrons and nuclei can be written, without approximation, as a Born–Oppenheimer (BO)-type product of a nuclear wave function, X ( R ), and an electronic one, Φ R ( r ), which depends parametrically on the nuclear configuration R . From the variational principle, we deduce formally exact equations for Φ R ( r ) and X ( R ). The algebraic structure of the exact nuclear equation coincides with the corresponding one in the adiabatic approximation. The electronic equation, however, contains terms not appearing in the adiabatic case, which couple the electronic and the nuclear wave functions and account for the electron–nuclear correlation beyond the BO level. It is proposed that these terms can be incorporated using an optimized local effective potential.

Стилі APA, Harvard, Vancouver, ISO та ін.

18

CHAKRABARTI, A., S. N. KARMAKAR, and R. K. MOITRA. "TWO-BAND FIBONACCI QUASICRYSTAL WITH HYBRIDIZATION: EXACT LOCAL GREEN’S FUNCTION USING THE RENORMALIZATION-GROUP METHOD." Modern Physics Letters B 04, no. 12 (July 10, 1990): 795–802. http://dx.doi.org/10.1142/s0217984990000982.

Повний текст джерела

Анотація:

In this paper we present a study of the electronic properties of a one-dimensional Fibonacci chain with two hybridizing bands. Our study is motivated by recent experiments with quasicrystals in which transition metal atoms occupy positions of icosahedral symmetry. Using a recently proposed real space renormalization group scheme we make an exact analytical study of the two-band problem. We examine the effect of hybridization on the energy spectrum, the wave functions and the density of states of the Fibonacci chain. We find that the spectrum continues to remain a Cantor set even in the presence of hybridization. We conclude therefore this property of the spectrum is a purely structural effect. We present our results on the electronic density of states and show how hybridization produces additional structures in the energy spectrum.

Стилі APA, Harvard, Vancouver, ISO та ін.

19

Cui, Bao Zhen, Ze Bing Wang, and Hong Xia Pan. "The Study of Local Wave Noise Reduction Based on the Correlation Analysis." Advanced Materials Research 588-589 (November 2012): 707–10. http://dx.doi.org/10.4028/www.scientific.net/amr.588-589.707.

Повний текст джерела

Анотація:

The signal can be divided into a number of intrinsic mode components (IMF) through local wave decomposition. The decomposition process is equivalent to the adaptive filter for signal. The frequencies of each IMF have reduced with the decomposition order. This paper established judgment criteria of signal, noise and pseudo component based on the local wave decomposition, used the characteristics of cross-correlation coefficient and autocorrelation sequence, combined with the power spectral density. The dominant mode function was extracted effectively and the final effects are used gear reducer in the JZQ250 of fault rolling bearing inner ring. It provides a new method for non-stationary signal adaptive noise reduction and fault diagnosis of rotating machinery.

Стилі APA, Harvard, Vancouver, ISO та ін.

20

HONG, SOON C., and JAE IL LEE. "ELECTRONIC STRUCTURE OF THE Mo(001) SURFACE: LOCAL DENSITY STUDY." International Journal of Modern Physics B 07, no. 01n03 (January 1993): 524–27. http://dx.doi.org/10.1142/s0217979293001104.

Повний текст джерела

Анотація:

LEED observed an incommensurate surface reconstruction for the Mo(001) surface and a recent photoemission experiment measured electronic structure of the Mo(001) surface at room and low temperature (52 K). Employing the all-electron local density full potential linearized augmented plane wave (FLAPW) method, we calculated the electronic structure of the Mo(001) surface. Two prominent LDOS peaks at the surface are found just below Fermi level and E b = 0.50 eV and they are confirmed to come from surface states along [Formula: see text] symmetry line. The surface states (just below Fermi level) with even symmetry show no energy dispersion while the surface states ( E b = 0.50 eV ) with odd symmetry have upward energy dispersion from [Formula: see text] to [Formula: see text]. The two bands of surface states fade off at [Formula: see text], which is very consistent with experiments. The work function is calculated to be 4.20 eV. We will present the character of charge densities of the surface states and compare to experiments.

Стилі APA, Harvard, Vancouver, ISO та ін.

21

Griffin, A. "Rigorous density functional theory for inhomogeneous Bose-condensed fluids." Canadian Journal of Physics 73, no. 11-12 (November 1, 1995): 755–62. http://dx.doi.org/10.1139/p95-111.

Повний текст джерела

Анотація:

The density functional theory originally developed by Hohenberg, Kohn, and Sham provides a rigorous conceptual framework for dealing with inhomogeneous interacting Fermi systems. We extend this approach to deal with inhomogeneous interacting Bose-condensed systems, limiting this presentation to setting up the formalism to deal with ground-state (T = 0) properties. The key new feature is that one must deal with energy functionals of both the local density n(r) and the local complex macroscopic wave function Φ(r) associated with the Bose broken-symmetry (the local condensate density is [Formula: see text]. Implementing the Kohn–Sham scheme, we reduce the problem to a gas of weakly interacting Bosons moving in self-consistent diagonal and off-diagonal one-body potentials. Our formalism should provide the basis for studies of the surface properties of liquid 4He as well as the properties of Bose-condensed atomic gases trapped in external potentials.

Стилі APA, Harvard, Vancouver, ISO та ін.

22

POLLS, A., and A. FABROCINI. "A MICROSCOPIC LOOK AT LIQUID HELIUM: THE 3He IMPURITY CASE." International Journal of Modern Physics B 15, no. 10n11 (May 10, 2001): 1575–90. http://dx.doi.org/10.1142/s0217979201006069.

Повний текст джерела

Анотація:

The description of the properties of liquid Helium is a challenge for any microscopic many-body theory. In this context, we study the ground state and the excitation spectrum of one 3 He impurity in liquid 4 He at T=0 with the aim of illustrating the power of the correlated basis function formalism in describing heavily correlated systems. The strong interatomic interaction and the large density require the theory to be pushed to a high degree of sophistication. A many-body correlation operator containing explicit two- and three-particle correlation functions is needed to obtain a realistic ground state wave function, whereas a perturbative expansion including up to two phonon correlated states must be enforced to study the impurity excitation energies. The theory describes accurately the experimental spectrum along all the available momentum range. As empirically shown by the experiments, a marked deviation from the quadratic Landau-Pomeranchuck behavior is found and the momentum dependent effective mass of the impurity increases of ~50% at q~1.7 Å-1 with respect to its q=0 value. Although the main emphasis is given to the correlated basis function theory, we present also comparisons with other methods, as diffusion Monte Carlo, variational Monte Carlo with shadow wave functions and time dependent correlations.

Стилі APA, Harvard, Vancouver, ISO та ін.

23

KYUNG, BUMSOO. "PRECURSOR OF ANTIFERROMAGNETIC BANDS IN THE HALF-FILLED TWO-DIMENSIONAL HUBBARD MODEL." International Journal of Modern Physics B 13, no. 27 (October 30, 1999): 3183–92. http://dx.doi.org/10.1142/s0217979299002940.

Повний текст джерела

Анотація:

We study the half-filled two-dimensional Hubbard model in the intermediate coupling regime. As temperature is decreased for a two-dimensional half-filled band, two-dimensional critical fluctuations give rise to a strong local maximum in | Im Σ(k F , ω)| at ω=0, leading to a split peak with a pseudogap inside in the spectral function and the density of states. The calculated energy dispersion is in good agreement with that of spin density wave approximation.

Стилі APA, Harvard, Vancouver, ISO та ін.

24

Zhu, Yuan Jiang, та Yun Liang Gao. "Density Function Theory Calculation of Crystal Properties and Electronic Structure of δ-Pu". Key Engineering Materials 727 (січень 2017): 712–17. http://dx.doi.org/10.4028/www.scientific.net/kem.727.712.

Повний текст джерела

Анотація:

In this paper, lattice constants, elastic properties and electronic structure of δ-Pu are investigated by means of plane wave pseudo-potential method (PWP) based on density function theory (DFT). A variety of density functional theory methods have been adopted to calculate the crystal structure and elastic property of δ-Pu, and it is found that the lattice constants, bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio ν calculated by spin polarization local density approximation (SP+LDA) method are in best agreement with experimental values. The electronic structure have been investigated within the framework of LDA+U, and the band structure, density of state (DOS) and partial density of state (PDOS) are calculated. Calculation results of elastic properties and electronic structure show that, δ-Pu shows obvious metallicity and well ductility, its electrons are strongly corrected and the DOS in the vicinity of the Fermi Level is mainly contributed by 5f electrons.

Стилі APA, Harvard, Vancouver, ISO та ін.

25

Jiang, T., and D. E. Ellis. "X-ray absorption near edge structures in cobalt oxides." Journal of Materials Research 11, no. 9 (September 1996): 2242–56. http://dx.doi.org/10.1557/jmr.1996.0285.

Повний текст джерела

Анотація:

Theoretical studies have been made of K-edge x-ray absorption near edge structure (XANES) of Co in CoO, Co(OH)2, CoTiO3, Co3O4, and CoAl2O4. Correlations of experimental near edge features with site symmetry, local geometry, local electronic structure, i.e., atomic configuration, charge transfer, and backscattering from neighboring atomic potentials are interpreted. The self-consistent Discrete Variational Xa Method (DV-Xα) within an embedded cluster technique has been used to generate the crystal potential. A multiple scattering (MS) approach is then used to solve for the final state wave function. The ground state DV wave functions are analyzed in terms of the projected density of states, whereas the final state MS continuum wave functions are analyzed through the concept of photoelectron trapping time.

Стилі APA, Harvard, Vancouver, ISO та ін.

26

OGATA, MASAO. "Electronic States and Mixing of Different Symmetry or Antiferromagnetism in Vortex Cores in dx2-y2-wave Superconductivity." International Journal of Modern Physics B 13, no. 29n31 (December 20, 1999): 3560–65. http://dx.doi.org/10.1142/s0217979299003428.

Повний текст джерела

Анотація:

The microscopic structure of vortices in high-Tc superconductors is studied using the two-dimensional t-J model. The spatial dependences of order parameters are determined self-consistently using the Gutzwiller approximation, in which the effect of correlation is into account. In the high-doping region, the pair potential has d x2-y2-wave nature and the local density of states in the vicinity of the core shows a zero-energy peak. However, in the low-doping region, a spatially oscillating (extended) s-wave-type order parameter is locally induced around the vortex core. As a result, the local density of states near the core shows a splitting of the zero-energy peak. This gives a possible explanation for the experimental data of scanning tunneling spectroscopy for YBCO. The possibility of the antiferromagnetic vortex core is also studied by modifying the Gutzwiller approximation. It is found that, close to the boundary to the antiferromagnetically ordered state, the antiferromagnetic correlation develops inside the vortex core, even if the bulk state is the pure d-wave state. In this case the local density of states near the core does not have a zero-energy peak but instead shows a gap-like feature, which can be observed experimentally. Finally the sign change of the charge of the vortex core as a function of the doping rate is found.

Стилі APA, Harvard, Vancouver, ISO та ін.

27

Lesku, John A., Alexei L. Vyssotski, Dolores Martinez-Gonzalez, Christiane Wilzeck, and Niels C. Rattenborg. "Local sleep homeostasis in the avian brain: convergence of sleep function in mammals and birds?" Proceedings of the Royal Society B: Biological Sciences 278, no. 1717 (January 5, 2011): 2419–28. http://dx.doi.org/10.1098/rspb.2010.2316.

Повний текст джерела

Анотація:

The function of the brain activity that defines slow wave sleep (SWS) and rapid eye movement (REM) sleep in mammals is unknown. During SWS, the level of electroencephalogram slow wave activity (SWA or 0.5–4.5 Hz power density) increases and decreases as a function of prior time spent awake and asleep, respectively. Such dynamics occur in response to waking brain use, as SWA increases locally in brain regions used more extensively during prior wakefulness. Thus, SWA is thought to reflect homeostatically regulated processes potentially tied to maintaining optimal brain functioning. Interestingly, birds also engage in SWS and REM sleep, a similarity that arose via convergent evolution, as sleeping reptiles and amphibians do not show similar brain activity. Although birds deprived of sleep show global increases in SWA during subsequent sleep, it is unclear whether avian sleep is likewise regulated locally. Here, we provide, to our knowledge, the first electrophysiological evidence for local sleep homeostasis in the avian brain. After staying awake watching David Attenborough's The Life of Birds with only one eye, SWA and the slope of slow waves (a purported marker of synaptic strength) increased only in the hyperpallium—a primary visual processing region—neurologically connected to the stimulated eye. Asymmetries were specific to the hyperpallium, as the non-visual mesopallium showed a symmetric increase in SWA and wave slope. Thus, hypotheses for the function of mammalian SWS that rely on local sleep homeostasis may apply also to birds.

Стилі APA, Harvard, Vancouver, ISO та ін.

28

Lacombe, C., J. L. Steinberg, C. C. Harvey, D. Hubert, A. Mangeney, and M. Moncuquet. "Density fluctuations measured by ISEE 1-2 in the Earth's magnetosheath and the resultant scattering of radio waves." Annales Geophysicae 15, no. 4 (April 30, 1997): 387–96. http://dx.doi.org/10.1007/s00585-997-0387-5.

Повний текст джерела

Анотація:

Abstract. Radio waves undergo angular scattering when they propagate through a plasma with fluctuating density. We show how the angular scattering coefficient can be calculated as a function of the frequency spectrum of the local density fluctuations. In the Earth's magnetosheath, the ISEE 1-2 propagation experiment measured the spectral power of the density fluctuations for periods in the range 300 to 1 s, which produce most of the scattering. The resultant local angular scattering coefficient can then be calculated for the first time with realistic density fluctuation spectra, which are neither Gaussian nor power laws. We present results on the variation of the local angular scattering coefficient during two crossings of the dayside magnetosheath, from the quasi-perpendicular bow shock to the magnetopause. For a radio wave at twice the local electron plasma frequency, the scattering coefficient in the major part of the magnetosheath is b(2fp) ≃ 0.5 – 4 × 10–9 rad2/m. The scattering coefficient is about ten times stronger in a thin sheet (0.1 to1RE) just downstream of the shock ramp, and close to the magnetopause.

Стилі APA, Harvard, Vancouver, ISO та ін.

29

Stoneback, R. A., and R. A. Heelis. "Identifying equatorial ionospheric irregularities using in situ ion drifts." Annales Geophysicae 32, no. 4 (April 15, 2014): 421–29. http://dx.doi.org/10.5194/angeo-32-421-2014.

Повний текст джерела

Анотація:

Abstract. Previous climatological investigations of ionospheric irregularity occurrence in the equatorial ionosphere have utilized in situ measurements of plasma density to identify the presence of an irregularity. Here we use the Morlet wavelet and C/NOFS to isolate perturbations in meridional ion drifts and generate irregularity occurrence maps as a function of local time, longitude, season, and solar activity. For the low solar activity levels in 2008, the distributions identified by velocity perturbations follow normalized density perturbation (ΔN/N) maps with large occurrences after midnight into dawn over all longitudes. The velocity and normalized density occurrence maps contract in both local time and longitude with increasing solar activity. By 2011 irregularities are confined to particular longitudes expected by alignment and a few hours of local time after sunset. The variation in the occurrence of the late night irregularities with solar activity is consistent with the presence of gravity wave seeding.

Стилі APA, Harvard, Vancouver, ISO та ін.

30

Santoliquido, Filippo, Michela Mapelli, Nicola Giacobbo, Yann Bouffanais, and M. Celeste Artale. "The cosmic merger rate density of compact objects: impact of star formation, metallicity, initial mass function, and binary evolution." Monthly Notices of the Royal Astronomical Society 502, no. 4 (February 3, 2021): 4877–89. http://dx.doi.org/10.1093/mnras/stab280.

Повний текст джерела

Анотація:

ABSTRACT We evaluate the redshift distribution of binary black hole (BBH), black hole–neutron star binary (BHNS), and binary neutron star (BNS) mergers, exploring the main sources of uncertainty: star formation rate (SFR) density, metallicity evolution, common envelope, mass transfer via Roche lobe overflow, natal kicks, core-collapse supernova model, and initial mass function. Among binary evolution processes, uncertainties on common envelope ejection have a major impact: the local merger rate density of BNSs varies from ∼103 to ∼20 Gpc−3 yr−1 if we change the common envelope efficiency parameter from αCE = 7 to 0.5, while the local merger rates of BBHs and BHNSs vary by a factor of ∼2–3. The BBH merger rate changes by one order of magnitude, when 1σ uncertainties on metallicity evolution are taken into account. In contrast, the BNS merger rate is almost insensitive to metallicity. Hence, BNSs are the ideal test bed to put constraints on uncertain binary evolution processes, such as common envelope and natal kicks. Only models assuming values of αCE ≳ 2 and moderately low natal kicks (depending on the ejected mass and the supernovae mechanism), result in a local BNS merger rate density within the 90 per cent credible interval inferred from the second gravitational-wave transient catalogue.

Стилі APA, Harvard, Vancouver, ISO та ін.

31

He, Ying, Xueling Chen, Zhongxian Liu, Dejian Yang, and Hai Zhang. "Simulation of Spatially Correlated Multipoint Ground Motions in a Saturated Alluvial Valley." Shock and Vibration 2021 (September 22, 2021): 1–11. http://dx.doi.org/10.1155/2021/7056096.

Повний текст джерела

Анотація:

Based on Biot’s theory, the boundary element method, and spectral representation method, an effective simulation method for multiple-station spatially correlated ground motions on both bedrock and surface is developed, incorporating the spectral density function, coherence function, and site transfer function that consider both the wave scattering effect and the medium saturation. The accuracy and feasibility of the present method are validated by a typical numerical example. Our results indicate that the local site conditions and the saturation property of the medium significantly affect the multipoint spatially correlated earthquake ground motions, especially in the long-period range. It is necessary to use spatially varying ground motions with the rational consideration of local site effects and medium saturation as input during the seismic analysis of large-span structures.

Стилі APA, Harvard, Vancouver, ISO та ін.

32

Legut, Dominik, and Mojmír Šob. "Ideal Tensile Strength of Ni₃Al and Fe₃Al with D0₃ Structure." Materials Science Forum 567-568 (December 2007): 77–80. http://dx.doi.org/10.4028/www.scientific.net/msf.567-568.77.

Повний текст джерела

Анотація:

The ideal tensile strength along the [111] direction in the Fe3Al and Ni3Al intermetallic compounds with the D03 structure has been calculated from the first principles using the fullpotential linearized augmented plane-wave method (FP LAPW) within the density functional theory (DFT). The strains corresponding to the maximum sustainable stresses in both materials were determined and compared. The behavior of atomic magnetic moments as a function of strain was analyzed. The tensile test simulations have been theoretically simulated employing both the local density approximation (LDA) and generalized gradient approximation (GGA) for the exchangecorrelation potential.

Стилі APA, Harvard, Vancouver, ISO та ін.

33

PEDERIVA, FRANCESCO. "DIFFUSION MONTE CARLO STUDY OF GROUND STATE PROPERTIES OF QUANTUM DOTS." International Journal of Modern Physics B 15, no. 10n11 (May 10, 2001): 1443–46. http://dx.doi.org/10.1142/s0217979201005933.

Повний текст джерела

Анотація:

We present the results of Diffusion Monte Carlo (DMC) calculations based on accurate multiconfiguration wave functions for N electrons (N≤13) confined to a parabolic quantum dot. The density and correlation energies have been computed and compared with the predictions of local spin density approximation theory (LSDA). We also computed the addition energy a function of the number of electrons in the dot, and compared them with the results of LSDA and Hartree Fock calculations. DMC results show a behavior qualitatively closer to the result of recent capacitance experiments.

Стилі APA, Harvard, Vancouver, ISO та ін.

34

Paez Gonzalez, Carlos Jose, Jorge Hernan Quintero Orozco, and Andrés Camilo García Castro. "Magnetic Field Effects on Charge and Current Density in Finite Monolayer Graphene." Revista Ingenierías Universidad de Medellín 20, no. 39 (June 16, 2021): 251–61. http://dx.doi.org/10.22395/rium.v20n39a14.

Повний текст джерела

Анотація:

In this work, we study the effects of an external magnetic field on the charge and current density in finite monolayer graphene, i.e., with zig-zag and armchair edges. We use the tight-binding model to include the effects of the magnetic field and the effect of the edges. By using the transmission probability and analyzing the local density of states (charge density) ob- tained from Green’s function method, we find an energy region where the wave functions are more localized in the edges and, consequently, the current flow across the borders. On the other hand, for energies close to Landau levels, the charge and current density are localized on the bulk of the system.

Стилі APA, Harvard, Vancouver, ISO та ін.

35

Ceccarelli, Emiliano, Giada Minelli, Viviana Egidi, and Giovanna Jona Jona Lasinio. "Assessment of Excess Mortality in Italy in 2020–2021 as a Function of Selected Macro-Factors." International Journal of Environmental Research and Public Health 20, no. 4 (February 5, 2023): 2812. http://dx.doi.org/10.3390/ijerph20042812.

Повний текст джерела

Анотація:

Background: Excess mortality (EM) can reliably capture the impact of a pandemic, this study aims at assessing the numerous factors associated with EM during the COVID-19 pandemic in Italy. Methods: Mortality records (ISTAT 2015–2021) aggregated in the 610 Italian Labour Market Areas (LMAs) were used to obtain the EM P-scores to associate EM with socioeconomic variables. A two-step analysis was implemented: (1) Functional representation of EM and clustering. (2) Distinct functional regression by cluster. Results: The LMAs are divided into four clusters: 1 low EM; 2 moderate EM; 3 high EM; and 4 high EM-first wave. Low-Income showed a negative association with EM clusters 1 and 4. Population density and percentage of over 70 did not seem to affect EM significantly. Bed availability positively associates with EM during the first wave. The employment rate positively associates with EM during the first two waves, becoming negatively associated when the vaccination campaign began. Conclusions: The clustering shows diverse behaviours by geography and time, the impact of socioeconomic characteristics, and local governments and health services’ responses. The LMAs allow to draw a clear picture of local characteristics associated with the spread of the virus. The employment rate trend confirmed that essential workers were at risk, especially during the first wave.

Стилі APA, Harvard, Vancouver, ISO та ін.

36

DRABLIA, S., H. MERADJI, S. GHEMID, N. BOUKHRIS, B. BOUHAFS, and G. NOUET. "ELECTRONIC AND OPTICAL PROPERTIES OF BaO, BaS, BaSe, BaTe AND BaPo COMPOUNDS UNDER HYDROSTATIC PRESSURE." Modern Physics Letters B 23, no. 26 (October 20, 2009): 3065–79. http://dx.doi.org/10.1142/s0217984909021235.

Повний текст джерела

Анотація:

We have performed first-principle full-potential (linear) augmented plane wave plus local orbital calculations (FP-L/APW + l0) with density functional theory (DFT) in local density approximation (LDA) and generalized gradient approximation (GGA), with the aim to determine and predict the electronic and optical properties of rocksalt BaO , BaS , BaSe , BaTe and BaPo compounds. First we present the main features of the electronic properties of these compounds, where the electronic band structure shows that the fundamental energy gap is indirect (Γ–X) for all compounds except for BaO which is direct (X–X). The different interband transitions have been determined from the imaginary part of the dielectric function. The real and imaginary parts of the dielectric function and the reflectivity are calculated. We have presented the assignment of the different optical transitions existing in these compounds from the imaginary part of the dielectric function spectra with respect to their correspondence in the electronic band. We have also calculated the pressure and volume dependence of the optical properties for these compounds.

Стилі APA, Harvard, Vancouver, ISO та ін.

37

WANG, HUAN-YOU, HUI XU, JIAN-RONG XIAO, and MINGJUN LI. "ELECTRONIC STRUCTURE, DIELECTRIC AND DYNAMICAL PROPERTIES OF ZINC-BLENDE AlN FROM FIRST PRINCIPLES CALCULATION." Modern Physics Letters B 21, no. 26 (November 10, 2007): 1775–84. http://dx.doi.org/10.1142/s0217984907014048.

Повний текст джерела

Анотація:

We have performed density-functional perturbation calculation for zinc-blende AlN using the pseudopotential plane-wave method. The results obtained using both the local-density approximate (LDA) and the generalized-gradient approximate (GGA) for exchange-correlation functional are compared. The ground state properties and response function properties for zinc-blende AlN , including the electronic band structure, charge density, Born effective charge, dielectric constant and vibrational properties are reported. Our results are basically in agreement with experimental data and theoretical values available, but the bandgap is underestimated and the first optical mode in the phonon band structure is overestimated. This can be attributed to the underestimation of the lattice parameter and selection of the pseudopotential.

Стилі APA, Harvard, Vancouver, ISO та ін.

38

Oshima, Mitsutaka, and Hiroshi Takenaka. "A P- and S-Wave Picking Technique Based on the Probabilistic Density Function of Seismic-Waveform Amplitude." Bulletin of the Seismological Society of America 110, no. 2 (February 25, 2020): 763–82. http://dx.doi.org/10.1785/0120190078.

Повний текст джерела

Анотація:

ABSTRACT Picking of P and S waves is a fundamental process in seismology, and various kinds of picking techniques have been developed. Seismic waveforms change dramatically depending on the magnitude, the mechanism of the earthquake, and the positional relationship between the hypocenter and the seismic station. The availability of various picking techniques is supposed to be helpful for appropriately dealing with a variety of seismic records. Hence, in addition to the revision of conventional techniques, the development of new picking techniques is worthwhile. In the present study, we developed a new stochastic technique to detect P and S waves based on the statistical amplitude distribution in the seismic record amplitude. In the proposed method, the probabilistic density function (PDF) of the amplitude is calculated for each segment of seismic records, and the similarity between the PDF of the amplitude and that of the Rayleigh or Gaussian distribution is evaluated by divergence. Because Rayleigh and Gaussian distributions are typically found in amplitude distributions of highly random waves, such as coda waves, the divergence indicates the randomness of the seismic records. P and S waves are found by tracing the temporal change of the divergence. We tested the proposed method using local seismic records for a series of seismic events that occurred before and after the 2016 Kumamoto earthquake. The mean absolute errors for picking P and S waves are 2.72×10−2 and 7.38×10−2 s, respectively. The proposed method is a simple and new statistical picking method that enables automatic detection of P- and S-wave arrivals.

Стилі APA, Harvard, Vancouver, ISO та ін.

39

Sera, Yasuaki, Takahiro Ueda, Hiroto Adachi, and Masanori Ichioka. "Relation of Superconducting Pairing Symmetry and Non-Magnetic Impurity Effects in Vortex States." Symmetry 12, no. 1 (January 18, 2020): 175. http://dx.doi.org/10.3390/sym12010175.

Повний текст джерела

Анотація:

Non-magnetic impurity scattering effects on the vortex core states are theoretically studied to clarify the contributions from the sign-change of the pairing function in anisotropic superconductors. The vortex states are calculated by the Eilenberger theory in superconductors with p x -wave pairing symmetry, as well as the corresponding anisotropic s-wave symmetry. From the spatial structure of the pair potential and the local electronic states around a vortex, we examine the differences between anisotropic superconductors with and without sign-change of the pairing function, and estimate how twofold symmetric vortex core images change with increasing the impurity scattering rate both in the Born and the unitary limits. We found that twofold symmetric vortex core image of zero-energy local density of states changes the orientation of the twofold symmetry with increasing the scattering rate when the sign change occurs in the pairing function. Without the sign change, the vortex core shape reduces to circular one with approaching dirty cases. These results of the impurity effects are valuable for identifying the pairing symmetry by observation of the vortex core image by the STM observation.

Стилі APA, Harvard, Vancouver, ISO та ін.

40

HADJI, S., S. BERRAH, and H. ABID. "OPTICAL PROPERTIES OF THE CUBIC AlxGa1-xN ALLOY." Modern Physics Letters B 27, no. 17 (June 17, 2013): 1350127. http://dx.doi.org/10.1142/s0217984913501273.

Повний текст джерела

Анотація:

In this paper, we present numerical calculations based on the full potential augmented plane wave (FP-LAPW) method within the local density approximation (LDA) to study the optical properties of the ternary alloy Al x Ga 1-x N . The shape of the dielectric function, the refractive index, and the absorption coefficient versus photon energy were presented. From the results, we deduce the possibility of this alloy to be used in the optoelectronic and photovololtaic area.

Стилі APA, Harvard, Vancouver, ISO та ін.

41

Mase, G. Thomas, and G. C. Johnson. "An Acoustoelastic Theory for Surface Waves in Anisotropic Media." Journal of Applied Mechanics 54, no. 1 (March 1, 1987): 127–35. http://dx.doi.org/10.1115/1.3172946.

Повний текст джерела

Анотація:

A theory for surface waves in an anisotropic material is developed in the framework of acoustoelasticity in which the material’s strain energy density is taken to be a cubic function in the strain. In order to relate the surface wave speeds to the applied stress, a configuration is introduced in which the effect of the local rotation is removed. The development shows that the surface wave speed can be determined from the eigenvalues of a particular real symmetric 2×2 matrix. Numerical results are given for uniaxial loading applied to aluminum and copper single crystals and to an ideal transversely isotropic aggregate of aluminum.

Стилі APA, Harvard, Vancouver, ISO та ін.

42

WANG, HUAN-YOU, HUI XU, JU-YING CAO, and MING-JUN LI. "AB INITIO THERMODYNAMICS OF ZINC-BLENDE ZnS, ZnSe." International Journal of Modern Physics B 25, no. 32 (December 30, 2011): 4553–61. http://dx.doi.org/10.1142/s0217979211052873.

Повний текст джерела

Анотація:

The density function perturbation theory (DFPT) is employed to study the linear thermal expansion and heat capacity at constant pressure (with the quasiharmonic approximation). The calculations are performed using a pseudopotential plane wave method and local density approximation for the exchange-correlation potential. The calculated results of linear thermal expansion coefficient and heat capacity at constant pressure for zinc-blende ZnS , ZnSe are compared with the available experimental data in a wide temperature range. Generally, in low-temperature range, they have good agreement. However, in high-temperature range, due to anharmonic effect and other reasons, lead to larger errors for these properties between the theoretical results and available experimental data.

Стилі APA, Harvard, Vancouver, ISO та ін.

43

Gómez i Blanch, G., and And M. J. Fullana i Alfonso. "On geometro dynamics in atomic stationary states." Revista Mexicana de Física 65, no. 2 (March 26, 2019): 148. http://dx.doi.org/10.31349/revmexfis.65.148.

Повний текст джерела

Анотація:

In a previous paper [G.Gomez Blanch and M.J.Fullana, 2017] we dened, in the frame of a geometro-dynamic approach, a metric corresponding to a lorentzian spacetime were the electron stationary trajectories in an hydrogenoid atom, derived from the de Broglie-Bohm model, are geodesics. In this paper we want to complete this purpose: we will determinate the remaining relevant geometrical elements of that approach and we will calculate the energetic density component of the energy-momentum tensor. We will discuss the meaning of the obtained results and their relationship with other geometro-dynamic approaches.Furthermore, we will derive a more general relationship between the lorentzian metric tensor and the wave function for general stationary states. The electron description by the wave function ψ in the Euclidean space and time is shown equivalent to the description by a metric tensor in an lorentzian manifold. In our approach, the particle acquires a determining role over thewave function, in a similar manner as the wave function determines the movement of the particle. This dialectic approach overcomes the de Broglie-Bohm model. And furthermore, a non local element (the quantum potential) is introduced in the model, that therefore goes beyond the relativistic locality.

Стилі APA, Harvard, Vancouver, ISO та ін.

44

HARMEL, M., H. KHACHAI, M. AMERI, R. KHENATA, N. BAKI, A. HADDOU, B. ABBAR, Ş. UǦUR, S. BIN OMRAN, and F. SOYALP. "DFT-BASEDAB INITIOSTUDY OF THE ELECTRONIC AND OPTICAL PROPERTIES OF CESIUM BASED FLUORO-PEROVSKITECsMF3(M = CaANDSr)." International Journal of Modern Physics B 26, no. 32 (December 11, 2012): 1250199. http://dx.doi.org/10.1142/s0217979212501998.

Повний текст джерела

Анотація:

Density functional theory (DFT) is performed to study the structural, electronic and optical properties of cubic fluoroperovskite AMF3( A = Cs ; M = Ca and Sr ) compounds. The calculations are based on the total-energy calculations within the full-potential linearized augmented plane wave (FP-LAPW) method. The exchange-correlation potential is treated by local density approximation (LDA) and generalized gradient approximation (GGA). The structural properties, including lattice constants, bulk modulus and their pressure derivatives are in very good agreement with the available experimental and theoretical data. The calculations of the electronic band structure, density of states and charge density reveal that compounds are both ionic insulators. The optical properties (namely: the real and the imaginary parts of the dielectric function ε(ω), the refractive index n(ω) and the extinction coefficient k(ω)) were calculated for radiation up to 40.0 eV.

Стилі APA, Harvard, Vancouver, ISO та ін.

45

Kaplun, M. V., E. V. Anikina, and V. P. Beskachko. "AB INITIO MODELLING OF A BILAYER GRAPHENE." Bulletin of the South Ural State University series "Mathematics. Mechanics. Physics" 14, no. 2 (2022): 64–71. http://dx.doi.org/10.14529/mmph220207.

Повний текст джерела

Анотація:

Using the electron density functional theory, numerical modelling of bilayer graphene has been performed. The structure and binding energy of the layers depending on the representation of the wave function of the system have been studied: plane waves (VASP package) and atomic-like orbitals (SIESTA package); and choice of approximation for the exchange-correlation (XC) functional. It has been shown that being in the free form the system creates a stable AB structure of bilayer graphene. The calculation of the layer binding energy has shown that the results of modelling performed with different basis for the wave function are consistent when using XC functionals corresponding to each other and considering the correction to the basis set superposition error in the tight binding method. As expected, the generalized gradient approximation (GGA) has shown underestimated values of the interaction energy of graphene layers. Comparison with experimental data has shown that the energy and geometric characteristics of bilayer graphene are best described by the local electron density approximation (LDA). The 2nd and 3rd generation semi-empirical Grimme corrections for GGA have given estimates of the binding energy higher than LDA, but also close to the experimental results.

Стилі APA, Harvard, Vancouver, ISO та ін.

46

Ravikumar, V., R. P. Rodrigues, and V. P. Dravid. "Direct imaging of spatially varying potential and charge across internal interfaces in solids." Proceedings, annual meeting, Electron Microscopy Society of America 53 (August 13, 1995): 316–17. http://dx.doi.org/10.1017/s0424820100137951.

Повний текст джерела

Анотація:

The importance of spatially varying potential (and thus charge) across lattice discontinuities in solids has been recognized in many technologically important systems, especially those containing electrically active interfaces, e.g. electroceramics. The presence of spatially varying potential across electroceramic interfaces has been indirectly deduced and analyzed using predominantly bulk measurement techniques like I-V, C-V curves and impedance spectroscopy. Direct imaging of spatially varying electrostatic potential profile and determination of the sign, magnitude and spatial distribution of the associated interface- and space- charge (and therefore defect density) in electroceramics have remained elusive.We have utilized the technique of transmission high energy electron holography to directly image and quantify the electrostatic potential across grain boundaries (GBs) in SrTiO3, a functional electroceramic. The phase of the exit wave function at the GB region can be altered by : (i) variation in local mean inner potential (related to the change in density of atoms at the GB), (ii) differential diffraction conditions across the interface, (iii) change in the local specimen thickness and, (iv) presence of local electrostatic (electrical charge) and magnetic potential.

Стилі APA, Harvard, Vancouver, ISO та ін.

47

Kosmas, T. S., Amand Faessler, F. Simkovic та J. D. Vergados. "Nuclear structure dependence of the coherent (μ-,e-) conversion matrix elements". HNPS Proceedings 4 (19 лютого 2020): 215. http://dx.doi.org/10.12681/hnps.2888.

Повний текст джерела

Анотація:

Coherent rates for the neutrinoless muon to electron conversion. (μ-, e-) in the presence of nuclei, are studied throughout the periodic table. The relevant ground state to ground state transition matrix elements are obtained in the context of the quasi-particle RPA. The results are discussed in view of the existing experimental data extracted at TRIUMF and PSI for 48Ti and 208Pb nuclei and compared with: (i) the single particle shell model results calculated with a determinantal ground state wave function and (ii) the results deduced in a local density approximation.

Стилі APA, Harvard, Vancouver, ISO та ін.

48

Anua, N. Najwa, R. Ahmed, A. Shaari, Ul Haq Bakhtiar, and Mazmira Binti Mohamad. "DFT Investigations of the Optical Properties of Gallium Arsenide." Advanced Materials Research 895 (February 2014): 429–38. http://dx.doi.org/10.4028/www.scientific.net/amr.895.429.

Повний текст джерела

Анотація:

Gallium Arsenide (GaAs) because of having unique characteristics like direct band gap, higher electron mobility and saturated electron velocity etcetera, has wide applications specifically in optoelectronic devices. In this research work we present a comprehensive density functional theory (DFT) based first principles study of optical properties of GaAs. Exchange correlation functional (XC) play a key role in the DFT investigations. A comparative study of the optical properties is presented based upon local density approximation (LDA) by Perdew and wang, Perdew-Burke-Ernzerhof parameterized generalized gradient approximation (GGA-PBE), Wu-Cohen parameterized GGA (GGA-WC) and Engel and Vosko proposed GGA (GGA-EV). Computations in this study have been performed by full potential (FP) linearized augmented plane wave (LAPW) plus local orbitals (lo) approach designed within DFT as realized in the computational code WIEN2k. Our investigations, for the optical properties of GaAs with mentioned XC potentials, cover detailed analysis of dielectric functions, absorption coefficient α (ω), energy loss functions, reflectivity R(ω), refractive index n (ω) and extinction coefficient k (ω). The analysis shows that the optical parameters calculated with GGA-PBE are comparatively reasonable and closer to the experimental results. Keywords: Density functional theory, local density approximation, gradient and other corrections, APW calculations, Dielectric function, absorption and reflection spectra PACS: 71.15.Mb, 71.15.Ap, 77.22.Ch, 78.40.Pg

Стилі APA, Harvard, Vancouver, ISO та ін.

49

Zhang, Lin, Jing Ba, and José M. Carcione. "A rock-physics model to determine the pore microstructure of cracked porous rocks." Geophysical Journal International 223, no. 1 (July 7, 2020): 622–31. http://dx.doi.org/10.1093/gji/ggaa327.

Повний текст джерела

Анотація:

SUMMARY Determining rock microstructure remains challenging, since a proper rock-physics model is needed to establish the relation between pore microstructure and elastic and transport properties. We present a model to estimate pore microstructure based on porosity, ultrasonic velocities and permeability, assuming that the microstructure consists on randomly oriented stiff equant pores and penny-shaped cracks. The stiff pore and crack porosity varying with differential pressure is estimated from the measured total porosity on the basis of a dual porosity model. The aspect ratio of pores and cracks and the crack density as a function of differential pressure are obtained from dry-rock P- and S-wave velocities, by using a differential effective medium model. These results are used to invert the pore radius from the matrix permeability by using a circular pore model. Above a crack density of 0.13, the crack radius can be estimated from permeability, and below that threshold, the radius is estimated from P-wave velocities, taking into account the wave dispersion induced by local fluid flow between pores and cracks. The approach is applied to experimental data for dry and saturated Fontainebleau sandstone and Chelmsford Granite.

Стилі APA, Harvard, Vancouver, ISO та ін.

50

Luo, Ying-Tao, Peng-Qi Li, Dong-Ting Li, Yu-Gui Peng, Zhi-Guo Geng, Shu-Huan Xie, Yong Li, Andrea Alù, Jie Zhu, and Xue-Feng Zhu. "Probability-Density-Based Deep Learning Paradigm for the Fuzzy Design of Functional Metastructures." Research 2020 (September 22, 2020): 1–11. http://dx.doi.org/10.34133/2020/8757403.

Повний текст джерела

Анотація:

In quantum mechanics, a norm-squared wave function can be interpreted as the probability density that describes the likelihood of a particle to be measured in a given position or momentum. This statistical property is at the core of the fuzzy structure of microcosmos. Recently, hybrid neural structures raised intense attention, resulting in various intelligent systems with far-reaching influence. Here, we propose a probability-density-based deep learning paradigm for the fuzzy design of functional metastructures. In contrast to other inverse design methods, our probability-density-based neural network can efficiently evaluate and accurately capture all plausible metastructures in a high-dimensional parameter space. Local maxima in probability density distribution correspond to the most likely candidates to meet the desired performances. We verify this universally adaptive approach in but not limited to acoustics by designing multiple metastructures for each targeted transmission spectrum, with experiments unequivocally demonstrating the effectiveness and generalization of the inverse design.

Стилі APA, Harvard, Vancouver, ISO та ін.

Статті в журналах з теми "Local Density Shadow Wave Function"

Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями