Pulse design without the rotating-wave approximation
NASA Astrophysics Data System (ADS)
Ibáñez, S.; Li, Yi-Chao; Chen, Xi; Muga, J. G.
2015-12-01
We design realizable time-dependent semiclassical pulses to invert the population of a two-level system faster than adiabatically when the rotating-wave approximation cannot be applied. Different approaches, based on the counterdiabatic method or on invariants, may lead to singularities in the pulse functions. Ways to avoid or cancel the singularities are put forward when the pulse spans few oscillations. For many oscillations an alternative numerical minimization method is proposed and demonstrated.
Quantum anti-Zeno effect without rotating wave approximation
Ai Qing; Sun, C. P.; Li Yong; Zheng Hang
2010-04-15
In this article, we systematically study the spontaneous decay phenomenon of a two-level system under the influences of both its environment and repetitive measurements. In order to clarify some well-established conclusions about the quantum Zeno effect (QZE) and the quantum anti-Zeno effect (QAZE), we do not use the rotating wave approximation (RWA) in obtaining an effective Hamiltonian. We examine various spectral distributions by making use of our present approach in comparison with other approaches. It is found that with respect to a bare excited state even without the RWA, the QAZE can still happen for some cases, for example, the interacting spectra of hydrogen. However, for a physical excited state, which is a renormalized dressed state of the atomic state, the QAZE disappears and only the QZE remains. These discoveries inevitably show a transition from the QZE to the QAZE as the measurement interval changes.
Symmetric rotating-wave approximation for the generalized single-mode spin-boson system
Albert, Victor V.; Scholes, Gregory D.; Brumer, Paul
2011-10-15
The single-mode spin-boson model exhibits behavior not included in the rotating-wave approximation (RWA) in the ultra and deep-strong coupling regimes, where counter-rotating contributions become important. We introduce a symmetric rotating-wave approximation that treats rotating and counter-rotating terms equally, preserves the invariances of the Hamiltonian with respect to its parameters, and reproduces several qualitative features of the spin-boson spectrum not present in the original rotating-wave approximation both off-resonance and at deep-strong coupling. The symmetric rotating-wave approximation allows for the treatment of certain ultra- and deep-strong coupling regimes with similar accuracy and mathematical simplicity as does the RWA in the weak-coupling regime. Additionally, we symmetrize the generalized form of the rotating-wave approximation to obtain the same qualitative correspondence with the addition of improved quantitative agreement with the exact numerical results. The method is readily extended to higher accuracy if needed. Finally, we introduce the two-photon parity operator for the two-photon Rabi Hamiltonian and obtain its generalized symmetric rotating-wave approximation. The existence of this operator reveals a parity symmetry similar to that in the Rabi Hamiltonian as well as another symmetry that is unique to the two-photon case, providing insight into the mathematical structure of the two-photon spectrum, significantly simplifying the numerics, and revealing some interesting dynamical properties.
NASA Astrophysics Data System (ADS)
O'Brien, Chris; Scully, Marlan O.
2016-01-01
In a straightforward manner, we utilize Floquet theory and adiabatic elimination to derive an analytic expression for a monochromatically driven two-level atom, without making the rotating wave approximation. We show that the counter-rotating terms dropped in the rotating wave approximation are responsible for three major effects. First an ac-Stark phase shift of the driven transition, second increased excited state population from far-detuned driving of the Lorentzian line, and third extra frequencies in the population dynamics that result in "wiggles." The analytic result agrees well with numerical simultations over a wide range of parameters.
Dynamics of Jaynes-Cummings Model in the Absence of Rotating-Wave Approximation
NASA Astrophysics Data System (ADS)
Fan, Yun-Xia; Liu, Tao; Feng, Mang; Wang, Ke-Lin
2007-05-01
The Jaynes-Cummings model (JCM) is studied in the absence of the rotating-wave approximation (RWA) by a coherent-state expansion technique. In comparison with the previous paper in which the coherent-state expansion was performed only to the third order, we carry out in this paper a complete expansion to demonstrate exactly the dynamics of the JCM without the RWA. Our study gives a systematic method to solve the non-RWA problem, which would be useful in various physical systems, e.g., in a system with an ultracold trapped ion experiencing the running waves of lasers.
Quantum speed limits in open systems: Non-Markovian dynamics without rotating-wave approximation
Sun, Zhe; Liu, Jing; Ma, Jian; Wang, Xiaoguang
2015-01-01
We derive an easily computable quantum speed limit (QSL) time bound for open systems whose initial states can be chosen as either pure or mixed states. Moreover, this QSL time is applicable to either Markovian or non-Markovian dynamics. By using of a hierarchy equation method, we numerically study the QSL time bound in a qubit system interacting with a single broadened cavity mode without rotating-wave, Born and Markovian approximation. By comparing with rotating-wave approximation (RWA) results, we show that the counter-rotating terms are helpful to increase evolution speed. The problem of non-Markovianity is also considered. We find that for non-RWA cases, increasing system-bath coupling can not always enhance the non-Markovianity, which is qualitatively different from the results with RWA. When considering the relation between QSL and non-Markovianity, we find that for small broadening widths of the cavity mode, non-Markovianity can increase the evolution speed in either RWA or non-RWA cases, while, for larger broadening widths, it is not true for non-RWA cases. PMID:25676589
Cavity losses for the dissipative Jaynes Cummings Hamiltonian beyond rotating wave approximation
NASA Astrophysics Data System (ADS)
Scala, M.; Militello, B.; Messina, A.; Maniscalco, S.; Piilo, J.; Suominen, K.-A.
2007-11-01
A microscopic derivation of the master equation for the Jaynes-Cummings model with cavity losses is given, taking into account the terms in the dissipator which vary with frequencies of the order of the vacuum Rabi frequency. Our approach allows us to single out physical contexts wherein the usual phenomenological dissipator turns out to be fully justified and constitutes an extension of our previous analysis (Scala et al 2007 Phys. Rev. A 75 013811), where a microscopic derivation was given in the framework of the rotating wave approximation.
Atom-field entanglement in the Jaynes-Cummings model without rotating wave approximation
NASA Astrophysics Data System (ADS)
Mirzaee, M.; Batavani, M.
2015-04-01
In this paper, we present a structure for obtaining the exact eigenfunctions and eigenvalues of the Jaynes-Cummings model (JCM) without the rotating wave approximation (RWA). We study the evolution of the system in the strong coupling region using the time evolution operator without RWA. The entanglement of the system without RWA is investigated using the Von Neumann entropy as an entanglement measure. It is interesting that in the weak coupling regime, the population of the atomic levels and Von Neumann entropy without RWA model shows a good agreement with the RWA whereas in strong coupling domain, the results of these two models are quite different.
Fast control of semiconductor qubits beyond the rotating-wave approximation
NASA Astrophysics Data System (ADS)
Song, Yang; Kestner, J. P.; Wang, Xin; Das Sarma, S.
2016-07-01
We present a theoretical study of single-qubit operations by oscillatory fields on various semiconductor platforms. We explicitly show how to perform faster gate operations by going beyond the universally used rotating-wave approximation (RWA) regime, while using only two sinusoidal pulses. We first show for specific published experiments how much error is currently incurred by implementing pulses designed using standard RWA. We then show that an even modest increase in gate speed would cause problems in using RWA for gate design in the singlet-triplet (ST) and resonant-exchange (RX) qubits. We discuss the extent to which analytically keeping higher orders in the perturbation theory would address the problem. More strikingly, we give a new prescription for gating with strong coupling far beyond the RWA regime. We perform numerical calculations for the phases and the durations of two consecutive pulses to realize the key Hadamard and π/8 gates with coupling strengths up to several times the qubit splitting. Working in this manifestly non-RWA regime, the gate operation speeds up by two to three orders of magnitude and nears the quantum speed limit without requiring complicated pulse shaping or optimal control sequences.
Chen Qinghu; Yang Yuan; Liu Tao; Wang Kelin
2010-11-15
Entanglement evolution of two independent Jaynes-Cummings atoms without the rotating-wave approximation (RWA) is studied by a numerically exact approach. Previous results based on the RWA are essentially modified in the strong-coupling regime (g{>=}0.1), which has been reached in the recent experiments on the flux qubit coupled to the LC resonator. For the initial Bell state with anticorrelated spins, entanglement sudden death (ESD) is absent in the RWA but does appear in the present numerical calculation without the RWA. Aperiodic entanglement evolution in the strong-coupling regime is observed. The strong atom-cavity coupling facilitates the ESD. The sign of the detuning plays an essential role in the entanglement evolution for strong coupling, which is irrelevant in the RWA. Analytical results based on an unitary transformation are also given, which could not modify the RWA picture essentially. It is suggested that the activation of the photons may be the origin of ESD in this system.
Coupling of exciton-polaritons in low-Q coupled microcavities beyond the rotating wave approximation
NASA Astrophysics Data System (ADS)
Liu, Bin; Rai, Prabin; Grezmak, John; Twieg, Robert J.; Singer, Kenneth D.
2015-10-01
We have demonstrated coupling between a pair of ultrastrong light-matter coupled microcavities composed of neat glassy organic dye films between metallic (silver) mirrors at room temperature. Based upon our modified coupled oscillator model, we have observed that the degeneracy between the Rabi splittings associated with the symmetric and antisymmetric cavity modes is broken by the higher-order antiresonant terms in the Hamiltonian associated with the breakdown of the rotating wave approximation in the ultrastrong coupling regime. These results are in quantitative agreement with both experiment and transfer matrix modeling. The component cavities are characterized by Q factors around 12 and display a large vacuum Rabi splitting around 1.12 eV between the upper and lower polariton branches, which is about 52 % of the excited state energy, thus indicating ultrastrong coupling in each individual cavity. This large splitting is due to the large oscillator strength of the neat dye glass. We have also observed large polariton-induced incidence-side asymmetry in reflection spectra in a coupled cavity pair with one cavity having no exciton.
Fano-Agarwal couplings and non-rotating wave approximation in single-photon timed Dicke subradiance
NASA Astrophysics Data System (ADS)
Mirza, Imran M.; Begzjav, Tuguldur
2016-04-01
Recently a new class of single-photon timed Dicke (TD) subradiant states has been introduced with possible applications in single-photon–based quantum information storage and on demand ultrafast retrieval (Scully M. O., Phys. Rev. Lett., 115 (2015) 243602). However, the influence of any kind of virtual processes on the decay of these new kind of subradiant states has been left as an open question. In the present paper, we focus on this problem in detail. In particular, we investigate how pure Fano-Agarwal couplings and other virtual processes arising from non-rotating wave approximation impact the decay of otherwise sub- and superradiant states. In addition to the overall virtual couplings among all TD states, we also focus on the dominant role played by the couplings between specific TD states.
Parallel SVD updating using approximate rotations
NASA Astrophysics Data System (ADS)
Goetze, Juergen; Rieder, Peter; Nossek, J. A.
1995-06-01
In this paper a parallel implementation of the SVD-updating algorithm using approximate rotations is presented. In its original form the SVD-updating algorithm had numerical problems if no reorthogonalization steps were applied. Representing the orthogonalmatrix V (right singular vectors) using its parameterization in terms of the rotation angles of n(n - 1)/2 plane rotations these reorthogonalization steps can be avoided during the SVD-updating algorithm. This results in a SVD-updating algorithm where all computations (matrix vector multiplication, QRD-updating, Kogbetliantz's algorithm) are entirely based on the evaluation and application of orthogonal plane rotations. Therefore, in this form the SVD-updating algorithm is amenable to an implementation using CORDIC-based approximate rotations. Using CORDIC-based approximate rotations the n(n - 1)/2 rotations representing V (as well as all other rotations) are only computed to a certain approximation accuracy (in the basis arctan 2i). All necessary computations required during the SVD-updating algorithm (exclusively rotations) are executed with the same accuracy, i.e., only r << w (w: wordlength) elementary orthonormal (mu) rotations are used per plane rotation. Simulations show the efficiency of the implementation using CORDIC-based approximate rotations.
Rotational waves in geodynamics
NASA Astrophysics Data System (ADS)
Gerus, Artyom; Vikulin, Alexander
2015-04-01
The rotation model of a geoblock with intrinsic momentum was constructed by A.V. Vikulin and A.G. Ivanchin [9, 10] to describe seismicity within the Pacific Ocean margin. It is based on the idea of a rotational motion of geoblocks as the parts of the rotating body of the Earth that generates rotary deformation waves. The law of the block motion was derived in the form of the sine-Gordon equation (SG) [5, 9]; the dimensionless form of the equation is: δ2θ δ2θ δξ2 - δη2 = sinθ, (1) where θ = β/2, ξ = k0z and η = v0k0t are dimensionless coordinates, z - length of the chain of masses (blocks), t - time, β - turn angle, ν0 - representative velocity of the process, k0 - wave number. Another case analyzed was a chain of nonuniformly rotating blocks, with deviation of force moments from equilibrium positions μ, considering friction forces α along boundaries, which better matched a real-life seismic process. As a result, the authors obtained the law of motion for a block in a chain in the form of the modified SG equation [8]: δ2θ δ2θ δθ- δξ2 - δ η2 = sin θ+ α δη + μδ(ξ)sin θ (2)
NASA Astrophysics Data System (ADS)
Sun, Zhe; Zhou, Longwen; Xiao, Gaoyang; Poletti, Dario; Gong, Jiangbin
2016-01-01
We investigate Landau-Zener processes modeled by a two-level quantum system, with its finite bias energy varied in time and in the presence of a single broadened cavity mode at zero temperature. By applying the hierarchy equation method to the Landau-Zener problem, we computationally study the survival fidelity of adiabatic states without Born, Markov, rotating-wave, or other perturbative approximations. With this treatment it also becomes possible to investigate cases with very strong system-bath coupling. Different from a previous study of infinite-time Landau-Zener processes, the fidelity of the time-evolving state as compared with instantaneous adiabatic states shows nonmonotonic dependence on the system-bath coupling and on the sweep rate of the bias. We then consider the effect of applying a counterdiabatic driving field, which is found to be useful in improving the fidelity only for sufficiently short Landau-Zener processes. Numerically exact results show that different counterdiabatic driving fields can have very different robustness against environment effects. Lastly, using a case study, we discuss the possibility of introducing a dynamical decoupling field in order to eliminate the decoherence effect of the environment and, at the same time, to retain the positive role of a counterdiabatic field. Our work indicates that finite-time Landau-Zener processes with counterdiabatic driving offer a fruitful testbed to understand controlled adiabatic processes in open systems.
Drift waves in rotating plasmas
Horton, W.; Liu, J.
1983-09-01
The stability of the electron drift wave is investigated in the presence of E x B plasma rotation typical of the central cell plasma in tandem mirrors. It is shown that a rotationally-driven drift wave may occur at low azimuthal mode numbers. Conditions for rotational instabilities are derived. Quasilinear formulas are given for the anomalous transport associated with the unstable fluctuations.
Blast waves in rotating media.
NASA Technical Reports Server (NTRS)
Rossner, L. F.
1972-01-01
The model investigated involves a cylindrically symmetric blast wave generated by an infinitely long line explosion in a cold and homogeneous gas rotating rigidly in its self-gravitational field. It is found that within the context of rotation in a gravitational field a blast wave will not adopt the one-zone form familiar from similarity solutions but, rather, a two-zone form. The inner compression zone arises as a response to the presence of the restoring force, which drives a rarefaction wave into the outer compression zone.
Constant Density Approximations for the Flow Behind Axisymmetric Shock Waves
NASA Technical Reports Server (NTRS)
Munson, Albert G.
1961-01-01
The incompressible rotational flow equations are used to obtain solutions for the flow behind axisymmetric shock waves with conic longitudinal sections. The nonlinear part of the term due to rotation is retained in the analysis. Numerical results for standoff distance and stagnation point velocity gradient are presented for the case in which the shock wave is a paraboloid, a sphere, or an oblate or prolate ellipsoid. A similarity parameter is proposed which correlates approximately the flow behind geometrically similar shock waves at different free-stream conditions.
Wave-driven Rotation in Supersonically Rotating Mirrors
A. Fetterman and N.J. Fisch
2010-02-15
Supersonic rotation in mirrors may be produced by radio frequency waves. The waves produce coupled diffusion in ion kinetic and potential energy. A population inversion along the diffusion path then produces rotation. Waves may be designed to exploit a natural kinetic energy source or may provide the rotation energy on their own. Centrifugal traps for fusion and isotope separation may benefit from this wave-driven rotation.
Slowly rotating scalar field wormholes: The second order approximation
Kashargin, P. E.; Sushkov, S. V.
2008-09-15
We discuss rotating wormholes in general relativity with a scalar field with negative kinetic energy. To solve the problem, we use the assumption about slow rotation. The role of a small dimensionless parameter plays the ratio of the linear velocity of rotation of the wormhole's throat and the velocity of light. We construct the rotating wormhole solution in the second-order approximation with respect to the small parameter. The analysis shows that the asymptotical mass of the rotating wormhole is greater than that of the nonrotating one, and the null energy condition violation in the rotating wormhole spacetime is weaker than that in the nonrotating one.
Dust waves in rotating planetary magnetospheres
Haque, Q.; Saleem, H.
2005-10-31
Low frequency electrostatic drift and acoustic waves are studied in rotating dusty plasmas. Linear dispersion relation is found. It is pointed out that rotation of the planet can introduce dust drift waves through Coriolis force in the planetary magnetospheres. This mode can couple with dust acoustic mode. Coriolis force effect may give rise to dipolar vortices in rotating dusty plasmas of planetary magnetospheres.
Molecular collisions 21: Semiclassical approximation to atom-symmetric top rotational excitation
NASA Technical Reports Server (NTRS)
Russell, D.; Curtiss, C. F.
1973-01-01
A distorted wave approximation to the T matrix for atom-symmetric top scattering was developed. The approximation is correct to first order in the part of the interaction potential responsible for transitions in the component of rotational angular momentum along the symmetry axis of the top. A semiclassical expression for this T matrix is derived by assuming large values of orbital and rotational angular momentum quantum numbers.
Detecting Gravitational Waves using Pade Approximants
NASA Astrophysics Data System (ADS)
Porter, E. K.; Sathyaprakash, B. S.
1998-12-01
We look at the use of Pade Approximants in defining a metric tensor for the inspiral waveform template manifold. By using this method we investigate the curvature of the template manifold and the number of templates needed to carry out a realistic search for a Gravitational Wave signal. By comparing this method with the normal use of Taylor Approximant waveforms we hope to show that (a) Pade Approximants are a superior method for calculating the inspiral waveform, and (b) the number of search templates needed, and hence computing power, is reduced.
Wave-Driven Rotation In Centrifugal Mirrors
Abraham J. Fetterman and Nathaniel J. Fisch
2011-03-28
Centrifugal mirrors use supersonic rotation to provide axial confinement and enhanced stability. Usually the rotation is produced using electrodes, but these electrodes have limited the rotation to the Alfven critical ionization velocity, which is too slow to be useful for fusion. Instead, the rotation could be produced using radio frequency waves. A fixed azimuthal ripple is a simple and efficient wave that could produce rotation by harnessing alpha particle energy. This is an extension of the alpha channeling effect. The alpha particle power and efficiency in a simulated devices is sufficient to produce rotation without external energy input. By eliminating the need for electrodes, this opens new opportunities for centrifugal traps.
Molecular collisions. 11: Semiclassical approximation to atom-symmetric top rotational excitation
NASA Technical Reports Server (NTRS)
Russell, D.; Curtiss, C. F.
1973-01-01
In a paper of this series a distorted wave approximation to the T matrix for atom-symmetric top scattering was developed which is correct to first order in the part of the interaction potential responsible for transitions in the component of rotational angular momentum along the symmetry axis of the top. A semiclassical expression for this T matrix is derived by assuming large values of orbital and rotational angular momentum quantum numbers.
Generalized stationary phase approximations for mountain waves
NASA Astrophysics Data System (ADS)
Knight, H.; Broutman, D.; Eckermann, S. D.
2016-04-01
Large altitude asymptotic approximations are derived for vertical displacements due to mountain waves generated by hydrostatic wind flow over arbitrary topography. This leads to new asymptotic analytic expressions for wave-induced vertical displacement for mountains with an elliptical Gaussian shape and with the major axis oriented at any angle relative to the background wind. The motivation is to understand local maxima in vertical displacement amplitude at a given height for elliptical mountains aligned at oblique angles to the wind direction, as identified in Eckermann et al. ["Effects of horizontal geometrical spreading on the parameterization of orographic gravity-wave drag. Part 1: Numerical transform solutions," J. Atmos. Sci. 72, 2330-2347 (2015)]. The standard stationary phase method reproduces one type of local amplitude maximum that migrates downwind with increasing altitude. Another type of local amplitude maximum stays close to the vertical axis over the center of the mountain, and a new generalized stationary phase method is developed to describe this other type of local amplitude maximum and the horizontal variation of wave-induced vertical displacement near the vertical axis of the mountain in the large altitude limit. The new generalized stationary phase method describes the asymptotic behavior of integrals where the asymptotic parameter is raised to two different powers (1/2 and 1) rather than just one power as in the standard stationary phase method. The vertical displacement formulas are initially derived assuming a uniform background wind but are extended to accommodate both vertical shear with a fixed wind direction and vertical variations in the buoyancy frequency.
NASA Astrophysics Data System (ADS)
Meath, William J.; Jagatap, B. N.
2011-10-01
One of the purposes of this paper is to develop an analytical many-level generalized rotating wave approximation (GRWA), including the effects of permanent dipoles, for the excitation of many-level molecules through the simultaneous absorption of two photons. Included are expressions for the two-photon laser-molecule coupling C, and its two components Cd and Cv corresponding to the direct permanent dipole and the virtual state excitation mechanisms, respectively, and related observables such as the time-dependent populations of the initial and final states of the excitation process and resonance profiles. This GRWA treatment also includes an energy shift parameter ɛ, which causes shifts in the position of the resonance energy as the laser intensity increases. The effects of permanent dipoles are very different in Cv and ɛ versus Cd. These effects have been discussed previously for Cd using analytic two-level RWA approaches. The analytical results for Cv and ɛ obtained here are new as is their use in discussing the influence of permanent dipoles in the parts of the two-photon excitation process involving virtual states. In the absence of permanent dipoles Cd is zero whereas Cv and ɛ are not; they equal the corresponding perturbation theory results. The GRWA and perturbative results are related by Bessel function damping functions which, for dipolar molecules, damp out the divergence of the perturbative results as the laser intensity increases. Illustrative examples are given for a two-photon excitation involving a model chromophore which has a significant virtual state contribution through both the laser-molecule coupling and the energy shift parameter.
Magnetized stratified rotating shear waves
NASA Astrophysics Data System (ADS)
Salhi, A.; Lehner, T.; Godeferd, F.; Cambon, C.
2012-02-01
We present a spectral linear analysis in terms of advected Fourier modes to describe the behavior of a fluid submitted to four constraints: shear (with rate S), rotation (with angular velocity Ω), stratification, and magnetic field within the linear spectral theory or the shearing box model in astrophysics. As a consequence of the fact that the base flow must be a solution of the Euler-Boussinesq equations, only radial and/or vertical density gradients can be taken into account. Ertel's theorem no longer is valid to show the conservation of potential vorticity, in the presence of the Lorentz force, but a similar theorem can be applied to a potential magnetic induction: The scalar product of the density gradient by the magnetic field is a Lagrangian invariant for an inviscid and nondiffusive fluid. The linear system with a minimal number of solenoidal components, two for both velocity and magnetic disturbance fields, is eventually expressed as a four-component inhomogeneous linear differential system in which the buoyancy scalar is a combination of solenoidal components (variables) and the (constant) potential magnetic induction. We study the stability of such a system for both an infinite streamwise wavelength (k1=0, axisymmetric disturbances) and a finite one (k1≠0, nonaxisymmetric disturbances). In the former case (k1=0), we recover and extend previous results characterizing the magnetorotational instability (MRI) for combined effects of radial and vertical magnetic fields and combined effects of radial and vertical density gradients. We derive an expression for the MRI growth rate in terms of the stratification strength, which indicates that purely radial stratification can inhibit the MRI instability, while purely vertical stratification cannot completely suppress the MRI instability. In the case of nonaxisymmetric disturbances (k1≠0), we only consider the effect of vertical stratification, and we use Levinson's theorem to demonstrate the stability of the
Magnetized stratified rotating shear waves.
Salhi, A; Lehner, T; Godeferd, F; Cambon, C
2012-02-01
We present a spectral linear analysis in terms of advected Fourier modes to describe the behavior of a fluid submitted to four constraints: shear (with rate S), rotation (with angular velocity Ω), stratification, and magnetic field within the linear spectral theory or the shearing box model in astrophysics. As a consequence of the fact that the base flow must be a solution of the Euler-Boussinesq equations, only radial and/or vertical density gradients can be taken into account. Ertel's theorem no longer is valid to show the conservation of potential vorticity, in the presence of the Lorentz force, but a similar theorem can be applied to a potential magnetic induction: The scalar product of the density gradient by the magnetic field is a Lagrangian invariant for an inviscid and nondiffusive fluid. The linear system with a minimal number of solenoidal components, two for both velocity and magnetic disturbance fields, is eventually expressed as a four-component inhomogeneous linear differential system in which the buoyancy scalar is a combination of solenoidal components (variables) and the (constant) potential magnetic induction. We study the stability of such a system for both an infinite streamwise wavelength (k(1) = 0, axisymmetric disturbances) and a finite one (k(1) ≠ 0, nonaxisymmetric disturbances). In the former case (k(1) = 0), we recover and extend previous results characterizing the magnetorotational instability (MRI) for combined effects of radial and vertical magnetic fields and combined effects of radial and vertical density gradients. We derive an expression for the MRI growth rate in terms of the stratification strength, which indicates that purely radial stratification can inhibit the MRI instability, while purely vertical stratification cannot completely suppress the MRI instability. In the case of nonaxisymmetric disturbances (k(1) ≠ 0), we only consider the effect of vertical stratification, and we use Levinson's theorem to demonstrate the
Wave-particle Interactions In Rotating Mirrors
Abraham J. Fetterman and Nathaniel J. Fisch
2011-01-11
Wave-particle interactions in E×B rotating plasmas feature an unusual effect: particles are diffused by waves in both potential energy and kinetic energy. This wave-particle interaction generalizes the alpha channeling effect, in which radio frequency waves are used to remove alpha particles collisionlessly at low energy. In rotating plasmas, the alpha particles may be removed at low energy through the loss cone, and the energy lost may be transferred to the radial electric field. This eliminates the need for electrodes in the mirror throat, which have presented serious technical issues in past rotating plasma devices. A particularly simple way to achieve this effect is to use a high azimuthal mode number perturbation on the magnetic field. Rotation can also be sustained by waves in plasmas without a kinetic energy source. This type of wave has been considered for plasma centrifuges used for isotope separation. Energy may also be transferred from the electric field to particles or waves, which may be useful for ion heating and energy generation.
Gravitational wave burst signal from core collapse of rotating stars
Dimmelmeier, Harald; Ott, Christian D.; Marek, Andreas; Janka, H.-Thomas
2008-09-15
We present results from detailed general relativistic simulations of stellar core collapse to a proto-neutron star, using two different microphysical nonzero-temperature nuclear equations of state as well as an approximate description of deleptonization during the collapse phase. Investigating a wide variety of rotation rates and profiles as well as masses of the progenitor stars and both equations of state, we confirm in this very general setup the recent finding that a generic gravitational wave burst signal is associated with core bounce, already known as type I in the literature. The previously suggested type II (or 'multiple-bounce') waveform morphology does not occur. Despite this reduction to a single waveform type, we demonstrate that it is still possible to constrain the progenitor and postbounce rotation based on a combination of the maximum signal amplitude and the peak frequency of the emitted gravitational wave burst. Our models include to sufficient accuracy the currently known necessary physics for the collapse and bounce phase of core-collapse supernovae, yielding accurate and reliable gravitational wave signal templates for gravitational wave data analysis. In addition, we assess the possibility of nonaxisymmetric instabilities in rotating nascent proto-neutron stars. We find strong evidence that in an iron core-collapse event the postbounce core cannot reach sufficiently rapid rotation to become subject to a classical bar-mode instability. However, many of our postbounce core models exhibit sufficiently rapid and differential rotation to become subject to the recently discovered dynamical instability at low rotation rates.
Inertial modes of rigidly rotating neutron stars in Cowling approximation
Kastaun, Wolfgang
2008-06-15
In this article, we investigate inertial modes of rigidly rotating neutron stars, i.e. modes for which the Coriolis force is dominant. This is done using the assumption of a fixed spacetime (Cowling approximation). We present frequencies and eigenfunctions for a sequence of stars with a polytropic equation of state, covering a broad range of rotation rates. The modes were obtained with a nonlinear general relativistic hydrodynamic evolution code. We further show that the eigenequations for the oscillation modes can be written in a particularly simple form for the case of arbitrary fast but rigid rotation. Using these equations, we investigate some general characteristics of inertial modes, which are then compared to the numerically obtained eigenfunctions. In particular, we derive a rough analytical estimate for the frequency as a function of the number of nodes of the eigenfunction, and find that a similar empirical relation matches the numerical results with unexpected accuracy. We investigate the slow rotation limit of the eigenequations, obtaining two different sets of equations describing pressure and inertial modes. For the numerical computations we only considered axisymmetric modes, while the analytic part also covers nonaxisymmetric modes. The eigenfunctions suggest that the classification of inertial modes by the quantum numbers of the leading term of a spherical harmonic decomposition is artificial in the sense that the largest term is not strongly dominant, even in the slow rotation limit. The reason for the different structure of pressure and inertial modes is that the Coriolis force remains important in the slow rotation limit only for inertial modes. Accordingly, the scalar eigenequation we obtain in that limit is spherically symmetric for pressure modes, but not for inertial modes.
On Plasma Rotation Induced by Traveling Fast Alfvin Waves
F.W. Perkins; R.B. White; and V.S. Chan
2001-08-09
Absorption of fast Alfven waves by the minority fundamental ion-cyclotron resonance, coupled with finite banana width physics, generates torque distributions and ultimately rotational shear layers in the bulk plasma, even when the toroidal wavenumber k(subscript ''phi'') = n/R of the fast wave vanishes (n=0) and cyclotron absorption introduces no angular momentum nor canonical angular momentum [F.W. Perkins, R.B. White, P.T. Bonoli, and V.S. Chan, Phys. Plasmas 8 (2001) 2181]. The present work extends these results to travelling waves with non-zero n where heating directly introduces angular momentum. Since tokamak fast-wave antennas have approximately one wavelength per toroidal field coil, the toroidal mode number n lies in the range n = 10-20, independent of machine size. A zero-dimensional analysis shows that the rotation rate arising from direct torque is comparable to that of the rotational shear layer and has the same scaling. Nondimensional rotation profiles for n = (-10, 10) show modest changes from the n = 0 case in the expected direction. For a balanced antenna spectrum, the nondimensional rotational profile (averaged over n = -10, 10) lies quite close to the n = 0 profile.
Millimetre Wave with Rotational Orbital Angular Momentum
Zhang, Chao; Ma, Lu
2016-01-01
Orbital angular momentum (OAM) has been widely studied in fibre and short-range communications. The implementation of millimetre waves with OAM is expected to increase the communication capacity. Most experiments demonstrate the distinction of OAM modes by receiving all of the energy in the surface vertical to the radiation axis in space. However, the reception of OAM is difficult in free space due to the non-zero beam angle and divergence of energy. The reception of OAM in the space domain in a manner similar to that in optical fibres (i.e., receiving all of the energy rings vertical to the radiation axis) is impractical, especially for long-distance transmission. Here, we fabricate a prototype of the antenna and demonstrate that rather than in the space domain, the OAM can be well received in the time domain via a single antenna by rotating the OAM wave at the transmitter, i.e., the radio wave with rotational OAM. The phase and frequency measured in the experiment reveal that for different OAM modes, the received signals act as a commonly used orthogonal frequency division multiplexing (OFDM) signal in the time domain. This phase rotation has promising prospects for use in the practical reception of different OAMs of millimetre waves in long-distance transmission. PMID:27596746
Millimetre Wave with Rotational Orbital Angular Momentum.
Zhang, Chao; Ma, Lu
2016-01-01
Orbital angular momentum (OAM) has been widely studied in fibre and short-range communications. The implementation of millimetre waves with OAM is expected to increase the communication capacity. Most experiments demonstrate the distinction of OAM modes by receiving all of the energy in the surface vertical to the radiation axis in space. However, the reception of OAM is difficult in free space due to the non-zero beam angle and divergence of energy. The reception of OAM in the space domain in a manner similar to that in optical fibres (i.e., receiving all of the energy rings vertical to the radiation axis) is impractical, especially for long-distance transmission. Here, we fabricate a prototype of the antenna and demonstrate that rather than in the space domain, the OAM can be well received in the time domain via a single antenna by rotating the OAM wave at the transmitter, i.e., the radio wave with rotational OAM. The phase and frequency measured in the experiment reveal that for different OAM modes, the received signals act as a commonly used orthogonal frequency division multiplexing (OFDM) signal in the time domain. This phase rotation has promising prospects for use in the practical reception of different OAMs of millimetre waves in long-distance transmission. PMID:27596746
Gravito-inertial waves in a differentially rotating spherical shell
NASA Astrophysics Data System (ADS)
Mirouh, G. M.; Baruteau, C.; Rieutord, M.; Ballot, J.
2016-08-01
The gravito-inertial waves propagating over a shellular baroclinic flow inside a rotating spherical shell are analysed using the Boussinesq approximation. The wave properties are examined by computing paths of characteristics in the non-dissipative limit, and by solving the full dissipative eigenvalue problem using a high-resolution spectral method. Gravito-inertial waves are found to obey a mixed-type second-order operator and to be often focused around short-period attractors of characteristics or trapped in a wedge formed by turning surfaces and boundaries. We also find eigenmodes that show a weak dependence with respect to viscosity and heat diffusion just like truly regular modes. Some axisymmetric modes are found unstable and likely destabilized by baroclinic instabilities. Similarly, some non-axisymmetric modes that meet a critical layer (or corotation resonance) can turn unstable at sufficiently low diffusivities. In all cases, the instability is driven by the differential rotation. For many modes of the spectrum, neat power laws are found for the dependence of the damping rates with diffusion coefficients, but the theoretical explanation for the exponent values remains elusive in general. The eigenvalue spectrum turns out to be very rich and complex, which lets us suppose an even richer and more complex spectrum for rotating stars or planets that own a differential rotation driven by baroclinicity.
A consistent collinear triad approximation for operational wave models
NASA Astrophysics Data System (ADS)
Salmon, J. E.; Smit, P. B.; Janssen, T. T.; Holthuijsen, L. H.
2016-08-01
In shallow water, the spectral evolution associated with energy transfers due to three-wave (or triad) interactions is important for the prediction of nearshore wave propagation and wave-driven dynamics. The numerical evaluation of these nonlinear interactions involves the evaluation of a weighted convolution integral in both frequency and directional space for each frequency-direction component in the wave field. For reasons of efficiency, operational wave models often rely on a so-called collinear approximation that assumes that energy is only exchanged between wave components travelling in the same direction (collinear propagation) to eliminate the directional convolution. In this work, we show that the collinear approximation as presently implemented in operational models is inconsistent. This causes energy transfers to become unbounded in the limit of unidirectional waves (narrow aperture), and results in the underestimation of energy transfers in short-crested wave conditions. We propose a modification to the collinear approximation to remove this inconsistency and to make it physically more realistic. Through comparison with laboratory observations and results from Monte Carlo simulations, we demonstrate that the proposed modified collinear model is consistent, remains bounded, smoothly converges to the unidirectional limit, and is numerically more robust. Our results show that the modifications proposed here result in a consistent collinear approximation, which remains bounded and can provide an efficient approximation to model nonlinear triad effects in operational wave models.
Scattering of electromagnetic wave by dielectric cylinder in eikonal approximation
NASA Astrophysics Data System (ADS)
Syshchenko, V. V.
2016-07-01
The scattering of the plane electromagnetic wave on a spatially extended, fiber lake target is considered. The formula for the scattering cross section is obtained using the approximation analogous to eikonal one in quantum mechanics.
Waves and vortices in rotating stratified turbulence
NASA Astrophysics Data System (ADS)
Pouquet, Annick; Herbert, Corentin; Marino, Raffaele; Rosenberg, Duane
2015-04-01
The interactions between vortices and waves is a long-standing problem in fluid turbulence. It can lead to a self-sustaining process that is dominant, for example in pipe flows, and to the prediction of large-scale coherent structures such as baroclinic jets in planetary atmospheres, and it can also be used as a control tool for the onset of turbulence. Similarly, the dynamics of the atmosphere and the ocean is dominated by complex interactions between nonlinear eddies and waves due to a combination of rotation and stratification (characterized respectively by frequencies f and N), as well as shear layers. The waves are faster at large scales, and this leads to a quasi-geostrophic quasi-linear regime in which there is a balance between pressure gradient and the Coriolis and gravity forces. The range of scales in these geophysical flows before dissipation prevails is such that other regimes can arise in which turbulence comes into play, with the eddy turn-over time becoming comparable to the wave period, and for which isotropy recovers for sufficiently high Reynolds numbers. One may decompose the flow-- observational, experimental or numerical, in terms of the normal modes that it supports, i.e. the inertia-gravity waves and the (slow, zero frequency) vortical modes carrying the potential vorticity, thanks to the existence of a small parameter, as for example the fluctuation around a mean flow or the ratio of the wave period to the eddy turn-over time. In this context an ensemble of data sets of rotating stratified turbulence will be analyzed, stemming from accurate direct numerical simulations of the Boussinesq equations at high resolution, up to 40963 grid points, using high-performance computing. These flows all support a constant-flux bi-directional cascade of energy towards both the large scales and the small scales. The parameter space includes the Reynolds number, the Prandtl number(s), and the Rossby and Froude numbers, and a universal response to a variety
Experiments on nonlinear coastal shelf waves in a rotating annulus
NASA Astrophysics Data System (ADS)
Stewart, Andrew; Dellar, Paul; Johnson, Ted
2010-05-01
In many coastal regions, the ocean depth increases very rapidly at a 'shelf break' running approximately parallel to the coastline. A shelf break marks the edge of the continental shelf, and separates the deep ocean from the relatively shallow near-coastal ocean. Shelf breaks play an important rôle in steering coastal currents, such as the Aghulas current which flows southwest along the eastern coast of Africa at speeds of up to 1 ms-1. To investigate the effect of shelf breaks in stabilising coastal currents, we have carried out laboratory experiments to generate nonlinear topographic Rossby waves that propagate along a shelf break in the presence of a mean current. Our experiments use an annular channel in a rotating cylindrical tank. We model the shelf break with a tank floor that undergoes a sharp drop at a certain radius Rh. The tank was filled with homogeneous fluid, and set rotating with constant angular velocity until the fluid inside rotated as a solid body. We then induced horizontal perturbations to the fluid, which caused Taylor columns to move inwards and outwards across the shelf. Conservation of potential vorticity forces these columns to acquire relative vorticity as they cross the shelf, which allows waves to propagate around the tank. These waves are known as topographic Rossby shelf waves. The large-scale flow around shelf breaks has been the subject of a series of theoretical investigations. These commonly approximate the sharp drop in the depth by a discontinuity, on the assumption that the horizontal length scale of the flow is much larger than the width of the shelf break. However, the fluid is still assumed to move in columns, as in shallow water theory, even as it crosses the shelf. Our present work aims to consolidate a theoretical model for nonlinear waves propagating along a depth discontinuity in the context of our laboratory experiments. We assume that rotational effects are dominant, and that fluid velocities are small compared with
The Inhomogeneous Waves in a Rotating Piezoelectric Body
Chen, Si
2013-01-01
This paper presents the analysis and numerical results of rotation, propagation angle, and attenuation angle upon the waves propagating in the piezoelectric body. Via considering the centripetal and Coriolis accelerations in the piezoelectric equations with respect to a rotating frame of reference, wave velocities and attenuations are derived and plotted graphically. It is demonstrated that rotation speed vector can affect wave velocities and make the piezoelectric body behaves as if it was damping. Besides, the effects of propagation angle and attenuation angle are presented. Critical point is found when rotation speed is equal to wave frequency, around which wave characteristics change drastically. PMID:24298219
Revisiting the envelope approximation: Gravitational waves from bubble collisions
NASA Astrophysics Data System (ADS)
Weir, David J.
2016-06-01
We study the envelope approximation and its applicability to first-order phase transitions in the early Universe. We demonstrate that the power laws seen in previous studies exist independently of the nucleation rate. We also compare the envelope approximation prediction to results from large-scale phase transition simulations. For phase transitions where the contribution to gravitational waves from scalar fields dominates over that from the coupled plasma of light particles, the envelope approximation is in agreement, giving a power spectrum of the same form and order of magnitude. In all other cases the form and amplitude of the gravitational wave power spectrum is markedly different and new techniques are required.
Parabolic approximation method for fast magnetosonic wave propagation in tokamaks
Phillips, C.K.; Perkins, F.W.; Hwang, D.Q.
1985-07-01
Fast magnetosonic wave propagation in a cylindrical tokamak model is studied using a parabolic approximation method in which poloidal variations of the wave field are considered weak in comparison to the radial variations. Diffraction effects, which are ignored by ray tracing mthods, are included self-consistently using the parabolic method since continuous representations for the wave electromagnetic fields are computed directly. Numerical results are presented which illustrate the cylindrical convergence of the launched waves into a diffraction-limited focal spot on the cyclotron absorption layer near the magnetic axis for a wide range of plasma confinement parameters.
Gravitational wave asteroseismology with fast rotating neutron stars
Gaertig, Erich; Kokkotas, Kostas D.
2011-03-15
We investigate damping and growth times of the quadrupolar f mode for rapidly rotating stars and a variety of different polytropic equations of state in the Cowling approximation. This is the first study of the damping/growth time of these types of oscillations for fast-rotating neutron stars in a relativistic treatment where the spacetime degrees of freedom of the perturbations are neglected. We use these frequencies and damping/growth times to create robust empirical formulae which can be used for gravitational-wave asteroseismology. The estimation of the damping/growth time is based on the quadrupole formula and our results agree very well with Newtonian ones in the appropriate limit.
Various approximations made in augmented-plane-wave calculations
NASA Astrophysics Data System (ADS)
Bacalis, N. C.; Blathras, K.; Thomaides, P.; Papaconstantopoulos, D. A.
1985-10-01
The effects of various approximations used in performing augmented-plane-wave calculations were studied for elements of the fifth and sixth columns of the Periodic Table, namely V, Nb, Ta, Cr, Mo, and W. Two kinds of approximations have been checked: (i) variation of the number of k points used to iterate to self-consistency, and (ii) approximations for the treatment of the core states. In addition a comparison between relativistic and nonrelativistic calculations is made, and an approximate method of calculating the spin-orbit splitting is given.
Nuclear Rotations and the Born-Oppenheimer Approximation
Zettili, Nouredine
2011-10-27
We deal here with the application of the Nuclear Born Oppenheimer (NBO) method to the description of nuclear rotations. As an edifying illustration, we apply the NBO formalism to study the rotational motion of nuclei which are axially-symmetric and even, but whose shells are not closed. We focus, in particular, on the derivation of expressions for the rotational energy and for the moment of inertia. Additionally, we examine the connection between the NBO method and the self-consistent cranking (SCC) model. Finally, we compare the moment of inertia generated by the NBO method with the Thouless-Valantin formula and hence establish a connection between the NBO method and the large body of experimental data.
Atmospheric planetary waves induced by solar rotation
NASA Technical Reports Server (NTRS)
Krivolutsky, A. A.
1989-01-01
It is known that there are variations in the atmospheric processes with a period close to that of the rotation of the Sun (27 days). The variations are discovered in tropospheric processes, rainfalls, geopotential and in stratosphere. The main theoretical problem is the identification of the physical process by which these heterogeneous solar and meteorological phenomena are connected. Ivanovsky and Krivolutsky proposed that the periodic heating of the ozone layer by the short wave radiation would be the reason of excitation the 27-day oscillations. It was also assumed that excitement takes place in condition of resonance with an excited mode corresponding to the conditions present in the stratospheric circulations. The possibility is discussed of the resonant excitation and presentation is made of the data analysis results which support this idea.
Approximate method for controlling solid elastic waves by transformation media
NASA Astrophysics Data System (ADS)
Hu, Jin; Chang, Zheng; Hu, Gengkai
2011-11-01
By idealizing a general mapping as a series of local affine ones, we derive approximately transformed material parameters necessary to control solid elastic waves within classical elasticity theory. The transformed elastic moduli are symmetric, and can be used with Navier's equation to manipulate elastic waves. It is shown numerically that the method can provide a powerful tool to control elastic waves in solids in case of high frequency or small material gradient. Potential applications can be anticipated in nondestructive testing, structure impact protection, petroleum exploration, and seismology.
Freely tunable broadband polarization rotator for terahertz waves.
Fan, Ren-Hao; Zhou, Yu; Ren, Xiao-Ping; Peng, Ru-Wen; Jiang, Shang-Chi; Xu, Di-Hu; Xiong, Xiang; Huang, Xian-Rong; Wang, Mu
2015-02-18
A freely tunable polarization rotator for broadband terahertz waves is demonstrated using a three-rotating-layer metallic grating structure, which can conveniently rotate the polarization of a linearly polarized terahertz wave to any desired direction with nearly perfect conversion efficiency. This low-cost, high-efficiency, and freely tunable device has potential applications as material analysis, wireless communication, and THz imaging. PMID:25545177
Impact of rotation on stochastic excitation of gravity and gravito-inertial waves in stars
NASA Astrophysics Data System (ADS)
Mathis, S.; Neiner, C.; Tran Minh, N.
2014-05-01
Context. Gravity waves (or their signatures) are detected in stars thanks to helio- and asteroseismology, and they may play an important role in the evolution of stellar angular momentum. Moreover, a previous observational study of the CoRoT target HD 51452 demonstrated the potential strong impact of rotation on the stochastic excitation of gravito-inertial waves in stellar interiors. Aims: Our goal is to explore and unravel the action of rotation on the stochastic excitation of gravity and gravito-inertial waves in stars. Methods: The dynamics of gravito-inertial waves in stellar interiors in both radiation and in convection zones is described with a local non-traditional f-plane model. The coupling of these waves with convective turbulent flows, which leads to their stochastic excitation, is studied in this framework. Results: First, we find that in the super-inertial regime in which the wave frequency is twice as high as the rotation frequency (σ > 2Ω), the evanescence of gravito-inertial waves in convective regions decreases with decreasing wave frequency. Next, in the sub-inertial regime (σ < 2Ω), gravito-inertial waves become purely propagative inertial waves in convection zones. Simultaneously, turbulence in convective regions is modified by rotation. Indeed, the turbulent energy cascade towards small scales is slowed down, and in the case of rapid rotation, strongly anisotropic turbulent flows are obtained that can be understood as complex non-linear triadic interactions of propagative inertial waves. These different behaviours, due to the action of the Coriolis acceleration, strongly modify the wave coupling with turbulent flows. On one hand, turbulence weakly influenced by rotation is coupled with evanescent gravito-inertial waves. On the other hand, rapidly rotating turbulence is intrinsically and strongly coupled with sub-inertial waves. Finally, to study these mechanisms, the traditional approximation cannot be assumed because it does not properly
Janzen, V.P.; Andrews, H.R.; Ball, G.C.
1996-12-31
There is now widespread evidence for the smooth termination of rotational bands in A {approx_equal} 110 nuclei at spins of 40-to-50{Dirac_h}s. The characteristics of these bands are compared to those of bands recently observed to high spin in {sup 64}Zn and {sup 48}Cr, studied with the 8{pi} {gamma}-ray spectrometer coupled to the Chalk River miniball charged-particle-detector array.
Vortex wave interaction in a rotating stratified fluid: WKB simulations
NASA Astrophysics Data System (ADS)
Moulin, F. Y.; Flór, J.-B.
2006-09-01
In this paper we present ray-tracing results on the interaction of inertia gravity waves with the velocity field of a vortex in a rotating stratified fluid. We consider rays that interact with a Rankine-type vortex with a Gaussian vertical distribution of vertical vorticity. The rays are traced, solving the WKB equations in cylindrical coordinates for vortices with different aspect ratios. The interactions are governed by the value of Fr R/lambda where Fr is the vortex Froude number, R its radius, and lambda the incident wavelength. The Froude number is defined as Fr {=} U_{max}/(NR) with U_{max} the maximum azimuthal velocity and N the buoyancy frequency. When Fr R/lambda {>} 1, part of the incident wave field strongly decreases in wavelength while its energy is trapped. The vortex aspect ratio, H/R, determines which part of this incident wave field is trapped, and where its energy accumulates in the vortex. Increasing values of Fr R/lambda are shown to be associated with a narrowing of the trapping region and an increase of the energy amplification of trapped rays. In the inviscid approximation, the infinite energy amplification predicted for unidirectional flows is retrieved in the limit Fr R/lambda {->} infty. When viscous damping is taken into account, the maximal amplification of the wave energy becomes a function of Fr R/lambda and a Reynolds number, Re_{wave} {=} sqrt{U_L(2+U_H^2}/nu) k(2) , with U_L and U_H typical values of the shear in, respectively, the radial and vertical directions; the kinematic viscosity is nu, and the wavenumber k, for the incident waves. In a sequel paper, we compare WKB simulations with experimental results.
Exact Faraday rotation in the cylindrical Einstein-Maxwell waves
Arafah, M.R.; Fakioglu, S.; Halilsoy, M. )
1990-07-15
We obtain the exact behavior of the cross-polarized cylindrical Einstein-Maxwell waves that generalizes the well-known Einstein-Rosen waves. In the presence of the second mode of polarization the outgoing waves interact with the incoming ones to exhibit an analogous effect of the Faraday rotation.
Freely-tunable broadband polarization rotator for terahertz waves
NASA Astrophysics Data System (ADS)
Peng, Ru-Wen; Fan, Ren-Hao; Zhou, Yu; Jiang, Shang-Chi; Xiong, Xiang; Huang, Xian-Rong; Wang, Mu
It is known that commercially-available terahertz (THz) emitters usually generate linearly polarized waves only along certain directions, but in practice, a polarization rotator that is capable of rotating the polarization of THz waves to any direction is particularly desirable and it will have various important applications. In this work, we demonstrate a freely tunable polarization rotator for broadband THz waves using a three-rotating-layer metallic grating structure, which can conveniently rotate the polarization of a linearly polarized THz wave to any desired direction with nearly perfect conversion efficiency. The device performance has been experimentally demonstrated by both THz transmission spectra and direct imaging. The polarization rotation originates from multi wave interference in the three-layer grating structure based on the scattering-matrix analysis. We can expect that this active broadband polarization rotator has wide applications in analytical chemistry, biology, communication technology, imaging, etc.. Reference: R. H. Fan, Y. Zhou, X. P. Ren, R. W. Peng, S. C. Jiang, D. H. Xu, X. Xiong, X. R. Huang, and Mu Wang, Advanced Materials 27,1201(2015). Freely-tunable broadband polarization rotator for terahertz waves.
Anisotropic electromagnetic wave propagation modeling using parabolic approximations
NASA Astrophysics Data System (ADS)
Brent, R. I.; Siegmann, W. L.; Jacobson, M. J.; Jacyna, G. M.
1990-12-01
A new method for the investigation of anisotropic electromagnetic wave propagation in the atmosphere is developed using parabolic approximations. Model equations for the electric field components are formulated which include the effects of both the inhomogeneous atmosphere and the static magnetic field of the earth. Application of parabolic-type approximations produces different systems of coupled parabolic equations. Each is valid for different relative magnitudes of components of the electric field. All admissible cases are then synthesized into one system which can be numerically examined, yielding solutions without a priori knowledge of electric field ratios. A specific example is presented and examined to understand static magnetic field effects on electromagnetic wave propagation. The influences of the earth's magnetic field are discussed and displayed in terms of electric components and the Poynting vector. Results demonstrate that the geomagnetic field can significantly influence HF atmospheric propagation.
Emitting waves from heterogeneity by a rotating electric field.
Zhao, Ye-Hua; Lou, Qin; Chen, Jiang-Xing; Sun, Wei-Gang; Ma, Jun; Ying, He-Ping
2013-09-01
In a generic model of excitable media, we simulate wave emission from a heterogeneity (WEH) induced by an electric field. Based on the WEH effect, a rotating electric field is proposed to terminate existed spatiotemporal turbulence. Compared with the effects resulted by a periodic pulsed electric field, the rotating electric field displays several improvements, such as lower required intensity, emitting waves on smaller obstacles, and shorter suppression time. Furthermore, due to rotation of the electric field, it can automatically source waves from the boundary of an obstacle with small curvature. PMID:24089977
NASA Astrophysics Data System (ADS)
Borchert, Sebastian; Achatz, Ulrich; Rieper, Felix; Fruman, Mark
2013-04-01
We use a numerical model of the classic differentially heated rotating annulus experiment to study the spontaneous emission of gravity waves (GWs) from jet stream imbalances, which is a major source of these waves in the atmosphere for which no satisfactory parameterization exists. Atmospheric observations are the main tool for the testing and verification of theoretical concepts but have their limitations. Given their specific potential for yielding reproducible data and for studying process dependence on external system parameters, laboratory experiments are an invaluable complementary tool. Experiments with a rotating annulus exhibiting a jet modulated by large-scale waves due to baroclinic instability have already been used to study GWs: Williams et al (2008) observed spontaneously emitted interfacial GWs in a two-layer flow, and Jacoby et al (2011) detected GWs emitted from boundary-layer instabilities in a differentially heated rotating annulus. Employing a finite-volume code for the numerical simulation of a continuously stratified liquid in a differentially heated rotating annulus, we here investigate the GWs in a wide and shallow annulus with relatively large temperature difference between inner and outer cylinder walls. In this atmosphere-like regime where the Brunt-Vaisala frequency is larger than the inertial frequency, various analyses suggest a distinct gravity wave activity. To identify regions of GW emission we decompose the flow into the geostrophic and ageostrophic part through the inversion of the quasi-geostrophic potential vorticity (e.g. Verkley, 2009). The analysis of the geostrophic sources of the ageostrophic flow indicates that, in addition to boundary layer instabilities, spontaneous imbalance in the jet region acts as an important source mechanism. Jacoby, T. N. L., Read, P. L., Williams, P. D. and Young, R. M. B., 2011: Generation of inertia-gravity waves in the rotating thermal annulus by a localised boundary layer instability. Geophys
An approximate solution for the free vibrations of rotating uniform cantilever beams
NASA Technical Reports Server (NTRS)
Peters, D. A.
1973-01-01
Approximate solutions are obtained for the uncoupled frequencies and modes of rotating uniform cantilever beams. The frequency approximations for flab bending, lead-lag bending, and torsion are simple expressions having errors of less than a few percent over the entire frequency range. These expressions provide a simple way of determining the relations between mass and stiffness parameters and the resultant frequencies and mode shapes of rotating uniform beams.
Curvilinear parabolic approximation for surface wave transformation with wave current interaction
NASA Astrophysics Data System (ADS)
Shi, Fengyan; Kirby, James T.
2005-04-01
The direct coordinate transformation method, which only transforms independent variables and retains Cartesian dependent variables, may not be an appropriate method for the purpose of simplifying the curvilinear parabolic approximation of the vector form of the wave-current equation given by Kirby [Higher-order approximations in the parabolic equation method for water waves, J. Geophys. Res. 91 (1986) 933-952]. In this paper, the covariant-contravariant tensor method is used for the curvilinear parabolic approximation. We use the covariant components of the wave number vector and contravariant components of the current velocity vector so that the derivation of the curvilinear equation closely follows the higher-order approximation in rectangular Cartesian coordinates in Kirby [Higher-order approximations in the parabolic equation method for water waves, J. Geophys. Res. 91 (1986) 933-952]. The resulting curvilinear equation can be easily implemented using the existing model structure and numerical schemes adopted in the Cartesian parabolic wave model [J.T. Kirby, R.A. Dalrymple, F. Shi, Combined Refraction/Diffraction Model REF/DIF 1, Version 2.6. Documentation and User's Manual, Research Report, Center for Applied Coastal Research, Department of Civil and Environmental Engineering, University of Delaware, Newark, 2004]. Several examples of wave simulations in curvilinear coordinate systems, including a case with wave-current interaction, are shown with comparisons to theoretical solutions or measurement data.
The Submillimeter-wave Rotational Spectra of Interstellar Molecules
NASA Technical Reports Server (NTRS)
Herbst, Eric; DeLucia, Frank C.; Butler, R. A. H.; Winnewisser, M.; Winnewisser, G.; Fuchs, U.; Groner, P.; Sastry, K. V. L. N.
2002-01-01
We discuss past and recent progress in our long-term laboratory program concerning the submillimeter-wave rotational spectroscopy of known and likely interstellar molecules, especially those associated with regions of high-mass star formation. Our program on the use of spectroscopy to study rotationally inelastic collisions of interstellar interest is also briefly mentioned.
Alpha Channeling in Rotating Plasma with Stationary Waves
A. Fetterman and N.J. Fisch
2010-02-15
An extension of the alpha channeling effect to supersonically rotating mirrors shows that the rotation itself can be driven using alpha particle energy. Alpha channeling uses radiofrequency waves to remove alpha particles collisionlessly at low energy. We show that stationary magnetic fields with high nθ can be used for this purpose, and simulations show that a large fraction of the alpha energy can be converted to rotation energy.
Comparison of gravitational wave detector network sky localization approximations
NASA Astrophysics Data System (ADS)
Grover, K.; Fairhurst, S.; Farr, B. F.; Mandel, I.; Rodriguez, C.; Sidery, T.; Vecchio, A.
2014-02-01
Gravitational waves emitted during compact binary coalescences are a promising source for gravitational-wave detector networks. The accuracy with which the location of the source on the sky can be inferred from gravitational-wave data is a limiting factor for several potential scientific goals of gravitational-wave astronomy, including multimessenger observations. Various methods have been used to estimate the ability of a proposed network to localize sources. Here we compare two techniques for predicting the uncertainty of sky localization—timing triangulation and the Fisher information matrix approximations—with Bayesian inference on the full, coherent data set. We find that timing triangulation alone tends to overestimate the uncertainty in sky localization by a median factor of 4 for a set of signals from nonspinning compact object binaries ranging up to a total mass of 20M⊙, and the overestimation increases with the mass of the system. We find that average predictions can be brought to better agreement by the inclusion of phase consistency information in timing-triangulation techniques. However, even after corrections, these techniques can yield significantly different results to the full analysis on specific mock signals. Thus, while the approximate techniques may be useful in providing rapid, large scale estimates of network localization capability, the fully coherent Bayesian analysis gives more robust results for individual signals, particularly in the presence of detector noise.
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…
Rotation-induced nonlinear wavepackets in internal waves
Whitfield, A. J. Johnson, E. R.
2014-05-15
The long time effect of weak rotation on an internal solitary wave is the decay into inertia-gravity waves and the eventual formation of a localised wavepacket. Here this initial value problem is considered within the context of the Ostrovsky, or the rotation-modified Korteweg-de Vries (KdV), equation and a numerical method for obtaining accurate wavepacket solutions is presented. The flow evolutions are described in the regimes of relatively-strong and relatively-weak rotational effects. When rotational effects are relatively strong a second-order soliton solution of the nonlinear Schrödinger equation accurately predicts the shape, and phase and group velocities of the numerically determined wavepackets. It is suggested that these solitons may form from a local Benjamin-Feir instability in the inertia-gravity wave-train radiated when a KdV solitary wave rapidly adjusts to the presence of strong rotation. When rotational effects are relatively weak the initial KdV solitary wave remains coherent longer, decaying only slowly due to weak radiation and modulational instability is no longer relevant. Wavepacket solutions in this regime appear to consist of a modulated KdV soliton wavetrain propagating on a slowly varying background of finite extent.
A large-amplitude rotational wave in the Venusian ionosheath
NASA Technical Reports Server (NTRS)
Fedorov, A. O.; Vaisberg, O. L.; Sagdeev, R. Z.; Galeev, A. A.; Intriligator, D. S.
1991-01-01
Results are reported of a preliminary analysis of a large-amplitude rotational wave in the Venusian ionosheath. The results are based on an analysis of the Pioneer Venus Orbiter plasma and magnetic field observations from six orbits in the first (1979) tail season. This wave appears to be the standing super-Alfvenic wing. It is located within the shocked plasma flow outside the boundary of the tail. The rotation of the magnetic field by about 90 deg across the wave occurs through several successive cycles making the wave similar to the group velocity wing consisting of phase velocity waves. The transition through the wave is accompanied by the vector change of the plasma velocity with the magnitude of the plasma velocity jump comparable to the vector jump of the Alfven velocity. The observed super-Alfvenic wing appears to originate upstream and closer to the planet, possibly near the upper boundary of the magnetic barrier on the dayside.
Extreme-ultraviolet observations of global coronal wave rotation
Attrill, G. D. R.; Long, D. M.; Green, L. M.; Harra, L. K.; Van Driel-Gesztelyi, L.
2014-11-20
We present evidence of global coronal wave rotation in EUV data from SOHO/EIT, STEREO/EUVI, and SDO/AIA. The sense of rotation is found to be consistent with the helicity of the source region (clockwise for positive helicity, anticlockwise for negative helicity), with the source regions hosting sigmoidal structures. We also study two coronal wave events observed by SDO/AIA where no clear rotation (or sigmoid) is observed. The selected events show supporting evidence that they all originate with flux rope eruptions. We make comparisons across this set of observations (both with and without clear sigmoidal structures). On examining the magnetic configuration of the source regions, we find that the nonrotation events possess a quadrupolar magnetic configuration. The coronal waves that do show a rotation originate from bipolar source regions.
Stochastic excitation of gravity waves in rapidly rotating massive stars
NASA Astrophysics Data System (ADS)
Mathis, S.; Neiner, C.
2015-01-01
Stochastic gravity waves have been recently detected and characterised in stars thanks to space asteroseismology and they may play an important role in the evolution of stellar angular momentum. In this context, the observational study of the CoRoT hot Be star HD 51452 suggests a potentially strong impact of rotation on stochastic excitation of gravito-inertial waves in rapidly rotating stars. In this work, we present our results on the action of the Coriolis acceleration on stochastic wave excitation by turbulent convection. We study the change of efficiency of this mechanism as a function of the waves' Rossby number and we demonstrate that the excitation presents two different regimes for super-inertial and sub-inertial frequencies. Consequences for rapidly rotating early-type stars and the transport of angular momentum in their interiors are discussed.
Fast computation of rotation-invariant image features by an approximate radial gradient transform.
Takacs, Gabriel; Chandrasekhar, Vijay; Tsai, Sam S; Chen, David; Grzeszczuk, Radek; Girod, Bernd
2013-08-01
We present the radial gradient transform (RGT) and a fast approximation, the approximate RGT (ARGT). We analyze the effects of the approximation on gradient quantization and histogramming. The ARGT is incorporated into the rotation-invariant fast feature (RIFF) algorithm. We demonstrate that, using the ARGT, RIFF extracts features 16× faster than SURF while achieving a similar performance for image matching and retrieval. PMID:23204286
Hopf Bifurcation from Rotating Waves and Patterns in Physical Space
NASA Astrophysics Data System (ADS)
Golubitsky, M.; LeBlanc, V. G.; Melbourne, I.
2000-02-01
Hopf bifurcations from time periodic rotating waves to two frequency tori have been studied for a number of years by a variety of authors including Rand and Renardy. Rotating waves are solutions to partial differential equations where time evolution is the same as spatial rotation. Thus rotating waves can exist mathematically only in problems that have at least SO (2) symmetry. In this paper we study the effect on this Hopf bifurcation when the problem has more than SO (2) symmetry. These effects manifest themselves in physical space and not in phase space. We use as motivating examples the experiments of Gorman et al . on porous plug burner flames, of Swinney et al . on the Taylor-Couette system, and of a variety of people on meandering spiral waves in the Belousov-Zhabotinsky reaction. In our analysis we recover and complete Rand's classification of modulated wavy vortices in the Taylor-Couette system. It is both curious and intriguing that the spatial manifestations of the two frequency motions in each of these experiments is different, and it is these differences that we seek to explain. In particular, we give a mathematical explanation of the differences between the nonuniform rotation of cellular flames in Gorman's experiments and the meandering of spiral waves in the Belousov-Zhabotinsky reaction. Our approach is based on the center bundle construction of Krupa with compact group actions and its extension to noncompact group actions by Sandstede, Scheel, and Wulff.
NASA Astrophysics Data System (ADS)
Luo, Hongjun; Kolb, Dietmar; Flad, Heinz-Jurgen; Hackbusch, Wolfgang; Koprucki, Thomas
2002-08-01
We have studied various aspects concerning the use of hyperbolic wavelets and adaptive approximation schemes for wavelet expansions of correlated wave functions. In order to analyze the consequences of reduced regularity of the wave function at the electron-electron cusp, we first considered a realistic exactly solvable many-particle model in one dimension. Convergence rates of wavelet expansions, with respect to L2 and H1 norms and the energy, were established for this model. We compare the performance of hyperbolic wavelets and their extensions through adaptive refinement in the cusp region, to a fully adaptive treatment based on the energy contribution of individual wavelets. Although hyperbolic wavelets show an inferior convergence behavior, they can be easily refined in the cusp region yielding an optimal convergence rate for the energy. Preliminary results for the helium atom are presented, which demonstrate the transferability of our observations to more realistic systems. We propose a contraction scheme for wavelets in the cusp region, which reduces the number of degrees of freedom and yields a favorable cost to benefit ratio for the evaluation of matrix elements.
Millimetre wave rotational spectrum of glycolic acid
NASA Astrophysics Data System (ADS)
Kisiel, Zbigniew; Pszczółkowski, Lech; Białkowska-Jaworska, Ewa; Charnley, Steven B.
2016-03-01
The pure rotational spectrum of glycolic acid, CH2OHCOOH, was studied in the region 115-318 GHz. For the most stable SSC conformer, transitions in all vibrational states up to 400 cm-1 have been measured and their analysis is reported. The data sets for the ground state, v21 = 1 , and v21 = 2 have been considerably extended. Immediately higher in vibrational energy are two triads of interacting vibrational states and their rotational transitions have been assigned and successfully fitted with coupled Hamiltonians accounting for Fermi and Coriolis resonances. The derived energy level spacings establish that the vibrational frequency of the ν21 mode is close to 100 cm-1. The existence of the less stable AAT conformer in the near 50 °C sample used in our experiment was also confirmed and additional transitions have been measured.
Thermal Rossby waves in a rotating annulus. Their stability.
Pino, D; Net, M; Sánchez, J; Mercader, I
2001-05-01
Nonlinear thermal convection in a fast rotating annulus about its axis, with slightly inclined ends, radial gravity and heating, is studied numerically for a fluid of Prandtl number sigma=0.7 and different values of the radius ratio and rotation rate. The properties of the rotating waves that appear after the Hopf bifurcation of the conductive state are analyzed. Near the critical Rayleigh number, different types of solutions with the same wave number coexist, and they are classified as a function of their connection with the two types of modes identified in the linear analysis for this Prandtl number. For different rotation rates, the stability of the primary solutions as a function of the radius ratio is also studied. The shape of the stability regions and the type of dominant disturbances that limit these regions are very sensitive to the proximity to the value of the radius ratio for which the type of dominant mode changes. PMID:11415011
On the SPH Approximations in Modeling Water Waves
NASA Astrophysics Data System (ADS)
Szmidt, Kazimierz
2014-10-01
This paper presents an examination of approximation aspects of the Smoothed Particle Hydrodynamics (SPH) in modeling the water wave phenomenon. Close attention is paid on consistency of the SPH formulation and its relation with a correction technique applied to improve the method accuracy. The considerations are confined to flow fields within finite domains with a free surface and fixed solid boundaries with free slip boundary conditions. In spite of a wide application of the SPH method in fluid mechanics, the appropriate modeling of the boundaries is still not clear. For solid straight line boundaries, a natural way is to use additional (virtual, ghost) particles outside the boundary and take into account mirror reflection of associated field variables. Such a method leads to good results, except for a vicinity of solid horizontal bottoms where, because of the SPH approximations in the description of pressure, a stratification of the fluid material particles may occur. In order to illustrate the last phenomenon, some numerical tests have been made. These numerical experiments show that the solid fluid bottom attracts the material particles and thus, to prevent these particles from penetration into the bottom, a mutual exchange of positions of real and ghost particles has been used in a computation procedure.
Can the slow-rotation approximation be used in electromagnetic observations of black holes?
NASA Astrophysics Data System (ADS)
Ayzenberg, Dimitry; Yagi, Kent; Yunes, Nicolás
2016-05-01
Future electromagnetic observations of black holes (BHs) may allow us to test general relativity (GR) in the strong-field regime. Such tests, however, require knowledge of rotating BH solutions in modified gravity theories, a class of which does not admit the Kerr metric as a solution. Several rotating BH solutions in modified theories have only been found in the slow-rotation approximation (i.e. assuming the spin angular momentum is much smaller than the mass squared). We here investigate whether the systematic error due to the approximate nature of these BH metrics is small enough relative to the observational error to allow their use in electromagnetic observations to constrain deviations from GR. We address this by considering whether electromagnetic observables constructed from a slow-rotation approximation to the Kerr metric can fit observables constructed from the full Kerr metric with systematic errors smaller than current observational errors. We focus on BH shadow and continuum spectrum observations, as these are the least influenced by accretion disk physics, with current observational errors of about 10%. We find that the fractional systematic error introduced by using a second-order, slowly rotating Kerr metric is at most 2% for shadows created by BHs with dimensionless spins χ ≤slant 0.6. We also find that the systematic error introduced by using the slowly rotating Kerr metric as an exact metric when constructing continuum spectrum observables is negligible for BHs with dimensionless spins of χ ≲ 0.9. Our results suggest that the modified gravity solutions found in the slow-rotation approximation may be used to constrain realistic deviations from GR with continuum spectrum and BH shadow observations.
Inertial wave beams and inertial wave modes in a rotating cylinder with time-modulated rotation rate
NASA Astrophysics Data System (ADS)
Borcia, Ion D.; Ghasemi V., Abouzar; Harlander, Uwe
2014-05-01
Inertial gravity waves play an crucial role in atmospheres, oceans, and the fluid inside of planets and moons. In the atmosphere, the effect of rotation is neglected for small wavelength and the waves bear the character of internal gravity waves. For long waves, the hydrostatic assumption is made which in turn makes the atmosphere inelastic with respect to inertial motion. In contrast, in the Earth's interior, pure inertial waves are considered as an important fundamental part of the motion. Moreover, as the deep ocean is nearly homogeneous, there the inertial gravity waves bear the character of inertial waves. Excited at the oceans surface mainly due to weather systems the waves can propagate downward and influence the deep oceans motion. In the light of the aforesaid it is important to understand better fundamental inertial wave dynamics. We investigate inertial wave modes by experimental and numerical methods. Inertial modes are excited in a fluid filled rotating annulus by modulating the rotation rate of the outer cylinder and the upper and lower lids. This forcing leads to inertial wave beams emitted from the corner regions of the annulus due to periodic motions in the boundary layers (Klein et al., 2013). When the forcing frequency matches with the eigenfrequency of the rotating annulus the beam pattern amplitude is increasing, the beams broaden and mode structures can be observed (Borcia et al., 2013a). The eigenmodes are compared with analytical solutions of the corresponding inviscid problem (Borcia et al, 2013b). In particular for the pressure field a good agreement can be found. However, shear layers related to the excited wave beams are present for all frequencies. This becomes obvious in particular in the experimental visualizations that are done by using Kalliroscope particles, highlighting relative motion in the fluid. Comparing the eigenfrequencies we find that relative to the analytical frequencies, the experimental and numerical ones show a small
NASA Technical Reports Server (NTRS)
Stallcop, J. R.
1974-01-01
Semiclassical collisions of an atom with a rigid-rotor molecule are examined in the sudden approximation. The rotational transition probability is shown to be invariant with respect to the choice of orientation for the molecular coordinate system; this fact contradicts recently reported results of a computer analysis. The present analysis may lead to an improved interpretation of recent molecular beam measurements.
NASA Technical Reports Server (NTRS)
Stallcop, J. R.
1974-01-01
The impact parameter method and the sudden approximation are applied to determine the total probability of inelastic rotational transitions arising from a collision of an atom and a homonuclear diatomic molecule at large impact parameters. An analytical approximation to this probability is found for conditions where the electron exchange or overlap forces dominate the scattering. An approximate upper bound to the range of impact parameters for which rotational scattering can be important is determined. In addition, an estimate of the total inelastic cross section is found at conditions for which a statistical model describes the scattering well. The results of this analysis are applied to Ar-O2 collisions and may be readily applied to other combinations of atoms and molecules.
The flow field in a rotating detonation-wave engine
NASA Astrophysics Data System (ADS)
Kailasanath, Kazhikathra; Schwer, Douglas
2011-11-01
Rotating detonation-wave engines (RDE) are a form of continuous detonation-wave engine. They potentially provide further gains than an intermittent or pulsed detonation-wave engine (PDE). However, significantly less work has been on this concept when compared to the PDE. In this talk, we present the detailed flow field in an idealized RDE, primarily consisting of two concentric cylinders. A premixed detonable mixture is injected into the annulus between the two concentric cylinders. Once a detonation is initiated, it keeps travelling around in the annulus as long as there is fresh detonable mixture ahead of it. Hence, the injection process is critically important to the stability and performance of the RDE. Furthermore, we show that the flow field is quite complex consisting of multiple shock waves and the outflow is primarily axial, although the detonation-wave is travelling around circumferentially. Sponsored by the NRL 6.1 Computational Physics Task Area.
Reeves, Daniel B.; Weaver, John B.
2015-01-01
Magnetic nanoparticles are promising tools for a host of therapeutic and diagnostic medical applications. The dynamics of rotating magnetic nanoparticles in applied magnetic fields depend strongly on the type and strength of the field applied. There are two possible rotation mechanisms and the decision for the dominant mechanism is often made by comparing the equilibrium relaxation times. This is a problem when particles are driven with high-amplitude fields because they are not necessarily at equilibrium at all. Instead, it is more appropriate to consider the “characteristic timescales” that arise in various applied fields. Approximate forms for the characteristic time of Brownian particle rotations do exist and we show agreement between several analytical and phenomenological-fit models to simulated data from a stochastic Langevin equation approach. We also compare several approximate models with solutions of the Fokker-Planck equation to determine their range of validity for general fields and relaxation times. The effective field model is an excellent approximation, while the linear response solution is only useful for very low fields and frequencies for realistic Brownian particle rotations. PMID:26130846
Reeves, Daniel B. Weaver, John B.
2015-06-21
Magnetic nanoparticles are promising tools for a host of therapeutic and diagnostic medical applications. The dynamics of rotating magnetic nanoparticles in applied magnetic fields depend strongly on the type and strength of the field applied. There are two possible rotation mechanisms and the decision for the dominant mechanism is often made by comparing the equilibrium relaxation times. This is a problem when particles are driven with high-amplitude fields because they are not necessarily at equilibrium at all. Instead, it is more appropriate to consider the “characteristic timescales” that arise in various applied fields. Approximate forms for the characteristic time of Brownian particle rotations do exist and we show agreement between several analytical and phenomenological-fit models to simulated data from a stochastic Langevin equation approach. We also compare several approximate models with solutions of the Fokker-Planck equation to determine their range of validity for general fields and relaxation times. The effective field model is an excellent approximation, while the linear response solution is only useful for very low fields and frequencies for realistic Brownian particle rotations.
Flow patterns of rotating time-dependent Hartree-Fock wave packets
NASA Astrophysics Data System (ADS)
Rosina, M.; Bouten, M.; Van Leuven, P.
1982-12-01
A soluble model (Elliott's model in two dimensions) is used to study how well flow patterns and features of rotational motion are represented by the time-dependent Hartree-Fock approximation. Due to the spreading of the wave packet in the exact Schrödinger time-evolution, the agreement is good only for phenomena which probe the current during a short time interval.
Inertial waves and wave attractors in a rotating annulus with inner or outer cylinder libration
NASA Astrophysics Data System (ADS)
Seelig, Torsten; Borcia, Ion D.; Klein, Marten; Ghasemi, Abozar; Will, Andreas; Egbers, Christoph; Schaller, Eberhard; Harlander, Uwe
2013-04-01
Inertial waves exist in rotating flows and are an ubiquitous phenomena in geophysical and astrophysical flows. Excitation mechanisms of inertial waves and wave attractors are the subject of recent publications [1, 2, 3]. Our research is focussed on the experimental and numerical study of inertial waves occuring in a homogeneous liquid confined between two coaxial co-rotating cylinders. The inner one has an inclined wall (frustum), in order to focus wave-energy [2]. Both cylinders rotate with mean angular velocity ?. Inertial waves are excited due to superimposed periodic oscillations with frequencies 0 ˜ ? ˜ 2? of (i) the inner or (ii) the outer cylinder together with the upper and lower lid of the cavity. The first results exhibit an agreement of wave reflection and attractor geometries between theory [2], numerical simulations and measurements. Further, we present similarities and differences between the cases of inner and outer cylinder libration. [1] Boisson, J., Lamriben, C., Maas, L.R.M., Cortet, P.P., Moisy, F.: Inertial waves and modes excited by the libration of a rotating cube. Physics of Fluids 24(076602), 1-18 (2012) [2] Borcia, I.D., Harlander, U.: Inertial waves in a rotating annulus with inclined inner cylinder: comparing the spectrum of wave attractor frequency bands and the eigenspectrum in the limit of zero inclination. Theor. Comput. Fluid Dyn. (2012). DOI 10.1007/s00162-012-0278-6 [3] Lopez, J.M., Marques, F.: Instabilities and inertial waves generated in a librating cylinder. Journal of Fluid Mechanics 687, 171-193. DOI 10.1017/jfm.2011.378
Heinemann, Tobias; Quataert, Eliot E-mail: eliot@berkeley.edu
2014-09-01
We derive the conductivity tensor for axisymmetric perturbations of a hot, collisionless, and charge-neutral plasma in the shearing sheet approximation. Our results generalize the well-known linear Vlasov theory for uniform plasmas to differentially rotating plasmas and can be used for wide range of kinetic stability calculations. We apply these results to the linear theory of the magneto-rotational instability (MRI) in collisionless plasmas. We show analytically and numerically how the general kinetic theory results derived here reduce in appropriate limits to previous results in the literature, including the low-frequency guiding center (or 'kinetic MHD') approximation, Hall magnetohydrodynamics (MHD), and the gyro-viscous approximation. We revisit the cold plasma model of the MRI and show that, contrary to previous results, an initially unmagnetized collisionless plasma is linearly stable to axisymmetric perturbations in the cold plasma approximation. In addition to their application to astrophysical plasmas, our results provide a useful framework for assessing the linear stability of differentially rotating plasmas in laboratory experiments.
Analysis of unsteady wave processes in a rotating channel
NASA Technical Reports Server (NTRS)
Larosiliere, L. M.; Mawid, M.
1993-01-01
The impact of passage rotation on the gas dynamic wave processes is analyzed through a numerical simulation of ideal shock-tube flow in a closed rotating-channel. Initial conditions are prescribed by assuming homentropic solid-body rotation. Relevant parameters of the problem such as wheel Mach number, hub-to-tip radius ratio, length-to-tip radius ratio, diaphragm temperature ratio, and diaphragm pressure ratio are varied. The results suggest possible criteria for assessing the consequences of passage rotation on the wave processes, and they may therefore be applicable to pressure-exchange wave rotors. It is shown that for a fixed geometry and initial conditions, the contact interface acquires a distorted three-dimensional time-dependent orientation at non-zero wheel Mach numbers. At a fixed wheel Mach number, the level of distortion depends primarily on the density ratio across the interface as well as the hub-to-tip radius ratio. Rarefaction fronts, shocks, and contact interfaces are observed to propagate faster with increasing wheel Mach number.
On the toroidal plasma rotations induced by lower hybrid waves
Guan Xiaoyin; Fisch, Nathaniel J.; Qin Hong; Liu Jian
2013-02-15
A theoretical model is developed to explain the plasma rotations induced by lower hybrid waves in Alcator C-Mod. In this model, torodial rotations are driven by the Lorentz force on the bulk-electron flow across flux surfaces, which is a response of the plasma to the resonant-electron flow across flux surfaces induced by the lower hybrid waves. The flow across flux surfaces of the resonant electrons and the bulk electrons are coupled through the radial electric field initiated by the resonant electrons, and the friction between ions and electrons transfers the toroidal momentum to ions from electrons. An improved quasilinear theory with gyrophase dependent distribution function is developed to calculate the perpendicular resonant-electron flow. Toroidal rotations are determined using a set of fluid equations for bulk electrons and ions, which are solved numerically by a finite-difference method. Numerical results agree well with the experimental observations in terms of flow profile and amplitude. The model explains the strong correlation between torodial flow and internal inductance observed experimentally, and predicts both counter-current and co-current flows, depending on the perpendicular wave vectors of the lower hybrid waves.
On the Toroidal Plasma Rotations Induced by Lower Hybrid Waves
Guan, Xiaoyin; Qin, Hong; Liu, Jian; Fisch, Nathaniel J.
2012-11-14
A theoretical model is developed to explain the plasma rotations induced by lower hybrid waves in Alcator C-Mod. In this model, torodial rotations are driven by the Lorentz force on the bulk electron flow across flux surfaces, which is a response of the plasma to the resonant-electron flow across flux surfaces induced by the lower hybrid waves. The flow across flux surfaces of the resonant electrons and the bulk electrons are coupled through the radial electric fi eld initiated by the resonant electrons, and the friction between ions and electrons transfers the toroidal momentum to ions from electrons. An improved quasilinear theory with gyrophase dependent distribution function is developed to calculate the perpendicular resonant-electron flow. Toroidal rotations are determined using a set of fluid equations for bulk electrons and ions, which are solved numerically by a fi nite- difference method. Numerical results agree well with the experimental observations in terms of flow pro file and amplitude. The model explains the strong correlation between torodial flow and internal inductance observed experimentally, and predicts both counter-current and co-current flows, depending on the perpendicular wave vectors of the lower hybrid waves. __________________________________________________
NASA Technical Reports Server (NTRS)
Green, S.
1979-01-01
The infinite order sudden (IOS) approximation is extended to rotational excitation of symmetric tops by collisions with atoms. After development of a formalism for 'primitive' or 'one-ended' tops, proper parity-adapted linear combinations describing real rotors are considered and modifications needed for asymmetric rigid rotors are noted. The generalized spectroscopic relaxation cross sections are discussed. IOS calculations for NH3-He and H2CO-He are performed and compared with more accurate calculations, and the IOS approximation is found to provide a reasonably accurate description.
Gravitational wave extraction in simulations of rotating stellar core collapse
Reisswig, C.; Ott, C. D.; Sperhake, U.; Schnetter, E.
2011-03-15
We perform simulations of general relativistic rotating stellar core collapse and compute the gravitational waves (GWs) emitted in the core-bounce phase of three representative models via multiple techniques. The simplest technique, the quadrupole formula (QF), estimates the GW content in the spacetime from the mass-quadrupole tensor only. It is strictly valid only in the weak-field and slow-motion approximation. For the first time, we apply GW extraction methods in core collapse that are fully curvature based and valid for strongly radiating and highly relativistic sources. These techniques are not restricted to weak-field and slow-motion assumptions. We employ three extraction methods computing (i) the Newman-Penrose (NP) scalar {Psi}{sub 4}, (ii) Regge-Wheeler-Zerilli-Moncrief master functions, and (iii) Cauchy-characteristic extraction (CCE) allowing for the extraction of GWs at future null infinity, where the spacetime is asymptotically flat and the GW content is unambiguously defined. The latter technique is the only one not suffering from residual gauge and finite-radius effects. All curvature-based methods suffer from strong nonlinear drifts. We employ the fixed-frequency integration technique as a high-pass waveform filter. Using the CCE results as a benchmark, we find that finite-radius NP extraction yields results that agree nearly perfectly in phase, but differ in amplitude by {approx}1%-7% at core bounce, depending on the model. Regge-Wheeler-Zerilli-Moncrief waveforms, while, in general, agreeing in phase, contain spurious high-frequency noise of comparable amplitudes to those of the relatively weak GWs emitted in core collapse. We also find remarkably good agreement of the waveforms obtained from the QF with those obtained from CCE. The results from QF agree very well in phase and systematically underpredict peak amplitudes by {approx}5%-11%, which is comparable to the NP results and is certainly within the uncertainties associated with core collapse
Arc-Polarized, Nonlinear Alfven Waves and Rotational Discontinuities: Directions of Propogation?
NASA Technical Reports Server (NTRS)
Tsurutani, B. T.; Ho, C. M.; Sakurai, R.; Arballo, J. K.; Riley, P.; Balogh, A.
1996-01-01
Large amplitude, noncompressive Alfven waves and rotational discontinuities are shown to be arc-polarized. The slowly rotating Alfven wave portion plus the fast rotating discontinuity comprise 360(deg) in phase rotation. The magnetic field vector perturbation lies in a plane. There are two (or more) possible interpretations to the observations.
Neural rotational speed control for wave energy converters
NASA Astrophysics Data System (ADS)
Amundarain, M.; Alberdi, M.; Garrido, A. J.; Garrido, I.
2011-02-01
Among the benefits arising from an increasing use of renewable energy are: enhanced security of energy supply, stimulation of economic growth, job creation and protection of the environment. In this context, this study analyses the performance of an oscillating water column device for wave energy conversion in function of the stalling behaviour in Wells turbines, one of the most widely used turbines in wave energy plants. For this purpose, a model of neural rotational speed control system is presented, simulated and implemented. This scheme is employed to appropriately adapt the speed of the doubly-fed induction generator coupled to the turbine according to the pressure drop entry, so as to avoid the undesired stalling behaviour. It is demonstrated that the proposed neural rotational speed control design adequately matches the desired relationship between the slip of the doubly-fed induction generator and the pressure drop input, improving the power generated by the turbine generator module.
Primordial gravitational waves measurements and anisotropies of CMB polarization rotation
NASA Astrophysics Data System (ADS)
Li, Si-Yu; Xia, Jun-Qing; Li, Mingzhe; Li, Hong; Zhang, Xinmin
2015-12-01
Searching for the signal of primordial gravitational waves in the B-modes (BB) power spectrum is one of the key scientific aims of the cosmic microwave background (CMB) polarization experiments. However, this could be easily contaminated by several foreground issues, such as the interstellar dust grains and the galactic cyclotron electrons. In this paper we study another mechanism, the cosmic birefringence, which can be introduced by a CPT-violating interaction between CMB photons and an external scalar field. Such kind of interaction could give rise to the rotation of the linear polarization state of CMB photons, and consequently induce the CMB BB power spectrum, which could mimic the signal of primordial gravitational waves at large scales. With the recently released polarization data of BICEP2 and the joint analysis data of BICEP2/Keck Array and Planck, we perform a global fitting analysis on constraining the tensor-to-scalar ratio r by considering the polarization rotation angle [ α (n ˆ)] which can be separated into a background isotropic part [ α bar ] and a small anisotropic part [ Δα (n ˆ)]. Since the data of BICEP2 and Keck Array experiments have already been corrected by using the "self-calibration" method, here we mainly focus on the effects from the anisotropies of CMB polarization rotation angle. We find that including Δα (n ˆ) in the analysis could slightly weaken the constraints on the tensor-to-scalar ratio r, when using current CMB polarization measurements. We also simulate the mock CMB data with the BICEP3-like sensitivity. Very interestingly, we find that if the effects of the anisotropic polarization rotation angle could not be taken into account properly in the analysis, the constraints on r will be dramatically biased. This implies that we need to break the degeneracy between the anisotropies of the CMB polarization rotation angle and the CMB primordial tensor perturbations, in order to measure the signal of primordial gravitational
NASA Technical Reports Server (NTRS)
Poole, L. R.
1975-01-01
A study of the effects of using different methods for approximating bottom topography in a wave-refraction computer model was conducted. Approximation techniques involving quadratic least squares, cubic least squares, and constrained bicubic polynomial interpolation were compared for computed wave patterns and parameters in the region of Saco Bay, Maine. Although substantial local differences can be attributed to use of the different approximation techniques, results indicated that overall computed wave patterns and parameter distributions were quite similar.
Evolution of nonlinear ion-acoustic solitary wave propagation in rotating plasma
Das, G. C.; Nag, Apratim
2006-08-15
A simple unmagnetized plasma rotating around an axis at an angle {theta} with the propagation direction of the acoustic mode has been taken. The nonlinear wave mode has been derived as an equivalent Sagdeev potential equation. A special procedure, known as the tanh method, has been developed to study the nonlinear wave propagation in plasma dynamics. Further, under small amplitude approximation, the nonlinear plasma acoustic mode has been exploited to study the evolution of soliton propagation in the plasma. The main emphasis has been given to the interaction of Coriolis force on the changes of coherent structure of the soliton. The solitary wave solution finds the different nature of solitons called compressive and rarefactive solitons as well as its explosions or collapses along with soliton dynamics and these have been showing exciting observations in exhibiting a narrow wave packet with the generation of high electric pressure and the growth of high energy which, in turn, yields the phenomena of radiating soliton in dynamics.
Analytical approximation of transit time scattering due to magnetosonic waves
NASA Astrophysics Data System (ADS)
Bortnik, J.; Thorne, R. M.; Ni, B.; Li, J.
2015-03-01
Recent test particle simulations have shown that energetic electrons traveling through fast magnetosonic (MS) wave packets can experience an effect which is specifically associated with the tight equatorial confinement of these waves, known as transit time scattering. However, such test particle simulations can be computationally cumbersome and offer limited insight into the dominant physical processes controlling the wave-particle interactions, that is, in determining the effects of the various wave parameters and equatorial confinement on the particle scattering. In this paper, we show that such nonresonant effects can be effectively captured with a straightforward analytical treatment that is made possible with a set of reasonable, simplifying assumptions. It is shown that the effect of the wave confinement, which is not captured by the standard quasi-linear theory approach, acts in such a way as to broaden the range of particle energies and pitch angles that can effectively resonate with the wave. The resulting diffusion coefficients can be readily incorporated into global diffusion models in order to test the effects of transit time scattering on the dynamical evolution of radiation belt fluxes.
Generation of Whistler Wave by a Rotating Magnetic Field Source
NASA Astrophysics Data System (ADS)
Karavaev, A.; Papadopoulos, K.; Shao, X.; Sharma, A. S.; Gigliotti, A.; Gekelman, W.; Pribyl, P.; Vincena, S.
2008-12-01
The interaction of Rotating Magnetic Fields (RMF) with plasmas is a fundamental plasma physics problem with implications to fusion related Field-Reversed Configurations (FRC), space propulsion, astronaut protection from cosmic rays in long interstellar travel, control of the energetic population in the radiation belts and near zone processes in pulsar magnetospheres. In this paper we report recent experiments on the generation of whistler waves with a new type RMF-based antenna. The experiments were conducted on UCLA's Large Plasma Device (LAPD). The Rotating Magnetic Field (RMF) is created using poly-phased loop antennas. A number of parameter combinations, e.g. plasma density, background magnetic field, and driving current, were used. It was found that RMF created by a two phase-delayed loop antenna drives significant currents along the ambient magnetic field. The measured amplitude of induced wave field was proportional to the square-root of the plasma density. The spatial decay rate for the wave perturbation across the background magnetic field was found to scale with the plasma skin depth. A small amplitude second harmonic was also measured. The paper will also present analytic and simulation results that account for the experimental results; in particular, the scaling of the induced magnetic field as a function of the RMF and plasma parameters and the spatial decay rate of magnetic field. Applications of RMF as an efficient radiation source of plasma waves in space plasmas will be discussed. This work was sponsored by ONR MURI Grant 5-28828
A wave model interpretation of the evolution of rotational discontinuities
NASA Technical Reports Server (NTRS)
Vasquez, Bernard J.; Cargill, Peter J.
1993-01-01
A hybrid numerical code is employed to trace the evolution of rotational discontinuities (RDs). An extensive parameter variation is carried out, with particular emphasis on beta, Ti/Te, theta sub B (the angle between the normal and total magnetic field), and the helicity of the RD. The RD structure is shown to have features in common with the evolution of both strongly modulated nonlinear wave packets and linear dispersive wave propagation in oblique magnetic fields. For small theta sub B, the RD disperses linearly, giving fast and Alfven waves upstream and downstream, respectively, and the familiar S-shaped hodograms. At larger theta sub B, nonlinearity becomes important and strong coupling to a compressional (sonic) component can occur in the main current layer. The results are applied to RDs observed in the solar wind and at the magnetopause.
Piezoelectric tube rotation effect owing to surface acoustic wave excitation
NASA Astrophysics Data System (ADS)
Biryukov, Sergey V.; Sotnikov, Andrei; Schmidt, Hagen
2016-03-01
It is shown experimentally that a macroscopic cylindrical solid shaped like a piezoelectric tube can be rotated due to the excitation of surface acoustic waves (SAWs) with different amplitudes propagating in opposite directions along the solid's surface. A unidirectional SAW transducer covering the whole cylindrical surface has been used for ac voltage excitation of waves with unequal amplitudes in both directions. The pattern of such a transducer consists of a periodic comb structure with two electrodes of different width per period. An external torque is not applied to the tube and, from the outside, its movement looks like a motion under the action of an internal force. The observed mechanical response of the piezoelectric cylindrical tube to excitation of waves is due to an angular momentum of SAWs, the value of which has been directly calculated from experimental results.
An approximate solution to the stress and deformation states of functionally graded rotating disks
NASA Astrophysics Data System (ADS)
Sondhi, Lakshman; Sanyal, Shubhashis; Saha, Kashi Nath; Bhowmick, Shubhankar
2016-07-01
The present work employs variational principle to investigate the stress and deformation states and estimate the limit angular speed of functionally graded high-speed rotating annular disks of constant thickness. Assuming a series approximation following Galerkin's principle, the solution of the governing equation is obtained. In the present study, elasticity modulus and density of the disk material are taken as power function of radius with the gradient parameter ranging between 0.0 and 1.0. Results obtained from numerical solutions are validated with benchmark results and are found to be in good agreement. The results are reported in dimensional form and presented graphically. The results provide a substantial insight in understanding the behavior of FGM rotating disks with constant thickness and different gradient parameter. Furthermore, the stress and deformation state of the disk at constant angular speed and limit angular speed is investigated to explain the existence of optimum gradient parameters.
NASA Astrophysics Data System (ADS)
Luo, Tao
1997-01-01
This paper concerns the large time behavior toward planar rarefaction waves of solutions for the relaxation approximation of conservation laws in several dimensions. It is shown that a planar rarefaction wave is nonlinear stable in the sense that it is an asymptotic attractor for the relaxation approximation of conservation laws.
Wave packet dynamics in the optimal superadiabatic approximation
NASA Astrophysics Data System (ADS)
Betz, V.; Goddard, B. D.; Manthe, U.
2016-06-01
We explain the concept of superadiabatic representations and show how in the context of electronically non-adiabatic transitions they lead to an explicit formula that can be used to predict transitions at avoided crossings. Based on this formula, we present a simple method for computing wave packet dynamics across avoided crossings. Only knowledge of the adiabatic potential energy surfaces near the avoided crossing is required for the computation. In particular, this means that no diabatization procedure is necessary, the adiabatic electronic energies can be computed on the fly, and they only need to be computed to higher accuracy when an avoided crossing is detected. We test the quality of our method on the paradigmatic example of photo-dissociation of NaI, finding very good agreement with results of exact wave packet calculations.
NASA Astrophysics Data System (ADS)
Van Gorder, Robert A.
2015-09-01
In a recent paper, we give a study of the purely rotational motion of general stationary states in the two-dimensional local induction approximation (2D-LIA) governing superfluid turbulence in the low-temperature limit [B. Svistunov, "Superfluid turbulence in the low-temperature limit," Phys. Rev. B 52, 3647 (1995)]. Such results demonstrated that variety of stationary configurations are possible from vortex filaments exhibiting purely rotational motion in addition to commonly discussed configurations such as helical or planar states. However, the filaments (or, more properly, waves along these filaments) can also exhibit translational motion along the axis of orientation. In contrast to the study on vortex configurations for purely rotational stationary states, the present paper considers non-stationary states which exhibit a combination of rotation and translational motions. These solutions can essentially be described as waves or disturbances which ride along straight vortex filament lines. As expected from our previous work, there are a number of types of structures that can be obtained under the 2D-LIA. We focus on non-stationary states, as stationary states exhibiting translation will essentially take the form of solutions studied in [R. A. Van Gorder, "General rotating quantum vortex filaments in the low-temperature Svistunov model of the local induction approximation," Phys. Fluids 26, 065105 (2014)], with the difference being translation along the reference axis, so that qualitative appearance of the solution geometry will be the same (even if there are quantitative differences). We discuss a wide variety of general properties of these non-stationary solutions and derive cases in which they reduce to known stationary states. We obtain various routes to Kelvin waves along vortex filaments and demonstrate that if the phase and amplitude of a disturbance both propagate with the same wave speed, then Kelvin waves will result. We also consider the self
Van Gorder, Robert A.
2015-09-15
In a recent paper, we give a study of the purely rotational motion of general stationary states in the two-dimensional local induction approximation (2D-LIA) governing superfluid turbulence in the low-temperature limit [B. Svistunov, “Superfluid turbulence in the low-temperature limit,” Phys. Rev. B 52, 3647 (1995)]. Such results demonstrated that variety of stationary configurations are possible from vortex filaments exhibiting purely rotational motion in addition to commonly discussed configurations such as helical or planar states. However, the filaments (or, more properly, waves along these filaments) can also exhibit translational motion along the axis of orientation. In contrast to the study on vortex configurations for purely rotational stationary states, the present paper considers non-stationary states which exhibit a combination of rotation and translational motions. These solutions can essentially be described as waves or disturbances which ride along straight vortex filament lines. As expected from our previous work, there are a number of types of structures that can be obtained under the 2D-LIA. We focus on non-stationary states, as stationary states exhibiting translation will essentially take the form of solutions studied in [R. A. Van Gorder, “General rotating quantum vortex filaments in the low-temperature Svistunov model of the local induction approximation,” Phys. Fluids 26, 065105 (2014)], with the difference being translation along the reference axis, so that qualitative appearance of the solution geometry will be the same (even if there are quantitative differences). We discuss a wide variety of general properties of these non-stationary solutions and derive cases in which they reduce to known stationary states. We obtain various routes to Kelvin waves along vortex filaments and demonstrate that if the phase and amplitude of a disturbance both propagate with the same wave speed, then Kelvin waves will result. We also consider the self
Millimeter Wave Tunneling-Rotational Spectrum of Phenol
NASA Astrophysics Data System (ADS)
Kolesnikova, L.; Daly, A. M.; Alonso, J. L.; Tercero, B.; Cernicharo, J.
2013-06-01
The millimeter wave spectra of phenol in the vibrational ground state and the first excited states of the bending and torsion vibrational modes have been studied in the frequency regions of 140 - 170 GHz and 280 - 360 GHz. The internal rotation of the hydroxyl group is responsible for the observed tunneling splitting into two substates (v_{t}, v_{b})^{+} and (v_{t}, v_{b})^{-} and more than 3500 distinct tunneling-rotational ^{b}R- and ^{b}Q-type transitions between them were measured and analyzed. Furthermore, accidental near degeneracies of the (+) and (-) energy levels were observed in case of the ground state and the v_{b} = 1 excited state and the analysis using a two-state effective Hamiltonian including tunneling-rotational Coriolis terms was performed. The spectroscopic constants for the first excited states of the bending and the torsion vibrational modes have been determined for the first time. The analysis of the microwave data provided very precise values of the spectroscopic constants necessary for the astrophysical search of phenol. We report a tentative detection for this molecule in the IRAM 30m line survey of Orion KL.
The millimeter wave tunneling-rotational spectrum of phenol
NASA Astrophysics Data System (ADS)
Kolesniková, L.; Daly, A. M.; Alonso, J. L.; Tercero, B.; Cernicharo, J.
2013-07-01
The millimeter wave spectra of phenol in the vibrational ground state and the first excited states of the bending and torsion vibrational modes have been studied in the frequency regions of 140-170 GHz and 280-360 GHz. The internal rotation of the hydroxyl group is responsible for the observed tunneling splitting into two substates (vt, vb)+ and (vt, vb)- and more than 3500 distinct tunneling-rotational bR- and bQ-type transitions between them were measured and analyzed. Furthermore, accidental near degeneracies of the (±) and (-) energy levels were observed in case of the ground state and the vb = 1 excited state and the analysis using a two-state effective Hamiltonian including tunneling-rotational Coriolis-like terms was performed. The analysis of the microwave data provided very precise values of the spectroscopic constants necessary for the astrophysical search of phenol. We report a tentative detection for this molecule in the IRAM 30m line survey of Orion KL.
Lower Hybrid Wave Induced Rotation on Alcator C-Mod
NASA Astrophysics Data System (ADS)
Parker, Ron; Podpaly, Yuri; Rice, John; Schmidt, Andrea
2009-11-01
Injection of RF power in the vicinity of the lower hybrid frequency has been observed to cause strong counter current rotation in Alcator C-Mod plasmas [1,2]. The spin-up rate is consistent with the rate at which momentum is injected by the LH waves, and also the rate at which fast electron momentum is transferred to the ions. A momentum diffusivity of ˜ 0.1 m^2/s is sufficient to account for the observed steady-state rotation. This value is also comparable with that derived from an analysis of rotation induced by RF mode conversion [3]. Radial force balance requires a radial electric field, suggesting a buildup of negative charge in the plasma core. This may be the result of an inward pinch of the LH produced fast electrons, as would be expected for resonant trapped particles. Analysis of the fast-electron-produced bremsstrahlung during LH power modulation experiments yields an inward pinch velocity of ˜ 1 m/s, consistent with the estimated trapped particle pinch velocity. [4pt] [1] A. Ince-Cushman, et.al., Phys. Rev. Lett., 102, 035002 (2009)[0pt] [2] J. E. Rice, et. al., Nucl. Fusion 49, 025004 (2009)[0pt] [3] Y. Lin, et.al., this meeting
Phase mixed rotation magnetoconvection and Taylor's condition III. Wave trains
NASA Astrophysics Data System (ADS)
Ewen, Susan A.; Soward, Andrew M.
Nonlinear amplitude equations governing the radial modulation of quasi-geostrophic convective rolls, which occur in a rapidly rotating self-gravitating sphere permeated by a weak azimuthal magnetic field (small Elsasser number), were derived in Part I. Stationary and travelling pulse solutions were obtained in Part II. That analysis is extended here; wave train solutions are sought and their stability tested. Special features of the equations include: nonlinear diffusion and dispersion; also phase mixing, which leads to a lack of translational invariance of the system. In spite of the latter, the underlying structure of the wave trains sought is spatially periodic on a length L, but modulated by a time dependent Floquet exponent. Consequently, a Fourier representation is employed and the time evolution of the Fourier coefficients is determined numerically. It is shown that pulses confined to lengths l(< L) can be superimposed non-interactively to form wave trains. The numerical demonstration relies on establishing that the pseudo-energy based on the time averaged wave train amplitude coincides with the corresponding pulse energy E calculated in Part II. When l and L are comparable some pulse interaction can be inferred. Available numerical evidence suggests that wave trains, and by implication pulses, are unstable. The geophysical implications are discussed. All finite amplitude solutions pertain to the Ekman regime in which the modified Taylor's condition is satisfied by small magnetic field perturbations. Only in the infinite amplitude limit do the solutions determine true Taylor states. It is anticipated that following instability in the Ekman regime convection equilibrates in some large amplitude Taylor state, which is determined when additional ageostrophic effects are taken into account. Analysis of that state lies outside the range of validity of our amplitude equations.
Exhaust Gas Emissions from a Rotating Detonation-wave Engine
NASA Astrophysics Data System (ADS)
Kailasanath, Kazhikathra; Schwer, Douglas
2015-11-01
Rotating detonation-wave engines (RDE) are a form of continuous detonation-wave engines. They potentially provide further gains in performance than an intermittent or pulsed detonation-wave engine (PDE). The overall flow field in an idealized RDE, primarily consisting of two concentric cylinders, has been discussed in previous meetings. Because of the high pressures involved and the lack of adequate reaction mechanisms for this regime, previous simulations have typically used simplified chemistry models. However, understanding the exhaust species concentrations in propulsion devices is important for both performance considerations as well as estimating pollutant emissions. Progress towards addressing this need will be discussed in this talk. In this approach, an induction parameter model is used for simulating the detonation but a more detailed finite-chemistry model including NOx chemistry is used in the expansion flow region, where the pressures are lower and the uncertainties in the chemistry model are greatly reduced. Results show that overall radical concentrations in the exhaust flow are substantially lower than from earlier predictions with simplified models. The performance of a baseline hydrogen/air RDE increased from 4940 s to 5000 s with the expansion flow chemistry, due to recombination of radicals and more production of H2O, resulting in additional heat release. Work sponsored by the Office of Naval Research.
Lisicki, Maciej; Cichocki, Bogdan; Rogers, Simon A; Dhont, Jan K G; Lang, Peter R
2014-06-28
In this article we extend recent experimental developments [Rogers et al., Phys. Rev. Lett., 2012, 109, 098305] by providing a suitable theoretical framework for the derivation of exact expressions for the first cumulant (initial decay rate) of the correlation function measured in Evanescent Wave Dynamic Light Scattering (EWDLS) experiments. We focus on a dilute suspension of optically anisotropic spherical Brownian particles diffusing near a planar hard wall. In such a system, translational and rotational diffusion are hindered by hydrodynamic interactions with the boundary which reflects the flow incident upon it, affecting the motion of colloids. The validity of the approximation by the first cumulant for moderate times is assessed by juxtaposition to Brownian dynamics simulations, and compared with experimental results. The presented method for the analysis of experimental data allows the determination of penetration-depth-averaged rotational diffusion coefficients of spherical colloids at low density. PMID:24788942
NASA Astrophysics Data System (ADS)
Borchert, S.; Achatz, U.; Rieper, F.; Fruman, M. D.
2012-04-01
We use a numerical model of the classic differentially heated rotating annulus experiment to study the spontaneous emission of gravity waves (GWs) from jet stream imbalances, which is a major source of these waves in the atmosphere for which no satisfactory parameterization exists. Atmospheric observations are the main tool for the testing and verification of theoretical concepts but have their limitations. Given their specific potential for yielding reproducible data and for studying process dependence on external system parameters, laboratory experiments are an invaluable complementary tool. Experiments with a rotating annulus exhibiting a jet modulated by large-scale waves due to baroclinic instability have already been used to study GWs: Williams et al (2008) observed spontaneously emitted interfacial GWs in a two-layer flow, and Jacoby et al (2011) detected GWs emitted from boundary-layer instabilities in a differentially heated rotating annulus. Employing a new finite-volume code for the numerical simulation of a continuously stratified liquid in a differentially heated rotating annulus, we here investigate whether such an experiment might be useful for studies of spontaneous imbalance. A major problem was the identification of experimental parameters yielding an atmosphere-like regime where the Brunt-Vaisala frequency is larger than the inertial frequency, so that energy transport by the lowest-frequency waves is predominantly horizontal while high-frequency GWs transport energy vertically. We show that this is indeed the case for a wide and shallow annulus with relatively large temperature difference between the inner and outer cylinder walls. We also show that this set-up yields a conspicuous signal in the horizontal divergence field close to the meandering jet. Various analyses support the notion that this signal is predominantly due to GWs superposed on a geostrophic flow. Jacoby, T. N. L., Read, P. L., Williams, P. D. and Young, R. M. B., 2011
The use of the plane wave fluid-structure interaction loading approximation in NASTRAN
NASA Technical Reports Server (NTRS)
Dawson, R. L.
1991-01-01
The Plane Wave Approximation (PWA) is widely used in finite element analysis to implement the loading generated by an underwater shock wave. The method required to implement the PWA in NASTRAN is presented along with example problems. A theoretical background is provided and the limitations of the PWA are discussed.
The millimeter-wave rotational spectrum of tertiary butyl isocyanide
NASA Astrophysics Data System (ADS)
Kisiel, Z.
1992-02-01
The millimeter-wave rotational spectrum of tertiary butyl isocyanide, (CH 3) 3CNC, was measured in the ground state and in the first excited state of the doubly degenerate CNC bending mode vβ. Accurate spectroscopic constants for both states have been determined from frequency measurements spanning the range 146-333 GHz. The results are compared with those for tertiary butyl cyanide, for which improved ground state sextic distortion constants are reported. The experimental quartic centrifugal distortion constants and the Coriolis coupling constant ξβ are well reproduced by a rudimentary force field calculation. Coriolis coupling constants for bending modes of linear segments attached to symmetric top C3 v molecules based on a tetrahedrally substituted carbon atom are compared and factors responsible for changes in their values are identified and discussed.
Gravitational wave signatures from low-mode spiral instabilities in rapidly rotating supernova cores
NASA Astrophysics Data System (ADS)
Kuroda, Takami; Takiwaki, Tomoya; Kotake, Kei
2014-02-01
We study properties of gravitational waves (GWs) from the rotating core collapse of a 15M⊙ star by performing three-dimensional general-relativistic hydrodynamic simulations with an approximate neutrino transport. By parametrically changing the precollapse angular momentum, we focus on the effects of rotation on the GW signatures in the early postbounce evolution. Regarding three-flavor neutrino transport, we solve the energy-averaged set of radiation energy and momentum based on the Thorne's momentum formalism. In addition to the gravitational quadrupole radiation from matter motions, we take into account GWs from anisotropic neutrino emission. With these computations, our results present supporting evidence for the previous anticipation that nonaxisymmetric instabilities play an essential role in determining the postbounce GW signatures. During prompt convection, we find that the waveforms show narrow-band and highly quasiperiodic signals which persist until the end of simulations. We point out that such features reflect the growth of the one-armed spiral modes. The typical frequency of the quasiperiodic waveforms can be well explained by the propagating acoustic waves between the stalled shock and the rotating proto-neutron star surface, which suggests the appearance of the standing-accretion-shock instability. Although the GW signals exhibit strong variability between the two polarizations and different observer directions, they are within the detection limits of next-generation detectors such as KAGRA and Advanced LIGO, if the source with sufficient angular momentum is located in our Galaxy.
NASA Astrophysics Data System (ADS)
Zhou, Yong; Ni, Sidao; Chu, Risheng; Yao, Huajian
2016-06-01
Numerical solvers of wave equations have been widely used to simulate global seismic waves including PP waves for modeling 410/660 km discontinuity and Rayleigh waves for imaging crustal structure. In order to avoid extra computation cost due to ocean water effects, these numerical solvers usually adopt water column approximation, whose accuracy depends on frequency and needs to be investigated quantitatively. In this paper, we describe a unified representation of accurate and approximate forms of the equivalent water column boundary condition as well as the free boundary condition. Then we derive an analytical form of the PP-wave reflection coefficient with the unified boundary condition, and quantify the effects of water column approximation on amplitude and phase shift of the PP waves. We also study the effects of water column approximation on phase velocity dispersion of the fundamental mode Rayleigh wave with a propagation matrix method. We find that with the water column approximation: (1) The error of PP amplitude and phase shift is less than 5% and 9 ° at periods greater than 25 s for most oceanic regions. But at periods of 15 s or less, PP is inaccurate up to 10% in amplitude and a few seconds in time shift for deep oceans. (2) The error in Rayleigh wave phase velocity is less than 1% at periods greater than 30 s in most oceanic regions, but the error is up to 2% for deep oceans at periods of 20 s or less. This study confirms that the water column approximation is only accurate at long periods and it needs to be improved at shorter periods.
NASA Astrophysics Data System (ADS)
Zhou, Yong; Ni, Sidao; Chu, Risheng; Yao, Huajian
2016-08-01
Numerical solvers of wave equations have been widely used to simulate global seismic waves including PP waves for modelling 410/660 km discontinuity and Rayleigh waves for imaging crustal structure. In order to avoid extra computation cost due to ocean water effects, these numerical solvers usually adopt water column approximation, whose accuracy depends on frequency and needs to be investigated quantitatively. In this paper, we describe a unified representation of accurate and approximate forms of the equivalent water column boundary condition as well as the free boundary condition. Then we derive an analytical form of the PP-wave reflection coefficient with the unified boundary condition, and quantify the effects of water column approximation on amplitude and phase shift of the PP waves. We also study the effects of water column approximation on phase velocity dispersion of the fundamental mode Rayleigh wave with a propagation matrix method. We find that with the water column approximation: (1) The error of PP amplitude and phase shift is less than 5 per cent and 9° at periods greater than 25 s for most oceanic regions. But at periods of 15 s or less, PP is inaccurate up to 10 per cent in amplitude and a few seconds in time shift for deep oceans. (2) The error in Rayleigh wave phase velocity is less than 1 per cent at periods greater than 30 s in most oceanic regions, but the error is up to 2 per cent for deep oceans at periods of 20 s or less. This study confirms that the water column approximation is only accurate at long periods and it needs to be improved at shorter periods.
NASA Astrophysics Data System (ADS)
Tikhomolov, Evgeniy
1996-12-01
A rotating fluid layer, heated from below, with a deformable upper and nondeformable lower stress free surfaces is considered in the Boussinesq approximation. The system of the differential equations that governs the long-scale Rossby waves and short-scale convection is obtained in the rapid-rotation approximation. Long-scale flows are unstable due to heating and deformation of the upper surface. The neutral stability curves for Rossby waves and convection are obtained for linearized version of the equations. In a slightly supercritical regime the amplitude equations for convection and Rossby waves are derived by the use of the method of multiscale expansions. The properties of the amplitude equations are discussed. The existence of the two weakly supercritical stationary convection regimes is shown by numerical integration of the equations in the rapid-rotation approximation. In one of them, the amplitude of short-scale convection is modulated due to long-scale deformation of the upper surface associated with the excitation of the Rossby wave. In the other regime, the presence of deformation gives rise to alternating regions with and without convection.
NASA Astrophysics Data System (ADS)
Mathis, S.; de Brye, N.
2012-04-01
Context. With the progress of observational constraints on dynamical processes in stars, it becomes necessary to understand the angular momentum and the rotation profile history. In this context, internal waves constitute an efficient transport mechanism over long distances in stellar radiation zones. Indeed, they could be one of the mechanisms responsible for the quasi-flat rotation profile of the solar radiative region up to 0.2 R⊙. Aims: Angular momentum transport induced by internal waves depends on the properties of their excitation regions and of their dissipation during propagation. Then, the bottom of convective envelopes (the top of convective cores, respectively) are differentially rotating magnetic layers while radiation zones may host fossil magnetic fields. It is therefore necessary to understand the modification of internal wave mechanisms by both rotation and magnetic fields. Methods: We continue our previous work by proceeding step by step. We analytically built a complete formalism that treats the angular momentum transport by internal waves while taking into account both the Coriolis acceleration and the Lorentz force in a non-perturbative way for an axisymmetric toroidal field. We assumed a uniform Alfvén frequency and a weak differential rotation to isolate the transport properties as a function of the Rossby and Elsasser numbers. Results: We examined the different possible approximations to describe low-frequency internal waves modified by the Coriolis acceleration and the Lorentz force in a deep spherical shell. The complete structure of these waves, which become magneto-gravito-inertial waves, is given assuming the quasi-linear approximation first in the adiabatic case and then in the dissipative one. Vertical and equatorial trapping phenomena appear that favor retrograde waves. The efficiency of the induced transport as a function of the Rossby and Elsasser numbers is then obtained. Conclusions: A complete study of the transport of
The choice of optimal Discrete Interaction Approximation to the kinetic integral for ocean waves
NASA Astrophysics Data System (ADS)
Polnikov, V. G.
A lot of discrete configurations for the four-wave nonlinear interaction processes have been calculated and tested by the method proposed earlier in the frame of the concept of Fast Discrete Interaction Approximation to the Hasselmann's kinetic integral (Polnikov and Farina, 2002). It was found that there are several simple configurations, which are more efficient than the one proposed originally in Hasselmann et al. (1985). Finally, the optimal multiple Discrete Interaction Approximation (DIA) to the kinetic integral for deep-water waves was found. Wave spectrum features have been intercompared for a number of different configurations of DIA, applied to a long-time solution of kinetic equation. On the basis of this intercomparison the better efficiency of the configurations proposed was confirmed. Certain recommendations were given for implementation of new approximations to the wave forecast practice.
Approximate analytical time-domain Green's functions for the Caputo fractional wave equation.
Kelly, James F; McGough, Robert J
2016-08-01
The Caputo fractional wave equation [Geophys. J. R. Astron. Soc. 13, 529-539 (1967)] models power-law attenuation and dispersion for both viscoelastic and ultrasound wave propagation. The Caputo model can be derived from an underlying fractional constitutive equation and is causal. In this study, an approximate analytical time-domain Green's function is derived for the Caputo equation in three dimensions (3D) for power law exponents greater than one. The Green's function consists of a shifted and scaled maximally skewed stable distribution multiplied by a spherical spreading factor 1/(4πR). The approximate one dimensional (1D) and two dimensional (2D) Green's functions are also computed in terms of stable distributions. Finally, this Green's function is decomposed into a loss component and a diffraction component, revealing that the Caputo wave equation may be approximated by a coupled lossless wave equation and a fractional diffusion equation. PMID:27586735
Periodic standing-wave approximation: Overview and three-dimensional scalar models
Andrade, Zeferino; Beetle, Christopher; Blinov, Alexey; Bromley, Benjamin; Burko, Lior M.; Cranor, Maria; Price, Richard H.; Owen, Robert
2004-09-15
The periodic standing-wave method for binary inspiral computes the exact numerical solution for periodic binary motion with standing gravitational waves, and uses it as an approximation to slow binary inspiral with outgoing waves. Important features of this method presented here are: (i) the mathematical nature of the 'mixed' partial differential equations to be solved (ii) the meaning of standing waves in the method (iii) computational difficulties, and (iv) the 'effective linearity' that ultimately justifies the approximation. The method is applied to three-dimensional nonlinear scalar model problems, and the numerical results are used to demonstrate extraction of the outgoing solution from the standing-wave solution, and the role of effective linearity.
ANALYTIC APPROXIMATE SEISMOLOGY OF PROPAGATING MAGNETOHYDRODYNAMIC WAVES IN THE SOLAR CORONA
Goossens, M.; Soler, R.; Arregui, I.
2012-12-01
Observations show that propagating magnetohydrodynamic (MHD) waves are ubiquitous in the solar atmosphere. The technique of MHD seismology uses the wave observations combined with MHD wave theory to indirectly infer physical parameters of the solar atmospheric plasma and magnetic field. Here, we present an analytical seismological inversion scheme for propagating MHD waves. This scheme uses the observational information on wavelengths and damping lengths in a consistent manner, along with observed values of periods or phase velocities, and is based on approximate asymptotic expressions for the theoretical values of wavelengths and damping lengths. The applicability of the inversion scheme is discussed and an example is given.
Dust Rotation Effects on DIA Surface Waves in a Semi-bounded Lorentzian Plasma
Lee, Myoung-Jae
2008-09-07
The dispersion relation for a dust ion-acoustic (DIA) surface wave is kinetically derived for the semi-bounded Lorentzian plasma containing elongated and rotating charged dust particles. The DIA surface wave frequency is found to be decreased as the dust rotational frequency increases.
Rotation-vibrational states of H3+ and the adiabatic approximation.
Alijah, Alexander; Hinze, Juergen
2006-11-15
We discuss recent progress in the calculation and identification of rotation-vibrational states of H3+ at intermediate energies up to 13,000 cm(-1). Our calculations are based on the potential energy surface of Cencek et al. which is of sub-microhartree accuracy. As this surface includes diagonal adiabatic and relativistic corrections to the fixed nuclei electronic energies, the remaining discrepancies between our calculated and experimental data should be due to the neglect of non-adiabatic coupling to excited electronic states in the calculations. To account for this, our calculated energy values were adjusted empirically by a simple correction formula. Based on our understanding of the adiabatic approximation, we suggest two new approaches to account for the off-diagonal adiabatic correction, which should work; however, they have not been tested yet for H3+. Theoretical predictions made for the above-barrier energy region of recent experimental interest are accurate to 0.35 cm(-1) or better. PMID:17015396
The critical layer for gravity waves in sheared rotating stratified flows
NASA Astrophysics Data System (ADS)
Millet, Christophe; Lott, Francois
2012-11-01
We re-examined the propagation of gravity waves through a critical layer surrounded by two inertial levels in the case of a constant vertically sheared flow. This problem involves a transition from balanced (where the quasi-geostrophic approximation applies) to sheared gravity waves. The three-dimensional disturbance is described analytically using both an exact solution and a WKB approximation valid for large Richardson numbers. In contradiction with past studies which show that there is finite reflection and did not analyse the transmission (Yamanaka and Tanaka, 1984), we find that reflection is extremely too small to be significant. The reasons that previous authors made incorrect evaluations are related to the fact that (i) the equations yielding to these results are extremely involved and (ii) the values of reflection and transmission coefficients are exponentially small or null, e.g. quite difficult to cross check numerically. Interestingly, these values are exactly like in the much simpler non-rotating case analysed by Booker and Bretherton (1966). Some practical implications for the problem of the emission of gravity waves by potential vorticity anomalies, analysed recently in Lott et al. (2013), are also discussed.
Faraday rotation, band splitting, and one-way propagation of plasmon waves on a nanoparticle chain
NASA Astrophysics Data System (ADS)
Pike, N. A.; Stroud, D.
2016-03-01
We calculate the dispersion relations of plasmonic waves propagating along a chain of semiconducting or metallic nanoparticles in the presence of both a static magnetic field B and a liquid crystalline host. The dispersion relations are obtained using the quasistatic approximation and a dipole-dipole approximation to treat the interaction between surface plasmons on different nanoparticles. For plasmons propagating along a particle chain in a nematic liquid crystalline host with both B and the director parallel to the chain, we find a small, but finite, Faraday rotation angle. For B perpendicular to the chain, but director still parallel to the chain, the field couples the longitudinal and one of the two transverse plasmonic branches. This coupling is shown to split the two branches at the zero field crossing by an amount proportional to |B | . In a cholesteric liquid crystal host and an applied magnetic field parallel to the chain, the dispersion relations for left- and right-moving waves are found to be different. For some frequencies, the plasmonic wave propagates only in one of the two directions.
Generation of magnetoacoustic zonal flows by Alfven waves in a rotating plasma
Mikhailovskii, A. B.; Lominadze, J. G.; Churikov, A. P.; Erokhin, N. N.; Tsypin, V. S.; Smolyakov, A. I.; Galvao, R. M. O.
2007-08-15
Analytical theory of nonlinear generation of magnetoacoustic zonal flows in a rotating plasma is developed. As the primary modes causing such a generation, a totality of the Alfven waves are considered, along with the kinetic, inertial, and rotational. It is shown that in all these cases of the Alfven waves the generation is possible if the double plasma rotation frequency exceeds the zonal flow frequency.
NASA Astrophysics Data System (ADS)
López-Ruiz, Alejandro; Solari, Sebastián; Ortega-Sánchez, Miguel; Losada, Miguel
2015-12-01
This work presents a simple and relatively quick methodology to obtain the nearshore wave angle. The method is especially valuable for curvilinear coasts where Snell's law may provide excessively inaccurate results. We defined a correction factor, K, that depends on the geometry of the coast and on the wave climate. The values of this coefficient were obtained minimizing the differences with a sophisticated numerical model. The limitations and performance of the methodology are further discussed. The procedure was applied to a beach in Southern Spain to analyze the influence of shoreline geometry on nearshore wave directionality. Offshore and nearshore distributions of wave period and directions were analyzed, and the results showed that the geometry of the coast played a crucial role in the directionality of the nearshore waves, which also plays an important role in hydrodynamics. The methodology presented here is able to analyze and quantify the importance of this directionality without a noticeable computational cost, even when a long time series of wave data are considered. Hence, this methodology constitutes a useful and efficient tool for practical applications in Coastal and Ocean Engineering, such as sedimentary, wave energy, and wave climate studies.
Ellis, J. A.; Siemens, X.; Van Haasteren, R.
2013-05-20
Direct detection of gravitational waves by pulsar timing arrays will become feasible over the next few years. In the low frequency regime (10{sup -7} Hz-10{sup -9} Hz), we expect that a superposition of gravitational waves from many sources will manifest itself as an isotropic stochastic gravitational wave background. Currently, a number of techniques exist to detect such a signal; however, many detection methods are computationally challenging. Here we introduce an approximation to the full likelihood function for a pulsar timing array that results in computational savings proportional to the square of the number of pulsars in the array. Through a series of simulations we show that the approximate likelihood function reproduces results obtained from the full likelihood function. We further show, both analytically and through simulations, that, on average, this approximate likelihood function gives unbiased parameter estimates for astrophysically realistic stochastic background amplitudes.
NASA Astrophysics Data System (ADS)
Wei, Xing
2016-09-01
To understand magnetic effects on dynamical tides, we study the rotating magnetohydrodynamic (MHD) flow driven by harmonic forcing. The linear responses are analytically derived in a periodic box under the local WKB approximation. Both the kinetic and Ohmic dissipations at the resonant frequencies are calculated, and the various parameters are investigated. Although magnetic pressure may be negligible compared to thermal pressure, the magnetic field can be important for the first-order perturbation, e.g., dynamical tides. It is found that the magnetic field splits the resonant frequency, namely the rotating hydrodynamic flow has only one resonant frequency, but the rotating MHD flow has two, one positive and the other negative. In the weak field regime the dissipations are asymmetric around the two resonant frequencies and this asymmetry is more striking with a weaker magnetic field. It is also found that both the kinetic and Ohmic dissipations at the resonant frequencies are inversely proportional to the Ekman number and the square of the wavenumber. The dissipation at the resonant frequency on small scales is almost equal to the dissipation at the non-resonant frequencies, namely the resonance takes its effect on the dissipation at intermediate length scales. Moreover, the waves with phase propagation that is perpendicular to the magnetic field are much more damped. It is also interesting to find that the frequency-averaged dissipation is constant. This result suggests that in compact objects, magnetic effects on tidal dissipation should be considered.
NASA Astrophysics Data System (ADS)
Kong, Dali; Zhang, Keke; Schubert, Gerald
2015-12-01
In an important paper, Roberts (1963b) studied the hydrostatic equilibrium of an isolated, self-gravitating, rapidly rotating polytropic gaseous body based on a controversial assumption/approximation that all (outer and internal) equidensity surfaces are in the shape of oblate spheroids whose eccentricities are a function of the equatorial radius and whose axes of symmetry are parallel to the rotation axis. We compute the three-dimensional, finite-element, fully self-consistent, continuous solution for a rapidly rotating polytropic gaseous body with Jupiter-like parameters without making any prior assumptions about its outer shape and internal structure. Upon partially relaxing the Roberts' approximation by assuming that only the outer equidensity surface is in the shape of an oblate spheroid, we also compute a finite-element solution with the same parameters without making any prior assumptions about its internal structure. It is found that all equidensity surfaces of the fully self-consistent solution differ only slightly from the oblate spheroidal shape. It is also found that the characteristic difference between the fully self-consistent solution and the outer-spheroidal-shape solution is insignificantly small. Our results suggest that the Roberts' assumption of spheroidal equidensity surfaces represents a reasonably accurate approximation for rotating polytropic gaseous bodies with Jupiter-like parameters. The numerical accuracy of our finite-element solution is checked by an exact analytic solution based on the Green's function using the spheroidal wave function. The three different solutions in non-spherical geometries - the fully self-consistent numerical solution, the numerical solution with the outer spheroidal shape and the exact analytical solution - can also serve as a useful benchmark for other solutions based on different numerical methods.
The Detectability of Millimeter-wave Molecular Rotational Transitions
NASA Astrophysics Data System (ADS)
Liszt, Harvey S.; Pety, Jerome
2016-06-01
Elaborating on a formalism that was first expressed some 40 years ago, we consider the brightness of low-lying millimeter-wave rotational lines of strongly polar molecules at the threshold of detectability. We derive a simple expression relating the brightness to the line-of-sight integral of the product of the total gas and molecular number densities and a suitably defined temperature-dependent excitation rate into the upper level of the transition. Detectability of a line is contingent only on the ability of a molecule to channel enough of the ambient thermal energy into the line, and the excitation can be computed in bulk by summing over rates without solving the multi-level rate equations, or computing optical depths and excitation temperatures. Results for {{HCO}}+, HNC, and CS are compared with escape-probability solutions of the rate equations using closed-form expressions for the expected range of validity of our ansatz, with the result that gas number densities as high as {10}4 {{{cm}}}-3 or optical depths as high as 100 can be accommodated in some cases. For densities below a well-defined upper bound, the range of validity of the discussion can be cast as an upper bound on the line brightness which is 0.3 K for the J = 1–0 lines and 0.8–1.7 K for the J = 2–1 lines of these species. The discussion casts new light on the interpretation of line brightnesses under conditions of weak excitation, simplifies derivation of physical parameters, and eliminates the need to construct grids of numerical solutions of the rate equations.
Dispersion relation for small amplitude sound waves in rotating newtonian fluids.
NASA Astrophysics Data System (ADS)
Marín-Antuña, José; Hernández-Rodríguez, Arezky; Sotolongo-Costa, Oscar
1996-11-01
For a rotating newtonian fluid (which is viscous and compressible), the linearized Navier-Stokes equation, the continuity equation and the equation for isoentropic process are simultaneosly considered to obtain an equation for pressure waves. This equation is solved to get the dispersion law for such waves. In the dispersion law an adimensional parameter τ is used, which is given by the relation between the characteristic damping wave time and the period of the fluid rotation. The limit of a viscous compressible static fluid is obtained. The numerical results of the dispersion relation are given for different values of the angle between the direction of the wave propagation and the rotation axis and for the values of τ. The existence of gaps and of a typical wave guide effect are reported. The dispersion relation of the modes are given for the real and the imaginary parts of the wave vector.
Experimental observation of steady inertial wave turbulence in deep rotating flows
NASA Astrophysics Data System (ADS)
Yarom, Ehud; Sharon, Eran
2015-11-01
We present experimental evidence of inertial wave turbulence in deep rotating fluid. Experiments were performed in a rotating cylindrical water tank, where previous work showed statistics similar to 2D turbulence (specifically an inverse energy cascade). Using Fourier analysis of high resolution data in both space (3D) and time we show that most of the energy of a steady state flow is contained around the inertial wave dispersion relation. The nonlinear interaction between the waves is manifested by the widening of the time spectrum around the dispersion relation. We show that as the Rossby number increases so does the spectrum width, with a strong dependence on wave number. Our results suggest that in some parameters range, rotating turbulence velocity field can be represented as a field of interacting waves (wave turbulence). Such formalism may provide a better understanding of the flow statistics. This work was supported by the Israel Science Foundation, Grant No. 81/12.
Van Raemdonck, Mario; Alcoba, Diego R; Poelmans, Ward; De Baerdemacker, Stijn; Torre, Alicia; Lain, Luis; Massaccesi, Gustavo E; Van Neck, Dimitri; Bultinck, Patrick
2015-09-14
A class of polynomial scaling methods that approximate Doubly Occupied Configuration Interaction (DOCI) wave functions and improve the description of dynamic correlation is introduced. The accuracy of the resulting wave functions is analysed by comparing energies and studying the overlap between the newly developed methods and full configuration interaction wave functions, showing that a low energy does not necessarily entail a good approximation of the exact wave function. Due to the dependence of DOCI wave functions on the single-particle basis chosen, several orbital optimisation algorithms are introduced. An energy-based algorithm using the simulated annealing method is used as a benchmark. As a computationally more affordable alternative, a seniority number minimising algorithm is developed and compared to the energy based one revealing that the seniority minimising orbital set performs well. Given a well-chosen orbital basis, it is shown that the newly developed DOCI based wave functions are especially suitable for the computationally efficient description of static correlation and to lesser extent dynamic correlation. PMID:26374017
NASA Astrophysics Data System (ADS)
Van Raemdonck, Mario; Alcoba, Diego R.; Poelmans, Ward; De Baerdemacker, Stijn; Torre, Alicia; Lain, Luis; Massaccesi, Gustavo E.; Van Neck, Dimitri; Bultinck, Patrick
2015-09-01
A class of polynomial scaling methods that approximate Doubly Occupied Configuration Interaction (DOCI) wave functions and improve the description of dynamic correlation is introduced. The accuracy of the resulting wave functions is analysed by comparing energies and studying the overlap between the newly developed methods and full configuration interaction wave functions, showing that a low energy does not necessarily entail a good approximation of the exact wave function. Due to the dependence of DOCI wave functions on the single-particle basis chosen, several orbital optimisation algorithms are introduced. An energy-based algorithm using the simulated annealing method is used as a benchmark. As a computationally more affordable alternative, a seniority number minimising algorithm is developed and compared to the energy based one revealing that the seniority minimising orbital set performs well. Given a well-chosen orbital basis, it is shown that the newly developed DOCI based wave functions are especially suitable for the computationally efficient description of static correlation and to lesser extent dynamic correlation.
One-way approximation for the simulation of weak shock wave propagation in atmospheric flows.
Gallin, Louis-Jonardan; Rénier, Mathieu; Gaudard, Eric; Farges, Thomas; Marchiano, Régis; Coulouvrat, François
2014-05-01
A numerical scheme is developed to simulate the propagation of weak acoustic shock waves in the atmosphere with no absorption. It generalizes the method previously developed for a heterogeneous medium [Dagrau, Rénier, Marchiano, and Coulouvrat, J. Acoust. Soc. Am. 130, 20-32 (2011)] to the case of a moving medium. It is based on an approximate scalar wave equation for potential, rewritten in a moving time frame, and separated into three parts: (i) the linear wave equation in a homogeneous and quiescent medium, (ii) the effects of atmospheric winds and of density and speed of sound heterogeneities, and (iii) nonlinearities. Each effect is then solved separately by an adapted method: angular spectrum for the wave equation, finite differences for the flow and heterogeneity corrections, and analytical method in time domain for nonlinearities. To keep a one-way formulation, only forward propagating waves are kept in the angular spectrum part, while a wide-angle parabolic approximation is performed on the correction terms. The numerical process is validated in the case of guided modal propagation with a shear flow. It is then applied to the case of blast wave propagation within a boundary layer flow over a flat and rigid ground. PMID:24815240
Localized waves supported by the rotating waveguide array.
Zhang, Xiao; Ye, Fangwei; Kartashov, Yaroslav V; Vysloukh, Victor A; Chen, Xianfeng
2016-09-01
We show that truncated rotating square waveguide arrays support new types of localized modes that exist even in the linear case, in complete contrast to localized excitations in nonrotating arrays requiring nonlinearity for their existence and forming above the energy flow threshold. These new modes appear either around an array center, since the rotation leads to the emergence of the effective attractive potential with a minimum at the rotation axis, or in the array corners, in which case localization occurs due to competition between the centrifugal force and total internal reflection at the interface of the truncated array. The degree of localization of the central and corner modes mediated by the rotation increases with the rotation frequency. The stable rotating soliton families bifurcating from linear modes are analyzed in both focusing and defocusing media. PMID:27607984
NASA Technical Reports Server (NTRS)
Zhu, P. Y.; Fung, A. K.
1986-01-01
The effective medium approximation (EMA) formalism developed for scalar wave calculations in solid state physics is generalized to electromagnetic wave scattering in a dense random medium. Results are applied to compute the effective propagation constant in a dense medium involving discrete spherical scatterers. When compared with a common quasicrystalline approximation (QCA), it is found that EMA accounts for backward scattering and the effect of correlation among three scatterers which are not available in QCA. It is also found that there is not much difference in the calculated normalized phase velocity between the use of these two approximations. However, there is a significant difference in the computed effective loss tangent in a nonabsorptive random medium. The computed effective loss tangent using EMA and measurements from a snow medium are compared, showing good agreement.
Gravity jitter effected slosh waves and the stability of a rotating bubble under microgravity
NASA Technical Reports Server (NTRS)
Hung, R. J.; Lee, C. C.; Leslie, F. W.
1991-01-01
The instability of liquid and gas interface can be induced by the pressure of longitudinal and lateral accelerations, vehicle vibration, and rotational fields of spacecraft in a microgravity environment. Characteristics of slosh waves excited by the restoring force field of gravity jitters have been investigated. Results show that lower frequency gravity jitters excite slosh wave with higher ratio of maximum amplitude to wave length than that of the slosh waves generated by the higher frequency gravity jitters.
NASA Astrophysics Data System (ADS)
Lähivaara, Timo; Ward, Nicholas F. Dudley; Huttunen, Tomi; Koponen, Janne; Kaipio, Jari P.
2014-01-01
Recently, it has been proposed that spontaneous seismic activity could be used in the estimation of hydrological parameters of aquifers such as permeability and storage. Approximate wave propagation models such as ray tracing, which are commonly used in hydrological parameter estimation with active sources and backscattering geometry, are not feasible with passive seismological imaging. With respect to full wave propagation models, the most accurate known model for aquifers is the poroelastic model while bedrock is usually modelled as an elastic medium. Using a poroelastic model in the forward model can be a computationally impractical choice. In this paper, we carry out a feasibility study in which we attempt to estimate the aquifer depth and water table using a highly approximate elastic model also for the aquifer. We adopt the Bayesian approximation error approach in which a statistical model is constructed for the errors that are induced by using model approximations such as sparse meshing and simplified physical models. We consider the problem in a simple two-dimensional geometry and show that straightforward adoption of approximate models leads to inconsistent parameter estimates, that is, the true parameters have essentially vanishing posterior density. On the other hand, using the Bayesian approximation error approach, the parameter estimates are consistent.
Equation of State Dependence of Gravitational Waves from Rapidly Rotating Core-Collapse
NASA Astrophysics Data System (ADS)
Richers, Sherwood; Ott, Christian D.; Abdikamalov, Ernazar
2016-03-01
We carry out axisymmetric simulations of rotating core-collapse, exploring over 92 precollapse rotational configurations and 18 different finite-temperature microphysical equations of state (EOS) using the general-relativistic hydrodynamical code CoCoNuT. Our focus is on gravitational wave (GW) emission. We find that the GW wave signature depends systematically on the rotation rate of the inner core at bounce and the compactness of the protoneutron star (PNS), set by the EOS and rotation. The GW signal from core bounce is almost independent of the EOS. However, the frequency of the post-bounce ring down signal from the fundamental quadrupole oscillation mode of the PNS is dependent on both rotation and the EOS, increasing with rotation rate and compactness. We will discuss the origin of the EOS-dependent f-mode frequency variation and its potential observability with Advanced LIGO.
Geometric phases of the Faraday rotation of electromagnetic waves in magnetized plasmas
Liu Jian; Qin Hong
2012-10-15
Geometric phases of circularly polarized electromagnetic waves in nonuniform magnetized plasmas is studied theoretically. The variation of the propagation direction of circularly polarized waves results in a geometric phase, which also contributes to the Faraday rotation, in addition to the standard dynamical phase. The origin and properties of the geometric phase are investigated. The influence of the geometric phase to plasma diagnostics using the Faraday rotation is discussed as an application of the theory.
Geometric Phase Of The Faraday Rotation Of Electromagnetic Waves In Magnetized Plasma
Jian Liu and Hong Qin
2011-11-07
The geometric phase of circularly polarized electromagnetic waves in nonuniform magnetized plasmas is studied theoretically. The variation of the propagation direction of circularly polarized waves results in a geometric phase, which also contributes to the Faraday rotation, in addition to the standard dynamical phase. The origin and properties of the geometric phase is investigated. The in uence of the geometric phase to plasma diagnostics using Faraday rotation is also discussed as an application of the theory.
Rotational manipulation of single cells and organisms using acoustic waves
Ahmed, Daniel; Ozcelik, Adem; Bojanala, Nagagireesh; Nama, Nitesh; Upadhyay, Awani; Chen, Yuchao; Hanna-Rose, Wendy; Huang, Tony Jun
2016-01-01
The precise rotational manipulation of single cells or organisms is invaluable to many applications in biology, chemistry, physics and medicine. In this article, we describe an acoustic-based, on-chip manipulation method that can rotate single microparticles, cells and organisms. To achieve this, we trapped microbubbles within predefined sidewall microcavities inside a microchannel. In an acoustic field, trapped microbubbles were driven into oscillatory motion generating steady microvortices which were utilized to precisely rotate colloids, cells and entire organisms (that is, C. elegans). We have tested the capabilities of our method by analysing reproductive system pathologies and nervous system morphology in C. elegans. Using our device, we revealed the underlying abnormal cell fusion causing defective vulval morphology in mutant worms. Our acoustofluidic rotational manipulation (ARM) technique is an easy-to-use, compact, and biocompatible method, permitting rotation regardless of optical, magnetic or electrical properties of the sample under investigation. PMID:27004764
Rotational manipulation of single cells and organisms using acoustic waves.
Ahmed, Daniel; Ozcelik, Adem; Bojanala, Nagagireesh; Nama, Nitesh; Upadhyay, Awani; Chen, Yuchao; Hanna-Rose, Wendy; Huang, Tony Jun
2016-01-01
The precise rotational manipulation of single cells or organisms is invaluable to many applications in biology, chemistry, physics and medicine. In this article, we describe an acoustic-based, on-chip manipulation method that can rotate single microparticles, cells and organisms. To achieve this, we trapped microbubbles within predefined sidewall microcavities inside a microchannel. In an acoustic field, trapped microbubbles were driven into oscillatory motion generating steady microvortices which were utilized to precisely rotate colloids, cells and entire organisms (that is, C. elegans). We have tested the capabilities of our method by analysing reproductive system pathologies and nervous system morphology in C. elegans. Using our device, we revealed the underlying abnormal cell fusion causing defective vulval morphology in mutant worms. Our acoustofluidic rotational manipulation (ARM) technique is an easy-to-use, compact, and biocompatible method, permitting rotation regardless of optical, magnetic or electrical properties of the sample under investigation. PMID:27004764
Effect on plasma rotation of lower hybrid (LH) waves in Alcator C-Mod
Lee, J. P.; Barnes, M.; Parker, R. R.; Rice, J. E.; Parra, F. I.; Bonoli, P. T.; Reinke, M. L.
2014-02-12
The injection of LH waves for current drive into a tokamak changes the ion toroidal rotation. In Alcator C-Mod, the direction of the steady state rotation change due to LH waves depends on the plasma current and the density. The change in rotation can be estimated by balancing the external torque of lower hybrid waves with the turbulent radial transport of the momentum. For high plasma current, the turbulent pinch and diffusion of the injected counter-current momentum are sufficient to explain the rotation change. However, for low plasma current, the change in the the intrinsic momentum transport (residual stress) for a non-rotating state is required to explain the co-current rotation change. Accordingly, we investigate the intrinsic momentum transport for the non-rotating state when diamagnetic flow and ExB flow cancel each other. The change in the intrinsic momentum transport due to lower hybrid waves is significant when the plasma current is low, which may explain the rotation reversal for low plasma current. The effect of changed q (safety factor) profile by lower hybrid on the intrinsic momentum transport is estimated by gyrokinetics.
Approximate entropy analysis of short-term HFECG based on wave mode
NASA Astrophysics Data System (ADS)
Ning, Xinbao; Xu, Yinlin; Wang, Jun; Ma, Xiaofei
2005-02-01
An improved approximate entropy (ApEn) algorithm based on wave mode is proposed by analyzing and modifying ApEn, so that the irregular analysis can be applied to analyze the short-term series, which contain a great deal of detailed information and fluctuate slowly but in a wide range, such as high-frequency electrocardiogram (HFECG). By analyzing the complexity of HFECG, a conclusion can be drawn that ApEn algorithm based on wave mode can obviously distinguish heart diseases from the healthy group. Therefore, it is of significance for diagnosing myocardial infarction in time.
NASA Astrophysics Data System (ADS)
Huang, Chao-Chun; Wang, Daw-Wei; Wu, Wen-Chin
2010-04-01
We investigate the condensate wave function and elementary excitations of strongly interacting bosonic polar molecules in a harmonic trap, treating the scattering amplitude beyond the standard first Born approximation (FBA). By using an appropriate trial wave function in the variational method, effects of the leading-order correction beyond the FBA have been investigated and shown to be significantly enhanced when the system is close to the phase boundary of collapse. How such a leading-order effect of going beyond the FBA can be observed in a realistic experiment is also discussed.
Calkins, Michael A.; Julien, Keith; Marti, Philippe
2015-01-01
The linear theory for rotating compressible convection in a plane layer geometry is presented for the astrophysically relevant case of low Prandtl number gases. When the rotation rate of the system is large, the flow remains geostrophically balanced for all stratification levels investigated and the classical (i.e. incompressible) asymptotic scaling laws for the critical parameters are recovered. For sufficiently small Prandtl numbers, increasing stratification tends to further destabilize the fluid layer, decrease the critical wavenumber and increase the oscillation frequency of the convective instability. In combination, these effects increase the relative magnitude of the time derivative of the density perturbation contained in the conservation of mass equation to non-negligible levels; the resulting convective instabilities occur in the form of compressional quasi-geostrophic oscillations. We find that the anelastic equations, which neglect this term, cannot capture these instabilities and possess spuriously growing eigenmodes in the rapidly rotating, low Prandtl number regime. It is shown that the Mach number for rapidly rotating compressible convection is intrinsically small for all background states, regardless of the departure from adiabaticity. PMID:25792951
A WKB approximation of elastic waves travelling on a shell of revolution
NASA Astrophysics Data System (ADS)
Morsbøl, J. O.; Sorokin, S. V.; Peake, N.
2016-08-01
This paper is concerned with the elastic waveguide properties of an infinite pipe with circular cross section whose radius varies slowly along its length. The equations governing the elastodynamics of such shells are derived analytically, approximated asymptotically in the limit of slow axial variation, and solved by means of the WKB-method (Wentzel-Kramers-Brillouin). From the derived solution the dispersion relation, modal coefficients, and wave amplification at each location along the structure are extracted, allowing identification of which types of waves are able to propagate along the structure at a given frequency. A key feature in the formulation of the model and the solution is that the radius and its variation are not specified in advance. Two characteristic examples of shells of revolution are presented to illustrate some general features of the waveguide properties, demonstrating how the evolution of the waves depends on the axial variation of the shell radius. It is explained how local resonances can be excited by the travelling waves and how strong amplifications of displacement can be produced. Specifically, for the axial/breathing wave it is shown that a local resonance is excited at the location where the frequency of the travelling wave and the radius of the shell exactly match the ring-frequency.
Electromagnetic waves propagation nearby rotating gravitating astrophysical object with atmosphere
NASA Astrophysics Data System (ADS)
Gladyshev, V. O.; Tereshin, A. A.; Fomin, I. V.; Chelnokov, M. B.; Kauts, V. L.; Gladysheva, T. M.; Bazleva, D. D.
The aim of the article to explore the effects of gravitational lensing and attraction of electromagnetic radiation in the description of the propagation of radiation nearby the atmospheres of rotating astrophysical objects.
Effects of different wave free surface approximations on the response of a TLP in deep water
Mekha, B.B.; Johnson, C.P.; Roesset, J.M.
1994-12-31
This paper is based on work conducted at the Offshore Technology Research Center to investigate the relative importance of different types of nonlinearities on the dynamic response of tension leg platforms. A time domain solution using Morison`s equation with several modifications and allowing to include or neglect various sources of nonlinearities was implemented and used in the dynamic analysis. This paper focuses on the non-linear effect of evaluating the wave forces up to the free surface using different approximate methods. A TLP hull model with time varying tendon forces is subjected to regular and irregular waves with and without current. The effects on calculating the wave kinematics up to the mean water level or up to the actual free surface, making use of various extrapolation or stretching techniques are then discussed.
Black-hole quasinormal resonances: Wave analysis versus a geometric-optics approximation
NASA Astrophysics Data System (ADS)
Hod, Shahar
2009-09-01
It has long been known that null unstable geodesics are related to the characteristic modes of black holes—the so-called quasinormal resonances. The basic idea is to interpret the free oscillations of a black hole in the eikonal limit in terms of null particles trapped at the unstable circular orbit and slowly leaking out. The real part of the complex quasinormal resonances is related to the angular velocity at the unstable null geodesic. The imaginary part of the resonances is related to the instability time scale (or the inverse Lyapunov exponent) of the orbit. While this geometric-optics description of the black-hole quasinormal resonances in terms of perturbed null rays is very appealing and intuitive, it is still highly important to verify the validity of this approach by directly analyzing the Teukolsky wave equation which governs the dynamics of perturbation waves in the black-hole spacetime. This is the main goal of the present paper. We first use the geometric-optics technique of perturbing a bundle of unstable null rays to calculate the resonances of near-extremal Kerr black holes in the eikonal approximation. We then directly solve the Teukolsky wave equation (supplemented by the appropriate physical boundary conditions) and show that the resultant quasinormal spectrum obtained directly from the wave analysis is in accord with the spectrum obtained from the geometric-optics approximation of perturbed null rays.
NASA Astrophysics Data System (ADS)
Vargas-Magaña, Rosa; Panayotaros, Panayotis
2015-11-01
We study the problem of wave propagation in a long-wave asymptotic regime over variable bottom of an ideal irrotational fluid in the framework of the Hamiltonian formulation in which the non-local Dirichlet-Neumann (DtN) operator appears explicitly in the Hamiltonian. We propose a non-local Hamiltonian model for bidirectional wave propagation in shallow water that involves pseudodifferential operators that approximate the DtN operator for variable depth. These models generalize the Boussinesq system as they include the exact dispersion relation in the case of constant depth. We present results for the normal modes and eigenfrequencies of the linearized problem. We see that variable topography introduces effects such as steepening of normal modes with increasing variation of depth, as well as amplitude modulation of the normal modes in certain wavelength ranges. Numerical integration shows that the constant depth nonlocal Boussinesq model with quadratic nonlinearity can capture the evolution obtained with higher order approximations of the DtN operator. In the case of variable depth we observe certain oscillations in width of the crest and also some interesting textures in the evolution of wave crests during the passage from obstacles.
Approximation to cutoffs of higher modes of Rayleigh waves for a layered earth model
Xu, Y.; Xia, J.; Miller, R.D.
2009-01-01
A cutoff defines the long-period termination of a Rayleigh-wave higher mode and, therefore is a key characteristic of higher mode energy relationship to several material properties of the subsurface. Cutoffs have been used to estimate the shear-wave velocity of an underlying half space of a layered earth model. In this study, we describe a method that replaces the multilayer earth model with a single surface layer overlying the half-space model, accomplished by harmonic averaging of velocities and arithmetic averaging of densities. Using numerical comparisons with theoretical models validates the single-layer approximation. Accuracy of this single-layer approximation is best defined by values of the calculated error in the frequency and phase velocity estimate at a cutoff. Our proposed method is intuitively explained using ray theory. Numerical results indicate that a cutoffs frequency is controlled by the averaged elastic properties within the passing depth of Rayleigh waves and the shear-wave velocity of the underlying half space. ?? Birkh??user Verlag, Basel 2009.
Finite Larmor Radius approximation for waves propagation in cylindrical plasma configurations
NASA Astrophysics Data System (ADS)
Galeotti, Laura; Ceccherini, Francesco; Brambilla, Marco; Barnes, Daniel C.; Pegoraro, Francesco
2011-10-01
We present an analytical derivation in cylindrical geometry of the Finite Larmor Radius approximation for the wave equations in the cyclotron frequency range and show a set of numerical results obtained with a new extended version of the code FELICE, which allows for arbitrary profiles of field, densities and temperatures. Obtaining a cylindrical FLR approximation is of great relevance for studying the wave propagation in plasma configurations like FRC's and theta-pinches in particular. The generic configuration we consider can be divided in the radial direction in two regions, i.e, a ``plasma region'' and a ``vacuum region''. In the former the wave propagation is computed numerically from the FRL approximation found, in the latter instead a general analytical solution has been calculated and implemented in the code. A detailed description on how to ensure both the overall causality of the propagation process and the correct matching conditions for the antenna surface and the vacuum/plasma surface is shown as well.
Observation of Co and Counter Rotation Produced by Lower Hybrid Waves in Alcator C-Mod
Parker, R. R.; Podpaly, Y.; Lee, J.; Reinke, M. L.; Rice, J. E.; Bonoli, P. T.; Meneghini, O.; Shiraiwa, S.; Wallace, G. M.; Wilson, J. R.
2011-12-23
Lower hybrid waves launched uni-directionally into tokamak plasmas impart momentum to the electrons. This momentum can be transferred to the ions, leading to substantial counter current rotation. Observations of LH-induced counter rotation have been previously reported [1], and the initial rate of increase has been found to be consistent with the calculated rate of wave momentum injection [2]. However, in recent experiments in Alcator C-Mod it has been found that application of LH waves to relatively low current (I{sub p}{approx}0.4-0.6 MA) plasmas can result in a co-current change of rotation, which implies a different mechanism than that described above. This appears to be linked to the so-called intrinsic rotation commonly observed in Alcator C-Mod and other tokamaks [3]. In addition to the change in direction at low current, some dependence on the magnetic configuration (USL vs. LSN) has been observed.
Energy transfer by inertial waves during the buildup of turbulence in a rotating system.
Kolvin, Itamar; Cohen, Kobi; Vardi, Yuval; Sharon, Eran
2009-01-01
We study the transition from fluid at rest to turbulence in a rotating tank. The energy is transported by inertial wave packets through the fluid volume. These high amplitude waves propagate at velocities consistent with those calculated from linearized theory [H. P. Greenspan, (Cambridge University Press, Cambridge, England, 1968)]. A "front" in the temporal evolution of the energy power spectrum indicates a time scale for energy transport at the linear wave speed. Nonlinear energy transfer between modes is governed by a different, longer, time scale. The observed mechanisms can lead to significant differences between rotating and two-dimensional turbulent flows. PMID:19257200
Sa, Paulo M.; Tome, Brigitte
2006-08-15
Recently, it was shown that differential rotation is an unavoidable feature of nonlinear r-modes. We investigate the influence of this differential rotation on the detectability of gravitational waves emitted by a newly born, hot, rapidly-rotating neutron star, as it spins down due to the r-mode instability. We conclude that gravitational radiation may be detected by the advanced laser interferometer detector LIGO if the amount of differential rotation at the time the r-mode instability becomes active is not very high.
Berkel, M. van; Tamura, N.; Ida, K.; Hogeweij, G. M. D.; Zwart, H. J.; Inagaki, S.; Baar, M. R. de
2014-11-15
In this paper, a number of new explicit approximations are introduced to estimate the perturbative diffusivity (χ), convectivity (V), and damping (τ) in cylindrical geometry. For this purpose, the harmonic components of heat waves induced by localized deposition of modulated power are used. The approximations are based on the heat equation in cylindrical geometry using the symmetry (Neumann) boundary condition at the plasma center. This means that the approximations derived here should be used only to estimate transport coefficients between the plasma center and the off-axis perturbative source. If the effect of cylindrical geometry is small, it is also possible to use semi-infinite domain approximations presented in Part I and Part II of this series. A number of new approximations are derived in this part, Part III, based upon continued fractions of the modified Bessel function of the first kind and the confluent hypergeometric function of the first kind. These approximations together with the approximations based on semi-infinite domains are compared for heat waves traveling towards the center. The relative error for the different derived approximations is presented for different values of the frequency, transport coefficients, and dimensionless radius. Moreover, it is shown how combinations of different explicit formulas can be used to estimate the transport coefficients over a large parameter range for cases without convection and damping, cases with damping only, and cases with convection and damping. The relative error between the approximation and its underlying model is below 2% for the case, where only diffusivity and damping are considered. If also convectivity is considered, the diffusivity can be estimated well in a large region, but there is also a large region in which no suitable approximation is found. This paper is the third part (Part III) of a series of three papers. In Part I, the semi-infinite slab approximations have been treated. In Part II
Hybrid simulations of rotational discontinuities. [Alfven wave propagation in astrophysics
NASA Technical Reports Server (NTRS)
Goodrich, C. C.; Cargill, P. J.
1991-01-01
1D hybrid simulations of rotational discontinuities (RDs) are presented. When the angle between the discontinuity normal and the magnetic field (theta-BN) is 30 deg, the RD broadens into a quasi-steady state of width 60-80 c/omega-i. The hodogram has a characteristic S-shape. When theta-BN = 60 deg, the RD is much narrower (10 c/omega-i). For right handed rotations, the results are similar to theta-BN = 30 deg. For left handed rotations, the RD does not evolve much from its initial conditions and the S-shape in the hodogram is much less visible. The results can be understood in terms of matching a fast mode wavelike structure upstream of the RD with an intermediate mode one downstream.
The effect of nonlinear traveling waves on rotating machinery
NASA Astrophysics Data System (ADS)
Jauregui-Correa, Juan Carlos
2013-08-01
The effect of the housing stiffness on nonlinear traveling waves is presented in this work. It was found that the housing controls the synchronization of nonlinear elements and it allows nonlinear waves to travel through the structure. This phenomenon was observed in a gearbox with a soft housing, and the phenomenon was reproduced with a lump-mass dynamic model. The model included a pair of gears, the rolling bearings and the housing. The model considered all the nonlinear effects. Numerical and experimental results were analyzed with a time-frequency method using the Morlet wavelet function. A compound effect was observed when the nonlinear waves travel between the gears and the bearings: the waves increased the dynamic load amplitude and add another periodic load.
Absorption of inertia-gravity waves in vertically sheared rotating stratified flows
NASA Astrophysics Data System (ADS)
Millet, C.; Lott, F.
2012-12-01
It is well established that gravity waves have a substantial role on the large-scale atmospheric circulation, particularly in the middle atmosphere. In the present work, we re-examine the reflection and transmission of gravity waves through a critical layer surrounded by two inertial levels for the case of a constant vertically sheared flow. In this configuration, the vertical structure of the disturbance can be described as quasi-geostrophic from the critical layer up to the inertial levels, at which the Doppler-shifted frequency is equal to the Coriolis parameter. Near and beyond these levels, the balanced approximations do not apply and there is a transition from the quasi-geostrophic solution to propagating gravity waves. The three-dimensional disturbance solution is obtained analytically using both an exact method, in terms of hypergeometric functions, and a WKB approximation valid for large Richardson numbers; the latter includes an exponentially small term which captures the radiation feedback in the region between the inertial levels. We first focused on the homogeneous part of the disturbance equations, under the assumption of an unbounded domain. In contrast with past studies which show that there is a finite reflection and did not analyze the transmission (Yamanaka and Tanaka, 1984), we find that the reflection coefficient is too small to be significant and that the transmission coefficient is exactly like in the much simpler non-rotating case analyzed by Booker and Bretherton (1966). Our theoretical predictions are found to be in very good agreement with those obtained by numerically integrating the complete hydrostatic-Boussinesq equations with a small Rayleigh damping. The discrepancies between our results and those in Yamanaka and Tanaka (1984) are related to the fact that the solutions are given in term of multivalued functions and the values of the reflection and transmission coefficients are exponentially small, e.g. quite difficult to cross check
NASA Astrophysics Data System (ADS)
Singh, Baljeet
2016-01-01
The present paper is concerned with the propagation of plane waves in a rotating, transversely isotropic, two-temperature generalized thermoelastic solid half-space without energy dissipation. The governing equations are solved to show the existence of three plane waves in the x-z plane. The reflection of these plane waves from a thermally insulated free surface is also studied to obtain a system of three non-homogeneous equations in reflection coefficients of the reflected waves. The speeds and reflection coefficients are computed for a particular model of the half-space. The speeds and reflection coefficients of plane waves are shown graphically to observe the effects of anisotropy, two temperatures and rotation.
Hussain, Ibrar; Qadir, Asghar; Mahomed, F. M.
2009-06-15
Since gravitational wave spacetimes are time-varying vacuum solutions of Einstein's field equations, there is no unambiguous means to define their energy content. However, Weber and Wheeler had demonstrated that they do impart energy to test particles. There have been various proposals to define the energy content, but they have not met with great success. Here we propose a definition using 'slightly broken' Noether symmetries. We check whether this definition is physically acceptable. The procedure adopted is to appeal to 'approximate symmetries' as defined in Lie analysis and use them in the limit of the exact symmetry holding. A problem is noted with the use of the proposal for plane-fronted gravitational waves. To attain a better understanding of the implications of this proposal we also use an artificially constructed time-varying nonvacuum metric and evaluate its Weyl and stress-energy tensors so as to obtain the gravitational and matter components separately and compare them with the energy content obtained by our proposal. The procedure is also used for cylindrical gravitational wave solutions. The usefulness of the definition is demonstrated by the fact that it leads to a result on whether gravitational waves suffer self-damping.
Study of Rotating-Wave Electromagnetic Modes for Applications in Space Exploration
NASA Astrophysics Data System (ADS)
Velazco, J. E.
2016-08-01
Rotating waves are circularly polarized electromagnetic wave fields that behave like traveling waves but have discrete resonant frequencies of standing waves. In JPL's Communications Ground Systems Section (333), we are making use of this peculiar type of electromagnetic modes to develop a new generation of devices and instruments for direct applications in space exploration. In this article, we present a straightforward analysis about the phase velocity of these wave modes. A derivation is presented for the azimuthal phase velocity of transverse magnetic rotating modes inside cylindrical cavity resonators. Computer simulations and experimental measurements are also presented that corroborate the theory developed. It is shown that the phase velocity of rotating waves inside cavity resonators increases with radial position within the cavity and decreases when employing higher-order operating modes. The exotic features of rotating modes, once better understood, have the potential to enable the implementation of a plethora of new devices that range from amplifiers and frequency multipliers to electron accelerators and ion thrusters.
NASA Astrophysics Data System (ADS)
Medvedev, A. E.; Fomin, V. M.
1998-05-01
An approximate analytical model for calculation of the parameters of a steady gas flow inside a plane constricting channel formed by two symmetrically positioned wedges is suggested. A Mach configuration of shock waves (triple point) is formed in the channel when the wedge angles are larger than some critical value. The flow calculation in a constricting channel reduces to the solution of the iterative problem for a system of nonlinear algebraic equations. The configurations of shock waves, the slipstream, and the sonic line are described by the proposed model of a gas flow. A comparison of the results obtained using this model allows a fairly accurate calculation of the Mach stem and the length of the subsonic-flow region.
Electron-impact excitation of carbon and silicon in the distorted-wave approximation
NASA Technical Reports Server (NTRS)
Pindzola, M. S.; Bhatia, A. K.; Temkin, A.
1977-01-01
The 3P to 1D electron-impact excitation cross section within the ground configuration of both neutral carbon and silicon is calculated in the distorted-wave approximation of the two-state Hartree-Fock coupled equations. An essential element of the present treatment is that orthogonality to core orbitals is not assumed in deriving equations for the scattering orbitals. A local adiabatic polarization potential is also added to the distorted-wave equations. Both elements are necessary in getting good agreement with close-coupling results for carbon to low impacting energies. The agreement is sufficiently good that predictions for silicon should be accurate to within a factor of 2.
Salomons, E M
2000-10-01
The validity of the axisymmetric parabolic-equation (PE) method for line-of-sight sound propagation in a turbulent atmosphere is investigated. The axisymmetric PE method is a finite-difference method for solving a 2D parabolic wave equation, which follows from the 3D wave equation by the assumption of axial symmetry around the vertical axis through the source. It is found that this axisymmetric approximation has a considerable spurious effect on the fluctuations of the sound field. This is concluded from analytical expressions for the log-amplitude and phase variances, derived both for isotropic turbulence and for axisymmetric turbulence. The expressions for axisymmetric turbulence are compared with the results of numerical computations with the PE method. PMID:11051480
Quantum Lattice Fluctuations in the Charge Density Wave State beyond the Adiabatic Approximation
NASA Astrophysics Data System (ADS)
Shida, Keisuke; Watanabe, Yuko; Gomi, Hiroki; Takahashi, Akira; Tomita, Norikazu
2015-12-01
We have developed a tractable numerical method in which large-amplitude quantum lattice fluctuations can be described beyond the adiabatic approximation using the coherent state representation of phonons. A many-body wave function is constructed by the superposition of direct products of non-orthogonal Slater determinants for electrons and coherent states of phonons. Both orbitals in all the Slater determinants and the amplitudes of all the coherent states are simultaneously optimized. We apply the method to the one-dimensional Su-Schrieffer-Heeger model with the on-site and nearest-neighbor-site Coulomb interactions. It is shown the lattice fluctuations in doped charge density wave (CDW) systems are described by the translational and vibrational motion of lattice solitons. Such lattice solitons induce bond alternation in the doped CDW system while the lattice becomes equidistant in the half-filled CDW system.
Modelling vibrational-rotational interactions in intensities of v2 band of H2O by Pade approximants
NASA Astrophysics Data System (ADS)
Egorov, O. V.; Voitsekhovskaya, O. K.
2014-11-01
A semiempirical model in the form of Pade approximants, describing vibrational-rotational (VR) interactions in intensities of VR-lines of v2 water vapor (H2O) band, was developed. The corresponding to the C2v molecular symmetry group matrix elements, involved in the expansion of the transformed dipole moment, was applied to the derivation. The treatment of experimental intensities of v2 H2O band for transitions with ΔK = +/-1 and ΔK = +/-3 by means of obtained model results in decreasing the root mean square deviation (RMS) about two times (2.82 % instead of 6.20 %) in comparison to the traditional scheme.
On plasma rotation induced by waves in tokamaks
Guan, Xiaoyin; Dodin, I. Y.; Fisch, N. J.; Qin, Hong; Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 ; Liu, Jian
2013-10-15
The momentum conservation for resonant wave-particle interactions, now proven rigorously and for general settings, is applied to explain in simple terms how tokamak plasma is spun up by the wave momentum perpendicular to the dc magnetic field. The perpendicular momentum is passed through resonant particles to the dc field and, giving rise to the radial electric field, is accumulated as a Poynting flux; the bulk plasma is then accelerated up to the electric drift velocity proportional to that flux, independently of collisions. The presence of this collisionless acceleration mechanism permits varying the ratio of the average kinetic momentum absorbed by the resonant-particle and bulk distributions depending on the orientation of the wave vector. Both toroidal and poloidal forces are calculated, and a fluid model is presented that yields the plasma velocity at equilibrium.
Pilot-wave hydrodynamics in a rotating frame: Exotic orbits
Oza, Anand U.; Harris, Daniel M.; Rosales, Rodolfo R.; Bush, John W. M.; Wind-Willassen, Øistein
2014-08-15
We present the results of a numerical investigation of droplets walking on a rotating vibrating fluid bath. The drop's trajectory is described by an integro-differential equation, which is simulated numerically in various parameter regimes. As the forcing acceleration is progressively increased, stable circular orbits give way to wobbling orbits, which are succeeded in turn by instabilities of the orbital center characterized by steady drifting then discrete leaping. In the limit of large vibrational forcing, the walker's trajectory becomes chaotic, but its statistical behavior reflects the influence of the unstable orbital solutions. The study results in a complete regime diagram that summarizes the dependence of the walker's behavior on the system parameters. Our predictions compare favorably to the experimental observations of Harris and Bush [“Droplets walking in a rotating frame: from quantized orbits to multimodal statistics,” J. Fluid Mech. 739, 444–464 (2014)].
Rotation of weakly collisional plasmas in tokamaks, operated with Alfv{acute e}n waves
Tsypin, V.S.; Elfimov, A.G.; de Azevedo, C.A.; de Assis, A.S.
1996-12-01
The effect of the kinetic Alfv{acute e}n waves on weakly collisional plasma rotation in tokamaks has been studied for the plateau and banana regimes. The quasistationary rotation velocities and radial electric field have been found. The estimation of these quantities for the Phaedrus-T tokamak [S. Wukitch {ital et} {ital al}., Phys. Rev. Lett. {bold 77}, 294 (1996)] and for the Joint European Torus (JET) [A. Fasoli {ital et} {ital al}., Nucl. Fusion, {bold 36}, 258 (1996)] has been presented. It is shown that the kinetic Alfv{acute e}n waves, which are needed for current drive, change weakly the quasistationary rotation velocities and radial electric field, as found from the experimental data of these tokamaks. In conditions with increased rf power, the plasma rotation and radial electric field can essentially grow up. {copyright} {ital 1996 American Institute of Physics.}
Bruce, Neil C
2008-08-01
This paper presents a new formulation of the 3D Kirchhoff approximation that allows calculation of the scattering of vector waves from 2D rough surfaces containing structures with infinite slopes. This type of surface has applications, for example, in remote sensing and in testing or imaging of printed circuits. Some preliminary calculations for rectangular-shaped grooves in a plane are presented for the 2D surface method and are compared with the equivalent 1D surface calculations for the Kirchhoff and integral equation methods. Good agreement is found between the methods. PMID:18677363
Instabilities and waves on a columnar vortex in a strongly stratified and rotating fluid
NASA Astrophysics Data System (ADS)
Park, Junho; Billant, Paul
2013-08-01
This paper investigates the effect of the background rotation on the radiative instability of a columnar Rankine vortex in a strongly stratified fluid. We show that a cyclonic background rotation strongly stabilizes the radiative instability. The modes become neutral when the Rossby number Ro is below a critical value which depends on the azimuthal wavenumber of the wave. In the limit of small Rossby number, there exist fast neutral waves that are not captured by the quasi-geostrophic theory. In the presence of anticyclonic background rotation, the centrifugal instability dominates the radiative instability only when -400 ≲ Ro < -1. The numerical stability analysis is completed by asymptotic analyses for large wavenumbers which explain the properties and mechanisms of the waves and the instabilities. The stability of a continuous smoothed Rankine vortex is also investigated. The most amplified azimuthal wavenumber is then finite instead of infinite for the Rankine vortex.
Statistical physics approach to dendritic computation: The excitable-wave mean-field approximation
NASA Astrophysics Data System (ADS)
Gollo, Leonardo L.; Kinouchi, Osame; Copelli, Mauro
2012-01-01
We analytically study the input-output properties of a neuron whose active dendritic tree, modeled as a Cayley tree of excitable elements, is subjected to Poisson stimulus. Both single-site and two-site mean-field approximations incorrectly predict a nonequilibrium phase transition which is not allowed in the model. We propose an excitable-wave mean-field approximation which shows good agreement with previously published simulation results [Gollo , PLoS Comput. Biol.NERNET1553-734X10.1371/journal.pcbi.1000402 5, e1000402 (2009)] and accounts for finite-size effects. We also discuss the relevance of our results to experiments in neuroscience, emphasizing the role of active dendrites in the enhancement of dynamic range and in gain control modulation.
Lin, Jing-Fung
2008-09-01
A novel technique is presented for obtaining concurrent measurements of the linear and circular birefringence properties of an optical sample by using a rotating-wave-plate Stokes polarimeter to extract the 2x2 central elements of the corresponding Mueller matrix via two linearly polarized probe lights. For a compound sample comprising a half-wave plate in series with a quarter-wave plate, the measured values of the principal angle and retardance of the quarter-wave plate are found to have average normalized errors of 0.56% and 1.16%, respectively, while the measured value of the rotation angle of the half-wave plate has an error of just 0.39%. When analyzing glucose solutions with concentrations ranging from 0-1.2 g/dl positioned in front of a half-wave plate, the average normalized errors in the principal axis angle and retardance measurements of the half-wave plate are 0.69% and 2.65%, respectively, while the error in the rotation angle measurements of the glucose solutions is 2.13%. The correlation coefficient between the measured rotation angle and the concentration of the glucose solution is determined to be 0.99985, while the standard deviation is just 0.0022 deg. Overall the experimental results demonstrate the ability of the proposed system to obtain highly accurate measurements of the linear and circular birefringence properties of an optical sample and to decouple the relationship between the principal axis angle and the rotation angle. PMID:18758522
The transverse and rotational motions of magnetohydrodynamic kink waves in the solar atmosphere
Goossens, M.; Van Doorsselaere, T.; Soler, R.; Terradas, J.; Verth, G.
2014-06-10
Magnetohydrodynamic (MHD) kink waves have now been observed to be ubiquitous throughout the solar atmosphere. With modern instruments, they have now been detected in the chromosphere, interface region, and corona. The key purpose of this paper is to show that kink waves do not only involve purely transverse motions of solar magnetic flux tubes, but the velocity field is a spatially and temporally varying sum of both transverse and rotational motion. Taking this fact into account is particularly important for the accurate interpretation of varying Doppler velocity profiles across oscillating structures such as spicules. It has now been shown that, as well as bulk transverse motions, spicules have omnipresent rotational motions. Here we emphasize that caution should be used before interpreting the particular MHD wave mode/s responsible for these rotational motions. The rotational motions are not necessarily signatures of the classic axisymmetric torsional Alfvén wave alone, because kink motion itself can also contribute substantially to varying Doppler velocity profiles observed across these structures. In this paper, the displacement field of the kink wave is demonstrated to be a sum of its transverse and rotational components, both for a flux tube with a discontinuous density profile at its boundary, and one with a more realistic density continuum between the internal and external plasma. Furthermore, the Doppler velocity profile of the kink wave is forward modeled to demonstrate that, depending on the line of sight, it can either be quite distinct or very similar to that expected from a torsional Alfvén wave.
NASA Technical Reports Server (NTRS)
Mcaninch, G. L.; Myers, M. K.
1980-01-01
The parabolic approximation for the acoustic equations of motion is applied to the study of the sound field generated by a plane wave at or near grazing incidence to a finite impedance boundary. It is shown how this approximation accounts for effects neglected in the usual plane wave reflection analysis which, at grazing incidence, erroneously predicts complete cancellation of the incident field by the reflected field. Examples are presented which illustrate that the solution obtained by the parabolic approximation contains several of the physical phenomena known to occur in wave propagation near an absorbing boundary.
Hamiltonian structure for rotational capillary waves in stratified flows
NASA Astrophysics Data System (ADS)
Martin, Calin Iulian
2016-07-01
We show that the governing equations of two-dimensional water waves driven by surface tension propagating over two-layered stratified flows admit a Hamiltonian formulation. Moreover, the underlying flows that we consider here, have piecewise constant distribution of vorticity, the jump in vorticity being located along the interface separating the fluid of bigger density at the bottom from the lighter fluid adjacent to the free surface.
The Mm-Wave Rotational Spectrum of Glycolic Acid
NASA Astrophysics Data System (ADS)
Kisiel, Zbigniew; Pszczółkowski, Lech; Białkowska-Jaworska, Ewa; Charnley, Steven B.
2014-06-01
Glycolic acid, HOCH_2COOH is the simplest α-hydroxy acid. It is as yet undetected in the interstellar medium, but is known to be present in carbonaceous meteorites and in residues from UV-photolysed interstellar ice analogue mixtures. Prior rotational spectroscopy has been carried out up to 40 GHz for the main, SSC conformer, Presently we report the analysis of the rotational spectrum of glycolic acid on the basis of broadband measurements performed up to 318 GHz, and updated spectroscopic constants for the ground state and the first two excited states of the low-frequency ν21 torsional mode. We have used the AABS package to assign multiple further excited vibrational states of the SSC conformer. In particular, we have been able to assign the highly perturbed triad of ν14, ν20 and 3ν21 states. The triad has been fitted down to experimental accuracy with a coupled fit, which allowed us to pin down the hitherto elusive frequency of the ν21 mode. The experimental results make an interesting comparison with those of anharmonic force field calculations. We have also been able to extend the measurements for the AAT conformer. C.E.Blom, A.Bauder, Chem. Phys. Lett., 82, 492 (1981), J. Am. Chem. Soc., 104, 2993 (1982). H.Hasegawa, O.Ohashi, I.Yamaguchi, J. Mol. Spectrosc., 82, 205 (1982). P.D.Godfrey, F.M.Rodgers, R.D.Brown, J. Am. Chem. Soc., 119, 2232 (1997).
Numerical analysis of volume holograms with spherical reference wave based on Born approximation
NASA Astrophysics Data System (ADS)
Yoshida, S.; Yamamoto, M.
2013-05-01
Holographic Data Storage (HDS) is one of the next generation storage technologies that can actualize high data capacity and high data transfer rate. Since information is recorded 3-dimensionally in a thick medium, data capacity of the HDS is not constrained by diffraction limit. However, behavior of wavefront in an inhomogeneous thick medium is highly complex, and it is hard to handle propagation of wavefront in the medium analytically. Therefore, we establish a numerical technique for analysis of volume holograms. The proposed technique is based on the scalar diffraction theory, which is described as the volume integral equation. By applying Born approximation and angular spectrum method to the volume integral equation, the technique can be applicable for various problems. We analyze characteristics of the volume hologram with spherical reference wave, and confirm effectiveness of the proposed technique. Compared to conventional techniques such as coupled wave analysis, beam propagation method, and finite-difference time domain method, the proposed technique has application potentiality for various problems, and it is easy to implement. In this study, we show effectiveness of the proposed technique by applying to analysis of the volume hologram with spherical reference wave. It can be expected that the proposed technique may become a tool for design of HDS systems.
Anomalous incident-angle and elliptical-polarization rotation of an elastically refracted P-wave
Fa, Lin; Fa, Yuxiao; Zhang, Yandong; Ding, Pengfei; Gong, Jiamin; Li, Guohui; Li, Lijun; Tang, Shaojie; Zhao, Meishan
2015-01-01
We report a newly discovered anomalous incident-angle of an elastically refracted P-wave, arising from a P-wave impinging on an interface between two VTI media with strong anisotropy. This anomalous incident-angle is found to be located in the post-critical incident-angle region corresponding to a refracted P-wave. Invoking Snell’s law for a refracted P-wave provides two distinctive solutions before and after the anomalous incident-angle. For an inhomogeneously refracted and elliptically polarized P-wave at the anomalous incident-angle, its rotational direction experiences an acute variation, from left-hand elliptical to right-hand elliptical polarization. The new findings provide us an enhanced understanding of acoustical-wave scattering and lead potentially to widespread and novel applications. PMID:26244284
Computational resources to filter gravitational wave data with P-approximant templates
NASA Astrophysics Data System (ADS)
Porter, Edward K.
2002-08-01
The prior knowledge of the gravitational waveform from compact binary systems makes matched filtering an attractive detection strategy. This detection method involves the filtering of the detector output with a set of theoretical waveforms or templates. One of the most important factors in this strategy is knowing how many templates are needed in order to reduce the loss of possible signals. In this study, we calculate the number of templates and computational power needed for a one-step search for gravitational waves from inspiralling binary systems. We build on previous works by first expanding the post-Newtonian waveforms to 2.5-PN order and second, for the first time, calculating the number of templates needed when using P-approximant waveforms. The analysis is carried out for the four main first-generation interferometers, LIGO, GEO600, VIRGO and TAMA. As well as template number, we also calculate the computational cost of generating banks of templates for filtering GW data. We carry out the calculations for two initial conditions. In the first case we assume a minimum individual mass of 1 Msolar and in the second, we assume a minimum individual mass of 5 Msolar. We find that, in general, we need more P-approximant templates to carry out a search than if we use standard PN templates. This increase varies according to the order of PN-approximation, but can be as high as a factor of 3 and is explained by the smaller span of the P-approximant templates as we go to higher masses. The promising outcome is that for 2-PN templates, the increase is small and is outweighed by the known robustness of the 2-PN P-approximant templates.
NASA Astrophysics Data System (ADS)
Dalton, C. A.; Hjorleifsdottir, V.; Ekstrom, G.
2011-12-01
Surface-wave amplitudes provide the primary constraint on upper-mantle anelastic structure and are also sensitive to small-scale elastic structure through focusing effects. However, the use of amplitudes for seismic imaging presents several challenges. One, amplitudes are affected not only by propagation through anelastic and elastic heterogeneity but also by uncertainty in the source excitation, local receiver structure, and instrument response. Two, accounting for focusing and defocusing effects, which is important if amplitudes are to be used to study anelasticity, depends considerably on the chosen theoretical treatment. Three, multiple scattering of seismic energy by elastic heterogeneity can be mapped into attenuation, especially at high frequencies. With the objective of improving our ability to image mantle seismic attenuation using real amplitude observations, we investigate how approximations in the theoretical treatment of wave excitation and propagation influence the interpretation of amplitudes. We use a spectral-element wave-propagation solver (SPECFEM3D_GLOBE) to generate accurate seismograms for global Earth models containing one-dimensional attenuation structure and three-dimensional variations in seismic velocity. The seismograms are calculated for 42 realistically distributed earthquakes. Fundamental-mode Rayleigh wave amplitudes in the period range 50--200 seconds are measured using the approach of Ekström et al. (1997), for which PREM is the assumed Earth model. We show that using the appropriate local seismic structure at the source and receiver instead of PREM has a non-negligible effect on the amplitudes and improves their interpretation. The amplitudes due to focusing and defocusing effects are predicted for great-circle ray theory, exact ray theory (JWKB theory), and finite-frequency theory. We assess the ability of each theory to predict amplitudes that agree with those measured from the SPECFEM synthetics for an Earth model that
Quantum metrology with rotating matter waves in different geometries
Dunningham, J. A.; Cooper, J. J.; Hallwood, D. W.
2012-09-01
A promising practical application of entanglement is metrology, where quantum states can be used to make measurements beyond the shot noise limit. Here we consider how metrology schemes could be realised using atomic Bose-Einstein condensates (BECs) trapped in different potentials. In particular, we show that if a trapped BEC is rotated at just the right frequency, it can undergo a quantum phase transition characterised by large-scale entanglement spreading across the system. This simple process of stirring can generate interesting quantum states such as macroscopic superpositions of all the atoms flowing in opposite directions around a ring-shaped potential. We consider different trapping potentials and show how this leads to different entangled states. In particular, we find that by reducing the dimensionality of the system to one or two dimensions, it is possible to generate entangled states that are remarkably robust to the loss of atoms and so are ideally suited to precision measurement schemes.
NASA Astrophysics Data System (ADS)
Van Gorder, Robert A.
2014-11-01
In R. A. Van Gorder, "General rotating quantum vortex filaments in the low-temperature Svistunov model of the local induction approximation," Phys. Fluids 26, 065105 (2014) I discussed properties of generalized vortex filaments exhibiting purely rotational motion under the low-temperature Svistunov model of the local induction approximation. Such solutions are stationary in terms of translational motion. In the Comment [N. Hietala, "Comment on `General rotating quantum vortex filaments in the low-temperature Svistunov model of the local induction approximation' [Phys. Fluids 26, 065105 (2014)]," Phys. Fluids 26, 119101 (2014)], the author criticizes my paper for not including translational motion (although it was clearly stated that the filament motion was assumed rotational). As it turns out, if one is interested in studying the geometric structure of solutions (which was the point of my paper), one obtains the needed qualitative results on the structure of such solutions by studying the purely rotational case. Nevertheless, in this Response I shall discuss the vortex filaments that have both rotational and translational motions. I then briefly discuss why one might want to study such generalized rotating filament solutions, in contrast to simple the standard helical or planar examples (which are really special cases). I also discuss how one can study the time evolution of filaments which exhibit more complicated dynamics than pure translation and rotation. Doing this, one can study non-stationary solutions which initially appear purely rotational and gradually display other dynamics as the filaments evolve.
Rotational study of the CH4-CO complex: Millimeter-wave measurements and ab initio calculations.
Surin, L A; Tarabukin, I V; Panfilov, V A; Schlemmer, S; Kalugina, Y N; Faure, A; Rist, C; van der Avoird, A
2015-10-21
The rotational spectrum of the van der Waals complex CH4-CO has been measured with the intracavity OROTRON jet spectrometer in the frequency range of 110-145 GHz. Newly observed and assigned transitions belong to the K = 2-1 subband correlating with the rotationless jCH4 = 0 ground state and the K = 2-1 and K = 0-1 subbands correlating with the jCH4 = 2 excited state of free methane. The (approximate) quantum number K is the projection of the total angular momentum J on the intermolecular axis. The new data were analyzed together with the known millimeter-wave and microwave transitions in order to determine the molecular parameters of the CH4-CO complex. Accompanying ab initio calculations of the intermolecular potential energy surface (PES) of CH4-CO have been carried out at the explicitly correlated coupled cluster level of theory with single, double, and perturbative triple excitations [CCSD(T)-F12a] and an augmented correlation-consistent triple zeta (aVTZ) basis set. The global minimum of the five-dimensional PES corresponds to an approximately T-shaped structure with the CH4 face closest to the CO subunit and binding energy De = 177.82 cm(-1). The bound rovibrational levels of the CH4-CO complex were calculated for total angular momentum J = 0-6 on this intermolecular potential surface and compared with the experimental results. The calculated dissociation energies D0 are 91.32, 94.46, and 104.21 cm(-1) for A (jCH4 = 0), F (jCH4 = 1), and E (jCH4 = 2) nuclear spin modifications of CH4-CO, respectively. PMID:26493903
NASA Astrophysics Data System (ADS)
Freistühler, Heinrich; Liu, Tai-Ping
1993-04-01
This paper proves that certain non-classical shock waves in a rotationally invariant system of viscous conservation laws posses nonlinear large-time stability against sufficiently small perturbations. The result applies to small intermediate magnetohydrodynamic shocks in the presence of dissipation.
Continuation and stability of convective modulated rotating waves in spherical shells
NASA Astrophysics Data System (ADS)
Garcia, F.; Net, M.; Sánchez, J.
2016-01-01
Modulated rotating waves (MRW), bifurcated from the thermal-Rossby waves that arise at the onset of convection of a fluid contained in a rotating spherical shell, and their stability, are studied. For this purpose, Newton-Krylov continuation techniques are applied. Nonslip boundary conditions, an Ekman number E =10-4 , and a low Prandtl number fluid Pr=0.1 in a moderately thick shell of radius ratio η =0.35 , differentially heated, are considered. The MRW are obtained as periodic orbits by rewriting the equations of motion in the rotating frame of reference where the rotating waves become steady states. Newton-Krylov continuation allows us to obtain unstable MRW that cannot be found by using only time integrations, and identify regions of multistability. For instance, unstable MRW without any azimuthal symmetry have been computed. It is shown how they become stable in a small Rayleigh-number interval, in which two branches of traveling waves are also stable. The study of the stability of the MRW helps to locate and classify the large sequence of bifurcations, which takes place in the range analyzed. In particular, tertiary Hopf bifurcations giving rise to three-frequency stable solutions are accurately determined.
Continuation and stability of convective modulated rotating waves in spherical shells.
Garcia, F; Net, M; Sánchez, J
2016-01-01
Modulated rotating waves (MRW), bifurcated from the thermal-Rossby waves that arise at the onset of convection of a fluid contained in a rotating spherical shell, and their stability, are studied. For this purpose, Newton-Krylov continuation techniques are applied. Nonslip boundary conditions, an Ekman number E=10^{-4}, and a low Prandtl number fluid Pr=0.1 in a moderately thick shell of radius ratio η=0.35, differentially heated, are considered. The MRW are obtained as periodic orbits by rewriting the equations of motion in the rotating frame of reference where the rotating waves become steady states. Newton-Krylov continuation allows us to obtain unstable MRW that cannot be found by using only time integrations, and identify regions of multistability. For instance, unstable MRW without any azimuthal symmetry have been computed. It is shown how they become stable in a small Rayleigh-number interval, in which two branches of traveling waves are also stable. The study of the stability of the MRW helps to locate and classify the large sequence of bifurcations, which takes place in the range analyzed. In particular, tertiary Hopf bifurcations giving rise to three-frequency stable solutions are accurately determined. PMID:26871166
Energetic Particles and Upstream Waves at Co-rotating Shocks
NASA Astrophysics Data System (ADS)
Smith, Edward J.; Zhou, Xiaoyan
2010-03-01
We report a study of energetic ion acceleration at shocks bounding co-rotating interaction regions (CIRs). Archived data obtained by Ulysses magnetic field, solar wind and energetic particle investigations at low latitude CIRs have been assembled and analyzed. The statistical relations between various properties of 22 Forward shocks, energetic particles and upstream heliospheric magnetic field fluctuations are presented. No statistically significant correlations are found between the shock compression ratio, r, or the particle intensity, jp, or the energetic particle spectral index, s, and the shock normal-upstream field angle, θBn. Furthermore, a theoretical relation between the particle spectral index and shock compression is not consistent with the observed values of s and r. The particle intensities are poorly correlated with the power in upstream heliospheric magnetic field fluctuations contrary to our preliminary study of fewer shocks. We conclude that many of the expectations of Diffusive Shock Theory are not supported by this data set but it is too early to decide whether some key measurement is missing or the theory needs reconsideration.
Nonlinear Solver Approaches for the Diffusive Wave Approximation to the Shallow Water Equations
NASA Astrophysics Data System (ADS)
Collier, N.; Knepley, M.
2015-12-01
The diffusive wave approximation to the shallow water equations (DSW) is a doubly-degenerate, nonlinear, parabolic partial differential equation used to model overland flows. Despite its challenges, the DSW equation has been extensively used to model the overland flow component of various integrated surface/subsurface models. The equation's complications become increasingly problematic when ponding occurs, a feature which becomes pervasive when solving on large domains with realistic terrain. In this talk I discuss the various forms and regularizations of the DSW equation and highlight their effect on the solvability of the nonlinear system. In addition to this analysis, I present results of a numerical study which tests the applicability of a class of composable nonlinear algebraic solvers recently added to the Portable, Extensible, Toolkit for Scientific Computation (PETSc).
Potsika, Vassiliki T; Protopappas, Vasilios C; Vavva, Maria G; Polyzos, Demosthenes; Fotiadis, Dimitrios I
2013-01-01
The quantitative determination of wave dispersion and attenuation in bone is an open research area as the factors responsible for ultrasound absorption and scattering in composite biological tissues have not been completely explained. In this study, we use the iterative effective medium approximation (IEMA) proposed in [1] so as to calculate phase velocity and attenuation in media with properties similar to those of cancellous bones. Calculations are performed for a frequency range of 0.4-0.8 MHz and for different inclusions' volume concentrations and sizes. Our numerical results are compared with previous experimental findings so as to assess the effectiveness of IEMA. It was made clear that attenuation and phase velocity estimations could provide supplementary information for cancellous bone characterization. PMID:24111396
Van Gorder, Robert A.
2014-06-15
In his study of superfluid turbulence in the low-temperature limit, Svistunov [“Superfluid turbulence in the low-temperature limit,” Phys. Rev. B 52, 3647 (1995)] derived a Hamiltonian equation for the self-induced motion of a vortex filament. Under the local induction approximation (LIA), the Svistunov formulation is equivalent to a nonlinear dispersive partial differential equation. In this paper, we consider a family of rotating vortex filament solutions for the LIA reduction of the Svistunov formulation, which we refer to as the 2D LIA (since it permits a potential formulation in terms of two of the three Cartesian coordinates). This class of solutions holds the well-known Hasimoto-type planar vortex filament [H. Hasimoto, “Motion of a vortex filament and its relation to elastica,” J. Phys. Soc. Jpn. 31, 293 (1971)] as one reduction and helical solutions as another. More generally, we obtain solutions which are periodic in the space variable. A systematic analytical study of the behavior of such solutions is carried out. In the case where vortex filaments have small deviations from the axis of rotation, closed analytical forms of the filament solutions are given. A variety of numerical simulations are provided to demonstrate the wide range of rotating filament behaviors possible. Doing so, we are able to determine a number of vortex filament structures not previously studied. We find that the solution structure progresses from planar to helical, and then to more intricate and complex filament structures, possibly indicating the onset of superfluid turbulence.
Hubbard, L.M.; Miller, W.H.
1983-02-15
The semiclassical perturbation (SCP) approximation of Miller and Smith (Phys. Rev. A 17, 17 (1978)) is applied to the scattering of atoms and molecules from crystal surfaces. Specifically, diffraction of He from LiF, and diffraction and rotationally inelastic scattering of H/sub 2/ from LiF are treated, and the SCP model is seen to agree well with earlier coupled-channel and quantum sudden calculations. These tests of the SCP model are all for ''soft'' interaction potentials, e.g., of the Lennard-Jones Devonshire variety, but it is also shown that the model behaves correctly in the limit of an impulsive hard-wall potential function. The SCP picture thus appears to have a wide range of validity for describing the dynamics of gas-surface collisions.
Hayama, Kazuhiro; Kuroda, Takami; Nakamura, Ko; Yamada, Shoichi
2016-04-15
We propose to employ the circular polarization of gravitational waves emitted by core-collapse supernovae as an unequivocal indication of rapid rotation deep in their cores just prior to collapse. It has been demonstrated by three dimensional simulations that nonaxisymmetric accretion flows may develop spontaneously via hydrodynamical instabilities in the postbounce cores. It is not surprising, then, that the gravitational waves emitted by such fluid motions are circularly polarized. We show, in this Letter, that a network of the second generation detectors of gravitational waves worldwide may be able to detect such polarizations up to the opposite side of the Galaxy as long as the rotation period of the core is shorter than a few seconds prior to collapse. PMID:27127951
NASA Astrophysics Data System (ADS)
Hayama, Kazuhiro; Kuroda, Takami; Nakamura, Ko; Yamada, Shoichi
2016-04-01
We propose to employ the circular polarization of gravitational waves emitted by core-collapse supernovae as an unequivocal indication of rapid rotation deep in their cores just prior to collapse. It has been demonstrated by three dimensional simulations that nonaxisymmetric accretion flows may develop spontaneously via hydrodynamical instabilities in the postbounce cores. It is not surprising, then, that the gravitational waves emitted by such fluid motions are circularly polarized. We show, in this Letter, that a network of the second generation detectors of gravitational waves worldwide may be able to detect such polarizations up to the opposite side of the Galaxy as long as the rotation period of the core is shorter than a few seconds prior to collapse.
On strongly interacting internal waves in a rotating ocean and coupled Ostrovsky equations.
Alias, A; Grimshaw, R H J; Khusnutdinova, K R
2013-06-01
In the weakly nonlinear limit, oceanic internal solitary waves for a single linear long wave mode are described by the KdV equation, extended to the Ostrovsky equation in the presence of background rotation. In this paper we consider the scenario when two different linear long wave modes have nearly coincident phase speeds and show that the appropriate model is a system of two coupled Ostrovsky equations. These are systematically derived for a density-stratified ocean. Some preliminary numerical simulations are reported which show that, in the generic case, initial solitary-like waves are destroyed and replaced by two coupled nonlinear wave packets, being the counterpart of the same phenomenon in the single Ostrovsky equation. PMID:23822486
NASA Astrophysics Data System (ADS)
Wang, Ping; Lu, DongQiang
2013-11-01
An analytic approximation method known as the homotopy analysis method (HAM) is applied to study the nonlinear hydroelastic progressive waves traveling in an infinite elastic plate such as an ice sheet or a very large floating structure (VLFS) on the surface of deep water. A convergent analytical series solution for the plate deflection is derived by choosing the optimal convergencecontrol parameter. Based on the analytical solution the effects of different parameters are considered. We find that the plate deflection becomes lower with an increasing Young's modulus of the plate. The displacement tends to be flattened at the crest and be sharpened at the trough as the thickness of the plate increases, and the larger density of the plate also causes analogous results. Furthermore, it is shown that the hydroelastic response of the plate is greatly affected by the high-amplitude incident wave. The results obtained can help enrich our understanding of the nonlinear hydroelastic response of an ice sheet or a VLFS on the water surface.
Niekerk, D. D. van; Ventel, B. I. S. van der; Titus, N. P.; Hillhouse, G. C.
2011-04-15
We present a fully relativistic model for polarized inclusive quasielastic proton-nucleus scattering that includes relativistic distorted waves for the projectile and ejectile (RDWIA), as well as the relativistic random-phase approximation (RPA) applied to the target nucleus. Using a standard relativistic impulse approximation treatment of quasielastic scattering and a two-body Scalar, Pseudoscalar, Vector, Axial vector, Tensor (SPVAT) form of the current operator, it is shown how the behavior of the projectile/ejectile and target can be decoupled. Distortion effects are included via a full partial-wave expansion of the relativistic wave functions. Target correlations are included via the relativistic RPA applied to mean-field theory in quantum hadrodynamics. A number of novel analytical and numerical techniques are employed to aid in this highly nontrivial calculation. A baseline plane-wave calculation is performed for the reaction {sup 40}Ca(p-vector,p-vector{sup '}) at an energy of 500 MeV and an angle {theta}{sub c.m.}=40 deg. Here it is found that the effect of isoscalar correlations is a quenching of the cross section that is expected to become more pronounced at lower energies or for higher-density targets. A RDWIA calculation shows additional reduction and if isoscalar target correlations are included this effect is enhanced.
A new model for algebraic Rossby solitary waves in rotation fluid and its solution
NASA Astrophysics Data System (ADS)
Chen, Yao-Deng; Yang, Hong-Wei; Gao, Yu-Fang; Yin, Bao-Shu; Feng, Xing-Ru
2015-09-01
A generalized Boussinesq equation that includes the dissipation effect is derived to describe a kind of algebraic Rossby solitary waves in a rotating fluid by employing perturbation expansions and stretching transformations of time and space. Using this equation, the conservation laws of algebraic Rossby solitary waves are discussed. It is found that the mass, the momentum, the energy, and the velocity of center of gravity of the algebraic solitary waves are conserved in the propagation process. Finally, the analytical solution of the equation is generated. Based on the analytical solution, the properties of the algebraic solitary waves and the dissipation effect are discussed. The results point out that, similar to classic solitary waves, the dissipation can cause the amplitude and the speed of solitary waves to decrease; however, unlike classic solitary waves, the algebraic solitary waves can split during propagation and the decrease of the detuning parameter can accelerate the occurrence of the solitary waves fission phenomenon. Project supported by the Shandong Provincial Key Laboratory of Marine Ecology and Environment and Disaster Prevention and Mitigation Project, China (Grant No. 2012010), the National Natural Science Foundation of China (Grant Nos. 41205082 and 41476019), the Special Funds for Theoretical Physics of the National Natural Science Foundation of China (Grant No. 11447205), and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), China.
Partial Antisymmetry and Approximate Primitive Wave Functions for Interacting Electronic Groups.
NASA Astrophysics Data System (ADS)
Vergenz, Robert Allan
The partial antisymmetry (PA) theorem of W. H. Adams (Chem. Phys. Letters, 68, 511 (1979)) shows that if one can determine an N-electron eigenfunction of a certain non-linear operator, then one can use the eigenfunction, without using full antisymmetry (FA), to calculate an eigenvalue of the Schrodinger Hamiltonian for the system. The operator neither depends on nor commutes with the antisymmetrizer, but involves partial antisymmetrizers. This work provides an initial numerical test of a new approach to calculating approximate interatomic interaction energies based on the PA theorem. Interaction energies were calculated for X ^1Sigma^{+}_ {rm g} Ne_2, Li_2 and Na_2, X^1Sigma^{+} LiNa, X^2Sigma^{+} _{rm g} Li_2 ^{+}, x ^7Sigma ^{+}_{rm u} N_2, x ^3Sigma ^{+}_{rm u} Li_2 and Na_2, x ^3Sigma^{+} LiNa and ionic and covalent configurations of X ^1Sigma^{+} LiF, all at several internuclear distances. Spin-coupled products of single determinants approximated the atomic wave functions, and accurate HF atomic bases were used. Three methods were used: the conventional method based on FA, the PA approach, and a method based on a hybrid set of assumptions. Results were compared with accurate potential curves from the literature. In nine cases of the eleven, including both bonding and repulsive interactions, the PA approximation gave results that were better or roughly the same as those using FA. In these cases there is thus no penalty exacted for the use of PA, though it is shown to be easier to use.
Exact solutions of regular approximate relativistic wave equations for hydrogen-like atoms
NASA Astrophysics Data System (ADS)
van Leeuwen, R.; van Lenthe, E.; Baerends, E. J.; Snijders, J. G.
1994-07-01
Apart from relativistic effects originating from high kinetic energy of an electron in a flat potential, which are treated in first order by the Pauli Hamiltonian, there are relativistic effects even for low-energy electrons if they move in a strong Coulomb potential. The latter effects can be accurately treated already in the zeroth order of an expansion of the Foldy-Wouthuysen transformation, if the expansion is carefully chosen to be nondivergent for r→0 even for Coulomb potentials, as shown by Van Lenthe et al. [J. Chem. Phys. 99, 4597 (1993)] (cf. also Heully et al. [J. Phys. B 19, 2799 (1986)] and Chang et al. [Phys. Scr. 34, 394 (1986)]). In the present paper, it is shown that the solutions of the zeroth order of this two-component regular approximate (ZORA) equation for hydrogen-like atoms are simply scaled solutions of the large component of the Dirac wave function for this problem. The eigenvalues are related in a similar way. As a consequence, it is proven that under some restrictions, the ZORA Hamiltonian is bounded from below for Coulomb-like potentials. Also, an exact result for the first order regular approximate Hamiltonian is given. The method can also be used to obtain exact results for regular approximations of scalar relativistic equations, like the Klein-Gordon equation. The balance between relativistic effects originating from the Coulombic singularity in the potential (typically core penetrating s and p valence electrons in atoms and molecules) and from high kinetic energy (important for high-energy electrons in a flat potential and also for core-avoiding high angular momentum (d, f, and g states in atoms) are discussed.
Do inertial wave interactions control the rate of energy dissipation of rotating turbulence?
NASA Astrophysics Data System (ADS)
Cortet, Pierre-Philippe; Campagne, Antoine; Machicoane, Nathanael; Gallet, Basile; Moisy, Frederic
2015-11-01
The scaling law of the energy dissipation rate, ɛ ~U3 / L (with U and L the characteristic velocity and lengthscale), is one of the most robust features of fully developed turbulence. How this scaling is affected by a background rotation is still a controversial issue with importance for geo and astrophysical flows. At asymptotically small Rossby numbers Ro = U / ΩL , i.e. in the weakly nonlinear limit, wave-turbulence arguments suggest that ɛ should be reduced by a factor Ro . Such scaling has however never been evidenced directly, neither experimentally nor numerically. We report here direct measurements of the injected power, and therefore of ɛ, in an experiment where a propeller is rotating at a constant rate in a large volume of fluid rotating at Ω. In co-rotation, we find a transition between the wave-turbulence scaling at small Ro and the classical Kolmogorov law at large Ro . The transition between these two regimes is characterized from experiments varying the propeller and tank dimensions. In counter-rotation, the scenario is much richer with the observation of an additional peak of dissipation, similar to the one found in Taylor-Couette experiments.
Internal wave breather propagation under the influence of the Earth rotation
NASA Astrophysics Data System (ADS)
Talipova, Tatiana; Rouvinskaya, Ekaterina; Kurkina, Oxana
2015-04-01
The internal wave breather propagation under the influence of the Earth rotation is studied in the frames of the asymptotic model based on the Gardner equation as well as the fully nonlinear Euler equations. It is obtained that the amplitude and shape of short breathers depend on the Earth rotation very weakly but the wide breathers change the amplitude and shape sufficiently. This effect is studied in the model situation adapted to the Baltic Sea hydrological conditions. The rate of the breather amplitude damping upon the even bottom is shown.
Zhou, Zhennan
2014-09-01
In this paper, we approximate the semi-classical Schrödinger equation in the presence of electromagnetic field by the Hagedorn wave packets approach. By operator splitting, the Hamiltonian is divided into the modified part and the residual part. The modified Hamiltonian, which is the main new idea of this paper, is chosen by the fact that Hagedorn wave packets are localized both in space and momentum so that a crucial correction term is added to the truncated Hamiltonian, and is treated by evolving the parameters associated with the Hagedorn wave packets. The residual part is treated by a Galerkin approximation. We prove that, with the modified Hamiltonian only, the Hagedorn wave packets dynamics give the asymptotic solution with error O(ε{sup 1/2}), where ε is the scaled Planck constant. We also prove that, the Galerkin approximation for the residual Hamiltonian can reduce the approximation error to O(ε{sup k/2}), where k depends on the number of Hagedorn wave packets added to the dynamics. This approach is easy to implement, and can be naturally extended to the multidimensional cases. Unlike the high order Gaussian beam method, in which the non-constant cut-off function is necessary and some extra error is introduced, the Hagedorn wave packets approach gives a practical way to improve accuracy even when ε is not very small.
Uniform asymptotic approximations for transient waves due to an initial disturbance
NASA Astrophysics Data System (ADS)
Madsen, Per A.; Schäffer, Hemming A.; Fuhrman, David R.; Toledo, Yaron
2016-01-01
In this work, we first present a semianalytical method for the evolution of linear fully dispersive transient waves generated by an initial surface displacement and propagating over a constant depth. The procedure starts from Fourier and Hankel transforms and involves a combination of the method of stationary phase, the method of uniform asymptotic approximations and various Airy integral formulations. Second, we develop efficient convolution techniques expressed as single and double summations over the source area. These formulations are flexible, extremely fast, and highly accurate even for the dispersive tail of the transient waves. To verify the accuracy of the embedded dispersion properties, we consider test cases with sharp-edged disturbances in 1-D and 2-D. Furthermore, we consider the case of a relatively blunt Gaussian disturbance in 2-D. In all cases, the agreement between the convolution results and simulations with a high-order Boussinesq model is outstanding. Finally, we make an attempt to extend the convolution methods to geophysical tsunami problems taking into account, e.g., uneven bottom effects. Unfortunately, refraction/diffraction effects cannot easily be incorporated, so instead we focus on the incorporation of linear shoaling and its effect on travel time and temporal evolution of the surface elevation. The procedure is tested on data from the 2011 Japan tsunami. Convolution results are likewise compared to model simulations based on the nonlinear shallow water equations and both are compared with field observations from 10 deep water DART buoys. The near-field results are generally satisfactory, while the far-field results leave much to be desired.
Interplay of Waves and Eddies and Energy Exchange in Rotating Stratified Geophysical Flows
NASA Astrophysics Data System (ADS)
Pouquet, A.; Marino, R.; Rosenberg, D. L.; Herbert, C.
2015-12-01
We investigate the distribution of energy between wave and vortical modes as a function of scale in high resolution direct numerical simulations of rotating stratified Boussinesq flows with a unit aspect ratio, varying the dimensionless parameters in regimes in which wave turbulence prevails. The shift in scale from a vortex-dominated to a wave-dominated dynamics, characterized each by their Fourier spectra, is quantified by the wavenumber KR at which they cross. We examine the dependency of KR with parameters characteristics of the intrinsic dynamics of the flow such as Reynolds, Froude and Rossby numbers, and their combinations. Features of the energy exchange between potential and kinetic energy related to the interplay of wave modes and vortical modes are also explored and results recast in the context of geophysical flows.
NASA Astrophysics Data System (ADS)
Takagi, Seiji; Ueda, Tetsuo
2010-06-01
Pattern dynamics plays a fundamental role in biological functions from cell to organ in living systems, and the appearance of rotating waves can lead to pathological situations. Basic dynamics of rotating waves of contraction-relaxation activity under local perturbation is studied in a newly developed protoplasmic droplet of the Physarum plasmodium. A light pulse is applied by irradiating circularly a quarter of the droplet showing a single rotating wave. The oscillation pattern changes abruptly only when the irradiation is applied at a part of the droplet near the maximal contraction. The abrupt changes are as follows: the rotating wave disappears or is displaced when the irradiation area is very close to the center of the rotating wave, while new rotating waves are created when the irradiation area is far from the center of the rotating wave. These results support the hypothesis that the phase response curve has a discontinuous change (type 0 resetting) from delay to advance around the maximal contraction. The significance of the results is discussed in relation to “vulnerability” in excitable media and biological systems in general.
Rotating matter-wave beam splitters and consequences for atom gyrometers
Antoine, Charles
2007-09-15
The effect of a rotation on a matter-wave-laser beam splitter is studied and modeled. This modeling is shown to give important nontrivial corrections to the Sagnac phase shift of matter-wave gyrometers when the duration of the laser action cannot be neglected with respect to the propagation time between beam splitters. This result is illustrated on a Mach-Zehnder atom gyrometer (rate gyroscope) with running laser beam splitters. A quasiclassical description of the interferometer arms inside the beam splitters is proposed to interpret the corrected Sagnac phase shift in terms of an effective interferometer area.
Pilot-wave dynamics in a rotating frame: on the emergence of orbital quantization
NASA Astrophysics Data System (ADS)
Oza, Anand; Harris, Daniel; Rosales, Rodolfo; Bush, John
2013-11-01
We present the results of a theoretical investigation of droplets walking on a rotating vibrating fluid bath. The droplet's trajectory is described in terms of an integro-differential equation that incorporates the influence of its propulsive wave force. Predictions for the dependence of the orbital radius on the bath's rotation rate compare favorably with experimental data and capture the progression from continuous to quantized orbits as the vibrational acceleration is increased. The orbital quantization is rationalized by assessing the stability of the orbital solutions, and may be understood as resulting directly from the dynamic constraint imposed on the drop by its monochromatic guiding wave. The stability analysis also predicts the existence of wobbling orbital states reported in recent experiments, and the virtual absence of stable orbits in the limit of large vibrational forcing. The authors acknowledge the generous financial support of the NSF through Grant CBET-0966452.
Chiral vortical wave and induced flavor charge transport in a rotating quark-gluon plasma
NASA Astrophysics Data System (ADS)
Jiang, Yin; Huang, Xu-Guang; Liao, Jinfeng
2015-10-01
We show the existence of a new gapless collective excitation in a rotating fluid system with chiral fermions, named the chiral vortical wave (CVW). The CVW has its microscopic origin at the quantum anomaly and macroscopically arises from interplay between vector and axial charge fluctuations induced by vortical effects. The wave equation is obtained both from hydrodynamic current equations and from chiral kinetic theory, and its solutions show nontrivial CVW-induced charge transport from different initial conditions. Using the rotating quark-gluon plasma in heavy ion collisions as a concrete example, we show the formation of an induced flavor quadrupole in quark-gluon plasma and estimate the elliptic flow splitting effect for Λ baryons that may be experimentally measured.
Rotating black holes in a draining bathtub: Superradiant scattering of gravity waves
NASA Astrophysics Data System (ADS)
Richartz, Maurício; Prain, Angus; Liberati, Stefano; Weinfurtner, Silke
2015-06-01
In a draining rotating fluid flow background, surface perturbations behave as a scalar field on a rotating effective black hole spacetime. We propose a new model for the background flow which takes into account the varying depth of the water. Numerical integration of the associated Klein-Gordon equation using accessible experimental parameters shows that gravity waves in an appropriate frequency range are amplified through the mechanism of superradiance. Our numerical results suggest that the observation of this phenomenon in a common fluid mechanical system is within experimental reach. Unlike the case of wave scattering around Kerr black holes, which depends only on one dimensionless background parameter (the ratio a /M between the specific angular momentum and the mass of the black hole), our system depends on two dimensionless background parameters, namely the normalized angular velocity and surface gravity at the effective black hole horizon.
NASA Technical Reports Server (NTRS)
Gilbert, Kenneth E.; Di, Xiao; Wang, Lintao
1990-01-01
Weiner and Keast observed that in an upward-refracting atmosphere, the relative sound pressure level versus range follows a characteristic 'step' function. The observed step function has recently been predicted qualitatively and quantitatively by including the effects of small-scale turbulence in a parabolic equation (PE) calculation. (Gilbert et al., J. Acoust. Soc. Am. 87, 2428-2437 (1990)). The PE results to single-scattering calculations based on the distorted-wave Born approximation (DWBA) are compared. The purpose is to obtain a better understanding of the physical mechanisms that produce the step-function. The PE calculations and DWBA calculations are compared to each other and to the data of Weiner and Keast for upwind propagation (strong upward refraction) and crosswind propagation (weak upward refraction) at frequencies of 424 Hz and 848 Hz. The DWBA calculations, which include only single scattering from turbulence, agree with the PE calculations and with the data in all cases except for upwind propagation at 848 Hz. Consequently, it appears that in all cases except one, the observed step function can be understood in terms of single scattering from an upward-refracted 'skywave' into the refractive shadow zone. For upwind propagation at 848 Hz, the DWBA calculation gives levels in the shadow zone that are much below both the PE and the data.
NASA Astrophysics Data System (ADS)
Zeng, Bin; Chu, Wei; Li, Guihua; Yao, Jinping; Zhang, Haisu; Ni, Jielei; Jing, Chenrui; Xie, Hongqiang; Cheng, Ya
2014-04-01
Molecular rotational spectroscopy based on a strong-field-ionization-induced nitrogen laser is employed to investigate the time evolution of the rotational wave packet composed by a coherent superposition of quantum rotational states created in a field-free molecular alignment. We show that this technique uniquely allows real-time observation of the ultrafast dynamics of the molecular rotational wave packet. Our analysis also shows that there exist two channels of generation of the nitrogen laser, shedding light on the population inversion mechanism behind the air laser generated by intense femtosecond laser pulses.
Toroidal rotation of multiple species of ions in tokamak plasma driven by lower-hybrid-waves
Zuo Yang; Wang Shaojie; Pan Chengkang
2012-10-15
A numerical simulation is carried out to investigate the toroidal rotation of multiple species of ions and the radial electric field in a tokamak plasma driven by the lower-hybrid-wave (LHW). The theoretical model is based on the neoclassical transport theory associated with the anomalous transport model. Three species of ions (primary ion and two species of impurity ions) are taken into consideration. The predicted toroidal velocity of the trace impurities during the LHW injection agrees reasonably well with the experimental observation. It is shown that the toroidal rotation velocities of the trace impurity ions and the primary ions are close, therefore the trace impurity ions are representative of the primary ions in the toroidal rotation driven by the LHW.
Gravity jitters excited slosh waves in rotating propellant tank under microgravity environment
NASA Technical Reports Server (NTRS)
Hung, R. J.; Lee, C. C.; Leslie, Fred W.
1991-01-01
The dynamical behavior of fluids, in particular the effect of surface tension on partially-filled rotating fluids (cryogenic liquid helium and helium vapor) in a full-scale Gravity Probe-B Spacecraft propellant tank without probe imposed by various frequencies of gravity jitters have been investigated. Results disclose the conditions for the excitation of large amplitude slosh waves which shall be avoided in the design of cryogenic liquid propellant system.
Non-linear evolution of tidally forced inertial waves in rotating fluid bodies
NASA Astrophysics Data System (ADS)
Favier, B.; Barker, A. J.; Baruteau, C.; Ogilvie, G. I.
2014-03-01
We perform one of the first studies into the non-linear evolution of tidally excited inertial waves in a uniformly rotating fluid body, exploring a simplified model of the fluid envelope of a planet (or the convective envelope of a solar-type star) subject to the gravitational tidal perturbations of an orbiting companion. Our model contains a perfectly rigid spherical core, which is surrounded by an envelope of incompressible uniform density fluid. The corresponding linear problem was studied in previous papers which this work extends into the non-linear regime, at moderate Ekman numbers (the ratio of viscous to Coriolis accelerations). By performing high-resolution numerical simulations, using a combination of pseudo-spectral and spectral element methods, we investigate the effects of non-linearities, which lead to time-dependence of the flow and the corresponding dissipation rate. Angular momentum is deposited non-uniformly, leading to the generation of significant differential rotation in the initially uniformly rotating fluid, i.e. the body does not evolve towards synchronism as a simple solid body rotator. This differential rotation modifies the properties of tidally excited inertial waves, changes the dissipative properties of the flow and eventually becomes unstable to a secondary shear instability provided that the Ekman number is sufficiently small. Our main result is that the inclusion of non-linearities eventually modifies the flow and the resulting dissipation from what linear calculations would predict, which has important implications for tidal dissipation in fluid bodies. We finally discuss some limitations of our simplified model, and propose avenues for future research to better understand the tidal evolution of rotating planets and stars.
Roever, Christian; Bizouard, Marie-Anne; Christensen, Nelson; Dimmelmeier, Harald; Heng, Ik Siong; Meyer, Renate
2009-11-15
Presented in this paper is a technique that we propose for extracting the physical parameters of a rotating stellar core collapse from the observation of the associated gravitational wave signal from the collapse and core bounce. Data from interferometric gravitational wave detectors can be used to provide information on the mass of the progenitor model, precollapse rotation, and the nuclear equation of state. We use waveform libraries provided by the latest numerical simulations of rotating stellar core collapse models in general relativity, and from them create an orthogonal set of eigenvectors using principal component analysis. Bayesian inference techniques are then used to reconstruct the associated gravitational wave signal that is assumed to be detected by an interferometric detector. Posterior probability distribution functions are derived for the amplitudes of the principal component analysis eigenvectors, and the pulse arrival time. We show how the reconstructed signal and the principal component analysis eigenvector amplitude estimates may provide information on the physical parameters associated with the core collapse event.
NASA Astrophysics Data System (ADS)
Kumar, Rajneesh; Singh, Manjeet
2009-07-01
The present investigation is concerned with the propagation of plane waves at an imperfectly bonded interface of two orthotropic generalized thermoelastic rotating half-spaces with different elastic and thermal properties. The thermoelastic theory with one relaxation time developed by Lord and Shulman [A generalized dynamical theory of thermoelasticity, J. Mech. Phys. Solids 15 (1967) 299-309] is used to study the problem. The reflection and transmission coefficients of Quasi Longitudinal (QL-) wave, Quasi Thermal (T-mode) wave and Quasi Transverse (QT-) wave have been derived. The effect of rotation has been studied on the velocities of different waves. Some special cases of boundaries i.e. normal stiffness, transverse stiffness, thermal contact conductance, slip boundary and welded contact boundary have been deduced from an imperfect one. Impact of different boundaries has been studied graphically. It is observed that thermal properties, rotation and imperfect boundary have significant effect on the propagation of waves.
Sahin, Serkan; Korotkova, Olga
2009-06-15
Using scattering matrices and the angular spectrum representation of waves, we develop the analytical theory of scattering of random scalar waves from random collections of particles, valid under the first Born approximation. We demonstrate that in the calculation of far-field statistics, such as the spectral density and the spectral degree of coherence, the knowledge of the pair-structure factor of the collection is crucial. We illustrate our analytical approach by considering a numerical example involving scattering of two partially correlated plane waves from a random distribution of spheres. PMID:19529695
Generation of plasma rotation in a tokamak by ion-cyclotron absorption of fast Alfven waves
F.W. Perkins; R.B. White; P. Bonoli
2000-06-13
Control of rotation in tokamak plasmas provides a method for suppressing fine-scale turbulent transport by velocity shear and for stabilizing large-scale magnetohydrodynamic instabilities via a close-fitting conducting shell. The experimental discovery of rotation in a plasma heated by the fast-wave minority ion cyclotron process is important both as a potential control method for a fusion reactor and as a fundamental issue, because rotation arises even though this heating process introduces negligible angular momentum. This paper proposes and evaluates a mechanism which resolves this apparent conflict. First, it is assumed that angular momentum transport in a tokamak is governed by a diffusion equation with a no-slip boundary condition at the plasma surface and with a torque-density source that is a function of radius. When the torque density source consists of two separated regions of positive and negative torque density, a non-zero central rotation velocity results, even when the total angular momentum input vanishes. Secondly, the authors show that localized ion-cyclotron heating can generate regions of positive and negative torque density and consequently central plasma rotation.
Wang Shaojie
2011-10-15
A theoretical model is proposed to interpret the counter-current rotation driven by the lower-hybrid-wave observed in the tokamak lower-hybrid-wave parallel current drive experiments. It is found that ions absorb the toroidal momentum indirectly from the wave through collisional friction with the resonant electrons that directly take the momentum from the wave through Landau resonance. This momentum coupling pumps out the ions to produce a negative radial electric field and makes the plasma rotate in the counter-current direction.
Kilcrease, D. P.; Brookes, S.
2013-08-19
The modeling of NLTE plasmas requires the solution of population rate equations to determine the populations of the various atomic levels relevant to a particular problem. The equations require many cross sections for excitation, de-excitation, ionization and recombination. Additionally, a simple and computational fast way to calculate electron collisional excitation cross-sections for ions is by using the plane-wave Born approximation. This is essentially a high-energy approximation and the cross section suffers from the unphysical problem of going to zero near threshold. Various remedies for this problem have been employed with varying degrees of success. We present a correction procedure formore » the Born cross-sections that employs the Elwert–Sommerfeld factor to correct for the use of plane waves instead of Coulomb waves in an attempt to produce a cross-section similar to that from using the more time consuming Coulomb Born approximation. We compare this new approximation with other, often employed correction procedures. Furthermore, we also look at some further modifications to our Born Elwert procedure and its combination with Y.K. Kim's correction of the Coulomb Born approximation for singly charged ions that more accurately approximate convergent close coupling calculations.« less
Kilcrease, D. P.; Brookes, S.
2013-08-19
The modeling of NLTE plasmas requires the solution of population rate equations to determine the populations of the various atomic levels relevant to a particular problem. The equations require many cross sections for excitation, de-excitation, ionization and recombination. Additionally, a simple and computational fast way to calculate electron collisional excitation cross-sections for ions is by using the plane-wave Born approximation. This is essentially a high-energy approximation and the cross section suffers from the unphysical problem of going to zero near threshold. Various remedies for this problem have been employed with varying degrees of success. We present a correction procedure for the Born cross-sections that employs the Elwert–Sommerfeld factor to correct for the use of plane waves instead of Coulomb waves in an attempt to produce a cross-section similar to that from using the more time consuming Coulomb Born approximation. We compare this new approximation with other, often employed correction procedures. Furthermore, we also look at some further modifications to our Born Elwert procedure and its combination with Y.K. Kim's correction of the Coulomb Born approximation for singly charged ions that more accurately approximate convergent close coupling calculations.
Educing the emission mechanism of internal gravity waves in the differentially heat rotating annulus
NASA Astrophysics Data System (ADS)
Rolland, Joran; Hien, Steffen; Achatz, Ulrich; Borchert, Sebastian; Fruman, Mark
2016-04-01
Understanding the lifecycle of gravity waves is fundamental to a good comprehension of the dynamics of the atmosphere. In this lifecycle, the emission mechanisms may be the most elusive. Indeed, while the emission of gravity waves by orography or convection is well understood, the so-called spontaneous emission is still a quite open topic of investigation [1]. This type of emission usually occur very near jet-front systems in the troposphere. In this abstract, we announce our numerical study of the question. Model systems of the atmosphere which can be easily simulated or built in a laboratory have always been an important part of the study of atmospheric dynamics, alongside global simulations, in situ measurements and theory. In the case of the study of the spontaneous emission of gravity waves near jet-front systems, the differentially heated rotating annulus set up has been proposed and extensively used. It comprises of an annular tank containing water: the inner cylinder is kept at a cold temperature while the outer cylinder is kept at a warm temperature. The whole system is rotating. Provided the values of the control parameters (temperature, rotation rate, gap between the cylinders, height of water) are well chosen, the resulting flow mimics the troposphere at midlatitudes: it has a jet stream, and a baroclinic lifecycle develops on top of it. A very reasonable ratio of Brunt-Väisälä frequency over rotation rate of the system can be obtained, so as to be as close to the atmosphere as possible. Recent experiments as well as earlier numerical simulations in our research group have shown that gravity waves are indeed emitted in this set up, in particular near the jet front system of the baroclinic wave [2]. After a first experimental stage of characterising the emitted wavepacket, we focused our work on testing hypotheses on the gravity wave emission mechanism: we have tested and validated the hypothesis of spontaneous imbalance generated by the flow in
Transfer induced by core excitation within an extended distorted-wave Born approximation method
NASA Astrophysics Data System (ADS)
Gómez-Ramos, M.; Moro, A. M.; Gómez-Camacho, J.; Thompson, I. J.
2015-07-01
Background: Dynamic core-excitation effects have been found to be of importance in breakup reactions and may be of relevance when obtaining spectroscopic information from transfer reactions. Purpose: In this paper we extend the distorted-wave Born approximation (DWBA) formalism in order to allow for noncentral components in the core-core term appearing in the transition operator, which allows for dynamic core-excitation effects. Then we study these effects by applying the formalism to different (d ,p ) reactions. Methods: The expression of the nonlocal kernels required for the evaluation of the DWBA amplitudes has been extended so as to include noncentral parts in the core-core interaction. The DWBA scattering amplitude is then obtained by solving the corresponding inhomogeneous equation, with the new computed kernels, and the usual outgoing boundary conditions. A new DWBA code has been developed for this purpose. Results: For 10Be(d ,p ) 11Be , core-excitation effects are found to be almost negligible (<3 %) . The importance of this effect has been found to depend to a large extent on the excitation energy of the core. This has been confirmed in the 30Ne(d ,p ) 31Ne case, for which the excitation energy of the first 2+ state is 0.8 MeV, and the effect of core excitation increases to ≈10 % . Conclusions: We find dynamic core-excitation effects in transfer reactions to have small contributions to cross sections, in general. However, they should not be neglected, since they may modify the spectroscopic information obtained from these reactions and may become of importance in reactions with nuclei with a core with high deformation and low excitation energy.
NASA Astrophysics Data System (ADS)
Aubourg, Quentin; Mordant, Nicolas
2016-04-01
energy cascade is clearly observed consistently with previous measurements. A large amount of data permits us to use higher order statistical tools to investigate directly the resonant interactions. We observe a strong presence of triadic interactions in our system, confirming the foundations of the weak wave turbulence theory. A significant part of these interactions are non-local and enable coupling between capillary and gravity waves. We also emphasize the role of approximate resonances that are made possible by the nonlinear spectral widening. The quasi-resonances increase significantly the number of wave interactions and in particular open the possibility of observing 3-wave coupling among gravity waves although 3-wave exact resonances are prohibited. These effects are being currently investigated in a larger size experiment using a 13m in diameter wave flume. Our observation raise the question of the importance of these approximate resonances of gravity waves in energy transfers both in the theory and in the ocean.
Wave generation by fracture initiation and propagation in geomaterials with internal rotations
NASA Astrophysics Data System (ADS)
Esin, Maxim; Pasternak, Elena; Dyskin, Arcady; Xu, Yuan
2016-04-01
Crack or fracture initiation and propagation in geomaterials are sources of waves and is important in both stability and fracture (e.g. hydraulic fracture) monitoring. Many geomaterials consist of particles or other constituents capable of rotating with respect to each other, either due to the absence of the binder phase (fragmented materials) or due to extensive damage of the cement between the constituents inflicted by previous loading. In investigating the wave generated in fracturing it is important to distinguish between the cases when the fracture is instantaneously initiated to its full length or propagates from a smaller initial crack. We show by direct physical experiments and discrete element modelling of 2D arrangements of unbonded disks that under compressive load fractures are initiated instantaneously as a result of the material instability and localisation. Such fractures generate waves as a single impulse impact. When the fractures propagate, they produce a sequence of impulses associated with the propagation steps. This manifests itself as acoustic (microseismic) emission whose temporal pattern contains the information of the fracture geometry, such as fractal dimension of the fracture. The description of this process requires formulating criteria of crack growth capable of taking into account the internal rotations. We developed an analytical solution based on the Cosserat continuum where each point of body has three translational and three rotational degrees of freedom. When the Cosserat characteristic lengths are comparable with the grain sizes, the simplified equations of small-scale Cosserat continuum can be used. We established that the order of singularity of the main asymptotic term for moment stress is higher than the order of singularity for conventional stress. Therefore, the mutual rotation of particles and related bending and/or twisting of the bonds between the particles represent an unconventional mechanism of crack propagation.
NASA Astrophysics Data System (ADS)
von Larcher, Thomas; Harlander, Uwe; Alexandrov, Kiril; Wang, Yongtai
2010-05-01
Experiments on baroclinic wave instabilities in a rotating cylindrical gap have been long performed, e.g., to unhide regular waves of different zonal wave number, to better understand the transition to the quasi-chaotic regime, and to reveal the underlying dynamical processes of complex wave flows. We present the application of appropriate multivariate data analysis methods on time series data sets acquired by the use of non-intrusive measurement techniques of a quite different nature. While the high accurate Laser-Doppler-Velocimetry (LDV ) is used for measurements of the radial velocity component at equidistant azimuthal positions, a high sensitive thermographic camera measures the surface temperature field. The measurements are performed at particular parameter points, where our former studies show that kinds of complex wave patterns occur [1, 2]. Obviously, the temperature data set has much more information content as the velocity data set due to the particular measurement techniques. Both sets of time series data are analyzed by using multivariate statistical techniques. While the LDV data sets are studied by applying the Multi-Channel Singular Spectrum Analysis (M - SSA), the temperature data sets are analyzed by applying the Empirical Orthogonal Functions (EOF ). Our goal is (a) to verify the results yielded with the analysis of the velocity data and (b) to compare the data analysis methods. Therefor, the temperature data are processed in a way to become comparable to the LDV data, i.e. reducing the size of the data set in such a manner that the temperature measurements would imaginary be performed at equidistant azimuthal positions only. This approach initially results in a great loss of information. But applying the M - SSA to the reduced temperature data sets enable us to compare the methods. [1] Th. von Larcher and C. Egbers, Experiments on transitions of baroclinic waves in a differentially heated rotating annulus, Nonlinear Processes in Geophysics
NASA Astrophysics Data System (ADS)
Lee, Myoung-Jae; Jung, Young-Dae
2016-05-01
The dispersion relation for modified dust ion-acoustic surface waves in the magnetized dusty plasma containing the rotating dust grains is derived, and the effects of magnetic field configuration on the resonant growth rate are investigated. We present the results that the resonant growth rates of the wave would increase with the ratio of ion plasma frequency to cyclotron frequency as well as with the increase of wave number for the case of perpendicular magnetic field configuration when the ion plasma frequency is greater than the dust rotation frequency. For the parallel magnetic field configuration, we find that the instability occurs only for some limited ranges of the wave number and the ratio of ion plasma frequency to cyclotron frequency. The resonant growth rate is found to decrease with the increase of the wave number. The influence of dust rotational frequency on the instability is also discussed.
Stability of steady rotational water-waves of finite amplitude on arbitrary shear currents
NASA Astrophysics Data System (ADS)
Seez, William; Abid, Malek; Kharif, Christian
2016-04-01
A versatile solver for the two-dimensional Euler equations with an unknown free-surface has been developed. This code offers the possibility to calculate two-dimensional, steady rotational water-waves of finite amplitude on an arbitrary shear current. Written in PYTHON the code incorporates both pseudo-spectral and finite-difference methods in the discretisation of the equations and thus allows the user to capture waves with large steepnesses. As such it has been possible to establish that, in a counter-flowing situation, the existence of wave solutions is not guaranteed and depends on a pair of parameters representing mass flux and vorticity. This result was predicted, for linear solutions, by Constantin. Furthermore, experimental comparisons, both with and without vorticity, have proven the precision of this code. Finally, waves propagating on top of highly realistic shear currents (exponential profiles under the surface) have been calculated following current profiles such as those used by Nwogu. In addition, a stability analysis routine has been developed to study the stability regimes of base waves calculated with the two-dimensional code. This linear stability analysis is based on three dimensional perturbations of the steady situation which lead to a generalised eigenvalue problem. Common instabilities of the first and second class have been detected, while a third class of wave-instability appears due to the presence of strong vorticity. {1} Adrian Constantin and Walter Strauss. {Exact steady periodic water waves with vorticity}. Communications on Pure and Applied Mathematics, 57(4):481-527, April 2004. Okey G. Nwogu. {Interaction of finite-amplitude waves with vertically sheared current fields}. Journal of Fluid Mechanics, 627:179, May 2009.
Monitoring Rotational Components of Seismic Waves with a Ring Laser Interferometer
NASA Astrophysics Data System (ADS)
Gakundi, Jackson; Dunn, Robert
2015-04-01
It has been known for decades that seismic waves can introduce rotation in the surface of the Earth. There are historic records of tombstones in Japan being rotated after large earthquakes. Until fairly recently, the primary way to detect ground rotation from earthquakes was with an array of several seismographs. The development of large ring laser interferometers has provided a way for a single instrument to make extremely sensitive measurements of ground motion. In this poster, a diagram of a large ring laser will be presented. For comparison, seismograms recorded with a ring laser and a collocated standard seismograph will be presented. A major thrust of this research is the detection and analysis of seismic responses from directional drilling sites in Arkansas and Oklahoma. There are suggestions that the injection of pressurized water used to fracture gas bearing shale may cause small earthquakes. The Arkansas Oil and Gas Commission ordered the closing of certain waste water disposal wells in North Central Arkansas. Apparently, these wells injected waste water into a previously unknown fault causing it to slip. An attempt is being made to determine if the seismic wave patterns from earthquakes generated near directional drilling sites differ from those generated miles away.
NASA Technical Reports Server (NTRS)
Boardsen, Scott A.; Slavin, James A.; Anderson, Brian J.; Korth, Haje; Schriver, David; Solomon, Sean C.
2012-01-01
We summarize observations by the MESSENGER spacecraft of highly coherent waves at frequencies between 0.4 and 5 Hz in Mercury's inner magnetosphere. This survey covers the time period from 24 March to 25 September 2011, or 2.1 Mercury years. These waves typically exhibit banded harmonic structure that drifts in frequency as the spacecraft traverses the magnetic equator. The waves are seen at all magnetic local times, but their observed rate of occurrence is much less on the dayside, at least in part the result of MESSENGER's orbit. On the nightside, on average, wave power is maximum near the equator and decreases with increasing magnetic latitude, consistent with an equatorial source. When the spacecraft traverses the plasma sheet during its equatorial crossings, wave power is a factor of 2 larger than for equatorial crossings that do not cross the plasma sheet. The waves are highly transverse at large magnetic latitudes but are more compressional near the equator. However, at the equator the transverse component of these waves increases relative to the compressional component as the degree of polarization decreases. Also, there is a substantial minority of events that are transverse at all magnetic latitudes, including the equator. A few of these latter events could be interpreted as ion cyclotron waves. In general, the waves tend to be strongly linear and characterized by values of the ellipticity less than 0.3 and wave-normal angles peaked near 90 deg. Their maxima in wave power at the equator coupled with their narrow-band character suggests that these waves might be generated locally in loss cone plasma characterized by high values of the ratio beta of plasma pressure to magnetic pressure. Presumably both electromagnetic ion cyclotron waves and electromagnetic ion Bernstein waves can be generated by ion loss cone distributions. If proton beta decreases with increasing magnetic latitude along a field line, then electromagnetic ion Bernstein waves are predicted
Forced generation of solitary waves in a rotating fluid and their stability
NASA Astrophysics Data System (ADS)
Choi, Wooyoung
The primary objective of this graduate research is to study forced generation of solitary waves in a rotating fluid and their stability properties. For axisymmetric flow of a non-uniformly rotating fluid within a long cylindrical tube, an analysis is presented to predict the periodic generation of upstream-advancing vortex solitons by axisymmetric disturbance steadily moving with a transcritical velocity as a forcing agent. The phenomenon is simulated using the forced Korteweg-de Vries (fKdV) equation to model the amplitude function of the Stokes stream function for describing this family of rotating flows of an inviscid and incompressible fluid. The numerical results for the weakly nonlinear and weakly dispersive wave motion show that a sequence of well-defined axisymmetrical recirculating eddies is periodically produced and emitted to radiate upstream of the disturbance, soon becoming permanent in the form as a procession of vortex solitons, which we call vortons. Two primary flows, the Rankine vortex and the Burgers vortex, are adopted to exhibit in detail the process of producing the upstream vortons by the critical motion of a slender body moving along the central axis, with the Burgers vortex being found the more effective of the two in the generation of vortons. To investigate the evolution of free or forced waves within a tube of non-uniform radius, a new forced KdV equation is derived which models the variable geometry with variable coefficients. A set of section-mean conservation laws is derived specially for this class of rotational tube flows of an inviscid and incompressible fluid, in both differential and integral forms. A new aspect of stability theory is analyzed for possible instabilities of the axisymmetric solitary waves subject to non-axisymmetric disturbances. The present linear analysis based on the model equation involving the bending mode shows that the axisymmetric solitary wave is neutrally stable with respect to small bending mode
Haut, T. S.; Babb, T.; Martinsson, P. G.; Wingate, B. A.
2015-06-16
Our manuscript demonstrates a technique for efficiently solving the classical wave equation, the shallow water equations, and, more generally, equations of the form ∂u/∂t=Lu∂u/∂t=Lu, where LL is a skew-Hermitian differential operator. The idea is to explicitly construct an approximation to the time-evolution operator exp(τL)exp(τL) for a relatively large time-step ττ. Recently developed techniques for approximating oscillatory scalar functions by rational functions, and accelerated algorithms for computing functions of discretized differential operators are exploited. Principal advantages of the proposed method include: stability even for large time-steps, the possibility to parallelize in time over many characteristic wavelengths and large speed-ups over existingmore » methods in situations where simulation over long times are required. Numerical examples involving the 2D rotating shallow water equations and the 2D wave equation in an inhomogenous medium are presented, and the method is compared to the 4th order Runge–Kutta (RK4) method and to the use of Chebyshev polynomials. The new method achieved high accuracy over long-time intervals, and with speeds that are orders of magnitude faster than both RK4 and the use of Chebyshev polynomials.« less
Haut, T. S.; Babb, T.; Martinsson, P. G.; Wingate, B. A.
2015-06-16
Our manuscript demonstrates a technique for efficiently solving the classical wave equation, the shallow water equations, and, more generally, equations of the form ∂u/∂t=Lu∂u/∂t=Lu, where LL is a skew-Hermitian differential operator. The idea is to explicitly construct an approximation to the time-evolution operator exp(τL)exp(τL) for a relatively large time-step ττ. Recently developed techniques for approximating oscillatory scalar functions by rational functions, and accelerated algorithms for computing functions of discretized differential operators are exploited. Principal advantages of the proposed method include: stability even for large time-steps, the possibility to parallelize in time over many characteristic wavelengths and large speed-ups over existing methods in situations where simulation over long times are required. Numerical examples involving the 2D rotating shallow water equations and the 2D wave equation in an inhomogenous medium are presented, and the method is compared to the 4th order Runge–Kutta (RK4) method and to the use of Chebyshev polynomials. The new method achieved high accuracy over long-time intervals, and with speeds that are orders of magnitude faster than both RK4 and the use of Chebyshev polynomials.
An Exact Solution for Geophysical Edge Waves in the {β}-Plane Approximation
NASA Astrophysics Data System (ADS)
Ionescu-Kruse, Delia
2015-12-01
By taking into account the {β}-plane effects, we provide an exact nonlinear solution to the geophysical edge-wave problem within the Lagrangian framework. This solution describes trapped waves propagating eastward or westward along a sloping beach with the shoreline parallel to the Equator.
Tsai, Shang-Min; Gu, Pin-Gao; Dobbs-Dixon, Ian
2014-10-01
Three-dimensional (3D) equatorial trapped waves excited by stellar isolation and the resulting equatorial super-rotating jet in a vertical stratified atmosphere of a tidally locked hot Jupiter are investigated. Taking the hot Jupiter HD 189733b as a fiducial example, we analytically solve linear equations subject to stationary stellar heating with a uniform zonal-mean flow included. We also extract wave information in the final equilibrium state of the atmosphere from our radiative hydrodynamical simulation for HD 189733b. Our analytic wave solutions are able to qualitatively explain the 3D simulation results. Apart from previous wave studies, investigating the vertical structure of waves allows us to explore new wave features such as the wavefronts tilts related to the Rossby-wave resonance as well as dispersive equatorial waves. We also attempt to apply our linear wave analysis to explain some numerical features associated with the equatorial jet development seen in the general circulation model by Showman and Polvani. During the spin-up phase of the equatorial jet, the acceleration of the jet can be in principle boosted by the Rossby-wave resonance. However, we also find that as the jet speed increases, the Rossby-wave structure shifts eastward, while the Kelvin-wave structure remains approximately stationary, leading to the decline of the acceleration rate. Our analytic model of jet evolution implies that there exists only one stable equilibrium state of the atmosphere, possibly implying that the final state of the atmosphere is independent of initial conditions in the linear regime. Limitations of our linear model and future improvements are also discussed.
NASA Astrophysics Data System (ADS)
Tsai, Shang-Min; Dobbs-Dixon, Ian; Gu, Pin-Gao
2014-10-01
Three-dimensional (3D) equatorial trapped waves excited by stellar isolation and the resulting equatorial super-rotating jet in a vertical stratified atmosphere of a tidally locked hot Jupiter are investigated. Taking the hot Jupiter HD 189733b as a fiducial example, we analytically solve linear equations subject to stationary stellar heating with a uniform zonal-mean flow included. We also extract wave information in the final equilibrium state of the atmosphere from our radiative hydrodynamical simulation for HD 189733b. Our analytic wave solutions are able to qualitatively explain the 3D simulation results. Apart from previous wave studies, investigating the vertical structure of waves allows us to explore new wave features such as the wavefronts tilts related to the Rossby-wave resonance as well as dispersive equatorial waves. We also attempt to apply our linear wave analysis to explain some numerical features associated with the equatorial jet development seen in the general circulation model by Showman and Polvani. During the spin-up phase of the equatorial jet, the acceleration of the jet can be in principle boosted by the Rossby-wave resonance. However, we also find that as the jet speed increases, the Rossby-wave structure shifts eastward, while the Kelvin-wave structure remains approximately stationary, leading to the decline of the acceleration rate. Our analytic model of jet evolution implies that there exists only one stable equilibrium state of the atmosphere, possibly implying that the final state of the atmosphere is independent of initial conditions in the linear regime. Limitations of our linear model and future improvements are also discussed.
NASA Astrophysics Data System (ADS)
Shao, X.; Karavaev, A. V.; Sharma, A. S.; Papadopoulos, K.; Gumerov, N.; Gigliotti, A. F.; Gekelman, W. N.
2009-12-01
Injection of whistler waves into Earth's inner radiation belt to enhance precipitation of energetic electrons has been an active research area, and is referred to as RB Remediation (RBR). Most mechanisms of pitch angle scattering of energetic particles are based on gyro-resonant wave-particle interaction. Recent experiments and simulations show that Rotating Magnetic Field (RMF) antennas in plasmas can be efficient radiation sources of MHD and whistler waves. In experiments conducted in the Large Plasma Device (LAPD) at UCLA, poly-phased current loops drove the RMF antenna. These experiments, as well as simulations show that 75-85% of the radiation generated by the RMF antenna is in guided propagation. The whistler and MHD waves have non-local magnetic field gradients in the transverse direction and these provide ways to break the adiabatic invariants of electrons and precipitate them via a non-resonant scattering. In this paper simulations of non-resonant pitch angle scattering of energetic particles by waves generated by RMF sources are presented. Three-dimensional EMHD simulations are used to model whistlers and the resultant 3D electromagnetic fields are used in particle tracing codes to study pitch angle scattering. The simulations are carried out for a wide range of magnetic fields produced by RMF sources, including fields much larger than the ambient magnetic field in space plasma environments. This work was sponsored by ONR MURI Grant 5-28828
Full-dimensional quantum wave packet study of rotationally inelastic transitions in H2+H2 collision
NASA Astrophysics Data System (ADS)
Ying Lin, Shi; Guo, Hua
2002-09-01
We report full-dimensional accurate quantum dynamical calculations of the rotationally inelastic collision: para-H2(ν1=0,j1)=0+para- H2(ν2=0,j2)=0→para- H2(ν1=0,j1)'+para- H2(ν2=0,j2)', using a wave packet approach based on the Chebyshev polynomial expansion of Green's operator. The six-dimensional Hamiltonian within the coupled-states approximation is discretized in a mixed grid/basis representation and its action is computed in appropriate representations facilitated by a series of one-dimensional pseudo-spectral transformations. Both the parity and diatomic exchange symmetry are adapted. The S-matrix elements for the rotational transitions are obtained at all energies by the Fourier transform of Chebyshev correlation functions and used to compute transition probabilities, differential and integral cross sections, and state-resolved thermal rate constants. Results are compared for two recently proposed ab initio based potential energy surfaces and with previous quantum results.
Cooper Pairs with Broken Parity and Spin-Rotational Symmetries in d-Wave Superconductors
NASA Astrophysics Data System (ADS)
Lebed, A. G.
2006-01-01
Paramagnetic effects are shown to result in the appearance of a triplet component of order parameter in a vortex phase of a d-wave superconductor in the absence of impurities. This component, which breaks parity and spin-rotational symmetries of Cooper pairs, is expected to be of the order of unity in a number of modern superconductors such as organic, high Tc, and some others. A generic phase diagram of such type-IV superconductors, which are singlet ones at H=0 and in the Meissner phase, and characterized by singlet-triplet mixed Copper pairs Δs+iΔt with broken symmetries in a vortex phase, is discussed.
On the linear approximation of gravity wave saturation in the mesosphere
NASA Technical Reports Server (NTRS)
Chao, W. C.; Schoeberl, M. R.
1984-01-01
Lindzen's model of gravity wave breaking is shown to be inconsistent with the process of convective adjustment and associated turbulent outbreak. The K-theory turbulent diffusion model used by Lindzen implies a spatially uniform turbulent field which is not in agreement with the fact that gravity wave saturation and the associated convection produce turbulence only in restricted zones. The Lindzen model may be corrected to some extent by taking the turbulent Prandtl number for a diffusion acting on the wave itself to be very large. The eddy diffusion coefficients computed by Lindzen then become a factor of 2 larger and eddy transports of heat and constituents by wave fields vanish to first order.
Magnetic field effect on waves in a centrifuged layer of a rotating conducting viscous fluid
NASA Astrophysics Data System (ADS)
Klueva, N. V.; Sandalov, V. M.; Tkach, M. E.; Soldatov, I. N.
2015-05-01
This paper considers wave processes in a centrifuged layer of an incompressible viscous conducting fluid in an axial magnetic field in the cavity of a rapidly rotating infinite cylinder with insulating walls. Inertial modes (solutions of the linearized boundary-value problem of magnetohydrodynamics) are represented as a superposition of helical fields. Expressions for the vorticity parameters of the helical flows forming the inertial mode at a small Stewart number are given. Dispersion curves of inertial waves are constructed, and the influence of the magnetic field on the flow field is analyzed. The critical frequencies at which the lowest (surface) mode arises are determined. The spatial and temporal stability of the modes are investigated.
Shear flow driven drift waves and the counter-rotating vortices
Haque, Q.; Saleem, H.; Mirza, Arshad M.
2005-10-01
It is shown that the drift waves can become unstable due to the shear flow produced by externally applied electric field. The modified Rayleigh instability condition is obtained which is applicable to both electron-ion and electron-positron-ion plasmas. It is proposed that the shear flow driven drift waves can be responsible for large amplitude electrostatic fluctuations in tokamak edges. In the nonlinear regime the stationary structures may appear in electron-positron-ion plasmas as well as electron-ion plasmas. A particular form of the shear flow can give rise to counter-rotating dipole vortices and vortex chains. The speed and amplitude of the structures are affected by the presence of positrons in the electron ion plasma. The relevance of this investigation to laboratory and astrophysical plasmas is pointed out.
NASA Astrophysics Data System (ADS)
Zhao, Huijiang
2000-04-01
In this paper, we show that a strong planar rarefaction wave is nonlinear stable, namely it is an attractor for the relaxation approximation of the scalar conservation laws in several space dimensions. Compared with former results obtained by T. P. Liu (1987, Comm. Math. Phys.108, 153-175) and T. Luo (1997, J. Differential Equations133, 255-279), our main novelty lies in the fact that the planar rarefaction waves do not need to be small, and in the one-dimensional case, the initial disturbance can also be chosen arbitrarily large.
CORONAL FARADAY ROTATION FLUCTUATIONS AND A WAVE/TURBULENCE-DRIVEN MODEL OF THE SOLAR WIND
Hollweg, Joseph V.; Cranmer, Steven R.; Chandran, Benjamin D. G. E-mail: scranmer@cfa.harvard.ed
2010-10-20
Some recent models for coronal heating and the origin of the solar wind postulate that the source of energy and momentum consists of Alfven waves of solar origin dissipating via MHD turbulence. We use one of these models to predict the level of Faraday rotation fluctuations (FRFs) that should be imposed on radio signals passing through the corona. This model has the virtue of specifying the correlation length of the turbulence, knowledge of which is essential for calculating the FRFs; previous comparisons of observed FRFs with models suffered from the fact that the correlation length had to be guessed. We compare the predictions with measurements of FRFs obtained by the Helios radio experiment during occultations in 1975 through 1977, close to solar minimum. We show that only a small fraction of the FRFs are produced by density fluctuations; the bulk of the FRFs must be produced by coronal magnetic field fluctuations. The observed FRFs have periods of hours, suggesting that they are related to Alfven waves which are observed in situ by spacecraft throughout the solar wind; other evidence also suggests that the FRFs are due to coronal Alfven waves. We choose a model field line in an equatorial streamer which has background electron concentrations that match those inferred from the Helios occultation data. The predicted FRFs are found to agree very well with the Helios data. If the FRFs are in fact produced by Alfven waves with the assumed correlation length, our analysis leads us to conclude that wave-turbulence models should continue to be pursued with vigor. But since we cannot prove that the FRFs are produced by Alfven waves, we state the more conservative conclusion, still subject to the correctness of the assumed correlation length, that the corona contains long-period magnetic fluctuations with sufficient energy to heat the corona and drive the solar wind.
Transformation cloaking and radial approximations for flexural waves in elastic plates
NASA Astrophysics Data System (ADS)
Brun, M.; Colquitt, D. J.; Jones, I. S.; Movchan, A. B.; Movchan, N. V.
2014-09-01
It is known that design of elastic cloaks is much more challenging than that of acoustic cloaks, cloaks of electromagnetic waves or scalar problems of anti-plane shear. In this paper, we address fully the fourth-order problem and develop a model of a broadband invisibility cloak for channelling flexural waves in thin plates around finite inclusions. We also discuss an option to employ efficiently an elastic pre-stress and body forces to achieve such a result. An asymptotic derivation provides a rigorous link between the model in question and elastic wave propagation in thin solids. This is discussed in detail to show connection with non-symmetric formulations in vector elasticity studied in earlier work.
Separable wave equations for gravitoelectromagnetic perturbations of rotating charged black strings
NASA Astrophysics Data System (ADS)
Miranda, Alex S.; Morgan, Jaqueline; Kandus, Alejandra; Zanchin, Vilson T.
2015-12-01
Rotating charged black strings are exact solutions of four-dimensional Einstein-Maxwell equations with a negative cosmological constant and a non-trivial spacetime topology. According to the AdS/CFT correspondence, these black strings are dual to rotating thermal states of a strongly interacting quantum field theory with nonzero chemical potential that lives in a cylinder. The dynamics of linear fluctuations in the dual field theory can be studied from the perturbation equations for classical fields in a black-string spacetime. With this motivation in mind, we develop here a completely gauge and tetrad invariant perturbation approach to deal with the gravitoelectromagnetic fluctuations of rotating charged black strings in the presence of sources. As usual, for any charged black hole, a perturbation in the background electromagnetic field induces a metric perturbation and vice versa. In spite of this coupling and the non-vanishing angular momentum, we show that linearization of equations of the Newman-Penrose formalism leads to four separated second-order complex equations for suitable combinations of the spin coefficients, the Weyl and the Maxwell scalars. Then, we generalize the Chandrasekhar transformation theory by the inclusion of sources and apply it to reduce the perturbation problem to four decoupled inhomogeneous wave equations—a pair for each sector of perturbations. The radial part of such wave equations can be put into Schrödinger-like forms after Fourier transforming them with respect to time. We find that the resulting effective potentials form two pairs of supersymmetric partner potentials and, as a consequence, the fundamental variables of one perturbation sector are related to the variables of the other sector. The relevance of such a symmetry in connection to the AdS/CFT correspondence is discussed, and future applications of the pertubation theory developed here are outlined.
Davis, Edward D.
2004-09-01
Semiclassical transformation theory implies an integral representation for stationary-state wave functions {psi}{sub m}(q) in terms of angle-action variables ({theta},J). It is a particular solution of Schroedinger's time-independent equation when terms of order ({Dirac_h}/2{pi}){sup 2} and higher are omitted, but the preexponential factor A(q,{theta}) in the integrand of this integral representation does not possess the correct dependence on q. The origin of the problem is identified: the standard unitarity condition invoked in semiclassical transformation theory does not fix adequately in A(q,{theta}) a factor which is a function of the action J written in terms of q and {theta}. A prescription for an improved choice of this factor, based on successfully reproducing the leading behavior of wave functions in the vicinity of potential minima, is outlined. Exact evaluation of the modified integral representation via the residue theorem is possible. It yields wave functions which are not, in general, orthogonal. However, closed-form results obtained after Gram-Schmidt orthogonalization bear a striking resemblance to the exact analytical expressions for the stationary-state wave functions of the various potential models considered (namely, a Poeschl-Teller oscillator and the Morse oscillator)
NASA Astrophysics Data System (ADS)
Bijarnia, R.; Singh, B.
2016-05-01
The paper is concerned with the propagation of plane waves in a transversely isotropic two temperature generalized thermoelastic solid half-space with voids and rotation. The governing equations are modified in the context of Lord and Shulman theory of generalized thermoelasticity and solved to show the existence of four plane waves in the x - z plane. Reflection of these plane waves from thermally insulated stress free surface is also studied to obtain a system of four non-homogeneous equations. For numerical computations of speed and reflection coefficients, a particular material is modelled as transversely isotropic generalized thermoelastic solid half-space. The speeds of plane waves are computed against the angle of propagation to observe the effects of two temperature and rotation. Reflection coefficients of various reflected waves are also computed against the angle of incidence to observe the effects of various parameters.
NASA Astrophysics Data System (ADS)
Lasky, Paul D.; Bennett, Mark F.; Melatos, Andrew
2013-03-01
Hydrodynamic turbulence driven by crust-core differential rotation imposes a fundamental noise floor on gravitational wave observations of neutron stars. The gravitational wave emission peaks at the Kolmogorov decoherence frequency which, for reasonable values of the crust-core shear, ΔΩ, occurs near the most sensitive part of the frequency band for ground-based, long-baseline interferometers. We calculate the energy density spectrum of the stochastic gravitational wave background from a cosmological population of turbulent neutron stars generalizing previous calculations for individual sources. The spectrum resembles a piecewise power law, Ωgw(ν)=Ωανα, with α=-1 and 7 above and below the decoherence frequency respectively, and its normalization scales as Ωα∝(ΔΩ)7. Nondetection of a stochastic signal by Initial LIGO implies an upper limit on ΔΩ and hence by implication on the internal relaxation time scale for the crust and core to come into corotation, τd=ΔΩ/Ω˙, where Ω˙ is the observed electromagnetic spin-down rate, with τd≲107yr for accreting millisecond pulsars and τd≲105yr for radio-loud pulsars. Target limits on τd are also estimated for future detectors, namely Advanced LIGO and the Einstein Telescope, and are found to be astrophysically interesting.
Hard magnetic ferrite with a gigantic coercivity and high frequency millimetre wave rotation
Namai, Asuka; Yoshikiyo, Marie; Yamada, Kana; Sakurai, Shunsuke; Goto, Takashi; Yoshida, Takayuki; Miyazaki, Tatsuro; Nakajima, Makoto; Suemoto, Tohru; Tokoro, Hiroko; Ohkoshi, Shin-ichi
2012-01-01
Magnetic ferrites such as Fe3O4 and Fe2O3 are extensively used in a range of applications because they are inexpensive and chemically stable. Here we show that rhodium-substituted ε-Fe2O3, ε-RhxFe2−xO3 nanomagnets prepared by a nanoscale chemical synthesis using mesoporous silica as a template, exhibit a huge coercive field (Hc) of 27 kOe at room temperature. Furthermore, a crystallographically oriented sample recorded an Hc value of 31 kOe, which is the largest value among metal-oxide-based magnets and is comparable to those of rare-earth magnets. In addition, ε-RhxFe2−xO3 shows high frequency millimetre wave absorption up to 209 GHz. ε-Rh0.14Fe1.86O3 exhibits a rotation of the polarization plane of the propagated millimetre wave at 220 GHz, which is one of the promising carrier frequencies (the window of air) for millimetre wave wireless communications. PMID:22948817
Chemical Kinetics in the expansion flow field of a rotating detonation-wave engine
NASA Astrophysics Data System (ADS)
Kailasanath, Kazhikathra; Schwer, Douglas
2014-11-01
Rotating detonation-wave engines (RDE) are a form of continuous detonation-wave engines. They potentially provide further gains in performance than an intermittent or pulsed detonation-wave engine (PDE). The overall flow field in an idealized RDE, primarily consisting of two concentric cylinders, has been discussed in previous meetings. Because of the high pressures involved and the lack of adequate reaction mechanisms for this regime, previous simulations have typically used simplified chemistry models. However, understanding the exhaust species concentrations in propulsion devices is important for both performance considerations as well as estimating pollutant emissions. A key step towards addressing this need will be discussed in this talk. In this approach, an induction parameter model is used for simulating the detonation but a more detailed finite-chemistry model is used in the expansion flow region, where the pressures are lower and the uncertainties in the chemistry model are greatly reduced. Results show that overall radical concentrations in the exhaust flow are substantially lower than from earlier predictions with simplified models. The performance of a baseline hydrogen/air RDE increased from 4940 s to 5000 s with the expansion flow chemistry, due to recombination of radicals and more production of H2O, resulting in additional heat release.
The exhaust flow field of a rotating detonation-wave engine
NASA Astrophysics Data System (ADS)
Kailasanath, Kazhikathra; Schwer, Douglas
2012-11-01
Rotating detonation-wave engines (RDE) are a form of continuous detonation-wave engine. They potentially provide further gains than an intermittent or pulsed detonation-wave engine (PDE). However, significantly less work has been done on this concept when compared to the PDE. Last year, we presented the details of the injection system on the overall flow field in an RDE. In this talk, we focus on the effects of adding an exhaust plenum to this idealized RDE. While the overall exhaust flow shows that a recirculation zone sets up behind the RDE when a plenum is added, the net effect on the flow field within the RDE and on performance is found to be small. However, the slight modification to the flow field may impact the design of suitable nozzles for this device. This is explored further with the addition of a simple conical nozzle. This nozzle reduces the size of the recirculation zone and also reduces the temperature in the plume but has little effect on the flow field inside the RDE. Work Sponsored by ONR through NRL 6.1 Computational Physics Task Area.
Kim, S.
1994-12-31
Parallel iterative procedures based on domain decomposition techniques are defined and analyzed for the numerical solution of wave propagation by finite element and finite difference methods. For finite element methods, in a Lagrangian framework, an efficient way for choosing the algorithm parameter as well as the algorithm convergence are indicated. Some heuristic arguments for finding the algorithm parameter for finite difference schemes are addressed. Numerical results are presented to indicate the effectiveness of the methods.
Shubert, V. Alvin; Schmitz, David; Medcraft, Chris; Krin, Anna; Patterson, David; Doyle, John M.; Schnell, Melanie
2015-06-07
We apply chirality sensitive microwave three-wave mixing to 4-carvomenthenol, a molecule previously uncharacterized with rotational spectroscopy. We measure its rotational spectrum in the 2-8.5 GHz range and observe three molecular conformers. We describe our method in detail, from the initial step of spectral acquisition and assignment to the final step of determining absolute configuration and enantiomeric excess. Combining fitted rotational constants with dipole moment components derived from quantum chemical calculations, we identify candidate three-wave mixing cycles which were further tested using a double resonance method. Initial optimization of the three-wave mixing signal is done by varying the duration of the second excitation pulse. With known transition dipole matrix elements, absolute configuration can be directly determined from a single measurement.
Maris, Assimo; Calabrese, Camilla; Melandri, Sonia; Blanco, Susana
2015-01-14
The rotational spectrum of fluoren-9-one, a small oxygenated polycyclic aromatic hydrocarbon, has been recorded and assigned in the 52-74.4 GHz region. The determined small negative value of the inertia defect (-0.3 u Å(2)) has been explained in terms of vibrational-rotational coupling constants calculated at the B3LYP/cc-pVTZ level of theory. Vibrational anharmonic analysis together with second-order vibrational perturbation theory approximation was applied both to fluorenone and its reduced form, fluorene, to predict the mid- and near-infrared spectra. The data presented here give precise indication on the fluorenone ground state structure, allow for an accurate spectral characterization in the millimeter wave and infrared regions, and hopefully will facilitate extensive radio astronomical searches with large radio telescopes. PMID:25591363
NASA Astrophysics Data System (ADS)
Maranò, Stefano; Fäh, Donat
2014-01-01
The analysis of rotational seismic motions has received considerable attention in the last years. Recent advances in sensor technologies allow us to measure directly the rotational components of the seismic wavefield. Today this is achieved with improved accuracy and at an affordable cost. The analysis and the study of rotational motions are, to a certain extent, less developed than other aspects of seismology due to the historical lack of instrumental observations. This is due to both the technical challenges involved in measuring rotational motions and to the widespread belief that rotational motions are insignificant. This paper addresses the joint processing of translational and rotational motions from both the theoretical and the practical perspectives. Our attention focuses on the analysis of motions of both Rayleigh waves and Love waves from recordings of single sensors and from an array of sensors. From the theoretical standpoint, analysis of Fisher information (FI) allows us to understand how the different measurement types contribute to the estimation of quantities of geophysical interest. In addition, we show how rotational measurements resolve ambiguity on parameter estimation in the single sensor setting. We quantify the achievable estimation accuracy by means of Cramér-Rao bound (CRB). From the practical standpoint, a method for the joint processing of rotational and translational recordings to perform maximum likelihood (ML) estimation is presented. The proposed technique estimates parameters of Love waves and Rayleigh waves from single sensor or array recordings. We support and illustrate our findings with a comprehensive collection of numerical examples. Applications to real recordings are also shown.
Parker, R.; Bonoli, P. T.; Meneghini, O.; Porkolab, M.; Schmidt, A. E.; Shiraiwa, S.; Wallace, G.; Hubbard, A. E.; Hughes, J. W.; Ko, J.-S.; McDermott, R. M.; Reinke, M. L.; Rice, J. E.; Wilson, J. R.; Scott, S.
2009-11-26
Recent results from the lower hybrid current drive experiments on Alcator C-Mod are presented. These include i) MSE measurements of broadened LHCD current profiles; ii) development of counter rotation comparable to the rate of injected wave momentum; iii) modification of pedestals and rotation in H-mode; and iv) development of a new FEM-based code that models LH wave propagation from the RF source to absorption in the plasma. An improved antenna concept that will be used in the upcoming C-Mod campaigns is also briefly described.
NASA Astrophysics Data System (ADS)
Majda, Andrew J.; Khouider, Boualem; Frenkel, Yevgeniy
2015-02-01
Atmospheric convection has the striking capability to organize itself into a hierarchy of cloud clusters and super-clusters on scales ranging from the convective cell of a few kilometres to planetary scale disturbances such as the Madden-Julian oscillation. It is widely accepted that this phenomenon is due in large part to the two-way coupling between convective processes and equatorially trapped waves and planetary scale flows in general. However, the physical mechanisms responsible for this multiscale organization and the associated across-scale interactions are poorly understood. The two main peculiarities of the tropics are the vanishing of the Coriolis force at the equator and the abundance of mid-level moisture. Here we test the effect of these two physical properties on the organization of convection and its interaction with gravity waves in a simplified primitive equation model for flows parallel to the equator. Convection is represented by deterministic as well as stochastic multicloud models that are known to represent organized convection and convectively coupled waves quite well. It is found here that both planetary rotation and mid-troposphere moisture are important players in the diminishing of organized convection and convectively coupled gravity wave activity in the subtropics and mid-latitudes. The meridional mean circulation increases with latitude while the mean zonal circulation is much shallower and is dominated by mid-level jets, reminiscent of a second baroclinic mode circulation associated with a congestus mode instability in the model. This is consistent with the observed shallow Hadley and Walker circulations accompanied by congestus cloud decks in the higher latitude tropics and sub-tropics. Moreover, deep convection activity in the stochastic model simulations becomes very patchy and unorganized as the computational domain is pushed towards the subtropics and mid-latitudes. This is consistent with previous work based on cloud resolving
Lugovtsov, A E; Nikitin, S Yu; Priezzhev, A V
2008-06-30
A theoretical model is developed and an algorithm is proposed for calculating far-field light scattering by a transparent dielectric particle significantly larger than a wavelength. The accuracy of this algorithm is close to that of the discrete dipole approximation. The calculation time for this algorithm in the case of particles with the size parameter higher than 50 is much lower than that for the discrete dipole approximation. Scattering diagrams for spheroidal particles of different sizes, orientations and refractive indices are calculated. The proposed algorithm has a great potential for quick calculations of parameters of light scattering by large biological particles such as erythrocytes and their aggregates, bacteria, etc. (special issue devoted to application of laser technologies in biophotonics and biomedical studies)
Thermodynamics of a helicoidal magnetic structure in a spin-wave approximation
NASA Astrophysics Data System (ADS)
Borich, M. A.; Smagin, V. V.; Tankeyev, A. P.
2014-08-01
Specific features of the heat capacity, magnetization, and magnetic susceptibility of a chiral magnet caused by the magnon contribution have been studied. It has been shown that the local heat capacity and the magnetization are functions of the coordinates and that their behavior depends on the magnitude of an applied magnetic field. The temperature dependences of these quantities have been investigated. The results of the approximate analytical calculations and numerical calculations have been compared between themselves.
Căruntu, Bogdan
2014-01-01
The paper presents the optimal homotopy perturbation method, which is a new method to find approximate analytical solutions for nonlinear partial differential equations. Based on the well-known homotopy perturbation method, the optimal homotopy perturbation method presents an accelerated convergence compared to the regular homotopy perturbation method. The applications presented emphasize the high accuracy of the method by means of a comparison with previous results. PMID:25003150
NASA Technical Reports Server (NTRS)
Lou, Y. Q.
1987-01-01
This paper considers two-dimensional nonlinear MHD waves of large horizontal spatial scales for a thin magnetofluid layer on the surface of a rotating sphere. The 'shallow fluid' hydrodynamic equations are generalized to include the effects of magnetic fields, and it is shown that the resulting MHD equations can be reduced to a single scalar equation for a stream function involving several free functions. For special choices of these free functions, two kinds of finite-amplitude MHD waves are obtained, propagating in the azimuthal direction relative to the uniformly rotating background atmosphere in the presence of a background zonal magnetic field and a steady differential zonal flow. These two kinds of MHD waves are fundamentally due to the joint effects of the uniform rotation of the background atmosphere and background magnetic field; the first is an inertial wave of the Rossby (1939) and Haurwitz (1940) type, modified by the presence of the background zonal magnetic field, while the second is a magnetic Alfven-like wave which is modified by the uniform rotation of the background atmosphere.
NASA Technical Reports Server (NTRS)
Zimmermann, M.; Szedenits, E., Jr.
1979-01-01
An axially symmetric, torque-free rigid body, rotating and precessing, emits gravitational quadrupole radiation at two frequencies, omega and 2 omega, corresponding to the l = 2, m = 1,2 spherical harmonics. The paper presents explicitly the waveforms of the two polarizations at both frequencies. From observations of gravitational waves, one can derive information about the body's orientation and its precession amplitude. Electromagnetic radiation emitted by a spot fixed on the surface of the body arrives in pulses at a mean frequency Omega which is typically different from omega. If the body is not axially symmetric but the amplitude of the precession is small, the gravitational radiation at the lower frequency omega is split into two frequencies on either side of the electromagnetic pulse frequency. Explicit waveforms for the two polarizations in this case are also presented.
Approximation of traveling wave solutions in wall-bounded flows using resolvent modes
NASA Astrophysics Data System (ADS)
McKeon, Beverley; Graham, Michael; Moarref, Rashad; Park, Jae Sung; Sharma, Ati; Willis, Ashley
2014-11-01
Significant recent attention has been devoted to computing and understanding exact traveling wave solutions of the Navier-Stokes equations. These solutions can be interpreted as the state-space skeleton of turbulence and are attractive benchmarks for studying low-order models of wall turbulence. Here, we project such solutions onto the velocity response (or resolvent) modes supplied by the gain-based resolvent analysis outlined by McKeon & Sharma (JFM, 2010). We demonstrate that in both pipe (Pringle et al., Phil. Trans. R. Soc. A, 2009) and channel (Waleffe, JFM, 2001) flows, the solutions can be well-described by a small number of resolvent modes. Analysis of the nonlinear forcing modes sustaining these solutions reveals the importance of small amplitude forcing, consistent with the large amplifications admitted by the resolvent operator. We investigate the use of resolvent modes as computationally cheap ``seeds'' for the identification of further traveling wave solutions. The support of AFOSR under Grants FA9550-09-1-0701, FA9550-12-1-0469, FA9550-11-1-0094 and FA9550-14-1-0042 (program managers Rengasamy Ponnappan, Doug Smith and Gregg Abate) is gratefully acknowledged.
Squarr, Anna Julia; Brinkmann, Klaus; Chen, Baoyu; Steinbacher, Tim; Ebnet, Klaus; Rosen, Michael K.
2016-01-01
Directional cell movements during morphogenesis require the coordinated interplay between membrane receptors and the actin cytoskeleton. The WAVE regulatory complex (WRC) is a conserved actin regulator. Here, we found that the atypical cadherin Fat2 recruits the WRC to basal membranes of tricellular contacts where a new type of planar-polarized whip-like actin protrusion is formed. Loss of either Fat2 function or its interaction with the WRC disrupts tricellular protrusions and results in the formation of nonpolarized filopodia. We provide further evidence for a molecular network in which the receptor tyrosine phosphatase Dlar interacts with the WRC to couple the extracellular matrix, the membrane, and the actin cytoskeleton during egg elongation. Our data uncover a mechanism by which polarity information can be transduced from a membrane receptor to a key actin regulator to control collective follicle cell migration during egg elongation. 4D-live imaging of rotating MCF10A mammary acini further suggests an evolutionary conserved mechanism driving rotational motions in epithelial morphogenesis. PMID:26903538
NASA Astrophysics Data System (ADS)
Van Gorder, Robert A.
2016-05-01
Very recent experimental work has demonstrated the existence of Kelvin waves along quantized vortex filaments in superfluid helium. The possible configurations and motions of such filaments is of great physical interest, and Svistunov previously obtained a Hamiltonian formulation for the dynamics of quantum vortex filaments in the low-temperature limit under the assumption that the vortex filament is essentially aligned along one axis, resulting in a two-dimensional (2D) problem. It is standard to approximate the dynamics of thin filaments by employing the local induction approximation (LIA), and we show that by putting the two-dimensional LIA into correspondence with the first equation in the integrable Wadati-Konno-Ichikawa-Schimizu (WKIS) hierarchy, we immediately obtain solutions to the two-dimensional LIA, such as helix, planar, and self-similar solutions. These solutions are obtained in a rather direct manner from the WKIS equation and then mapped into the 2D-LIA framework. Furthermore, the approach can be coupled to existing inverse scattering transform results from the literature in order to obtain solitary wave solutions including the analog of the Hasimoto one-soliton for the 2D-LIA. One large benefit of the approach is that the correspondence between the 2D-LIA and the WKIS allows us to systematically obtain vortex filament solutions directly in the Cartesian coordinate frame without the need to solve back from curvature and torsion. Implications of the results for the physics of experimentally studied solitary waves, Kelvin waves, and postvortex reconnection events are mentioned.
Jarvis, Andrew J C; Cegla, Frederic B
2014-07-01
The challenge of accurately simulating how incident scalar waves interact with rough boundaries has made it an important area of research within many scientific disciplines. Conventional methods, which in the majority of cases focus only on scattering in two dimensions, often suffer from long simulation times or reduced accuracy, neglecting phenomena such as multiple scattering and surface self-shadowing. A simulation based on the scalar wave distributed point source method (DPSM) is presented as an alternative which is computationally more efficient than fully meshed numerical methods while obtaining greater accuracy than approximate analytical techniques. Comparison is made to simulated results obtained using the finite element method for a sinusoidally periodic surface where scattering only occurs in two dimensions, showing very good agreement (<0.2 dB). In addition to two-dimensional scattering, comparison to experimental results is also carried out for scattering in three dimensions when the surface has a Gaussian roughness distribution. Results indicate that for two-dimensional scattering and for rough surfaces with a correlation length equal to the incident wavelength (λ) and a root mean square height less than 0.2λ, the scalar wave approximation predicts reflected pulse shape change and envelope amplitudes generally to within 1 dB. Comparison between transducers within a three-element array also illustrate the sensitivity pulse amplitude can have to sensor position above a rough surface, differing by as much as 17 dB with a positional change of just 1.25λ. PMID:24960707
NASA Astrophysics Data System (ADS)
Olano, C. A.
2009-11-01
Context: Using certain simplifications, Kompaneets derived a partial differential equation that states the local geometrical and kinematical conditions that each surface element of a shock wave, created by a point blast in a stratified gaseous medium, must satisfy. Kompaneets could solve his equation analytically for the case of a wave propagating in an exponentially stratified medium, obtaining the form of the shock front at progressive evolutionary stages. Complete analytical solutions of the Kompaneets equation for shock wave motion in further plane-parallel stratified media were not found, except for radially stratified media. Aims: We aim to analytically solve the Kompaneets equation for the motion of a shock wave in different plane-parallel stratified media that can reflect a wide variety of astrophysical contexts. We were particularly interested in solving the Kompaneets equation for a strong explosion in the interstellar medium of the Galactic disk, in which, due to intense winds and explosions of stars, gigantic gaseous structures known as superbubbles and supershells are formed. Methods: Using the Kompaneets approximation, we derived a pair of equations that we call adapted Kompaneets equations, that govern the propagation of a shock wave in a stratified medium and that permit us to obtain solutions in parametric form. The solutions provided by the system of adapted Kompaneets equations are equivalent to those of the Kompaneets equation. We solved the adapted Kompaneets equations for shock wave propagation in a generic stratified medium by means of a power-series method. Results: Using the series solution for a shock wave in a generic medium, we obtained the series solutions for four specific media whose respective density distributions in the direction perpendicular to the stratification plane are of an exponential, power-law type (one with exponent k=-1 and the other with k =-2) and a quadratic hyperbolic-secant. From these series solutions, we deduced
Wave-function frozen-density embedding: Approximate analytical nuclear ground-state gradients.
Heuser, Johannes; Höfener, Sebastian
2016-05-01
We report the derivation of approximate analytical nuclear ground-state uncoupled frozen density embedding (FDEu) gradients for the resolution of identity (RI) variant of the second-order approximate coupled cluster singles and doubles (RICC2) as well as density functional theory (DFT), and an efficient implementation thereof in the KOALA program. In order to guarantee a computationally efficient treatment, those gradient terms are neglected which would require the exchange of orbital information. This approach allows for geometry optimizations of single molecules surrounded by numerous molecules with fixed nuclei at RICC2-in-RICC2, RICC2-in-DFT, and DFT-in-DFT FDE level of theory using a dispersion correction, required due to the DFT-based treatment of the interaction in FDE theory. Accuracy and applicability are assessed by the example of two case studies: (a) the Watson-Crick pair adenine-thymine, for which the optimized structures exhibit a maximum error of about 0.08 Å for our best scheme compared to supermolecular reference calculations, (b) carbon monoxide on a magnesium oxide surface model, for which the error amount up to 0.1 Å for our best scheme. Efficiency is demonstrated by successively including environment molecules and comparing to an optimized conventional supermolecular implementation, showing that the method is able to outperform conventional RICC2 schemes already with a rather small number of environment molecules, gaining significant speed up in computation time. PMID:26804310
Non-Hermitian wave packet approximation for coupled two-level systems in weak and intense fields
NASA Astrophysics Data System (ADS)
Puthumpally-Joseph, Raiju; Sukharev, Maxim; Charron, Eric
2016-04-01
We introduce a non-Hermitian Schrödinger-type approximation of optical Bloch equations for two-level systems. This approximation provides a complete and accurate description of the coherence and decoherence dynamics in both weak and strong laser fields at the cost of losing accuracy in the description of populations. In this approach, it is sufficient to propagate the wave function of the quantum system instead of the density matrix, providing that relaxation and dephasing are taken into account via automatically adjusted time-dependent gain and decay rates. The developed formalism is applied to the problem of scattering and absorption of electromagnetic radiation by a thin layer comprised of interacting two-level emitters.
Non-Hermitian wave packet approximation for coupled two-level systems in weak and intense fields.
Puthumpally-Joseph, Raiju; Sukharev, Maxim; Charron, Eric
2016-04-21
We introduce a non-Hermitian Schrödinger-type approximation of optical Bloch equations for two-level systems. This approximation provides a complete and accurate description of the coherence and decoherence dynamics in both weak and strong laser fields at the cost of losing accuracy in the description of populations. In this approach, it is sufficient to propagate the wave function of the quantum system instead of the density matrix, providing that relaxation and dephasing are taken into account via automatically adjusted time-dependent gain and decay rates. The developed formalism is applied to the problem of scattering and absorption of electromagnetic radiation by a thin layer comprised of interacting two-level emitters. PMID:27389211
The Half Wave Plate Rotator for the BLAST-TNG Balloon-Borne Telescope
NASA Astrophysics Data System (ADS)
Setiawan, Hananiel; Ashton, Peter; Novak, Giles; Angilè, Francesco E.; Devlin, Mark J.; Galitzki, Nicholas; Ade, Peter; Doyle, Simon; Pascale, Enzo; Pisano, Giampaolo; Tucker, Carole E.
2016-01-01
The Next Generation Balloon-borne Large Aperture Submillimeter Telescope (BLAST-TNG) is an experiment designed to map magnetic fields in molecular clouds in order to study their role in the star formation process. The telescope will be launched aboard a high-altitude balloon in December 2016 for a 4-week flight from McMurdo station in Antarctica. BLAST-TNG will measure the polarization of submillimeter thermal emission from magnetically aligned interstellar dust grains, using large format arrays of kinetic inductance detectors operating in three bands centered at 250, 350, and 500 microns, with sub-arcminute angular resolution. The optical system includes an achromatic Half Wave Plate (HWP), mounted in a Half Wave Plate rotator (HWPr). The HWP and HWPr will operate at 4 K temperature to reduce thermal noise in our measurements, so it was crucial to account for the effects of thermal contraction at low temperature in the HWPr design. It was also equally important for the design to meet torque requirements while minimizing the power from friction and conduction dissipated at the 4 K stage. We also discuss our plan for cold testing the HWPr using a repurposed cryostat with a Silicon Diode thermometer read out by an EDAS-CE Ethernet data acquisition system.
NASA Astrophysics Data System (ADS)
Nielsen, S. K.; Salewski, M.; Westerhof, E.; Bongers, W.; Korsholm, S. B.; Leipold, F.; Oosterbeek, J. W.; Moseev, D.; Stejner, M.; the TEXTOR Team
2013-11-01
Anomalous scattering of high power millimetre waves from gyrotrons at 140 and 110 GHz is investigated for plasma with rotating islands at TEXTOR. The magnetic field and plasma density influence the spectral content of the scattered waves and their power levels significantly. Anomalous strong scattering occurs in two density regimes, one at low densities and one at high densities, that also depend on the magnetic field. The two regimes are separated by a quiescent regime without anomalous scattering. Investigations suggest that scattering in the high-density regime is generated at the low-field side intersection of the gyrotron beam and the island position. The transition from the quiescent regime to the high-density regime occurs when the gyrotron frequency is twice the upper hybrid frequency at this position. There is some evidence that the scattering in the low-density regime is generated near the plasma centre. Under this assumption all the observed scattering is generated when the gyrotron frequency is near or below twice the upper hybrid frequency.
Bijker, R.; Dieperink, A.E.L.
1982-12-01
It is shown that the dominance of ..beta --> gamma.. and ..gamma -->..g over ..beta -->..gE2 transitions in the SU(3) limit of the interacting-boson-approximation model, reported by Warner and Casten can be explained simply in terms of properties of the intrinsic E2 matrix elements.
Surin, L. A.; Tarabukin, I. V.; Panfilov, V. A.; Schlemmer, S.; Kalugina, Y. N.; Faure, A.; Rist, C.; Avoird, A. van der
2015-10-21
The rotational spectrum of the van der Waals complex CH{sub 4}–CO has been measured with the intracavity OROTRON jet spectrometer in the frequency range of 110–145 GHz. Newly observed and assigned transitions belong to the K = 2–1 subband correlating with the rotationless j{sub CH4} = 0 ground state and the K = 2–1 and K = 0–1 subbands correlating with the j{sub CH4} = 2 excited state of free methane. The (approximate) quantum number K is the projection of the total angular momentum J on the intermolecular axis. The new data were analyzed together with the known millimeter-wave and microwave transitions in order to determine the molecular parameters of the CH{sub 4}–CO complex. Accompanying ab initio calculations of the intermolecular potential energy surface (PES) of CH{sub 4}–CO have been carried out at the explicitly correlated coupled cluster level of theory with single, double, and perturbative triple excitations [CCSD(T)-F12a] and an augmented correlation-consistent triple zeta (aVTZ) basis set. The global minimum of the five-dimensional PES corresponds to an approximately T-shaped structure with the CH{sub 4} face closest to the CO subunit and binding energy D{sub e} = 177.82 cm{sup −1}. The bound rovibrational levels of the CH{sub 4}–CO complex were calculated for total angular momentum J = 0–6 on this intermolecular potential surface and compared with the experimental results. The calculated dissociation energies D{sub 0} are 91.32, 94.46, and 104.21 cm{sup −1} for A (j{sub CH4} = 0), F (j{sub CH4} = 1), and E (j{sub CH4} = 2) nuclear spin modifications of CH{sub 4}–CO, respectively.
NASA Astrophysics Data System (ADS)
Fujita, Ryuichi
2015-03-01
We compute the energy flux of the gravitational waves radiated by a particle of mass μ in circular orbits around a rotating black hole of mass M up to the 11th post-Newtonian order (11PN), i.e. v^{22} beyond the leading Newtonian approximation where v is the orbital velocity of the particle [L. Blanchet, Living Rev. Relativity 5, 3 (2002)]. By comparing the PN results for the energy flux with high-precision numerical results in black hole perturbation theory, we find the region of validity in the PN approximation becomes larger with increasing PN order. If one requires the relative error of the energy flux in the PN approximation to be less than 10^{-5}, the energy flux at 11PN (4PN) can be used for v⪉ 0.33 (v ⪉ 0.13). The region of validity can be further extended to v⪉ 0.4 if one applies a resummation method to the energy flux at 11PN. We then compare the orbital phase during a two-year inspiral from the PN results with the high-precision numerical results. We find that, for late (early) inspirals when q≤ 0.3 (q≤ 0.9), where q is the dimensionless spin parameter of the black hole, the difference in the phase is less than 1 (10^{-4}) rad and hence these inspirals may be detected in the data analysis for space detectors such as eLISA/New Gravitational wave Observatory by the PN templates. We also compute the energy flux radiated into the event horizon for a particle in circular orbits around a non-rotating black hole at 22.5PN, i.e. v^{45} beyond the leading Newtonian approximation, which is comparable to the PN order derived in our previous work for the energy flux to infinity at 22PN.
Mok, Jinsik
2014-01-01
Summary This study is motivated in part to better understand multiplexing in wireless communications, which employs photons carrying varying angular momenta. In particular, we examine both transverse electric (TE) and transverse magnetic (TM) waves in either co-rotations or counter-rotations. To this goal, we analyze both Poynting-vector flows and orbital and spin parts of the energy flow density for the combined fields. Consequently, we find not only enhancements but also cancellations between the two modes. To our surprise, the photon spins in the azimuthal direction exhibit a complete annihilation for the counter-rotational case even if the intensities of the colliding waves are of different magnitudes. In contrast, the orbital flow density disappears only if the two intensities satisfy a certain ratio. In addition, the concepts of spin sifters and enantiomer sorting are illustrated. PMID:25383300
NASA Astrophysics Data System (ADS)
Mourenas, D.; Artemyev, A. V.; Agapitov, O. V.; Krasnoselskikh, V.; Li, W.
2014-12-01
The distribution of trapped energetic electrons inside the Earth's radiation belts is the focus of intense studies aiming at better describing the evolution of the space environment in the presence of various disturbances induced by the solar wind or by an enhanced lightning activity. Such studies are usually performed by means of comparisons with full numerical simulations solving the Fokker-Planck quasi-linear diffusion equation for the particle distribution function. Here we present for the first time approximate but realistic analytical solutions for the electron distribution, which are shown to be in good agreement with exact numerical solutions in situations where resonant scattering of energetic electrons by whistler mode hiss, lightning-generated or chorus waves, is the dominant process. Quiet time distributions are well recovered, as well as the evolution of energized relativistic electron distributions during disturbed geomagnetic conditions. It is further shown that careful comparisons between the analytical solutions and measured distributions may allow to infer important bounce- and drift-averaged wave characteristics (such as wave amplitude). It could also help to improve the global understanding of underlying physical phenomena.
Van Gorder, Robert A
2015-05-01
The Hasimoto transformation between the classical LIA (local induction approximation, a model approximating the motion of a thin vortex filament) and the nonlinear Schrödinger equation (NLS) has proven very useful in the past, since it allows one to construct new solutions to the LIA once a solution to the NLS is known. In the present paper, the quantum form of the LIA (which includes mutual friction effects) is put into correspondence with a type of complex nonlinear dispersive partial differential equation (PDE) with cubic nonlinearity (similar in form to a Ginsburg-Landau equation, with additional nonlinear terms). Transforming the quantum LIA in such a way enables one to obtain quantum vortex filament solutions once solutions to this dispersive PDE are known. From our quantum Hasimoto transformation, we determine the form and behavior of Stokes waves, a standing one-soliton, traveling waves, and similarity solutions under normal and binormal friction effects. The quantum Hasimoto transformation is useful when normal fluid velocity is relatively weak, so for the case where the normal fluid velocity is dominant we resort to other approaches. We exhibit a number of solutions that exist only in the presence of the normal fluid velocity and mutual friction terms (which would therefore not exist in the limit taken to obtain the classical LIA, decaying into line filaments under such a limit), examples of which include normal fluid driven helices, stationary and propagating topological solitons, and a vortex ring whose radius varies inversely with the normal fluid magnitude. We show that, while chaos may not be impossible under the quantum LIA, it should not be expected to arise from traveling waves along quantum vortex filaments under the quantum LIA formulation. PMID:26066272
NASA Astrophysics Data System (ADS)
Van Gorder, Robert A.
2015-05-01
The Hasimoto transformation between the classical LIA (local induction approximation, a model approximating the motion of a thin vortex filament) and the nonlinear Schrödinger equation (NLS) has proven very useful in the past, since it allows one to construct new solutions to the LIA once a solution to the NLS is known. In the present paper, the quantum form of the LIA (which includes mutual friction effects) is put into correspondence with a type of complex nonlinear dispersive partial differential equation (PDE) with cubic nonlinearity (similar in form to a Ginsburg-Landau equation, with additional nonlinear terms). Transforming the quantum LIA in such a way enables one to obtain quantum vortex filament solutions once solutions to this dispersive PDE are known. From our quantum Hasimoto transformation, we determine the form and behavior of Stokes waves, a standing one-soliton, traveling waves, and similarity solutions under normal and binormal friction effects. The quantum Hasimoto transformation is useful when normal fluid velocity is relatively weak, so for the case where the normal fluid velocity is dominant we resort to other approaches. We exhibit a number of solutions that exist only in the presence of the normal fluid velocity and mutual friction terms (which would therefore not exist in the limit taken to obtain the classical LIA, decaying into line filaments under such a limit), examples of which include normal fluid driven helices, stationary and propagating topological solitons, and a vortex ring whose radius varies inversely with the normal fluid magnitude. We show that, while chaos may not be impossible under the quantum LIA, it should not be expected to arise from traveling waves along quantum vortex filaments under the quantum LIA formulation.
Lee, J. P.; Wright, J. C.; Bonoli, P. T.; Parker, R. R.; Catto, P. J.; Podpaly, Y. A.; Rice, J. E.; Reinke, M. L.
2011-12-23
Significant ion toroidal rotation (50km/s) has been measured by X-Ray spectroscopy for impurities in Alcator C-Mod during lower hybrid (LH) RF power injection. We investigate the relation between the computed toroidal momentum input from LH waves and the measured INITIAL change of ion toroidal rotation when the LH power is turned on. The relation may depend on the plasma current and magnetic configuration. Because of the fast build up time of the electron quasilinear plateau (<1 millisecond), the electron distribution function rapidly reaches steady state in which the electrons transfer momentum to the ions. The LH wave momentum input is computed from the self consistent steady state electron distribution function and a bounce-averaged quasilinear diffusion coefficient that are obtained by iterating a full wave code (TORLH) with a Fokker Plank code (CQL3D)
NASA Astrophysics Data System (ADS)
Marino, Raffaele; Rosenberg, Duane; Herbert, Corentin; Pouquet, Annick
2015-11-01
The interplay between waves and eddies in stably stratified rotating flows is investigated by means of world-class direct numerical simulations using up to 30723 grid points. Strikingly, we find that the shift from vortex- to wave-dominated dynamics occurs at a wave number k R which does not depend on the Reynolds number, suggesting that the partition of energy between wave and vortical modes is not sensitive to the development of turbulence at the smaller scales. We also show that k R is comparable to the wave number at which exchanges between kinetic and potential modes stabilize at close to equipartition, emphasizing the role of potential energy, as conjectured in the atmosphere and the oceans. Moreover, k R varies as the inverse of the Froude number as explained by the scaling prediction proposed, consistently with recent observations and modeling of the Mesosphere-Lower Thermosphere and of the ocean.
Data analysis for a rotating quarter-wave, far-infrared Stokes polarimeter.
Giudicotti, Leonardo; Brombin, Matteo
2007-05-10
Data analysis techniques are reviewed and extended for the measurement of the Stokes vector of partially or completely polarized radiation by the rotating quarter-wave method. It is shown that the conventional technique, based on the Fourier analysis of the recorded signal, can be efficiently replaced by a weighted least-squares best fit, so that the different accuracy of the measured data can be taken into account to calculate the measurement errors of the Stokes vector elements. Measurement errors for the polarization index P and for the azimuth and ellipticity angles psi and chi of the radiation are also calculated by propagation error theory. For those cases in which the above technique gives a nonphysical Stokes vector (i.e., with a polarization degree of P>1) a constrained least-squares best fit is introduced, and it is shown that in this way a Stokes vector with P = 1 (rather than P
Zhang, Zhaojun; Zhang, Dong H
2014-10-14
Seven-dimensional time-dependent wave packet calculations have been carried out for the title reaction to obtain reaction probabilities and cross sections for CHD3 in J0 = 1, 2 rotationally excited initial states with k0 = 0 - J0 (the projection of CHD3 rotational angular momentum on its C3 axis). Under the centrifugal sudden (CS) approximation, the initial states with the projection of the total angular momentum on the body fixed axis (K0) equal to k0 are found to be much more reactive, indicating strong dependence of reactivity on the orientation of the reagent CHD3 with respect to the relative velocity between the reagents H and CHD3. However, at the coupled-channel (CC) level this dependence becomes much weak although in general the K0 specified cross sections for the K0 = k0 initial states remain primary to the overall cross sections, implying the Coriolis coupling is important to the dynamics of the reaction. The calculated CS and CC integral cross sections obtained after K0 averaging for the J0 = 1, 2 initial states with all different k0 are essentially identical to the corresponding CS and CC results for the J0 = 0 initial state, meaning that the initial rotational excitation of CHD3 up to J0 = 2, regardless of its initial k0, does not have any effect on the total cross sections for the title reaction, and the errors introduced by the CS approximation on integral cross sections for the rotationally excited J0 = 1, 2 initial states are the same as those for the J0 = 0 initial state. PMID:25318724
NASA Technical Reports Server (NTRS)
Poole, L. R.
1976-01-01
The Langley Research Center and Virginia Institute of Marine Science wave refraction computer model was applied to the Baltimore Canyon region of the mid-Atlantic continental shelf. Wave refraction diagrams for a wide range of normally expected wave periods and directions were computed by using three bottom topography approximation techniques: quadratic least squares, cubic least squares, and constrained bicubic interpolation. Mathematical or physical interpretation of certain features appearing in the computed diagrams is discussed.
Radial extracorporeal shock-wave therapy in rotator cuff calcific tendinosis
Mangone, Giuseppe; Veliaj, Altin; Postiglione, Marco; Viliani, Tamara; Pasquetti, Pietro
2010-01-01
The objective of the study is to evaluate the effectiveness of Radial Extracorporeal Shock-wave Therapy (RESWT) compared with High Power LASER Therapy (HPLT) for the treatment of patients with Rotator Cuff Calcific Tendinosis (RCCT). RCCT is widely diffused, it is painful and invalidating. It is an important public health problem with social and economic implications. The most common therapeutic approach is a physiotherapic one. Both HPLT and RESWT give positive results. There is a debate on which is to be preferred. Therefore there is need to obtain scientific evidence to support either case. An observational study was carried out in the period between October 2008 and September 2009 in our outpatient clinic with 62 patients, divided into 3 groups: group A 36 patients treated only with RESWT, group B 26 patients treated only with HPLT and group C 16 patients with only short term improvement with HPLT retreated with RESWT. Patients were evaluated with Constant-Murley scale before and after treatment (immediately, 1 month and 3 months) for mean constant score, pain and range of movement. Data were examined statistically with SPSS. Criteria for inclusion and exclusion were defined. Patients treated with HPLT have shown good clinical results but have returned to original syndrome 1 month after treatment. RESWT has given improvement after treatment extended in time (3 months) in terms of pain and recover of functionality with a limited number of applications. The evidence collected indicates that RESWT is the method of choice. PMID:22460011
Gravitational Waves from Rotating Neutron Stars and Evaluation of fast Chirp Transform Techniques
NASA Technical Reports Server (NTRS)
Strohmayer, Tod E.; White, Nicholas E. (Technical Monitor)
2000-01-01
X-ray observations suggest that neutron stars in low mass X-ray binaries (LMXB) are rotating with frequencies from 300 - 600 Hz. These spin rates are significantly less than the break-up rates for essentially all realistic neutron star equations of state, suggesting that some process may limit the spin frequencies of accreting neutron stars to this range. If the accretion induced spin up torque is in equilibrium with gravitational radiation losses, these objects could be interesting sources of gravitational waves. I present a brief summary of current measurements of neutron star spins in LMXBs based on the observations of high-Q oscillations during thermonuclear bursts (so called 'burst oscillations'). Further measurements of neutron star spins will be important in exploring the gravitational radiation hypothesis in more detail. To this end I also present a study of fast chirp transform (FCT) techniques as described by Jenet and Prince in the context of searching for the chirping signals observed during X-ray bursts.
NASA Astrophysics Data System (ADS)
Korona, Tatiana
2012-02-01
A possibility to calculate electron affinities (EAs) by a software devised for electron excitations is exploited to examine the accuracy of a partly local EA-EOM-CCSD method. In the proposed approach local approximations are applied to the ground-state coupled cluster wave function, while the EAs themselves are obtained in a full configurational space. The results of a numerical test for 14 molecules show that already with standard local settings the method reproduces the nonlocal EAs with the average error of 0.009 eV. Since the EA-EOM step of the calculation requires less computational resources than the computation of the CCSD ground state, the proposed hybrid approach can become a valuable tool for obtaining the EAs for molecules, which are too large for a canonical CCSD calculation, but still small enough for the EA-EOM step to be performed in a nonlocal way.
NASA Technical Reports Server (NTRS)
Stiehl, A. L.; Haberman, R. C.; Cowles, J. H.
1988-01-01
An approximate method to compute the maximum deformation and permanent set of a beam subjected to shock wave laoding in vacuo and in water was investigated. The method equates the maximum kinetic energy of the beam (and water) to the elastic plastic work done by a static uniform load applied to a beam. Results for the water case indicate that the plastic deformation is controlled by the kinetic energy of the water. The simplified approach can result in significant savings in computer time or it can expediently be used as a check of results from a more rigorous approach. The accuracy of the method is demonstrated by various examples of beams with simple support and clamped support boundary conditions.
NASA Astrophysics Data System (ADS)
Aguiar-González, Borja; Gerkema, Theo
2015-04-01
We derive a new two-fluid layer model consisting of a set of forced rotation-modified Boussinesq equations for studying the generation and evolution of strongly nonlinear weakly nonhydrostatic dispersive interfacial waves in a rotating ocean. The forcing for internal tide generation is due to tide-topography interaction (an oscillating non-flat bottom mimicking a barotropic tidal flow over topography). The resulting model forms a generalization of the Miyata-Choi-Camassa (MCC) equations, to which we add topography, tidal forcing and Coriolis dispersion due to Earth's rotation. Solitons are generated by disintegration of the first-mode of the internal tide. Because of strong non-linearity, they can attain a table-shaped form. Our moving (accelerating) topography is not an inertial frame and, hence, the transformation to a frame at rest is not simply a Galilean transformation. The effect of this transformation is discussed and is shown to be slight for the parameters under consideration. The set of equations is solved numerically using finite-difference methods. Numerical experiments using these equations are a useful tool for exploring and interpreting the conditions under which full nonlinearity becomes important for soliton generation. In particular, this is the case for table-top solitons when approaching the theoretical maximum amplitude and the appearance of nonlinearities when the two-layer system consists of two layers of equal thickness. At the early stage of the strongly nonlinear disintegration of an internal tide into table-top solitons, we observe that the low mode internal tide splits up into two different groups of rank-ordered solitons: a train of depressions on the leading edge and a train of elevations, after the former packet, with initially smaller amplitudes. Evolving in time, the largest elevations reach the smaller depressions in the train ahead, and three leading solitons at the front attain almost equal amplitudes. The table-top soliton
NASA Astrophysics Data System (ADS)
McGurn, A. R.; Maradudin, A. A.
2001-10-01
Two computer simulation studies of the speckle correlations in the light scattered from a volume disordered dielectric medium consisting of a random array of dielectric spheres are made. In both studies light is treated in the scalar wave approximation, and the wavelength of the light is taken to be much greater than the radius of the dielectric spheres. In one study, the scattering medium is formed by placing dielectric spheres of radius R and dielectric constant ɛ randomly in space. The spheres occupy space uniformly, under the provision that no two spheres overlap. In a second study, the scattering medium is formed by placing dielectric spheres of radius R and dielectric constant ɛ randomly on the vertices of a simple cubic lattice so that a fixed fraction of the vertices is occupied by the spheres. The lattice constant of the simple cubic lattice is taken to be of the order of magnitude of the wavelength of light in vacuum. In both studies the the volume filling fraction is the same, and the region outside the spheres is vacuum. The field equations are integrated numerically to determine the scattered fields, and these fields are used to calculate the speckle correlation function defined by C(q-->,k-->\\|q',k')=<[I(q-->\\|k-->)-\\|k-->)>][I(q'\\|k')-. Here I(q-->\\|k-->) is proportional to the differential scattering coefficient for the elastic scattering of light of wave vector k--> into light of wave vector q-->, and < > indicates an average over an ensemble of random systems. Results are presented for C(q-->,k-->\\|q',k') with particular attention paid to regions of k--> space in which either the C(1) or C(10) contributions dominate the correlator.
NASA Technical Reports Server (NTRS)
Bassom, Andrew P.; Hall, Philip
1989-01-01
There are many fluid flows where the onset of transition can be caused by different instability mechanisms which compete among themselves. The interaction is considered of two types of instability mode (at an asymptotically large Reynolds number) which can occur in the flow above a rotating disc. In particular, the interaction is examined between lower branch Tollmien-Schlichting (TS) waves and the upper branch, stationary, inviscid crossflow vortex whose asymptotic structure has been described by Hall (1986). This problem is studied in the context of investigating the effect of the vortex on the stability characteristics of a small TS wave. Essentially, it is found that the primary effect is felt through the modification to the mean flow induced by the presence of the vortex. Initially, the TS wave is taken to be linear in character and it is shown (for the cases of both a linear and a nonlinear stationary vortex) that the vortex can exhibit both stabilizing and destabilizing effects on the TS wave and the nature of this influence is wholly dependent upon the orientation of this latter instability. Further, the problem is examined with a larger TS wave, whose size is chosen so as to ensure that this mode is nonlinear in its own right. An amplitude equation for the evolution of the TS wave is derived which admits solutions corresponding to finite amplitude, stable, traveling waves.
NASA Technical Reports Server (NTRS)
Bassom, Andrew P.; Hall, Philip
1990-01-01
There are many fluid flows where the onset of transition can be caused by different instability mechanisms which compete among themselves. The interaction is considered of two types of instability mode (at an asymptotically large Reynolds number) which can occur in the flow above a rotating disc. In particular, the interaction is examined between lower branch Tollmien-Schlichting (TS) waves and the upper branch, stationary, inviscid crossflow vortex whose asymptotic structure has been described by Hall (1986). This problem is studied in the context of investigating the effect of the vortex on the stability characteristics of a small TS wave. Essentially, it is found that the primary effect is felt through the modification to the mean flow induced by the presence of the vortex. Initially, the TS wave is taken to be linear in character and it is shown (for the cases of both a linear and a nonlinear stationary vortex) that the vortex can exhibit both stabilizing and destabilizing effects on the TS wave and the nature of this influence is wholly dependent upon the orientation of this latter instability. Further, the problem is examined with a larger TS wave, whose size is chosen so as to ensure that this mode is nonlinear in its own right. An amplitude equation for the evolution of the TS wave is derived which admits solutions corresponding to finite amplitude, stable, traveling waves.
Inertia gravity waves in a rotating, differentially heated annulus with an upper free surface
NASA Astrophysics Data System (ADS)
Randriamampianina, Anthony; Harlander, Uwe; Vincze, Miklos; von Larcher, Thomas; Viazzo, Stephane
2015-04-01
Inertia gravity waves (IGWs) are ubiquitous in the atmosphere and oceans, and are known to play a fundamental role in a wide variety of processes, among others the induction and modulation of turbulence. Observations and simulations have revealed their spontaneous occurrence simultaneously with the onset of baroclinic instability, recognized to be one of the dominant energetic processes in the large-scale atmospheric and oceanic circulations. In spite of intensive research activities these last decades, the generation mechanism and the propagation of IGWs, as well as their interaction with large-scale structures triggering locally chaotic motions, remain poorly understood. A better understanding of these phenomena is therefore mandatory for the development of IGW's parameterization schemes actually required for numerical global weather prediction. A combined laboratory experiment and direct numerical simulations study is proposed for the detailed investigations of instabilities arising within a differentially heated rotating annulus, the baroclinic cavity. The configuration corresponds to an experimental setup used at BTU, Cottbus Senftenberg, Germany [1], characterized by an open upper surface and filled with water (Pr = 7). Infrared thermography and simultaneous kalliroscope visualization in horizontal planes, illuminated by a laser sheet, have been applied to detect the surface signatures of IGWs. These findings confirmed the computations carried out by three different numerical approaches, using either spectral methods, high order compact finite difference scheme (M2P2, Marseille), or the EULAG code (Freie Universitaet Berlin). These small-scale features have been observed in addition to those developing along the inner cold cylinder, previously identified by simulations in a closed cavity, filled with a liquid defined by Pr = 16 [2]. These new IGWs show characteristics similar to the ones obtained by [3] at the exit of the meandering jet between the cyclonic
Surin, L. A.; Potapov, A.; Schlemmer, S.; Dolgov, A. A.; Tarabukin, I. V.; Panfilov, V. A.; Kalugina, Y. N.; Faure, A.; Avoird, A. van der
2015-03-21
The rotational spectrum of the van der Waals complex NH{sub 3}–CO has been measured with the intracavity OROTRON jet spectrometer in the frequency range of 112–139 GHz. Newly observed and assigned transitions belong to the K = 0–0, K = 1–1, K = 1–0, and K = 2–1 subbands correlating with the rotationless (j{sub k}){sub NH3} = 0{sub 0} ground state of free ortho-NH{sub 3} and the K = 0–1 and K = 2–1 subbands correlating with the (j{sub k}){sub NH3} = 1{sub 1} ground state of free para-NH{sub 3}. The (approximate) quantum number K is the projection of the total angular momentum J on the intermolecular axis. Some of these transitions are continuations to higher J values of transition series observed previously [C. Xia et al., Mol. Phys. 99, 643 (2001)], the other transitions constitute newly detected subbands. The new data were analyzed together with the known millimeter-wave and microwave transitions in order to determine the molecular parameters of the ortho-NH{sub 3}–CO and para-NH{sub 3}–CO complexes. Accompanying ab initio calculations of the intermolecular potential energy surface (PES) of NH{sub 3}–CO has been carried out at the explicitly correlated coupled cluster level of theory with single, double, and perturbative triple excitations and an augmented correlation-consistent triple zeta basis set. The global minimum of the five-dimensional PES corresponds to an approximately T-shaped structure with the N atom closest to the CO subunit and binding energy D{sub e} = 359.21 cm{sup −1}. The bound rovibrational levels of the NH{sub 3}–CO complex were calculated for total angular momentum J = 0–6 on this intermolecular potential surface and compared with the experimental results. The calculated dissociation energies D{sub 0} are 210.43 and 218.66 cm{sup −1} for ortho-NH{sub 3}–CO and para-NH{sub 3}–CO, respectively.
Sugimoto, Norihiko
2015-12-15
Inertia-gravity wave radiation from the merging of two co-rotating vortices is investigated numerically in a rotating shallow water system in order to focus on cyclone–anticyclone asymmetry at different values of the Rossby number (Ro). A numerical study is conducted on a model using a spectral method in an unbounded domain to estimate the gravity wave flux with high accuracy. Continuous gravity wave radiation is observed in three stages of vortical flows: co-rotating of the vortices, merging of the vortices, and unsteady motion of the merged vortex. A cyclone–anticyclone asymmetry appears at all stages at smaller Ro (≤20). Gravity waves from anticyclones are always larger than those from cyclones and have a local maximum at smaller Ro (∼2) compared with that for an idealized case of a co-rotating vortex pair with a constant rotation rate. The source originating in the Coriolis acceleration has a key role in cyclone–anticyclone asymmetry in gravity waves. An additional important factor is that at later stages, the merged axisymmetric anticyclone rotates faster than the elliptical cyclone due to the effect of the Rossby deformation radius, since a rotation rate higher than the inertial cutoff frequency is required to radiate gravity waves.
NASA Astrophysics Data System (ADS)
Sugimoto, Norihiko
2015-12-01
Inertia-gravity wave radiation from the merging of two co-rotating vortices is investigated numerically in a rotating shallow water system in order to focus on cyclone-anticyclone asymmetry at different values of the Rossby number (Ro). A numerical study is conducted on a model using a spectral method in an unbounded domain to estimate the gravity wave flux with high accuracy. Continuous gravity wave radiation is observed in three stages of vortical flows: co-rotating of the vortices, merging of the vortices, and unsteady motion of the merged vortex. A cyclone-anticyclone asymmetry appears at all stages at smaller Ro (≤20). Gravity waves from anticyclones are always larger than those from cyclones and have a local maximum at smaller Ro (˜2) compared with that for an idealized case of a co-rotating vortex pair with a constant rotation rate. The source originating in the Coriolis acceleration has a key role in cyclone-anticyclone asymmetry in gravity waves. An additional important factor is that at later stages, the merged axisymmetric anticyclone rotates faster than the elliptical cyclone due to the effect of the Rossby deformation radius, since a rotation rate higher than the inertial cutoff frequency is required to radiate gravity waves.
NASA Astrophysics Data System (ADS)
Heilmann, René; Gräfe, Markus; Nolte, Stefan; Szameit, Alexander
2014-02-01
Chip-based photonic quantum computing is an emerging technology that promises much speedup over conventional computers at small integration volumes. Particular interest is thereby given to polarisation-encoded photonic qubits, and many protocols have been developed for this encoding. However, arbitrary wave plate operation on chip are not available so far, preventing from the implementation of integrated universal quantum computing algorithms. In our work we close this gap and present Hadamard, Pauli-X, and rotation gates of high fidelity for photonic polarisation qubits on chip by employing a reorientation of the optical axis of birefringent waveguides. The optical axis of the birefringent waveguide is rotated due to the impact of an artificial stress field created by an additional modification close to the waveguide. By adjusting this length of the defect along the waveguide, the retardation between ordinary and extraordinary field components is precisely tunable including half-wave plate and quarter-wave plate operations. Our approach demonstrates the full range control of orientation and strength of the induced birefringence and thus allows arbitrary wave plate operations without affecting the degree of polarisation or introducing additional losses to the waveguides. The implemented gates are tested with classical and quantum light.
Machicoane, Nathanaël; Cortet, Pierre-Philippe; Moisy, Frédéric; Voisin, Bruno
2015-06-15
We analyze theoretically and experimentally the far-field viscous decay of a two-dimensional inertial wave beam emitted by a harmonic line source in a rotating fluid. By identifying the relevant conserved quantities along the wave beam, we show how the beam structure and decay exponent are governed by the multipole order of the source. Two wavemakers are considered experimentally, a pulsating and an oscillating cylinder, aiming to produce a monopole and a dipole source, respectively. The relevant conserved quantity which discriminates between these two sources is the instantaneous flow rate along the wave beam, which is non-zero for the monopole and zero for the dipole. For each source, the beam structure and decay exponent, measured using particle image velocimetry, are in good agreement with the predictions.
NASA Astrophysics Data System (ADS)
Nath, Gorakh
2016-07-01
The propagation of a strong cylindrical shock wave in a self-gravitating and rotational axisymmetric dusty gas, having variable azimuthal and axial fluid velocities is investigated. The dusty gas is assumed to be a mixture of small solid particles and perfect gas. The equilibrium flow conditions are assumed to be maintained. The density of the mixture and the fluid velocities in the ambient medium are assumed to be varying and obeying an exponential law. The shock wave moves with variable velocity and the total energy of the wave is non-constant. Non-similarity solutions are obtained and the effects of variation of the mass concentration of solid particles in the mixture, the ratio of the density of solid particles to the initial density of the gas, and the gravitational parameter on the flow variables in the region behind the shock are investigated at a given time. Also, a comparison between the isothermal and adiabatic flow is made.
Optimal rotated staggered-grid finite-difference schemes for elastic wave modeling in TTI media
NASA Astrophysics Data System (ADS)
Yang, Lei; Yan, Hongyong; Liu, Hong
2015-11-01
The rotated staggered-grid finite-difference (RSFD) is an effective approach for numerical modeling to study the wavefield characteristics in tilted transversely isotropic (TTI) media. But it surfaces from serious numerical dispersion, which directly affects the modeling accuracy. In this paper, we propose two different optimal RSFD schemes based on the sampling approximation (SA) method and the least-squares (LS) method respectively to overcome this problem. We first briefly introduce the RSFD theory, based on which we respectively derive the SA-based RSFD scheme and the LS-based RSFD scheme. Then different forms of analysis are used to compare the SA-based RSFD scheme and the LS-based RSFD scheme with the conventional RSFD scheme, which is based on the Taylor-series expansion (TE) method. The contrast in numerical accuracy analysis verifies the greater accuracy of the two proposed optimal schemes, and indicates that these schemes can effectively widen the wavenumber range with great accuracy compared with the TE-based RSFD scheme. Further comparisons between these two optimal schemes show that at small wavenumbers, the SA-based RSFD scheme performs better, while at large wavenumbers, the LS-based RSFD scheme leads to a smaller error. Finally, the modeling results demonstrate that for the same operator length, the SA-based RSFD scheme and the LS-based RSFD scheme can achieve greater accuracy than the TE-based RSFD scheme, while for the same accuracy, the optimal schemes can adopt shorter difference operators to save computing time.
Robert, Jean-Luc; Fink, Mathias
2009-01-01
The decomposition of the time reversal operator, known by the French acronym DORT, is widely used to detect, locate, and focus on scatterers in various domains such as underwater acoustics, medical ultrasound, and nondestructive evaluation. In the case of point-scatterers, the theory is well understood: The number of nonzero eigenvalues is equal to the number of scatterers, and the eigenvectors correspond to the scatterers Green's function. In the case of extended objects, however, the formalism is not as simple. It is shown here that, in the Fraunhofer approximation, analytical solutions can be found and that the solutions are functions called prolate spheroidal wave-functions. These functions have been studied in information theory as a basis of band-limited and time-limited signals. They also arise in optics. The theoretical solutions are compared to simulation results. Most importantly, the intuition that for an extended objects, the number of nonzero eigenvalues is proportional to the number of resolution cell in the object is justified. The case of three-dimensional objects imaged by a two-dimensional array is also dealt with. Comparison with previous solutions is made, and an application to super-resolution of scatterers is presented. PMID:19173409
Liu, Yi; Bławzdziewicz, Jerzy; Cichocki, Bogdan; Dhont, Jan K G; Lisicki, Maciej; Wajnryb, Eligiusz; Young, Y-N; Lang, Peter R
2015-10-01
In this article we report on a study of the near-wall dynamics of suspended colloidal hard spheres over a broad range of volume fractions. We present a thorough comparison of experimental data with predictions based on a virial approximation and simulation results. We find that the virial approach describes the experimental data reasonably well up to a volume fraction of ϕ≈ 0.25 which provides us with a fast and non-costly tool for the analysis and prediction of evanescent wave DLS data. Based on this we propose a new method to assess the near-wall self-diffusion at elevated density. Here, we qualitatively confirm earlier results [Michailidou, et al., Phys. Rev. Lett., 2009, 102, 068302], which indicate that many-particle hydrodynamic interactions are diminished by the presence of the wall at increasing volume fractions as compared to bulk dynamics. Beyond this finding we show that this diminishment is different for the particle motion normal and parallel to the wall. PMID:26264420
NASA Astrophysics Data System (ADS)
Sarwar, S.; Rashidi, M. M.
2016-07-01
This paper deals with the investigation of the analytical approximate solutions for two-term fractional-order diffusion, wave-diffusion, and telegraph equations. The fractional derivatives are defined in the Caputo sense, whose orders belong to the intervals [0,1], (1,2), and [1,2], respectively. In this paper, we extended optimal homotopy asymptotic method (OHAM) for two-term fractional-order wave-diffusion equations. Highly approximate solution is obtained in series form using this extended method. Approximate solution obtained by OHAM is compared with the exact solution. It is observed that OHAM is a prevailing and convergent method for the solutions of nonlinear-fractional-order time-dependent partial differential problems. The numerical results rendering that the applied method is explicit, effective, and easy to use, for handling more general fractional-order wave diffusion, diffusion, and telegraph problems.
Lin, Chih-Ming; Angot, Ludovic
2008-06-15
The first Born approximation is applied to calculate the angular selectivity for different positions on the reconstructed image as a function of the object beam's optical axis angle theta(ob) and reference beam angle theta(rw) for a holographic data storage system that records the Fourier transform holograms in a medium with an infinite plane-wave reference beam. Results are compared with those calculated by the coupled-wave theory. PMID:18552937
NASA Astrophysics Data System (ADS)
Dagrau, Franck; Coulouvrat, François; Marchiano, Régis; Héron, Nicolas
2008-06-01
Dassault Aviation as a civil aircraft manufacturer is studying the feasibility of a supersonic business jet with the target of an "acceptable" sonic boom at the ground level, and in particular in case of focusing. A sonic boom computational process has been performed, that takes into account meteorological effects and aircraft manoeuvres. Turn manoeuvres and aircraft acceleration create zones of convergence of rays (caustics) which are the place of sound amplification. Therefore two elements have to be evaluated: firstly the geometrical position of the caustics, and secondly the noise level in the neighbourhood of the caustics. The modelling of the sonic boom propagation is based essentially on the assumptions of geometrical acoustics. Ray tracing is obtained according to Fermat's principle as paths that minimise the propagation time between the source (the aircraft) and the receiver. Wave amplitude and time waveform result from the solution of the inviscid Burgers' equation written along each individual ray. The "age variable" measuring the cumulative nonlinear effects is linked to the ray tube area. Caustics are located as the place where the ray tube area vanishes. Since geometrical acoustics does not take into account diffraction effects, it breaks down in the neighbourhood of caustics where it would predict unphysical infinite pressure amplitude. The aim of this study is to describe an original method for computing the focused noise level. The approach involves three main steps that can be summarised as follows. The propagation equation is solved by a forward marching procedure split into three successive steps: linear propagation in a homogeneous medium, linear perturbation due to the weak heterogeneity of the medium, and non-linear effects. The first step is solved using an "exact" angular spectrum algorithm. Parabolic approximation is applied only for the weak perturbation due to the heterogeneities. Finally, non linear effects are performed by solving the
NASA Astrophysics Data System (ADS)
Briquet, M.; Neiner, C.; Petit, P.; Leroy, B.; de Batz, B.
2016-03-01
Aims: The main-sequence B-type star ζ Cassiopeiae is known as a N-rich star with a magnetic field discovered with the Musicos spectropolarimeter. We model the magnetic field of the star by means of 82 new spectropolarimetric observations of higher precision to investigate the field strength, topology, and effect. Methods: We gathered data with the Narval spectropolarimeter installed at Télescope Bernard Lyot (TBL; Pic du Midi, France) and applied the least-squares deconvolution technique to measure the circular polarisation of the light emitted from ζ Cas. We used a dipole oblique rotator model to determine the field configuration by fitting the longitudinal field measurements and by synthesizing the measured Stokes V profiles. We also made use of the Zeeman-Doppler imaging technique to map the stellar surface and to deduce the difference in rotation rate between the pole and equator. Results: ζ Cas exhibits a polar field strength Bpol of 100-150 G, which is the weakest polar field observed so far in a massive main-sequence star. Surface differential rotation is ruled out by our observations and the field of ζ Cas is strong enough to enforce rigid internal rotation in the radiative zone according to theory. Thus, the star rotates as a solid body in the envelope. Conclusions: We therefore exclude rotationally induced mixing as the cause of the surface N-enrichment. We discuss that the transport of chemicals from the core to the surface by internal gravity waves is the most plausible explanation for the nitrogen overabundance at the surface of ζ Cas. Based on observations obtained at the Télescope Bernard Lyot (USR5026) operated by the Observatoire Midi-Pyrénées, Université de Toulouse (Paul Sabatier), Centre National de la Recherche Scientifique (CNRS) of France.
Optical Ramsey spectroscopy in a rotating frame: Sagnac effect in a matter-wave interferometer
Riehle, F.; Kisters, T.; Witte, A.; Helmcke, J. ); Borde, C.J. Laboratoire de Physique des Lasers, Universite Paris, Villetaneuse, France )
1991-07-08
A calcium atomic beam excited in an optical Ramsey geometry was rotated about an axis perpendicular to the plane defined by the laser beams and the atomic beam. A frequency shift of the Ramsey fringes of several kHz has been measured which is proportional to the rotation frequency of the apparatus and to the distance between the laser beams. The results can be interpreted in three equivalent ways as the Sagnac effect in a calcium-atomic-beam interferometer: in the rotating frame of the laser beams either along straight paths or along the curved trajectories of the atoms, or in the inertial atomic frame.
Magnetopause surface waves triggered by a rotating IMF with the global MHD SWMF/BAT-S-RUS model
NASA Astrophysics Data System (ADS)
Andriyas, T.; Spencer, E. A.
2010-12-01
The solar wind driving of magnetopause surface waves is only partly understood. In particular we do not have a picture of the magnetopause surface wave properties and behavior when a magnetic cloud event, which sometimes involves a rotating IMF, impinges on the magnetosphere. Here we investigate the effect of a twisting or rotational IMF under moderate solar wind velocity (about 500 km/s) upon the magnetosphere with the Global MHD BATS-R-US code. Synthetic solar wind data is constructed to simulate the most important features of a magnetic cloud event, but without including shock features. A sinusoidally varying By component accompanied by a cosinusoidally varying Bz component of the IMF is input into the model with magnitude 10-20 nT. The synthetic data is representative of the magnetic cloud event that occurred on October 3-7 2000. We use the results of the simulation to infer the modes, properties, and particularly the phase speed and wavelength of the surface wave structures.
NASA Astrophysics Data System (ADS)
Yokozawa, Takaaki; Asano, Mitsuhiro; Kayano, Tsubasa; Suwa, Yudai; Kanda, Nobuyuki; Koshio, Yusuke; Vagins, Mark R.
2015-10-01
The next time a core-collapse supernova (SN) explodes in our galaxy, various detectors will be ready and waiting to detect its emissions of gravitational waves (GWs) and neutrinos. Current numerical simulations have successfully introduced multi-dimensional effects to produce exploding SN models, but thus far the explosion mechanism is not well understood. In this paper, we focus on an investigation of progenitor core rotation via comparison of the start time of GW emission and that of the neutronization burst. The GW and neutrino detectors are assumed to be, respectively, the KAGRA detector and a co-located gadolinium-loaded water Cherenkov detector, either EGADS or GADZOOKS!. Our detection simulation studies show that for a nearby SN (0.2 kpc) we can confirm the lack of core rotation close to 100% of the time, and the presence of core rotation about 90% of the time. Using this approach there is also the potential to confirm rotation for considerably more distant Milky Way SN explosions.
NASA Astrophysics Data System (ADS)
Bryan, Sean; Ade, Peter; Amiri, Mandana; Benton, Steven; Bihary, Richard; Bock, James; Bond, J. Richard; Chiang, H. Cynthia; Contaldi, Carlo; Crill, Brendan; Dore, Olivier; Elder, Benjamin; Filippini, Jeffrey; Fraisse, Aurelien; Gambrel, Anne; Gandilo, Natalie; Gudmundsson, Jon; Hasselfield, Matthew; Halpern, Mark; Hilton, Gene; Holmes, Warren; Hristov, Viktor; Irwin, Kent; Jones, William; Kermish, Zigmund; Lawrie, Craig; MacTavish, Carrie; Mason, Peter; Megerian, Krikor; Moncelsi, Lorenzo; Montroy, Thomas; Morford, Tracy; Nagy, Johanna; Netterfield, C. Barth; Padilla, Ivan; Rahlin, Alexandra S.; Reintsema, Carl; Riley, Daniel C.; Ruhl, John; Runyan, Marcus; Saliwanchik, Benjamin; Shariff, Jamil; Soler, Juan; Trangsrud, Amy; Tucker, Carole; Tucker, Rebecca; Turner, Anthony; Wen, Shyang; Wiebe, Donald; Young, Edward
2016-01-01
We describe the cryogenic half-wave plate rotation mechanisms built for and used in Spider, a polarization-sensitive balloon-borne telescope array that observed the cosmic microwave background at 95 GHz and 150 GHz during a stratospheric balloon flight from Antarctica in January 2015. The mechanisms operate at liquid helium temperature in flight. A three-point contact design keeps the mechanical bearings relatively small but allows for a large (305 mm) diameter clear aperture. A worm gear driven by a cryogenic stepper motor allows for precise positioning and prevents undesired rotation when the motors are depowered. A custom-built optical encoder system monitors the bearing angle to an absolute accuracy of ±0.1∘. The system performed well in Spider during its successful 16 day flight.
Bryan, Sean; Ade, Peter; Amiri, Mandana; Benton, Steven; Bihary, Richard; Bock, James; Bond, J Richard; Chiang, H Cynthia; Contaldi, Carlo; Crill, Brendan; Dore, Olivier; Elder, Benjamin; Filippini, Jeffrey; Fraisse, Aurelien; Gambrel, Anne; Gandilo, Natalie; Gudmundsson, Jon; Hasselfield, Matthew; Halpern, Mark; Hilton, Gene; Holmes, Warren; Hristov, Viktor; Irwin, Kent; Jones, William; Kermish, Zigmund; Lawrie, Craig; MacTavish, Carrie; Mason, Peter; Megerian, Krikor; Moncelsi, Lorenzo; Montroy, Thomas; Morford, Tracy; Nagy, Johanna; Netterfield, C Barth; Padilla, Ivan; Rahlin, Alexandra S; Reintsema, Carl; Riley, Daniel C; Ruhl, John; Runyan, Marcus; Saliwanchik, Benjamin; Shariff, Jamil; Soler, Juan; Trangsrud, Amy; Tucker, Carole; Tucker, Rebecca; Turner, Anthony; Wen, Shyang; Wiebe, Donald; Young, Edward
2016-01-01
We describe the cryogenic half-wave plate rotation mechanisms built for and used in Spider, a polarization-sensitive balloon-borne telescope array that observed the cosmic microwave background at 95 GHz and 150 GHz during a stratospheric balloon flight from Antarctica in January 2015. The mechanisms operate at liquid helium temperature in flight. A three-point contact design keeps the mechanical bearings relatively small but allows for a large (305 mm) diameter clear aperture. A worm gear driven by a cryogenic stepper motor allows for precise positioning and prevents undesired rotation when the motors are depowered. A custom-built optical encoder system monitors the bearing angle to an absolute accuracy of ±0.1(∘). The system performed well in Spider during its successful 16 day flight. PMID:26827333
NASA Technical Reports Server (NTRS)
Hung, R. J.; Lee, C. C.; Leslie, F. W.
1991-01-01
The dynamical behavior of fluids, in particular the effect of surface tension on partially-filled rotating fluids, in a full-scale Gravity Probe-B Spacecraft propellant dewar tank imposed by various frequencies of gravity jitters have been investigated. Results show that fluid stress distribution exerted on the outer and inner walls of rotating dewar are closely related to the characteristics of slosh waves excited on the liquid-vapor interface in the rotating dewar tank. This can provide a set of tool for the spacecraft dynamic control leading toward the control of spacecraft unbalance caused by the uneven fluid stress distribution due to slosh wave excitations.
NASA Astrophysics Data System (ADS)
Guenel, M.; Baruteau, C.; Mathis, S.; Rieutord, M.
2016-05-01
Context. Star-planet tidal interactions may result in the excitation of inertial waves in the convective region of stars. In low-mass stars, their dissipation plays a prominent role in the long-term orbital evolution of short-period planets. Turbulent convection can sustain differential rotation in their envelopes with an equatorial acceleration (as in the Sun) or deceleration, which can modify the propagation properties of the waves. Aims: We explore in this first paper the general propagation properties of free linear inertial waves in a differentially rotating homogeneous fluid inside a spherical shell. We assume that the angular velocity background flow depends on the latitudinal coordinate alone, close to what is expected in the external convective envelope of low-mass stars. Methods: We use an analytical approach in the inviscid case to get the dispersion relation, from which we compute the characteristic trajectories along which energy propagates. This allows us to study the existence of attractor cycles and infer the different families of inertial modes. We also use high-resolution numerical calculations based on a spectral method for the viscous problem. Results: We find that modes that propagate in the whole shell (D modes) behave the same way as with solid-body rotation. However, another family of inertial modes exists (DT modes), which can only propagate in a restricted part of the convective zone. Our study shows that they are less common than D modes and that the characteristic rays and shear layers often focus towards a wedge - or point-like attractor. More importantly, we find that for non-axisymmetric oscillation modes, shear layers may cross a corotation resonance with a local accumulation of kinetic energy. Their damping rate scales very differently from the value we obtain for standard D modes, and we show an example where it is independent of viscosity (Ekman number) in the astrophysical regime in which it is small.
NASA Astrophysics Data System (ADS)
Guenel, M.; Baruteau, C.; Mathis, S.; Rieutord, M.
2016-04-01
Context. Star-planet tidal interactions may result in the excitation of inertial waves in the convective region of stars. In low-mass stars, their dissipation plays a prominent role in the long-term orbital evolution of short-period planets. Turbulent convection can sustain differential rotation in their envelopes with an equatorial acceleration (as in the Sun) or deceleration, which can modify the propagation properties of the waves. Aims: We explore in this first paper the general propagation properties of free linear inertial waves in a differentially rotating homogeneous fluid inside a spherical shell. We assume that the angular velocity background flow depends on the latitudinal coordinate alone, close to what is expected in the external convective envelope of low-mass stars. Methods: We use an analytical approach in the inviscid case to get the dispersion relation, from which we compute the characteristic trajectories along which energy propagates. This allows us to study the existence of attractor cycles and infer the different families of inertial modes. We also use high-resolution numerical calculations based on a spectral method for the viscous problem. Results: We find that modes that propagate in the whole shell (D modes) behave the same way as with solid-body rotation. However, another family of inertial modes exists (DT modes), which can only propagate in a restricted part of the convective zone. Our study shows that they are less common than D modes and that the characteristic rays and shear layers often focus towards a wedge - or point-like attractor. More importantly, we find that for non-axisymmetric oscillation modes, shear layers may cross a corotation resonance with a local accumulation of kinetic energy. Their damping rate scales very differently from the value we obtain for standard D modes, and we show an example where it is independent of viscosity (Ekman number) in the astrophysical regime in which it is small.
Mushtaq, A.; Shah, H.A.
2005-07-15
The purpose of this work is to investigate the linear and nonlinear properties of the ion-acoustic waves (IAW), propagating obliquely to an external magnetic field in a weakly relativistic, rotating, and magnetized electron-positron-ion plasma. The Zakharov-Kuznetsov equation is derived by employing the reductive perturbation technique for this wave in the nonlinear regime. This equation admits the solitary wave solution. The amplitude and width of this solitary wave have been discussed with the effects of obliqueness, relativity, ion temperature, positron concentration, magnetic field, and rotation of the plasma and it is observed that for IAW these parameters affect the propagation properties of solitary waves and these plasmas behave differently from the simple electron-ion plasmas. Likewise, the current density and electric field of these waves are investigated for their dependence on the above-mentioned parameters.
NASA Technical Reports Server (NTRS)
Neugebauer, M.; Buti, B.
1990-01-01
Results are presented of a study designed to confirm the suspected relation between Alfven solitons (steepened Afven waves) and rotational discontinuities (RDs) in the solar wind. The ISEE 3 data were used to search for the predicted correlations between the beta value of plasma, the sense of polarization of the discontinuity, and changes of the magnetic field strength and plasma density across the discontinuity. No statistically significant evidence was found for the evolution of RDs from Alfven solitons. A possibility is suggested that the observations made could have been far from the regions in which the RDs were formed.
Sebek, Michael; Tönjes, Ralf; Kiss, István Z
2016-02-12
We perform experiments and phase model simulations with a ring network of oscillatory electrochemical reactions to explore the effect of random connections and nonisochronicity of the interactions on the pattern formation. A few additional links facilitate the emergence of the fully synchronized state. With larger nonisochronicity, complex rotating waves or persistent irregular phase dynamics can derail the convergence to global synchronization. The observed long transients of irregular phase dynamics exemplify the possibility of a sudden onset of hypersynchronous behavior without any external stimulus or network reorganization. PMID:26919024
Müller, Tobias M; Gurevich, Boris
2005-04-01
An important dissipation mechanism for waves in randomly inhomogeneous poroelastic media is the effect of wave-induced fluid flow. In the framework of Biot's theory of poroelasticity, this mechanism can be understood as scattering from fast into slow compressional waves. To describe this conversion scattering effect in poroelastic random media, the dynamic characteristics of the coherent wavefield using the theory of statistical wave propagation are analyzed. In particular, the method of statistical smoothing is applied to Biot's equations of poroelasticity. Within the accuracy of the first-order statistical smoothing an effective wave number of the coherent field, which accounts for the effect of wave-induced flow, is derived. This wave number is complex and involves an integral over the correlation function of the medium's fluctuations. It is shown that the known one-dimensional (1-D) result can be obtained as a special case of the present 3-D theory. The expression for the effective wave number allows to derive a model for elastic attenuation and dispersion due to wave-induced fluid flow. These wavefield attributes are analyzed in a companion paper. PMID:15898626
NASA Astrophysics Data System (ADS)
Porter, Edward K.
2005-09-01
In this study, we apply post-Newtonian (T-approximants) and resummed post-Newtonian (P-approximants) to the case of a test particle in equatorial orbit around a Kerr black hole. We compare the two approximants by measuring their effectualness (i.e., larger overlaps with the exact signal) and faithfulness (i.e., smaller biases while measuring the parameters of the signal) with the exact (numerical) waveforms. We find that in the case of prograde orbits, T-approximant templates obtain an effectualness of ~0.99 for spins q <= 0.75. For 0.75 < q < 0.95, the effectualness drops to about 0.82. The P-approximants achieve effectualness of >0.99 for all spins up to q = 0.95. The bias in the estimation of parameters is much lower in the case of P-approximants than T-approximants. We find that P-approximants are both effectual and faithful and should be more effective than T-approximants as a detection template family when q > 0. For q < 0, both T- and P-approximants perform equally well so that either of them could be used as a detection template family. However, for parameter estimation, the P-approximant templates still outperform the T-approximants.
The Millimeter-Wave Spectrum of Methacrolein. Torsion-Rotation Effects in the Excited States
NASA Astrophysics Data System (ADS)
Zakharenko, Olena; Motiyenko, R. A.; Aviles Moreno, Juan-Ramon; Huet, T. R.
2015-06-01
Last year we reported the analysis of the rotational spectrum of s-trans conformer of methacrolein CH2=C(CH3)CHO in the ground vibrational state. In this talk we report the study of its low lying excited vibrational states. The study is based on room-temperature absorption spectra of methacrolein recorded in the frequency range 150 - 465 GHz using the spectrometer in Lille. The new results include assignment of the first excited torsional state (131 cm-1), and the joint analysis of the vt = 0 and vt = 1 states, that allowed us to improve the model in the frame of Rho-Axis-Method (RAM) Hamiltonian and to remove some strong correlations between parameters. Also we assigned the first excited vibrational state of the skeletal torsion mode (170 cm-1). The inverse sequence of A and E tunneling substates as well as anomalous A-E splittings observed for the rotational lines of vsk = 1 state clearly indicate a coupling between methyl torsion and skeletal torsion. However we were able to fit within experimental accuracy the rotational lines of vsk = 1 state using the RAM Hamiltonian. Because of the inversion of the A and E tunneling substates the rotational lines of the vsk = 1 states were assumed to belong to a virtual first excited torsional state. Finally, we assigned several low-Ka rotational transitions of the excited vibrational states above 200 cm-1 but their analysis is complicated by different rotation-vibration interactions. In particular there is an evidence of the Fermi-type resonance between the second excited torsional state and the first excited state of the in-plane skeletal bending mode (265 cm-1). Support from the French Laboratoire d'Excellence CaPPA (Chemical and Physical Properties of the Atmosphere) through contract ANR-10-LABX-0005 of the Programme d'Investissements d'Avenir is acknowledged. Zakharenko O. et al., 69th ISMS, 2014, TI01
Stability and slosh wave for rotating bubble due to gravity-jitters under microgravity
NASA Technical Reports Server (NTRS)
Hung, R. J.; Lee, C. C.; Leslie, F. W.
1990-01-01
Time-dependent fluid behaviors in microgravity environments are examined with particular attention given to the dynamics of bubble configurations. The initial bubble profiles, computed from the steady-state formulation, are used as the initial input for the time dependent computation. The parameters considered are liquid density and its kinematic viscosity, gas density and its kinematic viscosity, surface tension coefficient, angular velocity, and gravity environment. This computer algorithm can be used to simulate the fluid behavior in a microgravity environment, in particular the excitation of slosh waves due to different frequencies of gravity jitters. Results show that lower-frequency gravity jitters excite slosh waves with a higher ratio of maximum amplitude to wave length than that of the slosh waves generated by the higher frequency gravity jitters.
Hamiltonian Formulation for Wave-Current Interactions in Stratified Rotational Flows
NASA Astrophysics Data System (ADS)
Constantin, A.; Ivanov, R. I.; Martin, C.-I.
2016-09-01
We show that the Hamiltonian framework permits an elegant formulation of the nonlinear governing equations for the coupling between internal and surface waves in stratified water flows with piecewise constant vorticity.
NASA Astrophysics Data System (ADS)
Miller, B.; O'Shaughnessy, R.; Littenberg, T. B.; Farr, B.
2015-08-01
Reliable low-latency gravitational wave parameter estimation is essential to target limited electromagnetic follow-up facilities toward astrophysically interesting and electromagnetically relevant sources of gravitational waves. In this study, we examine the trade-off between speed and accuracy. Specifically, we estimate the astrophysical relevance of systematic errors in the posterior parameter distributions derived using a fast-but-approximate waveform model, SpinTaylorF2 (stf2), in parameter estimation with lalinference_mcmc. Though efficient, the stf2 approximation to compact binary inspiral employs approximate kinematics (e.g., a single spin) and an approximate waveform (e.g., frequency domain versus time domain). More broadly, using a large astrophysically motivated population of generic compact binary merger signals, we report on the effectualness and limitations of this single-spin approximation as a method to infer parameters of generic compact binary sources. For most low-mass compact binary sources, we find that the stf2 approximation estimates compact binary parameters with biases comparable to systematic uncertainties in the waveform. We illustrate by example the effect these systematic errors have on posterior probabilities most relevant to low-latency electromagnetic follow-up: whether the secondary has a mass consistent with a neutron star (NS); whether the masses, spins, and orbit are consistent with that neutron star's tidal disruption; and whether the binary's angular momentum axis is oriented along the line of sight.
Effect of rotational wave packets on the stimulated emission of nitrogen with light filament
NASA Astrophysics Data System (ADS)
Arissian, Ladan; Kamer, Brian; Rasoulof, Amin
2016-06-01
We measure forward emission of the nitrogen ion excited by light filaments at 800 nm. The radiation strongly depends on light polarization and orbital angular momentum. In all cases the rotational distribution of nitrogen molecules plays an essential role in the 428 nm stimulated emission.
Hall effects on the Walén relation in rotational discontinuities and Alfvén waves
NASA Astrophysics Data System (ADS)
Wu, B. H.; Lee, L. C.
2000-08-01
For Alfvénic fluctuations in magnetohydrodynamics (MHD) the perturbed transverse velocity Vt and magnetic field Bt can be related by the Walén relation, Vt = ±Bt/(μ0ρ)1/2 ≡;±VAt, where ρ is the plasma density, VAt is the transverse Alfvén velocity, and the plus (minus) sign is for antiparallel (parallel) propagation. However, observations of Vt and Bt for Alfvén waves and rotational discontinuities in the solar wind and at the magnetopause showed an obvious deviation from the relation. In this paper, modifications of the Walén relation for linear and nonlinear Alfvén waves and rotational discontinuities (RDs) are examined in the Hall-MHD formulation. Let Vit (≈ Vt) be the transverse ion velocity and Vet be the transverse electron velocity. It is found that Vit = ±Bt(z)/(μ0ρ1)1/2 = ±(ρ(z)/ρ1)1/2 VAt(z) and Vet = ±(ρ1/μ0)1/2Bt(z)/ρ(z) = ±(ρ1/ρ(z))1/2 VAt(z)for RDs in Hall-MHD, where ρ1 is the upstream plasma density. The ion and electron Walén ratios are defined as Ai = Vit/VAt and Ae = Vet/VAt, respectively. It is found in Hall-MHD that ?, AiAe = 1 and Ai < 1 (Ai > 1) for Alfvén waves and RDs with right-hand (left-hand) polarization. The Hall dispersive effect may modify the ion Walén ratio by ΔAi≈±0.14 for the magnetopause RDs and by ΔAi≈±0.07 for the interplanetary RDs.
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.
Unpinning of rotating spiral waves in cardiac tissues by circularly polarized electric fields
NASA Astrophysics Data System (ADS)
Feng, Xia; Gao, Xiang; Pan, De-Bei; Li, Bing-Wei; Zhang, Hong
2014-04-01
Spiral waves anchored to obstacles in cardiac tissues may cause lethal arrhythmia. To unpin these anchored spirals, comparing to high-voltage side-effect traditional therapies, wave emission from heterogeneities (WEH) induced by the uniform electric field (UEF) has provided a low-voltage alternative. Here we provide a new approach using WEH induced by the circularly polarized electric field (CPEF), which has higher success rate and larger application scope than UEF, even with a lower voltage. And we also study the distribution of the membrane potential near an obstacle induced by CPEF to analyze its mechanism of unpinning. We hope this promising approach may provide a better alternative to terminate arrhythmia.
Stauber, Douglas A.
1985-01-01
A Born approximation is used to linearize the relationship, in the horizontal-wavenumber and frequency domains, between lateral perturbations of modulus and density in a layered half-space and the acoustic wave field observed at the surface when a plane wave is incident from below. The resulting equations can be used to perform a linear inversion of observed acoustic wave fields to obtain lateral perturbations in modulus and density. Since modulus and density effects are separated, gravity observations can be included in the inversion procedure without any assumptions about the relationship between density and acoustic velocity. Tests with synthetic data sets reveal that the inversion method gives useful results when the spatial scales of the inhomogeneities are smaller than several acoustic wavelengths. Refs.
The Dissipation Range in Rotating Turbulence
NASA Technical Reports Server (NTRS)
Rubinstein, Robert; Zhou, Ye
1999-01-01
The dissipation range energy balance of the direct interaction approximation is applied to rotating turbulence when rotation effects persist well into the dissipation range. Assuming that RoRe (exp 1/2) is much less than 1 and that three-wave interactions are dominant, the dissipation range is found to be concentrated in the wavevector plane perpendicular to the rotation axis. This conclusion is consistent with previous analyses of inertial range energy transfer in rotating turbulence, which predict the accumulation of energy in those scales.
NASA Technical Reports Server (NTRS)
Glytsis, Elias N.; Brundrett, David L.; Gaylord, Thomas K.
1993-01-01
A review of the rigorous coupled-wave analysis as applied to the diffraction of electro-magnetic waves by gratings is presented. The analysis is valid for any polarization, angle of incidence, and conical diffraction. Cascaded and/or multiplexed gratings as well as material anisotropy can be incorporated under the same formalism. Small period rectangular groove gratings can also be modeled using approximately equivalent uniaxial homogeneous layers (effective media). The ordinary and extraordinary refractive indices of these layers depend on the gratings filling factor, the refractive indices of the substrate and superstrate, and the ratio of the freespace wavelength to grating period. Comparisons of the homogeneous effective medium approximations with the rigorous coupled-wave analysis are presented. Antireflection designs (single-layer or multilayer) using the effective medium models are presented and compared. These ultra-short period antireflection gratings can also be used to produce soft x-rays. Comparisons of the rigorous coupled-wave analysis with experimental results on soft x-ray generation by gratings are also included.
A solar dynamo surface wave at the interface between convection and nonuniform rotation
NASA Astrophysics Data System (ADS)
Parker, E. N.
1993-05-01
A simple dynamo surface wave is presented to illustrate the basic principles of a dynamo operating in the thin layer of shear and suppressed eddy diffusion beneath the cyclonic convection in the convection zone of the sun. It is shown that the restriction of the shear delta(Omega)/delta(r) to a region below the convective zone provides the basic mode with a greatly reduced turbulent diffusion coefficient in the region of strong azimuthal field. The dynamo takes on the character of a surface wave tied to the lower surface z = 0 of the convective zone. There is a substantial body of evidence suggesting a fibril state for the principal flux bundles beneath the surface of the sun, with fundamental implications for the solar dynamo.
NASA Technical Reports Server (NTRS)
Lawless, Patrick B.; Fleeter, Sanford
1993-01-01
A simple model for the stability zones of a low speed centrifugal compressor is developed, with the goal of understanding the driving mechanism for the changes in stalling behavior predicted for, and observed in, the Purdue Low Speed Centrifugal Research Compressor Facility. To this end, earlier analyses of rotating stall suppression in centrifugal compressors are presented in a reduced form that preserves the essential parameters of the model that affect the stalling behavior of the compressor. The model is then used to illuminate the relationship between compressor geometry, expected mode shape, and regions of amplification for weak waves which are indicative of the susceptibility of the system to rotating stall. The results demonstrate that increasing the stagger angle of the diffuser vanes, and consequently the diffusion path length, results in the compressor moving towards a condition where higher-order spatial modes are excited during stall initiation. Similarly, flow acceleration in the diffuser section caused by an increase in the number of diffuser vanes also results in the excitation of higher modes.
NASA Technical Reports Server (NTRS)
Cicon, D. E.; Sofrin, T. G.
1995-01-01
This report describes a procedure for enhancing the use of the basic rotating microphone system so as to determine the forward propagating mode components of the acoustic field in the inlet duct at the microphone plane in order to predict more accurate far-field radiation patterns. In addition, a modification was developed to obtain, from the same microphone readings, the forward acoustic modes generated at the fan face, which is generally some distance downstream of the microphone plane. Both these procedures employ computer-simulated calibrations of sound propagation in the inlet duct, based upon the current radiation code. These enhancement procedures were applied to previously obtained rotating microphone data for the 17-inch ADP fan. The forward mode components at the microphone plane were obtained and were used to compute corresponding far-field directivities. The second main task of the program involved finding the forward wave modes generated at the fan face in terms of the same total radial mode structure measured at the microphone plane. To obtain satisfactory results with the ADP geometry it was necessary to limit consideration to the propagating modes. Sensitivity studies were also conducted to establish guidelines for use in other fan configurations.
Chemical Analysis of Exhaled Human Breath Using High Resolution Mm-Wave Rotational Spectra
NASA Astrophysics Data System (ADS)
Guo, Tianle; Branco, Daniela; Thomas, Jessica; Medvedev, Ivan; Dolson, David; Nam, Hyun-Joo; O, Kenneth
2014-06-01
High resolution rotational spectroscopy enables chemical sensors that are both sensitive and highly specific, which is well suited for analysis of expired human breath. We have previously reported on detection of breath ethanol, methanol, acetone, and acetaldehyde using THz sensors. This paper will outline our present efforts in this area, with specific focus on our ongoing quest to correlate levels of blood glucose with concentrations of a few breath chemicals known to be affected by elevated blood sugar levels. Prospects, challenges and future plans will be outlined and discussed. Fosnight, A.M., B.L. Moran, and I.R. Medvedev, Chemical analysis of exhaled human breath using a terahertz spectroscopic approach. Applied Physics Letters, 2013. 103(13): p. 133703-5.
Calculator Function Approximation.
ERIC Educational Resources Information Center
Schelin, Charles W.
1983-01-01
The general algorithm used in most hand calculators to approximate elementary functions is discussed. Comments on tabular function values and on computer function evaluation are given first; then the CORDIC (Coordinate Rotation Digital Computer) scheme is described. (MNS)
NASA Astrophysics Data System (ADS)
Amaro-Seoane, P.; Eichhorn, C.; Porter, E. K.; Spurzem, R.
2010-02-01
The dynamical evolution of binaries of intermediate-mass black holes (IMBHs; massive black holes with a mass ranging between 102 and 104Msolar) in stellar clusters has recently received an increasing amount of attention. This is at least partially due to the fact that if the binary is hard enough to evolve to the phase at which it will start emitting gravitational waves (GWs) efficiently, there is a good probability that it will be detectable by future space-borne detectors like Laser Interferometer Space Antenna. We study this evolution in the presence of rotation in the cluster by carrying out a series of simulations of an equal-mass binary of IMBHs embedded in a stellar distribution with different rotational parameters. The survey indicates that eccentricities and inclinations are primarily determined by the initial conditions of the IMBHs and the influence of dynamical friction, even though they are finally perturbed by the scattering of field stars. In particular, the eccentricity is strongly connected to the initial IMBHs velocities, and values of ~0.7 up to 0.9 are reached for low initial velocities, while almost circular orbits result if the initial velocities are increased. Evidence suggests a dependency of the eccentricity on the rotation parameter. We found only weak changes in the inclination, with slight variations of the orientation of the angular momentum vector of the binary. Counter-rotation simulations yield remarkably different results in eccentricity. A Monte Carlo study indicates that these sources will be detectable by a detector such as Laser Interferometer Space Antenna (LISA) with median signal-to-noise ratios (SNR) of between 10 and 20 over a three-year period, although some events had SNR of 300 or greater. Furthermore, one should also be able to estimate the chirp mass with median fractional errors of 10-4, reduced mass of the order of 10-3 and luminosity distance of the order of 10-1. Finally, these sources will have a median angular
Stability properties of a rotating astigmatic optical cavity
NASA Astrophysics Data System (ADS)
Habraken, Steven J. M.; Nienhuis, Gerard
2009-02-01
We study the effects of rotation on the stability properties of an astigmatic two-mirror cavity. We show that rotation can both stabilize and destabilize a cavity and investigate the effects of such a rotationally-induced transition on the spatial structure and the orbital angular momentum of the cavity modes. Our method relies on the connection between ray and wave optics and is exact within the time-dependent paraxial approximation.
NASA Astrophysics Data System (ADS)
Uberna, Radoslaw; Khalil, Munira; Williams, Richard M.; Papanikolas, John M.; Leone, Stephen R.
1998-06-01
Femtosecond laser pulse amplitude/phase masking techniques are employed to control the formation and detection of rotational wave packets in the electronic E 1Σg+ state of lithium dimer. The wave packets are prepared by coherent excitation of rovibronic E 1Σg+(νE,JE) states of Li2 from a single intermediate state, A 1Σu+(νA=11,JA=28), and probed by time-resolved photoionization. In the detection step, the wave packet is projected onto the X 2Σg+ state of Li2+. New resonance structure in the X 2Σu+ ionic state continuum is obtained by measuring the wave packet signal modulation amplitude as a function of the frequencies removed from the spectrally dispersed probe pulse by insertion of a wire mask in a single-grating pulse shaper. A split glass phase mask inserted into the pulse shaper is used to produce step function changes in the spectral phase of the pulse. The phase relation among the wave packet states is varied by changing the relative phases of spectral components in the pump pulse and is monitored by measuring the changes in the phase of the rotational wave packet recurrences using an unmodified probe pulse. By altering the relative phases among the wave packet components, the spatial distribution of the initial wave packet probability density is varied, resulting in phase-dependent "alignment" of the probability density in angular space. Phase changes in the signal recurrences are also observed when a phase modified pulse is used in the wave packet detection step after wave packet preparation with an unmodified pulse. The formation and detection of the wave packets is discussed in terms of quantum interference between different excitation routes. The relative phase factors encoded in a single optical pulse (pump or probe) are transferred into the interference term of the measured signal through the molecule-photon interaction.
Supersymmetric configurations in the rotating D1-D5 system andpp-waves
NASA Astrophysics Data System (ADS)
Maoz, Liat
Two families of supersymmetric configurations are considered. One is the 1/4 supersymmetric D1--D5 system with angular momentum, and the other is a family of pp-waves of type IIB string theory with some supersymmetry. In the first part of the thesis some configurations of the D1--D5 system are examined which give conical singularities in AdS 3 as their near horizon limit. It is shown that they can be made non-singular by adding angular momentum to the brane system. The smooth asymptotically flat solutions constructed this way are used to obtain global AdS 3 as the near horizon geometry. Using the relation of the D1--D5 system to the oscillating string, a large family of supergravity solutions is constructed which describe BPS excitations on AdS3 x S 3 with angular momentum on S3. These solutions take into account the full back reaction on the metric, and can be viewed as Kaluza-Klein monopole "supertubes", which are completely non-singular geometries. The different chiral primaries of the dual CFT are identified with these different supergravity solutions. This part is adapted from the papers [1], [2]. In its second part, a general class of supersymmetric pp-wave solutions of type IIB string theory is constructed, such that the superstring worldsheet action in light cone gauge is that of an interacting massive field theory. It is shown that when the light cone Lagrangian has (2.2) supersymmetry, one can find backgrounds that lead to arbitrary superpotentials on the worldsheet. Both flat and curved transverse spaces are considered. In particular, the background giving rise to the N = 2 sine Gordon theory on the worldsheet is analyzed. Massive mirror symmetry relates it to the deformed CP1 model (or sausage model) which seems to elude a purely supergravity target space interpretation. These are results which appeared in the paper [3].
NASA Technical Reports Server (NTRS)
Parrett, A. V.; Eversman, W.
1984-01-01
The problem of acoustic radiation from turbofan engine inlets in flow has not lent itself fully to analysis by numerical means because of the large domains and high frequencies involved. The current work has extended the use of finite elements and wave envelope elements, elements which simulate decay and wavelike behaviour in their interpolation functions, from the no-flow case in which they have been proven, to cases incorporating mean flow. By employing an irrotational mean flow assumption, the acoustics problem has been posed in an axisymmetric formulation in terms of acoustic velocity potential, thus minimizing computer solution storage requirements. The results obtained from the numerical procedures agree well with known analytical solutions, static experimental jet engines inflow data, and also with flight test results.
NASA Technical Reports Server (NTRS)
Draine, B. T.; Goodman, Jeremy
1993-01-01
We derive the dispersion relation for electromagnetic waves propagating on a lattice of polarizable points. From this dispersion relation we obtain a prescription for choosing dipole polarizabilities so that an infinite lattice with finite lattice spacing will mimic a continuum with dielectric constant. The discrete dipole approximation is used to calculate scattering and absorption by a finite target by replacing the target with an array of point dipoles. We compare different prescriptions for determining the dipole polarizabilities. We show that the most accurate results are obtained when the lattice dispersion relation is used to set the polarizabilities.
NASA Astrophysics Data System (ADS)
Adamson, P.
The propagation of s- and p-polarised electromagnetic plane waves in a N-layer system of anisotropic films on isotropic and homogeneous absorbing substrate is investigated in the long-wavelength limit. The analytical expressions are obtained for the reflection (transmission) coefficients and ellipsometric angles of an anisotropic multilayer system. All analytical results are correlated with the numerical solution of the reflection problem on the basis of rigorous electromagnetic theory for anisotropic layered systemsE The possibilities of using obtained approximate formulae for resolving the inverse problem for ultrathin anisotropic dielectric films upon absorbing substrates are discussed.
NASA Astrophysics Data System (ADS)
Adamson, P.
2010-07-01
The reflection of s- and p-polarised electromagnetic plane waves from an N-layer system of anisotropic dielectric films upon transparent homogeneous substrate is investigated in the long-wavelength approximation. The analytical expressions are obtained for the amplitude reflection (transmission) coefficients, reflectances (transmittances), and ellipsometric angles of an anisotropic multilayer thin-film system. All analytical results are in agreement with the numerical solution of the reflection problem for anisotropic stratified medium. The possibilities of using obtained expressions for resolving the inverse problem for ultrathin anisotropic films upon isotropic substrates are discussed.
NASA Astrophysics Data System (ADS)
Aulenbacher, Uwe; Rech, Klaus; Sedlmeier, Johannes; Pratisto, Hans; Wellig, Peter
2014-10-01
Ground based millimeter wave radar sensors offer the potential for a weather-independent automatic ground surveillance at day and night, e.g. for camp protection applications. The basic principle and the experimental verification of a radar system concept is described, which by means of an extreme off-axis positioning of the antenna(s) combines azimuthal mechanical beam steering with the formation of a circular-arc shaped synthetic aperture (SA). In automatic ground surveillance the function of search and detection of moving ground targets is performed by means of the conventional mechanical scan mode. The rotated antenna structure designed as a small array with two or more RX antenna elements with simultaneous receiver chains allows to instantaneous track multiple moving targets (monopulse principle). The simultaneously operated SAR mode yields areal images of the distribution of stationary scatterers. For ground surveillance application this SAR mode is best suited for identifying possible threats by means of change detection. The feasibility of this concept was tested by means of an experimental radar system comprising of a 94 GHz (W band) FM-CW module with 1 GHz bandwidth and two RX antennas with parallel receiver channels, placed off-axis at a rotating platform. SAR mode and search/track mode were tested during an outdoor measurement campaign. The scenery of two persons walking along a road and partially through forest served as test for the capability to track multiple moving targets. For SAR mode verification an image of the area composed of roads, grassland, woodland and several man-made objects was reconstructed from the measured data.
Gao, Q. D.; Budny, R. V.
2015-03-15
By using gyro-Landau fluid transport model (GLF23), time-dependent integrated modeling is carried out using TRANSP to explore the dynamic process of internal transport barrier (ITB) formation in the neutral beam heating discharges. When the current profile is controlled by LHCD (lower hybrid current drive), with appropriate neutral beam injection, the nonlinear interplay between the transport determined gradients in the plasma temperature (T{sub i,e}) and toroidal velocity (V{sub ϕ}) and the E×B flow shear (including q-profile) produces transport bifurcations, generating spontaneously a stepwise growing ITB. In the discharge, the constraints imposed by the wave propagation condition causes interplay of the LH driven current distribution with the plasma configuration modification, which constitutes non-linearity in the LH wave deposition. The non-linear effects cause bifurcation in LHCD, generating two distinct quasi-stationary reversed magnetic shear configurations. The change of current profile during the transition period between the two quasi-stationary states results in increase of the E×B shearing flow arising from toroidal rotation. The turbulence transport suppression by sheared E×B flow during the ITB development is analysed, and the temporal evolution of some parameters characterized the plasma confinement is examined. Ample evidence shows that onset of the ITB development is correlated with the enhancement of E×B shearing rate caused by the bifurcation in LHCD. It is suggested that the ITB triggering is associated with the non-linear effects of the LH power deposition.
Zhang, Zhaojun; Zhang, Dong H.
2014-10-14
Seven-dimensional time-dependent wave packet calculations have been carried out for the title reaction to obtain reaction probabilities and cross sections for CHD{sub 3} in J{sub 0} = 1, 2 rotationally excited initial states with k{sub 0} = 0 − J{sub 0} (the projection of CHD{sub 3} rotational angular momentum on its C{sub 3} axis). Under the centrifugal sudden (CS) approximation, the initial states with the projection of the total angular momentum on the body fixed axis (K{sub 0}) equal to k{sub 0} are found to be much more reactive, indicating strong dependence of reactivity on the orientation of the reagent CHD{sub 3} with respect to the relative velocity between the reagents H and CHD{sub 3}. However, at the coupled-channel (CC) level this dependence becomes much weak although in general the K{sub 0} specified cross sections for the K{sub 0} = k{sub 0} initial states remain primary to the overall cross sections, implying the Coriolis coupling is important to the dynamics of the reaction. The calculated CS and CC integral cross sections obtained after K{sub 0} averaging for the J{sub 0} = 1, 2 initial states with all different k{sub 0} are essentially identical to the corresponding CS and CC results for the J{sub 0} = 0 initial state, meaning that the initial rotational excitation of CHD{sub 3} up to J{sub 0} = 2, regardless of its initial k{sub 0}, does not have any effect on the total cross sections for the title reaction, and the errors introduced by the CS approximation on integral cross sections for the rotationally excited J{sub 0} = 1, 2 initial states are the same as those for the J{sub 0} = 0 initial state.
NASA Astrophysics Data System (ADS)
Harms, Enno; Lukes-Gerakopoulos, Georgios; Bernuzzi, Sebastiano; Nagar, Alessandro
2016-02-01
We present a new computation of the asymptotic gravitational wave energy fluxes emitted by a spinning particle in circular equatorial orbits about a Kerr black hole. The particle dynamics is computed in the pole-dipole approximation, solving the Mathisson-Papapetrou equations with the Tulczyjew spin-supplementary-condition. The fluxes are computed, for the first time, by solving the 2 +1 Teukolsky equation in the time-domain using hyperboloidal and horizon-penetrating coordinates. Denoting by M the black hole mass and by μ the particle mass, we cover dimensionless background spins a /M =(0 ,±0.9 ) and dimensionless particle spins -0.9 ≤S /μ2≤+0.9 . Our results span orbits of Boyer-Lindquist coordinate radii 4 ≤r /M ≤30 ; notably, we investigate the strong-field regime, in some cases even beyond the last-stable-orbit. We compare our numerical results for the gravitational wave fluxes with the 2.5th order accurate post-Newtonian (PN) prediction obtained analytically by Tanaka et al. [Phys. Rev. D 54, 3762 (1996)]: we find an unambiguous trend of the PN-prediction toward the numerical results when r is large. At r /M =30 the fractional agreement between the full numerical flux, approximated as the sum over the modes m =1 , 2, 3, and the PN prediction is ≲0.5 % in all cases tested. This is close to our fractional numerical accuracy (˜0.2 %). For smaller radii, the agreement between the 2.5PN prediction and the numerical result progressively deteriorates, as expected. Our numerical data will be essential to develop suitably resummed expressions of PN-analytical fluxes in order to improve their accuracy in the strong-field regime.
Antonini, Fabio; Murray, Norman; Mikkola, Seppo
2014-01-20
Coalescing black hole (BH) binaries forming in the dense core of globular clusters (GCs) are expected to be one of the brightest sources of gravitational wave (GW) radiation for the next generation of ground-based laser interferometers. Favorable conditions for a merger are initiated by the Kozai resonance in which the gravitational interaction with a third distant object, typically another BH, induces quasi-periodic variations of the inner BH binary eccentricity. In this article we perform high precision three-body simulations of the long-term evolution of hierarchical BH triples and investigate the conditions that lead to the merging of the BH binary and the way it might become an observable source of GW radiation. We find that the secular orbit average treatment, which was adopted in previous works, does not reliably describe the dynamics of these systems if the binary is orbited by the outer BH on a highly inclined orbit at a moderate distance. We show that 50% of coalescing BH binaries driven by the Kozai mechanism in GCs will have eccentricities larger than 0.1, with 10% of them being extremely eccentric, (1 – e) ≲ 10{sup –4}, when they first chirp in the frequency band of ground-based laser interferometers. This implies that a large fraction of such GW sources could be missed if conventional quasi-circular templates are used for analysis of GW detector data. The efficient detection of all coalescing BH binaries in GCs will therefore require template banks of eccentric inspiral waveforms for matched-filtering and dedicated search strategies.
NASA Astrophysics Data System (ADS)
Antonini, Fabio; Murray, Norman; Mikkola, Seppo
2014-01-01
Coalescing black hole (BH) binaries forming in the dense core of globular clusters (GCs) are expected to be one of the brightest sources of gravitational wave (GW) radiation for the next generation of ground-based laser interferometers. Favorable conditions for a merger are initiated by the Kozai resonance in which the gravitational interaction with a third distant object, typically another BH, induces quasi-periodic variations of the inner BH binary eccentricity. In this article we perform high precision three-body simulations of the long-term evolution of hierarchical BH triples and investigate the conditions that lead to the merging of the BH binary and the way it might become an observable source of GW radiation. We find that the secular orbit average treatment, which was adopted in previous works, does not reliably describe the dynamics of these systems if the binary is orbited by the outer BH on a highly inclined orbit at a moderate distance. We show that 50% of coalescing BH binaries driven by the Kozai mechanism in GCs will have eccentricities larger than 0.1, with 10% of them being extremely eccentric, (1 - e) <~ 10-4, when they first chirp in the frequency band of ground-based laser interferometers. This implies that a large fraction of such GW sources could be missed if conventional quasi-circular templates are used for analysis of GW detector data. The efficient detection of all coalescing BH binaries in GCs will therefore require template banks of eccentric inspiral waveforms for matched-filtering and dedicated search strategies.
NASA Astrophysics Data System (ADS)
Wan, X.; Tse, P. W.; Xu, G. H.; Tao, T. F.; Zhang, Q.
2016-04-01
Most previous studies on nonlinear Lamb waves are conducted using mode pairs that satisfying strict phase velocity matching and non-zero power flux criteria. However, there are some limitations in existence. First, strict phase velocity matching is not existed in the whole frequency bandwidth; Second, excited center frequency is not always exactly equal to the true phase-velocity-matching frequency; Third, mode pairs are isolated and quite limited in number; Fourth, exciting a single desired primary mode is extremely difficult in practice and the received signal is quite difficult to process and interpret. And few attention has been paid to solving these shortcomings. In this paper, nonlinear S0 mode Lamb waves at low-frequency range satisfying approximate phase velocity matching is proposed for the purpose of overcoming these limitations. In analytical studies, the secondary amplitudes with the propagation distance considering the fundamental frequency, the maximum cumulative propagation distance (MCPD) with the fundamental frequency and the maximum linear cumulative propagation distance (MLCPD) using linear regression analysis are investigated. Based on analytical results, approximate phase velocity matching is quantitatively characterized as the relative phase velocity deviation less than a threshold value of 1%. Numerical studies are also conducted using tone burst as the excitation signal. The influences of center frequency and frequency bandwidth on the secondary amplitudes and MCPD are investigated. S1-S2 mode with the fundamental frequency at 1.8 MHz, the primary S0 mode at the center frequencies of 100 and 200 kHz are used respectively to calculate the ratios of nonlinear parameter of Al 6061-T6 to Al 7075-T651. The close agreement of the computed ratios to the actual value verifies the effectiveness of nonlinear S0 mode Lamb waves satisfying approximate phase velocity matching for characterizing the material nonlinearity. Moreover, the ratios derived from
NASA Astrophysics Data System (ADS)
Boss, Alan P.; Keiser, Sandra A.
2015-08-01
Both astronomical observations of the interaction of Type II supernova remnants (SNRs) with dense interstellar clouds as well as cosmochemical studies of the abundances of daughter products of short-lived radioisotopes (SLRIs) formed by supernova nucleosynthesis support the hypothesis that the Solar System's SLRIs may have been derived from a supernova. This paper continues a series devoted to examining whether or not such a shock wave could have triggered the dynamical collapse of a dense, presolar cloud core and simultaneously injected sufficient abundances of SLRIs to explain the cosmochemical evidence. Here, we examine the effects of shock waves striking clouds whose spin axes are oriented perpendicular, rather than parallel, to the direction of propagation of the shock front. The models start with 2.2 {M}⊙ cloud cores and shock speeds of 20 or 40 km s-1. Central protostars and protoplanetary disks form in all models, although with their disk spin axes aligned somewhat randomly. The disks derive most of their angular momentum not from the initial cloud rotation, but from the Rayleigh-Taylor fingers that also inject shock wave SLRIs. Injection efficiencies, fi, the fraction of the incident shock wave material injected into the collapsing cloud core, are ˜0.04-0.1 in these models, similar to when the rotation axis is parallel to the shock propagation direction. Evidently, altering the rotation axis orientation has only a minor effect on the outcome, strengthening the case for this scenario as an explanation for the Solar System's SLRIs.
NASA Astrophysics Data System (ADS)
Lee, Jongsuh; Wang, Semyung; Kindt, Peter; Pluymers, Bert; Desmet, Wim
2016-02-01
Natural frequencies, mode shapes and modal damping values are the most important parameters to describe the noise and vibration behavior of a mechanical system. For rotating machinery, however, the directivity of the propagation wave and the wave length of each mode should also be taken into account. Generally, the information on directivity and wave length is obtained on the basis of the mode shape result, which is estimated from several measurements measured at different locations. In this research, the accurate directivity and wave length results will be observed by calculating the phase difference at two different locations. The limitation of the proposed method, which arises from the difference between the assumed ring model and the real tire, will be explained, and a method to address the limitation is introduced. The proposed method is verified by applying it to experimental measurements, and a brief explanation of the obtained results is provided.
NASA Astrophysics Data System (ADS)
Tagoshi, H.; Mano, S.; Takasugi, E.
Gravitational waves from coalescing compact binaries are the most promising candidates which will be able to be detected by the near-future, ground based laser interferometric gravitational wave detectors such as LIGO, VIRGO, TAMA, GEO600 etc. The standard method to calculate inspiraling wave forms from coalescing binaries is the post-Newtonian expansion of the Einstein equations, in which the orbital velocity v of binaries is assumed to be small compared to the speed of light. Then, we calculate the post-Newtonian expansion of the gravitational wave luminosities from a test particle in circular orbit around a rotating black hole. We consider both the gravitational wave at infinity and the black hole absorption of the wave. The calculation is based on the post-Newtonian Techniques for the Teukolsky equation. This calculation is limited to cases when one star is a test particle. However, we can calculate the very high orders of the post-Newtonian expansion in this case. Then these calculation is very helpful for the more general calculations of the post-Newtonian expansion. Using the results, we discuss the convergence property of the post-Newtonian expansion. We also discuss the effects of those high order post-Newtonian effect of gravitational wave emission to the orbital evolution of coalescing compact binaries.
NASA Astrophysics Data System (ADS)
Schou, Jesper; Beck, John G.
2001-01-01
Simple convection models estimate the depth of supergranulation at approximately 15,000 km which suggests that supergranules should rotate at the rate of the plasma in the outer 2% of the Sun by radius. Previous measurements (Snodgrass & Ulrich, 1990; Beck & Schou, 2000) found that supergranules rotate significantly faster than this, with a size-dependent rotation rate. We expand on previous work and show that the torsional oscillation signal seen in the supergranules tracks that obtained for normal modes. We also find that the amplitudes and lifetimes of the supergranulation are size dependent.
NASA Technical Reports Server (NTRS)
Elleman, D. D.; Croonquist, A. P.; Wang, T. G. (Inventor)
1983-01-01
A system is described for acoustically controlled rotation of a levitated object, which avoids deformation of a levitated liquid object. Acoustic waves of the same wavelength are directed along perpendicular directions across the object, and with the relative phases of the acoustic waves repeatedly switched so that one wave alternately leads and lags the other by 90 deg. The amount of torque for rotating the object, and the direction of rotation, are controlled by controlling the proportion of time one wave leads the other and selecting which wave leads the other most of the time.
Boss, Alan P.; Keiser, Sandra A.
2014-06-10
A key test of the supernova triggering and injection hypothesis for the origin of the solar system's short-lived radioisotopes is to reproduce the inferred initial abundances of these isotopes. We present here the most detailed models to date of the shock wave triggering and injection process, where shock waves with varied properties strike fully three-dimensional, rotating, dense cloud cores. The models are calculated with the FLASH adaptive mesh hydrodynamics code. Three different outcomes can result: triggered collapse leading to fragmentation into a multiple protostar system; triggered collapse leading to a single protostar embedded in a protostellar disk; or failure to undergo dynamic collapse. Shock wave material is injected into the collapsing clouds through Rayleigh-Taylor fingers, resulting in initially inhomogeneous distributions in the protostars and protostellar disks. Cloud rotation about an axis aligned with the shock propagation direction does not increase the injection efficiency appreciably, as the shock parameters were chosen to be optimal for injection even in the absence of rotation. For a shock wave from a core-collapse supernova, the dilution factors for supernova material are in the range of ∼10{sup –4} to ∼3 × 10{sup –4}, in agreement with recent laboratory estimates of the required amount of dilution for {sup 60}Fe and {sup 26}Al. We conclude that a type II supernova remains as a promising candidate for synthesizing the solar system's short-lived radioisotopes shortly before their injection into the presolar cloud core by the supernova's remnant shock wave.
Wave motions in a stably-neutrally stratified ocean
NASA Astrophysics Data System (ADS)
Reznik, G. M.
2015-11-01
Wave spectrum of rotating stably-neutrally stratified fluid consisting of the stably stratified upper layer and the homogeneous lower one is studied. The density and other fields are assumed to be continuous at the interface between the layers. The study does not use the traditional (when the horizontal component of the Earth's rotation is neglected) and hydrostatic approximations. The spectrum is rather complicated and consists of the super-inertial internal waves, the sub-inertial gyroscopic waves, and the sub- and super-inertial internal inertio-gravity waves. In the long-wave approximation the internal and internal inertio-gravity waves span both the layers, whereas the gyroscopic waves are localized in the lower layer and are close to the inertial oscillations. The sub-inertial wave motions observed in the nearly barotropic deep Western Mediterranean can be related to the gyroscopic waves.
Oscillations of rapidly rotating relativistic stars
Gaertig, Erich; Kokkotas, Kostas D.
2008-09-15
Nonaxisymmetric oscillations of rapidly rotating relativistic stars are studied using the Cowling approximation. The oscillation spectra have been estimated by Fourier transforming the evolution equations describing the perturbations. This is the first study of its kind and provides information on the effect of fast rotation on the oscillation spectra while it offers the possibility of studying the complete problem by including space-time perturbations. Our study includes both axisymmetric and nonaxisymmetric perturbations and provides limits for the onset of the secular bar mode rotational instability. We also present approximate formulas for the dependence of the oscillation spectrum from rotation. The results suggest that it is possible to extract the relativistic star's parameters from the observed gravitational wave spectrum.
NASA Astrophysics Data System (ADS)
Wassermann, J. M.; Wietek, A.; Hadziioannou, C.; Igel, H.
2014-12-01
Microzonation, i.e. the estimation of (shear) wave velocity profiles of the upper few 100m in dense 2D surface grids is one of the key methods to understand the variation in seismic hazard caused by ground shaking events. In this presentation we introduce a novel method for estimating the Love-wave phase velocity dispersion by using ambient noise recordings. We use the vertical component of rotational motions inherently present in ambient noise and the well established relation to simultaneous recordings of transverse acceleration. In this relation the frequency dependent phase velocity of a plane SH (or Love)-type wave acts as a proportionality factor between the anti-correlated amplitudes of both measures. In a first step we used synthetic data sets with increasing complexity to evaluate the proposed technique and the developed algorithm to extract the direction and amplitude of the incoming ambient noise wavefield measured at a single site. Since reliable weak rotational motion sensors are not yet readily available, we apply array derived rotation measurements in order to test our method. We next use the technique to analyze different real data sets of ambient noise measurements as well as seismic recordings at active volcanoes and compare these results with findings of the Spatial AutoCorrelation technique which was applied to the same data set. We demonstrate that the newly developed technique shows comparable results to more classical, strictly array based methods. Furthermore, we show that as soon as portable weak motion rotational motion sensors are available, a single 6C-station approach will be feasible, not only for microzonation but also for general array applications, with performance comparable to more classical techniques. An important advantage, especially in urban environments, is that with this approach, the number of seismic stations needed is drastically reduced.
NASA Astrophysics Data System (ADS)
Deng, Junjie; Zhang, Wenyan; Harff, Jan; Schneider, Ralf; Dudzinska-Nowak, Joanna; Terefenko, Pawel; Giza, Andrzej; Furmanczyk, Kazimierz
2014-01-01
Comparison between historical maps from the 1900s, 1980s and a modern map from the 2000s of the Pomeranian Bight at the southern Baltic Sea indicates that a major part of the coastline has been suffering continuous erosion. This also holds for a major part of other coasts on a global scale. Quantifying coastal geomorphological changes on a decadal-to-centennial temporal scale thus needs to be intensified for coastal protection activities and integrated coastal zone management. This study applies an estimation of sediment mass balance including the investigation of sediment source-to-sink transport. In the case of absent historical survey data, a numerical approach, namely the Dynamic Equilibrium Shore Model (DESM), is developed to approximate the historical morphology and to estimate sediment budget of wave-dominated coasts based on the information of historical coastline configuration derived from maps, a high-resolution modern Digital Elevation Model (DEM) and relative sea-level change. The basic concept of the model is a dynamic equilibrium of the coastal cross-shore profiles adapting to sediment mass balancing of a semi-enclosed coastal area, in which the unknown parameters of the cross-shore profile shapes are calculated by numerical iterations. The model is applied at the Pomeranian Bight, in order to validate its capability in reflecting the pattern of bed level change and estimating sediment mass volume. Two tests of the model are conducted in approximating historical DEMs in 1980s and ca. 1900. The changes of approximated DEMs from past to present are then respectively compared with the ones derived from a nautical sea chart in 1980s, and the ones produced by a complex morphodynamic model that uses the approximated DEM at ca. 1900 as a starting point to hindcast the coastal morphological evolution of the research area. The deposition/erosion patterns along the coastline are consistent in both comparisons. The pre-conditions and limitations of the model are
NASA Technical Reports Server (NTRS)
Choi, B. H.; Poe, R. T.
1977-01-01
A detailed vibrational-rotational (V-R) close-coupling formulation of electron-diatomic-molecule scattering is developed in which the target molecular axis is chosen to be the z-axis and the resulting coupled differential equation is solved in the moving body-fixed frame throughout the entire interaction region. The coupled differential equation and asymptotic boundary conditions in the body-fixed frame are given for each parity, and procedures are outlined for evaluating V-R transition cross sections on the basis of the body-fixed transition and reactance matrix elements. Conditions are discussed for obtaining identical results from the space-fixed and body-fixed formulations in the case where a finite truncated basis set is used. The hybrid theory of Chandra and Temkin (1976) is then reformulated, relevant expressions and formulas for the simultaneous V-R transitions of the hybrid theory are obtained in the same forms as those of the V-R close-coupling theory, and distorted-wave Born-approximation expressions for the cross sections of the hybrid theory are presented. A close-coupling approximation that conserves the internuclear axis component of the incident electronic angular momentum (l subscript z-prime) is derived from the V-R close-coupling formulation in the moving body-fixed frame.
Kusaka, A; Essinger-Hileman, T; Appel, J W; Gallardo, P; Irwin, K D; Jarosik, N; Nolta, M R; Page, L A; Parker, L P; Raghunathan, S; Sievers, J L; Simon, S M; Staggs, S T; Visnjic, K
2014-02-01
We evaluate the modulation of cosmic microwave background polarization using a rapidly rotating, half-wave plate (HWP) on the Atacama B-Mode Search. After demodulating the time-ordered-data (TOD), we find a significant reduction of atmospheric fluctuations. The demodulated TOD is stable on time scales of 500-1000 s, corresponding to frequencies of 1-2 mHz. This facilitates recovery of cosmological information at large angular scales, which are typically available only from balloon-borne or satellite experiments. This technique also achieves a sensitive measurement of celestial polarization without differencing the TOD of paired detectors sensitive to two orthogonal linear polarizations. This is the first demonstration of the ability to remove atmospheric contamination at these levels from a ground-based platform using a rapidly rotating HWP. PMID:24593374
Calculation of rotational transition probabilities in molecular collisions - Application to N2 + N2
NASA Technical Reports Server (NTRS)
Itikawa, Y.
1975-01-01
A computational method is proposed to obtain rotational transition probabilities in collisions between two diatomic molecules. The potential method of Rabitz and an exponential approximation are used to solve the semiclassical coupled equations without invoking any perturbational technique. The collision trajectory is determined in the classical modified-wave-number approximation. The method can treat systems involving strong interactions and provide probabilities for transitions even with a multiquantum jump. A simultaneous transition in the rotational states of both molecules, i.e., the rotational-rotational energy transfer, is taken into account. An application to the system N2 + N2 is presented.
NASA Technical Reports Server (NTRS)
Fitzjarrald, D. E.
1982-01-01
A novel form of streak photography based on a light-speckle technique has been used to investigate wave-amplitude vacillation in a thermally driven rotating cylindrical annulus of fluid. The technique is evaluated and found to be an excellent way to measure a 2-dimensional field of velocity without introducing probes into the fluid. The results are compared with previous work with the exception that the kinetic energy is significantly higher. The relation between eddy and mean motion, momentum transport, and period of the vacillation cycle appear similar in the two studies.
NASA Astrophysics Data System (ADS)
Ma, Jianxin
2016-07-01
A full-duplex radio-over fiber (RoF) link scheme based on single sideband (SSB) optical millimeter (mm)-wave signal with polarization-rotated optical carrier is proposed to realize the source-free colorless base station (BS), in which a polarization beam splitter (PBS) is used to abstract part of the optical carrier for conveying the uplink data. Since the optical carrier for the uplink does not bear the downlink signal, no cross-talk from the downlink contaminates the uplink signal. The simulation results demonstrate that both down- and up-links maintain good performance. The mm-wave signal distribution network based on the proposed full duplex fiber link scheme can use the uniform source-free colorless BSs, which makes the access system very simpler.
Mushtaq, A.; Shah, H.A.; Rubab, N.; Murtaza, G.
2006-06-15
The characteristics of obliquely propagating Dust Acoustic Waves (DAWs) in rotating and magnetized dusty plasma in the dayside tropical mesosphere are examined by incorporating adiabatic dust charge fluctuations. A Korteweg-de Vries equation is derived, which may support a nonlinear dust acoustic wave on a very slow time scale. The meteoritic dust in mesospheric plasmas on the dayside is charged positively due to photo- and thermionic emissions. The dynamics of the DAW with electronic, ionic, thermionic, and photoelectric currents along with obliqueness and effective gyrofrequency are studied. It is observed that the amplitude of the soliton depends directly on the obliqueness {theta} and dust charge variation, respectively, while the width is modified inversely with these parameters. It is also observed that the effective gyrofrequency modifies the width inversely.
Communication: Creation of molecular vibrational motions via the rotation-vibration coupling
Shu, Chuan-Cun; Henriksen, Niels E.
2015-06-14
Building on recent advances in the rotational excitation of molecules, we show how the effect of rotation-vibration coupling can be switched on in a controlled manner and how this coupling unfolds in real time after a pure rotational excitation. We present the first examination of the vibrational motions which can be induced via the rotation-vibration coupling after a pulsed rotational excitation. A time-dependent quantum wave packet calculation for the HF molecule shows how a slow (compared to the vibrational period) rotational excitation leads to a smooth increase in the average bond length whereas a fast rotational excitation leads to a non-stationary vibrational motion. As a result, under field-free postpulse conditions, either a stretched stationary bond or a vibrating bond can be created due to the coupling between the rotational and vibrational degrees of freedom. The latter corresponds to a laser-induced breakdown of the adiabatic approximation for rotation-vibration coupling.
NASA Astrophysics Data System (ADS)
Short, Mitchell R.
Nanotechnology has become so widely used it can be found in every aspect of life, from cell-phones and computers, to cars, and even athletic socks. As it permeates so many markets, the need for supplemental technologies has also increased. One such needed technology is in the area of nanoscale characterization. Current imaging methods are advanced; however, they do not have the capabilities to characterize the size, shape, composition, and arrangement of nanostructures and nanoparticles in a real-time, unobtrusive manner. The Polarized-Surface-Wave-Scattering system (PSWSS) is a method being researched at the University of Utah that can provide such characterization, although in order for the PSWSS to function accurately through inversion techniques, a predictive forward model must be developed and validated. This work explores the discrete dipole approximation with surface interaction (DDA-SI), an open source MATLAB toolbox, as a predictive model to calculate electromagnetic scattering by objects on a surface illuminated by an evanescent wave generated by total internal reflection (TIR). Far-field scattering predictions via DDA-SI are validated against scaled microwave experimental results for two objects on a surface: a sphere with a diameter of lambda/1.92 and a cube with a side length of lambda/1.785, where lambda refers to the wavelength. A good agreement between experiments and simulations is observed, especially when modified Fresnel reflection coefficients are employed by DDA-SI. Programs to calculate the amplitude scattering matrix and Mueller matrix elements have been also been created. Additionally, the sensitivity of four Mueller matrix elements (M11, M12, M21, and M22) to the particle size, material (gold and silver), shape (sphere and cube), and interparticle spacing, is analyzed. It is found that these four elements are sensitive to changes in shape and interparticle spacing, whereas prove insufficient to difference in material and sizes smaller than
NASA Astrophysics Data System (ADS)
Farhat, M.; Guenneau, S.; Enoch, S.
2011-03-01
We propose a finite elements algorithm to solve a fourth order partial differential equation governing the propagation of time-harmonic bending waves in thin elastic plates. Specially designed perfectly matched layers are implemented to deal with the infinite extent of the plates. These are deduced from a geometric transform in the biharmonic equation. To numerically illustrate the power of elastodynamic transformations, we analyze the elastic response of an elliptic invisibility cloak surrounding a clamped obstacle in the presence of a cylindrical excitation i.e. a concentrated point force. Elliptic cloaking for flexural waves involves a density and an orthotropic Young's modulus which depend on the radial and azimuthal positions, as deduced from a coordinates transformation for circular cloaks in the spirit of Pendry et al. [Science 312, 1780 (2006)], but with a further stretch of a coordinate axis. We find that a wave radiated by a concentrated point force located a couple of wavelengths away from the cloak is almost unperturbed in magnitude and in phase. However, when the point force lies within the coating, it seems to radiate from a shifted location. Finally, we emphasize the versatility of transformation elastodynamics with the design of an elliptic cloak which rotates the wavevector of a flexural wave within its core.
Farhat, M.; Guenneau, S.; Enoch, S.
2011-03-20
We propose a finite elements algorithm to solve a fourth order partial differential equation governing the propagation of time-harmonic bending waves in thin elastic plates. Specially designed perfectly matched layers are implemented to deal with the infinite extent of the plates. These are deduced from a geometric transform in the biharmonic equation. To numerically illustrate the power of elastodynamic transformations, we analyze the elastic response of an elliptic invisibility cloak surrounding a clamped obstacle in the presence of a cylindrical excitation i.e. a concentrated point force. Elliptic cloaking for flexural waves involves a density and an orthotropic Young's modulus which depend on the radial and azimuthal positions, as deduced from a coordinates transformation for circular cloaks in the spirit of Pendry et al. [Science 312, 1780 (2006)], but with a further stretch of a coordinate axis. We find that a wave radiated by a concentrated point force located a couple of wavelengths away from the cloak is almost unperturbed in magnitude and in phase. However, when the point force lies within the coating, it seems to radiate from a shifted location. Finally, we emphasize the versatility of transformation elastodynamics with the design of an elliptic cloak which rotates the wavevector of a flexural wave within its core.
Shantiaee, Yazdan; Dianat, Omid; Paymanpour, Payam; Nahvi, Golnaz; Ketabi, Mohammad Ali; Kolahi Ahari, Golbarg
2015-01-01
Introduction: The aim of this study was to compare the changes that occur in the danger zone (DZ) after preparation of curved mesiobuccal (MB) canals of mandibular first molars with WaveOne instruments in two different movements [reciprocation (RCP) and counter-clockwise rotation (CCWR)] by means of cone-beam computed tomography (CBCT). Methods and Materials: MB canals of 30 mandibular molars were randomly divided into 2 groups (n=15); WaveOne/RCP and WaveOne/CCWR. Pre- and post-instrumentation CBCT images were assessed for changes in the dentin thickness in DZ (2 and 4 mm below the highest point of the root furcation) in both groups. Data was analyzed using the repeated measures ANOVA test. Results: There was no statistically significant difference between two experimental groups in terms of remaining dentin thickness at 2 and 4 mm levels below the highest point of the furcation (P>0.05). Conclusion: The efficacy of WaveOne instrument on changes of the dentin thickness in the DZ was not affected by different file movements. PMID:26213536
NASA Astrophysics Data System (ADS)
Clary, D. C.; Connor, J. N. L.
Rotationally adiabatic distorted wave (RADW) and vibrationally adiabatic distorted wave (VADW) calculations of total and differential cross sections are reported for the three-dimensional H + H2(v=0, j=0) →H2(v'=0, j') + H and D + H2(v=0, j=0) →DH(v'=0, j') + H chemical reactions. Both the Porter-Karplus (PK) and the Siegbahn-Liu-Truhlar-Horowitz (SLTH) potential energy surfaces are used. The RADW results for D+H2 on the SLTH potential surface agree well with those obtained by Yung et al. In calculations using the PK surface, we obtain poor agreement with the RADW results reported for the H + H2 reaction by Choi and Tang, and for the D + H2 reaction by Tang and Choi. Reasons for these discrepancies are discussed. The absolute total RADW cross sections for the H + H2 reaction using both potential surfaces fall well below those obtained in accurate quantum calculations while the VADW total cross sections are smaller in magnitude than the RADW cross sections. The RADW and VADW results for relative rotational population distributions and for normalized differential cross sections are almost identical, and agree well with accurate quantum calculations for these quantities for the H + H2 reaction using the PK potential surface.
NASA Astrophysics Data System (ADS)
Blednov, O.; Girka, I.; Girka, V.; Pavlenko, I.; Sydora, R.
2014-12-01
The initial stage of interaction between a gyrating beam of electrons, which move along Larmor orbits in a narrow gap between a cylindrical plasma layer and an internal screen of a metal coaxial waveguide and electromagnetic eigen waves, is studied theoretically. These waves are extraordinary polarized ones; they propagate along the azimuthal angle across an axial external steady magnetic field in the electron cyclotron frequency range. The numerical analysis shows that the excitation process is stable enough in respect to changing plasma waveguide parameters. The wider the plasma layer, the broader the range of plasma waveguide parameters within which effective wave excitation takes place. The main influence on the excitation of these modes is performed by the applied axial magnetic field, namely: its increase leads to an increase of growth rate and a broadening of the range of the waveguide parameters within which wave excitation is effective.
NASA Astrophysics Data System (ADS)
Rabinovich, B. I.
2006-03-01
Based on a mathematical model described in [1], some new aspects of the dynamics of a thin planar plasma ring rotating in the magnetic field of a central body are considered. The dipole field is considered assuming that the dipole has a small eccentricity, and the dipole axis is inclined at a small angle to the central body’s axis of rotation. Emphasis is placed on the problem of stability of the ring’s stationary rotation. Unlike [1], the disturbed motion is considered which has a character of eddy magneto-gyroscopic waves. The original mathematical model is reduced to a system of finite-difference equations whose asymptotic analytical solution is obtained. It is demonstrated that some “elite” rings characterized by integral quantum numbers are long-living, while “lethal” or unstable rings (antirings) are associated with half-integer quantum numbers. As a result, an evolutionally rife rotating ring of magnetized plasma turns out to be stratified into a large number of narrow elite rings separated by gaps whose positions correspond to antirings. The regions of possible existence of elite rings in near-central body space are considered. Quantum numbers determining elite eigenvalues of the mean sector velocity (normalized in a certain manner) of a ring coincide with the quantum numbers appearing in the solution to the Schrödinger equation for a hydrogen atom. Perturbations of elite orbits corresponding to these quantum numbers satisfy the de Brogli quantum-mechanical condition. This is one more illustration of the isomorphism of quantization in microcosm and macrocosm.
NASA Astrophysics Data System (ADS)
Adcock, T. A. A.; Taylor, P. H.
2016-01-01
The non-linear Schrödinger equation and its higher order extensions are routinely used for analysis of extreme ocean waves. This paper compares the evolution of individual wave-packets modelled using non-linear Schrödinger type equations with packets modelled using fully non-linear potential flow models. The modified non-linear Schrödinger Equation accurately models the relatively large scale non-linear changes to the shape of wave-groups, with a dramatic contraction of the group along the mean propagation direction and a corresponding extension of the width of the wave-crests. In addition, as extreme wave form, there is a local non-linear contraction of the wave-group around the crest which leads to a localised broadening of the wave spectrum which the bandwidth limited non-linear Schrödinger Equations struggle to capture. This limitation occurs for waves of moderate steepness and a narrow underlying spectrum.
Laser-driven isomerization of HCN → HNC: the importance of rotational excitation.
Sun, Zhaopeng; Zheng, Yujun
2015-03-26
We report a time-dependent quantum wave packet theory, which is employed to interpret the isomerization dynamics of HCN molecules induced by an intense picosecond infrared laser field. Considering the molecular rotational degrees of the freedom, the wave functions are expanded in terms of molecular rotational bases. Our full-dimensional quantum model includes the full Coriolis coupling in the molecular kinetic energy Hamiltonian and dipole approximation in interaction terms. The numerical results show that the field-induced molecule rotational excitation plays an important role in the isomerization dynamical process. Some phenomena appear such as two-step two-photon absorption and highly oscillatory structure in rotational state distributions. The centrifugal sudden (CS) approximation calculation is also carried out and compared in this work; it is shown that the Coriolis couplings may lead to a significant decrease in the isomerization rate but highly enhanced molecular rotational excitation. PMID:25746130
NASA Astrophysics Data System (ADS)
Shirota, D.; Bindu, V. H.; Oguro, M.; Eto, W.; Ota, M.; Maeno, K.
When a space vehicle re-enters from the space into the atmosphere, the hypersonic shock wave is generated in front of the vehicle. The surface of the vehicle is exposed to the hypersonic non-equilibrium flow with strong radiative heating.
ERIC Educational Resources Information Center
Greenslade, Thomas B., Jr.
1981-01-01
Discusses theory of the rotating mirror, its use in measuring the velocity of the electrical signal in wires, and the velocity of light. Concludes with a description of the manometric flame apparatus developed for analyzing sound waves. (SK)
Twu, Ruey-Ching; Wang, Jhao-Sheng
2016-04-01
An optical phase interrogation is proposed to study reflection-induced linear polarization rotation in a common-path homodyne interferometer. This optical methodology can also be applied to the measurement of the refractive index variation of a liquid solution. The performance of the refractive index sensing structure is discussed theoretically, and the experimental results demonstrated a very good ability based on the proposed schemes. Compared with a conventional common-path heterodyne interferometer, the proposed homodyne interferometer with only a single channel reduced the usage of optic elements. PMID:27192320
Wave Journal Bearing. Part 1: Analysis
NASA Technical Reports Server (NTRS)
Dimofte, Florin
1995-01-01
A wave journal bearing concept features a waved inner bearing diameter of the non-rotating bearing side and it is an alternative to the plain journal bearing. The wave journal bearing has a significantly increased load capacity in comparison to the plain journal bearing operating at the same eccentricity. It also offers greater stability than the plain circular bearing under all operating conditions. The wave bearing's design is relatively simple and allows the shaft to rotate in either direction. Three wave bearings are sensitive to the direction of an applied stationary side load. Increasing the number of waves reduces the wave bearing's sensitivity to the direction of the applied load relative to the wave. However, the range in which the bearing performance can be varied decreases as the number of waves increases. Therefore, both the number and the amplitude of the waves must be properly selected to optimize the wave bearing design for a specific application. It is concluded that the stiffness of an air journal bearing, due to hydrodynamic effect, could be doubled and made to run stably by using a six or eight wave geometry with a wave amplitude approximately half of the bearing radial clearance.
NASA Astrophysics Data System (ADS)
Lebed, Andrei
2006-03-01
Paramagnetic effects are shown to result in the appearance of a triplet component of order parameter in vortex phases of d- and s-wave singlet superconductors in the absence of impurities. This component, which breaks both parity and spin-rotational symmetries of Cooper pairs, is expected to be of the order of unity in a number of modern superconductors such as high-Tc, organic, MgB2, and some others. A generic phase diagram of such type-IV superconductors [1], which are singlet ones at H=0 and in the Meissner phase and characterized by singlet-triplet mixed Copper pairs, δs+iδt, in a vortex phase, is suggested. [1] A.G. Lebed, Physical Review Letters, accepted (2006).
NASA Astrophysics Data System (ADS)
Nath, Gorakh
2016-07-01
Self-similar solutions are obtained for one-dimensional adiabatic flow behind a magnetogasdynamics cylindrical shock wave propagating in a rotational axisymmetric non ideal gas with increasing energy and conductive and radiative heat fluxes in presence of an azimuthal magnetic field. The fluid velocities and the azimuthal magnetic field in the ambient medium are assume to be varying and obeying power laws. In order to find the similarity solutions the angular velocity of the ambient medium is taken to be decreasing as the distance from the axis increases. The heat conduction is expressed in terms of Fourier's law and the radiation is considered to be the diffusion type for an optically thick grey gas model. The thermal conductivity and the absorption coefficient are assumed to vary with temperature and density. The effects of the presence of radiation and conduction, the non-idealness of the gas and the magnetic field on the shock propagation and the flow behind the shock are investigated.
San-Fabián, Emilio; Moscardó, Federico
2014-07-01
Spin-projected spin polarized Møller-Plesset and spin polarized coupled clusters calculations have been made to estimate the cyclobutadiene automerization, the ethylene torsion barriers in their ground state, and the gap between the singlet and triplet states of ethylene. The results have been obtained optimizing the geometries at MP4 and/or CCSD levels, by an extensive Gaussian basis set. A comparative analysis with more complex calculations, up to MP5 and CCSDTQP, together with others from the literature, have also been made, showing the efficacy of using spin-polarized wave functions as a reference wave function for Møller-Plesset and coupled clusters calculations, in such problems. PMID:24817406
Nonlinear wave interactions in shallow water magnetohydrodynamics of astrophysical plasma
NASA Astrophysics Data System (ADS)
Klimachkov, D. A.; Petrosyan, A. S.
2016-05-01
The rotating magnetohydrodynamic flows of a thin layer of astrophysical and space plasmas with a free surface in a vertical external magnetic field are considered in the shallow water approximation. The presence of a vertical external magnetic field changes significantly the dynamics of wave processes in an astrophysical plasma, in contrast to a neutral fluid and a plasma layer in an external toroidal magnetic field. There are three-wave nonlinear interactions in the case under consideration. Using the asymptotic method of multiscale expansions, we have derived nonlinear equations for the interaction of wave packets: three magneto- Poincare waves, three magnetostrophic waves, two magneto-Poincare and one magnetostrophic waves, and two magnetostrophic and one magneto-Poincare waves. The existence of decay instabilities and parametric amplification is predicted. We show that a magneto-Poincare wave decays into two magneto-Poincare waves, a magnetostrophic wave decays into two magnetostrophic waves, a magneto-Poincare wave decays into one magneto-Poincare and one magnetostrophic waves, and a magnetostrophic wave decays into one magnetostrophic and one magneto-Poincare waves. There are the following parametric amplification mechanisms: the parametric amplification of magneto-Poincare waves, the parametric amplification of magnetostrophic waves, the amplification of a magneto-Poincare wave in the field of a magnetostrophic wave, and the amplification of a magnetostrophic wave in the field of a magneto-Poincare wave. The instability growth rates and parametric amplification factors have been found for the corresponding processes.
Rotational-vibrational coupling in the theory of electron-molecule scattering
NASA Technical Reports Server (NTRS)
Temkin, A.; Sullivan, E. C.
1974-01-01
The adiabatic-nuclei approximation of vibrational-rotational excitation of homonuclear diatomic molecules can be simply augmented to describe the vibrational-rotational coupling by including the dependence of the vibrational wave function on j. Appropriate formulas are given, and the theory, is applied to e-H2 excitation, whereby it is shown that deviations from the simple Born-Oppenheimer approximation measured by Wong and Schultz can be explained. More important, it can be seen that the inclusion of the j-dependent centrifugal term is essential for transitions involving high-rotational quantum numbers.
A fully nonlinear, mixed spectral and finite difference model for thermally driven, rotating flows
NASA Technical Reports Server (NTRS)
Miller, Timothy L.; Lu, Huei-Iin; Butler, Karen A.
1992-01-01
Finite difference in time and the meridional plane, in conjunction with a spectral technique in the azimuthal direction, are used to approximate the Navier-Stokes equations in a model that can simulate a variety of thermally driven rotating flows in cylindrical and spherical geometries. Axisymmetric flow, linearized waves relative to a fixed or changing axisymmetric flow, nonlinear waves without wave-wave interaction, and fully nonlinear 3D flow, can in this way be calculated. A reexamination is conducted of the steady baroclinic wave case previously treated by Williams (1971) and Quon (1976).
Far-infrared rotational emission by carbon monoxide
NASA Technical Reports Server (NTRS)
Mckee, C. F.; Storey, J. W. V.; Watson, D. M.; Green, S.
1981-01-01
Accurate theoretical collisional excitation rates are used to determine the emissivities of CO rotational lines 10 to the 4th power/cu cm n(H2), 100 K T 2000 K, and J 50. An approximate analytic expression for the emissitivities which is valid over most of this region is obtained. Population inversions in the lower rotational levels occur for densities n(H2) approximately 10 (to the 3rd to 5th power)/cu cm and temperatures T approximately 50 K. Interstellar shocks observed edge on are a potential source of millimeter wave CO maser emission. The CO rotational cooling function suggested by Hollenbach and McKee (1979) is verified, and accurate numerical values given. Application of these results to other linear molecules should be straightforward.
NASA Astrophysics Data System (ADS)
Zhang, Shen; Wang, Hongwei; Kang, Wei; Zhang, Ping; He, X. T.
2016-04-01
An extended first-principles molecular dynamics (FPMD) method based on Kohn-Sham scheme is proposed to elevate the temperature limit of the FPMD method in the calculation of dense plasmas. The extended method treats the wave functions of high energy electrons as plane waves analytically and thus expands the application of the FPMD method to the region of hot dense plasmas without suffering from the formidable computational costs. In addition, the extended method inherits the high accuracy of the Kohn-Sham scheme and keeps the information of electronic structures. This gives an edge to the extended method in the calculation of mixtures of plasmas composed of heterogeneous ions, high-Z dense plasmas, lowering of ionization potentials, X-ray absorption/emission spectra, and opacities, which are of particular interest to astrophysics, inertial confinement fusion engineering, and laboratory astrophysics.
Passamonti, Andrea; Bruni, Marco; Gualtieri, Leonardo; Sopuerta, Carlos F.
2006-04-15
We investigate the nonlinear coupling between radial and nonradial oscillations of static spherically-symmetric neutron stars as a possible mechanism for the generation of gravitational waves that may lead to observable signatures. In this paper we concentrate on the axial sector of the nonradial perturbations. By using a multiparameter perturbative framework we introduce a complete description of the nonlinear coupling between radial and axial nonradial oscillations; we study the gauge-invariant character of the associated perturbative variables and develop a computational scheme to evolve the nonlinear coupling perturbations in the time domain. We present results of simulations corresponding to different physical situations and discuss the dynamical behavior of this nonlinear coupling. Of particular interest is the occurrence of signal amplifications in the form of resonance phenomena when a frequency associated with the radial pulsations is close to a frequency associated with one of the axial w-modes of the star. Finally, we mention possible extensions of this work and improvements towards more astrophysically motivated scenarios.
NASA Astrophysics Data System (ADS)
Agarwal, Smriti; Bisht, Amit Singh; Singh, Dharmendra; Pathak, Nagendra Prasad
2014-12-01
Millimetre wave imaging (MMW) is gaining tremendous interest among researchers, which has potential applications for security check, standoff personal screening, automotive collision-avoidance, and lot more. Current state-of-art imaging techniques viz. microwave and X-ray imaging suffers from lower resolution and harmful ionizing radiation, respectively. In contrast, MMW imaging operates at lower power and is non-ionizing, hence, medically safe. Despite these favourable attributes, MMW imaging encounters various challenges as; still it is very less explored area and lacks suitable imaging methodology for extracting complete target information. Keeping in view of these challenges, a MMW active imaging radar system at 60 GHz was designed for standoff imaging application. A C-scan (horizontal and vertical scanning) methodology was developed that provides cross-range resolution of 8.59 mm. The paper further details a suitable target identification and classification methodology. For identification of regular shape targets: mean-standard deviation based segmentation technique was formulated and further validated using a different target shape. For classification: probability density function based target material discrimination methodology was proposed and further validated on different dataset. Lastly, a novel artificial neural network based scale and rotation invariant, image reconstruction methodology has been proposed to counter the distortions in the image caused due to noise, rotation or scale variations. The designed neural network once trained with sample images, automatically takes care of these deformations and successfully reconstructs the corrected image for the test targets. Techniques developed in this paper are tested and validated using four different regular shapes viz. rectangle, square, triangle and circle.
Spin waves in ultracold gases with exchange and spin-orbit interactions
Andreeva, T. L.; Rubin, P. L.
2012-08-15
The dynamics of spin waves in ultracold gases is investigated with allowance for exchange and spin-orbit interaction. The exact basis of atomic states is used taking into account all rotational quantum numbers of the atom. The dispersion relation for spin waves is obtained for fermions and bosons in the hydro-dynamic approximation.
NASA Astrophysics Data System (ADS)
Bi, Lei; Yang, Ping
2016-07-01
The accuracy of the physical-geometric optics (PG-O) approximation is examined for the simulation of electromagnetic scattering by nonspherical dielectric particles. This study seeks a better understanding of the tunneling effect on the phase matrix by employing the invariant imbedding method to rigorously compute the zeroth-order Debye series, from which the tunneling efficiency and the phase matrix corresponding to the diffraction and external reflection are obtained. The tunneling efficiency is shown to be a factor quantifying the relative importance of the tunneling effect over the Fraunhofer diffraction near the forward scattering direction. Due to the tunneling effect, different geometries with the same projected cross section might have different diffraction patterns, which are traditionally assumed to be identical according to the Babinet principle. For particles with a fixed orientation, the PG-O approximation yields the external reflection pattern with reasonable accuracy, but ordinarily fails to predict the locations of peaks and minima in the diffraction pattern. The larger the tunneling efficiency, the worse the PG-O accuracy is at scattering angles less than 90°. If the particles are assumed to be randomly oriented, the PG-O approximation yields the phase matrix close to the rigorous counterpart, primarily due to error cancellations in the orientation-average process. Furthermore, the PG-O approximation based on an electric field volume-integral equation is shown to usually be much more accurate than the Kirchhoff surface integral equation at side-scattering angles, particularly when the modulus of the complex refractive index is close to unity. Finally, tunneling efficiencies are tabulated for representative faceted particles.
NASA Technical Reports Server (NTRS)
Adamson, T. C., Jr.; Messiter, A. F.
1981-01-01
The asymptotic description of the interaction between a normal shock wave and a turbulent boundary layer is reviewed. The layers necessary in a rational analysis of the interaction are discussed with emphasis on the differences from an interaction with a laminar boundary layer, the uncoupling of solutions for the distribution of pressure and skin friction at the wall, and the role of the Reynolds shear stress in these solutions. The accuracy of asymptotic solutions in flows at Reynolds numbers of technical interest is discussed. Solutions for the distribution of pressure and skin friction at the wall and the shape of the shock are considered for the case where the flow is near separation. For the pressure and skin friction, it is possible to write two simplified partial solutions, one valid at the beginning of the interaction and one valid somewhat downstream of the shock wave. A solution composed of these two parts and a linear interpolation between them appears to give good comparison with experiment; one unknown constant, independent of the parameters of the interaction, must be found from experiment. The simplified relations are presented. Comparison of numerical computations with experimental data indicates a possible value for the constant and shows quite satisfactory results.
Huisstede, Bionka M A; Gebremariam, Lukas; van der Sande, Renske; Hay, Elaine M; Koes, Bart W
2011-10-01
Extracorporeal shock-wave therapy (ESWT) is suggested as a treatment alternative for calcific and non-calcific rotator cuff tendinosis (RC-tendinosis), which may decrease the need for surgery. In this study we assessed the evidence for effectiveness of ESWT for these disorders. The Cochrane Library, PubMed, Embase, Pedro, and Cinahl were searched for relevant systematic reviews and RCTs. Two reviewers independently extracted data and assessed the methodological quality. Seventeen RCTs (11 calcific, 6 non-calcific) were included. For calcific RC-tendinosis, strong evidence was found for effectiveness in favour of high-ESWT versus low-ESWT in short-term. Moderate evidence was found in favour of high-ESWT versus placebo in short-, mid- and long-term and versus low-ESWT in mid- and long-term. Moreover, high-ESWT was more effective (moderate evidence) with focus on calcific deposit versus focus on tuberculum major in short- and long-term. RSWT was more effective (moderate evidence) than placebo in mid-term. For non-calcific RC-tendinosis, no strong or moderate evidence was found in favour of low-, mid- or high-ESWT versus placebo, each other, or other treatments. This review shows that only high-ESWT is effective for treating calcific RC-tendinosis. No evidence was found for the effectiveness of ESWT to treat non-calcific RC-tendinosis. PMID:21396877
Beyond the Kirchhoff approximation
NASA Technical Reports Server (NTRS)
Rodriguez, Ernesto
1989-01-01
The three most successful models for describing scattering from random rough surfaces are the Kirchhoff approximation (KA), the small-perturbation method (SPM), and the two-scale-roughness (or composite roughness) surface-scattering (TSR) models. In this paper it is shown how these three models can be derived rigorously from one perturbation expansion based on the extinction theorem for scalar waves scattering from perfectly rigid surface. It is also shown how corrections to the KA proportional to the surface curvature and higher-order derivatives may be obtained. Using these results, the scattering cross section is derived for various surface models.
An approximate Riemann solver for magnetohydrodynamics (that works in more than one dimension)
NASA Technical Reports Server (NTRS)
Powell, Kenneth G.
1994-01-01
An approximate Riemann solver is developed for the governing equations of ideal magnetohydrodynamics (MHD). The Riemann solver has an eight-wave structure, where seven of the waves are those used in previous work on upwind schemes for MHD, and the eighth wave is related to the divergence of the magnetic field. The structure of the eighth wave is not immediately obvious from the governing equations as they are usually written, but arises from a modification of the equations that is presented in this paper. The addition of the eighth wave allows multidimensional MHD problems to be solved without the use of staggered grids or a projection scheme, one or the other of which was necessary in previous work on upwind schemes for MHD. A test problem made up of a shock tube with rotated initial conditions is solved to show that the two-dimensional code yields answers consistent with the one-dimensional methods developed previously.
Probing the Spectrum of 10BE in the Approximation of the SU(3) Leading Representation
NASA Astrophysics Data System (ADS)
Lashko, Yuliya; Filippov, Gennady F.; Korennov, Sergei; Katō, Kiyoshi
2002-09-01
A realization of the approximation of the SU(3) leading representation with the microscopic Hamiltonian and a nucleon-nucleon interaction is presented in detail. An effective Hamiltonian reproducing results of calculations with some known potentials is constructed. It is shown that its structure is quite similar to that of the triaxial rotator, and the wave functions in the Elliott's scheme are linear combinations of Wigner's D-functions although they should be properly normalized.
The torsional and rotation-torsion spectra of CD2HOH
NASA Astrophysics Data System (ADS)
Ndao, M.; Kwabia Tchana, F.; Coudert, L. H.; Motiyenko, R. A.; Margulès, L.; Barros, J.; Manceron, L.; Roy, P.
2016-08-01
The torsional and rotation-torsion spectra of the doubly deuterated species of methanol CD2HOH have been analyzed using submillimeter wave, terahertz, and far infrared spectra. 101 torsional subbands, with subband centers ranging from 2.3 to 626 cm-1, were assigned. Analysis of these yielded kinetic energy and hindering potential parameters of the torsional Hamiltonian describing the large amplitude internal rotation of the CD2H methyl group with respect to the hydroxyl group. 3271 rotation and rotation-torsion transitions, involving the 24 torsional levels up to e1 with 3 ⩽ K ⩽ 10 , were assigned and fitted approximating the rotational energy of each torsional level with a Taylor-type expansion in J (J + 1) . The rotational structure of 48 torsional subbands involving torsional levels higher than e1 has also been analyzed. In most cases, only the Q branch could be observed and assigned.
NASA Astrophysics Data System (ADS)
D'Yachkov, P. N.; Makaev, D. V.
2007-11-01
Every carbon single-walled nanotube (SWNT) can be generated by first mapping only two nearest-neighbor C atoms onto a surface of a cylinder and then using the rotational and helical symmetry operators to determine the remainder of the tubule [C. T. White , Phys. Rev. B 47, 5485 (1993)]. With account of these symmetries, we developed a symmetry-adapted version of a linear augmented cylindrical wave method. In this case, the cells contain only two carbon atoms, and the ab initio theory becomes applicable to any SWNT independent of the number of atoms in a translational unit cell. The approximations are made in the sense of muffin-tin (MT) potentials and local-density-functional theory only. An electronic potential is suggested to be spherically symmetrical in the regions of atoms and constant in an interspherical region up to the two essentially impenetrable cylinder-shaped potential barriers. To construct the basis wave functions, the solutions of the Schrödinger equation for the interspherical and MT regions of the tubule were sewn together using a theorem of addition for cylindrical functions, the resulting basis functions being continuous and differentiable anywhere in the system. With account of analytical equations for these functions, the overlap and Hamiltonian integrals are calculated, which permits determination of electronic structure of nanotube. We have calculated the total band structures and densities of states of the chiral and achiral, semiconducting, semimetallic, and metallic carbon SWNTs (13, 0), (12, 2), (11, 3), (10, 5), (9, 6), (8, 7), (7, 7), (12, 4), and (100, 99) containing up to the 118 804 atoms per translational unit cell. Even for the (100, 99) system with huge unit cell, the band structure can be easily calculated and the results can be presented in the standard form of four curves for the valence band plus one curve for the low-energy states of conduction band. About 150 functions produce convergence of the band structures better then
NASA Astrophysics Data System (ADS)
Lehner, M.; Jungen, M.
2015-02-01
A three-dimensional wave packet method, based on Lanczos tridiagonalization of the Hamiltonian, is introduced and applied to the three-particle predissociation of rotating D3 and H3 3{{ }2}{{A}\\prime } (2sa1\\prime ). The time-dependent propagation calculations on the (diabatic) ground state potential energy surfaces include the non-adiabatic transition from the excited initial state. Results for the eight lowest vibrational levels are presented as Dalitz plots and compared to momentum correlation measurements.
Blum, Kenneth; Chen, Amanda LC; Chen, Thomas JH; Waite, Roger L; Downs, B William; Braverman, Eric R; Kerner, Mallory M; Savarimuthu, Stella M; DiNubile, Nicholas
2009-01-01
Background Albeit other prospective randomized controlled clinical trials on H-Wave Device Stimulation (HWDS), this is the first randomized double-blind Placebo controlled prospective study that assessed the effects of HWDS on range of motion and strength testing in patients who underwent rotator cuff reconstruction. Methods Twenty-two patients were randomly assigned into one of two groups: 1) H-Wave device stimulation (HWDS); 2) Sham-Placebo Device (PLACEBO). All groups received the same postoperative dressing and the same device treatment instructions. Group I was given HWDS which they were to utilize for one hour twice a day for 90 days postoperatively. Group II was given the same instructions with a Placebo device (PLACEBO). Range of motion was assessed by using one-way ANOVA with a Duncan Multiple Range Test for differences between the groups preoperatively, 45 days postoperatively, and 90 days postoperatively by using an active/passive scale for five basic ranges of motions: Forward Elevation, External Rotation (arm at side), External Rotation (arm at 90 degrees abduction), Internal Rotation (arm at side), and Internal Rotation (arm at 90 degrees abduction). The study also evaluated postoperative changes in strength by using the Medical Research Council (MRC) grade assessed strength testing. Results Patients who received HWDS compared to PLACEBO demonstrated, on average, significantly improved range of motion. Results confirm a significant difference for external rotation at 45 and 90 days postoperatively; active range at 45 days postoperatively (p = 0.007), active at 90 days postoperatively (p = 0.007). Internal rotation also demonstrated significant improvement compared to PLACEBO at 45 and 90 days postoperatively; active range at 45 days postoperatively (p = 0.007), and active range at 90 days postoperatively (p = 0.006). There was no significant difference between the two groups for strength testing. Conclusion HWDS compared to PLACEBO induces a
The Titan -1:0 Nodal Bending Wave in Saturn's Ring C.
Rosen, P A; Lissauer, J J
1988-08-01
The most prominent oscillatory feature observed in the Voyager 1 radio occultation of Saturn's rings is identified as a one-armed spiral bending wave excited by Titan's -1:0 nodal inner vertical resonance. Ring partides in a bending wave move in coherently inclined orbits, warping the local mean plane of the rings. The Titan -1:0 wave is the only known bending wave that propagates outward, away from Saturn, and the only spiral wave yet observed in which the wave pattern rotates opposite to the orbital direction of the ring particles. It is also the first bending wave identified in ring C. Modeling the observed feature with existing bending wave theory gives a surface mass density of approximately 0.4 g/cm(2) outside the wave region and a local ring thickness of [unknown]5 meters, and suggests that surface mass density is not constant in the wave region. PMID:17839081
Contained Modes In Mirrors With Sheared Rotation
Abraham J. Fetterman and Nathaniel J. Fisch
2010-10-08
In mirrors with E × B rotation, a fixed azimuthal perturbation in the lab frame can appear as a wave in the rotating frame. If the rotation frequency varies with radius, the plasma-frame wave frequency will also vary radially due to the Doppler shift. A wave that propagates in the high rotation plasma region might therefore be evanescent at the plasma edge. This can lead to radially localized Alfven eigenmodes with high azimuthal mode numbers. Contained Alfven modes are found both for peaked and non-peaked rotation profiles. These modes might be useful for alpha channeling or ion heating, as the high azimuthal wave number allows the plasma wave frequency in the rotating frame to exceed the ion cyclotron frequency. __________________________________________________
A perturbative approach to the numerical simulation of rotational collapse of neutron stars
NASA Astrophysics Data System (ADS)
Sperhake, Ulrich
2003-04-01
The collapse of rotating stars/stellar cores has attracted a lot of attention in the past and is considered among the most promising sources of detectable gravitational waves. We approach the numerical simulation of such scenarios in the slow rotation approximation by evolving gauge invariant second order perturbations on the background of a spherically symmetric collapsing neutron star. Our project thus represents a generalization to 'neutron stars with barotropic equations of state' of work by Cunningham, Price and Moncrief who applied this idea to the analytic background solution for Oppenheimer-Snyder dust collapse. In the slow rotation approximation this approach enables us to obtain fully relativistic simulations of rotating collapsing stars within a well understood numerical framework.
Seismic shear waves as Foucault pendulum
NASA Astrophysics Data System (ADS)
Snieder, Roel; Sens-Schönfelder, Christoph; Ruigrok, Elmer; Shiomi, Katsuhiko
2016-03-01
Earth's rotation causes splitting of normal modes. Wave fronts and rays are, however, not affected by Earth's rotation, as we show theoretically and with observations made with USArray. We derive that the Coriolis force causes a small transverse component for P waves and a small longitudinal component for S waves. More importantly, Earth's rotation leads to a slow rotation of the transverse polarization of S waves; during the propagation of S waves the particle motion behaves just like a Foucault pendulum. The polarization plane of shear waves counteracts Earth's rotation and rotates clockwise in the Northern Hemisphere. The rotation rate is independent of the wave frequency and is purely geometric, like the Berry phase. Using the polarization of ScS and ScS2 waves, we show that the Foucault-like rotation of the S wave polarization can be observed. This can affect the determination of source mechanisms and the interpretation of observed SKS splitting.
Crawford, R J; Kearns, M P
2003-10-01
Rotational moulding promises designers attractive economics and a low-pressure process. The benefits of rotational moulding are compared here with other manufacturing methods such as injection and blow moulding. PMID:14603714
Astronomers combined 146 exposures taken by NASA's Hubble SpaceTelescope to make this 73-frame movie of the asteroid Vesta's rotation.Vesta completes a rotation every 5.34 hours.âº Asteroid and...
Nonaxisymmetric oscillations of differentially rotating relativistic stars
Passamonti, Andrea; Stavridis, Adamantios; Kokkotas, Kostas D.
2008-01-15
Nonaxisymmetric oscillations of differentially rotating stars are studied using both slow rotation and Cowling approximation. The equilibrium stellar models are relativistic polytropes where differential rotation is described by the relativistic j-constant rotation law. The oscillation spectrum is studied versus three main parameters: the stellar compactness M/R, the degree of differential rotation A, and the number of maximum couplings l{sub max}. It is shown that the rotational splitting of the nonaxisymmetric modes are strongly enhanced by increasing the compactness of the star and the degree of differential rotation. Finally, we investigate the relation between the fundamental quadrupole mode and the corotation band of differentially rotating stars.
NASA Astrophysics Data System (ADS)
Sakurai, Kotaro; Bindu, Venigalla Hima; Niinomi, Shota; Ota, Masanori; Maeno, Kazuo
2010-09-01
Coherent Anti-Stokes Raman Spectroscopy (CARS) method is commonly used for measuring molecular structure or condition. In the aerospace technology, this method is applies to measure the temperature in thermic fluid with relatively long time duration of millisecond or sub millisecond. On the other hand, vibrational/rotational temperatures behind hypervelocity shock wave are important for heat-shield design in phase of reentry flight. The non-equilibrium flow with radiative heating from strongly shocked air ahead of the vehicles plays an important role on the heat flux to the wall surface structure as well as convective heating. In this paper CARS method is applied to measure the vibrational/rotational temperature of N2 behind hypervelocity shock wave. The strong shock wave in front of the reentering space vehicles can be experimentally realigned by free-piston, double-diaphragm shock tube with low density test gas. However CARS measurement is difficult for our experiment. Our measurement needs very short pulse which order of nanosecond and high power laser for CARS method. It is due to our measurement object is the momentary phenomena which velocity is 7km/s. In addition the observation section is low density test gas, and there is the strong background light behind the shock wave. So we employ the CARS method with high power, order of 1J/pulse, and very short pulse (10ns) laser. By using this laser the CARS signal can be acquired even in the strong radiation area. Also we simultaneously try to use the CCD camera to obtain total radiation with CARS method.
Peralta, J.; López-Valverde, M. A.; Imamura, T.; Read, P. L.; Luz, D.; Piccialli, A.
2014-07-01
This paper is the second in a two-part study devoted to developing tools for a systematic classification of the wide variety of atmospheric waves expected on slowly rotating planets with atmospheric superrotation. Starting with the primitive equations for a cyclostrophic regime, we have deduced the analytical solution for the possible waves, simultaneously including the effect of the metric terms for the centrifugal force and the meridional shear of the background wind. In those cases where the conditions for the method of the multiple scales in height are met, these wave solutions are also valid when vertical shear of the background wind is present. A total of six types of waves have been found and their properties were characterized in terms of the corresponding dispersion relations and wave structures. In this second part, we study the waves' solutions when several atmospheric approximations are applied: Lamb, surface, and centrifugal waves. Lamb and surface waves are found to be quite similar to those in a geostrophic regime. By contrast, centrifugal waves turn out to be a special case of Rossby waves that arise in atmospheres in cyclostrophic balance. Finally, we use our results to identify the nature of the waves behind atmospheric periodicities found in polar and lower latitudes of Venus's atmosphere.
NASA Astrophysics Data System (ADS)
Peralta, J.; Imamura, T.; Read, P. L.; Luz, D.; Piccialli, A.; López-Valverde, M. A.
2014-07-01
This paper is the second in a two-part study devoted to developing tools for a systematic classification of the wide variety of atmospheric waves expected on slowly rotating planets with atmospheric superrotation. Starting with the primitive equations for a cyclostrophic regime, we have deduced the analytical solution for the possible waves, simultaneously including the effect of the metric terms for the centrifugal force and the meridional shear of the background wind. In those cases where the conditions for the method of the multiple scales in height are met, these wave solutions are also valid when vertical shear of the background wind is present. A total of six types of waves have been found and their properties were characterized in terms of the corresponding dispersion relations and wave structures. In this second part, we study the waves' solutions when several atmospheric approximations are applied: Lamb, surface, and centrifugal waves. Lamb and surface waves are found to be quite similar to those in a geostrophic regime. By contrast, centrifugal waves turn out to be a special case of Rossby waves that arise in atmospheres in cyclostrophic balance. Finally, we use our results to identify the nature of the waves behind atmospheric periodicities found in polar and lower latitudes of Venus's atmosphere.
Decay of helical Kelvin waves on a quantum vortex filament
Van Gorder, Robert A.
2014-07-15
We study the dynamics of helical Kelvin waves moving along a quantum vortex filament driven by a normal fluid flow. We employ the vector form of the quantum local induction approximation (LIA) due to Schwarz. For an isolated filament, this is an adequate approximation to the full Hall-Vinen-Bekarevich-Khalatnikov dynamics. The motion of such Kelvin waves is both translational (along the quantum vortex filament) and rotational (in the plane orthogonal to the reference axis). We first present an exact closed form solution for the motion of these Kelvin waves in the case of a constant amplitude helix. Such solutions exist for a critical wave number and correspond exactly to the Donnelly-Glaberson instability, so perturbations of such solutions either decay to line filaments or blow-up. This leads us to consider helical Kelvin waves which decay to line filaments. Unlike in the case of constant amplitude helical solutions, the dynamics are much more complicated for the decaying helical waves, owing to the fact that the rate of decay of the helical perturbations along the vortex filament is not constant in time. We give an analytical and numerical description of the motion of decaying helical Kelvin waves, from which we are able to ascertain the influence of the physical parameters on the decay, translational motion along the filament, and rotational motion, of these waves (all of which depend nonlinearly on time). One interesting finding is that the helical Kelvin waves do not decay uniformly. Rather, such waves decay slowly for small time scales, and more rapidly for large time scales. The rotational and translational velocity of the Kelvin waves depend strongly on this rate of decay, and we find that the speed of propagation of a helical Kelvin wave along a quantum filament is large for small time while the wave asymptotically slows as it decays. The rotational velocity of such Kelvin waves along the filament will increase over time, asymptotically reaching a finite
NASA Astrophysics Data System (ADS)
Hashimoto, S.; Iwamoto, Y.; Sato, T.; Niita, K.; Boudard, A.; Cugnon, J.; David, J.-C.; Leray, S.; Mancusi, D.
2014-08-01
A new approach to describing neutron spectra of deuteron-induced reactions in the Monte Carlo simulation for particle transport has been developed by combining the Intra-Nuclear Cascade of Liège (INCL) and the Distorted Wave Born Approximation (DWBA) calculation. We incorporated this combined method into the Particle and Heavy Ion Transport code System (PHITS) and applied it to estimate (d,xn) spectra on natLi, 9Be, and natC targets at incident energies ranging from 10 to 40 MeV. Double differential cross sections obtained by INCL and DWBA successfully reproduced broad peaks and discrete peaks, respectively, at the same energies as those observed in experimental data. Furthermore, an excellent agreement was observed between experimental data and PHITS-derived results using the combined method in thick target neutron yields over a wide range of neutron emission angles in the reactions. We also applied the new method to estimate (d,xp) spectra in the reactions, and discussed the validity for the proton emission spectra.
NASA Astrophysics Data System (ADS)
Golubiatnikov, G. Yu; Belov, S. P.; Lapinov, A. V.
2016-01-01
The absolute error of determining the center frequency of the molecule spectral line during a single measurement, which is obtained by fitting the line shape to the model profile, is usually significantly smaller than the statistical spread in the frequencies of the repeated measurements. We discuss the possible causes of the systematic errors leading to an increase in the uncertainty of measurements of the line-center frequency. For an example of the multiple spectral measurements of the rotational transitions of the 16O12C32S molecule in the millimeter- and submillimeter-wave ranges (with a frequency of up to 522 GHz), by the Lamb-dip method, we determine the absolute error of the performed measurements, which amounts to 0 .4 kHz. New precision values of the center frequencies of the rotational transitions of the 16O12C32S molecule and more accurate values of the rotational constants, which are calculated using the measured frequencies, are presented.
General-relativistic rotation laws in rotating fluid bodies
NASA Astrophysics Data System (ADS)
Mach, Patryk; Malec, Edward
2015-06-01
We formulate new general-relativistic extensions of Newtonian rotation laws for self-gravitating stationary fluids. They have been used to rederive, in the first post-Newtonian approximation, the well-known geometric dragging of frames. We derive two other general-relativistic weak-field effects within rotating tori: the recently discovered dynamic antidragging and a new effect that measures the deviation from the Keplerian motion and/or the contribution of the fluids self-gravity. One can use the rotation laws to study the uniqueness and the convergence of the post-Newtonian approximations as well as the existence of the post-Newtonian limits.
NASA Technical Reports Server (NTRS)
Roberts, Glyn O.
1991-01-01
Undesired gravitational effects such as convection or sedimentation in a fluid can sometimes be avoided or decreased by the use of a closed chamber uniformly rotated about a horizontal axis. In a previous study, the spiral orbits of a heavy or buoyant particle in a uniformly rotating fluid were determined. The particles move in circles, and spiral in or out under the combined effects of the centrifugal force and centrifugal buoyancy. A optimization problem for the rotation rate of a cylindrical reactor rotated about its axis and containing distributed particles was formulated and solved. Related studies in several areas are addressed. A computer program based on the analysis was upgraded by correcting some minor errors, adding a sophisticated screen-and-printer graphics capability and other output options, and by improving the automation. The design, performance, and analysis of a series of experiments with monodisperse polystyrene latex microspheres in water were supported to test the theory and its limitations. The theory was amply confirmed at high rotation rates. However, at low rotation rates (1 rpm or less) the assumption of uniform solid-body rotation of the fluid became invalid, and there were increasingly strong secondary motions driven by variations in the mean fluid density due to variations in the particle concentration. In these tests the increase in the mean fluid density due to the particles was of order 0.015 percent. To a first approximation, these flows are driven by the buoyancy in a thin crescent-shaped depleted layer on the descending side of the rotating reactor. This buoyancy distribution is balanced by viscosity near the walls, and by the Coriolis force in the interior. A full analysis is beyond the scope of this study. Secondary flows are likely to be stronger for buoyant particles, which spiral in towards the neutral point near the rotation axis under the influence of their centrifugal buoyancy. This is because the depleted layer is
ERIC Educational Resources Information Center
Lekner, John
2008-01-01
Any free-particle wavepacket solution of Schrodinger's equation can be converted by differentiations to wavepackets rotating about the original direction of motion. The angular momentum component along the motion associated with this rotation is an integral multiple of [h-bar]. It is an "intrinsic" angular momentum: independent of origin and…
Isotropic and anisotropic surface wave cloaking techniques
NASA Astrophysics Data System (ADS)
McManus, T. M.; La Spada, L.; Hao, Y.
2016-04-01
In this paper we compare two different approaches for surface waves cloaking. The first technique is a unique application of Fermat’s principle and requires isotropic material properties, but owing to its derivation is limited in its applicability. The second technique utilises a geometrical optics approximation for dealing with rays bound to a two dimensional surface and requires anisotropic material properties, though it can be used to cloak any smooth surface. We analytically derive the surface wave scattering behaviour for both cloak techniques when applied to a rotationally symmetric surface deformation. Furthermore, we simulate both using a commercially available full-wave electromagnetic solver and demonstrate a good level of agreement with their analytically derived solutions. Our analytical solutions and simulations provide a complete and concise overview of two different surface wave cloaking techniques.
Analytical Solution for the Anisotropic Rabi Model: Effects of Counter-Rotating Terms
Zhang, Guofeng; Zhu, Hanjie
2015-01-01
The anisotropic Rabi model, which was proposed recently, differs from the original Rabi model: the rotating and counter-rotating terms are governed by two different coupling constants. This feature allows us to vary the counter-rotating interaction independently and explore the effects of it on some quantum properties. In this paper, we eliminate the counter-rotating terms approximately and obtain the analytical energy spectrums and wavefunctions. These analytical results agree well with the numerical calculations in a wide range of the parameters including the ultrastrong coupling regime. In the weak counter-rotating coupling limit we find out that the counter-rotating terms can be considered as the shifts to the parameters of the Jaynes-Cummings model. This modification shows the validness of the rotating-wave approximation on the assumption of near-resonance and relatively weak coupling. Moreover, the analytical expressions of several physics quantities are also derived, and the results show the break-down of the U(1)-symmetry and the deviation from the Jaynes-Cummings model. PMID:25736827
Wang, Bin; Qian, Zhenghua; Li, Nian; Sarraf, Hamid
2016-01-01
We propose the use of thickness-twist (TT) wave modes of an AT-cut quartz crystal plate resonator for measurement of material parameters, such as stiffness, density and material gradient, of a functionally graded material (FGM) layer on its surface, whose material property varies exponentially in thickness direction. A theoretical analysis of dispersion relations for TT waves is presented using Mindlin's plate theory, with displacement mode shapes plotted, and the existence of face-shear (FS) wave modes discussed. Through numerical examples, the effects of material parameters (stiffness, density and material gradient) on dispersion curves, cutoff frequencies and mode shapes are thoroughly examined, which can act as a theoretical reference for measurements of unknown properties of FGM layer. PMID:26254981
Effects of reactant rotational excitations on H2 + NH2 → H + NH3 reactivity
NASA Astrophysics Data System (ADS)
Song, Hongwei; Guo, Hua
2014-12-01
Rotational mode specificity of the title reaction is examined using an initial state selected time-dependent wave packet method on an accurate ab initio based global potential energy surface. This penta-atomic reaction presents an ideal system to test several dynamical approximations, which might be useful for future quantum dynamics studies of polyatomic reactions, particularly with rotationally excited reactants. The first approximation involves a seven-dimensional (7D) model in which the two non-reactive N-H bonds are fixed at their equilibrium geometry. The second is the centrifugal sudden (CS) approximation within the 7D model. Finally, the J-shifting (JS) model is tested, again with the fixed N-H bonds. The spectator-bond approximation works very well in the energy range studied, while the centrifugal sudden and J-shifting integral cross sections (ICSs) agree satisfactorily with the coupled-channel counterparts in the low collision energy range, but deviate at the high energies. The calculated integral cross sections indicate that the rotational excitation of H2 somewhat inhibits the reaction while the rotational excitations of NH2 have little effect. These findings are compared with the predictions of the sudden vector projection model. Finally, a simple model is proposed to predict rotational mode specificity using K-averaged reaction probabilities.
NASA Astrophysics Data System (ADS)
Groner, P.
2009-06-01
The rotational spectrum of methyl carbamate in the first excited torsional state (up to 149 GHz) has been analyzed recently for rotational quantum number J up to 20 together with transitions in the ground state. An extended analysis of the rotational spectrum in the ground state between 10 and 371 GHz with over 6000 transitions with J up to 60 has also been published. In the spectra recorded at that time by the FASSST method, about 3000 transitions belonging to the first torsional excited state of the methyl group have now been assigned and analyzed, about half of them belonging to the E torsional species. Both the newly assigned and previously published transitions have been used to fit less than 45 spectroscopic parameters of an effective rotational Hamiltonian for such systems, achieving a dimensionless standard deviation of 1.33. A somewhat unexpected result was the value of the {ρ} parameter of 0.063628(20) which differed significantly from the value obtained for the ground state of 0.058791(15). The discrepancy will be investigated in the near future. Hopefully, a resolution of the problem can be achieved by a combined fit of all excited and ground state transitions using common {ρ} and {β} parameters with {β} as the angle between the {ρ}-axis and the a principal axis. V. Ilyushin, E. Alekseev, J. Demaison, I. Kleiner, J. Mol. Spectrosc. 240, 127 (2006). P. Groner, M. Winnewisser, I. R. Medvedev, F. C. De Lucia, E. Herbst, K. V. L. N. Sastry, Astrophys. J. Suppl. Ser. 169, 28 (2007). P. Groner, J. Chem. Phys. 107, 4483 (1997).
NASA Astrophysics Data System (ADS)
Lakhin, V. P.; Sorokina, E. A.; Ilgisonis, V. I.; Konovaltseva, L. V.
2015-12-01
A set of reduced linear equations for the description of low-frequency perturbations in toroidally rotating plasma in axisymmetric tokamak is derived in the framework of ideal magnetohydrodynamics. The model suitable for the study of global geodesic acoustic modes (GGAMs) is designed. An example of the use of the developed model for derivation of the integral conditions for GGAM existence and of the corresponding dispersion relation is presented. The paper is dedicated to the memory of academician V.D. Shafranov.
Lakhin, V. P.; Sorokina, E. A. E-mail: vilkiae@gmail.com; Ilgisonis, V. I.; Konovaltseva, L. V.
2015-12-15
A set of reduced linear equations for the description of low-frequency perturbations in toroidally rotating plasma in axisymmetric tokamak is derived in the framework of ideal magnetohydrodynamics. The model suitable for the study of global geodesic acoustic modes (GGAMs) is designed. An example of the use of the developed model for derivation of the integral conditions for GGAM existence and of the corresponding dispersion relation is presented. The paper is dedicated to the memory of academician V.D. Shafranov.
Flow shear suppression of turbulence using externally driven ion Bernstein and Alfven waves
Biglari, H.; Ono, M. . Plasma Physics Lab.); Diamond, P.H. . Dept. of Physics); Craddock, G.G. )
1991-01-01
The utilization of externally-launched radio-frequency waves as a means of active confinement control through the generation of sheared poloidal flows is explored. For low-frequency waves, kinetic Alfven waves are proposed, and are shown to drive sheared E {times} B flows as a result of the radial variation in the electromagnetic Reynolds stress. In the high frequency regime, ion Bernstein waves are considered, and shown to generate sheared poloidal rotation through the ponderomotive force. In either case, it is shown that modest amounts of absorbed power ({approximately} few 100 kW) are required to suppress turbulence in a region of several cm radial width. 9 refs.
Nonlinear Spatial Landau Damping of Plasma Waves Beating at Plasma Angular Velocity
NASA Astrophysics Data System (ADS)
Kabantsev, A. A.; Driscoll, C. F.
2014-10-01
Experiments on pure electron plasmas characterize the nonlinear beat between two counter-propagating plasma waves, and the spatial Landau damping of the beat wave at the wave/rotation critical radius. The two plasma waves are (mθ = 1 ,kz = 1 , ω =ω* +/-ω1) , giving the beat wave with (mθ = 2 , ω = 2ω*) . The beat wave is resonant with the plasma rotation Ω (r) at radius r* where Ω (r*) =ω* . The net effect of this resonance is an energy exchange through wave-particle interaction between the two primary plasma waves and the background plasma rotation. Initial excitation of only one of the waves leads first to its fast sharing of energy with the other wave, and then followed by a slower combined decay of both waves. In contrast, initial excitation of both waves to (approximately) the same amplitude leads to three alternative scenarios: 1) both plasma waves may show the slow and synchronous decay evolution; 2) one of the waves may decay faster, with temporarily arrested decay of the other; 3) it may switch back and forth (seemingly randomly) between the first two types of evolution. Interestingly, wave/particle energy flow can be reversed when the plasma density profile is made to have a positive density gradient at r*. In this case, spontaneous excitation (instability) of both ω =ω* +/-ω1 plasma waves is observed. Supported by NSF/DoE Partnership Grants PHY-0903877 and DE-SC000245, and DOE/HEDLP Grant DE-SC0008693.
NASA Astrophysics Data System (ADS)
Dziembowski, W.
Sunspot observations made by Johannes Hevelius in 1642 - 1644 are the first ones providing significant information about the solar differential rotation. In modern astronomy the determination of the rotation rate is done in a routine way by measuring positions of various structures on the solar surface as well as by studying the Doppler shifts of spectral lines. In recent years a progress in helioseismology enabled determination of the rotation rate in the layers inaccessible for direct observations. There are still uncertainties concerning, especially, the temporal variations of the rotation rate and its behaviour in the radiative interior. We are far from understanding the observations. Theoretical works have not yet resulted in a satisfactory model for the angular momentum transport in the convective zone.
NASA Astrophysics Data System (ADS)
Fletcher, N. H.; Tarnopolsky, A. Z.; Lai, J. C. S.
2002-03-01
Free rotational aerophones such as the bullroarer, which consists of a wooden slat whirled around on the end of a string, and which emits a loud pulsating roar, have been used in many ancient and traditional societies for ceremonial purposes. This article presents an experimental and theoretical investigation of this instrument. The aerodynamics of rotational behavior is elucidated, and relates slat rotation frequency to slat width and velocity through the air. Analysis shows that sound production is due to generation of an oscillating-rotating dipole across the slat, the role of the vortices shed by the slat being relatively minor. Apparent discrepancies between the behavior of a bullroarer slat and a slat mounted on an axle in a wind tunnel are shown to be due to viscous friction in the bearings of the wind-tunnel experiment.
Michalsky, J.; Harrison, L.
1994-07-18
Our ARM goal is to help improve both longwave and shortwave models used in GCMs by providing improved radiometric shortwave data. The inference of cloud cover and optical properties of clouds is another goal of this research effort. At the Atmospheric Sciences Research Center (ASRC) in Albany, New York, we are acquiring downwelling shortwave, including direct and diffuse irradiance, at six wavelengths, plus downwelling longwave, upwelling and downwelling broadband shortwave, and aerosol optical depth that we combine with National Weather Service surface and upper air data as a model test data set for ARM researchers. The major objective of our program has been to develop two spectral versions of the rotating shadowband radiometer (RSR). The multi-filter rotating shadowband radiometer (MFRSR) contains six filtered, narrow-passband detectors, and one unfiltered silicon detector that serves as a surrogate total shortwave sensor. The rotating shadowband spectroradiometer (RSS) contains a 256-channel diode array that spans the wavelengths 350-1050 nm with resolution varying between 0.6 nm and 8 nm. With some of the instrument development complete we are devoting more effort to analysis of the MFRSR data. Progress was made on several fronts this year, resulting in conference papers and submissions to refereed journals. Data from the ASRC roof has been used to develop corrections of the MFRSR shortwave sensor. SGP data has been used to develop and validate a retrieval technique for total column water vapor. Total column ozone has been estimated using MFRSR data, but validation at the SGP was not possible for lack of a suitable ozone column standard. Some progress has been made on cloud cover detection, but it is not yet implemented as a routine classification and reporting procedure.
Alpha channeling in a rotating plasma.
Fetterman, Abraham J; Fisch, Nathaniel J
2008-11-14
The wave-particle alpha-channeling effect is generalized to include rotating plasma. Specifically, radio frequency waves can resonate with alpha particles in a mirror machine with ExB rotation to diffuse the alpha particles along constrained paths in phase space. Of major interest is that the alpha-particle energy, in addition to amplifying the rf waves, can directly enhance the rotation energy which in turn provides additional plasma confinement in centrifugal fusion reactors. An ancillary benefit is the rapid removal of alpha particles, which increases the fusion reactivity. PMID:19113347
Rasin, A.
1994-04-01
We discuss the idea of approximate flavor symmetries. Relations between approximate flavor symmetries and natural flavor conservation and democracy models is explored. Implications for neutrino physics are also discussed.
NASA Technical Reports Server (NTRS)
Dickey, Jean O.
1995-01-01
The study of the Earth's rotation in space (encompassing Universal Time (UT1), length of day, polar motion, and the phenomena of precession and nutation) addresses the complex nature of Earth orientation changes, the mechanisms of excitation of these changes and their geophysical implications in a broad variety of areas. In the absence of internal sources of energy or interactions with astronomical objects, the Earth would move as a rigid body with its various parts (the crust, mantle, inner and outer cores, atmosphere and oceans) rotating together at a constant fixed rate. In reality, the world is considerably more complicated, as is schematically illustrated. The rotation rate of the Earth's crust is not constant, but exhibits complicated fluctuations in speed amounting to several parts in 10(exp 8) [corresponding to a variation of several milliseconds (ms) in the Length Of the Day (LOD) and about one part in 10(exp 6) in the orientation of the rotation axis relative to the solid Earth's axis of figure (polar motion). These changes occur over a broad spectrum of time scales, ranging from hours to centuries and longer, reflecting the fact that they are produced by a wide variety of geophysical and astronomical processes. Geodetic observations of Earth rotation changes thus provide insights into the geophysical processes illustrated, which are often difficult to obtain by other means. In addition, these measurements are required for engineering purposes. Theoretical studies of Earth rotation variations are based on the application of Euler's dynamical equations to the problem of finding the response of slightly deformable solid Earth to variety of surface and internal stresses.
Wave-driven Countercurrent Plasma Centrifuge
A.J. Fetterman and N.J. Fisch
2009-03-20
A method for driving rotation and a countercurrent flow in a fully ionized plasma centrifuge is described. The rotation is produced by radiofrequency waves near the cyclotron resonance. The wave energy is transferred into potential energy in a manner similar to the α channeling effect. The countercurrent flow may also be driven by radiofrequency waves. By driving both the rotation and the flow pattern using waves instead of electrodes, physical and engineering issues may be avoided.
Translational Symmetry-Breaking for Spiral Waves
NASA Astrophysics Data System (ADS)
LeBlanc, V. G.; Wulff, C.
2000-10-01
Spiral waves are observed in numerous physical situations, ranging from Belousov-Zhabotinsky (BZ) chemical reactions, to cardiac tissue, to slime-mold aggregates. Mathematical models with Euclidean symmetry have recently been developed to describe the dynamic behavior (for example, meandering) of spiral waves in excitable media. However, no physical experiment is ever infinite in spatial extent, so the Euclidean symmetry is only approximate. Experiments on spiral waves show that inhomogeneities can anchor spirals and that boundary effects (for example, boundary drifting) become very important when the size of the spiral core is comparable to the size of the reacting medium. Spiral anchoring and boundary drifting cannot be explained by the Euclidean model alone. In this paper, we investigate the effects on spiral wave dynamics of breaking the translation symmetry while keeping the rotation symmetry. This is accomplished by introducing a small perturbation in the five-dimensional center bundle equations (describing Hopf bifurcation from one-armed spiral waves) which is SO(2)-equivariant but not equivariant under translations. We then study the effects of this perturbation on rigid spiral rotation, on quasi-periodic meandering and on drifting.
NASA Technical Reports Server (NTRS)
1979-01-01
In aircraft turbine engine research, certain investigations require extremely precise measurement of the position of a rotating part, such as the rotor, a disc-like part of the engine's compressor which revolves around a shaft at extremely high speeds. For example, in studies of airflow velocity within a compressor, researchers need to know-for data correlation the instantaneous position of a given spot on the rotor each time a velocity measurement is made. Earlier methods of measuring rotor shaft angle required a physical connection to the shaft, which limited the velocity of the rotating object.
Three-hair relations for rotating stars: Nonrelativistic limit
Stein, Leo C.; Yagi, Kent; Yunes, Nicolás
2014-06-10
The gravitational field outside of astrophysical black holes is completely described by their mass and spin frequency, as expressed by the no-hair theorems. These theorems assume vacuum spacetimes, and thus they apply only to black holes and not to stars. Despite this, we analytically find that the gravitational potential of arbitrarily rapid, rigidly rotating stars can still be described completely by only their mass, spin angular momentum, and quadrupole moment. Although these results are obtained in the nonrelativistic limit (to leading order in a weak-field expansion of general relativity, GR), they are also consistent with fully relativistic numerical calculations of rotating neutron stars. This description of the gravitational potential outside the source in terms of just three quantities is approximately universal (independent of equation of state). Such universality may be used to break degeneracies in pulsar and future gravitational wave observations to extract more physics and test GR in the strong-field regime.
Far-infrared rotational emission by carbon monoxide
NASA Technical Reports Server (NTRS)
Mckee, C. F.; Storey, J. W. V.; Watson, D. M.; Green, S.
1982-01-01
Accurate theoretical collisional excitation rates are used to determine the emissivities of CO rotational lines for an H2 molecule content of at least 10,000/cu cm, temperature in the range 100-3000 K, and J not more than 60 under the assumption that the lines are optically thin. An approximate analytic expression for the emissivities which is valid in this region is obtained. Population inversions in the lower rotational levels occur for densities of molecular H2 around 1000-100,000/cu cm and temperatures T not more than about 50 K provided photon trapping is unimportant. Interstellar shocks observed edge-on are a potential source of weak millimeter-wave CO maser emission.
NASA Astrophysics Data System (ADS)
Cazzoli, G.; Cludi, L.; Cotti, G.; Dore, L.; Esposti, C. D.; Bellini, M.; Denatale, P.
1994-02-01
The milimeter-wave, submillimeter-wave. and FIR spectra of the ground state of CHF 3 have been observed and analyzed up to J = 78. The resulting spectroscopic constants are: B0/MHz = 10 348.8706(2), D J/kHz= 11.34482(13), D JK/kHz = -18.11765(50), H JJJ/Hz= 0.020069(24), H JJK/Hz = -0.08598(10), H KKJ/Hz 0.11372(27), L J/mHz = -0.669(16) × 10 -4, L JJK/mHz = 0.4953(80) × 10 -3, L JK/mHz = -0.1189(17) × 10 -2, and L JKK/mHz = -0.1115(31) × 10 -2. The splitting of the K = 3 ground state lines has been observed starting from the J = 29 ← 28 transition and the determined values of the splitting constants are h3/Hz = 0.29689(45) ×10 -2 and δ h3/Hz = -0.2054(52) × 10 -7.
A Translational Polarization Rotator
NASA Technical Reports Server (NTRS)
Chuss, David T.; Wollack, Edward J.; Pisano, Giampaolo; Ackiss, Sheridan; U-Yen, Kongpop; Ng, Ming wah
2012-01-01
We explore a free-space polarization modulator in which a variable phase introduction between right- and left-handed circular polarization components is used to rotate the linear polarization of the outgoing beam relative to that of the incoming beam. In this device, the polarization states are separated by a circular polarizer that consists of a quarter-wave plate in combination with a wire grid. A movable mirror is positioned behind and parallel to the circular polarizer. As the polarizer-mirror distance is separated, an incident liear polarization will be rotated through an angle that is proportional to the introduced phase delay. We demonstrate a prototype device that modulates Stokes Q and U over a 20% bandwidth.
Peralta, J.; López-Valverde, M. A.; Imamura, T.; Read, P. L.; Luz, D.; Piccialli, A.
2014-07-01
This paper is the first of a two-part study devoted to developing tools for a systematic classification of the wide variety of atmospheric waves expected on slowly rotating planets with atmospheric superrotation. Starting with the primitive equations for a cyclostrophic regime, we have deduced the analytical solution for the possible waves, simultaneously including the effect of the metric terms for the centrifugal force and the meridional shear of the background wind. In those cases when the conditions for the method of the multiple scales in height are met, these wave solutions are also valid when vertical shear of the background wind is present. A total of six types of waves have been found and their properties were characterized in terms of the corresponding dispersion relations and wave structures. In this first part, only waves that are direct solutions of the generic dispersion relation are studied—acoustic and inertia-gravity waves. Concerning inertia-gravity waves, we found that in the cases of short horizontal wavelengths, null background wind, or propagation in the equatorial region, only pure gravity waves are possible, while for the limit of large horizontal wavelengths and/or null static stability, the waves are inertial. The correspondence between classical atmospheric approximations and wave filtering has been examined too, and we carried out a classification of the mesoscale waves found in the clouds of Venus at different vertical levels of its atmosphere. Finally, the classification of waves in exoplanets is discussed and we provide a list of possible candidates with cyclostrophic regimes.
Effect of Rotation in Cloud Core Collapse
NASA Astrophysics Data System (ADS)
Tsuribe, T.
stage by rapid growth of a nonspherical first core. Second, to mimic fragmentation processes of primordial clouds, the equation of state is approximated by a simple polytropic relation with γ ˜ 1.1. A series of numerical and semianalytical calculations of the rotating collapse of an initially spherical cloud shows a criterion for fragmentation of rotating polytropic cloud cores with γ=1.1. Fragmentation during core collapse is not expected to take place if the cloud thermal energy is greater than 0.3 times its gravitational energy at the initial stage of runaway collapse. The collapse of the central small core will not be halted by centrifugal force since a nonaxisymmetric waves will appear and the flow will converge to a self-similar flow until γ exceeds 4/3. Finally, we take into account the detailed non-equilibrium chemical reactions for primordial gas that consists of pure hydrogen. The parameters of the collapse and the condition of the fragmentation are compared with those of isothermal clouds. It is shown that the geometrical flatness of the central region of the disc is a good indicator for predicting whether the clouds fragment or not. If the flatness is greater than the critical value, ˜ 4π, a cloud fragments into filaments and blobs. On the other hand, if the flatness is smaller than the critical value, fragmentation is not expected before the central core formation even if the cooling is efficient and the total mass becomes much greater than the local Jeans mass at the center.
Broadband Rotational Spectroscopy
NASA Astrophysics Data System (ADS)
Pate, Brooks
2014-06-01
The past decade has seen several major technology advances in electronics operating at microwave frequencies making it possible to develop a new generation of spectrometers for molecular rotational spectroscopy. High-speed digital electronics, both arbitrary waveform generators and digitizers, continue on a Moore's Law-like development cycle that started around 1993 with device bandwidth doubling about every 36 months. These enabling technologies were the key to designing chirped-pulse Fourier transform microwave (CP-FTMW) spectrometers which offer significant sensitivity enhancements for broadband spectrum acquisition in molecular rotational spectroscopy. A special feature of the chirped-pulse spectrometer design is that it is easily implemented at low frequency (below 8 GHz) where Balle-Flygare type spectrometers with Fabry-Perot cavity designs become technologically challenging due to the mirror size requirements. The capabilities of CP-FTMW spectrometers for studies of molecular structure will be illustrated by the collaborative research effort we have been a part of to determine the structures of water clusters - a project which has identified clusters up to the pentadecamer. A second technology trend that impacts molecular rotational spectroscopy is the development of high power, solid state sources in the mm-wave/THz regions. Results from the field of mm-wave chirped-pulse Fourier transform spectroscopy will be described with an emphasis on new problems in chemical dynamics and analytical chemistry that these methods can tackle. The third (and potentially most important) technological trend is the reduction of microwave components to chip level using monolithic microwave integrated circuits (MMIC) - a technology driven by an enormous mass market in communications. Some recent advances in rotational spectrometer designs that incorporate low-cost components will be highlighted. The challenge to the high-resolution spectroscopy community - as posed by Frank De
Impact of plasma poloidal rotation on resistive wall mode instability in toroidally rotating plasmas
Aiba, N.; Shiraishi, J.; Tokuda, S.
2011-02-15
Stability of resistive wall mode (RWM) is investigated in a cylindrical plasma and an axisymmetric toroidal plasma by taking into account not only toroidal rotation but also poloidal rotation. Since the Doppler shifted frequency is responsible for the RWM stability, the modification of this Doppler shifted frequency by poloidal rotation affects the rotation effect on RWM. When a poloidal rotation frequency is not so large, the effect of poloidal rotation on the RWM stability can be approximately treated with the modified toroidal rotation frequency. In a toroidal plasma, this modified frequency is determined by subtracting a toroidal component of the rotation parallel to the magnetic field from the toroidal rotation frequency. The poloidal rotation that counteracts the effect of the Doppler shift strongly reduces the stabilizing effect of toroidal rotation, but by changing the rotational direction, the poloidal rotation enhances this stabilizing effect. This trend is confirmed in not only a cylindrical plasma but also a toroidal plasma. This result indicates that poloidal rotation produces the dependence of the critical toroidal rotation frequency for stabilizing RWM on the rotational direction of toroidal rotation in the same magnetic configuration.
NASA Astrophysics Data System (ADS)
McCoy, Anne B.; Ford, Jason E.; Marlett, Melanie L.; Petit, Andrew S.
2014-06-01
In this work, an extension to diffusion Monte Carlo (DMC) is proposed, allowing for the simultaneous calculation of the energy and wave function of multiple rotationally excited states of floppy molecules. The total wave function is expanded into a set of Dirac δ-functions called walkers, while the rotational portion of the wave function is expanded in a symmetric top basis set. Each walker is given a rotational state vector containing coefficients for all states of interest. The positions of the atoms and the coefficients in the state vector evolve according to the split operator approximation of the quantum propagator. The method was benchmarked by comparing calculated rotation-vibration energies for H_3^+, H_2D^+, and H_3O^+ to experimental values. For low to moderate values of J, the resulting energies are within the statistical uncertainty of the calculation. Rotation-vibration coupling is captured through flexibility introduced in the form of the vibrational wave function. This coupling is found to increase with increasing J-values. Based on the success achieved through these systems, the method was applied to CH_5^+ and its deuterated isotopologues for v = 0, J ≥ 10. Based on these calculations, the energy level structure of CH_5^+ is found to resemble that for a of a spherical top, and excitations up to J = 10 displayed insignificant rotation-vibration coupling. Extensions of this approach that explicitly account for vibrations will also be discussed. ` A. S. Petit, J. E. Ford and A. B. McCoy, J. Phys. Chem. A, in press, K. D. Jordan Festschrift, DOI: 10.1021/jp408821a
Beyond the Kirchhoff approximation. II - Electromagnetic scattering
NASA Technical Reports Server (NTRS)
Rodriguez, Ernesto
1991-01-01
In a paper by Rodriguez (1981), the momentum transfer expansion was introduced for scalar wave scattering. It was shown that this expansion can be used to obtain wavelength-dependent curvature corrections to the Kirchhoff approximation. This paper extends the momentum transfer perturbation expansion to electromagnetic waves. Curvature corrections to the surface current are obtained. Using these results, the specular field and the backscatter cross section are calculated.
NASA Astrophysics Data System (ADS)
Chen, Zhenhua; Hoffmann, Mark R.
2012-07-01
A unitary wave operator, exp (G), G+ = -G, is considered to transform a multiconfigurational reference wave function Φ to the potentially exact, within basis set limit, wave function Ψ = exp (G)Φ. To obtain a useful approximation, the Hausdorff expansion of the similarity transformed effective Hamiltonian, exp (-G)Hexp (G), is truncated at second order and the excitation manifold is limited; an additional separate perturbation approximation can also be made. In the perturbation approximation, which we refer to as multireference unitary second-order perturbation theory (MRUPT2), the Hamiltonian operator in the highest order commutator is approximated by a Møller-Plesset-type one-body zero-order Hamiltonian. If a complete active space self-consistent field wave function is used as reference, then the energy is invariant under orbital rotations within the inactive, active, and virtual orbital subspaces for both the second-order unitary coupled cluster method and its perturbative approximation. Furthermore, the redundancies of the excitation operators are addressed in a novel way, which is potentially more efficient compared to the usual full diagonalization of the metric of the excited configurations. Despite the loss of rigorous size-extensivity possibly due to the use of a variational approach rather than a projective one in the solution of the amplitudes, test calculations show that the size-extensivity errors are very small. Compared to other internally contracted multireference perturbation theories, MRUPT2 only needs reduced density matrices up to three-body even with a non-complete active space reference wave function when two-body excitations within the active orbital subspace are involved in the wave operator, exp (G). Both the coupled cluster and perturbation theory variants are amenable to large, incomplete model spaces. Applications to some widely studied model systems that can be problematic because of geometry dependent quasidegeneracy, H4, P4, and
NASA Technical Reports Server (NTRS)
Sharman, R. D.; Wurtele, M. G.
1983-01-01
Dynamics analogous to those of surface ship waves on water of finite depth are noted for the three-dimensional trapped lee wave modes produced by an isolated obstacle in a stratified fluid. This vertical trapping of wave energy is modeled by uniform upstream flow and stratification, bounded above by a rigid lid, and by a semiinfinite fluid of uniform stability whose wind velocity increases exponentially with height, representing the atmosphere. While formal asymptotic solutions are produced, limited quantitative usefulness is obtained through them because of the limitations of the approximations and the infinity of modes in the solution. Time-dependent numerical models are accordingly developed for both surface ship waves and internal and atmospheric ship waves, yielding a variety of results.
NASA Technical Reports Server (NTRS)
Dutta, Soumitra
1988-01-01
A model for approximate spatial reasoning using fuzzy logic to represent the uncertainty in the environment is presented. Algorithms are developed which can be used to reason about spatial information expressed in the form of approximate linguistic descriptions similar to the kind of spatial information processed by humans. Particular attention is given to static spatial reasoning.
NASA Astrophysics Data System (ADS)
Xu, Li-Hong; Lees, R. M.; Hao, Yun; Müller, H. S. P.; Endres, C. P.; Lewen, F.; Schlemmer, S.; Menten, K. M.
2014-09-01
Methanol is observed in a wide range of astrophysical sources throughout the universe, and comprehensive databases of the millimeter and THz spectra of CH3OH and its principal isotopologues represent important tools for the astronomical community. A previous combined analysis of microwave and millimeter wave spectra of 13CH3OH together with Fourier transform far-infrared spectra was limited to the first two torsional states, νt = 0 and 1, for J values up to 20. The limits on frequency and quantum number coverage have recently been extended by new millimeter and THz measurements on several different spectrometers in the Cologne laboratory in the frequency windows 34-70 GHz, 75-120 GHz, 240-340 GHz, 360-450 GHz and 1.12-1.50 THz. With the new data, the global treatment has now been expanded to include the first three torsional states for J values up to 30. The current 13CH3OH data set contains about 2300 microwave, millimeter-wave, sub-millimeter and THz lines and about 17,100 Fourier-transform far-infrared lines, representing the most recent available information in the quantum number ranges J ⩽ 30, K ⩽ 13 and νt ⩽ 2. The transitions have been successfully fitted to within the assigned measurement uncertainties of ±50 kHz for most of the frequency-measured (i.e. MW, MMW, Sub-MMW, THz) lines and ±6 MHz for the FIR lines. A convergent global fit was achieved using 103 adjustable parameters to reach an overall weighted standard deviation of 1.37. Our new C-13 methanol database is improved substantially compared to the existing one (Li-Hong et al., 1997), and will be available in the Cologne Database for Molecular Spectroscopy, CDMS (http://www.astro.uni-koeln.de/cdms/), in support of astronomical studies associated with results from HIFI (Heterodyne Instrument for the Far-Infrared) on the Herschel Space Observatory and new observations from SOFIA (Stratospheric Observatory For Infrared Astronomy) and ALMA (Atacama Large Millimeter/Submillimeter Array).
Comparing numerical and analytic approximate gravitational waveforms
NASA Astrophysics Data System (ADS)
Afshari, Nousha; Lovelace, Geoffrey; SXS Collaboration
2016-03-01
A direct observation of gravitational waves will test Einstein's theory of general relativity under the most extreme conditions. The Laser Interferometer Gravitational-Wave Observatory, or LIGO, began searching for gravitational waves in September 2015 with three times the sensitivity of initial LIGO. To help Advanced LIGO detect as many gravitational waves as possible, a major research effort is underway to accurately predict the expected waves. In this poster, I will explore how the gravitational waveform produced by a long binary-black-hole inspiral, merger, and ringdown is affected by how fast the larger black hole spins. In particular, I will present results from simulations of merging black holes, completed using the Spectral Einstein Code (black-holes.org/SpEC.html), including some new, long simulations designed to mimic black hole-neutron star mergers. I will present comparisons of the numerical waveforms with analytic approximations.
Haas, D A; Mailer, C; Robinson, B H
1993-01-01
Historically, the continuous wave electron paramagnetic resonance (CW-EPR) progressive saturation method has been used to obtain information on the spin-lattice relaxation time (T1e) and those processes, such as motion and spin exchange, that occur on a competitive timescale. For example, qualitative information on local dynamics and solvent accessibility of proteins and nucleic acids has been obtained by this method. However, making quantitative estimates of T1e from CW-EPR spectra have been frustrated by a lack of understanding of the role of T1e (and T2e) in the slow-motion regime. Theoretical simulation of the CW-EPR lineshapes in the slow-motion region under increasing power levels has been used in this work to test whether the saturation technique can produce quantitative estimates of the spin-lattice relaxation rates. A method is presented by which the correct T1e may be extracted from an analysis of the power-saturation rollover curve, regardless of the amount of inhomogeneous broadening or the rates of molecular reorientation. The range of motional correlation times from 10 to 200 ns should be optimal for extracting quantitative estimates of T1e values in spin-labeled biomolecules. The progressive-saturation rollover curve method should find wide application in those areas of biophysics where information on molecular interactions and solvent exposure as well as molecular reorientation rates are desired. PMID:8386009
NASA Technical Reports Server (NTRS)
Thompkins, W. T., Jr.
1982-01-01
A FORTRAN-IV computer program was developed for the calculation of the inviscid transonic/supersonic flow field in a fully three dimensional blade passage of an axial compressor rotor or stator. Rotors may have dampers (part span shrouds). MacCormack's explicit time marching method is used to solve the unsteady Euler equations on a finite difference mesh. This technique captures shocks and smears them over several grid points. Input quantities are blade row geometry, operating conditions and thermodynamic quanities. Output quantities are three velocity components, density and internal energy at each mesh point. Other flow quanities are calculated from these variables. A short graphics package is included with the code, and may be used to display the finite difference grid, blade geometry and static pressure contour plots on blade to blade calculation surfaces or blade suction and pressure surfaces. The flow in a low aspect ratio transonic compressor was analyzed and compared with high response total pressure probe measurements and gas fluorescence static density measurements made in the MIT blowdown wind tunnel. These comparisons show that the computed flow fields accurately model the measured shock wave locations and overall aerodynamic performance.
Rotational Energy Transfer in N2
NASA Technical Reports Server (NTRS)
Huo, Winifred M.
1994-01-01
Using the N2-N2 intermolecular potential of van der Avoird et al. rotational energy transfer cross sections have been calculated using both the coupled state (CS) and infinite order sudden (IOS) approximations. The rotational energy transfer rate constants at 300 K, calculated in the CS approximation, are in reasonable agreement with the measurements of Sitz and Farrow. The IOS approximation qualitatively reproduces the dependence of the rate constants on the rotational quantum numbers, but consistently overestimates their magnitudes. The treatment of exchange symmetry will be discussed.
NASA Technical Reports Server (NTRS)
Simsic, P. L.
1974-01-01
Excitation of neutral atoms by inelastic scattering of incident electrons in gaseous nebulae were investigated using Slater Wave functions to describe the initial and final states of the atom. Total cross sections using the Born Approximation are calculated for: Li(2s yields 2p), Na(3s yields 4p), k(4s yields 4p). The intensity of emitted radiation from gaseous nebulae is also calculated, and Maxwell distribution is employed to average the kinetic energy of electrons.
The effect of initial rotation in the N(2D) + H2 → NH(3Σ-) + H reaction
NASA Astrophysics Data System (ADS)
Karabulut, Ezman; Aslan, Emine; Kłos, Jacek; Bulut, Niyazi
2014-09-01
In this work, total reaction probabilities, integral cross sections and rate constants were calculated for selected initial rotational states of the H2 molecule in the N(2D) + H2 reaction. Time dependent wave packet method combined with Centrifugal Sudden approximation was used and followed by a flux analysis on recently developed NH2(12A‧‧) global potential energy surface. We also investigated the effect of the projection quantum number of the initial rotational state on the reactivity. Total reaction probabilities were calculated for all values of the total angular momentum, J, in the range from 0 to 40. The effects of the initial rotational excitation of the H2 reactant and of its projection quantum number on the behavior of rate constants were studied. The reaction rate constants are compared with previously published experimental and theoretical results. It was found that the initial rotation and its projection have a big effect on the integral cross sections.
Ott, C D; Dimmelmeier, H; Marek, A; Janka, H-T; Hawke, I; Zink, B; Schnetter, E
2007-06-29
We present 2D and 3D simulations of the collapse of rotating stellar iron cores in general relativity employing a nuclear equation of state and an approximate treatment of deleptonization. We compare fully general relativistic and conformally flat evolutions and find that the latter treatment is sufficiently accurate for the core-collapse supernova problem. We focus on gravitational wave (GW) emission from rotating collapse, bounce, and early postbounce phases. Our results indicate that the GW signature of these phases is much more generic than previously estimated. We also track the growth of a nonaxisymmetric instability in one model, leading to strong narrow-band GW emission. PMID:17678077
NASA Astrophysics Data System (ADS)
Van Gorder, Robert A.
2013-08-01
Very recently, Shivamoggi ["Vortex motion in superfluid 4He: Reformulation in the extrinsic vortex-filament coordinate space," Phys. Rev. B 84, 012506 (2011)], 10.1103/PhysRevB.84.012506 studied the extrinsic form of the local induction approximation (LIA) for the motion of a Kelvin wave on a vortex filament in superfluid 4He, and obtained some results in a cubic approximation. Presently, we study the motion of helical vortex filaments in superfluid 4He under the exact fully nonlinear LIA considered in potential form by Van Gorder ["Fully nonlinear local induction equation describing the motion of a vortex filament in superfluid 4He," J. Fluid Mech. 707, 585 (2012)], 10.1017/jfm.2012.308 and obtained from the Biot-Savart law through the equations of Hall and Vinen ["The rotation of liquid helium II. I. Experiments on the propagation of second sound in uniformly rotating helium II," Proc. R. Soc. London, Ser. A 238, 204 (1956)], 10.1098/rspa.1956.0214 including superfluid friction terms. Nonlinear dispersion relations governing the helical Kelvin wave on such a vortex filament are derived in exact form, from which we may exactly calculate the phase and group velocity of the Kelvin wave. With this, we classify the motion of a helical Kelvin wave on a vortex filament under the LIA. The dispersion relations and results, which follow are exact in nature, in contrast to most results in the literature, which are usually numerical approximations. As such, our results accurately capture the qualitative behavior of the Kelvin waves under the LIA. Extensions to other frameworks are discussed.
Upgrade of far-infrared laser-based Faraday rotation measurement on MST
Ding, W. X.; Brower, D. L.; Bergerson, W. F.; Lin, L.
2010-10-15
Recently, the far-infrared (FIR) laser ({lambda}{sub 0}=432 {mu}m) Faraday rotation measurement system on MST has been upgraded. The dc flowing-gas discharge CO{sub 2} pump laser is replaced by a rf-excited, sealed CO{sub 2} laser at 9.27 {mu}m (GEM select 100, Coherent Inc., Santa Clara, CA), which is subdivided equally into three parts to simultaneously pump three FIR cavities. The total infrared pump power is approximately 80 W on the 9R(20) line required to pump the formic acid molecule. Each FIR cavity produces {approx}12 mW, sufficient for 11 simultaneous chord interferometry-polarimetry operations. Three key issues [(1) conservation of circularly polarized wave, (2) colinearity of two probe waves, and (3) stability of intermediate frequencies between lasers] affecting the Faraday rotation measurement have been resolved experimentally.
Interactions between an idealized rotating string and stationary constraints
NASA Astrophysics Data System (ADS)
Yang, L.; Hutton, S. G.
1995-08-01
In this paper the dynamic interactions between an idealized rotating circular string and a stationary constraint, consisting of a spring, a damper, a mass or a frictional restraint, are discussed. The method of travelling waves is applied to develop the characteristic equation, and it is shown that this method is more general than the conventional method of separation of variables. The response of the string at its critical speed is examined, and it is shown that at the critical speed the string cannot vibrate freely. An approximate solution is generated using the Galerkin method to solve the eigenvalues effectively. The physics of the interactions between the string and the restraints is discussed on the basis of both analytical and approximate solutions.
Multistability in rotating spherical shell convection.
Feudel, F; Seehafer, N; Tuckerman, L S; Gellert, M
2013-02-01
The multiplicity of stable convection patterns in a rotating spherical fluid shell heated from the inner boundary and driven by a central gravity field is presented. These solution branches that arise as rotating waves (RWs) are traced for varying Rayleigh number while their symmetry, stability, and bifurcations are studied. At increased Rayleigh numbers all the RWs undergo transitions to modulated rotating waves (MRWs) which are classified by their spatiotemporal symmetry. The generation of a third frequency for some of the MRWs is accompanied by a further loss of symmetry. Eventually a variety of MRWs, three-frequency solutions, and chaotic saddles and attractors control the dynamics for higher Rayleigh numbers. PMID:23496624
Kinetic effect of toroidal rotation on the geodesic acoustic mode
Guo, W. Ye, L.; Zhou, D.; Xiao, X.; Wang, S.
2015-01-15
Kinetic effects of the toroidal rotation on the geodesic acoustic mode are theoretically investigated. It is found that when the toroidal rotation increases, the damping rate increases in the weak rotation regime due to the rotation enhancement of wave-particle interaction, and it decreases in the strong rotation regime due to the reduction of the number of resonant particles. Theoretical results are consistent with the behaviors of the geodesic acoustic mode recently observed in DIII-D and ASDEX-Upgrade. The kinetic damping effect of the rotation on the geodesic acoustic mode may shed light on the regulation of turbulence through the controlling the toroidal rotation.
Magnetization of the canted antiferromagnetic CoCO 3 in Abragam-Pryce approximation
NASA Astrophysics Data System (ADS)
Meshcheryakov, V. F.
2006-05-01
Weiss molecular field theory was used to calculate the magnetization of the canted antiferromagnetic CoCO 3 ( T=18.1 K). Wave functions of magnetic doublets near Co 2+ ground state in Abragam-Pryce approximation were determined. One of the crystal field variables, free Co 2+ ion isotropic exchange interaction inside, and between magnetic sublatticies, and rotation angle ϕ, characterizing nonequivalence ion Co 2+ positions, were used as parameters. From comparison with the experimental data exchange interaction anisotropy and g-factors g, g were obtained. At low temperatures T<40 K the coincidence of calculated and experimental results are good and g-factor values are almost the same as have been obtained from EPR data in Co(1%)+CdCO single crystals. At high temperatures in the paramagnetic region, experimental data differs from calculated ones by more than two times. It is shown that this discrepancy cannot be described within the frames of used approximations.
Vortices in a rotating Bose-Einstein condensate under extreme elongation
Sanchez-Lotero, P.; Palacios, J.J.
2005-10-15
We investigate a nonaxisymmetric rotating Bose-Einstein condensate (BEC) in the limit of rotation frequency for which the BEC transforms into a quasi-one-dimensional system. We compute the vortex lattice wave function by minimizing the Gross-Pitaevskii energy functional in the lowest Landau level approximation for different confinement potentials. The condensate typically presents a changing number of vortex rows as a function of the interaction strength or rotation-confinement ratio. More specifically, the vortex lattices can be classified into two classes according to their symmetry with respect to the longitudinal axis. These two classes correspond to different local minima of the energy functional and evolve independently as a function of the various parameters.
NASA Technical Reports Server (NTRS)
Dutta, Soumitra
1988-01-01
Much of human reasoning is approximate in nature. Formal models of reasoning traditionally try to be precise and reject the fuzziness of concepts in natural use and replace them with non-fuzzy scientific explicata by a process of precisiation. As an alternate to this approach, it has been suggested that rather than regard human reasoning processes as themselves approximating to some more refined and exact logical process that can be carried out with mathematical precision, the essence and power of human reasoning is in its capability to grasp and use inexact concepts directly. This view is supported by the widespread fuzziness of simple everyday terms (e.g., near tall) and the complexity of ordinary tasks (e.g., cleaning a room). Spatial reasoning is an area where humans consistently reason approximately with demonstrably good results. Consider the case of crossing a traffic intersection. We have only an approximate idea of the locations and speeds of various obstacles (e.g., persons and vehicles), but we nevertheless manage to cross such traffic intersections without any harm. The details of our mental processes which enable us to carry out such intricate tasks in such apparently simple manner are not well understood. However, it is that we try to incorporate such approximate reasoning techniques in our computer systems. Approximate spatial reasoning is very important for intelligent mobile agents (e.g., robots), specially for those operating in uncertain or unknown or dynamic domains.
Approximate kernel competitive learning.
Wu, Jian-Sheng; Zheng, Wei-Shi; Lai, Jian-Huang
2015-03-01
Kernel competitive learning has been successfully used to achieve robust clustering. However, kernel competitive learning (KCL) is not scalable for large scale data processing, because (1) it has to calculate and store the full kernel matrix that is too large to be calculated and kept in the memory and (2) it cannot be computed in parallel. In this paper we develop a framework of approximate kernel competitive learning for processing large scale dataset. The proposed framework consists of two parts. First, it derives an approximate kernel competitive learning (AKCL), which learns kernel competitive learning in a subspace via sampling. We provide solid theoretical analysis on why the proposed approximation modelling would work for kernel competitive learning, and furthermore, we show that the computational complexity of AKCL is largely reduced. Second, we propose a pseudo-parallelled approximate kernel competitive learning (PAKCL) based on a set-based kernel competitive learning strategy, which overcomes the obstacle of using parallel programming in kernel competitive learning and significantly accelerates the approximate kernel competitive learning for large scale clustering. The empirical evaluation on publicly available datasets shows that the proposed AKCL and PAKCL can perform comparably as KCL, with a large reduction on computational cost. Also, the proposed methods achieve more effective clustering performance in terms of clustering precision against related approximate clustering approaches. PMID:25528318
NASA Technical Reports Server (NTRS)
Sonnerup, B. U. O.; Ledley, B. G.
1974-01-01
Magnetic field data from the Goddard Space Flight Center magnetometer experiment on board Ogo 5 are analyzed by the minimum-variance technique for two magnetopause crossings, believed to provide the best evidence presently available of magnetopause rotational discontinuities. Approximate agreement with predictions from MHD and first-order orbit theory is found, but available low-energy electron data suggest the presence of significant non-MHD effects. The paper also illustrates an improved method for data interval selection, a new magnetopause hodogram representation, and the utility of data simulation.
Near-surface S-wave velocity measured with six-degree-of-freedom seismic sensor Rotaphone
NASA Astrophysics Data System (ADS)
Malek, Jiri; Brokesova, Johana
2015-04-01
An essential parameter in seismic engineering is the near-surface S-wave velocity. Rotaphone, a six-degree-of-freedom seismic sensor can be used with advantage to retrieve it from collocated rotational and translational measurements. Rotaphone consists of highly sensitive geophones connected to a conjoint datalogger. The geophones are mounted in parallel pairs to a rigid (metal) ground-based frame. The instrument is designed to measure short-period translational ground motion (velocity) and, in addition, differential motion between the paired geophones. The records of those differential motions are used to obtain rotational components. In-situ calibration of individual geophones is performed simultaneously with each measurement, which enables to reach high sensitivity and accuracy of rotational measurements. In our method we utilize seismic waves produced by anthropogenic source - a generator of S waves and rotational ground motions. The generator contains a fixed part (anchored to the ground), a revolving part and a braking mechanism for immediate braking of the rotational part, in which rotational seismic motions are generated by immediately stopping the revolving part, whereby energy is transmitted into the rock massive. The generator produces repeatedly identical source pulses. Due to identity of the source pulses, we can suppress noise by means of stacking data from many generator actions and thus increase the depth range and resolution. The phase velocity retrieval is based on matching relevant acceleration and rotation rate components. Thanks to a near-source distance and high-frequency content of the source pulses, well-known equations for plane-wave approximation must be replaced by more adequate equations relating the individual rotation rate components to the translational ones. These equations are derived under an assumption of spherical wave. The resulting S-wave phase velocity is compared to the value obtained by standard profile measurements. The
Rapidly rotating neutron star progenitors
NASA Astrophysics Data System (ADS)
Postnov, K. A.; Kuranov, A. G.; Kolesnikov, D. A.; Popov, S. B.; Porayko, N. K.
2016-08-01
Rotating proto-neutron stars can be important sources of gravitational waves to be searched for by present-day and future interferometric detectors. It was demonstrated by Imshennik that in extreme cases the rapid rotation of a collapsing stellar core may lead to fission and formation of a binary proto-neutron star which subsequently merges due to gravitational wave emission. In the present paper, we show that such dynamically unstable collapsing stellar cores may be the product of a former merger process of two stellar cores in a common envelope. We applied population synthesis calculations to assess the expected fraction of such rapidly rotating stellar cores which may lead to fission and formation of a pair of proto-neutron stars. We have used the BSE population synthesis code supplemented with a new treatment of stellar core rotation during the evolution via effective core-envelope coupling, characterized by the coupling time, τc. The validity of this approach is checked by direct MESA calculations of the evolution of a rotating 15 M⊙ star. From comparison of the calculated spin distribution of young neutron stars with the observed one, reported by Popov and Turolla, we infer the value τc ≃ 5 × 105 years. We show that merging of stellar cores in common envelopes can lead to collapses with dynamically unstable proto-neutron stars, with their formation rate being ˜0.1 - 1% of the total core collapses, depending on the common envelope efficiency.
Approximate analysis of electromagnetically coupled microstrip dipoles
NASA Astrophysics Data System (ADS)
Kominami, M.; Yakuwa, N.; Kusaka, H.
1990-10-01
A new dynamic analysis model for analyzing electromagnetically coupled (EMC) microstrip dipoles is proposed. The formulation is based on an approximate treatment of the dielectric substrate. Calculations of the equivalent impedance of two different EMC dipole configurations are compared with measured data and full-wave solutions. The agreement is very good.
Slow-Neutron Scattering by Rotators. II
NASA Technical Reports Server (NTRS)
Volkin, Howard C.
1960-01-01
The methods developed in a previous paper for extending the neutron scattering formalism of Zemach and Glauber to any type of molecular rotator have been employed to derive generalized forms generalized forms of the differential cross sections for rotator scattering. A mass-ratio expansion for the treatment of the high-energy limit is illustrated on the classical cross section and then employed in the treatment of the more general quantum-mechanical expression for the differential cross section. The results apply to an arbitrarily asymmetric rotator. The very low energy approximation is carried out for the symmetric rotator, and the procedure is compared with the explicit summing of the partial cross sections for individual rotational transitions. The inelastic correction to the static approximation for interference scattering is calculated to an accuracy of first order in the mass ratios for the case of the symmetric rotator.
Waves in strong centrifugal fields: dissipationless gas
NASA Astrophysics Data System (ADS)
Bogovalov, S. V.; Kislov, V. A.; Tronin, I. V.
2015-04-01
Linear waves are investigated in a rotating gas under the condition of strong centrifugal acceleration of the order 106 g realized in gas centrifuges for separation of uranium isotopes. Sound waves split into three families of the waves under these conditions. Dispersion equations are obtained. The characteristics of the waves strongly differ from the conventional sound waves on polarization, velocity of propagation and distribution of energy of the waves in space for two families having frequencies above and below the frequency of the conventional sound waves. The energy of these waves is localized in rarefied region of the gas. The waves of the third family were not specified before. They propagate exactly along the rotational axis with the conventional sound velocity. These waves are polarized only along the rotational axis. Radial and azimuthal motions are not excited. Energy of the waves is concentrated near the wall of the rotor where the density of the gas is largest.
Approximated solutions to Born-Infeld dynamics
NASA Astrophysics Data System (ADS)
Ferraro, Rafael; Nigro, Mauro
2016-02-01
The Born-Infeld equation in the plane is usefully captured in complex language. The general exact solution can be written as a combination of holomorphic and anti-holomorphic functions. However, this solution only expresses the potential in an implicit way. We rework the formulation to obtain the complex potential in an explicit way, by means of a perturbative procedure. We take care of the secular behavior common to this kind of approach, by resorting to a symmetry the equation has at the considered order of approximation. We apply the method to build approximated solutions to Born-Infeld electrodynamics. We solve for BI electromagnetic waves traveling in opposite directions. We study the propagation at interfaces, with the aim of searching for effects susceptible to experimental detection. In particular, we show that a reflected wave is produced when a wave is incident on a semi-space containing a magnetostatic field.
Modification of chirped laser pulses via delayed rotational nonlinearity
NASA Astrophysics Data System (ADS)
Romanov, D. A.; Odhner, J. H.; Levis, R. J.
2016-03-01
To interpret single-shot measurements of rotational revival patterns in molecular gases excited by an ultrashort laser pulse, an analytical description of the probe pulse modulation by the impulsively excited medium is developed. A femtosecond pump laser pulse prepares a rotational wavepacket in a gas-phase sample, and the resulting periodic revivals are mapped into the frequency domain by using a substantially chirped continuum probe pulse. Since the standard approximate descriptions of probe pulse propagation are inapplicable (such as the slowly varying envelope approximation and the slowly evolving wave approximation), we propose an approach capable of incorporating both the substantial chirp of the pulse and the temporal dispersion of the medium response. Theory is presented for the case where the frequency change of the probe during the probe pulse duration is comparable with the carrier frequency. Analytical expressions are obtained for the probe signal modulation over the pump-probe interaction region and for the resulting heterodyned transient birefringence spectra. The approach is illustrated using the case of nitrogen gas.
Approximating metal-insulator transitions
NASA Astrophysics Data System (ADS)
Danieli, Carlo; Rayanov, Kristian; Pavlov, Boris; Martin, Gaven; Flach, Sergej
2015-12-01
We consider quantum wave propagation in one-dimensional quasiperiodic lattices. We propose an iterative construction of quasiperiodic potentials from sequences of potentials with increasing spatial period. At each finite iteration step, the eigenstates reflect the properties of the limiting quasiperiodic potential properties up to a controlled maximum system size. We then observe approximate Metal-Insulator Transitions (MIT) at the finite iteration steps. We also report evidence on mobility edges, which are at variance to the celebrated Aubry-André model. The dynamics near the MIT shows a critical slowing down of the ballistic group velocity in the metallic phase, similar to the divergence of the localization length in the insulating phase.
Strong shock implosion, approximate solution
NASA Astrophysics Data System (ADS)
Fujimoto, Y.; Mishkin, E. A.; Alejaldre, C.
1983-01-01
The self-similar, center-bound motion of a strong spherical, or cylindrical, shock wave moving through an ideal gas with a constant, γ= cp/ cv, is considered and a linearized, approximate solution is derived. An X, Y phase plane of the self-similar solution is defined and the representative curved of the system behind the shock front is replaced by a straight line connecting the mappings of the shock front with that of its tail. The reduced pressure P(ξ), density R(ξ) and velocity U1(ξ) are found in closed, quite accurate, form. Comparison with numerically obtained results, for γ= {5}/{3} and γ= {7}/{5}, is shown.
Effects of mechanical rotation on spin currents.
Matsuo, Mamoru; Ieda, Jun'ichi; Saitoh, Eiji; Maekawa, Sadamichi
2011-02-18
We study the Pauli-Schrödinger equation in a uniformly rotating frame of reference to describe a coupling of spins and mechanical rotations. The explicit form of the spin-orbit interaction (SOI) with the inertial effects due to the mechanical rotation is presented. We derive equations of motion for a wave packet of electrons in two-dimensional planes subject to the SOI. The solution is a superposition of two cyclotron motions with different frequencies and a circular spin current is created by the mechanical rotation. The magnitude of the spin current is linearly proportional to the lower cyclotron frequency. PMID:21405528
Dasso, C. H.; Vitturi, A.
2009-06-15
We exploit a model describing the breakup of weakly bound nuclei that can be used as a laboratory for testing different prescriptions that have been advanced in the literature to take into account the nearby presence of continuum states. In the model, we follow the evolution of a single-particle wave function in one dimension, initially bound by a Woods-Saxon type potential and then perturbed by a time- and position-dependent external field. Proper choices of this potential can simulate the effect of the interaction between reaction partners in a nuclear collision. These processes generate inelastic excitation probabilities that--distributed over the bound and continuum states of the system--lead to either a partial or a total fragmentation of the final wave function.
Covariant approximation averaging
NASA Astrophysics Data System (ADS)
Shintani, Eigo; Arthur, Rudy; Blum, Thomas; Izubuchi, Taku; Jung, Chulwoo; Lehner, Christoph
2015-06-01
We present a new class of statistical error reduction techniques for Monte Carlo simulations. Using covariant symmetries, we show that correlation functions can be constructed from inexpensive approximations without introducing any systematic bias in the final result. We introduce a new class of covariant approximation averaging techniques, known as all-mode averaging (AMA), in which the approximation takes account of contributions of all eigenmodes through the inverse of the Dirac operator computed from the conjugate gradient method with a relaxed stopping condition. In this paper we compare the performance and computational cost of our new method with traditional methods using correlation functions and masses of the pion, nucleon, and vector meson in Nf=2 +1 lattice QCD using domain-wall fermions. This comparison indicates that AMA significantly reduces statistical errors in Monte Carlo calculations over conventional methods for the same cost.
Fast approximate motif statistics.
Nicodème, P
2001-01-01
We present in this article a fast approximate method for computing the statistics of a number of non-self-overlapping matches of motifs in a random text in the nonuniform Bernoulli model. This method is well suited for protein motifs where the probability of self-overlap of motifs is small. For 96% of the PROSITE motifs, the expectations of occurrences of the motifs in a 7-million-amino-acids random database are computed by the approximate method with less than 1% error when compared with the exact method. Processing of the whole PROSITE takes about 30 seconds with the approximate method. We apply this new method to a comparison of the C. elegans and S. cerevisiae proteomes. PMID:11535175
The Guiding Center Approximation
NASA Astrophysics Data System (ADS)
Pedersen, Thomas Sunn
The guiding center approximation for charged particles in strong magnetic fields is introduced here. This approximation is very useful in situations where the charged particles are very well magnetized, such that the gyration (Larmor) radius is small compared to relevant length scales of the confinement device, and the gyration is fast relative to relevant timescales in an experiment. The basics of motion in a straight, uniform, static magnetic field are reviewed, and are used as a starting point for analyzing more complicated situations where more forces are present, as well as inhomogeneities in the magnetic field -- magnetic curvature as well as gradients in the magnetic field strength. The first and second adiabatic invariant are introduced, and slowly time-varying fields are also covered. As an example of the use of the guiding center approximation, the confinement concept of the cylindrical magnetic mirror is analyzed.
Lucia, L.V.
1982-03-16
A wave action power plant powered by the action of water waves has a drive shaft rotated by a plurality of drive units, each having a lever pivotally mounted on and extending from said shaft and carrying a weight, in the form of a float, which floats on the waves and rocks the lever up and down on the shaft. A ratchet mechanism causes said shaft to be rotated in one direction by the weight of said float after it has been raised by wave and the wave has passed, leaving said float free to move downwardly by gravity and apply its full weight to pull down on the lever and rotate the drive shaft. There being a large number of said drive units so that there are always some of the weights pulling down on their respective levers while other weights are being lifted by waves and thereby causing continuous rotation of the drive shaft in one direction. The said levers are so mounted that they may be easily raised to bring the weights into a position wherein they are readily accessible for cleaning the bottoms thereof to remove any accumulation of barnacles, mollusks and the like. There is also provided means for preventing the weights from colliding with each other as they independently move up and down on the waves.
Monotone Boolean approximation
Hulme, B.L.
1982-12-01
This report presents a theory of approximation of arbitrary Boolean functions by simpler, monotone functions. Monotone increasing functions can be expressed without the use of complements. Nonconstant monotone increasing functions are important in their own right since they model a special class of systems known as coherent systems. It is shown here that when Boolean expressions for noncoherent systems become too large to treat exactly, then monotone approximations are easily defined. The algorithms proposed here not only provide simpler formulas but also produce best possible upper and lower monotone bounds for any Boolean function. This theory has practical application for the analysis of noncoherent fault trees and event tree sequences.
Bose-Einstein condensate in a rapidly rotating nonsymmetric trap
Fetter, Alexander L.
2010-03-15
A rapidly rotating Bose-Einstein condensate in a symmetric two-dimensional harmonic trap can be described with the lowest Landau-level set of single-particle states. The condensate wave function {psi}(x,y) is a Gaussian {proportional_to}exp(-r{sup 2}/2), multiplied by an analytic function f(z) of the complex variable z=x+iy. The criterion for a quantum phase transition to a non-superfluid correlated many-body state is usually expressed in terms of the ratio of the number of particles to the number of vortices. Here a similar description applies to a rapidly rotating nonsymmetric two-dimensional trap with arbitrary quadratic anisotropy ({omega}{sub x}{sup 2}<{omega}{sub y}{sup 2}). The corresponding condensate wave function {psi}(x,y) is a complex anisotropic Gaussian with a phase proportional to xy, multiplied by an analytic function f(z), where z=x+i{beta}{sub -}y is a stretched complex variable and 0{<=}{beta}{sub -{<=}}1 is a real parameter that depends on the trap anisotropy and the rotation frequency. Both in the mean-field Thomas-Fermi approximation and in the mean-field lowest Landau level approximation with many visible vortices, an anisotropic parabolic density profile minimizes the energy. An elongated condensate grows along the soft trap direction yet ultimately shrinks along the tight trap direction. The criterion for the quantum phase transition to a correlated state is generalized (1) in terms of N/L{sub z}, which suggests that a nonsymmetric trap should make it easier to observe this transition, or (2) in terms of a 'fragmented' correlated state, which suggests that a nonsymmetric trap should make it harder to observe this transition. An alternative scenario involves a crossover to a quasi one-dimensional condensate without visible vortices, as suggested by Aftalion et al., Phys. Rev. A 79, 011603(R) (2009).
NASA Technical Reports Server (NTRS)
1988-01-01
The NASA Bioreactor provides a low turbulence culture environment which promotes the formation of large, three-dimensional cell clusters. Due to their high level of cellular organization and specialization, samples constructed in the bioreactor more closely resemble the original tumor or tissue found in the body. NASA-sponsored bioreactor research has been instrumental in helping scientists to better understand normal and cancerous tissue development. In cooperation with the medical community, the bioreactor design is being used to prepare better models of human colon, prostate, breast and ovarian tumors. Cartilage, bone marrow, heart muscle, skeletal muscle, pancreatic islet cells, liver and kidney are just a few of the normal tissues currently being cultured in rotating bioreactors by investigators.
Approximating Integrals Using Probability
ERIC Educational Resources Information Center
Maruszewski, Richard F., Jr.; Caudle, Kyle A.
2005-01-01
As part of a discussion on Monte Carlo methods, which outlines how to use probability expectations to approximate the value of a definite integral. The purpose of this paper is to elaborate on this technique and then to show several examples using visual basic as a programming tool. It is an interesting method because it combines two branches of…
Multicriteria approximation through decomposition
Burch, C. |; Krumke, S.; Marathe, M.; Phillips, C.; Sundberg, E. |
1997-12-01
The authors propose a general technique called solution decomposition to devise approximation algorithms with provable performance guarantees. The technique is applicable to a large class of combinatorial optimization problems that can be formulated as integer linear programs. Two key ingredients of the technique involve finding a decomposition of a fractional solution into a convex combination of feasible integral solutions and devising generic approximation algorithms based on calls to such decompositions as oracles. The technique is closely related to randomized rounding. The method yields as corollaries unified solutions to a number of well studied problems and it provides the first approximation algorithms with provable guarantees for a number of new problems. The particular results obtained in this paper include the following: (1) The authors demonstrate how the technique can be used to provide more understanding of previous results and new algorithms for classical problems such as Multicriteria Spanning Trees, and Suitcase Packing. (2) They show how the ideas can be extended to apply to multicriteria optimization problems, in which they wish to minimize a certain objective function subject to one or more budget constraints. As corollaries they obtain first non-trivial multicriteria approximation algorithms for problems including the k-Hurdle and the Network Inhibition problems.
Multicriteria approximation through decomposition
Burch, C.; Krumke, S.; Marathe, M.; Phillips, C.; Sundberg, E.
1998-06-01
The authors propose a general technique called solution decomposition to devise approximation algorithms with provable performance guarantees. The technique is applicable to a large class of combinatorial optimization problems that can be formulated as integer linear programs. Two key ingredients of their technique involve finding a decomposition of a fractional solution into a convex combination of feasible integral solutions and devising generic approximation algorithms based on calls to such decompositions as oracles. The technique is closely related to randomized rounding. Their method yields as corollaries unified solutions to a number of well studied problems and it provides the first approximation algorithms with provable guarantees for a number of new problems. The particular results obtained in this paper include the following: (1) the authors demonstrate how the technique can be used to provide more understanding of previous results and new algorithms for classical problems such as Multicriteria Spanning Trees, and Suitcase Packing; (2) they also show how the ideas can be extended to apply to multicriteria optimization problems, in which they wish to minimize a certain objective function subject to one or more budget constraints. As corollaries they obtain first non-trivial multicriteria approximation algorithms for problems including the k-Hurdle and the Network Inhibition problems.
Gravitational radiation from rotating monopole-string systems
Babichev, E.; Dokuchaev, V.; Kachelriess, M.
2005-02-15
We study the gravitational radiation from a rotating monopole-antimonopole pair connected by a string. While at not too high frequencies the emitted gravitational spectrum is described asymptotically by P{sub n}{proportional_to}n{sup -1}, the spectrum is exponentially suppressed in the high-frequency limit, P{sub n}{proportional_to}exp(-n/n{sub cr}). Below n{sub cr}, the emitted spectrum of gravitational waves is very similar to the case of an oscillating monopole pair connected by a string, and we argue, therefore, that the spectrum found holds approximately for any moving monopole-string system. As an application, we discuss the stochastic gravitational wave background generated by monopole-antimonopole pairs connected by strings in the early Universe and gravitational wave bursts emitted at present by monopole-string networks. We confirm that advanced gravitational wave detectors have the potential to detect a signal for string tensions as small as G{mu}{approx}10{sup -13}.
Acoustic streaming flows and sample rotation control
NASA Astrophysics Data System (ADS)
Trinh, Eugene
1998-11-01
Levitated drops in a gas can be driven into rotation by altering their surrounding convective environment. When these drops are placed in an acoustic resonant chamber, the symmetry characteristics of the steady streaming flows in the vicinity of the drops determine the rotational motion of the freely suspended fluid particles. Using ultrasonic standing waves around 22 kHz and millimeter-size electrostatically levitated drops, we have investigated the correlation between the convective flow characteristics and their rotational behavior. The results show that accurate control of the drop rotation axis and rate can be obtained by carefully modifying the symmetry characteristics of the chamber, and that the dominant mechanism for rotation drive is the drag exerted by the air flow over the drop surface. In addition, we found that the rotational acceleration depends on the drop viscosity, suggesting that this torque is initially strongly influenced by differential flows within the drop itself. [Work sponsored by NASA].
The Maximum Mass of Rotating Strange Stars
NASA Astrophysics Data System (ADS)
Szkudlarek, M.; Gondek-Rosiń; ska, D.; Villain, L.; Ansorg, M.
2012-12-01
Strange quark stars are considered as a possible alternative to neutron stars as compact objects (e.g. Weber 2003). A hot compact star (a proto-neutron star or a strange star) born in a supernova explosion or a remnant of neutron stars binary merger are expected to rotate differentially and be important sources of gravitational waves. We present results of the first relativistic calculations of differentially rotating strange quark stars for broad ranges of degree of differential rotation and maximum densities. Using a highly accurate, relativistic code we show that rotation may cause a significant increase of maximum allowed mass of strange stars, much larger than in the case of neutron stars with the same degree of differential rotation. Depending on the maximum allowed mass a massive neutron star (strange star) can be temporarily stabilized by differential rotation or collapse to a black hole.
Optimizing the Zeldovich approximation
NASA Technical Reports Server (NTRS)
Melott, Adrian L.; Pellman, Todd F.; Shandarin, Sergei F.
1994-01-01
We have recently learned that the Zeldovich approximation can be successfully used for a far wider range of gravitational instability scenarios than formerly proposed; we study here how to extend this range. In previous work (Coles, Melott and Shandarin 1993, hereafter CMS) we studied the accuracy of several analytic approximations to gravitational clustering in the mildly nonlinear regime. We found that what we called the 'truncated Zeldovich approximation' (TZA) was better than any other (except in one case the ordinary Zeldovich approximation) over a wide range from linear to mildly nonlinear (sigma approximately 3) regimes. TZA was specified by setting Fourier amplitudes equal to zero for all wavenumbers greater than k(sub nl), where k(sub nl) marks the transition to the nonlinear regime. Here, we study the cross correlation of generalized TZA with a group of n-body simulations for three shapes of window function: sharp k-truncation (as in CMS), a tophat in coordinate space, or a Gaussian. We also study the variation in the crosscorrelation as a function of initial truncation scale within each type. We find that k-truncation, which was so much better than other things tried in CMS, is the worst of these three window shapes. We find that a Gaussian window e(exp(-k(exp 2)/2k(exp 2, sub G))) applied to the initial Fourier amplitudes is the best choice. It produces a greatly improved crosscorrelation in those cases which most needed improvement, e.g. those with more small-scale power in the initial conditions. The optimum choice of kG for the Gaussian window is (a somewhat spectrum-dependent) 1 to 1.5 times k(sub nl). Although all three windows produce similar power spectra and density distribution functions after application of the Zeldovich approximation, the agreement of the phases of the Fourier components with the n-body simulation is better for the Gaussian window. We therefore ascribe the success of the best-choice Gaussian window to its superior treatment
Approximate Quantum Cloaking and Almost-Trapped States
Greenleaf, Allan; Kurylev, Yaroslav; Lassas, Matti; Uhlmann, Gunther
2008-11-28
We describe potentials which act as approximate cloaks for matter waves. These potentials are derived from ideal cloaks for the conductivity and Helmholtz equations. At most energies E, if a potential is surrounded by an approximate cloak, then it becomes almost undetectable and unaltered by matter waves originating externally to the cloak. For certain E, however, the approximate cloaks are resonant, supporting wave functions almost trapped inside the cloaked region and negligible outside. Applications include dc or magnetically tunable ion traps and beam switches.
Energy Transfer in Rotating Turbulence
NASA Technical Reports Server (NTRS)
Cambon, Claude; Mansour, Nagi N.; Godeferd, Fabien S.; Rai, Man Mohan (Technical Monitor)
1995-01-01
The influence or rotation on the spectral energy transfer of homogeneous turbulence is investigated in this paper. Given the fact that linear dynamics, e.g. the inertial waves regime tackled in an RDT (Rapid Distortion Theory) fashion, cannot Affect st homogeneous isotropic turbulent flow, the study of nonlinear dynamics is of prime importance in the case of rotating flows. Previous theoretical (including both weakly nonlinear and EDQNM theories), experimental and DNS (Direct Numerical Simulation) results are gathered here and compared in order to give a self-consistent picture of the nonlinear effects of rotation on tile turbulence. The inhibition of the energy cascade, which is linked to a reduction of the dissipation rate, is shown to be related to a damping due to rotation of the energy transfer. A model for this effect is quantified by a model equation for the derivative-skewness factor, which only involves a micro-Rossby number Ro(sup omega) = omega'/(2(OMEGA))-ratio of rms vorticity and background vorticity as the relevant rotation parameter, in accordance with DNS and EDQNM results fit addition, anisotropy is shown also to develop through nonlinear interactions modified by rotation, in an intermediate range of Rossby numbers (Ro(omega) = (omega)' and Ro(omega)w greater than 1), which is characterized by a marco-Rossby number Ro(sup L) less than 1 and Ro(omega) greater than 1 which is characterized by a macro-Rossby number based on an integral lengthscale L and the micro-Rossby number previously defined. This anisotropy is mainly an angular drain of spectral energy which tends to concentrate energy in tile wave-plane normal to the rotation axis, which is exactly both the slow and the two-dimensional manifold. In Addition, a polarization of the energy distribution in this slow 2D manifold enhances horizontal (normal to the rotation axis) velocity components, and underlies the anisotropic structure of the integral lengthscales. Finally is demonstrated the
Quantum unidirectional rotation directly imaged with molecules
Mizuse, Kenta; Kitano, Kenta; Hasegawa, Hirokazu; Ohshima, Yasuhiro
2015-01-01
A gas-phase molecular ensemble coherently excited to have an oriented rotational angular momentum has recently emerged as an appropriate microscopic system to illustrate quantum mechanical behavior directly linked to classical rotational motion, which has a definite direction. To realize an intuitive visualization of such a unidirectional molecular rotation, we report high-resolution direct imaging of direction-controlled rotational wave packets in nitrogen molecules. The rotational direction was regulated by a pair of time-delayed, polarization-skewed laser pulses, introducing the dynamic chirality to the system. The subsequent spatiotemporal propagation was tracked by a newly developed Coulomb explosion imaging setup. From the observed molecular movie, time-dependent detailed nodal structures, instantaneous alignment, angular dispersion, and fractional revivals of the wave packet are fully characterized while the ensemble keeps rotating in one direction. The present approach, providing an accurate view on unidirectional rotation in quantum regime, will guide more sophisticated molecular manipulations by utilizing its capability in capturing highly structured spatiotemporal evolution of molecular wave packets. PMID:26601205