Theory and application of equivalent transformation relationships between plane wave and spherical wave

NASA Astrophysics Data System (ADS)

Wang, Yao; Yang, Zailin; Zhang, Jianwei; Yang, Yong

2017-10-01

Based on the governing equations and the equivalent models, we propose an equivalent transformation relationships between a plane wave in a one-dimensional medium and a spherical wave in globular geometry with radially inhomogeneous properties. These equivalent relationships can help us to obtain the analytical solutions of the elastodynamic issues in an inhomogeneous medium. The physical essence of the presented equivalent transformations is the equivalent relationships between the geometry and the material properties. It indicates that the spherical wave problem in globular geometry can be transformed into the plane wave problem in the bar with variable property fields, and its inverse transformation is valid as well. Four different examples of wave motion problems in the inhomogeneous media are solved based on the presented equivalent relationships. We obtain two basic analytical solution forms in Examples I and II, investigate the reflection behavior of inhomogeneous half-space in Example III, and exhibit a special inhomogeneity in Example IV, which can keep the traveling spherical wave in constant amplitude. This study implies that our idea makes solving the associated problem easier.

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.

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.

Ion-acoustic solitons do not exist in cylindrical and spherical geometries

NASA Astrophysics Data System (ADS)

Sheridan, T. E.

2017-09-01

We investigate the time evolution of one-dimensional, compressive, ion acoustic solitary waves for planar, cylindrical, and spherical geometries in a plasma of cold fluid ions and Boltzmann electrons. For cylindrical and spherical geometries, we show that inward (outward) going solitary waves cannot be localized (i.e., always have a tail) since the effect of a unipolar velocity perturbation is to shift ions inward (outward) to smaller (larger) radii, thereby increasing (decreasing) the local ion density. That is, there are no quasi-particle soliton states in the cylindrical and spherical cases. These results are confirmed and expanded using a plasma simulation for the cylindrical case. We initialize the system with an inward propagating planar soliton. We find supersonic solitary waves which increase in speed as they near the origin, while the wave amplitude increases as r-1/2. All solitary waves develop the predicted tail, but for larger amplitudes, the tail is unstable and evolves into an acoustic wave train.

Local spin density functional investigations of a manganite with perovskite-type derived structures

NASA Astrophysics Data System (ADS)

Matar, S. F.; Studer, F.; Siberchicot, B.; Subramanian, M. A.; Demazeau, G.; Etourneau, J.

1998-11-01

The electronic and magnetic structures of the perovskite CaMnO3 are self-consistently calculated assuming two crystal structures at the same formula unit volume within the local spin density functional theory and the augmented spherical wave (ASW) method. From the comparisons of energy differences between the different magnetic states the ground state configuration is an insulator with G-type ordering. This result together with the magnitudes of the magnetic moments are in agreement with experiment. The influence of mixing between Mn and O is found spin dependent from the analysis of the crystal orbital overlap population (COOP) which enable to describe the chemical bond. The calculations underline a feature of a half metallic ferromagnet which could be connected with the colossal magnetoresistance (CMR) property of related compounds.

Photographic laboratory studies of explosions.

NASA Technical Reports Server (NTRS)

Kamel, M. M.; Oppenheim, A. K.

1973-01-01

Description of a series of cinematographic studies of explosions made with a high-speed rotating-mirror streak camera which uses a high-frequency stroboscopic ruby laser as the light source. The results obtained mainly concern explosions initiated by focused laser irradiation from a pulsed neodymium laser in a detonating gas consisting essentially of an equimolar mixture of acetylene and oxygen at an initial pressure of 100 torr at room temperature. Among the most significant observations were observations of a spherical blast wave preceded by a Chapman-Jouguet detonation which is stabilized immediately after initiation, the merging of a spherical flame with a shock front of the blast wave in which the flame is propagating, the division of a spherical detonation front into a shock wave and flame, and the generation of shock waves by a network of spherical flames.

Spherical-wave expansions of piston-radiator fields.

PubMed

Wittmann, R C; Yaghjian, A D

1991-09-01

Simple spherical-wave expansions of the continuous-wave fields of a circular piston radiator in a rigid baffle are derived. These expansions are valid throughout the illuminated half-space and are useful for efficient numerical computation in the near-field region. Multipole coefficients are given by closed-form expressions which can be evaluated recursively.

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.

Detonation wave augmentation of gas turbines

NASA Technical Reports Server (NTRS)

Wortman, A.

1984-01-01

The results of a feasibility study that examined the effects of using detonation waves to augment the performance of gas turbines are reported. The central ideas were to reduce compressor requirements and to maintain high performance in jet engines. Gasdynamic equations were used to model the flows associated with shock waves generated by the detonation of fuel in detonator tubes. Shock wave attenuation to the level of Mach waves was found possible, thus eliminating interference with the compressor and the necessity of valves and seals. A preliminary parametric study of the performance of a compressor working at a 4:1 ratio in a conceptual design of a detonation wave augmented jet engine in subsonic flight indicated a clear superiority over conventional designs in terms of fuel efficiency and thrust.

Impulsive spherical gravitational waves

NASA Astrophysics Data System (ADS)

Aliev, A. N.; Nutku, Y.

2001-03-01

Penrose's identification with warp provides the general framework for constructing the continuous form of impulsive gravitational wave metrics. We present the two-component spinor formalism for the derivation of the full family of impulsive spherical gravitational wave metrics which brings out the power in identification with warp and leads to the simplest derivation of exact solutions. These solutions of the Einstein vacuum field equations are obtained by cutting Minkowski space into two pieces along a null cone and re-identifying them with warp which is given by an arbitrary nonlinear holomorphic transformation. Using two-component spinor techniques we construct a new metric describing an impulsive spherical gravitational wave where the vertex of the null cone lies on a worldline with constant acceleration.

Nonlinear Interaction of Waves in Rotating Spherical Layers

NASA Astrophysics Data System (ADS)

Zhilenko, D.; Krivonosova, O.; Gritsevich, M.

2018-01-01

Flows of a viscous incompressible fluid in a spherical layer that are due to rotational oscillations of its inner boundary at two frequencies with respect to the state of rest are numerically studied. It is found that an increase in the amplitude of oscillations of the boundary at the higher frequency can result in a significant enhancement of the low-frequency mode in a flow near the outer boundary. The direction of propagation of the low-frequency wave changes from radial to meridional, whereas the high-frequency wave propagates in the radial direction in a limited inner region of the spherical layer. The role of the meridional circulation in the energy exchange between spaced waves is demonstrated.

Expressions for the spherical-wave-structure function based on a bump spectrum model for the index of refraction

NASA Astrophysics Data System (ADS)

Richardson, Christina E.; Andrews, Larry C.

1991-07-01

New spectra models have recently been developed for the spatial power spectra of temperature and refractive index fluctuations in the atmospheric boundary layer showing the characteristic 'bump' just prior to the dissipation ranges. Theoretical work involving these new models has led to new expressions for the phase structure function associated with a plane optical wave, although most experimental work has involved spherical waves. Following techniques similar to those used for the plane wave analysis, new expressions valid in geometrical and diffraction regimes are developed here for the phase structure function of a spherical optical wave propagating through clear-air atmospheric turbulence. Useful asymptotic formulas for small separation distances and the inertial subrange are derived from these general expressions.

On the Interaction and Coalescence if Spherical Blast Waves

NASA Technical Reports Server (NTRS)

Kandula, Max; Freeman, Robert J.

2005-01-01

The scaling and similarity laws concerning the propagation of isolated spherical blast waves are briefly reviewed. Both point source explosions and high pressure gas explosions are considered. Test data on blast overpressure from the interaction and coalescence of spherical blast waves emanating from explosives in the form of shaped charges of different strength placed in the vicinity of a solid propellant stack are presented. These data are discussed with regard to the scaling laws concerning the decay of blast overpressure. The results point out the possibility of detecting source explosions from far-field pressure measurements.

Reappraisal of the corticothalamic and thalamocortical interactions that contribute to the augmenting response in the rat.

PubMed

Mishima, K; Ohta, M

1992-01-01

In urethane-anesthetized rats, low frequency electrical stimulation of the thalamic radiation (TR) evoked an augmenting response in the somatosensory cortex (SCx) which was followed by rhythmic slow waves. The augmenting response mainly consists of the incremental secondary response (II-response). Simultaneously, augmentation also occurs in the ventrobasal nucleus of thalamus (VB) on the late component responses, C- and D-waves, to TR stimulation. The latencies of these augmented responses were shorter for the C-wave and the accompanying unit discharges in the VB relay neurons than for the D-wave and the II-response. We hypothesized that the thalamo-cortico-thalamic reverberating circuit was crucial in generating the augmenting response in the SCx. To test this hypothesis, an attempt was made to block temporarily the corticothalamic glutamatergic transmission by means of microinjections of kynurenate (KYN), an antagonist of glutamate, into the VB with a dose of more than 2 mM. This local procedure blocked all of the augmenting phenomena completely with a full recovery after the duration that depended on the dose of KYN. Besides, in the stage of complete blocking of the II-response to the test TR stimuli, the augmentation was able to be restored by adding a short train of high frequency TR stimuli that mimicked a burst discharge of VB relay neurons. These results in support of the hypothesis would reappraise the functional significance of the reverberating circuit in augmentation that has recently been controversial.

Towards anti-causal Green's function for three-dimensional sub-diffraction focusing

NASA Astrophysics Data System (ADS)

Ma, Guancong; Fan, Xiying; Ma, Fuyin; de Rosny, Julien; Sheng, Ping; Fink, Mathias

2018-06-01

In causal physics, the causal Green's function describes the radiation of a point source. Its counterpart, the anti-causal Green's function, depicts a spherically converging wave. However, in free space, any converging wave must be followed by a diverging one. Their interference gives rise to the diffraction limit that constrains the smallest possible dimension of a wave's focal spot in free space, which is half the wavelength. Here, we show with three-dimensional acoustic experiments that we can realize a stand-alone anti-causal Green's function in a large portion of space up to a subwavelength distance from the focus point by introducing a near-perfect absorber for spherical waves at the focus. We build this subwavelength absorber based on membrane-type acoustic metamaterial, and experimentally demonstrate focusing of spherical waves beyond the diffraction limit.

Removal of pinned scroll waves in cardiac tissues by electric fields in a generic model of three-dimensional excitable media.

PubMed

Pan, De-Bei; Gao, Xiang; Feng, Xia; Pan, Jun-Ting; Zhang, Hong

2016-02-24

Spirals or scroll waves pinned to heterogeneities in cardiac tissues may cause lethal arrhythmias. To unpin these life-threatening spiral waves, methods of wave emission from heterogeneities (WEH) induced by low-voltage pulsed DC electric fields (PDCEFs) and circularly polarized electric fields (CPEFs) have been used in two-dimensional (2D) cardiac tissues. Nevertheless, the unpinning of scroll waves in three-dimensional (3D) cardiac systems is much more difficult than that of spiral waves in 2D cardiac systems, and there are few reports on the removal of pinned scroll waves in 3D cardiac tissues by electric fields. In this article, we investigate in detail the removal of pinned scroll waves in a generic model of 3D excitable media using PDCEF, AC electric field (ACEF) and CPEF, respectively. We find that spherical waves can be induced from the heterogeneities by these electric fields in initially quiescent excitable media. However, only CPEF can induce spherical waves with frequencies higher than that of the pinned scroll wave. Such higher-frequency spherical waves induced by CPEF can be used to drive the pinned scroll wave out of the cardiac systems. We hope this remarkable ability of CPEF can provide a better alternative to terminate arrhythmias caused by pinned scroll waves.

On the importance of local orbitals using second energy derivatives for d and f electrons

NASA Astrophysics Data System (ADS)

Karsai, Ferenc; Tran, Fabien; Blaha, Peter

2017-11-01

The all-electron linearized augmented plane wave (LAPW) methods are among the most accurate to solve the Kohn-Sham equations of density functional theory for periodic solids. In the LAPW methods, the unit cell is partitioned into spheres surrounding the atoms, inside which the wave functions are expanded into spherical harmonics, and the interstitial region, where the wave functions are expanded in Fourier series. Recently, Michalicek et al. (2013) reported an analysis of the so-called linearization error, which is inherent to the basis functions inside the spheres, and advocated the use of local orbital basis functions involving the second energy derivative of the radial part (HDLO). In the present work, we report the implementation of such basis functions into the WIEN2k code, and discuss in detail the improvement in terms of accuracy. From our tests, which involve atoms from the whole periodic table, it is concluded that for ground-state properties (e.g., equilibrium volume) the use of HDLO is necessary only for atoms with d or f electrons in the valence and large atomic spheres. For unoccupied states which are not too high above the Fermi energy, HDLO systematically improve the band structure, which may be of importance for the calculation of optical properties.

An Electron is the God Particle

NASA Astrophysics Data System (ADS)

Wolff, Milo

2001-04-01

Philosophers, Clifford, Mach, Einstein, Wyle, Dirac & Schroedinger, believed that only a wave structure of particles could satisfy experiment and fulfill reality. A quantum Wave Structure of Matter is described here. It predicts the natural laws more accurately and completely than classic laws. Einstein reasoned that the universe depends on particles which are "spherically, spatially extended in space." and "Hence a discrete material particle has no place as a fundamental concept in a field theory." Thus the discrete point particle was wrong. He deduced the true electron is primal because its force range is infinite. Now, it is found the electron's wave structure contains the laws of Nature that rule the universe. The electron plays the role of creator - the God particle. Electron structure is a pair of spherical outward/inward quantum waves, convergent to a center in 3D space. This wave pair creates a h/4pi quantum spin when the in-wave spherically rotates to become the out-wave. Both waves form a spinor satisfying the Dirac Equation. Thus, the universe is binary like a computer. Reference: http://members.tripod.com/mwolff

Huygens-Fresnel picture for electron-molecule elastic scattering★

NASA Astrophysics Data System (ADS)

Baltenkov, Arkadiy S.; Msezane, Alfred Z.

2017-11-01

The elastic scattering cross sections for a slow electron by C2 and H2 molecules have been calculated within the framework of the non-overlapping atomic potential model. For the amplitudes of the multiple electron scattering by a target the wave function of the molecular continuum is represented as a combination of a plane wave and two spherical waves generated by the centers of atomic spheres. This wave function obeys the Huygens-Fresnel principle according to which the electron wave scattering by a system of two centers is accompanied by generation of two spherical waves; their interaction creates a diffraction pattern far from the target. Each of the Huygens waves, in turn, is a superposition of the partial spherical waves with different orbital angular momenta l and their projections m. The amplitudes of these partial waves are defined by the corresponding phases of electron elastic scattering by an isolated atomic potential. In numerical calculations the s- and p-phase shifts are taken into account. So the number of interfering electron waves is equal to eight: two of which are the s-type waves and the remaining six waves are of the p-type with different m values. The calculation of the scattering amplitudes in closed form (rather than in the form of S-matrix expansion) is reduced to solving a system of eight inhomogeneous algebraic equations. The differential and total cross sections of electron scattering by fixed-in-space molecules and randomly oriented ones have been calculated as well. We conclude by discussing the special features of the S-matrix method for the case of arbitrary non-spherical potentials. Contribution to the Topical Issue "Low energy positron and electron interactions", edited by James Sullivan, Ron White, Michael Bromley, Ilya Fabrikant, and David Cassidy.

Simulation and scaling analysis of a spherical particle-laden blast wave

NASA Astrophysics Data System (ADS)

Ling, Y.; Balachandar, S.

2018-02-01

A spherical particle-laden blast wave, generated by a sudden release of a sphere of compressed gas-particle mixture, is investigated by numerical simulation. The present problem is a multiphase extension of the classic finite-source spherical blast-wave problem. The gas-particle flow can be fully determined by the initial radius of the spherical mixture and the properties of gas and particles. In many applications, the key dimensionless parameters, such as the initial pressure and density ratios between the compressed gas and the ambient air, can vary over a wide range. Parametric studies are thus performed to investigate the effects of these parameters on the characteristic time and spatial scales of the particle-laden blast wave, such as the maximum radius the contact discontinuity can reach and the time when the particle front crosses the contact discontinuity. A scaling analysis is conducted to establish a scaling relation between the characteristic scales and the controlling parameters. A length scale that incorporates the initial pressure ratio is proposed, which is able to approximately collapse the simulation results for the gas flow for a wide range of initial pressure ratios. This indicates that an approximate similarity solution for a spherical blast wave exists, which is independent of the initial pressure ratio. The approximate scaling is also valid for the particle front if the particles are small and closely follow the surrounding gas.

Simulation and scaling analysis of a spherical particle-laden blast wave

NASA Astrophysics Data System (ADS)

Ling, Y.; Balachandar, S.

2018-05-01

A spherical particle-laden blast wave, generated by a sudden release of a sphere of compressed gas-particle mixture, is investigated by numerical simulation. The present problem is a multiphase extension of the classic finite-source spherical blast-wave problem. The gas-particle flow can be fully determined by the initial radius of the spherical mixture and the properties of gas and particles. In many applications, the key dimensionless parameters, such as the initial pressure and density ratios between the compressed gas and the ambient air, can vary over a wide range. Parametric studies are thus performed to investigate the effects of these parameters on the characteristic time and spatial scales of the particle-laden blast wave, such as the maximum radius the contact discontinuity can reach and the time when the particle front crosses the contact discontinuity. A scaling analysis is conducted to establish a scaling relation between the characteristic scales and the controlling parameters. A length scale that incorporates the initial pressure ratio is proposed, which is able to approximately collapse the simulation results for the gas flow for a wide range of initial pressure ratios. This indicates that an approximate similarity solution for a spherical blast wave exists, which is independent of the initial pressure ratio. The approximate scaling is also valid for the particle front if the particles are small and closely follow the surrounding gas.

Formation and propagation of Love waves in a surface layer with a P-wave source. Technical report

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

Florence, A.L.; Miller, S.A.

The objective of this research is to investigate experimentally, and support with theoretical calculations, the formation and propagation of Love waves from a P-wave source due to scattering at material heterogeneities. The P-wave source is a spherical piezoelectric crystal cast in a surface layer of rock simulant overlaying a higher impedance granite substrate. Excitation of the piezoelectric crystal with a known voltage applies a spherical compressional pulse of known amplitude to the surrounding medium. Lateral heterogeneities cast in the surface layer convert incident P-wave energy into shear waves. The horizontally polarized shear waves (SH waves) trapped in the surface layermore » wave guide are the Love waves we will measure at the surface.« less

Analysis of scattering by a linear chain of spherical inclusions in an optical fiber

NASA Astrophysics Data System (ADS)

Chremmos, Ioannis D.; Uzunoglu, Nikolaos K.

2006-12-01

The scattering by a linear chain of spherical dielectric inclusions, embedded along the axis of an optical fiber, is analyzed using a rigorous integral equation formulation, based on the dyadic Green's function theory. The coupled electric field integral equations are solved by applying the Galerkin technique with Mie-type expansion of the field inside the spheres in terms of spherical waves. The analysis extends the previously studied case of a single spherical inhomogeneity inside a fiber to the multisphere-scattering case, by utilizing the classic translational addition theorems for spherical waves in order to analytically extract the direct-intersphere-coupling coefficients. Results for the transmitted and reflected power, on incidence of the fundamental HE11 mode, are presented for several cases.

Removal of pinned scroll waves in cardiac tissues by electric fields in a generic model of three-dimensional excitable media

PubMed Central

Pan, De-Bei; Gao, Xiang; Feng, Xia; Pan, Jun-Ting; Zhang, Hong

2016-01-01

Spirals or scroll waves pinned to heterogeneities in cardiac tissues may cause lethal arrhythmias. To unpin these life-threatening spiral waves, methods of wave emission from heterogeneities (WEH) induced by low-voltage pulsed DC electric fields (PDCEFs) and circularly polarized electric fields (CPEFs) have been used in two-dimensional (2D) cardiac tissues. Nevertheless, the unpinning of scroll waves in three-dimensional (3D) cardiac systems is much more difficult than that of spiral waves in 2D cardiac systems, and there are few reports on the removal of pinned scroll waves in 3D cardiac tissues by electric fields. In this article, we investigate in detail the removal of pinned scroll waves in a generic model of 3D excitable media using PDCEF, AC electric field (ACEF) and CPEF, respectively. We find that spherical waves can be induced from the heterogeneities by these electric fields in initially quiescent excitable media. However, only CPEF can induce spherical waves with frequencies higher than that of the pinned scroll wave. Such higher-frequency spherical waves induced by CPEF can be used to drive the pinned scroll wave out of the cardiac systems. We hope this remarkable ability of CPEF can provide a better alternative to terminate arrhythmias caused by pinned scroll waves. PMID:26905367

Tachycardia-dependent augmentation of "notched J waves" in a general patient population without ventricular fibrillation or cardiac arrest: not a repolarization but a depolarization abnormality?

PubMed

Aizawa, Yoshifusa; Sato, Masahito; Kitazawa, Hitoshi; Aizawa, Yoshiyasu; Takatsuki, Seiji; Oda, Eiji; Okabe, Masaaki; Fukuda, Keiichi

2015-02-01

J waves can be observed in individuals of the general population, but electrocardiographic characteristics are poorly understood. The purpose of this study was to examine the J-wave dynamicity in a general patient population. The responses of J waves (>0.1 mV above the isoelectric line in 2 contiguous leads) to varying RR intervals were analyzed. Patients with aborted sudden cardiac death, documented ventricular fibrillation, or a family history of sudden cardiac death were excluded. The J-wave amplitude was measured at baseline, in beats with short RR intervals in conducted atrial premature beats (APBs) or atrial stimulation during the electrophysiology study, and in the beats next to APBs with prolonged RR intervals. Mainly notched J waves were identified in 94 of 701 (24.5%) general patients (13.4%), and APBs were present in 23 of 94 (24.5%) patients. The mean baseline amplitude of J waves was 0.20 ± 0.06 mV at the baseline RR interval of 853 ± 152 ms, 0.25 ± 0.11 mV at the RR interval in the conducted APB of 545 ± 133 ms (P = .0018), and 0.19 ± 0.08 mV at the RR interval of 1146 ± 314 ms (P = .3102). The clinical characteristics were not different between patients with and without tachycardia-dependent augmentation of J waves. Augmentation of J waves was confirmed by the electrophysiology study: 0.28 ± 0.12 mV vs 0.42 ± 0.11 mV at baseline and in the beats of atrial stimulation, respectively (P = .0001). However, no bradycardia-dependent augmentation (>0.05 mV) was observed. Such tachycardia-dependent augmentation can represent depolarization abnormality rather than repolarization abnormality. J waves in a general patient population were augmented at shorter RR intervals, but not at prolonged RR intervals. Mechanistically, conduction delay is most likely responsible for this. Copyright © 2015 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.

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.

Experimental Investigation of Turbojet Thrust Augmentation Using an Ejector

DTIC Science & Technology

2007-03-01

mechanisms in which a particle can exchange energy. Thrust augmenting devices can be divided into two categories: ones that exchange net work or heat and...two categories from the energy equation discussion above. Thrust augmentation is achieved through turbulent entrainment where work and/or heat is...front sustained by compression waves from a trailing reaction zone. A deflagration wave is a subsonic flame front sustained by heat transfer

LETTER TO THE EDITOR: A disintegrating cosmic string

NASA Astrophysics Data System (ADS)

Griffiths, J. B.; Docherty, P.

2002-06-01

We present a simple sandwich gravitational wave of the Robinson-Trautman family. This is interpreted as representing a shock wave with a spherical wavefront which propagates into a Minkowski background minus a wedge (i.e. the background contains a cosmic string). The deficit angle (the tension) of the string decreases through the gravitational wave, which then ceases. This leaves an expanding spherical region of Minkowski space behind it. The decay of the cosmic string over a finite interval of retarded time may be considered to generate the gravitational wave.

Mean-square angle-of-arrival difference between two counter-propagating spherical waves in the presence of atmospheric turbulence.

PubMed

Chen, Chunyi; Yang, Huamin; Tong, Shoufeng; Lou, Yan

2015-09-21

The mean-square angle-of-arrival (AOA) difference between two counter-propagating spherical waves in atmospheric turbulence is theoretically formulated. Closed-form expressions for the path weighting functions are obtained. It is found that the diffraction and refraction effects of turbulent cells make negative and positive contributions to the mean-square AOA difference, respectively, and the turbulent cells located at the midpoint of the propagation path have no contributions to the mean-square AOA difference. If the mean-square AOA difference is separated into the refraction and diffraction parts, the refraction part always dominates the diffraction one, and the ratio of the diffraction part to the refraction one is never larger than 0.5 for any turbulence spectrum. Based on the expressions for the mean-square AOA difference, formulae for the correlation coefficient between the angles of arrival of two counter-propagating spherical waves in atmospheric turbulence are derived. Numerical calculations are carried out by considering that the turbulence spectrum has no path dependence. It is shown that the mean-square AOA difference always approximates to the variance of AOA fluctuations. It is found that the correlation coefficient between the angles of arrival in the x or y direction of two counter-propagating spherical waves ranges from 0.46 to 0.5, implying that the instantaneous angles of arrival of two counter-propagating spherical waves in atmospheric turbulence are far from being perfectly correlated even when the turbulence spectrum does not vary along the path.

Arterial Wave Reflection and Aortic Valve Calcification in an Elderly Community-Based Cohort

PubMed Central

Sera, Fusako; Russo, Cesare; Iwata, Shinichi; Jin, Zhezhen; Rundek, Tatjana; Elkind, Mitchell S.V.; Homma, Shunichi; Sacco, Ralph L.; Di Tullio, Marco R.

2015-01-01

Background Aortic valve calcification (AVC) without stenosis is common in the elderly, is associated with cardiovascular morbidity and mortality, and may progress to aortic valve stenosis. Arterial stiffness and pulse wave reflection are important components of proximal aortic hemodynamics, but their relationship with AVC is not established. Methods To investigate the relationship of arterial wave reflection and stiffness with AVC, pulse wave analysis and AVC evaluation by echocardiography were performed in 867 participants from the Cardiovascular Abnormalities and Brain Lesions (CABL) study. Participants were divided into 4 categories based on the severity and extent of AVC: 1) none or mild focal AVC; 2) mild diffuse AVC; 3) moderate-severe focal AVC; and 4) moderate-severe diffuse AVC. Central blood pressures and pulse pressure, total arterial compliance, augmentation index, and time to wave reflection were assessed using applanation tonometry. Results Indicators of arterial stiffness and wave reflection were significantly associated with AVC severity, except for central systolic and diastolic pressures and time to reflection. After adjustment for pertinent covariates (age, sex, race/ethnicity, and eGFR), only augmentation pressure (P = .02) and augmentation index (P = .002) were associated with the severity of AVC. Multivariable logistic regression analysis revealed that augmentation pressure (odds ratio per mmHg = 1.14; 95% confidence interval, 1.02–1.27; P = .02) and augmentation index (odds ratio per percentage point = 1.07; 95% confidence interval, 1.01–1.13; P = .02) were associated with an increase risk of moderate-severe diffuse AVC, even when central blood pressure value was included in the same model. Conclusions Arterial wave reflection is associated with AVC severity, independent of blood pressure values. Increased contribution of wave reflection to central blood pressure could be involved in the process leading to AVC. PMID:25600036

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.

A Spherical to Plane Wave Transformation Using a Reflectarray

NASA Technical Reports Server (NTRS)

Zaman, Afroz J.; Lee, Richard Q.

1997-01-01

A reflectarray has generally been used as a replacement for a reflector antenna. Using in this capacity, different configurations (prime focus, offset etc.) and various applications (dual frequency, scanning etc.) have been demonstrated with great success. Another potential application that has not been explored previously is the use of reflectarrays to compensate for phase errors in space power combining applications such as space-fed lens and power combining amplifier. In these applications, it is required to convert a spherical wave to a plane wave with proper phase correction added to each element of the reflectarray. This paper reports an experiment to investigate the feasibility of using a reflectarray as an alternative to a lens in space power combining. The experiment involves transforming a spherical wave from a orthomode horn to a plane wave at the horn aperture. The reflcctarray consists of square patches terminated in open stubs to provide necessary phase compensation. In this paper, preliminary results will be presented and the feasibility of such compensation scheme will be discussed.

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.

Acoustic manipulation of oscillating spherical bodies: Emergence of axial negative acoustic radiation force

NASA Astrophysics Data System (ADS)

Rajabi, Majid; Mojahed, Alireza

2016-11-01

In this paper, emergence of negative axial acoustic radiation force on a rigid oscillating spherical body is investigated for acoustic manipulation purposes. The problem of plane acoustic wave scattering from an oscillating spherical body submerged in an ideal acoustic fluid medium is solved. For the case of oscillating direction collinear with the wave propagation wave number vector (desired path), it has been shown that the acoustic radiation force, as a result of nonlinear acoustic wave interaction with bodies can be expressed as a linear function of incident wave field and the oscillation properties of the oscillator (i.e., amplitude and phase of oscillation). The negative (i.e., pulling effects) and positive (i.e., pushing effects) radiation force situations are divided in oscillation complex plane with a specific frequency-dependant straight line. This characteristic line defines the radiation force cancellation state. In order to investigate the stability of the mentioned manipulation strategy, the case of misaligned oscillation of sphere with the wave propagation direction is studied. The proposed methodology may suggest a novel concept of single-beam acoustic handling techniques based on smart carriers.

Exploration of high harmonic fast wave heating on the National Spherical Torus Experiment

NASA Astrophysics Data System (ADS)

Wilson, J. R.; Bell, R. E.; Bernabei, S.; Bitter, M.; Bonoli, P.; Gates, D.; Hosea, J.; LeBlanc, B.; Mau, T. K.; Medley, S.; Menard, J.; Mueller, D.; Ono, M.; Phillips, C. K.; Pinsker, R. I.; Raman, R.; Rosenberg, A.; Ryan, P.; Sabbagh, S.; Stutman, D.; Swain, D.; Takase, Y.; Wilgen, J.

2003-05-01

High harmonic fast wave (HHFW) heating has been proposed as a particularly attractive means for plasma heating and current drive in the high beta plasmas that are achievable in spherical torus (ST) devices. The National Spherical Torus Experiment (NSTX) [M. Ono, S. M. Kaye, S. Neumeyer et al., in Proceedings of the 18th IEEE/NPSS Symposium on Fusion Engineering, Albuquerque, 1999 (IEEE, Piscataway, NJ, 1999), p. 53] is such a device. An rf heating system has been installed on the NSTX to explore the physics of HHFW heating, current drive via rf waves and for use as a tool to demonstrate the attractiveness of the ST concept as a fusion device. To date, experiments have demonstrated many of the theoretical predictions for HHFW. In particular, strong wave absorption on electrons over a wide range of plasma parameters and wave parallel phase velocities, wave acceleration of energetic ions, and indications of current drive for directed wave spectra have been observed. In addition HHFW heating has been used to explore the energy transport properties of NSTX plasmas, to create H-mode discharges with a large fraction of bootstrap current and to control the plasma current profile during the early stages of the discharge.

Experimental investigation of blast mitigation and particle-blast interaction during the explosive dispersal of particles and liquids

NASA Astrophysics Data System (ADS)

Pontalier, Q.; Loiseau, J.; Goroshin, S.; Frost, D. L.

2018-04-01

The attenuation of a blast wave from a high-explosive charge surrounded by a layer of inert material is investigated experimentally in a spherical geometry for a wide range of materials. The blast wave pressure is inferred from extracting the blast wave velocity with high-speed video as well as direct measurements with pressure transducers. The mitigant consists of either a packed bed of particles, a particle bed saturated with water, or a homogeneous liquid. The reduction in peak blast wave overpressure is primarily dependent on the mitigant to explosive mass ratio, M/C, with the mitigant material properties playing a secondary role. Relative peak pressure mitigation reduces with distance and for low values of M/C (< 10) can return to unmitigated pressure levels in the mid-to-far field. Solid particles are more effective at mitigating the blast overpressure than liquids, particularly in the near field and at low values of M/C, suggesting that the energy dissipation during compaction, deformation, and fracture of the powders plays an important role. The difference in scaled arrival time of the blast and material fronts increases with M/C and scaled distance, with solid particles giving the largest separation between the blast wave and cloud of particles. Surrounding a high-explosive charge with a layer of particles reduces the positive-phase blast impulse, whereas a liquid layer has no influence on the impulse in the far field. Taking the total impulse due to the blast wave and material impact into account implies that the damage to a nearby structure may actually be augmented for a range of distances. These results should be taken into consideration in the design of explosive mitigant systems.

Experimental investigation of blast mitigation and particle-blast interaction during the explosive dispersal of particles and liquids

NASA Astrophysics Data System (ADS)

Pontalier, Q.; Loiseau, J.; Goroshin, S.; Frost, D. L.

2018-05-01

The attenuation of a blast wave from a high-explosive charge surrounded by a layer of inert material is investigated experimentally in a spherical geometry for a wide range of materials. The blast wave pressure is inferred from extracting the blast wave velocity with high-speed video as well as direct measurements with pressure transducers. The mitigant consists of either a packed bed of particles, a particle bed saturated with water, or a homogeneous liquid. The reduction in peak blast wave overpressure is primarily dependent on the mitigant to explosive mass ratio, M/ C, with the mitigant material properties playing a secondary role. Relative peak pressure mitigation reduces with distance and for low values of M/ C (< 10) can return to unmitigated pressure levels in the mid-to-far field. Solid particles are more effective at mitigating the blast overpressure than liquids, particularly in the near field and at low values of M/ C, suggesting that the energy dissipation during compaction, deformation, and fracture of the powders plays an important role. The difference in scaled arrival time of the blast and material fronts increases with M/ C and scaled distance, with solid particles giving the largest separation between the blast wave and cloud of particles. Surrounding a high-explosive charge with a layer of particles reduces the positive-phase blast impulse, whereas a liquid layer has no influence on the impulse in the far field. Taking the total impulse due to the blast wave and material impact into account implies that the damage to a nearby structure may actually be augmented for a range of distances. These results should be taken into consideration in the design of explosive mitigant systems.

Shear wave induced resonance elastography of spherical masses with polarized torsional waves

NASA Astrophysics Data System (ADS)

Hadj Henni, Anis; Schmitt, Cédric; Trop, Isabelle; Cloutier, Guy

2012-03-01

Shear wave induced resonance (SWIR) is a technique for dynamic ultrasound elastography of confined mechanical inclusions. It was developed for breast tumor imaging and tissue characterization. This method relies on the polarization of torsional shear waves modeled with the Helmholtz equation in spherical coordinates. To validate modeling, an invitro set-up was used to measure and image the first three eigenfrequencies and eigenmodes of a soft sphere. A preliminary invivo SWIR measurement on a breast fibroadenoma is also reported. Results revealed the potential of SWIR elastography to detect and mechanically characterize breast lesions for early cancer detection.

Shear wave induced resonance elastography of spherical masses with polarized torsional waves.

PubMed

Henni, Anis Hadj; Schmitt, Cédric; Trop, Isabelle; Cloutier, Guy

2012-03-26

Shear Wave Induced Resonance (SWIR) is a technique for dynamic ultrasound elastography of confined mechanical inclusions. It was developed for breast tumor imaging and tissue characterization. This method relies on the polarization of torsional shear waves modeled with the Helmholtz equation in spherical coordinates. To validate modeling, an in vitro set-up was used to measure and image the first three eigenfrequencies and eigenmodes of a soft sphere. A preliminary in vivo SWIR measurement on a breast fibroadenoma is also reported. Results revealed the potential of SWIR elastography to detect and mechanically characterize breast lesions for early cancer detection.

Symmetry of spherically converging shock waves through reflection, relating to the shock ignition fusion energy scheme.

PubMed

Davie, C J; Evans, R G

2013-05-03

We examine the properties of perturbed spherically imploding shock waves in an ideal fluid through the collapse, bounce, and development into an outgoing shock wave. We find broad conservation of the size and shape of ingoing and outgoing perturbations when viewed at the same radius. The outgoing shock recovers the velocity of the unperturbed shock outside the strongly distorted core. The results are presented in the context of the robustness of the shock ignition approach to inertial fusion energy.

Childhood Obesity Associates Haemodynamic and Vascular Changes That Result in Increased Central Aortic Pressure with Augmented Incident and Reflected Wave Components, without Changes in Peripheral Amplification

PubMed Central

Castro, Juan M.; García-Espinosa, Victoria; Curcio, Santiago; Arana, Maite; Chiesa, Pedro; Giachetto, Gustavo; Zócalo, Yanina; Bia, Daniel

2016-01-01

The aims were to determine if childhood obesity is associated with increased central aortic blood pressure (BP) and to characterize haemodynamic and vascular changes associated with BP changes in obese children and adolescents by means of analyzing changes in cardiac output (stroke volume, SV), arterial stiffness (aortic pulse wave velocity, PWV), peripheral vascular resistances (PVR), and net and relative contributions of reflected waves to the aortic pulse wave amplitude. We included 117 subjects (mean/range age: 10 (5–15) years, 49 females), who were obese (OB) or had normal weight (NW). Peripheral and central aortic BP, PWV, and pulse wave-derived parameters (augmentation index, amplitude of forward and backward components) were measured with tonometry (SphygmoCor) and oscillometry (Mobil-O-Graph). With independence of the presence of dyslipidemia, hypertension, or sedentarism, the aortic systolic and pulse BP were higher in OB than in NW subjects. The increase in central BP could not be explained by the elevation in the relative contribution of reflections to the aortic pressure wave and higher PVR or by an augmented peripheral reflection coefficient. Instead, the rise in central BP could be explained by an increase in the amplitude of both incident and reflect wave components associated to augmented SV and/or PWV. PMID:26881081

A spherical harmonic approach for the determination of HCP texture from ultrasound: A solution to the inverse problem

NASA Astrophysics Data System (ADS)

Lan, Bo; Lowe, Michael J. S.; Dunne, Fionn P. E.

2015-10-01

A new spherical convolution approach has been presented which couples HCP single crystal wave speed (the kernel function) with polycrystal c-axis pole distribution function to give the resultant polycrystal wave speed response. The three functions have been expressed as spherical harmonic expansions thus enabling application of the de-convolution technique to enable any one of the three to be determined from knowledge of the other two. Hence, the forward problem of determination of polycrystal wave speed from knowledge of single crystal wave speed response and the polycrystal pole distribution has been solved for a broad range of experimentally representative HCP polycrystal textures. The technique provides near-perfect representation of the sensitivity of wave speed to polycrystal texture as well as quantitative prediction of polycrystal wave speed. More importantly, a solution to the inverse problem is presented in which texture, as a c-axis distribution function, is determined from knowledge of the kernel function and the polycrystal wave speed response. It has also been explained why it has been widely reported in the literature that only texture coefficients up to 4th degree may be obtained from ultrasonic measurements. Finally, the de-convolution approach presented provides the potential for the measurement of polycrystal texture from ultrasonic wave speed measurements.

Resonance energy transfer: The unified theory via vector spherical harmonics

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

Grinter, Roger, E-mail: r.grinter@uea.ac.uk; Jones, Garth A., E-mail: garth.jones@uea.ac.uk

2016-08-21

In this work, we derive the well-established expression for the quantum amplitude associated with the resonance energy transfer (RET) process between a pair of molecules that are beyond wavefunction overlap. The novelty of this work is that the field of the mediating photon is described in terms of a spherical wave rather than a plane wave. The angular components of the field are constructed in terms of vector spherical harmonics while Hankel functions are used to define the radial component. This approach alleviates the problem of having to select physically correct solution from non-physical solutions, which seems to be inherentmore » in plane wave derivations. The spherical coordinate system allows one to easily decompose the photon’s fields into longitudinal and transverse components and offers a natural way to analyse near-, intermediate-, and far-zone RET within the context of the relative orientation of the transition dipole moments for the two molecules.« less

Sound Source Localization Using Non-Conformal Surface Sound Field Transformation Based on Spherical Harmonic Wave Decomposition

PubMed Central

Zhang, Lanyue; Ding, Dandan; Yang, Desen; Wang, Jia; Shi, Jie

2017-01-01

Spherical microphone arrays have been paid increasing attention for their ability to locate a sound source with arbitrary incident angle in three-dimensional space. Low-frequency sound sources are usually located by using spherical near-field acoustic holography. The reconstruction surface and holography surface are conformal surfaces in the conventional sound field transformation based on generalized Fourier transform. When the sound source is on the cylindrical surface, it is difficult to locate by using spherical surface conformal transform. The non-conformal sound field transformation by making a transfer matrix based on spherical harmonic wave decomposition is proposed in this paper, which can achieve the transformation of a spherical surface into a cylindrical surface by using spherical array data. The theoretical expressions of the proposed method are deduced, and the performance of the method is simulated. Moreover, the experiment of sound source localization by using a spherical array with randomly and uniformly distributed elements is carried out. Results show that the non-conformal surface sound field transformation from a spherical surface to a cylindrical surface is realized by using the proposed method. The localization deviation is around 0.01 m, and the resolution is around 0.3 m. The application of the spherical array is extended, and the localization ability of the spherical array is improved. PMID:28489065

Sample Design, Sample Augmentation, and Estimation for Wave 2 of the NSHAP

PubMed Central

English, Ned; Pedlow, Steven; Kwok, Peter K.

2014-01-01

Objectives. The sample for the second wave (2010) of National Social Life, Health, and Aging Project (NSHAP) was designed to increase the scientific value of the Wave 1 (2005) data set by revisiting sample members 5 years after their initial interviews and augmenting this sample where possible. Method. There were 2 important innovations. First, the scope of the study was expanded by collecting data from coresident spouses or romantic partners. Second, to maximize the representativeness of the Wave 2 data, nonrespondents from Wave 1 were again approached for interview in the Wave 2 sample. Results. The overall unconditional response rate for the Wave 2 panel was 74%; the conditional response rate of Wave 1 respondents was 89%; the conditional response rate of partners was 84%; and the conversion rate for Wave 1 nonrespondents was 26%. Discussion. The inclusion of coresident partners enhanced the study by allowing the examination of how intimate, household relationships are related to health trajectories and by augmenting the size of the NSHAP sample size for this and future waves. The uncommon strategy of returning to Wave 1 nonrespondents reduced potential bias by ensuring that to the extent possible the whole of the original sample forms the basis for the field effort. NSHAP Wave 2 achieved its field objectives of consolidating the panel, recruiting their resident spouses or romantic partners, and converting a significant proportion of Wave 1 nonrespondents. PMID:25360016

Acoustic manipulation of active spherical carriers: Generation of negative radiation force

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

Rajabi, Majid, E-mail: majid_rajabi@iust.ac.ir; Mojahed, Alireza

2016-09-15

This paper examines theoretically a novel mechanism of generating negative (pulling) radiation force for acoustic manipulation of spherical carriers equipped with piezoelectric actuators in its inner surface. In this mechanism, the spherical particle is handled by common plane progressive monochromatic acoustic waves instead of zero-/higher- order Bessel beams or standing waves field. The handling strategy is based on applying a spatially uniform harmonic electrical voltage at the piezoelectric actuator with the same frequency of handling acoustic waves, in order to change the radiation force effect from repulsive (away from source) to attractive (toward source). This study may be considered asmore » a start point for development of contact-free precise handling and entrapment technology of active carriers which are essential in many engineering and medicine applications.« less

Electron Bernstein waves in spherical torus plasmas

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

Saveliev, A. N.

2006-11-30

Propagation and absorption of the electron Bernstein waves (EBWs) in spherical tokamaks (STs) have been intensively discussed in recent years because the EBWs coupled with an externally launched electromagnetic beam seem to be the only opportunity for microwave plasma heating and current drive in the electron cyclotron (EC) frequency range in the STs. The whole problem of the electron Bernstein heating and current drive (EBWHCD) in spherical plasmas is naturally divided into three major parts: coupling of incident electromagnetic waves (EMWs) to the EBWs near the upper hybrid resonance (UHR) surface, propagation and absorption of the EBWs in the plasmamore » interior and generation of noninductive current driven by the EBWs. The present paper is a brief survey of the most important theoretical and numerical results on the issue of EBWs.« less

Approximation method for a spherical bound system in the quantum plasma

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

Mehramiz, A.; Sobhanian, S.; Mahmoodi, J.

2010-08-15

A system of quantum hydrodynamic equations has been used for investigating the dielectric tensor and dispersion equation of a semiconductor as a quantum magnetized plasma. Dispersion relations and their modifications due to quantum effects are derived for both longitudinal and transverse waves. The number of states and energy levels are analytically estimated for a spherical bound system embedded in a semiconductor quantum plasma. The results show that longitudinal waves decay rapidly and do not interact with the spherical bound system. The energy shifts caused by the spin-orbit interaction and the Zeeman effect are calculated.

Asynchronous arterial systolic expansion as a marker of vascular aging: assessment of the carotid artery with velocity vector imaging.

PubMed

Yang, Woo-In; Shim, Chi Y; Bang, Woo D; Oh, Chang M; Chang, Hyuk J; Chung, Namsik; Ha, Jong-Won

2011-12-01

Arterial elastic properties change with aging. Measurements of pulse wave velocity and augmentation index are useful for the evaluation of arterial stiffness. However, they likely represent only global characteristics of the arterial tree rather than local vascular alterations. The aim of this study was to evaluate whether local vascular properties assessed by velocity vector imaging differed with aging. Vascular properties of carotid arteries with ages were assessed in 100 healthy volunteers (52 men) ranging from 20 to 68 years using velocity vector imaging. The peak circumferential strain and strain rate of the six segments in left common carotid arteries were analyzed and the standard deviation of the time to peak circumferential strain and strain rate of the six segments, representing the synchronicity of the arterial expansion, were calculated. Central blood pressure, augmentation index and pulse wave velocity were assessed by commercially available radial artery tonometry, the SphygmoCor system (AtCor Medical, West Ryde, Australia). A validated generalized transfer function was used to acquire the central aortic pressures and pressure waveforms. Pulse wave velocity, augmentation index and velocity vector imaging parameters showed significant changes with age. However, the age-related changes in pulse wave velocity, augmentation index and velocity vector imaging parameters were different. The increase in pulse wave velocity was more prominent in older individuals, whereas the changes in augmentation index and carotid strain and strain rate were evident earlier, at the age of 30 years. Unlike augmentation index, which showed little change in older individuals, the standard deviation of time to peak strain and strain rate showed a steady increase from younger to older individuals. Asynchronous arterial expansion could be a useful discriminative marker of vascular aging independent of individual's age.

Spherical shock-wave propagation in three-dimensional granular packings.

PubMed

Xue, Kun; Bai, Chun-Hua

2011-02-01

We investigate numerically the spherical shock-wave propagation in an open dense granular packing perturbed by the sudden expansion of a spherical intruder in the interior of the pack, focusing on the correlation between geometrical fabrics and propagating properties. The measurements of the temporal and spatial variations in a variety of propagating properties define a consistent serrated wave substructure with characteristic length on the orders of particle diameters. Further inspection of particle packing reveals a well-defined particle layering that persists several particle diameters away from the intruder, although its dominant effects are only within one to two diameters. This interface-induced layering not only exactly coincides with the serrated wave profile, but also highlights the competition between two energy transmission mechanisms involving distinct transport speeds. The alternating dominances between these two mechanisms contribute to the nonlinear wave propagation on the particle scale. Moreover, the proliferation of intricate three-dimensional contact force networks suggests the anisotropic stress transmission, which is found to also arise from the localized packing structure in the vicinity of the intruder.

Shock waves raised by explosions in space as sources of ultra-high-energy cosmic rays

NASA Astrophysics Data System (ADS)

Kichigin, Gennadiy

2015-03-01

The paper discusses the possibility of particle acceleration up to ultrahigh energies in the relativistic waves generated by various explosive processes in the interstellar medium. We propose to use the surfatron mechanism of acceleration (surfing) of charged particles trapped in the front of relativistic waves as a generator of high-energy cosmic rays (CRs). Conditions under which surfing in these waves can be made are studied thoroughly. Ultra-high-energy CRs (up to 10^20 eV) are shown to be obtained due to the surfing in the relativistic plane and spherical waves. Surfing is supposed to take place in nonlinear Langmuir waves excited by powerful electromagnetic radiation or relativistic beams of charged particles, as well as in strong shock waves generated by relativistic jets or spherical formations that expand fast (fireballs).

Aortic stiffness predicts functional outcome in patients after ischemic stroke.

PubMed

Gasecki, Dariusz; Rojek, Agnieszka; Kwarciany, Mariusz; Kubach, Marlena; Boutouyrie, Pierre; Nyka, Walenty; Laurent, Stephane; Narkiewicz, Krzysztof

2012-02-01

Increased aortic stiffness (measured by carotid-femoral pulse wave velocity) and central augmentation index have been shown to independently predict cardiovascular events, including stroke. We studied whether pulse wave velocity and central augmentation index predict functional outcome after ischemic stroke. In a prospective study, we enrolled 99 patients with acute ischemic stroke (age 63.7 ± 12.4 years, admission National Institutes of Health Stroke Scale score 6.6 ± 6.6, mean ± SD). Carotid-femoral pulse wave velocity and central augmentation index (SphygmoCor) were measured 1 week after stroke onset. Functional outcome was evaluated 90 days after stroke using the modified Rankin Scale with modified Rankin Scale score of 0 to 1 considered an excellent outcome. In univariate analysis, low carotid-femoral pulse wave velocity (P=0.000001) and low central augmentation index (P=0.028) were significantly associated with excellent stroke outcome. Age, severity of stroke, presence of previous stroke, diabetes, heart rate, and peripheral pressures also predicted stroke functional outcome. In multivariate analysis, the predictive value of carotid-femoral pulse wave velocity (<9.4 m/s) remained significant (OR, 0.21; 95% CI, 0.06-0.79; P=0.02) after adjustment for age, National Institutes of Health Stroke Scale score on admission, and presence of previous stroke. By contrast, central augmentation index had no significant predictive value after adjustment. This study indicates that aortic stiffness is an independent predictor of functional outcome in patients with acute ischemic stroke.

Arterial wave reflection and aortic valve calcification in an elderly community-based cohort.

PubMed

Sera, Fusako; Russo, Cesare; Iwata, Shinichi; Jin, Zhezhen; Rundek, Tatjana; Elkind, Mitchell S V; Homma, Shunichi; Sacco, Ralph L; Di Tullio, Marco R

2015-04-01

Aortic valve calcification (AVC) without stenosis is common in the elderly, is associated with cardiovascular morbidity and mortality, and may progress to aortic valve stenosis. Arterial stiffness and pulse-wave reflection are important components of proximal aortic hemodynamics, but their relationship with AVC is not established. To investigate the relationship of arterial wave reflection and stiffness with AVC, pulse wave analysis and AVC evaluation by echocardiography were performed in 867 participants from the Cardiovascular Abnormalities and Brain Lesions study. Participants were divided into four categories on the basis of the severity and extent of AVC: (1) none or mild focal AVC, (2) mild diffuse AVC, (3) moderate to severe focal AVC, and (4) moderate to severe diffuse AVC. Central blood pressures and pulse pressure, total arterial compliance, augmentation index, and time to wave reflection were assessed using applanation tonometry. Indicators of arterial stiffness and wave reflection were significantly associated with AVC severity, except for central systolic and diastolic pressures and time to reflection. After adjustment for pertinent covariates (age, sex, race/ethnicity, and estimated glomerular filtration rate), only augmentation pressure (P = .02) and augmentation index (P = .002) were associated with the severity of AVC. Multivariate logistic regression analysis revealed that augmentation pressure (odds ratio per mm Hg, 1.14; 95% confidence interval, 1.02-1.27; P = .02) and augmentation index (odds ratio per percentage point, 1.07; 95% confidence interval, 1.01-1.13; P = .02) were associated with an increased risk for moderate to severe diffuse AVC, even when central blood pressure value was included in the same model. Arterial wave reflection is associated with AVC severity, independent of blood pressure values. Increased contribution of wave reflection to central blood pressure could be involved in the process leading to AVC. Copyright © 2015 American Society of Echocardiography. Published by Elsevier Inc. All rights reserved.

Exploration of High Harmonic Fast Wave Heating on the National Spherical Torus Experiment

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

J.R. Wilson; R.E. Bell; S. Bernabei

2003-02-11

High Harmonic Fast Wave (HHFW) heating has been proposed as a particularly attractive means for plasma heating and current drive in the high-beta plasmas that are achievable in spherical torus (ST) devices. The National Spherical Torus Experiment (NSTX) [Ono, M., Kaye, S.M., Neumeyer, S., et al., Proceedings, 18th IEEE/NPSS Symposium on Fusion Engineering, Albuquerque, 1999, (IEEE, Piscataway, NJ (1999), p. 53.)] is such a device. An radio-frequency (rf) heating system has been installed on NSTX to explore the physics of HHFW heating, current drive via rf waves and for use as a tool to demonstrate the attractiveness of the STmore » concept as a fusion device. To date, experiments have demonstrated many of the theoretical predictions for HHFW. In particular, strong wave absorption on electrons over a wide range of plasma parameters and wave parallel phase velocities, wave acceleration of energetic ions, and indications of current drive for directed wave spectra have been observed. In addition HHFW heating has been used to explore the energy transport properties of NSTX plasmas, to create H-mode (high-confinement mode) discharges with a large fraction of bootstrap current and to control the plasma current profile during the early stages of the discharge.« less

Augmented shock wave fracture/severance of materials

NASA Technical Reports Server (NTRS)

Schimmel, Morry L. (Inventor); Bement, Laurence J. (Inventor)

1995-01-01

The present invention related generally to severing materials, and more particularly to severing or weakening materials through explosively induced, augmented shock waves. Explosive cords are placed in grooves on the upper surface of the material to be severed or weakened. The explosive cords are initiated simultaneously to introduce explosive shock waves into the material. These shock waves progress toward the centerline between the explosive cords and the lower surface of the material. Intersecting and reflected waves produce a rarefaction zone on the centerline to fail the material in tension. A groove may also be cut in the lower surface of the material to aid in severing or weakening the material.

Regular and chaotic dynamics of non-spherical bodies. Zeldovich's pancakes and emission of very long gravitational waves

NASA Astrophysics Data System (ADS)

Bisnovatyi-Kogan, G. S.; Tsupko, O. Yu.

2015-10-01

> In this paper we review a recently developed approximate method for investigation of dynamics of compressible ellipsoidal figures. Collapse and subsequent behaviour are described by a system of ordinary differential equations for time evolution of semi-axes of a uniformly rotating, three-axis, uniform-density ellipsoid. First, we apply this approach to investigate dynamic stability of non-spherical bodies. We solve the equations that describe, in a simplified way, the Newtonian dynamics of a self-gravitating non-rotating spheroidal body. We find that, after loss of stability, a contraction to a singularity occurs only in a pure spherical collapse, and deviations from spherical symmetry prevent the contraction to the singularity through a stabilizing action of nonlinear non-spherical oscillations. The development of instability leads to the formation of a regularly or chaotically oscillating body, in which dynamical motion prevents the formation of the singularity. We find regions of chaotic and regular pulsations by constructing a Poincaré diagram. A real collapse occurs after damping of the oscillations because of energy losses, shock wave formation or viscosity. We use our approach to investigate approximately the first stages of collapse during the large scale structure formation. The theory of this process started from ideas of Ya. B. Zeldovich, concerning the formation of strongly non-spherical structures during nonlinear stages of the development of gravitational instability, known as `Zeldovich's pancakes'. In this paper the collapse of non-collisional dark matter and the formation of pancake structures are investigated approximately. Violent relaxation, mass and angular momentum losses are taken into account phenomenologically. We estimate an emission of very long gravitational waves during the collapse, and discuss the possibility of gravitational lensing and polarization of the cosmic microwave background by these waves.

Discontinuity-free edge-diffraction model for characterization of focused wave fields.

PubMed

Sedukhin, Andrey G

2010-03-01

A model of discontinuity-free edge diffraction is proposed that is valid in the framework of the scalar Debye approximation and describes the formation process and approximate structure of the stationary diffracted field of a monochromatic converging spherical wave of limited angular opening throughout the whole space about the focus. The field is represented semianalytically in terms of the sum of a direct quasi-spherical wave and two edge quasi-conical waves of the zeroth and first order. The angular spectrum amplitudes of all these waves have smooth continuous variations of the real and imaginary parts in polar angle and radius, the separable nonanalytic functions defining the polar-angle variations of the amplitudes being found by optimization techniques.

Analysis of Multi-Layered Materials Under High Velocity Impact Using CTH

DTIC Science & Technology

2008-03-01

of state . The other relationship deals with the deviatoric stress and is taken care of by the constitutive equations which are discussed in the next...models in CTH decompose the total stress tensor into the spherical and deviatoric parts. The spherical part of the stress tensor is the equation of state ...investigate the effects of wave propagation. Waves in rods are considered to create a state of

Measuring the radiation force of megahertz ultrasound acting on a solid spherical scatterer

NASA Astrophysics Data System (ADS)

Nikolaeva, A. V.; Tsysar, S. A.; Sapozhnikov, O. A.

2016-01-01

The paper considers the problem of precise measurement of the acoustic radiation force of an ultrasonic beam on targets in the form of solid spherical scatterers. Using known analytic relations, a numerical model is developed to perform calculations for different sizes of spherical scatterers and arbitrary frequencies of the incident acoustic wave. A novel method is proposed for measuring the radiation force, which is based on the principle of acoustic echolocation. The radiation force is measured experimentally in a wide range of incident wave intensities using two chosen methods differing in the way the location of the target is controlled.

Cylindrical and spherical solitary waves in an electron-acoustic plasma with vortex electron distribution

NASA Astrophysics Data System (ADS)

Demiray, Hilmi; El-Zahar, Essam R.

2018-04-01

We consider the nonlinear propagation of electron-acoustic waves in a plasma composed of a cold electron fluid, hot electrons obeying a trapped/vortex-like distribution, and stationary ions. The basic nonlinear equations of the above described plasma are re-examined in the cylindrical (spherical) coordinates by employing the reductive perturbation technique. The modified cylindrical (spherical) KdV equation with fractional power nonlinearity is obtained as the evolution equation. Due to the nature of nonlinearity, this evolution equation cannot be reduced to the conventional KdV equation. A new family of closed form analytical approximate solution to the evolution equation and a comparison with numerical solution are presented and the results are depicted in some 2D and 3D figures. The results reveal that both solutions are in good agreement and the method can be used to obtain a new progressive wave solution for such evolution equations. Moreover, the resulting closed form analytical solution allows us to carry out a parametric study to investigate the effect of the physical parameters on the solution behavior of the modified cylindrical (spherical) KdV equation.

Observation of beat oscillation generation by coupled waves associated with parametric decay during radio frequency wave heating of a spherical tokamak plasma.

PubMed

Nagashima, Yoshihiko; Oosako, Takuya; Takase, Yuichi; Ejiri, Akira; Watanabe, Osamu; Kobayashi, Hiroaki; Adachi, Yuuki; Tojo, Hiroshi; Yamaguchi, Takashi; Kurashina, Hiroki; Yamada, Kotaro; An, Byung Il; Kasahara, Hiroshi; Shimpo, Fujio; Kumazawa, Ryuhei; Hayashi, Hiroyuki; Matsuzawa, Haduki; Hiratsuka, Junichi; Hanashima, Kentaro; Kakuda, Hidetoshi; Sakamoto, Takuya; Wakatsuki, Takuma

2010-06-18

We present an observation of beat oscillation generation by coupled modes associated with parametric decay instability (PDI) during radio frequency (rf) wave heating experiments on the Tokyo Spherical Tokamak-2. Nearly identical PDI spectra, which are characterized by the coexistence of the rf pump wave, the lower-sideband wave, and the low-frequency oscillation in the ion-cyclotron range of frequency, are observed at various locations in the edge plasma. A bispectral power analysis was used to experimentally discriminate beat oscillation from the resonant mode for the first time. The pump and lower-sideband waves have resonant mode components, while the low-frequency oscillation is exclusively excited by nonlinear coupling of the pump and lower-sideband waves. Newly discovered nonlocal transport channels in spectral space and in real space via PDI are described.

Acoustically excited surface waves on empty or fluid-filled cylindrical and spherical shells

NASA Astrophysics Data System (ADS)

Ahyi, A. Claude; Cao, H.; Raju, P. K.; Werby, M. F.; Bao, X. L.; Überall, H.

2002-05-01

A comparative study is presented of the acoustical excitation of circumferential (surface) waves on fluid-immersed cylindrical or spherical metal shells, which may be either evacuated, or filled with the same or a different fluid. The excited surface waves can manifest themselves by the resonances apparent in the sound scattering amplitude, which they cause upon phase matching following repeated circumnavigations of the target object, or by their re-radiation into the external fluid in the manner of head waves. We plot dispersion curves versus frequency of the surface waves, which for evacuated shells have a generally rising character, while the fluid filling adds an additional set of circumferential waves that descend with frequency. The resonances of these latter waves may also be interpreted as being due to phase matching, but they may alternately be interpreted as constituting the eigenfrequencies of the internal fluid contained in an elastic enclosure.

Random Choice Solutions for Weak Spherical Shock-Wave Transitions of N-Waves in Air with Vibrational Excitation.

DTIC Science & Technology

1983-07-01

ionalI relaxat in dii icons whe-re kricrw-i aitMSo~lli-l-ic cirrd it ions could efc-tes for spherical I\\ -svrmetric wave s . bc obitani rd - It will lit...of cibirat jona 1 nonequ iiib rium cont rihuteCs to tr univ for weak waves. The rise times for the ieI ciCUlatijun for cases A5 , 81l, Cl and DI real...I ibrium thle c;iI itid ma iuum oci-rpressiire t I pIm1 atid in) :ompairisoni with c-ase A5 . hi ile almxost the same the half diii t iou tdI

Photoacoustic Effect Generated from an Expanding Spherical Source

NASA Astrophysics Data System (ADS)

Bai, Wenyu; Diebold, Gerald J.

2018-02-01

Although the photoacoustic effect is typically generated by amplitude-modulated continuous or pulsed radiation, the form of the wave equation for pressure that governs the generation of sound indicates that optical sources moving in an absorbing fluid can produce sound as well. Here, the characteristics of the acoustic wave produced by a radially symmetric Gaussian source expanding outwardly from the origin are found. The unique feature of the photoacoustic effect from the spherical source is a trailing compressive wave that arises from reflection of an inwardly propagating component of the wave. Similar to the one-dimensional geometry, an unbounded amplification effect is found for the Gaussian source expanding at the sound speed.

Central arterial stiffness is associated with systemic inflammation among Asians with type 2 diabetes.

PubMed

Zhang, Xiao; Liu, Jian Jun; Fang Sum, Chee; Ying, Yeoh Lee; Tavintharan, Subramaniam; Ng, Xiao Wei; Su, Chang; Low, Serena; Lee, Simon Bm; Tang, Wern Ee; Lim, Su Chi

2016-07-01

To examine the relationship between inflammation and central arterial stiffness in a type 2 diabetes Asian cohort. Central arterial stiffness was estimated by carotid-femoral pulse wave velocity and augmentation index. Linear regression model was used to evaluate the association of high-sensitivity C-reactive protein and soluble receptor for advanced glycation end products with pulse wave velocity and augmentation index. High-sensitivity C-reactive protein was analysed as a continuous variable and categories (<1, 1-3, and >3 mg/L). There is no association between high-sensitivity C-reactive protein and pulse wave velocity. Augmentation index increased with high-sensitivity C-reactive protein as a continuous variable (β = 0.328, p = 0.049) and categories (β = 1.474, p = 0.008 for high-sensitivity C-reactive protein: 1-3 mg/L and β = 1.323, p = 0.019 for high-sensitivity C-reactive protein: >3 mg/L) after multivariable adjustment. No association was observed between augmentation index and soluble receptor for advanced glycation end products. Each unit increase in natural log-transformed soluble receptor for advanced glycation end products was associated with 0.328 m/s decrease in pulse wave velocity after multivariable adjustment (p = 0.007). Elevated high-sensitivity C-reactive protein and decreased soluble receptor for advanced glycation end products are associated with augmentation index and pulse wave velocity, respectively, suggesting the potential role of systemic inflammation in the pathogenesis of central arterial stiffness in type 2 diabetes. © The Author(s) 2016.

Effect of Wave Reflection and Arterial Stiffness on the Risk of Development of Hypertension in Japanese Men.

PubMed

Tomiyama, Hirofumi; Komatsu, Shunsuke; Shiina, Kazuki; Matsumoto, Chisa; Kimura, Kazutaka; Fujii, Masatsune; Takahashi, Lisa; Chikamori, Taishiro; Yamashina, Akira

2018-05-08

We conducted analyses of repeated-measures data to examine whether pressure wave reflection acts additively or synergistically with arterial stiffness in the pathogenesis of hypertension. In 3172 middle-aged (42±9 years) healthy Japanese men without hypertension at the study baseline, systolic and diastolic blood pressures, brachial-ankle pulse wave velocity, and radial augmentation index were measured annually during a 9-year study period. Of these, 474 participants (15%) developed hypertension by the end of the study period. Binary logistic regression analysis demonstrated significant individual odds ratios for both baseline brachial-ankle pulse wave velocity and radial augmentation index for the development of hypertension. The rate of onset of hypertension during the study period was highest in the participant group with high values for both brachial-ankle pulse wave velocity and radial augmentation index at study baseline (262 of 965 participants: 27%). The generalized estimating equation analysis revealed that both radial augmentation index (estimate=0.06, SE=0.03, P =0.05) and brachial-ankle pulse wave velocity (estimate=0.07×10 -1 , SE=0.02×10 -1 , P <0.01) showed significant longitudinal association with new onset of hypertension, with no significant interaction. In Japanese men, abnormal wave reflection and increased arterial stiffness may be additively associated with the risk of new onset of hypertension. Abnormal wave reflection and elevated central blood pressure may be longitudinally associated with increase in arterial stiffness, and this longitudinal association may be a mechanism underlying the additive effect of these 2 variables on the risk of new onset of hypertension. © 2018 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley.

Droplet characteristic measurement in Fourier interferometry imaging and behavior at the rainbow angle.

PubMed

Briard, Paul; Saengkaew, Sawitree; Wu, Xuecheng; Meunier-Guttin-Cluzel, Siegfried; Chen, Linghong; Cen, Kefa; Gréhan, Gérard

2013-01-01

This paper presents the possibility of measuring the three-dimensional (3D) relative locations and diameters of a set of spherical particles and discusses the behavior of the light recorded around the rainbow angle, an essential step toward refractive index measurements. When a set of particles is illuminated by a pulsed incident wave, the particles act as spherical light wave sources. When the pulse duration is short enough to fix the particle location (typically about 10 ns), interference fringes between these different spherical waves can be recorded. The Fourier transform of the fringes divides the complex fringe systems into a series of spots, with each spot characterizing the interference between a pair of particles. The analyses of these spots (in position and shape) potentially allow the measurement of particle characteristics (3D relative position, particle diameter, and particle refractive index value).

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.

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.

Wave energy patterns of counterpulsation: a novel approach with wave intensity analysis.

PubMed

Lu, Pong-Jeu; Yang, Chi-Fu Jeffrey; Wu, Meng-Yu; Hung, Chun-Hao; Chan, Ming-Yao; Hsu, Tzu-Cheng

2011-11-01

In counterpulsation, diastolic augmentation increases coronary blood flow and systolic unloading reduces left ventricular afterload. We present a new approach with wave intensity analysis to revisit and explain counterpulsation principles. In an acute porcine model, a standard intra-aortic balloon pump was placed in descending aorta in 4 pigs. We measured pressure and velocity with probes in left anterior descending artery and aorta during and without intra-aortic balloon pump assistance. Wave intensities of aortic and left coronary waves were derived from pressure and flow measurements with synchronization correction. We identified predominating waves in counterpulsation. In the aorta, during diastolic augmentation, intra-aortic balloon inflation generated a backward compression wave, with a "pushing" effect toward the aortic root that translated to a forward compression wave into coronary circulation. During systolic unloading, intra-aortic balloon pump deflation generated a backward expansion wave that "sucked" blood from left coronary bed into the aorta. While this backward expansion wave translated to reduced left ventricular afterload, the "sucking" effect resulted in left coronary blood steal, as demonstrated by a forward expansion wave in left anterior descending coronary flow. The waves were sensitive to inflation and deflation timing, with just 25 ms delay from standard deflation timing leading to weaker forward expansion wave and less coronary regurgitation. Intra-aortic balloon pumps generate backward-traveling waves that predominantly drive aortic and coronary blood flow during counterpulsation. Wave intensity analysis of arterial circulations may provide a mechanism to explain diastolic augmentation and systolic unloading of intra-aortic balloon pump counterpulsation. Copyright © 2011 The American Association for Thoracic Surgery. Published by Mosby, Inc. All rights reserved.

Observation of interaction of shock wave with gas bubble by image converter camera

NASA Astrophysics Data System (ADS)

Yoshii, M.; Tada, M.; Tsuji, T.; Isuzugawa, Kohji

1995-05-01

When a spark discharge occurs at the first focal point of a semiellipsoid or a reflector located in water, a spherical shock wave is produced. A part of the wave spreads without reflecting on the reflector and is called direct wave in this paper. Another part reflects on the semiellipsoid and converges near the second focal point, that is named the focusing wave, and locally produces a high pressure. This phenomenon is applied to disintegrators of kidney stone. But it is concerned that cavitation bubbles induced in the body by the expansion wave following the focusing wave will injure human tissue around kidney stone. In this paper, in order to examine what happens when shock waves strike bubbles on human tissue, the aspect that an air bubble is truck by the spherical shock wave or its behavior is visualized by the schlieren system and its photographs are taken using an image converter camera. Besides,the variation of the pressure amplitude caused by the shock wave and the flow of water around the bubble is measured with a pressure probe.

Nonplanar ion acoustic waves with kappa-distributed electrons

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

Sahu, Biswajit

2011-06-15

Using the standard reductive perturbation technique, nonlinear cylindrical and spherical Kadomtsev-Petviashvili equations are derived for the propagation of ion acoustic solitary waves in an unmagnetized collisionless plasma with kappa distributed electrons and warm ions. The influence of kappa-distributed electrons and the effects caused by the transverse perturbation on cylindrical and spherical ion acoustic waves (IAWs) are investigated. It is observed that increase in the kappa distributed electrons (i.e., decreasing {kappa}) decreases the amplitude of the solitary electrostatic potential structures. The numerical results are presented to understand the formation of ion acoustic solitary waves with kappa-distributed electrons in nonplanar geometry. Themore » present investigation may have relevance in the study of propagation of IAWs in space and laboratory plasmas.« less

Hydrodynamic interactions of cilia on a spherical body

NASA Astrophysics Data System (ADS)

Nasouri, Babak; Elfring, Gwynn J.

2015-11-01

The emergence of metachronal waves in ciliated microorganisms can arise solely from the hydrodynamic interactions between the cilia. For a chain of cilia attached to a flat ciliate, it was observed that fluid forces can lead the system to form a metachronal wave. However, several microorganisms such as paramecium and volvox possess a curved shaped ciliate body. To understand the effect of this geometry on the formation of metachronal waves, we evaluate the hydrodynamic interactions of cilia near a large spherical body. Using a minimal model, we show that for a chain of cilia around the sphere, the embedded periodicity in the geometry leads the system to synchronize. We also report an emergent wave-like behavior when an asymmetry is introduced to the system.

Acoustical tweezers using single spherically focused piston, X-cut, and Gaussian beams.

PubMed

Mitri, Farid G

2015-10-01

Partial-wave series expansions (PWSEs) satisfying the Helmholtz equation in spherical coordinates are derived for circular spherically focused piston (i.e., apodized by a uniform velocity amplitude normal to its surface), X-cut (i.e., apodized by a velocity amplitude parallel to the axis of wave propagation), and Gaussian (i.e., apodized by a Gaussian distribution of the velocity amplitude) beams. The Rayleigh-Sommerfeld diffraction integral and the addition theorems for the Legendre and spherical wave functions are used to obtain the PWSEs assuming weakly focused beams (with focusing angle α ⩽ 20°) in the Fresnel-Kirchhoff (parabolic) approximation. In contrast with previous analytical models, the derived expressions allow computing the scattering and acoustic radiation force from a sphere of radius a without restriction to either the Rayleigh (a ≪ λ, where λ is the wavelength of the incident radiation) or the ray acoustics (a ≫λ) regimes. The analytical formulations are valid for wavelengths largely exceeding the radius of the focused acoustic radiator, when the viscosity of the surrounding fluid can be neglected, and when the sphere is translated along the axis of wave propagation. Computational results illustrate the analysis with particular emphasis on the sphere's elastic properties and the axial distance to the center of the concave surface, with close connection of the emergence of negative trapping forces. Potential applications are in single-beam acoustical tweezers, acoustic levitation, and particle manipulation.

Design and analysis of aspherical multilayer imaging X-ray microscope

NASA Technical Reports Server (NTRS)

Shealy, David L.; Jiang, WU; Hoover, Richard B.

1991-01-01

Spherical Schwarzschild microscopes for soft X-ray applications in microscopy and projection lithography employ two concentric spherical mirrors that are configured such that the third-order spherical aberration and coma are zero. Based on incoherent, sine-wave MTF calculations, the object-plane resolution of a magnification-factor-20 microscope is presently analyzed as a function of object height and numerical aperture of the primary for several spherical Schwarzschild, conic, and aspherical two-mirror microscope configurations.

Plane-wave decomposition by spherical-convolution microphone array

NASA Astrophysics Data System (ADS)

Rafaely, Boaz; Park, Munhum

2004-05-01

Reverberant sound fields are widely studied, as they have a significant influence on the acoustic performance of enclosures in a variety of applications. For example, the intelligibility of speech in lecture rooms, the quality of music in auditoria, the noise level in offices, and the production of 3D sound in living rooms are all affected by the enclosed sound field. These sound fields are typically studied through frequency response measurements or statistical measures such as reverberation time, which do not provide detailed spatial information. The aim of the work presented in this seminar is the detailed analysis of reverberant sound fields. A measurement and analysis system based on acoustic theory and signal processing, designed around a spherical microphone array, is presented. Detailed analysis is achieved by decomposition of the sound field into waves, using spherical Fourier transform and spherical convolution. The presentation will include theoretical review, simulation studies, and initial experimental results.

Coherent backscattering of light by complex random media of spherical scatterers: numerical solution

NASA Astrophysics Data System (ADS)

Muinonen, Karri

2004-07-01

Novel Monte Carlo techniques are described for the computation of reflection coefficient matrices for multiple scattering of light in plane-parallel random media of spherical scatterers. The present multiple scattering theory is composed of coherent backscattering and radiative transfer. In the radiative transfer part, the Stokes parameters of light escaping from the medium are updated at each scattering process in predefined angles of emergence. The scattering directions at each process are randomized using probability densities for the polar and azimuthal scattering angles: the former angle is generated using the single-scattering phase function, whereafter the latter follows from Kepler's equation. For spherical scatterers in the Rayleigh regime, randomization proceeds semi-analytically whereas, beyond that regime, cubic spline presentation of the scattering matrix is used for numerical computations. In the coherent backscattering part, the reciprocity of electromagnetic waves in the backscattering direction allows the renormalization of the reversely propagating waves, whereafter the scattering characteristics are computed in other directions. High orders of scattering (~10 000) can be treated because of the peculiar polarization characteristics of the reverse wave: after a number of scatterings, the polarization state of the reverse wave becomes independent of that of the incident wave, that is, it becomes fully dictated by the scatterings at the end of the reverse path. The coherent backscattering part depends on the single-scattering albedo in a non-monotonous way, the most pronounced signatures showing up for absorbing scatterers. The numerical results compare favourably to the literature results for nonabsorbing spherical scatterers both in and beyond the Rayleigh regime.

Density functional theory calculations of 95Mo NMR parameters in solid-state compounds.

PubMed

Cuny, Jérôme; Furet, Eric; Gautier, Régis; Le Pollès, Laurent; Pickard, Chris J; d'Espinose de Lacaillerie, Jean-Baptiste

2009-12-21

The application of periodic density functional theory-based methods to the calculation of (95)Mo electric field gradient (EFG) and chemical shift (CS) tensors in solid-state molybdenum compounds is presented. Calculations of EFG tensors are performed using the projector augmented-wave (PAW) method. Comparison of the results with those obtained using the augmented plane wave + local orbitals (APW+lo) method and with available experimental values shows the reliability of the approach for (95)Mo EFG tensor calculation. CS tensors are calculated using the recently developed gauge-including projector augmented-wave (GIPAW) method. This work is the first application of the GIPAW method to a 4d transition-metal nucleus. The effects of ultra-soft pseudo-potential parameters, exchange-correlation functionals and structural parameters are precisely examined. Comparison with experimental results allows the validation of this computational formalism.

Nonlinear Electromagnetic Waves and Spherical Arc-Polarized Waves in Space Plasmas

NASA Technical Reports Server (NTRS)

Tsurutani, B.; Ho, Christian M.; Arballo, John K.; Lakhina, Gurbax S.; Glassmeier, Karl-Heinz; Neubauer, Fritz M.

1997-01-01

We review observations of nonlinear plasma waves detected by interplanetary spacecraft. For this paper we will focus primarily on the phase-steepened properties of such waves. Plasma waves at comet Giacobini-Zinner measured by the International Cometary Explorer (ICE), at comets Halley and Grigg-Skjellerup measured by Giotto, and interplanetary Alfven waves measured by Ulysses, will be discussed and intercompared.

Spherical Harmonics Reveal Standing EEG Waves and Long-Range Neural Synchronization during Non-REM Sleep.

PubMed

Sivakumar, Siddharth S; Namath, Amalia G; Galán, Roberto F

2016-01-01

Previous work from our lab has demonstrated how the connectivity of brain circuits constrains the repertoire of activity patterns that those circuits can display. Specifically, we have shown that the principal components of spontaneous neural activity are uniquely determined by the underlying circuit connections, and that although the principal components do not uniquely resolve the circuit structure, they do reveal important features about it. Expanding upon this framework on a larger scale of neural dynamics, we have analyzed EEG data recorded with the standard 10-20 electrode system from 41 neurologically normal children and adolescents during stage 2, non-REM sleep. We show that the principal components of EEG spindles, or sigma waves (10-16 Hz), reveal non-propagating, standing waves in the form of spherical harmonics. We mathematically demonstrate that standing EEG waves exist when the spatial covariance and the Laplacian operator on the head's surface commute. This in turn implies that the covariance between two EEG channels decreases as the inverse of their relative distance; a relationship that we corroborate with empirical data. Using volume conduction theory, we then demonstrate that superficial current sources are more synchronized at larger distances, and determine the characteristic length of large-scale neural synchronization as 1.31 times the head radius, on average. Moreover, consistent with the hypothesis that EEG spindles are driven by thalamo-cortical rather than cortico-cortical loops, we also show that 8 additional patients with hypoplasia or complete agenesis of the corpus callosum, i.e., with deficient or no connectivity between cortical hemispheres, similarly exhibit standing EEG waves in the form of spherical harmonics. We conclude that spherical harmonics are a hallmark of spontaneous, large-scale synchronization of neural activity in the brain, which are associated with unconscious, light sleep. The analogy with spherical harmonics in quantum mechanics suggests that the variances (eigenvalues) of the principal components follow a Boltzmann distribution, or equivalently, that standing waves are in a sort of "thermodynamic" equilibrium during non-REM sleep. By extension, we speculate that consciousness emerges as the brain dynamics deviate from such equilibrium.

Spherical Harmonics Reveal Standing EEG Waves and Long-Range Neural Synchronization during Non-REM Sleep

PubMed Central

Sivakumar, Siddharth S.; Namath, Amalia G.; Galán, Roberto F.

2016-01-01

Previous work from our lab has demonstrated how the connectivity of brain circuits constrains the repertoire of activity patterns that those circuits can display. Specifically, we have shown that the principal components of spontaneous neural activity are uniquely determined by the underlying circuit connections, and that although the principal components do not uniquely resolve the circuit structure, they do reveal important features about it. Expanding upon this framework on a larger scale of neural dynamics, we have analyzed EEG data recorded with the standard 10–20 electrode system from 41 neurologically normal children and adolescents during stage 2, non-REM sleep. We show that the principal components of EEG spindles, or sigma waves (10–16 Hz), reveal non-propagating, standing waves in the form of spherical harmonics. We mathematically demonstrate that standing EEG waves exist when the spatial covariance and the Laplacian operator on the head's surface commute. This in turn implies that the covariance between two EEG channels decreases as the inverse of their relative distance; a relationship that we corroborate with empirical data. Using volume conduction theory, we then demonstrate that superficial current sources are more synchronized at larger distances, and determine the characteristic length of large-scale neural synchronization as 1.31 times the head radius, on average. Moreover, consistent with the hypothesis that EEG spindles are driven by thalamo-cortical rather than cortico-cortical loops, we also show that 8 additional patients with hypoplasia or complete agenesis of the corpus callosum, i.e., with deficient or no connectivity between cortical hemispheres, similarly exhibit standing EEG waves in the form of spherical harmonics. We conclude that spherical harmonics are a hallmark of spontaneous, large-scale synchronization of neural activity in the brain, which are associated with unconscious, light sleep. The analogy with spherical harmonics in quantum mechanics suggests that the variances (eigenvalues) of the principal components follow a Boltzmann distribution, or equivalently, that standing waves are in a sort of “thermodynamic” equilibrium during non-REM sleep. By extension, we speculate that consciousness emerges as the brain dynamics deviate from such equilibrium. PMID:27445777

Wave Amplitude Dependent Engineering Model of Propellant Slosh in Spherical Tanks

NASA Technical Reports Server (NTRS)

Brodnick, Jacob; Westra, Douglas G.; Eberhart, Chad J.; Yang, Hong Q.; West, Jeffrey S.

2016-01-01

Liquid propellant slosh is often a concern for the controllability of flight vehicles. Anti-slosh devices are traditionally included in propellant tank designs to limit the amount of sloshing allowed during flight. These devices and any necessary supports can be quite heavy to meet various structural requirements. Some of the burden on anti-slosh devices can be relieved by exploiting the nonlinear behavior of slosh waves in bare smooth wall tanks. A nonlinear regime slosh model for bare spherical tanks was developed through a joint analytical and experimental effort by NASA/MSFC. The developed slosh model accounts for the large damping inherent in nonlinear slosh waves which is more accurate and drives conservatism from vehicle stability analyses that use traditional bare tank slosh models. A more accurate slosh model will result in more realistic predicted slosh forces during flight reducing or removing the need for active controls during a maneuver or baffles in the tank design. Lower control gains and smaller or fewer tank baffles can reduce cost and system complexity while increasing vehicle performance. Both Computational Fluid Dynamics (CFD) simulation and slosh testing of three different spherical tank geometries were performed to develop the proposed slosh model. Several important findings were made during this effort in addition to determining the parameters to the nonlinear regime slosh model. The linear regime slosh damping trend for spherical tanks reported in NASA SP-106 was shown to be inaccurate for certain regions of a tank. Additionally, transition to the nonlinear regime for spherical tanks was only found to occur at very large wave amplitudes in the lower hemisphere and was a strong function of the propellant fill level in the upper hemisphere. The nonlinear regime damping trend was also found to be a function of the propellant fill level.

Analysis of Ultrasonic Wave Scattering for Characterization of Defects in Solids

DTIC Science & Technology

1976-05-01

embedded in a solid matrix.’ The results of this work have been partially reported in a paper sub- mitted to the "Journal of the Acoustical Society of...America." The abstract of this paper is presented here: a. "Scattering of Longitudinal Waves Incident on a Spherical Cavity in a Solid," B. R. Tittmann...F I 7 ... .OCT..9 UM... ... .. . ... U SCS7g. 31R 2. Scattering by a Spherical Inclusion During this past year the experimental portion of the

Spherical Harmonic Decomposition of Gravitational Waves Across Mesh Refinement Boundaries

NASA Technical Reports Server (NTRS)

Fiske, David R.; Baker, John; vanMeter, James R.; Centrella, Joan M.

2005-01-01

We evolve a linearized (Teukolsky) solution of the Einstein equations with a non-linear Einstein solver. Using this testbed, we are able to show that such gravitational waves, defined by the Weyl scalars in the Newman-Penrose formalism, propagate faithfully across mesh refinement boundaries, and use, for the first time to our knowledge, a novel algorithm due to Misner to compute spherical harmonic components of our waveforms. We show that the algorithm performs extremely well, even when the extraction sphere intersects refinement boundaries.

Short-scale turbulent fluctuations driven by the electron-temperature gradient in the national spherical torus experiment.

PubMed

Mazzucato, E; Smith, D R; Bell, R E; Kaye, S M; Hosea, J C; LeBlanc, B P; Wilson, J R; Ryan, P M; Domier, C W; Luhmann, N C; Yuh, H; Lee, W; Park, H

2008-08-15

Measurements with coherent scattering of electromagnetic waves in plasmas of the National Spherical Torus Experiment indicate the existence of turbulent fluctuations in the range of wave numbers k perpendicular rho(e)=0.1-0.4, corresponding to a turbulence scale length nearly equal to the collisionless skin depth. Experimental observations and agreement with numerical results from a linear gyrokinetic stability code support the conjecture that the observed turbulence is driven by the electron-temperature gradient.

Systematic Calibration for a Backpacked Spherical Photogrammetry Imaging System

NASA Astrophysics Data System (ADS)

Rau, J. Y.; Su, B. W.; Hsiao, K. W.; Jhan, J. P.

2016-06-01

A spherical camera can observe the environment for almost 720 degrees' field of view in one shoot, which is useful for augmented reality, environment documentation, or mobile mapping applications. This paper aims to develop a spherical photogrammetry imaging system for the purpose of 3D measurement through a backpacked mobile mapping system (MMS). The used equipment contains a Ladybug-5 spherical camera, a tactical grade positioning and orientation system (POS), i.e. SPAN-CPT, and an odometer, etc. This research aims to directly apply photogrammetric space intersection technique for 3D mapping from a spherical image stereo-pair. For this purpose, several systematic calibration procedures are required, including lens distortion calibration, relative orientation calibration, boresight calibration for direct georeferencing, and spherical image calibration. The lens distortion is serious on the ladybug-5 camera's original 6 images. Meanwhile, for spherical image mosaicking from these original 6 images, we propose the use of their relative orientation and correct their lens distortion at the same time. However, the constructed spherical image still contains systematic error, which will reduce the 3D measurement accuracy. Later for direct georeferencing purpose, we need to establish a ground control field for boresight/lever-arm calibration. Then, we can apply the calibrated parameters to obtain the exterior orientation parameters (EOPs) of all spherical images. In the end, the 3D positioning accuracy after space intersection will be evaluated, including EOPs obtained by structure from motion method.

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.

Dielectric Covered Planar Antennas

NASA Technical Reports Server (NTRS)

Llombart Juan, Nuria (Inventor); Lee, Choonsup (Inventor); Chattopadhyay, Goutam (Inventor); Gill, John J. (Inventor); Skalare, Anders J. (Inventor); Siegel, Peter H. (Inventor)

2014-01-01

An antenna element suitable for integrated arrays at terahertz frequencies is disclosed. The antenna element comprises an extended spherical (e.g. hemispherical) semiconductor lens, e.g. silicon, antenna fed by a leaky wave waveguide feed. The extended spherical lens comprises a substantially spherical lens adjacent a substantially planar lens extension. A couple of TE/TM leaky wave modes are excited in a resonant cavity formed between a ground plane and the substantially planar lens extension by a waveguide block coupled to the ground plane. Due to these modes, the primary feed radiates inside the lens with a directive pattern that illuminates a small sector of the lens. The antenna structure is compatible with known semiconductor fabrication technology and enables production of large format imaging arrays.

Wave field synthesis of moving virtual sound sources with complex radiation properties.

PubMed

Ahrens, Jens; Spors, Sascha

2011-11-01

An approach to the synthesis of moving virtual sound sources with complex radiation properties in wave field synthesis is presented. The approach exploits the fact that any stationary sound source of finite spatial extent radiates spherical waves at sufficient distance. The angular dependency of the radiation properties of the source under consideration is reflected by the amplitude and phase distribution on the spherical wave fronts. The sound field emitted by a uniformly moving monopole source is derived and the far-field radiation properties of the complex virtual source under consideration are incorporated in order to derive a closed-form expression for the loudspeaker driving signal. The results are illustrated via numerical simulations of the synthesis of the sound field of a sample moving complex virtual source.

NMR and NQR parameters of ethanol crystal

NASA Astrophysics Data System (ADS)

Milinković, M.; Bilalbegović, G.

2012-04-01

Electric field gradients and chemical shielding tensors of the stable monoclinic crystal phase of ethanol are computed. The projector-augmented wave (PAW) and gauge-including projector-augmented wave (GIPAW) models in the periodic plane-wave density functional theory are used. The crystal data from X-ray measurements, as well as the structures where either all atomic, or only hydrogen atom positions are optimized in the density functional theory are analyzed. These structural models are also studied by including the semi-empirical van der Waals correction to the density functional theory. Infrared spectra of these five crystal models are calculated.

The point explosion with radiation transport

NASA Astrophysics Data System (ADS)

Lin, Zhiwei; Zhang, Lu; Kuang, Longyu; Jiang, Shaoen

2017-10-01

Some amount of energy is released instantaneously at the origin to generate simultaneously a spherical radiative heat wave and a spherical shock wave in the point explosion with radiation transport, which is a complicated problem due to the competition between these two waves. The point explosion problem possesses self-similar solutions when only hydrodynamic motion or only heat conduction is considered, which are Sedov solution and Barenblatt solution respectively. The point explosion problem wherein both physical mechanisms of hydrodynamic motion and heat conduction are included has been studied by P. Reinicke and A.I. Shestakov. In this talk we numerically investigate the point explosion problem wherein both physical mechanisms of hydrodynamic motion and radiation transport are taken into account. The radiation transport equation in one dimensional spherical geometry has to be solved for this problem since the ambient medium is optically thin with respect to the initially extremely high temperature at the origin. The numerical results reveal a high compression of medium and a bi-peak structure of density, which are further theoretically analyzed at the end.

Sound Beams with Shockwave Pulses

NASA Astrophysics Data System (ADS)

Enflo, B. O.

2000-11-01

The beam equation for a sound beam in a diffusive medium, called the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation, has a class of solutions, which are power series in the transverse variable with the terms given by a solution of a generalized Burgers’ equation. A free parameter in this generalized Burgers’ equation can be chosen so that the equation describes an N-wave which does not decay. If the beam source has the form of a spherical cap, then a beam with a preserved shock can be prepared. This is done by satisfying an inequality containing the spherical radius, the N-wave pulse duration, the N-wave pulse amplitude, and the sound velocity in the fluid.

Tunable dielectric properties of mesoporous carbon hollow microspheres via textural properties.

PubMed

Xu, Hailong; Yin, Xiaowei; Li, Zhaochen; Liu, Chenglong; Wang, Zeyu; Li, Minghang; Zhang, Litong; Cheng, Laifei

2018-05-04

In this study, mesoporous carbon hollow microspheres (PCHMs) with tunable textural properties have been prepared through a facile hard template etching method. The PCHMs were characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction, Raman spectra, and nitrogen adsorption and desorption systems. Uniform PCHMs with shell thickness ranging from 23 nm to 55 nm are realized. PCHMs with different textural properties can regulate dielectric and electromagnetic (EM) wave absorption effectively. The composite of paraffin wax mixed with 10 wt% PCHMs (the shell thickness of PCHMs is 35 nm) exhibits a minimum coefficient value of -53.8 dB at 8.8 GHz, with a thickness of 3.4 mm. Besides, it is remarkable that the effective absorption bandwidth covers all the X band with as low as a 10 wt% filler ratio, compared with other spherical EM wave absorbers. The excellent EM wave absorption capability of PCHMs can be ascribed to the better impendence matching and strong EM wave attenuation constant based on tunable textural properties. Our results provide a facile strategy to tune dielectric properties of spherical carbon absorbers based on textural properties, and can be extended to other spherical absorbers.

Tunable dielectric properties of mesoporous carbon hollow microspheres via textural properties

NASA Astrophysics Data System (ADS)

Xu, Hailong; Yin, Xiaowei; Li, Zhaochen; Liu, Chenglong; Wang, Zeyu; Li, Minghang; Zhang, Litong; Cheng, Laifei

2018-05-01

In this study, mesoporous carbon hollow microspheres (PCHMs) with tunable textural properties have been prepared through a facile hard template etching method. The PCHMs were characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction, Raman spectra, and nitrogen adsorption and desorption systems. Uniform PCHMs with shell thickness ranging from 23 nm to 55 nm are realized. PCHMs with different textural properties can regulate dielectric and electromagnetic (EM) wave absorption effectively. The composite of paraffin wax mixed with 10 wt% PCHMs (the shell thickness of PCHMs is 35 nm) exhibits a minimum coefficient value of -53.8 dB at 8.8 GHz, with a thickness of 3.4 mm. Besides, it is remarkable that the effective absorption bandwidth covers all the X band with as low as a 10 wt% filler ratio, compared with other spherical EM wave absorbers. The excellent EM wave absorption capability of PCHMs can be ascribed to the better impendence matching and strong EM wave attenuation constant based on tunable textural properties. Our results provide a facile strategy to tune dielectric properties of spherical carbon absorbers based on textural properties, and can be extended to other spherical absorbers.

Wave equations in conformal gravity

NASA Astrophysics Data System (ADS)

Du, Juan-Juan; Wang, Xue-Jing; He, You-Biao; Yang, Si-Jiang; Li, Zhong-Heng

2018-05-01

We study the wave equation governing massless fields of all spins (s = 0, 1 2, 1, 3 2 and 2) in the most general spherical symmetric metric of conformal gravity. The equation is separable, the solution of the angular part is a spin-weighted spherical harmonic, and the radial wave function may be expressed in terms of solutions of the Heun equation which has four regular singular points. We also consider various special cases of the metric and find that the angular wave functions are the same for all cases, the actual shape of the metric functions affects only the radial wave function. It is interesting to note that each radial equation can be transformed into a known ordinary differential equation (i.e. Heun equation, or confluent Heun equation, or hypergeometric equation). The results show that there are analytic solutions for all the wave equations of massless spin fields in the spacetimes of conformal gravity. This is amazing because exact solutions are few and far between for other spacetimes.

The Use of Steady and Unsteady Detonation Waves for Propulsion Systems

NASA Technical Reports Server (NTRS)

Adelman, Henry G.; Menees, Gene P.; Cambier, Jean-Luc; Bowles, Jeffrey V.; Cavolowsky, John A. (Technical Monitor)

1995-01-01

Detonation wave enhanced supersonic combustors such as the Oblique Detonation Wave Engine (ODWE) are attractive propulsion concepts for hypersonic flight. These engines utilize detonation waves to enhance fuel-air mixing and combustion. The benefits of wave combustion systems include shorter and lighter engines which require less cooling and generate lower internal drag. These features allow air-breathing operation at higher Mach numbers than the diffusive burning scramjet delaying the need for rocket engine augmentation. A comprehensive vehicle synthesis code has predicted the aerodynamic characteristics and structural size and weight of a typical single-stage-to-orbit vehicle using an ODWE. Other studies have focused on the use of unsteady or pulsed detonation waves. For low speed applications, pulsed detonation engines (PDE) have advantages in low weight and higher efficiency than turbojets. At hypersonic speeds, the pulsed detonations can be used in conjunction with a scramjet type engine to enhance mixing and provide thrust augmentation.

Quality metric for spherical panoramic video

NASA Astrophysics Data System (ADS)

Zakharchenko, Vladyslav; Choi, Kwang Pyo; Park, Jeong Hoon

2016-09-01

Virtual reality (VR)/ augmented reality (AR) applications allow users to view artificial content of a surrounding space simulating presence effect with a help of special applications or devices. Synthetic contents production is well known process form computer graphics domain and pipeline has been already fixed in the industry. However emerging multimedia formats for immersive entertainment applications such as free-viewpoint television (FTV) or spherical panoramic video require different approaches in content management and quality assessment. The international standardization on FTV has been promoted by MPEG. This paper is dedicated to discussion of immersive media distribution format and quality estimation process. Accuracy and reliability of the proposed objective quality estimation method had been verified with spherical panoramic images demonstrating good correlation results with subjective quality estimation held by a group of experts.

Waves in Radial Gravity Using Magnetic Fluid

NASA Technical Reports Server (NTRS)

Ohlsen, D. R.; Hart, J. E.; Weidman, P. D.

1999-01-01

Terrestrial laboratory experiments studying various fluid dynamical processes are constrained, by being in an Earth laboratory, to have a gravitational body force which is uniform and unidirectional. Therefore fluid free-surfaces are horizontal and flat. Such free surfaces must have a vertical solid boundary to keep the fluid from spreading horizontally along a gravitational potential surface. In atmospheric, oceanic, or stellar fluid flows that have a horizontal scale of about one-tenth the body radius or larger, sphericity is important in the dynamics. Further, fluids in spherical geometry can cover an entire domain without any sidewall effects, i.e. have truly periodic boundary conditions. We describe spherical body-force laboratory experiments using ferrofluid. Ferrofluids are dilute suspensions of magnetic dipoles, for example magnetite particles of order 10 nm diameter, suspended in a carrier fluid. Ferrofluids are subject to an additional body force in the presence of an applied magnetic field gradient. We use this body force to conduct laboratory experiments in spherical geometry. The present study is a laboratory technique improvement. The apparatus is cylindrically axisymmetric. A cylindrical ceramic magnet is embedded in a smooth, solid, spherical PVC ball. The geopotential field and its gradient, the body force, were made nearly spherical by careful choice of magnet height-to-diameter ratio and magnet size relative to the PVC ball size. Terrestrial gravity is eliminated from the dynamics by immersing the "planet" and its ferrofluid "ocean" in an immiscible silicone oil/freon mixture of the same density. Thus the earth gravity is removed from the dynamics of the ferrofluid/oil interface and the only dynamically active force there is the radial magnetic gravity. The entire apparatus can rotate, and waves are forced on the ferrofluid surface by exterior magnets. The biggest improvement in technique is in the wave visualization. Fluorescing dye is added to the oil/freon mixture and an argon ion laser generates a horizontal light that can be scanned vertically. Viewed from above, the experiment is a black circle with wave deformations surrounded by a light background. A contour of the image intensity at any light sheet position gives the surface of the ferrofluid "ocean" at that "latitude". Radial displacements of the waves as a function of longitude are obtained by subtracting the contour line positions from a no-motion contour at that laser sheet latitude. The experiments are run by traversing the forcing magnet with the laser sheet height fixed and images are frame grabbed to obtain a time-series at one latitude. The experiment is then re-run with another laser-sheet height to generate a full picture of the three-dimensional wave structure in the upper hemisphere of the ball as a function of time. We concentrate here on results of laboratory studies of waves that are important in Earth's atmosphere and especially the ocean. To get oceanic scaling in the laboratory, the experiment must rotate rapidly (4-second rotation period) so that the wave speed is slow compared to the planetary rotation speed as in the ocean. In the Pacific Ocean, eastward propagating Kelvin waves eventually run into the South American coast. Theory predicts that some of the wave energy should scatter into coastal-trapped Kelvin waves that propagate north and south along the coast. Some of this coastal wave energy might then scatter into mid-latitude Rossby waves that propagate back westward. Satellite observations of the Pacific Ocean sea-surface temperature and height seem to show signatures of westward propagating mid-latitude Rossby waves, 5 to 10 years after the 1982-83 El Nino. The observational data is difficult to interpret unambiguously owing to the large range of motions that fill the ocean at shorter timescales. This series of reflections giving eastward, north- ward, and then westward traveling waves is observed cleanly in the laboratory experiments, confirming the theoretical expectations.

First Octahedral Spherical Hohlraum Energetics Experiment at the SGIII Laser Facility

NASA Astrophysics Data System (ADS)

Huo, Wen Yi; Li, Zhichao; Chen, Yao-Hua; Xie, Xufei; Ren, Guoli; Cao, Hui; Li, Shu; Lan, Ke; Liu, Jie; Li, Yongsheng; Li, Sanwei; Guo, Liang; Liu, Yonggang; Yang, Dong; Jiang, Xiaohua; Hou, Lifei; Du, Huabing; Peng, Xiaoshi; Xu, Tao; Li, Chaoguang; Zhan, Xiayu; Wang, Zhebin; Deng, Keli; Wang, Qiangqiang; Deng, Bo; Wang, Feng; Yang, Jiamin; Liu, Shenye; Jiang, Shaoen; Yuan, Guanghui; Zhang, Haijun; Jiang, Baibin; Zhang, Wei; Gu, Qianqian; He, Zhibing; Du, Kai; Deng, Xuewei; Zhou, Wei; Wang, Liquan; Huang, Xiaoxia; Wang, Yuancheng; Hu, Dongxia; Zheng, Kuixing; Zhu, Qihua; Ding, Yongkun

2018-04-01

The first octahedral spherical hohlraum energetics experiment is accomplished at the SGIII laser facility. For the first time, the 32 laser beams are injected into the octahedral spherical hohlraum through six laser entrance holes. Two techniques are used to diagnose the radiation field of the octahedral spherical hohlraum in order to obtain comprehensive experimental data. The radiation flux streaming out of laser entrance holes is measured by six flat-response x-ray detectors (FXRDs) and four M -band x-ray detectors, which are placed at different locations of the SGIII target chamber. The radiation temperature is derived from the measured flux of FXRD by using the blackbody assumption. The peak radiation temperature inside hohlraum is determined by the shock wave technique. The experimental results show that the octahedral spherical hohlraum radiation temperature is in the range of 170-182 eV with drive laser energies of 71 kJ to 84 kJ. The radiation temperature inside the hohlraum determined by the shock wave technique is about 175 eV at 71 kJ. For the flat-top laser pulse of 3 ns, the conversion efficiency of gas-filled octahedral spherical hohlraum from laser into soft x rays is about 80% according to the two-dimensional numerical simulation.

Cylindrical and spherical Akhmediev breather and freak waves in ultracold neutral plasmas

NASA Astrophysics Data System (ADS)

El-Tantawy, S. A.; El-Awady, E. I.

2018-01-01

The properties of cylindrical and spherical ion-acoustic breathers Akhmediev breather and freak waves in strongly coupled ultracold neutral plasmas (UNPs), whose constituents are inertial strongly coupled ions and weakly coupled Maxwellian electrons, are investigated numerically. Using the derivative expansion method, the basic set of fluid equations is reduced to a nonplanar (cylindrical and spherical)/modified nonlinear Schrödinger equation (mNLSE). The analytical solutions of the mNLSE were not possible until now, so their numerical solutions are obtained using the finite difference scheme with the help of the Dirichlet boundary conditions. Moreover, the criteria for the existence and propagation of breathers are discussed in detail. The geometrical effects due to the cylindrical and spherical geometries on the breather profile are studied numerically. It is found that the propagation of the ion-acoustic breathers in one-dimensional planar and nonplanar geometries is very different. Finally, our results may help to manipulate matter breathers experimentally in UNPs.

Distortion of ultrashort pulses caused by aberrations

NASA Astrophysics Data System (ADS)

Horváth, Z. L.; Kovács, A. P.; Bor, Zs.

The effect of the primary wave aberrations (spherical aberration, astigmatism and coma) on ultrashort pulses is studied by the Nijboer-Zernike theory. The results of the geometrical and the wave optical treatments are compared.

Cosmic dust-ion-acoustic waves, spherical modified Kadomtsev-Petviashvili model, and symbolic computation

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

Gao Yitian; Tian Bo; State Key Laboratory of Software Development Environment, Beijing University of Aeronautics and Astronautics, Beijing 100083

2006-11-15

The spherical modified Kadomtsev-Petviashvili (smKP) model is hereby derived with symbolic computation for the dust-ion-acoustic waves with zenith-angle perturbation in a cosmic dusty plasma. Formation and properties of both dark and bright smKP nebulons are obtained and discussed. The relevance of those smKP nebulons to the supernova shells and Saturn's F-ring is pointed out, and possibly observable nebulonic effects for the future cosmic plasma experiments are proposed. The difference of the smKP nebulons from other types of nebulons is also analyzed.

Wollaston prism phase-stepping point diffraction interferometer and method

DOEpatents

Rushford, Michael C.

2004-10-12

A Wollaston prism phase-stepping point diffraction interferometer for testing a test optic. The Wollaston prism shears light into reference and signal beams, and provides phase stepping at increased accuracy by translating the Wollaston prism in a lateral direction with respect to the optical path. The reference beam produced by the Wollaston prism is directed through a pinhole of a diaphragm to produce a perfect spherical reference wave. The spherical reference wave is recombined with the signal beam to produce an interference fringe pattern of greater accuracy.

Focusing of Finite-Amplitude Cylindrical and Spherical Sound Waves in a Viscous and Heat-Conducting Medium. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Chu, T.

1971-01-01

The focusing of acoustic pulses is studied analytically by considering the region of study in three parts: the converging, interaction and diverging regions. First, the linear problem of a pulse of infinitesimal amplitude is studied. For the spherical case, the expected phase change as a result of focusing is verified. The nonlinear case of finite-amplitude pulses leads to the development of M-waves, as determined by applying the method of matched-asymptotic expansions to Burges equation.

Connection between black-hole quasinormal modes and lensing in the strong deflection limit.

PubMed

Stefanov, Ivan Zh; Yazadjiev, Stoytcho S; Gyulchev, Galin G

2010-06-25

The purpose of the current Letter is to give some relations between gravitational lensing in the strong-deflection limit and the frequencies of the quasinormal modes of spherically symmetric, asymptotically flat black holes. On the one side, the relations obtained can give a physical interpretation of the strong-deflection limit parameters. On the other side, they also give an alternative method for the measurement of the frequencies of the quasinormal modes of spherically symmetric, asymptotically flat black holes. They could be applied to the localization of the sources of gravitational waves and could tell us what frequencies of the gravitational waves we could expect from a black hole acting simultaneously as a gravitational lens and a source of gravitational waves.

ON THE UNIVERSALITY OF THE GLOBAL DENSITY SLOPE-ANISOTROPY INEQUALITY

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

Van Hese, Emmanuel; Baes, Maarten; Dejonghe, Herwig, E-mail: emmanuel.vanhese@gmail.com, E-mail: maarten.baes@ugent.be, E-mail: herwig.dejonghe@ugent.be

2011-01-10

Recently, some intriguing results have led to speculations whether the central density slope-velocity dispersion anisotropy inequality (An and Evans) actually holds at all radii for spherical dynamical systems. We extend these studies by providing a complete analysis of the global slope-anisotropy inequality for all spherical systems in which the augmented density is a separable function of radius and potential. We prove that these systems indeed satisfy the global inequality if their central anisotropy is {beta}{sub 0} {<=} 1/2. Furthermore, we present several systems with {beta}{sub 0}>1/2 for which the inequality does not hold, thus demonstrating that the global density slope-anisotropymore » inequality is not a universal property. This analysis is a significant step toward an understanding of the relation for general spherical systems.« less

Initial decay of flow properties of planar, cylindrical and spherical blast waves

NASA Astrophysics Data System (ADS)

Sadek, H. S. I.; Gottlieb, J. J.

1983-10-01

Analytical expressions are presented for the initial decay of all major flow properties just behind planar, cylindrical, and spherical shock wave fronts whose trajectories are known as a function of either distance versus time or shock overpressure versus distance. These expressions give the time and/or distance derivatives of the flow properties not only along constant time and distance lines but also along positive and negative characteristic lines and a fluid-particle path. Conventional continuity, momentum and energy equations for the nonstationary motion of an inviscid, non-heat conducting, compressible gas are used in their derivation, along with the equation of state of a perfect gas. All analytical expressions are validated by comparing the results to those obtained indirectly from known self-similar solutions for planar, cylindrical and spherical shock-wave flows generated both by a sudden energy release and by a moving piston. Futhermore, time derivatives of pressure and flow velocity are compared to experimental data from trinitrotoluene (TNT), pentolite, ammonium nitrate-fuel oil (ANFO) and propane-oxygen explosions, and good agreement is obtained.

Calculation of the acoustic radiation force on coated spherical shells in progressive and standing plane waves.

PubMed

Mitri, F G

2006-07-01

In this paper, analytical equations are derived for the time-averaged radiation force induced by progressive and standing acoustic waves incident on elastic spherical shells covered with a layer of viscoelastic and sound-absorbing material. The fluid surrounding the shells is considered compressible and nonviscous. The incident field is assumed to be moderate so that the scattered field from the shells is taken to linear approximation. The analytical results are illustrated by means of a numerical example in which the radiation force function curves are displayed, with particular emphasis on the coating thickness and the content of the hollow region of the shells. The fluid-loading on the radiation force function curves is analysed as well. This study attempts to generalize the various treatments of radiation force due to both progressive and standing waves on spherically-shaped structures immersed in ideal fluids. The results show that various ways can be effectively used for damping resonance peaks, such as by changing the fluid in the interior hollow region of the shells or by changing the coating thickness.

Spectroscopy of a plasma formed in the vicinity of implosion of the shock wave generated by underwater electrical explosion of spherical wire array

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

Antonov, O.; Efimov, S.; Gurovich, V. Tz.

The results of visible spectroscopy of the plasma formed inside a copper capillary placed at the equatorial plane of an underwater electrically exploded spherical wire array (30 mm in diameter; 40 wires, each of 100 μm in diameter) are reported. In the experiments, a pulsed power generator with current amplitude of ∼300 kA and rise time of ∼1.1 μs was used to produce wire array explosion accompanied by the formation of a converging strong shock wave. The data obtained support the assumption of uniformity of the shock wave along the main path of its convergence. The spectroscopic measurements show that this rather simple methodmore » of formation of a converging strong shock wave can be used successfully for studying the shock wave's interaction with matter and the evaporation processes of atoms from a target.« less

Underwater optical communication performance for laser beam propagation through weak oceanic turbulence.

PubMed

Yi, Xiang; Li, Zan; Liu, Zengji

2015-02-20

In clean ocean water, the performance of a underwater optical communication system is limited mainly by oceanic turbulence, which is defined as the fluctuations in the index of refraction resulting from temperature and salinity fluctuations. In this paper, using the refractive index spectrum of oceanic turbulence under weak turbulence conditions, we carry out, for a horizontally propagating plane wave and spherical wave, analysis of the aperture-averaged scintillation index, the associated probability of fade, mean signal-to-noise ratio, and mean bit error rate. Our theoretical results show that for various values of the rate of dissipation of mean squared temperature and the temperature-salinity balance parameter, the large-aperture receiver leads to a remarkable decrease of scintillation and consequently a significant improvement on the system performance. Such an effect is more noticeable in the plane wave case than in the spherical wave case.

Spherical space Bessel-Legendre-Fourier localized modes solver for electromagnetic waves.

PubMed

Alzahrani, Mohammed A; Gauthier, Robert C

2015-10-05

Maxwell's vector wave equations are solved for dielectric configurations that match the symmetry of a spherical computational domain. The electric or magnetic field components and the inverse of the dielectric profile are series expansion defined using basis functions composed of the lowest order spherical Bessel function, polar angle single index dependant Legendre polynomials and azimuthal complex exponential (BLF). The series expressions and non-traditional form of the basis functions result in an eigenvalue matrix formulation of Maxwell's equations that are relatively compact and accurately solvable on a desktop PC. The BLF matrix returns the frequencies and field profiles for steady states modes. The key steps leading to the matrix populating expressions are provided. The validity of the numerical technique is confirmed by comparing the results of computations to those published using complementary techniques.

Numerical modeling of a spherical buoy moored by a cable in three dimensions

NASA Astrophysics Data System (ADS)

Zhu, Xiangqian; Yoo, Wan-Suk

2016-05-01

Floating facilities have been studied based on the static analysis of mooring cables over the past decades. To analyze the floating system of a spherical buoy moored by a cable with a higher accuracy than before, the dynamics of the cables are considered in the construction of the numerical modeling. The cable modeling is established based on a new element frame through which the hydrodynamic loads are expressed efficiently. The accuracy of the cable modeling is verified with an experiment that is conducted by a catenary chain moving in a water tank. In addition, the modeling of a spherical buoy is established with respect to a spherical coordinate in three dimensions, which can suffers the gravity, the variable buoyancy and Froude-Krylov loads. Finally, the numerical modeling for the system of a spherical buoy moored by a cable is established, and a virtual simulation is proceeded with the X- and Y-directional linear waves and the X-directional current. The comparison with the commercial simulation code ProteusDS indicates that the system is accurately analyzed by the numerical modeling. The tensions within the cable, the motions of the system, and the relationship between the motions and waves are illustrated according to the defined sea state. The dynamics of the cables should be considered in analyzing the floating system of a spherical buoy moored by a cable.

A Wave-Optics Approach to Paraxial Geometrical Laws Based on Continuity at Boundaries

ERIC Educational Resources Information Center

Linares, J.; Nistal, M. C.

2011-01-01

We present a derivation of the paraxial geometrical laws starting from a wave-optics approach, in particular by using simple continuity conditions of paraxial spherical waves at boundaries (discontinuities) between optical media. Paraxial geometrical imaging and magnification laws, under refraction and reflection at boundaries, are derived for…

Enhanced kidney stone fragmentation by short delay tandem conventional and modified lithotriptor shock waves: a numerical analysis.

PubMed

Tham, Leung-Mun; Lee, Heow Pueh; Lu, Chun

2007-07-01

We evaluated the effectiveness of modified lithotriptor shock waves using computer models. Finite element models were used to simulate the propagation of lithotriptor shock waves in human renal calculi in vivo. Kidney stones were assumed to be spherical, homogeneous, isotropic and linearly elastic, and immersed in a continuum fluid. Single and tandem shock wave pulses modified to intensify the collapse of cavitation bubbles near the stone surface to increase fragmentation efficiency and suppress the expansion of intraluminal bubbles for decreased vascular injury were analyzed. The effectiveness of the modified shock waves was assessed by comparing the states of loading in the renal calculi induced by these shock waves to those produced by conventional shock waves. Our numerical simulations revealed that modified shock waves produced marginally lower stresses in spherical renal calculi than those produced by conventional shock waves. Tandem pulses of conventional or modified shock waves produced peak stresses in the front and back halves of the renal calculi. However, the single shock wave pulses generated significant peak stresses in only the back halves of the renal calculi. Our numerical simulations suggest that for direct stress wave induced fragmentation modified shock waves should be as effective as conventional shock waves for fragmenting kidney stones. Also, with a small interval of 20 microseconds between the pulses tandem pulse lithotripsy using modified or conventional shock waves could be considerably more effective than single pulse lithotripsy for fragmenting kidney stones.

Influence of arterial wave reflection on carotid blood pressure and intima-media thickness in older endurance trained men and women with pre-hypertension.

PubMed

Heffernan, Kevin S; Jae, Sae Young; Tomayko, Emily; Ishaque, Muhammad R; Fernhall, Bo; Wilund, Kenneth R

2009-05-01

Increased carotid intima-media thickness (IMT) with aging is a significant predictor of mortality. Older endurance trained (ET) individuals have lower carotid artery stiffness but similar carotid IMT when compared to sedentary (SED) age-matched peers. The purpose of this study was to examine the contribution of arterial wave reflections to carotid hemodynamics and IMT in older ET and SED with pre-hypertension. Subjects consisted of endurance-trained master athletes and age-matched sedentary controls (mean age 67 years). Carotid artery Beta-stiffness index and IMT was assessed with ultrasonography. Carotid pressure and augmented pressure from wave reflections (obtained from pulse contour analysis) was measured with applanation tonometry. Carotid systolic blood pressure (SBP) and IMT were not different between groups (P>0.05). Carotid stiffness was significantly lower in ET versus SED (7.3 +/- 0.8 versus 9.9 +/- 0.6, P<0.05). Augmented pressure was significantly greater in ET versus SED (17.7 +/- 1.6 versus 13.3 +/- 1.5 mmHg, P<0.05). When adjusting for differences in resting heart rate, there were no group differences in augmented pressure. In conclusion, older ET persons with pre-hypertension have reduced carotid artery stiffness, but similar carotid SBP and carotid IMT when compared to SED. The lack of change in carotid SBP and IMT in older ET may be related to the inability of chronic exercise training to reduce bradycardia-related augmented pressure from wave reflections with aging.

Amplitude-phase characteristics of electromagnetic fields diffracted by a hole in a thin film with realistic optical properties

NASA Astrophysics Data System (ADS)

Dorofeyev, Illarion

2009-03-01

Characteristics of a quasi-spherical wave front of an electromagnetic field diffracted by a subwavelength hole in a thin film with real optical properties are studied. Related diffraction problem is solved in general by use of the scalar and vector Green's theorems and related Green's function of a boundary-value problem. Local phase deviations of a diffracted wave front from an ideal spherical front are calculated. Diffracted patterns are calculated for the coherent incident fields in case of holes array in a screen of perfect conductivity.

Combined approach to the Hubble Space Telescope wave-front distortion analysis

NASA Astrophysics Data System (ADS)

Roddier, Claude; Roddier, Francois

1993-06-01

Stellar images taken by the HST at various focus positions have been analyzed to estimate wave-front distortion. Rather than using a single algorithm, we found that better results were obtained by combining the advantages of various algorithms. For the planetary camera, the most accurate algorithms consistently gave a spherical aberration of -0.290-micron rms with a maximum deviation of 0.005 micron. Evidence was found that the spherical aberration is essentially produced by the primary mirror. The illumination in the telescope pupil plane was reconstructed and evidence was found for a slight camera misalignment.

A Variational Formulation for the Finite Element Analysis of Sound Wave Propagation in a Spherical Shell

NASA Technical Reports Server (NTRS)

Lebiedzik, Catherine

1995-01-01

Development of design tools to furnish optimal acoustic environments for lightweight aircraft demands the ability to simulate the acoustic system on a workstation. In order to form an effective mathematical model of the phenomena at hand, we have begun by studying the propagation of acoustic waves inside closed spherical shells. Using a fully-coupled fluid-structure interaction model based upon variational principles, we have written a finite element analysis program and are in the process of examining several test cases. Future investigations are planned to increase model accuracy by incorporating non-linear and viscous effects.

Cavity enhanced atomic magnetometry

PubMed Central

Crepaz, Herbert; Ley, Li Yuan; Dumke, Rainer

2015-01-01

Atom sensing based on Faraday rotation is an indispensable method for precision measurements, universally suitable for both hot and cold atomic systems. Here we demonstrate an all-optical magnetometer where the optical cell for Faraday rotation spectroscopy is augmented with a low finesse cavity. Unlike in previous experiments, where specifically designed multipass cells had been employed, our scheme allows to use conventional, spherical vapour cells. Spherical shaped cells have the advantage that they can be effectively coated inside with a spin relaxation suppressing layer providing long spin coherence times without addition of a buffer gas. Cavity enhancement shows in an increase in optical polarization rotation and sensitivity compared to single-pass configurations. PMID:26481853

Dynamic behaviour of a two-microbubble system under ultrasonic wave excitation.

PubMed

Huang, Xiao; Wang, Qian-Xi; Zhang, A-Man; Su, Jian

2018-05-01

Acoustic bubbles have wide and important applications in ultrasonic cleaning, sonochemistry and medical ultrasonics. A two-microbubble system (TMS) under ultrasonic wave excitation is explored in the present study, by using the boundary element method (BEM) based on the potential flow theory. A parametric study of the behaviour of a TMS has been carried out in terms of the amplitude and direction of ultrasound as well as the sizes and separation distance of the two bubbles. Three regimes of the dynamic behaviour of the TMS have been identified in terms of the pressure amplitude of the ultrasonic wave. When subject to a strong wave with the pressure amplitude of 1 atm or larger, the two microbubbles become non-spherical during the first cycle of oscillation, with two counter liquid jets formed. When subject to a weak wave with the pressure amplitude of less than 0.5 atm, two microbubbles may be attracted, repelled, or translate along the wave direction with periodic stable separation distance, depending on their size ratio. However, for the TMS under moderate waves, bubbles undergo both non-spherical oscillation and translation as well as liquid jet rebounding. Copyright © 2018 Elsevier B.V. All rights reserved.

Acoustic radiation force acting on elastic and viscoelastic spherical shells placed in a plane standing wave field.

PubMed

Mitri, F G

2005-08-01

The theory of the acoustic radiation force acting on elastic spherical shells suspended in a plane standing wave field is developed in relation to their thickness and the content of their hollow regions. The theory is modified to include the effect of a hysteresis type of absorption of compressional and shear waves in the material. The fluid-loading effect on the acoustic radiation force function Y(st) is analyzed as well. Results of numerical calculations are presented for a number of elastic and viscoelastic materials, with the hollow region filled with water or air. These results show how the damping due to absorption, the change of the interior fluid inside the shells' hollow regions, and the exterior fluid surrounding their structures, affect the acoustic radiation force.

Parallel decrease in arterial distensibility and in endothelium-dependent dilatation in young women with a history of pre-eclampsia.

PubMed

Pàez, Olga; Alfie, José; Gorosito, Marta; Puleio, Pablo; de Maria, Marcelo; Prieto, Noemì; Majul, Claudio

2009-10-01

Pre-eclampsia not only complicates 5 to 8% of pregnancies but also increases the risk of maternal cardiovascular disease and mortality later in life. We analyzed three different aspects of arterial function (pulse wave velocity, augmentation index, and flow-mediated dilatation), in 55 nonpregnant, normotensive women (18-33 years old) according to their gestational history: 15 nulliparous, 20 with a previous normotensive, and 20 formerly pre-eclamptic pregnancy. Former pre-eclamptic women showed a significantly higher augmentation index and pulse wave velocity (P < 0.001 and P < 0.05, respectively) and lower flow-mediated dilatation (p = 0.01) compared to control groups. In contrast, sublingual nitroglycerine elicited a comparable vasodilatory response in the three groups. The augmentation index correlated significantly with pulse wave velocity and flow-mediated dilatation (R = 0.28 and R = -0.32, respectively, P < 0.05 for both). No significant correlations were observed between augmentation index or flow-mediated dilatation with age, body mass index (BMI), brachial blood pressure, heart rate, or metabolic parameters (plasma cholesterol, glucose, insulin, or insulin resistance). Birth weight maintained a significantly inverse correlation with the augmentation index (R = -0.51, p < 0.002) but not with flow-mediated dilatation. Our findings revealed a parallel decrease in arterial distensibility and endothelium-dependent dilatation in women with a history of pre-eclampsia compared to nulliparous women and women with a previous normal pregnancy. A high augmentation index was the most consistent alteration associated with a history of pre-eclampsia. The study supports the current view that the generalized arterial dysfunction associated with pre-eclampsia persists subclinically after delivery.

Divergent effects of laughter and mental stress on arterial stiffness and central hemodynamics.

PubMed

Vlachopoulos, Charalambos; Xaplanteris, Panagiotis; Alexopoulos, Nikolaos; Aznaouridis, Konstantinos; Vasiliadou, Carmen; Baou, Katerina; Stefanadi, Elli; Stefanadis, Christodoulos

2009-05-01

To investigate the effect of laughter and mental stress on arterial stiffness and central hemodynamics. Arterial stiffness and wave reflections are independent predictors of cardiovascular risk. Chronic psychological stress is an independent risk factor for cardiovascular events, whereas acute stress deteriorates vascular function. Eighteen healthy individuals were studied on three occasions, according to a randomized, single-blind, crossover, sham procedure-controlled design. The effects of viewing a 30-minute segment of two films inducing laughter or stress were assessed. Carotid-femoral pulse wave velocity was used as an index of arterial stiffness; augmentation index was used as a measure of wave reflections. Laughter decreased pulse wave velocity (by 0.30 m/sec, p = .01), and augmentation index (by 2.72%, p = .05). Conversely, stress increased pulse wave velocity (by 0.29 m/sec, p = .05) and augmentation index (by 5.1%, p = .005). Laughter decreased cortisol levels by 1.67 microg/dl (p = .02), soluble P-selectin by 26 ng/ml (p = .02) and marginally von Willebrand factor (by 2.4%, p = .07) and increased total oxidative status (by 61 micromol/L, p < .001). Stress decreased interleukin-6 (by 0.11 pg/ml, p = .04) and increased total oxidative status (by 44 micromol/L, p = .007). Soluble CD40 ligand and fibrinogen remained unchanged. Positive (laughter) and negative (stress) behavioral interventions have divergent acute effects on arterial stiffness and wave reflections. These findings have important clinical implications extending the spectrum of lifestyle modifications that can ameliorate arterial function.

Classification and determination of cerebral biovailability of psychotropic drugs by quantitative "pharmaco-EEG" and psychometric investigations (studies with AX-A411-BS).

PubMed

Saletu, B; Grünberger, J; Linzmayer, L

1977-10-01

Utilizing computerized quantitative analysis of the human scalp recorded electroencephalogram (EEG), it is possible to classify psychotropic drugs. While neuroleptic compounds produce an increase of slow and decrease of fast activities, anxiolytic substances induce an augmentation of fast waves, decrease of alpha waves and--according to the sedative properties of the drug--an increase or decrease of slow waves. Antidepressants produce a concomitant augmentation of slow and fast activities as well as an attenuation of alpha waves. Nootropic substances attenuate slow activities, augment alpha and slow beta waves and decrease fast beta waves. The latter alterations are quite opposite to age-related changes. Since the main psychopharmacological classes seem to have characteristic pharmaco-EEG profiles, the method proved to be useful for determination of psychoactivity and cerebral bioavailability of newly developed substances as for instance AX-A411-BS, a new benzodiazepine. The latter substance was found to be CNS-active and was classified as anxiolytic. It induced dosedependent changes, which were barely visible in the 2nd hour post-drug, became quite obvious in the 4th hour and increased until the 8th hour after oral administration of one single dose. In the higher dosage range, slow activities came to the fore, indicating aoditional sedative properties. Psychometric tests measuring attention, psychomotor activity. mood, vigilance, extroversion, concentration aith a long-lasting effect. The implications of these methods are discussed.

Piezocomposite Actuator Arrays for Correcting and Controlling Wavefront Error in Reflectors

NASA Technical Reports Server (NTRS)

Bradford, Samuel Case; Peterson, Lee D.; Ohara, Catherine M.; Shi, Fang; Agnes, Greg S.; Hoffman, Samuel M.; Wilkie, William Keats

2012-01-01

Three reflectors have been developed and tested to assess the performance of a distributed network of piezocomposite actuators for correcting thermal deformations and total wave-front error. The primary testbed article is an active composite reflector, composed of a spherically curved panel with a graphite face sheet and aluminum honeycomb core composite, and then augmented with a network of 90 distributed piezoelectric composite actuators. The piezoelectric actuator system may be used for correcting as-built residual shape errors, and for controlling low-order, thermally-induced quasi-static distortions of the panel. In this study, thermally-induced surface deformations of 1 to 5 microns were deliberately introduced onto the reflector, then measured using a speckle holography interferometer system. The reflector surface figure was subsequently corrected to a tolerance of 50 nm using the actuators embedded in the reflector's back face sheet. Two additional test articles were constructed: a borosilicate at window at 150 mm diameter with 18 actuators bonded to the back surface; and a direct metal laser sintered reflector with spherical curvature, 230 mm diameter, and 12 actuators bonded to the back surface. In the case of the glass reflector, absolute measurements were performed with an interferometer and the absolute surface was corrected. These test articles were evaluated to determine their absolute surface control capabilities, as well as to assess a multiphysics modeling effort developed under this program for the prediction of active reflector response. This paper will describe the design, construction, and testing of active reflector systems under thermal loads, and subsequent correction of surface shape via distributed peizeoelctric actuation.

A novel embeddable spherical smart aggregate for structural health monitoring: part I. Fabrication and electrical characterization

NASA Astrophysics Data System (ADS)

Kong, Qingzhao; Fan, Shuli; Bai, Xiaolong; Mo, Y. L.; Song, Gangbing

2017-09-01

Recently developed piezoceramic-based transducers, known as smart aggregates (SAs), have shown their applicability and versatility in various applications of structural health monitoring (SHM). The lead zirconate titanate (PZT) patches embedded inside SAs have different modes that are more suitable for generating or receiving different types of stress waves (e.g. P and S waves, each of which has a unique role in SHM). However, due to the geometry of the 2D PZT patch, the embedded SA can only generate or receive the stress wave in a single direction and thus greatly limits its applications. This paper is the first of a series of two companion papers that introduces the authors’ latest work in developing a novel, embeddable spherical smart aggregate (SSA) for the health monitoring of concrete structures. In addition to the 1D guided wave produced by SA, the SSA embedded in concrete structures can generate or receive omni-directional stress waves that can significantly improve the detection aperture and provide additional functionalities in SHM. In the first paper (Part I), the detailed fabrication procedures with the help of 3D printing technology and electrical characterization of the proposed SSA is presented. The natural frequencies of the SSA were experimentally obtained and further compared with the numerical results. In addition, the influence of the components’ thickness (spherical piezoceramic shell and epoxy) and outer radius (spherical piezoceramic shell and protection concrete) on the natural frequencies of the SSA were analytically studied. The results will help elucidate the key parameters that determine the natural frequencies of the SSA. The natural frequencies of the SSA can thus be designed for suitability in the damage detection of concrete structures. In the second paper (Part II), further numerical and experimental verifications on the performance of the proposed SSA in concrete structures will be discussed.

NMR shieldings from density functional perturbation theory: GIPAW versus all-electron calculations

NASA Astrophysics Data System (ADS)

de Wijs, G. A.; Laskowski, R.; Blaha, P.; Havenith, R. W. A.; Kresse, G.; Marsman, M.

2017-02-01

We present a benchmark of the density functional linear response calculation of NMR shieldings within the gauge-including projector-augmented-wave method against all-electron augmented-plane-wave+local-orbital and uncontracted Gaussian basis set results for NMR shieldings in molecular and solid state systems. In general, excellent agreement between the aforementioned methods is obtained. Scalar relativistic effects are shown to be quite large for nuclei in molecules in the deshielded limit. The small component makes up a substantial part of the relativistic corrections.

NMR shieldings from density functional perturbation theory: GIPAW versus all-electron calculations.

PubMed

de Wijs, G A; Laskowski, R; Blaha, P; Havenith, R W A; Kresse, G; Marsman, M

2017-02-14

We present a benchmark of the density functional linear response calculation of NMR shieldings within the gauge-including projector-augmented-wave method against all-electron augmented-plane-wave+local-orbital and uncontracted Gaussian basis set results for NMR shieldings in molecular and solid state systems. In general, excellent agreement between the aforementioned methods is obtained. Scalar relativistic effects are shown to be quite large for nuclei in molecules in the deshielded limit. The small component makes up a substantial part of the relativistic corrections.

The numerical design of a spherical baroclinic experiment for Spacelab flights

NASA Technical Reports Server (NTRS)

Fowlis, W. W.; Roberts, G. O.

1982-01-01

The near-zero G environment of Spacelab is the basis of a true spherical experimental model of synoptic scale baroclinic atmospheric processes, using a radial dielectric body force analogous to gravity over a volume of liquid within two concentric spheres. The baroclinic motions are generated by corotating the spheres and imposing thermal boundary conditions, such that the liquid is subjected to a stable radial gradient and a latitudinal gradient. Owing to mathematical difficulties associated with the spherical geometry, quantitative design criteria can be acquired only by means of numerical models. The procedure adopted required the development of two computer codes based on the Navier-Stokes equations. The codes, of which the first calculates axisymmetric steady flow solutions and the second determines the growth or decay rates of linear wave perturbations with different wave numbers, are combined to generate marginal stability curves.

Modulational instability: Conservation laws and bright soliton solution of ion-acoustic waves in electron-positron-ion-dust plasmas

NASA Astrophysics Data System (ADS)

EL-Kalaawy, O. H.

2018-02-01

We consider the nonlinear propagation of non-planar (cylindrical and spherical) ion-acoustic (IA) envelope solitary waves in an unmagnetized plasma consisting of electron-positron-ion-dust plasma with two-electron temperature distributions in the context of the non-extensive statistics. The basic set of fluid equations is reduced to the modified nonlinear Schrödinger (MNLS) equation in cylindrical and spherical geometry by using the reductive perturbation method (RPM). It is found that the nature of the modulational instabilities would be significantly modified due to the effects of the non-extensive and other plasma parameters as well as cylindrical and spherical geometry. Conservation laws of the MNLS equation are obtained by Lie symmetry and multiplier method. A new exact solution (envelope bright soliton) is obtained by the extended homogeneous balance method. Finally, we study the results of this article.

On the rate of black hole binary mergers in galactic nuclei due to dynamical hardening

NASA Astrophysics Data System (ADS)

Leigh, N. W. C.; Geller, A. M.; McKernan, B.; Ford, K. E. S.; Mac Low, M.-M.; Bellovary, J.; Haiman, Z.; Lyra, W.; Samsing, J.; O'Dowd, M.; Kocsis, B.; Endlich, S.

2018-03-01

We assess the contribution of dynamical hardening by direct three-body scattering interactions to the rate of stellar-mass black hole binary (BHB) mergers in galactic nuclei. We derive an analytic model for the single-binary encounter rate in a nucleus with spherical and disc components hosting a super-massive black hole (SMBH). We determine the total number of encounters NGW needed to harden a BHB to the point that inspiral due to gravitational wave emission occurs before the next three-body scattering event. This is done independently for both the spherical and disc components. Using a Monte Carlo approach, we refine our calculations for NGW to include gravitational wave emission between scattering events. For astrophysically plausible models, we find that typically NGW ≲ 10. We find two separate regimes for the efficient dynamical hardening of BHBs: (1) spherical star clusters with high central densities, low-velocity dispersions, and no significant Keplerian component and (2) migration traps in discs around SMBHs lacking any significant spherical stellar component in the vicinity of the migration trap, which is expected due to effective orbital inclination reduction of any spherical population by the disc. We also find a weak correlation between the ratio of the second-order velocity moment to velocity dispersion in galactic nuclei and the rate of BHB mergers, where this ratio is a proxy for the ratio between the rotation- and dispersion-supported components. Because discs enforce planar interactions that are efficient in hardening BHBs, particularly in migration traps, they have high merger rates that can contribute significantly to the rate of BHB mergers detected by the advanced Laser Interferometer Gravitational-Wave Observatory.

Wave Augmented Diffuser for Centrifugal Compressor

NASA Technical Reports Server (NTRS)

Skoch, Gary J. (Inventor); Paxson, Daniel E. (Inventor)

2001-01-01

A wave augmented diffuser for a centrifugal compressor surrounds the outlet of an impeller that rotates on a drive shaft having an axis of rotation. The impeller brings flow in in an axial direction and imparts kinetic energy to the flow discharging it in radial and tangential directions. The flow is discharged into a plurality of circumferentially disposed wave chambers. The wave chambers are periodically opened and closed by a rotary valve such that the flow through the diffuser is unsteady. The valve includes a plurality of valve openings that are periodically brought into and out of fluid communication with the wave chambers. When the wave chambers are closed, a reflected compression wave moves upstream towards the diffuser bringing the flow into the wave chamber to rest. This action recovers the kinetic energy from the flow and limits any boundary layer growth. The flow is then discharged in an axial direction through an opening in the valve plate when the valve plate is rotated to an open position. The diffuser thus efficiently raises the static pressure of the fluid and discharges an axially directed flow at a radius that is predominantly below the maximum radius of the diffuser.

Numerical and theoretical analyses of underground explosion cavity decoupling

NASA Astrophysics Data System (ADS)

Jensen, R.; Aldridge, D. F.; Chael, E. P.

2013-12-01

It has long been established that the amplitudes of seismic waves radiated from an underground explosion can be reduced by detonating the explosive within a fluid-filled cavity of adequate size. Significant amplitude reduction occurs because the reflection coefficient at the fluid/rock interface (i.e., the cavity wall) is large. In fact, the DC frequency limit of the reflection coefficient for a spherically-diverging seismic wave incident upon a concentric spherical interface is -1.0, independent of radius of curvature and all material properties. In order to quantify to the degree of amplitude reduction expected in various realistic scenarios, we are conducting mathematical and numerical investigations into the so-called 'cavity decoupling problem' for a buried explosion. Our working tool is a numerical algorithm for simulating fully-coupled seismic and acoustic wave propagation in mixed solid/fluid media. Solution methodology involves explicit, time-domain, finite differencing of the elastodynamic velocity-stress partial differential system on a three-dimensional staggered spatial grid. Conditional logic is used to avoid shear stress updating within fluid zones; this approach leads to computational efficiency gains for models containing a significant proportion of ideal fluid. Numerical stability and accuracy are maintained at air/rock interfaces (where the contrast in mass density is on the order of 1 to 2000) via an FD operator 'order switching' formalism. The fourth-order spatial FD operator used throughout the bulk of the earth model is reduced to second-order in the immediate vicinity of a high-contrast interface. Point explosions detonated at the center of an air-filled or water-filled spherical cavity lead to strong resonant oscillations in radiated seismic energy, with period controlled by cavity radius and sound speed of the fill fluid. If the explosion is off-center, or the cavity is non-spherical, shear waves are generated in the surrounding elastic wholespace. Equilibrating the moment magnitudes of explosions for differing fill materials leads to misleading results in the amplitudes of the radiated elastic waves. The proper procedure entails equalizing the intrinsic energies of the explosions. Numerically-calculated results are in reasonable agreement with a theoretical model based on acoustic and elastic spherical wave propagation from a point center of symmetry. Sandia National Laboratories is a multi-program 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.

Development of fully non-inductive plasmas heated by medium and high-harmonic fast waves in the national spherical torus experiment upgrade

NASA Astrophysics Data System (ADS)

Taylor, G.; Poli, F.; Bertelli, N.; Harvey, R. W.; Hosea, J. C.; Mueller, D.; Perkins, R. J.; Phillips, C. K.; Raman, R.

2015-12-01

A major challenge for spherical tokamak development is to start-up and ramp-up the plasma current (Ip) without using a central solenoid. Experiments in the National Spherical Torus eXperiment (NSTX) demonstrated that 1.4 MW of 30 MHz high-harmonic fast wave (HHFW) power could generate an Ip = 300 kA H-mode discharge with a non-inductive Ip fraction, fNI ˜ 0.7. The discharge had an axial toroidal magnetic field (BT(0)) of 0.55 T, the maximum BT(0) available on NSTX. NSTX has undergone a major upgrade (NSTX-U), that will eventually allow the generation of BT(0) ≤ 1 T and Ip ≤ 2 MA plasmas. Full wave simulations of 30 MHz HHFW and medium harmonic fast wave (MHFW) heating in NSTX-U predict significantly reduced FW power loss in the plasma edge at the higher BT(0) achievable in NSTX-U. HHFW experiments will aim to generate stable, fNI ˜ 1, Ip = 300 kA H-mode plasmas and to ramp Ip from 250 to 400 kA with FW power. Time-dependent TRANSP simulations are used to develop non-inductive Ip ramp-up and sustainment using 30 MHz FW power. This paper presents results from these RF simulations and plans for developing non-inductive plasmas heated by FW power.

On the Exit Boundary Condition for One-Dimensional Calculations of Pulsed Detonation Engine Performance

NASA Technical Reports Server (NTRS)

Wilson, Jack; Paxson, Daniel E.

2002-01-01

In one-dimensional calculations of pulsed detonation engine (PDE) performance, the exit boundary condition is frequently taken to be a constant static pressure. In reality, for an isolated detonation tube, after the detonation wave arrives at the exit plane, there will be a region of high pressure, which will gradually return to ambient pressure as an almost spherical shock wave expands away from the exit, and weakens. Initially, the flow is supersonic, unaffected by external pressure, but later becomes subsonic. Previous authors have accounted for this situation either by assuming the subsonic pressure decay to be a relaxation phenomenon, or by running a two-dimensional calculation first, including a domain external to the detonation tube, and using the resulting exit pressure temporal distribution as the boundary condition for one-dimensional calculations. These calculations show that the increased pressure does affect the PDE performance. In the present work, a simple model of the exit process is used to estimate the pressure decay time. The planar shock wave emerging from the tube is assumed to transform into a spherical shock wave. The initial strength of the spherical shock wave is determined from comparison with experimental results. Its subsequent propagation, and resulting pressure at the tube exit, is given by a numerical blast wave calculation. The model agrees reasonably well with other, limited, results. Finally, the model was used as the exit boundary condition for a one-dimensional calculation of PDE performance to obtain the thrust wall pressure for a hydrogen-air detonation in tubes of length to diameter ratio (L/D) of 4, and 10, as well as for the original, constant pressure boundary condition. The modified boundary condition had no performance impact for values of L/D > 10, and moderate impact for L/D = 4.

The Numerical Studies Program for the Atmospheric General Circulation Experiment (AGCE) for Spacelab Flights

NASA Technical Reports Server (NTRS)

Fowlis, W. W. (Editor); Davis, M. H. (Editor)

1981-01-01

The atmospheric general circulation experiment (AGCE) numerical design for Spacelab flights was studied. A spherical baroclinic flow experiment which models the large scale circulations of the Earth's atmosphere was proposed. Gravity is simulated by a radial dielectric body force. The major objective of the AGCE is to study nonlinear baroclinic wave flows in spherical geometry. Numerical models must be developed which accurately predict the basic axisymmetric states and the stability of nonlinear baroclinic wave flows. A three dimensional, fully nonlinear, numerical model and the AGCE based on the complete set of equations is required. Progress in the AGCE numerical design studies program is reported.

Absolute Equation-of-State Measurement for Polystyrene from 25 - 60 Mbar Using a Spherically Converging Shock Wave

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

Glenzer, Siegfried

We have developed an experimental platform for the National Ignition Facility (NIF) that uses spherically converging shock waves for absolute equation of state (EOS) measurements along the principal Hugoniot. In this Letter we present radiographic compression measurements for polystyrene that were taken at shock pressures reaching 60 Mbar (6 TPa). This significantly exceeds previously published results obtained on the Nova laser [Cauble et al., Phys. Rev. Lett. 80, 1248 (1998)] at strongly improved precision, allowing to discriminate between different EOS models. We find excellent agreement with Kohn-Sham Density Functional Theory based molecular dynamics simulations.

Practical algorithms for simulation and reconstruction of digital in-line holograms.

PubMed

Latychevskaia, Tatiana; Fink, Hans-Werner

2015-03-20

Here we present practical methods for simulation and reconstruction of in-line digital holograms recorded with plane and spherical waves. The algorithms described here are applicable to holographic imaging of an object exhibiting absorption as well as phase-shifting properties. Optimal parameters, related to distances, sampling rate, and other factors for successful simulation and reconstruction of holograms are evaluated and criteria for the achievable resolution are worked out. Moreover, we show that the numerical procedures for the reconstruction of holograms recorded with plane and spherical waves are identical under certain conditions. Experimental examples of holograms and their reconstructions are also discussed.

On the generation of horizontal shear waves by underground explosions in jointed rocks

DOE PAGES

Vorobiev, Oleg; Ezzedine, Souheil; Antoun, Tarabay; ...

2015-02-04

This paper describes computational studies of non-spherical ground motions generated by spherical explosions in a heavily jointed granite formation. Various factors affecting the shear wave generation are considered, including joint spacing, orientation, persistence and properties. Simulations are performed both in 2D for a single joint set to elucidate the basic response mechanisms, and in 3D for multiple joint sets to realistically represent in situ conditions in a realistic geologic setting. The joints are modeled explicitly using both contact elements and weakness planes in the material. Simulations are performed both deterministically and stochastically to quantify the effects of geologic uncertainties onmore » near field ground motions. The mechanical properties of the rock and the joints as well as the joint spacing and orientation are taken from experimental test data and geophysical logs corresponding to the Climax Stock granitic outcrop, which is the geologic setting of the Source Physics Experiment (SPE). Agreement between simulation results and near field wave motion data from SPE enables newfound understanding of the origin and extent of non-spherical motions associated with underground explosions in fractured geologic media.« less

Transient Flows in a Pipe System with Pump Shut-Down and the Simultaneous Closing of a Spherical Valve

NASA Astrophysics Data System (ADS)

Zhang, Zh.

2016-11-01

Because of the limited value of the wave propagation speed in water the propagation of a pressure surge in transient flows can be tracked in the time series. This enables both the pressure head and the flow velocity in pipe flows to be determined as a function of both the coordinate along the pipe and the time. The propagation of the pressure surge includes both wave transmission and reflection. The latter occurs where the flow section is changed. The wave tracking method has been demonstrated as highly accurate and subsequently was applied to much more complex hydraulic systems, in which the pump is shut off and the spherical valve is simultaneously progressively closed. A combined four-quadrant characteristic of the pump and a spherical valve has been worked out, with which the computational procedure for the transient flow in the complex system could be significantly simplified. It has been demonstrated that not only the pressure surge in the hydraulic system but also the rotational speed of the pump could be satisfactorily computed. The computational algorithm has been demonstrated as quite simple, so that all calculations could be performed simply by means of the Microsoft Excel module.

On the completeness and the linear dependence of the Cartesian multipole series in representing the solution to the Helmholtz equation.

PubMed

Liu, Yangfan; Bolton, J Stuart

2016-08-01

The (Cartesian) multipole series, i.e., the series comprising monopole, dipoles, quadrupoles, etc., can be used, as an alternative to the spherical or cylindrical wave series, in representing sound fields in a wide range of problems, such as source radiation, sound scattering, etc. The proofs of the completeness of the spherical and cylindrical wave series in these problems are classical results, and it is also generally agreed that the Cartesian multipole series spans the same space as the spherical waves: a rigorous mathematical proof of that statement has, however, not been presented. In the present work, such a proof of the completeness of the Cartesian multipole series, both in two and three dimensions, is given, and the linear dependence relations among different orders of multipoles are discussed, which then allows one to easily extract a basis from the multipole series. In particular, it is concluded that the multipoles comprising the two highest orders in the series form a basis of the whole series, since the multipoles of all the lower source orders can be expressed as a linear combination of that basis.

Backscattering enhancement with a finite beam width for millimeter-wavelength weather radars

NASA Astrophysics Data System (ADS)

Kobayashi, Satoru; Tanelli, Simone; Iguchi, Toshio; Im, Eastwood

2004-12-01

Backscattering enhancement from random hydrometeors should increase as wavelengths of radars reach millimeter regions. For 95 GHz radars, the reflectivity of backscattering is expected to increase by 2 dB, due to multiple scattering including backscattering enhancement, for water droplets of diameter of 1 mm with a density of 5 x 103 m-3. Previous theoretical studies of backscattering enhancement considered infinitely extending plane waves. In this paper, we expand the theory to spherical waves with a Gaussian antenna pattern, including depolarizing effects. While the differences from the plane wave results are not great when the optical thickness is small, as the latter increases the differences become significant, and essentially depend on the ratio of radar footprint radius to the mean free path of hydrometeors. In this regime, for a radar footprint that is smaller than the mean free path, the backscattering-enhancement reflectivity corresponding to spherical waves is significantly less pronounced than in the case of the plane wave theory. Hence this reduction factor must be taken into account when analyzing radar reflectivity factors for use in remote sensing applications.

Inertial modes and their transition to turbulence in a differentially rotating spherical gap flow

NASA Astrophysics Data System (ADS)

Hoff, Michael; Harlander, Uwe; Andrés Triana, Santiago; Egbers, Christoph

2016-04-01

We present a study of inertial modes in a spherical shell experiment. Inertial modes are Coriolis-restored linear wave modes, often arise in rapidly-rotating fluids (e.g. in the Earth's liquid outer core [1]). Recent experimental works showed that inertial modes exist in differentially rotating spherical shells. A set of particular inertial modes, characterized by (l,m,ˆω), where l, m is the polar and azimuthal wavenumber and ˆω = ω/Ωout the dimensionless frequency [2], has been found. It is known that they arise due to eruptions in the Ekman boundary layer of the outer shell. But it is an open issue why only a few modes develop and how they get enhanced. Kelley et al. 2010 [3] showed that some modes draw their energy from detached shear layers (e.g. Stewartson layers) via over-reflection. Additionally, Rieutord et al. (2012) [4] found critical layers within the shear layers below which most of the modes cannot exist. In contrast to other spherical shell experiments, we have a full optical access to the flow. Therefore, we present an experimental study of inertial modes, based on Particle-Image-Velocimetry (PIV) data, in a differentially rotating spherical gap flow where the inner sphere is subrotating or counter-rotating at Ωin with respect to the outer spherical shell at Ωout, characterized by the Rossby number Ro = (Ωin - Ωout)/Ωout. The radius ratio of η = 1/3, with rin = 40mm and rout = 120mm, is close to that of the Earth's core. Our apparatus is running at Ekman numbers (E ≈ 10-5, with E = ν/(Ωoutrout2), two orders of magnitude higher than most of the other experiments. Based on a frequency-Rossby number spectrogram, we can partly confirm previous considerations with respect to the onset of inertial modes. In contrast, the behavior of the modes in the counter-rotation regime is different. We found a triad interaction between three dominant inertial modes, where one is a slow axisymmetric Rossby mode [5]. We show that the amplitude of the most dominant mode (l,m,ˆω) = (3,2,˜ 0.71) is increasing with increasing |Ro| until a critical Rossby number Rocrit. Accompanying with this is an increase of the zonal mean flow outside the tangent cylinder, leading to enhanced angular momentum transport. At the particular Rocrit, the wave mode, and the entire flow, breaks up into smaller-scale turbulence [6], together with a strong increase of the zonal mean flow inside the tangent cylinder. We found that the critical Rossby number scales approximately with E1/5. References [1] Aldridge, K. D.; Lumb, L. I. (1987): Inertial waves identified in the Earth's fluid outer core. Nature 325 (6103), S. 421-423. DOI: 10.1038/325421a0. [2] Greenspan, H. P. (1968): The theory of rotating fluids. London: Cambridge U.P. (Cambridge monographs on mechanics and applied mathematics). [3] Kelley, D. H.; Triana, S. A.; Zimmerman, D. S.; Lathrop, D. P. (2010): Selection of inertial modes in spherical Couette flow. Phys. Rev. E 81 (2), 26311. DOI: 10.1103/PhysRevE.81.026311. [4] Rieutord, M.; Triana, S. A.; Zimmerman, D. S.; Lathrop, D. P. (2012): Excitation of inertial modes in an experimental spherical Couette flow. Phys. Rev. E 86 (2), 026304. DOI: 10.1103/PhysRevE.86.026304. [5] Hoff, M., Harlander, U., Egbers, C. (2016): Experimental survey of linear and nonlinear inertial waves and wave instabilities in a spherical shell. J. Fluid Mech., (in print) [6] Kerswell, R. R. (1999): Secondary instabilities in rapidly rotating fluids: inertial wave breakdown. Journal of Fluid Mechanics 382, S. 283-306. DOI: 10.1017/S0022112098003954.

No regularity singularities exist at points of general relativistic shock wave interaction between shocks from different characteristic families.

PubMed

Reintjes, Moritz; Temple, Blake

2015-05-08

We give a constructive proof that coordinate transformations exist which raise the regularity of the gravitational metric tensor from C 0,1 to C 1,1 in a neighbourhood of points of shock wave collision in general relativity. The proof applies to collisions between shock waves coming from different characteristic families, in spherically symmetric spacetimes. Our result here implies that spacetime is locally inertial and corrects an error in our earlier Proc. R. Soc. A publication, which led us to the false conclusion that such coordinate transformations, which smooth the metric to C 1,1 , cannot exist. Thus, our result implies that regularity singularities (a type of mild singularity introduced in our Proc. R. Soc. A paper) do not exist at points of interacting shock waves from different families in spherically symmetric spacetimes. Our result generalizes Israel's celebrated 1966 paper to the case of such shock wave interactions but our proof strategy differs fundamentally from that used by Israel and is an extension of the strategy outlined in our original Proc. R. Soc. A publication. Whether regularity singularities exist in more complicated shock wave solutions of the Einstein-Euler equations remains open.

No regularity singularities exist at points of general relativistic shock wave interaction between shocks from different characteristic families

PubMed Central

Reintjes, Moritz; Temple, Blake

2015-01-01

We give a constructive proof that coordinate transformations exist which raise the regularity of the gravitational metric tensor from C0,1 to C1,1 in a neighbourhood of points of shock wave collision in general relativity. The proof applies to collisions between shock waves coming from different characteristic families, in spherically symmetric spacetimes. Our result here implies that spacetime is locally inertial and corrects an error in our earlier Proc. R. Soc. A publication, which led us to the false conclusion that such coordinate transformations, which smooth the metric to C1,1, cannot exist. Thus, our result implies that regularity singularities (a type of mild singularity introduced in our Proc. R. Soc. A paper) do not exist at points of interacting shock waves from different families in spherically symmetric spacetimes. Our result generalizes Israel's celebrated 1966 paper to the case of such shock wave interactions but our proof strategy differs fundamentally from that used by Israel and is an extension of the strategy outlined in our original Proc. R. Soc. A publication. Whether regularity singularities exist in more complicated shock wave solutions of the Einstein–Euler equations remains open. PMID:27547092

Properties of the Average Distribution of Equatorial Kelvin Waves Investigated with the GROGRAT Ray Tracer

DTIC Science & Technology

2009-01-01

spheric quasi-biennial oscillation ( QBO ). In this paper we combine several measured data sets with the Gravity wave Regional Or Global RAy Tracer (GROGRAT...equatorial wave modes and a broad spectrum of gravity waves (GWs) Kelvin waves are one of the main drivers of the quasi-biennial oscil- lation ( QBO ) of the...and dy- namics in the stratosphere and mesosphere (even at high lati- tudes) are modulated or influenced by the QBO , showing the importance of the

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

Compact range for variable-zone measurements

DOEpatents

Burnside, Walter D.; Rudduck, Roger C.; Yu, Jiunn S.

1988-08-02

A compact range for testing antennas or radar targets includes a source for directing energy along a feedline toward a parabolic reflector. The reflected wave is a spherical wave with a radius dependent on the distance of the source from the focal point of the reflector.

Compact range for variable-zone measurements

DOEpatents

Burnside, Walter D.; Rudduck, Roger C.; Yu, Jiunn S.

1988-01-01

A compact range for testing antennas or radar targets includes a source for directing energy along a feedline toward a parabolic reflector. The reflected wave is a spherical wave with a radius dependent on the distance of the source from the focal point of the reflector.

Dispersion of gravitational waves in cold spherical interstellar medium

NASA Astrophysics Data System (ADS)

Barta, Dániel; Vasúth, Mátyás

We investigate the propagation of locally plane, small-amplitude, monochromatic gravitational waves (GWs) through cold compressible interstellar gas in order to provide a more accurate picture of expected waveforms for direct detection. The quasi-isothermal gas is concentrated in a spherical symmetric cloud held together by self-gravitation. Gravitational waves can be treated as linearized perturbations on the background inner Schwarzschild spacetime. The perturbed quantities lead to the field equations governing the gas dynamics and describe the interaction of gravitational waves with matter. We have shown that the transport equation of these amplitudes provides numerical solutions for the frequency-alteration. The decrease in frequency is driven by the energy dissipating process of GW-matter interactions. The decrease is significantly smaller than the magnitude of the original frequency and too small to be detectable by present second-generation and planned third-generation detectors. It exhibits a power-law relationship between original and decreased frequencies. The frequency deviation was examined particularly for the transient signal GW150914.

Precision flyer initiator

DOEpatents

Frank, A.M.; Lee, R.S.

1998-05-26

A precision flyer initiator forms a substantially spherical detonation wave in a high explosive (HE) pellet. An explosive driver, such as a detonating cord, a wire bridge circuit or a small explosive, is detonated. A flyer material is sandwiched between the explosive driver and an end of a barrel that contains an inner channel. A projectile or ``flyer`` is sheared from the flyer material by the force of the explosive driver and projected through the inner channel. The flyer than strikes the HE pellet, which is supported above a second end of the barrel by a spacer ring. A gap or shock decoupling material delays the shock wave in the barrel from predetonating the HE pellet before the flyer. A spherical detonation wave is formed in the HE pellet. Thus, a shock wave traveling through the barrel fails to reach the HE pellet before the flyer strikes the HE pellet. The precision flyer initiator can be used in mining devices, well-drilling devices and anti-tank devices. 10 figs.

Precision flyer initiator

DOEpatents

Frank, Alan M.; Lee, Ronald S.

1998-01-01

A precision flyer initiator forms a substantially spherical detonation wave in a high explosive (HE) pellet. An explosive driver, such as a detonating cord, a wire bridge circuit or a small explosive, is detonated. A flyer material is sandwiched between the explosive driver and an end of a barrel that contains an inner channel. A projectile or "flyer" is sheared from the flyer material by the force of the explosive driver and projected through the inner channel. The flyer than strikes the HE pellet, which is supported above a second end of the barrel by a spacer ring. A gap or shock decoupling material delays the shock wave in the barrel from predetonating the HE pellet before the flyer. A spherical detonation wave is formed in the HE pellet. Thus, a shock wave traveling through the barrel fails to reach the HE pellet before the flyer strikes the HE pellet. The precision flyer initiator can be used in mining devices, well-drilling devices and anti-tank devices.

Arterial stiffness is associated to cardiorespiratory fitness and body mass index in young Swedish adults: The Lifestyle, Biomarkers, and Atherosclerosis study.

PubMed

Fernberg, Ulrika; Fernström, Maria; Hurtig-Wennlöf, Anita

2017-11-01

Background Early changes in the large muscular arteries are already associated with risk factors as hypertension and obesity in adolescence and young adulthood. The present study examines the association between arterial stiffness measurements, pulse wave velocity and augmentation index and lifestyle-related factors, body composition and cardiorespiratory fitness, in young, healthy, Swedish adults. Design This study used a population-based cross-sectional sample. Methods The 834 participants in the study were self-reported healthy, non-smoking, age 18-25 years. Augmentation index and pulse wave velocity were measured with applanation tonometry. Cardiorespiratory fitness was measured by ergometer bike test to estimate maximal oxygen uptake. Body mass index (kg/m 2 ) was calculated and categorised according to classification by the World Health Organisation. Results Young Swedish adults with obesity and low cardiorespiratory fitness have significantly higher pulse wave velocity and augmentation index than non-obese young adults with medium or high cardiorespiratory fitness. The observed U-shaped association between pulse wave velocity and body mass index categories in women indicates that it might be more beneficial to be normal weight than underweight when assessing the arterial stiffness with pulse wave velocity. The highest mean pulse wave velocity was found in overweight/obese individuals with low cardiorespiratory fitness. The lowest mean pulse wave velocity was found in normal weight individuals with high cardiorespiratory fitness. Cardiorespiratory fitness had a stronger effect than body mass index on arterial stiffness in multiple regression analyses. Conclusions The inverse association between cardiorespiratory fitness and arterial stiffness is observed already in young adults. The study result highlights the importance of high cardiorespiratory fitness, but also that underweight individuals may be a possible risk group that needs to be further studied.

Calculation of the Transition Matrix for the Scattering of Acoustic Waves from a Thin Elastic Spherical Shell Using the ATILA Finite Element Code

DTIC Science & Technology

1994-03-01

products of radial Hankel functions and spherical harmonics. The chosen driving frequency was 474 Hz, corresponding to a value of ka 1, where k is the...spherical harmonics. The chosen driving frequency was 474 Hz, corresponding to a value of ka = 1, where k is the wavenumber of sound in water and a is...wife Adriana for her support, understanding, and for her help in typing this thesis. vi I. INTRODUCTION The utilization of sonar systems in

A theoretical NMR study of selected benzazoles: Comparison of GIPAW and GIAO-PCM (DMSO) calculations.

PubMed

Marín-Luna, Marta; Alkorta, Ibon; Elguero, José

2018-03-01

This paper compares the absolute shieldings obtained by gauge-including-projected-augmented-wave (GIPAW) to those obtained by gauge-invariant atomic orbital/Becke, 3-parameter, Lee-Yang-Parr (GIAO/B3LYP)/6-311++G(d,p)-polarizable continuum model (PCM, dimethyl sulfoxide) for nine benzazoles (benzimidazoles, indazoles, and benzotriazoles) recorded in the solid-state. Three nuclei were explored, 13 C, 15 N, and 19 F, and the gauge-including-projected-augmented-wave approach only proved better for 15 N MAS NMR. Copyright © 2017 John Wiley & Sons, Ltd.

Compact range for variable-zone measurements

DOEpatents

Burnside, W.D.; Rudduck, R.C.; Yu, J.S.

1987-02-27

A compact range for testing antennas or radar targets includes a source for directing energy along a feedline toward a parabolic reflector. The reflected wave is a spherical wave with a radius dependent on the distance of the source from the focal point of the reflector. 2 figs.

A new two-metric theory of gravity with prior geometry

NASA Technical Reports Server (NTRS)

Lightman, A. P.; Lee, D. L.

1972-01-01

A theory is presented of gravity which has the same post-Newtonian (PN) as that of general relativity. The field equations, and a calculation of the PN limit of the theory are discussed along with the equations of stellar structure for static spherically symmetric stars. A special exterior spherically symmetric solution, time dependent solutions, conservations, and gravitational waves are analyzed.

Prospects for gravitational wave astronomy with next generation large-scale pulsar timing arrays

NASA Astrophysics Data System (ADS)

Wang, Yan; Mohanty, Soumya D.

2018-02-01

Next generation radio telescopes, namely the Five-hundred-meter Aperture Spherical Telescope (FAST) and the Square Kilometer Array (SKA), will revolutionize the pulsar timing arrays (PTAs) based gravitational wave (GW) searches. We review some of the characteristics of FAST and SKA, and the resulting PTAs, that are pertinent to the detection of gravitational wave signals from individual supermassive black hole binaries.

A study of nondiffracting Lommel beams propagating in a medium containing spherical scatterers

NASA Astrophysics Data System (ADS)

Belafhal, A.; Ez-zariy, L.; Hricha, Z.

2016-11-01

By means of the expansion of the nondiffracting beams on plane waves with help of the Whittaker integral, an exact analytical expression of the far-field form function of the scattering of the acoustic and optical nondiffracting Lommel beams propagating in a medium containing spherical particles, considered as rigid and single spheres, is investigated in this work. The form function of the scattering of the high order Bessel beam by a rigid and isolated sphere is deduced, from our finding, as a special case. The effects of the wave number-sphere radius product (ka) , the polar angle (φ) , the propagation half-cone angle (β) and the scattering angle (θ) on the far-field form function of the scattered wave have been analyzed and discussed numerically. The numerical results show that the illumination of a rigid sphere by Lommel beams produces asymmetrical scattering.

Contribution to study of interfaces instabilities in plane, cylindrical and spherical geometry

NASA Astrophysics Data System (ADS)

Toque, Nathalie

1996-12-01

This thesis proposes several experiments of hydrodynamical instabilities which are studied, numerically and theoretically. The experiments are in plane and cylindrical geometry. Their X-ray radiographies show the evolution of an interface between two solid media crossed by a detonation wave. These materials are initially solid. They become liquide under shock wave or stay between two phases, solid and liquid. The numerical study aims at simulating with the codes EAD and Ouranos, the interfaces instabilities which appear in the experiments. The experimental radiographies and the numerical pictures are in quite good agreement. The theoretical study suggests to modelise a spatio-temporal part of the experiments to obtain the quantitative development of perturbations at the interfaces and in the flows. The models are linear and in plane, cylindrical and spherical geometry. They preceed the inoming study of transition between linear and non linear development of instabilities in multifluids flows crossed by shock waves.

Spherical shock due to point explosion with varying energy

NASA Astrophysics Data System (ADS)

Singh, J. B.; Srivastava, S. K.

1983-05-01

The motion of a perfect gas behind a weak or strong spherical point-explosion shock wave in a nonuniform rest atmosphere is investigated analytically for the case of variable flow energy. The self-similar solutions derived are also adaptable to a uniform expanding piston. The solution is applied to the isothermal case, and the results of numerical integration are presented in graphs showing the density, velocity, and pressure distributions for different values of delta. The findings are considered significant for investigations of sonic booms, laser production of plasmas, high-altitude nuclear detonations, supernova explosions, and the sudden expansion of the solar corona, and for the laboratory production of high temperatures using shock waves.

Arterial pulse wave velocity but not augmentation index is associated with coronary artery disease extent and severity: implications for arterial transfer function applicability.

PubMed

Hope, Sarah A; Antonis, Paul; Adam, David; Cameron, James D; Meredith, Ian T

2007-10-01

The aim of this study was to test the hypothesis that coronary artery disease extent and severity are associated with central aortic pressure waveform characteristics. Although it is thought that central aortic pressure waveform characteristics, particularly augmentation index, may influence cardiovascular disease progression and predict cardiovascular risk, little is known of the relationship between central waveform characteristics and the severity and extent of coronary artery disease. Central aortic waveforms (2F Millar pressure transducer-tipped catheters) were acquired at the time of coronary angiography for suspected native coronary artery disease in 40 patients (24 male). The severity and extent of disease were assessed independently by two observers using two previously described scoring systems (modified Gensini's stenosis and Sullivan's extent scores). Relationships between disease scores, aortic waveform characteristics, aorto-radial pulse wave velocity and subject demographic features were assessed by regression techniques. Both extent and severity scores were associated with increasing age and male sex (P < 0.001), but no other risk factors. Both scores were independently associated with aorto-radial pulse wave velocity (P < 0.001), which entered a multiple regression model prior to age and sex. This association was not dependent upon blood pressure. Neither score was associated with central aortic augmentation index, by either simple or multiple linear regression techniques including heart rate, subject demographic features and cardiovascular risk factors. Aorto-radial pulse wave velocity, but not central aortic augmentation index, is associated with both the extent and severity of coronary artery disease. This has potentially important implications for applicability of a generalized arterial transfer function.

Spherical silicon-shell photonic band gap structures fabricated by laser-assisted chemical vapor deposition

NASA Astrophysics Data System (ADS)

Wang, H.; Yang, Z. Y.; Lu, Y. F.

2007-02-01

Laser-assisted chemical vapor deposition was applied in fabricating three-dimensional (3D) spherical-shell photonic band gap (PBG) structures by depositing silicon shells covering silica particles, which had been self-assembled into 3D colloidal crystals. The colloidal crystals of self-assembled silica particles were formed on silicon substrates using the isothermal heating evaporation approach. A continuous wave Nd:YAG laser (1064nm wavelength) was used to deposit silicon shells by thermally decomposing disilane gas. Periodic silicon-shell/silica-particle PBG structures were obtained. By removing the silica particles enclosed in the silicon shells using hydrofluoric acid, hollow spherical silicon-shell arrays were produced. This technique is capable of fabricating structures with complete photonic band gaps, which is predicted by simulations with the plane wave method. The techniques developed in this study have the potential to flexibly engineer the positions of the PBGs by varying both the silica particle size and the silicon-shell thickness. Ellipsometry was used to investigate the specific photonic band gaps for both structures.

Inviscid dynamics of a wet foam drop with monodisperse bubble size distribution

NASA Astrophysics Data System (ADS)

McDaniel, J. Gregory; Akhatov, Iskander; Holt, R. Glynn

2002-06-01

Motivated by recent experiments involving the acoustic levitation of foam drops, we develop a model for nonlinear oscillations of a spherical drop composed of monodisperse aqueous foam with void fraction below 0.1. The model conceptually divides a foam drop into many cells, each cell consisting of a spherical volume of liquid with a bubble at its center. By treating the liquid as incompressible and inviscid, a nonlinear equation is obtained for bubble motion due to a pressure applied at the outer radius of the liquid sphere. Upon linearizing this equation and connecting the cells at their outer radii, a wave equation is obtained with a dispersion relation for the sound waves in a bubbly liquid. For the spherical drop, this equation is solved by a normal mode expansion that yields the natural frequencies as functions of standard foam parameters. Numerical examples illustrate how the analysis may be used to extract foam parameters, such as void fraction and bubble radius, from the experimentally measured natural frequencies of a foam drop.

Cavitation studies in microgravity

NASA Astrophysics Data System (ADS)

Kobel, Philippe; Obreschkow, Danail; Farhat, Mohamed; Dorsaz, Nicolas; de Bosset, Aurele

The hydrodynamic cavitation phenomenon is a major source of erosion for many industrial systems such as cryogenic pumps for rocket propulsion, fast ship propellers, hydraulic pipelines and turbines. Erosive processes are associated with liquid jets and shockwaves emission fol-lowing the cavity collapse. Yet, fundamental understanding of these processes requires further cavitation studies inside various geometries of liquid volumes, as the bubble dynamics strongly depends the surrounding pressure field. To this end, microgravity represents a unique platform to produce spherical fluid geometries and remove the hydrostatic pressure gradient induced by gravity. The goal of our first experiment (flown on ESA's parabolic flight campaigns 2005 and 2006) was to study single bubble dynamics inside large spherical water drops (having a radius between 8 and 13 mm) produced in microgravity. The water drops were created by a micro-pump that smoothly expelled the liquid through a custom-designed injector tube. Then, the cavitation bubble was generated through a fast electrical discharge between two electrodes immersed in the liquid from above. High-speed imaging allowed to analyze the implications of isolated finite volumes and spherical free surfaces on bubble evolution, liquid jets formation and shock wave dynamics. Of particular interest are the following results: (A) Bubble lifetimes are shorter than in extended liquid volumes, which could be explain by deriving novel corrective terms to the Rayleigh-Plesset equation. (B) Transient crowds of micro-bubbles (smaller than 1mm) appeared at the instants of shockwaves emission. A comparison between high-speed visualizations and 3D N-particle simulations of a shock front inside a liquid sphere reveals that focus zones within the drop lead to a significantly increased density of induced cavitation. Considering shock wave crossing and focusing may hence prove crucially useful to understand the important process of cavitation erosion. The aim of our future microgravity experiment is to assess the direct effects of gravity on cavitation bubble collapse through a comparison of single cavitation bubbles collapsing in mi-crogravity, normal gravity, and hypergravity. In particular, we shall investigate the shape of the bubble in its final collapse stage and the amount of energy dissipated in the dominant collapse channels, such as liquid jet, shock wave, and rebound bubble. The highly spherical bubbles will be produced via a point-like plasma generated by a high power laser beam. One major hypothesis that we will test is an increase in shock wave energy with decreasing gravity as a consequence of the higher final sphericity and suppression of liquid jets. To support this, we introduce an analytical model for the gravity-perturbed asymmetric collapse of spherical bubbles, and demonstrate that all initially spherical bubbles develop a gravity-related vertical jet along their collapse.

A survey of electron Bernstein wave heating and current drive potential for spherical tokamaks

NASA Astrophysics Data System (ADS)

Urban, Jakub; Decker, Joan; Peysson, Yves; Preinhaelter, Josef; Shevchenko, Vladimir; Taylor, Gary; Vahala, Linda; Vahala, George

2011-08-01

The electron Bernstein wave (EBW) is typically the only wave in the electron cyclotron (EC) range that can be applied in spherical tokamaks for heating and current drive (H&CD). Spherical tokamaks (STs) operate generally in high-β regimes, in which the usual EC O- and X-modes are cut off. In this case, EBWs seem to be the only option that can provide features similar to the EC waves—controllable localized H&CD that can be used for core plasma heating as well as for accurate plasma stabilization. The EBW is a quasi-electrostatic wave that can be excited by mode conversion from a suitably launched O- or X-mode; its propagation further inside the plasma is strongly influenced by the plasma parameters. These rather awkward properties make its application somewhat more difficult. In this paper we perform an extensive numerical study of EBW H&CD performance in four typical ST plasmas (NSTX L- and H-mode, MAST Upgrade, NHTX). Coupled ray-tracing (AMR) and Fokker-Planck (LUKE) codes are employed to simulate EBWs of varying frequencies and launch conditions, which are the fundamental EBW parameters that can be chosen and controlled. Our results indicate that an efficient and universal EBW H&CD system is indeed viable. In particular, power can be deposited and current reasonably efficiently driven across the whole plasma radius. Such a system could be controlled by a suitably chosen launching antenna vertical position and would also be sufficiently robust.

Coherent electromagnetic waves in the presence of a half space of randomly distributed scatterers

NASA Technical Reports Server (NTRS)

Karam, M. A.; Fung, A. K.

1988-01-01

The present investigation of coherent field propagation notes, upon solving the Foldy-Twersky integral equation for a half-space of small spherical scatterers illuminated by a plane wave at oblique incidence, that the coherent field for a horizontally-polarized incident wave exhibits reflectivity and transmissivity consistent with the Fresnel formula for an equivalent continuous effective medium. In the case of a vertically polarized incident wave, both the vertical and longitudinal waves obtained for the coherent field have reflectivities and transmissivities that do not agree with the Fresnel formula.

Description of an α-cluster tail in 8Be and 20Ne: Delocalization of the α cluster by quantum penetration

NASA Astrophysics Data System (ADS)

Kanada-En'yo, Yoshiko

2014-10-01

We analyze the α-cluster wave functions in cluster states of ^8Be and ^{20}Ne by comparing the exact relative wave function obtained by the generator coordinate method (GCM) with various types of trial functions. For the trial functions, we adopt the fixed range shifted Gaussian of the Brink-Bloch (BB) wave function, the spherical Gaussian with the adjustable range parameter of the spherical Tohsaki-Horiuchi-Schuck-Röpke (sTHSR), the deformed Gaussian of the deformed THSR (dTHSR), and a function with the Yukawa tail (YT). The quality of the description of the exact wave function with a trial function is judged by the squared overlap between the trial function and the GCM wave function. A better result is obtained with the sTHSR wave function than the BB wave function, and further improvement can be made with the dTHSR wave function because these wave functions can describe the outer tail better. The YT wave function gives almost an equal quality to or even better quality than the dTHSR wave function, indicating that the outer tail of α-cluster states is characterized by the Yukawa-like tail rather than the Gaussian tail. In weakly bound α-cluster states with small α separation energy and the low centrifugal and Coulomb barriers, the outer tail part is the slowly damping function described well by the quantum penetration through the effective barrier. This outer tail characterizes the almost zero-energy free α gas behavior, i.e., the delocalization of the cluster.

Study of non-spherical bubble oscillations near a surface in a weak acoustic standing wave field.

PubMed

Xi, Xiaoyu; Cegla, Frederic; Mettin, Robert; Holsteyns, Frank; Lippert, Alexander

2014-04-01

The interaction of acoustically driven bubbles with a wall is important in many applications of ultrasound and cavitation, as the close boundary can severely alter the bubble dynamics. In this paper, the non-spherical surface oscillations of bubbles near a surface in a weak acoustic standing wave field are investigated experimentally and numerically. The translation, the volume, and surface mode oscillations of bubbles near a flat glass surface were observed by a high speed camera in a standing wave cell at 46.8 kHz. The model approach is based on a modified Keller-Miksis equation coupled to surface mode amplitude equations in the first order, and to the translation equations. Modifications are introduced due to the adjacent wall. It was found that a bubble's oscillation mode can change in the presence of the wall, as compared to the bubble in the bulk liquid. In particular, the wall shifts the instability pressure thresholds to smaller driving frequencies for fixed bubble equilibrium radii, or to smaller equilibrium radii for fixed excitation frequency. This can destabilize otherwise spherical bubbles, or stabilize bubbles undergoing surface oscillations in the bulk. The bubble dynamics observed in experiment demonstrated the same trend as the theoretical results.

Analysis of long wavelength electromagnetic scattering by a magnetized cold plasma prolate spheroid

NASA Astrophysics Data System (ADS)

Ahmadizadeh, Yadollah; Jazi, Bahram; Abdoli-Arani, Abbas

2013-08-01

Using dielectric permittivity tensor of the magnetized prolate plasma, the scattering of long wavelength electromagnetic waves from the mentioned object is studied. The resonance frequency and differential scattering cross section for the backward scattered waves are presented. Consistency between the resonance frequency in this configuration and results obtained for spherical plasma are investigated. Finally, the effective factors on obtained results such as incident wave polarization, the frequency of the incident wave, the plasma frequency and the cyclotron frequency are analyzed.

The jump-off velocity of an impulsively loaded spherical shell

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

Chabaud, Brandon M.; Brock, Jerry S.

2012-04-13

We consider a constant temperature spherical shell of isotropic, homogeneous, linearly elastic material with density {rho} and Lame coefficients {lambda} and {mu}. The inner and outer radii of the shell are r{sub i} and r{sub o}, respectively. We assume that the inside of the shell is a void. On the outside of the shell, we apply a uniform, time-varying pressure p(t). We also assume that the shell is initially at rest. We want to compute the jump-off time and velocity of the pressure wave, which are the first time after t = 0 at which the pressure wave from themore » outer surface reaches the inner surface. This analysis computes the jump-off velocity and time for both compressible and incompressible materials. This differs substantially from [3], where only incompressible materials are considered. We will consider the behavior of an impulsively loaded, exponentially decaying pressure wave p(t) = P{sub 0{sup e}}{sup -{alpha}t}, where {alpha} {ge} 0. We notice that a constant pressure wave P(t) = P{sub 0} is a special case ({alpha} = 0) of a decaying pressure wave. Both of these boundary conditions are considered in [3].« less

Simulations towards the achievement of non-inductive current ramp-up and sustainment in the National Spherical Torus Experiment Upgrade

DOE PAGES

Poli, F. M.; Andre, R. G.; Bertelli, N.; ...

2015-10-30

One of the goals of the National Spherical Torus Experiment Upgrade (NSTX-U) (Menard et al 2012 Nucl. Fusion 52 083015) is the demonstration of fully non-inductive start-up, current ramp-up and sustainment. This work discusses predictive simulations where the available heating and current drive systems are combined to maximize the non-inductive current and minimize the solenoidal contribution. Radio-frequency waves at harmonics higher than the ion cyclotron resonance (high-harmonic fast waves (HHFW)) and neutral beam injection are used to ramp the plasma current non-inductively starting from an initial Ohmic plasma. An interesting synergy is observed in the simulations between the HHFW andmore » electron cyclotron (EC) wave heating. Furthermore, time-dependent simulations indicate that, depending on the phasing of the HHFW antenna, EC wave heating can significantly increase the effectiveness of the radio-frequency power, by heating the electrons and increasing the current drive efficiency, thus relaxing the requirements on the level of HHFW power that needs to be absorbed in the core plasma to drive the same amount of fast-wave current.« less

High-harmonic fast magnetosonic wave coupling, propagation, and heating in a spherical torus plasma

NASA Astrophysics Data System (ADS)

Menard, J.; Majeski, R.; Kaita, R.; Ono, M.; Munsat, T.; Stutman, D.; Finkenthal, M.

1999-05-01

A novel rotatable two-strap antenna has been installed in the current drive experiment upgrade (CDX-U) [T. Jones, Ph.D. thesis, Princeton University (1995)] in order to investigate high-harmonic fast wave coupling, propagation, and electron heating as a function of strap angle and strap phasing in a spherical torus plasma. Radio-frequency-driven sheath effects are found to fit antenna loading trends at very low power and become negligible above a few kilowatts. At sufficiently high power, the measured coupling efficiency as a function of strap angle is found to agree favorably with cold plasma wave theory. Far-forward microwave scattering from wave-induced density fluctuations in the plasma core tracks the predicted fast wave loading as the antenna is rotated. Signs of electron heating during rf power injection have been observed in CDX-U with central Thomson scattering, impurity ion spectroscopy, and Langmuir probes. While these initial results appear promising, damping of the fast wave on thermal ions at high ion-cyclotron-harmonic number may compete with electron damping at sufficiently high ion β—possibly resulting in a significantly reduced current drive efficiency and production of a fast ion population. Preliminary results from ray-tracing calculations which include these ion damping effects are presented.

Propagation analysis of the helicity-drive Alfven wave in the HIST spherical torus plasmas

NASA Astrophysics Data System (ADS)

Hyobu, T.; Hanao, T.; Hirono, H.; Ito, K.; Matsumoto, K.; Nakayama, T.; Kikuchi, Y.; Fukumoto, N.; Nagata, M.

2012-10-01

Coaxial Helicity Injection is an efficient current-drive method used in spherical torus experiments. It is a key issue to investigate the dynamo mechanism required to maintain the plasmas. The behavior of a low frequency Alfven wave being possibly related to the dynamo current drive has been studied on HIST. The observed magnetic fluctuation with about 80 kHz propagates along the open flux column (OFC) region, spreading toward the core region. The parallel phase velocity is estimated at 321 km/s from the propagation velocity measured axially along the OFC. The parallel phase velocity agrees well to the Alfven velocity. The radial perpendicular propagation of the Alfven wave can be calculated by a theory based on cold or warm plasma approximation with the Hall term. The theoretical calculation indicates that there are two resonance points and is a cut-off point. These resonance and cut-off points agree well with the magnetic measurement. A part of fluctuation propagates slowly beyond the first resonance point. The wave polarization is left-handed near the resonance point and then converts to be nearly liner outside the resonance point. From these results, we speculate that the torsional Alfven wave evolves to the kinetic Alfven wave during the radial propagation.

Implementation of density functional theory method on object-oriented programming (C++) to calculate energy band structure using the projector augmented wave (PAW)

NASA Astrophysics Data System (ADS)

Alfianto, E.; Rusydi, F.; Aisyah, N. D.; Fadilla, R. N.; Dipojono, H. K.; Martoprawiro, M. A.

2017-05-01

This study implemented DFT method into the C++ programming language with object-oriented programming rules (expressive software). The use of expressive software results in getting a simple programming structure, which is similar to mathematical formula. This will facilitate the scientific community to develop the software. We validate our software by calculating the energy band structure of Silica, Carbon, and Germanium with FCC structure using the Projector Augmented Wave (PAW) method then compare the results to Quantum Espresso calculation’s results. This study shows that the accuracy of the software is 85% compared to Quantum Espresso.

Second-order spherical optoelectronic detector for 3D multi-particles wave emission and propagation in space time domains

NASA Astrophysics Data System (ADS)

Romano, Francesco; Cimmino, Rosario F.

2017-09-01

This paper concerns a feasibility study on a 2nd order spherical, or three-dimensional, angular momentum and linear momentum detector for photonic radiation applications. It has been developed in order to obtain a paraxial approximation of physical events observed under Coulomb gauge condition, which is essential to compute both the longitudinal and transverse rotational components of the observed 3-D vortex field, generally neglected by conventional detection systems under current usage. Since light and laser beams are neither full transversal or rotational phenomena, to measure directly and in the same time both the energy, mainly not-rotational, related to the relevant part of the linear momentum and the potential solenoidal energy (vortex), related to the angular momentum, 2nd order spherical, or 3-D, detector techniques are required. In addition, direct 2nd order measure techniques enable development of TEM + DEM [17] studies, therefore allowing for monochromatic complex wave detection with a paraxial accuracy in the relativistic time-space domain. Light and optic or Electromagnetic 2nd order 3-D AnM energy may usefully be used in tre-dimensional optical TEM, noTEM, DEM vortex or laser communications The paper illustrates an innovative quadratic order 3-D spherical model detector applied to directly measure a light source power spectrum and compares the performances of this innovative technique with those obtained with a traditional 1st order system. Results from a number of test experiments conducted in cooperation with INAF Observatories of ArcetriFlorence and Medicina-Bologna (Italy), and focused on telescopic observations of the inter-stellar electromagnetic radiations, are also summarized. The innovative quadratic-order spherical detector turns out to be optimal for optical and/or radio telescopes application, optical and optoelectronic sensors development and gravitational wave 2nd order detectors implementation. Although the proposed method is very innovative, it shows a very good adherence with results obtained with the conventional techniques in current usage.

Close-in Blast Waves from Spherical Charges*

NASA Astrophysics Data System (ADS)

Howard, William; Kuhl, Allen

2011-06-01

We study the close-in blast waves created by the detonation of spherical high explosives (HE) charges, via numerical simulations with our Arbitrary-Lagrange-Eulerian (ALE3D) code. We used a finely-resolved, fixed Eulerian 2-D mesh (200 μm per cell) to capture the detonation of the charge, the blast wave propagation in air, and the reflection of the blast wave from an ideal surface. The thermodynamic properties of the detonation products and air were specified by the Cheetah code. A programmed-burn model was used to detonate the charge at a rate based on measured detonation velocities. The results were analyzed to evaluate the: (i) free air pressure-range curves: Δps (R) , (ii) free air impulse curves, (iii) reflected pressure-range curves, and (iv) reflected impulse-range curves. A variety of explosives were studied. Conclusions are: (i) close-in (R < 10 cm /g 1 / 3) , each explosive had its own (unique) blast wave (e.g., Δps (R , HE) ~ a /Rn , where n is different for each explosive); (ii) these close-in blast waves do not scale with the ``Heat of Detonation'' of the explosive (because close-in, there is not enough time to fully couple the chemical energy to the air via piston work); (iii) instead they are related to the detonation conditions inside the charge. Scaling laws will be proposed for such close-in blast waves.

The dynamics of magnetic Rossby waves in spherical dynamo simulations: A signature of strong-field dynamos?

NASA Astrophysics Data System (ADS)

Hori, K.; Teed, R. J.; Jones, C. A.

2018-03-01

We investigate slow magnetic Rossby waves in convection-driven dynamos in rotating spherical shells. Quasi-geostrophic waves riding on a mean zonal flow may account for some of the geomagnetic westward drifts and have the potential to allow the toroidal field strength within the planetary fluid core to be estimated. We extend the work of Hori et al. (2015) to include a wider range of models, and perform a detailed analysis of the results. We find that a predicted dispersion relation matches well with the longitudinal drifts observed in our strong-field dynamos. We discuss the validity of our linear theory, since we also find that the nonlinear Lorentz terms influence the observed waveforms. These wave motions are excited by convective instability, which determines the preferred azimuthal wavenumbers. Studies of linear rotating magnetoconvection have suggested that slow magnetic Rossby modes emerge in the magnetostrophic regime, in which the Lorentz and Coriolis forces are in balance in the vorticity equation. We confirm this to be predominant balance for the slow waves we have detected in nonlinear dynamo systems. We also show that a completely different wave regime emerges if the magnetic field is not present. Finally we report the corresponding radial magnetic field variations observed at the surface of the shell in our simulations and discuss the detectability of these waves in the geomagnetic secular variation.

GEOSIM: A numerical model for geophysical fluid flow simulation

NASA Technical Reports Server (NTRS)

Butler, Karen A.; Miller, Timothy L.; Lu, Huei-Iin

1991-01-01

A numerical model which simulates geophysical fluid flow in a wide range of problems is described in detail, and comparisons of some of the model's results are made with previous experimental and numerical studies. The model is based upon the Boussinesq Navier-Stokes equations in spherical coordinates, which can be reduced to a cylindrical system when latitudinal walls are used near the pole and the ratio of latitudinal length to the radius of the sphere is small. The equations are approximated by finite differences in the meridional plane and spectral decomposition in the azimuthal direction. The user can specify a variety of boundary and initial conditions, and there are five different spectral truncation options. The results of five validation cases are presented: (1) the transition between axisymmetric flow and baroclinic wave flow in the side heated annulus; (2) the steady baroclinic wave of the side heated annulus; (3) the wave amplitude vacillation of the side heated annulus; (4) transition to baroclinic wave flow in a bottom heated annulus; and (5) the Spacelab Geophysical Fluid Flow Cell (spherical) experiment.

Multi-domain boundary element method for axi-symmetric layered linear acoustic systems

NASA Astrophysics Data System (ADS)

Reiter, Paul; Ziegelwanger, Harald

2017-12-01

Homogeneous porous materials like rock wool or synthetic foam are the main tool for acoustic absorption. The conventional absorbing structure for sound-proofing consists of one or multiple absorbers placed in front of a rigid wall, with or without air-gaps in between. Various models exist to describe these so called multi-layered acoustic systems mathematically for incoming plane waves. However, there is no efficient method to calculate the sound field in a half space above a multi layered acoustic system for an incoming spherical wave. In this work, an axi-symmetric multi-domain boundary element method (BEM) for absorbing multi layered acoustic systems and incoming spherical waves is introduced. In the proposed BEM formulation, a complex wave number is used to model absorbing materials as a fluid and a coordinate transformation is introduced which simplifies singular integrals of the conventional BEM to non-singular radial and angular integrals. The radial and angular part are integrated analytically and numerically, respectively. The output of the method can be interpreted as a numerical half space Green's function for grounds consisting of layered materials.

Phase function of a spherical particle when scattering an inhomogeneous electromagnetic plane wave.

PubMed

Frisvad, Jeppe Revall

2018-04-01

In absorbing media, electromagnetic plane waves are most often inhomogeneous. Existing solutions for the scattering of an inhomogeneous plane wave by a spherical particle provide no explicit expressions for the scattering components. In addition, current analytical solutions require evaluation of the complex hypergeometric function F 1 2 for every term of a series expansion. In this work, I develop a simpler solution based on associated Legendre functions with argument zero. It is similar to the solution for homogeneous plane waves but with new explicit expressions for the angular dependency of the far-field scattering components, that is, the phase function. I include recurrence formulas for practical evaluation and provide numerical examples to evaluate how well the new expressions match previous work in some limiting cases. The predicted difference in the scattering phase function due to inhomogeneity is not negligible for light entering an absorbing medium at an oblique angle. The presented theory could thus be useful for predicting scattering behavior in dye-based random lasing and in solar cell absorption enhancement.

Convergence of shock waves generated by underwater electrical explosion of cylindrical wire arrays between different boundary geometries

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

Yanuka, D.; Zinowits, H. E.; Krasik, Ya. E.

The results of experiments and numerical simulations of a shock wave propagating between either conical or parabolic bounding walls are presented. The shock wave was generated by a microsecond timescale underwater electrical explosion of a cylindrical wire array supplied by a current pulse having an amplitude of ∼230 kA and a rise time of ∼1 μs. It is shown that with the same energy density deposition into the exploding wire array, the shock wave converges faster between parabolic walls, and as a result, the pressure in the vicinity of convergence is ∼2.3 times higher than in the case of conical walls. Themore » results obtained are compared to those of earlier experiments [Antonov et al., Appl. Phys. Lett. 102, 124104 (2013)] with explosions of spherical wire arrays. It is shown that at a distance of ∼400 μm from the implosion origin the pressure obtained in the current experiments is higher than for the case of spherical wire arrays.« less

X ray microscope assembly and alignment support and advanced x ray microscope design and analysis

NASA Technical Reports Server (NTRS)

Shealy, David L.

1991-01-01

Considerable efforts have been devoted recently to the design, analysis, fabrication, and testing of spherical Schwarzschild microscopes for soft x ray application in microscopy and projection lithography. The spherical Schwarzschild microscope consists of two concentric spherical mirrors configured such that the third order spherical aberration and coma are zero. Since multilayers are used on the mirror substrates for x ray applications, it is desirable to have only two reflecting surfaces in a microscope. In order to reduce microscope aberrations and increase the field of view, generalized mirror surface profiles have been considered in this investigation. Based on incoherent and sine wave modulation transfer function (MTF) calculations, the object plane resolution of a microscope has been analyzed as a function of the object height and numerical aperture (NA) of the primary for several spherical Schwarzschild, conic, and aspherical head reflecting two mirror microscope configurations.

SUNIST Microwave Power System

NASA Astrophysics Data System (ADS)

Feng, Songlin; Yang, Xuanzong; Feng, Chunhua; Wang, Long; Rao, Jun; Feng, Kecheng

2005-06-01

Experiments on the start-up and formation of spherical tokamak plasmas by electron cyclotron heating alone without ohmic heating and electrode discharge assisted electron cyclotron wave current start-up will be carried out on the SUNIST (Sino United Spherical Tokamak) device. The 2.45 GHz/100kW/30 ms microwave power system and 1000 V/50 A power supply for electrode discharge are ready for experiments with non-inductive current drive.

Computerized ultrasound risk evaluation system

DOEpatents

Duric, Nebojsa; Littrup, Peter J.; Holsapple, III, Earle; Barter, Robert Henry; Moore, Thomas L.; Azevedo, Stephen G.; Ferguson, Sidney W.

2007-10-23

A method and system for examining tissue are provided in which the tissue is maintained in a position so that it may be insonified with a plurality of pulsed spherical or cylindrical acoustic waves. The insonifying acoustic waves are scattered by the tissue so that scattered acoustic radiation including a mix of reflected and transmitted acoustic waves is received. A representation of a portion of the tissue is then derived from the received scattered acoustic radiation.

Faraday Wave Turbulence on a Spherical Liquid Shell

NASA Technical Reports Server (NTRS)

Holt, R. Glynn; Trinh, Eugene H.

1996-01-01

Millimeter-radius liquid shells are acoustically levitated in an ultrasonic field. Capillary waves are observed on the shells. At low energies (minimal acoustic amplitude, thick shell) a resonance is observed between the symmetric and antisymmetric thin film oscillation modes. At high energies (high acoustic pressure, thin shell) the shell becomes fully covered with high-amplitude waves. Temporal spectra of scattered light from the shell in this regime exhibit a power-law decay indicative of turbulence.

Geometry of a naked singularity created by standing waves near a Schwarzschild horizon, and its application to the binary black hole problem

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

Mandel, Ilya

The most promising way to compute the gravitational waves emitted by binary black holes (BBHs) in their last dozen orbits, where post-Newtonian techniques fail, is a quasistationary approximation introduced by Detweiler and being pursued by Price and others. In this approximation the outgoing gravitational waves at infinity and downgoing gravitational waves at the holes' horizons are replaced by standing waves so as to guarantee that the spacetime has a helical Killing vector field. Because the horizon generators will not, in general, be tidally locked to the holes' orbital motion, the standing waves will destroy the horizons, converting the black holesmore » into naked singularities that resemble black holes down to near the horizon radius. This paper uses a spherically symmetric, scalar-field model problem to explore in detail the following BBH issues: (i) The destruction of a horizon by the standing waves. (ii) The accuracy with which the resulting naked singularity resembles a black hole. (iii) The conversion of the standing-wave spacetime (with a destroyed horizon) into a spacetime with downgoing waves by the addition of a 'radiation-reaction field'. (iv) The accuracy with which the resulting downgoing waves agree with the downgoing waves of a true black-hole spacetime (with horizon). The model problem used to study these issues consists of a Schwarzschild black hole endowed with spherical standing waves of a scalar field, whose wave frequency and near-horizon energy density are chosen to match those of the standing gravitational waves of the BBH quasistationary approximation. It is found that the spacetime metric of the singular, standing-wave spacetime, and its radiation-reaction-field-constructed downgoing waves are quite close to those for a Schwarzschild black hole with downgoing waves--sufficiently close to make the BBH quasistationary approximation look promising for non-tidally-locked black holes.« less

Fluidically Augmented Nozzles for Pulse Detonation Engine Applications

DTIC Science & Technology

2011-12-01

25 captured the flow soon after the leading shock wave passed through the diverging section of the nozzle. As can be seen, the “pillow” has begun to...35 Figure 25. Initial Detonation Wave Enters the Diverging Section of the Nozzle...charging the combustor with an appropriate fuel/air mixture. This mixture is then ignited, producing a flame that is initially a deflagration wave . A

Spin flip statistics and spin wave interference patterns in Ising ferromagnetic films: A Monte Carlo study.

PubMed

Acharyya, Muktish

2017-07-01

The spin wave interference is studied in two dimensional Ising ferromagnet driven by two coherent spherical magnetic field waves by Monte Carlo simulation. The spin waves are found to propagate and interfere according to the classic rule of interference pattern generated by two point sources. The interference pattern of spin wave is observed in one boundary of the lattice. The interference pattern is detected and studied by spin flip statistics at high and low temperatures. The destructive interference is manifested as the large number of spin flips and vice versa.

Wave aberrations in rhesus monkeys with vision-induced ametropias

PubMed Central

Ramamirtham, Ramkumar; Kee, Chea-su; Hung, Li-Fang; Qiao-Grider, Ying; Huang, Juan; Roorda, Austin; Smith, Earl L.

2007-01-01

The purpose of this study was to investigate the relationship between refractive errors and high-order aberrations in infant rhesus monkeys. Specifically, we compared the monochromatic wave aberrations measured with a Shack-Hartman wavefront sensor between normal monkeys and monkeys with vision-induced refractive errors. Shortly after birth, both normal monkeys and treated monkeys reared with optically induced defocus or form deprivation showed a decrease in the magnitude of high-order aberrations with age. However, the decrease in aberrations was typically smaller in the treated animals. Thus, at the end of the lens-rearing period, higher than normal amounts of aberrations were observed in treated eyes, both hyperopic and myopic eyes and treated eyes that developed astigmatism, but not spherical ametropias. The total RMS wavefront error increased with the degree of spherical refractive error, but was not correlated with the degree of astigmatism. Both myopic and hyperopic treated eyes showed elevated amounts of coma and trefoil and the degree of trefoil increased with the degree of spherical ametropia. Myopic eyes also exhibited a much higher prevalence of positive spherical aberration than normal or treated hyperopic eyes. Following the onset of unrestricted vision, the amount of high-order aberrations decreased in the treated monkeys that also recovered from the experimentally induced refractive errors. Our results demonstrate that high-order aberrations are influenced by visual experience in young primates and that the increase in high-order aberrations in our treated monkeys appears to be an optical byproduct of the vision-induced alterations in ocular growth that underlie changes in refractive error. The results from our study suggest that the higher amounts of wave aberrations observed in ametropic humans are likely to be a consequence, rather than a cause, of abnormal refractive development. PMID:17825347

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

Orbital volume augmentation using expandable hydrogel implants in acquired anophthalmia and phthisis bulbi.

PubMed

Kim, Esther Lee; Bernardino, Carlo Rob; Levin, Flora

2016-01-01

The purpose of this study is to describe our experience using expandable spherical hydrogel implants and injectable hydrogel pellets for orbital volume augmentation in cases of post-enucleation socket syndrome after acquired anophthalmia or phthisis bulbi. We retrospectively reviewed the clinical records of all adult patients who received an expandable hydrogel implant for orbital volume loss following enucleation or phthisis bulbi at the Emory Eye Center between 2004 and January 2007 and the Yale Eye Center between 2009 and 2011. The study included 9 women and 5 men with a mean age of 51.2 years old (range 35-76 years old). Follow-up spanned 6 to 71 months (median of 18.5 months). Four patients received spherical hydrogel implants and 10 patients received hydrogel pellet injections. On average, nine pellets (range 5-16) were placed in each patient over an average of 1.7 injections (range 1-3). Most commonly, five pellets were injected per session, as was the case for 13 of the 17 treatment sessions. Post-operative complications included 2 cases of pellet migration, one subcutaneously and one anteriorly due to insufficiently posterior implant placement, and 1 hospital admission for pain after injection of 10 pellets in one visit. All patients experienced an overall subjective improvement in cosmesis. Self-expandable hydrogel implants appear to offer several advantages over other existing options for orbital volume augmentation, as they are easy to place, generally well-tolerated, volume-titratable, and to the extent that our follow-up shows, may be a safe and durable means of treating orbital volume loss in patients with acquired anophthalmia and phthisis bulbi.

On mass transport in magmatic porosity waves

NASA Astrophysics Data System (ADS)

Jordan, J.; Hesse, M. A.; Rudge, J. F.

2017-12-01

Geochemical analyses of oceanic basalts indicate the mantle is lithologically heterogenous and subject to partial melting. Here we show that porosity waves-which arise naturally in models of buoyancy driven melt migration-transport mass and preserve geochemical signatures, at least partially. Prior studies of tracer transport in one dimensional porosity waves conclude that porosity waves do not transfer mass. However, it is well known that one-dimensional porosity waves are unstable in two and three dimensions and break up into sets of cylindrical or spherical porosity waves. We show that tracer transport in higher dimensional porosity waves is dramatically different than in one dimension. Lateral melt focusing into these high porosity regions leads to melt recirculating in the center of the wave. Melt focusing and recirculation are not resolvable in one dimension where no sustained transport is observed in numerical experiments of solitary porosity waves. In two and three dimensions, the recirculating melt is separated from the background melt-flow field by a circular or spherical dividing streamline and transported with the phase velocity of the porosity wave. The amount of melt focusing that occurs within any given porosity wave, and thus, the extent of the dividing streamline, and resultant volume of transported melt is extremely sensitive to the selection of porosity-permeability and porosity-rheology relationships. Therefore, we present a regime diagram spanning common parameterizations that illustrates the minimum amplitude and phase velocity required for a solitary porosity wave to transport mass as a function of material properties and common parameters used in magma dynamics and mid-ocean ridge models. The realization that solitary waves are capable of sustaining melt transport may require the reinterpretation of previous studies. For example, transport in porosity waves may allow melts that originated from the partial melting of fertile heterogeneities to retain their incompatible trace element signatures as they rise through the mantle. Porosity waves may also provide a mechanism for mixing melts derived from heterogeneities with ambient melts derived from different depths in the mantle.

Shock waves from non-spherically collapsing cavitation bubbles

NASA Astrophysics Data System (ADS)

Supponen, Outi; Obreschkow, Danail; Farhat, Mohamed

2017-11-01

Combining simultaneous high-speed imaging and hydrophone measurements, we uncover details of the multiple shock wave emission from laser-induced cavitation bubbles collapsing in a non-spherical way. For strongly deformed bubbles collapsing near a free surface, we identify the distinct shock waves caused by the jet impact onto the opposite bubble wall and by the individual collapses of the remaining bubble segments. The energy carried by each of these shocks depends on the level of bubble deformation, quantified by the anisotropy parameter ζ, the dimensionless equivalent of the Kelvin impulse. For jetting bubbles, at ζ < 0.01 , the jet impact hammer pressure is found to be the most energetic shock. Through statistical analysis of the experimental data and theoretical derivations, and by comparing bubbles deformed by different sources (variable gravity achieved on parabolic flights, and neighboring free and rigid surfaces), we find that the shock peak pressure may be approximated as the jet impact-induced water hammer as ph = 0.45 (ρc2 Δp) 1 / 2ζ-1 .

Hydrodynamic coupling of particle inclusions embedded in curved lipid bilayer membranes

DOE PAGES

Sigurdsson, Jon Karl; Atzberger, Paul J.

2016-06-27

Here, we develop theory and computational methods to investigate particle inclusions embedded within curved lipid bilayer membranes. We consider the case of spherical lipid vesicles where inclusion particles are coupled through (i) intramembrane hydrodynamics, (ii) traction stresses with the external and trapped solvent fluid, and (iii) intermonolayer slip between the two leaflets of the bilayer. We investigate relative to flat membranes how the membrane curvature and topology augment hydrodynamic responses. We show how both the translational and rotational mobility of protein inclusions are effected by the membrane curvature, ratio of intramembrane viscosity to solvent viscosity, and intermonolayer slip. For generalmore » investigations of many-particle dynamics, we also discuss how our approaches can be used to treat the collective diffusion and hydrodynamic coupling within spherical bilayers.« less

Hydrodynamic coupling of particle inclusions embedded in curved lipid bilayer membranes

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

Sigurdsson, Jon Karl; Atzberger, Paul J.

Here, we develop theory and computational methods to investigate particle inclusions embedded within curved lipid bilayer membranes. We consider the case of spherical lipid vesicles where inclusion particles are coupled through (i) intramembrane hydrodynamics, (ii) traction stresses with the external and trapped solvent fluid, and (iii) intermonolayer slip between the two leaflets of the bilayer. We investigate relative to flat membranes how the membrane curvature and topology augment hydrodynamic responses. We show how both the translational and rotational mobility of protein inclusions are effected by the membrane curvature, ratio of intramembrane viscosity to solvent viscosity, and intermonolayer slip. For generalmore » investigations of many-particle dynamics, we also discuss how our approaches can be used to treat the collective diffusion and hydrodynamic coupling within spherical bilayers.« less

Acoustic-to-Seismic Coupling Over Porous Ground Surfaces.

DTIC Science & Technology

1984-01-01

of sound into the ground is predicted for both spherical and plane acoustic waves incident upon two models of the ground viz i) a rigid porous solid...and soils of above-ground acoustic disturbances. Furthermore it is found possible to predict the results of model measurements using continuous and...saddle point 2.4 The geometrical wave 2.5 The lateral wave 2.6 Special cases 3. POINT TO POINT PROPAGATION MEASUREMENTS USING ACOUSTIC MODELLING " 3.0

Atomic collisions in the presence of laser radiation - Time dependence and the asymptotic wave function

NASA Technical Reports Server (NTRS)

Devries, P. L.; George, T. F.

1982-01-01

A time-dependent, wave-packet description of atomic collisions in the presence of laser radiation is extracted from the more conventional time-independent, stationary-state description. This approach resolves certain difficulties of interpretation in the time-independent approach which arise in the case of asymptotic near resonance. In the two-state model investigated, the approach predicts the existence of three spherically scattered waves in this asymptotically near-resonant case.

Time-Dependent Simulations of Fast-Wave Heated High-Non-Inductive-Fraction H-Mode Plasmas in the National Spherical Torus Experiment Upgrade

NASA Astrophysics Data System (ADS)

Taylor, Gary; Bertelli, Nicola; Gerhardt, Stefan P.; Hosea, Joel C.; Mueller, Dennis; Perkins, Rory J.; Poli, Francesca M.; Wilson, James R.; Raman, Roger

2017-10-01

30 MHz fast-wave heating may be an effective tool for non-inductively ramping low-current plasmas to a level suitable for initiating up to 12 MW of neutral beam injection on the National Spherical Tokamak Experiment Upgrade (NSTX-U). Previously on NSTX 30 MHz fast wave heating was shown to efficiently and rapidly heat electrons; at the NSTX maximum axial toroidal magnetic field (BT(0)) of 0.55 T, 1.4 MW of 30 MHz heating increased the central electron temperature from 0.2 to 2 keV in 30 ms and generated an H-mode plasma with a non-inductive fraction (fNI) ˜ 0.7 at a plasma current (Ip) of 300 kA. NSTX-U will operate at BT(0) up to 1 T, with up to 4 MW of 30 MHz power (Prf). Predictive TRANSP free boundary transport simulations, using the TORIC full wave spectral code to calculate the fast-wave heating and current drive, have been run for NSTX-U Ip = 300 kA H-mode plasmas. Favorable scaling of fNI with 30 MHz heating power is predicted, with fNI ≥ 1 for Prf ≥ 2 MW.

Numerical investigation of interactions of multiple spherical shock waves between themselves and with the underlying surface

NASA Astrophysics Data System (ADS)

Andrushchenko, V. A.; Murashkin, I. V.; Shevelev, Yu. D.

2016-06-01

Within the investigation of various aspects of asteroid and comet danger and, in particular, the explosion of several fragments of meteoroids in the atmosphere above the Earth surface, the toy problem about four point explosions in the case of their special arrangement above the underlying surface is numerically solved. Complex interactions of primary and secondary shock waves between themselves, with the hard surface, and with tangential discontinuities are examined. The structure of flow inside gas regions disturbed by the explosions—the occurrence of eddy structures in them and the influence of reflected shocks waves on them—are investigated. The tendency of the external wave fronts of each explosion to form a unified front and the tendency of their internal hot domains to merge into a joined configuration (where the second process proceeds a little later than the first one) is revealed. This unified front and joined configuration are qualitatively identical to the external internal structure for the solitary explosion. The specially arranged explosions are chosen because the effects of multiple diffraction, interference, and, the main thing, cumulation of spherical waves are manifested more clearly in this caseTwo variants with different altitude of the explosions above the surface are calculated.

Scanning dimensional measurement using laser-trapped microsphere with optical standing-wave scale

NASA Astrophysics Data System (ADS)

Michihata, Masaki; Ueda, Shin-ichi; Takahashi, Satoru; Takamasu, Kiyoshi; Takaya, Yasuhiro

2017-06-01

We propose a laser trapping-based scanning dimensional measurement method for free-form surfaces. We previously developed a laser trapping-based microprobe for three-dimensional coordinate metrology. This probe performs two types of measurements: a tactile coordinate and a scanning measurement in the same coordinate system. The proposed scanning measurement exploits optical interference. A standing-wave field is generated between the laser-trapped microsphere and the measured surface because of the interference from the retroreflected light. The standing-wave field produces an effective length scale, and the trapped microsphere acts as a sensor to read this scale. A horizontal scan of the trapped microsphere produces a phase shift of the standing wave according to the surface topography. This shift can be measured from the change in the microsphere position. The dynamics of the trapped microsphere within the standing-wave field was estimated using a harmonic model, from which the measured surface can be reconstructed. A spherical lens was measured experimentally, yielding a radius of curvature of 2.59 mm, in agreement with the nominal specification (2.60 mm). The difference between the measured points and a spherical fitted curve was 96 nm, which demonstrates the scanning function of the laser trapping-based microprobe for free-form surfaces.

Theory of wave propagation in partially saturated double-porosity rocks: a triple-layer patchy model

NASA Astrophysics Data System (ADS)

Sun, Weitao; Ba, Jing; Carcione, José M.

2016-04-01

Wave-induced local fluid flow is known as a key mechanism to explain the intrinsic wave dissipation in fluid-saturated rocks. Understanding the relationship between the acoustic properties of rocks and fluid patch distributions is important to interpret the observed seismic wave phenomena. A triple-layer patchy (TLP) model is proposed to describe the P-wave dissipation process in a double-porosity media saturated with two immiscible fluids. The double-porosity rock consists of a solid matrix with unique host porosity and inclusions which contain the second type of pores. Two immiscible fluids are considered in concentric spherical patches, where the inner pocket and the outer sphere are saturated with different fluids. The kinetic and dissipation energy functions of local fluid flow (LFF) in the inner pocket are formulated through oscillations in spherical coordinates. The wave propagation equations of the TLP model are based on Biot's theory and the corresponding Lagrangian equations. The P-wave dispersion and attenuation caused by the Biot friction mechanism and the local fluid flow (related to the pore structure and the fluid distribution) are obtained by a plane-wave analysis from the Christoffel equations. Numerical examples and laboratory measurements indicate that P-wave dispersion and attenuation are significantly influenced by the spatial distributions of both, the solid heterogeneity and the fluid saturation distribution. The TLP model is in reasonably good agreement with White's and Johnson's models. However, differences in phase velocity suggest that the heterogeneities associated with double-porosity and dual-fluid distribution should be taken into account when describing the P-wave dispersion and attenuation in partially saturated rocks.

Effect of omega-3 polyunsaturated fatty acid supplementation on central arterial stiffness and arterial wave reflections in young and older healthy adults

PubMed Central

Monahan, Kevin D; Feehan, Robert P; Blaha, Cheryl; McLaughlin, Daniel J

2015-01-01

Increased central arterial stiffness and enhanced arterial wave reflections may contribute to increased risk of cardiovascular disease development with advancing age. Omega-3 polyunsaturated fatty acid (n-3) ingestion may reduce cardiovascular risk via favorable effects exerted on arterial structure and function. We determined the effects of n-3 supplementation (4 g/day for 12 weeks) on important measures of central arterial stiffness (carotid-femoral pulse wave velocity; PWV) and arterial wave reflection (central augmentation index) in young (n = 12; 25 ± 1-year-old, mean ± SE) and older (n = 12; 66 ± 2) healthy adults. We hypothesized that n-3 supplementation would decrease carotid-femoral PWV and central augmentation index in older adults. Our results indicate that carotid-femoral PWV and central augmentation index were greater in older (988 ± 65 cm/sec and 33 ± 2%) than in young adults (656 ± 16 cm/sec and 3 ± 4%: both P < 0.05 compared to older) before the intervention (Pre). N-3 supplementation decreased carotid-femoral PWV in older (Δ-9 ± 2% Precompared to Post; P < 0.05), but not young adults (Δ2 ± 3%). Central augmentation index was unchanged by n-3 supplementation in young (3 ± 4 vs. 0 ± 4% for Pre and Post, respectively) and older adults (33 ± 2 vs. 35 ± 3%). Arterial blood pressure at rest, although increased with age, was not altered by n-3 supplementation in young or older adults. Collectively, these data indicate that 12 weeks of daily n-3 supplementation decreases an important measure of central arterial stiffness (carotid-femoral PWV) in older, but not young healthy adults. The mechanism underlying decreased central arterial stiffness with n-3 supplementation is unknown, but appears to be independent of effects on arterial blood pressure or arterial wave reflections. PMID:26109192

Bubbles with shock waves and ultrasound: a review.

PubMed

Ohl, Siew-Wan; Klaseboer, Evert; Khoo, Boo Cheong

2015-10-06

The study of the interaction of bubbles with shock waves and ultrasound is sometimes termed 'acoustic cavitation'. It is of importance in many biomedical applications where sound waves are applied. The use of shock waves and ultrasound in medical treatments is appealing because of their non-invasiveness. In this review, we present a variety of acoustics-bubble interactions, with a focus on shock wave-bubble interaction and bubble cloud phenomena. The dynamics of a single spherically oscillating bubble is rather well understood. However, when there is a nearby surface, the bubble often collapses non-spherically with a high-speed jet. The direction of the jet depends on the 'resistance' of the boundary: the bubble jets towards a rigid boundary, splits up near an elastic boundary, and jets away from a free surface. The presence of a shock wave complicates the bubble dynamics further. We shall discuss both experimental studies using high-speed photography and numerical simulations involving shock wave-bubble interaction. In biomedical applications, instead of a single bubble, often clouds of bubbles appear (consisting of many individual bubbles). The dynamics of such a bubble cloud is even more complex. We shall show some of the phenomena observed in a high-intensity focused ultrasound (HIFU) field. The nonlinear nature of the sound field and the complex inter-bubble interaction in a cloud present challenges to a comprehensive understanding of the physics of the bubble cloud in HIFU. We conclude the article with some comments on the challenges ahead.

Realistic Reflections for Marine Environments in Augmented Reality Training Systems

DTIC Science & Technology

2009-09-01

Static Backgrounds. Top: Agua Background. Bottom: Blue Background.............48 Figure 27. Ship Textures Used to Generate Reflections. In Order from...Like virtual simulations, augmented reality trainers can be configured to meet specific training needs and can be restarted and reused to train...Wave Distortion, Blurring and Shadow Many of the same methods outlined in Full Reflection shader were reused for the Physics shader. The same

Plasma instability in fast spherical discharge induced by a preionization

NASA Astrophysics Data System (ADS)

Antsiferov, P. S.; Dorokhin, L. A.

2015-04-01

As it was shown earlier, fast discharge (dI/dt ˜ 1012 A/s and Imax ≈ 40 kA) in a spherical cavity (Al2O3, inner diameter 11 mm, 4 mm apertures for the current supply) filled with working gas (Ar and Xe, pressure 80 Pa), results in the formation of a plasma with the form close to spherical. The physical mechanism can be the cumulation of a convergent shock wave, which was originated near the inner surface of the discharge cavity. It was also shown for the cylindrical fast discharge that the preionization influences the dynamics of the cylindrical convergent shock wave, its evolutions becomes faster. The present work is devoted to the study of the influence of the preionization on the plasma formation in the fast discharge with spherical geometry (Ar, 80 Pa). The inductive storage with plasma erosion opening switch was used as a current driver. The spatial structure of the discharge plasma was studied by means of a pin-hole camera with the microchannel plate (MCP) detector with time gate of 5 ns. The extreme ultra violet spectra were studied by means of the grazing incidence spectrometer with the same MCP detector with time gate of 20 ns. Beside the expected effects (reduction of the spherical plasma formation time and some increase of the electron temperature), the preionization of the discharge by the current 500 A results also in the development of the plasma instabilities and destruction of the compact plasma ball in several tens of nanoseconds. Possible mechanism of the instability is discussed.

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

Suzuki, Akihiro; Maeda, Keiichi; Shigeyama, Toshikazu

A two-dimensional special relativistic radiation-hydrodynamics code is developed and applied to numerical simulations of supernova shock breakout in bipolar explosions of a blue supergiant. Our calculations successfully simulate the dynamical evolution of a blast wave in the star and its emergence from the surface. Results of the model with spherical energy deposition show a good agreement with previous simulations. Furthermore, we calculate several models with bipolar energy deposition and compare their results with the spherically symmetric model. The bolometric light curves of the shock breakout emission are calculated by a ray-tracing method. Our radiation-hydrodynamic models indicate that the early partmore » of the shock breakout emission can be used to probe the geometry of the blast wave produced as a result of the gravitational collapse of the iron core.« less

Propagation of mechanical waves through a stochastic medium with spherical symmetry

NASA Astrophysics Data System (ADS)

Avendaño, Carlos G.; Reyes, J. Adrián

2018-01-01

We theoretically analyze the propagation of outgoing mechanical waves through an infinite isotropic elastic medium possessing spherical symmetry whose Lamé coefficients and density are spatial random functions characterized by well-defined statistical parameters. We derive the differential equation that governs the average displacement for a system whose properties depend on the radial coordinate. We show that such an equation is an extended version of the well-known Bessel differential equation whose perturbative additional terms contain coefficients that depend directly on the squared noise intensities and the autocorrelation lengths in an exponential decay fashion. We numerically solve the second order differential equation for several values of noise intensities and autocorrelation lengths and compare the corresponding displacement profiles with that of the exact analytic solution for the case of absent inhomogeneities.

Effect of anisotropy on intensity fluctuations in oceanic turbulence

NASA Astrophysics Data System (ADS)

Baykal, Yahya

2018-04-01

For an optical spherical wave propagating in an oceanic turbulent medium, the effect of anisotropy on the received intensity fluctuations is investigated. For different anisotropy factors, the variations of the scintillation index vs. the ratio that determines the relative strength of temperature and salinity in the index fluctuations, the rate of dissipation of the mean squared temperature, the rate of dissipation of the turbulent kinetic energy, viscosity, link length and the wavelength are plotted. It is found that, for all the oceanic turbulence and the link parameters of interest, as the medium becomes more anisotropic, the intensity of the optical spherical wave fluctuates less. It is concluded that the performance of an optical wireless communication systems (OWCS) operating in anisotropic oceanic turbulence is better than the performance of OWCS operating in isotropic oceanic turbulence.

Tachycardia-Induced J-Wave Changes in Patients With and Without Idiopathic Ventricular Fibrillation.

PubMed

Aizawa, Yoshiyasu; Takatsuki, Seiji; Nishiyama, Takahiko; Kimura, Takehiro; Kohsaka, Shun; Kaneko, Yoshiaki; Inden, Yasuya; Takahashi, Naohiko; Nagase, Satoshi; Aizawa, Yoshifusa; Fukuda, Keichi

2017-07-01

To know the underlying mechanisms of J waves, the response to atrial pacing was studied in patients with idiopathic ventricular fibrillation (IVF) and patients with non-IVF. In 8 patients with IVF, the J-wave amplitude was measured before, during, and after atrial pacing. All patients had episodes of ventricular fibrillation without structural heart disease. The responses of J waves were compared with those of the 17 non-IVF control subjects who revealed J waves but no history of cardiac arrest and underwent electrophysiological study. The IVF patients were younger than the non-IVF patients (28±10 versus 52±14 years, respectively; P =0.002) and had larger J waves with more extensive distribution. J waves decreased from 0.35±0.26 to 0.22±0.23 mV ( P =0.025) when the RR intervals were shortened from 782±88 to 573±162 ms ( P =0.001). A decrease (≥0.05 mV) in the J-wave amplitude was observed in 6 of the 8 patients. In addition, 1 patient showed a distinct reduction of J waves in the unipolar epicardial leads. In contrast, J waves were augmented in the 17 non-IVF subjects from 0.27±0.09 to 0.38±0.10 mV ( P <0.001): augmented in 9 and unchanged in the 8 subjects. The different response patterns of J waves to rapid pacing suggest different mechanisms: early repolarization in IVF patients and conduction delay in non-IVF patients. The response to atrial pacing was different between the IVF and non-IVF patients, which suggests the presence of different mechanisms for the genesis of J waves. © 2017 American Heart Association, Inc.

The Diurnal Profile of Central Hemodynamics in a General Uruguayan Population.

PubMed

Boggia, José; Luzardo, Leonella; Lujambio, Inés; Sottolano, Mariana; Robaina, Sebastián; Thijs, Lutgarde; Olascoaga, Alicia; Noboa, Oscar; Struijker-Boudier, Harry A; Safar, Michel E; Staessen, Jan A

2016-06-01

No previous population study assessed the diurnal profile of central arterial properties. In 167 participants (mean age, 56.1 years; 63.5% women), randomly recruited in Montevideo, Uruguay, we used the oscillometric Mobil-O-Graph 24-h PWA monitor to measure peripheral and central systolic (SBP), diastolic (DBP), and pulse (PP) pressures and central hemodynamics standardized to a heart rate of 75 bpm, including aortic pulse wave velocity, systolic augmentation (first/second peak × 100), and pressure amplification (peripheral PP/central PP). Over 24 hours, day and night, peripheral minus central differences in SBP/DBP and in PP averaged 12.2/-1.1, 14.0/-0.7, and 9.7/0.2mm Hg and 12.6, 14.7, and 9.5mm Hg, respectively (P < 0.001 except for nighttime DBP (P = 0.38)). The central-to-peripheral ratios of SBP, DBP, and PP were 0.89, 1.00, and 0.70 unadjusted, but after accounting for anthropometric characteristics decreased to 0.74, 0.97, and 0.63, respectively, with strong influence of height for SBP and DBP and of sex for PP. From day (10-20h) to nighttime (0-6h), peripheral (-10.4/-10.5 mm Hg) and central (-6.0/-11.3mm Hg) SBP/DBP, pulse wave velocity (-0.7 m/s) and pressure amplification (-0.05) decreased (P < 0.001), whereas central PP (+5.3mm Hg) and systolic augmentation (+2.3%) increased (P < 0.001). The diurnal rhythm of central pressure runs in parallel with that of peripheral pressure, but the nocturnal fall in SBP is smaller centrally than peripherally. pulse wave velocity, systolic augmentation, and pressure amplification loop through the day with high pulse wave velocity and pressure amplification but low systolic augmentation in the evening and opposite trends in the morning. © American Journal of Hypertension, Ltd 2015. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Relativistic scattered-wave theory. II - Normalization and symmetrization. [of Dirac wavefunctions

NASA Technical Reports Server (NTRS)

Yang, C. Y.

1978-01-01

Formalisms for normalization and symmetrization of one-electron Dirac scattered-wave wavefunctions are presented. The normalization integral consists of one-dimensional radial integrals for the spherical regions and an analytic expression for the intersphere region. Symmetrization drastically reduces the size of the secular matrix to be solved. Examples for planar Pb2Se2 and tetrahedral Pd4 are discussed.

Three-Dimensional Visualization of Wave Functions for Rotating Molecule: Plot of Spherical Harmonics

ERIC Educational Resources Information Center

Nagaoka, Shin-ichi; Teramae, Hiroyuki; Nagashima, Umpei

2013-01-01

At an early stage of learning quantum chemistry, undergraduate students usually encounter the concepts of the particle in a box, the harmonic oscillator, and then the particle on a sphere. Rotational levels of a diatomic molecule can be well approximated by the energy levels of the particle on a sphere. Wave functions for the particle in a…

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.

Torsional Alfvén Waves in a Dipolar Magnetic Field

NASA Astrophysics Data System (ADS)

Nataf, H. C.; Tigrine, Z.; Cardin, P.; Schaeffer, N.

2017-12-01

The discovery of torsional Alfvén waves in the Earth's core (Gillet et al, 2010) is a strong motivation for investigating the properties of these waves. Here, we report on the first experimental study of such waves. Alfvén waves are difficult to excite and observe in liquid metals because of their high magnetic diffusivity. Nevertheless, we obtained clear signatures of such diffusive waves in our DTS experiment. In this setup, some 40 liters of liquid sodium are contained between a ro = 210 mm-radius stainless steel outer shell, and a ri = 74 mm-radius copper inner sphere. Both spherical boundaries can rotate independently around a common vertical axis. The inner sphere shells a strong permanent magnet, which produces a nearly dipolar magnetic field whose intensity falls from 175 mT at ri to 8 mT at ro in the equatorial plane. We excite Alfvén waves in the liquid sodium by applying a sudden jerk of the inner sphere. To study the effect of global rotation, which leads to the formation of geostrophic torsional Alfvén waves, we spin the experiment at rotation rates fo = fi up to 15 Hz. The Alfvén wave produces a clear azimuthal magnetic signal on magnetometers installed in a sleeve inside the fluid. We also probe the associated azimuthal velocity field using ultrasound Doppler velocimetry. Electric potentials at the surface of the outer sphere turn out to be very revealing as well. In parallel, we use the XSHELLS magnetohydrodynamics spherical code to model torsional Alfvén waves in the experimental conditions, and beyond. We explore both linear and non-linear regimes. We observe a strong excitation of inertial waves in the equatorial plane, where the wave transits from a region of strong magnetic field to a region dominated by rotation (see figure of meridian map of azimuthal velocity). These novel observations should help deciphering the dynamics of Alfvén waves in planetary cores.

Caustics for spherical waves

DOE PAGES

de Rham, Claudia; Motohashi, Hayato

2017-03-07

We study the development of caustics in shift-symmetric scalar field theories by focusing on simple waves with an S O ( p ) -symmetry in an arbitrary number of space dimensions. We show that the pure Galileon, the DBI–Galileon, and the extreme-relativistic Galileon naturally emerge as the unique set of caustic-free theories, highlighting a link between the caustic-free condition for simple S O ( p ) -waves and the existence of either a global Galilean symmetry or a global (extreme-)relativistic Galilean symmetry.

Ground Truth, Magnitude Calibration, and Regional Phase Propagation and Detection in the Middle East and the Horn of Africa

DTIC Science & Technology

2008-09-01

Arabian Shield. Background The Arabian Shield consists of a late Proterozoic crystalline basement overlain by Tertiary and Quaternary volcanic...mantle structure under the Arabian Shield using body waves, we measured and inverted relative travel times from stations in Arabia. We augmented the...Rodgers, and A. Al-Amri (2008). S wave velocity structure of the Arabian Shield upper mantle from Rayleigh wave tomography, Geochem. Geophys

Changes in divergence-free grid turbulence interacting with a weak spherical shock wave

NASA Astrophysics Data System (ADS)

Kitamura, T.; Nagata, K.; Sakai, Y.; Sasoh, A.; Ito, Y.

2017-06-01

The characteristics of divergence-free grid turbulence interacting with a weak spherical shock wave with a Mach number of 1.05 are experimentally investigated. Turbulence-generating grids are used to generate nearly isotropic, divergence-free turbulence. The turbulent Reynolds number based on the Taylor microscale R eλ and the turbulent Mach number Mt are 49 ≤R eλ≤159 and 0.709 × 1 0-3≤Mt≤2.803 ×1 0-3, respectively. A spherical shock wave is generated by a diaphragmless shock tube. The instantaneous streamwise velocity before and after the interaction is measured by a hot wire probe. The results show that the root-mean-square value of streamwise velocity fluctuations (r.m.s velocity) increases and the streamwise integral length scale decreases after the interaction. The changes in the r.m.s velocity become small with the increase in R eλ and Mt for the same strength of the shock wave. This tendency is similar to that of the streamwise integral length scale. The continuous wavelet analysis shows that high intensity appears mainly in the low-frequency region and positive and negative wavelet coefficients appear periodically in time before the interaction, whereas such high intensity appears in both the low- and high-frequency regions after the interaction. The spectral analysis reveals that the energy at high wavenumbers increases after the interaction. The change in turbulence after the interaction is explained from the viewpoint of the initial turbulent Mach number. It is suggested that the change is more significant for initial divergence-free turbulence than for curl-free turbulence.

Penetration of steady fluid motions into an outer stable layer excited by MHD thermal convection in rotating spherical shells

NASA Astrophysics Data System (ADS)

Takehiro, Shin-ichi; Sasaki, Youhei

2018-03-01

Penetration of steady magneto-hydrodynamic (MHD) disturbances into an upper strongly stratified stable layer excited by MHD thermal convection in rotating spherical shells is investigated. The theoretical model proposed by Takehiro (2015) is reexamined in the case of steady fluid motion below the bottom boundary. Steady disturbances penetrate into a density stratified MHD fluid existing in the semi-infinite region in the vertical direction. The axis of rotation of the system is tilted with respect to the vertical. The basic magnetic field is uniform and may be tilted with respect to the vertical and the rotation axis. Linear dispersion relation shows that the penetration distance with zero frequency depends on the amplitude of Alfvén wave speed. When Alfvén wave speed is small, viscous diffusion becomes dominant and penetration distance is similar to the horizontal scale of the disturbance at the lower boundary. In contrast, when Alfvén wave speed becomes larger, disturbance can penetrate deeper, and penetration distance becomes proportional to the Alfvén wave speed and inversely proportional to the geometric average of viscous and magnetic diffusion coefficients and to the total horizontal wavenumber. The analytic expression of penetration distance is in good agreement with the extent of penetration of mean zonal flow induced by finite amplitude convection in a rotating spherical shell with an upper stably stratified layer embedded in an axially uniform basic magnetic field. The theory expects that the stable layer suggested in the upper part of the outer core of the earth could be penetrated completely by mean zonal flows excited by thermal/compositional convection developing below the stable layer.

The Bargmann-Wigner equations in spherical space

NASA Astrophysics Data System (ADS)

McKeon, D. G. C.; Sherry, T. N.

2006-01-01

The Bargmann-Wigner formalism is adapted to spherical surfaces embedded in three to eleven dimensions. This is demonstrated to generate wave equations in spherical space for a variety of antisymmetric tensor fields. Some of these equations are gauge invariant for particular values of the parameters characterizing them. For spheres embedded in three, four, and five dimensions, this gauge invariance can be generalized so as to become non-Abelian. This non-Abelian gauge invariance is shown to be a property of second-order models for two index antisymmetric tensor fields in any number of dimensions. The O(3) model is quantized and the two-point function is shown to vanish at the one-loop order.

Theoretical and experimental design studies for the Atmospheric General Circulation Experiment

NASA Technical Reports Server (NTRS)

Fowlis, W. W.; Hathaway, D. H.; Miller, T. L.; Roberts, G. O.; Kopecky, K. J.

1985-01-01

The major criterion for the Atmospheric General Circulation Experiment (AGCE) design is that it be possible to realize strong baroclinic instability in the spherical configuration chosen. A configuration was selected in which a hemispherical shell of fluid is subjected to latitudinal temperature gradients on its spherical boundaries and the latitudinal boundaries are insulators. Work in the laboratory with a cylindrical version of this configuration revealed more instabilities than baroclinic instability. Since researchers fully expect these additional instabilities to appear in the spherical configuration also, they decided to continue the laboratory cylindrical annulus studies. Four flow regimes were identified: an axisymmetric Hadley circulation, boundary layer convection, baroclinic waves and deep thermal convection. Regime diagrams were prepared.

Near-to-eye electroholography via guided-wave acousto-optics for augmented reality

NASA Astrophysics Data System (ADS)

Jolly, Sundeep; Savidis, Nickolaos; Datta, Bianca; Smalley, Daniel; Bove, V. Michael

2017-03-01

Near-to-eye holographic displays act to directly project wavefronts into a viewer's eye in order to recreate 3-D scenes for augmented or virtual reality applications. Recently, several solutions for near-to-eye electroholography have been proposed based on digital spatial light modulators in conjunction with supporting optics, such as holographic waveguides for light delivery; however, such schemes are limited by the inherent low space-bandwidth product available with current digital SLMs. In this paper, we depict a fully monolithic, integrated optical platform for transparent near-to-eye holographic display requiring no supporting optics. Our solution employs a guided-wave acousto-optic spatial light modulator implemented in lithium niobate in conjunction with an integrated Bragg-regime reflection volume hologram.

The transmission or scattering of elastic waves by an inhomogeneity of simple geometry: A comparison of theories

NASA Technical Reports Server (NTRS)

Sheu, Y. C.; Fu, L. S.

1983-01-01

The extended method of equivalent inclusions is applied to study the specific wave problems: (1) the transmission of elastic waves in an infinite medium containing a layer of inhomogeneity, and (2) the scattering of elastic waves in an infinite medium containing a perfect spherical inhomogeneity. Eigenstrains are expanded as a geometric series and a method of integration based on the inhomogeneous Helmholtz operator is adopted. This study compares results, obtained by using limited number of terms in the eigenstrain expansion, with exact solutions for the layer problem and that for a perfect sphere.

Simulation of wave propagation in three-dimensional random media

NASA Astrophysics Data System (ADS)

Coles, Wm. A.; Filice, J. P.; Frehlich, R. G.; Yadlowsky, M.

1995-04-01

Quantitative error analyses for the simulation of wave propagation in three-dimensional random media, when narrow angular scattering is assumed, are presented for plane-wave and spherical-wave geometry. This includes the errors that result from finite grid size, finite simulation dimensions, and the separation of the two-dimensional screens along the propagation direction. Simple error scalings are determined for power-law spectra of the random refractive indices of the media. The effects of a finite inner scale are also considered. The spatial spectra of the intensity errors are calculated and compared with the spatial spectra of

Stimulated Raman scattering of sub-millimeter waves in bismuth

NASA Astrophysics Data System (ADS)

Kumar, Pawan; Tripathi, V. K.

2007-12-01

A high-power sub-millimeter wave propagating through bismuth, a semimetal with non-spherical energy surfaces, parametrically excites a space-charge mode and a back-scattered electromagnetic wave. The free carrier density perturbation associated with the space-charge wave couples with the oscillatory velocity due to the pump to derive the scattered wave. The scattered and pump waves exert a pondermotive force on electrons and holes, driving the space-charge wave. The collisional damping of the decay waves determines the threshold for the parametric instability. The threshold intensity for 20 μm wavelength pump turns out to be ˜2×1012 W/cm2. Above the threshold, the growth rate scales increase with ωo, attain a maximum around ωo=6.5ωp, and, after this, falls off.

Value of the QRS complex in assessing left ventricular ejection fraction.

PubMed

Askenazi, J; Parisi, A F; Cohn, P F; Freedman, W B; Braunwald, E

1978-03-01

The relation between electrocardiographic findings and the angiographic left ventricular ejection fraction and the augmented ejection fraction after a premature ventricular contraction was investigated in 73 patients with documented chronic coronary artery disease. The patients were separated into four groups according to the presence or absence of abnormal Q waves. Twenty-four patients had diaphragmatic myocardial infarction, 21 had anterior myocardial infarction, 15 had both and 13 had no myocardial infarction. There was no statistically significant differences in cardiac index, left ventricular end-diastolic pressure or number of coronary vessels showing critical narrowing in the four groups. The sum of R waves (in mv) in leads aVL, aVF and V1 to V6 (sigmaR) was correlated with the ejection fraction (EF) and the augmented ejection fraction (EFa). EF in percent = 6.6 sigmaR mv + 9.4 (no. =73, r = 0.61); and EFa in percent = 8.6 sigmaR mv + 11.0 (no. = 73, r = 0.77). Among patients with sigmaR of less than 4.0 mv, augmented ejection fraction was less than 0.45 in 73 percent; among patients with sigmaR of 4.0 mv or more the augmented ejection fraction was greater than 0.45 in 93 percent (P less than 0.001). Thus, the sigmaR, calculated from six precordial and two augmented leads in patients with chronic coronary artery disease, correlated with both ejection fraction and augmented ejection fraction. The electrocardiogram in patients with coronary artery disease may prove useful as a simple, readily available and noninvasive guide in the assessment of left ventricular function in patients with coronary artery disease.

Gravitational Wave Experiments - Proceedings of the First Edoardo Amaldi Conference

NASA Astrophysics Data System (ADS)

Coccia, E.; Pizzella, G.; Ronga, F.

1995-07-01

The Table of Contents for the full book PDF is as follows: * Foreword * Notes on Edoardo Amaldi's Life and Activity * PART I. INVITED LECTURES * Sources and Telescopes * Sources of Gravitational Radiation for Detectors of the 21st Century * Neutrino Telescopes * γ-Ray Bursts * Space Detectors * LISA — Laser Interferometer Space Antenna for Gravitational Wave Measurements * Search for Massive Coalescing Binaries with the Spacecraft ULYSSES * Interferometers * The LIGO Project: Progress and Prospects * The VIRGO Experiment: Status of the Art * GEO 600 — A 600-m Laser Interferometric Gravitational Wave Antenna * 300-m Laser Interferometer Gravitational Wave Detector (TAMA300) in Japan * Resonant Detectors * Search for Continuous Gravitational Wave from Pulsars with Resonant Detector * Operation of the ALLEGRO Detector at LSU * Preliminary Results of the New Run of Measurements with the Resonant Antenna EXPLORER * Operation of the Perth Cryogenic Resonant-Bar Gravitational Wave Detector * The NAUTILUS Experiment * Status of the AURIGA Gravitational Wave Antenna and Perspectives for the Gravitational Waves Search with Ultracryogenic Resonant Detectors * Ultralow Temperature Resonant-Mass Gravitational Radiation Detectors: Current Status of the Stanford Program * Electromechanical Transducers and Bandwidth of Resonant-Mass Gravitational-Wave Detectors * Fully Numerical Data Analysis for Resonant Gravitational Wave Detectors: Optimal Filter and Available Information * PART II. CONTRIBUTED PAPERS * Sources and Telescopes * The Local Supernova Production * Periodic Gravitational Signals from Galactic Pulsars * On a Possibility of Scalar Gravitational Wave Detection from the Binary Pulsars PSR 1913+16 * Kazan Gravitational Wave Detector “Dulkyn”: General Concept and Prospects of Construction * Hierarchical Approach to the Theory of Detection of Periodic Gravitational Radiation * Application of Gravitational Antennae for Fundamental Geophysical Problems * On Production of Gravitational Radiation by Particle Accelerators and by High Power Lasers * NESTOR: An Underwater Cerenkov Detector for Neutrino Astronomy * A Cosmic-Ray Veto System for the Gravitational Wave Detector NAUTLUS * Interferometers * Development of a 20m Prototype Laser Interferometric Gravitational Wave Detector at NAO * Production of Higher-Order Light Modes by High Quality Optical Components * Vibration Isolation and Suspension Systems for Laser Interferometer Gravitational Wave Detectors * Quality Factors of Stainless Steel Pendulum Wires * Reduction of Suspension Thermal Noises in Laser Free Masses Gravitational Antenna by Correlation of the Output with Additional Optical Signal * Resonant Detectors * Regeneration Effects in a Resonant Gravitational Wave Detector * A Cryogenic Sapphire Transducer with Double Frequency Pumping for Resonant Mass GW Detectors * Effect of Parametric Instability of Gravitational Wave Antenna with Microwave Cavity Transducer * Resonators of Novel Geometry for Large Mass Resonant Transducers * Measurements on the Gravitational Wave Antenna ALTAIR Equipped with a BAE Transducer * The Rome BAE Transducer: Perspectives of its Application to Ultracryogenic Gravitational Wave Antennas * Behavior of a de SQUID Tightly Coupled to a High-Q Resonant Transducer * High Q-Factor LC Resonators for Optimal Coupling * Comparison Between Different Data Analysis Procedures for Gravitational Wave Pulse Detection * Supernova 1987A Rome Maryland Gravitational Radiation Antenna Observations * Analysis of the Data Recorded by the Maryland and Rome Gravitational-Wave Detectors and the Seismic Data from Moscow and Obninsk Station during SN1987A * Multitransducer Resonant Gravitational Antennas * Local Array of High Frequency Antennas * Interaction Cross-Sections for Spherical Resonant GW Antennae * Signal-To-Noise Analysis for a Spherical Gravitational Wave Antenna Instrumented with Multiple Transducers * On the Design of Ultralow Temperature Spherical Gravitational Wave Detectors * List of Participants

Nitrogen soft and hard X-ray emissions using different shapes of anodes in a 4-kJ plasma focus device

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

Mahtab, M., E-mail: m.mahtab.83@gmail.com; Habibi, M., E-mail: mortezahabibi@aut.ac.ir

2013-12-15

The effect of different anode tip geometries on the intensity of soft and hard X-rays emitted from a 4-kJ plasma focus device is investigated using five different anode tips. The shapes of the uppermost region of these anodes (tips) have been cylindrical-flat, cylindrical-hollow, spherical-convex, cone-flat, and cone-hollow. For time-resolved measurement of the emitted X-rays, several BPX-65 pin diodes covered by different filters and a fast plastic scintillator are used. Experimental results have shown that, the highest intensity of the both soft and hard X-ray is recorded in cone-flat, spherical-convex, and cone-hollow tips, respectively. The use of cone-flat anode tip hasmore » augmented the emitted X-ray three times.« less

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.

Propagation of diffuse light in a turbid medium with multiple spherical inhomogeneities.

PubMed

Pustovit, Vitaliy N; Markel, Vadim A

2004-01-01

We develop a fast and accurate solver for the forward problem of diffusion tomography in the case of several spherical inhomogeneities. The approach allows one to take into account multiple scattering of diffuse waves between different inhomogeneities. Theoretical results are illustrated with numerical examples; excellent numerical convergence and efficiency are demonstrated. The method is generalized for the case of additional planar diffuse-nondiffuse interfaces and is therefore applicable to the half-space and slab imaging geometries.

Assessment of Aerothermal Heating Augmentation Attributed to Surface Catalysis in High Enthalpy Shock Tunnel Flows

NASA Astrophysics Data System (ADS)

MacLean, M.; Holden, M.

2009-01-01

The effect of gas/surface interaction in making CFD predictions of convective heating has been considered with application to ground tests performed in high enthalpy shock tunnels where additional heating augmentation attributable to surface recombination has been observed for nitrogen, air and carbon dioxide flows. For test articles constructed of stainless steel and aluminum, measurements have been made with several types of heat transfer instrumentation including thin- film, calorimeter, and coaxial thermocouple sensors. These experiments have been modeled by computations made with the high quality, chemically reacting, Navier- Stokes solver, DPLR and the heating results compared. Some typical cases considered include results on an axisymmetric sphere-cone, axisymmetric spherical capsule, spherical capsule at angle of attack, and two- dimensional cylinder. In nitrogen flows, cases considered show a recombination probability on the order of 10-3, which agrees with published data. In many cases in air and CO2, measurements exceeding the predicted level of convective heating have been observed which are consistent with approximately complete recombination (to O2/N2 or CO2) on the surface of the model (sometimes called a super-catalytic wall). It has been recognized that the conclusion that this behavior is tied to an excessively high degree of catalytic efficiency is dependent on the current understanding of the freestream and shock-layer state of the gas.

A reflective optical transport system for ultraviolet Thomson scattering from electron plasma waves on OMEGA.

PubMed

Katz, J; Boni, R; Sorce, C; Follett, R; Shoup, M J; Froula, D H

2012-10-01

A reflective optical transport system has been designed for the OMEGA Thomson-scattering diagnostic. A Schwarzschild objective that uses two concentric spherical mirrors coupled to a Pfund objective provides diffraction-limited imaging across all reflected wavelengths. This enables the operator to perform Thomson-scattering measurements of ultraviolet (0.263 μm) light scattered from electron plasma waves.

Extended optical theorem in isotropic solids and its application to the elastic radiation force

NASA Astrophysics Data System (ADS)

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

2017-04-01

In this article, we derive the extended optical theorem for the elastic-wave scattering by a spherical inclusion (with and without absorption) in a solid matrix. This theorem expresses the extinction cross-section, i.e., the time-averaged power extracted from the incoming beam per its intensity, regarding the partial-wave expansion coefficients of the incident and scattered waves. We also establish the connection between the optical theorem and the elastic radiation force by a plane wave in a linear and isotropic solid. We obtain the absorption, scattering, and extinction efficiencies (the corresponding power per characteristic incident intensity per sphere cross-section area) for a plane wave and a spherically focused beam. We discuss to which extent the radiation force theory for plane waves can be used to the focused beam case. Considering an iron sphere embedded in an aluminum matrix, we numerically compute the scattering and elastic radiation force efficiencies. The radiation force on a stainless steel sphere embedded in a tissue-like medium (soft solid) is also computed. In this case, resonances are observed in the force as a function of the sphere size parameter (the wavenumber times the sphere radius). Remarkably, the relative difference between our findings and previous lossless liquid models is about 100% in the long-wavelength limit. Regarding some applications, the obtained results have a direct impact on ultrasound-based elastography techniques and ultrasonic nondestructive testing, as well as implantable devices activated by ultrasound.

Fully non-inductive second harmonic electron cyclotron plasma ramp-up in the QUEST spherical tokamak

NASA Astrophysics Data System (ADS)

Idei, H.; Kariya, T.; Imai, T.; Mishra, K.; Onchi, T.; Watanabe, O.; Zushi, H.; Hanada, K.; Qian, J.; Ejiri, A.; Alam, M. M.; Nakamura, K.; Fujisawa, A.; Nagashima, Y.; Hasegawa, M.; Matsuoka, K.; Fukuyama, A.; Kubo, S.; Shimozuma, T.; Yoshikawa, M.; Sakamoto, M.; Kawasaki, S.; Nakashima, H.; Higashijima, A.; Ide, S.; Maekawa, T.; Takase, Y.; Toi, K.

2017-12-01

Fully non-inductive second (2nd) harmonic electron cyclotron (EC) plasma current ramp-up was demonstrated with a newlly developed 28 GHz system in the QUEST spherical tokamak. A high plasma current of 54 kA was non-inductively ramped up and sustained stably for 0.9 s with a 270 kW 28 GHz wave. A higher plasma current of 66 kA was also non-inductively achieved with a slow ramp-up of the vertical field. We have achieved a significantly higher plasma current than those achieved previously with the 2nd harmonic EC waves. This fully non-inductive 2nd harmonic EC plasma ramp-up method might be useful for future burning plasma devices and fusion reactors, in particular for operations at half magnetic field with the same EC heating equipment.

The effects of electron thermal radiation on laser ablative shock waves from aluminum plasma into ambient air

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

Sai Shiva, S.; Leela, Ch.; Prem Kiran, P., E-mail: premkiranuoh@gmail.com, E-mail: prem@uohyd.ac.in

2016-05-15

The effect of electron thermal radiation on 7 ns laser ablative shock waves from aluminum (Al) plasma into an ambient atmospheric air has been numerically investigated using a one-dimensional, three-temperature (electron, ion, and radiation) radiation hydrodynamic code MULTI. The governing equations in Lagrangian form are solved using an implicit scheme for planar, cylindrical, and spherical geometries. The shockwave velocities (V{sub sw}) obtained numerically are compared with our experimental values obtained over the intensity range of 2.0 × 10{sup 10} to 1.4 × 10{sup 11 }W/cm{sup 2}. It is observed that the numerically obtained V{sub sw} is significantly influenced by the thermal radiation effects which are foundmore » to be dominant in the initial stage up to 2 μs depending on the input laser energy. Also, the results are found to be sensitive to the co-ordinate geometry used in the simulation (planar, cylindrical, and spherical). Moreover, it is revealed that shock wave undergoes geometrical transitions from planar to cylindrical nature and from cylindrical to spherical nature with time during its propagation into an ambient atmospheric air. It is also observed that the spatio-temporal evolution of plasma electron and ion parameters such as temperature, specific energy, pressure, electron number density, and mass density were found to be modified significantly due to the effects of electron thermal radiation.« less

Enhanced control of light and sound trajectories with three-dimensional gradient index lenses

NASA Astrophysics Data System (ADS)

Chang, T. M.; Dupont, G.; Enoch, S.; Guenneau, S.

2012-03-01

We numerically study the focusing and bending effects of light and sound waves through heterogeneous isotropic cylindrical and spherical devices. We first point out that transformation optics and acoustics show that the control of light requires spatially varying anisotropic permittivity and permeability, while the control of sound is achieved via spatially anisotropic density and isotropic compressibility. Moreover, homogenization theory applied to electromagnetic and acoustic periodic structures leads to such artificial (although not spatially varying) anisotropic permittivity, permeability and density. We stress that homogenization is thus a natural mathematical tool for the design of structured metamaterials. To illustrate the two-step geometric transform-homogenization approach, we consider the design of cylindrical and spherical electromagnetic and acoustic lenses displaying some artificial anisotropy along their optical axis (direction of periodicity of the structural elements). Applications are sought in the design of Eaton and Luneburg lenses bending light at angles ranging from 90° to 360°, or mimicking a Schwartzchild metric, i.e. a black hole. All of these spherical metamaterials are characterized by a refractive index varying inversely with the radius which is approximated by concentric layers of homogeneous material. We finally propose some structured cylindrical metamaterials consisting of infinitely conducting or rigid toroidal channels in a homogeneous bulk material focusing light or sound waves. The functionality of these metamaterials is demonstrated via full-wave three-dimensional computations using nodal elements in the context of acoustics, and finite edge-elements in electromagnetics.

Ion absorption of the high harmonic fast wave in the National Spherical Torus Experiment

NASA Astrophysics Data System (ADS)

Rosenberg, Adam Lewis

Ion absorption of the high harmonic fast wave in a spherical torus is of critical importance to assessing the viability of the wave as a means of heating and driving current. Analysis of recent NSTX shots has revealed that under some conditions when neutral beam and RF power are injected into the plasma simultaneously, a fast ion population with energy above the beam injection energy is sustained by the wave. In agreement with modeling, these experiments find the RF-induced fast ion tail strength and neutron rate at lower B-fields to be less enhanced, likely due to a larger β profile, which promotes greater off-axis absorption where the fast ion population is small. Ion loss codes find the increased loss fraction with decreased B insufficient to account for the changes in tail strength, providing further evidence that this is an RF interaction effect. Though greater ion absorption is predicted with lower k∥, surprisingly little variation in the tail was observed, along with a neutron rate enhancement with higher k∥. Data from the neutral particle analyzer, neutron detectors, x-ray crystal spectrometer, and Thomson scattering is presented, along with results from the TRANSP transport analysis code, ray-tracing codes HPRT and CURRAY, full-wave code and AORSA, quasilinear code CQL3D, and ion loss codes EIGOL and CONBEAM.

Flow design and simulation of a gas compression system for hydrogen fusion energy production

NASA Astrophysics Data System (ADS)

Avital, E. J.; Salvatore, E.; Munjiza, A.; Suponitsky, V.; Plant, D.; Laberge, M.

2017-08-01

An innovative gas compression system is proposed and computationally researched to achieve a short time response as needed in engineering applications such as hydrogen fusion energy reactors and high speed hammers. The system consists of a reservoir containing high pressure gas connected to a straight tube which in turn is connected to a spherical duct, where at the sphere’s centre plasma resides in the case of a fusion reactor. Diaphragm located inside the straight tube separates the reservoir’s high pressure gas from the rest of the plenum. Once the diaphragm is breached the high pressure gas enters the plenum to drive pistons located on the inner wall of the spherical duct that will eventually end compressing the plasma. Quasi-1D and axisymmetric flow formulations are used to design and analyse the flow dynamics. A spike is designed for the interface between the straight tube and the spherical duct to provide a smooth geometry transition for the flow. Flow simulations show high supersonic flow hitting the end of the spherical duct, generating a return shock wave propagating upstream and raising the pressure above the reservoir pressure as in the hammer wave problem, potentially giving temporary pressure boost to the pistons. Good agreement is revealed between the two flow formulations pointing to the usefulness of the quasi-1D formulation as a rapid solver. Nevertheless, a mild time delay in the axisymmetric flow simulation occurred due to moderate two-dimensionality effects. The compression system is settled down in a few milliseconds for a spherical duct of 0.8 m diameter using Helium gas and a uniform duct cross-section area. Various system geometries are analysed using instantaneous and time history flow plots.

Functional significance of the pattern of renal sympathetic nerve activation.

PubMed

Dibona, G F; Sawin, L L

1999-08-01

To assess the renal functional significance of the pattern of renal sympathetic nerve activation, computer-generated stimulus patterns (delivered at constant integrated voltage) were applied to the decentralized renal sympathetic nerve bundle and renal hemodynamic and excretory responses determined in anesthetized rats. When delivered at the same integrated voltage, stimulus patterns resembling those observed in in vivo multifiber recordings of renal sympathetic nerve activity (diamond-wave patterns) produced greater renal vasoconstrictor responses than conventional square-wave patterns. Within diamond-wave patterns, increasing integrated voltage by increasing amplitude produced twofold greater renal vasoconstrictor responses than by increasing duration. With similar integrated voltages that were subthreshold for renal vasoconstriction, neither diamond- nor square-wave pattern altered glomerular filtration rate, whereas diamond- but not square-wave pattern reversibly decreased urinary sodium excretion by 25 +/- 3%. At the same number of pulses per second, intermittent stimulation produced faster and greater renal vasoconstriction than continuous stimulation. At the same number of pulses per second, increases in rest period during intermittent stimulation proportionally augmented the renal vasoconstrictor response compared with that observed with continuous stimulation; the maximum augmentation of 55% occurred at a rest period of 500 ms. These results indicate that the pattern of renal sympathetic nerve stimulation (activity) significantly influences the rapidity, magnitude, and selectivity of the renal vascular and tubular responses.

Converging shock wave focusing and interaction with a target

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

Nitishinskiy, M.; Efimov, S.; Antonov, O.

2016-04-15

Converging shock waves in liquids can be used efficiently in the research of the extreme state of matter and in various applications. In this paper, the recent results related to the interaction of a shock wave with plasma preliminarily formed in the vicinity of the shock wave convergence are presented. The shock wave is produced by the underwater electrical explosion of a spherical wire array. The plasma is generated prior to the shock wave's arrival by a low-pressure gas discharge inside a quartz capillary placed at the equatorial plane of the array. Analysis of the Stark broadening of H{sub α}more » and H{sub β} spectral lines and line-to-continuum ratio, combined with the ratio of the relative intensities of carbon C III/C II and silicon Si III/Si II lines, were used to determine the plasma density and temperature evolution. It was found that during the first ∼200 ns with respect to the beginning of the plasma compression by the shock wave and when the spectral lines are resolved, the plasma density increases from 2 × 10{sup 17 }cm{sup −3} to 5 × 10{sup 17 }cm{sup −3}, while the temperature remains at the same value of 3–4 eV. Further, following the model of an adiabatically imploding capillary, the plasma density increases >10{sup 19 }cm{sup −3}, leading to the continuum spectra obtained experimentally, and the plasma temperature >30 eV at radii of compression of ≤20 μm. The data obtained indicate that the shock wave generated by the underwater electrical explosion of a spherical wire array retains its uniformity during the main part of its convergence.« less

Ground Signatures of EMIC Waves obtained From a 3D Global Wave Model

NASA Astrophysics Data System (ADS)

Rankin, R.; Sydorenko, D.; Zong, Q.; Zhang, L.

2016-12-01

EMIC waves generated in the inner magnetosphere are important drivers of radiation belt particle loss. Van Allen Probes and ground observations of EMIC waves suggest that localized magnetospheric sources inject waves that are guided along geomagnetic field lines and then reflected and refracted in the low altitude magnetosphere [Kim, E.-H., and J. R. Johnson (2016), Geophys. Res. Lett., 43, 13-21, doi:10.1002/2015GL066978] before entering the ionosphere. The waves then spread horizontally within the F-region waveguide and propagate to the ground. To understand the observed properties of EMIC waves, a global 3D model of ULF waves in Earth's magnetosphere, ionosphere, and neutral atmosphere has been developed. The simulation domain extends from Earth's surface to a spherical boundary a few tens of thousands of km in radius. The model uses spherical coordinates and incorporates an overset Yin-Yang grid that eliminates the singularity at the polar axis and improves uniformity of the grid in the polar areas [Kageyama, A., and T. Sato (2004), Geochem. Geophys. Geosyst., 5, Q09005, doi:10.1029/2004GC000734]. The geomagnetic field in the model is general, but is dipole in this study. The plasma is described as a set of electron and multiple species ion conducting fluids. Realistic 3D density profiles of various ion species as well as thermospheric parameters are provided by the Canadian Ionosphere Atmosphere Model (C-IAM) [Martynenko O.V. et al. (2014), J. Atmos. Solar-Terr. Phys., 120, 51-61, doi:10.1016/j.jastp.2014.08.014]. The global ULF wave model is applied to study propagation of EMIC waves excited in the equatorial plane near L=7. Wave propagation along field lines, reflection and refraction in the zone of critical frequencies, and further propagation through the ionosphere to the ground are discussed.

Two space scatterer formalism calculation of bulk parameters of thunderclouds

NASA Technical Reports Server (NTRS)

Phanord, Dieudonne D.

1994-01-01

In a previous study, we used a modified two-space scatterer formalism of Twersky to establish for a cloud modeled as a statistically homogeneous distribution of spherical water droplets, the dispersion relations that determine its bulk propagation numbers and bulk indexes of refraction in terms of the vector equivalent scattering amplitude and the dyadic scattering amplitude of the single water droplet in isolation. The results were specialized to the forward direction of scattering while demanding that the scatterers preserve the incident polarization. We apply this approach to obtain specific numerical values for the macroscopic parameters of the cloud. We work with a cloud of density rho = 100 cm(exp -3), a wavelength lambda = 0.7774 microns, and with spherical water droplets of common radius alpha = 10 microns. In addition, the scattering medium is divided into three parts, the medium outside the cloud, moist air (the medium inside the cloud but outside the droplets), and the medium inside the spherical water droplets. The results of this report are applicable to a cloud of any geometry since the boundary does not interfere with the calculations. Also, it is important to notice the plane wave nature of the incidence wave in the moist atmosphere.

Numerical modeling of lower hybrid current drive in fully non-inductive plasma start-up experiments on TST-2

NASA Astrophysics Data System (ADS)

Tsujii, N.; Takase, Y.; Ejiri, A.; Shinya, T.; Togashi, H.; Yajima, S.; Yamazaki, H.; Moeller, C. P.; Roidl, B.; Sonehara, M.; Takahashi, W.; Toida, K.; Yoshida, Y.

2017-12-01

Non-inductive plasma start-up is a critical issue for spherical tokamaks since there is not enough room to provide neutron shielding for the center solenoid. Start-up using lower hybrid (LH) waves has been studied on the TST-2 spherical tokamak. Because of the low magnetic field of a spherical tokamak, the plasma density needs to be kept at a very low value during the plasma current ramp-up so that the plasma core remains accessible to the LH waves. However, we have found that higher density was required to sustain larger plasma current. The achievable plasma current was limited by the maximum operational toroidal field of TST-2. The existence of an optimum density for LH current drive and its toroidal field dependence is explained through a numerical simulation based on a ray tracing code and a Fokker-Planck solver. In order to access higher density at the same magnetic field, a top-launch antenna was recently installed in addition to the existing outboard-launch antenna. Increase in the density limit was observed when the power was launched from the top antenna, consistently with the numerical predictions.

Fully non-inductive plasma start-up with lower-hybrid waves using the outboard-launch and top-launch antennas on the TST-2 spherical tokamak

NASA Astrophysics Data System (ADS)

Tsujii, Naoto; Takase, Yuichi; Ejiri, Akira; Shinya, Takahiro; Yajima, Satoru; Yamazaki, Hibiki; Togashi, Hiro; Moeller, Charles P.; Roidl, Benedikt; Takahashi, Wataru; Toida, Kazuya; Yoshida, Yusuke

2017-10-01

Removal of the central solenoid is essential to realize an economical spherical tokamak fusion reactor, but non-inductive plasma start-up is a challenge. On the TST-2 spherical tokamak, non-inductive plasma start-up using lower-hybrid (LH) waves has been investigated. Using the capacitively-coupled combline (CCC) antenna installed at the outboard midplane, fully non-inductive plasma current ramp-up up to a quarter of that of the typical Ohmic discharges has been achieved. Although it was desirable to keep the density low during the plasma current ramp-up to avoid the LH density limit, it was recognized that there was a maximum current density that could be carried by a given electron density. Since the density needed to increase as the plasma current was ramped-up, the achievable plasma current was limited by the maximum operational toroidal field of TST-2. The top-launch CCC antenna was installed to access higher density with up-shift of the parallel index of refraction. Numerical analysis of LH current drive with the outboard-launch and top-launch antennas was performed and the results were qualitatively consistent with the experimental observations.

Signatures of Nonlinear Waves in Coronal Plumes and Holes

NASA Technical Reports Server (NTRS)

Ofman, Leon

1999-01-01

In recent Ultraviolet Coronagraph Spectrometer/Solar and Heliospheric Observatory (UVCS/SOHO) White Light Channel (WLC) observations we found quasi-periodic variations in the polarized brightness (pB) in the polar coronal holes at heliocentric distances of 1.9-2.45 solar radii. The motivation for the observation is the 2.5D Magnetohydrodynamics (MHD) model of solar wind acceleration by nonlinear waves, that predicts compressive fluctuations in coronal holes. To help identify the waves observed with the UVCS/WLC we model the propagation and dissipation of slow magnetosonic waves in polar plumes using 1D MHD code in spherical geometry, We find that the slow waves nonlinearly steepen in the gravitationally stratified plumes. The nonlinear steepening of the waves leads to enhanced dissipation due to compressive viscosity at the wave-fronts.

On hydromagnetic oscillations in a rotating cavity.

NASA Technical Reports Server (NTRS)

Gans, R. F.

1971-01-01

Time-dependent hydromagnetic phenomena in a rotating spherical cavity are investigated in the framework of an interior boundary-layer expansion. The first type of wave is a modification of the hydrodynamic inertial wave, the second is a pseudo-geostrophic wave and is involved in spinup, and the third is related to the MAC waves of Braginskii (1967). It is shown that the MAC waves must satisfy more than the usual normal boundary conditions, and that reference must be made to the boundary-layer solution to resolve the ambiguity regarding which conditions are to be taken. The boundary-layer structure is investigated in detail to display the interactions between applied field, viscosity, electrical conductivity, frequency and latitu de.

Generation of extreme state of water by spherical wire array underwater electrical explosion

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

Antonov, O.; Gilburd, L.; Efimov, S.

2012-10-15

The results of the first experiments on the underwater electrical explosion of a spherical wire array generating a converging strong shock wave are reported. Using a moderate pulse power generator with a stored energy of {<=}6 kJ and discharge current of {<=}500 kA with a rise-time of {approx}300 ns, explosions of Cu and Al wire arrays of different diameters and with a different number and diameter of wires were tested. Electrical, optical, and destruction diagnostics were used to determine the energy deposited into the array, the time-of-flight of the shock wave to the origin of the implosion, and the parametersmore » of water at that location. The experimental and numerical simulation results indicate that the convergence of the shock wave leads to the formation of an extreme state of water in the vicinity of the implosion origin that is characterized by pressure, temperature, and compression factors of (2 {+-} 0.2) Multiplication-Sign 10{sup 12} Pa, 8 {+-} 0.5 eV, and 7 {+-} 0.5, respectively.« less

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.

Amplitude-modulated acoustic radiation force experienced by elastic and viscoelastic spherical shells in progressive waves.

PubMed

Mitri, F G; Fellah, Z E A

2006-07-01

The dynamic acoustic radiation force resulting from a dual-frequency beam incident on spherical shells immersed in an inviscid fluid is examined theoretically in relation to their thickness and the contents of their interior hollow regions. The theory is modified to include a hysteresis type of absorption inside the shells' material. The results of numerical calculations are presented for stainless steel and absorbing lucite (PolyMethyMethacrylAte) shells with the hollow region filled with water or air. Significant differences occur when the interior fluid inside the hollow region is changed from water to air. It is shown that the dynamic radiation force function Yd deviates from the static radiation force function Yp when the modulation size parameter deltax = mid R:x2 - x1mid R: (x1 = k1a, x2 = k2a, k1 and k2 are the wave vectors of the incident ultrasound waves, and a is the outer radius of the shell) starts to exceed the width of the resonance peaks in the Yp curves.

Collapsing shells and black holes: a quantum analysis

NASA Astrophysics Data System (ADS)

Leal, P.; Bernardini, A. E.; Bertolami, O.

2018-06-01

The quantization of a spherically symmetric null shells is performed and extended to the framework of phase-space noncommutative (NC) quantum mechanics. This shell is considered to be inside a black hole event horizon. The encountered properties are investigated making use of the Israel junction conditions on the shell, considering that it is the boundary between two spherically symmetric spacetimes. Using this method, and considering two different Kantowski–Sachs spacetimes as a representation for the Schwarzschild spacetime, the relevant quantities on the shell are computed, such as its stress-energy tensor and the action for the whole spacetime. From the obtained action, the Wheeler–deWitt equation is deduced in order to provide the quantum framework for the system. Solutions for the wave function of the system are found on both the commutative and NC scenarios. It is shown that, on the commutative version, the wave function has a purely oscillatory behavior in the interior of the shell. In the NC setting, it is shown that the wave function vanishes at the singularity, as well as, at the event horizon of the black hole.

Escape of gravitational radiation from the field of massive bodies

NASA Technical Reports Server (NTRS)

Price, Richard H.; Pullin, Jorge; Kundu, Prasun K.

1993-01-01

We consider a compact source of gravitational waves of frequency omega in or near a massive spherically symmetric distribution of matter or a black hole. Recent calculations have led to apparently contradictory results for the influence of the massive body on the propagation of the waves. We show here that the results are in fact consistent and in agreement with the 'standard' viewpoint in which the high-frequency compact source produces the radiation as if in a flat background, and the background curvature affects the propagation of these waves.

Surface motion of a fluid planet induced by impacts

NASA Astrophysics Data System (ADS)

Ni, Sidao; Ahrens, Thomas J.

2006-10-01

In order to approximate the free-surface motion of an Earth-sized planet subjected to a giant impact, we have described the excitation of body and surface waves in a spherical compressible fluid planet without gravity or intrinsic material attenuation for a buried explosion source. Using the mode summation method, we obtained an analytical solution for the surface motion of the fluid planet in terms of an infinite series involving the products of spherical Bessel functions and Legendre polynomials. We established a closed form expression for the mode summation excitation coefficient for a spherical buried explosion source, and then calculated the surface motion for different spherical explosion source radii a (for cases of a/R = 0.001 to 0.035, R is the radius of the Earth) We also studied the effect of placing the explosion source at different radii r0 (for cases of r0/R = 0.90 to 0.96) from the centre of the planet. The amplitude of the quasi-surface waves depends substantially on a/R, and slightly on r0/R. For example, in our base-line case, a/R = 0.03, r0/R = 0.96, the free-surface velocity above the source is 0.26c, whereas antipodal to the source, the peak free surface velocity is 0.19c. Here c is the acoustic velocity of the fluid planet. These results can then be applied to studies of atmosphere erosion via blow-off caused by asteroid impacts.

Analysis of two colliding fractionally damped spherical shells in modelling blunt human head impacts

NASA Astrophysics Data System (ADS)

Rossikhin, Yury A.; Shitikova, Marina V.

2013-06-01

The collision of two elastic or viscoelastic spherical shells is investigated as a model for the dynamic response of a human head impacted by another head or by some spherical object. Determination of the impact force that is actually being transmitted to bone will require the model for the shock interaction of the impactor and human head. This model is indended to be used in simulating crash scenarios in frontal impacts, and provide an effective tool to estimate the severity of effect on the human head and to estimate brain injury risks. The model developed here suggests that after the moment of impact quasi-longitudinal and quasi-transverse shock waves are generated, which then propagate along the spherical shells. The solution behind the wave fronts is constructed with the help of the theory of discontinuities. It is assumed that the viscoelastic features of the shells are exhibited only in the contact domain, while the remaining parts retain their elastic properties. In this case, the contact spot is assumed to be a plane disk with constant radius, and the viscoelastic features of the shells are described by the fractional derivative standard linear solid model. In the case under consideration, the governing differential equations are solved analytically by the Laplace transform technique. It is shown that the fractional parameter of the fractional derivative model plays very important role, since its variation allows one to take into account the age-related changes in the mechanical properties of bone.

Effect of omega-3 polyunsaturated fatty acid supplementation on central arterial stiffness and arterial wave reflections in young and older healthy adults.

PubMed

Monahan, Kevin D; Feehan, Robert P; Blaha, Cheryl; McLaughlin, Daniel J

2015-06-01

Increased central arterial stiffness and enhanced arterial wave reflections may contribute to increased risk of cardiovascular disease development with advancing age. Omega-3 polyunsaturated fatty acid (n-3) ingestion may reduce cardiovascular risk via favorable effects exerted on arterial structure and function. We determined the effects of n-3 supplementation (4 g/day for 12 weeks) on important measures of central arterial stiffness (carotid-femoral pulse wave velocity; PWV) and arterial wave reflection (central augmentation index) in young (n = 12; 25 ± 1-year-old, mean ± SE) and older (n = 12; 66 ± 2) healthy adults. We hypothesized that n-3 supplementation would decrease carotid-femoral PWV and central augmentation index in older adults. Our results indicate that carotid-femoral PWV and central augmentation index were greater in older (988 ± 65 cm/sec and 33 ± 2%) than in young adults (656 ± 16 cm/sec and 3 ± 4%: both P < 0.05 compared to older) before the intervention (Pre). N-3 supplementation decreased carotid-femoral PWV in older (∆-9 ± 2% Precompared to Post; P < 0.05), but not young adults (∆2 ± 3%). Central augmentation index was unchanged by n-3 supplementation in young (3 ± 4 vs. 0 ± 4% for Pre and Post, respectively) and older adults (33 ± 2 vs. 35 ± 3%). Arterial blood pressure at rest, although increased with age, was not altered by n-3 supplementation in young or older adults. Collectively, these data indicate that 12 weeks of daily n-3 supplementation decreases an important measure of central arterial stiffness (carotid-femoral PWV) in older, but not young healthy adults. The mechanism underlying decreased central arterial stiffness with n-3 supplementation is unknown, but appears to be independent of effects on arterial blood pressure or arterial wave reflections. © 2015 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.

Projector Augmented-Wave formulation of response to strain and electric field perturbation within the density-functional perturbation theory

NASA Astrophysics Data System (ADS)

Martin, Alexandre; Torrent, Marc; Caracas, Razvan

2015-03-01

A formulation of the response of a system to strain and electric field perturbations in the pseudopotential-based density functional perturbation theory (DFPT) has been proposed by D.R Hamman and co-workers. It uses an elegant formalism based on the expression of DFT total energy in reduced coordinates, the key quantity being the metric tensor and its first and second derivatives. We propose to extend this formulation to the Projector Augmented-Wave approach (PAW). In this context, we express the full elastic tensor including the clamped-atom tensor, the atomic-relaxation contributions (internal stresses) and the response to electric field change (piezoelectric tensor and effective charges). With this we are able to compute the elastic tensor for all materials (metals and insulators) within a fully analytical formulation. The comparison with finite differences calculations on simple systems shows an excellent agreement. This formalism has been implemented in the plane-wave based DFT ABINIT code. We apply it to the computation of elastic properties and seismic-wave velocities of iron with impurity elements. By analogy with the materials contained in meteorites, tested impurities are light elements (H, O, C, S, Si).

Modeling the Effects of Transbasin Nonlinear Internal Waves Through the South China Sea Basin

DTIC Science & Technology

2013-06-01

sound propagation through the SCS needs to be developed to help maintain tactical superiority. This model will provide valuable information for...METHODOLOGY A. ACOUSTIC MODEL 1. Ray Trace Theory Modeling of sound propagation through the ocean requires solving the governing spherical wave equation...arrival structure simulation code. The model permits the study of the physics and phenomenology of sound propagation though the SCS

Diagnostic Analysis Of Ultrasound Data

DOEpatents

Chambers, David H.; Mast, Jeffrey; Azevedo, Stephen G.; Wuebbeling, Frank; Natterer, Frank; Duric, Neb; Littrup, Peter J.; Holsapple, Earle

2006-01-10

A method and apparatus are provided for investigating tissue in which acoustic data are derived from scattering a plurality of pulsed spherical or cylindrical acoustic waves from a plurality of transmission elements through the tissue to a plurality of receiving elements. The acoustic data, which include a mix of reflected and transmitted acoustic waves, are received and digitized, and a representation of a portion of the tissue is generated from the digitized acoustic data.

Sound wave generation by a spherically symmetric outburst and AGN feedback in galaxy clusters II: impact of thermal conduction.

NASA Astrophysics Data System (ADS)

Tang, Xiaping; Churazov, Eugene

2018-04-01

We analyze the impact of thermal conduction on the appearance of a shock-heated gas shell which is produced when a spherically symmetric outburst of a supermassive black hole inflates bubbles of relativistic plasma at the center of a galaxy cluster. The presence of the hot and low-density shell can be used as an ancillary indicator for a high rate of energy release during the outburst, which is required to drive strong shocks into the gas. Here we show that conduction can effectively erase such shell, unless the diffusion of electrons is heavily suppressed. We conclude that a more robust proxy to the energy release rate is the ratio between the shock radius and bubble radius. We also revisited the issue of sound waves dissipation induced by thermal conduction in a scenario, where characteristic wavelength of the sound wave is set by the total energy of the outburst. For a fiducial short outburst model, the dissipation length does not exceed the cooling radius in a typical cluster, provided that the conduction is suppressed by a factor not larger than ˜100. For quasi-continuous energy injection neither the shock-heated shell nor the outgoing sound wave are important and the role of conduction is subdominant.

Linear Transformation of Electromagnetic Wave Beams of the Electron-Cyclotron Range in Toroidal Magnetic Configurations

NASA Astrophysics Data System (ADS)

Khusainov, T. A.; Shalashov, A. G.; Gospodchikov, E. D.

2018-05-01

The field structure of quasi-optical wave beams tunneled through the evanescence region in the vicinity of the plasma cutoff in a nonuniform magnetoactive plasma is analyzed. This problem is traditionally associated with the process of linear transformation of ordinary and extraordinary waves. An approximate analytical solution is constructed for a rather general magnetic configuration applicable to spherical tokamaks, optimized stellarators, and other magnetic confinement systems with a constant plasma density on magnetic surfaces. A general technique for calculating the transformation coefficient of a finite-aperture wave beam is proposed, and the physical conditions required for the most efficient transformation are analyzed.

Fully vectorial accelerating diffraction-free Helmholtz beams.

PubMed

Aleahmad, Parinaz; Miri, Mohammad-Ali; Mills, Matthew S; Kaminer, Ido; Segev, Mordechai; Christodoulides, Demetrios N

2012-11-16

We show that new families of diffraction-free nonparaxial accelerating optical beams can be generated by considering the symmetries of the underlying vectorial Helmholtz equation. Both two-dimensional transverse electric and magnetic accelerating wave fronts are possible, capable of moving along elliptic trajectories. Experimental results corroborate these predictions when these waves are launched from either the major or minor axis of the ellipse. In addition, three-dimensional spherical nondiffracting field configurations are presented along with their evolution dynamics. Finally, fully vectorial self-similar accelerating optical wave solutions are obtained via oblate-prolate spheroidal wave functions. In all occasions, these effects are illustrated via pertinent examples.

Gravitational field of a concentrated mass in Jordan—Brans—Dicke theory

NASA Astrophysics Data System (ADS)

Arutyunyan, G. G.; Papoyan, V. V.

1994-04-01

The problem of determining the gravitational field of a static, spherically symmetric, self-gravitating object is formulated. The small number of physically applicable exact solutions of the equations in Jordan—Brans—Dicke theory is augmented with new exact solutions describing the external gravitational field of the given body. Once a solution has been found, it can be rewritten in modified curvature, homogeneous, and other coordinates by appropriate gauging. In a special case the solution coincides with the well-known Schwarzschild solution.

Fusion yield: Guderley model and Tsallis statistics

NASA Astrophysics Data System (ADS)

Haubold, H. J.; Kumar, D.

2011-02-01

The reaction rate probability integral is extended from Maxwell-Boltzmann approach to a more general approach by using the pathway model introduced by Mathai in 2005 (A pathway to matrix-variate gamma and normal densities. Linear Algebr. Appl. 396, 317-328). The extended thermonuclear reaction rate is obtained in the closed form via a Meijer's G-function and the so-obtained G-function is represented as a solution of a homogeneous linear differential equation. A physical model for the hydrodynamical process in a fusion plasma-compressed and laser-driven spherical shock wave is used for evaluating the fusion energy integral by integrating the extended thermonuclear reaction rate integral over the temperature. The result obtained is compared with the standard fusion yield obtained by Haubold and John in 1981 (Analytical representation of the thermonuclear reaction rate and fusion energy production in a spherical plasma shock wave. Plasma Phys. 23, 399-411). An interpretation for the pathway parameter is also given.

Model Scaling of Hydrokinetic Ocean Renewable Energy Systems

NASA Astrophysics Data System (ADS)

von Ellenrieder, Karl; Valentine, William

2013-11-01

Numerical simulations are performed to validate a non-dimensional dynamic scaling procedure that can be applied to subsurface and deeply moored systems, such as hydrokinetic ocean renewable energy devices. The prototype systems are moored in water 400 m deep and include: subsurface spherical buoys moored in a shear current and excited by waves; an ocean current turbine excited by waves; and a deeply submerged spherical buoy in a shear current excited by strong current fluctuations. The corresponding model systems, which are scaled based on relative water depths of 10 m and 40 m, are also studied. For each case examined, the response of the model system closely matches the scaled response of the corresponding full-sized prototype system. The results suggest that laboratory-scale testing of complete ocean current renewable energy systems moored in a current is possible. This work was supported by the U.S. Southeast National Marine Renewable Energy Center (SNMREC).

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.

Acoustically mediated long-range interaction among multiple spherical particles exposed to a plane standing wave

NASA Astrophysics Data System (ADS)

Zhang, Shenwei; Qiu, Chunyin; Wang, Mudi; Ke, Manzhu; Liu, Zhengyou

2016-11-01

In this work, we study the acoustically mediated interaction forces among multiple well-separated spherical particles trapped in the same node or antinode plane of a standing wave. An analytical expression of the acoustic interaction force is derived, which is accurate even for the particles beyond the Rayleigh limit. Interestingly, the multi-particle system can be decomposed into a series of independent two-particle systems described by pairwise interactions. Each pairwise interaction is a long-range interaction, as characterized by a soft oscillatory attenuation (at the power exponent of n = -1 or -2). The vector additivity of the acoustic interaction force, which is not well expected considering the nonlinear nature of the acoustic radiation force, is greatly useful for exploring a system consisting of a large number of particles. The capability of self-organizing a big particle cluster can be anticipated through such acoustically controllable long-range interaction.

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

Boreyko, Jonathan B; Mruetusatorn, Prachya; Sarles, Stephen A

Droplet interface bilayers (DIBs) are a robust platform for studying synthetic cellular membranes; however, to date no DIBs have been produced at cellular length scales. Here, we create microscale droplet interface bilayers ( DIBs) at the interface between aqueous femtoliter-volume droplets within an oil-filled microfluidic channel. The uniquely large area-to-volume ratio of the droplets results in strong evaporation effects, causing the system to transition through three distinct regimes. First, the two adjacent droplets shrink into the shape of a single spherical droplet, where an augmented lipid bilayer partitions two hemi-spherical volumes. In the second regime, the combined effects of themore » shrinking monolayers and growing bilayer force the confined bilayer to buckle to conserve its mass. Finally, at a bending moment corresponding to a critical shear stress, the buckling bilayer fissions a vesicle to regulate its shape and stress. The DIBs produced here enable evaporation-induced bilayer dynamics reminiscent of endo- and exocytosis in cells.« less

On macromolecular refinement at subatomic resolution withinteratomic scatterers

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

Afonine, Pavel V.; Grosse-Kunstleve, Ralf W.; Adams, Paul D.

2007-11-09

A study of the accurate electron density distribution in molecular crystals at subatomic resolution, better than {approx} 1.0 {angstrom}, requires more detailed models than those based on independent spherical atoms. A tool conventionally used in small-molecule crystallography is the multipolar model. Even at upper resolution limits of 0.8-1.0 {angstrom}, the number of experimental data is insufficient for the full multipolar model refinement. As an alternative, a simpler model composed of conventional independent spherical atoms augmented by additional scatterers to model bonding effects has been proposed. Refinement of these mixed models for several benchmark datasets gave results comparable in quality withmore » results of multipolar refinement and superior of those for conventional models. Applications to several datasets of both small- and macro-molecules are shown. These refinements were performed using the general-purpose macromolecular refinement module phenix.refine of the PHENIX package.« less

On macromolecular refinement at subatomic resolution with interatomic scatterers

PubMed Central

Afonine, Pavel V.; Grosse-Kunstleve, Ralf W.; Adams, Paul D.; Lunin, Vladimir Y.; Urzhumtsev, Alexandre

2007-01-01

A study of the accurate electron-density distribution in molecular crystals at subatomic resolution (better than ∼1.0 Å) requires more detailed models than those based on independent spherical atoms. A tool that is conventionally used in small-molecule crystallography is the multipolar model. Even at upper resolution limits of 0.8–1.0 Å, the number of experimental data is insufficient for full multipolar model refinement. As an alternative, a simpler model composed of conventional independent spherical atoms augmented by additional scatterers to model bonding effects has been proposed. Refinement of these mixed models for several benchmark data sets gave results that were comparable in quality with the results of multipolar refinement and superior to those for conventional models. Applications to several data sets of both small molecules and macromolecules are shown. These refinements were performed using the general-purpose macromolecular refinement module phenix.refine of the PHENIX package. PMID:18007035

On macromolecular refinement at subatomic resolution with interatomic scatterers.

PubMed

Afonine, Pavel V; Grosse-Kunstleve, Ralf W; Adams, Paul D; Lunin, Vladimir Y; Urzhumtsev, Alexandre

2007-11-01

A study of the accurate electron-density distribution in molecular crystals at subatomic resolution (better than approximately 1.0 A) requires more detailed models than those based on independent spherical atoms. A tool that is conventionally used in small-molecule crystallography is the multipolar model. Even at upper resolution limits of 0.8-1.0 A, the number of experimental data is insufficient for full multipolar model refinement. As an alternative, a simpler model composed of conventional independent spherical atoms augmented by additional scatterers to model bonding effects has been proposed. Refinement of these mixed models for several benchmark data sets gave results that were comparable in quality with the results of multipolar refinement and superior to those for conventional models. Applications to several data sets of both small molecules and macromolecules are shown. These refinements were performed using the general-purpose macromolecular refinement module phenix.refine of the PHENIX package.

Impact of seasonality and air pollutants on carotid-femoral pulse wave velocity and wave reflection in hypertensive patients

PubMed Central

Stea, Francesco; Massetti, Luciano; Taddei, Stefano; Ghiadoni, Lorenzo; Modesti, Pietro Amedeo

2017-01-01

Objective The effects of seasonality on blood pressure (BP) and cardiovascular (CV) events are well established, while the influence of seasonality and other environmental factors on arterial stiffness and wave reflection has never been analyzed. This study evaluated whether seasonality (daily number of hours of light) and acute variations in outdoor temperature and air pollutants may affect carotid-femoral pulse wave velocity (PWV) and pressure augmentation. Design and method 731 hypertensive patients (30–88 years, 417 treated) were enrolled in a cross-sectional study during a 5-year period. PWV, central BP, Augmentation Index (AIx) and Augmentation Pressure (AP) were measured in a temperature-controlled (22–24°C) room. Data of the local office of the National Climatic Data Observatory were used to estimate meteorological conditions and air pollutants (PM10, O3, CO, N2O) exposure on the same day. Results PWV (mean value 8.5±1.8 m/s) was related to age (r = 0.467, p<0.001), body mass index (r = 0.132, p<0.001), central systolic (r = 0.414, p<0.001) and diastolic BP (r = 0.093, p = 0.013), daylight hours (r = -0.176, p<0.001), mean outdoor temperature (r = -0.082, p = 0.027), O3 (r = -0.135, p<0.001), CO (r = 0.096, p = 0.012), N2O (r = 0.087, p = 0.022). In multiple linear regression analysis, adjusted for confounders, PWV remained independently associated only with daylight hours (β = -0.170; 95% CI: -0.273 to -0.067, p = 0.001). No significant correlation was found between pressure augmentation and daylight hours, mean temperature or air pollutants. The relationship was stronger in untreated patients and women. Furthermore, a positive, independent association between O3 levels and PWV emerged in untreated patients (β: 0.018; p = 0.029; CI: 0.002 to 0.034) and in women (β: 0.027; p = 0.004; CI: 0.009 to 0.045). Conclusions PWV showed a marked seasonality in hypertensive patients. Environmental O3 levels may acutely reduce arterial stiffness in hypertensive women and in untreated patients. PMID:28231259

Effect of acoustic field parameters on arc acoustic binding during ultrasonic wave-assisted arc welding.

PubMed

Xie, Weifeng; Fan, Chenglei; Yang, Chunli; Lin, Sanbao

2016-03-01

As a newly developed arc welding method, power ultrasound has been successfully introduced into arc and weld pool during ultrasonic wave-assisted arc welding process. The advanced process for molten metals can be realized by utilizing additional ultrasonic field. Under the action of the acoustic wave, the plasma arc as weld heat source is regulated and its characteristics make an obvious change. Compared with the conventional arc, the ultrasonic wave-assisted arc plasma is bound significantly and becomes brighter. To reveal the dependence of the acoustic binding force on acoustic field parameters, a two-dimensional acoustic field model for ultrasonic wave-assisted arc welding device is established. The influences of the radiator height, the central pore radius, the radiator radius, and curvature radius or depth of concave radiator surface are discussed using the boundary element method. Then the authors analyze the resonant mode by this relationship curve between acoustic radiation power and radiator height. Furthermore, the best acoustic binding ability is obtained by optimizing the geometric parameters of acoustic radiator. In addition, three concave radiator surfaces including spherical cap surface, paraboloid of revolution, and rotating single curved surface are investigated systematically. Finally, both the calculation and experiment suggest that, to obtain the best acoustic binding ability, the ultrasonic wave-assisted arc welding setup should be operated under the first resonant mode using a radiator with a spherical cap surface, a small central pore, a large section radius and an appropriate curvature radius. Copyright © 2015 Elsevier B.V. All rights reserved.

Total Internal Reflection Ultrasonic Sensor for Detection of Subsurface Flaws: Proof of Concept

DTIC Science & Technology

2010-01-01

34 Tv001 Ve group (ray) velocity of the elastic wave X1, X2, X3 crystallographic coordinates x, y, z Descartes ’ coordinates tied to the transducer y0...TeO2 prism. 1.2.1. Orientation of directions and planes of interest with respect to Descartes ’ and Spherical coordinates. 1.2.2. Reflection of the...spect to Descartes ’ and Spherical coordi- nates. , (1.2.1) lili uuv Γ=ρ 2 where ρ is the crystal density and the symmetrical second rank Christoffel

Numerical simulation of MHD turbulence in three dimensions

NASA Technical Reports Server (NTRS)

Goldstein, M. L.; Roberts, D. A.; Deane, A.

1997-01-01

The evolution of Alfvenic turbulence in 3D spherical geometry can now be studied. In simulations, a fast stream is sandwiched between two slower streams. The inflow is both supersonic and superAlfvenic. Alfven waves entering the box are convected into the medium and interact nonlinearly with the velocity shear and with any structures (i.e., flux tubes) that might be present. These initial simulations suggest that velocity shear, even in spherical geometry, is able to drive a turbulent cascade which results in approximately Kolmogoroff-like power spectra.

Association between Refractive Errors and Ocular Biometry in Iranian Adults

PubMed Central

Hashemi, Hassan; Khabazkhoob, Mehdi; Emamian, Mohammad Hassan; Shariati, Mohammad; Miraftab, Mohammad; Yekta, Abbasali; Ostadimoghaddam, Hadi; Fotouhi, Akbar

2015-01-01

Purpose: To investigate the association between ocular biometrics such as axial length (AL), anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD) and corneal power (CP) with different refractive errors. Methods: In a cross-sectional study on the 40 to 64-year-old population of Shahroud, random cluster sampling was performed. Ocular biometrics were measured using the Allegro Biograph (WaveLight AG, Erlangen, Germany) for all participants. Refractive errors were determined using cycloplegic refraction. Results: In the first model, the strongest correlations were found between spherical equivalent with axial length and corneal power. Spherical equivalent was strongly correlated with axial length in high myopic and high hyperopic cases, and with corneal power in high hyperopic cases; 69.5% of variability in spherical equivalent was attributed to changes in these variables. In the second model, the correlations between vitreous chamber depth and corneal power with spherical equivalent were stronger in myopes than hyperopes, while the correlations between lens thickness and anterior chamber depth with spherical equivalent were stronger in hyperopic cases than myopic ones. In the third model, anterior chamber depth + lens thickness correlated with spherical equivalent only in moderate and severe cases of hyperopia, and this index was not correlated with spherical equivalent in moderate to severe myopia. Conclusion: In individuals aged 40-64 years, corneal power and axial length make the greatest contribution to spherical equivalent in high hyperopia and high myopia. Anterior segment biometric components have a more important role in hyperopia than myopia. PMID:26730304

Linear perturbations in spherically symmetric dust cosmologies including a cosmological constant

NASA Astrophysics Data System (ADS)

Meyer, Sven; Bartelmann, Matthias

2017-12-01

We study the dynamical behaviour of gauge-invariant linear perturbations in spherically symmetric dust cosmologies including a cosmological constant. In contrast to spatially homogeneous FLRW models, the reduced degree of spatial symmetry causes a non-trivial dynamical coupling of gauge-invariant quantities already at first order perturbation theory and the strength and influence of this coupling on the spacetime evolution is investigated here. We present results on the underlying dynamical equations augmented by a cosmological constant and integrate them numerically. We also present a method to derive cosmologically relevant initial variables for this setup. Estimates of angular power spectra for each metric variable are computed and evaluated on the central observer's past null cone. By comparing the full evolution to the freely evolved initial profiles, the coupling strength will be determined for a best fit radially inhomogeneous patch obtained in previous works (see [1]). We find that coupling effects are not noticeable within the cosmic variance limit and can therefore safely be neglected for a relevant cosmological scenario. On the contrary, we find very strong coupling effects in a best fit spherical void model matching the distance redshift relation of SNe which is in accordance with previous findings using parametric void models.

Interaction model between a liquid film and a spherical probe

NASA Astrophysics Data System (ADS)

Ledesma Alonso, Rene; Legendre, Dominique; Tordjeman, Philippe

2012-11-01

To find a liquid surface profile, when performing AFM measurements, probe interaction effects should be identified. Herein, the behavior of a liquid film free surface (thickness E, surface tension γ and density difference Δρ), disposed over a flat surface and in the presence of a spherical probe (radius R) is forecast. A bump-like surface shape is observed, due to the probe/film interaction (characterized by the Hamaker constant Hpl). In addition, the attraction between the film and the substrate (depicted by Hsl) opposes the axial and radial deformation ranges. Several parameters portray the equilibrium shape: Bond Bo = (ΔρgR2) / γ and modified Hamaker Ha = 4Hpl / (3 πγR2) numbers, Hamaker ratio A =Hls /Hpl , separation distance D / R and film thickness E / R . We focus on the effect of geometry, nevertheless special attention is given to the role of physical parameters. Employing an augmented Young-Laplace equation, the equilibrium profile is described by a strongly non-linear ODE. A critical distance, below which the irreversible wetting process of the spherical probe occurs, is predicted. Our results provide simple relationships between parameters, which determine the optimal scanning conditions over liquid films.

The Third Wave of Democratization in Indonesia

DTIC Science & Technology

2000-03-01

Dewan Perwakilan Rakyat (House of the Representatives) augmented by delegates from the regional territories and the groups in accordance with...unlimited THE THIRD WAVE OF DEMOCRATIZATION IN INDONESIA Azizan bin Md Delin Lieutenant Colonel, Malaysian Army LL B. (Hons), UiTM, Malaysia , 1996...Article 2(1) of the 1945 Constitution reads: "The Majelis Permusyawaratan Rakyat (People’s Consultative Assembly) shall consist of members of the

Broken Ergodicity in MHD Turbulence in a Spherical Domain

NASA Technical Reports Server (NTRS)

Shebalin, John V.; wang, Yifan

2011-01-01

Broken ergodicity (BE) occurs in Fourier method numerical simulations of ideal, homogeneous, incompressible magnetohydrodynamic (MHD) turbulence. Although naive statistical theory predicts that Fourier coefficients of fluid velocity and magnetic field are zero-mean random variables, numerical simulations clearly show that low-wave-number coefficients have non-zero mean values that can be very large compared to the associated standard deviation. In other words, large-scale coherent structure (i.e., broken ergodicity) in homogeneous MHD turbulence can spontaneously grow out of random initial conditions. Eigenanalysis of the modal covariance matrices in the probability density functions of ideal statistical theory leads to a theoretical explanation of observed BE in homogeneous MHD turbulence. Since dissipation is minimal at the largest scales, BE is also relevant for resistive magnetofluids, as evidenced in numerical simulations. Here, we move beyond model magnetofluids confined by periodic boxes to examine BE in rotating magnetofluids in spherical domains using spherical harmonic expansions along with suitable boundary conditions. We present theoretical results for 3-D and 2-D spherical models and also present computational results from dynamical simulations of 2-D MHD turbulence on a rotating spherical surface. MHD turbulence on a 2-D sphere is affected by Coriolus forces, while MHD turbulence on a 2-D plane is not, so that 2-D spherical models are a useful (and simpler) intermediate stage on the path to understanding the much more complex 3-D spherical case.

Bubbles with shock waves and ultrasound: a review

PubMed Central

Ohl, Siew-Wan; Klaseboer, Evert; Khoo, Boo Cheong

2015-01-01

The study of the interaction of bubbles with shock waves and ultrasound is sometimes termed ‘acoustic cavitation'. It is of importance in many biomedical applications where sound waves are applied. The use of shock waves and ultrasound in medical treatments is appealing because of their non-invasiveness. In this review, we present a variety of acoustics–bubble interactions, with a focus on shock wave–bubble interaction and bubble cloud phenomena. The dynamics of a single spherically oscillating bubble is rather well understood. However, when there is a nearby surface, the bubble often collapses non-spherically with a high-speed jet. The direction of the jet depends on the ‘resistance' of the boundary: the bubble jets towards a rigid boundary, splits up near an elastic boundary, and jets away from a free surface. The presence of a shock wave complicates the bubble dynamics further. We shall discuss both experimental studies using high-speed photography and numerical simulations involving shock wave–bubble interaction. In biomedical applications, instead of a single bubble, often clouds of bubbles appear (consisting of many individual bubbles). The dynamics of such a bubble cloud is even more complex. We shall show some of the phenomena observed in a high-intensity focused ultrasound (HIFU) field. The nonlinear nature of the sound field and the complex inter-bubble interaction in a cloud present challenges to a comprehensive understanding of the physics of the bubble cloud in HIFU. We conclude the article with some comments on the challenges ahead. PMID:26442143

Biomechanical Analysis of an Expandable Lumbar Interbody Spacer.

PubMed

Soriano-Baron, Hector; Newcomb, Anna G U S; Malhotra, Devika; Palma, Atilio E; Martinez-Del-Campo, Eduardo; Crawford, Neil R; Theodore, Nicholas; Kelly, Brian P; Kaibara, Taro

2018-06-01

Recently developed expandable interbody spacers are widely accepted in spinal surgery; however, the resulting biomechanical effects of their use have not yet been fully studied. We analyzed the biomechanical effects of an expandable polyetheretherketone interbody spacer inserted through a bilateral posterior approach with and without different modalities of posterior augmentation. Biomechanical nondestructive flexibility testing was performed in 7 human cadaveric lumbar (L2-L5) specimens followed by axial compressive loading. Each specimen was tested under 6 conditions: 1) intact, 2) bilateral L3-L4 cortical screw/rod (CSR) alone, 3) WaveD alone, 4) WaveD + CSR, 5) WaveD + bilateral L3-L4 pedicle screw/rod (PSR), and 6) WaveD + CSR/PSR, where CSR/PSR was a hybrid construct comprising bilateral cortical-level L3 and pedicle-level L4 screws interconnected by rods. The range of motion (ROM) with the interbody spacer alone decreased significantly compared with the intact condition during flexion-extension (P = 0.02) but not during lateral bending or axial rotation (P ≥ 0.19). The addition of CSR or PSR to the interbody spacer alone condition significantly decreased the ROM compared with the interbody spacer alone (P ≤ 0.002); and WaveD + CSR, WaveD + PSR, and WaveD + CSR/PSR (hybrid) (P ≥ 0.29) did not differ. The axial compressive stiffness (resistance to change in foraminal height during compressive loading) with the interbody spacer alone did not differ from the intact condition (P = 0.96), whereas WaveD + posterior instrumentation significantly increased compressive stiffness compared with the intact condition and the interbody spacer alone (P ≤ 0.001). The WaveD alone significantly reduced ROM during flexion-extension while maintaining the axial compressive stiffness. CSR, PSR, and CSR/PSR hybrid constructs were all effective in augmenting the expandable interbody spacer system and improving its stability. Copyright © 2018 Elsevier Inc. All rights reserved.

Increased aortic wave reflection contributes to higher systolic blood pressure in adolescents born preterm.

PubMed

Kowalski, Remi R; Beare, Richard; Mynard, Jonathan P; Cheong, Jeanie L Y; Doyle, Lex W; Smolich, Joseph J; Cheung, Michael M H

2018-03-29

To evaluate the wave reflection characteristics in the aortic arch and common carotid artery of ex-preterm adolescents and assess their relationship to central blood pressure in a cohort followed prospectively since birth. Central blood pressures, pulse wave velocity, augmentation index, microvascular reactive hyperemia, arterial distensibility, compliance and stiffness index, and also aortic and carotid wave intensity were measured in 18-year-olds born extremely preterm at below 28 weeks' gestation (n = 76) and term-born controls (n = 42). Compared with controls, ex-preterm adolescents had higher central systolic (111 ± 11 vs. 105 ± 10 mmHg; P < 0.001) and diastolic blood pressures (73 ± 7 vs. 67 ± 7 mmHg; P < 0.001). Although conventional measures of arterial function and biomechanics such as pulse wave velocity and augmentation index were no different between groups, wave intensity analysis revealed elevated backward compression wave area (-0.39 ± 0.21 vs. -0.29 ± 0.17 W/m/s × 10; P = 0.03), backward compression wave pressure change (9.0 ± 3.5 vs. 6.6 ± 2.5 mmHg; P = 0.001) and reflection index (0.44 ± 0.15 vs. 0.32 ± 0.08; P < 0.001) in the aorta of ex-preterm adolescents compared with controls. These changes were less pronounced in the carotid artery. On multivariable analysis, forward and backward compression wave areas were the only biomechanical variables associated with central systolic pressure. Ex-preterm adolescents demonstrate elevated wave reflection indices in the aortic arch, which correlate with central systolic pressure. Wave intensity analysis may provide a sensitive novel marker of evolving vascular dysfunction in ex-preterm survivors.

Flow above and within granular media composed of spherical and non-spherical particles - using a 3D numerical model

NASA Astrophysics Data System (ADS)

Bartzke, Gerhard; Kuhlmann, Jannis; Huhn, Katrin

2016-04-01

The entrainment of single grains and, hence, their erosion characteristics are dependent on fluid forcing, grain size and density, but also shape variations. To quantitatively describe and capture the hydrodynamic conditions around individual grains, researchers commonly use empirical approaches such as laboratory flume tanks. Nonetheless, it is difficult with such physical experiments to measure the flow velocities in the direct vicinity or within the pore spaces of sediments, at a sufficient resolution and in a non-invasive way. As a result, the hydrodynamic conditions in the water column, at the fluid-porous interface and within pore spaces of a granular medium of various grain shapes is not yet fully understood. For that reason, there is a strong need for numerical models, since these are capable of quantifying fluid speeds within a granular medium. A 3D-SPH (Smooth Particle Hydrodynamics) numerical wave tank model was set up to provide quantitative evidence on the flow velocities in the direct vicinity and in the interior of granular beds composed of two shapes as a complementary method to the difficult task of in situ measurement. On the basis of previous successful numerical wave tank models with SPH, the model geometry was chosen in dimensions of X=2.68 [m], Y=0.48 [m], and Z=0.8 [m]. Three suites of experiments were designed with a range of particle shape models: (1) ellipsoids with the long axis oriented in the across-stream direction, (2) ellipsoids with the long axis oriented in the along-stream direction, and (3) spheres. Particle diameters ranged from 0.04 [m] to 0.08 [m]. A wave was introduced by a vertical paddle that accelerated to 0.8 [m/s] perpendicular to the granular bed. Flow measurements showed that the flow velocity values into the beds were highest when the grains were oriented across the stream direction and lowest in case when the grains were oriented parallel to the stream, indicating that the model was capable to simulate simultaneously the flow into and within a granular medium composed of spherical and non-spherical shapes under wave forcing. It is concluded that variations in grain shape orientation within a bed appear to control the amount of flow that can be accumulated by the pores, which was illustrated in a conceptual model.

White coat hypertension is more risky than prehypertension: important role of arterial wave reflections.

PubMed

Sung, Shih-Hsien; Cheng, Hao-Min; Wang, Kang-Ling; Yu, Wen-Chung; Chuang, Shao-Yuan; Ting, Chih-Tai; Lakatta, Edward G; Yin, Frank C P; Chou, Pesus; Chen, Chen-Huan

2013-06-01

Arterial aging may link cardiovascular risk to white coat hypertension (WCH). The aims of the present study were to investigate the role of arterial aging in the white coat effect, defined as the difference between office and 24-hour ambulatory systolic blood pressures, and to compare WCH with prehypertension (PH) with respect to target organ damage and long-term cardiovascular mortality. A total of 1257 never-been-treated volunteer subjects from a community-based survey were studied. WCH and PH were defined by office and 24-hour ambulatory blood pressures. Left ventricular mass index, carotid intima-media thickness, estimated glomerular filtration rate, carotid-femoral pulse wave velocity, carotid augmentation index, amplitude of the reflection pressure wave, and 15-year cardiovascular mortality were determined. Subjects with WCH were significantly older and had greater body mass index, blood pressure values, intima-media thickness, carotid-femoral pulse wave velocity, augmentation index, amplitude of the backward pressure wave, and a lower estimated glomerular filtration rate than PH. Amplitude of the backward pressure wave was the most important independent correlate of the white coat effect in multivariate analysis (model r(2)=0.451; partial r(2)/model r(2)=90.5%). WCH had significantly greater cardiovascular mortality than PH (hazard ratio, 2.94; 95% confidence interval, 1.09-7.91), after accounting for age, sex, body mass index, smoking, fasting plasma glucose, and total cholesterol/high-density lipoprotein-cholesterol ratio. Further adjustment of the model for amplitude of the backward pressure wave eliminated the statistical significance of the WCH effect. In conclusion, the white coat effect is mainly caused by arterial aging. WCH carries higher risk for cardiovascular mortality than PH, probably via enhanced wave reflections that accompany arterial aging.

Experimental study of inertial waves in a spherical shell induced by librations of the inner sphere

NASA Astrophysics Data System (ADS)

Hoff, Michael; Harlander, Uwe; Jahangir, Saad; Egbers, Christoph

2015-04-01

Many planetary bodies do not rotate with a constant velocity but undergo rotations with superposed oscillations called longitudinal librations. This is the case e.g. for the Earth's moon, Mars' moon, Mercury and many other moons of Jupiter and Saturn and some of them have a solid inner core and a molten outer core. It is worth to know the interaction between the libration of the core and the interior of the fluid to understand tidal heating, fluid mixing, and the generation of magnetic fields. Here we present an experimental investigation of inertial waves in a spherical shell. The shell rotates with a mean angular velocity Ω around its vertical axis overlaid by a time periodic oscillation of the inner sphere in the range 0 < ω < 2Ω, in order to excite inertial waves with a known frequency. We want to show the influence of the libration amplitude ɛ on different libration frequencies ω and how efficient libration is, to excite inertial waves in the given frequency range. For low ω and high ɛ instability starts to grow and, beside the excited inertial waves, several low frequency structures can be found. Quantitative PIV analyses of the horizontal plane in the co-rotation frame show clear spiral structures with different wave numbers for high libration amplitudes due to strong shear, similar to differential rotation. Another question, we like to address, is whether high libration amplitudes can also excite very low frequency Rossby wave structures? If the frequency increases, it can be seen from Poincaré plots that large attractor windows for inertial waves appear. We want to show PIV analyses for such flows dominated by wave attractors. It is known that for large excitation frequencies subharmonic parametric instability starts to grow and triads will be excited. Our experimental data show hints for the existence of triads and preliminary results will be discussed.

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.

Determination of NMR chemical shifts for cholesterol crystals from first-principles

NASA Astrophysics Data System (ADS)

Kucukbenli, Emine; de Gironcoli, Stefano

2011-03-01

Solid State Nuclear Magnetic Resonance (NMR) is a powerful tool in crystallography when combined with theoretical predictions. So far, empirical calculations of spectra have been employed for an unambiguous identification. However, many complex systems are outside the scope of these methods. Our implementation of ultrasoft and projector augmented wave pseudopotentials within ab initio gauge including projector augmented plane wave (GIPAW) method in Quantum Espresso simulation package allows affordable calculations of NMR spectra for systems of thousands of electrons. We report here the first ab initio determination of NMR spectra for several crystal structures of cholesterol. Cholesterol crystals, the main component of human gallstones, are of interest to medical research as their structural properties can shed light on the pathologies of gallbladder. With our application we show that ab initio calculations can be employed to aid NMR crystallography.

Numerical relativity in spherical coordinates with the Einstein Toolkit

NASA Astrophysics Data System (ADS)

Mewes, Vassilios; Zlochower, Yosef; Campanelli, Manuela; Ruchlin, Ian; Etienne, Zachariah B.; Baumgarte, Thomas W.

2018-04-01

Numerical relativity codes that do not make assumptions on spatial symmetries most commonly adopt Cartesian coordinates. While these coordinates have many attractive features, spherical coordinates are much better suited to take advantage of approximate symmetries in a number of astrophysical objects, including single stars, black holes, and accretion disks. While the appearance of coordinate singularities often spoils numerical relativity simulations in spherical coordinates, especially in the absence of any symmetry assumptions, it has recently been demonstrated that these problems can be avoided if the coordinate singularities are handled analytically. This is possible with the help of a reference-metric version of the Baumgarte-Shapiro-Shibata-Nakamura formulation together with a proper rescaling of tensorial quantities. In this paper we report on an implementation of this formalism in the Einstein Toolkit. We adapt the Einstein Toolkit infrastructure, originally designed for Cartesian coordinates, to handle spherical coordinates, by providing appropriate boundary conditions at both inner and outer boundaries. We perform numerical simulations for a disturbed Kerr black hole, extract the gravitational wave signal, and demonstrate that the noise in these signals is orders of magnitude smaller when computed on spherical grids rather than Cartesian grids. With the public release of our new Einstein Toolkit thorns, our methods for numerical relativity in spherical coordinates will become available to the entire numerical relativity community.

Wave field restoration using three-dimensional Fourier filtering method.

PubMed

Kawasaki, T; Takai, Y; Ikuta, T; Shimizu, R

2001-11-01

A wave field restoration method in transmission electron microscopy (TEM) was mathematically derived based on a three-dimensional (3D) image formation theory. Wave field restoration using this method together with spherical aberration correction was experimentally confirmed in through-focus images of amorphous tungsten thin film, and the resolution of the reconstructed phase image was successfully improved from the Scherzer resolution limit to the information limit. In an application of this method to a crystalline sample, the surface structure of Au(110) was observed in a profile-imaging mode. The processed phase image showed quantitatively the atomic relaxation of the topmost layer.

A theoretical study of hot plasma spheroids in the presence of low-frequency electromagnetic waves

NASA Astrophysics Data System (ADS)

Ahmadizadeh, Y.; Jazi, B.; Barjesteh, S.

2016-07-01

While taking into account thermal motion of electrons, scattering of electromagnetic waves with low frequency from hot plasma spheroids is investigated. In this theoretical research, ions are heavy to respond to electromagnetic fluctuations. The solution of scalar wave equation in spheroidal coordinates for electric potential inside the plasma spheroids are obtained. The variations of resonance frequencies vs. Debye length are studied and consistency between the obtained results in this paper and the results for the well-known plasma objects such as plasma column and spherical plasma have been proved.

Dielectric magnetic microparticles as photomagnonic cavities: Enhancing the modulation of near-infrared light by spin waves

NASA Astrophysics Data System (ADS)

Almpanis, Evangelos

2018-05-01

The coupling between spin waves and optical Mie resonances inside a dielectric magnetic spherical particle, which acts simultaneously as a photonic and magnonic (photomagnonic) cavity, is investigated by means of numerical calculations accurate to arbitrary order in the magnetooptical coupling coefficient. Isolated dielectric magnetic particles with diameters of just a few microns support high-Q optical Mie resonances at near-infrared frequencies and localized spin waves, providing an ultrasmall and compact platform in the emerging field of cavity optomagnonics. Our results predict the occurrence of strong interaction effects, beyond the linear-response approximation, which lead to enhanced modulation of near-infrared light by spin waves through multimagnon absorption and emission mechanisms.

The 24-hour pulse wave velocity, aortic augmentation index, and central blood pressure in normotensive volunteers

PubMed Central

Kuznetsova, Tatyana Y; Korneva, Viktoria A; Bryantseva, Evgeniya N; Barkan, Vitaliy S; Orlov, Artemy V; Posokhov, Igor N; Rogoza, Anatoly N

2014-01-01

The purpose of this study was to examine the pulse wave velocity, aortic augmentation index corrected for heart rate 75 (AIx@75), and central systolic and diastolic blood pressure during 24-hour monitoring in normotensive volunteers. Overall, 467 subjects (206 men and 261 women) were recruited in this study. Participants were excluded from the study if they were less than 19 years of age, had blood test abnormalities, had a body mass index greater than 2 7.5 kg/m2, had impaired glucose tolerance, or had hypotension or hypertension. Ambulatory blood pressure monitoring (ABPM) with the BPLab® device was performed in each subject. ABPM waveforms were analyzed using the special automatic Vasotens® algorithm, which allows the calculation of pulse wave velocity, AIx@75, central systolic and diastolic blood pressure for “24-hour”, “awake”, and “asleep” periods. Circadian rhythms and sex differences in these indexes were identified. Pending further validation in prospective outcome-based studies, our data may be used as preliminary diagnostic values for the BPLab ABPM additional index in adult subjects. PMID:24812515

Shallow-water sloshing in a moving vessel with variable cross-section and wetting-drying using an extension of George's well-balanced finite volume solver

NASA Astrophysics Data System (ADS)

Alemi Ardakani, Hamid; Bridges, Thomas J.; Turner, Matthew R.

2016-06-01

A class of augmented approximate Riemann solvers due to George (2008) [12] is extended to solve the shallow-water equations in a moving vessel with variable bottom topography and variable cross-section with wetting and drying. A class of Roe-type upwind solvers for the system of balance laws is derived which respects the steady-state solutions. The numerical solutions of the new adapted augmented f-wave solvers are validated against the Roe-type solvers. The theory is extended to solve the shallow-water flows in moving vessels with arbitrary cross-section with influx-efflux boundary conditions motivated by the shallow-water sloshing in the ocean wave energy converter (WEC) proposed by Offshore Wave Energy Ltd. (OWEL) [1]. A fractional step approach is used to handle the time-dependent forcing functions. The numerical solutions are compared to an extended new Roe-type solver for the system of balance laws with a time-dependent source function. The shallow-water sloshing finite volume solver can be coupled to a Runge-Kutta integrator for the vessel motion.

A 1D-2D Shallow Water Equations solver for discontinuous porosity field based on a Generalized Riemann Problem

NASA Astrophysics Data System (ADS)

Ferrari, Alessia; Vacondio, Renato; Dazzi, Susanna; Mignosa, Paolo

2017-09-01

A novel augmented Riemann Solver capable of handling porosity discontinuities in 1D and 2D Shallow Water Equation (SWE) models is presented. With the aim of accurately approximating the porosity source term, a Generalized Riemann Problem is derived by adding an additional fictitious equation to the SWEs system and imposing mass and momentum conservation across the porosity discontinuity. The modified Shallow Water Equations are theoretically investigated, and the implementation of an augmented Roe Solver in a 1D Godunov-type finite volume scheme is presented. Robust treatment of transonic flows is ensured by introducing an entropy fix based on the wave pattern of the Generalized Riemann Problem. An Exact Riemann Solver is also derived in order to validate the numerical model. As an extension of the 1D scheme, an analogous 2D numerical model is also derived and validated through test cases with radial symmetry. The capability of the 1D and 2D numerical models to capture different wave patterns is assessed against several Riemann Problems with different wave patterns.

Modelling sheet-flow sediment transport in wave-bottom boundary layers using discrete-element modelling.

PubMed

Calantoni, Joseph; Holland, K Todd; Drake, Thomas G

2004-09-15

Sediment transport in oscillatory boundary layers is a process that drives coastal geomorphological change. Most formulae for bed-load transport in nearshore regions subsume the smallest-scale physics of the phenomena by parametrizing interactions amongst particles. In contrast, we directly simulate granular physics in the wave-bottom boundary layer using a discrete-element model comprised of a three-dimensional particle phase coupled to a one-dimensional fluid phase via Newton's third law through forces of buoyancy, drag and added mass. The particulate sediment phase is modelled using discrete particles formed to approximate natural grains by overlapping two spheres. Both the size of each sphere and the degree of overlap can be varied for these composite particles to generate a range of non-spherical grains. Simulations of particles having a range of shapes showed that the critical angle--the angle at which a grain pile will fail when tilted slowly from rest--increases from approximately 26 degrees for spherical particles to nearly 39 degrees for highly non-spherical composite particles having a dumbbell shape. Simulations of oscillatory sheet flow were conducted using composite particles with an angle of repose of approximately 33 degrees and a Corey shape factor greater than about 0.8, similar to the properties of beach sand. The results from the sheet-flow simulations with composite particles agreed more closely with laboratory measurements than similar simulations conducted using spherical particles. The findings suggest that particle shape may be an important factor for determining bed-load flux, particularly for larger bed slopes.

Effects of phenytoin on N100 augmenting/reducing and the late positive complex of the event-related potential: a topographic analysis.

PubMed

Pritchard, W S; Barratt, E S; Faulk, D M; Brandt, M E; Bryant, S G

1986-01-01

The effects of 100 mg of phenytoin on the topographic distribution of augmenting/reducing (amplitude response/nonresponse to increases in stimulus intensity) of the visual N100 component of the event-related potential (ERP) were examined. In normal subjects, visual N100 augmenting is associated with impulsivity and attentional distraction. Effects of phenytoin on the topographic distributions of the P300 and slow-wave cognitive ERP components were also examined. Subjects counted the total number of light flashes presented at two highly discriminable but equiprobable intensities. Results indicated that phenytoin had a significant reducing effect on the intensity response of N100 at the vertex and anterior temporal electrode sites, and approached significance at the frontal pole. That is, at these loci N100 showed less of an increase in amplitude (or, in some subjects, more of a decrease) in going from baseline to drug than in going from baseline to placebo. Results also indicated that phenytoin significantly enhanced the amplitude of the frontal, negative portion of slow wave, but not the posterior, positive portion or the P300 component. These findings are consistent with behavioral evidence that phenytoin reduces impulsivity and improves concentration.

Controlled rotation and translation of spherical particles or living cells by surface acoustic waves.

PubMed

Bernard, Ianis; Doinikov, Alexander A; Marmottant, Philippe; Rabaud, David; Poulain, Cédric; Thibault, Pierre

2017-07-11

We show experimental evidence of the acoustically-assisted micromanipulation of small objects like solid particles or blood cells, combining rotation and translation, using high frequency surface acoustic waves. This was obtained from the leakage in a microfluidic channel of two standing waves arranged perpendicularly in a LiNbO 3 piezoelectric substrate working at 36.3 MHz. By controlling the phase lag between the emitters, we could, in addition to translation, generate a swirling motion of the emitting surface which, in turn, led to the rapid rotation of spherical polystyrene Janus beads suspended in the channel and of human red and white blood cells up to several rounds per second. We show that these revolution velocities are compatible with a torque caused by the acoustic streaming that develops at the particles surface, like that first described by [F. Busse et al., J. Acoust. Soc. Am., 1981, 69(6), 1634-1638]. This device, based on standard interdigitated transducers (IDTs) adjusted to emit at equal frequencies, opens a way to a large range of applications since it allows the simultaneous control of the translation and rotation of hard objects, as well as the investigation of the response of cells to shear stress.

Modulated acoustic radiation pressure and stress-coupling projections

NASA Astrophysics Data System (ADS)

Marston, Philip L.; Thiessen, David B.

2005-09-01

Low-frequency deformation can be induced at a single frequency using radiation stress oscillations of double-sideband suppressed-carrier ultrasound [P. L. Marston and R. E. Apfel, J. Acoust. Soc. Am. 67, 27 (1980)]. The transducer voltage is proportional to a product of low- and high-frequency sine waves. To anticipate the shape and magnitude of induced deformations, it is helpful to expand the distribution of the radiation stress on the object to be deformed as a series of projections [P. L. Marston, J. Acoust. Soc. Am. 67, 15 (1980)]. Stress projections are also useful for unmodulated waves: the radiation force is an example. In addition to spherical and nearly spherical objects, recent experiments and calculations have concerned cylindrical objects [S. F. Morse, D. B. Thiessen, and P. L. Marston, Phys. Fluids 8, 3 (1996); W. Wei, D. B. Thiessen, and P. L. Marston, J. Acoust. Soc. Am. 116, 202 (2004)]. In standing waves the following projections are nonvanishing in the low acoustic frequency limit for appropriately situated dense objects: radial projection [M. J. Marr-Lyon, D. B. Thiessen, and P. L. Marston, Phys. Rev. Lett. 86, 2293 (2001)] and quadrupole projection [P. L. Marston et al., J. Acoust. Soc. Am. 69, 1499 (1981)].

The effect of rock fabric on P-wave velocity distribution in amphibolites

NASA Astrophysics Data System (ADS)

Vajdová, V.; Přikryl, R.; Pros, Z.; Klíma, K.

1999-07-01

This study presents contribution to the laboratory investigation of elastic properties and rock fabric of amphibolites. P-wave velocity was determined on four spherical samples prepared from a shallow borehole core. The measurement was conducted in 132 directions under various conditions of hydrostatic pressure (up to 400 MPa). The rock fabric was investigated by image analysis of thin sections that enabled precise determination of grain size, modal composition and shape parameters of rock-forming minerals. Laboratory measurement of P-waves revealed pseudoorthorhombic symmetry of rock fabric in amphibolites studied. This symmetry reflects rocks' macro- and microfabric. Maximum P-wave velocity corresponds to the macroscopically visible stretching lineation. Minimum P-wave velocity is oriented perpendicular to the foliation plane. The average grain size is the main microstructural factor controlling mean P-wave velocity.

An HLLC Riemann solver for resistive relativistic magnetohydrodynamics

NASA Astrophysics Data System (ADS)

Miranda-Aranguren, S.; Aloy, M. A.; Rembiasz, T.

2018-05-01

We present a new approximate Riemann solver for the augmented system of equations of resistive relativistic magnetohydrodynamics that belongs to the family of Harten-Lax-van Leer contact wave (HLLC) solvers. In HLLC solvers, the solution is approximated by two constant states flanked by two shocks separated by a contact wave. The accuracy of the new approximate solver is calibrated through 1D and 2D test problems.

Stability of stagnation via an expanding accretion shock wave

NASA Astrophysics Data System (ADS)

Velikovich, A. L.; Murakami, M.; Taylor, B. D.; Giuliani, J. L.; Zalesak, S. T.; Iwamoto, Y.

2016-05-01

Stagnation of a cold plasma streaming to the center or axis of symmetry via an expanding accretion shock wave is ubiquitous in inertial confinement fusion (ICF) and high-energy-density plasma physics, the examples ranging from plasma flows in x-ray-generating Z pinches [Maron et al., Phys. Rev. Lett. 111, 035001 (2013)] to the experiments in support of the recently suggested concept of impact ignition in ICF [Azechi et al., Phys. Rev. Lett. 102, 235002 (2009); Murakami et al., Nucl. Fusion 54, 054007 (2014)]. Some experimental evidence indicates that stagnation via an expanding shock wave is stable, but its stability has never been studied theoretically. We present such analysis for the stagnation that does not involve a rarefaction wave behind the expanding shock front and is described by the classic ideal-gas Noh solution in spherical and cylindrical geometry. In either case, the stagnated flow has been demonstrated to be stable, initial perturbations exhibiting a power-law, oscillatory or monotonic, decay with time for all the eigenmodes. This conclusion has been supported by our simulations done both on a Cartesian grid and on a curvilinear grid in spherical coordinates. Dispersion equation determining the eigenvalues of the problem and explicit formulas for the eigenfunction profiles corresponding to these eigenvalues are presented, making it possible to use the theory for hydrocode verification in two and three dimensions.

Stability of stagnation via an expanding accretion shock wave

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

Velikovich, A. L.; Giuliani, J. L.; Murakami, M.

Stagnation of a cold plasma streaming to the center or axis of symmetry via an expanding accretion shock wave is ubiquitous in inertial confinement fusion (ICF) and high-energy-density plasma physics, the examples ranging from plasma flows in x-ray-generating Z pinches [Maron et al., Phys. Rev. Lett. 111, 035001 (2013)] to the experiments in support of the recently suggested concept of impact ignition in ICF [Azechi et al., Phys. Rev. Lett. 102, 235002 (2009); Murakami et al., Nucl. Fusion 54, 054007 (2014)]. Some experimental evidence indicates that stagnation via an expanding shock wave is stable, but its stability has never beenmore » studied theoretically. We present such analysis for the stagnation that does not involve a rarefaction wave behind the expanding shock front and is described by the classic ideal-gas Noh solution in spherical and cylindrical geometry. In either case, the stagnated flow has been demonstrated to be stable, initial perturbations exhibiting a power-law, oscillatory or monotonic, decay with time for all the eigenmodes. This conclusion has been supported by our simulations done both on a Cartesian grid and on a curvilinear grid in spherical coordinates. Dispersion equation determining the eigenvalues of the problem and explicit formulas for the eigenfunction profiles corresponding to these eigenvalues are presented, making it possible to use the theory for hydrocode verification in two and three dimensions.« less

Effects of Earth's curvature in full-wave modeling of VLF propagation

NASA Astrophysics Data System (ADS)

Qiu, L.; Lehtinen, N. G.; Inan, U. S.; Stanford VLF Group

2011-12-01

We show how to include curvature in the full-wave finite element approach to calculate ELF/VLF wave propagation in horizontally stratified earth-ionosphere waveguide. A general curvilinear stratified system is considered, and the numerical solutions of full-wave method in curvilinear system are compared with the analytic solutions in the cylindrical and spherical waveguides filled with an isotropic medium. We calculate the attenuation and height gain for modes in the Earth-ionosphere waveguide, taking into account the anisotropicity of ionospheric plasma, for different assumptions about the Earth's curvature, and quantify the corrections due to the curvature. The results are compared with the results of previous models, such as LWPC, as well as with ground and satellite observations, and show improved accuracy compared with full-wave method without including the curvature effect.

Rayleigh-Taylor instability at spherical interfaces between viscous fluids: Fluid/vacuum interface

DOE PAGES

Terrones, Guillermo; Carrara, Mark D.

2015-05-01

For a spherical interface of radius R separating two different homogeneous regions of incompressible viscous fluids under the action of a radially directed acceleration, we perform a linear stability analysis in terms of spherical surface harmonics Y n to derive the dispersion relation. The instability behavior is investigated by computing the growth rates and the most-unstable modes as a function of the spherical harmonic degree n. This general methodology is applicable to the entire parameter space spanned by the Atwood number, the viscosity ratio, and the dimensionless number B = (α RΡ² 2/μ² ²)¹ /³ R (where α R, Ρmore » 2 and μ 2 are the local radial acceleration at the interface, and the density and viscosity of the denser overlying fluid, respectively). While the mathematical formulation here is general, this paper focuses on instability that arises at a spherical viscous fluid/vacuum interface as there is a great deal to be learned from the effects of one-fluid viscosity and sphericity alone. To quantify and understand the effect that curvature and radial accelerationhave on the Rayleigh-Taylor instability, a comparison of the growth rates, under homologous driving conditions, between the planar and spherical interfaces is performed. The derived dispersion relation for the planar interface accounts for an underlying finite fluid region of thickness L and normal acceleration α R. Under certain conditions, the development of the most-unstable modes at a spherical interface can take place via the superposition of two adjacent spherical harmonics Y n and Y n+1. This bimodality in the evolution of disturbances in the linear regime does not have a counterpart in the planar configuration where the most-unstable modes are associated with a unique wave number.« less

Analytical method for analysis of electromagnetic scattering from inhomogeneous spherical structures using duality principles

NASA Astrophysics Data System (ADS)

Kiani, M.; Abdolali, A.; Safari, M.

2018-03-01

In this article, an analytical approach is presented for the analysis of electromagnetic (EM) scattering from radially inhomogeneous spherical structures (RISSs) based on the duality principle. According to the spherical symmetry, similar angular dependencies in all the regions are considered using spherical harmonics. To extract the radial dependency, the system of differential equations of wave propagation toward the inhomogeneity direction is equated with the dual planar ones. A general duality between electromagnetic fields and parameters and scattering parameters of the two structures is introduced. The validity of the proposed approach is verified through a comprehensive example. The presented approach substitutes a complicated problem in spherical coordinate to an easy, well posed, and previously solved problem in planar geometry. This approach is valid for all continuously varying inhomogeneity profiles. One of the major advantages of the proposed method is the capability of studying two general and applicable types of RISSs. As an interesting application, a class of lens antenna based on the physical concept of the gradient refractive index material is introduced. The approach is used to analyze the EM scattering from the structure and validate strong performance of the lens.

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.

Momentum and energy transport by waves in the solar atmosphere and solar wind

NASA Technical Reports Server (NTRS)

Jacques, S. A.

1977-01-01

The fluid equations for the solar wind are presented in a form which includes the momentum and energy flux of waves in a general and consistent way. The concept of conservation of wave action is introduced and is used to derive expressions for the wave energy density as a function of heliocentric distance. The explicit form of the terms due to waves in both the momentum and energy equations are given for radially propagating acoustic, Alfven, and fast mode waves. The effect of waves as a source of momentum is explored by examining the critical points of the momentum equation for isothermal spherically symmetric flow. We find that the principal effect of waves on the solutions is to bring the critical point closer to the sun's surface and to increase the Mach number at the critical point. When a simple model of dissipation is included for acoustic waves, in some cases there are multiple critical points.

Instantaneous axial force of a high-order Bessel vortex beam of acoustic waves incident upon a rigid movable sphere.

PubMed

Mitri, F G; Fellah, Z E A

2011-08-01

The present investigation examines the instantaneous force resulting from the interaction of an acoustical high-order Bessel vortex beam (HOBVB) with a rigid sphere. The rigid sphere case is important in fluid dynamics applications because it perfectly simulates the interaction of instantaneous sound waves in a reduced gravity environment with a levitated spherical liquid soft drop in air. Here, a closed-form solution for the instantaneous force involving the total pressure field as well as the Bessel beam parameters is obtained for the case of progressive, stationary and quasi-stationary waves. Instantaneous force examples for progressive waves are computed for both a fixed and a movable rigid sphere. The results show how the instantaneous force per unit cross-sectional surface and unit pressure varies versus the dimensionless frequency ka (k is the wave number in the fluid medium and a is the sphere's radius), the half-cone angle β and the order m of the HOBVB. It is demonstrated here that the instantaneous force is determined only for (m,n) = (0,1) (where n is the partial-wave number), and vanishes for m>0 because of symmetry. In addition, the instantaneous force and normalized amplitude velocity results are computed and compared with those of a rigid immovable (fixed) sphere. It is shown that they differ significantly for ka values below 5. The proposed analysis may be of interest in the analysis of instantaneous forces on spherical particles for particle manipulation, filtering, trapping and drug delivery. The presented solutions may also serve as a method for comparison to other solutions obtained by strictly numerical or asymptotic approaches. Copyright © 2011 Elsevier B.V. All rights reserved.

Shear Wave Generation by Explosions in Anisotropic Crystalline Rock

NASA Astrophysics Data System (ADS)

Rogers-Martinez, M. A.; Sammis, C. G.; Stroujkova, A. F.

2015-12-01

The use of seismic waves to discriminate between earthquakes and underground explosions is complicated by the observation that explosions routinely radiate strong S waves. Whether these S waves are primarily generated by non-linear processes at the source, or by mode conversions and scattering along the path remains an open question. It has been demonstrated that S waves are generated at the source by any mechanism that breaks the spherical symmetry of the explosion. Examples of such mechanisms include tectonic shear stress, spall, and anisotropy in the emplacement medium. Many crystalline rock massifs are transversely isotropic because they contain aligned fractures over a range of scales from microfractures at the grain scale (called the rift) to regional sets of joints. In this study we use a micromechanical damage mechanics to model the fracture damage patterns and seismic radiation generated by explosions in a material in which the initial distribution of fractures has a preferred direction. Our simulations are compared with a set of field experiments in a granite quarry in Barre, VT conducted by New England Research and Weston Geophysical. Barre granite has a strong rift plane of aligned microfractures. Our model captures two important results of these field studies: 1) the spatial extent of rock fracture and generation of S waves depends on the burn-rate of the explosion and 2) the resultant damage is anisotropic with most damage occurring in the preferred direction of the microfractures (the rift plane in the granite). The physical reason damage is enhanced in the rift direction is that the mode I stress intensity factor is large for each fracture in the array of parallel fractures in the rift plane. Tensile opening on the rift plane plus sliding on the preexisting fractures make strong non-spherical contributions to the moment tensor in the far-field.

Thrust Augmentation Measurements for a Pulse Detonation Engine Driven Ejector

NASA Technical Reports Server (NTRS)

Pal, S.; Santoro, Robert J.; Shehadeh, R.; Saretto, S.; Lee, S.-Y.

2005-01-01

Thrust augmentation results of an ongoing study of pulse detonation engine driven ejectors are presented and discussed. The experiments were conducted using a pulse detonation engine (PDE) setup with various ejector configurations. The PDE used in these experiments utilizes ethylene (C2H4) as the fuel, and an equi-molar mixture of oxygen and nitrogen as the oxidizer at an equivalence ratio of one. High fidelity thrust measurements were made using an integrated spring damper system. The baseline thrust of the PDE engine was first measured and agrees with experimental and modeling results found in the literature. Thrust augmentation measurements were then made for constant diameter ejectors. The parameter space for the study included ejector length, PDE tube exit to ejector tube inlet overlap distance, and straight versus rounded ejector inlets. The relationship between the thrust augmentation results and various physical phenomena is described. To further understand the flow dynamics, shadow graph images of the exiting shock wave front from the PDE were also made. For the studied parameter space, the results showed a maximum augmentation of 40%. Further increase in augmentation is possible if the geometry of the ejector is tailored, a topic currently studied by numerous groups in the field.

Identification and onset of inertial modes in the wide-gap spherical Couette system

NASA Astrophysics Data System (ADS)

Barik, A.; Wicht, J.; Triana, S. A.; Hoff, M.

2016-12-01

The spherical Couette system consists of two concentric rotating spheres with a fluid filling the shell in between. The system has been studied for a long time by fluid dynamicists and is ideal for studying flow instabilities due to differential rotation and the interaction of the same with magnetic fields - important for understanding dynamics of planetary and stellar interiors. The system is also a basis for a new generation of dynamo experiments because of its closer geometrical resemblance to real astrophysical objects as compared to past experiments. We simulate this system using the two different pseudo-spectral codes MagIC and XSHELLS. We focus here on a very interesting and general instability in this system - inertial modes. A rotating body of fluid is known to sustain oscillatory waves due to the restoring action of the Coriolis force. In a bounded container, these form a discrete spectrum called inertial modes. These modes have been analytically known for a rotating full sphere for over a century now. In a spherical shell, they cannot be formulated analytically. However, many of these inertial modes are observed in spherical Couette experiments as well as in simulations. Past studies have tried to explain the onset of these modes invoking wave over-reflection or critical layer instabilities on the cylinder tangent to the inner sphere. In this study, we present the inertial modes found in our simulations and try to explain their onset as secondary instabilities due to the destabilization of the fundamental non-axisymmetric instability, forming a triadic resonance with the fundamental instability. We run various simulations varying the rotation rate of the inner sphere, while keeping the rotation rate of the outer sphere constant. We track velocities and induced magnetic field and produce spectrograms similar to those of the experiments. Our results match very well the experimental data from spherical Couette set-ups at BTU Cottbus and the University of Maryland.

Spherical grating based x-ray Talbot interferometry.

PubMed

Cong, Wenxiang; Xi, Yan; Wang, Ge

2015-11-01

Grating interferometry is a state-of-the-art x-ray imaging approach, which can acquire information on x-ray attenuation, phase shift, and small-angle scattering simultaneously. Phase-contrast imaging and dark-field imaging are very sensitive to microstructural variation and offers superior contrast resolution for biological soft tissues. However, a common x-ray tube is a point-like source. As a result, the popular planar grating imaging configuration seriously restricts the flux of photons and decreases the visibility of signals, yielding a limited field of view. The purpose of this study is to extend the planar x-ray grating imaging theory and methods to a spherical grating scheme for a wider range of preclinical and clinical applications. A spherical grating matches the wave front of a point x-ray source very well, allowing the perpendicular incidence of x-rays on the grating to achieve a higher visibility over a larger field of view than the planer grating counterpart. A theoretical analysis of the Talbot effect for spherical grating imaging is proposed to establish a basic foundation for x-ray spherical gratings interferometry. An efficient method of spherical grating imaging is also presented to extract attenuation, differential phase, and dark-field images in the x-ray spherical grating interferometer. Talbot self-imaging with spherical gratings is analyzed based on the Rayleigh-Sommerfeld diffraction formula, featuring a periodic angular distribution in a polar coordinate system. The Talbot distance is derived to reveal the Talbot self-imaging pattern. Numerical simulation results show the self-imaging phenomenon of a spherical grating interferometer, which is in agreement with the theoretical prediction. X-ray Talbot interferometry with spherical gratings has a significant practical promise. Relative to planar grating imaging, spherical grating based x-ray Talbot interferometry has a larger field of view and improves both signal visibility and dose utilization for pre-clinical and clinical applications.

Spherical grating based x-ray Talbot interferometry

PubMed Central

Cong, Wenxiang; Xi, Yan; Wang, Ge

2015-01-01

Purpose: Grating interferometry is a state-of-the-art x-ray imaging approach, which can acquire information on x-ray attenuation, phase shift, and small-angle scattering simultaneously. Phase-contrast imaging and dark-field imaging are very sensitive to microstructural variation and offers superior contrast resolution for biological soft tissues. However, a common x-ray tube is a point-like source. As a result, the popular planar grating imaging configuration seriously restricts the flux of photons and decreases the visibility of signals, yielding a limited field of view. The purpose of this study is to extend the planar x-ray grating imaging theory and methods to a spherical grating scheme for a wider range of preclinical and clinical applications. Methods: A spherical grating matches the wave front of a point x-ray source very well, allowing the perpendicular incidence of x-rays on the grating to achieve a higher visibility over a larger field of view than the planer grating counterpart. A theoretical analysis of the Talbot effect for spherical grating imaging is proposed to establish a basic foundation for x-ray spherical gratings interferometry. An efficient method of spherical grating imaging is also presented to extract attenuation, differential phase, and dark-field images in the x-ray spherical grating interferometer. Results: Talbot self-imaging with spherical gratings is analyzed based on the Rayleigh–Sommerfeld diffraction formula, featuring a periodic angular distribution in a polar coordinate system. The Talbot distance is derived to reveal the Talbot self-imaging pattern. Numerical simulation results show the self-imaging phenomenon of a spherical grating interferometer, which is in agreement with the theoretical prediction. Conclusions: X-ray Talbot interferometry with spherical gratings has a significant practical promise. Relative to planar grating imaging, spherical grating based x-ray Talbot interferometry has a larger field of view and improves both signal visibility and dose utilization for pre-clinical and clinical applications. PMID:26520741

Spherical grating based x-ray Talbot interferometry

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

Cong, Wenxiang, E-mail: congw@rpi.edu, E-mail: xiy2@rpi.edu, E-mail: wangg6@rpi.edu; Xi, Yan, E-mail: congw@rpi.edu, E-mail: xiy2@rpi.edu, E-mail: wangg6@rpi.edu; Wang, Ge, E-mail: congw@rpi.edu, E-mail: xiy2@rpi.edu, E-mail: wangg6@rpi.edu

2015-11-15

Purpose: Grating interferometry is a state-of-the-art x-ray imaging approach, which can acquire information on x-ray attenuation, phase shift, and small-angle scattering simultaneously. Phase-contrast imaging and dark-field imaging are very sensitive to microstructural variation and offers superior contrast resolution for biological soft tissues. However, a common x-ray tube is a point-like source. As a result, the popular planar grating imaging configuration seriously restricts the flux of photons and decreases the visibility of signals, yielding a limited field of view. The purpose of this study is to extend the planar x-ray grating imaging theory and methods to a spherical grating scheme formore » a wider range of preclinical and clinical applications. Methods: A spherical grating matches the wave front of a point x-ray source very well, allowing the perpendicular incidence of x-rays on the grating to achieve a higher visibility over a larger field of view than the planer grating counterpart. A theoretical analysis of the Talbot effect for spherical grating imaging is proposed to establish a basic foundation for x-ray spherical gratings interferometry. An efficient method of spherical grating imaging is also presented to extract attenuation, differential phase, and dark-field images in the x-ray spherical grating interferometer. Results: Talbot self-imaging with spherical gratings is analyzed based on the Rayleigh–Sommerfeld diffraction formula, featuring a periodic angular distribution in a polar coordinate system. The Talbot distance is derived to reveal the Talbot self-imaging pattern. Numerical simulation results show the self-imaging phenomenon of a spherical grating interferometer, which is in agreement with the theoretical prediction. Conclusions: X-ray Talbot interferometry with spherical gratings has a significant practical promise. Relative to planar grating imaging, spherical grating based x-ray Talbot interferometry has a larger field of view and improves both signal visibility and dose utilization for pre-clinical and clinical applications.« less

Relationships between 24-h blood pressure variability and 24-h central arterial pressure, pulse wave velocity and augmentation index in hypertensive patients.

PubMed

Omboni, Stefano; Posokhov, Igor N; Rogoza, Anatoly N

2017-04-01

Twenty-four-h blood pressure variability (BPV) predicts cardiovascular complications in hypertension, but its association with pulse wave indices (central arterial pressure, pulse wave velocity (PWV) and augmentation index (AIx)) is poorly understood. In the present study, we assessed the degree of the effect of 24-h BPV on 24-h pulse wave indices. Brachial blood pressure was measured non-invasively over the 24 h with an electronic, oscillometric, automated device (BPLab) in 661 uncomplicated treated or untreated hypertensive patients. Digitalized oscillometric waveforms were analyzed with a validated algorithm to obtain pulse wave indices. Twenty-four-h BPV was calculated as the unweighted (SDu) or weighted s.d. (SDw) of the mean blood pressure or as the average real variability (ARV). Twenty-four-h systolic BPV showed a direct and significant relationship with the central arterial systolic pressure (r=0.28 SDu, r=0.40 SDw, r=0.34 ARV), PWV (r=0.10 SDu, r=0.21 SDw, r=0.19 ARV) and AIx (r=0.17 SDu, r=0.27 SDw, r=0.23 ARV). After adjustment for age, sex, body mass index, antihypertensive treatment and 24-h systolic blood pressure, the relationship lost some power but was still significant for all measures, except for the AIx. Pulse wave indices were higher in patients with high BPV than in those with low BPV: after adjustment, these differences were abolished for the AIx. The diastolic BPV showed a weak association with the pulse wave indices. In conclusion, in hypertensive patients, 24-h systolic BPV is moderately and independently associated with 24-h central arterial pressure and stiffness.

Changes in Central Aortic Pressure Levels, Wave Components and Determinants Associated with High Peripheral Blood Pressure States in Childhood: Analysis of Hypertensive Phenotype.

PubMed

García-Espinosa, Victoria; Curcio, Santiago; Marotta, Marco; Castro, Juan M; Arana, Maite; Peluso, Gonzalo; Chiesa, Pedro; Giachetto, Gustavo; Bia, Daniel; Zócalo, Yanina

2016-10-01

The aims were to determine whether children's high peripheral blood pressure states (HBP) are associated with increased central aortic blood pressure (BP) and to characterize hemodynamic and vascular changes associated with HBP in terms of changes in cardiac output (stroke volume, SV), arterial stiffness (aortic pulse wave velocity, PWV), peripheral vascular resistances (PVR) and net and relative contributions of reflected waves to the aortic pulse amplitude. We included 154 subjects (mean age 11; range 4-16 years) assigned to one of two groups: normal peripheral BP (NBP, n = 101), defined as systolic and diastolic BP < 90th percentile, or high BP (HBP, n = 53), defined as average systolic and/or diastolic BP levels ≥90th percentile (curves for sex, age and body height). The HBP group included children with hypertensive and pre-hypertensive BP levels. After a first analysis, groups were compared excluding obese and dyslipidemic children. Peripheral and central aortic BP, PWV and pulse wave-derived parameters (augmentation index, forward and backward wave components' amplitude) were measured using gold-standard techniques, applanation tonometry (SphygmoCor) and oscillometry (Mobil-O-Graph). Independent of the presence of dyslipidemia and/or obesity, aortic systolic and pulse BP were higher in HBP than in NBP children. The increase in central BP could not be explained by an increase in the relative contribution of reflections to the aortic pressure wave, higher PVR or by an augmented peripheral reflection coefficient. Instead, the rise in central BP would be explained by an increase in the amplitude of both incident and reflected wave components.

Noninvasive Shock Wave Treatment for Capsular Contractures After Breast Augmentation: A Rabbit Study.

PubMed

Chen, Po Chou; Kuo, Shyh Ming; Jao, Jo Chi; Yang, Shiou Wen; Hsu, Ching Wen; Wu, Yu Chiuan

2016-06-01

Capsular contracture is the most common complication of breast augmentation. Although numerous procedures are intended to prevent capsular contracture, their efficacy does not satisfy surgeons or patients. In the present study, we used shock waves to develop innovative protocols to treat capsular contracture in rabbits. We used shock waves to treat capsular contracture in a rabbit model. Six clinical parameters were evaluated to determine the treatment efficacy of shock waves on the pathological histology of capsular contracture. Dual-flip-angle T1-mapping magnetic resonance imaging was used to confirm the pathological findings. Among the parameters, myxoid change, vascular proliferation, and lymphoplasma cell infiltration around the capsule increased more after treatment than they did in a control group. Capsular thickness, inner thinner collagen layer, and capsule wall collagen deposition decreased after shock wave treatment; only the inner thinner collagen layer and capsule wall collagen deposition changed significantly. The MRI findings for both scar thickness and water content were consistent with pathological biology findings. This was the first pilot study and trial to treat capsular contractures using shock waves. We found that shock waves can cause changes in the structure or the composition of capsular contracture. We conclude that the treatment could decrease water content, loosen structure, decrease collagen deposition, and might alleviate scar formation from capsular contracture. We believe that the treatment could be a viable remedy for capsular contractures. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Thermal invisibility based on scattering cancellation and mantle cloaking

PubMed Central

Farhat, M.; Chen, P.-Y.; Bagci, H.; Amra, C.; Guenneau, S.; Alù, A.

2015-01-01

We theoretically and numerically analyze thermal invisibility based on the concept of scattering cancellation and mantle cloaking. We show that a small object can be made completely invisible to heat diffusion waves, by tailoring the heat conductivity of the spherical shell enclosing the object. This means that the thermal scattering from the object is suppressed, and the heat flow outside the object and the cloak made of these spherical shells behaves as if the object is not present. Thermal invisibility may open new vistas in hiding hot spots in infrared thermography, military furtivity, and electronics heating reduction. PMID:25928664

Merging black holes in non-spherical nuclear star clusters

NASA Astrophysics Data System (ADS)

Petrovich, Cristobal

2018-04-01

The Milky Way and a significant fraction of galaxies are observed to host a central Massive Black Hole (MBH) embedded in a non-spherical nuclear star cluster. I will discuss the orbital evolution of stellar binaries in these environments and argue that their merger rates are expected to be greatly enhanced when the effect from cluster potential is taken into account in the binary-MBH triple system. I will apply our results to compact-object binary mergers mediated by gravitational wave radiation and show that this merger channel can contribute significantly to the LIGO/Virgo detections.

A Study of the Nearfield of an Excited Spherical Shell.

DTIC Science & Technology

1980-03-17

8217 tte exact wave harmonic series and the approximate Geometrical Theory of Diffraction (GTD) were used to predict the acoustic near field of an elastic...rr) )1/3 n 4 n14 XV e i+ (424 (ka) (2h (ka) nn an1 % Tte SkaI/ rA’ (k)2 nn in Ap ndi B]. =Q (ikc)~ (4.25)h(1 (a n Tn whee i adeayftore fo acosi prpaa3o...Approach to Scattering from Elastic Spherical Shells," NUC TP425, September 1974, Naval Undersea Center, San Diego, California. 36. Pathak, P. H. and

Type 2 diabetes is associated with increased pulse wave velocity measured at different sites of the arterial system but not augmentation index in a Chinese population.

PubMed

Zhang, Minghua; Bai, Yongyi; Ye, Ping; Luo, Leiming; Xiao, Wenkai; Wu, Hongmei; Liu, Dejun

2011-10-01

Patients with type 2 diabetes have increased stiffness of central elastic arteries. However, whether peripheral muscular artery stiffness is equally affected by the disease remains sparsely examined. Moreover, the association between pulse wave velocity (PWV) and augmentation index (AIx) in diabetes is poorly understood. Type 2 diabetes is associated with the alterations in arterial stiffness (PWV and AIx) in a community-based population. A total of 79 Chinese patients with type 2 diabetes and 79 sex-, age- (±3 years), and body mass index- (±2 kg/m(2) ) matched healthy controls were studied. Carotid-femoral pulse wave velocity (CF-PWV), carotid-radial pulse wave velocity (CR-PWV), and carotid-ankle pulse wave velocity (CA-PWV) were calculated from tonometry waveforms and body surface measurements, whereas AIx was assessed using pulse wave analyses. In univariate analysis, patients with type 2 diabetes showed increased CF-PWV (P < 0.001), CR-PWV (P = 0.012), and CA-PWV (P = 0.016), and lower AIx (P = 0.017) than the control group. In multiple linear regression models adjusting for covariates, type 2 diabetes remained a significant determinant of CF-PWV. Fasting glucose was associated with CR-PWV but was not related to CA-PWV or AIx. Our findings suggest that patients with type 2 diabetes have increased central and peripheral artery stiffness, but preserved AIx compared to controls. Diabetes was a predictor of central artery stiffness, and glucose was a determinant of peripheral artery stiffness. © 2011 Wiley Periodicals, Inc.

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.

Adaptation of the projector-augmented-wave formalism to the treatment of orbital-dependent exchange-correlation functionals

NASA Astrophysics Data System (ADS)

Xu, Xiao; Holzwarth, N. A. W.

2011-10-01

This paper presents the formulation and numerical implementation of a self-consistent treatment of orbital-dependent exchange-correlation functionals within the projector-augmented-wave method of Blöchl [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.50.17953 50, 17953 (1994)] for electronic structure calculations. The methodology is illustrated with binding energy curves for C in the diamond structure and LiF in the rock salt structure, by comparing results from the Hartree-Fock (HF) formalism and the optimized effective potential formalism in the so-called KLI approximation [Krieger, Li, and Iafrate, Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.45.101 45, 101 (1992)] with those of the local density approximation. While the work here uses pure Fock exchange only, the formalism can be extended to treat orbital-dependent functionals more generally.

Cd in SnO: Probing structural effects on the electronic structure of doped oxide semiconductors through the electric field gradient at the Cd nucleus

NASA Astrophysics Data System (ADS)

Errico, Leonardo A.; Rentería, Mario; Petrilli, Helena M.

2007-04-01

We perform an ab initio study of the electric field gradient (EFG) at the nucleus of Cd impurities at substitutional Sn sites in crystalline SnO. The full-potential linearized-augmented plane wave and the projector augmented wave methods used here allow us to treat the electronic structure of the doped system and the atomic relaxations introduced by the impurities in the host in a fully self-consistent way using a supercell approach in a state-of-the-art way. Effects of the impurity charge state on the electronic and structural properties are also discussed. Since the EFG is a very subtle quantity, its determination is very useful to probe ground-state properties such as the charge density. We show that the EFG is very sensitive to structural relaxations induced by the impurity. Our theoretical predictions are compared with available experimental results.

Crystal structures of tiotropium bromide and its monohydrate in view of combined solid-state nuclear magnetic resonance and gauge-including projector-augmented wave studies.

PubMed

Pindelska, Edyta; Szeleszczuk, Lukasz; Pisklak, Dariusz Maciej; Majka, Zbigniew; Kolodziejski, Waclaw

2015-07-01

Tiotropium bromide is an anticholinergic bronchodilator used in the management of chronic obstructive pulmonary disease. The crystal structures of this compound and its monohydrate have been previously solved and published. However, in this paper, we showed that those structures contain some major errors. Our methodology based on combination of the solid-state nuclear magnetic resonance (NMR) spectroscopy and quantum mechanical gauge-including projector-augmented wave (GIPAW) calculations of NMR shielding constants enabled us to correct those errors and obtain reliable structures of the studied compounds. It has been proved that such approach can be used not only to perform the structural analysis of a drug substance and to identify its polymorphs, but also to verify and optimize already existing crystal structures. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

Computational investigations of the band structure, and thermodynamic and optical features of thorium-based oxide ThGeO4 using the full-potential linearized augmented plane-wave plus local orbital approach

NASA Astrophysics Data System (ADS)

Chiker, F.; Khachai, H.; Mathieu, C.; Bin-Omran, S.; Kada, Belkacem; Sun, Xiao-Wei; Sandeep; Rai, D. P.; Khenata, R.

2018-05-01

In this study, first-principles investigations were performed using the full-potential linearized augmented plane-wave method of the structural and optoelectronic properties of thorium germinate (ThGeO4), a high-K dielectric material. Under ambient conditions, the structural properties calculated for ThGeO4 in the zircon phase were in excellent agreement with the available experimental data. Furthermore, using the modified Becke -Johnson correction method, the calculated band gaps and optical constants accurately described this compound. Finally, the thermal properties were predicted over a temperature range of 0-700 K and pressures up to 11 GPa using the quasi-harmonic Debye model, where the variations in the heat capacity, primitive cell volume, and thermal expansion coefficients were determined successfully.

Shallow Water Quasi-Geostrophic Theory on the Sphere

NASA Astrophysics Data System (ADS)

Schubert, Wayne H.; Taft, Richard K.; Silvers, Levi G.

2009-02-01

Quasi-geostrophic theory forms the basis for much of our understanding of mid-latitude atmospheric dynamics. The theory is typically presented in either its f-plane form or its β-plane form. However, for many applications, including diagnostic use in global climate modeling, a fully spherical version would be most useful. Such a global theory does in fact exist and has for many years, but few in the scientific community seem to have ever been aware of it. In the context of shallow water dynamics, it is shown that the spherical version of quasigeostrophic theory is easily derived (re-derived) based on a partitioning of the flow between nondivergent and irrotational components, as opposed to a partitioning between geostrophic and ageostrophic components. In this way, the invertibility principle is expressed as a relation between the streamfunction and the potential vorticity, rather than between the geopotential and the potential vorticity. This global theory is then extended by showing that the invertibility principle can be solved analytically using spheroidal harmonic transforms, an advancement that greatly improves the usefulness of this "forgotten" theory. When the governing equation for the time evolution of the potential vorticity is linearized about a state of rest, a simple Rossby-Haurwitz wave dispersion relation is derived and examined. These waves have a horizontal structure described by spheroidal harmonics, and the Rossby-Haurwitz wave frequencies are given in terms of the eigenvalues of the spheroidal harmonic operator. Except for sectoral harmonics with low zonal wavenumber, the quasi-geostrophic Rossby-Haurwitz frequencies agree very well with those calculated from the primitive equations. One of the many possible applications of spherical quasi-geostrophic theory is to the study of quasi-geostrophic turbulence on the sphere. In this context, the theory is used to derive an anisotropic Rhines barrier in three-dimensional wavenumber space.

A generic set of HF antennas for use with spherical model expansions

NASA Astrophysics Data System (ADS)

Katal, Nedim

1990-03-01

An antenna engineering handbook and database program has been constructed by engineers at the Lawrence Livermore National Laboratory (LLNL) using the Numerical Electromagnetics Code (NEC) antenna modeling program to prepare data performance on tactical field communication antennas used by the Army. It is desirable to have this information installed on a personnel computer (PC), using relational database techniques to select antennas based on performance criteria. This thesis obtains and analyses current distributions and radiation pattern data by using NEC for the following set of four (4) high frequency (HF) tactical generic antennas to be used in future spherical mode expansion work: a quarter wavelength basic whip, a one-wavelength horizontal quad Loop, a 564-foot longwire, and a sloping vee beam dipole. The results of this study show that the basic whip antenna provides good groundwave communication, but it has poor near vertical incident skywave (NVIS) performance. The current distribution has the characteristics of standing waves. The horizontal quad loop antenna is good for night vision imaging systems (NVIS) and medium range skywave communications. The current distribution is sinusoidal and continuous around the loop. The long wire antenna allows short, medium and long range communications and a standing wave current distribution occurs along the antenna axis due to non-termination. The sloping vee beam antenna favors long range communication and the current distribution is mainly that of travelling sinusoidal waves. Because of their well-known efficiency, the basic whip and quad loop can be used as reference standards for the spherical mode expansion work. The longwire and sloping vee beam antenna are unwieldy, but they are effective as base station antennas.

Decoherence and Determinism in a One-Dimensional Cloud-Chamber Model

NASA Astrophysics Data System (ADS)

Sparenberg, Jean-Marc; Gaspard, David

2018-03-01

The hypothesis (Sparenberg et al. in EPJ Web Conf 58:01016, [1]. https://doi.org/10.1051/epjconf/20135801016) that the particular linear tracks appearing in the measurement of a spherically-emitting radioactive source in a cloud chamber are determined by the (random) positions of atoms or molecules inside the chamber is further explored in the framework of a recently established one-dimensional model (Carlone et al. Comm Comput Phys 18:247, [2]. https://doi.org/10.4208/cicp.270814.311214a). In this model, meshes of localized spins 1/2 play the role of the cloud-chamber atoms and the spherical wave is replaced by a linear superposition of two wave packets moving from the origin to the left and to the right, evolving deterministically according to the Schrödinger equation. We first revisit these results using a time-dependent approach, where the wave packets impinge on a symmetric two-sided detector. We discuss the evolution of the wave function in the configuration space and stress the interest of a non-symmetric detector in a quantum-measurement perspective. Next we use a time-independent approach to study the scattering of a plane wave on a single-sided detector. Preliminary results are obtained, analytically for the single-spin case and numerically for up to 8 spins. They show that the spin-excitation probabilities are sometimes very sensitive to the parameters of the model, which corroborates the idea that the measurement result could be determined by the atom positions. The possible origin of decoherence and entropy increase in future models is finally discussed.

Comparison of laboratory and ambulatory measures of central blood pressure and pulse wave reflection: hitting the target or missing the mark?

PubMed

Burns, Matthew J; Seed, Jeremy D; Incognito, Anthony V; Doherty, Connor J; Notay, Karambir; Millar, Philip J

2018-04-01

Prior studies demonstrating clinical significance of noninvasive estimates of central blood pressure (BP) and pulse wave reflection have relied primarily on discrete resting measures. The aim of this study was to compare central BP and pulse wave reflection measures sampled during a single resting laboratory visit against those obtained under ambulatory conditions. The secondary aim was to investigate the reproducibility of ambulatory central BP and pulse wave reflection measurements. Forty healthy participants (21 males; 24 ± 3 years) completed three measurements of brachial artery pulse wave analysis (Oscar 2 with SphygmoCor Inside) in the laboratory followed by 24 hours of ambulatory monitoring. Seventeen participants repeated the 24-hour ambulatory monitoring visit after at least 1 week. Ambulatory measures were divided into daytime (9 AM-9 PM), nighttime (1 AM-6 AM), and 24-hour periods. Compared with laboratory measurements, central systolic BP, augmentation pressure, and augmentation index (with and without heart rate normalization) were higher (all P < .01) during daytime and 24-hour periods but lower during the nighttime period (all P < .001). The drop in nighttime brachial systolic BP was larger than central systolic pressure (Δ -20 ± 6 vs. -15 ± 6 mm Hg; P < .0001). Repeat ambulatory measurements of central BP and pulse wave reflection displayed good-to-excellent intraclass correlation coefficients (r = 0.58-0.86; all P < .01), although measures of pulse wave reflection had higher coefficients of variation (14%-41%). The results highlight absolute differences in central BP and pulse wave reflection between discrete laboratory and ambulatory conditions. The use of ambulatory measures of central BP and pulse wave reflection warrant further investigation for clinical prognostic value. Copyright © 2018 American Heart Association. Published by Elsevier Inc. All rights reserved.

Cross-sectional relations of arterial stiffness, pressure pulsatility, wave reflection, and arterial calcification.

PubMed

Tsao, Connie W; Pencina, Karol M; Massaro, Joseph M; Benjamin, Emelia J; Levy, Daniel; Vasan, Ramachandran S; Hoffmann, Udo; O'Donnell, Christopher J; Mitchell, Gary F

2014-11-01

Arterial hemodynamics and vascular calcification are associated with increased risk for cardiovascular disease, but their inter-relations remain unclear. We sought to examine the associations of arterial stiffness, pressure pulsatility, and wave reflection with arterial calcification in individuals free of prevalent cardiovascular disease. Framingham Heart Study Third Generation and Offspring Cohort participants free of cardiovascular disease underwent applanation tonometry to measure arterial stiffness, pressure pulsatility, and wave reflection, including carotid-femoral pulse wave velocity, central pulse pressure, forward wave amplitude, and augmentation index. Participants in each cohort (n=1905, 45±6 years and n=1015, 65±9 years, respectively) underwent multidetector computed tomography to assess the presence and quantity of thoracic aortic calcification, abdominal aortic calcification, and coronary artery calcification. In multivariable-adjusted models, both higher carotid-femoral pulse wave velocity and central pulse pressure were associated with greater thoracic aortic calcification and abdominal aortic calcification, whereas higher augmentation index was associated with abdominal aortic calcification. Among the tonometry measures, carotid-femoral pulse wave velocity was the strongest correlate of all calcification measures in multivariable-adjusted models (odds ratio per SD for thoracic aortic calcification, 2.69 [95% confidence interval, 2.17-3.35]; abdominal aortic calcification, 1.47 [95% confidence interval, 1.26-1.73]; and coronary artery calcification, 1.48 [95% confidence interval, 1.28-1.72]; all P<0.001, respectively). We observed stronger relations of carotid-femoral pulse wave velocity, central pulse pressure, and forward wave amplitude with nearly all continuous calcification measures in the younger Third Generation Cohort as compared with the Offspring Cohort. In community-dwelling individuals without prevalent cardiovascular disease, abnormal central arterial hemodynamics were positively associated with vascular calcification and were observed at younger ages than previously recognized. The mechanisms of these associations may be bidirectional and deserve further study. © 2014 American Heart Association, Inc.

Compressible instability of rapidly expanding spherical material interfaces

NASA Astrophysics Data System (ADS)

Mankbadi, Mina Reda

The focus herein is on the instability of a material interface formed during an abrupt release of concentrated energy as in detonative combustion, explosive dispersals, and inertial-confinement fusion. These applications are modeled as a spherical shock-tube in which high-pressure gas initially contained in a small spherical shell is suddenly released. A forward-moving shock and an inward-moving secondary shock are formed, and between them a material interface develops that separates high-density fluid from the low-density one. The wrinkling of this interface controls mixing and energy release. The interface's stability is studied with and without the inclusion of metalized particulates. A numerical scheme is developed to discretize the full nonlinear equations of the base flow, and the 3D linearized perturbed flow equations. Linearization is followed by spherical harmonic decomposition of the disturbances, thereby reducing the 3D computational domain to one-dimensional radial domain. The 3D physical nature of the disturbances is maintained throughout the procedure. An extended Roe-Pike scheme coupled with a WENO scheme is developed to capture the discontinuities and accurately predict the disturbances. In Chapter 2, the contact interface's stability is analyzed in the inviscid single-phase. The disturbances grow exponentially and the growth rate is insensitive to the radial initial-disturbance profile. For wave numbers less than 100, the results are in accordance with previous theories but clarify that compressibility reduces the growth rate. Unlike the classical RTI, the growth rate reaches saturation at high wavenumbers. The parametric studies show that for specific ratios of initial pressure and temperature, the instability can be eliminated altogether. Chapter 3 discusses the full effects of viscosity and thermal diffusivity. Although Prandtl number effects are minimal, viscous effects dampen the high-wave numbers. For a given Reynolds number there is a peak wave number at which the disturbances are most amplified. In Chapter 4, the multiphase case with metalized particles is investigated. The quasi steady gas-particle interaction forces and heat transfer decelerate the contact interface and reduce its Atwood number, which results in reducing the growth of the interfacial instabilities. A parametric study of the multiphase instability is presented to assist in controlling the instability.

Acoustically enhanced heat exchange and drying apparatus

DOEpatents

Bramlette, T.T.; Keller, J.O.

1987-07-10

A heat transfer drying apparatus includes an acoustically augmented heat transfer chamber for receiving material to be dried. The chamber includes a first heat transfer gas inlet, a second heat transfer gas inlet, a material inlet, and a gas outlet which also serves as a dried material and gas outlet. A non-pulsing first heat transfer gas source provides a first drying gas to the acoustically augmented heat transfer chamber through the first heat transfer gas inlet. A valveless, continuous second heat transfer gas source provides a second drying gas to the acoustically augmented heat transfer chamber through the second heat transfer gas inlet. The second drying gas also generates acoustic waves which bring about acoustical coupling with the gases in the acoustically augmented heat transfer chamber. The second drying gas itself oscillates at an acoustic frequency of approximately 180 Hz due to fluid mechanical motion in the gas. The oscillations of the second heat transfer gas coupled to the first heat transfer gas in the acoustically augmented heat transfer chamber enhance heat and mass transfer by convection within the chamber. 3 figs.

[Alterations in arterial compliance of dyslipidemic patients].

PubMed

Clara, Fernando Mario; Corral, Pablo; Blanco, Gustavo Hector; Scandurra, Adriana Graciela; Meschino, Gustavo Javier

2015-01-01

We studied the alteration on the distensibility of the arterial walls caused by dyslipidemia LDLc dependent, along the decades of life, by means of a study of the radial artery pulse wave. We made an analysis of the radial artery pulse wave records acquired by means a movement displacement sensor, placed on radial palpation area. We recruited 100 dyslipidemic men without other cardiovascular risk factors, between the 3rd and the 6th decade. We identified the reflected wave in the records and we computed the augmentation index in order to quantify its amplitude and position. This index is useful to assess the endothelial dysfunction. Besides, we defined a velocity coefficient as the ratio between the size of the individuals and the delay time between the peak of the systolic wave and the arrival of the reflected wave. Results were compared against those obtained in a group of 161 healthy volunteers. We found that dyslipidemic patients presented augmentation index values similar to controls until the fourth decade, increasing thereafter with significant differences only in the 6th decade. No significant differences were found in the velocity index in any of the ages studied. We conclude that alterations produced by dyslipidemia take decades to manifest, and they begin affecting the mechanism of vasodilation of distal arteries with highest proportion of smooth muscle, without altering the proximal conduit arteries with more elastin content. Copyright © 2013 Sociedad Española de Arteriosclerosis. Published by Elsevier España. All rights reserved.

Quasicrystalline structures and uses thereof

DOEpatents

Steinhardt, Paul J; Chaikin, Paul Michael; Man, Weining

2013-12-03

This invention relates generally to the field of quasicrystalline structures. In preferred embodiments, the stopgap structure is more spherically symmetric than periodic structures facilitating the formation of stopgaps in nearly all directions because of higher rotational symmetries. More particularly, the invention relates to the use of quasicrystalline structures for optical, mechanical, electrical and magnetic purposes. In some embodiments, the invention relates to manipulating, controlling, modulating and directing waves including electromagnetic, sound, spin, and surface waves, for pre-selected range of wavelengths propagating in multiple directions.

Quasicrystalline structures and uses thereof

DOEpatents

Steinhardt, Paul Joseph [Princeton, NJ; Chaikin, Paul Michael [New York, NY; Man, Weining [San Francisco, CA

2011-11-22

This invention relates generally to the field of quasicrystalline structures. In preferred embodiments, the stopgap structure is more spherically symmetric than periodic structures facilitating the formation of stopgaps in nearly all directions because of higher rotational symmetries. More particularly, the invention relates to the use of quasicrystalline structures for optical, mechanical, electrical and magnetic purposes. In some embodiments, the invention relates to manipulating, controlling, modulating and directing waves including electromagnetic, sound, spin, and surface waves, for a pre-selected range of wavelengths propagating in multiple directions.

Quasicrystalline structures and uses thereof

DOEpatents

Steinhardt, Paul Joseph; Chaikin, Paul Michael; Man, Weining

2017-02-14

This invention relates generally to the field of quasicrystalline structures. In preferred embodiments, the stopgap structure is more spherically symmetric than periodic structures facilitating the formation of stopgaps in nearly all directions because of higher rotational symmetries. More particularly, the invention relates to the use of quasicrystalline structures for optical, mechanical, electrical and magnetic purposes. In some embodiments, the invention relates to manipulating, controlling, modulating and directing waves including electromagnetic, sound, spin, and surface waves, for pre-selected range of wavelengths propagating in multiple directions.

Multilayer Volume Holographic Optical Memory

NASA Technical Reports Server (NTRS)

Markov, Vladimir; Millerd, James; Trolinger, James; Norrie, Mark; Downie, John; Timucin, Dogan; Lau, Sonie (Technical Monitor)

1998-01-01

We demonstrate a scheme for volume holographic storage based on the features of shift selectivity of a speckle reference wave hologram. The proposed recording method allows more efficient use of the recording medium and increases the storage density in comparison with spherical or plane-wave reference beams. Experimental results of multiple hologram storage and replay in a photorefractive crystal of iron-doped lithium niobate are presented. The mechanism of lateral and longitudinal shift selectivity are described theoretically and shown to agree with experimental measurements.

Aircraft noise propagation. [sound diffraction by wings

NASA Technical Reports Server (NTRS)

Hadden, W. J.; Pierce, A. D.

1978-01-01

Sound diffraction experiments conducted at NASA Langley Research Center to study the acoustical implications of the engine over wing configuration (noise-shielding by wing) and to provide a data base for assessing various theoretical approaches to the problem of aircraft noise reduction are described. Topics explored include the theory of sound diffraction around screens and wedges; the scattering of spherical waves by rectangular patches; plane wave diffraction by a wedge with finite impedence; and the effects of ambient flow and distribution sources.

Diffractive Alvarez lens

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

Barton, Ian M.; Dixit, Sham N.; Summers, Leslie J.

2000-01-01

A diffractive Alvarez lens is demonstrated that consists of two separate phase plates, each having complementary 16-level surface-relief profiles that contain cubic phase delays. Translation of these two components in the plane of the phase plates is shown to produce a variable astigmatic focus. Both spherical and cylindrical phase profiles are demonstrated with good accuracy, and the discrete surface-relief features are shown to cause less than {lambda}/10 wave-front aberration in the transmitted wave front over a 40 mmx80 mm region. (c) 2000 Optical Society of America.

Simulation of wave propagation in three-dimensional random media

NASA Technical Reports Server (NTRS)

Coles, William A.; Filice, J. P.; Frehlich, R. G.; Yadlowsky, M.

1993-01-01

Quantitative error analysis for simulation of wave propagation in three dimensional random media assuming narrow angular scattering are presented for the plane wave and spherical wave geometry. This includes the errors resulting from finite grid size, finite simulation dimensions, and the separation of the two-dimensional screens along the propagation direction. Simple error scalings are determined for power-law spectra of the random refractive index of the media. The effects of a finite inner scale are also considered. The spatial spectra of the intensity errors are calculated and compared to the spatial spectra of intensity. The numerical requirements for a simulation of given accuracy are determined for realizations of the field. The numerical requirements for accurate estimation of higher moments of the field are less stringent.

Treadmill walking with load carriage increases aortic pressure wave reflection.

PubMed

Ribeiro, Fernando; Oliveira, Nórton L; Pires, Joana; Alves, Alberto J; Oliveira, José

2014-01-01

The study examined the effects of treadmill walking with load carriage on derived measures of central pressure and augmentation index in young healthy subjects. Fourteen male subjects (age 31.0 ± 1.0 years) volunteered in this study. Subjects walked 10 minutes on a treadmill at a speed of 5 km/h carrying no load during one session and a load of 10% of their body weight on both upper limbs in two water carboys with handle during the other session. Pulse wave analysis was performed at rest and immediately after exercise in the radial artery of the right upper limb by applanation tonometry. The main result indicates that walking with load carriage sharply increased augmentation index at 75 bpm (-5.5 ± 2.2 to -1.4 ± 2.2% vs. -5.2 ± 2.8 to -5.5 ± 2.1%, p<0.05), and also induced twice as high increments in central pulse pressure (7.4 ± 1.5 vs. 3.1 ± 1.4 mmHg, p<0.05) and peripheral (20.5 ± 2.7 vs. 10.3 ± 2.5 mmHg, p<0.05) and central systolic pressure (14.7 ± 2.1 vs. 7.4 ± 2.0 mmHg, p<0.05). Walking with additional load of 10% of their body weight (aerobic exercise accompanied by upper limb isometric contraction) increases derived measures of central pressure and augmentation index, an index of wave reflection and arterial stiffness. Copyright © 2013 Sociedade Portuguesa de Cardiologia. Published by Elsevier España. All rights reserved.

PERFECTLY MATCHED LAYERS FOR ELASTIC WAVES IN CYLINDRICAL AND SPHERICAL COORDINATES. (R825225)

EPA Science Inventory

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

Improvement in airborne position measurements based on an ultrasonic linear-period-modulated wave by 1-bit signal processing

NASA Astrophysics Data System (ADS)

Thong-un, Natee; Hirata, Shinnosuke; Kurosawa, Minoru K.

2015-07-01

In this paper, we describe an expansion of the airborne ultrasonic systems for object localization in the three-dimensional spaces of navigation. A system, which revises the microphone arrangement and algorithm, can expand the object-position measurement from +90° in a previous method up to +180° for both the elevation and azimuth angles. The proposed system consists of a sound source and four acoustical receivers. Moreover, the system is designed to utilize low-cost devices, and low-cost computation relying on 1-bit signal processing is used to support the real-time application on a field-programmable gate array (FPGA). An object location is identified using spherical coordinates. A spherical object, which has a curved surface, is considered a target for this system. The transmit pulse to the target is a linear-period-modulated ultrasonic wave with a chirp rate of 50-20 kHz. Statistical evaluation of this work is the experimental investigation under repeatability.

Acoustic wavefield and Mach wave radiation of flashing arcs in strombolian explosion measured by image luminance

NASA Astrophysics Data System (ADS)

Genco, Riccardo; Ripepe, Maurizio; Marchetti, Emanuele; Bonadonna, Costanza; Biass, Sebastien

2014-10-01

Explosive activity often generates visible flashing arcs in the volcanic plume considered as the evidence of the shock-front propagation induced by supersonic dynamics. High-speed image processing is used to visualize the pressure wavefield associated with flashing arcs observed in strombolian explosions. Image luminance is converted in virtual acoustic signal compatible with the signal recorded by pressure transducer. Luminance variations are moving with a spherical front at a 344.7 m/s velocity. Flashing arcs travel at the sound speed already 14 m above the vent and are not necessarily the evidence of a supersonic explosive dynamics. However, seconds later, the velocity of small fragments increases, and the spherical acousto-luminance wavefront becomes planar recalling the Mach wave radiation generated by large scale turbulence in high-speed jet. This planar wavefront forms a Mach angle of 55° with the explosive jet axis, suggesting an explosive dynamics moving at Mo = 1.22 Mach number.

Extinction by a Homogeneous Spherical Particle in an Absorbing Medium

NASA Technical Reports Server (NTRS)

Mishchenko, Michael I.; Videen, Gorden; Yang, Ping

2017-01-01

We use a recent computer implementation of the first principles theory of electromagnetic scattering to compute far-field extinction by a spherical particle embedded in an absorbing unbounded host. Our results show that the suppressing effect of increasing absorption inside the host medium on the ripple structure of the extinction efficiency factor as a function of the size parameter is similar to the well-known effect of increasing absorption inside a particle embedded in a nonabsorbing host. However, the accompanying effects on the interference structure of the extinction efficiency curves are diametrically opposite. As a result, sufficiently large absorption inside the host medium can cause negative particulate extinction. We offer a simple physical explanation of the phenomenon of negative extinction consistent with the interpretation of the interference structure as being the result of interference of the field transmitted by the particle and the diffracted field due to an incomplete wave front resulting from the blockage of the incident plane wave by the particle's geometrical projection.

Buckling Instability Causes Inertial Thrust for Spherical Swimmers at All Scales

NASA Astrophysics Data System (ADS)

Djellouli, Adel; Marmottant, Philippe; Djeridi, Henda; Quilliet, Catherine; Coupier, Gwennou

2017-12-01

Microswimmers, and among them aspirant microrobots, generally have to cope with flows where viscous forces are dominant, characterized by a low Reynolds number (Re). This implies constraints on the possible sequences of body motion, which have to be nonreciprocal. Furthermore, the presence of a strong drag limits the range of resulting velocities. Here, we propose a swimming mechanism which uses the buckling instability triggered by pressure waves to propel a spherical, hollow shell. With a macroscopic experimental model, we show that a net displacement is produced at all Re regimes. An optimal displacement caused by nontrivial history effects is reached at intermediate Re. We show that, due to the fast activation induced by the instability, this regime is reachable by microscopic shells. The rapid dynamics would also allow high-frequency excitation with standard traveling ultrasonic waves. Scale considerations predict a swimming velocity of order 1 cm /s for a remote-controlled microrobot, a suitable value for biological applications such as drug delivery.

Robust signal recovery using the prolate spherical wave functions and maximum correntropy criterion

NASA Astrophysics Data System (ADS)

Zou, Cuiming; Kou, Kit Ian

2018-05-01

Signal recovery is one of the most important problem in signal processing. This paper proposes a novel signal recovery method based on prolate spherical wave functions (PSWFs). PSWFs are a kind of special functions, which have been proved having good performance in signal recovery. However, the existing PSWFs based recovery methods used the mean square error (MSE) criterion, which depends on the Gaussianity assumption of the noise distributions. For the non-Gaussian noises, such as impulsive noise or outliers, the MSE criterion is sensitive, which may lead to large reconstruction error. Unlike the existing PSWFs based recovery methods, our proposed PSWFs based recovery method employs the maximum correntropy criterion (MCC), which is independent of the noise distribution. The proposed method can reduce the impact of the large and non-Gaussian noises. The experimental results on synthetic signals with various types of noises show that the proposed MCC based signal recovery method has better robust property against various noises compared to other existing methods.

Artificial excitation of ELF waves with frequency of Schumann resonance

NASA Astrophysics Data System (ADS)

Streltsov, A. V.; Guido, T.; Tulegenov, B.; Labenski, J.; Chang, C.-L.

2014-11-01

We report results from the experiment aimed at the artificial excitation of extremely low-frequency (ELF) electromagnetic waves with frequencies corresponding to the frequency of Schumann resonance. Electromagnetic waves with these frequencies can form a standing pattern inside the spherical cavity formed by the surface of the Earth and the ionosphere. In the experiment the ELF waves were excited by heating the ionosphere with X-mode HF electromagnetic waves generated at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska. The experiment demonstrates that heating of the ionosphere can excite relatively large-amplitude electromagnetic waves with frequencies in the range 7.8-8.0 Hz when the ionosphere has a strong F layer, the frequency of the HF radiation is in the range 3.20-4.57 MHz, and the electric field greater than 5 mV/m is present in the ionosphere.

The Next Wave: Humans, Computers, and Redefining Reality

NASA Technical Reports Server (NTRS)

Little, William

2018-01-01

The Augmented/Virtual Reality (AVR) Lab at KSC is dedicated to " exploration into the growing computer fields of Extended Reality and the Natural User Interface (it is) a proving ground for new technologies that can be integrated into future NASA projects and programs." The topics of Human Computer Interface, Human Computer Interaction, Augmented Reality, Virtual Reality, and Mixed Reality are defined; examples of work being done in these fields in the AVR Lab are given. Current new and future work in Computer Vision, Speech Recognition, and Artificial Intelligence are also outlined.

Do cyanobacteria swim using traveling surface waves?

PubMed Central

Ehlers, K M; Samuel, A D; Berg, H C; Montgomery, R

1996-01-01

Bacteria that swim without the benefit of flagella might do so by generating longitudinal or transverse surface waves. For example, swimming speeds of order 25 microns/s are expected for a spherical cell propagating longitudinal waves of 0.2 micron length, 0.02 micron amplitude, and 160 microns/s speed. This problem was solved earlier by mathematicians who were interested in the locomotion of ciliates and who considered the undulations of the envelope swept out by ciliary tips. A new solution is given for spheres propagating sinusoidal waveforms rather than Legendre polynomials. The earlier work is reviewed and possible experimental tests are suggested. Images Fig. 1 PMID:8710872

Cloaks for suppression or enhancement of scattering of diffuse photon density waves

NASA Astrophysics Data System (ADS)

Renthlei, Lalruatfela; Ramakrishna, S. Anantha; Wanare, Harshawardhan

2018-07-01

Enhancement of wave-like characteristics of heavily damped diffuse photon density waves in a random medium by amplification can induce strongly localised resonances. These resonances can be used to either suppress or enhance scattering from an inhomogeneity in the random medium by cloaking the inhomogeneous region by a shell of random medium with the correct levels of absorption or amplification. A spherical core-shell structure consisting of a shell of a random amplifying medium is shown to enhance or suppress specific resonant modes. A shell with an absorbing random medium is also shown to suppress scattering which can also be used for cloaking the core region.

Les résonances d'un trou noir de Schwarzschild.

NASA Astrophysics Data System (ADS)

Bachelot, A.; Motet-Bachelot, A.

1993-09-01

This paper is devoted to the theoretical and computational investigations of the scattering frequencies of scalar, electromagnetic, gravitational waves around a spherical black hole. The authors adopt a time dependent approach: construction of wave operators for the hyperbolic Regge-Wheeler equation; asymptotic completeness; outgoing and incoming spectral representations; meromorphic continuation of the Heisenberg matrix; approximation by dumping and cut-off of the potentials and interpretation of the semi group Z(t) in the framework of the membrane paradigma. They develop a new procedure for the computation of the resonances by the spectral analysis of the transient scattered wave, based on Prony's algorithm.

VHF electromagnetic wave propagation

NASA Astrophysics Data System (ADS)

Gole, P.

Theoretical and experimental study of large-scale VHF propagation characteristics is presented. Certain phenomena that are difficult to model, such as the effects of ground near the antenna, are examined from a purely experimental point of view. The characteristics of electromagnetic waves over a spherical surface and through a medium having a certain refractive index, such as is the case for waves propagated over the earth's surface, are analytically described. Two mathematical models are used, one for the case of the receiver being within the radioelectric horizon of the transmitter and the other for when it is not. Propagation phenomena likely to increase the false alarm probability of an air surveillance radar are briefly considered.

Gravitational waves from rotating and precessing rigid bodies. 2: General solutions and computationally useful formulae

NASA Technical Reports Server (NTRS)

Zimmerman, M.

1979-01-01

The classical mechanics results for free precession which are needed in order to calculate the weak field, slow-motion, quadrupole-moment gravitational waves are reviewed. Within that formalism, algorithms are given for computing the exact gravitational power radiated and waveforms produced by arbitrary rigid-body freely-precessing sources. The dominant terms are presented in series expansions of the waveforms for the case of an almost spherical object precessing with a small wobble angle. These series expansions, which retain the precise frequency dependence of the waves, may be useful for gravitational astronomers when freely-precessing sources begin to be observed.

Application of optical interferometry in focused acoustic field measurement

NASA Astrophysics Data System (ADS)

Wang, Yuebing; Sun, Min; Cao, Yonggang; Zhu, Jiang

2018-07-01

Optical interferometry has been successfully applied in measuring acoustic pressures in plane-wave fields and spherical-wave fields. In this paper, the "effective" refractive index for focused acoustic fields was developed, through numerical simulation and experiments, the feasibility of the optical method in measuring acoustic fields of focused transducers was proved. Compared with the results from a membrane hydrophone, it was concluded that the optical method has good spatial resolution and is suitable for detecting focused fields with fluctuant distributions. The influences of a few factors (the generated lamb wave, laser beam directivity, etc.) were analyzed, and corresponding suggestions were proposed for effective application of this technology.

Wave energy and intertidal productivity

PubMed Central

Leigh, Egbert G.; Paine, Robert T.; Quinn, James F.; Suchanek, Thomas H.

1987-01-01

In the northeastern Pacific, intertidal zones of the most wave-beaten shores receive more energy from breaking waves than from the sun. Despite severe mortality from winter storms, communities at some wave-beaten sites produce an extraordinary quantity of dry matter per unit area of shore per year. At wave-beaten sites of Tatoosh Island, WA, sea palms, Postelsia palmaeformis, can produce > 10 kg of dry matter, or 1.5 × 108 J, per m2 in a good year. Extraordinarily productive organisms such as Postelsia are restricted to wave-beaten sites. Intertidal organisms cannot transform wave energy into chemical energy, as photosynthetic plants transform solar energy, nor can intertidal organisms “harness” wave energy. Nonetheless, wave energy enhances the productivity of intertidal organisms. On exposed shores, waves increase the capacity of resident algae to acquire nutrients and use sunlight, augment the competitive ability of productive organisms, and protect intertidal residents by knocking away their enemies or preventing them from feeding. PMID:16593813

Two-dimensional wave patterns of spreading depolarization: Retracting, re-entrant, and stationary waves

NASA Astrophysics Data System (ADS)

Dahlem, Markus A.; Graf, Rudolf; Strong, Anthony J.; Dreier, Jens P.; Dahlem, Yuliya A.; Sieber, Michaela; Hanke, Wolfgang; Podoll, Klaus; Schöll, Eckehard

2010-06-01

We present spatio-temporal characteristics of spreading depolarizations (SD) in two experimental systems: retracting SD wave segments observed with intrinsic optical signals in chicken retina, and spontaneously occurring re-entrant SD waves that repeatedly spread across gyrencephalic feline cortex observed by laser speckle flowmetry. A mathematical framework of reaction-diffusion systems with augmented transmission capabilities is developed to explain the emergence and transitions between these patterns. Our prediction is that the observed patterns are reaction-diffusion patterns controlled and modulated by weak nonlocal coupling such as long-range, time-delayed, and global coupling. The described spatio-temporal characteristics of SD are of important clinical relevance under conditions of migraine and stroke. In stroke, the emergence of re-entrant SD waves is believed to worsen outcome. In migraine, retracting SD wave segments cause neurological symptoms and transitions to stationary SD wave patterns may cause persistent symptoms without evidence from noninvasive imaging of infarction.

Artificial Excitation of Schumann Resonance with HAARP

NASA Astrophysics Data System (ADS)

Streltsov, A. V.; Chang, C. L.

2014-12-01

We report results from the experiment aimed at the artificial excitation of extremely-low-frequency (ELF) electromagnetic waves with frequencies corresponding to the frequency of Schumann resonance (typically, 7.5 - 8.0 Hz frequency range). Electromagnetic waves with these frequencies can form a standing pattern inside the spherical cavity formed by the surface of the earth and the ionosphere. In the experiment the ELF waves were excited by heating the ionosphere with X-mode HF electromagnetic waves generated by the High Frequency Active Auroral Research Program (HAARP) facility in Alaska. The experiment demonstrates that heating of the ionosphere can excite relatively large-amplitude electromagnetic waves with frequencies in the range of the Schumann resonance, when the ionosphere has a strong F-layer and an electric field greater than 5 mV/m is present in the E-region.

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

El-Labany, S. K., E-mail: skellabany@hotmail.com; Zedan, N. A., E-mail: nesreenplasma@yahoo.com; El-Taibany, W. F., E-mail: eltaibany@hotmail.com, E-mail: eltaibany@du.edu.eg

The nonplanar amplitude modulation of dust acoustic (DA) envelope solitary waves in a strongly coupled dusty plasma (SCDP) has been investigated. By using a reductive perturbation technique, a modified nonlinear Schrödinger equation (NLSE) including the effects of geometry, polarization, and ion superthermality is derived. The modulational instability (MI) of the nonlinear DA wave envelopes is investigated in both planar and nonplanar geometries. There are two stable regions for the DA wave propagation strongly affected by polarization and ion superthermality. Moreover, it is found that the nonlinear DA waves in spherical geometry are the more structurally stable. The larger growth ratemore » of the nonlinear DA MI is observed in the cylindrical geometry. The salient characteristics of the MI in the nonplanar geometries cannot be found in the planar one. The DA wave propagation and the NLSE solutions are investigated both analytically and numerically.« less

Impact of Primary Spherical Aberration, Spatial Frequency and Stiles Crawford Apodization on Wavefront determined Refractive Error: A Computational Study

PubMed Central

Xu, Renfeng; Bradley, Arthur; Thibos, Larry N.

2013-01-01

Purpose We tested the hypothesis that pupil apodization is the basis for central pupil bias of spherical refractions in eyes with spherical aberration. Methods We employed Fourier computational optics in which we vary spherical aberration levels, pupil size, and pupil apodization (Stiles Crawford Effect) within the pupil function, from which point spread functions and optical transfer functions were computed. Through-focus analysis determined the refractive correction that optimized retinal image quality. Results For a large pupil (7 mm), as spherical aberration levels increase, refractions that optimize the visual Strehl ratio mirror refractions that maximize high spatial frequency modulation in the image and both focus a near paraxial region of the pupil. These refractions are not affected by Stiles Crawford Effect apodization. Refractions that optimize low spatial frequency modulation come close to minimizing wavefront RMS, and vary with level of spherical aberration and Stiles Crawford Effect. In the presence of significant levels of spherical aberration (e.g. C40 = 0.4 µm, 7mm pupil), low spatial frequency refractions can induce −0.7D myopic shift compared to high SF refraction, and refractions that maximize image contrast of a 3 cycle per degree square-wave grating can cause −0.75D myopic drift relative to refractions that maximize image sharpness. Discussion Because of small depth of focus associated with high spatial frequency stimuli, the large change in dioptric power across the pupil caused by spherical aberration limits the effective aperture contributing to the image of high spatial frequencies. Thus, when imaging high spatial frequencies, spherical aberration effectively induces an annular aperture defining that portion of the pupil contributing to a well-focused image. As spherical focus is manipulated during the refraction procedure, the dimensions of the annular aperture change. Image quality is maximized when the inner radius of the induced annulus falls to zero, thus defining a circular near paraxial region of the pupil that determines refraction outcome. PMID:23683093

Rotary wave-ejector enhanced pulse detonation engine

NASA Astrophysics Data System (ADS)

Nalim, M. R.; Izzy, Z. A.; Akbari, P.

2012-01-01

The use of a non-steady ejector based on wave rotor technology is modeled for pulse detonation engine performance improvement and for compatibility with turbomachinery components in hybrid propulsion systems. The rotary wave ejector device integrates a pulse detonation process with an efficient momentum transfer process in specially shaped channels of a single wave-rotor component. In this paper, a quasi-one-dimensional numerical model is developed to help design the basic geometry and operating parameters of the device. The unsteady combustion and flow processes are simulated and compared with a baseline PDE without ejector enhancement. A preliminary performance assessment is presented for the wave ejector configuration, considering the effect of key geometric parameters, which are selected for high specific impulse. It is shown that the rotary wave ejector concept has significant potential for thrust augmentation relative to a basic pulse detonation engine.

Method for preparing spherical ferrite beads and use thereof

DOEpatents

Lauf, Robert J.; Anderson, Kimberly K.; Montgomery, Frederick C.; Collins, Jack L.

2002-01-01

The invention allows the fabrication of small, dense, highly polished spherical beads of hexagonal ferrites with selected compositions for use in nonreciprocal microwave and mm-wave devices as well as in microwave absorbent or reflective coatings, composites, and the like. A porous, generally spherical bead of hydrous iron oxide is made by a sol-gel process to form a substantially rigid bead having a generally fine crystallite size and correspondingly finely distributed internal porosity. The resulting gel bead is washed and hydrothermally reacted with a soluble alkaline earth salt (typically Ba or Sr) under conditions of elevated temperature and pressure to convert the bead into a mixed hydrous iron-alkaline earth oxide while retaining the generally spherical shape. This mixed oxide bead is then washed, dried, and calcined to produce the desired (BaFe.sub.12 O.sub.19 or SrFe.sub.12 O.sub.19) crystal structure. The calcined bead is then sintered to form a dense bead of the BaFe.sub.12 O.sub.19 and SrFe.sub.12 O.sub.19 phase suitable for polishing and incorporation into various microwave devices and components.

Over-Water Aspects of Ground-Effect Vehicles

NASA Technical Reports Server (NTRS)

Kuhn, Richard E.; Carter, Arthur W.; Schade, Robert O.

1960-01-01

The large thrust augmentation obtainable with annular-jet configurations in ground proximity has led to the serious investigation of ground-effect machines. The basic theoretical work on these phenomena has been done by Chaplin and Boehler. Large thrust-augmentation factors, however, can be obtained only at very low heights, that is, of the order of a few percent of the diameter of the vehicle. To take advantage of this thrust augmentation therefore the vehicle must be either very large or must operate over very smooth terrain. Over-land uses of these vehicles then will probably be rather limited. The water, however, is inherently smooth and those irregularities that do exist, that is waves, are statistically known. It appears therefore that some practical application of ground-effect machines may be made in over-water application.

Optimal secondary source position in exterior spherical acoustical holophony

NASA Astrophysics Data System (ADS)

Pasqual, A. M.; Martin, V.

2012-02-01

Exterior spherical acoustical holophony is a branch of spatial audio reproduction that deals with the rendering of a given free-field radiation pattern (the primary field) by using a compact spherical loudspeaker array (the secondary source). More precisely, the primary field is known on a spherical surface surrounding the primary and secondary sources and, since the acoustic fields are described in spherical coordinates, they are naturally subjected to spherical harmonic analysis. Besides, the inverse problem of deriving optimal driving signals from a known primary field is ill-posed because the secondary source cannot radiate high-order spherical harmonics efficiently, especially in the low-frequency range. As a consequence, a standard least-squares solution will overload the transducers if the primary field contains such harmonics. Here, this is avoided by discarding the strongly decaying spherical waves, which are identified through inspection of the radiation efficiency curves of the secondary source. However, such an unavoidable regularization procedure increases the least-squares error, which also depends on the position of the secondary source. This paper deals with the above-mentioned questions in the context of far-field directivity reproduction at low and medium frequencies. In particular, an optimal secondary source position is sought, which leads to the lowest reproduction error in the least-squares sense without overloading the transducers. In order to address this issue, a regularization quality factor is introduced to evaluate the amount of regularization required. It is shown that the optimal position improves significantly the holophonic reconstruction and maximizes the regularization quality factor (minimizes the amount of regularization), which is the main general contribution of this paper. Therefore, this factor can also be used as a cost function to obtain the optimal secondary source position.

Ultrasonic power transfer from a spherical acoustic wave source to a free-free piezoelectric receiver: Modeling and experiment

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

Shahab, S.; Gray, M.; Erturk, A., E-mail: alper.erturk@me.gatech.edu

2015-03-14

Contactless powering of small electronic components has lately received growing attention for wireless applications in which battery replacement or tethered charging is undesired or simply impossible, and ambient energy harvesting is not a viable solution. As an alternative to well-studied methods of contactless energy transfer, such as the inductive coupling method, the use of ultrasonic waves transmitted and received by piezoelectric devices enables larger power transmission distances, which is critical especially for deep-implanted electronic devices. Moreover, energy transfer by means of acoustic waves is well suited in situations where no electromagnetic fields are allowed. The limited literature of ultrasonic acousticmore » energy transfer is mainly centered on proof-of-concept experiments demonstrating the feasibility of this method, lacking experimentally validated modeling efforts for the resulting multiphysics problem that couples the source and receiver dynamics with domain acoustics. In this work, we present fully coupled analytical, numerical, and experimental multiphysics investigations for ultrasonic acoustic energy transfer from a spherical wave source to a piezoelectric receiver bar that operates in the 33-mode of piezoelectricity. The fluid-loaded piezoelectric receiver under free-free mechanical boundary conditions is shunted to an electrical load for quantifying the electrical power output for a given acoustic source strength of the transmitter. The analytical acoustic-piezoelectric structure interaction modeling framework is validated experimentally, and the effects of system parameters are reported along with optimal electrical loading and frequency conditions of the receiver.« less

Fully pseudospectral solution of the conformally invariant wave equation near the cylinder at spacelike infinity. III: nonspherical Schwarzschild waves and singularities at null infinity

NASA Astrophysics Data System (ADS)

Frauendiener, Jörg; Hennig, Jörg

2018-03-01

We extend earlier numerical and analytical considerations of the conformally invariant wave equation on a Schwarzschild background from the case of spherically symmetric solutions, discussed in Frauendiener and Hennig (2017 Class. Quantum Grav. 34 045005), to the case of general, nonsymmetric solutions. A key element of our approach is the modern standard representation of spacelike infinity as a cylinder. With a decomposition into spherical harmonics, we reduce the four-dimensional wave equation to a family of two-dimensional equations. These equations can be used to study the behaviour at the cylinder, where the solutions turn out to have, in general, logarithmic singularities at infinitely many orders. We derive regularity conditions that may be imposed on the initial data, in order to avoid the first singular terms. We then demonstrate that the fully pseudospectral time evolution scheme can be applied to this problem leading to a highly accurate numerical reconstruction of the nonsymmetric solutions. We are particularly interested in the behaviour of the solutions at future null infinity, and we numerically show that the singularities spread to null infinity from the critical set, where the cylinder approaches null infinity. The observed numerical behaviour is consistent with similar logarithmic singularities found analytically on the critical set. Finally, we demonstrate that even solutions with singularities at low orders can be obtained with high accuracy by virtue of a coordinate transformation that converts solutions with logarithmic singularities into smooth solutions.

Plasma current start-up using the lower hybrid wave on the TST-2 spherical tokamak

NASA Astrophysics Data System (ADS)

Takase, Y.; Ejiri, A.; Inada, T.; Moeller, C. P.; Shinya, T.; Tsujii, N.; Yajima, S.; Furui, H.; Homma, H.; Imamura, K.; Nakamura, K.; Nakamura, K.; Sonehara, M.; Takeuchi, T.; Togashi, H.; Tsuda, S.; Yoshida, Y.

2015-12-01

Non-inductive plasma current start-up, ramp-up and sustainment by waves in the lower hybrid wave (LHW) frequency range at 200 MHz were investigated on the TST-2 spherical tokamak (R0 ≤ 0.38 m, a ≤ 0.25 m, Bt0 ≤ 0.3T, Ip ≤ 0.14 MA). Experimental results obtained using three types of antenna were compared. Both the highest plasma current (Ip = 18 kA) and the highest current drive figure of merit ηCD≡n¯eIpR0/PRF=1.4 ×1017 A/W/m2 were achieved using the capacitively-coupled combline (CCC) antenna, designed to excite the LHW with a sharp and highly directional wavenumber spectrum. For Ip greater than about 5 kA, high energy electrons accelerated by the LHW become the dominant carrier of plasma current. The low value of ηCD observed so far are believed to be caused by a rapid loss of energetic electrons and parasitic losses of the LHW energy in the plasma periphery. ηCD is expected to improve by an order of magnitude by increasing the plasma current to improve energetic electron confinement. In addition, edge power losses are expected to be reduced by increasing the toroidal magnetic field to improve wave accessibility to the plasma core, and by launching the LHW from the inboard upper region of the torus to achieve better single-pass absorption.

Collisionless relaxation in spiral galaxy models

NASA Technical Reports Server (NTRS)

Hohl, F.

1974-01-01

The increase in random kinetic energy of stars by rapidly fluctuating gravitational fields (collisionless or violent relaxation) in disk galaxy models is investigated for three interaction potentials of the stars corresponding to (1) point stars, (2) rod stars of length 2 kpc, and (3) uniform density spherical stars of radius 2 kpc. To stabilize the galaxy against the large scale bar forming instability, a fixed field corresponding to a central core or halo component of stars was added with the stars containing at most 20 percent of the total mass of the galaxy. Considerable heating occurred for both the point stars and the rod stars, whereas the use of spherical stars resulted in a very low heating rate. The use of spherical stars with the resulting low heating rate will be desirable for the study of large scale galactic stability or density wave propagation, since collective heating effects will no longer mask the phenomena under study.

Synthetic Landau Levels and Spinor Vortex Matter on a Haldane Spherical Surface with a Magnetic Monopole.

PubMed

Zhou, Xiang-Fa; Wu, Congjun; Guo, Guang-Can; Wang, Ruquan; Pu, Han; Zhou, Zheng-Wei

2018-03-30

We present a flexible scheme to realize exact flat Landau levels on curved spherical geometry in a system of spinful cold atoms. This is achieved by applying the Floquet engineering of a magnetic quadrupole field to create a synthetic monopole field in real space. The system can be exactly mapped to the electron-monopole system on a sphere, thus realizing Haldane's spherical geometry for fractional quantum Hall physics. This method works for either bosons or fermions. We investigate the ground-state vortex pattern for an s-wave interacting atomic condensate by mapping this system to the classical Thompson's problem. The distortion and stability of the vortex pattern are further studied in the presence of dipolar interaction. Our scheme is compatible with the current experimental setup, and may serve as a promising route of investigating quantum Hall physics and exotic spinor vortex matter on curved space.

Efficient Terahertz Wide-Angle NUFFT-Based Inverse Synthetic Aperture Imaging Considering Spherical Wavefront.

PubMed

Gao, Jingkun; Deng, Bin; Qin, Yuliang; Wang, Hongqiang; Li, Xiang

2016-12-14

An efficient wide-angle inverse synthetic aperture imaging method considering the spherical wavefront effects and suitable for the terahertz band is presented. Firstly, the echo signal model under spherical wave assumption is established, and the detailed wavefront curvature compensation method accelerated by 1D fast Fourier transform (FFT) is discussed. Then, to speed up the reconstruction procedure, the fast Gaussian gridding (FGG)-based nonuniform FFT (NUFFT) is employed to focus the image. Finally, proof-of-principle experiments are carried out and the results are compared with the ones obtained by the convolution back-projection (CBP) algorithm. The results demonstrate the effectiveness and the efficiency of the presented method. This imaging method can be directly used in the field of nondestructive detection and can also be used to provide a solution for the calculation of the far-field RCSs (Radar Cross Section) of targets in the terahertz regime.

Black hole and cosmos with multiple horizons and multiple singularities in vector-tensor theories

NASA Astrophysics Data System (ADS)

Gao, Changjun; Lu, Youjun; Yu, Shuang; Shen, You-Gen

2018-05-01

A stationary and spherically symmetric black hole (e.g., Reissner-Nordström black hole or Kerr-Newman black hole) has, at most, one singularity and two horizons. One horizon is the outer event horizon and the other is the inner Cauchy horizon. Can we construct static and spherically symmetric black hole solutions with N horizons and M singularities? The de Sitter cosmos has only one apparent horizon. Can we construct cosmos solutions with N horizons? In this article, we present the static and spherically symmetric black hole and cosmos solutions with N horizons and M singularities in the vector-tensor theories. Following these motivations, we also construct the black hole solutions with a firewall. The deviation of these black hole solutions from the usual ones can be potentially tested by future measurements of gravitational waves or the black hole continuum spectrum.

Compton scattering study of electron momentum distribution in lithium fluoride using 662 keV gamma radiations

NASA Astrophysics Data System (ADS)

Vijayakumar, R.; Shivaramu; Ramamurthy, N.; Ford, M. J.

2008-12-01

Here we report the first ever 137Cs Compton spectroscopy study of lithium fluoride. The spherical average Compton profiles of lithium fluoride are deduced from Compton scattering measurements on poly crystalline sample at gamma ray energy of 662 keV. To compare the experimental data, we have computed the spherical average Compton profiles using self-consistent Hartree-Fock wave functions employed on linear combination of atomic orbital (HF-LCAO) approximation. The directional Compton profiles and their anisotropic effects are also calculated using the same HF-LCAO approximation. The experimental spherical average profiles are found to be in good agreement with the corresponding HF-LCAO calculations and in qualitative agreement with Hartree-Fock free atom values. The present experimental isotropic and calculated directional profiles are also compared with the available experimental isotropic and directional Compton profiles using 59.54 and 159 keV γ-rays.

Synthetic Landau Levels and Spinor Vortex Matter on a Haldane Spherical Surface with a Magnetic Monopole

NASA Astrophysics Data System (ADS)

Zhou, Xiang-Fa; Wu, Congjun; Guo, Guang-Can; Wang, Ruquan; Pu, Han; Zhou, Zheng-Wei

2018-03-01

We present a flexible scheme to realize exact flat Landau levels on curved spherical geometry in a system of spinful cold atoms. This is achieved by applying the Floquet engineering of a magnetic quadrupole field to create a synthetic monopole field in real space. The system can be exactly mapped to the electron-monopole system on a sphere, thus realizing Haldane's spherical geometry for fractional quantum Hall physics. This method works for either bosons or fermions. We investigate the ground-state vortex pattern for an s -wave interacting atomic condensate by mapping this system to the classical Thompson's problem. The distortion and stability of the vortex pattern are further studied in the presence of dipolar interaction. Our scheme is compatible with the current experimental setup, and may serve as a promising route of investigating quantum Hall physics and exotic spinor vortex matter on curved space.

Monoenergetic electron parameters in a spheroid bubble model

NASA Astrophysics Data System (ADS)

Sattarian, H.; Sh., Rahmatallahpur; Tohidi, T.

2013-02-01

A reliable analytical expression for the potential of plasma waves with phase velocities near the speed of light is derived. The presented spheroid cavity model is more consistent than the previous spherical and ellipsoidal models and it explains the mono-energetic electron trajectory more accurately, especially at the relativistic region. The maximum energy of electrons is calculated and it is shown that the maximum energy of the spheroid model is less than that of the spherical model. The electron energy spectrum is also calculated and it is found that the energy distribution ratio of electrons ΔE/E for the spheroid model under the conditions reported here is half that of the spherical model and it is in good agreement with the experimental value in the same conditions. As a result, the quasi-mono-energetic electron output beam interacting with the laser plasma can be more appropriately described with this model.

Rigid rotators. [deriving the time-independent energy states associated with rotational motions of the molecule

NASA Technical Reports Server (NTRS)

1976-01-01

The two-particle, steady-state Schroedinger equation is transformed to center of mass and internuclear distance vector coordinates, leading to the free particle wave equation for the kinetic energy motion of the molecule and a decoupled wave equation for a single particle of reduced mass moving in a spherical potential field. The latter describes the vibrational and rotational energy modes of the diatomic molecule. For fixed internuclear distance, this becomes the equation of rigid rotator motion. The classical partition function for the rotator is derived and compared with the quantum expression. Molecular symmetry effects are developed from the generalized Pauli principle that the steady-state wave function of any system of fundamental particles must be antisymmetric. Nuclear spin and spin quantum functions are introduced and ortho- and para-states of rotators, along with their degeneracies, are defined. Effects of nuclear spin on entropy are deduced. Next, rigid polyatomic rotators are considered and the partition function for this case is derived. The patterns of rotational energy levels for nonlinear molecules are discussed for the spherical symmetric top, for the prolate symmetric top, for the oblate symmetric top, and for the asymmetric top. Finally, the equilibrium energy and specific heat of rigid rotators are derived.

Quantum Analogies in the Interaction between Acoustic Waves and Bubble Clouds

NASA Astrophysics Data System (ADS)

Parrales, Miguel A.; Rodriguez-Rodriguez, Javier

2014-11-01

Analogies between quantum mechanical and acoustical propagation phenomena have a great interest in academic research due to their ability to shed light on some complex quantum effects, which are impossible to visualize directly in the macroscopic world. In this talk, we describe a number of these analogies concerning the acoustic behavior of bubble clouds. Firstly, we show that the structure of the collective oscillation modes of a spherical bubble cloud resembles that of the atomic orbitals of a hydrogen atom. Secondly, we present an analogy between some perturbation methods used in quantum-electrodynamics and the computation of the acoustic response of the randomly distributed bubble cloud by considering the contribution to the total scattered pressure of the multiple scattering paths that take place inside the clouds. As an application of this analogy, we obtain the scattering cross-section of a diluted cloud, which remarkably mimics the quantum scattering of an neutron wave when passing through an atomic nucleus. Finally, we numerically reproduce the behavior of an electron in a covalent bond between two hydrogen atoms by simulating the acoustic wave propagation through two neighboring spherical bubble assemblages. Funded by the Spanish Ministry of Economy and Competitiveness through Grants DPI2011-28356-C03-01 and DPI2011-28356-C03-02.

Natural oscillations of a gas bubble in a liquid-filled cavity located in a viscoelastic medium

NASA Astrophysics Data System (ADS)

Doinikov, Alexander A.; Marmottant, Philippe

2018-04-01

The present study is motivated by cavitation phenomena that occur in the stems of trees. The internal pressure in tree conduits can drop down to significant negative values. This drop gives rise to cavitation bubbles, which undergo high-frequency eigenmodes. The aim of the present study is to determine the parameters of the bubble natural oscillations. To this end, a theory is developed that describes the pulsation of a spherical bubble located at the center of a spherical cavity surrounded by an infinite solid medium. It is assumed that the medium inside the bubble is a gas-vapor mixture, the cavity is filled with a compressible viscous liquid, and the medium surrounding the cavity behaves as a viscoelastic solid. The theoretical solution takes into account the outgoing acoustic wave produced by the bubble pulsation, the incoming wave caused by reflection from the liquid-solid boundary, and the outgoing wave propagating in the solid. A dispersion equation for the calculation of complex wavenumbers of the bubble eigenmodes is derived. Approximate analytical solutions to the dispersion equation are found. Numerical simulations are performed to reveal the effect of different physical parameters on the resonance frequency and the attenuation coefficient of the bubble oscillations.

Fast discharge in a spherical cavity

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

Antsiferov, P. S., E-mail: Ants@isan.troitsk.ru; Dorokhin, L. A.

2014-04-15

The work is devoted to the study of the plasma, created by a fast discharge in a spherical cavity. The discharge was driven by an inductive storage with plasma erosion opening switch (dI/dt ∼10{sup 12} A/s). The plasma was produced in a spherical cavity (alumina, 11 mm diameter). Xe, Ar, and He at the pressure 80 Pa were used as working gases. The time evolution of the spatial structure and of extreme ultraviolet (EUV) spectra of the discharge plasma was studied by means of micro channel plate detector. The discharges with Xe and Ar resulted in the stable appearance of the spherically shapedmore » plasma with the diameter about 1–3 mm. The plasma emission in the EUV region lasts ∼500 ns. The EUV spectrum of Ar discharge at the moment of maximum of the electron temperature T{sub e} contains the lines of Ar X (ionization potential 478.7 eV), that indicates a value of T{sub e} in the range 50–100 eV. The mechanism of plasma appearance can be the cumulation of the convergent spherical shock wave, generated by fast heat deposition and magnetic pressure in working media near the inner surface of the discharge volume.« less

Coherent Backscattering by Polydisperse Discrete Random Media: Exact T-Matrix Results

NASA Technical Reports Server (NTRS)

Mishchenko, Michael I.; Dlugach, Janna M.; Mackowski, Daniel W.

2011-01-01

The numerically exact superposition T-matrix method is used to compute, for the first time to our knowledge, electromagnetic scattering by finite spherical volumes composed of polydisperse mixtures of spherical particles with different size parameters or different refractive indices. The backscattering patterns calculated in the far-field zone of the polydisperse multiparticle volumes reveal unequivocally the classical manifestations of the effect of weak localization of electromagnetic waves in discrete random media, thereby corroborating the universal interference nature of coherent backscattering. The polarization opposition effect is shown to be the least robust manifestation of weak localization fading away with increasing particle size parameter.

Local-area simulations of rotating compressible convection and associated mean flows

NASA Technical Reports Server (NTRS)

Hurlburt, Neal E.; Brummell, N. H.; Toomre, Juri

1995-01-01

The dynamics of compressible convection within a curved local segment of a rotating spherical shell are considered in relation to the turbulent redistribution of angular momentum within the solar convection zone. Current supercomputers permit fully turbulent flows to be considered within the restricted geometry of local area models. By considering motions in a curvilinear geometry in which the Coriolos parameters vary with latitude, Rossby waves which couple with the turbulent convection are thought of as being possible. Simulations of rotating convection are presented in such a curved local segment of a spherical shell using a newly developed, sixth-order accurate code based on compact finite differences.

An investigation of the forward scattering theorem

NASA Technical Reports Server (NTRS)

Karam, M. A.; Fung, A. K.

1987-01-01

The calculation of an EM wave's extinction loss during propagation within an inhomogeneous medium, as in active and passive remote sensing modeling, can be undertaken either through the summation of the scattering and absorption losses or through the use of the forward scattering theorem. Attention is presently given to the similarities and differences of these two approaches as a function of dielectric properties of a spherical scatterer and the incident frequency. Scattering loss is obtainable by integrating the magnitude-squared of the scattered field over a spherical surface surrounding the scatterer; the scattered field and the field within the scatterer are computed according to Mie theory.

Acoustic radiation force control: Pulsating spherical carriers.

PubMed

Rajabi, Majid; Mojahed, Alireza

2018-02-01

The interaction between harmonic plane progressive acoustic beams and a pulsating spherical radiator is studied. The acoustic radiation force function exerted on the spherical body is derived as a function of the incident wave pressure and the monopole vibration characteristics (i.e., amplitude and phase) of the body. Two distinct strategies are presented in order to alter the radiation force effects (i.e., pushing and pulling states) by changing its magnitude and direction. In the first strategy, an incident wave field with known amplitude and phase is considered. It is analytically shown that the zero- radiation force state (i.e., radiation force function cancellation) is achievable for specific pulsation characteristics belong to a frequency-dependent straight line equation in the plane of real-imaginary components (i.e., Nyquist Plane) of prescribed surface displacement. It is illustrated that these characteristic lines divide the mentioned displacement plane into two regions of positive (i.e., pushing) and negative (i.e., pulling) radiation forces. In the second strategy, the zero, negative and positive states of radiation force are obtained through adjusting the incident wave field characteristics (i.e., amplitude and phase) which insonifies the radiator with prescribed pulsation characteristics. It is proved that zero radiation force state occurs for incident wave pressure characteristics belong to specific frequency-dependent circles in Nyquist plane of incident wave pressure. These characteristic circles divide the Nyquist plane into two distinct regions corresponding to positive (out of circles) and negative (in the circles) values of radiation force function. It is analytically shown that the maximum amplitude of negative radiation force is exactly equal to the amplitude of the (positive) radiation force exerted upon the sphere in the passive state, by the same incident field. The developed concepts are much more deepened by considering the required power supply for distinct cases of zero, negative and positive radiation force states along with the frequency dependent asymmetry index. In addition, considering the effect of phase difference between the incident wave field and the pulsating object, and its possible variation with respect to spatial position of object, some practical points about the spatial average of generated radiation force, the optimal state of operation, the stability of zero radiation force states and the possibly of precise motion control are discussed. This work would extend the novel concept of smart carriers to and may be helpful for robust single-beam acoustic handling techniques. Furthermore, the shown capability of precise motion control may be considered as a new way toward smart acoustic driven micro-mechanisms and micro-machines. Copyright © 2017 Elsevier B.V. All rights reserved.

The structure of shock wave in a gas consisting of ideally elastic, rigid spherical molecules

NASA Technical Reports Server (NTRS)

Cheremisin, F. G.

1972-01-01

Principal approaches are examined to the theoretical study of the shock layer structure. The choice of a molecular model is discussed and three procedures are formulated. These include a numerical calculation method, solution of the kinetic relaxation equation, and solution of the Boltzmann equation.

YASEIS: Yet Another computer program to calculate synthetic SEISmograms for a spherically multi-layered Earth model

NASA Astrophysics Data System (ADS)

Ma, Yanlu

2013-04-01

Although most researches focus on the lateral heterogeneity of 3D Earth nowadays, a spherically multi-layered model where the parameters depend only on depth still represents a good first order approximation of real Earth. Such 1D models could be used as starting models for seismic tomographic inversion or as background model where the source mechanisms are inverted. The problem of wave propagation in a spherically layered model had been solved theoretically long time ago (Takeuchi and Saito, 1972). The existing computer programs such as Mineos (developed by G. Master, J. Woodhouse and F. Gilbert), Gemini (Friederich and Dalkolmo 1995), DSM (Kawai et. al. 2006) and QSSP (Wang 1999) tackled the computational aspects of the problem. A new simple and fast program for computing the Green's function of a stack of spherical dissipative layers is presented here. The analytical solutions within each homogeneous spherical layer are joined through the continuous boundary conditions and propagated from the center of model up to the level of source depth. Another solution is built by propagating downwardly from the free surface of model to the source level. The final solution is then constructed in frequency domain from the previous two solutions to satisfy the discontinuities of displacements and stresses at the source level which are required by the focal mechanism. The numerical instability in the propagator approach is solved by complementing the matrix propagating with an orthonormalization procedure (Wang 1999). Another unstable difficulty due to the high attenuation in the upper mantle low velocity zone is overcome by switching the bases of solutions from the spherical Bessel functions to the spherical Hankel functions when necessary. We compared the synthetic seismograms obtained from the new program YASEIS with those computed by Gemini and QSSP. In the range of near distances, the synthetics by a reflectivity code for the horizontally layers are also compared with those from YASEIS. Finally the static displacements in the source region are computed by choosing a very small frequency value in YASEIS which is designed for computing the dynamic response, and compared with the results in a homogeneous half-space model (Okada 1992). [1] Friederich, W. and J. Dalkolmo (1995). Complete synthetic seismograms for a spherically symmetric Earth a numerical computation of the Green's function in the frequency domain, Geophys. J. Int., vol. 122, 537-550. [2] Kawai, K., N. Takeuchi, and R.J. Geller (2006). Complete synthetic seismograms up to 2Hz for transversely isotropic spherically symmetric media, Geophys. J. Int., vol. 164, 411-424. [3] Okada, Y. (1992). Internal deformation due to shear and tensile faults in a half space, Bull. Seismol. Soc. Am., vol. 82, no. 2, 1018-1040. [4] Takeuchi, H. and M. Saito (1972). Seismic surface waves, Methods in computational physics, vol. II, 217-295. [5] Wang, R. (1999). A simple orthonormalization method for stable and efficient computation of Green's functions, Bull. Seismol. Soc. Am., vol. 89, no. 3, 733-741.

A simple approach to the joint inversion of seismic body and surface waves applied to the southwest U.S.

NASA Astrophysics Data System (ADS)

West, Michael; Gao, Wei; Grand, Stephen

2004-08-01

Body and surface wave tomography have complementary strengths when applied to regional-scale studies of the upper mantle. We present a straight-forward technique for their joint inversion which hinges on treating surface waves as horizontally-propagating rays with deep sensitivity kernels. This formulation allows surface wave phase or group measurements to be integrated directly into existing body wave tomography inversions with modest effort. We apply the joint inversion to a synthetic case and to data from the RISTRA project in the southwest U.S. The data variance reductions demonstrate that the joint inversion produces a better fit to the combined dataset, not merely a compromise. For large arrays, this method offers an improvement over augmenting body wave tomography with a one-dimensional model. The joint inversion combines the absolute velocity of a surface wave model with the high resolution afforded by body waves-both qualities that are required to understand regional-scale mantle phenomena.

Finite element solution of transient fluid-structure interaction problems

NASA Technical Reports Server (NTRS)

Everstine, Gordon C.; Cheng, Raymond S.; Hambric, Stephen A.

1991-01-01

A finite element approach using NASTRAN is developed for solving time-dependent fluid-structure interaction problems, with emphasis on the transient scattering of acoustic waves from submerged elastic structures. Finite elements are used for modeling both structure and fluid domains to facilitate the graphical display of the wave motion through both media. For the liquid, the use of velocity potential as the fundamental unknown results in a symmetric matrix equation. The approach is illustrated for the problem of transient scattering from a submerged elastic spherical shell subjected to an incident tone burst. The use of an analogy between the equations of elasticity and the wave equation of acoustics, a necessary ingredient to the procedure, is summarized.

Vector matter waves in two-component Bose-Einstein condensates with spatially modulated nonlinearities

NASA Astrophysics Data System (ADS)

Xu, Si-Liu; He, Jun-Rong; Xue, Li; Belić, Milivoj R.

2018-02-01

We demonstrate three-dimensional (3D) vector solitary waves in the coupled (3 + 1)-D nonlinear Gross-Pitaevskii equations with variable nonlinearity coefficients. The analysis is carried out in spherical coordinates, providing novel localized solutions that depend on three modal numbers, l, m, and n. Using the similarity transformation (ST) method in 3D, vector solitary waves are built with the help of a combination of harmonic and trapping potentials, including multipole solutions and necklace rings. In general, the solutions found are stable for low values of the modal numbers; for values larger than 2, the solutions are found to be unstable. Variable nonlinearity allows the utilization of soliton management methods.

Anisotropic models of the upper mantle

NASA Technical Reports Server (NTRS)

Regan, J.; Anderson, D. L.

1983-01-01

Long period Rayleigh wave and Love wave dispersion data, particularly for oceanic areas, were not simultaneously satisfied by an isotropic structure. Available phase and group velocity data are inverted by a procedure which includes the effects of transverse anisotropy, an elastic dispersion, sphericity, and gravity. The resulting models, for the average Earth, average ocean and oceanic regions divided according to the age of the ocean floor, are quite different from previous results which ignore the above effects. The models show a low velocity zone with age dependent anisotropy and velocities higher than derived in previous surface wave studies. The correspondence between the anisotropy variation with age and a physical model based on flow aligned olivine is suggested.

Conical wave propagation and diffraction in two-dimensional hexagonally packed granular lattices

DOE PAGES

Chong, C.; Kevrekidis, P. G.; Ablowitz, M. J.; ...

2016-01-25

We explore linear and nonlinear mechanisms for conical wave propagation in two-dimensional lattices in the realm of phononic crystals. As a prototypical example, a statically compressed granular lattice of spherical particles arranged in a hexagonal packing configuration is analyzed. Upon identifying the dispersion relation of the underlying linear problem, the resulting diffraction properties are considered. Analysis both via a heuristic argument for the linear propagation of a wave packet and via asymptotic analysis leading to the derivation of a Dirac system suggests the occurrence of conical diffraction. This analysis is valid for strong precompression, i.e., near the linear regime. Formore » weak precompression, conical wave propagation is still possible, but the resulting expanding circular wave front is of a nonoscillatory nature, resulting from the complex interplay among the discreteness, nonlinearity, and geometry of the packing. Lastly, the transition between these two types of propagation is explored.« less

Near-Infrared 1064 nm Laser Modulates Migratory Dendritic Cells To Augment the Immune Response to Intradermal Influenza Vaccine.

PubMed

Morse, Kaitlyn; Kimizuka, Yoshifumi; Chan, Megan P K; Shibata, Mai; Shimaoka, Yusuke; Takeuchi, Shu; Forbes, Benjamin; Nirschl, Christopher; Li, Binghao; Zeng, Yang; Bronson, Roderick T; Katagiri, Wataru; Shigeta, Ayako; Sîrbulescu, Ruxandra F; Chen, Huabiao; Tan, Rhea Y Y; Tsukada, Kosuke; Brauns, Timothy; Gelfand, Jeffrey; Sluder, Ann; Locascio, Joseph J; Poznansky, Mark C; Anandasabapathy, Niroshana; Kashiwagi, Satoshi

2017-08-15

Brief exposure of skin to near-infrared (NIR) laser light has been shown to augment the immune response to intradermal vaccination and thus act as an immunologic adjuvant. Although evidence indicates that the NIR laser adjuvant has the capacity to activate innate subsets including dendritic cells (DCs) in skin as conventional adjuvants do, the precise immunological mechanism by which the NIR laser adjuvant acts is largely unknown. In this study we sought to identify the cellular target of the NIR laser adjuvant by using an established mouse model of intradermal influenza vaccination and examining the alteration of responses resulting from genetic ablation of specific DC populations. We found that a continuous wave (CW) NIR laser adjuvant broadly modulates migratory DC (migDC) populations, specifically increasing and activating the Lang + and CD11b - Lang - subsets in skin, and that the Ab responses augmented by the CW NIR laser are dependent on DC subsets expressing CCR2 and Langerin. In comparison, a pulsed wave NIR laser adjuvant showed limited effects on the migDC subsets. Our vaccination study demonstrated that the efficacy of the CW NIR laser is significantly better than that of the pulsed wave laser, indicating that the CW NIR laser offers a desirable immunostimulatory microenvironment for migDCs. These results demonstrate the unique ability of the NIR laser adjuvant to selectively target specific migDC populations in skin depending on its parameters, and highlight the importance of optimization of laser parameters for desirable immune protection induced by an NIR laser-adjuvanted vaccine. Copyright © 2017 by The American Association of Immunologists, Inc.

Relations of Arterial Stiffness and Brachial Flow-Mediated Dilation With New-Onset Atrial Fibrillation: The Framingham Heart Study.

PubMed

Shaikh, Amir Y; Wang, Na; Yin, Xiaoyan; Larson, Martin G; Vasan, Ramachandran S; Hamburg, Naomi M; Magnani, Jared W; Ellinor, Patrick T; Lubitz, Steven A; Mitchell, Gary F; Benjamin, Emelia J; McManus, David D

2016-09-01

The relations of measures of arterial stiffness, pulsatile hemodynamic load, and endothelial dysfunction to atrial fibrillation (AF) remain poorly understood. To better understand the pathophysiology of AF, we examined associations between noninvasive measures of vascular function and new-onset AF. The study sample included participants aged ≥45 years from the Framingham Heart Study offspring and third-generation cohorts. Using Cox proportional hazards regression models, we examined relations between incident AF and tonometry measures of arterial stiffness (carotid-femoral pulse wave velocity), wave reflection (augmentation index), pressure pulsatility (central pulse pressure), endothelial function (flow-mediated dilation), resting brachial arterial diameter, and hyperemic flow. AF developed in 407/5797 participants in the tonometry sample and 270/3921 participants in the endothelial function sample during follow-up (median 7.1 years, maximum 10 years). Higher augmentation index (hazard ratio, 1.16; 95% confidence interval, 1.02-1.32; P=0.02), baseline brachial artery diameter (hazard ratio, 1.20; 95% confidence interval, 1.01-1.43; P=0.04), and lower flow-mediated dilation (hazard ratio, 0.79; 95% confidence interval, 0.63-0.99; P=0.04) were associated with increased risk of incident AF. Central pulse pressure, when adjusted for age, sex, and hypertension (hazard ratio, 1.14; 95% confidence interval, 1.02-1.28; P=0.02) was associated with incident AF. Higher pulsatile load assessed by central pulse pressure and greater apparent wave reflection measured by augmentation index were associated with increased risk of incident AF. Vascular endothelial dysfunction may precede development of AF. These measures may be additional risk factors or markers of subclinical cardiovascular disease associated with increased risk of incident AF. © 2016 American Heart Association, Inc.

Reliability of oscillometric central hemodynamic responses to an orthostatic challenge.

PubMed

Stoner, Lee; Bonner, Chantel; Credeur, Daniel; Lambrick, Danielle; Faulkner, James; Wadsworth, Daniel; Williams, Michelle A

2015-08-01

Monitoring central hemodynamic responses to an orthostatic challenge may provide important insight into autonomic nervous system function. Oscillometric pulse wave analysis devices have recently emerged, presenting clinically viable options for investigating central hemodynamic properties. The purpose of the current study was to determine whether oscillometric pulse wave analysis can be used to reliably (between-day) assess central blood pressure and central pressure augmentation (augmentation index) responses to a 5 min orthostatic challenge (modified tilt-table). Twenty healthy adults (26.4 y (SD 5.2), 55% F, 24.7 kg/m(2) (SD 3.8)) were tested on 3 different mornings in the fasted state, separated by a maximum of 7 days. Central hemodynamic variables were assessed on the left arm using an oscillometric device. Repeated measures analysis of variance indicated a significant main effect of the modified tilt-table for all central hemodynamic variables (P < 0.001). In response to the tilt, central diastolic pressure increased by 4.5 mmHg (CI: 2.6, 6.4), central systolic blood pressure increased by 2.3 (CI: 4.4, 0.16) mmHg, and augmentation index decreased by an absolute - 5.3%, (CI: -2.7, -7.9%). The intra-class correlation coefficient values for central diastolic pressure (0.83-0.86), central systolic blood pressure (0.80-0.87) and AIx (0.79-0.82) were above the 0.75 criterion in both the supine and tilted positions, indicating excellent between-day reliability. Central hemodynamic responses to an orthostatic challenge can be assessed with acceptable between-day reliability using oscillometric pulse wave analysis. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Strong scattering of short-period seismic waves by the core-mantle boundary and the P-diffracted wave

NASA Astrophysics Data System (ADS)

Bataille, Klaus; Lund, Fernando

We interpret the long-tail-in-time (up to 3 minutes) decay of short-period Pdiff as being due to multiple scattering within D″, which, for this purpose, is assumed to be an heterogeneous region with a low velocity zone just next to the core-mantle boundary. A simple multiple scattering theory, generalized for a two-dimensional spherical geometry, provides good agreement with observations for values of the scattering and attenuation coefficients (η) of about 10-3 km-1.

Theoretical investigation of resonance frequencies in long wavelength electromagnetic wave scattering process from plasma prolate and oblate spheroids placed in a dielectric layer

NASA Astrophysics Data System (ADS)

Ahmadizadeh, Y.; Jazi, B.; Abdoli-Arani, A.

2014-01-01

Response of a prolate spheroid plasma and/or an oblate spheroid plasma in presence of long wavelength electromagnetic wave has been studied. The resonance frequencies of these objects are obtained and it is found that they reduce to the resonance frequency of spherical cold plasma. Moreover, the resonant frequencies of prolate spheroid plasma and oblate spheroid plasma covered by a dielectric are investigated as well. Furthermore, their dependency on dielectric permittivity and geometry dimensions is simulated.

Universal test fixture for monolithic mm-wave integrated circuits calibrated with an augmented TRD algorithm

NASA Technical Reports Server (NTRS)

Romanofsky, Robert R.; Shalkhauser, Kurt A.

1989-01-01

The design and evaluation of a novel fixturing technique for characterizing millimeter wave solid state devices is presented. The technique utilizes a cosine-tapered ridge guide fixture and a one-tier de-embedding procedure to produce accurate and repeatable device level data. Advanced features of this technique include nondestructive testing, full waveguide bandwidth operation, universality of application, and rapid, yet repeatable, chip-level characterization. In addition, only one set of calibration standards is required regardless of the device geometry.

Body-wave traveltime and amplitude shifts from asymptotic travelling wave coupling

USGS Publications Warehouse

Pollitz, F.

2006-01-01

We explore the sensitivity of finite-frequency body-wave traveltimes and amplitudes to perturbations in 3-D seismic velocity structure relative to a spherically symmetric model. Using the approach of coupled travelling wave theory, we consider the effect of a structural perturbation on an isolated portion of the seismogram. By convolving the spectrum of the differential seismogram with the spectrum of a narrow window taper, and using a Taylor's series expansion for wavenumber as a function of frequency on a mode dispersion branch, we derive semi-analytic expressions for the sensitivity kernels. Far-field effects of wave interactions with the free surface or internal discontinuities are implicitly included, as are wave conversions upon scattering. The kernels may be computed rapidly for the purpose of structural inversions. We give examples of traveltime sensitivity kernels for regional wave propagation at 1 Hz. For the direct SV wave in a simple crustal velocity model, they are generally complicated because of interfering waves generated by interactions with the free surface and the Mohorovic??ic?? discontinuity. A large part of the interference effects may be eliminated by restricting the travelling wave basis set to those waves within a certain range of horizontal phase velocity. ?? Journal compilation ?? 2006 RAS.

Charged and uncharged vortices in quasiclassical theory

NASA Astrophysics Data System (ADS)

Masaki, Yusuke; Kato, Yusuke

2018-03-01

The charging effect of a superconducting vortex core is very important for transport properties of superconducting vortices. The chiral p-wave superconductor, known as a topological superconductor (SC), has a Majorana fermion in a vortex core and the charging effect has been studied using microscopic Bogoliubov{de Gennes (BdG) theory. According to calculations based on the BdG theory, one type of the vortex is charged as well as the vortex of the s-wave SC, while the other is uncharged. We reproduce this interesting charging effect using an augmented quasiclassical theory in chiral p-wave SCs, by which we can deal with particle-hole asymmetry in the quasiclassical approximation.

GIPAW (gauge including projected augmented wave) and local dynamics in 13C and 29Si solid state NMR: the study case of silsesquioxanes (RSiO1.5)8.

PubMed

Gervais, Christel; Bonhomme-Coury, Laure; Mauri, Francesco; Babonneau, Florence; Bonhomme, Christian

2009-08-28

Octameric silsesquioxanes (RSiO(1.5))(8) are versatile and interesting nano building blocks, suitable for the synthesis of nanocomposites with controlled porosity. In this paper, we revisit the (29)Si and (13)C solid state NMR spectroscopy for this class of materials, by using GIPAW (gauge including projected augmented wave) first principles calculations [Pickard & Mauri, Phys. Rev. B, 2001, 63, 245101]. Full tensorial data, including the chemical shift anisotropies (CSA) and the absolute orientation of the corresponding principal axes systems (PAS), were calculated. Subsequent averaging of the calculated tensors (due to fast reorientation of the R groups around the Si-C bonds) allowed for the interpretation of the strong reduction of CSA and dipolar couplings for these derivatives. Good agreement was observed between the averaged calculated data and the experimental parameters. Interesting questions related to the interplay between X-ray crystallography and solid state NMR are raised and will be emphasized.

Global excitation of wave phenomena in a dissipative multiconstituent medium. I - Transfer function of the earth's thermosphere. II - Impulsive perturbations in the earth's thermosphere

NASA Technical Reports Server (NTRS)

Mayr, H. G.; Harris, I.; Herrero, F. A.; Varosi, F.

1984-01-01

A transfer function approach is taken in constructing a spectral model of the acoustic-gravity wave response in a multiconstituent thermosphere. The model is then applied to describing the thermospheric response to various sources around the globe. Zonal spherical harmonics serve to model the horizontal variations in propagating waves which, when integrated with respect to height, generate a transfer function for a vertical source distribution in the thermosphere. Four wave components are characterized as resonance phenomena and are associated with magnetic activity and ionospheric disturbances. The waves are either trapped or propagate, the latter becoming significant when possessing frequencies above 3 cycles/day. The energy input is distributed by thermospheric winds. The disturbances decay slowly, mainly due to heat conduction and diffusion. Gravity waves appear abruptly and are connected to a sudden switching on or off of a source. Turn off of a source coincides with a reversal of the local atmospheric circulation.

Estimation of Supersonic Stage Separation Aerodynamics of Winged-Body Launch Vehicles Using Response Surface Methods

NASA Technical Reports Server (NTRS)

Erickson, Gary E.; Deloach, Richard

2008-01-01

A collection of statistical and mathematical techniques referred to as response surface methodology was used to estimate the longitudinal stage separation aerodynamic characteristics of a generic, bimese, winged multi-stage launch vehicle configuration using data obtained on small-scale models at supersonic speeds in the NASA Langley Research Center Unitary Plan Wind Tunnel. The simulated Mach 3 staging was dominated by multiple shock wave interactions between the orbiter and booster vehicles throughout the relative spatial locations of interest. This motivated a partitioning of the overall inference space into several contiguous regions within which the separation aerodynamics were presumed to be well-behaved and estimable using cuboidal and spherical central composite designs capable of fitting full second-order response functions. The primary goal was to approximate the underlying overall aerodynamic response surfaces of the booster vehicle in belly-to-belly proximity to the orbiter vehicle using relatively simple, lower-order polynomial functions that were piecewise-continuous across the full independent variable ranges of interest. The quality of fit and prediction capabilities of the empirical models were assessed in detail, and the issue of subspace boundary discontinuities was addressed. The potential benefits of augmenting the central composite designs to full third order using computer-generated D-optimality criteria were also evaluated. The usefulness of central composite designs, the subspace sizing, and the practicality of fitting low-order response functions over a partitioned inference space dominated by highly nonlinear and possibly discontinuous shock-induced aerodynamics are discussed.

Global-Scale P-Wave Tomography Designed for Accurate Prediction of Regional and Teleseismic Travel Times for Middle East Events

DTIC Science & Technology

2010-09-01

latitude-longitude grid. Building a spherical tessellation mesh involves recursive subdivision of triangular facets of an initial polyhedron (in our...of our local database at Lawrence Livermore National Laboratory (Ruppert et al. 2005) and the publicly available Engdahl-van der Hilst-Buland (EHB

Calculations of the Sound Scattering of Hyperbolic Frequency Modulated Chirped Pulses from Fluid-filled Spherical Shell Sonar Targets

DTIC Science & Technology

2010-02-01

calculated the target strength of the most intense partial wave, a quantity termed the “effective target strength” by Kaduchak and Loeffler (1998...ed., United States Naval Institute, Annapolis, 417 pp. Kaduchak, G. and Loeffler , C.M. (1998). “Relationship between material parameters and

Massive graviton geons

NASA Astrophysics Data System (ADS)

Aoki, Katsuki; Maeda, Kei-ichi; Misonoh, Yosuke; Okawa, Hirotada

2018-02-01

We find vacuum solutions such that massive gravitons are confined in a local spacetime region by their gravitational energy in asymptotically flat spacetimes in the context of the bigravity theory. We call such self-gravitating objects massive graviton geons. The basic equations can be reduced to the Schrödinger-Poisson equations with the tensor "wave function" in the Newtonian limit. We obtain a nonspherically symmetric solution with j =2 , ℓ=0 as well as a spherically symmetric solution with j =0 , ℓ=2 in this system where j is the total angular momentum quantum number and ℓ is the orbital angular momentum quantum number, respectively. The energy eigenvalue of the Schrödinger equation in the nonspherical solution is smaller than that in the spherical solution. We then study the perturbative stability of the spherical solution and find that there is an unstable mode in the quadrupole mode perturbations which may be interpreted as the transition mode to the nonspherical solution. The results suggest that the nonspherically symmetric solution is the ground state of the massive graviton geon. The massive graviton geons may decay in time due to emissions of gravitational waves but this timescale can be quite long when the massive gravitons are nonrelativistic and then the geons can be long-lived. We also argue possible prospects of the massive graviton geons: applications to the ultralight dark matter scenario, nonlinear (in)stability of the Minkowski spacetime, and a quantum transition of the spacetime.

On computing special functions in marine engineering

NASA Astrophysics Data System (ADS)

Constantinescu, E.; Bogdan, M.

2015-11-01

Important modeling applications in marine engineering conduct us to a special class of solutions for difficult differential equations with variable coefficients. In order to be able to solve and implement such models (in wave theory, in acoustics, in hydrodynamics, in electromagnetic waves, but also in many other engineering fields), it is necessary to compute so called special functions: Bessel functions, modified Bessel functions, spherical Bessel functions, Hankel functions. The aim of this paper is to develop numerical solutions in Matlab for the above mentioned special functions. Taking into account the main properties for Bessel and modified Bessel functions, we shortly present analytically solutions (where possible) in the form of series. Especially it is studied the behavior of these special functions using Matlab facilities: numerical solutions and plotting. Finally, it will be compared the behavior of the special functions and point out other directions for investigating properties of Bessel and spherical Bessel functions. The asymptotic forms of Bessel functions and modified Bessel functions allow determination of important properties of these functions. The modified Bessel functions tend to look more like decaying and growing exponentials.

Electromagnetic scattering by a uniaxial anisotropic sphere located in an off-axis Bessel beam.

PubMed

Qu, Tan; Wu, Zhen-Sen; Shang, Qing-Chao; Li, Zheng-Jun; Bai, Lu

2013-08-01

Electromagnetic scattering of a zero-order Bessel beam by an anisotropic spherical particle in the off-axis configuration is investigated. Based on the spherical vector wave functions, the expansion expression of the zero-order Bessel beam is derived, and its convergence is numerically discussed in detail. Utilizing the tangential continuity of the electromagnetic fields, the expressions of scattering coefficients are given. The effects of the conical angle of the wave vector components of the zero-order Bessel beam, the ratio of the radius of the sphere to the central spot radius of the zero-order Bessel beam, the shift of the beam waist center position along both the x and y axes, the permittivity and permeability tensor elements, and the loss of the sphere on the radar cross section (RCS) are numerically analyzed. It is revealed that the maximum RCS appears in the conical direction or neighboring direction when the sphere is illuminated by a zero-order Bessel beam. Furthermore, the RCS will decrease and the symmetry is broken with the shift of the beam waist center.

Injection of Compact Torus into the HIST spherical torus plasmas

NASA Astrophysics Data System (ADS)

Sugawara, M.; Katsumoto, S.; Kikuchi, Y.; Fukumoto, N.; Nagata, M.

2006-10-01

The three-dimensional interaction of a spheromak-like compact torus (CT) plasma with spherical torus (ST) plasmas has been experimentally studied to understand magnetic reconnection, helicity current drive, particle fuelling and Alfvén wave excitation [1]. We have examined how the sign of helicity (Co-HI and Counter-HI) of the injected CT influences on the ST plasmas on HIST [2]. The dynamics of the CT have been identified to be significantly different between the both injection cases. Time-frequency analysis shows that the fluctuation induced in the co-HI case has the maximum spectral amplitude at around 300 -- 400 kHz that may indicate the magnetic reconnection. In this case, the CT particle is released quickly at a periphery region, but on the other hand, for the counter-HI case, the CT could penetrate deeply into the core region as accompanied by Alfvén wave due to no magnetic reconnection. [1] M. Nagata, et al., Nucl. Fusion 45, 1056 (2005) [2] M. Nagata, et al., Physics of Plasmas 10, 2932 (2003)

Acoustic manipulation: Bessel beams and active carriers

NASA Astrophysics Data System (ADS)

Rajabi, Majid; Mojahed, Alireza

2017-10-01

In this paper, we address the interaction of zero-order acoustic Bessel beams as an acoustic manipulation tool, with an active spherical shell, as a carrier in drug, agent, or material delivery systems, in order to investigate the controllability of exerted acoustic radiation force as the driver. The active body is comprised of a spherical elastic shell stimulated in its monopole mode of vibrations with the same frequency as the incident wave field via an internally bonded and spatially uniformly excited piezoelectric actuator. The main aim of this work is to examine the performance of a nondiffracting and self-reconstructing zero-order Bessel beam to obtain the full manipulability condition of active carriers in comparison with the case of a plane wave field. The results unveil some unique potentials of the Bessel beams in the company of active carriers, with emphasis on the consumed power of the actuation system. This paper will widen the path toward the single-beam robust acoustic manipulation techniques and may lead to the prospect of combined tweezers and fields, with applications in delivery systems, microswimmers, and trapper designs.

On the generation of tangential ground motion by underground explosions in jointed rocks

NASA Astrophysics Data System (ADS)

Vorobiev, Oleg; Ezzedine, Souheil; Antoun, Tarabay; Glenn, Lewis

2015-03-01

This paper describes computational studies of tangential ground motions generated by spherical explosions in a heavily jointed granite formation. Various factors affecting the shear wave generation are considered, including joint spacing, orientation and frictional properties. Simulations are performed both in 2-D for a single joint set to elucidate the basic response mechanisms, and in 3-D for multiple joint sets to realistically represent in situ conditions in a realistic geological setting. The joints are modelled explicitly using both contact elements and weakness planes in the material. Simulations are performed both deterministically and stochastically to quantify the effects of geological uncertainties on near field ground motions. The mechanical properties of the rock and the joints as well as the joint spacing and orientation are taken from experimental test data and geophysical logs corresponding to the Climax Stock granitic outcrop, which is the geological setting of the source physics experiment (SPE). Agreement between simulation results and near field wave motion data from SPE enables newfound understanding of the origin and extent of non-spherical motions associated with underground explosions in fractured geological media.

Second-harmonic generation from a thin spherical layer and No-generation conditions

NASA Astrophysics Data System (ADS)

Kapshai, V. N.; Shamyna, A. A.

2017-09-01

In the Rayleigh-Gans-Debye approximation, we solve the problem of second-harmonic generation by an elliptically polarized electromagnetic wave incident on the surface of a spherical particle that is coated by an optically nonlinear layer and is placed in a dielectric. The formulas obtained characterize the spatial distribution of the electric field of the second harmonic in the far-field zone. The most general form of the second-order dielectric susceptibility tensor is considered, which contains four independent components, with three of them being nonchiral and one, chiral. Consistency and inconsistencies between the obtained solution and formulas from works of other authors are found. We analyze the directivity patterns that characterize the spatial distribution of the generated radiation for the nonchiral layer and their dependences on the anisotropy and ellipticity coefficients of the incident wave. It is found that, with increasing radius of the nonlinear layer, the generated radiation becomes more directional. Combinations of parameters for which no radiation is generated are revealed. Based on this, we propose methods for experimental determination of the anisotropy coefficients.

Radiation torque on an absorptive spherical drop centered on an acoustic helicoidal Bessel beam

NASA Astrophysics Data System (ADS)

Zhang, Likun; Marston, Philip L.

2009-11-01

Circularly polarized electromagnetic waves carry axial angular momentum and analysis shows that the axial radiation torque on an illuminated sphere is proportional to the power absorbed by the sphere [1]. Helicoidal acoustic beams also carry axial angular momentum and absorption of such a beam should also produce an axial radiation torque [2]. In the present work the acoustic radiation torque on solid spheres and spherical drops centered on acoustic helicoidal Bessel beams is examined. The torque is predicted to be proportional to the ratio of the absorbed power to the acoustic frequency. Depending on the beam helicity, the torque is parallel or anti-parallel to the beam axis. The analysis uses a relation between the scattering and the partial wave coefficients for a sphere in a helicoidal Bessel beam. Calculations suggest that beams with a low topological charge are more efficient for generating torques on solid spheres.[4pt] [1] P. L. Marston and J. H. Crichton, Phys. Rev. A. 30, 2508-2516 (1984).[0pt] [2] B. T. Hefner and P. L. Marston, J. Acoust. Soc. Am. 106, 3313-3316 (1999).

Assessment of central haemomodynamics from a brachial cuff in a community setting

PubMed Central

2012-01-01

Background Large artery stiffening and wave reflections are independent predictors of adverse events. To date, their assessment has been limited to specialised techniques and settings. A new, more practical method allowing assessment of central blood pressure from waveforms recorded using a conventional automated oscillometric monitor has recently been validated in laboratory settings. However, the feasibility of this method in a community based setting has not been assessed. Methods One-off peripheral and central haemodynamic (systolic and diastolic blood pressure (BP) and pulse pressure) and wave reflection parameters (augmentation pressure (AP) and index, AIx) were obtained from 1,903 volunteers in an Austrian community setting using a transfer-function like method (ARCSolver algorithm) and from waveforms recorded with a regular oscillometric cuff. We assessed these parameters for known differences and associations according to gender and age deciles from <30 years to >80 years in the whole population and a subset with a systolic BP < 140 mmHg. Results We obtained 1,793 measures of peripheral and central BP, PP and augmentation parameters. Age and gender associations with central haemodynamic and augmentation parameters reflected those previously established from reference standard non-invasive techniques under specialised settings. Findings were the same for patients with a systolic BP below 140 mmHg (i.e. normotensive). Lower values for AIx in the current study are possibly due to differences in sampling rates, detection frequency and/or averaging procedures and to lower numbers of volunteers in younger age groups. Conclusion A novel transfer-function like algorithm, using brachial cuff-based waveform recordings, provides robust and feasible estimates of central systolic pressure and augmentation in community-based settings. PMID:22734820

A Geophysical Flow Experiment in a Compressible Critical Fluid

NASA Technical Reports Server (NTRS)

Hegseth, John; Garcia, Laudelino

1996-01-01

The first objective of this experiment is to build an experimental system in which, in analogy to a geophysical system, a compressible fluid in a spherical annulus becomes radially stratified in density through an A.C. electric field. When this density gradient is demonstrated, the system will be augmented so that the fluid can be driven by heating and rotation and tested in preparation for a microgravity experiment. This apparatus consists of a spherical capacitor filled with critical fluid in a temperature controlled environment. To make the fluid critical, the apparatus will be operated near the critical pressure, critical density, and critical temperature of the fluid. This will result in a highly compressible fluid because of the properties of the fluid near its critical point. A high voltage A.C. source applied across the capacitor will create a spherically symmetric central force because of the dielectric properties of the fluid in an electric field gradient. This central force will induce a spherically symmetric density gradient that is analogous to a geophysical fluid system. To generate such a density gradient the system must be small (approx. 1 inch diameter). This small cell will also be capable of driving the critical fluid by heating and rotation. Since a spherically symmetric density gradient can only be made in microgravity, another small cell, of the same geometry, will be built that uses incompressible fluid. The driving of the fluid by rotation and heating in these small cells will be developed. The resulting instabilities from the driving in these two systems will then be studied. The second objective is to study the pattern forming instabilities (bifurcations) resulting from the well controlled experimental conditions in the critical fluid cell. This experiment will come close to producing conditions that are geophysically similar and will be studied as the driving parameters are changed.

Nonlinear hydrodynamic stability and transition; Proceedings of the IUTAM Symposium, Nice, France, Sept. 3-7, 1990

NASA Astrophysics Data System (ADS)

Theoretical and experimental research on nonlinear hydrodynamic stability and transition is presented. Bifurcations, amplitude equations, pattern in experiments, and shear flows are considered. Particular attention is given to bifurcations of plane viscous fluid flow and transition to turbulence, chaotic traveling wave covection, chaotic behavior of parametrically excited surface waves in square geometry, amplitude analysis of the Swift-Hohenberg equation, traveling wave convection in finite containers, focus instability in axisymmetric Rayleigh-Benard convection, scaling and pattern formation in flowing sand, dynamical behavior of instabilities in spherical gap flows, and nonlinear short-wavelength Taylor vortices. Also discussed are stability of a flow past a two-dimensional grid, inertia wave breakdown in a precessing fluid, flow-induced instabilities in directional solidification, structure and dynamical properties of convection in binary fluid mixtures, and instability competition for convecting superfluid mixtures.

The transmission or scattering of elastic waves by an inhomogeneity of simple geometry: A comparison of theories

NASA Technical Reports Server (NTRS)

Sheu, Y. C.; Fu, L. S.

1982-01-01

The extended method of equivalent inclusion developed is applied to study the specific wave problems of the transmission of elastic waves in an infinite medium containing a layer of inhomogeneity, and of the scattering of elastic waves in an infinite medium containing a perfect spherical inhomogeneity. The eigenstrains are expanded as a geometric series and the method of integration for the inhomogeneous Helmholtz operator given by Fu and Mura is adopted. The results obtained by using a limited number of terms in the eigenstrain expansion are compared with exact solutions for the layer problem and for a perfect sphere. Two parameters are singled out for this comparison: the ratio of elastic moduli, and the ratio of the mass densities. General trends for three different situations are shown.

A multiple scattering theory for EM wave propagation in a dense random medium

NASA Technical Reports Server (NTRS)

Karam, M. A.; Fung, A. K.; Wong, K. W.

1985-01-01

For a dense medium of randomly distributed scatterers an integral formulation for the total coherent field has been developed. This formulation accounts for the multiple scattering of electromagnetic waves including both the twoand three-particle terms. It is shown that under the Markovian assumption the total coherent field and the effective field have the same effective wave number. As an illustration of this theory, the effective wave number and the extinction coefficient are derived in terms of the polarizability tensor and the pair distribution function for randomly distributed small spherical scatterers. It is found that the contribution of the three-particle term increases with the particle size, the volume fraction, the frequency and the permittivity of the particle. This increase is more significant with frequency and particle size than with other parameters.

Elastic Parameters of West Bohemian Granites under Hydrostatic Pressure

NASA Astrophysics Data System (ADS)

Pros, Z.; Lokajíček, T.; Přikryl, R.; Špičák, A.; Vajdová, V.; Klíma, K.

The West Bohemian seismoactive region is situated near the contact of the Moldanu bian, Bohemian and Saxothuringian units in which a large volume is occupied by granitoid massifs. The spatial distribution of P-wave velocities and the rock fabric of five representative samples from these massifs were studied. The P-wave velocities were measured on spherical samples in 132 independent directions under hydrostatic pressure up to 400 MPa, using the pulse-transmission method. The pressure of 400 MPa corresponds to a depth of about 15 km in the area under study. The changes of P-wave velocity were correlated with the preferred orientations of the main rock fabric elements, i.e., rock forming minerals and microcracks. The values of the P-wave velocity from laboratory measurements on granite samples fit the velocity model used by seismologists in the West Bohemian seismoactive region.

MLFMA-accelerated Nyström method for ultrasonic scattering - Numerical results and experimental validation

NASA Astrophysics Data System (ADS)

Gurrala, Praveen; Downs, Andrew; Chen, Kun; Song, Jiming; Roberts, Ron

2018-04-01

Full wave scattering models for ultrasonic waves are necessary for the accurate prediction of voltage signals received from complex defects/flaws in practical nondestructive evaluation (NDE) measurements. We propose the high-order Nyström method accelerated by the multilevel fast multipole algorithm (MLFMA) as an improvement to the state-of-the-art full-wave scattering models that are based on boundary integral equations. We present numerical results demonstrating improvements in simulation time and memory requirement. Particularly, we demonstrate the need for higher order geom-etry and field approximation in modeling NDE measurements. Also, we illustrate the importance of full-wave scattering models using experimental pulse-echo data from a spherical inclusion in a solid, which cannot be modeled accurately by approximation-based scattering models such as the Kirchhoff approximation.

The Acceleration of Charged Particles at a Spherical Shock Moving through an Irregular Magnetic Field

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

Giacalone, J.

We investigate the physics of charged-particle acceleration at spherical shocks moving into a uniform plasma containing a turbulent magnetic field with a uniform mean. This has applications to particle acceleration at astrophysical shocks, most notably, to supernovae blast waves. We numerically integrate the equations of motion of a large number of test protons moving under the influence of electric and magnetic fields determined from a kinematically defined plasma flow associated with a radially propagating blast wave. Distribution functions are determined from the positions and velocities of the protons. The unshocked plasma contains a magnetic field with a uniform mean andmore » an irregular component having a Kolmogorov-like power spectrum. The field inside the blast wave is determined from Maxwell’s equations. The angle between the average magnetic field and unit normal to the shock varies with position along its surface. It is quasi-perpendicular to the unit normal near the sphere’s equator, and quasi-parallel to it near the poles. We find that the highest intensities of particles, accelerated by the shock, are at the poles of the blast wave. The particles “collect” at the poles as they approximately adhere to magnetic field lines that move poleward from their initial encounter with the shock at the equator, as the shock expands. The field lines at the poles have been connected to the shock the longest. We also find that the highest-energy protons are initially accelerated near the equator or near the quasi-perpendicular portion of the shock, where the acceleration is more rapid.« less

Acoustic wave simulation using an overset grid for the global monitoring system

NASA Astrophysics Data System (ADS)

Kushida, N.; Le Bras, R.

2017-12-01

The International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) has been monitoring hydro-acoustic and infrasound waves over the globe. Because of the complex natures of the oceans and the atmosphere, computer simulation can play an important role in understanding the observed signals. In this regard, methods which depend on partial differential equations and require minimum modelling, are preferable. So far, to our best knowledge, acoustic wave propagation simulations based on partial differential equations on such a large scale have not been performed (pp 147 - 161 of ref [1], [2]). The main difficulties in building such simulation codes are: (1) considering the inhomogeneity of medium including background flows, (2) high aspect ratio of computational domain, (3) stability during long time integration. To overcome these difficulties, we employ a two-dimensional finite different (FDM) scheme on spherical coordinates with the Yin-Yang overset grid[3] solving the governing equation of acoustic waves introduces by Ostashev et. al.[4]. The comparison with real recording examples in hydro-acoustic will be presented at the conference. [1] Paul C. Etter: Underwater Acoustic Modeling and Simulation, Fourth Edition, CRC Press, 2013. [2] LIAN WANG et. al.: REVIEW OF UNDERWATER ACOUSTIC PROPAGATION MODELS, NPL Report AC 12, 2014. [3] A. Kageyama and T. Sato: "Yin-Yang grid": An overset grid in spherical geometry, Geochem. Geophys. Geosyst., 5, Q09005, 2004. [4] Vladimir E. Ostashev et. al: Equations for finite-difference, time-domain simulation of sound propagation in moving inhomogeneous media and numerical implementation, Acoustical Society of America. DOI: 10.1121/1.1841531, 2005.

Magnetogasdynamic spherical shock wave in a non-ideal gas under gravitational field with conductive and radiative heat fluxes

NASA Astrophysics Data System (ADS)

Nath, G.; Vishwakarma, J. P.

2016-11-01

Similarity solutions are obtained for the flow behind a spherical shock wave in a non-ideal gas under gravitational field with conductive and radiative heat fluxes, in the presence of a spatially decreasing azimuthal magnetic field. The shock wave is driven by a piston moving with time according to power law. The radiation is considered to be of the diffusion type for an optically thick grey gas model and the heat conduction is expressed in terms of Fourier's law for heat conduction. Similarity solutions exist only when the surrounding medium is of constant density. The gas is assumed to have infinite electrical conductivity and to obey a simplified van der Waals equation of state. It is shown that an increase of the gravitational parameter or the Alfven-Mach number or the parameter of the non-idealness of the gas decreases the compressibility of the gas in the flow-field behind the shock, and hence there is a decrease in the shock strength. The pressure and density vanish at the inner surface (piston) and hence a vacuum is formed at the center of symmetry. The shock waves in conducting non-ideal gas under gravitational field with conductive and radiative heat fluxes can be important for description of shocks in supernova explosions, in the study of a flare produced shock in the solar wind, central part of star burst galaxies, nuclear explosion etc. The solutions obtained can be used to interpret measurements carried out by space craft in the solar wind and in neighborhood of the Earth's magnetosphere.

A hybrid-drive nonisobaric-ignition scheme for inertial confinement fusion

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

He, X. T., E-mail: xthe@iapcm.ac.cn; Center for Applied Physics and Technology, HEDPS, Peking University, Beijing 100871; IFSA Collaborative Innovation Center of MoE, Shanghai Jiao-Tong University, Shanghai 200240

A new hybrid-drive (HD) nonisobaric ignition scheme of inertial confinement fusion (ICF) is proposed, in which a HD pressure to drive implosion dynamics increases via increasing density rather than temperature in the conventional indirect drive (ID) and direct drive (DD) approaches. In this HD (combination of ID and DD) scheme, an assembled target of a spherical hohlraum and a layered deuterium-tritium capsule inside is used. The ID lasers first drive the shock to perform a spherical symmetry implosion and produce a large-scale corona plasma. Then, the DD lasers, whose critical surface in ID corona plasma is far from the radiationmore » ablation front, drive a supersonic electron thermal wave, which slows down to a high-pressure electron compression wave, like a snowplow, piling up the corona plasma into high density and forming a HD pressurized plateau with a large width. The HD pressure is several times the conventional ID and DD ablation pressure and launches an enhanced precursor shock and a continuous compression wave, which give rise to the HD capsule implosion dynamics in a large implosion velocity. The hydrodynamic instabilities at imploding capsule interfaces are suppressed, and the continuous HD compression wave provides main pdV work large enough to hotspot, resulting in the HD nonisobaric ignition. The ignition condition and target design based on this scheme are given theoretically and by numerical simulations. It shows that the novel scheme can significantly suppress implosion asymmetry and hydrodynamic instabilities of current isobaric hotspot ignition design, and a high-gain ICF is promising.« less

Sound wave generation by a spherically symmetric outburst and AGN feedback in galaxy clusters

NASA Astrophysics Data System (ADS)

Tang, Xiaping; Churazov, Eugene

2017-07-01

We consider the evolution of an outburst in a uniform medium under spherical symmetry, having in mind active galactic nucleus feedback in the intracluster medium. For a given density and pressure of the medium, the spatial structure and energy partition at a given time tage (since the onset of the outburst) are fully determined by the total injected energy Einj and the duration tb of the outburst. We are particularly interested in the late phase evolution when the strong shock transforms into a sound wave. We studied the energy partition during such transition with different combinations of Einj and tb. For an instantaneous outburst with tb → 0, which corresponds to the extension of classic Sedov-Taylor solution with counter-pressure, the fraction of energy that can be carried away by sound waves is ≲12 per cent of Einj. As tb increases, the solution approaches the 'slow piston' limit, with the fraction of energy in sound waves approaching zero. We then repeat the simulations using radial density and temperature profiles measured in Perseus and M87/Virgo clusters. We find that the results with a uniform medium broadly reproduce an outburst in more realistic conditions once proper scaling is applied. We also develop techniques to map intrinsic properties of an outburst (Einj, tb and tage) to the observables like the Mach number of the shock and radii of the shock and ejecta. For the Perseus cluster and M87, the estimated (Einj, tb and tage) agree with numerical simulations tailored for these objects with 20-30 per cent accuracy.

Three-dimensional liquid flattened Luneburg lens with ultra-wide viewing angle and frequency band

NASA Astrophysics Data System (ADS)

Wu, Lingling; Tian, Xiaoyong; Yin, Ming; Li, Dichen; Tang, Yiping

2013-08-01

Traditional Luneburg lens is a dielectric spherical antenna. It can focus the incoming collimated electromagnetic waves on its spherical surface, which causes the incompatibility with the planar feeding and receiving devices. Furthermore, the difficulties in the fabrication process also limited its applications. In this paper, a three-dimensional flattened Luneburg lens with a field-of-view angle up to 180° has been realized based on a liquid medium approach and a 3D-printing process. The fabricated three-dimensional lens showed a broadband transmission characteristic from 12.4 GHz to 18 GHz. The performance of the proposed lens was demonstrated by simulation and experimental results.

Embedded Spherical Localization for Micro Underwater Vehicles Based on Attenuation of Electro-Magnetic Carrier Signals

PubMed Central

Duecker, Daniel-André; Geist, A. René; Hengeler, Michael; Kreuzer, Edwin; Pick, Marc-André; Rausch, Viktor; Solowjow, Eugen

2017-01-01

Self-localization is one of the most challenging problems for deploying micro autonomous underwater vehicles (μAUV) in confined underwater environments. This paper extends a recently-developed self-localization method that is based on the attenuation of electro-magnetic waves, to the μAUV domain. We demonstrate a compact, low-cost architecture that is able to perform all signal processing steps present in the original method. The system is passive with one-way signal transmission and scales to possibly large μAUV fleets. It is based on the spherical localization concept. We present results from static and dynamic position estimation experiments and discuss the tradeoffs of the system. PMID:28445419

On the determination of the electromagnetic field upon scattering by a small inhomogeneous spherical object

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

Shalashov, A. G., E-mail: ags@appl.sci-nnov.ru; Gospodchikov, E. D.

An efficient and fairly simple method of solving the problem of the incidence of a plane electromagnetic wave on an inhomogeneous object with specified spherically symmetric distributions of its electric permittivity and magnetic permeability is presented. The fields inside the object and the integrated scattering and absorption cross sections are found by assuming the object to be small compared to the vacuum wavelength. Since no constraints are imposed on the scales of the fields inside the object, the method is suitable for investigating complex cases, including those associated with the local amplification and absorption of the electromagnetic field in inhomogeneousmore » resonant media.« less

[Acoustic Levitation Methods and Apparatus

NASA Technical Reports Server (NTRS)

Barmatz, M. B.; Jacobi, N. (Inventor)

1982-01-01

Methods are described for acoustically levitating objects within chambers of spherical and cylindrical shape. The wavelengths for chambers of particular dimensions are given, for generating standing wave patterns of any of a variety of modes within the chambers. For a spherical chamber the lowest resonant mode is excited by applying a wavelength of 3.02R, where R is the chamber radius. The two lowest pure radial modes for that chamber, are excited by applying wavelengths of 1.40R and 0.814R. For a cylindrical chamber of radius R, the lowest mode is at a wavelength of 3.41R, and the lowest pure radial modes are at wavelengths of 1.64R and 0.896R.

Embedded Spherical Localization for Micro Underwater Vehicles Based on Attenuation of Electro-Magnetic Carrier Signals.

PubMed

Duecker, Daniel-André; Geist, A René; Hengeler, Michael; Kreuzer, Edwin; Pick, Marc-André; Rausch, Viktor; Solowjow, Eugen

2017-04-26

Self-localization is one of the most challenging problems for deploying micro autonomous underwater vehicles ( μ AUV) in confined underwater environments. This paper extends a recently-developed self-localization method that is based on the attenuation of electro-magnetic waves, to the μ AUV domain. We demonstrate a compact, low-cost architecture that is able to perform all signal processing steps present in the original method. The system is passive with one-way signal transmission and scales to possibly large μ AUV fleets. It is based on the spherical localization concept. We present results from static and dynamic position estimation experiments and discuss the tradeoffs of the system.

Morphology of ductile metals eroded by a jet of spherical particles impinging at normal incidence

NASA Technical Reports Server (NTRS)

Veerabhadra Rao, P.; Young, S. G.; Buckley, D. H.

1983-01-01

Scanning electron microscopy and energy-dispersive X-ray spectroscopy are used, together with surface profile measurements, in the present morphological study of the erosion of an aluminum alloy and copper by the normal impact of spherical glass erodent particles. The morphology of the damage pattern is a manifestation of the flow pattern of erodent particles, and yields insight into the mechanisms that may be active at different stages of erosion. The simultaneous appearance of radial cracks and concentric rings is reported, together with wave crests which contain an accumulation of metallic flakes. A preliminary analysis is advanced to explain the formation of the various damage patterns observed.

Scattering theory derivation of a 3D acoustic cloaking shell.

PubMed

Cummer, Steven A; Popa, Bogdan-Ioan; Schurig, David; Smith, David R; Pendry, John; Rahm, Marco; Starr, Anthony

2008-01-18

Through acoustic scattering theory we derive the mass density and bulk modulus of a spherical shell that can eliminate scattering from an arbitrary object in the interior of the shell--in other words, a 3D acoustic cloaking shell. Calculations confirm that the pressure and velocity fields are smoothly bent and excluded from the central region as for previously reported electromagnetic cloaking shells. The shell requires an anisotropic mass density with principal axes in the spherical coordinate directions and a radially dependent bulk modulus. The existence of this 3D cloaking shell indicates that such reflectionless solutions may also exist for other wave systems that are not isomorphic with electromagnetics.

Analytical study of the effects of clouds on the light produced by lightning

NASA Technical Reports Server (NTRS)

Phanord, Dieudonne D.

1990-01-01

Researchers consider the scattering of visible and infrared light due to lightning by cubic, cylindrical and spherical clouds. The researchers extend to cloud physics the work by Twersky for single and multiple scattering of electromagnetic waves. They solve the interior problem separately to obtain the bulk parameters for the scatterer equivalent to the ensemble of spherical droplets. With the interior solution or the equivalent medium approach, the multiple scattering problem is reduced to that of a single scatterer in isolation. Hence, the computing methods of Wiscombe or Bohren specialized to Mie scattering with the possibility for absorption were used to generate numerical results in short computer time.

Asymptotic behavior and interpretation of virtual states: The effects of confinement and of basis sets

NASA Astrophysics Data System (ADS)

Boffi, Nicholas M.; Jain, Manish; Natan, Amir

2016-02-01

A real-space high order finite difference method is used to analyze the effect of spherical domain size on the Hartree-Fock (and density functional theory) virtual eigenstates. We show the domain size dependence of both positive and negative virtual eigenvalues of the Hartree-Fock equations for small molecules. We demonstrate that positive states behave like a particle in spherical well and show how they approach zero. For the negative eigenstates, we show that large domains are needed to get the correct eigenvalues. We compare our results to those of Gaussian basis sets and draw some conclusions for real-space, basis-sets, and plane-waves calculations.

Invisible waves and hidden realms: augmented reality and experimental art

NASA Astrophysics Data System (ADS)

Ruzanka, Silvia

2012-03-01

Augmented reality is way of both altering the visible and revealing the invisible. It offers new opportunities for artistic exploration through virtual interventions in real space. In this paper, the author describes the implementation of two art installations using different AR technologies, one using optical marker tracking on mobile devices and one integrating stereoscopic projections into the physical environment. The first artwork, De Ondas y Abejas (The Waves and the Bees), is based on the widely publicized (but unproven) hypothesis of a link between cellphone radiation and the phenomenon of bee colony collapse disorder. Using an Android tablet, viewers search out small fiducial markers in the shape of electromagnetic waves hidden throughout the gallery, which reveal swarms of bees scattered on the floor. The piece also creates a generative soundscape based on electromagnetic fields. The second artwork, Urban Fauna, is a series of animations in which features of the urban landscape become plants and animals. Surveillance cameras become flocks of birds while miniature cellphone towers, lampposts, and telephone poles grow like small seedlings in time-lapse animation. The animations are presented as small stereoscopic projections, integrated into the physical space of the gallery. These two pieces explore the relationship between nature and technology through the visualization of invisible forces and hidden alternate realities.

Wave Propagation in Non-Stationary Statistical Mantle Models at the Global Scale

NASA Astrophysics Data System (ADS)

Meschede, M.; Romanowicz, B. A.

2014-12-01

We study the effect of statistically distributed heterogeneities that are smaller than the resolution of current tomographic models on seismic waves that propagate through the Earth's mantle at teleseismic distances. Current global tomographic models are missing small-scale structure as evidenced by the failure of even accurate numerical synthetics to explain enhanced coda in observed body and surface waveforms. One way to characterize small scale heterogeneity is to construct random models and confront observed coda waveforms with predictions from these models. Statistical studies of the coda typically rely on models with simplified isotropic and stationary correlation functions in Cartesian geometries. We show how to construct more complex random models for the mantle that can account for arbitrary non-stationary and anisotropic correlation functions as well as for complex geometries. Although this method is computationally heavy, model characteristics such as translational, cylindrical or spherical symmetries can be used to greatly reduce the complexity such that this method becomes practical. With this approach, we can create 3D models of the full spherical Earth that can be radially anisotropic, i.e. with different horizontal and radial correlation functions, and radially non-stationary, i.e. with radially varying model power and correlation functions. Both of these features are crucial for a statistical description of the mantle in which structure depends to first order on the spherical geometry of the Earth. We combine different random model realizations of S velocity with current global tomographic models that are robust at long wavelengths (e.g. Meschede and Romanowicz, 2014, GJI submitted), and compute the effects of these hybrid models on the wavefield with a spectral element code (SPECFEM3D_GLOBE). We finally analyze the resulting coda waves for our model selection and compare our computations with observations. Based on these observations, we make predictions about the strength of unresolved small-scale structure and extrinsic attenuation.

Measurements and modeling of acoustic scattering from partially and completely buried spherical shells

NASA Astrophysics Data System (ADS)

Tesei, A.; Maguer, A.; Fox, W. L. J.; Lim, R.; Schmidt, H.

2002-11-01

The use of low-frequency sonars (2-15 kHz) is explored to better exploit scattering features of buried targets that can contribute to their detection and classification. Compared to conventional mine countermeasure sonars, sound penetrates better into the sediment at these frequencies, and the excitation of structural waves in the targets is enhanced. The main contributions to target echo are the specular reflection, geometric diffraction effects, and the structural response, with the latter being particularly important for man-made elastic objects possessing particular symmetries such as bodies of revolution. The resonance response derives from elastic periodic phenomena such as surface circumferential waves revolving around the target. The GOATS'98 experiment, conducted jointly by SACLANTCEN and MIT off the island of Elba, involved controlled monostatic measurements of scattering by spherical shells which were partially and completely buried in sand, and suspended in the water column. The analysis mainly addresses a study of the effect of burial on the dynamics of backscattered elastic waves, which can be clearly identified in the target responses, and is based on the comparison of measurements with appropriate scattering models. Data interpretation results are in good agreement with theory. This positive result demonstrates the applicability of low-frequency methodologies based on resonance analysis to the classification of buried objects. copyright 2002 Acoustical Society of America.

Capillary waves with surface viscosity

NASA Astrophysics Data System (ADS)

Shen, Li; Denner, Fabian; Morgan, Neal; van Wachem, Berend; Dini, Daniele

2017-11-01

Experiments over the last 50 years have suggested a correlation between the surface (shear) viscosity and the stability of a foam or emulsion. With recent techniques allowing more accurate measurements of the elusive surface viscosity, we examine this link theoretically using small-amplitude capillary waves in the presence of the Marangoni effect and surface viscosity modelled via the Boussinesq-Scriven model. The surface viscosity effect is found to contribute a damping effect on the amplitude of the capillary wave with subtle differences to the effect of the convective-diffusive Marangoni transport. The general wave dispersion is augmented to take into account the Marangoni and surface viscosity effects, and a first-order correction to the critical damping wavelength is derived. The authors acknowledge the financial support of the Shell University Technology Centre for fuels and lubricants.

Irreversible transport in the stratosphere by internal waves of short vertical wavelength

NASA Technical Reports Server (NTRS)

Danielsen, Edwin F.; Hipskind, R. S.; Starr, Walter L.; Vedder, James F.; Gaines, Steven E.; Kley, Dieter; Kelley, Ken K.

1991-01-01

Measurements performed during stratospheric flights of the U-2 aircraft confirm that cross-jet transport is dominated by waves, not by large-scale circulations. Monotonic gradients of trace constituents normal to the jet axis, with upper stratospheric tracers increasing poleward and tropospheric tracers increasing equatorward, are augmented by large-scale confluence as the jet intensifies during cyclogenesis. These gradients are rotated, intensified, and significantly increased in areas as their mixing ratio surfaces are folded by the differential transport of a very low frequency transverse wave. The quasi-horizontal transport produces a laminar structure with stable layers rich in upper stratospheric tracers alternating vertically with less stable layers rich in tropospheric tracers. The transport proceeds toward irreversibility at higher frequency, shear-gravity waves extend the folding to smaller horizontal scales.

Search for gravitational waves associated with the August 2006 timing glitch of the Vela pulsar

NASA Astrophysics Data System (ADS)

Abadie, J.; Abbott, B. P.; Abbott, R.; Adhikari, R.; Ajith, P.; Allen, B.; Allen, G.; Amador Ceron, E.; Amin, R. S.; Anderson, S. B.; Anderson, W. G.; Arain, M. A.; Araya, M.; Aso, Y.; Aston, S.; Aufmuth, P.; Aulbert, C.; Babak, S.; Baker, P.; Ballmer, S.; Barker, D.; Barr, B.; Barriga, P.; Barsotti, L.; Barton, M. A.; Bartos, I.; Bassiri, R.; Bastarrika, M.; Behnke, B.; Benacquista, M.; Bennett, M. F.; Betzwieser, J.; Beyersdorf, P. T.; Bilenko, I. A.; Billingsley, G.; Biswas, R.; Black, E.; Blackburn, J. K.; Blackburn, L.; Blair, D.; Bland, B.; Bock, O.; Bodiya, T. P.; Bondarescu, R.; Bork, R.; Born, M.; Bose, S.; Brady, P. R.; Braginsky, V. B.; Brau, J. E.; Breyer, J.; Bridges, D. O.; Brinkmann, M.; Britzger, M.; Brooks, A. F.; Brown, D. A.; Bullington, A.; Buonanno, A.; Burmeister, O.; Byer, R. L.; Cadonati, L.; Cain, J.; Camp, J. B.; Cannizzo, J.; Cannon, K. C.; Cao, J.; Capano, C.; Cardenas, L.; Caudill, S.; Cavaglià, M.; Cepeda, C.; Chalermsongsak, T.; Chalkley, E.; Charlton, P.; Chatterji, S.; Chelkowski, S.; Chen, Y.; Christensen, N.; Chua, S. S. Y.; Chung, C. T. Y.; Clark, D.; Clark, J.; Clayton, J. H.; Conte, R.; Cook, D.; Corbitt, T. R. C.; Cornish, N.; Coward, D.; Coyne, D. C.; Creighton, J. D. E.; Creighton, T. D.; Cruise, A. M.; Culter, R. M.; Cumming, A.; Cunningham, L.; Dahl, K.; Danilishin, S. L.; Danzmann, K.; Daudert, B.; Davies, G.; Daw, E. J.; Dayanga, T.; Debra, D.; Degallaix, J.; Dergachev, V.; Desalvo, R.; Dhurandhar, S.; Díaz, M.; Donovan, F.; Dooley, K. L.; Doomes, E. E.; Drever, R. W. P.; Driggers, J.; Dueck, J.; Duke, I.; Dumas, J.-C.; Edgar, M.; Edwards, M.; Effler, A.; Ehrens, P.; Etzel, T.; Evans, M.; Evans, T.; Fairhurst, S.; Faltas, Y.; Fan, Y.; Fazi, D.; Fehrmann, H.; Finn, L. S.; Flasch, K.; Foley, S.; Forrest, C.; Fotopoulos, N.; Frede, M.; Frei, M.; Frei, Z.; Freise, A.; Frey, R.; Fricke, T. T.; Friedrich, D.; Fritschel, P.; Frolov, V. V.; Fulda, P.; Fyffe, M.; Garofoli, J. A.; Ghosh, S.; Giaime, J. A.; Giampanis, S.; Giardina, K. D.; Goetz, E.; Goggin, L. M.; González, G.; Goßler, S.; Grant, A.; Gras, S.; Gray, C.; Greenhalgh, R. J. S.; Gretarsson, A. M.; Grosso, R.; Grote, H.; Grunewald, S.; Gustafson, E. K.; Gustafson, R.; Hage, B.; Hallam, J. M.; Hammer, D.; Hammond, G. D.; Hanna, C.; Hanson, J.; Harms, J.; Harry, G. M.; Harry, I. W.; Harstad, E. D.; Haughian, K.; Hayama, K.; Hayler, T.; Heefner, J.; Heng, I. S.; Heptonstall, A.; Hewitson, M.; Hild, S.; Hirose, E.; Hoak, D.; Hodge, K. A.; Holt, K.; Hosken, D. J.; Hough, J.; Howell, E.; Hoyland, D.; Hughey, B.; Husa, S.; Huttner, S. H.; Ingram, D. R.; Isogai, T.; Ivanov, A.; Johnson, W. W.; Jones, D. I.; Jones, G.; Jones, R.; Ju, L.; Kalmus, P.; Kalogera, V.; Kandhasamy, S.; Kanner, J.; Katsavounidis, E.; Kawabe, K.; Kawamura, S.; Kawazoe, F.; Kells, W.; Keppel, D. G.; Khalaidovski, A.; Khalili, F. Y.; Khan, R.; Khazanov, E.; Kim, H.; King, P. J.; Kissel, J. S.; Klimenko, S.; Kokeyama, K.; Kondrashov, V.; Kopparapu, R.; Koranda, S.; Kozak, D.; Kringel, V.; Krishnan, B.; Kuehn, G.; Kullman, J.; Kumar, R.; Kwee, P.; Lam, P. K.; Landry, M.; Lang, M.; Lantz, B.; Lastzka, N.; Lazzarini, A.; Leaci, P.; Lei, M.; Leindecker, N.; Leonor, I.; Lin, H.; Lindquist, P. E.; Littenberg, T. B.; Lockerbie, N. A.; Lodhia, D.; Lormand, M.; Lu, P.; Lubiński, M.; Lucianetti, A.; Lück, H.; Lundgren, A.; Machenschalk, B.; Macinnis, M.; Mageswaran, M.; Mailand, K.; Mak, C.; Mandel, I.; Mandic, V.; Márka, S.; Márka, Z.; Markosyan, A.; Markowitz, J.; Maros, E.; Martin, I. W.; Martin, R. M.; Marx, J. N.; Mason, K.; Matichard, F.; Matone, L.; Matzner, R. A.; Mavalvala, N.; McCarthy, R.; McClelland, D. E.; McGuire, S. C.; McIntyre, G.; McKechan, D. J. A.; Mehmet, M.; Melatos, A.; Melissinos, A. C.; Mendell, G.; Menéndez, D. F.; Mercer, R. A.; Merrill, L.; Meshkov, S.; Messenger, C.; Meyer, M. S.; Miao, H.; Miller, J.; Mino, Y.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Miyakawa, O.; Moe, B.; Mohanty, S. D.; Mohapatra, S. R. P.; Moreno, G.; Mors, K.; Mossavi, K.; Mowlowry, C.; Mueller, G.; Müller-Ebhardt, H.; Mukherjee, S.; Mullavey, A.; Munch, J.; Murray, P. G.; Nash, T.; Nawrodt, R.; Nelson, J.; Newton, G.; Nishida, E.; Nishizawa, A.; O'Dell, J.; O'Reilly, B.; O'Shaughnessy, R.; Ochsner, E.; Ogin, G. H.; Oldenburg, R.; Ottaway, D. J.; Ottens, R. S.; Overmier, H.; Owen, B. J.; Page, A.; Pan, Y.; Pankow, C.; Papa, M. A.; Patel, P.; Pathak, D.; Pedraza, M.; Pekowsky, L.; Penn, S.; Peralta, C.; Perreca, A.; Pickenpack, M.; Pinto, I. M.; Pitkin, M.; Pletsch, H. J.; Plissi, M. V.; Postiglione, F.; Principe, M.; Prix, R.; Prokhorov, L.; Puncken, O.; Quetschke, V.; Raab, F. J.; Rabeling, D. S.; Radkins, H.; Raffai, P.; Raics, Z.; Rakhmanov, M.; Raymond, V.; Reed, C. M.; Reed, T.; Rehbein, H.; Reid, S.; Reitze, D. H.; Riesen, R.; Riles, K.; Roberts, P.; Robertson, N. A.; Robinson, C.; Robinson, E. L.; Roddy, S.; Röver, C.; Rollins, J.; Romano, J. D.; Romie, J. H.; Rowan, S.; Rüdiger, A.; Ryan, K.; Sakata, S.; Sammut, L.; Sancho de La Jordana, L.; Sandberg, V.; Sannibale, V.; Santamaría, L.; Santostasi, G.; Saraf, S.; Sarin, P.; Sathyaprakash, B. S.; Sato, S.; Satterthwaite, M.; Saulson, P. R.; Savage, R.; Schilling, R.; Schnabel, R.; Schofield, R.; Schulz, B.; Schutz, B. F.; Schwinberg, P.; Scott, J.; Scott, S. M.; Searle, A. C.; Seifert, F.; Sellers, D.; Sengupta, A. S.; Sergeev, A.; Shapiro, B.; Shawhan, P.; Shoemaker, D. H.; Sibley, A.; Siemens, X.; Sigg, D.; Sintes, A. M.; Skelton, G.; Slagmolen, B. J. J.; Slutsky, J.; Smith, J. R.; Smith, M. R.; Smith, N. D.; Somiya, K.; Sorazu, B.; Speirits, F.; Stein, A. J.; Stein, L. C.; Steplewski, S.; Stochino, A.; Stone, R.; Strain, K. A.; Strigin, S.; Stroeer, A.; Stuver, A. L.; Summerscales, T. Z.; Sung, M.; Susmithan, S.; Sutton, P. J.; Szokoly, G. P.; Talukder, D.; Tanner, D. B.; Tarabrin, S. P.; Taylor, J. R.; Taylor, R.; Thorne, K. A.; Thorne, K. S.; Thüring, A.; Titsler, C.; Tokmakov, K. V.; Torres, C.; Torrie, C. I.; Traylor, G.; Trias, M.; Turner, L.; Ugolini, D.; Urbanek, K.; Vahlbruch, H.; Vallisneri, M.; van den Broeck, C.; van der Sluys, M. V.; van Veggel, A. A.; Vass, S.; Vaulin, R.; Vecchio, A.; Veitch, J.; Veitch, P. J.; Veltkamp, C.; Villar, A.; Vorvick, C.; Vyachanin, S. P.; Waldman, S. J.; Wallace, L.; Wanner, A.; Ward, R. L.; Wei, P.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Wen, L.; Wen, S.; Wessels, P.; West, M.; Westphal, T.; Wette, K.; Whelan, J. T.; Whitcomb, S. E.; Whiting, B. F.; Wilkinson, C.; Willems, P. A.; Williams, H. R.; Williams, L.; Willke, B.; Wilmut, I.; Winkelmann, L.; Winkler, W.; Wipf, C. C.; Wiseman, A. G.; Woan, G.; Wooley, R.; Worden, J.; Yakushin, I.; Yamamoto, H.; Yamamoto, K.; Yeaton-Massey, D.; Yoshida, S.; Zanolin, M.; Zhang, L.; Zhang, Z.; Zhao, C.; Zotov, N.; Zucker, M. E.; Zweizig, J.; Buchner, S.

2011-02-01

The physical mechanisms responsible for pulsar timing glitches are thought to excite quasinormal mode oscillations in their parent neutron star that couple to gravitational-wave emission. In August 2006, a timing glitch was observed in the radio emission of PSR B0833-45, the Vela pulsar. At the time of the glitch, the two colocated Hanford gravitational-wave detectors of the Laser Interferometer Gravitational-wave observatory (LIGO) were operational and taking data as part of the fifth LIGO science run (S5). We present the first direct search for the gravitational-wave emission associated with oscillations of the fundamental quadrupole mode excited by a pulsar timing glitch. No gravitational-wave detection candidate was found. We place Bayesian 90% confidence upper limits of 6.3×10-21 to 1.4×10-20 on the peak intrinsic strain amplitude of gravitational-wave ring-down signals, depending on which spherical harmonic mode is excited. The corresponding range of energy upper limits is 5.0×1044 to 1.3×1045erg.

Search for Gravitational Waves Associated with the August 2006 Timing Glitch of the Vela Pulsar

NASA Technical Reports Server (NTRS)

Camp, J. B.; Cannizzo, J.; Stroeer, A.

2011-01-01

The physical mechanisms responsible for pulsar timing glitches are thought to excite quasinormal mode oscillations in their parent neutron star that couple to gravitational-wave emission, In August 2006, a timing glitch was observed in the radio emission of PSR B0833-45, the Vela pulsar. At the time of the glitch, the two colocated Hanford gravitational-wave detectors of the Laser Interferometer Gravitational-wave observatory (LIGO) were operational and taking data as part of the fifth LIGO science run (S5). We present the first direct search for the gravitational-wave emission associated with oscillations of the fundamental quadrupole mode excited by a pulsar timing glitch. No gravitational-wave detection candidate was found. We place Bayesian 90% confidence upper limits of 6,3 x 10(exp -21) to 1.4 x 10(exp -20) on the peak: intrinsic strain amplitude of gravitational-wave ring-down signals, depending on which spherical harmonic mode is excited. The corresponding range of energy upper limits is 5.0 x 10(exp 44) to 1.3 x 10(exp 45) erg.

A numerical analysis of transient planetary waves and the vertical structure in a meso-strato-troposphere model, part 1.4A

NASA Technical Reports Server (NTRS)

Zhang, K. S.; Sasamori, T.

1984-01-01

The structure of unstable planetary waves is computed by a quasi-geostrophic model extending from the surface up to 80 km by means of eigenvalue-eigenfunction techniques in spherical coordinates. Three kinds of unstable modes of distinct phase speeds and vertical structures are identified in the winter climate state: (1) the deep Green mode with its maximum amplitude in the stratosphere; (2) the deep Charney mode with its maximum amplitude in the troposphere: and (3) the shallow Charney mode which is largely confined to the troposphere. Both the Green mode and the deep Charney mode are characterized by very slow phase speeds. They are mainly supported by upward wave energy fluxes, but the local baroclinic energy conversion within the stratosphere also contributes in supporting these deep modes. The mesosphere and the troposphere are dynamically independent in the summer season decoupled by the deep stratospheric easterly. The summer mesosphere supports the easterly unstable waves 1-4. Waves 3 and 4 are identified with the observed mesospheric 2-day wave and 1.7-day wave, respectively.

Simulation and Analysis of Converging Shock Wave Test Problems

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

Ramsey, Scott D.; Shashkov, Mikhail J.

2012-06-21

Results and analysis pertaining to the simulation of the Guderley converging shock wave test problem (and associated code verification hydrodynamics test problems involving converging shock waves) in the LANL ASC radiation-hydrodynamics code xRAGE are presented. One-dimensional (1D) spherical and two-dimensional (2D) axi-symmetric geometric setups are utilized and evaluated in this study, as is an instantiation of the xRAGE adaptive mesh refinement capability. For the 2D simulations, a 'Surrogate Guderley' test problem is developed and used to obviate subtleties inherent to the true Guderley solution's initialization on a square grid, while still maintaining a high degree of fidelity to the originalmore » problem, and minimally straining the general credibility of associated analysis and conclusions.« less

Rapid calculation of acoustic fields from arbitrary continuous-wave sources.

PubMed

Treeby, Bradley E; Budisky, Jakub; Wise, Elliott S; Jaros, Jiri; Cox, B T

2018-01-01

A Green's function solution is derived for calculating the acoustic field generated by phased array transducers of arbitrary shape when driven by a single frequency continuous wave excitation with spatially varying amplitude and phase. The solution is based on the Green's function for the homogeneous wave equation expressed in the spatial frequency domain or k-space. The temporal convolution integral is solved analytically, and the remaining integrals are expressed in the form of the spatial Fourier transform. This allows the acoustic pressure for all spatial positions to be calculated in a single step using two fast Fourier transforms. The model is demonstrated through several numerical examples, including single element rectangular and spherically focused bowl transducers, and multi-element linear and hemispherical arrays.

Exploration of spherical torus physics in the NSTX device

NASA Astrophysics Data System (ADS)

Ono, M.; Kaye, S. M.; Peng, Y.-K. M.; Barnes, G.; Blanchard, W.; Carter, M. D.; Chrzanowski, J.; Dudek, L.; Ewig, R.; Gates, D.; Hatcher, R. E.; Jarboe, T.; Jardin, S. C.; Johnson, D.; Kaita, R.; Kalish, M.; Kessel, C. E.; Kugel, H. W.; Maingi, R.; Majeski, R.; Manickam, J.; McCormack, B.; Menard, J.; Mueller, D.; Nelson, B. A.; Nelson, B. E.; Neumeyer, C.; Oliaro, G.; Paoletti, F.; Parsells, R.; Perry, E.; Pomphrey, N.; Ramakrishnan, S.; Raman, R.; Rewoldt, G.; Robinson, J.; Roquemore, A. L.; Ryan, P.; Sabbagh, S.; Swain, D.; Synakowski, E. J.; Viola, M.; Williams, M.; Wilson, J. R.; NSTX Team

2000-03-01

The National Spherical Torus Experiment (NSTX) is being built at Princeton Plasma Physics Laboratory to test the fusion physics principles for the spherical torus concept at the MA level. The NSTX nominal plasma parameters are R0 = 85 cm, a = 67 cm, R/a >= 1.26, Bt = 3 kG, Ip = 1 MA, q95 = 14, elongation κ <= 2.2, triangularity δ <= 0.5 and a plasma pulse length of up to 5 s. The plasma heating/current drive tools are high harmonic fast wave (6 MW, 5 s), neutral beam injection (5 MW, 80 keV, 5 s) and coaxial helicity injection. Theoretical calculations predict that NSTX should provide exciting possibilities for exploring a number of important new physics regimes, including very high plasma β, naturally high plasma elongation, high bootstrap current fraction, absolute magnetic well and high pressure driven sheared flow. In addition, the NSTX programme plans to explore fully non-inductive plasma startup as well as a dispersive scrape-off layer for heat and particle flux handling.

Receiving sensitivity and transmitting voltage response of a fluid loaded spherical piezoelectric transducer with an elastic coating.

PubMed

George, Jineesh; Ebenezer, D D; Bhattacharyya, S K

2010-10-01

A method is presented to determine the response of a spherical acoustic transducer that consists of a fluid-filled piezoelectric sphere with an elastic coating embedded in infinite fluid to electrical and plane-wave acoustic excitations. The exact spherically symmetric, linear, differential, governing equations are used for the interior and exterior fluids, and elastic and piezoelectric materials. Under acoustic excitation and open circuit boundary condition, the equation governing the piezoelectric sphere is homogeneous and the solution is expressed in terms of Bessel functions. Under electrical excitation, the equation governing the piezoelectric sphere is inhomogeneous and the complementary solution is expressed in terms of Bessel functions and the particular integral is expressed in terms of a power series. Numerical results are presented to illustrate the effect of dimensions of the piezoelectric sphere, fluid loading, elastic coating and internal material losses on the open-circuit receiving sensitivity and transmitting voltage response of the transducer.

Frequency dependence of the acoustic field generated from a spherical cavity transducer with open ends

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

Li, Faqi; Zeng, Deping; He, Min

2015-12-15

Resolution of high intensity focused ultrasound (HIFU) focusing is limited by the wave diffraction. We have developed a spherical cavity transducer with two open ends to improve the focusing precision without sacrificing the acoustic intensity (App Phys Lett 2013; 102: 204102). This work aims to theoretically and experimentally investigate the frequency dependence of the acoustic field generated from the spherical cavity transducer with two open ends. The device emits high intensity ultrasound at the frequency ranging from 420 to 470 kHz, and the acoustic field is measured by a fiber optic probe hydrophone. The measured results shows that the sphericalmore » cavity transducer provides high acoustic intensity for HIFU treatment only in its resonant modes, and a series of resonant frequencies can be choosen. Furthermore, a finite element model is developed to discuss the frequency dependence of the acoustic field. The numerical simulations coincide well with the measured results.« less

Distinct turbulence sources and confinement features in the spherical tokamak plasma regime

DOE PAGES

Wang, W. X.; Ethier, S.; Ren, Y.; ...

2015-10-30

New turbulence contributions to plasma transport and confinement in the spherical tokamak (ST) regime are identified through nonlinear gyrokinetic simulations. The drift wave Kelvin-Helmholtz (KH) mode characterized by intrinsic mode asymmetry is shown to drive significant ion thermal transport in strongly rotating national spherical torus experiment (NSTX) L-modes. The long wavelength, quasi-coherent dissipative trapped electron mode (TEM) is destabilized in NSTX H-modes despite the presence of strong E x B shear, providing a robust turbulence source dominant over collisionless TEM. Dissipative trapped electron mode (DTEM)-driven transport in the NSTX parametric regime is shown to increase with electron collision frequency, offeringmore » one possible source for the confinement scaling observed in experiments. There exists a turbulence-free regime in the collision-induced collisionless trapped electron mode to DTEM transition for ST plasmas. In conclusion, this predicts a natural access to a minimum transport state in the low collisionality regime that future advanced STs may cover.« less

Multiple-cycle Simulation of a Pulse Detonation Engine Ejector

NASA Technical Reports Server (NTRS)

Yungster, S.; Perkins, H. D.

2002-01-01

This paper presents the results of a study involving single and multiple-cycle numerical simulations of various PDE-ejector configurations utilizing hydrogen-oxygen mixtures. The objective was to investigate the thrust, impulse and mass flow rate characteristics of these devices. The results indicate that ejector systems can utilize the energy stored in the strong shock wave exiting the detonation tube to augment the impulse obtained from the detonation tube alone. Impulse augmentation ratios of up to 1.9 were achieved. The axial location of the converging-diverging ejectors relative to the end of the detonation tube were shown to affect the performance of the system.

Elastic medium equivalent to Fresnel's double-refraction crystal.

PubMed

Carcione, José M; Helbig, Klaus

2008-10-01

In 1821, Fresnel obtained the wave surface of an optically biaxial crystal, assuming that light waves are vibrations of the ether in which longitudinal vibrations (P waves) do not propagate. An anisotropic elastic medium mathematically analogous to Fresnel's crystal exists. The medium has four elastic constants: a P-wave modulus, associated with a spherical P wave surface, and three elastic constants, c(44), c(55), and c(66), associated with the shear waves, which are mathematically equivalent to the three dielectric permittivity constants epsilon(11), epsilon(22), and epsilon(33) as follows: mu(0)epsilon(11)<==>rho/c(44), mu(0)epsilon(22)<==>rho/c(55), mu(0)epsilon(33)<==>rho/c(66), where mu(0) is the magnetic permeability of vacuum and rho is the mass density. These relations also represent the equivalence between the elastic and electromagnetic wave velocities along the principal axes of the medium. A complete mathematical equivalence can be obtained by setting the P-wave modulus equal to zero, but this yields an unstable elastic medium (the hypothetical ether). To obtain stability the P-wave velocity has to be assumed infinite (incompressibility). Another equivalent Fresnel's wave surface corresponds to a medium with anomalous polarization. This medium is physically unstable even for a nonzero P-wave modulus.

A Numerical Model for Wind-Wave Prediction in Deep Water.

DTIC Science & Technology

1983-01-01

amounts of gage data are available. Additionally, if all steps are modeled correctly, factors such as direction and angular spreading, which are not...spherical orthogonal system if large oceanic areas are to be modeled. The wave model requires a rect- angular grid and wind input at each of the...RM22CNFREQ+1)u1. DO 70 Im1,NFREG 70 SINF(I)uTWOPI*690/(TWOPIIFF(l))3S5 C DO 17 ItJ𔃻,100 VST =O,4851.4$IU USTwVST 19 ZOaCl/UST+C2*UST$UST-C3 UST1= VST /ALOG

Effect of Surface Roughness on Characteristics of Spherical Shock Waves

NASA Technical Reports Server (NTRS)

Huber, Paul W.; McFarland, Donald R.

1959-01-01

Measurements of peak overpressure and Mach stem height were made at four burst heights. Data were obtained with instrumentation capable of directly observing the variation of shock wave movement with time. Good similarity of free air shock peak overpressure with larger scale data was found to exist. The net effect of surface roughness on shock peak overpressures slightly. Surface roughness delayed the Mach stem formation at the greatest charge height and lowered the growth at all burst heights. A similarity parameter was found which approximately correlates the triple point path at different burst heights.

Effects of nonthermal distribution of electrons and polarity of net dust-charge number density on nonplanar dust-ion-acoustic solitary waves.

PubMed

Mamun, A A; Shukla, P K

2009-09-01

Effects of the nonthermal distribution of electrons as well as the polarity of the net dust-charge number density on nonplanar (viz. cylindrical and spherical) dust-ion-acoustic solitary waves (DIASWs) are investigated by employing the reductive perturbation method. It is found that the basic features of the DIASWs are significantly modified by the effects of nonthermal electron distribution, polarity of net dust-charge number density, and nonplanar geometry. The implications of our results in some space and laboratory dusty plasma environments are briefly discussed.

The non-radiating component of the field generated by a finite monochromatic scalar source distribution

NASA Astrophysics Data System (ADS)

Hoenders, Bernhard J.; Ferwerda, Hedzer A.

1998-09-01

We separate the field generated by a spherically symmetric bounded scalar monochromatic source into a radiative and non-radiative part. The non-radiative part is obtained by projecting the total field on the space spanned by the non-radiating inhomogeneous modes, i.e. the modes which satisfy the inhomogeneous wave equation. Using residue techniques, introduced by Cauchy, we obtain an explicit analytical expression for the non-radiating component. We also identify the part of the source distribution which corresponds to this non-radiating part. The analysis is based on the scalar wave equation.

Laboratory Approach to the Study of Elastic Anisotropy on Rock Samples

NASA Astrophysics Data System (ADS)

Pros, Z.; Lokajíček, T.; Klíma, K.

The experimental approach (hardware and software) to the study of the elastic an isotropy of rocks on spherical samples under hydrostatic pressure up to 400 MPa is discussed. A substantial innovation of the existing measuring system and processing methods enabled us to make a detailed investigation and evaluation of the kinematic as well as dynamic parameters of elastic waves propagating through anisotropic media. The innovation is based on digital recording of the wave pattern with a high sampling density of both time and amplitude. Several options and results obtained with the innovated laboratory equipment are presented.

An axion-like scalar field environment effect on binary black hole merger

NASA Astrophysics Data System (ADS)

Yang, Qing; Ji, Li-Wei; Hu, Bin; Cao, Zhou-Jian; Cai, Rong-Gen

2018-06-01

The environment, such as an accretion disk, could modify the signal of the gravitational wave from astrophysical black hole binaries. In this article, we model the matter field around intermediate-mass binary black holes by means of an axion-like scalar field and investigate their joint evolution. In detail, we consider equal mass binary black holes surrounded by a shell of axion-like scalar field both in spherically symmetric and non-spherically symmetric cases, and with different strengths of the scalar field. Our result shows that the environmental scalar field could essentially modify the dynamics. Firstly, in the spherically symmetric case, with increase of the scalar field strength, the number of circular orbits for the binary black hole is reduced. This means that the scalar field could significantly accelerate the merger process. Secondly, once the scalar field strength exceeds a certain critical value, the scalar field could collapse into a third black hole with its mass being larger than that of the binary. Consequently, the new black hole that collapses from the environmental scalar field could accrete the binary promptly and the binary collides head-on with each other. In this process, there is almost no quadrupole signal produced, and, consequently, the gravitational wave is greatly suppressed. Thirdly, when the scalar field strength is relatively smaller than the critical value, the black hole orbit could develop eccentricity through accretion of the scalar field. Fourthly, during the initial stage of the inspiral, the gravitational attractive force from the axion-like scalar field could induce a sudden turn in the binary orbits, hence resulting in a transient wiggle in the gravitational waveform. Finally, in the non-spherical case, the scalar field could gravitationally attract the binary moving toward the center of mass for the scalar field and slow down the merger process.

Myocardial effects of local shock wave therapy in a Langendorff model.

PubMed

Becker, M; Goetzenich, A; Roehl, A B; Huebel, C; de la Fuente, M; Dietz-Laursonn, K; Radermacher, K; Rossaint, R; Hein, M

2014-01-01

Applying shock waves to the heart has been reported to stimulate the heart and alter cardiac function. We hypothesized that shock waves could be used to diagnose regional viability. We used a Langendorff model to investigate the acute effects of shock waves at different energy levels and times related to systole, cycle duration and myocardial function. We found only a small time window to use shock waves. Myocardial fibrillation or extrasystolic beats will occur if the shock wave is placed more than 15 ms before or 30 ms after the onset of systole. Increased contractility and augmented relaxation were observed after the second beat, and these effects decreased after prolonging the shock wave delay from 15 ms before to 30 ms after the onset of systole. An energy dependency could be found only after short delays (-15 ms). The involved processes might include post-extrasystolic potentiation and simultaneous pacing. In summary, we found that low-energy shock waves can be a useful tool to stimulate the myocardium at a distance and influence function. Copyright © 2013 Elsevier B.V. All rights reserved.

On macromolecular refinement at subatomic resolution with interatomic scatterers

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

Afonine, Pavel V., E-mail: pafonine@lbl.gov; Grosse-Kunstleve, Ralf W.; Adams, Paul D.

2007-11-01

Modelling deformation electron density using interatomic scatters is simpler than multipolar methods, produces comparable results at subatomic resolution and can easily be applied to macromolecules. A study of the accurate electron-density distribution in molecular crystals at subatomic resolution (better than ∼1.0 Å) requires more detailed models than those based on independent spherical atoms. A tool that is conventionally used in small-molecule crystallography is the multipolar model. Even at upper resolution limits of 0.8–1.0 Å, the number of experimental data is insufficient for full multipolar model refinement. As an alternative, a simpler model composed of conventional independent spherical atoms augmented bymore » additional scatterers to model bonding effects has been proposed. Refinement of these mixed models for several benchmark data sets gave results that were comparable in quality with the results of multipolar refinement and superior to those for conventional models. Applications to several data sets of both small molecules and macromolecules are shown. These refinements were performed using the general-purpose macromolecular refinement module phenix.refine of the PHENIX package.« less

High-Intensity Interval Cycling Exercise on Wave Reflection and Pulse Wave Velocity.

PubMed

Kingsley, J Derek; Tai, Yu Lun; Vaughan, Jeremiah A; Mayo, Xián

2017-05-01

Kingsley, JD, Tai, YL, Vaughan, J, and Mayo, X. High-intensity interval cycling exercise on wave reflection and pulse wave velocity. J Strength Cond Res 31(5): 1313-1320, 2017-The purpose of this study was to assess the effects of high-intensity exercise on wave reflection and aortic stiffness. Nine young, healthy men (mean ± SD: age: 22 ± 2 years) participated in the study. The high-intensity interval cycling exercise consisted of 3 sets of Wingate Anaerobic Tests (WATs) with 7.5% of bodyweight as resistance and 2 minutes of rest between each set. Measurements were taken at rest and 1 minute after completion of the WATs. Brachial and aortic blood pressures, as well as wave reflection characteristics, were measured through pulse wave analysis. Aortic stiffness was assessed through carotid-femoral pulse wave velocity (cfPWV). A repeated-measures analysis of variance was used to investigate the effects of the WATs on blood pressure and vascular function across time. There was no change in brachial or aortic systolic pressure from rest to recovery. There was a significant (p ≤ 0.05) decrease in brachial diastolic pressure (rest: 73 ± 6 mm Hg; recovery: 67 ± 9 mm Hg) and aortic diastolic pressure (rest: 75 ± 6 mm Hg; recovery: 70 ± 9 mm Hg) from rest to recovery. In addition, there was no significant change in the augmentation index (rest: 111.4 ± 6.5%; recovery: 109.8 ± 5.8%, p = 0.65) from rest to recovery. However, there was a significant (p ≤ 0.05) increase in the augmentation index normalized at 75 b·min (rest: 3.29 ± 9.82; recovery 21.21 ± 10.87) during recovery compared with rest. There was no change in cfPWV (rest: 5.3 ± 0.8 m·s; recovery: 5.7 ± 0.5m·s; p = 0.09) in response to the WAT. These data demonstrate that high-intensity interval cycling exercise with short rest periods has a nonsignificant effect on vascular function.

Effects of intra-aortic counterpulsation on aortic wall energetics and damping: in vivo experiments.

PubMed

Fischer, Edmundo I Cabrera; Bia, Daniel; Camus, Juan M; Zócalo, Yanina; de Forteza, Eduardo; Armentano, Ricardo L

2008-01-01

Intra-aortic balloon pumping (IABP) could modify the arterial biomechanics; however, its effects on arterial wall properties have not been fully explored. This dynamical study was designed to characterize the pressure-dependent and smooth muscle-dependent effects of IABP on aortic wall energetics in an in vivo animal model. Intra-aortic balloon pumping (1:2) was performed in six anesthetized sheep in which aortic pressure and diameter signals were measured in basal, augmented (during balloon inflation), and assisted (postaugmented) beats. Energy dissipation values in augmented and assisted beats were significantly higher than those observed in basal state (p < 0.05). Assisted beats showed a significant increase of wall damping with respect to basal and augmented beats (p < 0.05). Intra-aortic balloon pumping resulted in a significant increase of pulse wave velocity (p < 0.05) in augmented beats with respect to basal state (6.3 +/- 0.8 vs. 5.2 +/- 0.5 m x s(-1)); whereas values observed in assisted beats were significantly (p < 0.05) lower than those observed in augmented beats (4.9 +/- 0.5 vs. 6.3 +/- 0.8 m x s(-1)). Our findings show that IABP determined the pressure and smooth muscle-dependent changes in arterial wall energetics and damping properties in this animal model.

The Role of Shabansky Orbits in Compression-Related Electromagnetic Ion Cyclotron Wave Growth (Postprint)

DTIC Science & Technology

2012-03-15

compressing the field. Equation (5) uses a geocentric spherical coordinate system with units of length in Earth radii. It is clear that setting b1 = 0...in a complementary approach to the one used by McCollough et al. [2009]. 3. Anisotropy Arising From Magnetic Field Configuration [21] McCollough et al

Measurement of spatio-temporal field distribution of THz pulses in electro-optic crystal by interferometry method

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

Chizhov, P A; Ushakov, A A; Bukin, V V

2015-05-31

We propose a scheme for measuring the spatial distribution of the THz pulse electric field strength in an electro-optic crystal using optical interferometry. The resulting images of the field distribution from a test source with a spherical wave front are presented. (extreme light fields and their applications)

Salient features of solitary waves in dusty plasma under the influence of Coriolis force

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

Das, G. C.; Nag, Apratim; Department of Physics, G. C. College, Silchar-788004

The main interest is to study the nonlinear acoustic wave in rotating dusty plasma augmented through the derivation of a modified Sagdeev potential equation. Small rotation causes the interaction of Coriolis force in the dynamical system, and leads to the complexity in the derivation of the nonlinear wave equation. As a result, the finding of solitary wave propagation in dusty plasma ought to be of merit. However, the nonlinear wave equation has been successfully solved by the use of the hyperbolic method. Main emphasis has been given to the changes on the evolution and propagation of soliton, and the variationmore » caused by the dusty plasma constituents as well as by the Coriolis force have been highlighted. Some interesting nonlinear wave behavior has been found which can be elaborately studied for the interest of laboratory and space plasmas. Further, to support the theoretical investigations, numeric plasma parameters have been taken for finding the inherent features of solitons.« less

The influence of polarization on millimeter wave propagation through rain. Ph.D Thesis. Interim Report

NASA Technical Reports Server (NTRS)

Wiley, P. H.; Bostian, C. W.; Stutzman, W. L.

1973-01-01

The influence of polarization on millimeter wave propagation is investigated from both an experimental and a theoretical viewpoint. First, previous theoretical and experimental work relating to the attenuation and depolarization of millimeter waves by rainfall is discussed. Considerable detail is included in the literature review. Next, a theoretical model is developed to predict the cross polarization level during rainfall from the path average rain rate and the scattered field from a single raindrop. Finally, data from the VPI and SU depolarization experiment are presented as verification of the new model, and a comparison is made with other theories and experiments. Aspects of the new model are: (1) spherical rather than plane waves are assumed, (2) the average drop diameter is used rather than a drop size distribution, and (3) it is simple enough so that the effect which changing one or more parameters has on the crosspolarization level is easily seen.

Dynamics of anisotropic particles under waves

NASA Astrophysics Data System (ADS)

Dibenedetto, Michelle; Ouellette, Nicholas; Koseff, Jeffrey

2017-11-01

We present results on anisotropic particles in wavy flows in order to gain insight into the transport and mixing of microplastic particles in the near-shore environment. From theory and numerical simulations, we find that the rate of alignment of the particles is not constant and depends strongly on their initial orientation; thus, variations in initial particle orientation result in dispersion of anisotropic-particle plumes. We find that this dispersion is a function of the particle's eccentricity and the ratio of the settling and wave time scales. Experiments in which non-spherical particles of various shapes are released under surface gravity waves were also performed. Our main goal is to explore the effects of particle shape under various wave scenarios. We vary the aspect ratio of the particle in our experiments while holding other variables constant. Our results demonstrate that particle shape can be important when predicting transport.

Wave-driven dynamo action in spherical magnetohydrodynamic systems.

PubMed

Reuter, K; Jenko, F; Tilgner, A; Forest, C B

2009-11-01

Hydrodynamic and magnetohydrodynamic numerical studies of a mechanically forced two-vortex flow inside a sphere are reported. The simulations are performed in the intermediate regime between the laminar flow and developed turbulence, where a hydrodynamic instability is found to generate internal waves with a characteristic m=2 zonal wave number. It is shown that this time-periodic flow acts as a dynamo, although snapshots of the flow as well as the mean flow are not dynamos. The magnetic fields' growth rate exhibits resonance effects depending on the wave frequency. Furthermore, a cyclic self-killing and self-recovering dynamo based on the relative alignment of the velocity and magnetic fields is presented. The phenomena are explained in terms of a mixing of nonorthogonal eigenstates of the time-dependent linear operator of the magnetic induction equation. The potential relevance of this mechanism to dynamo experiments is discussed.

Nonlinear Propagation of Alfven Waves Driven by Observed Photospheric Motions: Application to the Coronal Heating and Spicule Formation

NASA Astrophysics Data System (ADS)

Matsumoto, Takuma; Shibata, Kazunari

We have performed MHD simulations of Alfven wave propagation along an open ux tube in the solar atmosphere. In our numerical model, Alfven waves are generated by the photospheric granular motion. As the wave generator, we used a derived temporal spectrum of the photo-spheric granular motion from G-band movies of Hinode/SOT. It is shown that the total energy ux at the corona becomes larger and the transition region height becomes higher in the case when we use the observed spectrum rather than white/pink noise spectrum as the wave gener-ator. This difference can be explained by the Alfven wave resonance between the photosphere and the transition region. After performing Fourier analysis on our numerical results, we have found that the region between the photosphere and the transition region becomes an Alfven wave resonant cavity. We have conrmed that there are at least three resonant frequencies, 1, 3 and 5 mHz, in our numerical model. Alfven wave resonance is one of the most effective mechanisms to explain the dynamics of the spicules and the sufficient energy ux to heat the corona.

Shock wave and flame front induced detonation in a rapid compression machine

NASA Astrophysics Data System (ADS)

Wang, Y.; Qi, Y.; Xiang, S.; Mével, R.; Wang, Z.

2018-05-01

The present study focuses on one mode of detonation initiation observed in a rapid compression machine (RCM). This mode is referred to as shock wave and flame front-induced detonation (SWFID). Experimental high-speed imaging and two-dimensional numerical simulations with skeletal chemistry are combined to unravel the dominant steps of detonation initiation under SWFID conditions. It is shown that the interaction between the shock wave generated by the end-gas auto-ignition and the spherical flame creates a region of high pressure and temperature which enables the acceleration of the flame front and the detonation onset. The experimental observation lacks adequate spatial and temporal resolution despite good reproducibility of the detonation onset. Based on the numerical results, phenomenological interpretation of the event within the framework of shock wave refraction indicates that the formation of a free-precursor shock wave at the transition between regular and irregular refraction may be responsible for detonation onset. The present results along with previous findings on shock wave reflection-induced detonation in the RCM indicate that super-knock occurs after the interaction of the shock wave generated by end-gas auto-ignition with the RCM walls, preignition flame, or another shock wave.

Wave number selection in the presence of noise: Experimental results

NASA Astrophysics Data System (ADS)

Zhilenko, Dmitry; Krivonosova, Olga; Gritsevich, Maria; Read, Peter

2018-05-01

In this study, we consider how the wave number selection in spherical Couette flow, in the transition to azimuthal waves after the first instability, occurs in the presence of noise. The outer sphere was held stationary, while the inner sphere rotational speed was increased linearly from a subcritical flow to a supercritical one. In a supercritical flow, one of two possible flow states, each with different azimuthal wave numbers, can appear depending upon the initial and final Reynolds numbers and the acceleration value. Noise perturbations were added by introducing small disturbances into the rotational speed signal. With an increasing noise amplitude, a change in the dominant wave number from m to m ± 1 was found to occur at the same initial and final Reynolds numbers and acceleration values. The flow velocity measurements were conducted by using laser Doppler anemometry. Using these results, the role of noise as well as the behaviour of the amplitudes of the competing modes in their stages of damping and growth were determined.

Acoustic Waves in a Three-Dimensional Stratified Atmosphere

NASA Astrophysics Data System (ADS)

Kalkofen, W.; Massaglia, S.; Bodo, G.; Rossi, P.

2000-05-01

We investigate the propagation of acoustic waves in a three-dimensional, nonmagnetic, isothermal atmosphere stratified in plane-parallel layers in a study of oscillations in chromospheric calcium bright points. We present analytic results for the linear and numerical results for the nonlinear evolution of a disturbance. An impulsively excited acoustic disturbance emanates from a point source and propagates outward as a spherical acoustic wave, amplifying exponentially in the upward direction. A significant wave amplitude is found only in a relatively narrow cone about the vertical. The amplitude of the wave and the opening angle of the cone decrease with time. Because of the lateral spread of the upward-propagating energy, the decay is faster in 2D and 3D simulations than in 1D. We discuss observational consequences of this scenario, some of which are not anticipated from 1D calculations. We acknowledge support from NASA, NSF and the Ministero per l'Università e la Ricerca Scientifica e Tecnologica.

Wave Phenomena in Reaction-Diffusion Systems

NASA Astrophysics Data System (ADS)

Steinbock, Oliver; Engel, Harald

2013-12-01

Pattern formation in excitable and oscillatory reaction-diffusion systems provides intriguing examples for the emergence of macroscopic order from molecular reaction events and Brownian motion. Here we review recent results on several aspects of excitation waves including anomalous dispersion, vortex pinning, and three-dimensional scroll waves. Anomalies in the speed-wavelength dependence of pulse trains include nonmonotonic behavior, bistability, and velocity gaps. We further report on the hysteresis effects during the pinning-depinning transition of twodimensional spiral waves. The pinning of three-dimensional scroll waves shows even richer dynamic complexity, partly due to the possibility of geometric and topological mismatches between the unexcitable, pinning heterogeneities and the one-dimensional rotation backbone of the vortex. As examples we present results on the pinning of scroll rings to spherical, C-shaped, and genus-2-type heterogeneities. We also review the main results of several experimental studies employing the Belousov-Zhabotinsky reaction and briefly discuss the biomedical relevance of this research especially in the context of cardiology.

A study of phase explosion of metal using high power Nd:YAG laser ablation

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

Yoh, Jack J.; Lee, H. H.; Choi, J. H.

2007-12-12

The interaction of high-power pulsed-laser beam with metal targets in air from 1.06 {mu}m, 5 ns, 3 J/pulse max, Nd:YAG pulsed laser is investigated together with hydrodynamic theories of laser-supported detonation (LSD) wave and multi-material reactive Euler equations. The high speed blast wave generated by the laser ablation of metal reaches maximum velocity of several thousand meters per second. The apparently similar flow conditions to those of reactive shock wave allow one to apply the equations of motion for energetic materials and to understand the explosive behavior of metal vaporization upon laser ablation. The characteristic time at which planar tomore » spherical wave transition occurs is confirmed at low (20 mJ/pulse) to higher (200 mJ/pulse) beam intensities. The flow structure behind the leading shock wave during the early planar shock state is confirmed by the high-resolution multi-material hydrocode originally developed for shock compression of condensed matter.« less

Collapse of a nanoscopic void triggered by a spherically symmetric traveling sound wave.

PubMed

Hołyst, Robert; Litniewski, Marek; Garstecki, Piotr

2012-05-01

Molecular-dynamics simulations of the Lennard-Jones fluid (up to 10(7) atoms) are used to analyze the collapse of a nanoscopic bubble. The collapse is triggered by a traveling sound wave that forms a shock wave at the interface. The peak temperature T(max) in the focal point of the collapse is approximately ΣR(0)(a), where Σ is the surface density of energy injected at the boundary of the container of radius R(0) and α ≈ 0.4-0.45. For Σ = 1.6 J/m(2) and R(0) = 51 nm, the shock wave velocity, which is proportional to √Σ, reaches 3400 m/s (4 times the speed of sound in the liquid); the pressure at the interface, which is proportional to Σ, reaches 10 GPa; and T(max) reaches 40,000 K. The Rayleigh-Plesset equation together with the time of the collapse can be used to estimate the pressure at the front of the shock wave.

Dynamics of Laser-Driven Shock Waves in Solid Targets

NASA Astrophysics Data System (ADS)

Aglitskiy, Y.; Karasik, M.; Velikovich, A. L.; Serlin, V.; Weaver, J.; Schmitt, A. J.; Obenschain, S. P.; Grun, J.; Metzler, N.; Zalesak, S. T.; Gardner, J. H.; Oh, J.; Harding, E. C.

2009-11-01

Accurate shock timing is a key issue of both indirect- and direct-drive laser fusions. The experiments on the Nike laser at NRL presented here were made possible by improvements in the imaging capability of our monochromatic x-ray diagnostics based on Bragg reflection from spherically curved crystals. Side-on imaging implemented on Nike makes it possible to observe dynamics of the shock wave and ablation front in laser-driven solid targets. We can choose to observe a sequence of 2D images or a continuous time evolution of an image resolved in one spatial dimension. A sequence of 300 ps snapshots taken using vanadium backlighter at 5.2 keV reveals propagation of a shock wave in a solid plastic target. The shape of the shock wave reflects the intensity distribution in the Nike beam. The streak records with continuous time resolution show the x-t trajectory of a laser-driven shock wave in a 10% solid density DVB foam.

Numerical Study of Wave Propagation in a Non-Uniform Flow

NASA Technical Reports Server (NTRS)

Povitsky, Alex; Bushnell, Dennis M. (Technical Monitor)

2000-01-01

The propagation of acoustic waves originating from cylindrical and spherical pulses, in a non-uniform mean flow, and in the presence of a reflecting wall is investigated by Hardin and Pope approach using compact approximation of spatial derivatives. The 2-D and 3-D stagnation flows and a flow around a cylinder are taken as prototypes of real world flows with strong gradients of mean pressure and velocity. The intensity and directivity of acoustic wave patterns appear to be quite different from the benchmark solutions obtained in a static environment for the same geometry. The physical reasons for amplification and weakening of sound are discussed in terms of dynamics of wave profile and redistribution of acoustic energy and its potential and kinetic components. For an acoustic wave in the flow around a cylinder, the observed mean acoustic pressure is approximately doubled (upstream pulse position) and halved (downstream pulse position) in comparison with the sound propagation in static ambient conditions.

Physical exercise, fitness and dietary pattern and their relationship with circadian blood pressure pattern, augmentation index and endothelial dysfunction biological markers: EVIDENT study protocol

PubMed Central

2010-01-01

Background Healthy lifestyles may help to delay arterial aging. The purpose of this study is to analyze the relationship of physical activity and dietary pattern to the circadian pattern of blood pressure, central and peripheral blood pressure, pulse wave velocity, carotid intima-media thickness and biological markers of endothelial dysfunction in active and sedentary individuals without arteriosclerotic disease. Methods/Design Design: A cross-sectional multicenter study with six research groups. Subjects: From subjects of the PEPAF project cohort, in which 1,163 who were sedentary became active, 1,942 were sedentary and 2,346 were active. By stratified random sampling, 1,500 subjects will be included, 250 in each group. Primary measurements: We will evaluate height, weight, abdominal circumference, clinical and ambulatory blood pressure with the Radial Pulse Wave Acquisition Device (BPro), central blood pressure and augmentation index with Pulse Wave Application Software (A-Pulse) and SphymgoCor System Px (Pulse Wave Analysis), pulse wave velocity (PWV) with SphymgoCor System Px (Pulse Wave Velocity), nutritional pattern with a food intake frequency questionnaire, physical activity with the 7-day PAR questionnaire and accelerometer (Actigraph GT3X), physical fitness with the cycle ergometer (PWC-170), carotid intima-media thickness by ultrasound (Micromax), and endothelial dysfunction biological markers (endoglin and osteoprotegerin). Discussion Determining that sustained physical activity and the change from sedentary to active as well as a healthy diet improve circadian pattern, arterial elasticity and carotid intima-media thickness may help to propose lifestyle intervention programs. These interventions could improve the cardiovascular risk profile in some parameters not routinely assessed with traditional risk scales. From the results of this study, interventional approaches could be obtained to delay vascular aging that combine physical exercise and diet. Trial Registration Clinical Trials.gov Identifier: NCT01083082 PMID:20459634

Post-exercise effects on aortic wave reflection derived from wave separation analysis in young- to middle-aged pre-hypertensives and hypertensives.

PubMed

Millen, Aletta M E; Woodiwiss, Angela J; Norton, Gavin R

2016-07-01

Decreases in brachial blood pressure (BP) may occur for several hours following a bout of exercise. Although aortic backward waves predict cardiovascular damage independent of brachial BP, whether decreases in aortic backward waves also occur post-exercise in young-to-middle-aged hypertensives, the extent to which these changes exceed brachial BP changes, and the best method of identifying these changes is uncertain. We examined aortic function at baseline and 15-min post-exercise in 20 pre-hypertensive or hypertensive men and women (age 45 ± 7 years). Central aortic pressure, forward (Pf) and backward (Pb) wave pressures, the reflection index (RI) and augmentation pressure (AP) and index (AIx) were determined using applanation tonometry, and SphygmoCor software. Decreases in central aortic (p < 0.001) but not brachial systolic BP and pulse pressure (PP) occurred post-exercise. In addition, decreases in post-exercise (baseline versus post-exercise) Pb (19 ± 4 vs 13 ± 3 mm Hg p < 0.0001), RI (72.9 ± 22.1 vs 47.6 ± 12.8 %, p < 0.0001), AIx (26.3 ± 10.8 vs 7.8 ± 11.6 %, p < 0.0001) and AP (9.9 ± 3.9 vs 2.8 ± 3.9 mm Hg, p < 0.0001), but not Pf, were noted. However, decreases in AIx were not correlated with decreases in Pb, and whilst decreases in aortic PP correlated with decreases in Pb (p < 0.0001), no correlations were noted with decreases in AP or AIx. In young-to-middle-aged pre-hypertensive and hypertensive individuals, aortic backward waves decrease post-exercise; this change is not reflected in brachial BP measurements and is poorly indexed by measures of pressure augmentation.

Simulation of a flexible spinning vehicle

NASA Technical Reports Server (NTRS)

Baudry, W. A.

1972-01-01

Results are presented of experimental investigation of the controlled and uncontrolled dynamical behavior of a rotating or artificial gravity space station including flexible body effects. A dynamically scaled model was supported by a spherical air bearing which provided a nearly moment free environment. Reaction jet system were provided for spin-up and spin-down and for damping of wobble motion. Two single-gimbal gyros were arranged as a control moment gyro wobble damping system. Remotely controllable movable masses were provided to simulate mass shift disturbances such as arise from crew motions. An active mass balance wobble damping system which acted to minimize the wobble motions induced by crew motions was also installed. Flexible body effects were provided by a pair of inertia augmentation booms. Inertia augmentation booms are contemplated for use on rotating space stations to cause the spin axis moment of inertia to be the largest of the three moments of inertia as is necessary to assure gyroscopic stability. Test runs were made with each of the control systems with the booms locked (rigid body) and unlocked (flexible body).

A computationally tractable version of the collective model

NASA Astrophysics Data System (ADS)

Rowe, D. J.

2004-05-01

A computationally tractable version of the Bohr-Mottelson collective model is presented which makes it possible to diagonalize realistic collective models and obtain convergent results in relatively small appropriately chosen subspaces of the collective model Hilbert space. Special features of the proposed model are that it makes use of the beta wave functions given analytically by the softened-beta version of the Wilets-Jean model, proposed by Elliott et al., and a simple algorithm for computing SO(5)⊃SO(3) spherical harmonics. The latter has much in common with the methods of Chacon, Moshinsky, and Sharp but is conceptually and computationally simpler. Results are presented for collective models ranging from the spherical vibrator to the Wilets-Jean and axially symmetric rotor-vibrator models.

Natural Divertor Spherical Tokamak Plasmas with bean shape and ergodic limiter

NASA Astrophysics Data System (ADS)

Ribeiro, Celso; Herrera, Julio; Chavez, Esteban; Tritz, Kevin

2013-10-01

The former spherical tokamak (ST) MEDUSA (Madison EDUcation Small Aspect.ratio tokamak, R < 0.14 m, a < 0.10 m, BT < 0.5T, Ip < 40 kA, 3 ms pulse) is being recommissioned in Costa Rica Institute of Technology. The main objectives of the MEDUSA-CR project are training and to clarify several issues in relevant physics for conventional and mainly STs, including beta studies in bean-shaped ST plasmas, transport, heating and current drive via Alfvén wave, and natural divertor STs with ergodic magnetic limiter. We report here improvements in the self-consistency of these equilibrium comparisons and a preliminary study of their MHD stability beta limits. VIE-ITCR, IAEA-CRP contract 17592, National Instruments of Costa Rica.

Deconvolving the wedge: maximum-likelihood power spectra via spherical-wave visibility modelling

NASA Astrophysics Data System (ADS)

Ghosh, A.; Mertens, F. G.; Koopmans, L. V. E.

2018-03-01

Direct detection of the Epoch of Reionization (EoR) via the red-shifted 21-cm line will have unprecedented implications on the study of structure formation in the infant Universe. To fulfil this promise, current and future 21-cm experiments need to detect this weak EoR signal in the presence of foregrounds that are several orders of magnitude larger. This requires extreme noise control and improved wide-field high dynamic-range imaging techniques. We propose a new imaging method based on a maximum likelihood framework which solves for the interferometric equation directly on the sphere, or equivalently in the uvw-domain. The method uses the one-to-one relation between spherical waves and spherical harmonics (SpH). It consistently handles signals from the entire sky, and does not require a w-term correction. The SpH coefficients represent the sky-brightness distribution and the visibilities in the uvw-domain, and provide a direct estimate of the spatial power spectrum. Using these spectrally smooth SpH coefficients, bright foregrounds can be removed from the signal, including their side-lobe noise, which is one of the limiting factors in high dynamics-range wide-field imaging. Chromatic effects causing the so-called `wedge' are effectively eliminated (i.e. deconvolved) in the cylindrical (k⊥, k∥) power spectrum, compared to a power spectrum computed directly from the images of the foreground visibilities where the wedge is clearly present. We illustrate our method using simulated Low-Frequency Array observations, finding an excellent reconstruction of the input EoR signal with minimal bias.

The nature of spherical collapse and a study of black hole dynamics

NASA Astrophysics Data System (ADS)

Nampalliwar, Sourabh

Gravitational waves and singularities are two of the most significant predictions of General Relativity. Binary systems are the most promising sources of gravitational waves that are expected to be detected with the current ground-based and upcoming space-based gravitational wave detectors. During the merger of binary compact objects, an important stage is the plunge. A small part of the gravitational waveform, it marks the end of early inspiral and determines the quasinormal ringing (QNR) of the final product of the merger. It is also the part of the waveform where most of the gravitational energy is released. But, unlike early inspiral and late ringdown, it is poorly understood in terms of phenomenology. This thesis introduces a novel approach combining the Fourier domain Green's function in the particle perturbation approximation and a simple model to understand this crucial stage. The resulting understanding is successful in explaining QNR for a Schwarzschild black hole and opens a new approach to understanding binary inspiral. It holds the promise of a much improved understanding, and improved efficiency in making astrophysical estimates of gravitational wave source strength. Singularities are known to be the ultimate fate of all massive stars undergoing gravitational collapse. The cosmic censorship hypothesis predicts that all these singularities are generically covered by event horizons, i.e., all collapsing stars, if they result in a singularity, end up as black holes. Although several theoretical examples of non-hidden (naked) singularities have been found, the question of the genericity of naked singularities is far from settled. This thesis presents a study of the causal structure of spherically symmetric models of dust collapse and its perturbations to investigate the genericity of naked singularities.

Quick reproduction of blast-wave flow-field properties of nuclear, TNT, and ANFO explosions

NASA Astrophysics Data System (ADS)

Groth, C. P. T.

1986-04-01

In many instances, extensive blast-wave flow-field properties are required in gasdynamics research studies of blast-wave loading and structure response, and in evaluating the effects of explosions on their environment. This report provides a very useful computer code, which can be used in conjunction with the DNA Nuclear Blast Standard subroutines and code, to quickly reconstruct complete and fairly accurate blast-wave data for almost any free-air (spherical) and surface-burst (hemispherical) nuclear, trinitrotoluene (TNT), or ammonium nitrate-fuel oil (ANFO) explosion. This code is capable of computing all of the main flow properties as functions of radius and time, as well as providing additional information regarding air viscosity, reflected shock-wave properties, and the initial decay of the flow properties just behind the shock front. Both spatial and temporal distributions of the major blast-wave flow properties are also made readily available. Finally, provisions are also included in the code to provide additional information regarding the peak or shock-front flow properties over a range of radii, for a specific explosion of interest.