plane-wave born approximation: Topics by Science.gov

Sample records for plane-wave born approximation

Correction of the near threshold behavior of electron collisional excitation cross-sections in the plane-wave Born approximation

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.
Correction of the near threshold behavior of electron collisional excitation cross-sections in the plane-wave Born approximation

DOE PAGES

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
Direct pair production in heavy-ion--atom collisions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anholt, R.; Jakubassa-Amundsen, D.H.; Amundsen, P.A.

1983-02-01

Direct pair production in approx.5-MeV/amu heavy-ion--atom collisions with uranium target atoms is calculated with the plane-wave Born approximation and the semiclassical approximation. Briggs's approximation is used to obtain the electron and positron wave functions. Since pair production involves high momentum transfer q from the moving projectile to the vacuum, use is made of a high-q approximation to greatly simplify the numerical computations. Coulomb deflection of the projectile, the effect of finite nuclear size on the elec- tronic wave functions, and the energy loss by the projectile exciting the pair are all taken into account in these calculations.
Second Order Born Effects in the Perpendicular Plane Ionization of Xe (5p) Atoms

NASA Astrophysics Data System (ADS)

Purohit, G.; Singh, Prithvi; Patidar, Vinod

We report triple differential cross section (TDCS) results for the perpendicular plane ionization of xenon atoms at incident electron energies 5, 10, 20, 30, and 40 eV above ionization potential. The TDCS calculation have been preformed within the modified distorted wave Born approximation formalism including the second order Born (SBA) amplitude. We compare the (e, 2e) TDCS result of our calculation with the very recent measurements of Nixon and Murray [Phys. Rev. A 85, 022716 (2012)] and relativistic DWBA-G results of Illarionov and Stauffer [J. Phys. B: At. Mol. Opt. Phys. 45, 225202 (2012)] and discuss the process contributing to structure seen in the differential cross section.
Topics in electron capture by fast ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsin, S.H.

1987-01-01

The post-collision interaction (PCI) model was applied, together with the eikonal approximation, to study the (n = 2,3) capture cross sections in p + H(ls) collisions. The results indeed improve the previous eikonal calculations for l = 0 cases, and agree quite well with present experimental data. Calculations using the strong-potential Born (SPB) approximation, with the Sil and McGuire technique, for capture into the np, nd levels are also presented. While these cross sections are smaller than cross sections for capture into the ns levels at high velocities, nevertheless the Thomas peak is clearly evident in both the absolute valuemore » m = 2, absolute value m = 1 and m = 0 magnetic substates in p + H(ls) collisions. Also calculated were corrections to the SPB using the Distorted-Wave Born formalism of Taulbjerg and Briggs. In the sense of a plane-wave Born expansion, all terms of the third Born approximation and all single switching fourth Born terms are included, but a peaking approximation is needed to reduce the calculation to tractable form. Effects of the higher terms are most visible in the valley between the Thomas peak and the forward peak. The Thomas peak is visible in the correction term, even though it includes no second Born contributions.« less
Perturbations of the seismic reflectivity of a fluid-saturated depth-dependent poroelastic medium.

PubMed

de Barros, Louis; Dietrich, Michel

2008-03-01

Analytical formulas are derived to compute the first-order effects produced by plane inhomogeneities on the point source seismic response of a fluid-filled stratified porous medium. The derivation is achieved by a perturbation analysis of the poroelastic wave equations in the plane-wave domain using the Born approximation. This approach yields the Frechet derivatives of the P-SV- and SH-wave responses in terms of the Green's functions of the unperturbed medium. The accuracy and stability of the derived operators are checked by comparing, in the time-distance domain, differential seismograms computed from these analytical expressions with complete solutions obtained by introducing discrete perturbations into the model properties. For vertical and horizontal point forces, it is found that the Frechet derivative approach is remarkably accurate for small and localized perturbations of the medium properties which are consistent with the Born approximation requirements. Furthermore, the first-order formulation appears to be stable at all source-receiver offsets. The porosity, consolidation parameter, solid density, and mineral shear modulus emerge as the most sensitive parameters in forward and inverse modeling problems. Finally, the amplitude-versus-angle response of a thin layer shows strong coupling effects between several model parameters.
Measurements of the scattering of sound by a line vortex

NASA Technical Reports Server (NTRS)

Horne, W. C.

1983-01-01

This paper presents measurements of the phase and magnitude of the scattered field arising from the incidence of a monochromatic plane sound field as a steady vortex. The amplitude of the scattered field was found to vary linearly with the vortex strength, and with the incident wave amplitude and frequency as predicted by solutions based on the Born approximation. The scattered field was observed to be nonsingular in the incidence direction, and this was similar to predictions by the Parabolic Equation Method (PEM) rather than the Born approximation, which predicts singular behavior in the incidence direction.
L-shell x-ray production cross sections of Ni, Cu, Ge, As, Rb, Sr, Y, Zr, and Pd by (0. 25--2. 5)-MeV protons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duggan, J.L.; Kocur, P.M.; Price, J.L.

1985-10-01

L-shell x-ray production cross sections by /sub 1//sup 1/H/sup +/ ions are reported. The data are compared to the first Born approximation (plane-wave Born approximation for direct ionization and Oppenheimer-Brinkman-Kramers approximation for electron capture) and to the ECPSSR (energy-loss and Coulomb-deflection effects, perturbed stationary-state approximation with relativistic correction) theory. The energy of the protons ranged from 0.25 to 2.5 MeV in steps of 0.25 MeV. The targets used in these measurements were /sub 28/Ni, /sub 29/Cu, /sub 32/Ge, /sub 33/As, /sub 37/Rb, /sub 38/Sr, /sub 39/Y, /sub 40/Zr, and /sub 46/Pd. The first Born theory generally agrees with the datamore » found in the literature at high energies and overpredicts them below 1.5 MeV. The ECPSSR predictions are in better agreement with experimental cross sections. At 0.25 MeV our data, however, are underestimated by this theory and tend to agree with the first Born approximation.« less
On the Scattering of Sound by a Rectilinear Vortex

NASA Astrophysics Data System (ADS)

HOWE, M. S.

1999-11-01

A re-examination is made of the two-dimensional interaction of a plane, time-harmonic sound wave with a rectilinear vortex of small core diameter at low Mach number. Sakov [1] and Ford and Smith [2] have independently resolved the “infinite forward scatter” paradox encountered in earlier applications of the Born approximation to this problem. The first order scattered field (Born approximation) has nulls in the forward and back scattering directions, but the interaction of the wave with non-acoustically compact components of the vortex velocity field causes wavefront distortion, and the phase of the incident wave to undergo a significant variation across a parabolic domain whose axis extends along the direction of forward scatter from the vortex core. The transmitted wave crests of the incident wave become concave and convex, respectively, on opposite sides of the axis of the parabola, and focusing and defocusing of wave energy produces corresponding increases and decreases in wave amplitude. Wave front curvature decreases with increasing distance from the vortex core, with the result that the wave amplitude and phase are asymptotically equal to the respective values they would have attained in the absence of the vortex. The transverse acoustic dipole generated by translational motion of the vortex at the incident wave acoustic particle velocity, and the interaction of the incident wave with acoustically compact components of the vortex velocity field, are responsible for a system of cylindrically spreading, scattered waves outside the parabolic domain.
S-Wave Dispersion Relations: Exact Left Hand E-Plane Discontinuity from the Born Series

NASA Technical Reports Server (NTRS)

Bessis, D.; Temkin, A.

1999-01-01

We show, for a superposition of Yukawa potentials, that the left hand cut discontinuity in the complex E plane of the (S-wave) scattering amplitude is given exactly, in an interval depending on n, by the discontinuity of the Born series stopped at order n. This also establishes an inverse and unexpected correspondence of the Born series at positive high energies and negative low energies. We can thus construct a viable dispersion relation (DR) for the partial (S-) wave amplitude. The high numerical precision achievable by the DR is demonstrated for the exponential potential at zero scattering energy. We also briefly discuss the extension of our results to Field Theory.
Experimental and theoretical double differential cross sections for electron impact ionization of methane

NASA Astrophysics Data System (ADS)

Yavuz, Murat; Ozer, Zehra Nur; Ulu, Melike; Champion, Christophe; Dogan, Mevlut

2016-04-01

Experimental and theoretical double differential cross sections (DDCSs) for electron-induced ionization of methane (CH4) are here reported for primary energies ranging from 50 eV to 350 eV and ejection angles between 25° and 130°. Experimental DDCSs are compared with theoretical predictions performed within the first Born approximation Coulomb wave. In this model, the initial molecular state is described by using single center wave functions, the incident (scattered) electron being described by a plane wave, while a Coulomb wave function is used for modeling the secondary ejected electron. A fairly good agreement may be observed between theory and experiment with nevertheless an expected systematic overestimation of the theory at low-ejection energies (<50 eV).
Condition for invariant spectrum of an electromagnetic wave scattered from an anisotropic random media.

PubMed

Li, Jia; Wu, Pinghui; Chang, Liping

2015-08-24

Within the accuracy of the first-order Born approximation, sufficient conditions are derived for the invariance of spectrum of an electromagnetic wave, which is generated by the scattering of an electromagnetic plane wave from an anisotropic random media. We show that the following restrictions on properties of incident fields and the anisotropic media must be simultaneously satisfied: 1) the elements of the dielectric susceptibility matrix of the media must obey the scaling law; 2) the spectral components of the incident field are proportional to each other; 3) the second moments of the elements of the dielectric susceptibility matrix of the media are inversely proportional to the frequency.
Accurate Cross Sections for Microanalysis.

PubMed

Rez, Peter

2002-01-01

To calculate the intensity of x-ray emission in electron beam microanalysis requires a knowledge of the energy distribution of the electrons in the solid, the energy variation of the ionization cross section of the relevant subshell, the fraction of ionizations events producing x rays of interest and the absorption coefficient of the x rays on the path to the detector. The theoretical predictions and experimental data available for ionization cross sections are limited mainly to K shells of a few elements. Results of systematic plane wave Born approximation calculations with exchange for K, L, and M shell ionization cross sections over the range of electron energies used in microanalysis are presented. Comparisons are made with experimental measurement for selected K shells and it is shown that the plane wave theory is not appropriate for overvoltages less than 2.5 V.
Triple differential cross-sections of Ne (2s2) in coplanar to perpendicular plane geometry

NASA Astrophysics Data System (ADS)

Chen, L. Q.; Khajuria, Y.; Chen, X. J.; Xu, K. Z.

2003-10-01

The distorted wave Born approximation (DWBA) with the spin averaged static exchange potential has been used to calculate the triple differential cross-sections (TDCSs) for Ne (2s^2) ionization by electron impact in coplanar to perpendicular plane symmetric geometry at 110.5 eV incident electron energy. The present theoretical results at gun angles Psi = 0^circ (coplanar symmetric geometry) and Psi = 90^circ (perpendicular plane geometry) are in satisfactory agreement with the available experimental data. A deep interference minimum appears in the TDCS in the coplanar symmetric geometry and a strong peak at scattering angle xi = 90^circ caused by the single collision mechanism has been observed in the perpendicular plane geometry. The TDCSs at the gun angles Psi = 30^circ, and Psi = 60^circ are predicted.
Born approximation for scattering by evanescent waves: Comparison with exact scattering by an infinite fluid cylinder

NASA Astrophysics Data System (ADS)

Marston, Philip L.

2004-05-01

In some situations, evanescent waves can be an important component of the acoustic field within the sea bottom. For this reason (as well as to advance the understanding of scattering processes) it can be helpful to examine the modifications to scattering theory resulting from evanescence. Modifications to ray theory were examined in a prior approximation [P. L. Marston, J. Acoust. Soc. Am. 113, 2320 (2003)]. The new research concerns the modifications to the low-frequency Born approximation and confirmation by comparison with the exact two-dimensional scattering by a fluid cylinder. In the case of a circular cylinder having the same density as the surroundings but having a compressibility contrast with the surroundings, the Born approximation with a nonevanescent incident wave gives only monopole scattering. When the cylinder has a density contrast and the same compressibility as the surroundings the regular Born approximation gives only dipole scattering (with the dipole oriented along to the incident wavevector). In both cases when the Born approximation is modified to include the evanescence of the incident wave, an additional dipole scattering term is evident. In each case the new dipole is oriented along to the decay axis of the evanescent wave. [Research supported by ONR.
Electronic wave function and binding effects in M-shell ionization of gold by protons

NASA Astrophysics Data System (ADS)

Pajek, M.; Banaś, D.; Jabłoński, Ł.; Mukoyama, T.

2018-02-01

The measured M-X-ray production cross sections for protons, which are used in the particle induced X-ray emission (PIXE) technique, are systematically underestimated for low impact energies by the ECPSSR and ECUSAR theories. These theories, which are based on the plane wave Born approximation (PWBA) and use the screened hydrogenic wave functions, include corrections for the projectile Coulomb deflection and electron relativistic and binding effects. In the present paper, in order to interpret the observed disagreement at low impact energies, the systematic calculations of the M-shell ionization cross sections for gold were performed using the semiclassical (SCA) and the binary encounter (BEA) approximations in order to identify a role of the electronic wave function and electron binding effects. In these calculations the different wave functions, from nonrelativistic hydrogenic to selfconsistent Dirac-Hartree-Fock, were considered and the binding effect was treated within extreme separated- (SA) and united-atoms (UA) limits. The results are discussed in details and the observed discrepancies are attributed to inadequate description of the electron binding effect at the lowest impact energies for which the molecular approach is required.
Distorted-wave methods for electron capture in ion-atom collisions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burgdoerfer, J.; Taulbjerg, K.

1986-05-01

Distorted-wave methods for electron capture are discussed with emphasis on the surface term in the T matrix and on the properties of the associated integral equations. The surface term is generally nonvanishing if the distorted waves are sufficiently accurate to include parts of the considered physical process. Two examples are considered in detail. If distorted waves of the strong-potential Born-approximation (SPB) type are employed the surface term supplies the first-Born-approximation part of the T matrix. The surface term is shown to vanish in the continuum-distorted-wave (CDW) method. The integral kernel is in either case free of the dangerous disconnected termsmore » discussed by Greider and Dodd but the CDW theory is peculiar in the sense that its first-order approximation (CDW1) excludes a specific on-shell portion of the double-scattering term that is closely connected with the classical Thomas process. The latter is described by the second-order term in the CDW series. The distorted-wave Born approximation with SPB waves is shown to be free of divergences. In the limit of asymmetric collisions the DWB suggests a modification of the SPB approximation to avoid the divergence problem recently identified by Dewangan and Eichler.« less
Electron- and proton-induced ionization of pyrimidine

DOE PAGES

Champion, Christophe; Quinto, Michele; Weck, Philippe F

2015-03-27

This present work describes a quantum-mechanically based model of the electron- and proton-induced ionization of isolated pyrimidine molecules. The impact energies range from the target ionization threshold up to ~1 keV for electrons and from 10 keV up to 10 MeV for protons. The cross-section calculations are performed within the 1st Born approximation in which the ejected electron is described by a Coulomb wave whereas the incident and the scattered projectiles are both described by plane waves. The pyrimidine target is described using the Gaussian 09 software package. Furthermore, our theoretical predictions obtained are in good agreement with experimental absolutemore » total cross sections, while large discrepancies are observed between existing semi-empirical models and the present calculations.« less
Non-perturbative aspects of particle acceleration in non-linear electrodynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burton, David A.; Flood, Stephen P.; Wen, Haibao

2015-04-15

We undertake an investigation of particle acceleration in the context of non-linear electrodynamics. We deduce the maximum energy that an electron can gain in a non-linear density wave in a magnetised plasma, and we show that an electron can “surf” a sufficiently intense Born-Infeld electromagnetic plane wave and be strongly accelerated by the wave. The first result is valid for a large class of physically reasonable modifications of the linear Maxwell equations, whilst the second result exploits the special mathematical structure of Born-Infeld theory.
Microwave beam broadening due to turbulent plasma density fluctuations within the limit of the Born approximation and beyond

NASA Astrophysics Data System (ADS)

Köhn, A.; Guidi, L.; Holzhauer, E.; Maj, O.; Poli, E.; Snicker, A.; Weber, H.

2018-07-01

Plasma turbulence, and edge density fluctuations in particular, can under certain conditions broaden the cross-section of injected microwave beams significantly. This can be a severe problem for applications relying on well-localized deposition of the microwave power, like the control of MHD instabilities. Here we investigate this broadening mechanism as a function of fluctuation level, background density and propagation length in a fusion-relevant scenario using two numerical codes, the full-wave code IPF-FDMC and the novel wave kinetic equation solver WKBeam. The latter treats the effects of fluctuations using a statistical approach, based on an iterative solution of the scattering problem (Born approximation). The full-wave simulations are used to benchmark this approach. The Born approximation is shown to be valid over a large parameter range, including ITER-relevant scenarios.

Track structure: time evolution from physics to chemistry.

PubMed

Dingfelder, M

2006-01-01

This review discusses interaction cross sections of charged particles (electrons, protons, light ions) with atoms and molecules. The focus is on biological relevant targets like liquid water which serves as a substitute of soft tissue in most Monte Carlo codes. The spatial distribution of energy deposition patterns by different radiation qualities and their importance to the time evolution from the physical to the chemical stage or radiation response is discussed. The determination of inelastic interaction cross sections for charged particles in condensed matter is discussed within the relativistic plane-wave Born approximation and semi-empirical models. The dielectric-response-function of liquid water is discussed.
/sub 1//sup 1/H/sup +/- and /sub 2//sup 4/He/sup +/-induced M-shell x-ray-production cross sections for selected elements in the rare-earth region

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mehta, R.; Duggan, J.L.; Price, J.L.

1983-12-01

The measurements of M-shell x-ray-production cross sections induced by /sub 1//sup 1/H/sup +/ and /sub 2//sup 4/He/sup +/ ions are compared to the first-Born-approximation and ECPSSR (energy loss, Coulomb-deflection effects; perturbed-stationary-state approximation, with relativistic corrections) theories. Most of the reported experimental data were measured in our laboratory and the other measurements were taken from the literature. The data from our laboratory were for incident H/sup +/ and He/sup +/ ions in the energy range from 0.25 to 2.5 MeV. The M-shell x-ray-production cross sections were measured for the following thin targets: /sub 59/Pr, /sub 60/Nd, /sub 63/Eu, /sub 64/Gd, /submore » 66/Dy, /sub 67/Ho, /sub 68/Er, /sub 70/Yb, and /sub 72/Hf. The data from the literature were for protons and He/sup +/ ions in the energy range from 30 keV to 40 MeV. These data were for the following elements: /sub 54/Xe, /sub 59/Pr, /sub 60/Nd, /sub 62/Sm, /sub 63/Eu, /sub 64/Gd, /sub 65/Tb, /sub 66/Dy, /sub 67/Ho, /sub 68/Er, /sub 70/Yb, /sub 72/Hf, /sub 73/Ta, /sub 74/W, /sub 78/Pt, /sub 79/Au, /sub 80/Hg, /sub 82/Pb, /sub 83/Bi, and /sub 92/U. The first-Born-approximation calculations of the ionization cross section were made using the plane-wave Born approximation for direct ionization and the Oppenheimer-Brinkman-Kramers approximation of Nikolaev for electron capture. The ECPSSR theory of Brandt and Lapicki (Phys. Rev. A 23, 1717 (1981)) goes beyond the first Born approximation and accounts for the energy loss, Coulomb deflection, and relativistic effects in the perturbed-stationary-state theory. The first Born approximation overpredicts all measurements. The ECPSSR theory predicts the M-shell production cross sections correctly for Z/sub 2/>70 and energies per ..mu..>0.25 MeV/..mu...« less
Track-structure simulations for charged particles.

PubMed

Dingfelder, Michael

2012-11-01

Monte Carlo track-structure simulations provide a detailed and accurate picture of radiation transport of charged particles through condensed matter of biological interest. Liquid water serves as a surrogate for soft tissue and is used in most Monte Carlo track-structure codes. Basic theories of radiation transport and track-structure simulations are discussed and differences compared to condensed history codes highlighted. Interaction cross sections for electrons, protons, alpha particles, and light and heavy ions are required input data for track-structure simulations. Different calculation methods, including the plane-wave Born approximation, the dielectric theory, and semi-empirical approaches are presented using liquid water as a target. Low-energy electron transport and light ion transport are discussed as areas of special interest.
Absolute cross-section measurements of inner-shell ionization

NASA Astrophysics Data System (ADS)

Schneider, Hans; Tobehn, Ingo; Ebel, Frank; Hippler, Rainer

1994-12-01

Cross section ratios for K- and L-shell ionization of thin silver and gold targets by positron and electron impact have been determined at projectile energies of 30 70 keV. The experimental results are confirmed by calculations in plane wave Born approximation (PWBA) which include an electron exchange term and account for the deceleration or acceleration of the incident projectile in the nuclear field of the target atom. We report first absolute cross sections for K- and L-shell ionization of silver and gold targets by lepton impact in the threshold region. We have measured the corresponding cross sections for electron (e-) impact with an electron gun and the same experimental set-up.
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.
Electron- and proton-induced ionization of pyrimidine

NASA Astrophysics Data System (ADS)

Champion, Christophe; Quinto, Michele A.; Weck, Philippe F.

2015-05-01

The present work describes a quantum-mechanically based model of the electron- and proton-induced ionization of isolated pyrimidine molecules. The impact energies range from the target ionization threshold up to ~1 keV for electrons and from 10 keV up to 10 MeV for protons. The cross-section calculations are performed within the 1st Born approximation in which the ejected electron is described by a Coulomb wave whereas the incident and the scattered projectiles are both described by plane waves. The pyrimidine target is described using the Gaussian 09 software package. The theoretical predictions obtained are in good agreement with experimental absolute total cross sections, while large discrepancies are observed between existing semi-empirical models and the present calculations. Contribution to the Topical Issue "COST Action Nano-IBCT: Nano-scale Processes Behind Ion-Beam Cancer Therapy", edited by Andrey Solov'yov, Nigel Mason, Gustavo García, Eugene Surdutovich.
Scattering and absorption of massless scalar waves by Born-Infeld black holes

NASA Astrophysics Data System (ADS)

Sanchez, Pablo Alejandro; Bretón, Nora; Bergliaffa, Santiago Esteban Perez

2018-06-01

We present the results of a study of the scattering of massless planar scalar waves by a Born-Infeld black hole. The scattering and absorption cross sections are calculated using partial-wave methods. The numerical results are checked by reproducing those of the Reissner-Nordstrom black hole, and also using several approximations, with which our results are in very good agreement. The dependence of these phenomena on the effective potential, the charge of the black hole, and the value of the Born-Infeld parameter is discussed.
Phenomenological Study of Interaction between Solar Acoustic Waves and Sunspots from Measured Scattered Wavefunctions

NASA Astrophysics Data System (ADS)

Yang, Ming-Hsu; Chou, Dean-Yi; Zhao, Hui; Liang, Zhi-Chao

2012-08-01

The solar acoustic waves around a sunspot are modified because of the interaction with the sunspot. The interaction can be viewed as that the sunspot, excited by the incident wave, generates the scattered wave, and the scattered wave is added to the incident wave to form the total wave around the sunspot. We define an interaction parameter, which could be complex, describing the interaction between the acoustic waves and the sunspot. The scattered wavefunction on the surface can be expressed as a two-dimensional integral of the product of the Green's function, the wavefunction, and the two-dimensional interaction parameter over the sunspot area for the Born approximation of different orders. We assume a simple model for the two-dimensional interaction parameter distribution: its absolute value is axisymmetric with a Gaussian distribution and its phase is a constant. The measured scattered wavefunctions of various modes for NOAAs 11084 and 11092 are fitted to the theoretical scattered wavefunctions to determine the three model parameters, magnitude, Gaussian radius, and phase, for the Born approximation of different orders. The three model parameters converge to some values at high-order Born approximations. The result of the first-order Born approximation is significantly different from the convergent value in some cases. The rate of convergence depends on the sunspot size and wavelength. It converges more rapidly for the smaller sunspot and longer wavelength. The magnitude increases with mode frequency and degree for each radial order. The Gaussian radius is insensitive to frequency and degree. The spatial range of the interaction parameter is greater than that of the continuum intensity deficit, but smaller than that of the acoustic power deficit of the sunspot. The phase versus phase speed falls into a small range. This suggests that the phase could be a function phase speed. NOAAs 11084 and 11092 have a similar magnitude and phase, although the ratio of their sizes is 0.75.
131 iodine gamma dose determination in the thyroid gland using two geometrical shapes: a comparative study

NASA Astrophysics Data System (ADS)

Betka, A.; Bentabet, A.; Azbouche, A.; Fenineche, N.; Adjiri, A.; Dib, A.

2015-05-01

In order to study the internal gamma dose, we used a Monte Carlo code ‘Penelope’ simulation with two geometrical models (cylindrical and spherical). The deposited energy was determined via the loss of energy calculated from the quantum theory for inelastic collisions based on the first-order (plane-wave) Born approximation for charged particles with individual atoms and molecules. Our results show that the cylindrical geometry is more suitable for carrying out such a study. Moreover, we developed an analytical expression for the 131 iodine gamma dose (the energy deposited per photon absorbed dose). This latter could be considered as an important tool for evaluating the gamma dose without going through stochastic models.
Variationally consistent approximation scheme for charge transfer

NASA Technical Reports Server (NTRS)

Halpern, A. M.

1978-01-01

The author has developed a technique for testing various charge-transfer approximation schemes for consistency with the requirements of the Kohn variational principle for the amplitude to guarantee that the amplitude is correct to second order in the scattering wave functions. Applied to Born-type approximations for charge transfer it allows the selection of particular groups of first-, second-, and higher-Born-type terms that obey the consistency requirement, and hence yield more reliable approximation to the amplitude.
Quantum scattering beyond the plane-wave approximation

NASA Astrophysics Data System (ADS)

Karlovets, Dmitry

2017-12-01

While a plane-wave approximation in high-energy physics works well in a majority of practical cases, it becomes inapplicable for scattering of the vortex particles carrying orbital angular momentum, of Airy beams, of the so-called Schrödinger cat states, and their generalizations. Such quantum states of photons, electrons and neutrons have been generated experimentally in recent years, opening up new perspectives in quantum optics, electron microscopy, particle physics, and so forth. Here we discuss the non-plane-wave effects in scattering brought about by the novel quantum numbers of these wave packets. For the well-focused electrons of intermediate energies, already available at electron microscopes, the corresponding contribution can surpass that of the radiative corrections. Moreover, collisions of the cat-like superpositions of such focused beams with atoms allow one to probe effects of the quantum interference, which have never played any role in particle scattering.
Submillimeter wave survey of the galactic plane. Ph.D. Thesis - Maryland Univ.

NASA Technical Reports Server (NTRS)

Cheung, L. H.

1980-01-01

The survey measured, over virtually the entire galactic plane, the distribution and basic physical conditions of the coolest dust component of the interstellar medium. The instrument designed for observations of extended, low surface brightness continuum emission consisted of a balloon borne, gyro stablized, 1.2 m Cassegrain telescope and a liquid cooled photometer. The design, integration, tests, and flight operation of the survey are presented.
Scattering of an electromagnetic light wave from a quasi-homogeneous medium with semisoft boundary

NASA Astrophysics Data System (ADS)

Zhou, Jianyang; Zhao, Daomu

2016-08-01

Based on the first-order Born approximation, the scattering of an electromagnetic plane wave from a relatively more realistic random medium, a quasi-homogeneous medium with semisoft boundary, has been investigated. The analytic expressions for the spectral density, the spectral degree of coherence and the spectral degree of polarization have been derived, and the effects of the characteristics of the medium and the polarization of the incident light wave on the far-zone scattered field are determined. The numerical simulations indicate that, with the increasing of the edge softness M of the medium, the spectral density presents a pattern with interference fringes, and the number, position and width of interference fringes can be modified by the parameter. It is also found that there is an obvious value saltation in the coherence profile. Besides, unlike the intensity and the coherence are significantly affected by the properties of the medium, the polarization of the scattered field is irrelevant to them due to the quasi-homogeneity and isotropy of the medium, and it is only connected with the polarization of the incident light.
An integrated model to simulate the scattering of ultrasounds by inclusions in steels.

PubMed

Darmon, Michel; Calmon, Pierre; Bèle, Bertrand

2004-04-01

We present a study performed to model and predict the ultrasonic response of alumina inclusions in steels. The Born and the extended quasistatic approximations have been applied and modified to improve their accuracy in the framework of this application. The modified Born approximation, called "doubly distorted wave (D(2)W) Born approximation" allowing to deal with various inclusion shapes, has been selected to be implemented in the CIVA software. The model reliability has been evaluated by comparison with Ying and Truell's exact analytical solution. In parallel, measurements have been carried out upon both natural and artificial alumina inclusions.
On Born approximation in black hole scattering

NASA Astrophysics Data System (ADS)

Batic, D.; Kelkar, N. G.; Nowakowski, M.

2011-12-01

A massless field propagating on spherically symmetric black hole metrics such as the Schwarzschild, Reissner-Nordström and Reissner-Nordström-de Sitter backgrounds is considered. In particular, explicit formulae in terms of transcendental functions for the scattering of massless scalar particles off black holes are derived within a Born approximation. It is shown that the conditions on the existence of the Born integral forbid a straightforward extraction of the quasi normal modes using the Born approximation for the scattering amplitude. Such a method has been used in literature. We suggest a novel, well defined method, to extract the large imaginary part of quasinormal modes via the Coulomb-like phase shift. Furthermore, we compare the numerically evaluated exact scattering amplitude with the Born one to find that the approximation is not very useful for the scattering of massless scalar, electromagnetic as well as gravitational waves from black holes.
Complex space monofilar approximation of diffraction currents on a conducting half plane

NASA Technical Reports Server (NTRS)

Lindell, I. V.

1987-01-01

Simple approximation of diffraction surface currents on a conducting half plane, due to an incoming plane wave, is obtained with a line current (monofile) in complex space. When compared to an approximating current at the edge, the diffraction pattern is seen to improve by an order of magnitude for a minimal increase of computation effort. Thus, the inconvient Fresnel integral functions can be avoided for quick calculations of diffracted fields and the accuracy is good in other directions than along the half plane. The method can be applied to general problems involving planar metal edges.
A plane wave generation method by wave number domain point focusing.

PubMed

Chang, Ji-Ho; Choi, Jung-Woo; Kim, Yang-Hann

2010-11-01

A method for generation of a wave-field that is a plane wave is described. This method uses an array of loudspeakers phased so that the field in the wave-number domain is nearly concentrated at a point, this point being at the wave-number vector of the desired plane wave. The method described here for such a wave-number concentration makes use of an expansion in spherical harmonics, and requires a relatively small number of measurement points for a good approximate achievement of a plane wave. The measurement points are on a spherical surface surrounding the array of loudspeakers. The input signals for the individual loudspeakers can be derived without a matrix inversion or without explicit assumptions about the loudspeakers. The mathematical development involves spherical harmonics and three-dimensional Fourier transforms. Some numerical examples are given, with various assumptions concerning the nature of the loudspeakers, that support the premise that the method described in the present paper may be useful in applications.
Quantum-mechanical predictions of electron-induced ionization cross sections of DNA components

NASA Astrophysics Data System (ADS)

Champion, Christophe

2013-05-01

Ionization of biomolecules remains still today rarely investigated on both the experimental and the theoretical sides. In this context, the present work appears as one of the first quantum mechanical approaches providing a multi-differential description of the electron-induced ionization process of the main DNA components for impact energies ranging from the target ionization threshold up to about 10 keV. The cross section calculations are here performed within the 1st Born approximation framework in which the ejected electron is described by a Coulomb wave whereas the incident and the scattered electrons are both described by a plane wave. The biological targets of interest, namely, the DNA nucleobases and the sugar-phosphate backbone, are here described by means of the GAUSSIAN 09 system using the restricted Hartree-Fock method with geometry optimization. The theoretical predictions also obtained have shown a reasonable agreement with the experimental total ionization cross sections while huge discrepancies have been pointed out with existing theoretical models, mainly developed within a semi-classical framework.
Electron-pair-production cross section in the tip region of the positron spectrum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sud, K.K.; Sharma, D.K.

1984-11-01

The radial integrals for electron-pair production in a point Coulomb potential have been expressed by Sud, Sharma, and Sud in terms of the matrix generalization of the GAMMA function. Two new partial differential equations in photon energy satisfied by the matrix GAMMA function are obtained. We have obtained, on integrating the partial differential equations, accurate radial integrals as a function of photon energy for the pair production by intermediate-energy photons. The cross section in the tip region of the spectrum are calculated for photons of energy 5.0 to 10.0 MeV for /sup 92/U. The new technique results in extensive savingmore » in computer time as the basic radial integrals in terms of the hypergeometric function F/sub 2/ are computed at one photon energy for each pair of partial waves. The results of our calculations are compared with plane-wave Born-approximation results and with the calculations of Dugne and of Deck, Moroi, and Alling.« less
A numerical comparison with an exact solution for the transient response of a cylinder immersed in a fluid. [computer simulated underwater tests to determine transient response of a submerged cylindrical shell

NASA Technical Reports Server (NTRS)

Giltrud, M. E.; Lucas, D. S.

1979-01-01

The transient response of an elastic cylindrical shell immersed in an acoustic media that is engulfed by a plane wave is determined numerically. The method applies to the USA-STAGS code which utilizes the finite element method for the structural analysis and the doubly asymptotic approximation for the fluid-structure interaction. The calculations are compared to an exact analysis for two separate loading cases: a plane step wave and an exponentially decaying plane wave.

Sound pressure distribution within natural and artificial human ear canals: forward stimulation.

PubMed

Ravicz, Michael E; Tao Cheng, Jeffrey; Rosowski, John J

2014-12-01

This work is part of a study of the interaction of sound pressure in the ear canal (EC) with tympanic membrane (TM) surface displacement. Sound pressures were measured with 0.5-2 mm spacing at three locations within the shortened natural EC or an artificial EC in human temporal bones: near the TM surface, within the tympanic ring plane, and in a plane transverse to the long axis of the EC. Sound pressure was also measured at 2-mm intervals along the long EC axis. The sound field is described well by the size and direction of planar sound pressure gradients, the location and orientation of standing-wave nodal lines, and the location of longitudinal standing waves along the EC axis. Standing-wave nodal lines perpendicular to the long EC axis are present on the TM surface >11-16 kHz in the natural or artificial EC. The range of sound pressures was larger in the tympanic ring plane than at the TM surface or in the transverse EC plane. Longitudinal standing-wave patterns were stretched. The tympanic-ring sound field is a useful approximation of the TM sound field, and the artificial EC approximates the natural EC.
Electron-Impact Cross Sections for Dipole- and Spin-Allowed Excitations of Hydrogen, Helium, and Lithium.

PubMed

Stone, Philip M; Kim, Yong-Ki; Desclaux, J P

2002-01-01

Electron-impact excitation cross sections are presented for the dipole- and spin allowed transitions from the ground states to the np (2)P states for hydrogen and lithium, and to the 1snp (1)P states for helium, n = 2 through 10. Two scaling formulas developed earlier by Kim [Phys. Rev. A 64, 032713 (2001)] for plane-wave Born cross sections are used. The scaled Born cross sections are in excellent agreement with available theoretical and experimental data.
Variation in Differential and Total Cross Sections Due to Different Radial Wave Functions

ERIC Educational Resources Information Center

Williamson, W., Jr.; Greene, T.

1976-01-01

Three sets of analytical wave functions are used to calculate the Na (3s---3p) transition differential and total electron excitation cross sections by Born approximations. Results show expected large variations in values. (Author/CP)
Density functional calculations of multiphonon capture cross sections at defects in semiconductors

NASA Astrophysics Data System (ADS)

Barmparis, Georgios D.; Puzyrev, Yevgeniy S.; Zhang, X.-G.; Pantelides, Sokrates T.

2014-03-01

The theory of electron capture cross sections by multiphonon processes in semiconductors has a long and controversial history. Here we present a comprehensive theory and describe its implementation for realistic calculations. The Born-Oppenheimer and the Frank-Condon approximations are employed. The transition probability of an incoming electron is written as a product of an instantaneous electronic transition in the initial defect configuration and the line shape function (LSF) that describes the multiphonon processes that lead to lattice relaxation. The electronic matrix elements are calculated using the Projector Augmented Wave (PAW) method which yields the true wave functions while still employing a plane-wave basis. The LSF is calculated by employing a Monte Carlo method and the real phonon modes of the defect, calculated using density functional theory in the PAW scheme. Initial results of the capture cross section for a prototype system, namely a triply hydrogenated vacancy in Si are presented. The results are relevant for modeling device degradation by hot electron effects. This work is supported in part by the Samsung Advanced Institute of Technology (SAIT)'s Global Research Outreach (GRO) Program and by the LDRD program at ORNL.
On periodic geophysical water flows with discontinuous vorticity in the equatorial f-plane approximation

NASA Astrophysics Data System (ADS)

Martin, Calin Iulian

2017-12-01

We are concerned here with geophysical water waves arising as the free surface of water flows governed by the f-plane approximation. Allowing for an arbitrary bounded discontinuous vorticity, we prove the existence of steady periodic two-dimensional waves of small amplitude. We illustrate the local bifurcation result by means of an analysis of the dispersion relation for a two-layered fluid consisting of a layer of constant non-zero vorticity γ1 adjacent to the surface situated above another layer of constant non-zero vorticity γ2≠γ1 adjacent to the bed. For certain vorticities γ1,γ2, we also provide estimates for the wave speed c in terms of the speed at the surface of the bifurcation inducing laminar flows. This article is part of the theme issue 'Nonlinear water waves'.
Coded Excitation Plane Wave Imaging for Shear Wave Motion Detection

PubMed Central

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
Attenuation characteristics of the fundamental modes that propagate in buried iron water pipes.

PubMed

Long, R; Lowe, M; Cawley, P

2003-09-01

The attenuation of the fundamental non-torsional modes that propagate down buried iron water pipes has been studied. The mode shapes, mode attenuation due to leakage into the surrounding medium and the scattering of the modes as they interact with pipe joints and fittings have been investigated. In the low frequency region the mode predicted to dominate over significant propagation distances approximates a plane wave in the water within the pipe. The established acoustic technique used to locate leaks in buried iron water pipes assumes that leak noise propagates as a single non-dispersive mode at a velocity related to the low frequency asymptote of this water borne mode. Experiments have been conducted on buried water mains at test sites in the UK to verify the attenuation and velocity dispersion predictions.
Relativistic Atomic Data for Lines in Ge-Like Sm and Eu Ions

NASA Astrophysics Data System (ADS)

Nagy, O.; El Sayed, Fatma

2012-11-01

Energies, wavelengths, transition probabilities, and oscillator strengths have been calculated for the 4s24p2 - 4s4p3, 4s24p2 - 4s24p4d and 4s4p3 - 4p4 allowed transitions in heavy Ge-like Sm and Eu ions. The fully relativistic Multiconfiguration Dirac-Fock (MCDF) method taking into account both the correlations within the n = 4 complex and the quantum electrodynamic (QED) effects have been used in the calculations. MCDFGME code is used to calculate electron impact excitation cross sections for the 4s24p2 - 4s4p3, and 4s24p2 - 4s24p4d transitions with plane-wave Born approximation. The results of SmXXXI and Eu XXXII are compared with HFR method results.
Performance of different theories for the angular distribution of bremsstrahlung produced by keV electrons incident upon a target

NASA Astrophysics Data System (ADS)

Omar, Artur; Andreo, Pedro; Poludniowski, Gavin

2018-07-01

Different theories of the intrinsic bremsstrahlung angular distribution (i.e., the shape function) have been evaluated using Monte Carlo calculations for various target materials and incident electron energies between 20 keV and 300 keV. The shape functions considered were the plane-wave first Born approximation cross sections (i) 2BS [high-energy result, screened nucleus], (ii) 2BN [general result, bare nucleus], (iii) KM [2BS modified to emulate 2BN], and (iv) SIM [leading term of 2BN]; (v) expression based on partial-waves expansion, KQP; and (vi) a uniform spherical distribution, UNI [a common approximation in certain analytical models]. The shape function was found to have an important impact on the bremsstrahlung emerging from thin foil targets in which the incident electrons undergo few elastic scatterings before exiting the target material. For thick transmission and reflection targets the type of shape function had less importance, as the intrinsic bremsstrahlung angular distribution was masked by the diffuse directional distribution of multiple scattered electrons. Predictions made using the 2BN and KQP theories were generally in good agreement, suggesting that the effect of screening and the constraints of the Born approximation on the intrinsic angular distribution may be acceptable. The KM and SIM shape functions deviated notably from KQP for low electron energies (< 50 keV), while 2BS and UNI performed poorly over most of the energy range considered; the 2BS shape function was found to be too forward-focused in emission, while UNI was not forward-focused enough. The results obtained emphasize the importance of the intrinsic bremsstrahlung angular distribution for theoretical predictions of x-ray emission, which is relevant in various applied disciplines, including x-ray crystallography, electron-probe microanalysis, security and industrial inspection, medical imaging, as well as low- and medium (orthovoltage) energy radiotherapy.
Basis for paraxial surface-plasmon-polariton packets

NASA Astrophysics Data System (ADS)

Martinez-Herrero, Rosario; Manjavacas, Alejandro

2016-12-01

We present a theoretical framework for the study of surface-plasmon polariton (SPP) packets propagating along a lossy metal-dielectric interface within the paraxial approximation. Using a rigorous formulation based on the plane-wave spectrum formalism, we introduce a set of modes that constitute a complete basis set for the solutions of Maxwell's equations for a metal-dielectric interface in the paraxial approximation. The use of this set of modes allows us to fully analyze the evolution of the transversal structure of SPP packets beyond the single plane-wave approximation. As a paradigmatic example, we analyze the case of a Gaussian SPP mode, for which, exploiting the analogy with paraxial optical beams, we introduce a set of parameters that characterize its propagation.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Watanabe, N.; Takahashi, M.

We report a collision dynamics study on ionization-excitation processes of He and H{sub 2} by means of (e, 2e) electron momentum spectroscopy. The two-step mechanism, one of the second-order terms of the plane-wave Born series model, has been found to play a particular role in the processes at an incident electron energy of 1.2 keV.
Direct Measurement of Wave Kernels in Time-Distance Helioseismology

NASA Technical Reports Server (NTRS)

Duvall, T. L., Jr.

2006-01-01

Solar f-mode waves are surface-gravity waves which propagate horizontally in a thin layer near the photosphere with a dispersion relation approximately that of deep water waves. At the power maximum near 3 mHz, the wavelength of 5 Mm is large enough for various wave scattering properties to be observable. Gizon and Birch (2002,ApJ,571,966)h ave calculated kernels, in the Born approximation, for the sensitivity of wave travel times to local changes in damping rate and source strength. In this work, using isolated small magnetic features as approximate point-sourc'e scatterers, such a kernel has been measured. The observed kernel contains similar features to a theoretical damping kernel but not for a source kernel. A full understanding of the effect of small magnetic features on the waves will require more detailed modeling.
GW/Bethe-Salpeter calculations for charged and model systems from real-space DFT

NASA Astrophysics Data System (ADS)

Strubbe, David A.

GW and Bethe-Salpeter (GW/BSE) calculations use mean-field input from density-functional theory (DFT) calculations to compute excited states of a condensed-matter system. Many parts of a GW/BSE calculation are efficiently performed in a plane-wave basis, and extensive effort has gone into optimizing and parallelizing plane-wave GW/BSE codes for large-scale computations. Most straightforwardly, plane-wave DFT can be used as a starting point, but real-space DFT is also an attractive starting point: it is systematically convergeable like plane waves, can take advantage of efficient domain parallelization for large systems, and is well suited physically for finite and especially charged systems. The flexibility of a real-space grid also allows convenient calculations on non-atomic model systems. I will discuss the interfacing of a real-space (TD)DFT code (Octopus, www.tddft.org/programs/octopus) with a plane-wave GW/BSE code (BerkeleyGW, www.berkeleygw.org), consider performance issues and accuracy, and present some applications to simple and paradigmatic systems that illuminate fundamental properties of these approximations in many-body perturbation theory.
Treatment of Ion-Atom Collisions Using a Partial-Wave Expansion of the Projectile Wavefunction

ERIC Educational Resources Information Center

Wong, T. G.; Foster, M.; Colgan, J.; Madison, D. H.

2009-01-01

We present calculations of ion-atom collisions using a partial-wave expansion of the projectile wavefunction. Most calculations of ion-atom collisions have typically used classical or plane-wave approximations for the projectile wavefunction, since partial-wave expansions are expected to require prohibitively large numbers of terms to converge…
Diagonal Born-Oppenheimer correction for coupled-cluster wave-functions

NASA Astrophysics Data System (ADS)

Shamasundar, K. R.

2018-06-01

We examine how geometry-dependent normalisation freedom of electronic wave-functions affects extraction of a meaningful diagonal Born-Oppenheimer correction (DBOC) to the ground-state Born-Oppenheimer potential energy surface (PES). By viewing this freedom as a kind of gauge-freedom, it is shown that DBOC and the resulting associated mass-dependent adiabatic PES are gauge-invariant quantities. A sum-over-states (SOS) formula for DBOC which explicitly exhibits this invariance is derived. A biorthogonal formulation suitable for DBOC computations using standard unnormalised coupled-cluster (CC) wave-functions is presented. This is shown to lead to a biorthogonal version of SOS formula with similar properties. On this basis, different computational schemes for evaluating DBOC using approximate CC wave-functions are derived. One of this agrees with the formula used in the current literature. The connection to adiabatic-to-diabatic transformations in non-adiabatic dynamics is explored and complications arising from biorthogonal nature of CC theory are identified.
Sound pressure distribution within natural and artificial human ear canals: Forward stimulation

PubMed Central

Ravicz, Michael E.; Tao Cheng, Jeffrey; Rosowski, John J.

2014-01-01

This work is part of a study of the interaction of sound pressure in the ear canal (EC) with tympanic membrane (TM) surface displacement. Sound pressures were measured with 0.5–2 mm spacing at three locations within the shortened natural EC or an artificial EC in human temporal bones: near the TM surface, within the tympanic ring plane, and in a plane transverse to the long axis of the EC. Sound pressure was also measured at 2-mm intervals along the long EC axis. The sound field is described well by the size and direction of planar sound pressure gradients, the location and orientation of standing-wave nodal lines, and the location of longitudinal standing waves along the EC axis. Standing-wave nodal lines perpendicular to the long EC axis are present on the TM surface >11–16 kHz in the natural or artificial EC. The range of sound pressures was larger in the tympanic ring plane than at the TM surface or in the transverse EC plane. Longitudinal standing-wave patterns were stretched. The tympanic-ring sound field is a useful approximation of the TM sound field, and the artificial EC approximates the natural EC. PMID:25480061
Gaussian and Airy wave packets of massive particles with orbital angular momentum

NASA Astrophysics Data System (ADS)

Karlovets, Dmitry V.

2015-01-01

While wave-packet solutions for relativistic wave equations are oftentimes thought to be approximate (paraxial), we demonstrate, by employing a null-plane- (light-cone-) variable formalism, that there is a family of such solutions that are exact. A scalar Gaussian wave packet in the transverse plane is generalized so that it acquires a well-defined z component of the orbital angular momentum (OAM), while it may not acquire a typical "doughnut" spatial profile. Such quantum states and beams, in contrast to the Bessel states, may have an azimuthal-angle-dependent probability density and finite uncertainty of the OAM, which is determined by the packet's width. We construct a well-normalized Airy wave packet, which can be interpreted as a one-particle state for a relativistic massive boson, show that its center moves along the same quasiclassical straight path, and, which is more important, spreads with time and distance exactly as a Gaussian wave packet does, in accordance with the uncertainty principle. It is explained that this fact does not contradict the well-known "nonspreading" feature of the Airy beams. While the effective OAM for such states is zero, its uncertainty (or the beam's OAM bandwidth) is found to be finite, and it depends on the packet's parameters. A link between exact solutions for the Klein-Gordon equation in the null-plane-variable formalism and the approximate ones in the usual approach is indicated; generalizations of these states for a boson in the external field of a plane electromagnetic wave are also presented.
Integrated focal plane arrays for millimeter-wave astronomy

NASA Astrophysics Data System (ADS)

Bock, James J.; Goldin, Alexey; Hunt, Cynthia; Lange, Andrew E.; Leduc, Henry G.; Day, Peter K.; Vayonakis, Anastasios; Zmuidzinas, Jonas

2002-02-01

We are developing focal plane arrays of bolometric detectors for sub-millimeter and millimeter-wave astrophysics. We propose a flexible array architecture using arrays of slot antennae coupled via low-loss superconducting Nb transmission line to microstrip filters and antenna-coupled bolometers. By combining imaging and filtering functions with transmission line, we are able to realize unique structures such as a multi-band polarimeter and a planar, dispersive spectrometer. Micro-strip bolometers have significantly smaller active volume than standard detectors with extended absorbers, and can realize higher sensitivity and speed of response. The integrated array has natural immunity to stray radiation or spectral leaks, and minimizes the suspended mass operating at 0.1-0.3 K. We also discuss future space-borne spectroscopy and polarimetry applications. .
Fully differential cross sections for the single ionization of helium by fast ions: Classical model calculations

NASA Astrophysics Data System (ADS)

Sarkadi, L.

2018-04-01

Fully differential cross sections (FDCSs) have been calculated for the single ionization of helium by 1- and 3-MeV proton and 100-MeV/u C6 + ion impact using the classical trajectory Monte Carlo (CTMC) method in the nonrelativistic, three-body approximation. The calculations were made employing a Wigner-type model in which the quantum-mechanical position distribution of the electron is approximated by a weighted integral of the microcanonical distribution over a range of the binding energy of the electron. In the scattering plane, the model satisfactorily reproduces the observed shape of the binary peak. In the region of the peak the calculated FDCSs agree well with the results of continuum-distorted-wave calculations for all the investigated collisions. For 1-MeV proton impact the experimentally observed shift of the binary peak with respect to the first Born approximation is compared with the shifts obtained by different higher-order quantum-mechanical theories and the present CTMC method. The best result was achieved by CTMC, but still a large part of the shift remained unexplained. Furthermore, it was found that the classical theory failed to reproduce the shape of the recoil peak observed in the experiments, it predicts a much narrower peak. This indicates that the formation of the recoil peak is dominated by quantum-mechanical effects. For 100-MeV/u C6 + ion impact the present CTMC calculations confirmed the existence of the "double-peak" structure of the angular distribution of the electron in the plane perpendicular to the momentum transfer, in accordance with the observation, the prediction of an incoherent semiclassical model, and previous CTMC results. This finding together with wave-packet calculations suggests that the "C6 + puzzle" may be solved by considering the loss of the projectile coherence. Experiments to be conducted using ion beams of anisotropic coherence are proposed for a more differential investigation of the ionization dynamics.
On periodic geophysical water flows with discontinuous vorticity in the equatorial f-plane approximation.

PubMed

Martin, Calin Iulian

2018-01-28

We are concerned here with geophysical water waves arising as the free surface of water flows governed by the f -plane approximation. Allowing for an arbitrary bounded discontinuous vorticity, we prove the existence of steady periodic two-dimensional waves of small amplitude. We illustrate the local bifurcation result by means of an analysis of the dispersion relation for a two-layered fluid consisting of a layer of constant non-zero vorticity γ 1 adjacent to the surface situated above another layer of constant non-zero vorticity γ 2 ≠ γ 1 adjacent to the bed. For certain vorticities γ 1 , γ 2 , we also provide estimates for the wave speed c in terms of the speed at the surface of the bifurcation inducing laminar flows.This article is part of the theme issue 'Nonlinear water waves'. © 2017 The Author(s).

Second-order numerical solution of time-dependent, first-order hyperbolic equations

NASA Technical Reports Server (NTRS)

Shah, Patricia L.; Hardin, Jay

1995-01-01

A finite difference scheme is developed to find an approximate solution of two similar hyperbolic equations, namely a first-order plane wave and spherical wave problem. Finite difference approximations are made for both the space and time derivatives. The result is a conditionally stable equation yielding an exact solution when the Courant number is set to one.
Lattice dynamical and dielectric properties of L-amino acids

NASA Astrophysics Data System (ADS)

Tulip, P. R.; Clark, S. J.

2006-08-01

We present the results of ab initio calculations of the lattice dynamical and dielectric properties of the L-amino acids L-alanine, L-leucine, and L-isoleucine. Normal-mode frequencies and dielectric permittivity tensors are obtained using density-functional perturbation theory implemented within the plane-wave pseudopotential approximation. IR spectra are calculated and are used to analyze the effects of intermolecular interactions and zwitterionization upon the lattice dynamics. It is found that vibronic modes associated with the carboxy and amino functional groups undergo modification from their free-molecule values due to the presence of hydrogen bonds. The role of macroscopic electric fields set up by zone-center normal modes in the lattice dynamics is investigated by analysis of the Born effective charge. Calculated permittivity tensors are found to be greater than would be obtained by a naive use of the isolated molecular values, indicating the role of intermolecular interactions in increasing molecular polarizability.
Efficient evaluation of Coulomb integrals in a mixed Gaussian and plane-wave basis using the density fitting and Cholesky decomposition.

PubMed

Čársky, Petr; Čurík, Roman; Varga, Štefan

2012-03-21

The objective of this paper is to show that the density fitting (resolution of the identity approximation) can also be applied to Coulomb integrals of the type (k(1)(1)k(2)(1)|g(1)(2)g(2)(2)), where k and g symbols refer to plane-wave functions and gaussians, respectively. We have shown how to achieve the accuracy of these integrals that is needed in wave-function MO and density functional theory-type calculations using mixed Gaussian and plane-wave basis sets. The crucial issues for achieving such a high accuracy are application of constraints for conservation of the number electrons and components of the dipole moment, optimization of the auxiliary basis set, and elimination of round-off errors in the matrix inversion. © 2012 American Institute of Physics
On Periodic Water Waves with Coriolis Effects and Isobaric Streamlines

NASA Astrophysics Data System (ADS)

Matioc, Anca-Voichita; Matioc, Bogdan-Vasile

2012-10-01

In this paper we prove that solutions of the f-plane approximation for equatorial geophysical deep water waves, which have the property that the pressure is constant along the streamlines and do not possess stagnation points, are Gerstner-type waves. Furthermore, for waves traveling over a flat bed, we prove that there are only laminar flow solutions with these properties.
Computation of tightly-focused laser beams in the FDTD method

PubMed Central

Çapoğlu, İlker R.; Taflove, Allen; Backman, Vadim

2013-01-01

We demonstrate how a tightly-focused coherent TEMmn laser beam can be computed in the finite-difference time-domain (FDTD) method. The electromagnetic field around the focus is decomposed into a plane-wave spectrum, and approximated by a finite number of plane waves injected into the FDTD grid using the total-field/scattered-field (TF/SF) method. We provide an error analysis, and guidelines for the discrete approximation. We analyze the scattering of the beam from layered spaces and individual scatterers. The described method should be useful for the simulation of confocal microscopy and optical data storage. An implementation of the method can be found in our free and open source FDTD software (“Angora”). PMID:23388899
Computation of tightly-focused laser beams in the FDTD method.

PubMed

Capoğlu, Ilker R; Taflove, Allen; Backman, Vadim

2013-01-14

We demonstrate how a tightly-focused coherent TEMmn laser beam can be computed in the finite-difference time-domain (FDTD) method. The electromagnetic field around the focus is decomposed into a plane-wave spectrum, and approximated by a finite number of plane waves injected into the FDTD grid using the total-field/scattered-field (TF/SF) method. We provide an error analysis, and guidelines for the discrete approximation. We analyze the scattering of the beam from layered spaces and individual scatterers. The described method should be useful for the simulation of confocal microscopy and optical data storage. An implementation of the method can be found in our free and open source FDTD software ("Angora").
Calculation of the total electron excitation cross section in the Born approximation using Slater wave functions for the Li (2s yields 2p), Li (2s yields 3p), Na (3s yields 4p), Mg (3p yields 4s), Ca (4s yields 4p) and K (4s yields 4p) excitations. M.S. Thesis

NASA Technical Reports Server (NTRS)

Simsic, P. L.

1974-01-01

Excitation of neutral atoms by inelastic scattering of incident electrons in gaseous nebulae were investigated using Slater Wave functions to describe the initial and final states of the atom. Total cross sections using the Born Approximation are calculated for: Li(2s yields 2p), Na(3s yields 4p), k(4s yields 4p). The intensity of emitted radiation from gaseous nebulae is also calculated, and Maxwell distribution is employed to average the kinetic energy of electrons.
Solitary waves in shallow water hydrodynamics and magnetohydrodynamics in rotating spherical coordinates

NASA Astrophysics Data System (ADS)

London, Steven D.

2018-01-01

In a recent paper (London, Geophys. Astrophys. Fluid Dyn. 2017, vol. 111, pp. 115-130, referred to as L1), we considered a perfect electrically conducting rotating fluid in the presence of an ambient toroidal magnetic field, governed by the shallow water magnetohydrodynamic (MHD) equations in a modified equatorial ?-plane approximation. In conjunction with a WKB type approximation, we used a multiple scale asymptotic scheme, previously developed by Boyd (J. Phys. Oceanogr. 1980, vol. 10, pp. 1699-1717) for equatorial solitary hydrodynamic waves, and found solitary MHD waves. In this paper, as in L1, we apply a WKB type approximation in order to extend the results of L1 from the modified ?-plane to the full spherical geometry. We have included differential rotation in the analysis in order to make the results more relevant to the solar case. In addition, we consider the case of hydrodynamic waves on the rotating sphere in the presence of a differential rotation intended to roughly model the varying large scale currents in the oceans and atmosphere. In the hydrodynamic case, we find the usual equatorial solitary waves as found by Boyd, as well as waves in bands away from the equator for sufficiently strong currents. In the MHD case, we find basically the same equatorial waves found in L1. L1 also found non-equatorial modes; no such modes are found in the full spherical geometry.
Ultrasonic measurements of the reflection coefficient at a water/polyurethane foam interface.

PubMed

Sagers, Jason D; Haberman, Michael R; Wilson, Preston S

2013-09-01

Measured ultrasonic reflection coefficients as a function of normal incidence angle are reported for several samples of polyurethane foam submerged in a water bath. Three reflection coefficient models are employed as needed in this analysis to approximate the measured data: (1) an infinite plane wave impinging on an elastic halfspace, (2) an infinite plane wave impinging on a single fluid layer overlying a fluid halfspace, and (3) a finite acoustic beam impinging on an elastic halfspace. The compressional wave speed in each sample is calculated by minimizing the sum of squared error (SSE) between the measured and modeled data.
Theoretical atomic physics code development I: CATS: Cowan Atomic Structure Code

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abdallah, J. Jr.; Clark, R.E.H.; Cowan, R.D.

An adaptation of R.D. Cowan's Atomic Structure program, CATS, has been developed as part of the Theoretical Atomic Physics (TAPS) code development effort at Los Alamos. CATS has been designed to be easy to run and to produce data files that can interface with other programs easily. The CATS produced data files currently include wave functions, energy levels, oscillator strengths, plane-wave-Born electron-ion collision strengths, photoionization cross sections, and a variety of other quantities. This paper describes the use of CATS. 10 refs.
Generation of an incident focused light pulse in FDTD.

PubMed

Capoğlu, Ilker R; Taflove, Allen; Backman, Vadim

2008-11-10

A straightforward procedure is described for accurately creating an incident focused light pulse in the 3-D finite-difference time-domain (FDTD) electromagnetic simulation of the image space of an aplanatic converging lens. In this procedure, the focused light pulse is approximated by a finite sum of plane waves, and each plane wave is introduced into the FDTD simulation grid using the total-field/scattered-field (TF/SF) approach. The accuracy of our results is demonstrated by comparison with exact theoretical formulas.
Generation of an incident focused light pulse in FDTD

PubMed Central

Çapoğlu, İlker R.; Taflove, Allen; Backman, Vadim

2009-01-01

A straightforward procedure is described for accurately creating an incident focused light pulse in the 3-D finite-difference time-domain (FDTD) electromagnetic simulation of the image space of an aplanatic converging lens. In this procedure, the focused light pulse is approximated by a finite sum of plane waves, and each plane wave is introduced into the FDTD simulation grid using the total-field/scattered-field (TF/SF) approach. The accuracy of our results is demonstrated by comparison with exact theoretical formulas. PMID:19582013
Transition between free-space Helmholtz equation solutions with plane sources and parabolic wave equation solutions.

PubMed

Mahillo-Isla, R; Gonźalez-Morales, M J; Dehesa-Martínez, C

2011-06-01

The slowly varying envelope approximation is applied to the radiation problems of the Helmholtz equation with a planar single-layer and dipolar sources. The analyses of such problems provide procedures to recover solutions of the Helmholtz equation based on the evaluation of solutions of the parabolic wave equation at a given plane. Furthermore, the conditions that must be fulfilled to apply each procedure are also discussed. The relations to previous work are given as well.
Trapped waves on the mid-latitude β-plane

NASA Astrophysics Data System (ADS)

Paldor, Nathan; Sigalov, Andrey

2008-08-01

A new type of approximate solutions of the Linearized Shallow Water Equations (LSWE) on the mid-latitude β-plane, zonally propagating trapped waves with Airy-like latitude-dependent amplitude, is constructed in this work, for sufficiently small radius of deformation. In contrast to harmonic Poincare and Rossby waves, these newly found trapped waves vanish fast in the positive half-axis, and their zonal phase speed is larger than that of the corresponding harmonic waves for sufficiently large meridional domains. Our analysis implies that due to the smaller radius of deformation in the ocean compared with that in the atmosphere, the trapped waves are relevant to observations in the ocean whereas harmonic waves typify atmospheric observations. The increase in the zonal phase speed of trapped Rossby waves compared with that of harmonic ones is consistent with recent observations that showed that Sea Surface Height features propagated westwards faster than the phase speed of harmonic Rossby waves.
A diffraction correction for storage and loss moduli imaging using radiation force based elastography.

PubMed

Budelli, Eliana; Brum, Javier; Bernal, Miguel; Deffieux, Thomas; Tanter, Mickaël; Lema, Patricia; Negreira, Carlos; Gennisson, Jean-Luc

2017-01-07

Noninvasive evaluation of the rheological behavior of soft tissues may provide an important diagnosis tool. Nowadays, available commercial ultrasound systems only provide shear elasticity estimation by shear wave speed assessment under the hypothesis of a purely elastic model. However, to fully characterize the rheological behavior of tissues, given by its storage (G') and loss (G″) moduli, it is necessary to estimate both: shear wave speed and shear wave attenuation. Most elastography techniques use the acoustic radiation force to generate shear waves. For this type of source the shear waves are not plane and a diffraction correction is needed to properly estimate the shear wave attenuation. The use of a cylindrical wave approximation to evaluate diffraction has been proposed by other authors before. Here the validity of such approximation is numerically and experimentally revisited. Then, it is used to generate images of G' and G″ in heterogeneous viscoelastic mediums. A simulation algorithm based on the anisotropic and viscoelastic Green's function was used to establish the validity of the cylindrical approximation. Moreover, two experiments were carried out: a transient elastography experiment where plane shear waves were generated using a vibrating plate and a SSI experiment that uses the acoustic radiation force to generate shear waves. For both experiments the shear wave propagation was followed with an ultrafast ultrasound scanner. Then, the shear wave velocity and shear wave attenuation were recovered from the phase and amplitude decay versus distance respectively. In the SSI experiment the cylindrical approximation was applied to correct attenuation due to diffraction effects. The numerical and experimental results validate the use of a cylindrical correction to assess shear wave attenuation. Finally, by applying the cylindrical correction G' and G″ images were generated in heterogeneous phantoms and a preliminary in vivo feasibility study was carried out in the human liver.
A diffraction correction for storage and loss moduli imaging using radiation force based elastography

NASA Astrophysics Data System (ADS)

Budelli, Eliana; Brum, Javier; Bernal, Miguel; Deffieux, Thomas; Tanter, Mickaël; Lema, Patricia; Negreira, Carlos; Gennisson, Jean-Luc

2017-01-01

Noninvasive evaluation of the rheological behavior of soft tissues may provide an important diagnosis tool. Nowadays, available commercial ultrasound systems only provide shear elasticity estimation by shear wave speed assessment under the hypothesis of a purely elastic model. However, to fully characterize the rheological behavior of tissues, given by its storage (G‧) and loss (G″) moduli, it is necessary to estimate both: shear wave speed and shear wave attenuation. Most elastography techniques use the acoustic radiation force to generate shear waves. For this type of source the shear waves are not plane and a diffraction correction is needed to properly estimate the shear wave attenuation. The use of a cylindrical wave approximation to evaluate diffraction has been proposed by other authors before. Here the validity of such approximation is numerically and experimentally revisited. Then, it is used to generate images of G‧ and G″ in heterogeneous viscoelastic mediums. A simulation algorithm based on the anisotropic and viscoelastic Green’s function was used to establish the validity of the cylindrical approximation. Moreover, two experiments were carried out: a transient elastography experiment where plane shear waves were generated using a vibrating plate and a SSI experiment that uses the acoustic radiation force to generate shear waves. For both experiments the shear wave propagation was followed with an ultrafast ultrasound scanner. Then, the shear wave velocity and shear wave attenuation were recovered from the phase and amplitude decay versus distance respectively. In the SSI experiment the cylindrical approximation was applied to correct attenuation due to diffraction effects. The numerical and experimental results validate the use of a cylindrical correction to assess shear wave attenuation. Finally, by applying the cylindrical correction G‧ and G″ images were generated in heterogeneous phantoms and a preliminary in vivo feasibility study was carried out in the human liver.
Electron-impact ionization of Ne (2 p ) and Ar (3 p ) at intermediate energies: Role of the postcollision interaction

NASA Astrophysics Data System (ADS)

Hu, Xiaoqing; Gao, Cong-Zhang; Chen, Zhanbin; Wang, Jianguo; Wu, Yong; Wang, Yang

2017-11-01

We present the absolute triple differential cross section (TDCS) for single ionization of Ne (2 p ) at an impact energy of 599.6 eV and Ar (3 p ) at 195 eV. The role of the postcollision interaction (PCI) is studied using a high-order distorted-wave Born approximation model with a continuum distorted-waves expansion. Both the second- and third-order effects are considered in the present calculations, and the third-order distorted wave Born approximation model is reported in the (e ,2 e ) reaction. The calculated results show satisfactory agreement with experimental data. The magnitude of the absolute TDCS is enhanced by a factor 2-3 when the strength factor γ of the PCI amplitude is summarized just from 0 to 2. This proves that the PCI plays an important role in the absolute TDCS of the (e ,2 e ) reaction in the intermediate-energy region.
Photoelectron wave function in photoionization: Plane wave or Coulomb wave? [Does photoionization of neutral targets produce Coulomb or plane waves?

DOE PAGES

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
Approximate non-linear multiparameter inversion for multicomponent single and double P-wave scattering in isotropic elastic media

NASA Astrophysics Data System (ADS)

Ouyang, Wei; Mao, Weijian

2018-03-01

An asymptotic quadratic true-amplitude inversion method for isotropic elastic P waves is proposed to invert medium parameters. The multicomponent P-wave scattered wavefield is computed based on a forward relationship using second-order Born approximation and corresponding high-frequency ray theoretical methods. Within the local double scattering mechanism, the P-wave transmission factors are elaborately calculated, which results in the radiation pattern for P-waves scattering being a quadratic combination of the density and Lamé's moduli perturbation parameters. We further express the elastic P-wave scattered wavefield in a form of generalized Radon transform (GRT). After introducing classical backprojection operators, we obtain an approximate solution of the inverse problem by solving a quadratic non-linear system. Numerical tests with synthetic data computed by finite-differences scheme demonstrate that our quadratic inversion can accurately invert perturbation parameters for strong perturbations, compared with the P-wave single-scattering linear inversion method. Although our inversion strategy here is only syncretized with P-wave scattering, it can be extended to invert multicomponent elastic data containing both P-wave and S-wave information.
The effect of an infinite plane-wave approximation on calculations for second-harmonic generation in a one-dimensional nonlinear crystal

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.

Quantitative molecular orbital energies within a G0W0 approximation

NASA Astrophysics Data System (ADS)

Sharifzadeh, S.; Tamblyn, I.; Doak, P.; Darancet, P. T.; Neaton, J. B.

2012-09-01

Using many-body perturbation theory within a G 0 W 0 approximation, with a plane wave basis set and using a starting point based on density functional theory within the generalized gradient approximation, we explore routes for computing the ionization potential (IP), electron affinity (EA), and fundamental gap of three gas-phase molecules — benzene, thiophene, and (1,4) diamino-benzene — and compare with experiments. We examine the dependence of the IP and fundamental gap on the number of unoccupied states used to represent the dielectric function and the self energy, as well as the dielectric function plane-wave cutoff. We find that with an effective completion strategy for approximating the unoccupied subspace, and a well converged dielectric function kinetic energy cutoff, the computed IPs and EAs are in excellent quantitative agreement with available experiment (within 0.2 eV), indicating that a one-shot G 0 W 0 approach can be very accurate for calculating addition/removal energies of small organic molecules.
Transmission of sound across a vortex layer enclosing a cylindrical column of jet

NASA Technical Reports Server (NTRS)

Luh, R.; Chao, C. C.

1982-01-01

An approximate solution to the problem of transmission of sound across a cylindrical vortex was obtained. Results are considerably different from the plane vortex sheet case because of the added role played by the curvature of the jet. In comparison with the plane case, the specularly transmitted waves are more complex and require some numerical integration. Resonance waves are identically predicted for M 2, but there is also a wave field whose modified effect appears to extend the region of resonance just as the instability waves cover a region in space and time. The instability waves are predicted to exist for all Mach numbers but vanish for wavelengths that are large compared to the jet radius. The region of propagation is similarly wavelength dependent.
Approximate nonlinear multiparameter inversion for multicomponent single and double P-wave scattering in isotropic elastic media

NASA Astrophysics Data System (ADS)

Ouyang, Wei; Mao, Weijian

2018-07-01

An asymptotic quadratic true-amplitude inversion method for isotropic elastic P waves is proposed to invert medium parameters. The multicomponent P-wave scattered wavefield is computed based on a forward relationship using second-order Born approximation and corresponding high-frequency ray theoretical methods. Within the local double scattering mechanism, the P-wave transmission factors are elaborately calculated, which results in the radiation pattern for P-wave scattering being a quadratic combination of the density and Lamé's moduli perturbation parameters. We further express the elastic P-wave scattered wavefield in a form of generalized Radon transform. After introducing classical backprojection operators, we obtain an approximate solution of the inverse problem by solving a quadratic nonlinear system. Numerical tests with synthetic data computed by finite-differences scheme demonstrate that our quadratic inversion can accurately invert perturbation parameters for strong perturbations, compared with the P-wave single-scattering linear inversion method. Although our inversion strategy here is only syncretized with P-wave scattering, it can be extended to invert multicomponent elastic data containing both P- and S-wave information.
Strong potential wave functions with elastic channel distortion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Macek, J.; Taulbjerg, K.

1989-06-01

The strong-potential Born approximation is analyzed in a channel-distorted-wave approach. Channel-distorted SPB wave functions are reduced to a conventional form in which the standard off-energy-shell factor /ital g/ has been replaced by a modified factor ..gamma.., which represents a suitable average of /ital g/ over the momentum distribution of the distorted-channel function. The modified factor is evaluated in a physically realistic model for the distortion potential, and it is found that ..gamma.. is well represented by a slowly varying phase factor. The channel-distorted SPB approximation is accordingly identical to the impulse approximation if the phase variation of ..gamma.. can bemore » ignored. This is generally the case in applications to radiative electron capture and to a good approximation for ordinary capture at not too small velocities.« less
Improved distorted wave theory with the localized virial conditions

NASA Astrophysics Data System (ADS)

Hahn, Y. K.; Zerrad, E.

2009-12-01

The distorted wave theory is operationally improved to treat the full collision amplitude, such that the corrections to the distorted wave Born amplitude can be systematically calculated. The localized virial conditions provide the tools necessary to test the quality of successive approximations at each stage and to optimize the solution. The details of the theoretical procedure are explained in concrete terms using a collisional ionization model and variational trial functions. For the first time, adjustable parameters associated with an approximate scattering solution can be fully determined by the theory. A small number of linear parameters are introduced to examine the convergence property and the effectiveness of the new approach.
Born scattering of long-period body waves

NASA Astrophysics Data System (ADS)

Dalkolmo, Jörg; Friederich, Wolfgang

2000-09-01

The Born approximation is applied to the modelling of the propagation of deeply turning long-period body waves through heterogeneities in the lowermost mantle. We use an exact Green's function for a spherically symmetric earth model that also satisfies the appropriate boundary conditions at internal boundaries and the surface of the earth. The scattered displacement field is obtained by a numerical quadrature of the product of the Green's function, the exciting wavefield and structural perturbations. We study three examples: scattering of long-period P waves from a plume rising from the core-mantle boundary (CMB), generation of long-period precursors to PKIKP by strong, localized scatterers at the CMB, and propagation of core-diffracted P waves through large-scale heterogeneities in D''. The main results are as follows: (1) the signals scattered from a realistic plume are small with relative amplitudes of less than 2 per cent at a period of 20s, rendering plume detection a fairly difficult task; (2) strong heterogeneities at the CMB of appropriate size may produce observable long-period precursors to PKIKP in spite of the presence of a diffraction from the PKP-B caustic; (3) core-diffracted P waves (Pdiff) are sensitive to structure in D'' far off the geometrical ray path and also far beyond the entry and exit points of the ray into and out of D'' sensitivity kernels exhibit ring-shaped patterns of alternating sign reminiscent of Fresnel zones; (4) Pdiff also shows a non-negligible sensitivity to shear wave velocity in D'' (5) down to periods of 40s, the Born approximation is sufficiently accurate to allow waveform modelling of Pdiff through large-scale heterogeneities in D'' of up to 5 per cent.
Hydrodynamic waves in films flowing under an inclined plane

NASA Astrophysics Data System (ADS)

Rohlfs, Wilko; Pischke, Philipp; Scheid, Benoit

2017-04-01

This study addresses the fluid dynamics of two-dimensional falling films flowing underneath an inclined plane using the weighted integral boundary layer (WIBL) model and direct numerical simulations (DNSs). Film flows under an inclined plane are subject to hydrodynamic and Rayleigh-Taylor instabilities, leading to the formation of two- and three-dimensional waves, rivulets, and eventually dripping. The latter can only occur in film flows underneath an inclined plane such that the gravitational force acts in a destabilizing manner by pulling liquid into the gaseous atmosphere. The DNSs are performed using the solver interFoam of the open-source code OpenFOAM with a gradient limiter approach that avoids artificial oversharpening of the interface. We find good agreement between the two model approaches for wave amplitude and wave speed irrespectively of the orientation of the gravitational force and before the onset of dripping. The latter cannot be modeled with the WIBL model by nature as it is a single-value model. However, for large-amplitude solitarylike waves, the WIBL model fails to predict the velocity field within the wave, which is confirmed by a balance of viscous dissipation and the change in potential energy. In the wavy film flows, different flow features can occur such as circulating waves, i.e., circulating eddies in the main wave hump, or flow reversal, i.e., rotating vortices in the capillary minima of the wave. A phase diagram for all flow features is presented based on results of the WIBL model. Regarding the transition to circulating waves, we show that a critical ratio between the maximum and substrate film thickness (approximately 2.5) is also universal for film flows underneath inclined planes (independent of wavelength, inclination, viscous dissipation, and Reynolds number).
Variable-permittivity linear inverse problem for the H(sub z)-polarized case

NASA Technical Reports Server (NTRS)

Moghaddam, M.; Chew, W. C.

1993-01-01

The H(sub z)-polarized inverse problem has rarely been studied before due to the complicated way in which the unknown permittivity appears in the wave equation. This problem is equivalent to the acoustic inverse problem with variable density. We have recently reported the solution to the nonlinear variable-permittivity H(sub z)-polarized inverse problem using the Born iterative method. Here, the linear inverse problem is solved for permittivity (epsilon) and permeability (mu) using a different approach which is an extension of the basic ideas of diffraction tomography (DT). The key to solving this problem is to utilize frequency diversity to obtain the required independent measurements. The receivers are assumed to be in the far field of the object, and plane wave incidence is also assumed. It is assumed that the scatterer is weak, so that the Born approximation can be used to arrive at a relationship between the measured pressure field and two terms related to the spatial Fourier transform of the two unknowns, epsilon and mu. The term involving permeability corresponds to monopole scattering and that for permittivity to dipole scattering. Measurements at several frequencies are used and a least squares problem is solved to reconstruct epsilon and mu. It is observed that the low spatial frequencies in the spectra of epsilon and mu produce inaccuracies in the results. Hence, a regularization method is devised to remove this problem. Several results are shown. Low contrast objects for which the above analysis holds are used to show that good reconstructions are obtained for both permittivity and permeability after regularization is applied.
Estimation of spin contamination error in dissociative adsorption of Au2 onto MgO(0 0 1) surface: First application of approximate spin projection (AP) method to plane wave basis

NASA Astrophysics Data System (ADS)

Tada, Kohei; Koga, Hiroaki; Okumura, Mitsutaka; Tanaka, Shingo

2018-06-01

Spin contamination error in the total energy of the Au2/MgO system was estimated using the density functional theory/plane-wave scheme and approximate spin projection methods. This is the first investigation in which the errors in chemical phenomena on a periodic surface are estimated. The spin contamination error of the system was 0.06 eV. This value is smaller than that of the dissociation of Au2 in the gas phase (0.10 eV). This is because of the destabilization of the singlet spin state due to the weakening of the Au-Au interaction caused by the Au-MgO interaction.
Acoustic resonance scattering from a multilayered cylindrical shell with imperfect bonding.

PubMed

Rajabi, M; Hasheminejad, Seyyed M

2009-12-01

The method of wave function expansion is adopted to study the three dimensional scattering of a time-harmonic plane progressive sound field obliquely incident upon a multi-layered hollow cylinder with interlaminar bonding imperfection. For the generality of solution, each layer is assumed to be cylindrically orthotropic. An approximate laminate model in the context of the modal state equations with variable coefficients along with the classical T-matrix solution technique is set up for each layer to solve for the unknown modal scattering and transmission coefficients. A linear spring model is used to describe the interlaminar adhesive bonding whose effects are incorporated into the global transfer matrix by introduction of proper interfacial transfer matrices. Following the classic acoustic resonance scattering theory (RST), the scattered field and response to surface waves are determined by constructing the partial waves and obtaining the non-resonance (backgrounds) and resonance components. The solution is first used to investigate the effect of interlayer imperfection of an air-filled and water submerged bilaminate aluminium cylindrical shell on the resonances associated with various modes of wave propagation (i.e., symmetric/asymmetric Lamb waves, fluid-borne A-type waves, Rayleigh and Whispering Gallery waves) appearing in the backscattered spectrum, according to their polarization and state of stress. An illustrative numerical example is also given for a multi-layered (five-layered) cylindrical shell for which the stiffness of the adhesive interlayers is artificially varied. The sensitivity of resonance frequencies associated with higher mode numbers to the stiffness coefficients is demonstrated to be a good measure of the bonding strength. Limiting cases are considered and fair agreements with solutions available in the literature are established.
Elastic and inelastic scattering of /sup 58/Ni+/sup 208/Pb at bombarding energies from 598 to 1011 MeV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beckerman, M.; Auble, R.L.; Bertrand, F.E.

1987-08-01

High-resolution measurements have been made of elastic and inelastic scattering of /sup 58/Ni+ /sup 208/Pb at four bombarding energies from 10.3 to 17.4 MeV/nucleon. The considerable inelastic strength observed for excitation energies up to at least 7 MeV is dominated by Coulomb-driven quadrupole transitions. Analyses were done using both the distorted-wave Born approximation and coupled-channels models. At the highest bombarding energies the data can be described equally well by distorted-wave Born approximations and coupled channels analyses. We find that B(E2) = 0.062 e/sup 2/b/sup 2/ for the 1.454 MeV 2/sup +/ state in /sup 58/Ni and B(E2) = 0.34 e/supmore » 2/b/sup 2/ for the 4.09 MeV 2/sup +/ state in /sup 208/Pb.« less
Born distorted-wave approximation applied to the H+ + He collisions at intermediate and high energies

NASA Astrophysics Data System (ADS)

Rahmanian, M.; Fathi, R.; Shojaei, F.

2017-11-01

The single-charge transfer process in collision of protons with helium atoms in their ground states is investigated. The model utilizes the second-order three-body Born distorted-wave approximation (BDW-3B) with correct Coulomb boundary conditions to calculate the differential and total cross sections at intermediate and high energies. The role of the passive electrons and electron-electron correlations are studied by comparing our results and the BDW-4B calculations with the complete perturbation potential. The present results are also compared with other theories, and the Thomas scattering mechanism is investigated. The obtained results are also compared with the recent experimental measurements. For the prior differential cross sections, the comparisons show better agreement with the experiments at smaller scattering angles. The agreement between the total cross sections and the BDW-4B results as well as the experimental data is good at higher impact energies.
The He+H¯→He p¯+e+ rearrangement

NASA Astrophysics Data System (ADS)

Todd, Allan C.; Armour, Edward A. G.

2006-06-01

In this paper, we present a summary of our work in progress on calculating cross sections for the He+H¯→He p¯+e+ rearrangement process in He H¯ scattering. This has involved a study of the system He p¯ within the Born-Oppenheimer (BO) approximation using the Rayleigh-Ritz variational method. This work has been reported in [A.C. Todd, E.A.G. Armour, J. Phys. B 38 (2005) 3367] and is summarised here. Similar calculations are in progress for the He+H¯ entrance channel. We intend to use the entrance channel and rearrangement channel wave functions to obtain the cross sections for the rearrangement using the distorted wave Born approximation T-matrix method described elsewhere in these proceedings [E.A.G. Armour, S. Jonsell, Y. Liu, A.C. Todd, these Proceedings, doi:10.1016/j.nimb.2006.01.049].
Multiplane wave imaging increases signal-to-noise ratio in ultrafast ultrasound imaging.

PubMed

Tiran, Elodie; Deffieux, Thomas; Correia, Mafalda; Maresca, David; Osmanski, Bruno-Felix; Sieu, Lim-Anna; Bergel, Antoine; Cohen, Ivan; Pernot, Mathieu; Tanter, Mickael

2015-11-07

Ultrafast imaging using plane or diverging waves has recently enabled new ultrasound imaging modes with improved sensitivity and very high frame rates. Some of these new imaging modalities include shear wave elastography, ultrafast Doppler, ultrafast contrast-enhanced imaging and functional ultrasound imaging. Even though ultrafast imaging already encounters clinical success, increasing even more its penetration depth and signal-to-noise ratio for dedicated applications would be valuable. Ultrafast imaging relies on the coherent compounding of backscattered echoes resulting from successive tilted plane waves emissions; this produces high-resolution ultrasound images with a trade-off between final frame rate, contrast and resolution. In this work, we introduce multiplane wave imaging, a new method that strongly improves ultrafast images signal-to-noise ratio by virtually increasing the emission signal amplitude without compromising the frame rate. This method relies on the successive transmissions of multiple plane waves with differently coded amplitudes and emission angles in a single transmit event. Data from each single plane wave of increased amplitude can then be obtained, by recombining the received data of successive events with the proper coefficients. The benefits of multiplane wave for B-mode, shear wave elastography and ultrafast Doppler imaging are experimentally demonstrated. Multiplane wave with 4 plane waves emissions yields a 5.8 ± 0.5 dB increase in signal-to-noise ratio and approximately 10 mm in penetration in a calibrated ultrasound phantom (0.7 d MHz(-1) cm(-1)). In shear wave elastography, the same multiplane wave configuration yields a 2.07 ± 0.05 fold reduction of the particle velocity standard deviation and a two-fold reduction of the shear wave velocity maps standard deviation. In functional ultrasound imaging, the mapping of cerebral blood volume results in a 3 to 6 dB increase of the contrast-to-noise ratio in deep structures of the rodent brain.
A rational explanation of wave-particle duality of light

NASA Astrophysics Data System (ADS)

Rashkovskiy, S. A.

2013-10-01

The wave-particle duality is a fundamental property of the nature. At the same time, it is one of the greatest mysteries of modern physics. This gave rise to a whole direction in quantum physics - the interpretation of quantum mechanics. The Wiener experiments demonstrating the wave-particle duality of light are discussed. It is shown that almost all interpretations of quantum mechanics allow explaining the double-slit experiments, but are powerless to explain the Wiener experiments. The reason of the paradox, associated with the wave-particle duality is analyzed. The quantum theory consists of two independent parts: (i) the dynamic equations describing the behavior of a quantum object (for example, the Schrodinger or Maxwell equations), and (ii) the Born's rule, the relation between the wave function and the probability of finding the particle at a given point. It is shown that precisely the Born's rule results in paradox in explaining the wave-particle duality. In order to eliminate this paradox, we propose a new rational interpretation of the wave-particle duality and associated new rule, connecting the corpuscular and wave properties of quantum objects. It is shown that this new rational interpretation of the wave-particle duality allows using the classic images of particle and wave in explaining the quantum mechanical and optical phenomena, does not result in paradox in explaining the doubleslit experiments and Wiener experiments, and does not contradict to the modern quantum mechanical concepts. It is shown that the Born's rule follows immediately from proposed new rules as an approximation.
Bumps of the wave structure function in non-Kolmogorov turbulence

NASA Astrophysics Data System (ADS)

Qiao, Chunhong; Lu, Lu; Zhang, Pengfei; Wang, Haitao; Huang, Honghua; Fan, Chengyu

2015-10-01

The analytical expressions for wave structure function of plane and spherical waves are derived both in the viscous dissipation and inertial range. Due to previously research, there is a discrepancy between theoretical results and the experimental datum in viscous dissipation range. In this paper, only considering the inertial range, taking plane waves for example, we give a comparison of results of WSF calculated by the analytical formula obtained in this paper and the numerical calculations of the definition at the fixed parameter (i.e., the generalized exponent α), it can be seen that the two results are in agreement with each other exactly. Based on non-Kolmogorov power spectrum, new characteristics for wave structure function (WSF) have been found for plane and spherical wave models when the different ratio of inner scale l0 and outer scale of turbulence L0 is obtained. In outer scale assumed finite case (i.e., L0 =1m), WSF obtains the maximum when α approximates to 3.3 both for plane and spherical wave models. In outer scale assumed infinite case (i.e., L0 = ∞), the WSF can be sorted into three parts, including two rapid-rising regions (i.e., 3.0 < α < 3.3 and 3.8 < α < 4.0 ) and one gently rising region (i.e., 3.3 < α < 3.8 ).Further, the changes of scaled WSF versus the ratio of separation distance and inner scale ( p/ l0 ) are investigated under mentioned above conditions for two models. In L0 = 1m case, both for plane and spherical waves, the value of α determines the bump position of WSF. In L0 = ∞ case, the bump of scaled WSF disappears when the generalized exponent has large values. The changings of scaled WSF monotonically increase as α increased when the generalized exponent is larger than11/3 for two models. Besides, the properties of spherical waves are similar to plane waves, except which the values of WSF and the scaled WSF are smaller than plane ones.
Gradient-index phononic crystal lens-based enhancement of elastic wave energy harvesting

NASA Astrophysics Data System (ADS)

Tol, S.; Degertekin, F. L.; Erturk, A.

2016-08-01

We explore the enhancement of structure-borne elastic wave energy harvesting, both numerically and experimentally, by exploiting a Gradient-Index Phononic Crystal Lens (GRIN-PCL) structure. The proposed GRIN-PCL is formed by an array of blind holes with different diameters on an aluminum plate, where the blind hole distribution is tailored to obtain a hyperbolic secant gradient profile of refractive index guided by finite-element simulations of the lowest asymmetric mode Lamb wave band diagrams. Under plane wave excitation from a line source, experimentally measured wave field validates the numerical simulation of wave focusing within the GRIN-PCL domain. A piezoelectric energy harvester disk located at the first focus of the GRIN-PCL yields an order of magnitude larger power output as compared to the baseline case of energy harvesting without the GRIN-PCL on the uniform plate counterpart.
Two-dimensional model of the interaction of a plane acoustic wave with nozzle edge and wing trailing edge.

PubMed

Faranosov, Georgy A; Bychkov, Oleg P

2017-01-01

The interaction of a plane acoustic wave with two-dimensional model of nozzle edge and trailing edge is investigated theoretically by means of the Wiener-Hopf technique. The nozzle edge and the trailing edge are simulated by two half-planes with offset edges. Shear layer behind the nozzle edge is represented by a vortex sheet supporting Kelvin-Helmholtz instability waves. The considered configuration combines two well-known models (nozzle edge and trailing edge), and reveals additional interesting physical aspects. To obtain the solution, the matrix Wiener-Hopf equation is solved in conjunction with a requirement that the full Kutta condition is imposed at the edges. Factorization of the kernel matrix is performed by the combination of Padé approximation and the pole removal technique. This procedure is used to obtain numerical results. The results indicate that the diffracted acoustic field may be significantly intensified due to scattering of hydrodynamic instability waves into sound waves provided that the trailing edge is close enough to the vortex sheet. Similar mechanism may be responsible for the intensification of jet noise near a wing.
Pseudopotential plane-wave calculation of the structural properties of yttrium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Y.; Chou, M.Y.

1991-11-01

The structural properties of hexagonal-close-packed yttrium are studied by using the plane-wave basis within the pseudopotential method and local-density-functional approximation. By employing a soft'' pseudopotential proposed by Troullier and Martins, satisfactory convergence is achieved with a plane-wave energy cutoff of 30--40 Ry for this early-transition-metal element. The overall results for the structural properties are in good agreement with experiment. It is found that the charge overlap between core and valence electrons has a substantial effect on the accuracy of the calculated structural properties. Two different calculations are performed with and without the outer-core 4{ital p} orbital included as a valencemore » state. In addition, as found in some other local-density calculations, the uncertainty in the results due to different exchange-correlation energy functionals may not be negligible in transition metals.« less
A standing wave linear ultrasonic motor operating in in-plane expanding and bending modes.

PubMed

Chen, Zhijiang; Li, Xiaotian; Ci, Penghong; Liu, Guoxi; Dong, Shuxiang

2015-03-01

A novel standing wave linear ultrasonic motor operating in in-plane expanding and bending modes was proposed in this study. The stator (or actuator) of the linear motor was made of a simple single Lead Zirconate Titanate (PZT) ceramic square plate (15 × 15 × 2 mm(3)) with a circular hole (D = 6.7 mm) in the center. The geometric parameters of the stator were computed with the finite element analysis to produce in-plane bi-mode standing wave vibration. The calculated results predicted that a driving tip attached at midpoint of one edge of the stator can produce two orthogonal, approximate straight-line trajectories, which can be used to move a slider in linear motion via frictional forces in forward or reverse direction. The investigations showed that the proposed linear motor can produce a six times higher power density than that of a previously reported square plate motor.

Photoelectron wave function in photoionization: plane wave or Coulomb wave?

PubMed

Gozem, Samer; Gunina, Anastasia O; Ichino, Takatoshi; Osborn, David L; Stanton, John F; Krylov, Anna I

2015-11-19

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 photoelectron 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. 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.
Interpretation of ES, CS, and IOS approximations within a translational--internal coupling scheme. IV. ES and IOS molecule--molecule cross sections

DOE Office of Scientific and Technical Information (OSTI.GOV)

Snider, R.F.; Parvatiyar, M.G.

1981-05-15

Properties of energy sudden and infinite order sudden translational--internal reduced S matrices are given for general molecule--molecule collisions. Formal similarities with the distorted wave Born approximation are discussed. Structural simplifications of energy dependent and kinetic cross sections associated with making the ES approximation are described. Conceptual difficulties associated with applying the ES and IOS approximations to kinetic processes dominated by energetically inelastic collisions are pointed out.
Coherence and dimensionality of intense spatiospectral twin beams

NASA Astrophysics Data System (ADS)

Peřina, Jan

2015-07-01

Spatiospectral properties of twin beams at their transition from low to high intensities are analyzed in parametric and paraxial approximations using decomposition into paired spatial and spectral modes. Intensity auto- and cross-correlation functions are determined and compared in the spectral and temporal domains as well as the transverse wave-vector and crystal output planes. Whereas the spectral, temporal, and transverse wave-vector coherence increases with the increasing pump intensity, coherence in the crystal output plane is almost independent of the pump intensity owing to the mode structure in this plane. The corresponding auto- and cross-correlation functions approach each other for larger pump intensities. The entanglement dimensionality of a twin beam is determined with a comparison of several approaches.
A class of reduced-order models in the theory of waves and stability.

PubMed

Chapman, C J; Sorokin, S V

2016-02-01

This paper presents a class of approximations to a type of wave field for which the dispersion relation is transcendental. The approximations have two defining characteristics: (i) they give the field shape exactly when the frequency and wavenumber lie on a grid of points in the (frequency, wavenumber) plane and (ii) the approximate dispersion relations are polynomials that pass exactly through points on this grid. Thus, the method is interpolatory in nature, but the interpolation takes place in (frequency, wavenumber) space, rather than in physical space. Full details are presented for a non-trivial example, that of antisymmetric elastic waves in a layer. The method is related to partial fraction expansions and barycentric representations of functions. An asymptotic analysis is presented, involving Stirling's approximation to the psi function, and a logarithmic correction to the polynomial dispersion relation.
Alignment error of mirror modules of advanced telescope for high-energy astrophysics due to wavefront aberrations

NASA Astrophysics Data System (ADS)

Zocchi, Fabio E.

2017-10-01

One of the approaches that is being tested for the integration of the mirror modules of the advanced telescope for high-energy astrophysics x-ray mission of the European Space Agency consists in aligning each module on an optical bench operated at an ultraviolet wavelength. The mirror module is illuminated by a plane wave and, in order to overcome diffraction effects, the centroid of the image produced by the module is used as a reference to assess the accuracy of the optical alignment of the mirror module itself. Among other sources of uncertainty, the wave-front error of the plane wave also introduces an error in the position of the centroid, thus affecting the quality of the mirror module alignment. The power spectral density of the position of the point spread function centroid is here derived from the power spectral density of the wave-front error of the plane wave in the framework of the scalar theory of Fourier diffraction. This allows the defining of a specification on the collimator quality used for generating the plane wave starting from the contribution to the error budget allocated for the uncertainty of the centroid position. The theory generally applies whenever Fourier diffraction is a valid approximation, in which case the obtained result is identical to that derived by geometrical optics considerations.
Born scattering and inversion sensitivities in viscoelastic transversely isotropic media

NASA Astrophysics Data System (ADS)

Moradi, Shahpoor; Innanen, Kristopher A.

2017-11-01

We analyse the scattering of seismic waves from anisotropic-viscoelastic inclusions using the Born approximation. We consider the specific case of Vertical Transverse Isotropic (VTI) media with low-loss attenuation and weak anisotropy such that second- and higher-order contributions from quality factors and Thomsen parameters are negligible. To accommodate the volume scattering approach, the viscoelastic VTI media is broken into a homogeneous viscoelastic reference medium with distributed inclusions in both viscoelastic and anisotropic properties. In viscoelastic reference media in which all propagations take place, wave modes are of P-wave type, SI-wave type and SII-wave type, all with complex slowness and polarization vectors. We generate expressions for P-to-P, P-to-SI, SI-to-SI and SII-to-SII scattering potentials, and demonstrate that they reduce to previously derived isotropic results. These scattering potential expressions are sensitivity kernels related to the Fréchet derivatives which provide the weights for multiparameter full waveform inversion updates.
Evidence of iridescence in TiO2 nanostructures: An approximation in plane wave expansion method

NASA Astrophysics Data System (ADS)

Quiroz, Heiddy P.; Barrera-Patiño, C. P.; Rey-González, R. R.; Dussan, A.

2016-11-01

Titanium dioxide nanotubes, TiO2 NTs, can be obtained by electrochemical anodization of Titanium sheets. After nanotubes are removed by mechanical stress, residual structures or traces on the surface of titanium sheets can be observed. These traces show iridescent effects. In this paper we carry out both experimental and theoretical study of those interesting and novel optical properties. For the experimental analysis we use angle resolved UV-vis spectroscopy while in the theoretical study is evaluated the photonic spectra using numerical simulations into the frequency-domain and the framework of the wave plane approximation. The iridescent effect is a strong property and independent of the sample. This behavior can be important to design new materials or compounds for several applications such as, cosmetic industry, optoelectronic devices, photocatalysis, sensors, among others.
A differential equation for the Generalized Born radii.

PubMed

Fogolari, Federico; Corazza, Alessandra; Esposito, Gennaro

2013-06-28

The Generalized Born (GB) model offers a convenient way of representing electrostatics in complex macromolecules like proteins or nucleic acids. The computation of atomic GB radii is currently performed by different non-local approaches involving volume or surface integrals. Here we obtain a non-linear second-order partial differential equation for the Generalized Born radius, which may be solved using local iterative algorithms. The equation is derived under the assumption that the usual GB approximation to the reaction field obeys Laplace's equation. The equation admits as particular solutions the correct GB radii for the sphere and the plane. The tests performed on a set of 55 different proteins show an overall agreement with other reference GB models and "perfect" Poisson-Boltzmann based values.
Evaluation of an Approximate Method for Incorporating Floating Docks in Harbor Wave Prediction Models

DTIC Science & Technology

2005-11-25

fact, Koutandos et al. (2004) even now have had to limit their work only to the x–z plane while using a similar approach. In this paper, therefore, we...breakwater Koutandos et al. (2004) have presented data pertaining to transmission coefficients for waves passing a fixed, infinitely long, floating...4. Values of A and B for determining α. Fig. 5. Wave height comparison with data presented in Koutandos et al. (2004). Fig. 6. Wave transmission past
Calculation of total electron excitation cross-sections and partial electron ionization cross-sections for the elements. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Green, T. J.

1973-01-01

Computer programs were used to calculate the total electron excitation cross-section for atoms and the partial ionization cross-section. The approximations to the scattering amplitude used are as follows: (1) Born, Bethe, and Modified Bethe for non-exchange excitation; (2) Ochkur for exchange excitation; and (3) Coulomb-Born of non-exchange ionization. The amplitudes are related to the differential cross-sections which are integrated to give the total excitation (or partial ionization) cross-section for the collision. The atomic wave functions used are Hartree-Fock-Slater functions for bound states and the coulomb wave function for the continuum. The programs are presented and the results are examined.
Joint Services Electronics Program. Appendix

DTIC Science & Technology

1992-11-01

the accu- clude surface waves, creeping waves, multiple racy, convergence, and CPU times for the MM diffractions, shadowing effects , etc. A second ad...Method which is an approximation to the true current J Jn= A /m on the strip. The next section will discuss the - computation of the far zone...to the cavity (0 part of the incident plane wave captured by interior E•,. After a background discussion of the aperture at the open end is divided
Corrections to the one-photon approximation in the 0+-->2+ transition of 12C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paul Gueye; Madeleine Bernheim; J. F. Danel

2001-04-18

Contribution of higher order effects to the one-photon exchange approximation were studied in the first excited state of 12C by comparing inclusive inelastic scattering cross sections of electrons and positrons obtained at the Saclay Linear Accelerator. The data were compared to a distorted wave Born approximation (DWBA)calculation. The results indicate an effect less than 2% within 2sigma, compatible with what was observed in recent elastic scattering measurements.
Second-order Born calculation of coplanar symmetric (e, 2e) process on Mg

NASA Astrophysics Data System (ADS)

Zhang, Yong-Zhi; Wang, Yang; Zhou, Ya-Jun

2014-06-01

The second-order distorted wave Born approximation (DWBA) method is employed to investigate the triple differential cross sections (TDCS) of coplanar doubly symmetric (e, 2e) collisions for magnesium at excess energies of 6 eV-20 eV. Comparing with the standard first-order DWBA calculations, the inclusion of the second-order Born term in the scattering amplitude improves the degree of agreement with experiments, especially for backward scattering region of TDCS. This indicates that the present second-order Born term is capable to give a reasonable correction to DWBA model in studying coplanar symmetric (e, 2e) problems of two-valence-electron target in low energy range.
Electron-Impact Cross Sections for Ground State to np Excitations of Sodium and Potassium.

PubMed

Stone, Philip M; Kim, Yong-Ki

2004-01-01

Cross sections for electron impact excitation of atoms are important for modeling of low temperature plasmas and gases. While there are many experimental and theoretical results for excitation to the first excited states, little information is available for excitation to higher states. We present here calculations of excitations from the ground state to the np levels of sodium (n = 3 through 11) and potassium (n = 4 through 12). We also present a calculation for a transition from the excited sodium level 3p to 3d to show the generality of the method. Scaling formulas developed earlier by Kim [Phys. Rev. A 64, 032713 (2001)] for plane-wave Born cross sections are used. These formulas have been shown to be remarkably accurate yet simple to use. We have used a core polarization potential in a Dirac-Fock wave function code to calculate target atom wave functions and a matching form of the dipole transition operator to calculate oscillator strengths and Born cross sections. The scaled Born results here for excitation to the first excited levels are in very good agreement with experimental and other theoretical data, and the results for excitation to the next few levels are in satisfactory agreement with the limited data available. The present results for excitation to the higher levels are believed to be the only data available.
Rupture dimensions of the 1998 Antarctic Earthquake from low-frequency waves

NASA Astrophysics Data System (ADS)

McGuire, Jeffrey J.; Zhao, Li; Jordan, Thomas H.

2000-08-01

We inverted frequency dependent phase and amplitude measurements from 1st orbit Rayleigh waves at global stations for the 1st and 2nd degree polynomial moments of the stress-glut rate tensor. The higher moments of the slip-rate distribution determine the fault plane and approximate rupture dimensions. The results show strong rupture propagation to the west with an average velocity of the instantaneous centroid of 3.6±.1 km/s. The rupture had a characteristic length of 178±46 km in the east-west direction and a characteristic duration of 48±2 s. The results are consistent with unilateral rupture on the east-west fault plane of the focal mechanism and rule out significant rupture on the north-south nodal plane.
Impulse approximation in nuclear pion production reactions: Absence of a one-body operator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bolton, Daniel R.; Miller, Gerald A.

2011-06-15

The impulse approximation of pion production reactions is studied by developing a relativistic formalism, consistent with that used to define the nucleon-nucleon potential. For plane wave initial states we find that the usual one-body (1B) expression O{sub 1B} is replaced by O{sub 2B}=-iK(m{sub {pi}}/2)O{sub 1B}/m{sub {pi}}, where K(m{sub {pi}}/2) is the sum of all irreducible contributions to nucleon-nucleon scattering with energy transfer of m{sub {pi}}/2. We show that O{sub 2B}{approx_equal}O{sub 1B} for plane wave initial states. For distorted waves, we find that the usual operator is replaced with a sum of two-body operators that are well approximated by the operatormore » O{sub 2B}. Our new formalism solves the (previously ignored) problem of energy transfer forbidding a one-body impulse operator. Using a purely one pion exchange deuteron, the net result is that the impulse amplitude for np{yields}d{pi}{sup 0} at threshold is enhanced by a factor of approximately two. This amplitude is added to the larger ''rescattering'' amplitude and, although experimental data remain in disagreement, the theoretical prediction of the threshold cross section is brought closer to (and in agreement with) the data.« less
Reflection and Transmission of Plane Electromagnetic Waves by a Geologic Layer.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aldridge, David F.

Electric field and magnetic field reflection and transmission responses generated by a plane wave normally incident onto a finite - thickness geologic layer are mathematically derived and numerically evaluated. A thin layer with enhanced electric current conductivity and/or magnetic permeability is a reasonable geophysical representation of a hydraulic fracture inject ed with a high - contrast proppant pack. Both theory and numerics indicate that backward - and forward - scattered electromagnetic wavefields are potentially observable in a field experiment, despite the extreme thinness of a fracture compared to a typical low - frequency electromagnetic wavelength. The First Born Approximation (FBA)more » representation of layer scattering, significant for inversion studies, is shown to be accurate for a thin layer with mild medium parameter (i.e., conductivity, permeability, and per mittivity) contrasts with the surrounding homogeneous wholespace. However, FBA scattering theory breaks down for thick layers and strong parameter contrasts. ACKNOWLEDGEMENTS Sandia National Laboratories is a multi - mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the US Department of Energy's National Nuclear Security Administration under contract DE - AC04 - 94AL85000. This research is conducted under the auspices of CRADA (Cooperative Research and Development Agreement) SC11/01780.00 between Carbo Ceramics Inc. and Sandia National Laboratories. The author acknowledges former Carbo R&D Vic e - President Mr. Chad Cannan and former SNL Geophysics Department manage r Ms. Amy Halloran for their interest i n and support of this work. Technical discussions with Project Manager and Principal Investigator Dr. Chester J. Weiss of the SNL Geophysics Department greatly benefited this work. Dr. Lewis C. Bartel, formerly with S NL and presently a consultant to Carbo Ceramics, provided many useful and intuitive insights, and is acknowledged as the originator of the concept underpinning a recent patent grant (Aldridge and Bartel, 2016) involving electromagnetic wave scattering.« less
Interference effects in phased beam tracing using exact half-space solutions.

PubMed

Boucher, Matthew A; Pluymers, Bert; Desmet, Wim

2016-12-01

Geometrical acoustics provides a correct solution to the wave equation for rectangular rooms with rigid boundaries and is an accurate approximation at high frequencies with nearly hard walls. When interference effects are important, phased geometrical acoustics is employed in order to account for phase shifts due to propagation and reflection. Error increases, however, with more absorption, complex impedance values, grazing incidence, smaller volumes and lower frequencies. Replacing the plane wave reflection coefficient with a spherical one reduces the error but results in slower convergence. Frequency-dependent stopping criteria are then applied to avoid calculating higher order reflections for frequencies that have already converged. Exact half-space solutions are used to derive two additional spherical wave reflection coefficients: (i) the Sommerfeld integral, consisting of a plane wave decomposition of a point source and (ii) a line of image sources located at complex coordinates. Phased beam tracing using exact half-space solutions agrees well with the finite element method for rectangular rooms with absorbing boundaries, at low frequencies and for rooms with different aspect ratios. Results are accurate even for long source-to-receiver distances. Finally, the crossover frequency between the plane and spherical wave reflection coefficients is discussed.
A New Algorithm with Plane Waves and Wavelets for Random Velocity Fields with Many Spatial Scales

NASA Astrophysics Data System (ADS)

Elliott, Frank W.; Majda, Andrew J.

1995-03-01

A new Monte Carlo algorithm for constructing and sampling stationary isotropic Gaussian random fields with power-law energy spectrum, infrared divergence, and fractal self-similar scaling is developed here. The theoretical basis for this algorithm involves the fact that such a random field is well approximated by a superposition of random one-dimensional plane waves involving a fixed finite number of directions. In general each one-dimensional plane wave is the sum of a random shear layer and a random acoustical wave. These one-dimensional random plane waves are then simulated by a wavelet Monte Carlo method for a single space variable developed recently by the authors. The computational results reported in this paper demonstrate remarkable low variance and economical representation of such Gaussian random fields through this new algorithm. In particular, the velocity structure function for an imcorepressible isotropic Gaussian random field in two space dimensions with the Kolmogoroff spectrum can be simulated accurately over 12 decades with only 100 realizations of the algorithm with the scaling exponent accurate to 1.1% and the constant prefactor accurate to 6%; in fact, the exponent of the velocity structure function can be computed over 12 decades within 3.3% with only 10 realizations. Furthermore, only 46,592 active computational elements are utilized in each realization to achieve these results for 12 decades of scaling behavior.
Metastable Bound States of Two-Dimensional Magnetoexcitons in the Lowest Landau Levels Approximation

NASA Astrophysics Data System (ADS)

Moskalenko, S. A.; Khadzhi, P. I.; Podlesny, I. V.; Dumanov, E. V.; Liberman, M. A.; Zubac, I. A.

2017-12-01

The possible existence of the two-dimensional bimagnetoexcitons and metastable bound states formed by two magnetoexcitons with opposite in-plane wave vectors k and -k has been studied. Magnetoexcitons taking part in the formation of molecules look as two electric dipoles with the arms oriented in-plane perpendicular to the respective wave vectors and with the length of the arms d=k(l_0)^2, where l_0 is the magnetic length. Two antiparallel dipoles moving with equal, yet antiparallel, wave vectors have the possibility of moving with equal probability in any direction of the plane, which is determined by the trial wave function of relative motion φ_n(|k|), depending on modulus k. The magnetoexcitons are composed of electrons and holes situated on the lowest Landau levels with the cyclotron energies greater than the binding energy of the 2D Wannier-Mott exciton. The description has been made in Landau gauge. The spin states of two electrons have been chosen in the form of antisymmetric or symmetric combinations with parameter η=+/-1. The effective spins of two heavy holes have been combined in the same resultant spinor states as the spin of the electrons. Because the projections of the both spinor states with η=+/-1 are equal to zero, the influence of the Zeeman splitting effect vanishes. In the case of trial wave function, the maximal density of the magnetoexcitons in the momentum space is concentrated on the in-plane ring. In the approximation of the lowest Landau levels, when the influence of the excited Landau levels is neglected, stable bound states of bimagnetoexcitons do not exist for both spin orientations. Instead, in the case of α=0.5 and Î·=1, a deep metastable bound state with the activation barrier comparable with two magnetoexciton ionization potentials 2I_l has been revealed. In the case of η=-1 and α=3.4, only a shallow metastable bound state can appear.

The propagation of the shock wave from a strong explosion in a plane-parallel stratified medium: the Kompaneets approximation

NASA Astrophysics Data System (ADS)

Olano, C. A.

2009-11-01

Context: Using certain simplifications, Kompaneets derived a partial differential equation that states the local geometrical and kinematical conditions that each surface element of a shock wave, created by a point blast in a stratified gaseous medium, must satisfy. Kompaneets could solve his equation analytically for the case of a wave propagating in an exponentially stratified medium, obtaining the form of the shock front at progressive evolutionary stages. Complete analytical solutions of the Kompaneets equation for shock wave motion in further plane-parallel stratified media were not found, except for radially stratified media. Aims: We aim to analytically solve the Kompaneets equation for the motion of a shock wave in different plane-parallel stratified media that can reflect a wide variety of astrophysical contexts. We were particularly interested in solving the Kompaneets equation for a strong explosion in the interstellar medium of the Galactic disk, in which, due to intense winds and explosions of stars, gigantic gaseous structures known as superbubbles and supershells are formed. Methods: Using the Kompaneets approximation, we derived a pair of equations that we call adapted Kompaneets equations, that govern the propagation of a shock wave in a stratified medium and that permit us to obtain solutions in parametric form. The solutions provided by the system of adapted Kompaneets equations are equivalent to those of the Kompaneets equation. We solved the adapted Kompaneets equations for shock wave propagation in a generic stratified medium by means of a power-series method. Results: Using the series solution for a shock wave in a generic medium, we obtained the series solutions for four specific media whose respective density distributions in the direction perpendicular to the stratification plane are of an exponential, power-law type (one with exponent k=-1 and the other with k =-2) and a quadratic hyperbolic-secant. From these series solutions, we deduced exact solutions for the four media in terms of elemental functions. The exact solution for shock wave propagation in a medium of quadratic hyperbolic-secant density distribution is very appropriate to describe the growth of superbubbles in the Galactic disk. Member of the Carrera del Investigador Científico del CONICET, Argentina.
Electromagnetic wave scattering from some vegetation samples

NASA Technical Reports Server (NTRS)

Karam, Mostafa A.; Fung, Adrian K.; Antar, Yahia M.

1988-01-01

For an incident plane wave, the field inside a thin scatterer (disk and needle) is estimated by the generalized Rayleigh-Gans (GRG) approximation. This leads to a scattering amplitude tensor equal to that obtained via the Rayleigh approximation (dipole term) with a modifying function. For a finite-length cylinder the inner field is estimated by the corresponding field for the same cylinder of infinite lenght. The effects of different approaches in estimating the field inside the scatterer on the backscattering cross section are illustrated numerically for a circular disk, a needle, and a finite-length cylinder as a function of the wave number and the incidence angle. Finally, the modeling predictions are compared with measurements.
A plane wave source with minimal harmonic distortion for investigating nonlinear acoustic properties

PubMed Central

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
Matter-wave diffraction approaching limits predicted by Feynman path integrals for multipath interference

NASA Astrophysics Data System (ADS)

Barnea, A. Ronny; Cheshnovsky, Ori; Even, Uzi

2018-02-01

Interference experiments have been paramount in our understanding of quantum mechanics and are frequently the basis of testing the superposition principle in the framework of quantum theory. In recent years, several studies have challenged the nature of wave-function interference from the perspective of Born's rule—namely, the manifestation of so-called high-order interference terms in a superposition generated by diffraction of the wave functions. Here we present an experimental test of multipath interference in the diffraction of metastable helium atoms, with large-number counting statistics, comparable to photon-based experiments. We use a variation of the original triple-slit experiment and accurate single-event counting techniques to provide a new experimental bound of 2.9 ×10-5 on the statistical deviation from the commonly approximated null third-order interference term in Born's rule for matter waves. Our value is on the order of the maximal contribution predicted for multipath trajectories by Feynman path integrals.
PARTICLE DISPLACEMENTS ON THE WALL OF A BOREHOLE FROM INCIDENT PLANE WAVES.

USGS Publications Warehouse

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.
Partial Wave Dispersion Relations: Application to Electron-Atom Scattering

NASA Technical Reports Server (NTRS)

Temkin, A.; Drachman, Richard J.

1999-01-01

In this Letter we propose the use of partial wave dispersion relations (DR's) as the way of solving the long-standing problem of correctly incorporating exchange in a valid DR for electron-atom scattering. In particular a method is given for effectively calculating the contribution of the discontinuity and/or poles of the partial wave amplitude which occur in the negative E plane. The method is successfully tested in three cases: (i) the analytically solvable exponential potential, (ii) the Hartree potential, and (iii) the S-wave exchange approximation for electron-hydrogen scattering.
Linear Elastic Waves - Series: Cambridge Texts in Applied Mathematics (No. 26)

NASA Astrophysics Data System (ADS)

Harris, John G.

2001-10-01

Wave propagation and scattering are among the most fundamental processes that we use to comprehend the world around us. While these processes are often very complex, one way to begin to understand them is to study wave propagation in the linear approximation. This is a book describing such propagation using, as a context, the equations of elasticity. Two unifying themes are used. The first is that an understanding of plane wave interactions is fundamental to understanding more complex wave interactions. The second is that waves are best understood in an asymptotic approximation where they are free of the complications of their excitation and are governed primarily by their propagation environments. The topics covered include reflection, refraction, the propagation of interfacial waves, integral representations, radiation and diffraction, and propagation in closed and open waveguides. Linear Elastic Waves is an advanced level textbook directed at applied mathematicians, seismologists, and engineers. Aimed at beginning graduate students Includes examples and exercises Has application in a wide range of disciplines
Inner Core Anisotropy: Can Seismic Observations be Reconciled with Ab Initio Calculations of Elasticity?

NASA Astrophysics Data System (ADS)

Song, X.; Jordan, T. H.

2016-12-01

Body-wave and normal-mode observations have revealed an inner-core structure that is radially layered, axially anisotropic, and hemispherically asymmetric. Previous theoretical studies have examined the consistency of these features with the elasticity of iron crystals thought to dominate inner-core composition, but a fully consistent model has been elusive. Here we compare the seismic observation with effective-medium models derived from ab initio calculations of the elasticity tensors for hcp-Fe and bcc-Fe. Our estimates are based on Jordan's (GJI, 2015) effective medium theory, which is derived from a self-consistent, second-order Born approximation. The theory provides closed-form expressions for the effective elastic parameters of 3D anisotropic, heterogeneous media in which the local anisotropy is a constant hexagonal stiffness tensor C stochastically oriented about a constant symmetry axis \\hat{s} and the statistics of the small-scale heterogeneities are transversely isotropic in the plane perpendicular to \\hat{s}. The stochastic model is then described by a dimensionless "aspect ratio of the heterogeneity", 0 ≤ η < ∞, and a dimensionless "orientation ratio of the anisotropy", 0 ≤ ξ < ∞. The latter determines the degree to which the axis of C is aligned with \\hat{s}. We compute the loci of models with \\hat{s} oriented along the Earth's rotational axis ( \\hat{s} = north) by varying ξ and η for various ab initio estimates of C. We show that a lot of widely used estimates of C are inconsistent with most published normal-mode models of inner-core anisotropy. In particular, if the P-wave fast axis aligns with the rotational axis, which is required to satisfy the body-wave observations, then these hcp-Fe models predict that the fast polarization of the S waves is in the plane perpendicular to \\hat{s}, which disagrees with most normal-mode models. We have attempted to resolve this discrepancy by examining alternative hcp-Fe models, including radially anisotropic distributions of stochastic anisotropy and heterogeneity (i.e., where \\hat{s} = \\hat{r}), as well as bcc-Fe models. Our calculations constrain the form of C needed to satisfy the seismological inferences.
First principles calculation of thermo-mechanical properties of thoria using Quantum ESPRESSO

NASA Astrophysics Data System (ADS)

Malakkal, Linu; Szpunar, Barbara; Zuniga, Juan Carlos; Siripurapu, Ravi Kiran; Szpunar, Jerzy A.

2016-05-01

In this work, we have used Quantum ESPRESSO (QE), an open source first principles code, based on density-functional theory, plane waves, and pseudopotentials, along with quasi-harmonic approximation (QHA) to calculate the thermo-mechanical properties of thorium dioxide (ThO2). Using Python programming language, our group developed qe-nipy-advanced, an interface to QE, which can evaluate the structural and thermo-mechanical properties of materials. We predicted the phonon contribution to thermal conductivity (kL) using the Slack model. We performed the calculations within local density approximation (LDA) and generalized gradient approximation (GGA) with the recently proposed version for solids (PBEsol). We employed a Monkhorst-Pack 5 × 5 × 5 k-points mesh in reciprocal space with a plane wave cut-off energy of 150 Ry to obtain the convergence of the structure. We calculated the dynamical matrices of the lattice on a 4 × 4 × 4 mesh. We have predicted the heat capacity, thermal expansion and the phonon contribution to thermal conductivity, as a function of temperature up to 1400K, and compared them with the previous work and known experimental results.
Pulse wave imaging using coherent compounding in a phantom and in vivo

NASA Astrophysics Data System (ADS)

Zacharias Apostolakis, Iason; McGarry, Matthew D. J.; Bunting, Ethan A.; Konofagou, Elisa E.

2017-03-01

Pulse wave velocity (PWV) is a surrogate marker of arterial stiffness linked to cardiovascular morbidity. Pulse wave imaging (PWI) is a technique developed by our group for imaging the pulse wave propagation in vivo. PWI requires high temporal and spatial resolution, which conventional ultrasonic imaging is unable to simultaneously provide. Coherent compounding is known to address this tradeoff and provides full aperture images at high frame rates. This study aims to implement PWI using coherent compounding within a GPU-accelerated framework. The results of the implemented method were validated using a silicone phantom against static mechanical testing. Reproducibility of the measured PWVs was assessed in the right common carotid of six healthy subjects (n = 6) approximately 10-15 mm before the bifurcation during two cardiac cycles over the course of 1-3 d. Good agreement of the measured PWVs (3.97 ± 1.21 m s-1, 4.08 ± 1.15 m s-1, p = 0.74) was obtained. The effects of frame rate, transmission angle and number of compounded plane waves on PWI performance were investigated in the six healthy volunteers. Performance metrics such as the reproducibility of the PWVs, the coefficient of determination (r 2), the SNR of the PWI axial wall velocities (\\text{SN}{{\\text{R}}{{\\text{v}_{\\text{PWI}}}}} ) and the percentage of lateral positions where the pulse wave appears to arrive at the same time-point, indicating inadequacy of the temporal resolution (i.e. temporal resolution misses) were used to evaluate the effect of each parameter. Compounding plane waves transmitted at 1° increments with a linear array yielded optimal performance, generating significantly higher r 2 and \\text{SN}{{\\text{R}}{{\\text{v}_{\\text{PWI}}}}} values (p ⩽ 0.05). Higher frame rates (⩾1667 Hz) produced improvements with significant gains in the r 2 coefficient (p ⩽ 0.05) and significant increase in both r 2 and \\text{SN}{{\\text{R}}{{\\text{v}_{\\text{PWI}}}}} from single plane wave imaging to 3-plane wave compounding (p ⩽ 0.05). Optimal performance was established at 2778 Hz with 3 plane waves and at 1667 Hz with 5 plane waves.
Single-scatter vector-wave scattering from surfaces with infinite slopes using the Kirchhoff approximation.

PubMed

Bruce, Neil C

2008-08-01

This paper presents a new formulation of the 3D Kirchhoff approximation that allows calculation of the scattering of vector waves from 2D rough surfaces containing structures with infinite slopes. This type of surface has applications, for example, in remote sensing and in testing or imaging of printed circuits. Some preliminary calculations for rectangular-shaped grooves in a plane are presented for the 2D surface method and are compared with the equivalent 1D surface calculations for the Kirchhoff and integral equation methods. Good agreement is found between the methods.
Vortices for K-shell ionization of carbon by electron impact

NASA Astrophysics Data System (ADS)

Ward, S. J.; Macek, J. H.

2014-05-01

Using the Coulomb-Born approximation, we obtained a deep minimum in the TDCS for K-shell ionization of carbon by electron impact. The minimum is due to a vortex in the velocity field. We considered the electron to be ejected in the scattering plane, which we took to be the xz -plane. The minimum was obtained for the kinematics of an incident energy Ei = 1801 . 2 eV , scattering angle θf =4° , energy of ejected electron Ek = 5 . 5 eV , and angle of the ejected electron θk =239° . We analyzed the importance of various multipole components in an expansion of the Coulomb-Born T-matrix. We also considered the electron ejected out of the scattering plane for Ei = 1801 . 2 eV and θf =4° and located the positions of vortices for small but nonzero values of ky, the y - component of the momentum of the ejected electron. We constructed the vortex line for the kinematics of Ei = 1801 . 2 eV and θf =4° . S. J. W. and J. H. M. acknowledge support from NSF under grant no. PHYS- 0968638 and from D.O.E. under grant number DE-FG02-02ER15283, respectively.
Factorization breaking of A d T for polarized deuteron targets in a relativistic framework

DOE PAGES

Jeschonnek, Sabine; Van Orden, J. W.

2017-04-17

We discuss the possible factorization of the tensor asymmetrymore » $$A^T_d$$ measured for polarized deuteron targets within a relativistic framework. We define a reduced asymmetry and find that factorization holds only in plane wave impulse approximation and if $p$-waves are neglected. Our numerical results show a strong factorization breaking once final state interactions are included. We also compare the $d$-wave content of the wave functions with the size of the factored, reduced asymmetry and find that there is no systematic relationship of this quantity to the d-wave probability of the various wave functions.« less
A numerical analysis of the Born approximation for image formation modeling of differential interference contrast microscopy for human embryos

NASA Astrophysics Data System (ADS)

Trattner, Sigal; Feigin, Micha; Greenspan, Hayit; Sochen, Nir

2008-03-01

The differential interference contrast (DIC) microscope is commonly used for the visualization of live biological specimens. It enables the view of the transparent specimens while preserving their viability, being a non-invasive modality. Fertility clinics often use the DIC microscope for evaluation of human embryos quality. Towards quantification and reconstruction of the visualized specimens, an image formation model for DIC imaging is sought and the interaction of light waves with biological matter is examined. In many image formation models the light-matter interaction is expressed via the first Born approximation. The validity region of this approximation is defined in a theoretical bound which limits its use to very small specimens with low dielectric contrast. In this work the Born approximation is investigated via the Helmholtz equation, which describes the interaction between the specimen and light. A solution on the lens field is derived using the Gaussian Legendre quadrature formulation. This numerical scheme is considered both accurate and efficient and has shortened significantly the computation time as compared to integration methods that required a great amount of sampling for satisfying the Whittaker - Shannon sampling theorem. By comparing the numerical results with the theoretical values it is shown that the theoretical bound is not directly relevant to microscopic imaging and is far too limiting. The numerical exhaustive experiments show that the Born approximation is inappropriate for modeling the visualization of thick human embryos.
The effect of density fluctuations on electron cyclotron beam broadening and implications for ITER

NASA Astrophysics Data System (ADS)

Snicker, A.; Poli, E.; Maj, O.; Guidi, L.; Köhn, A.; Weber, H.; Conway, G.; Henderson, M.; Saibene, G.

2018-01-01

We present state-of-the-art computations of propagation and absorption of electron cyclotron waves, retaining the effects of scattering due to electron density fluctuations. In ITER, injected microwaves are foreseen to suppress neoclassical tearing modes (NTMs) by driving current at the q=2 and q=3/2 resonant surfaces. Scattering of the beam can spoil the good localization of the absorption and thus impair NTM control capabilities. A novel tool, the WKBeam code, has been employed here in order to investigate this issue. The code is a Monte Carlo solver for the wave kinetic equation and retains diffraction, full axisymmetric tokamak geometry, determination of the absorption profile and an integral form of the scattering operator which describes the effects of turbulent density fluctuations within the limits of the Born scattering approximation. The approach has been benchmarked against the paraxial WKB code TORBEAM and the full-wave code IPF-FDMC. In particular, the Born approximation is found to be valid for ITER parameters. In this paper, we show that the radiative transport of EC beams due to wave scattering in ITER is diffusive unlike in present experiments, thus causing up to a factor of 2-4 broadening in the absorption profile. However, the broadening depends strongly on the turbulence model assumed for the density fluctuations, which still has large uncertainties.
Electromagnetic backscattering from a random distribution of lossy dielectric scatterers

NASA Technical Reports Server (NTRS)

Lang, R. H.

1980-01-01

Electromagnetic backscattering from a sparse distribution of discrete lossy dielectric scatterers occupying a region 5 was studied. The scatterers are assumed to have random position and orientation. Scattered fields are calculated by first finding the mean field and then by using it to define an equivalent medium within the volume 5. The scatterers are then viewed as being embedded in the equivalent medium; the distorted Born approximation is then used to find the scattered fields. This technique represents an improvement over the standard Born approximation since it takes into account the attenuation of the incident and scattered waves in the equivalent medium. The method is used to model a leaf canopy when the leaves are modeled by lossy dielectric discs.
Waveform inversion of mantle Love waves: The born seismogram approach

NASA Technical Reports Server (NTRS)

Tanimoto, T.

1983-01-01

Normal mode theory, extended to the slightly laterally heterogeneous Earth by the first-order Born approximation, is applied to the waveform inversion of mantle Love waves (200-500 sec) for the Earth's lateral heterogeneity at l=2 and a spherically symmetric anelasticity (Q sub mu) structure. The data are from the Global Digital Seismograph Network (GDSN). The l=2 pattern is very similar to the results of other studies that used either different methods, such as phase velocity measurements and multiplet location measurements, or a different data set, such as mantle Rayleigh waves from different instruments. The results are carefully analyzed for variance reduction and are most naturally explained by heterogeneity in the upper 420 km. Because of the poor resolution of the data set for the deep interior, however, a fairly large heterogeneity in the transition zones, of the order of up to 3.5% in shear wave velocity, is allowed. It is noteworthy that Love waves of this period range can not constrain the structure below 420 km and thus any model presented by similar studies below this depth are likely to be constrained by Rayleigh waves (spheroidal modes) only.
Waveform inversion of mantle Love waves - The Born seismogram approach

NASA Technical Reports Server (NTRS)

Tanimoto, T.

1984-01-01

Normal mode theory, extended to the slightly laterally heterogeneous earth by the first-order Born approximation, is applied to the waveform inversion of mantle Love waves (200-500 sec) for the earth's lateral heterogeneity at l = 2 and a spherically symmetric anelasticity (Q sub mu) structure. The data are from the Global Digital Seismograph Network (GDSN). The l = 2 pattern is very similar to the results of other studies that used either different methods, such as phase velocity measurements and multiplet location measurements, or a different data set, such as mantle Rayleigh waves from different instruments. The results are carefully analyzed for variance reduction and are most naturally explained by heterogeneity in the upper 420 km. Because of the poor resolution of the data set for the deep interior, however, a fairly large heterogeneity in the transition zones, of the order of up to 3.5 percent in shear wave velocity, is allowed. It is noteworthy that Love waves of this period range can not constrain the structure below 420 km and thus any model presented by similar studies below this depth are likely to be constrained by Rayleigh waves (spheroidal modes) only.
Scattering of electromagnetic waves from a half-space of randomly distributed discrete scatterers and polarized backscattering ratio law

NASA Technical Reports Server (NTRS)

Zhu, P. Y.

1991-01-01

The effective-medium approximation is applied to investigate scattering from a half-space of randomly and densely distributed discrete scatterers. Starting from vector wave equations, an approximation, called effective-medium Born approximation, a particular way, treating Green's functions, and special coordinates, of which the origin is set at the field point, are used to calculate the bistatic- and back-scatterings. An analytic solution of backscattering with closed form is obtained and it shows a depolarization effect. The theoretical results are in good agreement with the experimental measurements in the cases of snow, multi- and first-year sea-ice. The root product ratio of polarization to depolarization in backscattering is equal to 8; this result constitutes a law about polarized scattering phenomena in the nature.
Highly parallel implementation of non-adiabatic Ehrenfest molecular dynamics

NASA Astrophysics Data System (ADS)

Kanai, Yosuke; Schleife, Andre; Draeger, Erik; Anisimov, Victor; Correa, Alfredo

2014-03-01

While the adiabatic Born-Oppenheimer approximation tremendously lowers computational effort, many questions in modern physics, chemistry, and materials science require an explicit description of coupled non-adiabatic electron-ion dynamics. Electronic stopping, i.e. the energy transfer of a fast projectile atom to the electronic system of the target material, is a notorious example. We recently implemented real-time time-dependent density functional theory based on the plane-wave pseudopotential formalism in the Qbox/qb@ll codes. We demonstrate that explicit integration using a fourth-order Runge-Kutta scheme is very suitable for modern highly parallelized supercomputers. Applying the new implementation to systems with hundreds of atoms and thousands of electrons, we achieved excellent performance and scalability on a large number of nodes both on the BlueGene based ``Sequoia'' system at LLNL as well as the Cray architecture of ``Blue Waters'' at NCSA. As an example, we discuss our work on computing the electronic stopping power of aluminum and gold for hydrogen projectiles, showing an excellent agreement with experiment. These first-principles calculations allow us to gain important insight into the the fundamental physics of electronic stopping.

Comparisons of Calculations with PARTRAC and NOREC: Transport of Electrons in Liquid Water

PubMed Central

Dingfelder, M.; Ritchie, R. H.; Turner, J. E.; Friedland, W.; Paretzke, H. G.; Hamm, R. N.

2013-01-01

Monte Carlo computer models that simulate the detailed, event-by-event transport of electrons in liquid water are valuable for the interpretation and understanding of findings in radiation chemistry and radiation biology. Because of the paucity of experimental data, such efforts must rely on theoretical principles and considerable judgment in their development. Experimental verification of numerical input is possible to only a limited extent. Indirect support for model validity can be gained from a comparison of details between two independently developed computer codes as well as the observable results calculated with them. In this study, we compare the transport properties of electrons in liquid water using two such models, PARTRAC and NOREC. Both use interaction cross sections based on plane-wave Born approximations and a numerical parameterization of the complex dielectric response function for the liquid. The models are described and compared, and their similarities and differences are highlighted. Recent developments in the field are discussed and taken into account. The calculated stopping powers, W values, and slab penetration characteristics are in good agreement with one another and with other independent sources. PMID:18439039
Low-energy proton induced M X-ray production cross sections for 70Yb, 81Tl and 82Pb

NASA Astrophysics Data System (ADS)

Shehla; Mandal, A.; Kumar, Ajay; Roy Chowdhury, M.; Puri, Sanjiv; Tribedi, L. C.

2018-07-01

The cross sections for production of Mk (k = Mξ, Mαβ, Mγ, Mm1) X-rays of 70Yb, 81Tl and 82Pb induced by 50-250 keV protons have been measured in the present work. The experimental cross sections have been compared with the earlier reported values and those calculated using the ionization cross sections based on the ECPSSR (Perturbed (P) stationary(S) state(S), incident ion energy (E) loss, Coulomb (C) deflection and relativistic (R) correction) model, the X-ray emission rates based on the Dirac-Fock model, the fluorescence and Coster-Kronig yields based on the Dirac-Hartree-Slater (DHS) model. In addition, the present measured proton induced X-ray production cross sections have also been compared with those calculated using the Dirac-Hartree-Slater (DHS) model based ionization cross sections and those based on the Plane wave Born Approximation (PWBA). The measured M X-ray production cross sections are, in general, found to be higher than the ECPSSR and DHS model based values and lower than the PWBA model based cross sections.
Semiclassical Origin of Superdeformed Shell Structure in the Spheroidal Cavity Model

NASA Astrophysics Data System (ADS)

Arita, K.; Sugita, A.; Matsuyanagi, K.

1998-12-01

Classical periodic orbits responsible for emergence of the superdeformed shell structures of single-particle motion in spheroidal cavities are identified and their relative contributions to the shell structures are evaluated. Both prolate and oblate superdeformations (axis ratio approximately 2:1) as well as prolate hyperdeformation (axis ratio approximately 3:1) are investigated. Fourier transforms of quantum spectra clearly show that three-dimensional periodic orbits born out of bifurcations of planar orbits in the equatorial plane become predominant at large prolate deformations, while butterfly-shaped planar orbits bifurcated from linear orbits along the minor axis are important at large oblate deformations.
Time-dependent calculations of transfer ionization by fast proton-helium collision in one-dimensional kinematics

NASA Astrophysics Data System (ADS)

Serov, Vladislav V.; Kheifets, A. S.

2014-12-01

We analyze a transfer ionization (TI) reaction in the fast proton-helium collision H++He →H0+He2 ++ e- by solving a time-dependent Schrödinger equation (TDSE) under the classical projectile motion approximation in one-dimensional kinematics. In addition, we construct various time-independent analogs of our model using lowest-order perturbation theory in the form of the Born series. By comparing various aspects of the TDSE and the Born series calculations, we conclude that the recent discrepancies of experimental and theoretical data may be attributed to deficiency of the Born models used by other authors. We demonstrate that the correct Born series for TI should include the momentum-space overlap between the double-ionization amplitude and the wave function of the transferred electron.
Energy propagation by transverse waves in multiple flux tube systems using filling factors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Doorsselaere, T.; Gijsen, S. E.; Andries, J.

2014-11-01

In the last few years, it has been found that transverse waves are present at all times in coronal loops or spicules. Their energy has been estimated with an expression derived for bulk Alfvén waves in homogeneous media, with correspondingly uniform wave energy density and flux. The kink mode, however, is localized in space with the energy density and flux dependent on the position in the cross-sectional plane. The more relevant quantities for the kink mode are the integrals of the energy density and flux over the cross-sectional plane. The present paper provides an approximation to the energy propagated bymore » kink modes in an ensemble of flux tubes by means of combining the analysis of single flux tube kink oscillations with a filling factor for the tube cross-sectional area. This finally allows one to compare the expressions for energy flux of Alfvén waves with an ensemble of kink waves. We find that the correction factor for the energy in kink waves, compared to the bulk Alfvén waves, is between f and 2f, where f is the density filling factor of the ensemble of flux tubes.« less
Total Born approximation cross sections for single electron loss by atoms and ions colliding with atoms

NASA Technical Reports Server (NTRS)

Rule, D. W.

1977-01-01

The first born approximation (FBA) is applied to the calculation of single electron loss cross sections for various ions and atoms containing from one to seven electrons. Screened hydrogenic wave functions were used for the states of the electron ejected from the projectile, and Hartree-Fock elastic and incoherent scattering factors were used to describe the target. The effect of the target atom on the scaling of projectile ionization cross sections with respect to the projectile nuclear charge was explored in the case of hydrogen-like ions. Scaling of the cross section with respect to the target nuclear charge for electron loss by Fe (+25) in collision with neutral atoms ranging from H to Fe is also examined. These results were compared to those of the binary encounter approximation and to the FBA for the case of ionization by completely stripped target ions.
CYLINDRICAL WAVES OF FINITE AMPLITUDE IN DISSIPATIVE MEDIUM (in Russian)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Naugol'nykh, K.A.; Soluyan, S.I.; Khokhlov, R.V.

1962-07-01

Propagation of diverging and converging cylindrical waves in a nonlinear, viscous, heat conducting medium is analyzed using approximation methods. The KrylovBogolyubov method was used for small Raynold's numbers, and the method of S. I. Soluyan et al. (Vest. Mosk. Univ. ser. phys. and astronomy 3, 52-81, 1981), was used for large Raynold's numbers. The formation and dissipation of shock fronts and spatial dimensions of shock phenomena were analyzed. It is shown that the problem of finiteamplitude cylindrical wave propagation is identical to the problem of plane wave propagations in a medium with variable viscosity. (tr-auth)
Few-body quark dynamics for doubly heavy baryons and tetraquarks

NASA Astrophysics Data System (ADS)

Richard, Jean-Marc; Valcarce, Alfredo; Vijande, Javier

2018-03-01

We discuss the adequate treatment of the three- and four-body dynamics for the quark model picture of double-charm baryons and tetraquarks. We stress that the variational and Born-Oppenheimer approximations give energies very close to the exact ones, while the diquark approximation might be somewhat misleading. The Hall-Post inequalities also provide very useful lower bounds that exclude the possibility of stable tetraquarks for some mass ratios and some color wave functions.
Emissivity of half-space random media. [in passive remote sensing

NASA Technical Reports Server (NTRS)

Tsang, L.; Kong, J. A.

1976-01-01

Scattering of electromagnetic waves by a half-space random medium with three-dimensional correlation functions is studied with the Born approximation. The emissivity is calculated from a simple integral and is illustrated for various cases. The results are valid over a wavelength range smaller or larger than the correlation lengths.
New approach to description of (d,xn) spectra at energies below 50 MeV in Monte Carlo simulation by intra-nuclear cascade code with Distorted Wave Born Approximation

NASA Astrophysics Data System (ADS)

Hashimoto, S.; Iwamoto, Y.; Sato, T.; Niita, K.; Boudard, A.; Cugnon, J.; David, J.-C.; Leray, S.; Mancusi, D.

2014-08-01

A new approach to describing neutron spectra of deuteron-induced reactions in the Monte Carlo simulation for particle transport has been developed by combining the Intra-Nuclear Cascade of Liège (INCL) and the Distorted Wave Born Approximation (DWBA) calculation. We incorporated this combined method into the Particle and Heavy Ion Transport code System (PHITS) and applied it to estimate (d,xn) spectra on natLi, 9Be, and natC targets at incident energies ranging from 10 to 40 MeV. Double differential cross sections obtained by INCL and DWBA successfully reproduced broad peaks and discrete peaks, respectively, at the same energies as those observed in experimental data. Furthermore, an excellent agreement was observed between experimental data and PHITS-derived results using the combined method in thick target neutron yields over a wide range of neutron emission angles in the reactions. We also applied the new method to estimate (d,xp) spectra in the reactions, and discussed the validity for the proton emission spectra.
Lamb Wave Assessment of Fiber Volume Fraction in Composites

NASA Technical Reports Server (NTRS)

Seale, Michael D.; Smith, Barry T.; Prosser, W. H.; Zalameda, Joseph N.

1998-01-01

Among the various techniques available, ultrasonic Lamb waves offer a convenient method of examining composite materials. Since the Lamb wave velocity depends on the elastic properties of a material, an effective tool exists to evaluate composites by measuring the velocity of these waves. Lamb waves can propagate over long distances and are sensitive to the desired in-plane elastic properties of the material. This paper discusses a study in which Lamb waves were used to examine fiber volume fraction variations of approximately 0.40-0.70 in composites. The Lamb wave measurements were compared to fiber volume fractions obtained from acid digestion tests. Additionally, a model to predict the fiber volume fraction from Lamb wave velocity values was evaluated.
Diffraction and geometrical optical transfer functions: calculation time comparison

NASA Astrophysics Data System (ADS)

Díaz, José Antonio; Mahajan, Virendra N.

2017-08-01

In a recent paper, we compared the diffraction and geometrical optical transfer functions (OTFs) of an optical imaging system, and showed that the GOTF approximates the DOTF within 10% when a primary aberration is about two waves or larger [Appl. Opt., 55, 3241-3250 (2016)]. In this paper, we determine and compare the times to calculate the DOTF by autocorrelation or digital autocorrelation of the pupil function, and by a Fourier transform (FT) of the point-spread function (PSF); and the GOTF by a FT of the geometrical PSF and its approximation, the spot diagram. Our starting point for calculating the DOTF is the wave aberrations of the system in its pupil plane, and the ray aberrations in the image plane for the GOTF. The numerical results for primary aberrations and a typical imaging system show that the direct integrations are slow, but the calculation of the DOTF by a FT of the PSF is generally faster than the GOTF calculation by a FT of the spot diagram.
Efficient Calculation of Exact Exchange Within the Quantum Espresso Software Package

NASA Astrophysics Data System (ADS)

Barnes, Taylor; Kurth, Thorsten; Carrier, Pierre; Wichmann, Nathan; Prendergast, David; Kent, Paul; Deslippe, Jack

Accurate simulation of condensed matter at the nanoscale requires careful treatment of the exchange interaction between electrons. In the context of plane-wave DFT, these interactions are typically represented through the use of approximate functionals. Greater accuracy can often be obtained through the use of functionals that incorporate some fraction of exact exchange; however, evaluation of the exact exchange potential is often prohibitively expensive. We present an improved algorithm for the parallel computation of exact exchange in Quantum Espresso, an open-source software package for plane-wave DFT simulation. Through the use of aggressive load balancing and on-the-fly transformation of internal data structures, our code exhibits speedups of approximately an order of magnitude for practical calculations. Additional optimizations are presented targeting the many-core Intel Xeon-Phi ``Knights Landing'' architecture, which largely powers NERSC's new Cori system. We demonstrate the successful application of the code to difficult problems, including simulation of water at a platinum interface and computation of the X-ray absorption spectra of transition metal oxides.
Analysis of fluid-structure interaction in a frame pipe undergoing plastic deformations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khamlichi, A.; Jezequel, L.; Jacques, Y.

1995-11-01

Water hammer pressure waves of sufficiently large magnitude can cause plastic flexural deformations in a frame pipe. In this study, the authors propose a modelization of this problem based on plane wave approximation for the fluid equations and approximation of the structure motion by a single-degree-of-freedom elastic-plastic oscillator. Direct analytical integration of elastic-plastic equations through pipe sections, then over the pipe length is performed in order to identify the oscillator parameters. Comparison of the global load-displacement relationship obtained with the finite element solution was considered and has shown good agreement. Fluid-structure coupling is achieved by assuming elbows to act likemore » plane monopole sources, where localized jumps of fluid velocity occur and where net pressure forces are exerted on the structure. The authors have applied this method to analyze the fluid-structure interaction in this range of deformations. Energy exchange between the fluid and the structure and energy dissipation are quantified.« less
Theory of dissociative tunneling ionization

NASA Astrophysics Data System (ADS)

Svensmark, Jens; Tolstikhin, Oleg I.; Madsen, Lars Bojer

2016-05-01

We present a theoretical study of the dissociative tunneling ionization process. Analytic expressions for the nuclear kinetic energy distribution of the ionization rates are derived. A particularly simple expression for the spectrum is found by using the Born-Oppenheimer (BO) approximation in conjunction with the reflection principle. These spectra are compared to exact non-BO ab initio spectra obtained through model calculations with a quantum mechanical treatment of both the electronic and nuclear degrees of freedom. In the regime where the BO approximation is applicable, imaging of the BO nuclear wave function is demonstrated to be possible through reverse use of the reflection principle, when accounting appropriately for the electronic ionization rate. A qualitative difference between the exact and BO wave functions in the asymptotic region of large electronic distances is shown. Additionally, the behavior of the wave function across the turning line is seen to be reminiscent of light refraction. For weak fields, where the BO approximation does not apply, the weak-field asymptotic theory describes the spectrum accurately.
Electromagnetic and scalar diffraction by a right-angled wedge with a uniform surface impedance

NASA Technical Reports Server (NTRS)

Hwang, Y. M.

1974-01-01

The diffraction of an electromagnetic wave by a perfectly-conducting right-angled wedge with one surface covered by a dielectric slab or absorber is considered. The effect of the coated surface is approximated by a uniform surface impedance. The solution of the normally incident electromagnetic problem is facilitated by introducing two scalar fields which satisfy a mixed boundary condition on one surface of the wedge and a Neumann of Dirichlet boundary condition on the other. A functional transformation is employed to simplify the boundary conditions so that eigenfunction expansions can be obtained for the resulting Green's functions. The eigenfunction expansions are transformed into the integral representations which then are evaluated asymptotically by the modified Pauli-Clemmow method of steepest descent. A far zone approximation is made to obtain the scattered field from which the diffraction coefficient is found for scalar plane, cylindrical or sperical wave incident on the edge. With the introduction of a ray-fixed coordinate system, the dyadic diffraction coefficient for plane or cylindrical EM waves normally indicent on the edge is reduced to the sum of two dyads which can be written alternatively as a 2 X 2 diagonal matrix.
Edge turbulence effect on ultra-fast swept reflectometry core measurements in tokamak plasmas

NASA Astrophysics Data System (ADS)

Zadvitskiy, G. V.; Heuraux, S.; Lechte, C.; Hacquin, S.; Sabot, R.

2018-02-01

Ultra-fast frequency-swept reflectometry (UFSR) enables one to provide information about the turbulence radial wave-number spectrum and perturbation amplitude with good spatial and temporal resolutions. However, a data interpretation of USFR is quiet tricky. An iterative algorithm to solve this inverse problem was used in past works, Gerbaud (2006 Rev. Sci. Instrum. 77 10E928). For a direct solution, a fast 1D Helmholtz solver was used. Two-dimensional effects are strong and should be taken into account during data interpretation. As 2D full-wave codes are still too time consuming for systematic application, fast 2D approaches based on the Born approximation are of prime interest. Such methods gives good results in the case of small turbulence levels. However in tokamak plasmas, edge turbulence is usually very strong and can distort and broaden the probing beam Sysoeva et al (2015 Nucl. Fusion 55 033016). It was shown that this can change reflectometer phase response from the plasma core. Comparison between 2D full wave computation and the simplified Born approximation was done. The approximated method can provide a right spectral shape, but it is unable to describe a change of the spectral amplitude with an edge turbulence level. Computation for the O-mode wave with the linear density profile in the slab geometry and for realistic Tore-Supra density profile, based on the experimental data turbulence amplitude and spectrum, were performed to investigate the role of strong edge turbulence. It is shown that the spectral peak in the signal amplitude variation spectrum which rises with edge turbulence can be a signature of strong edge turbulence. Moreover, computations for misaligned receiving and emitting antennas were performed. It was found that the signal amplitude variation peak changes its position with a receiving antenna poloidal displacement.
Justification of Shallow-Water Theory

NASA Astrophysics Data System (ADS)

Ostapenko, V. V.

2018-01-01

The basic conservation laws of shallow-water theory are derived from multidimensional mass and momentum integral conservation laws describing the plane-parallel flow of an ideal incompressible fluid above the horizontal bottom. This conclusion is based on the concept of hydrostatic approximation, which generalizes the concept of long-wavelength approximation and is used for justifying the applicability of the shallow-water theory in the simulation of wave flows of fluid with hydraulic bores.
Crystallographic features of the approximant H (Mn7Si2V) phase in the Mn-Si-V alloy system

NASA Astrophysics Data System (ADS)

Nakayama, Kei; Komatsuzaki, Takumi; Koyama, Yasumasa

2018-07-01

The intermetallic compound H (Mn7Si2V) phase in the Mn-Si-V alloy system can be regarded as an approximant phase of the dodecagonal quasicrystal as one of the two-dimensional quasicrystals. To understand the features of the approximant H phase, in this study, the crystallographic features of both the H phase and the (σ → H) reaction in Mn-Si-V alloy samples were investigated, mainly by transmission electron microscopy. It was found that, in the H phase, there were characteristic structural disorders with respect to an array of a dodecagonal structural unit consisting of 19 dodecagonal atomic columns. Concretely, penetrated structural units consisting of two dodecagonal structural units were presumed to be typical of such disorders. An interesting feature of the (σ → H) reaction was that regions with a rectangular arrangement of penetrated structural units (RAPU) first appeared in the σ matrix as the initial state, and H regions were then nucleated in contact with RAPU regions. The subsequent conversion of RAPU regions into H regions eventually resulted in the formation of the approximant H state as the final state. Furthermore, atomic positions in both the H structure and the dodecagonal quasicrystal were examined using a simple plane-wave model with 12 plane waves.
Ultrasonic waves in classical gases

NASA Astrophysics Data System (ADS)

Magner, A. G.; Gorenstein, M. I.; Grygoriev, U. V.

2017-12-01

The velocity and absorption coefficient for the plane sound waves in a classical gas are obtained by solving the Boltzmann kinetic equation, which describes the reaction of the single-particle distribution function to a periodic external field. Within the linear response theory, the nonperturbative dispersion equation valid for all sound frequencies is derived and solved numerically. The results are in agreement with the approximate analytical solutions found for both the frequent- and rare-collision regimes. These results are also in qualitative agreement with the experimental data for ultrasonic waves in dilute gases.

Monochromatic plane-fronted waves in conformal gravity are pure gauge

NASA Astrophysics Data System (ADS)

Fabbri, Luca; Paranjape, M. B.

2011-05-01

We consider plane-fronted, monochromatic gravitational waves on a Minkowski background, in a conformally invariant theory of general relativity. By this we mean waves of the form: gμν=ημν+γμνF(k·x), where γμν is a constant polarization tensor, and kμ is a lightlike vector. We also assume the coordinate gauge condition |g|-1/4∂τ(|g|1/4gστ)=0 which is the conformal analog of the harmonic gauge condition gμνΓμνσ=-|g|-1/2∂τ(|g|1/2gστ)=0, where det⁡[gμν]≡g. Requiring additionally the conformal gauge condition g=-1 surprisingly implies that the waves are both transverse and traceless. Although the ansatz for the metric is eminently reasonable when considering perturbative gravitational waves, we show that the metric is reducible to the metric of Minkowski space-time via a sequence of coordinate transformations which respect the gauge conditions, without any perturbative approximation that γμν be small. This implies that we have, in fact, exact plane-wave solutions; however, they are simply coordinate/conformal artifacts. As a consequence, they carry no energy. Our result does not imply that conformal gravity does not have gravitational wave phenomena. A different, more generalized ansatz for the deviation, taking into account the fourth-order nature of the field equation, which has the form gμν=ημν+Bμν(n·x)G(k·x), indeed yields waves which carry energy and momentum [P. D. Mannheim, Gen. Relativ. Gravit.GRGVA80001-7701 43, 703 (2010)10.1007/s10714-010-1088-z]. It is just surprising that transverse, traceless, plane-fronted gravitational waves, those that would be used in any standard, perturbative, quantum analysis of the theory, simply do not exist.
Evaluation of a wave-vector-frequency-domain method for nonlinear wave propagation

PubMed Central

Jing, Yun; Tao, Molei; Clement, Greg T.

2011-01-01

A wave-vector-frequency-domain method is presented to describe one-directional forward or backward acoustic wave propagation in a nonlinear homogeneous medium. Starting from a frequency-domain representation of the second-order nonlinear acoustic wave equation, an implicit solution for the nonlinear term is proposed by employing the Green’s function. Its approximation, which is more suitable for numerical implementation, is used. An error study is carried out to test the efficiency of the model by comparing the results with the Fubini solution. It is shown that the error grows as the propagation distance and step-size increase. However, for the specific case tested, even at a step size as large as one wavelength, sufficient accuracy for plane-wave propagation is observed. A two-dimensional steered transducer problem is explored to verify the nonlinear acoustic field directional independence of the model. A three-dimensional single-element transducer problem is solved to verify the forward model by comparing it with an existing nonlinear wave propagation code. Finally, backward-projection behavior is examined. The sound field over a plane in an absorptive medium is backward projected to the source and compared with the initial field, where good agreement is observed. PMID:21302985
Elastic scattering of spin-polarized electrons and positrons from 23Na nuclei

NASA Astrophysics Data System (ADS)

Jakubassa-Amundsen, D. H.

2018-07-01

Differential cross sections and polarization correlations for the scattering of relativistic spin-polarized leptons from unpolarized ground-state sodium nuclei are calculated within the distorted-wave Born approximation (DWBA). Various nuclear ground-state charge distributions are probed. Besides potential scattering, also electric C2 and magnetic M1 and M3 transitions are taken into account. It is shown that even for a light nucleus such as 23Na there are considerable electron-positron differences at high collision energies and large scattering angles. In particular, the symmetry of the Sherman function with respect to a global sign change, as predicted by the second-order Born approximation when replacing electrons by positrons, is broken whenever the diffraction structures come into play beyond 100 MeV.
Frequency lock-in and phase synchronization of vortex shedding behind circular cylinder due to surface waves

NASA Astrophysics Data System (ADS)

Gunnoo, Hans; Abcha, Nizar; Ezersky, Alexander

2016-02-01

The influence of harmonic surface wave on non-regular Karman Vortex Street is investigated. In our experiments, Karman Street arises behind a vertical circular cylinder in a water flow and harmonic surface waves propagating upstream. It is found that surface waves can modify regimes of shedding in Karman Street: frequency lock-in and synchronization of vortex shedding can arise. Intensive surface waves can excite symmetric vortex street instead of chess-like street, and completely suppress shedding behind the cylinder. It is shown experimentally that such effects occur if frequency of harmonic surface wave is approximately twice higher than the frequency of vortex shedding. Region of frequency lock-in is found on the plane amplitude-frequency of surface wave.
Generalized self-similar unsteady gas flows behind the strong shock wave front

NASA Astrophysics Data System (ADS)

Bogatko, V. I.; Potekhina, E. A.

2018-05-01

Two-dimensional (plane and axially symmetric) nonstationary gas flows behind the front of a strong shock wave are considered. All the gas parameters are functions of the ratio of Cartesian coordinates to some degree of time tn, where n is a self-similarity index. The problem is solved in Lagrangian variables. It is shown that the resulting system of partial differential equations is suitable for constructing an iterative process. ¢he "thin shock layer" method is used to construct an approximate analytical solution of the problem. The limit solution of the problem is constructed. A formula for determining the path traversed by a gas particle in the shock layer along the front of a shock wave is obtained. A system of equations for determining the first approximation corrections is constructed.
Magnetic droplet soliton nucleation in oblique fields

NASA Astrophysics Data System (ADS)

Mohseni, Morteza; Hamdi, M.; Yazdi, H. F.; Banuazizi, S. A. H.; Chung, S.; Sani, S. R.; Åkerman, Johan; Mohseni, Majid

2018-05-01

We study the auto-oscillating magnetodynamics in orthogonal spin-torque nano-oscillators (STNOs) as a function of the out-of-plane (OOP) magnetic-field angle. In perpendicular fields and at OOP field angles down to approximately 50°, we observe the nucleation of a droplet. However, for field angles below 50°, experiments indicate that the droplet gives way to propagating spin waves, in agreement with our micromagnetic simulations. Theoretical calculations show that the physical mechanism behind these observations is the sign changing of spin-wave nonlinearity (SWN) by angle. In addition, we show that the presence of a strong perpendicular magnetic anisotropy free layer in the system reverses the angular dependence of the SWN and dynamics in STNOs with respect to the known behavior determined for the in-plane magnetic anisotropy free layer. Our results are of fundamental interest in understanding the rich dynamics of nanoscale solitons and spin-wave dynamics in STNOs.
Application of the Boundary Element Method to Elastic Wave Scattering Problems in Ultrasonic Nondestructive Evaluation.

NASA Astrophysics Data System (ADS)

Schafbuch, Paul Jay

The boundary element method (BEM) is used to numerically simulate the interaction of ultrasonic waves with material defects such as voids, inclusions, and open cracks. The time harmonic formulation is in 3D and therefore allows flaws of arbitrary shape to be modeled. The BEM makes such problems feasible because the underlying boundary integral equation only requires a surface (2D) integration and difficulties associated with the seemingly infinite extent of the host domain are not encountered. The computer code utilized in this work is built upon recent advances in elastodynamic boundary element theory such as a scheme for self adjusting integration order and singular integration regularization. Incident fields may be taken as compressional or shear plane waves or predicted by an approximate Gauss -Hermite beam model. The code is highly optimized for voids and has been coupled with computer aided engineering packages for automated flaw shape definition and mesh generation. Subsequent graphical display of intermediate results supports model refinement and physical interpretation. Final results are typically cast in a nondestructive evaluation (NDE) context as either scattering amplitudes or flaw signals (via a measurement model based on a reciprocity integral). The near field is also predicted which allows for improved physical insight into the scattering process and the evaluation of certain modeling approximations. The accuracy of the BEM approach is first examined by comparing its predictions to those of other models for single, isolated scatterers. The comparisons are with the predictions of analytical solutions for spherical defects and with MOOT and T-matrix calculations for axisymmetric flaws. Experimental comparisons are also made for volumetric shapes with different characteristic dimensions in all three directions, since no other numerical approach has yet produced results of this type. Theoretical findings regarding the fictitious eigenfrequency difficulty are substantiated through the analytical solution of a fundamental elastodynamics problem and corresponding BEM studies. Given the confidence in the BEM technique engendered by these comparisons, it is then used to investigate the modeling of "open", cracklike defects amenable to a volumetric formulation. The limits of applicability of approximate theories (e.g., quasistatic, Kirchhoff, and geometric theory of diffraction) are explored for elliptical cracks, from this basis. The problem of two interacting scatterers is then considered. Results from a fully implicit approach and from a more efficient hybrid scheme are compared with generalized Born and farfield approximate interaction theories.
Application of the boundary element method to elastic wave scattering problems in ultrasonic nondestructive evaluation

NASA Astrophysics Data System (ADS)

Schafbuch, Paul Jay

1991-02-01

The boundary element method (BEM) is used to numerically simulate the interaction of ultrasonic waves with material defects such as voids, inclusions, and open cracks. The time harmonic formulation is in 3D and therefore allows flaws of arbitrary shape to be modeled. The BEM makes such problems feasible because the underlying boundary integral equation only requires a surface (2D) integration and difficulties associated with the seemingly infinite extent of the host domain are not encountered. The computer code utilized in this work is built upon recent advances in elastodynamic boundary element theory such as a scheme for self adjusting integration order and singular integration regularization. Incident fields may be taken as compressional or shear plane waves or predicted by an approximate Gauss-Hermite beam model. The code is highly optimized for voids and has been coupled with computer aided engineering packages for automated flaw shape definition and mesh generation. Subsequent graphical display of intermediate results supports model refinement and physical interpretation. Final results are typically cast in a nondestructive evaluation (NDE) context as either scattering amplitudes or flaw signals (via a measurement model based on a reciprocity integral). The near field is also predicted which allows for improved physical insight into the scattering process and the evaluation of certain modeling approximations. The accuracy of the BEM approach is first examined by comparing its predictions to those of other models for single, isolated scatters. The comparisons are with the predictions of analytical solutions for spherical defects and with MOOT and T-matrix calculations for axisymmetric flaws. Experimental comparisons are also made for volumetric shapes with different characteristic dimensions in all three directions, since no other numerical approach has yet produced results of this type. Theoretical findings regarding the fictitious eigenfrequency difficulty are substantiated through the analytical solution of a fundamental elastodynamics problem and corresponding BEM studies. Given the confidence in the BEM technique engendered by these comparisons, it is then used to investigate the modeling of 'open', cracklike defects amenable to a volumetric formulation. The limits of applicability of approximate theories (e.g., quasistatic, Kirchhoff, and geometric theory of diffraction) are explored for elliptical cracks, from this basis. The problem of two interacting scatterers is then considered. Results from a fully implicit approach and from a more efficient hybrid scheme are compared with generalized Born and farfield approximate interaction theories.
High-temperature electronic structure with the Korringa-Kohn-Rostoker Green's function method

NASA Astrophysics Data System (ADS)

Starrett, C. E.

2018-05-01

Modeling high-temperature (tens or hundreds of eV), dense plasmas is challenging due to the multitude of non-negligible physical effects including significant partial ionization and multisite effects. These effects cause the breakdown or intractability of common methods and approximations used at low temperatures, such as pseudopotentials or plane-wave basis sets. Here we explore the Korringa-Kohn-Rostoker Green's function method at these high-temperature conditions. The method is all electron, does not rely on pseudopotentials, and uses a spherical harmonic basis set, and so avoids the aforementioned limitations. It is found to be accurate for solid density aluminum and iron plasmas when compared to a plane-wave method at low temperature, while being able to access high temperatures.
Wavespace-Based Coherent Deconvolution

NASA Technical Reports Server (NTRS)

Bahr, Christopher J.; Cattafesta, Louis N., III

2012-01-01

Array deconvolution is commonly used in aeroacoustic analysis to remove the influence of a microphone array's point spread function from a conventional beamforming map. Unfortunately, the majority of deconvolution algorithms assume that the acoustic sources in a measurement are incoherent, which can be problematic for some aeroacoustic phenomena with coherent, spatially-distributed characteristics. While several algorithms have been proposed to handle coherent sources, some are computationally intractable for many problems while others require restrictive assumptions about the source field. Newer generalized inverse techniques hold promise, but are still under investigation for general use. An alternate coherent deconvolution method is proposed based on a wavespace transformation of the array data. Wavespace analysis offers advantages over curved-wave array processing, such as providing an explicit shift-invariance in the convolution of the array sampling function with the acoustic wave field. However, usage of the wavespace transformation assumes the acoustic wave field is accurately approximated as a superposition of plane wave fields, regardless of true wavefront curvature. The wavespace technique leverages Fourier transforms to quickly evaluate a shift-invariant convolution. The method is derived for and applied to ideal incoherent and coherent plane wave fields to demonstrate its ability to determine magnitude and relative phase of multiple coherent sources. Multi-scale processing is explored as a means of accelerating solution convergence. A case with a spherical wave front is evaluated. Finally, a trailing edge noise experiment case is considered. Results show the method successfully deconvolves incoherent, partially-coherent, and coherent plane wave fields to a degree necessary for quantitative evaluation. Curved wave front cases warrant further investigation. A potential extension to nearfield beamforming is proposed.
Positronium formation in e+ plus H- collisions

NASA Technical Reports Server (NTRS)

Straton, Jack C.; Drachman, Richard J.

1990-01-01

Cross sections for positronium formation by capture from the negative hydrogen ion are given. Orthogonalization corrections to the Coulomb (First) Born Approximation (CBA) differential and total cross sections are calculated using approximate H- wave functions of both Lowdin and Chandrasekhar. Various methods of orthogonalizing the unbound projectile to the possible bound states are considered. It is found that treating the atomic nuclei as if they were isotopic spin projections of a single type of nucleon gives cross sections that are an improvement over the CBA.
Spatial-heterodyne sampling requirements in the off-axis pupil plane recording geometry for deep-turbulence wavefront sensing

NASA Astrophysics Data System (ADS)

Banet, Matthias T.; Spencer, Mark F.

2017-09-01

Spatial-heterodyne interferometry is a robust solution for deep-turbulence wavefront sensing. With that said, this paper analyzes the focal-plane array sampling requirements for spatial-heterodyne systems operating in the off-axis pupil plane recording geometry. To assess spatial-heterodyne performance, we use a metric referred to as the field-estimated Strehl ratio. We first develop an analytical description of performance with respect to the number of focal-plane array pixels across the Fried coherence diameter and then verify our results with wave-optics simulations. The analysis indicates that at approximately 5 focal-plane array pixels across the Fried coherence diameter, the field-estimated Strehl ratios begin to exceed 0:9 which is indicative of largely diffraction-limited results.
Statistics of optical vortex wander on propagation through atmospheric turbulence.

PubMed

Gu, Yalong

2013-04-01

The transverse position of an optical vortex on propagation through atmospheric turbulence is studied. The probability density of the optical vortex position on a transverse plane in the atmosphere is formulated in weak turbulence by using the Born approximation. With these formulas, the effect of aperture averaging on topological charge detection is investigated. These results provide quantitative guidelines for the design of an optimal detector of topological charge, which has potential application in optical vortex communication systems.
Kubo-Greenwood electrical conductivity formulation and implementation for projector augmented wave datasets

NASA Astrophysics Data System (ADS)

Calderín, L.; Karasiev, V. V.; Trickey, S. B.

2017-12-01

As the foundation for a new computational implementation, we survey the calculation of the complex electrical conductivity tensor based on the Kubo-Greenwood (KG) formalism (Kubo, 1957; Greenwood, 1958), with emphasis on derivations and technical aspects pertinent to use of projector augmented wave datasets with plane wave basis sets (Blöchl, 1994). New analytical results and a full implementation of the KG approach in an open-source Fortran 90 post-processing code for use with Quantum Espresso (Giannozzi et al., 2009) are presented. Named KGEC ([K]ubo [G]reenwood [E]lectronic [C]onductivity), the code calculates the full complex conductivity tensor (not just the average trace). It supports use of either the original KG formula or the popular one approximated in terms of a Dirac delta function. It provides both Gaussian and Lorentzian representations of the Dirac delta function (though the Lorentzian is preferable on basic grounds). KGEC provides decomposition of the conductivity into intra- and inter-band contributions as well as degenerate state contributions. It calculates the dc conductivity tensor directly. It is MPI parallelized over k-points, bands, and plane waves, with an option to recover the plane wave processes for their use in band parallelization as well. It is designed to provide rapid convergence with respect to k-point density. Examples of its use are given.
Nonlinear waves of a nonlocal modified KdV equation in the atmospheric and oceanic dynamical system

NASA Astrophysics Data System (ADS)

Tang, Xiao-yan; Liang, Zu-feng; Hao, Xia-zhi

2018-07-01

A new general nonlocal modified KdV equation is derived from the nonlinear inviscid dissipative and equivalent barotropic vorticity equation in a β-plane. The nonlocal property is manifested in the shifted parity and delayed time reversal symmetries. Exact solutions of the nonlocal modified KdV equation are obtained including periodic waves, kink waves, solitary waves, kink- and/or anti-kink-cnoidal periodic wave interaction solutions, which can be utilized to describe various two-place and time-delayed correlated events. As an illustration, a special approximate solution is applied to theoretically capture the salient features of two correlated dipole blocking events in atmospheric dynamical systems.
Modeling boundary measurements of scattered light using the corrected diffusion approximation

PubMed Central

Lehtikangas, Ossi; Tarvainen, Tanja; Kim, Arnold D.

2012-01-01

We study the modeling and simulation of steady-state measurements of light scattered by a turbid medium taken at the boundary. In particular, we implement the recently introduced corrected diffusion approximation in two spatial dimensions to model these boundary measurements. This implementation uses expansions in plane wave solutions to compute boundary conditions and the additive boundary layer correction, and a finite element method to solve the diffusion equation. We show that this corrected diffusion approximation models boundary measurements substantially better than the standard diffusion approximation in comparison to numerical solutions of the radiative transport equation. PMID:22435102
Heats of Segregation of BCC Binaries from Ab Initio and Quantum Approximate Calculations

NASA Technical Reports Server (NTRS)

Good, Brian S.

2003-01-01

We compare dilute-limit segregation energies for selected BCC transition metal binaries computed using ab initio and quantum approximate energy methods. Ab initio calculations are carried out using the CASTEP plane-wave pseudopotential computer code, while quantum approximate results are computed using the Bozzolo-Ferrante-Smith (BFS) method with the most recent parameters. Quantum approximate segregation energies are computed with and without atomistic relaxation. Results are discussed within the context of segregation models driven by strain and bond-breaking effects. We compare our results with full-potential quantum calculations and with available experimental results.
Whistler mode waves in the Jovian magnetosheath

NASA Technical Reports Server (NTRS)

Lin, Naiguo; Kellogg, P. J.; Thiessen, J. P.; Lengyel-Frey, D.; Tsurutani, B. T.; Phillips, J. L.

1994-01-01

During the Ulysses flyby of Jupiter in February 1992, the spacecraft traversed the Jovian magnetosheath for a few hours during the inbound pass and for aa few days during the outbound pass. Burstlike electomagnetic waves at frequencies of approximately 0.1-0.4 of the local electron cyclotron frequency have been observed by the Unified Radio and Plasma Wave (URAP) experiement. The waves were more often observed in the regions which were probably the outer or the middle magnetosheath, especially near the bow shock, and rarely seen in the magnetosphere/magnetosheath boundary layer. The propagation angles of the waves are estimated by comparing the measurements of the wave electric and magnetic fields in the spacecraft spin plane with the corresponding values calculated using the cold plasma dispersion relation under local field and plasma conditions. It is found that the waves propagate obliquely with wave angles between approximately 30 deg and 50 deg. These waves are likely to be the whistler mode waves which are excited by suprathermal electrons with a few hundred eV and a slight anisotropy (T(sub perp)/T(sub parallel) approximately 1.1-1.5). They are probably similar in nature to the lion roars observed in the Earth's magnetosheath. Signature of coupling between the mirror and the whistler mode have also been observed. The plasma conditions which favor the excitation of the whistler mode instability during the wave events exists as observed by the plasma experiement of Ulysses.
Extension of geometrical-optics approximation to on-axis Gaussian beam scattering. I. By a spherical particle.

PubMed

Xu, Feng; Ren, Kuan Fang; Cai, Xiaoshu

2006-07-10

The geometrical-optics approximation of light scattering by a transparent or absorbing spherical particle is extended from plane wave to Gaussian beam incidence. The formulas for the calculation of the phase of each ray and the divergence factor are revised, and the interference of all the emerging rays is taken into account. The extended geometrical-optics approximation (EGOA) permits one to calculate the scattering diagram in all directions from 0 degrees to 180 degrees. The intensities of the scattered field calculated by the EGOA are compared with those calculated by the generalized Lorenz-Mie theory, and good agreement is found. The surface wave effect in Gaussian beam scattering is also qualitatively analyzed by introducing a flux ratio factor. The approach proposed is particularly important to the further extension of the geometrical-optics approximation to the scattering of large spheroidal particles.
On the dipole approximation with error estimates

NASA Astrophysics Data System (ADS)

Boßmann, Lea; Grummt, Robert; Kolb, Martin

2018-01-01

The dipole approximation is employed to describe interactions between atoms and radiation. It essentially consists of neglecting the spatial variation of the external field over the atom. Heuristically, this is justified by arguing that the wavelength is considerably larger than the atomic length scale, which holds under usual experimental conditions. We prove the dipole approximation in the limit of infinite wavelengths compared to the atomic length scale and estimate the rate of convergence. Our results include N-body Coulomb potentials and experimentally relevant electromagnetic fields such as plane waves and laser pulses.

Wave theory in rotating systems: Schrödinger equations bridge the gaps between the equatorial β-plane and the spherical earth

NASA Astrophysics Data System (ADS)

Paldor, N.

2017-12-01

The concise and elegant wave theory developed on the equatorial β-plane by Matsuno (1966, M66 hereafter) is based on the formulation of a Schrödinger equation associated with the governing Linear Rotating Shallow Water Equations (LRSWE). The theory yields explicit expressions for the dispersion relations and meridional amplitude structures of all zonally propagating waves - Rossby, Inertia-Gravity, Kelvin and Yanai. In contrast, the spherical wave theory of Longuet-Higgins (1968) is a collection of asymptotic expansions in many sub-ranges e.g. large, small (and even negative) Lamb Number; high and low frequency; low-latitudes, etc. that rests upon extensive numerical solutions of several Ordinary Differential Equations. The difference between the two theories is highlighted by their lengths. The essential elements of the former planar study are completely revealed in just 3-4 pages including the derivation of explicit formulae for the phase speeds and amplitude meridional structures. In comtrast, the latter spherical theory contains 97 pages and the results of the numerical calculations are summarized in 30 pages of tables filled with numerical values and about 31 figures, each of which containing many separate curves! In my talk I will re-visit the wave problem on a sphere by developing several Schrödinger equations that approximate the governing eigenvalue equation associated with zonally propagating waves. Each of the Schrödinger equations approximates the original second order Ordinary Differential Equation in a different range of the 3 parameters: Lamb-Number, frequency and zonal wavenumber. As in M66, each of the Schrödinger equations yields explicit expressions for the dispersion relations and meridional amplitude structure of Rossby and Inertia-Gravity waves. In addition, the analysis shows that Yanai wave exists on a sphere even tough the zonal velocity is regular everywhere there (in contrast to the β-plane where the zonal velocity is singular everywhere) and that Kelvin waves do not exist as a separate mode (but the eastward propagating n=0 Inertia-Gravity is nearly non-dispersive). References Longuet-Higgins, M. S. Phil. Trans. Roy. Soc. London; 262, 511-607; 1968 Matsuno, T.; J. Met. Soc. Japan. 44(1), 25-43; 1966
Wave function continuity and the diagonal Born-Oppenheimer correction at conical intersections

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meek, Garrett A.; Levine, Benjamin G., E-mail: levine@chemistry.msu.edu

2016-05-14

We demonstrate that though exact in principle, the expansion of the total molecular wave function as a sum over adiabatic Born-Oppenheimer (BO) vibronic states makes inclusion of the second-derivative nonadiabatic energy term near conical intersections practically problematic. In order to construct a well-behaved molecular wave function that has density at a conical intersection, the individual BO vibronic states in the summation must be discontinuous. When the second-derivative nonadiabatic terms are added to the Hamiltonian, singularities in the diagonal BO corrections (DBOCs) of the individual BO states arise from these discontinuities. In contrast to the well-known singularities in the first-derivative couplingsmore » at conical intersections, these singularities are non-integrable, resulting in undefined DBOC matrix elements. Though these singularities suggest that the exact molecular wave function may not have density at the conical intersection point, there is no physical basis for this constraint. Instead, the singularities are artifacts of the chosen basis of discontinuous functions. We also demonstrate that continuity of the total molecular wave function does not require continuity of the individual adiabatic nuclear wave functions. We classify nonadiabatic molecular dynamics methods according to the constraints placed on wave function continuity and analyze their formal properties. Based on our analysis, it is recommended that the DBOC be neglected when employing mixed quantum-classical methods and certain approximate quantum dynamical methods in the adiabatic representation.« less
Wave function continuity and the diagonal Born-Oppenheimer correction at conical intersections

NASA Astrophysics Data System (ADS)

Meek, Garrett A.; Levine, Benjamin G.

2016-05-01

We demonstrate that though exact in principle, the expansion of the total molecular wave function as a sum over adiabatic Born-Oppenheimer (BO) vibronic states makes inclusion of the second-derivative nonadiabatic energy term near conical intersections practically problematic. In order to construct a well-behaved molecular wave function that has density at a conical intersection, the individual BO vibronic states in the summation must be discontinuous. When the second-derivative nonadiabatic terms are added to the Hamiltonian, singularities in the diagonal BO corrections (DBOCs) of the individual BO states arise from these discontinuities. In contrast to the well-known singularities in the first-derivative couplings at conical intersections, these singularities are non-integrable, resulting in undefined DBOC matrix elements. Though these singularities suggest that the exact molecular wave function may not have density at the conical intersection point, there is no physical basis for this constraint. Instead, the singularities are artifacts of the chosen basis of discontinuous functions. We also demonstrate that continuity of the total molecular wave function does not require continuity of the individual adiabatic nuclear wave functions. We classify nonadiabatic molecular dynamics methods according to the constraints placed on wave function continuity and analyze their formal properties. Based on our analysis, it is recommended that the DBOC be neglected when employing mixed quantum-classical methods and certain approximate quantum dynamical methods in the adiabatic representation.
Wave function continuity and the diagonal Born-Oppenheimer correction at conical intersections.

PubMed

Meek, Garrett A; Levine, Benjamin G

2016-05-14

We demonstrate that though exact in principle, the expansion of the total molecular wave function as a sum over adiabatic Born-Oppenheimer (BO) vibronic states makes inclusion of the second-derivative nonadiabatic energy term near conical intersections practically problematic. In order to construct a well-behaved molecular wave function that has density at a conical intersection, the individual BO vibronic states in the summation must be discontinuous. When the second-derivative nonadiabatic terms are added to the Hamiltonian, singularities in the diagonal BO corrections (DBOCs) of the individual BO states arise from these discontinuities. In contrast to the well-known singularities in the first-derivative couplings at conical intersections, these singularities are non-integrable, resulting in undefined DBOC matrix elements. Though these singularities suggest that the exact molecular wave function may not have density at the conical intersection point, there is no physical basis for this constraint. Instead, the singularities are artifacts of the chosen basis of discontinuous functions. We also demonstrate that continuity of the total molecular wave function does not require continuity of the individual adiabatic nuclear wave functions. We classify nonadiabatic molecular dynamics methods according to the constraints placed on wave function continuity and analyze their formal properties. Based on our analysis, it is recommended that the DBOC be neglected when employing mixed quantum-classical methods and certain approximate quantum dynamical methods in the adiabatic representation.
An array effect of wave energy farm buoys

NASA Astrophysics Data System (ADS)

Kweon, Hyuck-Min; Lee, Jung-Lyul

2012-12-01

An ocean buoy energy farm is considered for Green energy generation and delivery to small towns along the Korean coast. The present studypresents that the floating buoy-type energy farm appears to be sufficiently feasible fortrapping more energy compared to afixed cylinder duck array. It is also seen from the numerical resultsthat the resonated waves between spaced buoys are further trapped by floating buoy motion.Our numerical study is analyzed by a plane-wave approximation, in which evanescent mode effects are included in a modified mild-slope equation based on the scattering characteristics for a single buoy.
Single electron impact ionization of the methane molecule

NASA Astrophysics Data System (ADS)

Bouamoud, Mammar; Sahlaoui, Mohammed; Benmansour, Nour El Houda; Atomic and Molecular Collisions Team

2014-10-01

Triply differential cross sections (TDCS) results of electron-impact ionization of the inner 2a1 molecular orbital of CH4 are presented in the framework of the Second Born Approximation and compared with the experimental data performed in coplanar asymmetric geometry. The cross sections are averaged on the random orientations of the molecular target for accurate comparison with experiments and are compared also with the theoretical calculations of the Three Coulomb wave (3CW) model. Our results are in good agreement with experiments and 3CW results in the binary peak. In contrast the Second Born Approximation yields a significant higher values compared to the 3CW results for the recoil peak and seems to describe suitably the recoil region where higher order effects can occur with the participation of the recoiling ion in the collision process.
Surface charge conductivity of a topological insulator in a magnetic field: The effect of hexagonal warping

NASA Astrophysics Data System (ADS)

Akzyanov, R. S.; Rakhmanov, A. L.

2018-02-01

We investigate the influence of hexagonal warping on the transport properties of topological insulators. We study the charge conductivity within Kubo formalism in the first Born approximation using low-energy expansion of the Hamiltonian near the Dirac point. The effects of disorder, magnetic field, and chemical-potential value are analyzed in detail. We find that the presence of hexagonal warping significantly affects the conductivity of the topological insulator. In particular, it gives rise to the growth of the longitudinal conductivity with the increase of the disorder and anisotropic anomalous in-plane magnetoresistance. Hexagonal warping also affects the quantum anomalous Hall effect and anomalous out-of-plane magnetoresistance. The obtained results are consistent with the experimental data.
Catastrophe optics of sharp-edge diffraction.

PubMed

Borghi, Riccardo

2016-07-01

A classical problem of diffraction theory, namely plane wave diffraction by sharp-edge apertures, is here reformulated from the viewpoint of the fairly new subject of catastrophe optics. On using purely geometrical arguments, properly embedded into a wave optics context, uniform analytical estimates of the diffracted wavefield at points close to fold caustics are obtained, within paraxial approximation, in terms of the Airy function and its first derivative. Diffraction from parabolic apertures is proposed to test reliability and accuracy of our theoretical predictions.
Experimental and theoretical triple differential cross sections for electron-impact ionization of Ar (3p) for equal energy final state electrons

NASA Astrophysics Data System (ADS)

Amami, Sadek; Ozer, Zehra N.; Dogan, Mevlut; Yavuz, Murat; Varol, Onur; Madison, Don

2016-09-01

There have been several studies of electron-impact ionization of inert gases for asymmetric final state energy sharing and normally one electron has an energy significantly higher than the other. However, there have been relatively few studies examining equal energy final state electrons. Here we report experimental and theoretical triple differential cross sections for electron impact ionization of Ar (3p) for equal energy sharing of the outgoing electrons. Previous experimental results combined with some new measurements are compared with distorted wave born approximation (DWBA) results, DWBA results using the Ward-Macek (WM) approximation for the post collision interaction (PCI), and three-body distorted wave (3DW) which includes PCI without approximation. The results show that it is crucially important to include PCI in the calculation particularly for lower energies and that the WM approximation is valid only for high energies. The 3DW, on the other hand, is in reasonably good agreement with data down to fairly low energies.
Analytical expressions for the log-amplitude correlation function of a plane wave through anisotropic atmospheric refractive turbulence.

PubMed

Gudimetla, V S Rao; Holmes, Richard B; Smith, Carey; Needham, Gregory

2012-05-01

The effect of anisotropic Kolmogorov turbulence on the log-amplitude correlation function for plane-wave fields is investigated using analysis, numerical integration, and simulation. A new analytical expression for the log-amplitude correlation function is derived for anisotropic Kolmogorov turbulence. The analytic results, based on the Rytov approximation, agree well with a more general wave-optics simulation based on the Fresnel approximation as well as with numerical evaluations, for low and moderate strengths of turbulence. The new expression reduces correctly to previously published analytic expressions for isotropic turbulence. The final results indicate that, as asymmetry becomes greater, the Rytov variance deviates from that given by the standard formula. This deviation becomes greater with stronger turbulence, up to moderate turbulence strengths. The anisotropic effects on the log-amplitude correlation function are dominant when the separation of the points is within the Fresnel length. In the direction of stronger turbulence, there is an enhanced dip in the correlation function at a separation close to the Fresnel length. The dip is diminished in the weak-turbulence axis, suggesting that energy redistribution via focusing and defocusing is dominated by the strong-turbulence axis. The new analytical expression is useful when anisotropy is observed in relevant experiments. © 2012 Optical Society of America
Cross sections and rate coefficients for inner-shell excitation of Li-like ions with 6 < Z < 42

NASA Astrophysics Data System (ADS)

Safronova, U. I.; Safronova, M. S.; Kato, T.

1996-07-01

Excitation cross sections and rate coefficients by electron impact were calculated for the 1s22s-1s2s2p, 1s22s-1s2s2 and 1s22s-1s2p2 transitions of the Li-like ions (C IV, N V, O VI, Ne VIII, Mg X, Al XI, Si XII, S XIV, Ar XVI, Ca XVIII, Ti XX, Fe XXIV, Ni XXVI, Zn XXVIII, Ge XXX, Se XXXII, Kr XXXIV and Mo XXXX) in the Coulomb-Born approximation with exchange including relativistic effects and configuration interaction. Level energies, mixing coefficients and transition wavelengths and probabilities were also computed. Calculations performed by the 1/Z perturbation theory and Coulomb-Born approximation are compared with the R-matrix method and the distorted-wave approximation were Z is the nuclear charge. Formulae obtained for the angular factors of n-electron atomic system allow one to generalize this method to an arbitrary system of highly charged ions.
Role of the 3He optical model potential ambiguity in the distorted-wave Born approximation description of the 58Ni(3He, d)59Cu reaction at 130 MeV incident energy

NASA Astrophysics Data System (ADS)

Djaloeis, A.; Alderliesten, C.; Bojowald, J.; Mayer-Böricke, C.; Oelert, W.; Turek, P.

1983-04-01

Angular distributions of 58Ni(3He, d)59Cu transitions leading to the (0.0 MeV, 32-), (0.91 MeV, 52-), and (3.04 MeV, 92+) states in 59Cu have been measured at an incident energy of 130 MeV. The experimental data have been used to study mainly the role of the 3He optical model potential ambiguity in the distorted-wave Born approximation description of the reaction. Satisfactory fits to the data are obtained using a deep helion potential in standard local zero-range calculations. For a shallow 3He potential a comparable description can be achieved if the depth of the real part of the deuteron optical potential is reduced considerably, and nonlocality as well as finite-range corrections are taken into account. Under these conditions, the use of a 3He potential constructed according to the Johnson-Soper prescription yields similar results. NUCLEAR REACTIONS 58Ni (3He, d)59Cu, E=130 MeV; measured dσ(θ)dΩ. Enriched target; DWBA analysis; discussed reaction mechanism.
Three-dimensional waveform sensitivity kernels

NASA Astrophysics Data System (ADS)

Marquering, Henk; Nolet, Guust; Dahlen, F. A.

1998-03-01

The sensitivity of intermediate-period (~10-100s) seismic waveforms to the lateral heterogeneity of the Earth is computed using an efficient technique based upon surface-wave mode coupling. This formulation yields a general, fully fledged 3-D relationship between data and model without imposing smoothness constraints on the lateral heterogeneity. The calculations are based upon the Born approximation, which yields a linear relation between data and model. The linear relation ensures fast forward calculations and makes the formulation suitable for inversion schemes; however, higher-order effects such as wave-front healing are neglected. By including up to 20 surface-wave modes, we obtain Fréchet, or sensitivity, kernels for waveforms in the time frame that starts at the S arrival and which includes direct and surface-reflected body waves. These 3-D sensitivity kernels provide new insights into seismic-wave propagation, and suggest that there may be stringent limitations on the validity of ray-theoretical interpretations. Even recently developed 2-D formulations, which ignore structure out of the source-receiver plane, differ substantially from our 3-D treatment. We infer that smoothness constraints on heterogeneity, required to justify the use of ray techniques, are unlikely to hold in realistic earth models. This puts the use of ray-theoretical techniques into question for the interpretation of intermediate-period seismic data. The computed 3-D sensitivity kernels display a number of phenomena that are counter-intuitive from a ray-geometrical point of view: (1) body waves exhibit significant sensitivity to structure up to 500km away from the source-receiver minor arc; (2) significant near-surface sensitivity above the two turning points of the SS wave is observed; (3) the later part of the SS wave packet is most sensitive to structure away from the source-receiver path; (4) the sensitivity of the higher-frequency part of the fundamental surface-wave mode is wider than for its faster, lower-frequency part; (5) delayed body waves may considerably influence fundamental Rayleigh and Love waveforms. The strong sensitivity of waveforms to crustal structure due to fundamental-mode-to-body-wave scattering precludes the use of phase-velocity filters to model body-wave arrivals. Results from the 3-D formulation suggest that the use of 2-D and 1-D techniques for the interpretation of intermediate-period waveforms should seriously be reconsidered.
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.
Variational treatment of electron-polyatomic-molecule scattering calculations using adaptive overset grids

NASA Astrophysics Data System (ADS)

Greenman, Loren; Lucchese, Robert R.; McCurdy, C. William

2017-11-01

The complex Kohn variational method for electron-polyatomic-molecule scattering is formulated using an overset-grid representation of the scattering wave function. The overset grid consists of a central grid and multiple dense atom-centered subgrids that allow the simultaneous spherical expansions of the wave function about multiple centers. Scattering boundary conditions are enforced by using a basis formed by the repeated application of the free-particle Green's function and potential Ĝ0+V ̂ on the overset grid in a Born-Arnoldi solution of the working equations. The theory is shown to be equivalent to a specific Padé approximant to the T matrix and has rapid convergence properties, in both the number of numerical basis functions employed and the number of partial waves employed in the spherical expansions. The method is demonstrated in calculations on methane and CF4 in the static-exchange approximation and compared in detail with calculations performed with the numerical Schwinger variational approach based on single-center expansions. An efficient procedure for operating with the free-particle Green's function and exchange operators (to which no approximation is made) is also described.
Ab Initio study on structural, electronic, magnetic and dielectric properties of LSNO within Density Functional Perturbation Theory

NASA Astrophysics Data System (ADS)

Petersen, John; Bechstedt, Friedhelm; Furthmüller, Jürgen; Scolfaro, Luisa

LSNO (La2-xSrxNiO4) is of great interest due to its colossal dielectric constant (CDC) and rich underlying physics. While being an antiferromagnetic insulator, localized holes are present in the form of stripes in the Ni-O planes which are commensurate with the inverse of the Sr concentration. The stripes are a manifestation of charge density waves with period approximately 1/x and spin density waves with period approximately 2/x. Here, the spin ground state is calculated via LSDA + U with the PAW method implemented in VASP. Crystal structure and the effective Hubbard U parameter are optimized before calculating ɛ∞ within the independent particle approximation. ɛ∞ and the full static dielectric constant (including the lattice polarizability) ɛ0 are calculated within Density Functional Perturbation Theory.
Development of attenuation and diffraction corrections for linear and nonlinear Rayleigh surface waves radiating from a uniform line source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeong, Hyunjo, E-mail: hjjeong@wku.ac.kr; Cho, Sungjong; Zhang, Shuzeng

2016-04-15

In recent studies with nonlinear Rayleigh surface waves, harmonic generation measurements have been successfully employed to characterize material damage and microstructural changes, and found to be sensitive to early stages of damage process. A nonlinearity parameter of Rayleigh surface waves was derived and frequently measured to quantify the level of damage. The accurate measurement of the nonlinearity parameter generally requires making corrections for beam diffraction and medium attenuation. These effects are not generally known for nonlinear Rayleigh waves, and therefore not properly considered in most of previous studies. In this paper, the nonlinearity parameter for a Rayleigh surface wave ismore » defined from the plane wave displacement solutions. We explicitly define the attenuation and diffraction corrections for fundamental and second harmonic Rayleigh wave beams radiated from a uniform line source. Attenuation corrections are obtained from the quasilinear theory of plane Rayleigh wave equations. To obtain closed-form expressions for diffraction corrections, multi-Gaussian beam (MGB) models are employed to represent the integral solutions derived from the quasilinear theory of the full two-dimensional wave equation without parabolic approximation. Diffraction corrections are presented for a couple of transmitter-receiver geometries, and the effects of making attenuation and diffraction corrections are examined through the simulation of nonlinearity parameter determination in a solid sample.« less
Transversally periodic solitary gravity–capillary waves

PubMed Central

Milewski, Paul A.; Wang, Zhan

2014-01-01

When both gravity and surface tension effects are present, surface solitary water waves are known to exist in both two- and three-dimensional infinitely deep fluids. We describe here solutions bridging these two cases: travelling waves which are localized in the propagation direction and periodic in the transverse direction. These transversally periodic gravity–capillary solitary waves are found to be of either elevation or depression type, tend to plane waves below a critical transverse period and tend to solitary lumps as the transverse period tends to infinity. The waves are found numerically in a Hamiltonian system for water waves simplified by a cubic truncation of the Dirichlet-to-Neumann operator. This approximation has been proved to be very accurate for both two- and three-dimensional computations of fully localized gravity–capillary solitary waves. The stability properties of these waves are then investigated via the time evolution of perturbed wave profiles. PMID:24399922
The role of the complete Coriolis force in weakly stratified oceanic flows

NASA Astrophysics Data System (ADS)

Tort, M.; Winters, K. B.; Ribstein, B.; Zeitlin, V.

2016-02-01

Ocean dynamics is usually described using the primitive equations based on the so-called traditional approximation (TA), where the Coriolis force associated with the horizontal component of the planetary rotation is neglected (also called non-traditional (NT) part proportional to cosΦ, see Fig 1.). However, recent studies have shown that the NT part of the Coriolis force plays a non-negligible dynamical role in some particular oceanic flows (see Gerkema et al., 2008 for an extensive review of NT effects for geophysical and astrophysical flows). Here we explore the relevance of including the NT component of the Coriolis force in ocean models, by presenting particular results regarding two different mid-latitude flow configurations after relaxing the TA: Propagation of wind-induced near-inertial waves (NIWs). Under the TA, NIWs propagate toward the equator, the inertially poleward propagation being internally reflected at a depth-independent critical latitude. The combined effects of the NT Coriolis force and weak stratification in the deep ocean leads to the existence of waveguides for sub-inertial waves, which get trapped and propagate further poleward (Winters et al., 2011). Here we consider storm-induced NIWs and their evolution in a non-linear Boussinesq model on the β-plane in the NT approximation. Preliminary results are presented concerning the behavior of the waves in a weakly stratified mixed-layer, where NT effects are expected to be significant. Inertial instability. A detailed linear stability analysis of the Bickley jet at large Rossby numbers in the NT approximation on the f-plane is performed for long waves in a continuously stratified Boussinesq model. For a sufficiently weak stratification, both symmetric and asymmetric inertial instabilities have substantially higher growth rates than in the TA while no discernible differences between the two approximations are observed for strong enough stratifications (Tort et al., 2015).
Rotational-vibrational coupling in the theory of electron-molecule scattering

NASA Technical Reports Server (NTRS)

Temkin, A.; Sullivan, E. C.

1974-01-01

The adiabatic-nuclei approximation of vibrational-rotational excitation of homonuclear diatomic molecules can be simply augmented to describe the vibrational-rotational coupling by including the dependence of the vibrational wave function on j. Appropriate formulas are given, and the theory, is applied to e-H2 excitation, whereby it is shown that deviations from the simple Born-Oppenheimer approximation measured by Wong and Schultz can be explained. More important, it can be seen that the inclusion of the j-dependent centrifugal term is essential for transitions involving high-rotational quantum numbers.

Triple differential cross sections of magnesium in doubly symmetric geometry

NASA Astrophysics Data System (ADS)

S, Y. Sun; X, Y. Miao; Xiang-Fu, Jia

2016-01-01

A dynamically screened three-Coulomb-wave (DS3C) method is applied to study the single ionization of magnesium by electron impact. Triple differential cross sections (TDCS) are calculated in doubly symmetric geometry at incident energies of 13.65, 17.65, 22.65, 27.65, 37.65, 47.65, 57.65, and 67.65 eV. Comparisons are made with experimental data and theoretical predictions from a three-Coulomb-wave function (3C) approach and distorted-wave Born approximation (DWBA). The overall agreement between the predictions of the DS3C model and the DWBA approach with the experimental data is satisfactory. Project supported by the National Natural Science Foundation of China (Grant No. 11274215).
Kinematics and dynamics of green water on a fixed platform in a large wave basin in focusing wave and random wave conditions

NASA Astrophysics Data System (ADS)

Chuang, Wei-Liang; Chang, Kuang-An; Mercier, Richard

2018-06-01

Green water kinematics and dynamics due to wave impingements on a simplified geometry, fixed platform were experimentally investigated in a large, deep-water wave basin. Both plane focusing waves and random waves were employed in the generation of green water. The focusing wave condition was designed to create two consecutive plunging breaking waves with one impinging on the frontal vertical wall of the fixed platform, referred as wall impingement, and the other directly impinging on the deck surface, referred as deck impingement. The random wave condition was generated using the JONSWAP spectrum with a significant wave height approximately equal to the freeboard. A total of 179 green water events were collected in the random wave condition. By examining the green water events in random waves, three different flow types are categorized: collapse of overtopping wave, fall of bulk water, and breaking wave crest. The aerated flow velocity was measured using bubble image velocimetry, while the void fraction was measured using fiber optic reflectometry. For the plane focusing wave condition, measurements of impact pressure were synchronized with the flow velocity and void fraction measurements. The relationship between the peak pressures and the pressure rise times is examined. For the high-intensity impact in the deck impingement events, the peak pressures are observed to be proportional to the aeration levels. The maximum horizontal velocities in the green water events in random waves are well represented by the lognormal distribution. Ritter's solution is shown to quantitatively describe the green water velocity distributions under both the focusing wave condition and the random wave condition. A prediction equation for green water velocity distribution under random waves is proposed.
High-frequency techniques for RCS prediction of plate geometries

NASA Technical Reports Server (NTRS)

Balanis, Constantine A.; Polka, Lesley A.

1992-01-01

The principal-plane scattering from perfectly conducting and coated strips and rectangular plates is examined. Previous reports have detailed Geometrical Theory of Diffraction/Uniform Theory of Diffraction (GTD/UTD) solutions for these geometries. The GTD/UTD solution for the perfectly conducting plate yields monostatic radar cross section (RCS) results that are nearly identical to measurements and results obtained using the Moment Method (MM) and the Extended Physical Theory of Diffraction (EPTD). This was demonstrated in previous reports. The previous analysis is extended to bistatic cases. GTD/UTD results for the principal-plane scattering from a perfectly conducting, infinite strip are compared to MM and EPTD data. A comprehensive overview of the advantages and disadvantages of the GTD/UTD and of the EPTD and a detailed analysis of the results from both methods are provided. Several previous reports also presented preliminary discussions and results for a GTD/UTD model of the RCS of a coated, rectangular plate. Several approximations for accounting for the finite coating thickness, plane-wave incidence, and far-field observation were discussed. Here, these approximations are replaced by a revised wedge diffraction coefficient that implicitly accounts for a coating on a perfect conductor, plane-wave incidence, and far-field observation. This coefficient is computationally more efficient than the previous diffraction coefficient because the number of Maliuzhinets functions that must be calculated using numerical integration is reduced by a factor of 2. The derivation and the revised coefficient are presented in detail for the hard polarization case. Computations and experimental data are also included. The soft polarization case is currently under investigation.
The Bolocam Galactic Plane Survey

NASA Technical Reports Server (NTRS)

Glenn, Jason; Aguirre, James; Bally, John; Battersby, Cara; Bradley, Eric Todd; Cyganowski, Claudia; Dowell, Darren; Drosback, Meredith; Dunham, Miranda K.; Evans, Neal J., II;

2009-01-01

The Bolocam Galactic Plane Survey (BGPS) is a 1.1 millimeter continuum survey of the northern Galactic Plane made with Bolocam and the Caltech Submillimeter Observatory. The coverage totals 170 square degrees, comprised of a contiguous range from -10.5 deg is less than or equal to 90.5 deg, 0.5 deg is less than or equal to b is less than or equal to 0.5 deg, with extended coverage in b in selected regions, and four targeted regions in the outer Galaxy, including: IC1396, toward the Perseus arm at l is approximately 111 deg, W3/4/5, and Gem OB1. Depths of the maps range from 30 to 60 mJy beam (sup 1). Approximately 8,400 sources were detected and the maps and source catalog have been made publicly available. Millimeter-wave thermal dust emission reveals dense regions within molecular clouds, thus the BGPS serves as a database for studies of the dense interstellar medium and star formation within the Milky Way.

u d b \\xAF b \\xAF tetraquark resonances with lattice QCD potentials and the Born-Oppenheimer approximation

NASA Astrophysics Data System (ADS)

Bicudo, Pedro; Cardoso, Marco; Peters, Antje; Pflaumer, Martin; Wagner, Marc

2017-09-01

We study tetraquark resonances with lattice QCD potentials computed for a static b ¯b ¯ pair in the presence of two lighter quarks u d , the Born-Oppenheimer approximation and the emergent wave method. As a proof of concept we focus on the system with isospin I =0 , but consider different relative angular momenta l of the heavy quarks b ¯b ¯. For l =0 a bound state has already been predicted with quantum numbers I (JP)=0 (1+). Exploring various angular momenta we now compute the phase shifts and search for S and T matrix poles in the second Riemann sheet. We predict a tetraquark resonance for l =1 , decaying into two B mesons, with quantum numbers I (JP)=0 (1-) , mass m =10 57 6-4+4 MeV and decay width Γ =11 2-103+90 MeV .
High-frequency Born synthetic seismograms based on coupled normal modes

USGS Publications Warehouse

Pollitz, Fred F.

2011-01-01

High-frequency and full waveform synthetic seismograms on a 3-D laterally heterogeneous earth model are simulated using the theory of coupled normal modes. The set of coupled integral equations that describe the 3-D response are simplified into a set of uncoupled integral equations by using the Born approximation to calculate scattered wavefields and the pure-path approximation to modulate the phase of incident and scattered wavefields. This depends upon a decomposition of the aspherical structure into smooth and rough components. The uncoupled integral equations are discretized and solved in the frequency domain, and time domain results are obtained by inverse Fourier transform. Examples show the utility of the normal mode approach to synthesize the seismic wavefields resulting from interaction with a combination of rough and smooth structural heterogeneities. This approach is applied to an ∼4 Hz shallow crustal wave propagation around the site of the San Andreas Fault Observatory at Depth (SAFOD).
Internal swells in the tropics: Near-inertial wave energy fluxes and dissipation during CINDY

NASA Astrophysics Data System (ADS)

Soares, S. M.; Natarov, A.; Richards, K. J.

2016-05-01

A developing MJO event in the tropical Indian Ocean triggered wind disturbances that generated inertial oscillations in the surface mixed layer. Subsequent radiation of near-inertial waves below the mixed layer produced strong turbulence in the pycnocline. Linear plane wave dynamics and spectral analysis are used to explain these observations, with the ultimate goal of estimating the wave energy flux in relation to both the energy input by the wind and the dissipation by turbulence. The results indicate that the wave packets carry approximately 30-40% of the wind input of inertial kinetic energy, and propagate in an environment conducive to the occurrence of a critical level set up by a combination of vertical gradients in background relative vorticity and Doppler shifting of wave frequency. Turbulent kinetic energy dissipation measurements demonstrate that the waves lose energy as they propagate in the transition layer as well as in the pycnocline, where approaching this critical level may have dissipated approximately 20% of the wave packet energy in a single event. Our analysis, therefore, supports the notion that appreciable amounts of wind-induced inertial kinetic energy escape the surface boundary layer into the interior. However, a large fraction of wave energy is dissipated within the pycnocline, limiting its penetration into the abyssal ocean.
Time-Harmonic Gaussian Beams: Exact Solutions of the Helmhotz Equation in Free Space

NASA Astrophysics Data System (ADS)

Kiselev, A. P.

2017-12-01

An exact solution of the Helmholtz equation u xx + u yy + u zz + k 2 u = 0 is presented, which describes propagation of monochromatic waves in the free space. The solution has the form of a superposition of plane waves with a specific weight function dependent on a certain free parameter a. If ka→∞, the solution is localized in the Gaussian manner in a vicinity of a certain straight line and asymptotically coincides with the famous approximate solution known as the fundamental mode of a paraxial Gaussian beam. The asymptotics of the aforementioned exact solution does not include a backward wave.
Waves in a plane graphene - dielectric waveguide structure

NASA Astrophysics Data System (ADS)

Evseev, Dmitry A.; Eliseeva, Svetlana V.; Sementsov, Dmitry I.

2017-10-01

The features of the guided TE modes propagation have been investigated on the basis of computer simulations in a planar structure consisting of a set of alternating layers of dielectric and graphene. Within the framework of the effective medium approximation, the dispersion relations have been received for symmetric and antisymmetric waveguide modes, determined by the frequency range of their existence. The wave field distribution by structure, frequency dependences of the constants of propagation and transverse components of the wave vectors, as well as group and phase velocities of waveguide modes have been obtained, the effect of the graphene part in a structure on the waveguide mode behavior has been shown.
The Atomic Origin of the Reflection Law

ERIC Educational Resources Information Center

Prytz, Kjell

2016-01-01

It will be demonstrated how the reflection law may be derived on an atomic basis using the plane wave approximation together with Huygens' principle. The model utilized is based on the electric dipole character of matter originating from its molecular constituents. This approach is not new but has, since it was first introduced by Ewald and Oseen…
New conformal mapping for adaptive resolving of the complex singularities of Stokes wave

PubMed Central

Dyachenko, Sergey A.; A. Silantyev, Denis

2017-01-01

A new highly efficient method is developed for computation of travelling periodic waves (Stokes waves) on the free surface of deep water. A convergence of numerical approximation is determined by the complex singularities above the free surface for the analytical continuation of the travelling wave into the complex plane. An auxiliary conformal mapping is introduced which moves singularities away from the free surface thus dramatically speeding up numerical convergence by adapting the numerical grid for resolving singularities while being consistent with the fluid dynamics. The efficiency of that conformal mapping is demonstrated for the Stokes wave approaching the limiting Stokes wave (the wave of the greatest height) which significantly expands the family of numerically accessible solutions. It allows us to provide a detailed study of the oscillatory approach of these solutions to the limiting wave. Generalizations of the conformal mapping to resolve multiple singularities are also introduced. PMID:28690418
New conformal mapping for adaptive resolving of the complex singularities of Stokes wave.

PubMed

Lushnikov, Pavel M; Dyachenko, Sergey A; A Silantyev, Denis

2017-06-01

A new highly efficient method is developed for computation of travelling periodic waves (Stokes waves) on the free surface of deep water. A convergence of numerical approximation is determined by the complex singularities above the free surface for the analytical continuation of the travelling wave into the complex plane. An auxiliary conformal mapping is introduced which moves singularities away from the free surface thus dramatically speeding up numerical convergence by adapting the numerical grid for resolving singularities while being consistent with the fluid dynamics. The efficiency of that conformal mapping is demonstrated for the Stokes wave approaching the limiting Stokes wave (the wave of the greatest height) which significantly expands the family of numerically accessible solutions. It allows us to provide a detailed study of the oscillatory approach of these solutions to the limiting wave. Generalizations of the conformal mapping to resolve multiple singularities are also introduced.
Dynamic correlation effects in fully differential cross sections for 75-keV proton-impact ionization of helium

NASA Astrophysics Data System (ADS)

Niu, Xiaojie; Sun, Shiyan; Wang, Fujun; Jia, Xiangfu

2017-08-01

The effect of final-state dynamic correlation is investigated for helium single ionization by 75-keV proton impact analyzing fully differential cross sections (FDCS). The final state is represented by a continuum correlated wave (CCW-PT) function which accounts for the interaction between the projectile and the residual target ion (PT interaction). This continuum correlated wave function partially includes the correlation of electron-projectile and electron-target relative motion as coupling terms of the wave equation. The transition matrix is evaluated using the CCW-PT function and the Born initial state. The analytical expression of the transition matrix has been obtained. We have shown that this series is strongly convergent and analyzed the contribution of their different terms to the FDCS within the perturbation method. Illustrative computations are performed in the scattering plane and in the perpendicular plane. Both the correlation effects and the PT interaction are checked by the preset calculations. Our results are compared with absolute experimental data as well as other theoretical models. We have shown that the dynamic correlation plays an important role in the single ionization of atoms by proton impact at intermediate projectile energies, especially at large transverse momentum transfer. While overall agreement between theory and the experimental data is encouraging, detailed agreement is lacking. The need for more theoretical and experimental work is emphasized.
Plane Evanescent Waves and Interface Waves

NASA Astrophysics Data System (ADS)

Luppé, F.; Conoir, J. M.; El Kettani, M. Ech-Cherif; Lenoir, O.; Izbicki, J. L.; Duclos, J.; Poirée, B.

The evanescent plane wave formalism is used to obtain the characteristic equation of the normal vibration modes of a plane elastic solid embedded in a perfect fluid. Simple drawings of the real and imaginary parts of complex wave vectors make quite clear the choice of the Riemann sheets on which the roots of the characteristic equation are to be looked for. The generalized Rayleigh wave and the Scholte - Stoneley wave are then described. The same formalism is used to describe Lamb waves on an elastic plane plate immersed in water. The damping, due to energy leaking in the fluid, is shown to be directly given by the projection of evanescence vectors on the interface. Measured values of the damping coefficient are in good agreement with those derived from calculations. The width of the angular resonances associated to Lamb waves or Rayleigh waves is also directly related to this same evanescence vectors projection, as well as the excitation coefficient of a given Lamb wave excited by a plane incident wave. This study shows clearly the strong correlation between the resonance point of view and the wave one in plane interface problems.
Accuracy and efficiency considerations for wide-angle wavefield extrapolators and scattering operators

NASA Astrophysics Data System (ADS)

Thomson, C. J.

2005-10-01

Several observations are made concerning the numerical implementation of wide-angle one-way wave equations, using for illustration scalar waves obeying the Helmholtz equation in two space dimensions. This simple case permits clear identification of a sequence of physically motivated approximations of use when the mathematically exact pseudo-differential operator (PSDO) one-way method is applied. As intuition suggests, these approximations largely depend on the medium gradients in the direction transverse to the main propagation direction. A key point is that narrow-angle approximations are to be avoided in the interests of accuracy. Another key consideration stems from the fact that the so-called `standard-ordering' PSDO indicates how lateral interpolation of the velocity structure can significantly reduce computational costs associated with the Fourier or plane-wave synthesis lying at the heart of the calculations. A third important point is that the PSDO theory shows what approximations are necessary in order to generate an exponential one-way propagator for the laterally varying case, representing the intuitive extension of classical integral-transform solutions for a laterally homogeneous medium. This exponential propagator permits larger forward stepsizes. Numerical comparisons with Helmholtz (i.e. full) wave-equation finite-difference solutions are presented for various canonical problems. These include propagation along an interfacial gradient, the effects of a compact inclusion and the formation of extended transmitted and backscattered wave trains by model roughness. The ideas extend to the 3-D, generally anisotropic case and to multiple scattering by invariant embedding. It is concluded that the method is very competitive, striking a new balance between simplifying approximations and computational labour. Complicated wave-scattering effects are retained without the need for expensive global solutions, providing a robust and flexible modelling tool.
Surface Segregation Energies of BCC Binaries from Ab Initio and Quantum Approximate Calculations

NASA Technical Reports Server (NTRS)

Good, Brian S.

2003-01-01

We compare dilute-limit segregation energies for selected BCC transition metal binaries computed using ab initio and quantum approximate energy method. Ab initio calculations are carried out using the CASTEP plane-wave pseudopotential computer code, while quantum approximate results are computed using the Bozzolo-Ferrante-Smith (BFS) method with the most recent parameterization. Quantum approximate segregation energies are computed with and without atomistic relaxation. The ab initio calculations are performed without relaxation for the most part, but predicted relaxations from quantum approximate calculations are used in selected cases to compute approximate relaxed ab initio segregation energies. Results are discussed within the context of segregation models driven by strain and bond-breaking effects. We compare our results with other quantum approximate and ab initio theoretical work, and available experimental results.
Analysis of THG modes for femtosecond laser pulse

NASA Astrophysics Data System (ADS)

Trofimov, Vyacheslav A.; Sidorov, Pavel S.

2017-05-01

THG is used nowadays in many practical applications such as a substance diagnostics, and biological objects imaging, and etc. With developing of new materials and technology (for example, photonic crystal) an attention to THG process analysis grow. Therefore, THG features understanding are a modern problem. Early we have developed new analytical approach based on using the problem invariant for analytical solution construction of the THG process. It should be stressed that we did not use a basic wave non-depletion approximation. Nevertheless, a long pulse duration approximation and plane wave approximation has applied. The analytical solution demonstrates, in particular, an optical bistability property (and may other regimes of frequency tripling) for the third harmonic generation process. But, obviously, this approach does not reflect an influence of a medium dispersion on the frequency tripling. Therefore, in this paper we analyze THG efficiency of a femtosecond laser pulse taking into account a second order dispersion affect as well as self- and crossmodulation of the interacting waves affect on the frequency conversion process. Analysis is made using a computer simulation on the base of Schrödinger equations describing the process under consideration.
Nonviral transfection of suspension cells in ultrasound standing wave fields.

PubMed

Lee, Yu-Hsiang; Peng, Ching-An

2007-05-01

Ultrasound-induced cavitation has been widely used for delivering DNA vectors into cells. However, this approach may seriously disrupt cell membranes and cause lethal damage when cells are exposed to the inertial cavitation field. In this study, instead of using sonoporation, ultrasound standing wave fields (USWF) were explored for nonviral transfection of suspension cells. Acoustic resonance in a tubular chamber was generated from the interference of waves emitted from a piezoelectric transducer and consequently reflected from a borosilicate glass coverslip. The suspended K562 erythroleukemia cells were transfected by polyethyleneimine (PEI)/DNA complexes with and without exposure to 1-MHz USWF for 5 min. During USWF exposure, K562 cells moved to the pressure nodal planes first and formed cell bands by the primary radiation force. Nanometer-sized PEI/DNA complexes, circulated between nodal planes by acoustic microstreaming, then used the cell agglomerates as the nucleating sites on which to attach. After incubation at 37 degrees C for 48 h, the efficiency of nonviral transfection based on EGFP transgene expression was determined by fluorescent microscopy and fluorometry. Both studies showed that USWF brought suspended K562 cells and PEI/DNA complexes into close contact at the pressure nodal planes, yielding an approximately 10-fold increment of EGFP transgene expression compared with the group without ultrasonic treatment.
Nonlinear wave runup in long bays and firths: Samoa 2009 and Tohoku 2011 tsunamis

NASA Astrophysics Data System (ADS)

Didenkulova, I.; Pelinovsky, E.

2012-04-01

Last catastrophic tsunami events in Samoa on 29 September 2009 and in Japan on 11 March 2011 demonstrated that tsunami may experience abnormal amplification in long bays and firths and result in an unexpectedly high wave runup. The capital city Pago Pago, which is located at the toe of a narrow 4-km-long bay and represents the most characteristic example of a long and narrow bay, was considerably damaged during Samoa 2009 tsunami (destroyed infrastructures, boats and shipping containers carried inland into commercial areas, etc.) The runup height there reached 8 m over an inundation of 538 m at its toe, while the tsunami wave height measured by the tide-gauge at the entrance of the bay was at most 3 m. The same situation was observed during catastrophic Tohoku tsunami in Japan, which coast contains numerous long bays and firths, which experienced the highest wave runup and the strongest amplification. Such examples are villages: Ofunato, Ryori Bay, where the wave runup reached 30 m high, and Onagawa, where the wave amplified up to 17 m. Here we study the nonlinear dynamics of tsunami waves in an inclined U-shaped bay. Nonlinear shallow water equations can in this case be written in 1D form and solved analytically with the use of the hodograph transformation. This approach generalizes the well-known Carrier-Greenspan transformation for long wave runup on a plane beach. In the case of an inclined U-shaped bay it leads to the associated generalized wave equation for symmetrical wave in fractal space. In the special case of the channel of parabolic cross-section it is a spherical symmetrical linear wave equation. As a result, the solution of the Cauchy problem can be expressed in terms of elementary functions and has a simple form (with respect to analysis) for any kind of initial conditions. Wave regimes associated with various localized initial conditions, corresponding to problems of evolution and runup of tsunami, are considered and analyzed. Special attention is paid to the wave breaking criterion. Theoretical estimates of tsunami runup are applied to cases of 2009 Samoa and 2011 Tohoku tsunamis. The data of tide-gauges or computed tide-gauges are used to calculate wave runup for two approximations of the bottom topography: a plane beach and for a narrow bay. It is shown that theory of 1D runup on a plane beach underestimate the tsunami runup height and the influence of the narrow bay geometry should be taken into account. The differences in estimated shoreline velocity, travel time and wave breaking regime, calculated in the framework of these two approximations are also discussed. It is concluded that the wave runup in narrow bays should by calculated by the corresponding formulas, which should be taken into account by TEWS.
Three-nucleon force contribution in the distorted-wave theory of (d ,p ) reactions

NASA Astrophysics Data System (ADS)

Timofeyuk, N. K.

2018-05-01

The distorted-wave theory of A (d ,p )B reactions, widely used to analyze experimental data, is based on a Hamiltonian that includes only two-nucleon interactions. However, numerous studies of few-nucleon systems and many modern developments in nuclear structure theory show the importance of the three-nucleon (3 N ) force. The purpose of this paper is to study the contribution of the 3 N force of the simplest possible form to the A (d ,p )B reaction amplitude. This contribution is given by a new term that accounts for the interaction of the neutron and proton in the incoming deuteron with one of the target nucleons. This term involves a new type of nuclear matrix elements containing an infinite number of target excitations in addition to the main part associated with the traditional overlap function between A and B . The nuclear matrix elements are calculated for double-closed shell targets within a mean field theory where target excitations are shown to be equivalent to exchanges between valence and core nucleons. These matrix elements can be readily incorporated into available reaction codes if the 3 N interaction has a spin-independent zero-range form. Distorted-wave calculations are presented for a contact 3 N force with the volume integral fixed by the chiral effective field theory at the next-to-next-to-leading order. For this particular choice, the 3 N contribution is noticeable, especially at high deuteron incident energies. No 3 N effects are seen for incident energies below the Coulomb barrier. The finite range can significantly affect the 3 N contribution to the (d ,p ) cross sections. Finite-range studies require new formal developments and, therefore, their contribution is preliminarily assessed within the plane-wave Born approximation, together with sensitivity to the choice of the deuteron model.

Scattering of plane transverse waves by spherical inclusions in a poroelastic medium

NASA Astrophysics Data System (ADS)

Liu, Xu; Greenhalgh, Stewart; Zhou, Bing

2009-03-01

The scattering of plane transverse waves by a spherical inclusion embedded in an infinite poroelastic medium is treated for the first time in this paper. The vector displacement wave equations of Biot's theory are solved as an infinite series of vector spherical harmonics for the case of a plane S-wave impinging from a porous medium onto a spherical inclusion which itself is assumed to be another porous medium. Based on the single spherical scattering theory and dynamic composite elastic medium theory, the non-self-consistent shear wavenumber is derived for a porous rock having numerous spherical inclusions of another medium. The frequency dependences of the shear wave velocity and the shear wave attenuation have been calculated for both the patchy saturation model (inclusions having the same solid frame as the host but with a different pore fluid from the host medium) and the double porosity model (inclusions having a different solid frame than the host but the same pore fluid as the host medium) with dilute concentrations of identical inclusions. Unlike the case of incident P-wave scattering, we show that although the fluid and the heterogeneity of the rock determine the shear wave velocity of the composite, the attenuation of the shear wave caused by scattering is actually contributed by the heterogeneity of the rock for spherical inclusions. The scattering of incident shear waves in the patchy saturation model is quite different from that of the double porosity model. For the patchy saturation model, the gas inclusions do not significantly affect the shear wave dispersion characteristic of the water-filled host medium. However, the softer inclusion with higher porosity in the double porosity model can cause significant shear wave scattering attenuation which occurs at a frequency at which the wavelength of the shear wave is approximately equal to the characteristic size of the inclusion and depends on the volume fraction. Compared with analytic formulae for the low frequency limit of the shear velocity, our scattering model yields discrepancies within 4.0 per cent. All calculated shear velocities of the composite medium with dilute inclusion concentrations approach the high frequency limit of the host material.
Effects of dynamical screening on single ionization of potassium by electron impact in doubly symmetric geometry

NASA Astrophysics Data System (ADS)

Sun, S. Y.; Jia, X. F.; Miao, X. Y.; Zhang, J. F.

2014-03-01

The dynamically screened three-Coulomb-wave (DS3C) method is applied to study the single ionization of potassium by electron impact. Triple differential cross-sections (TDCS) are calculated in doubly symmetric geometry at excess energies of 6, 10, 15, 20, 30, 40, 50 and 60 eV. Comparisons are made with recent experimental data and theoretical predictions from a three-Coulomb-wave (3C) and distorted-wave Born approximation (DWBA). The DS3C method is able to reproduce most of the trend of experimental data and in good agreement with DWBA results. It is shown that the DS3C calculation provides much better shape and relative magnitude agreement with experiment.
Distorted-wave born approximation calculations for turbulence scattering in an upward-refracting atmosphere

NASA Technical Reports Server (NTRS)

Gilbert, Kenneth E.; Di, Xiao; Wang, Lintao

1990-01-01

Weiner and Keast observed that in an upward-refracting atmosphere, the relative sound pressure level versus range follows a characteristic 'step' function. The observed step function has recently been predicted qualitatively and quantitatively by including the effects of small-scale turbulence in a parabolic equation (PE) calculation. (Gilbert et al., J. Acoust. Soc. Am. 87, 2428-2437 (1990)). The PE results to single-scattering calculations based on the distorted-wave Born approximation (DWBA) are compared. The purpose is to obtain a better understanding of the physical mechanisms that produce the step-function. The PE calculations and DWBA calculations are compared to each other and to the data of Weiner and Keast for upwind propagation (strong upward refraction) and crosswind propagation (weak upward refraction) at frequencies of 424 Hz and 848 Hz. The DWBA calculations, which include only single scattering from turbulence, agree with the PE calculations and with the data in all cases except for upwind propagation at 848 Hz. Consequently, it appears that in all cases except one, the observed step function can be understood in terms of single scattering from an upward-refracted 'skywave' into the refractive shadow zone. For upwind propagation at 848 Hz, the DWBA calculation gives levels in the shadow zone that are much below both the PE and the data.
Heats of Segregation of BCC Binaries from ab Initio and Quantum Approximate Calculations

NASA Technical Reports Server (NTRS)

Good, Brian S.

2004-01-01

We compare dilute-limit heats of segregation for selected BCC transition metal binaries computed using ab initio and quantum approximate energy methods. Ab initio calculations are carried out using the CASTEP plane-wave pseudopotential computer code, while quantum approximate results are computed using the Bozzolo-Ferrante-Smith (BFS) method with the most recent LMTO-based parameters. Quantum approximate segregation energies are computed with and without atomistic relaxation, while the ab initio calculations are performed without relaxation. Results are discussed within the context of a segregation model driven by strain and bond-breaking effects. We compare our results with full-potential quantum calculations and with available experimental results.
Resonant triad in boundary-layer stability. Part 1: Fully nonlinear interaction

NASA Technical Reports Server (NTRS)

Mankbadi, Reda R.

1991-01-01

A first principles theory is developed to study the nonlinear spatial evolution of a near-resonance triad of instability waves in boundary layer transition. This triad consists of a plane wave at fundamental frequency and a pair of symmetrical, oblique waves at the subharmonic frequency. A low frequency, high Reynolds number asymptotic scaling leads to a distinct critical layer where nonlinearity first becomes important; the development of the triad's waves is determined by the critical layer's nonlinear, viscous dynamics. The resulting theory is fully nonlinear in that all nonlinearly generated oscillatory and nonoscillatory components are accounted for. The presence of the plane wave initially causes exponential of exponential growth of the oblique waves. However, the plane wave continues to follow the linear theory, even when the oblique waves' amplitude attains the same order of magnitude as that of the plane wave. A fully interactive stage then comes into effect when the oblique waves exceed a certain level compared to that of the plane wave. The oblique waves react back on the fundamental, slowing its growth rate. The oblique waves' saturation results from their self-interaction - a mechanism that does not require the presence of the plane wave. The oblique waves' saturation level is independent of their initial level, but decreases as the obliqueness angle increases.
Solutions of differential equations with regular coefficients by the methods of Richmond and Runge-Kutta

NASA Technical Reports Server (NTRS)

Cockrell, C. R.

1989-01-01

Numerical solutions of the differential equation which describe the electric field within an inhomogeneous layer of permittivity, upon which a perpendicularly-polarized plane wave is incident, are considered. Richmond's method and the Runge-Kutta method are compared for linear and exponential profiles of permittivities. These two approximate solutions are also compared with the exact solutions.
SYMBMAT: Symbolic computation of quantum transition matrix elements

NASA Astrophysics Data System (ADS)

Ciappina, M. F.; Kirchner, T.

2012-08-01

We have developed a set of Mathematica notebooks to compute symbolically quantum transition matrices relevant for atomic ionization processes. The utilization of a symbolic language allows us to obtain analytical expressions for the transition matrix elements required in charged-particle and laser induced ionization of atoms. Additionally, by using a few simple commands, it is possible to export these symbolic expressions to standard programming languages, such as Fortran or C, for the subsequent computation of differential cross sections or other observables. One of the main drawbacks in the calculation of transition matrices is the tedious algebraic work required when initial states other than the simple hydrogenic 1s state need to be considered. Using these notebooks the work is dramatically reduced and it is possible to generate exact expressions for a large set of bound states. We present explicit examples of atomic collisions (in First Born Approximation and Distorted Wave Theory) and laser-matter interactions (within the Dipole and Strong Field Approximations and different gauges) using both hydrogenic wavefunctions and Slater-Type Orbitals with arbitrary nlm quantum numbers as initial states. Catalogue identifier: AEMI_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEMI_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC license, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 71 628 No. of bytes in distributed program, including test data, etc.: 444 195 Distribution format: tar.gz Programming language: Mathematica Computer: Single machines using Linux or Windows (with cores with any clock speed, cache memory and bits in a word) Operating system: Any OS that supports Mathematica. The notebooks have been tested under Windows and Linux and with versions 6.x, 7.x and 8.x Classification: 2.6 Nature of problem: The notebooks generate analytical expressions for quantum transition matrix elements required in diverse atomic processes: ionization by ion, electron, or photon impact and ionization within the framework of strong field physics. In charged-particle collisions approaches based on perturbation theory enjoy widespread utilization. Accordingly, we have chosen the First Born Approximation and Distorted Wave theories as examples. In light-matter interactions, the main ingredient for many types of calculations is the dipole transition matrix in its different formulations, i.e. length, velocity, and acceleration gauges. In all these cases the transitions of interest occur between a bound state and a continuum state which can be described in different ways. With the notebooks developed in the present work it is possible to calculate transition matrix elements analytically for any set of quantum numbers nlm of initial hydrogenic states or Slater-Type Orbitals and for plane waves or Coulomb waves as final continuum states. Solution method: The notebooks employ symbolic computation to generate analytical expressions for transition matrix elements used in both collision and light-matter interaction physics. fba_hyd.nb - This notebook computes analytical expressions for the transition matrix of collision-induced ionization in the First Born Approximation (FBA). The transitions considered are from a bound hydrogenic state with arbitrary quantum numbers nlm to a continuum state represented by a plane wave (PW) or a Coulomb wave (CW). distorted_hyd.nb - This notebook computes analytical expressions for the transition matrix of collision-induced ionization in Distorted Wave (DW) theories. The transitions considered are from a (distorted) bound hydrogenic state with arbitrary quantum numbers nlm to a distorted-wave continuum state. The computations are based on scalar and vectorial integrals (see the text for details). dipoleLength_hyd.nb - This notebook computes analytical expressions for the dipole transition matrix in length gauge. The transitions considered are from a bound hydrogenic state with arbitrary quantum numbers nlm to a continuum state represented by a PW (the Strong Field Approximation (SFA)) or a CW (the Coulomb-Volkov Approximation (CVA)). dipoleVelocity_hyd.nb - This notebook computes analytical expressions for the dipole transition matrix in velocity gauge. The transitions considered are from a bound hydrogenic state with arbitrary quantum numbers nlm to a continuum state represented by a PW (the SFA) or a CW (the CVA). dipoleAcceleration_hyd.nb - This notebook computes analytical expressions for the dipole transition matrix in acceleration gauge. The transitions considered are from a bound hydrogenic state with arbitrary quantum numbers nlm to a continuum state represented by a PW (the SFA). For the case of the CVA we only include the transition from the 1s state to a continuum state represented by a CW. fba_STO.nb - This notebook computes analytical expressions for the transition matrix of collision-induced ionization in the FBA. The transitions considered are from a Slater-Type Orbital (STO) with arbitrary quantum numbers nlm to a continuum state represented by a PW or a CW. distorted_STO.nb - This notebook computes analytical expressions for the transition matrix of collision-induced ionization in DW theories. The transitions considered are from a (distorted) STO with arbitrary quantum numbers nlm to a distorted-wave continuum state. The computations are based on scalar and vectorial integrals (see the text for details). dipoleLength_STO.nb - This notebook computes analytical expressions for the dipole transition matrix in length gauge. The transitions considered are from an STO with arbitrary quantum numbers nlm to a continuum state represented by a PW (the SFA) or a CW (the CVA). dipoleVelocity_STO.nb - This notebook computes analytical expressions for the dipole transition matrix in velocity gauge. The transitions considered are from an STO with arbitrary quantum numbers nlm to a continuum state represented by a PW (the SFA) or a CW (the CVA). dipoleAcceleration_STO.nb - This notebook computes analytical expressions for the dipole transition matrix in acceleration gauge. The transitions considered are from an STO with arbitrary quantum numbers nlm to a continuum state represented by a PW (the SFA). The symbolic expressions obtained within each notebook can be exported to standard programming languages such as Fortran or C using the Format.m package (see the text and Ref. Sofroniou (1993) [16] for details). Running time: Computational times vary according to the transition matrix selected and quantum numbers nlm of the initial state used. The typical running time is several minutes, but it will take longer for large values of nlm.
Approximate optimal tracking control for near-surface AUVs with wave disturbances

NASA Astrophysics Data System (ADS)

Yang, Qing; Su, Hao; Tang, Gongyou

2016-10-01

This paper considers the optimal trajectory tracking control problem for near-surface autonomous underwater vehicles (AUVs) in the presence of wave disturbances. An approximate optimal tracking control (AOTC) approach is proposed. Firstly, a six-degrees-of-freedom (six-DOF) AUV model with its body-fixed coordinate system is decoupled and simplified and then a nonlinear control model of AUVs in the vertical plane is given. Also, an exosystem model of wave disturbances is constructed based on Hirom approximation formula. Secondly, the time-parameterized desired trajectory which is tracked by the AUV's system is represented by the exosystem. Then, the coupled two-point boundary value (TPBV) problem of optimal tracking control for AUVs is derived from the theory of quadratic optimal control. By using a recently developed successive approximation approach to construct sequences, the coupled TPBV problem is transformed into a problem of solving two decoupled linear differential sequences of state vectors and adjoint vectors. By iteratively solving the two equation sequences, the AOTC law is obtained, which consists of a nonlinear optimal feedback item, an expected output tracking item, a feedforward disturbances rejection item, and a nonlinear compensatory term. Furthermore, a wave disturbances observer model is designed in order to solve the physically realizable problem. Simulation is carried out by using the Remote Environmental Unit (REMUS) AUV model to demonstrate the effectiveness of the proposed algorithm.
A simplified method of evaluating the stress wave environment of internal equipment

NASA Technical Reports Server (NTRS)

Colton, J. D.; Desmond, T. P.

1979-01-01

A simplified method called the transfer function technique (TFT) was devised for evaluating the stress wave environment in a structure containing internal equipment. The TFT consists of following the initial in-plane stress wave that propagates through a structure subjected to a dynamic load and characterizing how the wave is altered as it is transmitted through intersections of structural members. As a basis for evaluating the TFT, impact experiments and detailed stress wave analyses were performed for structures with two or three, or more members. Transfer functions that relate the wave transmitted through an intersection to the incident wave were deduced from the predicted wave response. By sequentially applying these transfer functions to a structure with several intersections, it was found that the environment produced by the initial stress wave propagating through the structure can be approximated well. The TFT can be used as a design tool or as an analytical tool to determine whether a more detailed wave analysis is warranted.
Goedel, Penrose, anti-Mach: Extra supersymmetries of time-dependent plane waves

NASA Astrophysics Data System (ADS)

Blau, Matthias; Meessen, Patrick; O'Loughlin, Martin

2003-09-01

We prove that M-theory plane waves with extra supersymmetries are necessarily homogeneous (but possibly time-dependent), and we show by explicit construction that such time-dependent plane waves can admit extra supersymmetries. To that end we study the Penrose limits of Gödel-like metrics, show that the Penrose limit of the M-theory Gödel metric (with 20 supercharges) is generically a time-dependent homogeneous plane wave of the anti-Mach type, and display the four extra Killings spinors in that case. We conclude with some general remarks on the Killing spinor equations for homogeneous plane waves.
Small scatterers in the lower mantle observed at German broadband arrays

USGS Publications Warehouse

Thomas, C.; Weber, M.; Wicks, C.W.; Scherbaum, F.

1999-01-01

Seismograms of earthquakes from the South Pacific recorded at a German broadband array and network show precursors to PKPdf. These precursors mainly originate from off-path scattering of PKPab or a nearby PKPbc to P (for receiver-side scattering) or from scattering of P to PKPab or PKPbc on the PKPdf path (for source-side scattering). Standard array processing techniques based on plane wave approximations (such as vespagram or frequency-wavenumber analysis) are inadequate for investigating these precursors since scattered waves cannot be approximated as plane waves for arrays and networks larger than 300 x 300 km for short-period waves. We therefore develop a migration method to estimate the location of scatterers in the mantle, at the core-mantle boundary and at the top of the outer core. With our method we are able to find isolated scatterers at the source side and the receiver side, although the depth of the scatterer is not well constrained. However, from looking at the first possible arrival time of precursors at different depth and the region where scattering can take place (scattering volume), we believe that the location of the scatterers is in the lowermost mantle. Since we have detected scatterers in regions where ultralow-velocity zones have been discovered recently, we think that the precursor energy possibly originates from scattering at partial melt at the base of the mantle. Comparing results from broadband and band-pass-filtered data the detection of small-scale structure of the ultralow-velocity zones becomes possible. Copyright 1999 by the American Geophysical Union.
Forced sound transmission through a finite-sized single leaf panel subject to a point source excitation.

PubMed

Wang, Chong

2018-03-01

In the case of a point source in front of a panel, the wavefront of the incident wave is spherical. This paper discusses spherical sound waves transmitting through a finite sized panel. The forced sound transmission performance that predominates in the frequency range below the coincidence frequency is the focus. Given the point source located along the centerline of the panel, forced sound transmission coefficient is derived through introducing the sound radiation impedance for spherical incident waves. It is found that in addition to the panel mass, forced sound transmission loss also depends on the distance from the source to the panel as determined by the radiation impedance. Unlike the case of plane incident waves, sound transmission performance of a finite sized panel does not necessarily converge to that of an infinite panel, especially when the source is away from the panel. For practical applications, the normal incidence sound transmission loss expression of plane incident waves can be used if the distance between the source and panel d and the panel surface area S satisfy d/S>0.5. When d/S ≈0.1, the diffuse field sound transmission loss expression may be a good approximation. An empirical expression for d/S=0 is also given.
Surface acoustic wave micromotor with arbitrary axis rotational capability

NASA Astrophysics Data System (ADS)

Tjeung, Ricky T.; Hughes, Mark S.; Yeo, Leslie Y.; Friend, James R.

2011-11-01

A surface acoustic wave (SAW) actuated rotary motor is reported here, consisting of a millimeter-sized spherical metal rotor placed on the surface of a lead zirconate titanate piezoelectric substrate upon which the SAW is made to propagate. At the design frequency of 3.2 MHz and with a fixed preload of 41.1 μN, the maximum rotational speed and torque achieved were approximately 1900 rpm and 5.37 μN-mm, respectively, producing a maximum output power of 1.19 μW. The surface vibrations were visualized using laser Doppler vibrometry and indicate that the rotational motion arises due to retrograde elliptical motions of the piezoelectric surface elements. Rotation about orthogonal axes in the plane of the substrate has been obtained by using orthogonally placed interdigital electrodes on the substrate to generate SAW impinging on the rotor, offering a means to generate rotation about an arbitrary axis in the plane of the substrate.
Parametric resonant triad interactions in a free shear layer

NASA Technical Reports Server (NTRS)

Mallier, R.; Maslowe, S. A.

1993-01-01

We investigate the weakly nonlinear evolution of a triad of nearly-neutral modes superimposed on a mixing layer with velocity profile u bar equals Um + tanh y. The perturbation consists of a plane wave and a pair of oblique waves each inclined at approximately 60 degrees to the mean flow direction. Because the evolution occurs on a relatively fast time scale, the critical layer dynamics dominate the process and the amplitude evolution of the oblique waves is governed by an integro-differential equation. The long-time solution of this equation predicts very rapid (exponential of an exponential) amplification and we discuss the pertinence of this result to vortex pairing phenomena in mixing layers.
Spin waves in planar quasicrystal of Penrose tiling

NASA Astrophysics Data System (ADS)

Rychły, J.; Mieszczak, S.; Kłos, J. W.

2018-03-01

We investigated two-dimensional magnonic structures which are the counterparts of photonic quasicrystals forming Penrose tiling. We considered the slab composed of Ni (or Py) disks embedded in Fe (or Co) matrix. The disks are arranged in quasiperiodic Penrose-like structure. The infinite quasicrystal was approximated by its rectangular section with periodic boundary conditions applied. This approach allowed us to use the plane wave method to find the frequency spectrum of eigenmodes for spin waves and their spatial profiles. The calculated integrated density of states shows more distinctive magnonic gaps for the structure composed of materials of high magnetic contrast (Ni and Fe) and relatively high filling fraction. This proves the impact of quasiperiodic long-range order on the spectrum of spin waves. We also investigated the localization of spin wave eingenmodes resulting from the quasiperiodicity of the structure.
Topologically protected edge states for out-of-plane and in-plane bulk elastic waves.

PubMed

Huo, Shao-Yong; Chen, Jiu-Jiu; Huang, Hong-Bo

2018-04-11

Topological phononic insulators (TPnIs) show promise for application in the manipulation of acoustic waves for the design of low-loss transmission and perfectly integrated communication devices. Since solid phononic crystals exist as a transverse polarization mode and a mixed longitudinal-transverse polarization mode, the realization of topological edge states for both out-of-plane and in-plane bulk elastic waves is desirable to enhance the controllability of the edge waves in solid systems. In this paper, a two-dimensional (2D) solid/solid hexagonal-latticed phononic system that simultaneously supports the topologically protected edge states for out-of-plane and in-plane bulk elastic waves is investigated. Firstly, two pairs of two-fold Dirac cones, respectively corresponding to the out-of-plane and in-plane waves, are obtained at the same frequency by tuning the crystal parameters. Then, a strategy of zone folding is invoked to form double Dirac cones. By shrinking and expanding the steel scatterer, the lattice symmetry is broken, and band inversions induced, giving rise to an intriguing topological phase transition. Finally, the topologically protected edge states for both out-of-plane and in-plane bulk elastic waves, which can be simultaneously located at the frequency range from 1.223 to 1.251 MHz, are numerically observed. Robust pseudospin-dependent elastic edge wave propagation along arbitrary paths is further demonstrated. Our results will significantly broaden its practical application in the engineering field.
Topologically protected edge states for out-of-plane and in-plane bulk elastic waves

NASA Astrophysics Data System (ADS)

Huo, Shao-Yong; Chen, Jiu-Jiu; Huang, Hong-Bo

2018-04-01

Topological phononic insulators (TPnIs) show promise for application in the manipulation of acoustic waves for the design of low-loss transmission and perfectly integrated communication devices. Since solid phononic crystals exist as a transverse polarization mode and a mixed longitudinal-transverse polarization mode, the realization of topological edge states for both out-of-plane and in-plane bulk elastic waves is desirable to enhance the controllability of the edge waves in solid systems. In this paper, a two-dimensional (2D) solid/solid hexagonal-latticed phononic system that simultaneously supports the topologically protected edge states for out-of-plane and in-plane bulk elastic waves is investigated. Firstly, two pairs of two-fold Dirac cones, respectively corresponding to the out-of-plane and in-plane waves, are obtained at the same frequency by tuning the crystal parameters. Then, a strategy of zone folding is invoked to form double Dirac cones. By shrinking and expanding the steel scatterer, the lattice symmetry is broken, and band inversions induced, giving rise to an intriguing topological phase transition. Finally, the topologically protected edge states for both out-of-plane and in-plane bulk elastic waves, which can be simultaneously located at the frequency range from 1.223 to 1.251 MHz, are numerically observed. Robust pseudospin-dependent elastic edge wave propagation along arbitrary paths is further demonstrated. Our results will significantly broaden its practical application in the engineering field.
Relationship between strong-motion array parameters and the accuracy of source inversion and physical waves

USGS Publications Warehouse

Iida, M.; Miyatake, T.; Shimazaki, K.

1990-01-01

We develop general rules for a strong-motion array layout on the basis of our method of applying a prediction analysis to a source inversion scheme. A systematic analysis is done to obtain a relationship between fault-array parameters and the accuracy of a source inversion. Our study of the effects of various physical waves indicates that surface waves at distant stations contribute significantly to the inversion accuracy for the inclined fault plane, whereas only far-field body waves at both small and large distances contribute to the inversion accuracy for the vertical fault, which produces more phase interference. These observations imply the adequacy of the half-space approximation used throughout our present study and suggest rules for actual array designs. -from Authors
Tunable Snell's law for spin waves in heterochiral magnetic films

NASA Astrophysics Data System (ADS)

Mulkers, Jeroen; Van Waeyenberge, Bartel; Milošević, Milorad V.

2018-03-01

Thin ferromagnetic films with an interfacially induced DMI exhibit nontrivial asymmetric dispersion relations that lead to unique and useful magnonic properties. Here we derive an analytical expression for the magnon propagation angle within the micromagnetic framework and show how the dispersion relation can be approximated with a comprehensible geometrical interpretation in the k space of the propagation of spin waves. We further explore the refraction of spin waves at DMI interfaces in heterochiral magnetic films, after deriving a generalized Snell's law tunable by an in-plane magnetic field, that yields analytical expressions for critical incident angles. The found asymmetric Brewster angles at interfaces of regions with different DMI strengths, adjustable by magnetic field, support the conclusion that heterochiral ferromagnetic structures are an ideal platform for versatile spin-wave guides.
Scattering of three-dimensional plane waves in a self-reinforced half-space lying over a triclinic half-space

NASA Astrophysics Data System (ADS)

Gupta, Shishir; Pramanik, Abhijit; Smita; Pramanik, Snehamoy

2018-06-01

The phenomenon of plane waves at the intersecting plane of a triclinic half-space and a self-reinforced half-space is discussed with possible applications during wave propagation. Analytical expressions of the phase velocities of reflection and refraction for quasi-compressional and quasi-shear waves under initial stress are discussed carefully. The closest form of amplitude proportions on reflection and refraction factors of three quasi-plane waves are developed mathematically by applying appropriate boundary conditions. Graphics are sketched to exhibit the consequences of initial stress in the three-dimensional plane wave on reflection and refraction coefficients. Some special cases that coincide with the fundamental properties of several layers are designed to express the reflection and refraction coefficients.

Prevalence of direct-reaction mechanism in a deeply inelastic reaction, /sup 197/Au(/sup 19/F,/sup 12/B)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ishihara, M.; Shimoda, T.; Froehlich, H.

1979-07-09

Continuum cross sections and spin polarizations of /sup 12/B produced in the reaction /sup 197/Au(/sup 19/F,/sup 12/B) induced by 186-MeV/sup 19/F were measured. The observed data were reproduced very well in terms of a distorted-wave Born-approximation theory, indicating that this reaction transferring as many as seven nucleons proceeds as a direct process.
Ultrafast dynamic response of single crystal β-HMX

NASA Astrophysics Data System (ADS)

Zaug, Joseph M.; Armstrong, Michael R.; Crowhurst, Jonathan C.; Radousky, Harry B.; Ferranti, Louis; Swan, Raymond; Gross, Rick; Teslich, Nick E.; Wall, Mark A.; Austin, Ryan A.; Fried, Laurence E.

2017-01-01

We report results from ultrafast compression experiments conducted on β-HMX single crystals. Results consist of nominally 12 picosecond time-resolved wave profile data, (ultrafast time domain interferometry -TDI measurements), that were analyzed to determine high-velocity wave speeds as a function of piston velocity. TDI results are used to validate calculations of anisotropic stress-strain behavior of shocked loaded energetic materials. Our previous results derived using a 350 ps duration compression drive revealed anisotropic elastic wave response in single crystal β-HMX from (110) and (010) impact planes. Here we present results using a 1.05 ns duration compression drive with a 950 ps interferometry window to extend knowledge of the anisotropic dynamic response of β-HMX within eight microns of the initial impact plane. We observe two distinct wave profiles from (010) and three wave profiles from (010) impact planes. The (110) impact plane wave speeds typically exceed (010) impact plane wave speeds at the same piston velocities. The development of multiple hydrodynamic wave profiles begins at 20 GPa for the (110) impact plane and 28 GPa for the (10) impact plane. We compare our ultrafast TDI results with previous gun and plate impact results on β-HMX and PBX9501.
The influence of air-filled structures on wave propagation and beam formation of a pygmy sperm whale (Kogia breviceps) in horizontal and vertical planes.

PubMed

Song, Zhongchang; Zhang, Yu; Thornton, Steven W; Li, Songhai; Dong, Jianchen

2017-10-01

The wave propagation, sound field, and transmission beam pattern of a pygmy sperm whale (Kogia breviceps) were investigated in both the horizontal and vertical planes. Results suggested that the signals obtained at both planes were similarly characterized with a high peak frequency and a relatively narrow bandwidth, close to the ones recorded from live animals. The sound beam measured outside the head in the vertical plane was narrower than that of the horizontal one. Cases with different combinations of air-filled structures in both planes were used to study the respective roles in controlling wave propagation and beam formation. The wave propagations and beam patterns in the horizontal and vertical planes elucidated the important reflection effect of the spermaceti and vocal chambers on sound waves, which was highly significant in forming intensive forward sound beams. The air-filled structures, the forehead soft tissues and skull structures formed wave guides in these two planes for emitted sounds to propagate forward.
Bistability By Self-Reflection In A Saturable Absorber

NASA Astrophysics Data System (ADS)

Roso-Franco, Luis

1987-01-01

Propagation of laser light through a saturable absorber is theoretically studied. Computed steady state solutions of the Maxwell equations describing the unidimensional propagation of a plane monochromatic wave without introducing the slowly-varying envelope approximation are presented showing how saturation effects can influence the absorption of the field. At a certain range of refractive index and extintion coefficients, computed solutions display a very susprising behaviour, and a self-reflected wave appears inside the absorber. This can be useful for a new kind of biestable device, similar to a standard bistable cavity but with the back mirror self-induced by the light.
Evanescent waves and deaf bands in sonic crystals

NASA Astrophysics Data System (ADS)

Romero-García, V.; Garcia-Raffi, L. M.; Sánchez-Pérez, J. V.

2011-12-01

The properties of sonic crystals (SC) are theoretically investigated in this work by solving the inverse problem k(ω) using the extended plane wave expansion (EPWE). The solution of the resulting eigenvalue problem gives the complex band structure which takes into account both the propagating and the evanescent modes. In this work we show the complete mathematical formulation of the EPWE for SC and the supercell approximation for its use in both a complete SC and a SC with defects. As an example we show a novel interpretation of the deaf bands in a complete SC in good agreement with multiple scattering simulations.
Explicit inclusion of nonlocality in ( d , p ) transfer reactions

DOE PAGES

Titus, L. J.; Nunes, F. M.; Potel, G.

2016-01-06

Traditionally, nucleon-nucleus optical potentials are made local for convenience. In recent work we studied the effects of including nonlocal interactions explicitly in the final state for (d,p) reactions, within the distorted wave Born approximation. Our goal in this work is to develop an improved formalism for nonlocal interactions that includes deuteron breakup and to use it to study the effects of including nonlocal interactions in transfer (d,p) reactions, in both the deuteron and the proton channel. We extend the finite-range adiabatic distorted wave approximation to include nonlocal nucleon optical potentials. We apply our method to (d,p) reactions on 16O, 40Ca,more » 48Ca, 126Sn, 132Sn, and 208Pb at 10, 20 and 50 MeV. Here, we find that nonlocality in the deuteron scattering state reduces the amplitude of the wave function in the nuclear interior, and shifts the wave function outward. In many cases, this has the effect of increasing the transfer cross section at the first peak of the angular distributions. This increase was most significant for heavy targets and for reactions at high energies. Lastly, our systematic study shows that, if only local optical potentials are used in the analysis of experimental (d, p) transfer cross sections, the extracted spectroscopic factors may be incorrect by up to 40% due to the local approximation.« less
Single-Slit Diffraction: Transitioning from Geometric Optics to the Fraunhofer Regime

ERIC Educational Resources Information Center

Panuski, Christopher L.; Mungan, Carl E.

2016-01-01

Suppose a red laser beam (of wavelength ? equal to 0.660 µm) is expanded using an optical telescope into a collimated, approximately plane wave that is 5.68 mm in diameter. Pass that beam through a tall rectangular slit whose width "a" is gradually reduced from 3.30 to 0.100 mm. Look at its image on a screen located at a distance…
Absorption, scattering, and radiation force efficiencies in the longitudinal wave scattering by a small viscoelastic particle in an isotropic solid.

PubMed

Lopes, J H; Leão-Neto, J P; Silva, G T

2017-11-01

Analytical expressions of the absorption, scattering, and elastic radiation force efficiency factors are derived for the longitudinal plane wave scattering by a small viscoelastic particle in a lossless solid matrix. The particle is assumed to be much smaller than the incident wavelength, i.e., the so-called long-wavelength (Rayleigh) approximation. The efficiencies are dimensionless quantities that represent the absorbed and scattering powers and the elastic radiation force on the particle. In the quadrupole approximation, they are expressed in terms of contrast functions (bulk and shear moduli, and density) between the particle and solid matrix. The results for a high-density polyethylene particle embedded in an aluminum matrix agree with those obtained with the partial wave expansion method. Additionally, the connection between the elastic radiation force and forward scattering function is established through the optical theorem. The present results should be useful for ultrasound characterization of particulate composites, and the development of implanted devices activated by radiation force.
Projection operators for the Rossby and Poincare waves in a beta-plane approximation

NASA Astrophysics Data System (ADS)

Lebedkina, Anastasia; Ivan, Karpov; Sergej, Leble

2013-04-01

Study of the wave structure variations of atmospheric parameters is a due to a solving of number practical problems associated with the weather and the state of the environment requires knowledge of the spectral characteristics of atmospheric waves. Modern methods, for identification of wave disturbances in the atmosphere, based on the harmonic analysis of observations. The success of these application is determined by the presence of sets of experimental data obtained in the long-term (over the period of the wave) of the atmosphere on a large number of independent observation stations. Currently, the system of observation in the atmosphere, both terrestrial and satellite, unevenly covers the surface of the Earth and, despite the length of observation, doesn't solve the problem of identification of waves. Thus, the problem of identification wave disturbances conflicts fundamental difficulties, and solution needs in a new methods for the analysis of observations. The work complete a procedure to construct a projection operators for large-scale waves in the atmosphere. Advantage of this method is the ability to identify type of wave and its characteristics only on the base of a time series of observations. It means that the problem of waves identification can be solved on the basis of only one station observations. In the method assumed that the observed spatial and temporal structure of the atmosphere is determined by the superposition of different type waves. For each type of waves involved in this superposition, dispersion and polarization relations (between the components of the wave vector of the field) expect as known. Based on these assumptions, we can construct projection operators on the initial superposition state on the linear basis of vectors corresponding to the known type of atmospheric waves. The action of the design on the superposition state, which, in fact, is the result of observations, determine the amplitude and phase of the waves of a known type. The idea to use the polarization relations for the classification of waves originated in radio physics in the works of A. A. Novikov. In the theory of the electromagnetic field polarization relations is traditionally included in the analysis of wave phenomena. In the theory of acoustic-gravity waves, projection operators were introduced in a works of S. B. Leble. The object of study is a four-dimentional vector (components of the velocity, pressure and temperature). Based on these assumptions, we can construct the projection operators for superposition state on the linear basis, corresponding to the well-known type of waves. In this paper we consider procedure for construction of a projection operators for planetary Rossby and Poincare waves in the Earth's atmosphere in the approximation of the "beta-plane". In a result of work we constructed projection operators in this approximation for Poincare and Rossby waves. The tests for operators shown, that separation of the contribution of corresponding waves from source of the wave field is possible. Estimation accuracy of the operators and results of applying operators to the data TEC presented.
Quantitative determination of the lateral density and intermolecular correlation between proteins anchored on the membrane surfaces using grazing incidence small-angle X-ray scattering and grazing incidence X-ray fluorescence.

PubMed

Abuillan, Wasim; Vorobiev, Alexei; Hartel, Andreas; Jones, Nicola G; Engstler, Markus; Tanaka, Motomu

2012-11-28

As a physical model of the surface of cells coated with densely packed, non-crystalline proteins coupled to lipid anchors, we functionalized the surface of phospholipid membranes by coupling of neutravidin to biotinylated lipid anchors. After the characterization of fine structures perpendicular to the plane of membrane using specular X-ray reflectivity, the same membrane was characterized by grazing incidence small angle X-ray scattering (GISAXS). Within the framework of distorted wave Born approximation and two-dimensional Percus-Yevick function, we can analyze the form and structure factors of the non-crystalline, membrane-anchored proteins for the first time. As a new experimental technique to quantify the surface density of proteins on the membrane surface, we utilized grazing incidence X-ray fluorescence (GIXF). Here, the mean intermolecular distance between proteins from the sulfur peak intensities can be calculated by applying Abelé's matrix formalism. The characteristic correlation distance between non-crystalline neutravidin obtained by the GISAXS analysis agrees well with the intermolecular distance calculated by GIXF, suggesting a large potential of the combination of GISAXS and GIXF in probing the lateral density and correlation of non-crystalline proteins displayed on the membrane surface.
A feasibility study of the use of bounded beams resembling the shape of evanescent and inhomogeneous waves.

PubMed

Declercq, Nico F; Leroy, Oswald

2011-08-01

Plane waves are solutions of the visco-elastic wave equation. Their wave vector can be real for homogeneous plane waves or complex for inhomogeneous and evanescent plane waves. Although interesting from a theoretical point of view, complex wave vectors normally only emerge naturally when propagation or scattering is studied of sound under the appearance of damping effects. Because of the particular behavior of inhomogeneous and evanescent waves and their estimated efficiency for surface wave generation, bounded beams, experimentally mimicking their infinite counterparts similar to (wide) Gaussian beams imitating infinite harmonic plane waves, are of special interest in this report. The study describes the behavior of bounded inhomogeneous and bounded evanescent waves in terms of amplitude and phase distribution as well as energy flow direction. The outcome is of importance to the applicability of bounded inhomogeneous ultrasonic waves for nondestructive testing. Copyright © 2011. Published by Elsevier B.V.
Rogue waves of the Kundu-Eckhaus equation in a chaotic wave field.

PubMed

Bayindir, Cihan

2016-03-01

In this paper we study the properties of the chaotic wave fields generated in the frame of the Kundu-Eckhaus equation (KEE). Modulation instability results in a chaotic wave field which exhibits small-scale filaments with a free propagation constant, k. The average velocity of the filaments is approximately given by the average group velocity calculated from the dispersion relation for the plane-wave solution; however, direction of propagation is controlled by the β parameter, the constant in front of the Raman-effect term. We have also calculated the probabilities of the rogue wave occurrence for various values of propagation constant k and showed that the probability of rogue wave occurrence depends on k. Additionally, we have showed that the probability of rogue wave occurrence significantly depends on the quintic and the Raman-effect nonlinear terms of the KEE. Statistical comparisons between the KEE and the cubic nonlinear Schrödinger equation have also been presented.
The effective propagation constants of SH wave in composites reinforced by dispersive parallel nanofibers

NASA Astrophysics Data System (ADS)

Qiang, FangWei; Wei, PeiJun; Li, Li

2012-07-01

In the present paper, the effective propagation constants of elastic SH waves in composites with randomly distributed parallel cylindrical nanofibers are studied. The surface stress effects are considered based on the surface elasticity theory and non-classical interfacial conditions between the nanofiber and the host are derived. The scattering waves from individual nanofibers embedded in an infinite elastic host are obtained by the plane wave expansion method. The scattering waves from all fibers are summed up to obtain the multiple scattering waves. The interactions among random dispersive nanofibers are taken into account by the effective field approximation. The effective propagation constants are obtained by the configurational average of the multiple scattering waves. The effective speed and attenuation of the averaged wave and the associated dynamical effective shear modulus of composites are numerically calculated. Based on the numerical results, the size effects of the nanofibers on the effective propagation constants and the effective modulus are discussed.
Electromagnetic scattering and absorption by thin walled dielectric cylinders with application to ice crystals

NASA Technical Reports Server (NTRS)

Senior, T. B. A.; Weil, H.

1977-01-01

Important in the atmospheric heat balance are the reflection, transmission, and absorption of visible and infrared radiation by clouds and polluted atmospheres. Integral equations are derived to evaluate the scattering and absorption of electromagnetic radiation from thin cylindrical dielectric shells of arbitrary cross section when irradiated by a plane wave of any polarization incident in a plane perpendicular to the generators. Application of the method to infinitely long hexagonal cylinders has yielded numerical scattering and absorption data which simulate columnar sheath ice crystals. It is found that the numerical procedures are economical for cylinders having perimeters less than approximately fifteen free-space wavelengths.
Non-plane-wave Hartree-Fock states and nuclear homework potentials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gutierrez, G.; Plastino, A.; de Llano, M.

1979-12-01

It is shown that non-plane-wave single-particle Hartree-Fock orbitals giving rise to a ''spin-density-wave-like'' structure give lower energy than plane waves beyond a certain relatively low density in both nuclear and neutron matter with homework pair potentials v/sub 1/ and v/sub 2/.
Explosive plane-wave lens

DOEpatents

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.
Explosive plane-wave lens

DOEpatents

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.
High-frequency Born synthetic seismograms based on coupled normal modes

USGS Publications Warehouse

Pollitz, F.

2011-01-01

High-frequency and full waveform synthetic seismograms on a 3-D laterally heterogeneous earth model are simulated using the theory of coupled normal modes. The set of coupled integral equations that describe the 3-D response are simplified into a set of uncoupled integral equations by using the Born approximation to calculate scattered wavefields and the pure-path approximation to modulate the phase of incident and scattered wavefields. This depends upon a decomposition of the aspherical structure into smooth and rough components. The uncoupled integral equations are discretized and solved in the frequency domain, and time domain results are obtained by inverse Fourier transform. Examples show the utility of the normal mode approach to synthesize the seismic wavefields resulting from interaction with a combination of rough and smooth structural heterogeneities. This approach is applied to an ~4 Hz shallow crustal wave propagation around the site of the San Andreas Fault Observatory at Depth (SAFOD). ?? The Author Geophysical Journal International ?? 2011 RAS.
Design of 280 GHz feedhorn-coupled TES arrays for the balloon-borne polarimeter SPIDER

NASA Astrophysics Data System (ADS)

Hubmayr, Johannes; Austermann, Jason E.; Beall, James A.; Becker, Daniel T.; Benton, Steven J.; Bergman, A. Stevie; Bond, J. Richard; Bryan, Sean; Duff, Shannon M.; Duivenvoorden, Adri J.; Eriksen, H. K.; Filippini, Jeffrey P.; Fraisse, A.; Galloway, Mathew; Gambrel, Anne E.; Ganga, K.; Grigorian, Arpi L.; Gualtieri, Riccardo; Gudmundsson, Jon E.; Hartley, John W.; Halpern, M.; Hilton, Gene C.; Jones, William C.; McMahon, Jeffrey J.; Moncelsi, Lorenzo; Nagy, Johanna M.; Netterfield, C. B.; Osherson, Benjamin; Padilla, Ivan; Rahlin, Alexandra S.; Racine, B.; Ruhl, John; Rudd, T. M.; Shariff, J. A.; Soler, J. D.; Song, Xue; Ullom, Joel N.; Van Lanen, Jeff; Vissers, Michael R.; Wehus, I. K.; Wen, Shyang; Wiebe, D. V.; Young, Edward

2016-07-01

We describe 280 GHz bolometric detector arrays that instrument the balloon-borne polarimeter spider. A primary science goal of spider is to measure the large-scale B-mode polarization of the cosmic microwave background (cmb) in search of the cosmic-inflation, gravitational-wave signature. 280 GHz channels aid this science goal by constraining the level of B-mode contamination from galactic dust emission. We present the focal plane unit design, which consists of a 16x16 array of conical, corrugated feedhorns coupled to a monolithic detector array fabricated on a 150 mm diameter silicon wafer. Detector arrays are capable of polarimetric sensing via waveguide probe-coupling to a multiplexed array of transition-edge-sensor (TES) bolometers. The spider receiver has three focal plane units at 280 GHz, which in total contains 765 spatial pixels and 1,530 polarization sensitive bolometers. By fabrication and measurement of single feedhorns, we demonstrate 14.7° FHWM Gaussian-shaped beams with <1% ellipticity in a 30% fractional bandwidth centered at 280 GHz. We present electromagnetic simulations of the detection circuit, which show 94% band-averaged, single-polarization coupling efficiency, 3% reflection and 3% radiative loss. Lastly, we demonstrate a low thermal conductance bolometer, which is well-described by a simple TES model and exhibits an electrical noise equivalent power (NEP) = 2.6 x 10-17 W/√Hz, consistent with the phonon noise prediction.
Tissue elasticity of in vivo skeletal muscles measured in the transverse and longitudinal planes using shear wave elastography.

PubMed

Chino, Kentaro; Kawakami, Yasuo; Takahashi, Hideyuki

2017-07-01

The aim of the present study was to measure in vivo skeletal muscle elasticity in the transverse and longitudinal planes using shear wave elastography and then to compare the image stability, measurement values and measurement repeatability between these imaging planes. Thirty-one healthy males participated in this study. Tissue elasticity (shear wave velocity) of the medial gastrocnemius, rectus femoris, biceps brachii and rectus abdominis was measured in both the transverse and longitudinal planes using shear wave elastography. Image stability was evaluated by the standard deviation of the colour distribution in the shear wave elastography image. Measurement repeatability was assessed by the coefficient of variance obtained from three measurement values. Image stability of all tested muscles was significantly higher in the longitudinal plane (P<0·001), but measurement repeatability did not differ significantly between the imaging planes (P>0·05), except in the biceps brachii (P = 0·001). Measurement values of the medial gastrocnemius, rectus femoris and biceps brachii were significantly different between the imaging planes (P<0·001). Image stability and measurement values of shear wave elastography images varied with imaging plane, which indicates that imaging plane should be considered when measuring skeletal muscle tissue elasticity by shear wave elastography. © 2015 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd.

Plane-Wave Implementation and Performance of à-la-Carte Coulomb-Attenuated Exchange-Correlation Functionals for Predicting Optical Excitation Energies in Some Notorious Cases.

PubMed

Bircher, Martin P; Rothlisberger, Ursula

2018-06-12

Linear-response time-dependent density functional theory (LR-TD-DFT) has become a valuable tool in the calculation of excited states of molecules of various sizes. However, standard generalized-gradient approximation and hybrid exchange-correlation (xc) functionals often fail to correctly predict charge-transfer (CT) excitations with low orbital overlap, thus limiting the scope of the method. The Coulomb-attenuation method (CAM) in the form of the CAM-B3LYP functional has been shown to reliably remedy this problem in many CT systems, making accurate predictions possible. However, in spite of a rather consistent performance across different orbital overlap regimes, some pitfalls remain. Here, we present a fully flexible and adaptable implementation of the CAM for Γ-point calculations within the plane-wave pseudopotential molecular dynamics package CPMD and explore how customized xc functionals can improve the optical spectra of some notorious cases. We find that results obtained using plane waves agree well with those from all-electron calculations employing atom-centered bases, and that it is possible to construct a new Coulomb-attenuated xc functional based on simple considerations. We show that such a functional is able to outperform CAM-B3LYP in some cases, while retaining similar accuracy in systems where CAM-B3LYP performs well.
Upper Atmosphere Heating From Ocean-Generated Acoustic Wave Energy

DOE PAGES

Bowman, D. C.; Lees, J. M.

2018-04-27

We present that colliding sea surface waves generate the ocean microbarom, an acoustic signal that may transmit significant energy to the upper atmosphere. Previous estimates of acoustic energy flux from the ocean microbarom and mountain-wind interactions are on the order of 0.01 to 1 mW/m 2, heating the thermosphere by tens of Kelvins per day. We captured upgoing ocean microbarom waves with a balloon-borne infrasound microphone; the maximum acoustic energy flux was approximately 0.05 mW/m 2. This is about half the average value reported in previous ground-based microbarom observations spanning 8 years. The acoustic flux from the microbarom episode describedmore » here may have heated the thermosphere by several Kelvins per day while the source persisted. Lastly, we suggest that ocean wave models could be used to parameterize acoustically generated heating of the upper atmosphere based on sea state.« less
Upper Atmosphere Heating From Ocean-Generated Acoustic Wave Energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bowman, D. C.; Lees, J. M.

We present that colliding sea surface waves generate the ocean microbarom, an acoustic signal that may transmit significant energy to the upper atmosphere. Previous estimates of acoustic energy flux from the ocean microbarom and mountain-wind interactions are on the order of 0.01 to 1 mW/m 2, heating the thermosphere by tens of Kelvins per day. We captured upgoing ocean microbarom waves with a balloon-borne infrasound microphone; the maximum acoustic energy flux was approximately 0.05 mW/m 2. This is about half the average value reported in previous ground-based microbarom observations spanning 8 years. The acoustic flux from the microbarom episode describedmore » here may have heated the thermosphere by several Kelvins per day while the source persisted. Lastly, we suggest that ocean wave models could be used to parameterize acoustically generated heating of the upper atmosphere based on sea state.« less
Dirty two-band superconductivity with interband pairing order

NASA Astrophysics Data System (ADS)

Asano, Yasuhiro; Sasaki, Akihiro; Golubov, Alexander A.

2018-04-01

We study theoretically the effects of random nonmagnetic impurities on the superconducting transition temperature T c in a two-band superconductor characterized by an equal-time s-wave interband pairing order parameter. Because of the two-band degree of freedom, it is possible to define a spin-triplet s-wave pairing order parameter as well as a spin-singlet s-wave order parameter. The former belongs to odd-band-parity symmetry class, whereas the latter belongs to even-band-parity symmetry class. In a spin-singlet superconductor, T c is insensitive to the impurity concentration when we estimate the self-energy due to the random impurity potential within the Born approximation. On the other hand in a spin-triplet superconductor, T c decreases with the increase of the impurity concentration. We conclude that Cooper pairs belonging to odd-band-parity symmetry class are fragile under the random impurity potential even though they have s-wave pairing symmetry.
Nuclear Fusion Rate Study of a Muonic Molecule via Nuclear Threshold Resonances

NASA Astrophysics Data System (ADS)

Faghihi, F.; Eskandari, M. R.

This work follows our previous calculations of the ground state binding energy, size, and the effective nuclear charge of the muonic T3 molecule, using the Born-Oppenheimer adiabatic approximation. In our past articles, we showed that the system possesses two minimum positions, the first one at the muonic distance and the second at the atomic distance. Also, the symmetric planner vibrational model assumed between the two minima and the approximated potential were calculated. Following from the previous studies, we now calculate the fusion rate of the T3 muonic molecule according to the overlap integral of the resonance nuclear compound nucleus and the molecular wave functions.
The consequences of improperly describing oscillator strengths beyond the electric dipole approximation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lestrange, Patrick J.; Egidi, Franco; Li, Xiaosong, E-mail: xsli@uw.edu

2015-12-21

The interaction between a quantum mechanical system and plane wave light is usually modeled within the electric dipole approximation. This assumes that the intensity of the incident field is constant over the length of the system and transition probabilities are described in terms of the electric dipole transition moment. For short wavelength spectroscopies, such as X-ray absorption, the electric dipole approximation often breaks down. Higher order multipoles are then included to describe transition probabilities. The square of the magnetic dipole and electric quadrupole are often included, but this results in an origin-dependent expression for the oscillator strength. The oscillator strengthmore » can be made origin-independent if all terms through the same order in the wave vector are retained. We will show the consequences and potential pitfalls of using either of these two expressions. It is shown that the origin-dependent expression may violate the Thomas-Reiche-Kuhn sum rule and the origin-independent expression can result in negative transition probabilities.« less
The consequences of improperly describing oscillator strengths beyond the electric dipole approximation.

PubMed

Lestrange, Patrick J; Egidi, Franco; Li, Xiaosong

2015-12-21

The interaction between a quantum mechanical system and plane wave light is usually modeled within the electric dipole approximation. This assumes that the intensity of the incident field is constant over the length of the system and transition probabilities are described in terms of the electric dipole transition moment. For short wavelength spectroscopies, such as X-ray absorption, the electric dipole approximation often breaks down. Higher order multipoles are then included to describe transition probabilities. The square of the magnetic dipole and electric quadrupole are often included, but this results in an origin-dependent expression for the oscillator strength. The oscillator strength can be made origin-independent if all terms through the same order in the wave vector are retained. We will show the consequences and potential pitfalls of using either of these two expressions. It is shown that the origin-dependent expression may violate the Thomas-Reiche-Kuhn sum rule and the origin-independent expression can result in negative transition probabilities.
The consequences of improperly describing oscillator strengths beyond the electric dipole approximation

NASA Astrophysics Data System (ADS)

Lestrange, Patrick J.; Egidi, Franco; Li, Xiaosong

2015-12-01

The interaction between a quantum mechanical system and plane wave light is usually modeled within the electric dipole approximation. This assumes that the intensity of the incident field is constant over the length of the system and transition probabilities are described in terms of the electric dipole transition moment. For short wavelength spectroscopies, such as X-ray absorption, the electric dipole approximation often breaks down. Higher order multipoles are then included to describe transition probabilities. The square of the magnetic dipole and electric quadrupole are often included, but this results in an origin-dependent expression for the oscillator strength. The oscillator strength can be made origin-independent if all terms through the same order in the wave vector are retained. We will show the consequences and potential pitfalls of using either of these two expressions. It is shown that the origin-dependent expression may violate the Thomas-Reiche-Kuhn sum rule and the origin-independent expression can result in negative transition probabilities.
Numerical Study of Nonlinear Structures of Locally Excited Marangoni Convection in the Long-Wave Approximation

NASA Astrophysics Data System (ADS)

Wertgeim, Igor I.

2018-02-01

We investigate stationary and non-stationary solutions of nonlinear equations of the long-wave approximation for the Marangoni convection caused by a localized source of heat or a surface active impurity (surfactant) in a thin horizontal layer of a viscous incompressible fluid with a free surface. The distribution of heat or concentration flux is determined by the uniform vertical gradient of temperature or impurity concentration, distorted by the imposition of a slightly inhomogeneous heating or of surfactant, localized in the horizontal plane. The lower boundary of the layer is considered thermally insulated or impermeable, whereas the upper boundary is free and deformable. The equations obtained in the long-wave approximation are formulated in terms of the amplitudes of the temperature distribution or impurity concentration, deformation of the surface, and vorticity. For a simplification of the problem, a sequence of nonlinear equations is obtained, which in the simplest form leads to a nonlinear Schrödinger equation with a localized potential. The basic state of the system, its dependence on the parameters and stability are investigated. For stationary solutions localized in the region of the surface tension inhomogeneity, domains of parameters corresponding to different spatial patterns are delineated.
Born iterative reconstruction using perturbed-phase field estimates.

PubMed

Astheimer, Jeffrey P; Waag, Robert C

2008-10-01

A method of image reconstruction from scattering measurements for use in ultrasonic imaging is presented. The method employs distorted-wave Born iteration but does not require using a forward-problem solver or solving large systems of equations. These calculations are avoided by limiting intermediate estimates of medium variations to smooth functions in which the propagated fields can be approximated by phase perturbations derived from variations in a geometric path along rays. The reconstruction itself is formed by a modification of the filtered-backpropagation formula that includes correction terms to account for propagation through an estimated background. Numerical studies that validate the method for parameter ranges of interest in medical applications are presented. The efficiency of this method offers the possibility of real-time imaging from scattering measurements.
Vacuum electron acceleration by coherent dipole radiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Troha, A.L.; Van Meter, J.R.; Landahl, E.C.

1999-07-01

The validity of the concept of laser-driven vacuum acceleration has been questioned, based on an extrapolation of the well-known Lawson-Woodward theorem, which stipulates that plane electromagnetic waves cannot accelerate charged particles in vacuum. To formally demonstrate that electrons can indeed be accelerated in vacuum by focusing or diffracting electromagnetic waves, the interaction between a point charge and coherent dipole radiation is studied in detail. The corresponding four-potential exactly satisfies both Maxwell{close_quote}s equations and the Lorentz gauge condition everywhere, and is analytically tractable. It is found that in the far-field region, where the field distribution closely approximates that of a planemore » wave, we recover the Lawson-Woodward result, while net acceleration is obtained in the near-field region. The scaling of the energy gain with wave-front curvature and wave amplitude is studied systematically. {copyright} {ital 1999} {ital The American Physical Society}« less
Wind velocity profile reconstruction from intensity fluctuations of a plane wave propagating in a turbulent atmosphere.

PubMed

Banakh, V A; Marakasov, D A

2007-08-01

Reconstruction of a wind profile based on the statistics of plane-wave intensity fluctuations in a turbulent atmosphere is considered. The algorithm for wind profile retrieval from the spatiotemporal spectrum of plane-wave weak intensity fluctuations is described, and the results of end-to-end computer experiments on wind profiling based on the developed algorithm are presented. It is shown that the reconstructing algorithm allows retrieval of a wind profile from turbulent plane-wave intensity fluctuations with acceptable accuracy.
Testing the Ginzburg-Landau approximation for three-flavor crystalline color superconductivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mannarelli, Massimo; Sharma, Rishi; Rajagopal, Krishna

2006-06-01

It is an open challenge to analyze the crystalline color superconducting phases that may arise in cold dense, but not asymptotically dense, three-flavor quark matter. At present the only approximation within which it seems possible to compare the free energies of the myriad possible crystal structures is the Ginzburg-Landau approximation. Here, we test this approximation on a particularly simple 'crystal' structure in which there are only two condensates {approx}{delta}exp(iq{sub 2}{center_dot}r) and {approx}{delta}exp(iq{sub 3}{center_dot}r) whose position-space dependence is that of two plane waves with wave vectors q{sub 2} and q{sub 3} at arbitrary angles. For this case, we are able tomore » solve the mean-field gap equation without making a Ginzburg-Landau approximation. We find that the Ginzburg-Landau approximation works in the {delta}{yields}0 limit as expected, find that it correctly predicts that {delta} decreases with increasing angle between q{sub 2} and q{sub 3} meaning that the phase with q{sub 2} parallel q{sub 3} has the lowest free energy, and find that the Ginzburg-Landau approximation is conservative in the sense that it underestimates {delta} at all values of the angle between q{sub 2} and q{sub 3}.« less
Explosive plane-wave lens

DOEpatents

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.
Coupled-mode theory and Fano resonances in guided-mode resonant gratings: the conical diffraction mounting.

PubMed

Bykov, Dmitry A; Doskolovich, Leonid L; Soifer, Victor A

2017-01-23

We study resonances of guided-mode resonant gratings in conical mounting. By developing 2D time-dependent coupled-mode theory we obtain simple approximations of the transmission and reflection coefficients. Being functions of the incident light's frequency and in-plane wave vector components, the obtained approximations can be considered as multi-variable generalizations of the Fano line shape. We show that the approximations are in good agreement with the rigorously calculated transmission and reflection spectra. We use the developed theory to investigate angular tolerances of the considered structures and to obtain mode excitation conditions. In particular, we obtain the cross-polarization mode excitation conditions in the case of conical mounting.
Breakup processes in heavy-ion induced reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Udagawa, T.; Tamura, T.; Shimoda, T.

1979-11-01

Cross sections for breakup of /sup 20/Ne into /sup 16/O and ..cap alpha.. during scattering from /sup 40/Ca were calculated in terms of the distorted-wave Born approximation. The inclusive /sup 16/O cross section observed in the /sup 40/Ca(/sup 20/Ne,/sup 16/O) reaction was then found to be fitted very well by the sum of this breakup contribution and that of the ..cap alpha..-transfer reaction calculated in our previous work.
Resonating group method as applied to the spectroscopy of α-transfer reactions

NASA Astrophysics Data System (ADS)

Subbotin, V. B.; Semjonov, V. M.; Gridnev, K. A.; Hefter, E. F.

1983-10-01

In the conventional approach to α-transfer reactions the finite- and/or zero-range distorted-wave Born approximation is used in liaison with a macroscopic description of the captured α particle in the residual nucleus. Here the specific example of 16O(6Li,d)20Ne reactions at different projectile energies is taken to present a microscopic resonating group method analysis of the α particle in the final nucleus (for the reaction part the simple zero-range distorted-wave Born approximation is employed). In the discussion of suitable nucleon-nucleon interactions, force number one of the effective interactions presented by Volkov is shown to be most appropriate for the system considered. Application of the continuous analog of Newton's method to the evaluation of the resonating group method equations yields an increased accuracy with respect to traditional methods. The resonating group method description induces only minor changes in the structures of the angular distributions, but it does serve its purpose in yielding reliable and consistent spectroscopic information. NUCLEAR STRUCTURE 16O(6Li,d)20Ne; E=20 to 32 MeV; calculated B(E2); reduced widths, dσdΩ extracted α-spectroscopic factors. ZRDWBA with microscope RGM description of residual α particle in 20Ne; application of continuous analog of Newton's method; tested and applied Volkov force No. 1; direct mechanism.
Ab-initio calculation for cation vacancy formation energy in anti-fluorite structure

NASA Astrophysics Data System (ADS)

Saleel, V. P. Saleel Ahammad; Chitra, D.; Veluraja, K.; Eithiraj, R. D.

2018-04-01

Lithium oxide (Li2O) has been suggested as a suitable breeder blanket material for fusion reactors. Li+ vacancies are created by neutron irradiation, forming bulk defect complex whose extra character is experimentally unclear. We present a theoretical study of Li2O using density functional theory (DFT) with a plane-wave basis set. The generalized gradient approximation (GGA) and local-density approximation (LDA) were used for exchange and correlation. Here we address the total energy for defect free, cation defect, cation vacancy and vacancy formation energy in Li2O crystal in anti-fluorite structure.
Dynamics of coupled mode solitons in bursting neural networks

NASA Astrophysics Data System (ADS)

Nfor, N. Oma; Ghomsi, P. Guemkam; Moukam Kakmeni, F. M.

2018-02-01

Using an electrically coupled chain of Hindmarsh-Rose neural models, we analytically derived the nonlinearly coupled complex Ginzburg-Landau equations. This is realized by superimposing the lower and upper cutoff modes of wave propagation and by employing the multiple scale expansions in the semidiscrete approximation. We explore the modified Hirota method to analytically obtain the bright-bright pulse soliton solutions of our nonlinearly coupled equations. With these bright solitons as initial conditions of our numerical scheme, and knowing that electrical signals are the basis of information transfer in the nervous system, it is found that prior to collisions at the boundaries of the network, neural information is purely conveyed by bisolitons at lower cutoff mode. After collision, the bisolitons are completely annihilated and neural information is now relayed by the upper cutoff mode via the propagation of plane waves. It is also shown that the linear gain of the system is inextricably linked to the complex physiological mechanisms of ion mobility, since the speeds and spatial profiles of the coupled nerve impulses vary with the gain. A linear stability analysis performed on the coupled system mainly confirms the instability of plane waves in the neural network, with a glaring example of the transition of weak plane waves into a dark soliton and then static kinks. Numerical simulations have confirmed the annihilation phenomenon subsequent to collision in neural systems. They equally showed that the symmetry breaking of the pulse solution of the system leaves in the network static internal modes, sometime referred to as Goldstone modes.
Three-dimensional ground-motion simulations of earthquakes for the Hanford area, Washington

USGS Publications Warehouse

Frankel, Arthur; Thorne, Paul; Rohay, Alan

2014-01-01

This report describes the results of ground-motion simulations of earthquakes using three-dimensional (3D) and one-dimensional (1D) crustal models conducted for the probabilistic seismic hazard assessment (PSHA) of the Hanford facility, Washington, under the Senior Seismic Hazard Analysis Committee (SSHAC) guidelines. The first portion of this report demonstrates that the 3D seismic velocity model for the area produces synthetic seismograms with characteristics (spectral response values, duration) that better match those of the observed recordings of local earthquakes, compared to a 1D model with horizontal layers. The second part of the report compares the response spectra of synthetics from 3D and 1D models for moment magnitude (M) 6.6–6.8 earthquakes on three nearby faults and for a dipping plane wave source meant to approximate regional S-waves from a Cascadia great earthquake. The 1D models are specific to each site used for the PSHA. The use of the 3D model produces spectral response accelerations at periods of 0.5–2.0 seconds as much as a factor of 4.5 greater than those from the 1D models for the crustal fault sources. The spectral accelerations of the 3D synthetics for the Cascadia plane-wave source are as much as a factor of 9 greater than those from the 1D models. The differences between the spectral accelerations for the 3D and 1D models are most pronounced for sites with thicker supra-basalt sediments and for stations with earthquakes on the Rattlesnake Hills fault and for the Cascadia plane-wave source.

Dynamics of coupled mode solitons in bursting neural networks.

PubMed

Nfor, N Oma; Ghomsi, P Guemkam; Moukam Kakmeni, F M

2018-02-01

Using an electrically coupled chain of Hindmarsh-Rose neural models, we analytically derived the nonlinearly coupled complex Ginzburg-Landau equations. This is realized by superimposing the lower and upper cutoff modes of wave propagation and by employing the multiple scale expansions in the semidiscrete approximation. We explore the modified Hirota method to analytically obtain the bright-bright pulse soliton solutions of our nonlinearly coupled equations. With these bright solitons as initial conditions of our numerical scheme, and knowing that electrical signals are the basis of information transfer in the nervous system, it is found that prior to collisions at the boundaries of the network, neural information is purely conveyed by bisolitons at lower cutoff mode. After collision, the bisolitons are completely annihilated and neural information is now relayed by the upper cutoff mode via the propagation of plane waves. It is also shown that the linear gain of the system is inextricably linked to the complex physiological mechanisms of ion mobility, since the speeds and spatial profiles of the coupled nerve impulses vary with the gain. A linear stability analysis performed on the coupled system mainly confirms the instability of plane waves in the neural network, with a glaring example of the transition of weak plane waves into a dark soliton and then static kinks. Numerical simulations have confirmed the annihilation phenomenon subsequent to collision in neural systems. They equally showed that the symmetry breaking of the pulse solution of the system leaves in the network static internal modes, sometime referred to as Goldstone modes.
The EBEX experiment

NASA Astrophysics Data System (ADS)

Oxley, Paul; Ade, Peter A.; Baccigalupi, C.; deBernardis, Pierluigi; Cho, Hsiao-Mei; Devlin, Mark J.; Hanany, Shaul; Johnson, B. R.; Jones, T.; Lee, Adrian T.; Matsumura, T.; Miller, Amber D.; Milligan, M.; Renbarger, T.; Spieler, Helmuth G.; Stompor, R.; Tucker, Gregory S.; Zaldarriaga, Matias

2004-11-01

EBEX is a balloon-borne polarimeter designed to measure the intensity and polarization of the cosmic microwave background radiation. The measurements would probe the inflationary epoch that took place shortly after the big bang and would significantly improve constraints on the values of several cosmological parameters. EBEX is unique in its broad frequency coverage and in its ability to provide critical information about the level of polarized Galactic foregrounds which will be necessary for all future CMB polarization experiments. EBEX consists of a 1.5 m Dragone-type telescope that provides a resolution of less than 8 arcminutes over four focal planes each of 4 degree diffraction limited field of view at frequencies up to 450 GHz. The experiment is designed to accommodate 330 transition edge bolometric detectors per focal plane, for a total of up to 1320 detectors. EBEX will operate with frequency bands centered at 150, 250, 350, and 450 GHz. Polarimetry is achieved with a rotating achromatic half-wave plate. EBEX is currently in the design and construction phase, and first light is scheduled for 2008.
Integrated Lens Antennas for Multi-Pixel Receivers

NASA Technical Reports Server (NTRS)

Lee, Choonsup; Chattopadhyay, Goutam

2011-01-01

Future astrophysics and planetary experiments are expected to require large focal plane arrays with thousands of detectors. Feedhorns have excellent performance, but their mass, size, fabrication challenges, and expense become prohibitive for very large focal plane arrays. Most planar antenna designs produce broad beam patterns, and therefore require additional elements for efficient coupling to the telescope optics, such as substrate lenses or micromachined horns. An antenna array with integrated silicon microlenses that can be fabricated photolithographically effectively addresses these issues. This approach eliminates manual assembly of arrays of lenses and reduces assembly errors and tolerances. Moreover, an antenna array without metallic horns will reduce mass of any planetary instrument significantly. The design has a monolithic array of lens-coupled, leaky-wave antennas operating in the millimeter- and submillimeter-wave frequencies. Electromagnetic simulations show that the electromagnetic fields in such lens-coupled antennas are mostly confined in approximately 12 15 . This means that one needs to design a small-angle sector lens that is much easier to fabricate using standard lithographic techniques, instead of a full hyper-hemispherical lens. Moreover, this small-angle sector lens can be easily integrated with the antennas in an array for multi-pixel imager and receiver implementation. The leaky antenna is designed using double-slot irises and fed with TE10 waveguide mode. The lens implementation starts with a silicon substrate. Photoresist with appropriate thickness (optimized for the lens size) is spun on the substrate and then reflowed to get the desired lens structure. An antenna array integrated with individual lenses for higher directivity and excellent beam profile will go a long way in realizing multi-pixel arrays and imagers. This technology will enable a new generation of compact, low-mass, and highly efficient antenna arrays for use in multi-pixel receivers and imagers for future planetary and astronomical instruments. These antenna arrays can also be used in radars and imagers for contraband detection at stand-off distances. This will be enabling technology for future balloon-borne, smaller explorer class mission (SMEX), and other missions, and for a wide range of proposed planetary sounders and radars for planetary bodies.
Interpretation of ES, CS, and IOS approximations within a translational-internal coupling scheme. II. Application to atom--diatom kinetic cross sections

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coombe, D.A.; Snider, R.F.

1980-02-15

ES, CS, and IOS approximations to atom--diatom kinetic cross sections are derived. In doing so, reduced S-matrices in a translational-internal coupling scheme are stressed. This entails the insertion of recently obtained approximate reduced S-matrices in the translational-internal coupling scheme into previously derived general expressions for the kinetic cross sections. Of special interest is the structure (rotational j quantum number dependence) of the kinetic cross sections associated with the Senftleben Beenakker effects and of pure internal state relaxation phenomena. The viscomagnetic effect is used as an illustrative example. It is found in particular that there is a great similarity of structuremore » between the energy sudden (and IOS) approximation and the previously derived distorted wave Born results.« less
Research in Optical Sciences

DTIC Science & Technology

1990-03-12

where this is not so (see, e.g., the Jaynes - Cummings problem). This is why this model , and the closely related micromaser, remain exceedingly important...55 one calculates the plane- wave spectrum ( without 7.), one must arbitrarily impose nearly zero phase mismatch to obtain a similar spectrum.3" 2.7...taking approximately 3 CPU minutes. To model the intentionally introduced astigmatism, a phase term was added to the input wavefront at the cell entrance
First principle study of structural, electronic and fermi surface properties of aluminum praseodymium

NASA Astrophysics Data System (ADS)

Shugani, Mani; Aynyas, Mahendra; Sanyal, S. P.

2018-05-01

We present a structural, Electronic and Fermi surface properties of Aluminum Praseodymium (AlPr) using First-principles density functional calculation by using full potential linearized augmented plane wave (FP-LAPW) method within generalized gradient approximation (GGA). The ground state properties along with electronic and Fermi surface properties are studied. It is found that AlPr is metallic and the bonding between Al and Pr is covalent.
Propagation in Striated Media

DTIC Science & Technology

1976-05-01

random walk photon scattering, geometric optics refraction at a thin phase screen, plane wave scattering from a thin screen in the Fraunhofer limit and...significant cases. In the geometric optics regime the distribution of density of allowable multipath rays is gsslanly distributed and the power...3.1 Random Walk Approach to Scattering 10 3.2 Phase Screen Approximation to Strong Scattering 13 3.3 Ray Optics and Stationary Phase Analysis 21 3,3,1
Angular dependence of Raman scattering selection rules for long-wavelength optical phonons in short-period GaAs/AlAs superlattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Volodin, V. A., E-mail: volodin@isp.nsc.ru; Sachkov, V. A.; Sinyukov, M. P.

2016-07-15

The angular dependence of Raman scattering selection rules for optical phonons in short-period (001) GaAs/AlAs superlattices is calculated and experimentally studied. Experiments are performed using a micro-Raman setup, in the scattering geometry with the wavevectors of the incident and scattered light lying in the plane of superlattices (so-called in-plane geometry). Phonon frequencies are calculated using the Born model taking the Coulomb interaction into account in the rigid-ion approximation. Raman scattering spectra are calculated in the framework of the deformation potential and electro-optical mechanisms. Calculations show an angular dependence of the selection rules for optical phonons with different directions of themore » wavevectors. Drastic differences in the selection rules are found for experimental and calculated spectra. Presumably, these differences are due to the Fröhlich mechanism in Raman scattering for short-period superlattices.« less
High spatial resolution with zoomable saw-tooth refractive lenses?

NASA Astrophysics Data System (ADS)

Jark, Werner

2011-09-01

Refractive x-ray lenses can be assembled from two opposing saw-tooth structures, when they are inclined with respect to each other and almost touch at one end. An incident plane wave will then traverse a varying number of triangular prisms, which direct the beam towards the optical axis and focus it. Optically speaking the plane wave traverses a parabolic lens profile, which is approximated by trapezoidal segments. The parabolic profile will focus ideally, when a lens can be discussed in the "thin lens" approximation. Now the saw-tooth refractive lens is found to be too "thick". The residual aberrations limit the focusing capability to just submicrometer focusing, significantly above the limit in diffraction limited focusing. It is shown that the aberrations can be removed by introducing a variation into the originally constant saw-tooth angle. After this modification the lens can be operated in the diffraction limited regime. Spot sizes even below 0.1 micrometer are then feasible. This performance in terms of spatial resolution is found to be limited to focusing to microspots and is not available, when the saw-tooth refractive lens is used in an imaging setup. In this case the spatial resolution deteriorates rapidly with increasing off axis distance of the object to be imaged.
Expansions for infinite or finite plane circular time-reversal mirrors and acoustic curtains for wave-field-synthesis.

PubMed

Mellow, Tim; Kärkkäinen, Leo

2014-03-01

An acoustic curtain is an array of microphones used for recording sound which is subsequently reproduced through an array of loudspeakers in which each loudspeaker reproduces the signal from its corresponding microphone. Here the sound originates from a point source on the axis of symmetry of the circular array. The Kirchhoff-Helmholtz integral for a plane circular curtain is solved analytically as fast-converging expansions, assuming an ideal continuous array, to speed up computations and provide insight. By reversing the time sequence of the recording (or reversing the direction of propagation of the incident wave so that the point source becomes an "ideal" point sink), the curtain becomes a time reversal mirror and the analytical solution for this is given simultaneously. In the case of an infinite planar array, it is demonstrated that either a monopole or dipole curtain will reproduce the diverging sound field of the point source on the far side. However, although the real part of the sound field of the infinite time-reversal mirror is reproduced, the imaginary part is an approximation due to the missing singularity. It is shown that the approximation may be improved by using the appropriate combination of monopole and dipole sources in the mirror.
Finite-fault inversion of the Mw 5.9 2012 Emilia-Romagna earthquake (Northern Italy) using aftershocks as near-field Green's function approximations

NASA Astrophysics Data System (ADS)

Causse, Mathieu; Cultrera, Giovanna; Herrero, André; Courboulex, Françoise; Schiappapietra, Erika; Moreau, Ludovic

2017-04-01

On May 29, 2012 occurred a Mw 5.9 earthquake in the Emilia-Romagna region (Po Plain) on a thrust fault system. This shock, as well as hundreds of aftershocks, were recorded by 10 strong motion stations located less than 10 km away from the rupture plane, with 4 stations located within the surface rupture projection. The Po Plain is a very large EW trending syntectonic alluvial basin, delimited by the Alps and Apennines chains to the North and South. The Plio-Quaternary sedimentary sequence filling the Po Plain is characterized by an uneven thickness, ranging from several thousands of meters to a few tens of meters. This particular context results especially in a resonance basin below 1 Hz and strong surface waves, which makes it particularly difficult to model wave propagation and hence to obtain robust images of the rupture propagation. This study proposes to take advantage of the large set of recorded aftershocks, considered as point sources, to model wave propagation. Due to the heterogeneous distribution of the aftershocks on the fault plane, an interpolation technique is proposed to compute an approximation of the Green's function between each fault point and each strong motion station in the frequency range [0.2-1Hz]. We then use a Bayesian inversion technique (Monte Carlo Markov Chain algorithm) to obtain images of the rupture propagation from the strong motion data. We propose to retrieve the slip distribution by inverting the final slip value at some control points, which are allowed to move on the fault plane, and by interpolating the slip value between these points. We show that the use of 5 control points to describe the slip, coupled with the hypothesis of spatially constant rupture velocity and rise-time (that is 18 free source parameters), results in a good level of fit with the data. This indicates that despite their complexity, the strong motion data can be properly modeled up to 1 Hz using a relatively simple rupture. The inversion results also reveal that the rupture propagated slowly, at a speed of about 45% of the shear wave velocity.
On the asymptotic evolution of finite energy Airy wave functions.

PubMed

Chamorro-Posada, P; Sánchez-Curto, J; Aceves, A B; McDonald, G S

2015-06-15

In general, there is an inverse relation between the degree of localization of a wave function of a certain class and its transform representation dictated by the scaling property of the Fourier transform. We report that in the case of finite energy Airy wave packets a simultaneous increase in their localization in the direct and transform domains can be obtained as the apodization parameter is varied. One consequence of this is that the far-field diffraction rate of a finite energy Airy beam decreases as the beam localization at the launch plane increases. We analyze the asymptotic properties of finite energy Airy wave functions using the stationary phase method. We obtain one dominant contribution to the long-term evolution that admits a Gaussian-like approximation, which displays the expected reduction of its broadening rate as the input localization is increased.
C-plane Reconstructions from Sheaf Acquisition for Ultrasound Electrode Vibration Elastography.

PubMed

Ingle, Atul; Varghese, Tomy

2014-09-03

This paper presents a novel algorithm for reconstructing and visualizing ablated volumes using radiofrequency ultrasound echo data acquired with the electrode vibration elastography approach. The ablation needle is vibrated using an actuator to generate shear wave pulses that are tracked in the ultrasound image plane at different locations away from the needle. This data is used for reconstructing shear wave velocity maps for each imaging plane. A C-plane reconstruction algorithm is proposed which estimates shear wave velocity values on a collection of transverse planes that are perpendicular to the imaging planes. The algorithm utilizes shear wave velocity maps from different imaging planes that share a common axis of intersection. These C-planes can be used to generate a 3D visualization of the ablated region. Experimental validation of this approach was carried out using data from a tissue mimicking phantom. The shear wave velocity estimates were within 20% of those obtained from a clinical scanner, and a contrast of over 4 dB was obtained between the stiff and soft regions of the phantom.
Effects of volcano topography on seismic broad-band waveforms

NASA Astrophysics Data System (ADS)

Neuberg, Jürgen; Pointer, Tim

2000-10-01

Volcano seismology often deals with rather shallow seismic sources and seismic stations deployed in their near field. The complex stratigraphy on volcanoes and near-field source effects have a strong impact on the seismic wavefield, complicating the interpretation techniques that are usually employed in earthquake seismology. In addition, as most volcanoes have a pronounced topography, the interference of the seismic wavefield with the stress-free surface results in severe waveform perturbations that affect seismic interpretation methods. In this study we deal predominantly with the surface effects, but take into account the impact of a typical volcano stratigraphy as well as near-field source effects. We derive a correction term for plane seismic waves and a plane-free surface such that for smooth topographies the effect of the free surface can be totally removed. Seismo-volcanic sources radiate energy in a broad frequency range with a correspondingly wide range of different Fresnel zones. A 2-D boundary element method is employed to study how the size of the Fresnel zone is dependent on source depth, dominant wavelength and topography in order to estimate the limits of the plane wave approximation. This approximation remains valid if the dominant wavelength does not exceed twice the source depth. Further aspects of this study concern particle motion analysis to locate point sources and the influence of the stratigraphy on particle motions. Furthermore, the deployment strategy of seismic instruments on volcanoes, as well as the direct interpretation of the broad-band waveforms in terms of pressure fluctuations in the volcanic plumbing system, are discussed.
Transport Theory for Propagation and Reverberation

DTIC Science & Technology

2016-07-20

mentioned that our transport theory method is essentially 2-D (range and depth), so that out-of- plane forward scattering (a 3-D effect) is not treated...roughness spectrum, it is useful to consider scattering based on perturbation theory in some detail with a plane wave incident on the rough surface. The...the wave vector for the water wave. Let an incident acoustic plane wave have wave vector ki = kiH + kiz, where kiH denotes the horizontal component
Novel Aspects of Evolution of the Stokes Parameters for an Electromagnetic Wave in Anisotropic Media

NASA Astrophysics Data System (ADS)

Botet, R.; Kuratsuji, H.; Seto, R.

2006-08-01

Polarization of a plane electromagnetic wave travelling through a medium is studied in the slowly-varying field envelope approximation. It is shown that the problem is identical to the 4-momentum evolution of a negatively-charged massless relativistic particle in an electromagnetic field. The approach is exemplified by the resonant oscillations of circular polarization in a medium embedded in a static magnetic field and a modulated electric field. The effect of dissipation in the medium is discussed. It is shown that the Rabi oscillations are stable below a threshold depending on the absorption coefficient. Above it, oscillations disappear.
Theoretical investigations on structural, elastic and electronic properties of thallium halides

NASA Astrophysics Data System (ADS)

Singh, Rishi Pal; Singh, Rajendra Kumar; Rajagopalan, Mathrubutham

2011-04-01

Theoretical investigations on structural, elastic and electronic properties, viz. ground state lattice parameter, elastic moduli and density of states, of thallium halides (viz. TlCl and TlBr) have been made using the full potential linearized augmented plane wave method within the generalized gradient approximation (GGA). The ground state lattice parameter and bulk modulus and its pressure derivative have been obtained using optimization method. Young's modulus, shear modulus, Poisson ratio, sound velocities for longitudinal and shear waves, Debye average velocity, Debye temperature and Grüneisen parameter have also been calculated for these compounds. Calculated structural, elastic and other parameters are in good agreement with the available data.
Wave attenuation and mode dispersion in a waveguide coated with lossy dielectric material

NASA Technical Reports Server (NTRS)

Lee, C. S.; Chuang, S. L.; Lee, S. W.; Lo, Y. T.

1984-01-01

The modal attenuation constants in a cylindrical waveguide coated with a lossy dielectric material are studied as functions of frequency, dielectric constant, and thickness of the dielectric layer. A dielectric material best suited for a large attenuation is suggested. Using Kirchhoff's approximation, the field attenuation in a coated waveguide which is illuminated by a normally incident plane wave is also studied. For a circular guide which has a diameter of two wavelengths and is coated with a thin lossy dielectric layer (omega sub r = 9.1 - j2.3, thickness = 3% of the radius), a 3 dB attenuation is achieved within 16 diameters.
Effect of polarization force on the Jeans instability in collisional dusty plasmas

NASA Astrophysics Data System (ADS)

A, ABBASI; M, R. RASHIDIAN VAZIRI

2018-03-01

The Jeans instability in collisional dusty plasmas has been analytically investigated by considering the polarization force effect. Instabilities due to dust-neutral and ion-neutral drags can occur in electrostatic waves of collisional dusty plasmas with self-gravitating particles. In this study, the effect of gravitational force on heavy dust particles is considered in tandem with both the polarization and electrostatic forces. The theoretical framework has been developed and the dispersion relation and instability growth rate have been derived, assuming the plane wave approximation. The derived instability growth rate shows that, in collisional dusty plasmas, the Jeans instability strongly depends on the magnitude of the polarization force.
Methods And Apparatus For Acoustic Fiber Fractionation

DOEpatents

Brodeur, Pierre

1999-11-09

Methods and apparatus for acoustic fiber fractionation using a plane ultrasonic wave field interacting with water suspended fibers circulating in a channel flow using acoustic radiation forces to separate fibers into two or more fractions based on fiber radius, with applications of the separation concept in the pulp and paper industry. The continuous process relies on the use of a wall-mounted, rectangular cross-section piezoelectric ceramic transducer to selectively deflect flowing fibers as they penetrate the ultrasonic field. The described embodiment uses a transducer frequency of approximately 150 kHz. Depending upon the amount of dissolved gas in water, separation is obtained using a standing or a traveling wave field.

Optical generation of millimeter-wave pulses using a fiber Bragg grating in a fiber-optics system.

PubMed

Ye, Qing; Qu, Ronghui; Fang, Zujie

2007-04-10

A scheme is proposed to transform an optical pulse into a millimeter-wave frequency modulation pulse by using a weak fiber Bragg grating (FBG) in a fiber-optics system. The Fourier transformation method is used to obtain the required spectrum response function of the FBG for the Gaussian pulse, soliton pulse, and Lorenz shape pulse. On the condition of the first-order Born approximation of the weak fiber grating, the relation of the refractive index distribution and the spectrum response function of the FBG satisfies the Fourier transformation, and the corresponding refractive index distribution forms are obtained for single-frequency modulation and linear-frequency modulation millimeter-wave pulse generation. The performances of the designed fiber gratings are also studied by a numerical simulation method for a supershort pulse transmission.
Application of the ideas and techniques of classical fluid mechanics to some problems in physical oceanography.

PubMed

Johnson, R S

2018-01-28

This review makes a case for describing many of the flows observed in our oceans, simply based on the Euler equation, with (piecewise) constant density and with suitable boundary conditions. The analyses start from the Euler and mass conservation equations, expressed in a rotating, spherical coordinate system (but the f -plane and β -plane approximations are also mentioned); five examples are discussed. For three of them, a suitable non-dimensionalization is introduced, and a single small parameter is identified in each case. These three examples lead straightforwardly and directly to new results for: waves on the Pacific Equatorial Undercurrent (EUC) with a thermocline (in the f -plane); a nonlinear, three-dimensional model for EUC-type flows (in the β -plane); and a detailed model for large gyres. The other two examples are exact solutions of the complete system: a flow which corresponds to the underlying structure of the Pacific EUC; and a flow based on the necessary requirement to use a non-conservative body force, which produces the type of flow observed in the Antarctic Circumpolar Current. (All these examples have been discussed in detail in the references cited.) This review concludes with a few comments on how these solutions can be extended and expanded.This article is part of the theme issue 'Nonlinear water waves'. © 2017 The Author(s).
The influence of pore-fluid in the soil on ground vibrations from a tunnel embedded in a layered half-space

NASA Astrophysics Data System (ADS)

Yuan, Zonghao; Cao, Zhigang; Boström, Anders; Cai, Yuanqiang

2018-04-01

A computationally efficient semi-analytical solution for ground-borne vibrations from underground railways is proposed and used to investigate the influence of hydraulic boundary conditions at the scattering surfaces and the moving ground water table on ground vibrations. The arrangement of a dry soil layer with varying thickness resting on a saturated poroelastic half-space, which includes a circular tunnel subject to a harmonic load at the tunnel invert, creates the scenario of a moving water table for research purposes in this paper. The tunnel is modelled as a hollow cylinder, which is made of viscoelastic material and buried in the half-space below the ground water table. The wave field in the dry soil layer consists of up-going and down-going waves while the wave field in the tunnel wall consists of outgoing and regular cylindrical waves. The complete solution for the saturated half-space with a cylindrical hole is composed of down-going plane waves and outgoing cylindrical waves. By adopting traction-free boundary conditions on the ground surface and continuity conditions at the interfaces of the two soil layers and of the tunnel and the surrounding soil, a set of algebraic equations can be obtained and solved in the transformed domain. Numerical results show that the moving ground water table can cause an uncertainty of up to 20 dB for surface vibrations.
Matrix basis for plane and modal waves in a Timoshenko beam.

PubMed

Claeyssen, Julio Cesar Ruiz; Tolfo, Daniela de Rosso; Tonetto, Leticia

2016-11-01

Plane waves and modal waves of the Timoshenko beam model are characterized in closed form by introducing robust matrix basis that behave according to the nature of frequency and wave or modal numbers. These new characterizations are given in terms of a finite number of coupling matrices and closed form generating scalar functions. Through Liouville's technique, these latter are well behaved at critical or static situations. Eigenanalysis is formulated for exponential and modal waves. Modal waves are superposition of four plane waves, but there are plane waves that cannot be modal waves. Reflected and transmitted waves at an interface point are formulated in matrix terms, regardless of having a conservative or a dissipative situation. The matrix representation of modal waves is used in a crack problem for determining the reflected and transmitted matrices. Their euclidean norms are seen to be dominated by certain components at low and high frequencies. The matrix basis technique is also used with a non-local Timoshenko model and with the wave interaction with a boundary. The matrix basis allows to characterize reflected and transmitted waves in spectral and non-spectral form.
Large-scale laboratory study of breaking wave hydrodynamics over a fixed bar

NASA Astrophysics Data System (ADS)

van der A, Dominic A.; van der Zanden, Joep; O'Donoghue, Tom; Hurther, David; Cáceres, Iván.; McLelland, Stuart J.; Ribberink, Jan S.

2017-04-01

A large-scale wave flume experiment has been carried out involving a T = 4 s regular wave with H = 0.85 m wave height plunging over a fixed barred beach profile. Velocity profiles were measured at 12 locations along the breaker bar using LDA and ADV. A strong undertow is generated reaching magnitudes of 0.8 m/s on the shoreward side of the breaker bar. A circulation pattern occurs between the breaking area and the inner surf zone. Time-averaged turbulent kinetic energy (TKE) is largest in the breaking area on the shoreward side of the bar where the plunging jet penetrates the water column. At this location, and on the bar crest, TKE generated at the water surface in the breaking process reaches the bottom boundary layer. In the breaking area, TKE does not reduce to zero within a wave cycle which leads to a high level of "residual" turbulence and therefore lower temporal variation in TKE compared to previous studies of breaking waves on plane beach slopes. It is argued that this residual turbulence results from the breaker bar-trough geometry, which enables larger length scales and time scales of breaking-generated vortices and which enhances turbulence production within the water column compared to plane beaches. Transport of TKE is dominated by the undertow-related flux, whereas the wave-related and turbulent fluxes are approximately an order of magnitude smaller. Turbulence production and dissipation are largest in the breaker zone and of similar magnitude, but in the shoaling zone and inner surf zone production is negligible and dissipation dominates.
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.
First-principles investigation for some physical properties of some fluoroperovskites compounds ABF3 (A = K, Na; B = Mg, Zn)

NASA Astrophysics Data System (ADS)

Bakri, Badis; Driss, Zied; Berri, Saadi; Khenata, Rabah

2017-12-01

In this work, the structural, electronic and optical properties of fluoroperovskite ABF3 (A = K, Na; B = Mg, Zn) were studied using two different approaches: the full-potential linearized augmented plane wave method and the pseudo-potential plane wave scheme in the frame of generalized gradient approximation features such as the lattice constant, bulk modulus and its pressure derivative are reported. The ground state properties of these compounds such as the equilibrium lattice constant and the bulk modulus are in good agreement with the experimental results. The first principles calculations were performed to study the electronic structures of ABF3(A = K, Na; B = Mg, Zn) compounds and the results indicated that these four compounds are indirect band gap insulators. The optical properties are analysed and the source of some peaks in the spectra is discussed. Besides, the dielectric function, refractive index and extinction coefficient for radiation up to 25 eV have also been reported and discussed.
Trojan horse particle invariance studied with the {sup 6}Li(d,{alpha}){sup 4}He and {sup 7}Li(p,{alpha}){sup 4}He reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pizzone, R. G.; Spitaleri, C.; Lamia, L.

2011-04-15

The Trojan horse nucleus invariance for the binary reaction cross section extracted from the Trojan horse reaction was tested using the quasifree {sup 3}He({sup 6}Li,{alpha}{alpha})H and {sup 3}He({sup 7}Li,{alpha}{alpha}){sup 2}H reactions. The cross sections for the {sup 6}Li(d,{alpha}){sup 4}He and {sup 7}Li(p,{alpha}){sup 4}He binary processes were extracted in the framework of the plane wave approximation. They are compared with direct behaviors as well as with cross sections extracted from previous indirect investigations of the same binary reactions using deuteron as the Trojan horse nucleus instead of {sup 3}He. The very good agreement confirms the applicability of the plane wave approximationmore » which suggests the independence of the binary indirect cross section on the chosen Trojan horse nucleus, at least for the investigated cases.« less
Investigation of channeling and radiation of relativistic electrons in charged planes of the crystals with zinc blende structure

NASA Astrophysics Data System (ADS)

Maksyuta, N. V.; Vysotskii, V. I.; Efimenko, S. V.; Slinchenko, Y. A.

2018-04-01

In this paper the interaction potentials of relativistic electrons with the charged (2m+1, 2n+1, 2p+1) and (2m+1, 2n, 2p) planes (m, n, p=0,1,dot s, and Miller indices are mutually prime numbers) in the crystals with a zinc blende structure are calculated using Moliere approximation. It is shown that at the change of the type of used crystal plane (from the main (100) to the high-index charged planes), the structures of potential wells are transformed from non-unimodal to unimodal ones. In this case for the crystals constructed from ions with close nucleus charges, there arise so-called positron-like potential wells for the channeled electrons, i.e. with minima in the interplanar space. The influence of temperature factor on interaction potentials structures is also investigated. For the electrons with Lorentz-factors γ = 25, 50, 75 in the main (100) and (111) planes the transverse energy levels and corresponding wave functions in single planar approximation are found numerically. By means of these data the spectra of channeling radiation (CR) in dipole approximation are calculated for the electrons beams with a Lorentz-factor γ = 50 and an angular dispersion θ 0 ≈ 0,5 mrad, arising in the main charged (100) and (111) planes in ZnS, ZnSe and ZnTe crystals. It is shown that the CR generated at electron channeling along the (111) planes is more intense. It is shown also that spectra of CR arising in (111) planes of silicon and AlP crystals at using of channeled electron beam with γ = 25 and an angular dispersion θ 0 ≈ 0,5 mrad, due to similarity of structures of potential wells are identical. The spectra of CR at γ = 25, 50, 75 are calculated for a number of crystals with a zinc blende structure, namely AlP, AlAs, AlSb, GaP, GaAs, InP, InAs, InSb.
Channel correlation and BER performance analysis of coherent optical communication systems with receive diversity over moderate-to-strong non-Kolmogorov turbulence.

PubMed

Fu, Yulong; Ma, Jing; Tan, Liying; Yu, Siyuan; Lu, Gaoyuan

2018-04-10

In this paper, new expressions of the channel-correlation coefficient and its components (the large- and small-scale channel-correlation coefficients) for a plane wave are derived for a horizontal link in moderate-to-strong non-Kolmogorov turbulence using a generalized effective atmospheric spectrum which includes finite-turbulence inner and outer scales and high-wave-number "bump". The closed-form expression of the average bit error rate (BER) of the coherent free-space optical communication system is derived using the derived channel-correlation coefficients and an α-μ distribution to approximate the sum of the square root of arbitrarily correlated Gamma-Gamma random variables. Analytical results are provided to investigate the channel correlation and evaluate the average BER performance. The validity of the proposed approximation is illustrated by Monte Carlo simulations. This work will help with further investigation of the fading correlation in spatial diversity systems.
Quantum criticality and nodal superconductivity in the FeAs-based superconductor KFe2As2.

PubMed

Dong, J K; Zhou, S Y; Guan, T Y; Zhang, H; Dai, Y F; Qiu, X; Wang, X F; He, Y; Chen, X H; Li, S Y

2010-02-26

The in-plane resistivity rho and thermal conductivity kappa of the FeAs-based superconductor KFe2As2 single crystal were measured down to 50 mK. We observe non-Fermi-liquid behavior rho(T) approximately T{1.5} at H{c{2}}=5 T, and the development of a Fermi liquid state with rho(T) approximately T{2} when further increasing the field. This suggests a field-induced quantum critical point, occurring at the superconducting upper critical field H{c{2}}. In zero field, there is a large residual linear term kappa{0}/T, and the field dependence of kappa_{0}/T mimics that in d-wave cuprate superconductors. This indicates that the superconducting gaps in KFe2As2 have nodes, likely d-wave symmetry. Such a nodal superconductivity is attributed to the antiferromagnetic spin fluctuations near the quantum critical point.
Improved computational treatment of transonic flow about swept wings

NASA Technical Reports Server (NTRS)

Ballhaus, W. F.; Bailey, F. R.; Frick, J.

1976-01-01

Relaxation solutions to classical three-dimensional small-disturbance (CSD) theory for transonic flow about lifting swept wings are reported. For such wings, the CSD theory was found to be a poor approximation to the full potential equation in regions of the flow field that are essentially two-dimensional in a plane normal to the sweep direction. The effect of this deficiency on the capture of embedded shock waves in terms of (1) the conditions under which shock waves can exist and (2) the relations they must satisfy when they do exist is emphasized. A modified small-disturbance (MSD) equation, derived by retaining two previously neglected terms, was proposed and shown to be a consistent approximation to the full potential equation over a wider range of sweep angles. The effect of these extra terms is demonstrated by comparing CSD, MSD, and experimental wing surface pressures.
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.
Introduction to Radar Polarimetry

DTIC Science & Technology

1991-04-23

Coulomb force 11 1,2 Static etectric fields 13 1.3 Summary 15 2 ELECTROMAGNETIC WAVES 16 2.1 Harmonic plane waves 16 2.2 The average intensity of a...harmonic plane wave 17 2.3 Spherical harmonic waves 18 2.4 Summary 19 3 THE POLARIZATION OF AN ELECTROMAGNETIC WAVE 20 3.1 The polarization ellipse 20 3.2...CHANGE OF POLARIZATION 31 4.1 Simple examples 31 4.2 Scattering at a plane interface 33 4.3 Summary 36 5 THE SCATTERING MATRIX 37 5.1 Transmission
/sup 13/C(/sup 6/Li,t)/sup 16/O reaction in the 20--32 MeV incident energy range

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cunsolo, A.; Foti, A.; Imme, G.

1980-03-01

The reaction /sup 13/C(/sup 6/Li,t)/sup 16/O has been studied in the 20 --32 MeV incident energy range. Angular distributions have been measured at E/sup 6/Li/=28 MeV; the data have been analyzed in terms of Hauser-Feshbach and exact finite range distorted-wave Born-approximation theories. The extracted relative /sup 3/He spectroscopic strengths show a satisfactory independence from the optical model parameters.
Two-proton transfer reactions on even Ni and Zn isotopes

NASA Astrophysics Data System (ADS)

Boucenna, A.; Kraus, L.; Linck, I.; Chan, Tsan Ung

1990-10-01

New levels strongly excited by 112-MeV 12C ions on even Ni and Zn isotopes are Jπ assigned on kinematical and geometrical arguments, crude shell-model calculations, and distorted-wave Born approximation angular-distribution analysis. These tentative assignments are supported by the Bansal-French model. Because of the contribution of additional collective effects, the two-proton transfer reaction spectra are less selectively fed than those obtained with the analogous two-neutron transfer reactions induced on the same targets in a similar energy range.
Application of linearized inverse scattering methods for the inspection in steel plates embedded in concrete structures

NASA Astrophysics Data System (ADS)

Tsunoda, Takaya; Suzuki, Keigo; Saitoh, Takahiro

2018-04-01

This study develops a method to visualize the state of steel-concrete interface with ultrasonic testing. Scattered waves are obtained by the UT pitch-catch mode from the surface of the concrete. Discrete wavelet transform is applied in order to extract echoes scattered from the steel-concrete interface. Then Linearized Inverse Scattering Methods are used for imaging the interface. The results show that LISM with Born and Kirchhoff approximation provide clear images for the target.
Intermolecular shielding contributions studied by modeling the 13C chemical-shift tensors of organic single crystals with plane waves

PubMed Central

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
Twisted gravitational waves

NASA Astrophysics Data System (ADS)

Bini, Donato; Chicone, Carmen; Mashhoon, Bahram

2018-03-01

In general relativity (GR), linearized gravitational waves propagating in empty Minkowski spacetime along a fixed spatial direction have the property that the wave front is the Euclidean plane. Beyond the linear regime, exact plane waves in GR have been studied theoretically for a long time and many exact vacuum solutions of the gravitational field equations are known that represent plane gravitational waves. These have parallel rays and uniform wave fronts. It turns out, however, that GR also admits exact solutions representing gravitational waves propagating along a fixed direction that are nonplanar. The wave front is then nonuniform and the bundle of rays is twisted. We find a class of solutions representing nonplanar unidirectional gravitational waves and study some of the properties of these twisted waves.
Non-Born-Oppenheimer calculations of the pure vibrational spectrum of HeH+.

PubMed

Pavanello, Michele; Bubin, Sergiy; Molski, Marcin; Adamowicz, Ludwik

2005-09-08

Very accurate calculations of the pure vibrational spectrum of the HeH(+) ion are reported. The method used does not assume the Born-Oppenheimer approximation, and the motion of both the electrons and the nuclei are treated on equal footing. In such an approach the vibrational motion cannot be decoupled from the motion of electrons, and thus the pure vibrational states are calculated as the states of the system with zero total angular momentum. The wave functions of the states are expanded in terms of explicitly correlated Gaussian basis functions multipled by even powers of the internuclear distance. The calculations yielded twelve bound states and corresponding eleven transition energies. Those are compared with the pure vibrational transition energies extracted from the experimental rovibrational spectrum.

Born iterative reconstruction using perturbed-phase field estimates

PubMed Central

Astheimer, Jeffrey P.; Waag, Robert C.

2008-01-01

A method of image reconstruction from scattering measurements for use in ultrasonic imaging is presented. The method employs distorted-wave Born iteration but does not require using a forward-problem solver or solving large systems of equations. These calculations are avoided by limiting intermediate estimates of medium variations to smooth functions in which the propagated fields can be approximated by phase perturbations derived from variations in a geometric path along rays. The reconstruction itself is formed by a modification of the filtered-backpropagation formula that includes correction terms to account for propagation through an estimated background. Numerical studies that validate the method for parameter ranges of interest in medical applications are presented. The efficiency of this method offers the possibility of real-time imaging from scattering measurements. PMID:19062873
Stress wave calculations in composite plates using the fast Fourier transform.

NASA Technical Reports Server (NTRS)

Moon, F. C.

1973-01-01

The protection of composite turbine fan blades against impact forces has prompted the study of dynamic stresses in composites due to transient loads. The mathematical model treats the laminated plate as an equivalent anisotropic material. The use of Mindlin's approximate theory of crystal plates results in five two-dimensional stress waves. Three of the waves are flexural and two involve in-plane extensional strains. The initial value problem due to a transient distributed transverse force on the plate is solved using Laplace and Fourier transforms. A fast computer program for inverting the two-dimensional Fourier transform is used. Stress contours for various stresses and times after application of load are obtained for a graphite fiber-epoxy matrix composite plate. Results indicate that the points of maximum stress travel along the fiber directions.
Numerical modeling of the interaction of liquid drops and jets with shock waves and gas jets

NASA Astrophysics Data System (ADS)

Surov, V. S.

1993-02-01

The motion of a liquid drop (jet) and of the ambient gas is described, in the general case, by Navier-Stokes equations. An approximate solution to the interaction of a plane shock wave with a single liquid drop is presented. Based on the analysis, the general system of Navier-Stokes equations is reduced to two groups of equations, Euler equations for gas and Navier-Stokes equations for liquid; solutions to these equations are presented. The discussion also covers the modeling of the interaction of a shock wave with a drop screen, interaction of a liquid jet with a counterpropagating supersonic gas flow, and modeling of processes in a shock layer during the impact of a drop against an obstacle in gas flow.
Sauter-Schwinger pair creation dynamically assisted by a plane wave

NASA Astrophysics Data System (ADS)

Torgrimsson, Greger; Schneider, Christian; Schützhold, Ralf

2018-05-01

We study electron-positron pair creation by a strong and constant electric field superimposed with a weaker transversal plane wave which is incident perpendicularly (or under some angle). Comparing the fully nonperturbative approach based on the world-line instanton method with a perturbative expansion into powers of the strength of the weaker plane wave, we find good agreement—provided that the latter is carried out to sufficiently high orders. As usual for the dynamically assisted Sauter-Schwinger effect, the additional plane wave induces an exponential enhancement of the pair-creation probability if the combined Keldysh parameter exceeds a certain threshold.
Near ground measure and theoretical model of plane wave covariance of intensity in anisotropic turbulence.

PubMed

Beason, Melissa; Smith, Christopher; Coffaro, Joseph; Belichki, Sara; Spychalsky, Jonathon; Titus, Franklin; Crabbs, Robert; Andrews, Larry; Phillips, Ronald

2018-06-01

Experimental measurements were recently made which displayed characteristics of plane wave propagation through anisotropic optical turbulence. A near-plane wave beam was propagated a distance of 1 and 2 km at a height of 2 m above the concrete runway at the Shuttle Landing Facility, Kennedy Space Center, Florida, during January and February of 2017. The spatial-temporal fluctuations of the beam were recorded, and the covariance of intensity was calculated. These data sets were compared to a theoretical calculation of covariance of intensity for a plane wave.
First plasma wave observations at neptune.

PubMed

Gurnett, D A; Kurth, W S; Poynter, R L; Granroth, L J; Cairns, I H; Macek, W M; Moses, S L; Coroniti, F V; Kennel, C F; Barbosa, D D

1989-12-15

The Voyager 2 plasma wave instrument detected many familiar plasma waves during the encounter with Neptune, including electron plasma oscillations in the solar wind upstream of the bow shock, electrostatic turbulence at the bow shock, and chorus, hiss, electron cyclotron waves, and upper hybrid resonance waves in the inner magnetosphere. Low-frequency radio emissions, believed to be generated by mode conversion from the upper hybrid resonance emissions, were also observed propagating outward in a disklike beam along the magnetic equatorial plane. At the two ring plane crossings many small micrometer-sized dust particles were detected striking the spacecraft. The maximum impact rates were about 280 impacts per second at the inbound ring plane crossing, and about 110 impacts per second at the outbound ring plane crossing. Most of the particles are concentrated in a dense disk, about 1000 kilometers thick, centered on the equatorial plane. However, a broader, more tenuous distribution also extends many tens of thousands of kilometers from the equatorial plane, including over the northern polar region.
Screw-symmetric gravitational waves: A double copy of the vortex

NASA Astrophysics Data System (ADS)

Ilderton, A.

2018-07-01

Plane gravitational waves can admit a sixth 'screw' isometry beyond the usual five. The same is true of plane electromagnetic waves. From the point of view of integrable systems, a sixth isometry would appear to over-constrain particle dynamics in such waves; we show here, though, that no effect of the sixth isometry is independent of those from the usual five. Many properties of particle dynamics in a screw-symmetric gravitational wave are also seen in a (non-plane-wave) electromagnetic vortex; we make this connection explicit, showing that the screw-symmetric gravitational wave is the classical double copy of the vortex.
Accuracy & Computational Considerations for Wide--Angle One--way Seismic Propagators and Multiple Scattering by Invariant Embedding

NASA Astrophysics Data System (ADS)

Thomson, C. J.

2004-12-01

Pseudodifferential operators (PSDOs) yield in principle exact one--way seismic wave equations, which are attractive both conceptually and for their promise of computational efficiency. The one--way operators can be extended to include multiple--scattering effects, again in principle exactly. In practice approximations must be made and, as an example, the variable--wavespeed Helmholtz equation for scalar waves in two space dimensions is here factorized to give the one--way wave equation. This simple case permits clear identification of a sequence of physically reasonable approximations to be used when the mathematically exact PSDO one--way equation is implemented on a computer. As intuition suggests, these approximations hinge on the medium gradients in the direction transverse to the main propagation direction. A key point is that narrow--angle approximations are to be avoided in the interests of accuracy. Another key consideration stems from the fact that the so--called ``standard--ordering'' PSDO indicates how lateral interpolation of the velocity structure can significantly reduce computational costs associated with the Fourier or plane--wave synthesis lying at the heart of the calculations. The decision on whether a slow or a fast Fourier transform code should be used rests upon how many lateral model parameters are truly distinct. A third important point is that the PSDO theory shows what approximations are necessary in order to generate an exponential one--way propagator for the laterally varying case, representing the intuitive extension of classical integral--transform solutions for a laterally homogeneous medium. This exponential propagator suggests the use of larger discrete step sizes, and it can also be used to approach phase--screen like approximations (though the latter are not the main interest here). Numerical comparisons with finite--difference solutions will be presented in order to assess the approximations being made and to gain an understanding of computation time differences. The ideas described extend to the three--dimensional, generally anisotropic case and to multiple scattering by invariant embedding.
Radiation from a current filament driven by a traveling wave

NASA Technical Reports Server (NTRS)

Levine, D. M.; Meneghini, R.

1976-01-01

Solutions are presented for the electromagnetic fields radiated by an arbitrarily oriented current filament located above a perfectly conducting ground plane and excited by a traveling current wave. Both an approximate solution, valid in the fraunhofer region of the filament and predicting the radiation terms in the fields, and an exact solution, which predicts both near and far field components of the electromagnetic fields, are presented. Both solutions apply to current waveforms which propagate along the channel but are valid regardless of the actual waveshape. The exact solution is valid only for waves which propagate at the speed of light, and the approximate solution is formulated for arbitrary velocity of propagation. The spectrum-magnitude of the fourier transform-of the radiated fields is computed by assuming a compound exponential model for the current waveform. The effects of channel orientation and length, as well as velocity of propagation of the current waveform and location of the observer, are discussed. It is shown that both velocity of propagation and an effective channel length are important in determining the shape of the spectrum.
On a method computing transient wave propagation in ionospheric regions

NASA Technical Reports Server (NTRS)

Gray, K. G.; Bowhill, S. A.

1978-01-01

A consequence of an exoatmospheric nuclear burst is an electromagnetic pulse (EMP) radiated from it. In a region far enough away from the burst, where nonlinear effects can be ignored, the EMP can be represented by a large-amplitude narrow-time-width plane-wave pulse. If the ionosphere intervenes the origin and destination of the EMP, frequency dispersion can cause significant changes in the original pulse upon reception. A method of computing these dispersive effects of transient wave propagation is summarized. The method described is different from the standard transform techniques and provides physical insight into the transient wave process. The method, although exact, can be used in approximating the early-time transient response of an ionospheric region by a simple integration with only explicit knowledge of the electron density, electron collision frequency, and electron gyrofrequency required. As an illustration of the method, it is applied to a simple example and contrasted with the corresponding transform solution.
Relationship of scattering phase shifts to special radiation force conditions for spheres in axisymmetric wave-fields.

PubMed

Marston, Philip L; Zhang, Likun

2017-05-01

When investigating the radiation forces on spheres in complicated wave-fields, the interpretation of analytical results can be simplified by retaining the s-function notation and associated phase shifts imported into acoustics from quantum scattering theory. For situations in which dissipation is negligible, as taken to be the case in the present investigation, there is an additional simplification in that partial-wave phase shifts become real numbers that vanish when the partial-wave index becomes large and when the wave-number-sphere-radius product vanishes. By restricting attention to monopole and dipole phase shifts, transitions in the axial radiation force for axisymmetric wave-fields are found to be related to wave-field parameters for traveling and standing Bessel wave-fields by considering the ratio of the phase shifts. For traveling waves, the special force conditions concern negative forces while for standing waves, the special force conditions concern vanishing radiation forces. An intermediate step involves considering the functional dependence on phase shifts. An appendix gives an approximation for zero-force plane standing wave conditions. Connections with early investigations of acoustic levitation are mentioned and some complications associated with viscosity are briefly noted.
Precursor Wave Emission Enhanced by Weibel Instability in Relativistic Shocks

NASA Astrophysics Data System (ADS)

Iwamoto, Masanori; Amano, Takanobu; Hoshino, Masahiro; Matsumoto, Yosuke

2018-05-01

We investigated the precursor wave emission efficiency in magnetized purely perpendicular relativistic shocks in pair plasmas. We extended our previous study to include the dependence of upstream magnetic field orientations. We performed two-dimensional particle-in-cell simulations and focused on two magnetic field orientations: the magnetic field in the simulation plane (i.e., in-plane configuration) and that perpendicular to the simulation plane (i.e., out-of-plane configuration). Our simulations in the in-plane configuration demonstrated that not only extraordinary but also ordinary mode waves are excited. We quantified the emission efficiency as a function of the magnetization parameter σ e and found that the large-amplitude precursor waves are emitted for a wide range of σ e . We found that especially at low σ e , the magnetic field generated by Weibel instability amplifies the ordinary mode wave power. The amplitude is large enough to perturb the upstream plasma, and transverse density filaments are generated as in the case of the out-of-plane configuration investigated in the previous study. We confirmed that our previous conclusion holds regardless of upstream magnetic field orientations with respect to the two-dimensional simulation plane. We discuss the precursor wave emission in three dimensions and the feasibility of wakefield acceleration in relativistic shocks based on our results.
Matrix basis for plane and modal waves in a Timoshenko beam

PubMed Central

Tolfo, Daniela de Rosso; Tonetto, Leticia

2016-01-01

Plane waves and modal waves of the Timoshenko beam model are characterized in closed form by introducing robust matrix basis that behave according to the nature of frequency and wave or modal numbers. These new characterizations are given in terms of a finite number of coupling matrices and closed form generating scalar functions. Through Liouville’s technique, these latter are well behaved at critical or static situations. Eigenanalysis is formulated for exponential and modal waves. Modal waves are superposition of four plane waves, but there are plane waves that cannot be modal waves. Reflected and transmitted waves at an interface point are formulated in matrix terms, regardless of having a conservative or a dissipative situation. The matrix representation of modal waves is used in a crack problem for determining the reflected and transmitted matrices. Their euclidean norms are seen to be dominated by certain components at low and high frequencies. The matrix basis technique is also used with a non-local Timoshenko model and with the wave interaction with a boundary. The matrix basis allows to characterize reflected and transmitted waves in spectral and non-spectral form. PMID:28018668
Strong shock implosion, approximate solution

NASA Astrophysics Data System (ADS)

Fujimoto, Y.; Mishkin, E. A.; Alejaldre, C.

1983-01-01

The self-similar, center-bound motion of a strong spherical, or cylindrical, shock wave moving through an ideal gas with a constant, γ= cp/ cv, is considered and a linearized, approximate solution is derived. An X, Y phase plane of the self-similar solution is defined and the representative curved of the system behind the shock front is replaced by a straight line connecting the mappings of the shock front with that of its tail. The reduced pressure P(ξ), density R(ξ) and velocity U1(ξ) are found in closed, quite accurate, form. Comparison with numerically obtained results, for γ= {5}/{3} and γ= {7}/{5}, is shown.
Theory of inhomogeneous quantum systems. III. Variational wave functions for Fermi fluids

NASA Astrophysics Data System (ADS)

Krotscheck, E.

1985-04-01

We develop a general variational theory for inhomogeneous Fermi systems such as the electron gas in a metal surface, the surface of liquid 3He, or simple models of heavy nuclei. The ground-state wave function is expressed in terms of two-body correlations, a one-body attenuation factor, and a model-system Slater determinant. Massive partial summations of cluster expansions are performed by means of Born-Green-Yvon and hypernetted-chain techniques. An optimal single-particle basis is generated by a generalized Hartree-Fock equation in which the two-body correlations screen the bare interparticle interaction. The optimization of the pair correlations leads to a state-averaged random-phase-approximation equation and a strictly microscopic determination of the particle-hole interaction.
Density functional theory of electron transfer beyond the Born-Oppenheimer approximation: Case study of LiF.

PubMed

Li, Chen; Requist, Ryan; Gross, E K U

2018-02-28

We perform model calculations for a stretched LiF molecule, demonstrating that nonadiabatic charge transfer effects can be accurately and seamlessly described within a density functional framework. In alkali halides like LiF, there is an abrupt change in the ground state electronic distribution due to an electron transfer at a critical bond length R = R c , where an avoided crossing of the lowest adiabatic potential energy surfaces calls the validity of the Born-Oppenheimer approximation into doubt. Modeling the R-dependent electronic structure of LiF within a two-site Hubbard model, we find that nonadiabatic electron-nuclear coupling produces a sizable elongation of the critical R c by 0.5 bohr. This effect is very accurately captured by a simple and rigorously derived correction, with an M -1 prefactor, to the exchange-correlation potential in density functional theory, M = reduced nuclear mass. Since this nonadiabatic term depends on gradients of the nuclear wave function and conditional electronic density, ∇ R χ(R) and ∇ R n(r, R), it couples the Kohn-Sham equations at neighboring R points. Motivated by an observed localization of nonadiabatic effects in nuclear configuration space, we propose a local conditional density approximation-an approximation that reduces the search for nonadiabatic density functionals to the search for a single function y(n).
Waveguide Calibrator for Multi-Element Probe Calibration

NASA Technical Reports Server (NTRS)

Sommerfeldt, Scott D.; Blotter, Jonathan D.

2007-01-01

A calibrator, referred to as the spider design, can be used to calibrate probes incorporating multiple acoustic sensing elements. The application is an acoustic energy density probe, although the calibrator can be used for other types of acoustic probes. The calibrator relies on the use of acoustic waveguide technology to produce the same acoustic field at each of the sensing elements. As a result, the sensing elements can be separated from each other, but still calibrated through use of the acoustic waveguides. Standard calibration techniques involve placement of an individual microphone into a small cavity with a known, uniform pressure to perform the calibration. If a cavity is manufactured with sufficient size to insert the energy density probe, it has been found that a uniform pressure field can only be created at very low frequencies, due to the size of the probe. The size of the energy density probe prevents one from having the same pressure at each microphone in a cavity, due to the wave effects. The "spider" design probe is effective in calibrating multiple microphones separated from each other. The spider design ensures that the same wave effects exist for each microphone, each with an indivdual sound path. The calibrator s speaker is mounted at one end of a 14-cm-long and 4.1-cm diameter small plane-wave tube. This length was chosen so that the first evanescent cross mode of the plane-wave tube would be attenuated by about 90 dB, thus leaving just the plane wave at the termination plane of the tube. The tube terminates with a small, acrylic plate with five holes placed symmetrically about the axis of the speaker. Four ports are included for the four microphones on the probe. The fifth port is included for the pre-calibrated reference microphone. The ports in the acrylic plate are in turn connected to the probe sensing elements via flexible PVC tubes. These five tubes are the same length, so the acoustic wave effects are the same in each tube. The flexible nature of the tubes allows them to be positioned so that each tube terminates at one of the microphones of the energy density probe, which is mounted in the acrylic structure, or the calibrated reference microphone. Tests performed verify that the pressure did not vary due to bends in the tubes. The results of these tests indicate that the average sound pressure level in the tubes varied by only 0.03 dB as the tubes were bent to various angles. The current calibrator design is effective up to a frequency of approximately 4.5 kHz. This upper design frequency is largely due to the diameter of the plane-wave tubes.
A review of electron-nucleus bremsstrahlung cross sections between 1 and 10 MeV

NASA Astrophysics Data System (ADS)

Mangiarotti, A.; Martins, M. N.

2017-12-01

More than 80 years have passed since the first calculations of electron-nucleus bremsstrahlung cross sections were published by Sommerfeld, for non-relativistic electrons, and, independently, by Sauter, Bethe and Heitler, and Racah, for relativistic electrons. The Bethe-Heitler expression, that is based on the first Born approximation and includes the screening of the Coulomb field of the nucleus by the atomic electrons, has proven to work well at moderately high energies where the Landau-Pomeranchuk-Migdal effect is negligible. We review the current theoretical and experimental status with a highlight on electrons with kinetic energies between 1 and 10 MeV. The choice is motivated by the peculiar difficulties present in this energy region, where it is necessary to treat simultaneously the interaction with the Coulomb field beyond the first Born approximation and the effect of screening. A fully numerical approach within the S-matrix formalism has proven to be extremely difficult above a few MeV, because the number of partial waves needed for an accurate evaluation is prohibitively large. Here we focus on analytic results, including the more complex ones employing the Furry-Sommerfeld-Maue wave functions and taking into account the next-to-leading order, and discuss the advantages and limitations in light of the best available data. The influence of multiple scattering in the target is investigated under the actual experimental conditions. A comparison with the widely used cross section tabulations by Seltzer and Berger is also presented.
Noise Equalization for Ultrafast Plane Wave Microvessel Imaging.

PubMed

Song, Pengfei; Manduca, Armando; Trzasko, Joshua D; Chen, Shigao

2017-11-01

Ultrafast plane wave microvessel imaging significantly improves ultrasound Doppler sensitivity by increasing the number of Doppler ensembles that can be collected within a short period of time. The rich spatiotemporal plane wave data also enable more robust clutter filtering based on singular value decomposition. However, due to the lack of transmit focusing, plane wave microvessel imaging is very susceptible to noise. This paper was designed to: 1) study the relationship between ultrasound system noise (primarily time gain compensation induced) and microvessel blood flow signal and 2) propose an adaptive and computationally cost-effective noise equalization method that is independent of hardware or software imaging settings to improve microvessel image quality.
Theoretical derivation of laser-dressed atomic states by using a fractal space

NASA Astrophysics Data System (ADS)

Duchateau, Guillaume

2018-05-01

The derivation of approximate wave functions for an electron submitted to both a Coulomb and a time-dependent laser electric fields, the so-called Coulomb-Volkov (CV) state, is addressed. Despite its derivation for continuum states does not exhibit any particular problem within the framework of the standard theory of quantum mechanics (QM), difficulties arise when considering an initially bound atomic state. Indeed the natural way of translating the unperturbed momentum by the laser vector potential is no longer possible since a bound state does not exhibit a plane wave form explicitly including a momentum. The use of a fractal space permits to naturally define a momentum for a bound wave function. Within this framework, it is shown how the derivation of laser-dressed bound states can be performed. Based on a generalized eikonal approach, a new expression for the laser-dressed states is also derived, fully symmetric relative to the continuum or bound nature of the initial unperturbed wave function. It includes an additional crossed term in the Volkov phase which was not obtained within the standard theory of quantum mechanics. The derivations within this fractal framework have highlighted other possible ways to derive approximate laser-dressed states in QM. After comparing the various obtained wave functions, an application to the prediction of the ionization probability of hydrogen targets by attosecond XUV pulses within the sudden approximation is provided. This approach allows to make predictions in various regimes depending on the laser intensity, going from the non-resonant multiphoton absorption to tunneling and barrier-suppression ionization.

Damping of quasiparticles in a Bose-Einstein condensate coupled to an optical cavity

NASA Astrophysics Data System (ADS)

Kónya, G.; Szirmai, G.; Domokos, P.

2014-07-01

We present a general theory for calculating the damping rate of elementary density-wave excitations in a Bose-Einstein condensate strongly coupled to a single radiation field mode of an optical cavity. Thereby we give a detailed derivation of the huge resonant enhancement in the Beliaev damping of a density-wave mode, predicted recently by Kónya et al. [Phys. Rev. A 89, 051601(R) (2014), 10.1103/PhysRevA.89.051601]. The given density-wave mode constitutes the polaritonlike soft mode of the self-organization phase transition. The resonant enhancement takes place, in both the normal and the ordered phases, outside the critical region. We show that the large damping rate is accompanied by a significant frequency shift of this polariton mode. Going beyond the Born-Markov approximation and determining the poles of the retarded Green's function of the polariton, we reveal a strong coupling between the polariton and a collective mode in the phonon bath formed by the other density-wave modes.
Born approximation in linear-time invariant system

NASA Astrophysics Data System (ADS)

Gumjudpai, Burin

2017-09-01

An alternative way of finding the LTI’s solution with the Born approximation, is investigated. We use Born approximation in the LTI and in the transformed LTI in form of Helmholtz equation. General solution are considered as infinite series or Feynman graph. Slow-roll approximation are explored. Transforming the LTI system into Helmholtz equation, approximated general solution can be found for any given forms of force with its initial value.
Seismic scatterers in the mid-lower mantle beneath Tonga-Fiji

NASA Astrophysics Data System (ADS)

Kaneshima, Satoshi

2018-01-01

We analyze deep and intermediate-depth earthquakes at the Tonga-Fiji region in order to reveal the distribution of scattering objects in the mid-lower mantle. By array processing waveform data recorded at regional seismograph stations in the US, Alaska, and Japan, we investigate S-to-P scattering waves in the P coda, which arise from kilometer-scale chemically distinct objects in the mid-lower mantle beneath Tonga-Fiji. With ten scatterers previously reported by the author included, twenty-three mid-lower mantle scatterers have been detected below 900 km depth, while scatterers deeper than 1900 km have not been identified. Strong mid-lower mantle S-to-P scattering most frequently occurs at the scatterers located within a depth range between 1400 km and 1600 km. The number of scatterers decreases below 1600 km depth, and the deeper objects tend to be weaker. The scatterer distribution may reflect diminishing elastic anomalies of basaltic rocks with depth relative to the surrounding mantle rocks, which mineral physics has predicted to occur. The predominant occurrence of strong S-to-P scattering waves within a narrow depth range may reflect significant reduction of rigidity due to the ferro-elastic transformation of stishovite in basaltic rocks. Very large signals associated with mid-mantle scatterers are observed only for a small portion of the entire earthquake-array pairs. Such infrequent observations of large scattering signals, combined with quite large event-to-event differences in the scattering intensity for each scatterer, suggest both that the strong arrivals approximately represent ray theoretical S-to-P converted waves at objects with a plane geometry. The plane portions of the strong scatterers may often dip steeply, with the size exceeding 100 km. For a few strong scatterers, the range of receivers showing clear scattered waves varies substantially from earthquake-array pair to pair. Some of the scatterers are also observed at different arrays that have significantly different directions of incident waves to the scatterers. Furthermore, weak but coherent P-to-P scattered waves as well as S-to-P waves are observed for a few of the scatterers. These observations indicate that the locally plane scatterers also possess substantial topography.
Finite-surface method for the Maxwell equations with corner singularities

NASA Technical Reports Server (NTRS)

Vinokur, Marcel; Yarrow, Maurice

1994-01-01

The finite-surface method for the two-dimensional Maxwell equations in generalized coordinates is extended to treat perfect conductor boundaries with sharp corners. Known singular forms of the grid and the electromagnetic fields in the neighborhood of each corner are used to obtain accurate approximations to the surface and line integrals appearing in the method. Numerical results are presented for a harmonic plane wave incident on a finite flat plate. Comparisons with exact solutions show good agreement.
Experiment E89-044 on the Quasielastic 3He(e,e'p) Reaction at Jefferson Laboratory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Penel-Nottaris, Emilie

The Jefferson Lab Hall A E89-044 experiment has measured the 3He(e,e'p) reaction cross-sections. The extraction of the longitudinal and transverse response functions for the two-body break-up 3He(e,e'p)d reaction in parallel kinematics allows the study of the bound proton electromagnetic properties inside the 3He nucleus and the involved nuclear mechanisms beyond plane wave approximations.
Comparative In Situ Measurements of Plasma Instabilities in the Equatorial and Auroral Electrojets

NASA Technical Reports Server (NTRS)

Pfaff, Robert F.

2008-01-01

This presentation provides a comparison of in situ measurements of plasma instabilities gathered by rocket-borne probes in the equatorial and auroral electrojets. Specifically, using detailed measurements of the DC electric fields, current density, and plasma number density within the unstable daytime equatorial electrojet from Brazil (Guara Campaign) and in the auroral electrojet from Sweden (ERRIS Campaign), we present comparative observations and general conclusions regarding the observed physical properties of Farley-Buneman two-stream waves and large scale, gradient drift waves. The two stream observations reveal coherent-like waves propagating near the E x B direction but at reduced speeds (nearer to the presumed acoustic velocity) with wavelengths of approximately 5-10m in both the equatorial and auroral electrojet, as measured using the spaced-receiver technique. The auroral electrojet data generally shows extensions to shorter wavelengths, in concert with the fact that these waves are driven harder. With respect to gradient-drift driven waves, observations of this instability are much more pronounced in the equatorial electrojet, given the more favorable geometry for growth provided by the vertical gradient and horizontal magnetic field lines. We present new analysis of Guara rocket observations of electric field and plasma density data that reveal considerable structuring in the middle and lower portion of the electrojet (90-105 km) where the ambient plasma density gradient is unstable. Although the electric field amplitudes are largest (approximately 10-15 mV/m) in the zonal direction, considerable structure (approximately 5-10 mV/m) is also observed in the vertical electric field component as well, implying that the dominant large scale waves involve significant vertical interaction and coupling within the narrow altitude range where they are observed. Furthermore, a detailed examination of the phase of the waveforms show that on some, but not all occasions, locally enhanced eastward fields are associated with locally enhanced upwards (polarization) electric fields. The measurements are discussed in terms of theories involving the non-linear evolution and structuring of plasma waves.
Local Fitting of the Kohn-Sham Density in a Gaussian and Plane Waves Scheme for Large-Scale Density Functional Theory Simulations.

PubMed

Golze, Dorothea; Iannuzzi, Marcella; Hutter, Jürg

2017-05-09

A local resolution-of-the-identity (LRI) approach is introduced in combination with the Gaussian and plane waves (GPW) scheme to enable large-scale Kohn-Sham density functional theory calculations. In GPW, the computational bottleneck is typically the description of the total charge density on real-space grids. Introducing the LRI approximation, the linear scaling of the GPW approach with respect to system size is retained, while the prefactor for the grid operations is reduced. The density fitting is an O(N) scaling process implemented by approximating the atomic pair densities by an expansion in one-center fit functions. The computational cost for the grid-based operations becomes negligible in LRIGPW. The self-consistent field iteration is up to 30 times faster for periodic systems dependent on the symmetry of the simulation cell and on the density of grid points. However, due to the overhead introduced by the local density fitting, single point calculations and complete molecular dynamics steps, including the calculation of the forces, are effectively accelerated by up to a factor of ∼10. The accuracy of LRIGPW is assessed for different systems and properties, showing that total energies, reaction energies, intramolecular and intermolecular structure parameters are well reproduced. LRIGPW yields also high quality results for extended condensed phase systems such as liquid water, ice XV, and molecular crystals.
Electromagnetic Simulation of the Near-Field Distribution around a Wind Farm

DOE PAGES

Yang, Shang-Te; Ling, Hao

2013-01-01

An efficienmore » t approach to compute the near-field distribution around and within a wind farm under plane wave excitation is proposed. To make the problem computationally tractable, several simplifying assumptions are made based on the geometry problem. By comparing the approximations against full-wave simulations at 500 MHz, it is shown that the assumptions do not introduce significant errors into the resulting near-field distribution. The near fields around a 3 × 3 wind farm are computed using the developed methodology at 150 MHz, 500 MHz, and 3 GHz. Both the multipath interference patterns and the forward shadows are predicted by the proposed method.« less
Photoelectron Diffraction from Valence States of Oriented Molecules

NASA Astrophysics Data System (ADS)

Krüger, Peter

2018-06-01

The angular distribution of photoelectrons emitted from valence states of oriented molecules is investigated. The principles underlying the angular pattern formation are explained in terms of photoelectron wave interference, caused by initial state delocalization and final state photoelectron scattering. Computational approaches to photoelectron spectroscopy from molecules are briefly reviewed. Here a combination of molecular orbital calculations for the initial state and multiple scattering theory for the photoelectron final state is used and applied to the 3σ and 4σ orbitals of nitrogen and the highest occupied molecular orbital of pentacene. Appreciable perpendicular emission and circular dichroism in angular distributions is found, two effects that cannot be described by the popular plane wave approximation to the photoelectron final state.
Track structure simulations at relativistic energies: an update on cross section calculations

NASA Astrophysics Data System (ADS)

Dingfelder, Michael

Charged particle track structure simulations follow the primary, as well as all (produced) sec-ondary particles in an event-by-event matter, from starting or ejection energies down to total stopping. They provide detailed information on the spacial distributions of energy depositions, interaction types, and radical species produced. These quantities provide a starting point to describe the interaction of the radiation with matter of biological interest and to explore and estimate the effects of radiation quality on various biological responses of these systems. Of special interest is liquid water which serves as surrogate for soft tissue. Ionization and excitation cross sections for bare charged particles can be calculated within the framework of the (relativistic) plane-wave Born approximation or the (relativistic) Bethe approximation. Both theories rely on a realistic model of the dielectric response function of the material under consideration and need to address relativistic medium polarization effects like the Fermi-density effect in a consistent way. In this talk we will review and present new and updated aspects of charged particle cross section calculations for relativistic heavy ions with liquid water and other materials of biological interest. This includes an updated model for the dielectric response function of liquid water to better reflect new data from inelastic X-ray scattering (IXS) experiments using synchrotron radiation and a model for the dielectric response function of calcium, which serves as a bone surrogate. We will also discuss the implementation of relativistic effect, especially of the Fermi-density effect into the cross section calculations. This work is supported by the National Aeronautics and Space Administration (NASA), grant no. NNJ04HF39G.
Binary-encounter electrons observed at 0 degree in collisions of 1--2-MeV/amu H sup + , C sup 6+ , N sup 7+ , O sup 8+ , and F sup 9+ ions with H sub 2 and He targets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, D.H.; Richard, P.; Zouros, T.J.M.

The energy distribution of binary-encounter electrons (BEE) produced in collisions of 1--2 MeV/amu H{sup +} and bare C, N, O, and F ions with H{sub 2} and He gas targets is reported at 0{degree} with respect to the beam direction. These electrons result from ionization of the target due to hard collisions with the projectile and can thus be considered to be produced in a process analogous to elastic scattering of a free electron from a highly charged ion. An impulse-approximation (IA) model has been developed to describe this process in which quasifree'' target electrons undergo 180{degree} Rutherford scattering inmore » the projectile frame. The measured BEE double-differential production cross sections for bare ions were well described by this model and were found to scale with {ital Z}{sub {ital p}}{sup 2} and {ital E}{sub {ital p}}{sup {minus}({similar to}2.6--2.7)} where {ital Z}{sub {ital p}} and {ital E}{sub {ital p}} are the charge and energy of the projectile, respectively. An energy shift of the BEE below 4{ital t}, where {ital t} is the cusp electron energy, is observed and is also predicted by the IA treatment. A plane-wave Born approximation (PWBA) calculation for BEE production is also found to be in overall agreement with our data. However, the energy shift of the BEE peak could not be fully accounted for within this PWBA calculation.« less
Density functional theory of electron transfer beyond the Born-Oppenheimer approximation: Case study of LiF

NASA Astrophysics Data System (ADS)

Li, Chen; Requist, Ryan; Gross, E. K. U.

2018-02-01

We perform model calculations for a stretched LiF molecule, demonstrating that nonadiabatic charge transfer effects can be accurately and seamlessly described within a density functional framework. In alkali halides like LiF, there is an abrupt change in the ground state electronic distribution due to an electron transfer at a critical bond length R = Rc, where an avoided crossing of the lowest adiabatic potential energy surfaces calls the validity of the Born-Oppenheimer approximation into doubt. Modeling the R-dependent electronic structure of LiF within a two-site Hubbard model, we find that nonadiabatic electron-nuclear coupling produces a sizable elongation of the critical Rc by 0.5 bohr. This effect is very accurately captured by a simple and rigorously derived correction, with an M-1 prefactor, to the exchange-correlation potential in density functional theory, M = reduced nuclear mass. Since this nonadiabatic term depends on gradients of the nuclear wave function and conditional electronic density, ∇Rχ(R) and ∇Rn(r, R), it couples the Kohn-Sham equations at neighboring R points. Motivated by an observed localization of nonadiabatic effects in nuclear configuration space, we propose a local conditional density approximation—an approximation that reduces the search for nonadiabatic density functionals to the search for a single function y(n).
Migration of scattered teleseismic body waves

NASA Astrophysics Data System (ADS)

Bostock, M. G.; Rondenay, S.

1999-06-01

The retrieval of near-receiver mantle structure from scattered waves associated with teleseismic P and S and recorded on three-component, linear seismic arrays is considered in the context of inverse scattering theory. A Ray + Born formulation is proposed which admits linearization of the forward problem and economy in the computation of the elastic wave Green's function. The high-frequency approximation further simplifies the problem by enabling (1) the use of an earth-flattened, 1-D reference model, (2) a reduction in computations to 2-D through the assumption of 2.5-D experimental geometry, and (3) band-diagonalization of the Hessian matrix in the inverse formulation. The final expressions are in a form reminiscent of the classical diffraction stack of seismic migration. Implementation of this procedure demands an accurate estimate of the scattered wave contribution to the impulse response, and thus requires the removal of both the reference wavefield and the source time signature from the raw record sections. An approximate separation of direct and scattered waves is achieved through application of the inverse free-surface transfer operator to individual station records and a Karhunen-Loeve transform to the resulting record sections. This procedure takes the full displacement field to a wave vector space wherein the first principal component of the incident wave-type section is identified with the direct wave and is used as an estimate of the source time function. The scattered displacement field is reconstituted from the remaining principal components using the forward free-surface transfer operator, and may be reduced to a scattering impulse response upon deconvolution of the source estimate. An example employing pseudo-spectral synthetic seismograms demonstrates an application of the methodology.
Development of an Acoustic Levitation Linear Transportation System Based on a Ring-Type Structure.

PubMed

Thomas, Gilles P L; Andrade, Marco A B; Adamowski, Julio Cezar; Silva, Emilio Carlos Nelli

2017-05-01

A linear acoustic levitation transportation system based on a ring-type vibrator is presented. The system is composed by two 21-kHz Langevin transducers connected to a ring-shaped structure formed by two semicircular sections and two flat plates. In this system, a flexural standing wave is generated along the ring structure, producing an acoustic standing wave between the vibrating ring and a plane reflector located at a distance of approximately a half wavelength from the ring. The acoustic standing wave in air has a series of pressure nodes, where small particles can be levitated and transported. The ring-type transportation system was designed and analyzed by using the finite element method. Additionally, a prototype was built and the acoustic levitation and transport of a small polystyrene particle was demonstrated.
Procedure for noise prediction and optimization of advanced technology propellers

NASA Technical Reports Server (NTRS)

Jou, W. H.; Bernstein, S.

1979-01-01

The sound field due to a propeller operating at supersonic tip speed in a uniform flow was investigated. Using the fact that the wave front in a uniform stream is a convected sphere, the fundamental solution to the convected wave equation was easily obtained. The Fourier coefficients of the pressure signature were obtained by a far field approximation, and are expressed as an integral over the blade platform. It is shown that cones of silence exist fore and aft the propeller plane. The semiapex angles are shown. These angles are independent of the individual Mach components such as the flight Mach number and the rotation Mach number. The result is confirmed by the computation of the ray path of the emitted Mach waves. The Doppler amplification factor strengthens the signal behind the propeller while it weakens that upstream.
Floquet wave ultrasonic method for determination of single ply moduli in multidirectional composites.

PubMed

Wang, L; Rokhlin, S I

2002-09-01

An inversion method based on Floquet wave velocity in a periodic medium has been introduced to determine the single ply elastic moduli of a multi-ply composite. The stability of this algorithm is demonstrated by numerical simulation. The applicability of the plane wave approximation to the velocity measurement in the double-through-transmission self-reference method has been analyzed using a time-domain beam model. It shows that the finite width of the transmitter affects only the amplitudes of the signals and has almost no effect on the time delay. Using this method, the ply moduli for a multiply composite have been experimentally determined. While the paper focuses on elastic constant reconstruction from phase velocity measurements by the self-reference double-through-transmission method, the reconstruction methodology is also applicable to assessment of data collected by other methods.
Instability of quantum equilibrium in Bohm's dynamics

PubMed Central

Colin, Samuel; Valentini, Antony

2014-01-01

We consider Bohm's second-order dynamics for arbitrary initial conditions in phase space. In principle, Bohm's dynamics allows for ‘extended’ non-equilibrium, with initial momenta not equal to the gradient of phase of the wave function (as well as initial positions whose distribution departs from the Born rule). We show that extended non-equilibrium does not relax in general and is in fact unstable. This is in sharp contrast with de Broglie's first-order dynamics, for which non-standard momenta are not allowed and which shows an efficient relaxation to the Born rule for positions. On this basis, we argue that, while de Broglie's dynamics is a tenable physical theory, Bohm's dynamics is not. In a world governed by Bohm's dynamics, there would be no reason to expect to see an effective quantum theory today (even approximately), in contradiction with observation. PMID:25383020
First Principle Predictions of Isotopic Shifts in H2O

NASA Technical Reports Server (NTRS)

Schwenke, David W.; Kwak, Dochan (Technical Monitor)

2002-01-01

We compute isotope independent first and second order corrections to the Born-Oppenheimer approximation for water and use them to predict isotopic shifts. For the diagonal correction, we use icMRCI wavefunctions and derivatives with respect to mass dependent, internal coordinates to generate the mass independent correction functions. For the non-adiabatic correction, we use scaled SCF/CIS wave functions and a generalization of the Handy method to obtain mass independent correction functions. We find that including the non-adiabatic correction gives significantly improved results compared to just including the diagonal correction when the Born-Oppenheimer potential energy surface is optimized for H2O-16. The agreement with experimental results for deuterium and tritium containing isotopes is nearly as good as our best empirical correction, however, the present correction is expected to be more reliable for higher, uncharacterized levels.
Letters: Noise Equalization for Ultrafast Plane Wave Microvessel Imaging

PubMed Central

Song, Pengfei; Manduca, Armando; Trzasko, Joshua D.

2017-01-01

Ultrafast plane wave microvessel imaging significantly improves ultrasound Doppler sensitivity by increasing the number of Doppler ensembles that can be collected within a short period of time. The rich spatiotemporal plane wave data also enables more robust clutter filtering based on singular value decomposition (SVD). However, due to the lack of transmit focusing, plane wave microvessel imaging is very susceptible to noise. This study was designed to: 1) study the relationship between ultrasound system noise (primarily time gain compensation-induced) and microvessel blood flow signal; 2) propose an adaptive and computationally cost-effective noise equalization method that is independent of hardware or software imaging settings to improve microvessel image quality. PMID:28880169
Deriving micro- to macro-scale seismic velocities from ice-core c axis orientations

NASA Astrophysics Data System (ADS)

Kerch, Johanna; Diez, Anja; Weikusat, Ilka; Eisen, Olaf

2018-05-01

One of the great challenges in glaciology is the ability to estimate the bulk ice anisotropy in ice sheets and glaciers, which is needed to improve our understanding of ice-sheet dynamics. We investigate the effect of crystal anisotropy on seismic velocities in glacier ice and revisit the framework which is based on fabric eigenvalues to derive approximate seismic velocities by exploiting the assumed symmetry. In contrast to previous studies, we calculate the seismic velocities using the exact c axis angles describing the orientations of the crystal ensemble in an ice-core sample. We apply this approach to fabric data sets from an alpine and a polar ice core. Our results provide a quantitative evaluation of the earlier approximative eigenvalue framework. For near-vertical incidence our results differ by up to 135 m s-1 for P-wave and 200 m s-1 for S-wave velocity compared to the earlier framework (estimated 1 % difference in average P-wave velocity at the bedrock for the short alpine ice core). We quantify the influence of shear-wave splitting at the bedrock as 45 m s-1 for the alpine ice core and 59 m s-1 for the polar ice core. At non-vertical incidence we obtain differences of up to 185 m s-1 for P-wave and 280 m s-1 for S-wave velocities. Additionally, our findings highlight the variation in seismic velocity at non-vertical incidence as a function of the horizontal azimuth of the seismic plane, which can be significant for non-symmetric orientation distributions and results in a strong azimuth-dependent shear-wave splitting of max. 281 m s-1 at some depths. For a given incidence angle and depth we estimated changes in phase velocity of almost 200 m s-1 for P wave and more than 200 m s-1 for S wave and shear-wave splitting under a rotating seismic plane. We assess for the first time the change in seismic anisotropy that can be expected on a short spatial (vertical) scale in a glacier due to strong variability in crystal-orientation fabric (±50 m s-1 per 10 cm). Our investigation of seismic anisotropy based on ice-core data contributes to advancing the interpretation of seismic data, with respect to extracting bulk information about crystal anisotropy, without having to drill an ice core and with special regard to future applications employing ultrasonic sounding.

Wave function delocalization and large-amplitude vibrations of helium on corrugated aromatic microsurfaces: tetracene.He and pentacene.He van der Waals complexes.

PubMed

Xu, Minzhong; Bacić, Zlatko

2007-08-09

We report accurate quantum three-dimensional calculations of highly excited intermolecular vibrational states of the van der Waals (vdW) complexes tetracene.He and pentacene.He in the S1 excited electronic state. The aromatic molecules were taken to be rigid and the intermolecular potential energy surfaces (IPESs) were modeled as a sum of atom-atom Lennard-Jones pair potentials. The IPESs are corrugated in the direction of the long (x) axis of the aromatic molecules, due to the presence of the symmetrically equivalent global double minimum for tetracene.He, and a triple minimum (central global minimum and two equivalent local minima) for pentacene.He, on each side of the aromatic plane. Both IPESs have two additional minor equivalent local minima further away from the center of the molecule. The vdW vibrational states analyzed in this work cover about 80% of the well depths of the IPESs. The mode coupling is generally weak for those states whose out-of-plane (z) mode is unexcited. However, the z-mode fundamental is strongly coupled to the short-axis (y) in-plane mode, so that the pure z-mode excitation could not be identified. The He atom exhibits large in-plane spatial delocalizaton already in the ground vdW vibrational state, which increases rapidly upon the excitation of the in-plane x and y modes, with little hindrance by the corrugation of the aromatic microsurfaces. For the vdW vibrational energies considered, the He atom spatial delocalization reaches Deltax and Deltay values of approximately 5 and 4 A, respectively, and is limited only by the finite size of the aromatic substrates. Side-crossing delocalization of the wave functions on both sides of the molecular plane is found at excitation energies >30 cm(-1), giving rise to the energy splittings of the pairs of states symmetric/antisymmetric with respect to the aromatic plane; the splittings show strong vdW vibrational mode specificity.
Optimized norm-conserving Hartree-Fock pseudopotentials for plane-wave calculations

NASA Astrophysics Data System (ADS)

Al-Saidi, W. A.; Walter, E. J.; Rappe, A. M.

2008-02-01

We report Hartree-Fock (HF)-based pseudopotentials suitable for plane-wave calculations. Unlike typical effective core potentials, the present pseudopotentials are finite at the origin and exhibit rapid convergence in a plane-wave basis; the optimized pseudopotential method [A. M. Rappe , Phys. Rev. B 41, 1227 (1990)] improves plane-wave convergence. Norm-conserving HF pseudopotentials are found to develop long-range non-Coulombic behavior which does not decay faster than 1/r , and is nonlocal. This behavior, which stems from the nonlocality of the exchange potential, is remedied using a recently developed self-consistent procedure [J. R. Trail and R. J. Needs, J. Chem. Phys. 122, 014112 (2005)]. The resulting pseudopotentials slightly violate the norm conservation of the core charge. We calculated several atomic properties using these pseudopotentials, and the results are in good agreement with all-electron HF values. The dissociation energies, equilibrium bond lengths, and frequencies of vibration of several dimers obtained with these HF pseudopotentials and plane waves are also in good agreement with all-electron results.
Highly precise acoustic calibration method of ring-shaped ultrasound transducer array for plane-wave-based ultrasound tomography

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.
Grating tuned unstable resonator laser cavity

DOEpatents

Johnson, Larry C.

1982-01-01

An unstable resonator to be used in high power, narrow line CO.sub.2 pump lasers comprises an array of four reflectors in a ring configuration wherein spherical and planar wavefronts are separated from each other along separate optical paths and only the planar wavefronts are impinged on a plane grating for line tuning. The reflector array comprises a concave mirror for reflecting incident spherical waves as plane waves along an output axis to form an output beam. A plane grating on the output axis is oriented to reflect a portion of the output beam off axis onto a planar relay mirror spaced apart from the output axis in proximity to the concave mirror. The relay mirror reflects plane waves from the grating to impinge on a convex expanding mirror spaced apart from the output axis in proximity to the grating. The expanding mirror reflects the incident planar waves as spherical waves to illuminate the concave mirror. Tuning is provided by rotating the plane grating about an axis normal to the output axis.
The EBEX Experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oxley, P.; Ade, P.; Baccigalupi, C.

2005-01-06

EBEX is a balloon-borne polarimeter designed to measure the intensity and polarization of the cosmic microwave background radiation. The measurements would probe the inflationary epoch that took place shortly after the big bang and would significantly improve constraints on the values of several cosmological parameters. EBEX is unique in its broad frequency coverage and in its ability to provide critical information about the level of polarized Galactic foregrounds which will be necessary for all future CMB polarization experiments. EBEX consists of a 1.5 m Dragone-type telescope that provides a resolution of less than 8 arcminutes over four focal planes eachmore » of 4. diffraction limited field of view at frequencies up to 450 GHz. The experiment is designed to accommodate 330 transition edge bolometric detectors per focal plane, for a total of up to 1320 detectors. EBEX will operate with frequency bands centered at 150, 250, 350, and 450 GHz. Polarimetry is achieved with a rotating achromatic half-wave plate. EBEX is currently in the design and construction phase, and first light is scheduled for 2008.« less
The effect of guide-field and boundary conditions on collisionless magnetic reconnection in a stressed X-point collapse

DOE Office of Scientific and Technical Information (OSTI.GOV)

Graf von der Pahlen, J.; Tsiklauri, D.

2014-01-15

Works of Tsiklauri and Haruki [Phys. Plasmas 15, 102902 (2008); 14, 112905 (2007)] are extended by inclusion of the out-of-plane magnetic (guide) field. In particular, magnetic reconnection during collisionless, stressed X-point collapse for varying out-of-plane guide-fields is studied using a kinetic, 2.5D, fully electromagnetic, relativistic particle-in-cell numerical code. For zero guide-field, cases for both open and closed boundary conditions are investigated, where magnetic flux and particles are lost and conserved, respectively. It is found that reconnection rates, out-of-plane currents and density in the X-point increase more rapidly and peak sooner in the closed boundary case, but higher values are reachedmore » in the open boundary case. The normalized reconnection rate is fast: 0.10-0.25. In the open boundary case it is shown that an increase of guide-field yields later onsets in the reconnection peak rates, while in the closed boundary case initial peak rates occur sooner but are suppressed. The reconnection current changes similarly with increasing guide-field; however for low guide-fields the reconnection current increases, giving an optimal value for the guide-field between 0.1 and 0.2 times the in-plane field in both cases. Also, in the open boundary case, it is found that for guide-fields of the order of the in-plane magnetic field, the generation of electron vortices occurs. Possible causes of the vortex generation, based on the flow of decoupled particles in the diffusion region and localized plasma heating, are discussed. Before peak reconnection onset, oscillations in the out-of-plane electric field at the X-point are found, ranging in frequency from approximately 1 to 2 ω{sub pe} and coinciding with oscillatory reconnection. These oscillations are found to be part of a larger wave pattern in the simulation domain. Mapping the out-of-plane electric field along the central lines of the domain over time and applying a 2D Fourier transform reveal that the waves predominantly correspond to the ordinary and the extraordinary mode and hence may correspond to observable radio waves such as solar radio burst fine structure spikes.« less
Zr-92(d,p)Zr-93 and Zr-92(d,t)Zr-91

NASA Technical Reports Server (NTRS)

Baron, N.; Fink, C. L.; Christensen, P. R.; Nickels, J.; Torsteinsen, T.

1972-01-01

The structures of Zr-93 and Zr-91 were studied by the stripping reaction Zr-92(d,p)Zr-93 and the pick-up reaction Zr-92(d,t)Zr-91 using 13 MeV incident deuterons. The reaction product particles were detected by counter telescope. Typical spectra from the reactions were analyzed by a nonlinear least squares peak fitting program which included a background search. Spin and parity assignments to observed excited levels were made by comparing experimental angular distributions with distorted wave Born approximation calculations.
Two-proton transfer reactions on even Ni and Zn isotopes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boucenna, A.; Kraus, L.; Linck, I.

New levels strongly excited by 112-MeV {sup 12}C ions on even Ni and Zn isotopes are {ital J}{sup {pi}} assigned on kinematical and geometrical arguments, crude shell-model calculations, and distorted-wave Born approximation angular-distribution analysis. These tentative assignments are supported by the Bansal-French model. Because of the contribution of additional collective effects, the two-proton transfer reaction spectra are less selectively fed than those obtained with the analogous two-neutron transfer reactions induced on the same targets in a similar energy range.
Ultracold collisions between spin-orbit-coupled dipoles: General formalism and universality

NASA Astrophysics Data System (ADS)

Wang, Jia; Hougaard, Christiaan R.; Mulkerin, Brendan C.; Liu, Xia-Ji

2018-04-01

A theoretical study of the low-energy scattering properties of two aligned identical bosonic and fermionic dipoles in the presence of isotropic spin-orbit coupling is presented. A general treatment of particles with arbitrary (pseudo)spin is given in the framework of multichannel scattering. At ultracold temperatures and away from shape resonances or closed-channel dominated resonances, the cross section can be well described within the Born approximation to within corrections due to the s -wave scattering. We compare our findings with numerical calculations and find excellent agreement.
WavePacket: A Matlab package for numerical quantum dynamics. I: Closed quantum systems and discrete variable representations

NASA Astrophysics Data System (ADS)

Schmidt, Burkhard; Lorenz, Ulf

2017-04-01

WavePacket is an open-source program package for the numerical simulation of quantum-mechanical dynamics. It can be used to solve time-independent or time-dependent linear Schrödinger and Liouville-von Neumann-equations in one or more dimensions. Also coupled equations can be treated, which allows to simulate molecular quantum dynamics beyond the Born-Oppenheimer approximation. Optionally accounting for the interaction with external electric fields within the semiclassical dipole approximation, WavePacket can be used to simulate experiments involving tailored light pulses in photo-induced physics or chemistry. The graphical capabilities allow visualization of quantum dynamics 'on the fly', including Wigner phase space representations. Being easy to use and highly versatile, WavePacket is well suited for the teaching of quantum mechanics as well as for research projects in atomic, molecular and optical physics or in physical or theoretical chemistry. The present Part I deals with the description of closed quantum systems in terms of Schrödinger equations. The emphasis is on discrete variable representations for spatial discretization as well as various techniques for temporal discretization. The upcoming Part II will focus on open quantum systems and dimension reduction; it also describes the codes for optimal control of quantum dynamics. The present work introduces the MATLAB version of WavePacket 5.2.1 which is hosted at the Sourceforge platform, where extensive Wiki-documentation as well as worked-out demonstration examples can be found.
Shock wave polarizations and optical metrics in the Born and the Born–Infeld electrodynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Minz, Christoph, E-mail: christoph.minz@alumni.tu-berlin.de; Borzeszkowski, Horst-Heino von, E-mail: borzeszk@mailbox.tu-berlin.de; Chrobok, Thoralf, E-mail: tchrobok@mailbox.tu-berlin.de

We analyze the behavior of shock waves in nonlinear theories of electrodynamics. For this, by use of generalized Hadamard step functions of increasing order, the electromagnetic potential is developed in a series expansion near the shock wave front. This brings about a corresponding expansion of the respective electromagnetic field equations which allows for deriving relations that determine the jump coefficients in the expansion series of the potential. We compute the components of a suitable gauge-normalized version of the jump coefficients given for a prescribed tetrad compatible with the shock front foliation. The solution of the first-order jump relations shows that,more » in contrast to linear Maxwell’s electrodynamics, in general the propagation of shock waves in nonlinear theories is governed by optical metrics and polarization conditions describing the propagation of two differently polarized waves (leading to a possible appearance of birefringence). In detail, shock waves are analyzed in the Born and Born–Infeld theories verifying that the Born–Infeld model exhibits no birefringence and the Born model does. The obtained results are compared to those ones found in literature. New results for the polarization of the two different waves are derived for Born-type electrodynamics.« less
Born-Infeld corrections to Coulombian interactions.

PubMed

Ferraro, Rafael; Lipchak, María Evangelina

2008-04-01

Two-dimensional Born-Infeld electrostatic fields behaving as the superposition of two pointlike charges in the linearized (Maxwellian) limit are investigated by means of a nonholomorphic mapping of the complex plane. The changes in the Coulombian interaction between two charges in Born-Infeld theory are computed. Remarkably, the force between equal charges goes to zero as they approach each other.
Electron phonon interactions and intrinsic nonadiabatic state of superconductors

NASA Astrophysics Data System (ADS)

Baňacký, Pavol

2007-09-01

Study of band structure of YBa 2Cu 3O 7 has shown that electron coupling to A g, B 2g and B 3g modes results in fluctuation of saddle point of one of the CuO plane d-pσ band in Y point of 1st BZ across Fermi level. It represents breakdown of adiabatic Born-Oppenheimer approximation and transition of the system into intrinsic nonadiabatic state, ω > EF. Results show that system is stabilized in this state at distorted nuclear geometry. Stabilization effect is mainly due to strong dependence of the electronic motion on instantaneous nuclear momenta. On the lattice scale, the intrinsic nonadiabatic state is geometrically degenerate at broken translation symmetry - system has fluxional nuclear configuration of O2, O3 atoms in CuO planes. It enables formation of mobile bipolarons that can move in the lattice without dissipation. Described effects are absent in non-superconducting YBa 2Cu 3O 6.
Linear shoaling of free-surface waves in multi-layer non-hydrostatic models

NASA Astrophysics Data System (ADS)

Bai, Yefei; Cheung, Kwok Fai

2018-01-01

The capability to describe shoaling over sloping bottom is fundamental to modeling of coastal wave transformation. The linear shoaling gradient provides a metric to measure this property in non-hydrostatic models with layer-integrated formulations. The governing equations in Boussinesq form facilitate derivation of the linear shoaling gradient, which is in the form of a [ 2 P + 2 , 2 P ] expansion of the water depth parameter kd with P equal to 1 for a one-layer model and (4 N - 4) for an N-layer model. The expansion reproduces the analytical solution from Airy wave theory at the shallow water limit and maintains a reasonable approximation up to kd = 1.2 and 2 for the one and two-layer models. Additional layers provide rapid and monotonic convergence of the shoaling gradient into deep water. Numerical experiments of wave propagation over a plane slope illustrate manifestation of the shoaling errors through the transformation processes from deep to shallow water. Even though outside the zone of active wave transformation, shoaling errors from deep to intermediate water are cumulative to produce appreciable impact to the wave amplitude in shallow water.
40 MHz high-frequency ultrafast ultrasound imaging.

PubMed

Huang, Chih-Chung; Chen, Pei-Yu; Peng, Po-Hsun; Lee, Po-Yang

2017-06-01

Ultrafast high-frame-rate ultrasound imaging based on coherent-plane-wave compounding has been developed for many biomedical applications. Most coherent-plane-wave compounding systems typically operate at 3-15 MHz, and the image resolution for this frequency range is not sufficient for visualizing microstructure tissues. Therefore, the purpose of this study was to implement a high-frequency ultrafast ultrasound imaging operating at 40 MHz. The plane-wave compounding imaging and conventional multifocus B-mode imaging were performed using the Field II toolbox of MATLAB in simulation study. In experiments, plane-wave compounding images were obtained from a 256 channel ultrasound research platform with a 40 MHz array transducer. All images were produced by point-spread functions and cyst phantoms. The in vivo experiment was performed from zebrafish. Since high-frequency ultrasound exhibits a lower penetration, chirp excitation was applied to increase the imaging depth in simulation. The simulation results showed that a lateral resolution of up to 66.93 μm and a contrast of up to 56.41 dB were achieved when using 75-angles plane waves in compounding imaging. The experimental results showed that a lateral resolution of up to 74.83 μm and a contrast of up to 44.62 dB were achieved when using 75-angles plane waves in compounding imaging. The dead zone and compounding noise are about 1.2 mm and 2.0 mm in depth for experimental compounding imaging, respectively. The structure of zebrafish heart was observed clearly using plane-wave compounding imaging. The use of fewer than 23 angles for compounding allowed a frame rate higher than 1000 frames per second. However, the compounding imaging exhibits a similar lateral resolution of about 72 μm as the angle of plane wave is higher than 10 angles. This study shows the highest operational frequency for ultrafast high-frame-rate ultrasound imaging. © 2017 American Association of Physicists in Medicine.
Self-interaction corrected LDA + U investigations of BiFeO3 properties: plane-wave pseudopotential method

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.
Defect-mediated phonon dynamics in TaS2 and WSe2

PubMed Central

Cremons, Daniel R.; Plemmons, Dayne A.; Flannigan, David J.

2017-01-01

We report correlative crystallographic and morphological studies of defect-dependent phonon dynamics in single flakes of 1T-TaS2 and 2H-WSe2 using selected-area diffraction and bright-field imaging in an ultrafast electron microscope. In both materials, we observe in-plane speed-of-sound acoustic-phonon wave trains, the dynamics of which (i.e., emergence, propagation, and interference) are strongly dependent upon discrete interfacial features (e.g., vacuum/crystal and crystal/crystal interfaces). In TaS2, we observe cross-propagating in-plane acoustic-phonon wave trains of differing frequencies that undergo coherent interference approximately 200 ps after initial emergence from distinct interfacial regions. With ultrafast bright-field imaging, the properties of the interfering wave trains are observed to correspond to the beat frequency of the individual oscillations, while intensity oscillations of Bragg spots generated from selected areas within the region of interest match well with the real-space dynamics. In WSe2, distinct acoustic-phonon dynamics are observed emanating and propagating away from structurally dissimilar morphological discontinuities (vacuum/crystal interface and crystal terrace), and results of ultrafast selected-area diffraction reveal thickness-dependent phonon frequencies. The overall observed dynamics are well-described using finite element analysis and time-dependent linear-elastic continuum mechanics. PMID:28503630
Validation of Born Traveltime Kernels

NASA Astrophysics Data System (ADS)

Baig, A. M.; Dahlen, F. A.; Hung, S.

2001-12-01

Most inversions for Earth structure using seismic traveltimes rely on linear ray theory to translate observed traveltime anomalies into seismic velocity anomalies distributed throughout the mantle. However, ray theory is not an appropriate tool to use when velocity anomalies have scale lengths less than the width of the Fresnel zone. In the presence of these structures, we need to turn to a scattering theory in order to adequately describe all of the features observed in the waveform. By coupling the Born approximation to ray theory, the first order dependence of heterogeneity on the cross-correlated traveltimes (described by the Fréchet derivative or, more colourfully, the banana-doughnut kernel) may be determined. To determine for what range of parameters these banana-doughnut kernels outperform linear ray theory, we generate several random media specified by their statistical properties, namely the RMS slowness perturbation and the scale length of the heterogeneity. Acoustic waves are numerically generated from a point source using a 3-D pseudo-spectral wave propagation code. These waves are then recorded at a variety of propagation distances from the source introducing a third parameter to the problem: the number of wavelengths traversed by the wave. When all of the heterogeneity has scale lengths larger than the width of the Fresnel zone, ray theory does as good a job at predicting the cross-correlated traveltime as the banana-doughnut kernels do. Below this limit, wavefront healing becomes a significant effect and ray theory ceases to be effective even though the kernels remain relatively accurate provided the heterogeneity is weak. The study of wave propagation in random media is of a more general interest and we will also show our measurements of the velocity shift and the variance of traveltime compare to various theoretical predictions in a given regime.
An accelerated hologram calculation using the wavefront recording plane method and wavelet transform

NASA Astrophysics Data System (ADS)

Arai, Daisuke; Shimobaba, Tomoyoshi; Nishitsuji, Takashi; Kakue, Takashi; Masuda, Nobuyuki; Ito, Tomoyoshi

2017-06-01

Fast hologram calculation methods are critical in real-time holography applications such as three-dimensional (3D) displays. We recently proposed a wavelet transform-based hologram calculation called WASABI. Even though WASABI can decrease the calculation time of a hologram from a point cloud, it increases the calculation time with increasing propagation distance. We also proposed a wavefront recoding plane (WRP) method. This is a two-step fast hologram calculation in which the first step calculates the superposition of light waves emitted from a point cloud in a virtual plane, and the second step performs a diffraction calculation from the virtual plane to the hologram plane. A drawback of the WRP method is in the first step when the point cloud has a large number of object points and/or a long distribution in the depth direction. In this paper, we propose a method combining WASABI and the WRP method in which the drawbacks of each can be complementarily solved. Using a consumer CPU, the proposed method succeeded in performing a hologram calculation with 2048 × 2048 pixels from a 3D object with one million points in approximately 0.4 s.
Modal method for Second Harmonic Generation in nanostructures

NASA Astrophysics Data System (ADS)

Héron, S.; Pardo, F.; Bouchon, P.; Pelouard, J.-L.; Haïdar, R.

2015-05-01

Nanophotonic devices show interesting features for nonlinear response enhancement but numerical tools are mandatory to fully determine their behaviour. To address this need, we present a numerical modal method dedicated to nonlinear optics calculations under the undepleted pump approximation. It is brie y explained in the frame of Second Harmonic Generation for both plane waves and focused beams. The nonlinear behaviour of selected nanostructures is then investigated to show comparison with existing analytical results and study the convergence of the code.

Paraboloid-aspheric lenses free of spherical aberration

NASA Astrophysics Data System (ADS)

Lozano-Rincón, Ninfa del C.; Valencia-Estrada, Juan Camilo

2017-07-01

A method to design singlet paraboloid-aspheric lenses free of all orders of spherical aberration with maximum aperture is described. This work includes all parametric formulas to describe paraboloid-aspheric or aspheric-paraboloid lenses for any finite conjugated planes. It also includes the Schwarzchilds approximations (which can be used to calculate one rigorous propagation of light waves in physic optics) to design convex paraboloid-aspheric lenses for imaging an object at infinity, with explicit formulas to calculate thicknesses easily. The results were verified with software through ray tracing.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Verma, U. P.; Nayak, V.

Quantum mechanical first principle calculations have been performed to study the electronic and structural properties of TiN and TiAs in zinc blende (ZB) and rock salt (RS) structures. The full-potential linearized augmented plane wave (FP-LAPW) method has been used within the framework of density functional theory (DFT). The exchange correlation functional has been solved employing generalized gradient approximation (GGA). Our predicted results for lattice constants are in good agreement with the earlier findings. The electronic band structures of TiX are metallic in both the phases.
Two-dimensional noncontact transportation of small objects in air using flexural vibration of a plate.

PubMed

Kashima, Ryota; Koyama, Daisuke; Matsukawa, Mami

2015-12-01

This paper investigates a two-dimensional ultrasonic manipulation technique for small objects in air. The ultrasonic levitation system consists of a rectangular vibrating plate with four ultrasonic transducers and a reflector. The configuration of the vibrator, the resonant frequency, and the positions of the four transducers with step horns were determined from finite element analysis such that an intense acoustic standing-wave field could be generated between the plates. A lattice flexural vibration mode with a wavelength of 28.3 mm was excited on the prototype plate at 24.6 kHz. Small objects could get trapped in air along the horizontal nodal plane of the standing wave. By controlling the driving phase difference between the transducers, trapped objects could be transported without contact in a two-dimensional plane. When the phase difference was changed from 0° to 720°, the distance moved by a small particle in the orthogonal direction was approximately 29 mm, which corresponds with the wavelength of the flexural vibration on the vibrating plate.
First-Principles Study on the Structural and Magnetic Properties of Iron Hydride

NASA Astrophysics Data System (ADS)

Tsumuraya, Takao; Matsuura, Yasuyuki; Shishidou, Tatsuya; Oguchi, Tamio

2012-06-01

The magnetic and structural properties of iron hydride FeH with the double hexagonal close-packed (dhcp) and hexagonal close-packed (hcp) structures are investigated by first-principles density-functional theory calculations with a spin-polarized form of generalized gradient approximation. All the calculations are performed using all-electron full-potential linearized augmented plane wave method. Both dhcp and hcp FeH are ferromagnetic at ambient pressure. The ferromagnetic ordering of the dhcp structure collapses at a pressure of 48 GPa, while that of the hcp structure vanishes gradually from 48 GPa. The modification in the density of states (DOS) due to the applied pressure causes the collapse of the magnetization. The difference in magnetic moment reduction between dhcp and hcp FeH is attributed to their DOS around the Fermi level. The calculated magnetocrystalline anisotropy energies between in-plane and out-of-plane spin orientations are found to be 124 μeV/Fe for the dhcp structure, and 100 μeV/Fe for the hcp structure. The easy axis is in-plane direction for both structures.
Electromagnetic fields radiated from a lightning return stroke - Application of an exact solution to Maxwell's equations

NASA Technical Reports Server (NTRS)

Le Vine, D. M.; Meneghini, R.

1978-01-01

A solution is presented for the electromagnetic fields radiated by an arbitrarily oriented current filament over a conducting ground plane in the case where the current propagates along the filament at the speed of light, and this solution is interpreted in terms of radiation from lightning return strokes. The solution is exact in the fullest sense; no mathematical approximations are made, and the governing differential equations and boundary conditions are satisfied. The solution has the additional attribute of being specified in closed form in terms of elementary functions. This solution is discussed from the point of view of deducing lightning current wave forms from measurements of the electromagnetic fields and understanding the effects of channel tortuosity on the radiated fields. In addition, it is compared with two approximate solutions, the traditional moment approximation and the Fraunhofer approximation, and a set of criteria describing their applicability are presented and interpreted.
Electromagnetic Wave Excitation by a Longitudinal Slot in a Broad Wall of Rectangular Waveguide in the Presence of Passive Impedance Vibrators Outside the Waveguide

NASA Astrophysics Data System (ADS)

Berdnik, S. L.; Katrich, V. A.; Nesterenko, M. V.; Penkin, Yu. M.

2016-09-01

Purpose: A problem of electromagnetic wave diffraction by a longitudinal slot cut in a waveguide wide wall is solved. The slot is cut in a wide wall of a rectangular waveguide and radiates in a half-space above a perfectly conducting plane where two vertical impedance monopoles with arbitrary lengths placed with their bases placed on the plane. The paper is aimed at studying the electrodynamic characteristics of vibratorwaveguide-slot structures which allow to form the emission fields as that in a Clavin element with two identical passive ideally conducting monopoles of a fixed length located on a set distance from a slot center on both sides of a narrow halfwave slot. Design/methodology/approach: The problem is solved by a generalized method of induced electromotive and magnetomotive forces in approximation of electric currents in the vibrators and equivalent magnetic current in the slot by the functions obtained by the asymptotic averaging method. Findings: The influence of geometric parameters of the structure on the directional characteristics of Clavin type element is analyzed on the assumption of simultaneous account for relative level of sidelobes in the E-plane and beamwidth differences at -3 dB level in the main planes. It is shown that the directional characteristics and energy characteristics of the radiators: radiation and reflection coefficients, antenna directivity and gain can be varied within wide limits by changing the electrical length and/or distributed surface impedances of the vibrators, providing at that a low level of radiation within a slot plane. Conclusions: The results obtained can be useful when designing both small-size and multi-element antenna arrays with Clavin elements.
Inclusive breakup calculations in angular momentum basis: Application to 7Li+58Ni

NASA Astrophysics Data System (ADS)

Lei, Jin

2018-03-01

The angular momentum basis method is introduced to solve the inclusive breakup problem within the model proposed by Ichimura, Austern, and Vincent [Phys. Rev. C 32, 431 (1985), 10.1103/PhysRevC.32.431]. This method is based on the geometric transformation between different Jacobi coordinates, in which the particle spins can be included in a natural and efficient way. To test the validity of this partial wave expansion method, a benchmark calculation is done comparing with the one given by Lei and Moro [Phys. Rev. C 92, 044616 (2015), 10.1103/PhysRevC.92.044616]. In addition, using the distorted-wave Born approximation version of the IAV model, applications to 7Li+58Ni reactions at energies around Coulomb barrier are presented and compared with available data.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Scherrer, Arne; UMR 8640 ENS-CNRS-UPMC, Département de Chimie, 24 rue Lhomond, École Normale Supérieure, 75005 Paris; UPMC Université Paris 06, 4, Place Jussieu, 75005 Paris

The nuclear velocity perturbation theory (NVPT) for vibrational circular dichroism (VCD) is derived from the exact factorization of the electron-nuclear wave function. This new formalism offers an exact starting point to include correction terms to the Born-Oppenheimer (BO) form of the molecular wave function, similar to the complete-adiabatic approximation. The corrections depend on a small parameter that, in a classical treatment of the nuclei, is identified as the nuclear velocity. Apart from proposing a rigorous basis for the NVPT, we show that the rotational strengths, related to the intensity of the VCD signal, contain a new contribution beyond-BO that canmore » be evaluated with the NVPT and that only arises when the exact factorization approach is employed. Numerical results are presented for chiral and non-chiral systems to test the validity of the approach.« less
Experimental Study on Ultrasonic Computed Tomography Using Transducers Arrayed on the Internal Surface of a Cylinder

NASA Astrophysics Data System (ADS)

Kim, Jung-Soon; Kim, Moo-Joon; Kim, Jung-Ho; Ha, Kang-Lyeol

2005-06-01

In this study, ultrasonic array transducers with 32 vibrators arranged on the internal surface of a part of a cylinder were fabricated. The vibrators were operated by the piezoelectric transverse effect. By controlling the phase of the input signal for every vibrator, a quasi plane wave was synthesized. Using the fabricated array, inverse scattering ultrasonic computed tomography (UCT) was carried out with a phantom specimen after checking the plane wave generation. It was confirmed that the plane wave was synthesized successfully and a sound velocity image of the phantom was obtained by the plane wave. Consequently, it was noted that the array could be employed as a transmitter and receiver for data acquisition in UCT.
Amplitudes on plane waves from ambitwistor strings

NASA Astrophysics Data System (ADS)

Adamo, Tim; Casali, Eduardo; Mason, Lionel; Nekovar, Stefan

2017-11-01

In marked contrast to conventional string theory, ambitwistor strings remain solvable worldsheet theories when coupled to curved background fields. We use this fact to consider the quantization of ambitwistor strings on plane wave metric and plane wave gauge field backgrounds. In each case, the worldsheet model is anomaly free as a consequence of the background satisfying the field equations. We derive vertex operators (in both fixed and descended picture numbers) for gravitons and gluons on these backgrounds from the worldsheet CFT, and study the 3-point functions of these vertex operators on the Riemann sphere. These worldsheet correlation functions reproduce the known results for 3-point scattering amplitudes of gravitons and gluons in gravitational and gauge theoretic plane wave backgrounds, respectively.
Making waves round a structured cloak: lattices, negative refraction and fringes

PubMed Central

Colquitt, D. J.; Jones, I. S.; Movchan, N. V.; Movchan, A. B.; Brun, M.; McPhedran, R. C.

2013-01-01

Using the framework of transformation optics, this paper presents a detailed analysis of a non-singular square cloak for acoustic, out-of-plane shear elastic and electromagnetic waves. Analysis of wave propagation through the cloak is presented and accompanied by numerical illustrations. The efficacy of the regularized cloak is demonstrated and an objective numerical measure of the quality of the cloaking effect is provided. It is demonstrated that the cloaking effect persists over a wide range of frequencies. As a demonstration of the effectiveness of the regularized cloak, a Young's double slit experiment is presented. The stability of the interference pattern is examined when a cloaked and uncloaked obstacle are successively placed in front of one of the apertures. This novel link with a well-known quantum mechanical experiment provides an additional method through which the quality of cloaks may be examined. In the second half of the paper, it is shown that an approximate cloak may be constructed using a discrete lattice structure. The efficiency of the approximate lattice cloak is analysed and a series of illustrative simulations presented. It is demonstrated that effective cloaking may be obtained by using a relatively simple lattice structure, particularly, in the low-frequency regime. PMID:24062625
A frozen Gaussian approximation-based multi-level particle swarm optimization for seismic inversion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Jinglai, E-mail: jinglaili@sjtu.edu.cn; Lin, Guang, E-mail: lin491@purdue.edu; Computational Sciences and Mathematics Division, Pacific Northwest National Laboratory, Richland, WA 99352

2015-09-01

In this paper, we propose a frozen Gaussian approximation (FGA)-based multi-level particle swarm optimization (MLPSO) method for seismic inversion of high-frequency wave data. The method addresses two challenges in it: First, the optimization problem is highly non-convex, which makes hard for gradient-based methods to reach global minima. This is tackled by MLPSO which can escape from undesired local minima. Second, the character of high-frequency of seismic waves requires a large number of grid points in direct computational methods, and thus renders an extremely high computational demand on the simulation of each sample in MLPSO. We overcome this difficulty by threemore » steps: First, we use FGA to compute high-frequency wave propagation based on asymptotic analysis on phase plane; Then we design a constrained full waveform inversion problem to prevent the optimization search getting into regions of velocity where FGA is not accurate; Last, we solve the constrained optimization problem by MLPSO that employs FGA solvers with different fidelity. The performance of the proposed method is demonstrated by a two-dimensional full-waveform inversion example of the smoothed Marmousi model.« less
Fourier optics of constant-thickness three-dimensional objects on the basis of diffraction models

NASA Astrophysics Data System (ADS)

Chugui, Yu. V.

2017-09-01

Results of investigations of diffraction phenomena on constant-thickness three-dimensional objects with flat inner surfaces (thick plates) are summarized on the basis of our constructive theory of their calculation as applied to dimensional inspection. It is based on diffraction models of 3D objects with the use of equivalent diaphragms (distributions), which allow the Kirchhoff-Fresnel approximation to be effectively used. In contrast to available rigorous and approximate methods, the present approach does not require cumbersome calculations; it is a clearly arranged method, which ensures sufficient accuracy for engineering applications. It is found that the fundamental diffraction parameter for 3D objects of constant thickness d is the critical diffraction angle {θ _{cr}} = √ {λ /d} at which the effect of three-dimensionality on the spectrum of the 3D object becomes appreciable. Calculated Fraunhofer diffraction patterns (spectra) and images of constant-thickness 3D objects with absolutely absorbing, absolutely reflecting, and gray internal faces are presented. It is demonstrated that selection of 3D object fragments can be performed by choosing an appropriate configuration of the wave illuminating the object (plane normal or inclined waves, spherical waves).
On gravitational waves in Born-Infeld inspired non-singular cosmologies

NASA Astrophysics Data System (ADS)

Beltrán Jiménez, Jose; Heisenberg, Lavinia; Olmo, Gonzalo J.; Rubiera-Garcia, Diego

2017-10-01

We study the evolution of gravitational waves for non-singular cosmological solutions within the framework of Born-Infeld inspired gravity theories, with special emphasis on the Eddington-inspired Born-Infeld theory. We review the existence of two types of non-singular cosmologies, namely bouncing and asymptotically Minkowski solutions, from a perspective that makes their features more apparent. We study in detail the propagation of gravitational waves near these non-singular solutions and carefully discuss the origin and severity of the instabilities and strong coupling problems that appear. We also investigate the role of the adiabatic sound speed of the matter sector in the regularisation of the gravitational waves evolution. We extend our analysis to more general Born-Infeld inspired theories where analogous solutions are found. As a general conclusion, we obtain that the bouncing solutions are generally more prone to instabilities, while the asymptotically Minkowski solutions can be rendered stable, making them appealing models for the early universe.
On gravitational waves in Born-Infeld inspired non-singular cosmologies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiménez, Jose Beltrán; Heisenberg, Lavinia; Olmo, Gonzalo J.

We study the evolution of gravitational waves for non-singular cosmological solutions within the framework of Born-Infeld inspired gravity theories, with special emphasis on the Eddington-inspired Born-Infeld theory. We review the existence of two types of non-singular cosmologies, namely bouncing and asymptotically Minkowski solutions, from a perspective that makes their features more apparent. We study in detail the propagation of gravitational waves near these non-singular solutions and carefully discuss the origin and severity of the instabilities and strong coupling problems that appear. We also investigate the role of the adiabatic sound speed of the matter sector in the regularisation of themore » gravitational waves evolution. We extend our analysis to more general Born-Infeld inspired theories where analogous solutions are found. As a general conclusion, we obtain that the bouncing solutions are generally more prone to instabilities, while the asymptotically Minkowski solutions can be rendered stable, making them appealing models for the early universe.« less
Plasmon dispersion in strongly correlated superlattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, D.; Golden, K.I.; Kalman, G.

The dielectric response function of a strongly correlated superlattice is calculated in the quasilocalized charge (QLC) approximation. The resulting QLC static local-field correction, which contains both intralayer and interlayer pair-correlational effects, is identical to the correlational part of the third-frequency-moment sum-rule coefficient. This approximation treats the interlayer and intralayer couplings on an equal footing. The resulting dispersion relation is first analyzed to determine the effect of intralayer coupling on the out-of-phase acoustic-mode dispersion; in this approximation the interlayer coupling is suppressed and the mutual interaction of the layers is taken into account only through the average random-phase approximation (RPA) field.more » In the resulting mode dispersion, the onset of a finite-{ital k} ({ital k} being the in-plane wave number) reentrant low-frequency excitation developing (with decreasing {ital d}/{ital a}) into a dynamical instability is indicated ({ital a} being the in-plane Wigner-Seitz radius and {ital d} the distance between adjacent lattice planes). This dynamical instability parallels a static structural instability reported earlier both for a bilayer electron system and a superlattice and presumably indicates a structural change in the electron liquid. If one takes account of interlayer correlations beyond the RPA, the acoustic excitation spectrum is dramatically modified by the appearance of an energy gap which also has a stabilizing effect on the instability. We extend a previous energy gap study at {ital k}=0 [G. Kalman, Y. Ren, and K. I. Golden, Phys Rev. B {bold 50}, 2031 (1994)] to a calculation of the dispersion of the gapped acoustic excitation spectrum in the long-wavelength domain. {copyright} {ital 1996 The American Physical Society.}« less
Electric transition dipole moment in pre-Born-Oppenheimer molecular structure theory.

PubMed

Simmen, Benjamin; Mátyus, Edit; Reiher, Markus

2014-10-21

This paper presents the calculation of the electric transition dipole moment in a pre-Born-Oppenheimer framework. Electrons and nuclei are treated equally in terms of the parametrization of the non-relativistic total wave function, which is written as a linear combination of basis functions constructed from explicitly correlated Gaussian functions and the global vector representation. The integrals of the electric transition dipole moment are derived corresponding to these basis functions in both the length and the velocity representation. The calculations are performed in laboratory-fixed Cartesian coordinates without relying on coordinates which separate the center of mass from the translationally invariant degrees of freedom. The effect of the overall motion is eliminated through translationally invariant integral expressions. The electric transition dipole moment is calculated between two rovibronic levels of the H2 molecule assignable to the lowest rovibrational states of the X (1)Σ(g)(+) and B (1)Σ(u)(+) electronic states in the clamped-nuclei framework. This is the first evaluation of this quantity in a full quantum mechanical treatment without relying on the Born-Oppenheimer approximation.
Generation of remote adaptive torsional shear waves with an octagonal phased array to enhance displacements and reduce variability of shear wave speeds: comparison with quasi-plane shear wavefronts.

PubMed

Ouared, Abderrahmane; Montagnon, Emmanuel; Cloutier, Guy

2015-10-21

A method based on adaptive torsional shear waves (ATSW) is proposed to overcome the strong attenuation of shear waves generated by a radiation force in dynamic elastography. During the inward propagation of ATSW, the magnitude of displacements is enhanced due to the convergence of shear waves and constructive interferences. The proposed method consists in generating ATSW fields from the combination of quasi-plane shear wavefronts by considering a linear superposition of displacement maps. Adaptive torsional shear waves were experimentally generated in homogeneous and heterogeneous tissue mimicking phantoms, and compared to quasi-plane shear wave propagations. Results demonstrated that displacement magnitudes by ATSW could be up to 3 times higher than those obtained with quasi-plane shear waves, that the variability of shear wave speeds was reduced, and that the signal-to-noise ratio of displacements was improved. It was also observed that ATSW could cause mechanical inclusions to resonate in heterogeneous phantoms, which further increased the displacement contrast between the inclusion and the surrounding medium. This method opens a way for the development of new noninvasive tissue characterization strategies based on ATSW in the framework of our previously reported shear wave induced resonance elastography (SWIRE) method proposed for breast cancer diagnosis.
Ultrafast Ultrasound Imaging of Ocular Anatomy and Blood Flow

PubMed Central

Urs, Raksha; Ketterling, Jeffrey A.; Silverman, Ronald H.

2016-01-01

Purpose Ophthalmic ultrasound imaging is currently performed with mechanically scanned single-element probes. These probes have limited capabilities overall and lack the ability to image blood flow. Linear-array systems are able to detect blood flow, but these systems exceed ophthalmic acoustic intensity safety guidelines. Our aim was to implement and evaluate a new linear-array–based technology, compound coherent plane-wave ultrasound, which offers ultrafast imaging and depiction of blood flow at safe acoustic intensity levels. Methods We compared acoustic intensity generated by a 128-element, 18-MHz linear array operated in conventionally focused and plane-wave modes and characterized signal-to-noise ratio (SNR) and lateral resolution. We developed plane-wave B-mode, real-time color-flow, and high-resolution depiction of slow flow in postprocessed data collected continuously at a rate of 20,000 frames/s. We acquired in vivo images of the posterior pole of the eye by compounding plane-wave images acquired over ±10° and produced images depicting orbital and choroidal blood flow. Results With the array operated conventionally, Doppler modes exceeded Food and Drug Administration safety guidelines, but plane-wave modalities were well within guidelines. Plane-wave data allowed generation of high-quality compound B-mode images, with SNR increasing with the number of compounded frames. Real-time color-flow Doppler readily visualized orbital blood flow. Postprocessing of continuously acquired data blocks of 1.6-second duration allowed high-resolution depiction of orbital and choroidal flow over the cardiac cycle. Conclusions Newly developed high-frequency linear arrays in combination with plane-wave techniques present opportunities for the evaluation of ocular anatomy and blood flow, as well as visualization and analysis of other transient phenomena such as vessel wall motion over the cardiac cycle and saccade-induced vitreous motion. PMID:27428169
Application of the wavenumber jump condition to the normal and oblique interaction of a plane acoustic wave and a plane shock

NASA Technical Reports Server (NTRS)

Kleinstein, G. G.; Gunzburger, M. D.

1977-01-01

The kinematics of normal and oblique interactions between a plane acoustic wave and a plane shock wave are investigated separately using an approach whereby the shock is considered as a sharp discontinuity surface separating two half-spaces, so that the dispersion relation on either side of the shock and the wavenumber jump condition across a discontinuity surface completely specify the kinematics of the problem in the whole space independently of the acoustic-field dynamics. The normal interaction is analyzed for a stationary shock, and the spectral change of the incident wave is investigated. The normal interaction is then examined for the case of a shock wave traveling into an ambient region where an acoustic disturbance is propagating in the opposite direction. Detailed attention is given to the consequences of the existence of a critical shock speed above which the frequency of the transmitted wave becomes negative. Finally, the oblique interaction with a fixed shock is considered, and the existence and nature of the transmitted wave is investigated, particularly as a function of the angle of incidence.

Damage detection in composite panels based on mode-converted Lamb waves sensed using 3D laser scanning vibrometer

NASA Astrophysics Data System (ADS)

Pieczonka, Łukasz; Ambroziński, Łukasz; Staszewski, Wiesław J.; Barnoncel, David; Pérès, Patrick

2017-12-01

This paper introduces damage identification approach based on guided ultrasonic waves and 3D laser Doppler vibrometry. The method is based on the fact that the symmetric and antisymmetric Lamb wave modes differ in amplitude of the in-plane and out-of-plane vibrations. Moreover, the modes differ also in group velocities and normally they are well separated in time. For a given time window both modes can occur simultaneously only close to the wave source or to a defect that leads to mode conversion. By making the comparison between the in-plane and out-of-plane wave vector components the detection of mode conversion is possible, allowing for superior and reliable damage detection. Experimental verification of the proposed damage identification procedure is performed on fuel tank elements of Reusable Launch Vehicles designed for space exploration. Lamb waves are excited using low-profile, surface-bonded piezoceramic transducers and 3D scanning laser Doppler vibrometer is used to characterize the Lamb wave propagation field. The paper presents theoretical background of the proposed damage identification technique as well as experimental arrangements and results.
Analysis of the Localization of Michelson Interferometer Fringes Using Fourier Optics and Temporal Coherence

ERIC Educational Resources Information Center

Narayanamurthy, C. S.

2009-01-01

Fringes formed in a Michelson interferometer never localize in any plane, in the detector plane and in the localization plane. Instead, the fringes are assumed to localize at infinity. Except for some explanation in "Principles of Optics" by Born and Wolf (1964 (New York: Macmillan)), the fringe localization phenomena of Michelson's interferometer…
On the theory of the relativistic motion of a charged particle in the field of intense electromagnetic radiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Milant'ev, V. P., E-mail: vmilantiev@sci.pfu.edu.ru; Castillo, A. J., E-mail: vmilant@mail.ru

2013-04-15

Averaged relativistic equations of motion of a charged particle in the field of intense electromagnetic radiation have been obtained in the geometrical optics approximation using the Bogoliubov method. Constraints are determined under which these equations are valid. Oscillating additions to the smoothed dynamical variables of the particle have been found; they are reduced to known expressions in the case of the circularly and linearly polarized plane waves. It has been shown that the expressions for the averaged relativistic force in both cases contain new additional small terms weakening its action. The known difference between the expressions for the ponderomotive forcemore » in the cases of circularly and linearly polarized waves has been confirmed.« less
Radar cross section fundamentals for the aircraft designer

NASA Technical Reports Server (NTRS)

Stadmore, H. A.

1979-01-01

Various aspects of radar cross-section (RCS) techniques are summarized, with emphasis placed on fundamental electromagnetic phenomena, such as plane and spherical wave formulations, and the definition of RCS is given in the far-field sense. The basic relationship between electronic countermeasures and a signature level is discussed in terms of the detectability range of a target vehicle. Fundamental radar-signature analysis techniques, such as the physical-optics and geometrical-optics approximations, are presented along with examples in terms of aircraft components. Methods of analysis based on the geometrical theory of diffraction are considered and various wave-propagation phenomena are related to local vehicle geometry. Typical vehicle components are also discussed, together with their contribution to total vehicle RCS and their individual signature sensitivities.
Plane waves and structures in turbulent channel flow

NASA Technical Reports Server (NTRS)

Sirovich, L.; Ball, K. S.; Keefe, L. R.

1990-01-01

A direct simulation of turbulent flow in a channel is analyzed by the method of empirical eigenfunctions (Karhunen-Loeve procedure, proper orthogonal decomposition). This analysis reveals the presence of propagating plane waves in the turbulent flow. The velocity of propagation is determined by the flow velocity at the location of maximal Reynolds stress. The analysis further suggests that the interaction of these waves appears to be essential to the local production of turbulence via bursting or sweeping events in the turbulent boundary layer, with the additional suggestion that the fast acting plane waves act as triggers.
A projection-free method for representing plane-wave DFT results in an atom-centered basis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dunnington, Benjamin D.; Schmidt, J. R., E-mail: schmidt@chem.wisc.edu

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 strictmore » 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.« less
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)
Reduced-rank approximations to the far-field transform in the gridded fast multipole method

NASA Astrophysics Data System (ADS)

Hesford, Andrew J.; Waag, Robert C.

2011-05-01

The fast multipole method (FMM) has been shown to have a reduced computational dependence on the size of finest-level groups of elements when the elements are positioned on a regular grid and FFT convolution is used to represent neighboring interactions. However, transformations between plane-wave expansions used for FMM interactions and pressure distributions used for neighboring interactions remain significant contributors to the cost of FMM computations when finest-level groups are large. The transformation operators, which are forward and inverse Fourier transforms with the wave space confined to the unit sphere, are smooth and well approximated using reduced-rank decompositions that further reduce the computational dependence of the FMM on finest-level group size. The adaptive cross approximation (ACA) is selected to represent the forward and adjoint far-field transformation operators required by the FMM. However, the actual error of the ACA is found to be greater than that predicted using traditional estimates, and the ACA generally performs worse than the approximation resulting from a truncated singular-value decomposition (SVD). To overcome these issues while avoiding the cost of a full-scale SVD, the ACA is employed with more stringent accuracy demands and recompressed using a reduced, truncated SVD. The results show a greatly reduced approximation error that performs comparably to the full-scale truncated SVD without degrading the asymptotic computational efficiency associated with ACA matrix assembly.
Reduced-Rank Approximations to the Far-Field Transform in the Gridded Fast Multipole Method.

PubMed

Hesford, Andrew J; Waag, Robert C

2011-05-10

The fast multipole method (FMM) has been shown to have a reduced computational dependence on the size of finest-level groups of elements when the elements are positioned on a regular grid and FFT convolution is used to represent neighboring interactions. However, transformations between plane-wave expansions used for FMM interactions and pressure distributions used for neighboring interactions remain significant contributors to the cost of FMM computations when finest-level groups are large. The transformation operators, which are forward and inverse Fourier transforms with the wave space confined to the unit sphere, are smooth and well approximated using reduced-rank decompositions that further reduce the computational dependence of the FMM on finest-level group size. The adaptive cross approximation (ACA) is selected to represent the forward and adjoint far-field transformation operators required by the FMM. However, the actual error of the ACA is found to be greater than that predicted using traditional estimates, and the ACA generally performs worse than the approximation resulting from a truncated singular-value decomposition (SVD). To overcome these issues while avoiding the cost of a full-scale SVD, the ACA is employed with more stringent accuracy demands and recompressed using a reduced, truncated SVD. The results show a greatly reduced approximation error that performs comparably to the full-scale truncated SVD without degrading the asymptotic computational efficiency associated with ACA matrix assembly.
Reduced-Rank Approximations to the Far-Field Transform in the Gridded Fast Multipole Method

PubMed Central

Hesford, Andrew J.; Waag, Robert C.

2011-01-01

The fast multipole method (FMM) has been shown to have a reduced computational dependence on the size of finest-level groups of elements when the elements are positioned on a regular grid and FFT convolution is used to represent neighboring interactions. However, transformations between plane-wave expansions used for FMM interactions and pressure distributions used for neighboring interactions remain significant contributors to the cost of FMM computations when finest-level groups are large. The transformation operators, which are forward and inverse Fourier transforms with the wave space confined to the unit sphere, are smooth and well approximated using reduced-rank decompositions that further reduce the computational dependence of the FMM on finest-level group size. The adaptive cross approximation (ACA) is selected to represent the forward and adjoint far-field transformation operators required by the FMM. However, the actual error of the ACA is found to be greater than that predicted using traditional estimates, and the ACA generally performs worse than the approximation resulting from a truncated singular-value decomposition (SVD). To overcome these issues while avoiding the cost of a full-scale SVD, the ACA is employed with more stringent accuracy demands and recompressed using a reduced, truncated SVD. The results show a greatly reduced approximation error that performs comparably to the full-scale truncated SVD without degrading the asymptotic computational efficiency associated with ACA matrix assembly. PMID:21552350
Instabilities in dynamic anti-plane sliding of an elastic layer on a dissimilar elastic half-space

NASA Astrophysics Data System (ADS)

Kunnath, R.

2012-12-01

The stability of dynamic anti-plane sliding at an interface between an elastic layer and an elastic half-space with dissimilar elastic properties is studied. Friction at the interface is assumed to follow a rate- and state-dependent law, with a positive instantaneous dependence on slip velocity and a rate weakening behavior in the steady state. The perturbations are of the form exp(ikx+pt), where k is the wavenumber, x is the coordinate along the interface, p is the time response to the perturbation and t is time. The results of the stability analysis are shown in Figs. 1 and 2 with the velocity weakening parameter b/a=5, shear wave speed ratio cs'/cs=1.2, shear modulus ratio μ'/μ=1.2 and non-dimensional layer thickness H=100. The normalized instability growth rate and normalized phase velocity are plotted as a function of wavenumber. Fig.1 is for a non-dimensional unperturbed slip velocity ɛ=5 (rapid sliding) while Fig. 2 is for ɛ=0.05 (slow sliding). The results show the destabilization of interfacial waves. For slow sliding, destabilization of interfacial waves is still seen, indicating that the quasi-static approximation to slow sliding is not valid. This is in agreement with the result of Ranjith (Int. J. Solids and Struct., 2009, 46, 3086-3092) who predicted an instability of long-wavelength Love waves in slow sliding.
Control of Love waves by resonant metasurfaces.

PubMed

Palermo, Antonio; Marzani, Alessandro

2018-05-08

Metasurfaces of mechanical resonators have been successfully used to control in-plane polarized surface waves for filtering, waveguiding and lensing applications across different length scales. In this work, we extend the concept of metasurfaces to anti-plane surface waves existing in semi-infinite layered media, generally known as Love waves. By means of an effective medium approach, we derive an original closed-form dispersion relation for the metasurface. This relation reveals the possibility to control the Love waves dispersive properties by varying the resonators mechanical parameters. We exploit this capability to manipulate the metasurface refractive index and design two gradient index (GRIN) metalenses, i.e. a Luneburg lens and a Maxwell lens. We confirm the performance of the designed lenses using full 3D finite element simulations. Our work demonstrates the possibility of realizing wave control devices for anti-plane waves.
Gravitational Radiation of a Vibrating Physical String as a Model for the Gravitational Emission of an Astrophysical Plasma

NASA Astrophysics Data System (ADS)

Lewis, Ray A.; Modanese, Giovanni

Vibrating media offer an important testing ground for reconciling conflicts between General Relativity, Quantum Mechanics and other branches of physics. For sources like a Weber bar, the standard covariant formalism for elastic bodies can be applied. The vibrating string, however, is a source of gravitational waves which requires novel computational techniques, based on the explicit construction of a conserved and renormalized energy-momentum tensor. Renormalization (in a classical sense) is necessary to take into account the effect of external constraints, which affect the emission considerably. Our computation also relaxes usual simplifying assumptions like far-field approximation, spherical or plane wave symmetry, TT gauge and absence of internal interference. In a further step towards unification, the method is then adapted to give the radiation field of a transversal Alfven wave in a rarefied astrophysical plasma, where the tension is produced by an external static magnetic field.
Coherent scattering of a spherical wave from an irregular surface. [antenna pattern effects

NASA Technical Reports Server (NTRS)

Fung, A. K.

1983-01-01

The scattering of a spherical wave from a rough surface using the Kirchhoff approximation is considered. An expression representing the measured coherent scattering coefficient is derived. It is shown that the sphericity of the wavefront and the antenna pattern can become an important factor in the interpretation of ground-based measurements. The condition under which the coherent scattering-coefficient expression reduces to that corresponding to a plane wave incidence is given. The condition under which the result reduces to the standard image solution is also derived. In general, the consideration of antenna pattern and sphericity is unimportant unless the surface-height standard deviation is small, i.e., unless the coherent scattering component is significant. An application of the derived coherent backscattering coefficient together with the existing incoherent scattering coefficient to interpret measurements from concrete and asphalt surfaces is shown.
Wave-induced fluid flow in random porous media: Attenuation and dispersion of elastic waves

NASA Astrophysics Data System (ADS)

Müller, Tobias M.; Gurevich, Boris

2005-05-01

A detailed analysis of the relationship between elastic waves in inhomogeneous, porous media and the effect of wave-induced fluid flow is presented. Based on the results of the poroelastic first-order statistical smoothing approximation applied to Biot's equations of poroelasticity, a model for elastic wave attenuation and dispersion due to wave-induced fluid flow in 3-D randomly inhomogeneous poroelastic media is developed. Attenuation and dispersion depend on linear combinations of the spatial correlations of the fluctuating poroelastic parameters. The observed frequency dependence is typical for a relaxation phenomenon. Further, the analytic properties of attenuation and dispersion are analyzed. It is shown that the low-frequency asymptote of the attenuation coefficient of a plane compressional wave is proportional to the square of frequency. At high frequencies the attenuation coefficient becomes proportional to the square root of frequency. A comparison with the 1-D theory shows that attenuation is of the same order but slightly larger in 3-D random media. Several modeling choices of the approach including the effect of cross correlations between fluid and solid phase properties are demonstrated. The potential application of the results to real porous materials is discussed. .
Plane wave gravitons, curvature singularities and string physics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brooks, R.

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.
Non-Markovian quantum Brownian motion in one dimension in electric fields

NASA Astrophysics Data System (ADS)

Shen, H. Z.; Su, S. L.; Zhou, Y. H.; Yi, X. X.

2018-04-01

Quantum Brownian motion is the random motion of quantum particles suspended in a field (or an effective field) resulting from their collision with fast-moving modes in the field. It provides us with a fundamental model to understand various physical features concerning open systems in chemistry, condensed-matter physics, biophysics, and optomechanics. In this paper, without either the Born-Markovian or rotating-wave approximation, we derive a master equation for a charged-Brownian particle in one dimension coupled with a thermal reservoir in electric fields. The effect of the reservoir and the electric fields is manifested as time-dependent coefficients and coherent terms, respectively, in the master equation. The two-photon correlation between the Brownian particle and the reservoir can induce nontrivial squeezing dynamics to the particle. We derive a current equation including the source from the driving fields, transient current from the system flowing into the environment, and the two-photon current caused by the non-rotating-wave term. The presented results then are compared with that given by the rotating-wave approximation in the weak-coupling limit, and these results are extended to a more general quantum network involving an arbitrary number of coupled-Brownian particles. The presented formalism might open a way to better understand exactly the non-Markovian quantum network.
Methods in the study of discrete upper hybrid waves

NASA Astrophysics Data System (ADS)

Yoon, P. H.; Ye, S.; Labelle, J.; Weatherwax, A. T.; Menietti, J. D.

2007-11-01

Naturally occurring plasma waves characterized by fine frequency structure or discrete spectrum, detected by satellite, rocket-borne instruments, or ground-based receivers, can be interpreted as eigenmodes excited and trapped in field-aligned density structures. This paper overviews various theoretical methods to study such phenomena for a one-dimensional (1-D) density structure. Among the various methods are parabolic approximation, eikonal matching, eigenfunction matching, and full numerical solution based upon shooting method. Various approaches are compared against the full numerical solution. Among the analytic methods it is found that the eigenfunction matching technique best approximates the actual numerical solution. The analysis is further extended to 2-D geometry. A detailed comparative analysis between the eigenfunction matching and fully numerical methods is carried out for the 2-D case. Although in general the two methods compare favorably, significant differences are also found such that for application to actual observations it is prudent to employ the fully numerical method. Application of the methods developed in the present paper to actual geophysical problems will be given in a companion paper.
Collimation and Asymmetry of the Hot Blast Wave from the Recurrent Nova V745 Sco

NASA Astrophysics Data System (ADS)

Drake, Jeremy J.; Delgado, Laura; Laming, J. Martin; Starrfield, Sumner; Kashyap, Vinay; Orlando, Salvatore; Page, Kim L.; Hernanz, M.; Ness, J.-U.; Gehrz, R. D.; van Rossum, Daan; Woodward, Charles E.

2016-07-01

The recurrent symbiotic nova V745 Sco exploded on 2014 February 6 and was observed on February 22 and 23 by the Chandra X-ray Observatory Transmission Grating Spectrometers. By that time the supersoft source phase had already ended, and Chandra spectra are consistent with emission from a hot, shock-heated circumstellar medium with temperatures exceeding 107 K. X-ray line profiles are more sharply peaked than expected for a spherically symmetric blast wave, with a full width at zero intensity of approximately 2400 km s-1, an FWHM of 1200 ± 30 km s-1, and an average net blueshift of 165 ± 10 km s-1. The red wings of lines are increasingly absorbed toward longer wavelengths by material within the remnant. We conclude that the blast wave was sculpted by an aspherical circumstellar medium in which an equatorial density enhancement plays a role, as in earlier symbiotic nova explosions. Expansion of the dominant X-ray-emitting material is aligned close to the plane of the sky and is most consistent with an orbit seen close to face-on. Comparison of an analytical blast wave model with the X-ray spectra, Swift observations, and near-infrared line widths indicates that the explosion energy was approximately 1043 erg and confirms an ejected mass of approximately 10-7 M ⊙. The total mass lost is an order of magnitude lower than the accreted mass required to have initiated the explosion, indicating that the white dwarf is gaining mass and is a Type Ia supernova progenitor candidate.
Density functional theory calculations of III-N based semiconductors with mBJLDA

NASA Astrophysics Data System (ADS)

Gürel, Hikmet Hakan; Akıncı, Özden; Ünlü, Hilmi

2017-02-01

In this work, we present first principles calculations based on a full potential linear augmented plane-wave method (FP-LAPW) to calculate structural and electronic properties of III-V based nitrides such as GaN, AlN, InN in a zinc-blende cubic structure. First principles calculation using the local density approximation (LDA) and generalized gradient approximation (GGA) underestimate the band gap. We proposed a new potential called modified Becke-Johnson local density approximation (MBJLDA) that combines modified Becke-Johnson exchange potential and the LDA correlation potential to get better band gap results compared to experiment. We compared various exchange-correlation potentials (LSDA, GGA, HSE, and MBJLDA) to determine band gaps and structural properties of semiconductors. We show that using MBJLDA density potential gives a better agreement with experimental data for band gaps III-V nitrides based semiconductors.

Propagation of magnetostatic spin waves in an yttrium iron garnet film for out-of-plane magnetic fields

NASA Astrophysics Data System (ADS)

Bang, Wonbae; Lim, Jinho; Trossman, Jonathan; Tsai, C. C.; Ketterson, John B.

2018-06-01

We have observed the propagation of spin waves across a thin yttrium iron garnet film on (1 1 1) gadolinium gallium garnet for magnetic fields inclined with respect to the film plane. Two principle planes were studied: that for H in the plane defined by the wave vector k and the plane normal, n, with limiting forms corresponding to the Backward Volume and Forward Volume modes, and that for H in the plane perpendicular to k, with limiting forms corresponding to the Damon-Eshbach and Forward Volume modes. By exciting the wave at one edge of the film and observing the field dependence of the phase of the received signal at the opposing edge we determined the frequency vs. wavevector relation, ω = ω (k), of various propagating modes in the film. Avoided crossings are observed in the Damon-Eshbach and Forward Volume regimes when the propagating mode intersects the higher, exchange split, volume modes, leading to an extinction of the propagating mode; analysis of the resulting behavior allows a determination of the exchange parameter. The experimental results are compared with theoretical simulations.
Starburst-Driven Winds May Have Created Giant "Lobe" in Galactic Center

NASA Astrophysics Data System (ADS)

2004-06-01

An astronomer using the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT) has discovered that two prominent features rising out of the center of the Milky Way Galaxy are actually the distant edges of the same superstructure. This object, which has the appearance of a "lobe," may have been formed during an epoch of furious star formation. Lobe Galactic center radio image with lobe feature shown in outline. CREDIT: NRAO/AUI/NSF Yusef-Zadeh, et.al. (Click for Image w/o lines) Astronomer Casey Law of Northwestern University presented his results at the Denver, Colorado, meeting of the American Astronomical Society. "The center of our Galaxy is an incredibly dynamic place and morphologically very difficult to untangle" said Law. "Among the many features we see there, including supernova remnants, hot star-forming regions, and massive molecular clouds, are two very prominent columns of radio-emitting material that seem to erupt out of the plane of the Galaxy. The nature and origin of these features have been the subjects of much speculation, but with the new data from the Green Bank Telescope we're finally able to discern that they are in fact part of the same superstructure." Much of what we know about the center of our Galaxy has come from studies conducted on radio telescopes. The center of the Milky Way is, in fact, hidden from view to optical telescopes due to intervening clouds of dust and gas. Radio waves, however, are able to pass through the obscuring material and reveal details about the core of our Galaxy. Astronomers now know that this area of the Milky Way -- approximately 26,000 light-years from Earth -- is a densely packed region brimming with hot , young stars, supernova remnants, and more esoteric features -- like long radio-emitting filaments. At the center of it all is a remarkably radio-bright region known as Sagittarius A* (pronounced A-star), which is known to contain a supermassive black hole. Deciphering what all these features are and how they are formed are particularly difficult tasks. To help better understand the nature and possible connection of the columns in this study, Law studied data taken by a team of astronomers who used the GBT to create what is being called "the best single-dish survey of the Galactic center." The team made several maps of the Galactic center at multiple wavelengths, from as short as 3.6 centimeters to as long as 90 centimeters. By comparing an object at multiple radio frequencies (known as the spectral index), astronomers can produce a more complete picture of that object and also determine how the radio waves were produced. Hot bodies, such as stellar nurseries and even our Sun, generate radio waves across the radio spectrum. This is known as thermal emission, and it is characterized by stronger emission at shorter wavelengths. Other radio waves are generated by the acceleration of electrons within a magnetic field, which is the same process that causes quasars and pulsars to emit radio waves. This is known as non-thermal emission and it is characterized by stronger emission at longer wavelengths. "By looking at the features in the Galactic center at multiple frequencies," said Farhad Yusef-Zadeh of Northwestern University and a member of the observation team, "we can not only distinguish between thermal and non-thermal processes, but we can also compare and contrast different features to see if they are related." In looking at the lobe, which rises approximately 450 light-years above the Galactic center, Law determined that the spectral index of both sides of the lobe matched almost identically. "Early radio surveys of the galactic center suggested that the two columns eventually connected above the plane of the Galaxy," said Law. "But the clear correlation we now see between these two distant features strongly suggests that they are part of the same structure and produced by the same process." One of the leading explanations of how these features were produced is by a wind of energetic particles driven by an epoch of starburst near the Galactic center. Law speculates that approximately 10 million years ago, there was a furious period of star formation, with many stars being born and quickly dying in a series of supernovae. "At that time, something caused an acceleration of star formation near the very center of our Galaxy that thrust this material out of the plane of the Galaxy. The hot, young stars would have generated a lot of wind, and the supernovae would have contributed more energy," added Law. "This collective energy would have blown a lot of gas out of the disk for an extended period, eventually producing the features we see today." As the hot gas and particles shot out of the plane they would have "shocked" or energized the gas in the interstellar medium, which would have concentrated and amplified the ambient magnetic fields. The magnetic fields would then have accelerated electrons in the interstellar medium, producing the non-thermal radio profiles of the lobe. Earlier work done by other researchers estimates that this feature could contain approximately 5,000,000 solar masses of material, and that -- in the starburst model -- it would take the energy of possibly 10,000 supernovae to eject that amount of material out of the plane of the Galaxy and produce the feature seen in the lobe. In addition to Law and Yusef-Zadeh, the team that conducted the multiwavelength GBT survey included Douglas Roberts and Jack Hewitt of Northwestern University, and William Cotton and Ron Maddalena of the National Radio Astronomy Observatory. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. Additional image without outline is here.
Reprint of: Ionization probabilities of Ne, Ar, Kr, and Xe by proton impact for different initial states and impact energies

NASA Astrophysics Data System (ADS)

Montanari, C. C.; Miraglia, J. E.

2018-01-01

In this contribution we present ab initio results for ionization total cross sections, probabilities at zero impact parameter, and impact parameter moments of order +1 and -1 of Ne, Ar, Kr, and Xe by proton impact in an extended energy range from 100 keV up to 10 MeV. The calculations were performed by using the continuum distorted wave eikonal initial state approximation (CDW-EIS) for energies up to 1 MeV, and using the first Born approximation for larger energies. The convergence of the CDW-EIS to the first Born above 1 MeV is clear in the present results. Our inner-shell ionization cross sections are compared with the available experimental data and with the ECPSSR results. We also include in this contribution the values of the ionization probabilities at the origin, and the impact parameter dependence. These values have been employed in multiple ionization calculations showing very good description of the experimental data. Tables of the ionization probabilities are presented, disaggregated for the different initial bound states, considering all the shells for Ne and Ar, the M-N shells of Kr and the N-O shells of Xe.
Cavity Born-Oppenheimer Approximation for Correlated Electron-Nuclear-Photon Systems.

PubMed

Flick, Johannes; Appel, Heiko; Ruggenthaler, Michael; Rubio, Angel

2017-04-11

In this work, we illustrate the recently introduced concept of the cavity Born-Oppenheimer approximation [ Flick et al. PNAS 2017 , 10.1073/pnas.1615509114 ] for correlated electron-nuclear-photon problems in detail. We demonstrate how an expansion in terms of conditional electronic and photon-nuclear wave functions accurately describes eigenstates of strongly correlated light-matter systems. For a GaAs quantum ring model in resonance with a photon mode we highlight how the ground-state electronic potential-energy surface changes the usual harmonic potential of the free photon mode to a dressed mode with a double-well structure. This change is accompanied by a splitting of the electronic ground-state density. For a model where the photon mode is in resonance with a vibrational transition, we observe in the excited-state electronic potential-energy surface a splitting from a single minimum to a double minimum. Furthermore, for a time-dependent setup, we show how the dynamics in correlated light-matter systems can be understood in terms of population transfer between potential energy surfaces. This work at the interface of quantum chemistry and quantum optics paves the way for the full ab initio description of matter-photon systems.
The Relativistic Wave Vector

ERIC Educational Resources Information Center

Houlrik, Jens Madsen

2009-01-01

The Lorentz transformation applies directly to the kinematics of moving particles viewed as geometric points. Wave propagation, on the other hand, involves moving planes which are extended objects defined by simultaneity. By treating a plane wave as a geometric object moving at the phase velocity, novel results are obtained that illustrate the…
An anisotropic lens for transitioning plane waves between media of different permittivities

NASA Astrophysics Data System (ADS)

Stone, Alexander P.; Baum, Carl E.

1988-11-01

A particularly simple geometry is considered in which an inhomogeneous and anisotropic lens is specified for the transition of plane waves between media of different permittivities. The permittivities of the regions outside of the lens can be constant, but the permittivity of the lens region depends on position. Results are presented for a plane wave in the second medium propagating normally to the assumed plane boundary of that medium. The results for the case of normal incidence are then generalized to the case of nonnormal incidence. The conditions of transit time conservation and impedance matching are related to the Brewster angle.
Geometrical-optics approximation of forward scattering by gradient-index spheres.

PubMed

Li, Xiangzhen; Han, Xiang'e; Li, Renxian; Jiang, Huifen

2007-08-01

By means of geometrical optics we present an approximation method for acceleration of the computation of the scattering intensity distribution within a forward angular range (0-60 degrees ) for gradient-index spheres illuminated by a plane wave. The incident angle of reflected light is determined by the scattering angle, thus improving the approximation accuracy. The scattering angle and the optical path length are numerically integrated by a general-purpose integrator. With some special index models, the scattering angle and the optical path length can be expressed by a unique function and the calculation is faster. This method is proved effective for transparent particles with size parameters greater than 50. It fails to give good approximation results at scattering angles whose refractive rays are in the backward direction. For different index models, the geometrical-optics approximation is effective only for forward angles, typically those less than 60 degrees or when the refractive-index difference of a particle is less than a certain value.
Helicons in uniform fields. I. Wave diagnostics with hodograms

NASA Astrophysics Data System (ADS)

Urrutia, J. M.; Stenzel, R. L.

2018-03-01

The wave equation for whistler waves is well known and has been solved in Cartesian and cylindrical coordinates, yielding plane waves and cylindrical waves. In space plasmas, waves are usually assumed to be plane waves; in small laboratory plasmas, they are often assumed to be cylindrical "helicon" eigenmodes. Experimental observations fall in between both models. Real waves are usually bounded and may rotate like helicons. Such helicons are studied experimentally in a large laboratory plasma which is essentially a uniform, unbounded plasma. The waves are excited by loop antennas whose properties determine the field rotation and transverse dimensions. Both m = 0 and m = 1 helicon modes are produced and analyzed by measuring the wave magnetic field in three dimensional space and time. From Ampère's law and Ohm's law, the current density and electric field vectors are obtained. Hodograms for these vectors are produced. The sign ambiguity of the hodogram normal with respect to the direction of wave propagation is demonstrated. In general, electric and magnetic hodograms differ but both together yield the wave vector direction unambiguously. Vector fields of the hodogram normal yield the phase flow including phase rotation for helicons. Some helicons can have locally a linear polarization which is identified by the hodogram ellipticity. Alternatively the amplitude oscillation in time yields a measure for the wave polarization. It is shown that wave interference produces linear polarization. These observations emphasize that single point hodogram measurements are inadequate to determine the wave topology unless assuming plane waves. Observations of linear polarization indicate wave packets but not plane waves. A simple qualitative diagnostics for the wave polarization is the measurement of the magnetic field magnitude in time. Circular polarization has a constant amplitude; linear polarization results in amplitude modulations.
Geometrical optics in the near field: local plane-interface approach with evanescent waves.

PubMed

Bose, Gaurav; Hyvärinen, Heikki J; Tervo, Jani; Turunen, Jari

2015-01-12

We show that geometrical models may provide useful information on light propagation in wavelength-scale structures even if evanescent fields are present. We apply a so-called local plane-wave and local plane-interface methods to study a geometry that resembles a scanning near-field microscope. We show that fair agreement between the geometrical approach and rigorous electromagnetic theory can be achieved in the case where evanescent waves are required to predict any transmission through the structure.
Existence and Stability of Spatial Plane Waves for the Incompressible Navier-Stokes in R^3

NASA Astrophysics Data System (ADS)

Correia, Simão; Figueira, Mário

2018-03-01

We consider the three-dimensional incompressible Navier-Stokes equation on the whole space. We observe that this system admits a L^∞ family of global spatial plane wave solutions, which are connected with the two-dimensional equation. We then proceed to prove local well-posedness over a space which includes L^3(R^3) and these solutions. Finally, we prove L^3-stability of spatial plane waves, with no condition on their size.
Exciting surface plasmon polaritons in the Kretschmann configuration by a light beam

NASA Astrophysics Data System (ADS)

Vinogradov, A. P.; Dorofeenko, A. V.; Pukhov, A. A.; Lisyansky, A. A.

2018-06-01

We consider exciting surface plasmon polaritons in the Kretschmann configuration. Contrary to common belief, we show that a plane-wave incident at an angle greater than the angle of total internal reflection does not excite surface plasmon polaritons. These excitations do arise, however, if the incident light forms a narrow beam composed of an infinite number of plane waves. The surface plasmon polariton is formed at the geometrical edge of the beam as a result of interference of reflected plane waves.
Lee waves, benign and malignant

NASA Technical Reports Server (NTRS)

Wurtele, M. G.; Datta, A.

1992-01-01

The flow of an incompressible, stratified fluid over an obstacle will produce an oscillation in which buoyancy is the restoring force, called a gravity wave. For disturbances of this scale, the atmosphere may be treated as incompressible; and even the linear approximation will explain many of the phenomena observed in the lee of mountains. However, nonlinearities arise in two ways: (1) through the large (scaled) size of the mountain, and (2) from dynamically singular levels in the fluid field. These produce a complicated array of phenomena that present hazards to aircraft and to lee surface areas. If there is no dynamic barrier, these waves can penetrate vertically into the middle atmosphere (30-100 km attitude), where recent observations show them to be of a length scale that must involve the Coriolis force in any modeling. At these altitudes, the amplitude of the waves is very large, and the waves are studied with a view to their potential impact on the projected National Aerospace Plane. This paper presents the results of analyses and state-of-the-art numerical simulations, validated where possible by observational data.
Three-dimensional Fréchet sensitivity kernels for electromagnetic wave propagation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strickland, C. E.; Johnson, T. C.; Odom, R. I.

2015-08-28

Electromagnetic imaging methods are useful tools for monitoring subsurface changes in pore-fluid content and the associated changes in electrical permittivity and conductivity. The most common method for georadar tomography uses a high frequency ray-theoretic approximation that is valid when material variations are sufficiently small relative to the wavelength of the propagating wave. Georadar methods, however, often utilize electromagnetic waves that propagate within heterogeneous media at frequencies where ray theory may not be applicable. In this paper we describe the 3-D Fréchet sensitivity kernels for EM wave propagation. Various data functional types are formulated that consider all three components of themore » electric wavefield and incorporate near-, intermediate-, and far-field contributions. We show that EM waves exhibit substantial variations for different relative source-receiver component orientations. The 3-D sensitivities also illustrate out-of-plane effects that are not captured in 2-D sensitivity kernels and can influence results obtained using 2-D inversion methods to image structures that are in reality 3-D.« less
A physical model study of scattering of waves by aligned cracks: Comparison between experiment and theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ass'ad, J.M.; McDonald, J.A.; Kusky, T.M.

1993-04-01

An approximation to plane-wave propagation through a composite material is examined using a physical model with oriented but randomly distributed penny-shaped rubber inclusions within an isotropic epoxy resin matrix. A pulse transmission method is used to determine velocities of shear and compressional waves as a function of angle of incidence and crack density. The experimental and theoretical results of Hudson were compared and limitations within the crack parameters used in this study have been determined. Results from both polarized shear waves (S1, S2) compare favorably with the theory for a composite with up to 7% crack density, but theory andmore » experiment diverge at higher crack densities. On the other hand, compressional-wave velocities at low crack densities (1% and 3%) compare favorably with the theory. It is also shown that the velocity ratio V[sub p]/V[sub s] for two extreme cases, i.e. propagation normal and parallel to the cracks, as a function of crack density and porosity, has a strong directional dependence.« less
Spin dynamics of possible density wave states in the pseudogap phase of high-temperature superconductors

NASA Astrophysics Data System (ADS)

Hsu, Chen-Hsuan; Wang, Zhiqiang; Chakravarty, Sudip

2012-12-01

In a recent inelastic neutron scattering experiment in the pseudogap state of the high-temperature superconductor YBa2Cu3O6.6, an unusual “vertical” dispersion of the spin excitations with a large in-plane anisotropy was observed. In this paper, we discuss in detail the spin susceptibility of the singlet d-density wave, the triplet d-density wave as well as the more common spin density wave orders with hopping anisotropies. From numerical calculations within the framework of random phase approximation, we find nearly vertical dispersion relations for spin excitations with anisotropic incommensurability at low energy ω≤90meV, which are reminiscent of the experiments. At very high energy ω≥165meV, we also find energy-dependent incommensurability. Although there are some important differences between the three cases, unpolarized neutron measurements cannot discriminate between these alternate possibilities; the vertical dispersion, however, is a distinct feature of all three density wave states in contrast to the superconducting state, which shows an hour-glass shape dispersion.
Source Characterization of Microseismic Events using Empirical Green's Functions at the Basel EGS Project

NASA Astrophysics Data System (ADS)

Folesky, Jonas; Kummerow, Jörn

2015-04-01

The Empirical Green's Function (EGF) method uses pairs of events of high wave form similarity and adjacent hypocenters to decompose the influences of source time function, ray path, instrument site, and instrument response. The seismogram of the smaller event is considered as the Green's function which then can be deconvolved from the other seismogram. The result provides a reconstructed relative source time function (RSTF) of the larger event of that event pair. The comparison of the RSTFs at all stations of the observation systems produces information on the rupture process of the event based on an apparent directivity effect and possible changes in the RSTFs complexities. The Basel EGS dataset of 2006-2007 consists of about 2800 localized events of magnitudes between 0.0 < ML < 3.5 with event pairs of adequate magnitude difference for EGF analysis. The data has sufficient quality to analyse events with magnitudes down to ML = 0.0 for an apparent directivity effect although the approximate rupture duration for those events is of only a few milliseconds. The dataset shows a number of multiplets where fault plane solutions are known from earlier studies. Using the EGF method we compute rupture orientations for about 190 event pairs and compare them to the fault plane solutions of the multiplets. For the majority of events we observe a good consistency between the rupture direction found there and one of the previously determined nodal planes from fault plane solutions. In combination this resolves the fault plane ambiguity. Furthermore the rupture direction fitting yields estimates for projections of the rupture velocity on the horizontal plane. They seem to vary between the multiplets in the reservoir from 0.3 to 0.7 times the S-wave velocity. To our knowledge source characterization by EGF analysis has not yet been introduced to microseismic reservoirs with the data quality found in Basel. Our results show that EGF analysis can provide valuable additional insights on the distribution of rupture properties within the reservoir.
From the paddle to the beach - A Boussinesq shallow water numerical wave tank based on Madsen and Sørensen's equations

NASA Astrophysics Data System (ADS)

Orszaghova, Jana; Borthwick, Alistair G. L.; Taylor, Paul H.

2012-01-01

This article describes a one-dimensional numerical model of a shallow-water flume with an in-built piston paddle moving boundary wavemaker. The model is based on a set of enhanced Boussinesq equations and the nonlinear shallow water equations. Wave breaking is described approximately, by locally switching to the nonlinear shallow water equations when a critical wave steepness is reached. The moving shoreline is calculated as part of the solution. The piston paddle wavemaker operates on a movable grid, which is Lagrangian on the paddle face and Eulerian away from the paddle. The governing equations are, however, evolved on a fixed mapped grid, and the newly calculated solution is transformed back onto the moving grid via a domain mapping technique. Validation test results are compared against analytical solutions, confirming correct discretisation of the governing equations, wave generation via the numerical paddle, and movement of the wet/dry front. Simulations are presented that reproduce laboratory experiments of wave runup on a plane beach and wave overtopping of a laboratory seawall, involving solitary waves and compact wave groups. In practice, the numerical model is suitable for simulating the propagation of weakly dispersive waves and can additionally model any associated inundation, overtopping or inland flooding within the same simulation.
Investigation of the reconstruction accuracy of guided wave tomography using full waveform inversion

NASA Astrophysics Data System (ADS)

Rao, Jing; Ratassepp, Madis; Fan, Zheng

2017-07-01

Guided wave tomography is a promising tool to accurately determine the remaining wall thicknesses of corrosion damages, which are among the major concerns for many industries. Full Waveform Inversion (FWI) algorithm is an attractive guided wave tomography method, which uses a numerical forward model to predict the waveform of guided waves when propagating through corrosion defects, and an inverse model to reconstruct the thickness map from the ultrasonic signals captured by transducers around the defect. This paper discusses the reconstruction accuracy of the FWI algorithm on plate-like structures by using simulations as well as experiments. It was shown that this algorithm can obtain a resolution of around 0.7 wavelengths for defects with smooth depth variations from the acoustic modeling data, and about 1.5-2 wavelengths from the elastic modeling data. Further analysis showed that the reconstruction accuracy is also dependent on the shape of the defect. It was demonstrated that the algorithm maintains the accuracy in the case of multiple defects compared to conventional algorithms based on Born approximation.
From plane waves to local Gaussians for the simulation of correlated periodic systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Booth, George H., E-mail: george.booth@kcl.ac.uk; Tsatsoulis, Theodoros; Grüneis, Andreas, E-mail: a.grueneis@fkf.mpg.de

2016-08-28

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 themore » 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.« less
The elliptical Gaussian wave transformation due to diffraction by an elliptical hologram

NASA Astrophysics Data System (ADS)

Janicijevic, L.

1985-03-01

Realized as an interferogram of a spherical and a cylindrical wave, the elliptical hologram is treated as a plane diffracting grating which produces Fresnel diffraction of a simple astigmatic Gaussian incident wave. It is shown that if the principal axes of the incident beam coincide with the principal axes of the hologram, the diffracted wave field is composed of three different astigmatic Gaussian waves, with their waists situated in parallel but distinct planes. The diffraction pattern, observed on a transverse screen, is the result of the interference of the three diffracted wave components. It consists of three systems of overlapped second-order curves, whose shape depends on the distance of the observation screen from the hologram, as well as on the parameters of the incident wave beam and the hologram. The results are specialized for gratings in the form of circular and linear holograms and for the case of a stigmatic Gaussian incident wave, as well as for the normal plane-wave incidence on the three mentioned types of hologram.

Orbital dependent functionals: An atom projector augmented wave method implementation

NASA Astrophysics Data System (ADS)

Xu, Xiao

This thesis explores the formulation and numerical implementation of orbital dependent exchange-correlation functionals within electronic structure calculations. These orbital-dependent exchange-correlation functionals have recently received renewed attention as a means to improve the physical representation of electron interactions within electronic structure calculations. In particular, electron self-interaction terms can be avoided. In this thesis, an orbital-dependent functional is considered in the context of Hartree-Fock (HF) theory as well as the Optimized Effective Potential (OEP) method and the approximate OEP method developed by Krieger, Li, and Iafrate, known as the KLI approximation. In this thesis, the Fock exchange term is used as a simple well-defined example of an orbital-dependent functional. The Projected Augmented Wave (PAW) method developed by P. E. Blochl has proven to be accurate and efficient for electronic structure calculations for local and semi-local functions because of its accurate evaluation of interaction integrals by controlling multiple moments. We have extended the PAW method to treat orbital-dependent functionals in Hartree-Fock theory and the Optimized Effective Potential method, particularly in the KLI approximation. In the course of study we develop a frozen-core orbital approximation that accurately treats the core electron contributions for above three methods. The main part of the thesis focuses on the treatment of spherical atoms. We have investigated the behavior of PAW-Hartree Fock and PAW-KLI basis, projector, and pseudopotential functions for several elements throughout the periodic table. We have also extended the formalism to the treatment of solids in a plane wave basis and implemented PWPAW-KLI code, which will appear in future publications.
On the Mass of Atoms in Molecules: Beyond the Born-Oppenheimer Approximation

NASA Astrophysics Data System (ADS)

Scherrer, Arne; Agostini, Federica; Sebastiani, Daniel; Gross, E. K. U.; Vuilleumier, Rodolphe

2017-07-01

Describing the dynamics of nuclei in molecules requires a potential energy surface, which is traditionally provided by the Born-Oppenheimer or adiabatic approximation. However, we also need to assign masses to the nuclei. There, the Born-Oppenheimer picture does not account for the inertia of the electrons, and only bare nuclear masses are considered. Nowadays, experimental accuracy challenges the theoretical predictions of rotational and vibrational spectra and requires the participation of electrons in the internal motion of the molecule. More than 80 years after the original work of Born and Oppenheimer, this issue has still not been solved, in general. Here, we present a theoretical and numerical framework to address this problem in a general and rigorous way. Starting from the exact factorization of the electron-nuclear wave function, we include electronic effects beyond the Born-Oppenheimer regime in a perturbative way via position-dependent corrections to the bare nuclear masses. This maintains an adiabaticlike point of view: The nuclear degrees of freedom feel the presence of the electrons via a single potential energy surface, whereas the inertia of electrons is accounted for and the total mass of the system is recovered. This constitutes a general framework for describing the mass acquired by slow degrees of freedom due to the inertia of light, bounded particles; thus, it is applicable not only in electron-nuclear systems but in light-heavy nuclei or ions as well. We illustrate this idea with a model of proton transfer, where the light particle is the proton and the heavy particles are the oxygen atoms to which the proton is bounded. Inclusion of the light-particle inertia allows us to gain orders of magnitude in accuracy. The electron-nuclear perspective is adopted, instead, to calculate position-dependent mass corrections using density functional theory for a few polyatomic molecules at their equilibrium geometry. These data can serve as input for the computation of high-precision molecular spectra.
Isotropic transmission of magnon spin information without a magnetic field.

PubMed

Haldar, Arabinda; Tian, Chang; Adeyeye, Adekunle Olusola

2017-07-01

Spin-wave devices (SWD), which use collective excitations of electronic spins as a carrier of information, are rapidly emerging as potential candidates for post-semiconductor non-charge-based technology. Isotropic in-plane propagating coherent spin waves (magnons), which require magnetization to be out of plane, is desirable in an SWD. However, because of lack of availability of low-damping perpendicular magnetic material, a usually well-known in-plane ferrimagnet yttrium iron garnet (YIG) is used with a large out-of-plane bias magnetic field, which tends to hinder the benefits of isotropic spin waves. We experimentally demonstrate an SWD that eliminates the requirement of external magnetic field to obtain perpendicular magnetization in an otherwise in-plane ferromagnet, Ni 80 Fe 20 or permalloy (Py), a typical choice for spin-wave microconduits. Perpendicular anisotropy in Py, as established by magnetic hysteresis measurements, was induced by the exchange-coupled Co/Pd multilayer. Isotropic propagation of magnon spin information has been experimentally shown in microconduits with three channels patterned at arbitrary angles.
Isotropic transmission of magnon spin information without a magnetic field

PubMed Central

Haldar, Arabinda; Tian, Chang; Adeyeye, Adekunle Olusola

2017-01-01

Spin-wave devices (SWD), which use collective excitations of electronic spins as a carrier of information, are rapidly emerging as potential candidates for post-semiconductor non-charge-based technology. Isotropic in-plane propagating coherent spin waves (magnons), which require magnetization to be out of plane, is desirable in an SWD. However, because of lack of availability of low-damping perpendicular magnetic material, a usually well-known in-plane ferrimagnet yttrium iron garnet (YIG) is used with a large out-of-plane bias magnetic field, which tends to hinder the benefits of isotropic spin waves. We experimentally demonstrate an SWD that eliminates the requirement of external magnetic field to obtain perpendicular magnetization in an otherwise in-plane ferromagnet, Ni80Fe20 or permalloy (Py), a typical choice for spin-wave microconduits. Perpendicular anisotropy in Py, as established by magnetic hysteresis measurements, was induced by the exchange-coupled Co/Pd multilayer. Isotropic propagation of magnon spin information has been experimentally shown in microconduits with three channels patterned at arbitrary angles. PMID:28776033
A combined representation method for use in band structure calculations. 1: Method

NASA Technical Reports Server (NTRS)

Friedli, C.; Ashcroft, N. W.

1975-01-01

A representation was described whose basis levels combine the important physical aspects of a finite set of plane waves with those of a set of Bloch tight-binding levels. The chosen combination has a particularly simple dependence on the wave vector within the Brillouin Zone, and its use in reducing the standard one-electron band structure problem to the usual secular equation has the advantage that the lattice sums involved in the calculation of the matrix elements are actually independent of the wave vector. For systems with complicated crystal structures, for which the Korringa-Kohn-Rostoker (KKR), Augmented-Plane Wave (APW) and Orthogonalized-Plane Wave (OPW) methods are difficult to apply, the present method leads to results with satisfactory accuracy and convergence.
Global multiresolution models of surface wave propagation: comparing equivalently regularized Born and ray theoretical solutions

NASA Astrophysics Data System (ADS)

Boschi, Lapo

2006-10-01

I invert a large set of teleseismic phase-anomaly observations, to derive tomographic maps of fundamental-mode surface wave phase velocity, first via ray theory, then accounting for finite-frequency effects through scattering theory, in the far-field approximation and neglecting mode coupling. I make use of a multiple-resolution pixel parametrization which, in the assumption of sufficient data coverage, should be adequate to represent strongly oscillatory Fréchet kernels. The parametrization is finer over North America, a region particularly well covered by the data. For each surface-wave mode where phase-anomaly observations are available, I derive a wide spectrum of plausible, differently damped solutions; I then conduct a trade-off analysis, and select as optimal solution model the one associated with the point of maximum curvature on the trade-off curve. I repeat this exercise in both theoretical frameworks, to find that selected scattering and ray theoretical phase-velocity maps are coincident in pattern, and differ only slightly in amplitude.
Coherent structural trapping through wave packet dispersion during photoinduced spin state switching

NASA Astrophysics Data System (ADS)

Lemke, Henrik T.; Kjær, Kasper S.; Hartsock, Robert; van Driel, Tim B.; Chollet, Matthieu; Glownia, James M.; Song, Sanghoon; Zhu, Diling; Pace, Elisabetta; Matar, Samir F.; Nielsen, Martin M.; Benfatto, Maurizio; Gaffney, Kelly J.; Collet, Eric; Cammarata, Marco

2017-05-01

The description of ultrafast nonadiabatic chemical dynamics during molecular photo-transformations remains challenging because electronic and nuclear configurations impact each other and cannot be treated independently. Here we gain experimental insights, beyond the Born-Oppenheimer approximation, into the light-induced spin-state trapping dynamics of the prototypical [Fe(bpy)3]2+ compound by time-resolved X-ray absorption spectroscopy at sub-30-femtosecond resolution and high signal-to-noise ratio. The electronic decay from the initial optically excited electronic state towards the high spin state is distinguished from the structural trapping dynamics, which launches a coherent oscillating wave packet (265 fs period), clearly identified as molecular breathing. Throughout the structural trapping, the dispersion of the wave packet along the reaction coordinate reveals details of intramolecular vibronic coupling before a slower vibrational energy dissipation to the solution environment. These findings illustrate how modern time-resolved X-ray absorption spectroscopy can provide key information to unravel dynamic details of photo-functional molecules.
Plane wave packet formulation of atom-plus-diatom quantum reactive scattering.

PubMed

Althorpe, Stuart C

2004-07-15

We recently interpreted several reactive scattering experiments using a plane wave packet (PWP) formulation of quantum scattering theory [see, e.g., S. C. Althorpe, F. Fernandez-Alonso, B. D. Bean, J. D. Ayers, A. E. Pomerantz, R. N. Zare, and E. Wrede, Nature (London) 416, 67 (2002)]. This paper presents the first derivation of this formulation for atom-plus-diatom reactive scattering, and explains its relation to conventional time-independent reactive scattering. We generalize recent results for spherical-particle scattering [S. C. Althorpe, Phys. Rev. A 69, 042702 (2004)] to atom-rigid-rotor scattering in the space-fixed frame, atom-rigid-rotor scattering in the body-fixed frame, and finally A+BC rearrangement scattering. The reactive scattering is initiated by a plane wave packet, describing the A+BC reagents in center-of-mass scattering coordinates, and is detected by projecting onto a series of AC+B (or AB+C) plane wave "probe" packets. The plane wave packets are localized at the closest distance from the scattering center at which the interaction potential can be neglected. The time evolution of the initial plane wave packet provides a clear visualization of the scattering into space of the reaction products. The projection onto the probe packets yields the time-independent, state-to-state scattering amplitude, and hence the differential cross section. We explain how best to implement the PWP approach in a numerical computation, and illustrate this with a detailed application to the H+D2 reaction. (c) 2004 American Institute of Physics
Dynamic Structure Factor: An Introduction

NASA Astrophysics Data System (ADS)

Sturm, K.

1993-02-01

The doubly differential cross-section for weak inelastic scattering of waves or particles by manybody systems is derived in Born approximation and expressed in terms of the dynamic structure factor according to van Hove. The application of this very general scheme to scattering of neutrons, x-rays and high-energy electrons is discussed briefly. The dynamic structure factor, which is the space and time Fourier transform of the density-density correlation function, is a property of the many-body system independent of the external probe and carries information on the excitation spectrum of the system. The relation of the electronic structure factor to the density-density response function defined in linear-response theory is shown using the fluctuation-dissipation theorem. This is important for calculations, since the response function can be calculated approximately from the independent-particle response function in self-consistent field approximations, such as the random-phase approximation or the local-density approximation of the density functional theory. Since the density-density response function also determines the dielectric function, the dynamic structure can be expressed by the dielectric function.
A high frequency analysis of electromagnetic plane wave scattering by perfectly-conducting semi-infinite parallel plate and rectangular waveguides with absorber coated inner walls

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.
Hybrid Simulation of the Shock Wave Trailing the Moon

NASA Technical Reports Server (NTRS)

Israelevich, P.; Ofman, Leon

2012-01-01

A standing shock wave behind the Moon was predicted by Michel (1967) but never observed nor simulated. We use 1D hybrid code in order to simulate the collapse of the plasma-free cavity behind the Moon and for the first time to model the formation of this shock. Starting immediately downstream of the obstacle we consider the evolution of plasma expansion into the cavity in the frame of reference moving along with the solar wind. Well-known effects as electric charging of the cavity affecting the plasma flow and counterstreaming ion beams in the wake are reproduced. Near the apex of the inner Mach cone where the plasma flows from the opposite sides of the obstacle meet, a shock wave arises. We expect the shock to be produced at periods of high electron temperature solar wind streams (T(sub i) much less than T(sub e) approximately 100 eV). The shock is produced by the interaction of oppositely directed proton beams in the plane containing solar wind velocity and interplanetary magnetic field vectors. In the direction across the magnetic field and the solar wind velocity, the shock results from the interaction of the plasma flow with the region of the enhanced magnetic field inside the cavity that plays the role of the magnetic barrier. The appearance of the standing shock wave is expected at the distance of approximately 7R(sub M) downstream of the Moon.
Electron-impact excitation cross sections for the b /sup 3/. sigma. /sub u//sup +/ state of H/sub 2/

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khakoo, M.A.; Trajmar, S.; McAdams, R.

1987-04-01

Differential and integral cross sections for electron-impact excitation of the b /sup 3/..sigma../sub u//sup +/ state of H/sub 2/ have been determined in the 20--100-eV impact energy region. The calibration of the cross sections was achieved through the H/sub 2/ elastic scattering cross sections, which in turn were normalized to absolute He elastic scattering cross sections. Comparison is made with available experimental data and with theoretical results applying Born-Ochkur-Rudge, distorted-wave, and close-coupling approximations.
Breakup effects on alpha spectroscopic factors of 16O

NASA Astrophysics Data System (ADS)

Adhikari, S.; Basu, C.; Sugathan, P.; Jhinghan, A.; Behera, B. R.; Saneesh, N.; Kaur, G.; Thakur, M.; Mahajan, R.; Dubey, R.; Mitra, A. K.

2017-01-01

The triton angular distribution for the 12C(7Li,t)16O* reaction is measured at 20 MeV, populating discrete states of 16O. Continuum discretized coupled reaction channel calculations are used to to extract the alpha spectroscopic properties of 16O states instead of the distorted wave born approximation theory to include the effects of breakup on the transfer process. The alpha reduced width, spectroscopic factors and the asymptotic normalization constant (ANC) of 16O states are extracted. The error in the spectroscopic factor is about 35% and in that of the ANC about 27%.
Level structure of sup 52 Cr from the sup 51 V( sup 3 He, d ) reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Basher, M.A.; Siddique, H.R.; Husain, A.

1992-04-01

The {sup 51}V({sup 3}He,{ital d}){sup 52}Cr reaction has been studied at 15 MeV using the tandem Van de Graaff accelerator and the multichannel magnetic spectrograph of the Nuclear Physics Laboratory, Oxford. Angular distributions have been measured for levels up to {ital E}{sub {ital x}}=8.6 MeV over the laboratory angular range {theta}=3.75{degree}--71.25{degree}. Data are analyzed in terms of the distorted wave Born approximation theory of the direct reaction. The {ital l} transfers and the spectroscopic factors are obtained.
24Na at Ex=4.7 -5.9 MeV from 22Ne(3He,p )

NASA Astrophysics Data System (ADS)

Fortune, H. T.

2018-04-01

Abstract. Analysis of data from the 22Ne(3He,p ) 24Na reaction has been extended to include 18 angular distributions for states between 4.7 and 5.9 MeV. A distorted-wave Born-approximation analysis allows the determination of ℓ value(s) for most of them. Results for Jπ are compared with previous information. In general, agreement is good. Some apparent disagreements between current and past results are indicative of population of a different state in this reaction than the nearby one listed in the compilation.
Self-consistent-field perturbation theory for the Schröautdinger equation

NASA Astrophysics Data System (ADS)

Goodson, David Z.

1997-06-01

A method is developed for using large-order perturbation theory to solve the systems of coupled differential equations that result from the variational solution of the Schröautdinger equation with wave functions of product form. This is a noniterative, computationally efficient way to solve self-consistent-field (SCF) equations. Possible applications include electronic structure calculations using products of functions of collective coordinates that include electron correlation, vibrational SCF calculations for coupled anharmonic oscillators with selective coupling of normal modes, and ab initio calculations of molecular vibration spectra without the Born-Oppenheimer approximation.
Absolute instabilities of travelling wave solutions in a Keller-Segel model

NASA Astrophysics Data System (ADS)

Davis, P. N.; van Heijster, P.; Marangell, R.

2017-11-01

We investigate the spectral stability of travelling wave solutions in a Keller-Segel model of bacterial chemotaxis with a logarithmic chemosensitivity function and a constant, sublinear, and linear consumption rate. Linearising around the travelling wave solutions, we locate the essential and absolute spectrum of the associated linear operators and find that all travelling wave solutions have parts of the essential spectrum in the right half plane. However, we show that in the case of constant or sublinear consumption there exists a range of parameters such that the absolute spectrum is contained in the open left half plane and the essential spectrum can thus be weighted into the open left half plane. For the constant and sublinear consumption rate models we also determine critical parameter values for which the absolute spectrum crosses into the right half plane, indicating the onset of an absolute instability of the travelling wave solution. We observe that this crossing always occurs off of the real axis.
Space-Borne Radio-Sounding Investigations Facilitated by the Virtual Wave Observatory (VWO)

NASA Technical Reports Server (NTRS)

Benson, Robert F.; Fung, Shing F.; Bilitza,Dieter; Garcia, Leonard N.; Shao, Xi; Galkin, Ivan A.

2011-01-01

The goal of the Virtual Wave Observatory (VWO) is to provide userfriendly access to heliophysics wave data. While the VWO initially emphasized the vast quantity of wave data obtained from passive receivers, the VWO infrastructure can also be used to access active sounder data sets. Here we use examples from some half-million Alouette-2, ISIS-1, and ISIS-2 digital topside-sounder ionograms to demonstrate the desirability of such access to the actual ionograms for investigations of both natural and sounder-stimulated plasma-wave phenomena. By this demonstration, we wish to encourage investigators to make other valuable space-borne sounder data sets accessible via the VWO.
Evanescent-Wave Filtering in Images Using Remote Terahertz Structured Illumination

NASA Astrophysics Data System (ADS)

Flammini, M.; Pontecorvo, E.; Giliberti, V.; Rizza, C.; Ciattoni, A.; Ortolani, M.; DelRe, E.

2017-11-01

Imaging with structured illumination allows for the retrieval of subwavelength features of an object by conversion of evanescent waves into propagating waves. In conditions in which the object plane and the structured-illumination plane do not coincide, this conversion process is subject to progressive filtering of the components with high spatial frequency when the distance between the two planes increases, until the diffraction-limited lateral resolution is restored when the distance exceeds the extension of evanescent waves. We study the progressive filtering of evanescent waves by developing a remote super-resolution terahertz imaging system operating at a wavelength λ =1.00 mm , based on a freestanding knife edge and a reflective confocal terahertz microscope. In the images recorded with increasing knife-edge-to-object-plane distance, we observe the transition from a super-resolution of λ /17 ≃60 μ m to the diffraction-limited lateral resolution of Δ x ≃λ expected for our confocal microscope. The extreme nonparaxial conditions are analyzed in detail, exploiting the fact that, in the terahertz frequency range, the knife edge can be positioned at a variable subwavelength distance from the object plane. Electromagnetic simulations of radiation scattering by the knife edge reproduce the experimental super-resolution achieved.
A harmonic adiabatic approximation to calculate highly excited vibrational levels of ``floppy molecules''

NASA Astrophysics Data System (ADS)

Lauvergnat, David; Nauts, André; Justum, Yves; Chapuisat, Xavier

2001-04-01

The harmonic adiabatic approximation (HADA), an efficient and accurate quantum method to calculate highly excited vibrational levels of molecular systems, is presented. It is well-suited to applications to "floppy molecules" with a rather large number of atoms (N>3). A clever choice of internal coordinates naturally suggests their separation into active, slow, or large amplitude coordinates q', and inactive, fast, or small amplitude coordinates q″, which leads to an adiabatic (or Born-Oppenheimer-type) approximation (ADA), i.e., the total wave function is expressed as a product of active and inactive total wave functions. However, within the framework of the ADA, potential energy data concerning the inactive coordinates q″ are required. To reduce this need, a minimum energy domain (MED) is defined by minimizing the potential energy surface (PES) for each value of the active variables q', and a quadratic or harmonic expansion of the PES, based on the MED, is used (MED harmonic potential). In other words, the overall picture is that of a harmonic valley about the MED. In the case of only one active variable, we have a minimum energy path (MEP) and a MEP harmonic potential. The combination of the MED harmonic potential and the adiabatic approximation (harmonic adiabatic approximation: HADA) greatly reduces the size of the numerical computations, so that rather large molecules can be studied. In the present article however, the HADA is applied to our benchmark molecule HCN/CNH, to test the validity of the method. Thus, the HADA vibrational energy levels are compared and are in excellent agreement with the ADA calculations (adiabatic approximation with the full PES) of Light and Bačić [J. Chem. Phys. 87, 4008 (1987)]. Furthermore, the exact harmonic results (exact calculations without the adiabatic approximation but with the MEP harmonic potential) are compared to the exact calculations (without any sort of approximation). In addition, we compare the densities of the bending motion during the HCN/CNH isomerization, computed with the HADA and the exact wave function.

Investigation of standing wave formation in a human skull for a clinical prototype of a large-aperture, transcranial MR-guided Focused Ultrasound (MRgFUS) phased array: An experimental and simulation study

PubMed Central

Song, Junho; Pulkkinen, Aki; Huang, Yuexi; Hynynen, Kullervo

2014-01-01

Standing wave formation in an ex vivo human skull was investigated using a clinical prototype of a 30 cm diameter with 15 cm radius of curvature, low frequency (230 kHz), hemispherical transcranial Magnetic Resonance guided Focused Ultrasound (MRgFUS) phased-array. Experimental and simulation studies were conducted with changing aperture size and f-number configurations of the phased array, and qualitatively and quantitatively examined the acoustic pressure variation at the focus due to standing waves. The results demonstrated that the nodes and anti-nodes of standing wave produced by the small aperture array were clearly seen at approximately every 3 mm. The effect of the standing wave became more pronounced as the focus was moved closer to skull base. However, a sharp focus was seen for the full array, and there was no such standing wave pattern in the acoustic plane or near the skull base. This study showed that the fluctuation pressure amplitude would be greatly reduced by using a large-scale, hemispherical phased array with a low f-number. PMID:22049360
The Existence of Topological Edge States in Honeycomb Plasmonic Lattices

NASA Astrophysics Data System (ADS)

Wang, Li

In this paper, we investigate the band properties of 2D honeycomb plasmonic lattices consisting of metallic nanoparticles. By means of the coupled dipole method and quasi-static approximation, we theoretically analyze the band structures stemming from near-field interaction of localized surface plasmon polaritons for both the infinite lattice and ribbons. Naturally, the interaction of point dipoles decouples into independent out-of-plane and in-plane polarizations. For the out-of-plane modes, both the bulk spectrum and the range of the momentum k∥ where edge states exist in ribbons are similar to the electronic bands in graphene. Nevertheless, the in-plane polarized modes show significant differences, which do not only possess additional non-flat edge states in ribbons, but also have different distributions of the flat edge states in reciprocal space. For in-plane polarized modes, we derived the bulk-edge correspondence, namely, the relation between the number of flat edge states at a fixed k∥, Zak phases of the bulk bands and the winding number associated with the bulk hamiltonian, and verified it through four typical ribbon boundaries, i.e. zigzag, bearded zigzag, armchair, and bearded armchair. Our approach gives a new topological understanding of edge states in such plasmonic systems, and may also apply to other 2D vector wave systems.
Heisenberg-Langevin versus quantum master equation

NASA Astrophysics Data System (ADS)

Boyanovsky, Daniel; Jasnow, David

2017-12-01

The quantum master equation is an important tool in the study of quantum open systems. It is often derived under a set of approximations, chief among them the Born (factorization) and Markov (neglect of memory effects) approximations. In this article we study the paradigmatic model of quantum Brownian motion of a harmonic oscillator coupled to a bath of oscillators with a Drude-Ohmic spectral density. We obtain analytically the exact solution of the Heisenberg-Langevin equations, with which we study correlation functions in the asymptotic stationary state. We compare the exact correlation functions to those obtained in the asymptotic long time limit with the quantum master equation in the Born approximation with and without the Markov approximation. In the latter case we implement a systematic derivative expansion that yields the exact asymptotic limit under the factorization approximation only. We find discrepancies that could be significant when the bandwidth of the bath Λ is much larger than the typical scales of the system. We study the exact interaction energy as a proxy for the correlations missed by the Born approximation and find that its dependence on Λ is similar to the discrepancy between the exact solution and that of the quantum master equation in the Born approximation. We quantify the regime of validity of the quantum master equation in the Born approximation with or without the Markov approximation in terms of the system's relaxation rate γ , its unrenormalized natural frequency Ω and Λ : γ /Ω ≪1 and also γ Λ /Ω2≪1 . The reliability of the Born approximation is discussed within the context of recent experimental settings and more general environments.
On the estimation of ice thickness from scattering observations

NASA Astrophysics Data System (ADS)

Williams, T. D.; Squire, V. A.

2010-04-01

This paper is inspired by the proposition that it may be possible to extract descriptive physical parameters - in particular the ice thickness, of a sea-ice field from ocean wave information. The motivation is that mathematical theory describing wave propagation in such media has reached a point where the inherent heterogeneity, expressed as pressure ridge keels and sails, leads, thickness variations and changes of material property and draught, can be fully assimilated exactly or through approximations whose limitations are understood. On the basis that leads have the major wave scattering effect for most sea-ice [Williams, T.D., Squire, V.A., 2004. Oblique scattering of plane flexural-gravity waves by heterogeneities in sea ice. Proc. R. Soc. Lon. Ser.-A 460 (2052), 3469-3497], a model two dimensional sea-ice sheet composed of a large number of such features, randomly dispersed, is constructed. The wide spacing approximation is used to predict how wave trains of different period will be affected, after first establishing that this produces results that are very close to the exact solution. Like Kohout and Meylan [Kohout, A.L., Meylan, M.H., 2008. An elastic plate model for wave attenuation and ice floe breaking in the marginal ice zone. J. Geophys. Res. 113, C09016, doi:10.1029/2007JC004434], we find that on average the magnitude of a wave transmitted by a field of leads decays exponentially with the number of leads. Then, by fitting a curve based on this assumption to the data, the thickness of the ice sheet is obtained. The attenuation coefficient can always be calculated numerically by ensemble averaging but in some cases more rapidly computed approximations work extremely well. Moreover, it is found that the underlying thickness can be determined to good accuracy by the method as long as Archimedean draught is correctly provided for, suggesting that waves can indeed be effective as a remote sensing agent to measure ice thickness in areas where pressure ridges are not sizeable, i.e. away from coastal regions of high deformation.
Numerical Investigation of Three-dimensional Instability of Standing Waves

NASA Astrophysics Data System (ADS)

Zhu, Qiang; Liu, Yuming; Yue, Dick K. P.

2002-11-01

We study the three-dimensional instability of finite-amplitude standing waves under the influence of gravity using the transition matrix method. For accurate calculation of the transition matrices, we apply an efficient high-order spectral element method for nonlinear wave dynamics in complex domain. We consider two types of standing waves: (a) plane standing waves; and (b) standing waves in a circular tank. For the former, in addition to the confirmation of the side-band-like instability, we find a new three-dimensional instability for arbitrary base standing waves. The dominant component of the unstable disturbance is an oblique standing wave, with an arbitrary angle relative to the base flow, whose frequency is approximately equal to that of the base standing wave. Based on direct simulations, we confirm such a three-dimensional instability and show the occurrence of the Fermi-Pasta-Ulam recurrence phenomenon during nonlinear evolution. For the latter, we find that beyond a threshold wave steepness, the standing wave with frequency Ω becomes unstable to a small three-dimensional disturbance, which contains two dominant standing-wave components with frequencies ω1 and ω_2, provided that 2Ω ω1 + ω_2. The threshold wave steepness is found to decrease/increase as the radial/azimuthal wavenumber of the base standing wave increases. We show that the instability of standing waves in rectangular and circular tanks is caused by third-order quartet resonances between base flow and disturbance.
The reflection and diffraction of internal waves from the junction of a slit and a half-space, with application to submarine canyons

NASA Astrophysics Data System (ADS)

Grimshaw, R. H. J.; Baines, P. G.; Bell, R. C.

1985-07-01

We consider the three-dimensional reflection and diffraction properties of internal waves in a continuously stratified rotating fluid which are incident on the junction of a vertical slit and a half-space. This geometry is a model for submarine canyons on continental slopes in the ocean, where various physical phenomena embodying reflection and diffraction effects have been observed. Three types of incident wave are considered: (1) Kelvin waves in the slit (canyon); (2) Kelvin waves on the slope; and (3) plane internal waves incident from the half-space (ocean). These are scattered into Kelvin and Poincaré waves in the slit, a Kelvin wave on the slope and Poincaré waves in the half-space. Most of the discussion is centered around case (1). Various properties of the wave field are calculated for ranges of the parameters c/ cot θ, γα and ƒ/ω where cot θ is the topographic slope, c is the internal wave ray slope, α is the canyon half-width, γ is the down-slope wave-number, ƒ is the Coriolis parameter and ω is the wave frequency. Analytical results are obtained for small γα and some approximate results for larger values of γα. The results show that significant wave trapping may occur in oceanic situations, and that submarine canyons may act as source regions for internal Kelvin waves on the continental slope.
Probing the smearing effect by a pointlike graviton in the plane-wave matrix model

DOE Office of Scientific and Technical Information (OSTI.GOV)

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.
Applicability of geometrical optics to in-plane liquid-crystal configurations.

PubMed

Sluijter, M; Xu, M; Urbach, H P; de Boer, D K G

2010-02-15

We study the applicability of geometrical optics to inhomogeneous dielectric nongyrotropic optically anisotropic media typically found in in-plane liquid-crystal configurations with refractive indices n(o)=1.5 and n(e)=1.7. To this end, we compare the results of advanced ray- and wave-optics simulations of the propagation of an incident plane wave to a special anisotropic configuration. Based on the results, we conclude that for a good agreement between ray and wave optics, a maximum change in optical properties should occur over a distance of at least 20 wavelengths.
A parallel orbital-updating based plane-wave basis method for electronic structure calculations

NASA Astrophysics Data System (ADS)

Pan, Yan; Dai, Xiaoying; de Gironcoli, Stefano; Gong, Xin-Gao; Rignanese, Gian-Marco; Zhou, Aihui

2017-11-01

Motivated by the recently proposed parallel orbital-updating approach in real space method [1], we propose a parallel orbital-updating based plane-wave basis method for electronic structure calculations, for solving the corresponding eigenvalue problems. In addition, we propose two new modified parallel orbital-updating methods. Compared to the traditional plane-wave methods, our methods allow for two-level parallelization, which is particularly interesting for large scale parallelization. Numerical experiments show that these new methods are more reliable and efficient for large scale calculations on modern supercomputers.
Solid explosive plane-wave lenses pressed-to-shape with dies

DOE Office of Scientific and Technical Information (OSTI.GOV)

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.
RCS measurements, transformations, and comparisons under cylindrical and plane wave illumination

NASA Astrophysics Data System (ADS)

Vokura, V. J.; Balanis, Constantine A.; Birtcher, Craig R.

1994-03-01

Monostatic RCS measurements of a long bar (at X-band) and of a scale model aircraft (at C-band) were performed under the quasi-plane wave illumination produced by a dual parabolic-cylinder CATR. At Arizona State University's ElectroMagnetic Anechoic Chamber (EMAC) facility, these measurements were repeated under the cylindrical wave illumination produced by a March Microwave Single-Plane Collimating Range (SPCR). The SPRC measurements were corrected using corrected using the 'reference target method.' The corrected SPCR measurements are in good agreement with the CATR measurements.
Seismic Wave Propagation in Fully Anisotropic Axisymmetric Media: Applications and Practical Considerations

NASA Astrophysics Data System (ADS)

van Driel, Martin; Nissen-Meyer, Tarje; Stähler, Simon; Waszek, Lauren; Hempel, Stefanie; Auer, Ludwig; Deuss, Arwen

2014-05-01

We present a numerical method to compute high-frequency 3D elastic waves in fully anisotropic axisymmetric media. The method is based on a decomposition of the wavefield into a series of uncoupled 2D equations, for which the dependence of the wavefield on the azimuth can be solved analytically. The remaining 2D problems are then solved using a spectral element method (AxiSEM). AxiSEM was recently published open-source (Nissen-Meyer et al. 2014) as a production ready code capable to compute global seismic wave propagation up to frequencies of ~2Hz. It accurately models visco-elastic dissipation and anisotropy (van Driel et al., submitted to GJI) and runs efficiently on HPC resources using up to 10K cores. At very short period, the Fresnel Zone of body waves is narrow and sensitivity is focused around the geometrical ray. In cases where the azimuthal variations of structural heterogeneity exhibit long spatial wavelengths, so called 2.5D simulations (3D wavefields in 2D models) provide a good approximation. In AxiSEM, twodimensional variations in the source-receiver plane are effectively modelled as ringlike structures extending in the out-of-plane direction. In contrast to ray-theory, which is widely used in high-frequency applications, AxiSEM provides complete waveforms, thus giving access to frequency dependency, amplitude variations, and peculiar wave effects such as diffraction and caustics. Here we focus on the practical implications of the inherent axisymmetric geometry and show how the 2.5D-features of our method method can be used to model realistic anisotropic structures, by applying it to problems such as the D" region and the inner core.
Novel high-gain, improved-bandwidth, finned-ladder V-band Traveling-Wave Tube slow-wave circuit design

NASA Technical Reports Server (NTRS)

Kory, Carol L.; Wilson, Jeffrey D.

1994-01-01

The V-band frequency range of 59-64 GHz is a region of the millimeter-wave spectrum that has been designated for inter-satellite communications. As a first effort to develop a high-efficiency V-band Traveling-Wave Tube (TWT), variations on a ring-plane slow-wave circuit were computationally investigated to develop an alternative to the more conventional ferruled coupled-cavity circuit. The ring-plane circuit was chosen because of its high interaction impedance, large beam aperture, and excellent thermal dissipation properties. Despite these advantages, however, low bandwidth and high voltage requirements have, until now, prevented its acceptance outside the laboratory. In this paper, the three-dimensional electrodynamic simulation code MAFIA (solution of MAxwell's Equation by the Finite-Integration-Algorithm) is used to investigate methods of increasing the bandwidth and lowering the operating voltage of the ring-plane circuit. Calculations of frequency-phase dispersion, beam on-axis interaction impedance, attenuation and small-signal gain per wavelength were performed for various geometric variations and loading distributions of the ring-plane TWT slow-wave circuit. Based on the results of the variations, a circuit termed the finned-ladder TWT slow-wave circuit was designed and is compared here to the scaled prototype ring-plane and a conventional ferruled coupled-cavity TWT circuit over the V-band frequency range. The simulation results indicate that this circuit has a much higher gain, significantly wider bandwidth, and a much lower voltage requirement than the scaled ring-plane prototype circuit, while retaining its excellent thermal dissipation properties. The finned-ladder circuit has a much larger small-signal gain per wavelength than the ferruled coupled-cavity circuit, but with a moderate sacrifice in bandwidth.
Understanding the power reflection and transmission coefficients of a plane wave at a planar interface

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.
Use of complex frequency plane to design broadband and sub-wavelength absorbers.

PubMed

Romero-García, V; Theocharis, G; Richoux, O; Pagneux, V

2016-06-01

The reflection of sound of frequency below 1 kHz, by a rigid-backed structure that contains sub-wavelength resonators is studied in this work. In particular, only single mode reflected waves are considered, an approximation which is accurate in this low frequency regime. A method of analysis of absorption that uses the structure of the reflection coefficient in the complex frequency plane is proposed. In the absence of losses, the reflection coefficient supports pairs of poles and zeros that are complex conjugate and which have imaginary parts linked to the energy leakage by radiation. When losses are introduced and balanced to the leakage, the critical coupling condition is satisfied and total absorption is obtained. Examples of a slot resonator and of multiple Helmholtz resonators are analyzed to obtain both narrow and broadband total absorption.
Mica-dominated seismic properties of mid-crust beneath west Yunnan (China) and geodynamic implications

NASA Astrophysics Data System (ADS)

Shao, Tongbin; Ji, Shaocheng; Oya, Shoma; Michibayashi, Katsuyoshi; Wang, Qian

2016-05-01

Measurements of crystallographic preferred orientations (CPO) and calculations of P- and S-wave velocities (Vp and Vs) and anisotropy were conducted on three quartz-mica schists and one felsic mylonite, which are representative of typical metamorphic rocks deformed in the middle crust beneath the southeastern Tibetan plateau. Results show that the schists have Vp anisotropy (AVp) ranging from 16.4% to 25.5% and maximum Vs anisotropy [AVs(max)] between 21.6% and 37.8%. The mylonite has lower AVp and AVs(max) but slightly higher foliation anisotropy, which are 13.2%, 18.5%, and 3.07%, respectively, due to the lower content and CPO strength of mica. With increasing mica content, the deformed rocks tend to form transverse isotropy (TI) with fast velocities in the foliation plane and slow velocities normal to the foliation. However, the presence of prismatic minerals (e.g., amphibole and sillimanite) forces the overall symmetry to deviate from TI. An increase in feldspar content reduces the bulk anisotropy caused by mica or quartz because the fast-axis of feldspar aligns parallel to the slow-axis of mica and/or quartz. The effect of quartz on seismic properties of mica-bearing rocks is complex, depending on its content and prevailing slip system. The greatest shear-wave splitting and fastest Vp both occur for propagation directions within the foliation plane, consistent with the fast Pms (S-wave converted from P-wave at the Moho) polarization directions in the west Yunnan where mica/amphibole-bearing rocks have developed pervasive subvertical foliation and subhorizontal lineation. The fast Pms directions are perpendicular to the approximately E-W orienting fast SKS (S-wave traversing the core as P-wave) directions, indicating a decoupling at the Moho interface between the crust and mantle beneath the region. The seismic data are inconsistent with the model of crustal channel flow as the latter should produce a subhorizontal foliation where vertically incident shear waves suffer little splitting.
Strings on AdS_3 x S^3 and the Plane-Wave Limit. Issues on PP-Wave/CFT Holography

NASA Astrophysics Data System (ADS)

Zapata, Oswaldo

2005-10-01

In this thesis we give explicit results for bosonic string amplitudes on AdS_3 x S^3 and the corresponding plane-wave limit. We also analyze the consequences of our approach for understanding holography in this set up, as well as its possible generalization to other models.
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…
Microwave Heating of Metal Power Clusters

NASA Astrophysics Data System (ADS)

Rybakov, K. I.; Semenov, V. E.; Volkovskaya, I. I.

2018-01-01

The results of simulating the rapid microwave heating of spherical clusters of metal particles to the melting point are reported. In the simulation, the cluster is subjected to a plane electromagnetic wave. The cluster size is comparable to the wavelength; the perturbations of the field inside the cluster are accounted for within an effective medium approximation. It is shown that the time of heating in vacuum to the melting point does not exceed 1 s when the electric field strength in the incident wave is about 2 kV/cm at a frequency of 24 GHz or 5 kV/cm at a frequency of 2.45 GHz. The obtained results demonstrate feasibility of using rapid microwave heating for the spheroidization of metal particles with an objective to produce high-quality powders for additive manufacturing technologies.
Plane waves in magneto-thermoelastic anisotropic medium based on (L-S) theory under the effect of Coriolis and centrifugal forces

NASA Astrophysics Data System (ADS)

Alesemi, Meshari

2018-04-01

The objective of this research is to illustrate the effectiveness of the thermal relaxation time based on the theory of Lord-Shulman (L-S), Coriolis and Centrifugal Forces on the reflection coefficients of plane waves in an anisotropic magneto-thermoelastic medium. Assuming the elastic medium is rotating with stable angular velocity and the imposed magnetic field is parallel to the boundary of the half-space. The basic equations of a transversely isotropic rotating magneto-thermoelastic medium are formulated according to thermoelasticity theory of Lord-Shulman (L-S). Next to that, getting the velocity equation which is illustrated to show existence of three quasi-plane waves propagating in the medium. The amplitude ratios coefficients of these plane waves have been given and then computed numerically and plotted graphically to demonstrate the influences of the rotation on the Zinc material.

Imaging electrical conductivity, permeability, and/or permittivity contrasts using the Born Scattering Inversion (BSI)

NASA Astrophysics Data System (ADS)

Darrh, A.; Downs, C. M.; Poppeliers, C.

2017-12-01

Born Scattering Inversion (BSI) of electromagnetic (EM) data is a geophysical imaging methodology for mapping weak conductivity, permeability, and/or permittivity contrasts in the subsurface. The high computational cost of full waveform inversion is reduced by adopting the First Born Approximation for scattered EM fields. This linearizes the inverse problem in terms of Born scattering amplitudes for a set of effective EM body sources within a 3D imaging volume. Estimation of scatterer amplitudes is subsequently achieved by solving the normal equations. Our present BSI numerical experiments entail Fourier transforming real-valued synthetic EM data to the frequency-domain, and minimizing the L2 residual between complex-valued observed and predicted data. We are testing the ability of BSI to resolve simple scattering models. For our initial experiments, synthetic data are acquired by three-component (3C) electric field receivers distributed on a plane above a single point electric dipole within a homogeneous and isotropic wholespace. To suppress artifacts, candidate Born scatterer locations are confined to a volume beneath the receiver array. Also, we explore two different numerical linear algebra algorithms for solving the normal equations: Damped Least Squares (DLS), and Non-Negative Least Squares (NNLS). Results from NNLS accurately recover the source location only for a large dense 3C receiver array, but fail when the array is decimated, or is restricted to horizontal component data. Using all receiver stations and all components per station, NNLS results are relatively insensitive to a sub-sampled frequency spectrum, suggesting that coarse frequency-domain sampling may be adequate for good target resolution. Results from DLS are insensitive to diminishing array density, but contain spatially oscillatory structure. DLS-generated images are consistently centered at the known point source location, despite an abundance of surrounding structure.
Exploring Near-Field Radiative Heat Transfer for Thermo-photovoltaic Applications

NASA Astrophysics Data System (ADS)

Ganjeh, Yashar; Song, Bai; Sadat, Seid; Thompson, Dakotah; Fiorino, Anthony; Reddy, Pramod; Meyhofer, Edgar

2014-03-01

Understanding near-field radiative heat transfer (NFRHT) is critical for developing efficient thermo-photovoltaic devices. Theoretical predictions suggest that when the spatial separation of two parallel planes at different temperatures is less than their Wien's thermal wavelength, thermal transport via radiation can be greatly enhanced. The radiative heat flow across nanoscale gaps is predicted to be orders-of-magnitude higher than that given by Stefan-Boltzmann law, due to contribution of evanescent waves. In order to test these predictions, a novel experimental platform was designed and built enabling parallelization of two planar surfaces (50 μm by 50 μm) with 500 microradian resolution in their relative orientation. This platform was used to probe NFRHT between two planes and also between a plane and a sphere. It was found that, when a 50 μm diameter silica sphere was approximately 20 nm away from a 50 by 50 μm2 silica plane, a significant increase in radiative heat transfer coefficient was observed. This increase is 3 orders of magnitude higher than the value predicted by the blackbody limit. Other setups, including Au spheres and planes, and the plane-plane geometries are currently being investigated. 1) Army Research office (W911NF-12-1-0612), 2) NSF Thermal Transport Prcesses (CBET 1235691), 3) Center for Solar and Thermal Energy conversion, funded by the US Department of Energy, Office of Science, Basic Energy Sciences under award no. DE-SC0000957.
Innovative Technologies for Maskless Lithography and Non-Conventional Patterning

DTIC Science & Technology

2008-08-01

wave sources are used and quantitative data is produced on the local field intensities and scattered plane and plasmon wave amplitudes and phases...transistors”, Transducers 2007, Lyon, France, 3EH5.P, 2007. 9. D. Huang and V. Subramanian “Iodine-doped pentacene schottky diodes for high-frequency RFID...wave sources are used and quantitative data is produced on the local field intensities and scattered plane and plasmon wave amplitudes and phases
Reflection coefficient of qP, qS and SH at a plane boundary between viscoelastic TTI media

NASA Astrophysics Data System (ADS)

Wang, Hongwei; Peng, Suping

2016-01-01

This paper introduces a calculation method for the effective elastic stiffness tensor matrix of the viscous-elastic TTI medium based on the Chapman theory. We then obtain the phase velocity formula and seismic wave polarization formula of the viscous-elastic TTI medium, by solving the Christoffel equation; solve the phase angle of reflection and transmission wave through the numerical method in accordance with the wave slowness ellipsoid; on the basis of this assumption, and assuming that qP, qS and SH waves occurred simultaneously at the viscous-elastic anisotropic interface, establish the sixth-order Zoeppritz equation in accordance with the boundary conditions; establish the models for the upper and lower media which are viscous-elastic HTI, TTI, etc., on the basis of the sixth-order Zoeppritz equation; and study the impact of fracture dip angle, azimuth angle and frequency on the reflection coefficient. From this we obtain the following conclusions: the reflection coefficient can identify the fracture strike and dip when any information pertaining to the media is unknown; dispersion phenomenon is obvious on the axial plane of symmetry and weakened in the plane vertical to the axial plane of symmetry; the vertical-incidence longitudinal wave can stimulate the qS wave when the dip angle is not 0° or 90° under the condition of coincidence between the symmetry planes of the upper and lower media; when the symmetry planes of the upper and lower media do not coincide and the dip angle is not 0° or 90°, then the vertical-incidence qP will stimulate the qS and SH waves at the same time; the dip angle can cause the reflection coefficient curve to have a more obvious dispersion phenomenon, while the included angle between the symmetry planes of the upper and lower media will weaken the dispersion except SH; and the intercept of reflection coefficient is affected by the fracture dip and included angle between the symmetry planes of the upper and lower media.
Forward volume and surface magnetostatic modes in an yttrium iron garnet film for out-of-plane magnetic fields: Theory and experiment

NASA Astrophysics Data System (ADS)

Lim, Jinho; Bang, Wonbae; Trossman, Jonathan; Amanov, Dovran; Ketterson, John B.

2018-05-01

We present experimental and theoretical results on the propagation of magnetostatic spin waves in a film of yttrium iron garnet (YIG) for out-of-plane magnetic fields for which propagation in opposite directions is nonreciprocal in the presence of a metal layer. The plane studied is defined by the film normal n and n × k where k is the wave vector of the mode. Spin waves in this setting are classified as forward volume waves or surface waves and display non-reciprocity in the presence of an adjacent metal layer except for when H//n. The measurements are carried out in a transmission geometry, and a microwave mixer is used to measure the change of phase, and with it the evolution of wavevector, of the arriving spin wave with external magnetic field.
Detecting the chaotic nature in a transitional boundary layer using symbolic information-theory quantifiers.

PubMed

Zhang, Wen; Liu, Peiqing; Guo, Hao; Wang, Jinjun

2017-11-01

The permutation entropy and the statistical complexity are employed to study the boundary-layer transition induced by the surface roughness. The velocity signals measured in the transition process are analyzed with these symbolic quantifiers, as well as the complexity-entropy causality plane, and the chaotic nature of the instability fluctuations is identified. The frequency of the dominant fluctuations has been found according to the time scales corresponding to the extreme values of the symbolic quantifiers. The laminar-turbulent transition process is accompanied by the evolution in the degree of organization of the complex eddy motions, which is also characterized with the growing smaller and flatter circles in the complexity-entropy causality plane. With the help of the permutation entropy and the statistical complexity, the differences between the chaotic fluctuations detected in the experiments and the classical Tollmien-Schlichting wave are shown and discussed. It is also found that the chaotic features of the instability fluctuations can be approximated with a number of regular sine waves superimposed on the fluctuations of the undisturbed laminar boundary layer. This result is related to the physical mechanism in the generation of the instability fluctuations, which is the noise-induced chaos.
Detecting the chaotic nature in a transitional boundary layer using symbolic information-theory quantifiers

NASA Astrophysics Data System (ADS)

Zhang, Wen; Liu, Peiqing; Guo, Hao; Wang, Jinjun

2017-11-01

The permutation entropy and the statistical complexity are employed to study the boundary-layer transition induced by the surface roughness. The velocity signals measured in the transition process are analyzed with these symbolic quantifiers, as well as the complexity-entropy causality plane, and the chaotic nature of the instability fluctuations is identified. The frequency of the dominant fluctuations has been found according to the time scales corresponding to the extreme values of the symbolic quantifiers. The laminar-turbulent transition process is accompanied by the evolution in the degree of organization of the complex eddy motions, which is also characterized with the growing smaller and flatter circles in the complexity-entropy causality plane. With the help of the permutation entropy and the statistical complexity, the differences between the chaotic fluctuations detected in the experiments and the classical Tollmien-Schlichting wave are shown and discussed. It is also found that the chaotic features of the instability fluctuations can be approximated with a number of regular sine waves superimposed on the fluctuations of the undisturbed laminar boundary layer. This result is related to the physical mechanism in the generation of the instability fluctuations, which is the noise-induced chaos.
Compressed modes for variational problems in mathematical physics and compactly supported multiresolution basis for the Laplace operator

NASA Astrophysics Data System (ADS)

Ozolins, Vidvuds; Lai, Rongjie; Caflisch, Russel; Osher, Stanley

2014-03-01

We will describe a general formalism for obtaining spatially localized (``sparse'') solutions to a class of problems in mathematical physics, which can be recast as variational optimization problems, such as the important case of Schrödinger's equation in quantum mechanics. Sparsity is achieved by adding an L1 regularization term to the variational principle, which is shown to yield solutions with compact support (``compressed modes''). Linear combinations of these modes approximate the eigenvalue spectrum and eigenfunctions in a systematically improvable manner, and the localization properties of compressed modes make them an attractive choice for use with efficient numerical algorithms that scale linearly with the problem size. In addition, we introduce an L1 regularized variational framework for developing a spatially localized basis, compressed plane waves (CPWs), that spans the eigenspace of a differential operator, for instance, the Laplace operator. Our approach generalizes the concept of plane waves to an orthogonal real-space basis with multiresolution capabilities. Supported by NSF Award DMR-1106024 (VO), DOE Contract No. DE-FG02-05ER25710 (RC) and ONR Grant No. N00014-11-1-719 (SO).
Theoretical calculation of electron-positron momentum density in YBa 2Cu 3O 7-δ

NASA Astrophysics Data System (ADS)

Massidda, S.

1990-07-01

We present calculations of the electron-positron momentum density for the high- Tc superconductor YBa 2Cu 3O 7-δ for δ=0 and for the insulating parent compound YBa 2Cu 3O 6, based on first-principle electronic structure calculations performed within the local density approximation (LDA) using the full potential linearized augmented plane wave (FLAPW) method. Our results indicate a small overlap of the positron wave function with the CuO 2 plane electrons and, as a consequence, relatively small signals due to the related Fermi surfaces. By contrast, the present calculations show, after the folding of Umklapp terms according to Lock, Crisp and West, clear Fermi surface breaks arising from the Cu-O chain bands. No general agreement with existing experiments allows a clear definition of Fermi surface structures in the latter. A comparison of the calculated momentum with the experimental two-dimensional angular correlation of annihilation radiation (2D-ACAR) recently measured in Geneva shows an overall agreement for the insulating compound, despite the spurious LDA metallic state, and possibly suggests the importance of O vacancies in experiments performed on non-stoichiometric YBa 2Cu 3O 7-δ samples.
Electronic and optical properties of Praseodymium trifluoride

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saini, Sapan Mohan, E-mail: smsaini.phy@nitrr.ac.in

2014-10-24

We report the role of f- states on electronic and optical properties of Praseodymium trifluoride (PrF{sub 3}) compound. Full potential linearized augmented plane wave (FPLAPW) method with the inclusion of spin orbit coupling has been used. We employed the local spin density approximation (LSDA) and Coulomb-corrected local spin density approximation (LSDA+U). LSDA+U is known for treating the highly correlated 4f electrons properly. Our theoretical investigation shows that LSDA+U approximation reproduce the correct insulating ground state of PrF{sub 3}. On the other hand there is no significant difference of reflectivity calculated by LSDA and LSDA+U. We find that the reflectivity formore » PrF{sub 3} compound stays low till around 7 eV which is consistent with their large energy gaps. Our calculated reflectivity compares well with the experimental data. The results are analyzed in the light of transitions involved.« less
Performance of Gas Scintillation Proportional Counter Array for High-Energy X-Ray Observatory

NASA Technical Reports Server (NTRS)

Gubarev, Mikhail; Ramsey, Brian; Apple, Jeffery

2004-01-01

A focal plane array of high-pressure gas scintillation proportional counters (GSPC) for a High Energy X-Ray Observatory (HERO) is developed at the Marshall Space Flight Center. The array is consisted from eight GSPCs and is a part of balloon born payload scheduled to flight in May 2004. These detectors have an active area of approximately 20 square centimeters, and are filled with a high pressure (10(exp 6) Pa) xenon-helium mixture. Imaging is via crossed-grid position-sensitive phototubes sensitive in the UV region. The performance of the GSPC is well matched to that of the telescopes x-ray optics which have response to 75 keV and a focal spot size of approximately 500 microns. The detector's energy resolution, 4% FWHM at 60 keV, is adequate for resolving the broad spectral lines of astrophysical importance and for accurate continuum measurements. Results of the on-earth detector calibration will be presented and in-flight detector performance will be provided, as available.
Air-coupled ultrasonic through-transmission thickness measurements of steel plates.

PubMed

Waag, Grunde; Hoff, Lars; Norli, Petter

2015-02-01

Non-destructive ultrasonic testing of steel structures provide valuable information in e.g. inspection of pipes, ships and offshore structures. In many practical applications, contact measurements are cumbersome or not possible, and air-coupled ultrasound can provide a solution. This paper presents air-coupled ultrasonic through-transmission measurements on a steel plate with thicknesses 10.15 mm; 10.0 mm; 9.8 mm. Ultrasound pulses were transmitted from a piezoelectric transducer at normal incidence, through the steel plate, and were received at the opposite side. The S1, A2 and A3 modes of the plate are excited, with resonance frequencies that depend on the material properties and the thickness of the plate. The results show that the resonances could be clearly identified after transmission through the steel plate, and that the frequencies of the resonances could be used to distinguish between the three plate thicknesses. The S1-mode resonance was observed to be shifted 10% down compared to a simple plane wave half-wave resonance model, while the A2 and S2 modes were found approximately at the corresponding plane-wave resonance frequencies. A model based on the angular spectrum method was used to predict the response of the through-transmission setup. This model included the finite aperture of the transmitter and receiver, and compressional and shear waves in the solid. The model predicts the frequencies of the observed modes of the plate to within 1%, including the down-shift of the S1-mode. Copyright © 2014 Elsevier B.V. All rights reserved.
In-duct identification of fluid-borne source with high spatial resolution

NASA Astrophysics Data System (ADS)

Heo, Yong-Ho; Ih, Jeong-Guon; Bodén, Hans

2014-11-01

Source identification of acoustic characteristics of in-duct fluid machinery is required for coping with the fluid-borne noise. By knowing the acoustic pressure and particle velocity field at the source plane in detail, the sound generation mechanism of a fluid machine can be understood. The identified spatial distribution of the strength of major radiators would be useful for the low noise design. Conventional methods for measuring the source in a wide duct have not been very helpful in investigating the source properties in detail because their spatial resolution is improper for the design purpose. In this work, an inverse method to estimate the source parameters with a high spatial resolution is studied. The theoretical formulation including the evanescent modes and near-field measurement data is given for a wide duct. After validating the proposed method to a duct excited by an acoustic driver, an experiment on a duct system driven by an air blower is conducted in the presence of flow. A convergence test for the evanescent modes is performed to find the necessary number of modes to regenerate the measured pressure field precisely. By using the converged modal amplitudes, very-close near-field pressure to the source is regenerated and compared with the measured pressure, and the maximum error was -16.3 dB. The source parameters are restored from the converged modal amplitudes. Then, the distribution of source parameters on the driver and the blower is clearly revealed with a high spatial resolution for kR<1.84 in which range only plane waves can propagate to far field in a duct. Measurement using a flush mounted sensor array is discussed, and the removal of pure radial modes in the modeling is suggested.
COLLIMATION AND ASYMMETRY OF THE HOT BLAST WAVE FROM THE RECURRENT NOVA V745 Sco

DOE Office of Scientific and Technical Information (OSTI.GOV)

Drake, Jeremy J.; Kashyap, Vinay; Delgado, Laura

The recurrent symbiotic nova V745 Sco exploded on 2014 February 6 and was observed on February 22 and 23 by the Chandra X-ray Observatory Transmission Grating Spectrometers. By that time the supersoft source phase had already ended, and Chandra spectra are consistent with emission from a hot, shock-heated circumstellar medium with temperatures exceeding 10{sup 7} K. X-ray line profiles are more sharply peaked than expected for a spherically symmetric blast wave, with a full width at zero intensity of approximately 2400 km s{sup 1}, an FWHM of 1200 ± 30 km s{sup 1}, and an average net blueshift of 165more » ± 10 km s{sup 1}. The red wings of lines are increasingly absorbed toward longer wavelengths by material within the remnant. We conclude that the blast wave was sculpted by an aspherical circumstellar medium in which an equatorial density enhancement plays a role, as in earlier symbiotic nova explosions. Expansion of the dominant X-ray-emitting material is aligned close to the plane of the sky and is most consistent with an orbit seen close to face-on. Comparison of an analytical blast wave model with the X-ray spectra, Swift observations, and near-infrared line widths indicates that the explosion energy was approximately 10{sup 43} erg and confirms an ejected mass of approximately 10{sup 7} M {sub ⊙}. The total mass lost is an order of magnitude lower than the accreted mass required to have initiated the explosion, indicating that the white dwarf is gaining mass and is a Type Ia supernova progenitor candidate.« less
Polarization independent and tunable plasmonic structure for mimicking electromagnetically induced transparency in the reflectance spectrum

NASA Astrophysics Data System (ADS)

Guo, B. S.; Loo, Y. L.; Ong, C. K.

2017-10-01

This paper proposes a plasmonic metamaterial that is able to mimic electromagnetically induced transparency in the reflectance spectrum within the GHz frequency range. Each meta-atom consists of a cross-slot structure as the bright resonator positioned on one side of the FR-4 substrate, and four spiral structures as the dark resonator located on the opposite side. Free space experimental results demonstrate that at normal incidence of plane wave, the metamaterial possesses the properties of tunability and polarization independence. In addition, based on simulation results the metamaterial also possesses slow wave property, with group refractive index of 56; and refractive-index-based sensing capability, with figure of merit of 6.1. In the strong coupling configuration, the plasma frequency and coupling constant of the metamaterial were calculated to be approximately 5.4 × 1010 rad s-1 and 9.8 × 109 rad s-1 respectively. While the respective damping constants of the bright resonator and dark resonator were calculated to be approximately 4.6 × 1010 rad s-1 and 1.9 × 1010 rad s-1.
Sound field reconstruction within an entire cavity by plane wave expansions using a spherical microphone array.

PubMed

Wang, Yan; Chen, Kean

2017-10-01

A spherical microphone array has proved effective in reconstructing an enclosed sound field by a superposition of spherical wave functions in Fourier domain. It allows successful reconstructions surrounding the array, but the accuracy will be degraded at a distance. In order to extend the effective reconstruction to the entire cavity, a plane-wave basis in space domain is used owing to its non-decaying propagating characteristic and compared with the conventional spherical wave function method in a low frequency sound field within a cylindrical cavity. The sensitivity to measurement noise, the effects of the numbers of plane waves, and measurement positions are discussed. Simulations show that under the same measurement conditions, the plane wave function method is superior in terms of reconstruction accuracy and data processing efficiency, that is, the entire sound field imaging can be achieved by only one time calculation instead of translations of local sets of coefficients with respect to every measurement position into a global one. An experiment was conducted inside an aircraft cabin mock-up for validation. Additionally, this method provides an alternative possibility to recover the coefficients of high order spherical wave functions in a global coordinate system without coordinate translations with respect to local origins.
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…
Magnetic antenna excitation of whistler modes. III. Group and phase velocities of wave packets

NASA Astrophysics Data System (ADS)

Urrutia, J. M.; Stenzel, R. L.

2015-07-01

The properties of whistler modes excited by single and multiple magnetic loop antennas have been investigated in a large laboratory plasma. A single loop excites a wavepacket, but an array of loops across the ambient magnetic field B0 excites approximate plane whistler modes. The single loop data are measured. The array patterns are obtained by linear superposition of experimental data shifted in space and time, which is valid in a uniform plasma and magnetic field for small amplitude waves. Phasing the array changes the angle of wave propagation. The antennas are excited by an rf tone burst whose propagating envelope and oscillations yield group and phase velocities. A single loop antenna with dipole moment across B0 excites wave packets whose topology resembles m = 1 helicon modes, but without radial boundaries. The phase surfaces are conical with propagation characteristics of Gendrin modes. The cones form near the antenna with comparable parallel and perpendicular phase velocities. A physical model for the wave excitation is given. When a wave burst is applied to a phased antenna array, the wave front propagates both along the array and into the plasma forming a "whistler wing" at the front. These laboratory observations may be relevant for excitation and detection of whistler modes in space plasmas.
Examining Coherency Scales, Substructure, and Propagation of Whistler Mode Chorus Elements With Magnetospheric Multiscale (MMS)

NASA Astrophysics Data System (ADS)

Turner, D. L.; Lee, J. H.; Claudepierre, S. G.; Fennell, J. F.; Blake, J. B.; Jaynes, A. N.; Leonard, T.; Wilder, F. D.; Ergun, R. E.; Baker, D. N.; Cohen, I. J.; Mauk, B. H.; Strangeway, R. J.; Hartley, D. P.; Kletzing, C. A.; Breuillard, H.; Le Contel, O.; Khotyaintsev, Yu. V.; Torbert, R. B.; Allen, R. C.; Burch, J. L.; Santolik, O.

2017-11-01

Whistler mode chorus waves are a naturally occurring electromagnetic emission observed in Earth's magnetosphere. Here, for the first time, data from NASA's Magnetospheric Multiscale (MMS) mission were used to analyze chorus waves in detail, including the calculation of chorus wave normal vectors, fi>k. A case study was examined from a period of substorm activity around the time of a conjunction between the MMS constellation and NASA's Van Allen Probes mission on 07 April 2016. Chorus wave activity was simultaneously observed by all six spacecraft over a broad range of L shells (5.5 < L < 8.5), magnetic local time (06:00 < MLT < 09:00), and magnetic latitude (-32° < MLAT < -15°), implying a large chorus active region. Eight chorus elements and their substructure were analyzed in detail with MMS. These chorus elements were all lower band and rising tone emissions, right-handed and nearly circularly polarized, and propagating away from the magnetic equator when they were observed at MMS (MLAT -31°). Most of the elements had "hook"-like signatures on their wave power spectra, characterized by enhanced wave power at flat or falling frequency following the peak, and all the elements exhibited complex and well-organized substructure observed consistently at all four MMS spacecraft at separations up to 70 km (60 km perpendicular and 38 km parallel to the background magnetic field). The waveforms in field-aligned coordinates also demonstrated that these waves were all phase coherent, allowing for the direct calculation of fi>k. Error estimates on calculated fi>k revealed that the plane wave approximation was valid for six of the eight elements and most of the subelements. The wave normal vectors were within 20-30° from the direction antiparallel to the background field for all elements and changed from subelement to subelement through at least two of the eight elements. The azimuthal angle of fi>k in the perpendicular plane was oriented earthward and was oblique to that of the Poynting vector, which has implications for the validity of cold plasma theory.
Globally Convergent Inverse Reconstruction Algorithm for Detection of IEDs via Imaging of Spatially Distributed Dielectric Constants using Microwave

DTIC Science & Technology

2010-04-27

Dirichlet boundary data DP̃ (x, y) at the entire plane P̃ . Then one can solve the following boundary value problem in the half space below P̃ ∆w − s2w...which we wanted to be a plane wave when reaching the bottom side of the prism of Figure 1, where measurements were conducted. But actually this 14 was a...initializing wave field is a plane wave. On the other hand, a visual inspection of the output experimental data has revealed to us that actually we had a

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