Alfvénic wave packets collision in a kinetic plasma

NASA Astrophysics Data System (ADS)

Pezzi, Oreste; Parashar, Tulasi N.; Servidio, Sergio; Valentini, Francesco; Malara, Francesco; Matthaeus, William H.; Veltri, Pierluigi

2016-04-01

The problem of two colliding and counter-propagating Alfvénic wave packets has been investigated in detail since the late Seventies. In particular Moffatt [1] and Parker [2] showed that, in the framework of the incompressible magnetohydrodynamics (MHD), nonlinear interactions can develop only during the overlapping of the two packets. Here we describe a similar problem in the framework of the kinetic physics. The collision of two quasi-Alfvénic packets has been analyzed by means of MHD, Hall-MHD and kinetic simulations performed with two different hybrid codes: a PIC code [3] and a Vlasov-Maxwell code [4]. Due to the huge computational cost, only a 2D-3V phase space is allowed (two dimensions in the physical space, three dimensions in the velocity space). Preliminary results suggest that, as well as in the MHD case, the most relevant nonlinear effects occur during the overlapping of the two packets. For both the PIC and Vlasov cases, strong temperature anisotropies are present during the evolution of the wave packets. Moreover, due to the absence of numerical noise, Vlasov simulations show that the collision of the counter-propagating solitary waves produces a significant beam in the velocity distribution functions [5], which, instead, cannot be appreciated in PIC simulations. We remark that, beyond the interest of studying a well-known MHD problem in the realm of the kinetic physics, our results allows also to compare different numerical codes. [1] H.K. Moffatt, Field generation in electrically conducting fluids (Cambridge University Press, 1978). [2] E.N. Parker, Cosmical magnetic fields: their origin and their activity (Oxford University Press, 1979). [3] T.N. Parashar, M.A. Shay, P.A. Cassak and W.H. Matthaeus, Physics of Plasmas 16, 032310 (2009). [4] F. Valentini, P. Trávníček, F. Califano, P. Hellinger & A. Mangeney, Journal of Computational Physics 225, 753-770 (2007). [5] J. He, C. Tu, E. Marsch, C.H. Chen, L. Wang, Z. Pei, L. Zhang, C.S. Salem and S

Airy Wave Packets Accelerating in Space-Time

NASA Astrophysics Data System (ADS)

Kondakci, H. Esat; Abouraddy, Ayman F.

2018-04-01

Although diffractive spreading is an unavoidable feature of all wave phenomena, certain waveforms can attain propagation invariance. A lesser-explored strategy for achieving optical self-similar propagation exploits the modification of the spatiotemporal field structure when observed in reference frames moving at relativistic speeds. For such an observer, it is predicted that the associated Lorentz boost can bring to a halt the axial dynamics of a wave packet of an arbitrary profile. This phenomenon is particularly striking in the case of a self-accelerating beam—such as an Airy beam—whose peak normally undergoes a transverse displacement upon free propagation. Here we synthesize an acceleration-free Airy wave packet that travels in a straight line by deforming its spatiotemporal spectrum to reproduce the impact of a Lorentz boost. The roles of the axial spatial coordinate and time are swapped, leading to "time diffraction" manifested in self-acceleration observed in the propagating Airy wave-packet frame.

Runge-Lenz wave packet in multichannel Stark photoionization

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

Texier, F.

2005-01-01

In a previous slow photoionization experiment, modulations of ionization rings were manifested for Xe in a constant electric field. The present quantum calculation reveals that the modulation is an effect of the multichannel core scattering and of tunneling waves through the Coulomb-Stark potential barrier: the barrier reduces the number of oscillations that is observed relatively to the number of oscillations of the short range wave functions, and the nonhydrogenic core phase shifts modify the position of the ionization rings. We find a hidden difference, in the ionization process, for two close values of the energy depending on the resonance withmore » the barrier. The ionization intensity is interpreted as a Runge-Lenz wave packet; thus, we can relate the quantum modulation to the classical Coulomb-Stark trajectories. The Runge-Lenz wave packet differs from a usual temporal wave packet because its components are eigenstates of the Runge-Lenz vector z projection and its evolution is not temporal but spatial.« less

Nonlinear critical-layer evolution of a forced gravity wave packet

NASA Astrophysics Data System (ADS)

Campbell, L. J.; Maslowe, S. A.

2003-10-01

In this paper, numerical simulations are presented of the nonlinear critical-layer evolution of a forced gravity wave packet in a stratified shear flow. The wave packet, localized in the horizontal direction, is forced at the lower boundary of a two-dimensional domain and propagates vertically towards the critical layer. The wave mean-flow interactions in the critical layer are investigated numerically and contrasted with the results obtained using a spatially periodic monochromatic forcing. With the horizontally localized forcing, the net absorption of the disturbance at the critical layer continues for large time and the onset of the nonlinear breakdown is delayed compared with the case of monochromatic forcing. There is an outward flux of momentum in the horizontal direction so that the horizontal extent of the packet increases with time. The extent to which this happens depends on a number of factors including the amplitude and horizontal length of the forcing. It is also seen that the prolonged absorption of the disturbance stabilizes the solution to the extent that it is always convectively stable; the local Richardson number remains positive well into the nonlinear regime. In this respect, our results for the localized forcing differ from those in the case of monochromatic forcing where significant regions with negative Richardson number appear.

WavePacket: A Matlab package for numerical quantum dynamics.II: Open quantum systems, optimal control, and model reduction

NASA Astrophysics Data System (ADS)

Schmidt, Burkhard; Hartmann, Carsten

2018-07-01

WavePacket is an open-source program package for numeric simulations in quantum dynamics. It can solve time-independent or time-dependent linear Schrödinger and Liouville-von Neumann-equations in one or more dimensions. Also coupled equations can be treated, which allows, e.g., to simulate molecular quantum dynamics beyond the Born-Oppenheimer approximation. Optionally accounting for the interaction with external electric fields within the semi-classical dipole approximation, WavePacket can be used to simulate experiments involving tailored light pulses in photo-induced physics or chemistry. Being highly versatile and offering visualization of quantum dynamics 'on the fly', WavePacket is well suited for teaching or research projects in atomic, molecular and optical physics as well as in physical or theoretical chemistry. Building on the previous Part I [Comp. Phys. Comm. 213, 223-234 (2017)] which dealt with closed quantum systems and discrete variable representations, the present Part II focuses on the dynamics of open quantum systems, with Lindblad operators modeling dissipation and dephasing. This part also describes the WavePacket function for optimal control of quantum dynamics, building on rapid monotonically convergent iteration methods. Furthermore, two different approaches to dimension reduction implemented in WavePacket are documented here. In the first one, a balancing transformation based on the concepts of controllability and observability Gramians is used to identify states that are neither well controllable nor well observable. Those states are either truncated or averaged out. In the other approach, the H2-error for a given reduced dimensionality is minimized by H2 optimal model reduction techniques, utilizing a bilinear iterative rational Krylov algorithm. The present work describes the MATLAB version of WavePacket 5.3.0 which is hosted and further developed at the Sourceforge platform, where also extensive Wiki-documentation as well as numerous

Phase Structure of Strong-Field Tunneling Wave Packets from Molecules.

PubMed

Liu, Ming-Ming; Li, Min; Wu, Chengyin; Gong, Qihuang; Staudte, André; Liu, Yunquan

2016-04-22

We study the phase structure of the tunneling wave packets from strong-field ionization of molecules and present a molecular quantum-trajectory Monte Carlo model to describe the laser-driven dynamics of photoelectron momentum distributions of molecules. Using our model, we reproduce and explain the alignment-dependent molecular frame photoelectron spectra of strong-field tunneling ionization of N_{2} reported by M. Meckel et al. [Nat. Phys. 10, 594 (2014)]. In addition to modeling the low-energy photoelectron angular distributions quantitatively, we extract the phase structure of strong-field molecular tunneling wave packets, shedding light on its physical origin. The initial phase of the tunneling wave packets at the tunnel exit depends on both the initial transverse momentum distribution and the molecular internuclear distance. We further show that the ionizing molecular orbital has a critical effect on the initial phase of the tunneling wave packets. The phase structure of the photoelectron wave packet is a key ingredient for modeling strong-field molecular photoelectron holography, high-harmonic generation, and molecular orbital imaging.

Minimal position-velocity uncertainty wave packets in relativistic and non-relativistic quantum mechanics

NASA Astrophysics Data System (ADS)

Al-Hashimi, M. H.; Wiese, U.-J.

2009-12-01

We consider wave packets of free particles with a general energy-momentum dispersion relation E(p). The spreading of the wave packet is determined by the velocity v=∂pE. The position-velocity uncertainty relation ΔxΔv⩾12|<∂p2E>| is saturated by minimal uncertainty wave packets Φ(p)=Aexp(-αE(p)+βp). In addition to the standard minimal Gaussian wave packets corresponding to the non-relativistic dispersion relation E(p)=p2/2m, analytic calculations are presented for the spreading of wave packets with minimal position-velocity uncertainty product for the lattice dispersion relation E(p)=-cos(pa)/ma2 as well as for the relativistic dispersion relation E(p)=p2+m2. The boost properties of moving relativistic wave packets as well as the propagation of wave packets in an expanding Universe are also discussed.

Initial dynamics of the Norrish Type I reaction in acetone: probing wave packet motion.

PubMed

Brogaard, Rasmus Y; Sølling, Theis I; Møller, Klaus B

2011-02-10

The Norrish Type I reaction in the S(1) (nπ*) state of acetone is a prototype case of ketone photochemistry. On the basis of results from time-resolved mass spectrometry (TRMS) and photoelectron spectroscopy (TRPES) experiments, it was recently suggested that after excitation the wave packet travels toward the S(1) minimum in less than 30 fs and stays there for more than 100 picoseconds [Chem. Phys. Lett.2008, 461, 193]. In this work we present simulated TRMS and TRPES signals based on ab initio multiple spawning simulations of the dynamics during the first 200 fs after excitation, getting quite good agreement with the experimental signals. We can explain the ultrafast decay of the experimental signals in the following manner: the wave packet simply travels, mainly along the deplanarization coordinate, out of the detection window of the ionizing probe. This window is so narrow that subsequent revival of the signal due to the coherent deplanarization vibration is not observed, meaning that from the point of view of the experiment the wave packets travels directly to the S(1) minimum. This result stresses the importance of pursuing a closer link to the experimental signal when using molecular dynamics simulations in interpreting experimental results.

Magnetic helicity conservation and inverse energy cascade in electron magnetohydrodynamic wave packets.

PubMed

Cho, Jungyeon

2011-05-13

Electron magnetohydrodynamics (EMHD) provides a fluidlike description of small-scale magnetized plasmas. An EMHD wave propagates along magnetic field lines. The direction of propagation can be either parallel or antiparallel to the magnetic field lines. We numerically study propagation of three-dimensional (3D) EMHD wave packets moving in one direction. We obtain two major results. (1) Unlike its magnetohydrodynamic (MHD) counterpart, an EMHD wave packet is dispersive. Because of this, EMHD wave packets traveling in one direction create opposite-traveling wave packets via self-interaction and cascade energy to smaller scales. (2) EMHD wave packets traveling in one direction clearly exhibit inverse energy cascade. We find that the latter is due to conservation of magnetic helicity. We compare inverse energy cascade in 3D EMHD turbulence and two-dimensional (2D) hydrodynamic turbulence.

Study on acceleration processes of the radiation belt electrons through interaction with sub-packet chorus waves in parallel propagation

NASA Astrophysics Data System (ADS)

Hiraga, R.; Omura, Y.

2017-12-01

By recent observations, chorus waves include fine structures such as amplitude fluctuations (i.e. sub-packet structure), and it has not been verified in detail yet how energetic electrons are efficiently accelerated under the wave features. In this study, we firstly focus on the acceleration process of a single electron: how it experiences the efficient energy increase by interaction with sub-packet chorus waves in parallel propagation along the Earth's magnetic field. In order to reproduce the chorus waves as seen by the latest observations by Van Allen Probes (Foster et al. 2017), the wave model amplitude in our simulation is structured such that when the wave amplitude nonlinearly grows to reach the optimum amplitude, it starts decreasing until crossing the threshold. Once it crosses the threshold, the wave dissipates and a new wave rises to repeat the nonlinear growth and damping in the same manner. The multiple occurrence of this growth-damping cycle forms a saw tooth-like amplitude variation called sub-packet. This amplitude variation also affects the wave frequency behavior which is derived by the chorus wave equations as a function of the wave amplitude (Omura et al. 2009). It is also reasonable to assume that when a wave packet diminishes and the next wave rises, it has a random phase independent of the previous wave. This randomness (discontinuity) in phase variation is included in the simulation. Through interaction with such waves, dynamics of energetic electrons were tracked. As a result, some electrons underwent an efficient acceleration process defined as successive entrapping, in which an electron successfully continues to surf the trapping potential generated by consecutive wave packets. When successive entrapping occurs, an electron trapped and de-trapped (escape the trapping potential) by a single wave packet falls into another trapping potential generated by the next wave sub-packet and continuously accelerated. The occurrence of successive

Steering attosecond electron wave packets with light.

PubMed

Kienberger, R; Hentschel, M; Uiberacker, M; Spielmann, Ch; Kitzler, M; Scrinzi, A; Wieland, M; Westerwalbesloh, Th; Kleineberg, U; Heinzmann, U; Drescher, M; Krausz, F

2002-08-16

Photoelectrons excited by extreme ultraviolet or x-ray photons in the presence of a strong laser field generally suffer a spread of their energies due to the absorption and emission of laser photons. We demonstrate that if the emitted electron wave packet is temporally confined to a small fraction of the oscillation period of the interacting light wave, its energy spectrum can be up- or downshifted by many times the laser photon energy without substantial broadening. The light wave can accelerate or decelerate the electron's drift velocity, i.e., steer the electron wave packet like a classical particle. This capability strictly relies on a sub-femtosecond duration of the ionizing x-ray pulse and on its timing to the phase of the light wave with a similar accuracy, offering a simple and potentially single-shot diagnostic tool for attosecond pump-probe spectroscopy.

Time-dependent wave packet simulations of transport through Aharanov-Bohm rings with an embedded quantum dot.

PubMed

Kreisbeck, C; Kramer, T; Molina, R A

2017-04-20

We have performed time-dependent wave packet simulations of realistic Aharonov-Bohm (AB) devices with a quantum dot embedded in one of the arms of the interferometer. The AB ring can function as a measurement device for the intrinsic transmission phase through the quantum dot, however, care has to be taken in analyzing the influence of scattering processes in the junctions of the interferometer arms. We consider a harmonic quantum dot and show how the Darwin-Fock spectrum emerges as a unique pattern in the interference fringes of the AB oscillations.

Trajectory description of the quantum–classical transition for wave packet interference

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

Chou, Chia-Chun, E-mail: ccchou@mx.nthu.edu.tw

2016-08-15

The quantum–classical transition for wave packet interference is investigated using a hydrodynamic description. A nonlinear quantum–classical transition equation is obtained by introducing a degree of quantumness ranging from zero to one into the classical time-dependent Schrödinger equation. This equation provides a continuous description for the transition process of physical systems from purely quantum to purely classical regimes. In this study, the transition trajectory formalism is developed to provide a hydrodynamic description for the quantum–classical transition. The flow momentum of transition trajectories is defined by the gradient of the action function in the transition wave function and these trajectories follow themore » main features of the evolving probability density. Then, the transition trajectory formalism is employed to analyze the quantum–classical transition of wave packet interference. For the collision-like wave packet interference where the propagation velocity is faster than the spreading speed of the wave packet, the interference process remains collision-like for all the degree of quantumness. However, the interference features demonstrated by transition trajectories gradually disappear when the degree of quantumness approaches zero. For the diffraction-like wave packet interference, the interference process changes continuously from a diffraction-like to collision-like case when the degree of quantumness gradually decreases. This study provides an insightful trajectory interpretation for the quantum–classical transition of wave packet interference.« less

Quantum-shutter approach to tunneling time scales with wave packets

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

Yamada, Norifumi; Garcia-Calderon, Gaston; Villavicencio, Jorge

2005-07-15

The quantum-shutter approach to tunneling time scales [G. Garcia-Calderon and A. Rubio, Phys. Rev. A 55, 3361 (1997)], which uses a cutoff plane wave as the initial condition, is extended to consider certain type of wave packet initial conditions. An analytical expression for the time-evolved wave function is derived. The time-domain resonance, the peaked structure of the probability density (as the function of time) at the exit of the barrier, originally found with the cutoff plane wave initial condition, is studied with the wave packet initial conditions. It is found that the time-domain resonance is not very sensitive to themore » width of the packet when the transmission process occurs in the tunneling regime.« less

Collisions of two Alfvénic wave packets in a kinetic plasma

NASA Astrophysics Data System (ADS)

Pezzi, O.; Servidio, S.; Valentini, F.; Parashar, T.; Malara, F.; Matthaeus, W. H.; Veltri, P.

2016-12-01

The problem of two colliding and counter-propagating Alfvénic wave packets has been investigated in detail since the late Seventies. In particular Moffatt [1] and Parker [2] showed that, in the framework of the incompressible magnetohydrodynamics (MHD), nonlinear interactions can develop only during the overlapping of the two packets. Here we describe a similar problem in the framework of the kinetic physics. The collision of two quasi-Alfvénic packets has been analyzed by means of MHD, Hall-MHD and kinetic simulations performed with two different hybrid codes: a PIC code [3] and a Vlasov-Maxwell code [4]. Due to the huge computational cost, only a 2D-3V phase space is allowed (two dimensions in the physical space, three dimensions in the velocity space). Preliminary results suggest that, as well as in the MHD case, the most relevant nonlinear effects occur during the overlapping of the two packets. For both the PIC and Vlasov cases, strong temperature anisotropies are present during the evolution of the wave packets. Moreover, due to the absence of numerical noise, Vlasov simulations show that the collision of the counter-propagating solitary waves produces a significant beam in the velocity distribution functions [5], which, instead, cannot be appreciated in PIC simulations. We remark that, beyond the interest of studying a well-known MHD problem in the realm of the kinetic physics, our results allows also to compare different numerical codes. [1] H.K. Moffatt, Field generation in electrically conducting fluids (Cambridge University Press, 1978). [2] E.N. Parker, Cosmical magnetic fields: their origin and their activity (Oxford University Press, 1979). [3] T.N. Parashar, M.A. Shay, P.A. Cassak and W.H. Matthaeus, Physics of Plasmas 16, 032310 (2009). [4] F. Valentini, P. Trávníček, F. Califano, P. Hellinger & A. Mangeney, Journal of Computational Physics 225, 753-770 (2007). [5] J. He, C. Tu, E. Marsch, C.H. Chen, L. Wang, Z. Pei, L. Zhang, C.S. Salem and S

WavePacket: A Matlab package for numerical quantum dynamics. I: Closed quantum systems and discrete variable representations

NASA Astrophysics Data System (ADS)

Schmidt, Burkhard; Lorenz, Ulf

2017-04-01

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

Spatiotemporal Airy Ince-Gaussian wave packets in strongly nonlocal nonlinear media.

PubMed

Peng, Xi; Zhuang, Jingli; Peng, Yulian; Li, DongDong; Zhang, Liping; Chen, Xingyu; Zhao, Fang; Deng, Dongmei

2018-03-08

The self-accelerating Airy Ince-Gaussian (AiIG) and Airy helical Ince-Gaussian (AihIG) wave packets in strongly nonlocal nonlinear media (SNNM) are obtained by solving the strongly nonlocal nonlinear Schrödinger equation. For the first time, the propagation properties of three dimensional localized AiIG and AihIG breathers and solitons in the SNNM are demonstrated, these spatiotemporal wave packets maintain the self-accelerating and approximately non-dispersion properties in temporal dimension, periodically oscillating (breather state) or steady (soliton state) in spatial dimension. In particular, their numerical experiments of spatial intensity distribution, numerical simulations of spatiotemporal distribution, as well as the transverse energy flow and the angular momentum in SNNM are presented. Typical examples of the obtained solutions are based on the ratio between the input power and the critical power, the ellipticity and the strong nonlocality parameter. The comparisons of analytical solutions with numerical simulations and numerical experiments of the AiIG and AihIG optical solitons show that the numerical results agree well with the analytical solutions in the case of strong nonlocality.

Coherent wave packet dynamics in a double-well potential in cavity

NASA Astrophysics Data System (ADS)

Zheng, Li; Li, Gang; Ding, Ming-Song; Wang, Yong-Liang; Zhang, Yun-Cui

2018-02-01

We investigate the coherent wave packet dynamics of a two-level atom trapped in a symmetric double-well potential in a near-resonance cavity. Prepared on one side of the double-well potential, the atom wave packet oscillates between the left and right wells, while recoil induced by the emitted photon from the atom entangles the atomic internal and external degrees of freedom. The collapse and revival of the tunneling occurs. Adjusting the width of the wave packets, one can modify the tunneling frequency and suppress the tunneling.

Propagation velocity of Alfven wave packets in a dissipative plasma

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

Amagishi, Y.; Nakagawa, H.; Tanaka, M.

1994-09-01

We have experimentally studied the behavior of Alfven wave packets in a dissipative plasma due to ion--neutral-atom collisions. It is urged that the central frequency of the packet is observed to gradually decrease with traveling distance in the absorption range of frequencies because of a differential damping among the Fourier components, and that the measured average velocity of its peak amplitude is not accounted for by the conventional group velocity, but by the prediction derived by Tanaka, Fujiwara, and Ikegami [Phys. Rev. A 34, 4851 (1986)]. Furthermore, when the initial central frequency is close to the critical frequency in themore » anomalous dispersion, the wave packet apparently collapses when traveling along the magnetic field; however, we have found that it is decomposed into another two wave packets with the central frequencies being higher or lower than the critical frequency.« less

Nonlinear saturation of wave packets excited by low-energy electron horseshoe distributions.

PubMed

Krafft, C; Volokitin, A

2013-05-01

Horseshoe distributions are shell-like particle distributions that can arise in space and laboratory plasmas when particle beams propagate into increasing magnetic fields. The present paper studies the stability and the dynamics of wave packets interacting resonantly with electrons presenting low-energy horseshoe or shell-type velocity distributions in a magnetized plasma. The linear instability growth rates are determined as a function of the ratio of the plasma to the cyclotron frequencies, of the velocity and the opening angle of the horseshoe, and of the relative thickness of the shell. The nonlinear stage of the instability is investigated numerically using a symplectic code based on a three-dimensional Hamiltonian model. Simulation results show that the dynamics of the system is mainly governed by wave-particle interactions at Landau and normal cyclotron resonances and that the high-order normal cyclotron resonances play an essential role. Specific features of the dynamics of particles interacting simultaneously with two or more waves at resonances of different natures and orders are discussed, showing that such complex processes determine the main characteristics of the wave spectrum's evolution. Simulations with wave packets presenting quasicontinuous spectra provide a full picture of the relaxation of the horseshoe distribution, revealing two main phases of the evolution: an initial stage of wave energy growth, characterized by a fast filling of the shell, and a second phase of slow damping of the wave energy, accompanied by final adjustments of the electron distribution. The influence of the density inhomogeneity along the horseshoe on the wave-particle dynamics is also discussed.

Localizing high-lying Rydberg wave packets with two-color laser fields

NASA Astrophysics Data System (ADS)

Larimian, Seyedreza; Lemell, Christoph; Stummer, Vinzenz; Geng, Ji-Wei; Roither, Stefan; Kartashov, Daniil; Zhang, Li; Wang, Mu-Xue; Gong, Qihuang; Peng, Liang-You; Yoshida, Shuhei; Burgdörfer, Joachim; Baltuška, Andrius; Kitzler, Markus; Xie, Xinhua

2017-08-01

We demonstrate control over the localization of high-lying Rydberg wave packets in argon atoms with phase-locked orthogonally polarized two-color laser fields. With a reaction microscope, we measure ionization signals of high-lying Rydberg states induced by a weak dc field and blackbody radiation as a function of the relative phase between the two-color fields. We find that the dc-field-ionization yield of high-lying Rydberg argon atoms oscillates with the relative two-color phase with a period of 2 π while the photoionization signal by blackbody radiation shows a period of π . Accompanying simulations show that these observations are a clear signature of the asymmetric localization of electrons recaptured into very elongated (low angular momentum) high-lying Rydberg states after conclusion of the laser pulse. Our findings thus open an effective pathway to control the localization of high-lying Rydberg wave packets.

Communication: Quantum molecular dynamics simulation of liquid para-hydrogen by nuclear and electron wave packet approach.

PubMed

Hyeon-Deuk, Kim; Ando, Koji

2014-05-07

Liquid para-hydrogen (p-H2) is a typical quantum liquid which exhibits strong nuclear quantum effects (NQEs) and thus anomalous static and dynamic properties. We propose a real-time simulation method of wave packet (WP) molecular dynamics (MD) based on non-empirical intra- and inter-molecular interactions of non-spherical hydrogen molecules, and apply it to condensed-phase p-H2. The NQEs, such as WP delocalization and zero-point energy, are taken into account without perturbative expansion of prepared model potential functions but with explicit interactions between nuclear and electron WPs. The developed MD simulation for 100 ps with 1200 hydrogen molecules is realized at feasible computational cost, by which basic experimental properties of p-H2 liquid such as radial distribution functions, self-diffusion coefficients, and shear viscosities are all well reproduced.

Excited-state vibronic wave-packet dynamics in H2 probed by XUV transient four-wave mixing

NASA Astrophysics Data System (ADS)

Cao, Wei; Warrick, Erika R.; Fidler, Ashley; Leone, Stephen R.; Neumark, Daniel M.

2018-02-01

The complex behavior of a molecular wave packet initiated by an extreme ultraviolet (XUV) pulse is investigated with noncollinear wave mixing spectroscopy. A broadband XUV pulse spanning 12-16 eV launches a wave packet in H2 comprising a coherent superposition of multiple electronic and vibrational levels. The molecular wave packet evolves freely until a delayed few-cycle optical laser pulse arrives to induce nonlinear signals in the XUV via four-wave mixing (FWM). The angularly resolved FWM signals encode rich energy exchange processes between the optical laser field and the XUV-excited molecule. The noncollinear geometry enables spatial separation of ladder and V- or Λ-type transitions induced by the optical field. Ladder transitions, in which the energy exchange with the optical field is around 3 eV, appear off axis from the incident XUV beam. Each vibrationally revolved FWM line probes a different part of the wave packet in energy, serving as a promising tool for energetic tomography of molecular wave packets. V- or Λ-type transitions, in which the energy exchange is well under 1 eV, result in on-axis nonlinear signals. The first-order versus third-order interference of the on-axis signal serves as a mapping tool of the energy flow pathways. Intra- and interelectronic potential energy curve transitions are decisively identified. The current study opens possibilities for accessing complete dynamic information in XUV-excited complex systems.

Annular wave packets at Dirac points in graphene and their probability-density oscillation.

PubMed

Luo, Ji; Valencia, Daniel; Lu, Junqiang

2011-12-14

Wave packets in graphene whose central wave vector is at Dirac points are investigated by numerical calculations. Starting from an initial Gaussian function, these wave packets form into annular peaks that propagate to all directions like ripple-rings on water surface. At the beginning, electronic probability alternates between the central peak and the ripple-rings and transient oscillation occurs at the center. As time increases, the ripple-rings propagate at the fixed Fermi speed, and their widths remain unchanged. The axial symmetry of the energy dispersion leads to the circular symmetry of the wave packets. The fixed speed and widths, however, are attributed to the linearity of the energy dispersion. Interference between states that, respectively, belong to two branches of the energy dispersion leads to multiple ripple-rings and the probability-density oscillation. In a magnetic field, annular wave packets become confined and no longer propagate to infinity. If the initial Gaussian width differs greatly from the magnetic length, expanding and shrinking ripple-rings form and disappear alternatively in a limited spread, and the wave packet resumes the Gaussian form frequently. The probability thus oscillates persistently between the central peak and the ripple-rings. If the initial Gaussian width is close to the magnetic length, the wave packet retains the Gaussian form and its height and width oscillate with a period determined by the first Landau energy. The wave-packet evolution is determined jointly by the initial state and the magnetic field, through the electronic structure of graphene in a magnetic field. © 2011 American Institute of Physics

Cherenkov Radiation Control via Self-accelerating Wave-packets.

PubMed

Hu, Yi; Li, Zhili; Wetzel, Benjamin; Morandotti, Roberto; Chen, Zhigang; Xu, Jingjun

2017-08-18

Cherenkov radiation is a ubiquitous phenomenon in nature. It describes electromagnetic radiation from a charged particle moving in a medium with a uniform velocity larger than the phase velocity of light in the same medium. Such a picture is typically adopted in the investigation of traditional Cherenkov radiation as well as its counterparts in different branches of physics, including nonlinear optics, spintronics and plasmonics. In these cases, the radiation emitted spreads along a "cone", making it impractical for most applications. Here, we employ a self-accelerating optical pump wave-packet to demonstrate controlled shaping of one type of generalized Cherenkov radiation - dispersive waves in optical fibers. We show that, by tuning the parameters of the wave-packet, the emitted waves can be judiciously compressed and focused at desired locations, paving the way to such control in any physical system.

Thermal averages in a quantum point contact with a single coherent wave packet.

PubMed

Heller, E J; Aidala, K E; LeRoy, B J; Bleszynski, A C; Kalben, A; Westervelt, R M; Maranowski, K D; Gossard, A C

2005-07-01

A novel formal equivalence between thermal averages of coherent properties (e.g., conductance) and time averages of a single wave packet arises for Fermi gases and certain geometries. In the case of one open channel in a quantum point contact (QPC), only one wave packet history, with the wave packet width equal to the thermal length, completely determines the thermally averaged conductance. The formal equivalence moreover allows very simple physical interpretations of interference features surviving under thermal averaging. Simply put, pieces of the thermal wave packet returning to the QPC along independent paths must arrive at the same time in order to interfere. Remarkably, one immediate result of this approach is that higher temperature leads to narrower wave packets and therefore better resolution of events in the time domain. In effect, experiments at 4.2 K are performing time-gated experiments at better than a gigahertz. Experiments involving thermally averaged ballistic conductance in 2DEGS are presented as an application of this picture.

Plane wave packet formulation of atom-plus-diatom quantum reactive scattering.

PubMed

Althorpe, Stuart C

2004-07-15

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

Communication: Quantum molecular dynamics simulation of liquid para-hydrogen by nuclear and electron wave packet approach

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

Hyeon-Deuk, Kim, E-mail: kim@kuchem.kyoto-u.ac.jp; Japan Science and Technology Agency, PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012; Ando, Koji

2014-05-07

Liquid para-hydrogen (p-H{sub 2}) is a typical quantum liquid which exhibits strong nuclear quantum effects (NQEs) and thus anomalous static and dynamic properties. We propose a real-time simulation method of wave packet (WP) molecular dynamics (MD) based on non-empirical intra- and inter-molecular interactions of non-spherical hydrogen molecules, and apply it to condensed-phase p-H{sub 2}. The NQEs, such as WP delocalization and zero-point energy, are taken into account without perturbative expansion of prepared model potential functions but with explicit interactions between nuclear and electron WPs. The developed MD simulation for 100 ps with 1200 hydrogen molecules is realized at feasible computationalmore » cost, by which basic experimental properties of p-H{sub 2} liquid such as radial distribution functions, self-diffusion coefficients, and shear viscosities are all well reproduced.« less

Pump-dump iterative squeezing of vibrational wave packets.

PubMed

Chang, Bo Y; Sola, Ignacio R

2005-12-22

The free motion of a nonstationary vibrational wave packet in an electronic potential is a source of interesting quantum properties. In this work we propose an iterative scheme that allows continuous stretching and squeezing of a wave packet in the ground or in an excited electronic state, by switching the wave function between both potentials with pi pulses at certain times. Using a simple model of displaced harmonic oscillators and delta pulses, we derive the analytical solution and the conditions for its possible implementation and optimization in different molecules and electronic states. We show that the main constraining parameter is the pulse bandwidth. Although in principle the degree of squeezing (or stretching) is not bounded, the physical resources increase quadratically with the number of iterations, while the achieved squeezing only increases linearly.

Gaussian and Airy wave packets of massive particles with orbital angular momentum

NASA Astrophysics Data System (ADS)

Karlovets, Dmitry V.

2015-01-01

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

Stochastic Acceleration of Ions Driven by Pc1 Wave Packets

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Sibeck, D. G.; Tel'nikhin, A. A.; Kronberg, T. K.

2015-01-01

The stochastic motion of protons and He(sup +) ions driven by Pc1 wave packets is studied in the context of resonant particle heating. Resonant ion cyclotron heating typically occurs when wave powers exceed 10(exp -4) nT sq/Hz. Gyroresonance breaks the first adiabatic invariant and energizes keV ions. Cherenkov resonances with the electrostatic component of wave packets can also accelerate ions. The main effect of this interaction is to accelerate thermal protons to the local Alfven speed. The dependencies of observable quantities on the wave power and plasma parameters are determined, and estimates for the heating extent and rate of particle heating in these wave-particle interactions are shown to be in reasonable agreement with known empirical data.

Propagation velocity of Alfvén wave packets in a dissipative plasma

NASA Astrophysics Data System (ADS)

Amagishi, Yoshimitsu; Nakagawa, Hiroyuki; Tanaka, Masayoshi

1994-09-01

We have experimentally studied the behavior of Alfvén wave packets in a dissipative plasma due to ion-neutral-atom collisions. It is urged that the central frequency of the packet is observed to gradually decrease with traveling distance in the absorption range of frequencies because of a differential damping among the Fourier components, and that the measured average velocity of its peak amplitude is not accounted for by the conventional group velocity, but by the prediction derived by Tanaka, Fujiwara, and Ikegami [Phys. Rev. A 34, 4851 (1986)]. Furthermore, when the initial central frequency is close to the critical frequency in the anomalous dispersion, the wave packet apparently collapses when traveling along the magnetic field; however, we have found that it is decomposed into another two wave packets with the central frequencies being higher or lower than the critical frequency.

Attosecond transient absorption of a bound wave packet coupled to a smooth continuum

DOE PAGES

Dahlström, Jan Marcus; Pabst, Stefan; Lindroth, Eva

2017-10-16

Here, we investigate the possibility of using transient absorption of a coherent bound electron wave packet in hydrogen as an attosecond pulse characterization technique. In a recent work, we have shown that photoionization of such a coherent bound electron wave packet opens up for pulse characterization with unprecedented temporal accuracy—independent of the atomic structure—with maximal photoemission at all kinetic energies given a wave packet with zero relative phase. Here, we perform numerical propagation of the time-dependent Schrödinger equation and analytical calculations based on perturbation theory to show that the energy-resolved maximal absorption of photons from the attosecond pulse does not uniquely occur at a zero relative phase of the initial wave packet. Instead, maximal absorption occurs at different relative wave packet phases, distributed as a non-monotonous function with a smoothmore » $$-\\pi /2$$ shift across the central photon energy (given a Fourier-limited Gaussian pulse). Similar results are also found in helium. Our finding is surprising, because it implies that the energy-resolved photoelectrons are not mapped one-to-one with the energy-resolved absorbed photons of the attosecond pulse.« less

Attosecond transient absorption of a bound wave packet coupled to a smooth continuum

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

Dahlström, Jan Marcus; Pabst, Stefan; Lindroth, Eva

Here, we investigate the possibility of using transient absorption of a coherent bound electron wave packet in hydrogen as an attosecond pulse characterization technique. In a recent work, we have shown that photoionization of such a coherent bound electron wave packet opens up for pulse characterization with unprecedented temporal accuracy—independent of the atomic structure—with maximal photoemission at all kinetic energies given a wave packet with zero relative phase. Here, we perform numerical propagation of the time-dependent Schrödinger equation and analytical calculations based on perturbation theory to show that the energy-resolved maximal absorption of photons from the attosecond pulse does not uniquely occur at a zero relative phase of the initial wave packet. Instead, maximal absorption occurs at different relative wave packet phases, distributed as a non-monotonous function with a smoothmore » $$-\\pi /2$$ shift across the central photon energy (given a Fourier-limited Gaussian pulse). Similar results are also found in helium. Our finding is surprising, because it implies that the energy-resolved photoelectrons are not mapped one-to-one with the energy-resolved absorbed photons of the attosecond pulse.« less

Resonance-assisted decay of nondispersive wave packets.

PubMed

Wimberger, Sandro; Schlagheck, Peter; Eltschka, Christopher; Buchleitner, Andreas

2006-07-28

We present a quantitative semiclassical theory for the decay of nondispersive electronic wave packets in driven, ionizing Rydberg systems. Statistically robust quantities are extracted combining resonance-assisted tunneling with subsequent transport across chaotic phase space and a final ionization step.

Self-action of Bessel wave packets in a system of coupled light guides and formation of light bullets

NASA Astrophysics Data System (ADS)

Balakin, A. A.; Mironov, V. A.; Skobelev, S. A.

2017-01-01

The self-action of two-dimensional and three-dimensional Bessel wave packets in a system of coupled light guides is considered using the discrete nonlinear Schrödinger equation. The features of the self-action of such wave fields are related to their initial strong spatial inhomogeneity. The numerical simulation shows that for the field amplitude exceeding a critical value, the development of an instability typical of a medium with the cubic nonlinearity is observed. Various regimes are studied: the self-channeling of a wave beam in one light guide at powers not strongly exceeding a critical value, the formation of the "kaleidoscopic" picture of a wave packet during the propagation of higher-power radiation along a stratified medium, the formation of light bullets during competition between self-focusing and modulation instabilities in the case of three-dimensional wave packets, etc. In the problem of laser pulse shortening, the situation is considered when the wave-field stratification in the transverse direction dominates. This process is accompanied by the self-compression of laser pulses in well enough separated light guides. The efficiency of conversion of the initial Bessel field distribution to two flying parallel light bullets is about 50%.

Dynamics of coupled plasmon polariton wave packets excited at a subwavelength slit in optically thin metal films

NASA Astrophysics Data System (ADS)

Wang, Lei-Ming; Zhang, Lingxiao; Seideman, Tamar; Petek, Hrvoje

2012-10-01

We study by numerical simulations the excitation and propagation dynamics of coupled surface plasmon polariton (SPP) wave packets (WPs) in optically thin Ag films and a bulk Ag/vacuum interface under the illumination of a subwavelength slit by 400 nm continuous wave (cw) and femtosecond pulsed light. The generated surface fields include contributions from both SPPs and quasicylindrical waves, which dominate in different regimes. We explore aspects of the coupled SPP modes in Ag thin films, including symmetry, propagation, attenuation, and the variation of coupling with incident angle and film thickness. Simulations of the electromagnetic transients initiated with femtosecond pulses reveal new features of coupled SPP WP generation and propagation in thin Ag films. Our results show that, under pulsed excitation, the SPP modes in an Ag thin film break up into two distinct bound surface wave packets characterized by marked differences in symmetries, group velocities, attenuation lengths, and dispersion properties. The nanometer spatial and femtosecond temporal scale excitation and propagation dynamics of the coupled SPP WPs are revealed in detail by movies recording the evolution of their transient field distributions.

Spectro-spatial analysis of wave packet propagation in nonlinear acoustic metamaterials

NASA Astrophysics Data System (ADS)

Zhou, W. J.; Li, X. P.; Wang, Y. S.; Chen, W. Q.; Huang, G. L.

2018-01-01

The objective of this work is to analyze wave packet propagation in weakly nonlinear acoustic metamaterials and reveal the interior nonlinear wave mechanism through spectro-spatial analysis. The spectro-spatial analysis is based on full-scale transient analysis of the finite system, by which dispersion curves are generated from the transmitted waves and also verified by the perturbation method (the L-P method). We found that the spectro-spatial analysis can provide detailed information about the solitary wave in short-wavelength region which cannot be captured by the L-P method. It is also found that the optical wave modes in the nonlinear metamaterial are sensitive to the parameters of the nonlinear constitutive relation. Specifically, a significant frequency shift phenomenon is found in the middle-wavelength region of the optical wave branch, which makes this frequency region behave like a band gap for transient waves. This special frequency shift is then used to design a direction-biased waveguide device, and its efficiency is shown by numerical simulations.

Generalized Gaussian wave packet dynamics: Integrable and chaotic systems.

PubMed

Pal, Harinder; Vyas, Manan; Tomsovic, Steven

2016-01-01

The ultimate semiclassical wave packet propagation technique is a complex, time-dependent Wentzel-Kramers-Brillouin method known as generalized Gaussian wave packet dynamics (GGWPD). It requires overcoming many technical difficulties in order to be carried out fully in practice. In its place roughly twenty years ago, linearized wave packet dynamics was generalized to methods that include sets of off-center, real trajectories for both classically integrable and chaotic dynamical systems that completely capture the dynamical transport. The connections between those methods and GGWPD are developed in a way that enables a far more practical implementation of GGWPD. The generally complex saddle-point trajectories at its foundation are found using a multidimensional Newton-Raphson root search method that begins with the set of off-center, real trajectories. This is possible because there is a one-to-one correspondence. The neighboring trajectories associated with each off-center, real trajectory form a path that crosses a unique saddle; there are exceptions that are straightforward to identify. The method is applied to the kicked rotor to demonstrate the accuracy improvement as a function of ℏ that comes with using the saddle-point trajectories.

Wave-packet formation at the zero-dispersion point in the Gardner-Ostrovsky equation.

PubMed

Whitfield, A J; Johnson, E R

2015-05-01

The long-time effect of weak rotation on an internal solitary wave is the decay into inertia-gravity waves and the eventual emergence of a coherent, steadily propagating, nonlinear wave packet. There is currently no entirely satisfactory explanation as to why these wave packets form. Here the initial value problem is considered within the context of the Gardner-Ostrovsky, or rotation-modified extended Korteweg-de Vries, equation. The linear Gardner-Ostrovsky equation has maximum group velocity at a critical wave number, often called the zero-dispersion point. It is found here that a nonlinear splitting of the wave-number spectrum at the zero-dispersion point, where energy is shifted into the modulationally unstable regime of the Gardner-Ostrovsky equation, is responsible for the wave-packet formation. Numerical comparisons of the decay of a solitary wave in the Gardner-Ostrovsky equation and a derived nonlinear Schrödinger equation at the zero-dispersion point are used to confirm the spectral splitting.

High-order-harmonic generation from solids: The contributions of the Bloch wave packets moving at the group and phase velocities

NASA Astrophysics Data System (ADS)

Du, Tao-Yuan; Huang, Xiao-Huan; Bian, Xue-Bin

2018-01-01

We study numerically the Bloch electron wave-packet dynamics in periodic potentials to simulate laser-solid interactions. We introduce an alternative perspective in the coordinate space combined with the motion of the Bloch electron wave packets moving at group and phase velocities under the laser fields. This model interprets the origins of the two contributions (intra- and interband transitions) in the high-order harmonic generation (HHG) processes by investigating the local and global behaviours of the wave packets. It also elucidates the underlying physical picture of the HHG intensity enhancement by means of carrier-envelope phase, chirp, and inhomogeneous fields. It provides a deep insight into the emission of high-order harmonics from solids. This model is instructive for experimental measurements and provides an alternative avenue to distinguish mechanisms of the HHG from solids in different laser fields.

Coupled wave-packets for non-adiabatic molecular dynamics: a generalization of Gaussian wave-packet dynamics to multiple potential energy surfaces

DOE PAGES

White, Alexander James; Tretiak, Sergei; Mozyrsky, Dima V.

2016-04-25

Accurate simulation of the non-adiabatic dynamics of molecules in excited electronic states is key to understanding molecular photo-physical processes. Here we present a novel method, based on a semiclassical approximation, that is as efficient as the commonly used mean field Ehrenfest or ad hoc surface hopping methods and properly accounts for interference and decoherence effects. This novel method is an extension of Heller's thawed Gaussian wave-packet dynamics that includes coupling between potential energy surfaces. By studying several standard test problems we demonstrate that the accuracy of the method can be systematically improved while maintaining high efficiency. The method is suitablemore » for investigating the role of quantum coherence in the non-adiabatic dynamics of many-atom molecules.« less

Energy and Information Transfer Via Coherent Exciton Wave Packets

NASA Astrophysics Data System (ADS)

Zang, Xiaoning

Electronic excitons are bound electron-hole states that are generated when light interacts with matter. Such excitations typically entangle with phonons and rapidly decohere; the resulting electronic state dynamics become diffusive as a result. However, if the exciton-phonon coupling can be reduced, it may be possible to construct excitonic wave packets that offer a means of efficiently transmitting information and energy. This thesis is a combined theory/computation investigation to design condensed matter systems which support the requisite coherent transport. Under the idealizing assumption that exciton-phonon entanglement could be completely suppressed, the majority of this thesis focuses on the creation and manipulation of exciton wave packets in quasi-one-dimensional systems. While each site could be a silicon quantum dot, the actual implementation focused on organic molecular assemblies for the sake of computational simplicity, ease of experimental implementation, potential for coherent transport, and promise because of reduced structural uncertainty. A laser design was derived to create exciton wave packets with tunable shape and speed. Quantum interference was then exploited to manipulate these packets to block, pass, and even dissociate excitons based on their energies. These developments allow exciton packets to be considered within the arena of quantum information science. The concept of controllable excitonic wave packets was subsequently extended to consider molecular designs that allow photons with orbital angular momentum to be absorbed to create excitons with a quasi-angular momentum of their own. It was shown that a well-defined measure of topological charge is conserved in such light-matter interactions. Significantly, it was also discovered that such molecules allow photon angular momenta to be combined and later emitted. This amounts to a new way of up/down converting photonic angular momentum without relying on nonlinear optical materials. The

Symmetry and conservation laws in semiclassical wave packet dynamics

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

Ohsawa, Tomoki, E-mail: tomoki@utdallas.edu

2015-03-15

We formulate symmetries in semiclassical Gaussian wave packet dynamics and find the corresponding conserved quantities, particularly the semiclassical angular momentum, via Noether’s theorem. We consider two slightly different formulations of Gaussian wave packet dynamics; one is based on earlier works of Heller and Hagedorn and the other based on the symplectic-geometric approach by Lubich and others. In either case, we reveal the symplectic and Hamiltonian nature of the dynamics and formulate natural symmetry group actions in the setting to derive the corresponding conserved quantities (momentum maps). The semiclassical angular momentum inherits the essential properties of the classical angular momentum asmore » well as naturally corresponds to the quantum picture.« less

The exact thermal rotational spectrum of a two-dimensional rigid rotor obtained using Gaussian wave packet dynamics

NASA Technical Reports Server (NTRS)

Reimers, J. R.; Heller, E. J.

1985-01-01

The exact thermal rotational spectrum of a two-dimensional rigid rotor is obtained using Gaussian wave packet dynamics. The spectrum is obtained by propagating, without approximation, infinite sets of Gaussian wave packets. These sets are constructed so that collectively they have the correct periodicity, and indeed, are coherent states appropriate to this problem. Also, simple, almost classical, approximations to full wave packet dynamics are shown to give results which are either exact or very nearly exact. Advantages of the use of Gaussian wave packet dynamics over conventional linear response theory are discussed.

Engineering and manipulating exciton wave packets

NASA Astrophysics Data System (ADS)

Zang, Xiaoning; Montangero, Simone; Carr, Lincoln D.; Lusk, Mark T.

2017-05-01

When a semiconductor absorbs light, the resulting electron-hole superposition amounts to a uncontrolled quantum ripple that eventually degenerates into diffusion. If the conformation of these excitonic superpositions could be engineered, though, they would constitute a new means of transporting information and energy. We show that properly designed laser pulses can be used to create such excitonic wave packets. They can be formed with a prescribed speed, direction, and spectral make-up that allows them to be selectively passed, rejected, or even dissociated using superlattices. Their coherence also provides a handle for manipulation using active, external controls. Energy and information can be conveniently processed and subsequently removed at a distant site by reversing the original procedure to produce a stimulated emission. The ability to create, manage, and remove structured excitons comprises the foundation for optoexcitonic circuits with application to a wide range of quantum information, energy, and light-flow technologies. The paradigm is demonstrated using both tight-binding and time-domain density functional theory simulations.

Wave-variable framework for networked robotic systems with time delays and packet losses

NASA Astrophysics Data System (ADS)

Puah, Seng-Ming; Liu, Yen-Chen

2017-05-01

This paper investigates the problem of networked control system for nonlinear robotic manipulators under time delays and packet loss by using passivity technique. With the utilisation of wave variables and a passive remote controller, the networked robotic system is demonstrated to be stable with guaranteed position regulation. For the input/output signals of robotic systems, a discretisation block is exploited to convert continuous-time signals to discrete-time signals, and vice versa. Subsequently, we propose a packet management, called wave-variable modulation, to cope with the proposed networked robotic system under time delays and packet losses. Numerical examples and experimental results are presented to demonstrate the performance of the proposed wave-variable-based networked robotic systems.

Self-action of Bessel wave packets in a system of coupled light guides and formation of light bullets

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

Balakin, A. A., E-mail: balakin.alexey@yandex.ru; Mironov, V. A.; Skobelev, S. A., E-mail: sk.sa1981@gmail.com

The self-action of two-dimensional and three-dimensional Bessel wave packets in a system of coupled light guides is considered using the discrete nonlinear Schrödinger equation. The features of the self-action of such wave fields are related to their initial strong spatial inhomogeneity. The numerical simulation shows that for the field amplitude exceeding a critical value, the development of an instability typical of a medium with the cubic nonlinearity is observed. Various regimes are studied: the self-channeling of a wave beam in one light guide at powers not strongly exceeding a critical value, the formation of the “kaleidoscopic” picture of a wavemore » packet during the propagation of higher-power radiation along a stratified medium, the formation of light bullets during competition between self-focusing and modulation instabilities in the case of three-dimensional wave packets, etc. In the problem of laser pulse shortening, the situation is considered when the wave-field stratification in the transverse direction dominates. This process is accompanied by the self-compression of laser pulses in well enough separated light guides. The efficiency of conversion of the initial Bessel field distribution to two flying parallel light bullets is about 50%.« less

Laser control of electronic transitions of wave packet by using quadratically chirped pulses.

PubMed

Zou, Shiyang; Kondorskiy, Alexey; Mil'nikov, Gennady; Nakamura, Hiroki

2005-02-22

An effective scheme is proposed for the laser control of wave packet dynamics. It is demonstrated that by using specially designed quadratically chirped pulses, fast and nearly complete excitation of wave packet can be achieved without significant distortion of its shape. The parameters of the laser pulse can be estimated analytically from the Zhu-Nakamura theory of nonadiabatic transition. If the wave packet is not too narrow or not too broad, then the scheme is expected to be utilizable for multidimensional systems. The scheme is applicable to various processes such as simple electronic excitation, pump-dump, and selective bond breaking, and it is actually numerically demonstrated to work well by taking diatomic and triatomic molecules (LiH, NaK, H(2)O) as examples.

Laser control of electronic transitions of wave packet by using quadratically chirped pulses

NASA Astrophysics Data System (ADS)

Zou, Shiyang; Kondorskiy, Alexey; Mil'nikov, Gennady; Nakamura, Hiroki

2005-02-01

An effective scheme is proposed for the laser control of wave packet dynamics. It is demonstrated that by using specially designed quadratically chirped pulses, fast and nearly complete excitation of wave packet can be achieved without significant distortion of its shape. The parameters of the laser pulse can be estimated analytically from the Zhu-Nakamura theory of nonadiabatic transition. If the wave packet is not too narrow or not too broad, then the scheme is expected to be utilizable for multidimensional systems. The scheme is applicable to various processes such as simple electronic excitation, pump-dump, and selective bond breaking, and it is actually numerically demonstrated to work well by taking diatomic and triatomic molecules (LiH, NaK, H2O) as examples.

Direct observation of isolated Damon-Eshbach and backward volume spin-wave packets in ferromagnetic microstripes

PubMed Central

Wessels, Philipp; Vogel, Andreas; Tödt, Jan-Niklas; Wieland, Marek; Meier, Guido; Drescher, Markus

2016-01-01

The analysis of isolated spin-wave packets is crucial for the understanding of magnetic transport phenomena and is particularly interesting for applications in spintronic and magnonic devices, where isolated spin-wave packets implement an information processing scheme with negligible residual heat loss. We have captured microscale magnetization dynamics of single spin-wave packets in metallic ferromagnets in space and time. Using an optically driven high-current picosecond pulse source in combination with time-resolved scanning Kerr microscopy probed by femtosecond laser pulses, we demonstrate phase-sensitive real-space observation of spin-wave packets in confined permalloy (Ni80Fe20) microstripes. Impulsive excitation permits extraction of the dynamical parameters, i.e. phase- and group velocities, frequencies and wave vectors. In addition to well-established Damon-Eshbach modes our study reveals waves with counterpropagating group- and phase-velocities. Such unusual spin-wave motion is expected for backward volume modes where the phase fronts approach the excitation volume rather than emerging out of it due to the negative slope of the dispersion relation. These modes are difficult to excite and observe directly but feature analogies to negative refractive index materials, thus enabling model studies of wave propagation inside metamaterials. PMID:26906113

Propagation of Gaussian wave packets in complex media and application to fracture characterization

NASA Astrophysics Data System (ADS)

Ding, Yinshuai; Zheng, Yingcai; Zhou, Hua-Wei; Howell, Michael; Hu, Hao; Zhang, Yu

2017-08-01

Knowledge of the subsurface fracture networks is critical in probing the tectonic stress states and flow of fluids in reservoirs containing fractures. We propose to characterize fractures using scattered seismic data, based on the theory of local plane-wave multiple scattering in a fractured medium. We construct a localized directional wave packet using point sources on the surface and propagate it toward the targeted subsurface fractures. The wave packet behaves as a local plane wave when interacting with the fractures. The interaction produces multiple scattering of the wave packet that eventually travels up to the surface receivers. The propagation direction and amplitude of the multiply scattered wave can be used to characterize fracture density, orientation and compliance. Two key aspects in this characterization process are the spatial localization and directionality of the wave packet. Here we first show the physical behaviour of a new localized wave, known as the Gaussian Wave Packet (GWP), by examining its analytical solution originally formulated for a homogenous medium. We then use a numerical finite-difference time-domain (FDTD) method to study its propagation behaviour in heterogeneous media. We find that a GWP can still be localized and directional in space even over a large propagation distance in heterogeneous media. We then propose a method to decompose the recorded seismic wavefield into GWPs based on the reverse-time concept. This method enables us to create a virtually recorded seismic data using field shot gathers, as if the source were an incident GWP. Finally, we demonstrate the feasibility of using GWPs for fracture characterization using three numerical examples. For a medium containing fractures, we can reliably invert for the local parameters of multiple fracture sets. Differing from conventional seismic imaging such as migration methods, our fracture characterization method is less sensitive to errors in the background velocity model

Hybridization effects on wave packet dynamics in topological insulator thin films.

PubMed

Yar, Abdullah; Naeem, Muhammad; Khan, Safi Ullah; Sabeeh, Kashif

2017-11-22

Theoretical study of electron wave packet dynamics in topological insulator (TI) thin films is presented. We have investigated real space trajectories and spin dynamics of electron wave packets in TI thin films. Our focus is on the role of hybridization between the electronic states of the two surfaces. This allows us to access the crossover regime of a thick film with no hybridization to a thin film with finite hybridization. We show that the electron wave packet undergoes side-jump motion in addition to zitterbewegung. The oscillation frequency of zitterbewegung can be tuned by the strength of hybridization, which in turn can be tuned by the thickness of the film. We find that the spin expectations also exhibit zitterbewegung tunable by hybridization. We also show that it is possible to obtain persistent zitterbewegung, oscillations which do not decay, in both the real space trajectories as well as spin dynamics. The zitterbewegung oscillation frequency in TI thin films falls in a parameter regime where it might be possible to observe these effects using present day experimental techniques.

Phase Coupling in Langmuir Wave Packets: Evidence for Four Wave Interactions in Solar Type III Radio Bursts

NASA Technical Reports Server (NTRS)

Thejappa, G.; MacDowall, R. J.; Bergamo, M.

2012-01-01

The four wave interaction process, known as the oscillating two stream instability (OTSI) is considered as one of the mechanisms responsible for stabilizing the electron beams associated with solar type III radio bursts. It has been reported that (1) an intense localized Langmuir wave packet associated with a type III burst contains the spectral characteristics of the OTSI: (a) a resonant peak at the local electron plasma frequency, f(sub pe), (b) a Stokes peak at a frequency slightly lower than f(sub pe), (c) anti-Stokes peak at a frequency slightly higher than f(sub pe), and (d) a low frequency enhancement below a few hundred Hz, (2) the frequencies and wave numbers of these spectral components satisfy the resonance conditions of the OTSI, and (3) the peak intensity of the wave packet is well above the thresholds for the OTSI as well as spatial collapse of envelope solitons. Here, for the first time, applying the trispectral analysis on this wave packet, we show that the tricoherence, which measures the degree of coherent four-wave coupling amongst the observed spectral components exhibits a peak. This provides an additional evidence for the OTSI and related spatial collapse of Langmuir envelope solitons in type III burst sources.

Pressure fluctuations beneath turbulent spots and instability wave packets in a hypersonic boundary layer.

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

Beresh, Steven Jay; Casper, Katya M.; Schneider, Steven P.

2010-12-01

The development of turbulent spots in a hypersonic boundary layer was studied on the nozzle wall of the Boeing/AFOSR Mach-6 Quiet Tunnel. Under quiet flow conditions, the nozzle wall boundary layer remains laminar and grows very thick over the long nozzle length. This allows the development of large turbulent spots that can be readily measured with pressure transducers. Measurements of naturally occurring wave packets and developing turbulent spots were made. The peak frequencies of these natural wave packets were in agreement with second-mode computations. For a controlled study, the breakdown of disturbances created by spark and glow perturbations were studiedmore » at similar freestream conditions. The spark perturbations were the most effective at creating large wave packets that broke down into turbulent spots. The flow disturbances created by the controlled perturbations were analyzed to obtain amplitude criteria for nonlinearity and breakdown as well as the convection velocities of the turbulent spots. Disturbances first grew into linear instability waves and then quickly became nonlinear. Throughout the nonlinear growth of the wave packets, large harmonics are visible in the power spectra. As breakdown begins, the peak amplitudes of the instability waves and harmonics decrease into the rising broad-band frequencies. Instability waves are still visible on either side of the growing turbulent spots during this breakdown process.« less

A Gaussian wave packet phase-space representation of quantum canonical statistics

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

Coughtrie, David J.; Tew, David P.

2015-07-28

We present a mapping of quantum canonical statistical averages onto a phase-space average over thawed Gaussian wave-packet (GWP) parameters, which is exact for harmonic systems at all temperatures. The mapping invokes an effective potential surface, experienced by the wave packets, and a temperature-dependent phase-space integrand, to correctly transition from the GWP average at low temperature to classical statistics at high temperature. Numerical tests on weakly and strongly anharmonic model systems demonstrate that thermal averages of the system energy and geometric properties are accurate to within 1% of the exact quantum values at all temperatures.

Universal potential-barrier penetration by initially confined wave packets

NASA Astrophysics Data System (ADS)

Granot, Er'El; Marchewka, Avi

2007-07-01

The dynamics of an initially sharp-boundary wave packet in the presence of an arbitrary potential barrier is investigated. It is shown that the penetration through the barrier is universal in the sense that it depends only on the values of the wave function and its derivatives at the boundary. The dependence on the derivatives vanishes at long distances from the barrier, where the dynamics is governed solely by the initial value of the wave function at the boundary.

Wave packet analysis and break-up length calculations for an accelerating planar liquid jet

NASA Astrophysics Data System (ADS)

Turner, M. R.; Healey, J. J.; Sazhin, S. S.; Piazzesi, R.

2012-02-01

This paper examines the process of transition to turbulence within an accelerating planar liquid jet. By calculating the propagation and spatial evolution of disturbance wave packets generated at a nozzle where the jet emerges, we are able to estimate break-up lengths and break-up times for different magnitudes of acceleration and different liquid to air density ratios. This study uses a basic jet velocity profile that has shear layers in both air and the liquid either side of the fluid interface. The shear layers are constructed as functions of velocity which behave in line with our CFD simulations of injecting diesel jets. The non-dimensional velocity of the jet along the jet centre-line axis is assumed to take the form V (t) = tanh(at), where the parameter a determines the magnitude of the acceleration. We compare the fully unsteady results obtained by solving the unsteady Rayleigh equation to those of a quasi-steady jet to determine when the unsteady effects are significant and whether the jet can be regarded as quasi-steady in typical operating conditions for diesel engines. For a heavy fluid injecting into a lighter fluid (density ratio ρair/ρjet = q < 1), it is found that unsteady effects are mainly significant at early injection times where the jet velocity profile is changing fastest. When the shear layers in the jet thin with time, the unsteady effects cause the growth rate of the wave packet to be smaller than the corresponding quasi-steady jet, whereas for thickening shear layers the unsteady growth rate is larger than that of the quasi-steady jet. For large accelerations (large a), the unsteady effect remains at later times but its effect on the growth rate of the wave packet decreases as the time after injection increases. As the rate of acceleration is reduced, the range of velocity values for which the jet can be considered as quasi-steady increases until eventually the whole jet can be considered quasi-steady. For a homogeneous jet (q = 1), the

Monte Carlo wave packet study of negative ion mediated vibrationally inelastic scattering of NO from the metal surface

NASA Astrophysics Data System (ADS)

Li, Shenmin; Guo, Hua

2002-09-01

The scattering dynamics of vibrationally excited NO from a metal surface is investigated theoretically using a dissipative model that includes both the neutral and negative ion states. The Liouville-von Neumann equation is solved numerically by a Monte Carlo wave packet method, in which the wave packet is allowed to "jump" between the neutral and negative ion states in a stochastic fashion. It is shown that the temporary population of the negative ion state results in significant changes in vibrational dynamics, which eventually lead to vibrationally inelastic scattering of NO. Reasonable agreement with experiment is obtained with empirical potential energy surfaces. In particular, the experimentally observed facile multiquantum relaxation of the vibrationally highly excited NO is reproduced. The simulation also provides interesting insight into the scattering dynamics.

The exact eigenfunctions and eigenvalues of a two-dimensional rigid rotor obtained using Gaussian wave packet dynamics

NASA Technical Reports Server (NTRS)

Reimers, J. R.; Heller, E. J.

1985-01-01

Exact eigenfunctions for a two-dimensional rigid rotor are obtained using Gaussian wave packet dynamics. The wave functions are obtained by propagating, without approximation, an infinite set of Gaussian wave packets that collectively have the correct periodicity, being coherent states appropriate to this rotational problem. This result leads to a numerical method for the semiclassical calculation of rovibrational, molecular eigenstates. Also, a simple, almost classical, approximation to full wave packet dynamics is shown to give exact results: this leads to an a posteriori justification of the De Leon-Heller spectral quantization method.

Collective neutrino oscillations and neutrino wave packets

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

Akhmedov, Evgeny; Lindner, Manfred; Kopp, Joachim, E-mail: akhmedov@mpi-hd.mpg.de, E-mail: jkopp@uni-mainz.de, E-mail: lindner@mpi-hd.mpg.de

Effects of decoherence by wave packet separation on collective neutrino oscillations in dense neutrino gases are considered. We estimate the length of the wave packets of neutrinos produced in core collapse supernovae and the expected neutrino coherence length, and then proceed to consider the decoherence effects within the density matrix formalism of neutrino flavour transitions. First, we demonstrate that for neutrino oscillations in vacuum the decoherence effects are described by a damping term in the equation of motion of the density matrix of a neutrino as a whole (as contrasted to that of the fixed-momentum components of the neutrino densitymore » matrix). Next, we consider neutrino oscillations in ordinary matter and dense neutrino backgrounds, both in the adiabatic and non-adiabatic regimes. In the latter case we study two specific models of adiabaticity violation—one with short-term and another with extended non-adiabaticity. It is demonstrated that, while in the adiabatic case a damping term is present in the equation of motion of the neutrino density matrix (just like in the vacuum oscillation case), no such term in general appears in the non-adiabatic regime.« less

Energy-flux characterization of conical and space-time coupled wave packets

NASA Astrophysics Data System (ADS)

Lotti, A.; Couairon, A.; Faccio, D.; Trapani, P. Di

2010-02-01

We introduce the concept of energy density flux as a characterization tool for the propagation of ultrashort laser pulses with spatiotemporal coupling. In contrast with calculations for the Poynting vector, those for energy density flux are derived in the local frame moving at the velocity of the envelope of the wave packet under examination and do not need knowledge of the magnetic field. We show that the energy flux defined from a paraxial propagation equation follows specific geometrical connections with the phase front of the optical wave packet, which demonstrates that the knowledge of the phase fronts amounts to the measurement of the energy flux. We perform a detailed numerical study of the energy density flux in the particular case of conical waves, with special attention paid to stationary-envelope conical waves (X or O waves). A full characterization of linear conical waves is given in terms of their energy flux. We extend the definition of this concept to the case of nonlinear propagation in Kerr media with nonlinear losses.

Delocalization of charge and current in a chiral quasiparticle wave packet

NASA Astrophysics Data System (ADS)

Sarkar, Subhajit

2018-03-01

A chiral quasiparticle wave packet (c-QPWP) is defined as a conventional superposition of chiral quasiparticle states corresponding to an interacting electron system in two dimensions (2D) in the presence of Rashba spin-orbit coupling (RSOC). I investigate its internal structure via studying the charge and the current densities within the first-order perturbation in the electron-electron interaction. It is found that the c-QPWP contains a localized charge which is less than the magnitude of the bare charge and the remaining charge resides at the system boundary. The amount of charge delocalized turns out to be inversely proportional to the degenerate Fermi velocity v0(=√{α2+2 μ /m }) when RSOC (with strength α ) is weak, and therefore externally tunable. For strong RSOC, the magnitudes of both the delocalized charge and the current further strongly depend on the direction of propagation of the wave packet. Both the charge and the current densities consist of an anisotropic r-2 tail away from the center of the wave packet. Possible implications of such delocalizations in real systems corresponding to 2D semiconductor heterostructure are also discussed within the context of particle injection experiments.

Information hiding and retrieval in Rydberg wave packets using half-cycle pulses

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

Murray, J. M.; Pisharody, S. N.; Wen, H.

We demonstrate an information hiding and retrieval scheme with the relative phases between states in a Rydberg wave packet acting as the bits of a data register. We use a terahertz half-cycle pulse (HCP) to transfer phase-encoded information from an optically accessible angular momentum manifold to another manifold which is not directly accessed by our laser pulses, effectively hiding the information from our optical interferometric measurement techniques. A subsequent HCP acting on these wave packets reintroduces the information back into the optically accessible data register manifold which can then be read out.

Amplitudes and frequency sweep rates of wave packets of whistler-mode chorus observed by the Cluster spacecraft

NASA Astrophysics Data System (ADS)

Macusova, E.; Santolik, O.; Pickett, J. S.; Gurnett, D. A.; Cornilleau-Wehrlin, N.; Demekhov, A. G.; Titova, E. E.

2013-12-01

Whistler-mode chorus is one of the most intense electromagnetic wave emissions observed in the inner magnetosphere, usually outside the plasmasphere. These waves play an important role in wave-particle interactions. They are usually generated close to the geomagnetic equator in a wide range of L-shells, and they propagate toward larger magnetic latitudes. Whistler-mode chorus is sometimes composed of two frequency bands separated by a gap at one half of the electron cyclotron frequency. At short time scales (on the order of hundreds of milliseconds) chorus consist of different discrete spectral shapes: rising tones, falling tones, constant frequency tones, and hooks. Our survey is based on high time resolution measurements collected by the WBD instrument onboard four Cluster spacecraft. We analyze time intervals containing different types of spectral shapes occurring at different L-shells, and at different latitudes relative to the chorus source region, as it is determined from measurements of the STAFF-SA instrument. Each of these events includes a large number of individual wave packets (between a few hundreds to a few thousands). For each individual wave packet we determine the frequency sweep rate and the average amplitude. Our results confirm previous conclusions of numerical simulations, theoretical predictions, and case studies showing that the amplitude of chorus wave packets increases with an increasing frequency sweep rate. The amplitude also increases as the wave forming chorus propagate away from the equator. The scatter of obtained values of frequency sweep rates and amplitudes is much larger closer to the Earth than at larger radial distances. This work receives EU support through the FP7-Space grant agreement no 284520 for the MAARBLE collaborative research project.

Determination of the effective transverse coherence of the neutron wave packet as employed in reflectivity investigations of condensed-matter structures. II. Analysis of elastic scattering using energy-gated wave packets with an application to neutron reflection from ruled gratings

NASA Astrophysics Data System (ADS)

Berk, N. F.

2014-03-01

We present a general approach to analyzing elastic scattering for those situations where the incident beam is prepared as an incoherent ensemble of wave packets of a given arbitrary shape. Although wave packets, in general, are not stationary solutions of the Schrödinger equation, the analysis of elastic scattering data treats the scattering as a stationary-state problem. We thus must gate the wave packet, coherently distorting its shape in a manner consistent with the elastic condition. The resulting gated scattering amplitudes (e.g., reflection coefficients) thus are weighted coherent sums of the constituent plane-wave scattering amplitudes, with the weights determined by the shape of the incident wave packet as "filtered" by energy gating. We develop the gating formalism in general and apply it to the problem of neutron scattering from ruled gratings described by Majkrzak et al. in a companion paper. The required exact solution of the associated problem of plane-wave reflection from gratings also is derived.

Femtosecond laser spectroscopy on the vibrational wave packet dynamics of the A 1Σ+ state of NaK

NASA Astrophysics Data System (ADS)

Berg, L.-E.; Beutter, M.; Hansson, T.

1996-05-01

The vibrational wave packet dynamics of a heteronuclear diatomic alkali molecule in an excited state, the A 1Σ+ state of gaseous NaK, has been measured for the first time. At λpump = 790 nm, a wave packet oscillation period of 442 fs and dephasing within 10 ps has been observed. This dynamics has been analysed by calculation of Franck-Condon factors and difference potentials. It is from this seen that initially the pump pulse prepares a wave packet at the inner turning point of the A-state. The wave packet then evolves in time and is probed at the outer turning point by a transition to the E-state with subsequent fluorescence detection.

Extended wave-packet model to calculate energy-loss moments of protons in matter

NASA Astrophysics Data System (ADS)

Archubi, C. D.; Arista, N. R.

2017-12-01

In this work we introduce modifications to the wave-packet method proposed by Kaneko to calculate the energy-loss moments of a projectile traversing a target which is represented in terms of Gaussian functions for the momentum distributions of electrons in the atomic shells. These modifications are introduced using the Levine and Louie technique to take into account the energy gaps corresponding to the different atomic levels of the target. We use the extended wave-packet model to evaluate the stopping power, the energy straggling, the inverse mean free path, and the ionization cross sections for protons in several targets, obtaining good agreements for all these quantities on an extensive energy range that covers low-, intermediate-, and high-energy regions. The extended wave-packet model proposed here provides a method to calculate in a very straightforward way all the significant terms of the inelastic interaction of light ions with any element of the periodic table.

Wave-packet rectification in nonlinear electronic systems: A tunable Aharonov-Bohm diode

PubMed Central

Li, Yunyun; Zhou, Jun; Marchesoni, Fabio; Li, Baowen

2014-01-01

Rectification of electron wave-packets propagating along a quasi-one dimensional chain is commonly achieved via the simultaneous action of nonlinearity and longitudinal asymmetry, both confined to a limited portion of the chain termed wave diode. However, it is conceivable that, in the presence of an external magnetic field, spatial asymmetry perpendicular to the direction of propagation suffices to ensure rectification. This is the case of a nonlinear ring-shaped lattice with different upper and lower halves (diode), which is attached to two elastic chains (leads). The resulting device is mirror symmetric with respect to the ring vertical axis, but mirror asymmetric with respect to the chain direction. Wave propagation along the two diode paths can be modeled for simplicity by a discrete Schrödinger equation with cubic nonlinearities. Numerical simulations demonstrate that, thanks to the Aharonov-Bohm effect, such a diode can be operated by tuning the magnetic flux across the ring. PMID:24691462

Quantum spreading of a self-gravitating wave-packet in singularity free gravity

NASA Astrophysics Data System (ADS)

Buoninfante, Luca; Lambiase, Gaetano; Mazumdar, Anupam

2018-01-01

In this paper we will study for the first time how the wave-packet of a self-gravitating meso-scopic system spreads in theories beyond Einstein's general relativity. In particular, we will consider a ghost-free infinite derivative gravity, which resolves the 1 / r singularity in the potential - such that the gradient of the potential vanishes within the scale of non-locality. We will show that a quantum wave-packet spreads faster for a ghost-free and singularity-free gravity as compared to the Newtonian case, therefore providing us a unique scenario for testing classical and quantum properties of short-distance gravity in a laboratory in the near future.

Propagation of arbitrary initial wave packets in a quantum parametric oscillator: Instability zones for higher order moments

NASA Astrophysics Data System (ADS)

Biswas, Subhadip; Chattopadhyay, Rohitashwa; Bhattacharjee, Jayanta K.

2018-05-01

We consider the dynamics of a particle in a parametric oscillator with a view to exploring any quantum feature of the initial wave packet that shows divergent (in time) behaviour for parameter values where the classical motion dynamics of the mean position is bounded. We use Ehrenfest's theorem to explore the dynamics of nth order moment which reduces exactly to a linear non autonomous differential equation of order n + 1. It is found that while the width and skewness of the packet is unbounded exactly in the zones where the classical motion is unbounded, the kurtosis of an initially non-gaussian wave packet can become infinitely large in certain additional zones. This implies that the shape of the wave packet can change drastically with time in these zones.

Generic short-time propagation of sharp-boundaries wave packets

NASA Astrophysics Data System (ADS)

Granot, E.; Marchewka, A.

2005-11-01

A general solution to the "shutter" problem is presented. The propagation of an arbitrary initially bounded wave function is investigated, and the general solution for any such function is formulated. It is shown that the exact solution can be written as an expression that depends only on the values of the function (and its derivatives) at the boundaries. In particular, it is shown that at short times (t << 2mx2/hbar, where x is the distance to the boundaries) the wave function propagation depends only on the wave function's values (or its derivatives) at the boundaries of the region. Finally, we generalize these findings to a non-singular wave function (i.e., for wave packets with finite-width boundaries) and suggest an experimental verification.

Transmission and reflection of charge-density wave packets in a quantum Hall edge controlled by a metal gate

NASA Astrophysics Data System (ADS)

Matsuura, Masahiro; Mano, Takaaki; Noda, Takeshi; Shibata, Naokazu; Hotta, Masahiro; Yusa, Go

2018-02-01

Quantum energy teleportation (QET) is a proposed protocol related to quantum vacuum. The edge channels in a quantum Hall system are well suited for the experimental verification of QET. For this purpose, we examine a charge-density wave packet excited and detected by capacitively coupled front gate electrodes. We observe the waveform of the charge packet, which is proportional to the time derivative of the applied square voltage wave. Further, we study the transmission and reflection behaviors of the charge-density wave packet by applying a voltage to another front gate electrode to control the path of the edge state. We show that the threshold voltages where the dominant direction is switched in either transmission or reflection for dense and sparse wave packets are different from the threshold voltage where the current stops flowing in an equilibrium state.

Study of the wave packet treatment of neutrino oscillation at Daya Bay

NASA Astrophysics Data System (ADS)

Daya Bay Collaboration

2017-09-01

The disappearance of reactor \\bar{ν }_e observed by the Daya Bay experiment is examined in the framework of a model in which the neutrino is described by a wave packet with a relative intrinsic momentum dispersion σ _{rel}. Three pairs of nuclear reactors and eight antineutrino detectors, each with good energy resolution, distributed among three experimental halls, supply a high-statistics sample of \\bar{ν }_e acquired at nine different baselines. This provides a unique platform to test the effects which arise from the wave packet treatment of neutrino oscillation. The modified survival probability formula was used to fit Daya Bay data, providing the first experimental limits: 2.38 × 10^{-17}< σ _{rel} < 0.23. Treating the dimensions of the reactor cores and detectors as constraints, the limits are improved: 10^{-14} ≲ σ _ {rel} < 0.23, and an upper limit of σ _ {rel}<0.20 (which corresponds to σ _x ≳ 10^{-11} {cm }) is obtained. All limits correspond to a 95% C.L. Furthermore, the effect due to the wave packet nature of neutrino oscillation is found to be insignificant for reactor antineutrinos detected by the Daya Bay experiment thus ensuring an unbiased measurement of the oscillation parameters sin ^22θ _{13} and Δ m^2_{32} within the plane wave model.

Spectra of KeV Protons Related to Ion-Cyclotron Wave Packets

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Sibeck, D. G.; Tel'Nikhin, A. A.; Kronberg, T. K.

2017-01-01

We use the Fokker-Planck-Kolmogorov equation to study the statistical aspects of stochastic dynamics of the radiation belt (RB) protons driven by nonlinear electromagnetic ion-cyclotron (EMIC) wave packets. We obtain the spectra of keV protons scattered by these waves that showsteeping near the gyroresonance, the signature of resonant wave-particle interaction that cannot be described by a simple power law. The most likely mechanism for proton precipitation events in RBs is shown to be nonlinear wave-particle interaction, namely, the scattering of RB protons into the loss cone by EMIC waves.

A classical phase r-centroid approach to molecular wave packet dynamics illustrating the danger of using an incomplete set of initial states for thermal averaging

NASA Astrophysics Data System (ADS)

Hansson, Tony

1999-08-01

An inexpensive semiclassical method to simulate time-resolved pump-probe spectroscopy on molecular wave packets is applied to NaK molecules at high temperature. The method builds on the introduction of classical phase factors related to the r-centroids for vibronic transitions and assumes instantaneous laser-molecule interaction. All observed quantum mechanical features are reproduced - for short times where experimental data are available even quantitatively. Furthermore, it is shown that fully quantum dynamical molecular wave packet calculations on molecules at elevated temperatures, which do not include all rovibrational states, must be regarded with caution, as they easily might yield even qualitatively incorrect results.

Gaussian variational ansatz in the problem of anomalous sea waves: Comparison with direct numerical simulation

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

Ruban, V. P., E-mail: ruban@itp.ac.ru

2015-05-15

The nonlinear dynamics of an obliquely oriented wave packet on a sea surface is analyzed analytically and numerically for various initial parameters of the packet in relation to the problem of the so-called rogue waves. Within the Gaussian variational ansatz applied to the corresponding (1+2)-dimensional hyperbolic nonlinear Schrödinger equation (NLSE), a simplified Lagrangian system of differential equations is derived that describes the evolution of the coefficients of the real and imaginary quadratic forms appearing in the Gaussian. This model provides a semi-quantitative description of the process of nonlinear spatiotemporal focusing, which is one of the most probable mechanisms of roguemore » wave formation in random wave fields. The system of equations is integrated in quadratures, which allows one to better understand the qualitative differences between linear and nonlinear focusing regimes of a wave packet. Predictions of the Gaussian model are compared with the results of direct numerical simulation of fully nonlinear long-crested waves.« less

A model with chaotic scattering and reduction of wave packets

NASA Astrophysics Data System (ADS)

Guarneri, Italo

2018-03-01

Some variants of Smilansky’s model of a particle interacting with harmonic oscillators are examined in the framework of scattering theory. A dynamical proof is given of the existence of wave operators. Analysis of a classical version of the model provides a transparent picture for the spectral transition to which the quantum model owes its renown, and for the underlying dynamical behaviour. The model is thereby classified as an extreme case of chaotic scattering, with aspects related to wave packet reduction and irreversibility.

Resonant tunneling of spin-wave packets via quantized states in potential wells.

PubMed

Hansen, Ulf-Hendrik; Gatzen, Marius; Demidov, Vladislav E; Demokritov, Sergej O

2007-09-21

We have studied the tunneling of spin-wave pulses through a system of two closely situated potential barriers. The barriers represent two areas of inhomogeneity of the static magnetic field, where the existence of spin waves is forbidden. We show that for certain values of the spin-wave frequency corresponding to the quantized spin-wave states existing in the well formed between the barriers, the tunneling has a resonant character. As a result, transmission of spin-wave packets through the double-barrier structure is much more efficient than the sequent tunneling through two single barriers.

Time-Dependent Wave Packet Dynamics Calculations of Cross Sections for Ultracold Scattering of Molecules

NASA Astrophysics Data System (ADS)

Huang, Jiayu; Liu, Shu; Zhang, Dong H.; Krems, Roman V.

2018-04-01

Because the de Broglie wavelength of ultracold molecules is very large, the cross sections for collisions of molecules at ultracold temperatures are always computed by the time-independent quantum scattering approach. Here, we report the first accurate time-dependent wave packet dynamics calculation for reactive scattering of ultracold molecules. Wave packet dynamics calculations can be applied to molecular systems with more dimensions and provide real-time information on the process of bond rearrangement and/or energy exchange in molecular collisions. Our work thus makes possible the extension of rigorous quantum calculations of ultracold reaction properties to polyatomic molecules and adds a new powerful tool for the study of ultracold chemistry.

Time-Dependent Wave Packet Dynamics Calculations of Cross Sections for Ultracold Scattering of Molecules.

PubMed

Huang, Jiayu; Liu, Shu; Zhang, Dong H; Krems, Roman V

2018-04-06

Because the de Broglie wavelength of ultracold molecules is very large, the cross sections for collisions of molecules at ultracold temperatures are always computed by the time-independent quantum scattering approach. Here, we report the first accurate time-dependent wave packet dynamics calculation for reactive scattering of ultracold molecules. Wave packet dynamics calculations can be applied to molecular systems with more dimensions and provide real-time information on the process of bond rearrangement and/or energy exchange in molecular collisions. Our work thus makes possible the extension of rigorous quantum calculations of ultracold reaction properties to polyatomic molecules and adds a new powerful tool for the study of ultracold chemistry.

Wave-packet continuum-discretization approach to ion-atom collisions including rearrangement: Application to differential ionization in proton-hydrogen scattering

NASA Astrophysics Data System (ADS)

Abdurakhmanov, I. B.; Bailey, J. J.; Kadyrov, A. S.; Bray, I.

2018-03-01

In this work, we develop a wave-packet continuum-discretization approach to ion-atom collisions that includes rearrangement processes. The total scattering wave function is expanded using a two-center basis built from wave-packet pseudostates. The exact three-body Schrödinger equation is converted into coupled-channel differential equations for time-dependent expansion coefficients. In the asymptotic region these time-dependent coefficients represent transition amplitudes for all processes including elastic scattering, excitation, ionization, and electron capture. The wave-packet continuum-discretization approach is ideal for differential ionization studies as it allows one to generate pseudostates with arbitrary energies and distribution. The approach is used to calculate the double differential cross section for ionization in proton collisions with atomic hydrogen. Overall good agreement with experiment is obtained for all considered cases.

Body frame close coupling wave packet approach to gas phase atom-rigid rotor inelastic collisions

NASA Technical Reports Server (NTRS)

Sun, Y.; Judson, R. S.; Kouri, D. J.

1989-01-01

The close coupling wave packet (CCWP) method is formulated in a body-fixed representation for atom-rigid rotor inelastic scattering. For J greater than j-max (where J is the total angular momentum and j is the rotational quantum number), the computational cost of propagating the coupled channel wave packets in the body frame is shown to scale approximately as N exp 3/2, where N is the total number of channels. For large numbers of channels, this will be much more efficient than the space frame CCWP method previously developed which scales approximately as N-squared under the same conditions.

Decoherence and surface hopping: When can averaging over initial conditions help capture the effects of wave packet separation?

NASA Astrophysics Data System (ADS)

Subotnik, Joseph E.; Shenvi, Neil

2011-06-01

Fewest-switches surface hopping (FSSH) is a popular nonadiabatic dynamics method which treats nuclei with classical mechanics and electrons with quantum mechanics. In order to simulate the motion of a wave packet as accurately as possible, standard FSSH requires a stochastic sampling of the trajectories over a distribution of initial conditions corresponding, e.g., to the Wigner distribution of the initial quantum wave packet. Although it is well-known that FSSH does not properly account for decoherence effects, there is some confusion in the literature about whether or not this averaging over a distribution of initial conditions can approximate some of the effects of decoherence. In this paper, we not only show that averaging over initial conditions does not generally account for decoherence, but also why it fails to do so. We also show how an apparent improvement in accuracy can be obtained for a fortuitous choice of model problems, even though this improvement is not possible, in general. For a basic set of one-dimensional and two-dimensional examples, we find significantly improved results using our recently introduced augmented FSSH algorithm.

Imaging and control of interfering wave packets in a dissociating molecule.

PubMed

Skovsen, Esben; Machholm, Mette; Ejdrup, Tine; Thøgersen, Jan; Stapelfeldt, Henrik

2002-09-23

Using two identical 110 femtosecond (fs) optical pulses separated by 310 fs, we launch two dissociative wave packets in I2. We measure the square of the wave function as a function of both the internuclear separation, /Psi(R)/(2), and of the internuclear velocity, /Psi(v(R))/(2), by ionizing the dissociating molecule with an intense 20 fs probe pulse. Strong interference is observed in both /Psi(R)/(2) and in /Psi(v(R))/(2). The interference, and therefore the shape of the wave function, is controlled through the phase difference between the two dissociation pulses in good agreement with calculations.

Real-time dynamics of Auger wave packets and decays in ultrafast charge migration processes

NASA Astrophysics Data System (ADS)

Covito, F.; Perfetto, E.; Rubio, A.; Stefanucci, G.

2018-06-01

The Auger decay is a relevant recombination channel during the first few femtoseconds of molecular targets impinged by attosecond XUV or soft x-ray pulses. Including this mechanism in time-dependent simulations of charge-migration processes is a difficult task, and Auger scatterings are often ignored altogether. In this work we present an advance of the current state-of-the-art by putting forward a real-time approach based on nonequilibrium Green's functions suitable for first-principles calculations of molecules with tens of active electrons. To demonstrate the accuracy of the method we report comparisons against accurate grid simulations of one-dimensional systems. We also predict a highly asymmetric profile of the Auger wave packet, with a long tail exhibiting ripples temporally spaced by the inverse of the Auger energy.

Persistent nuclear wave packet oscillation coexistent with incoherent vibrational population at excited F centers in KI.

PubMed

Koyama, Takeshi; Takahashi, Youtarou; Nakajima, Makoto; Suemoto, Tohru

2006-06-14

We investigated nuclear wave packet dynamics in the excited state of KI F centers at 10 K using time-resolved luminescence spectroscopy. Observed transient spectrum is divided into oscillatory and non-oscillatory components. The former lasts over 11 ps without appreciable damping and is attributed to the oscillation of the wave packet consisting mainly of the A(1g) mode around the center. The non-oscillatory part rises quickly after photo-excitation exhibiting a cooling of incoherent vibrational population. This behavior suggests the fast energy dissipation due to the dephasing of the bulk phonon modes.

Coherent structural trapping through wave packet dispersion during photoinduced spin state switching

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

Lemke, Henrik T.; Kjær, Kasper S.; Hartsock, Robert

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

Coherent structural trapping through wave packet dispersion during photoinduced spin state switching

DOE PAGES

Lemke, Henrik T.; Kjær, Kasper S.; Hartsock, Robert; ...

2017-05-24

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

Coherent structural trapping through wave packet dispersion during photoinduced spin state switching

NASA Astrophysics Data System (ADS)

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

2017-05-01

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

Study of diffusion of wave packets in a square lattice under external fields along the discrete nonlinear Schrödinger equation

NASA Astrophysics Data System (ADS)

de Brito, P. E.; Nazareno, H. N.

2012-09-01

The object of the present work is to analyze the effect of nonlinearity on wave packet propagation in a square lattice subject to a magnetic and an electric field in the Hall configuration, by using the Discrete Nonlinear Schrödinger Equation (DNLSE). In previous works we have shown that without the nonlinear term, the presence of the magnetic field induces the formation of vortices that remain stationary, while a wave packet is introduced in the system. As for the effect of an applied electric field, it was shown that the vortices propagate in a direction perpendicular to the electric field, similar behavior as presented in the classical treatment, we provide a quantum mechanics explanation for that. We have performed the calculations considering first the action of the magnetic field as well as the nonlinearity. The results indicate that for low values of the nonlinear parameter U the vortices remain stationary while preserving the form. For greater values of the parameter the picture gets distorted, the more so, the greater the nonlinearity. As for the inclusion of the electric field, we note that for small U, the wave packet propagates perpendicular to the applied field, until for greater values of U the wave gets partially localized in a definite region of the lattice. That is, for strong nonlinearity the wave packet gets partially trapped, while the tail of it can propagate through the lattice. Note that this tail propagation is responsible for the over-diffusion for long times of the wave packet under the action of an electric field. We have produced short films that show clearly the time evolution of the wave packet, which can add to the understanding of the dynamics.

Theoretical prediction of a rotating magnon wave packet in ferromagnets.

PubMed

Matsumoto, Ryo; Murakami, Shuichi

2011-05-13

We theoretically show that the magnon wave packet has a rotational motion in two ways: a self-rotation and a motion along the boundary of the sample (edge current). They are similar to the cyclotron motion of electrons, but unlike electrons the magnons have no charge and the rotation is not due to the Lorentz force. These rotational motions are caused by the Berry phase in momentum space from the magnon band structure. Furthermore, the rotational motion of the magnon gives an additional correction term to the magnon Hall effect. We also discuss the Berry curvature effect in the classical limit of long-wavelength magnetostatic spin waves having macroscopic coherence length.

LANGMUIR WAVE DECAY IN INHOMOGENEOUS SOLAR WIND PLASMAS: SIMULATION RESULTS

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

Krafft, C.; Volokitin, A. S.; Krasnoselskikh, V. V., E-mail: catherine.krafft@u-psud.fr

2015-08-20

Langmuir turbulence excited by electron flows in solar wind plasmas is studied on the basis of numerical simulations. In particular, nonlinear wave decay processes involving ion-sound (IS) waves are considered in order to understand their dependence on external long-wavelength plasma density fluctuations. In the presence of inhomogeneities, it is shown that the decay processes are localized in space and, due to the differences between the group velocities of Langmuir and IS waves, their duration is limited so that a full nonlinear saturation cannot be achieved. The reflection and the scattering of Langmuir wave packets on the ambient and randomly varying density fluctuationsmore » lead to crucial effects impacting the development of the IS wave spectrum. Notably, beatings between forward propagating Langmuir waves and reflected ones result in the parametric generation of waves of noticeable amplitudes and in the amplification of IS waves. These processes, repeated at different space locations, form a series of cascades of wave energy transfer, similar to those studied in the frame of weak turbulence theory. The dynamics of such a cascading mechanism and its influence on the acceleration of the most energetic part of the electron beam are studied. Finally, the role of the decay processes in the shaping of the profiles of the Langmuir wave packets is discussed, and the waveforms calculated are compared with those observed recently on board the spacecraft Solar TErrestrial RElations Observatory and WIND.« less

Radiation from an electron beam in magnetized plasma: excitation of a whistler mode wave packet by interacting, higher-frequency, electrostatic-wave eigenmodes

NASA Astrophysics Data System (ADS)

Brenning, N.; Axnäs, I.; Koepke, M.; Raadu, M. A.; Tennfors, E.

2017-12-01

Infrequent, bursty, electromagnetic, whistler-mode wave packets, excited spontaneously in the laboratory by an electron beam from a hot cathode, appear transiently, each with a time duration τ around ∼1 μs. The wave packets have a center frequency f W that is broadly distributed in the range 7 MHz < f W < 40 MHz. They are excited in a region with separate electrostatic (es) plasma oscillations at values of f hf, 200 MHz < f hf < 500 MHz, that are hypothesized to match eigenmode frequencies of an axially localized hf es field in a well-defined region attached to the cathode. Features of these es-eigenmodes that are studied include: the mode competition at times of transitions from one dominating es-eigenmode to another, the amplitude and spectral distribution of simultaneously occurring es-eigenmodes that do not lead to a transition, and the correlation of these features with the excitation of whistler mode waves. It is concluded that transient coupling of es-eigenmode pairs at f hf such that | {{{f}}}1,{{h}{{f}}}-{{{f}}}2,{{h}{{f}}}| = {f}{{W}}< {f}{{g}{{e}}} can explain both the transient lifetime and the frequency spectra of the whistler-mode wave packets (f W) as observed in lab. The generalization of the results to bursty whistler-mode excitation in space from electron beams, created on the high potential side of double layers, is discussed.

Characterizing the astrophysical S factor for 12C+12C fusion with wave-packet dynamics

NASA Astrophysics Data System (ADS)

Diaz-Torres, Alexis; Wiescher, Michael

2018-05-01

A quantitative study of the astrophysically important subbarrier fusion of 12C+12C is presented. Low-energy collisions are described in the body-fixed reference frame using wave-packet dynamics within a nuclear molecular picture. A collective Hamiltonian drives the time propagation of the wave packet through the collective potential-energy landscape. The fusion imaginary potential for specific dinuclear configurations is crucial for understanding the appearance of resonances in the fusion cross section. The theoretical subbarrier fusion cross sections explain some observed resonant structures in the astrophysical S factor. These cross sections monotonically decline towards stellar energies. The structures in the data that are not explained are possibly due to cluster effects in the nuclear molecule, which need to be included in the present approach.

Wave packet interferometry and quantum state reconstruction by acousto-optic phase modulation

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

Tekavec, Patrick F.; Dyke, Thomas R.; Marcus, Andrew H.

2006-11-21

Studies of wave packet dynamics often involve phase-selective measurements of coherent optical signals generated from sequences of ultrashort laser pulses. In wave packet interferometry (WPI), the separation between the temporal envelopes of the pulses must be precisely monitored or maintained. Here we introduce a new (and easy to implement) experimental scheme for phase-selective measurements that combines acousto-optic phase modulation with ultrashort laser excitation to produce an intensity-modulated fluorescence signal. Synchronous detection, with respect to an appropriately constructed reference, allows the signal to be simultaneously measured at two phases differing by 90 deg. Our method effectively decouples the relative temporal phasemore » from the pulse envelopes of a collinear train of optical pulse pairs. We thus achieve a robust and high signal-to-noise scheme for WPI applications, such as quantum state reconstruction and electronic spectroscopy. The validity of the method is demonstrated, and state reconstruction is performed, on a model quantum system - atomic Rb vapor. Moreover, we show that our measurements recover the correct separation between the absorptive and dispersive contributions to the system susceptibility.« less

Expansion of a quantum wave packet in a one-dimensional disordered potential in the presence of a uniform bias force

NASA Astrophysics Data System (ADS)

Crosnier de Bellaistre, C.; Trefzger, C.; Aspect, A.; Georges, A.; Sanchez-Palencia, L.

2018-01-01

We study numerically the expansion dynamics of an initially confined quantum wave packet in the presence of a disordered potential and a uniform bias force. For white-noise disorder, we find that the wave packet develops asymmetric algebraic tails for any ratio of the force to the disorder strength. The exponent of the algebraic tails decays smoothly with that ratio and no evidence of a critical behavior on the wave density profile is found. Algebraic localization features a series of critical values of the force-to-disorder strength where the m th position moment of the wave packet diverges. Below the critical value for the m th moment, we find fair agreement between the asymptotic long-time value of the m th moment and the predictions of diagrammatic calculations. Above it, we find that the m th moment grows algebraically in time. For correlated disorder, we find evidence of systematic delocalization, irrespective to the model of disorder. More precisely, we find a two-step dynamics, where both the center-of-mass position and the width of the wave packet show transient localization, similar to the white-noise case, at short time and delocalization at sufficiently long time. This correlation-induced delocalization is interpreted as due to the decrease of the effective de Broglie wavelength, which lowers the effective strength of the disorder in the presence of finite-range correlations.

Estimating TCP Packet Loss Ratio from Sampled ACK Packets

NASA Astrophysics Data System (ADS)

Yamasaki, Yasuhiro; Shimonishi, Hideyuki; Murase, Tutomu

The advent of various quality-sensitive applications has greatly changed the requirements for IP network management and made the monitoring of individual traffic flows more important. Since the processing costs of per-flow quality monitoring are high, especially in high-speed backbone links, packet sampling techniques have been attracting considerable attention. Existing sampling techniques, such as those used in Sampled NetFlow and sFlow, however, focus on the monitoring of traffic volume, and there has been little discussion of the monitoring of such quality indexes as packet loss ratio. In this paper we propose a method for estimating, from sampled packets, packet loss ratios in individual TCP sessions. It detects packet loss events by monitoring duplicate ACK events raised by each TCP receiver. Because sampling reveals only a portion of the actual packet loss, the actual packet loss ratio is estimated statistically. Simulation results show that the proposed method can estimate the TCP packet loss ratio accurately from a 10% sampling of packets.

A Simulated Spectrum of Convectively Generated Gravity Waves: Propagation from the Tropopause to the Mesopause and Effects on the Middle Atmosphere

NASA Technical Reports Server (NTRS)

Alexander, Joan

1996-01-01

This work evaluates the interaction of a simulated spectrum of convectively generated gravity waves with realistic middle atmosphere mean winds. The wave spectrum is derived from the nonlinear convection model described by Alexander et al. that simulated a two-dimensional midlatitude squall line. This spectrum becomes input to a linear ray tracing model for evaluation of wave propagation as a function of height through climatological background wind and buoyancy frequency profiles. The energy defined by the spectrum as a function of wavenumber and frequency is distributed spatially and temporally into wave packets for the purpose of estimating wave amplitudes at the lower boundary of the ray tracing model. A wavelet analysis provides an estimate of these wave packet widths in space and time. Without this redistribution of energies into wave packets the Fourier analysis alone inaccurately assumes the energy is evenly distributed throughout the storm model domain. The growth with height of wave amplitudes is derived from wave action flux conservation coupled to a convective instability saturation condition. Mean flow accelerations and wave energy dissipation profiles are derived from this analysis and compared to parameterized estimates of gravity wave forcing, providing a measure of the importance of the storm source to global gravity wave forcing. The results suggest that a single large convective storm system like the simulated squall line could provide a significant fraction of the zonal mean gravity wave forcing at some levels, particularly in the mesosphere. The vertical distributions of mean flow acceleration and energy dissipation do not much resemble the parameterized profiles in form because of the peculiarities of the spectral properties of the waves from the storm source. The ray tracing model developed herein provides a tool for examining the role of convectively generated waves in middle atmosphere physics.

A Simulated Spectrum of Convectively Generated Gravity Waves: Propagation from the Tropopause to the Mesopause and Effects on the Middle Atmosphere

NASA Technical Reports Server (NTRS)

Alexander, M. Joan

1996-01-01

This work evaluates the interaction of a simulated spectrum of convectively generated gravity waves with realistic middle atmosphere mean winds. The wave spectrum is derived from the nonlinear convection model described by Alexander et al. [1995] that simulated a two-dimensional midlatitude squall line. This spectrum becomes input to a linear ray tracing model for evaluation of wave propagation as a function of height through climatological background wind and buoyancy frequency profiles. The energy defined by the spectrum as a function of wavenumber and frequency is distributed spatially and temporally into wave packets for the purpose of estimating wave amplitudes at the lower boundary of the ray tracing model. A wavelet analysis provides an estimate of these wave packet widths in space and time. Without this redistribution of energies into wave packets the Fourier analysis alone inaccurately assumes the energy is evenly distributed throughout the storm model domain. The growth with height of wave amplitudes is derived from wave action flux conservation coupled to a convective instability saturation condition. Mean flow accelerations and wave energy dissipation profiles are derived from this analysis and compared to parameterized estimates of gravity wave forcing, providing a measure of the importance of the storm source to global gravity wave forcing. The results suggest that a single large convective storm system like the simulated squall line could provide a significant fraction of the zonal mean gravity wave forcing at some levels, particularly in the mesosphere. The vertical distributions of mean flow acceleration and energy dissipation do not much resemble the parameterized profiles in form because of the peculiarities of the spectral properties of the waves from the storm source. The ray tracing model developed herein provides a tool for examining the role of convectively generated waves in middle atmosphere physics.

Evolution of a localized Langmuir packet in the solar wind and on auroral field lines

NASA Technical Reports Server (NTRS)

Roth, I.; Muschietti, L.; Brown, E. F.; Gray, P. C.

1994-01-01

Langmuir emissions in space are reported to be clumpy and intermittent. The high-frequency wave power appears concentrated in spatial packets, whether amidst the solar wind or on auroral field lines. Due to the plasma motion relative to the spacecraft, determining the source for the wave free energy in the three-dimensional electron distribution function has always been difficult, since the unstable features pass by the detector in presumably too short time to be measured. The range of unstable phase velocities and growth rates have generally been estimated rather than determined by unequivocal measurements. The analysis of wave-particle interactions in a space environment has taken recently a new turn with the development of wave correlators on board rockets and satellites. Such instruments seek to identify correlations between the phase of the wave-field and the fluxes of energetic particles. The data interpretation is complex, however, it must be backed by a detailed theoretical understanding of the wave-particle interaction, including the phase relation for inhomogeneous packets. To this end Langmuir packets interacting with fast electrons can be studied in the appropriate regime by means of particle-in-cell simulations, provided that one succeeds in reducing the level of the fluctuations, enhancing the signal-to-noise ratio, and incorporating the appropriate boundary conditions. The first results of such simulations are presented here as a test and expansion of previous analysis.

Coherent Nuclear Wave Packets in Q States by Ultrafast Internal Conversions in Free Base Tetraphenylporphyrin.

PubMed

Kim, So Young; Joo, Taiha

2015-08-06

Persistence of vibrational coherence in electronic transition has been noted especially in biochemical systems. Here, we report the dynamics between electronic excited states in free base tetraphenylporphyrin (H2TPP) by time-resolved fluorescence with high time resolution. Following the photoexcitation of the B state, ultrafast internal conversion occurs to the Qx state directly as well as via the Qy state. Unique and distinct coherent nuclear wave packet motions in the Qx and Qy states are observed through the modulation of the fluorescence intensity in time. The instant, serial internal conversions from the B to the Qy and Qx states generate the coherent wave packets. Theory and experiment show that the observed vibrational modes involve the out-of-plane vibrations of the porphyrin ring that are strongly coupled to the internal conversion of H2TPP.

Recovery time in quantum dynamics of wave packets

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

Strekalov, M. L., E-mail: strekalov@kinetics.nsc.ru

2017-01-15

A wave packet formed by a linear superposition of bound states with an arbitrary energy spectrum returns arbitrarily close to the initial state after a quite long time. A method in which quantum recovery times are calculated exactly is developed. In particular, an exact analytic expression is derived for the recovery time in the limiting case of a two-level system. In the general case, the reciprocal recovery time is proportional to the Gauss distribution that depends on two parameters (mean value and variance of the return probability). The dependence of the recovery time on the mean excitation level of themore » system is established. The recovery time is the longest for the maximal excitation level.« less

Evidence of spectrally broad Gravity Wave packet propagation and dispersion in the mesopause region observed by the Na lidar and Mesospheric Temperature Mapper above Logan, Utah

NASA Astrophysics Data System (ADS)

Yuan, T.; Heale, C. J.; Snively, J. B.

2016-12-01

Utilizing observations from the Na lidar at Utah State University and the nearby Mesospheric Temperature Mapper (MTM) at Bear Lake Observatory (BLO) [41.9°N, 111.4°W], we investigate a unique case of vertical dispersion for a spectrally broad gravity wave packet in the mesopause region over Logan, Utah (41.7°N, 111.8°W) that occurred on September 2nd, 2011, to study the waves' evolution as a packet propagates upward. The lidar observed temperature perturbation was dominated by close to a 1-hour modulation at 100 km during the early hours, but gradually evolved into a 1.5-hour modulation during the second half of the night. The vertical wavelength also decreased simultaneously, while the vertical group and phase velocities of the packet apparently slowed, as it was approaching a critical level during the second half of the night. A two-dimensional numerical model is utilized to simulate the observed GW processes, finding that the location of the lidar relative to the source can strongly influence which portion of the spectrum can be observed at a particular location relative to a source.

The Nosé–Hoover looped chain thermostat for low temperature thawed Gaussian wave-packet dynamics

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

Coughtrie, David J.; Tew, David P.

2014-05-21

We have used a generalised coherent state resolution of the identity to map the quantum canonical statistical average for a general system onto a phase-space average over the centre and width parameters of a thawed Gaussian wave packet. We also propose an artificial phase-space density that has the same behaviour as the canonical phase-space density in the low-temperature limit, and have constructed a novel Nosé–Hoover looped chain thermostat that generates this density in conjunction with variational thawed Gaussian wave-packet dynamics. This forms a new platform for evaluating statistical properties of quantum condensed-phase systems that has an explicit connection to themore » time-dependent Schrödinger equation, whilst retaining many of the appealing features of path-integral molecular dynamics.« less

Vibrational wave packets in the B 1Πu and D 1Σu+ states of Cs2: Determination of improved Cs2+(X) and Cs2(B) spectroscopic constants

NASA Astrophysics Data System (ADS)

Oldenburg, A. L.; John, P. C.; Eden, J. G.

2000-12-01

Vibrational wave packets in the B 1Πu and D 1Σu+ excited states of Cs2 have been studied on the ˜100 fs time scale by pump-probe laser spectroscopy. The temporal behavior of the wave packets was monitored by photoionizing the electronically excited molecule with a time-delayed probe pulse and recording the time and energy-integrated photoelectron signal as a function of time delay between the pump and probe pulses. For the B 1Σu+ experiments, wave packets were produced by exciting the B 1Σu+←X 1Σg+ transition in the ˜740-790 nm region and subsequently detected by photoionizing the molecule at wavelengths between 565 nm and 600 nm. By simulating the experimentally observed transients with the density matrix formalism (and explicitly accounting for laser chirp and |Δv|>1 coherences), improved values for the equilibrium internuclear separation for the Cs2(B1Πu) state and Te for the Cs2+(X) state were determined to be Re(B 1Πu)=4.93±0.03 Å and Te[Cs2+(X)]=29 930±100 cm-1, respectively. Similar experiments were conducted for the D 1Σu+ state. Wave packets composed of vibrational levels (v'≈40-50) perturbed by the bound 2 3Πou state were produced on the D 1Σu+ potential surface by driving the D 1Σu+←X 1Σg+ transition in the 575-610 nm spectral interval.

The coupled three-dimensional wave packet approach to reactive scattering

NASA Astrophysics Data System (ADS)

Marković, Nikola; Billing, Gert D.

1994-01-01

A recently developed scheme for time-dependent reactive scattering calculations using three-dimensional wave packets is applied to the D+H2 system. The present method is an extension of a previously published semiclassical formulation of the scattering problem and is based on the use of hyperspherical coordinates. The convergence requirements are investigated by detailed calculations for total angular momentum J equal to zero and the general applicability of the method is demonstrated by solving the J=1 problem. The inclusion of the geometric phase is also discussed and its effect on the reaction probability is demonstrated.

Fast simulation of packet loss rates in a shared buffer communications switch

NASA Technical Reports Server (NTRS)

Chang, Cheng-Shang; Heidelberger, Philip; Shahabuddin, Perwez

1993-01-01

This paper describes an efficient technique for estimating, via simulation, the probability of buffer overflows in a queueing model that arises in the analysis of ATM (Asynchronous Transfer Mode) communication switches. There are multiple streams of (autocorrelated) traffic feeding the switch that has a buffer of finite capacity. Each stream is designated as either being of high or low priority. When the queue length reaches a certain threshold, only high priority packets are admitted to the switch's buffer. The problem is to estimate the loss rate of high priority packets. An asymptotically optimal importance sampling approach is developed for this rare event simulation problem. In this approach, the importance sampling is done in two distinct phases. In the first phase, an importance sampling change of measure is used to bring the queue length up to the threshold at which low priority packets get rejected. In the second phase, a different importance sampling change of measure is used to move the queue length from the threshold to the buffer capacity.

Vibrational wave packet dynamics in NaK: The A 1Σ+ state

NASA Astrophysics Data System (ADS)

Andersson, L. Mauritz; Karlsson, Hans O.; Goscinski, Osvaldo; Berg, Lars-Erik; Beutter, Matthias; Hansson, Tony

1999-02-01

A combined experimental and theoretical study of the vibrational wave packet dynamics for the NaK molecule in the A 1Σ+ state is presented. The experiment utilises a 790 nm one-colour femtosecond pump-probe scheme with detection of a previously not reported dissociation pathway of the 3 1Π+ state, leading to the Na(3p)+K(4s) product channel. The dissociation is suggested to proceed via either collisionally mediated processes or a molecular cascading process via the 4 1Σ+ state, which crosses several states correlating to the Na(3p)+K(4s) limit. Time-dependent quantum mechanical calculations are used for studying the dynamics in detail. Simulations are performed both for 790 nm and for 766 nm, to relate also to earlier studies. The previous interpretations of the probe processes are revised. Inclusion of vibrational and rotational temperature effects are shown to be crucial for explaining the shape of the signal and the vibrational period, and leads to excellent agreement with the experiments.

Regional-specific Stochastic Simulation of Spatially-distributed Ground-motion Time Histories using Wavelet Packet Analysis

NASA Astrophysics Data System (ADS)

Huang, D.; Wang, G.

2014-12-01

Stochastic simulation of spatially distributed ground-motion time histories is important for performance-based earthquake design of geographically distributed systems. In this study, we develop a novel technique to stochastically simulate regionalized ground-motion time histories using wavelet packet analysis. First, a transient acceleration time history is characterized by wavelet-packet parameters proposed by Yamamoto and Baker (2013). The wavelet-packet parameters fully characterize ground-motion time histories in terms of energy content, time- frequency-domain characteristics and time-frequency nonstationarity. This study further investigates the spatial cross-correlations of wavelet-packet parameters based on geostatistical analysis of 1500 regionalized ground motion data from eight well-recorded earthquakes in California, Mexico, Japan and Taiwan. The linear model of coregionalization (LMC) is used to develop a permissible spatial cross-correlation model for each parameter group. The geostatistical analysis of ground-motion data from different regions reveals significant dependence of the LMC structure on regional site conditions, which can be characterized by the correlation range of Vs30 in each region. In general, the spatial correlation and cross-correlation of wavelet-packet parameters are stronger if the site condition is more homogeneous. Using the regional-specific spatial cross-correlation model and cokriging technique, wavelet packet parameters at unmeasured locations can be best estimated, and regionalized ground-motion time histories can be synthesized. Case studies and blind tests demonstrated that the simulated ground motions generally agree well with the actual recorded data, if the influence of regional-site conditions is considered. The developed method has great potential to be used in computational-based seismic analysis and loss estimation in a regional scale.

Coriolis-coupled wave packet dynamics of H + HLi reaction.

PubMed

Padmanaban, R; Mahapatra, S

2006-05-11

We investigated the effect of Coriolis coupling (CC) on the initial state-selected dynamics of H+HLi reaction by a time-dependent wave packet (WP) approach. Exact quantum scattering calculations were obtained by a WP propagation method based on the Chebyshev polynomial scheme and ab initio potential energy surface of the reacting system. Partial wave contributions up to the total angular momentum J=30 were found to be necessary for the scattering of HLi in its vibrational and rotational ground state up to a collision energy approximately 0.75 eV. For each J value, the projection quantum number K was varied from 0 to min (J, K(max)), with K(max)=8 until J=20 and K(max)=4 for further higher J values. This is because further higher values of K do not have much effect on the dynamics and also because one wishes to maintain the large computational overhead for each calculation within the affordable limit. The initial state-selected integral reaction cross sections and thermal rate constants were calculated by summing up the contributions from all partial waves. These were compared with our previous results on the title system, obtained within the centrifugal sudden and J-shifting approximations, to demonstrate the impact of CC on the dynamics of this system.

Optimal laser pulse design for transferring the coherent nuclear wave packet of H+2

NASA Astrophysics Data System (ADS)

Zhang, Jun; He, Guang-Qiang; He, Feng

2014-07-01

Within the Franck-Condon approximation, the single ionisation of H2 leaves H+2 in a coherent superposition of 19 nuclear vibrational states. We numerically design an optimal laser pulse train to transfer such a coherent nuclear wave packet to the ground vibrational state of H+2. Frequency analysis of the designed optimal pulse reveals that the transfer principle is mainly an anti-Stokes transition, i.e. the H+2 in 1sσg with excited nuclear vibrational states is first pumped to 2pσg state by the pulse at an appropriate time, and then dumped back to 1sσg with lower excited or ground vibrational states. The simulation results show that the population of the ground state after the transfer is more than 91%. To the best of our knowledge, this is the highest transition probability when the driving laser field is dozens of femtoseconds.

Exact wave packet dynamics of singlet fission in unsubstituted and substituted polyene chains within long-range interacting models

NASA Astrophysics Data System (ADS)

Prodhan, Suryoday; Ramasesha, S.

2017-08-01

Singlet fission (SF) is a potential pathway for significant enhancement of efficiency in organic solar cells (OSC). In this paper, we study singlet fission in a pair of polyene molecules in two different stacking arrangements employing exact many-body wave packet dynamics. In the noninteracting model, the SF yield is absent. The individual molecules are treated within Hubbard and Pariser-Parr-Pople (PPP) models and the interaction between them involves transfer terms, intersite electron repulsions, and site-charge-bond-charge repulsion terms. Initial wave packet is constructed from excited singlet state of one molecule and ground state of the other. Time development of this wave packet under the influence of intermolecular interactions is followed within the Schrödinger picture by an efficient predictor-corrector scheme. In unsubstituted Hubbard and PPP chains, 2 1A excited singlet state leads to significant SF yield while the 1 1B state gives negligible fission yield. On substitution by donor-acceptor groups of moderate strength, the lowest excited state will have sufficient 2 1A character and hence results in significant SF yield. Because of rapid internal conversion, the nature of the lowest excited singlet will determine the SF contribution to OSC efficiency. Furthermore, we find the fission yield depends considerably on the stacking arrangement of the polyene molecules.

Rydberg wave packets in static electric fields initiated with far infrared pulses

NASA Astrophysics Data System (ADS)

Robicheaux, F.; Lankhuijzen, G. M.; Rella, C.; Noordam, L. D.

1998-05-01

We perform experimental and theoretical studies of transitions from bound atomic Rydberg Stark states in a static electric field to autoionizing states. The transitions are induced by a broadband, tunable free electron laser pulse (1-5 ps width). The systematics of the wave packet properties are investigated when the initial state is the lowest energy state or highest energy state of the n-manifold. We show that the recently proposed electron gun is realized for Rb giving an AC electron current with a 20 ps period.

Scattering of an electronic wave packet by a one-dimensional electron-phonon-coupled structure

NASA Astrophysics Data System (ADS)

Brockt, C.; Jeckelmann, E.

2017-02-01

We investigate the scattering of an electron by phonons in a small structure between two one-dimensional tight-binding leads. This model mimics the quantum electron transport through atomic wires or molecular junctions coupled to metallic leads. The electron-phonon-coupled structure is represented by the Holstein model. We observe permanent energy transfer from the electron to the phonon system (dissipation), transient self-trapping of the electron in the electron-phonon-coupled structure (due to polaron formation and multiple reflections at the structure edges), and transmission resonances that depend strongly on the strength of the electron-phonon coupling and the adiabaticity ratio. A recently developed TEBD algorithm, optimized for bosonic degrees of freedom, is used to simulate the quantum dynamics of a wave packet launched against the electron-phonon-coupled structure. Exact results are calculated for a single electron-phonon site using scattering theory and analytical approximations are obtained for limiting cases.

Acoustic wave propagation in a temporal evolving shear-layer for low-Mach number perturbations

NASA Astrophysics Data System (ADS)

Hau, Jan-Niklas; Müller, Björn

2018-01-01

We study wave packets with the small perturbation/gradient Mach number interacting with a smooth shear-layer in the linear regime of small amplitude perturbations. In particular, we investigate the temporal evolution of wave packets in shear-layers with locally curved regions of variable size using non-modal linear analysis and direct numerical simulations of the two-dimensional gas-dynamical equations. Depending on the wavenumber of the initially imposed wave packet, three different types of behavior are observed: (i) The wave packet passes through the shear-layer and constantly transfers energy back to the mean flow. (ii) It is turned around (or reflected) within the sheared region and extracts energy from the base flow. (iii) It is split into two oppositely propagating packages when reaching the upper boundary of the linearly sheared region. The conducted direct numerical simulations confirm that non-modal linear stability analysis is able to predict the wave packet dynamics, even in the presence of non-linearly sheared regions. In the light of existing studies in this area, we conclude that the sheared regions are responsible for the highly directed propagation of linearly generated acoustic waves when there is a dominating source, as it is the case for jet flows.

Effects of packet retransmission with finite packet lifetime on traffic capacity in scale-free networks

NASA Astrophysics Data System (ADS)

Jiang, Zhong-Yuan; Ma, Jian-Feng

Existing routing strategies such as the global dynamic routing [X. Ling, M. B. Hu, R. Jiang and Q. S. Wu, Phys. Rev. E 81, 016113 (2010)] can achieve very high traffic capacity at the cost of extremely long packet traveling delay. In many real complex networks, especially for real-time applications such as the instant communication software, extremely long packet traveling time is unacceptable. In this work, we propose to assign a finite Time-to-Live (TTL) parameter for each packet. To guarantee every packet to arrive at its destination within its TTL, we assume that a packet is retransmitted by its source once its TTL expires. We employ source routing mechanisms in the traffic model to avoid the routing-flaps induced by the global dynamic routing. We compose extensive simulations to verify our proposed mechanisms. With small TTL, the effects of packet retransmission on network traffic capacity are obvious, and the phase transition from flow free state to congested state occurs. For the purpose of reducing the computation frequency of the routing table, we employ a computing cycle Tc within which the routing table is recomputed once. The simulation results show that the traffic capacity decreases with increasing Tc. Our work provides a good insight into the understanding of effects of packet retransmission with finite packet lifetime on traffic capacity in scale-free networks.

Tuning the group delay of optical wave packets in liquid-crystal light valves

NASA Astrophysics Data System (ADS)

Bortolozzo, U.; Residori, S.; Huignard, J. P.

2009-05-01

By performing two-wave mixing experiments in a liquid-crystal light valve, optical pulses are slowed down to group velocities as slow as a few tenths of mm/s, corresponding to a very large group index. We present experiments and model of the slow-light process occurring in the liquid-crystal light valve, showing that this is characterized by multiple-beam diffraction in the Raman-Nath regime. Depending on the initial frequency detuning between pump and signal, the different output order beams are distinguished by different group delays. The group delay can be tuned by changing the main parameters of the experiment: the detuning between the pump and the input wave packet, the strength of the nonlinearity, and the intensity of the pump beam.

Semiclassical wave packet treatment of scattering resonances: application to the delta zero-point energy effect in recombination reactions.

PubMed

Vetoshkin, Evgeny; Babikov, Dmitri

2007-09-28

For the first time Feshbach-type resonances important in recombination reactions are characterized using the semiclassical wave packet method. This approximation allows us to determine the energies, lifetimes, and wave functions of the resonances and also to observe a very interesting correlation between them. Most important is that this approach permits description of a quantum delta-zero-point energy effect in recombination reactions and reproduces the anomalous rates of ozone formation.

Wave packet dynamics, time scales and phase diagram in the IBM-Lipkin-Meshkov-Glick model

NASA Astrophysics Data System (ADS)

Castaños, Octavio; de los Santos, Francisco; Yáñez, Rafael; Romera, Elvira

2018-02-01

We derive the phase diagram of a scalar two-level boson model by studying the equilibrium and stability properties of its energy surface. The plane of control parameters is enlarged with respect to previous studies. We then analyze the time evolution of wave packets centered around the ground state at various quantum phase transition boundary lines. In particular, classical and revival times are computed numerically.

Simmons Insurance Agency. A Clerk-Typist Position Simulation. Student Packet IV. Office Occupations.

ERIC Educational Resources Information Center

Georgia State Univ., Atlanta.

This is the fourth of five student packets forming part of a position simulation developed for use in an office applications laboratory at the postsecondary level. The purpose of the simulation is to give the student an opportunity to become familiar with the tasks and duties performed by a clerk-typist working for an independent insurance agency.…

Accurate quantum wave packet calculations for the F + HCl → Cl + HF reaction on the ground 1(2)A' potential energy surface.

PubMed

Bulut, Niyazi; Kłos, Jacek; Alexander, Millard H

2012-03-14

We present converged exact quantum wave packet calculations of reaction probabilities, integral cross sections, and thermal rate coefficients for the title reaction. Calculations have been carried out on the ground 1(2)A' global adiabatic potential energy surface of Deskevich et al. [J. Chem. Phys. 124, 224303 (2006)]. Converged wave packet reaction probabilities at selected values of the total angular momentum up to a partial wave of J = 140 with the HCl reagent initially selected in the v = 0, j = 0-16 rovibrational states have been obtained for the collision energy range from threshold up to 0.8 eV. The present calculations confirm an important enhancement of reactivity with rotational excitation of the HCl molecule. First, accurate integral cross sections and rate constants have been calculated and compared with the available experimental data.

Time dependent three-dimensional body frame quantal wave packet treatment of the H + H2 exchange reaction on the Liu-Siegbahn-Truhlar-Horowitz (LSTH) surface

NASA Technical Reports Server (NTRS)

Neuhauser, Daniel; Baer, Michael; Judson, Richard S.; Kouri, Donald J.

1989-01-01

The first successful application of the three-dimensional quantum body frame wave packet approach to reactive scattering is reported for the H + H2 exchange reaction on the LSTH potential surface. The method used is based on a procedure for calculating total reaction probabilities from wave packets. It is found that converged, vibrationally resolved reactive probabilities can be calculated with a grid that is not much larger than required for the pure inelastic calculation. Tabular results are presented for several energies.

Time-reversal-symmetric single-photon wave packets for free-space quantum communication.

PubMed

Trautmann, N; Alber, G; Agarwal, G S; Leuchs, G

2015-05-01

Readout and retrieval processes are proposed for efficient, high-fidelity quantum state transfer between a matter qubit, encoded in the level structure of a single atom or ion, and a photonic qubit, encoded in a time-reversal-symmetric single-photon wave packet. They are based on controlling spontaneous photon emission and absorption of a matter qubit on demand in free space by stimulated Raman adiabatic passage. As these processes do not involve mode selection by high-finesse cavities or photon transport through optical fibers, they offer interesting perspectives as basic building blocks for free-space quantum-communication protocols.

Wave packet dynamics for a system with position and time-dependent effective mass in an infinite square well

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

Vubangsi, M.; Tchoffo, M.; Fai, L. C.

The problem of a particle with position and time-dependent effective mass in a one-dimensional infinite square well is treated by means of a quantum canonical formalism. The dynamics of a launched wave packet of the system reveals a peculiar revival pattern that is discussed. .

Glider Observations of Internal Tide Packets on the Australian Northwest Shelf

NASA Astrophysics Data System (ADS)

Book, J. W.; Steinberg, C. R.; Brinkman, R. M.; Jones, N. L.; Lowe, R.; Ivey, G. N.; Pattiaratchi, C. B.; Rice, A. E.

2016-02-01

The rapid profiling capabilities (less than 10 minutes per profile in 100 m of water excluding surfacing times) of autonomous gliders were utilized to study the structure of non-linear internal tide packets on the Australian Northwest Shelf. A total of five gliders were deployed on the shelf from 11 February - 21 April 2012 with more than 2900 glider CTD profiles collected during the final three weeks of this time period when the internal tide activity was intense. In general the internal tide packets showed high degrees of non-linearity, for example in one case a glider observed a 62 m rise of the 28° isotherm over 2.25 hours in a shelf location of 90 meters water depth. In addition to the glider measurements, moored strings of CTD sensors were used to measure the internal tide packets at fixed positions and the results show that the wave packets vary significantly with respect to their structure and arrival times from one tidal period to the next. This fact complicates interpretation of the glider data as wave packet spatial evolution is non-stationary and cannot be simply recovered from repeat glider visits to the same location. Furthermore, the packets were found to move at speeds near or greater (e.g., 0.55 m/s) than the speed that the gliders were moving. Despite these challenges, the gliders offer the only resource that can measure the spatial structure of the wave packets beyond the scope of our limited mooring positions. Therefore, we have implemented methods such as time-augmented empirical orthogonal functions to combine these glider measurements with the fixed mooring measurements in order to better understand the spatial and temporal patterns of the wave packet evolution over the slope and shelf of this region.

Internal Gravity Waves Forced by an Isolated Mountain

NASA Astrophysics Data System (ADS)

Nikitina, L.; Campbell, L.

2009-12-01

Density-stratified fluid flow over topography such as mountains, hills and ridges may give rise to internal gravity waves which transport and distribute energy away from their source and have profound effects on the general circulation of the atmosphere and ocean. Much of our knowledge of internal gravity wave dynamics has been acquired from theoretical studies involving mathematical analyses of simplified forms of the governing equations, as well as numerical simulations at varying levels of approximation. In this study, both analytical and numerical methods are used to examine the nonlinear dynamics of gravity waves forced by an isolated mountain. The topography is represented by a lower boundary condition on a two-dimensional rectangular domain and the waves are represented as a perturbation to the background shear flow, thus allowing the use of weakly-nonlinear and multiple-scale asymptotic analyzes. The waves take the form of a packet, localized in the horizontal direction and comprising a continuous spectrum of horizontal wavenumbers centered at zero. For horizontally-localized wave packets, such as those forced by a mountain range with multiple peaks, there are generally two horizontal scales, the fast (short) scale which is defined by the oscillations within the packet and the slow (large) scale which is defined by the horizontal extent of the packet. In the case of an isolated mountain that we examine here, the multiple-scaling procedure is simplified by the absence of a fast spatial scale. The problem is governed by two small parameters that define the height and width of the mountain and approximate solutions are derived in terms of these parameters. Numerical solutions are also carried out to simulate nonlinear critical-level interactions such as the transfer of energy to the background flow by the wave packet, wave reflection and static instability and, eventually, wave breaking leading to turbulence. It is found that for waves forced by an isolated

Path-integral analysis of the time delay for wave-packet scattering and the status of complex tunneling times

NASA Astrophysics Data System (ADS)

Sokolovski, D.; Connor, J. N. L.

1990-12-01

The wave-packet simulation (WPS) method for calculating the time a tunneling particle spends inside a one-dimensional potential barrier is reexamined using the Feynman path-integral technique. Following earlier work by Sokolovski and Baskin [Phys. Rev. A 36, 4604 (1987)], the tunneling (or traversal) time tTpack is defined as a matrix element of a classical nonlocal functional between two states that represent the initial and transmitted wave packets. These states do not lie on the same orbit in Hilbert space; as a result, tTpack is complex-valued. It is shown that RetTpack reduces to the standard WPS result, tTphase, for conditions similar to those employed in the conventional WPS analysis. Similarly, ImtTpack is shown to contain information about the energy dependence of the transmission probability. Under semiclassical conditions, ImtTpack reduces to the well-known Wentzel-Kramers-Brillouin expression for the tunneling time. It is shown there are different definitions for the traversal time of a classical moving object, whose size is comparable to the width of the region of interest. In the quantum case, these different definitions correspond to different ways of analyzing the WPS experiment. The path-integral approach demonstrates that the tunneling-time problem is one of understanding the physical significance of complex-valued off-orbit matrix elements of an operator or functional. The physical content of complex-valued tunneling times is discussed. It is emphasized that the use of complex tunneling times includes real-time approaches as a special case. Nevertheless, there is a limitation in the description of tunneling experiments using tunneling times, whether real or complex. The path-integral approach does not supply a universal traversal time, analogous to a classical time, that can be used in quantum situations. It is demonstrated that the often expressed hope of finding a well-defined and universal real tunneling time is erroneous.

Near-Resonant Raman Amplification in the Rotational Quantum Wave Packets of Nitrogen Molecular Ions Generated by Strong Field Ionization

NASA Astrophysics Data System (ADS)

Liu, Zhaoxiang; Yao, Jinping; Chen, Jinming; Xu, Bo; Chu, Wei; Cheng, Ya

2018-02-01

The generation of laserlike narrow bandwidth emissions from nitrogen molecular ions (N2+ ) generated in intense near- and mid infrared femtosecond laser fields has aroused much interest because of the mysterious physics underlying such a phenomenon. Here, we perform a pump-probe measurement on the nonlinear interaction of rotational quantum wave packets of N2+ generated in midinfrared (e.g., at a wavelength centered at 1580 nm) femtosecond laser fields with an ultrashort probe pulse whose broad spectrum overlaps both P - and R -branch rotational transition lines between the electronic states N2+(B2Σu+,v'=0 ) and N2+(X2Σg+,v =0 ) . The results indicate the occurrence of highly efficient near-resonant stimulated Raman scattering in the quantum wave packets of N2+ ions generated in strong laser fields in the midinfrared region, of which the underlying mechanism is different from that of the air lasers generated in atmospheric environment when pumping with 800 nm intense pulses.

Preparing isolated vibrational wave packets with light-induced molecular potentials by chirped laser pulses

NASA Astrophysics Data System (ADS)

Vatasescu, Mihaela

2012-05-01

We consider a specific wave packet preparation arising from the control of tunneling in the 0g-(6s,6p3/2) double well potential of a Cs2 cold molecule with chirped laser pulses. Such a possibility to manipulate the population dynamics in the 0g-(6s,6p3/2) potential appears in a pump-dump scheme designed to form cold molecules by photoassociation of two cold cesium atoms. The initial population in the 0g-(6s,6p3/2) double well is a wave packet prepared in the outer well at large interatomic distances (94 a0) by a photoassociation step with a first chirped pulse, being a superposition of several vibrational states whose energies surround the energy of a tunneling resonance. Our present work is focused on a second delayed chirped pulse, coupling the 0g-(6s,6p3/2) surface with the a3Σu+(6s,6s) one in the zone of the double well barrier (15 a0) and creating deeply bound cold molecules in the a3Σu+(6s,6s) state. We explore the parameters choice (intensity, duration, chirp rate and sign) for this second pulse, showing that picoseconds pulses with a negative chirp can lead to trapping of population in the inner well in strongly bound vibrational states, out of the resonant tunneling able to transfer it back to the outer well.

Magnetic antenna excitation of whistler modes. III. Group and phase velocities of wave packets

NASA Astrophysics Data System (ADS)

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

2015-07-01

The properties of whistler modes excited by single and multiple magnetic loop antennas have been investigated in a large laboratory plasma. A single loop excites a wavepacket, but an array of loops across the ambient magnetic field B0 excites approximate plane whistler modes. The single loop data are measured. The array patterns are obtained by linear superposition of experimental data shifted in space and time, which is valid in a uniform plasma and magnetic field for small amplitude waves. Phasing the array changes the angle of wave propagation. The antennas are excited by an rf tone burst whose propagating envelope and oscillations yield group and phase velocities. A single loop antenna with dipole moment across B0 excites wave packets whose topology resembles m = 1 helicon modes, but without radial boundaries. The phase surfaces are conical with propagation characteristics of Gendrin modes. The cones form near the antenna with comparable parallel and perpendicular phase velocities. A physical model for the wave excitation is given. When a wave burst is applied to a phased antenna array, the wave front propagates both along the array and into the plasma forming a "whistler wing" at the front. These laboratory observations may be relevant for excitation and detection of whistler modes in space plasmas.

Improving the resolution for Lamb wave testing via a smoothed Capon algorithm

NASA Astrophysics Data System (ADS)

Cao, Xuwei; Zeng, Liang; Lin, Jing; Hua, Jiadong

2018-04-01

Lamb wave testing is promising for damage detection and evaluation in large-area structures. The dispersion of Lamb waves is often unavoidable, restricting testing resolution and making the signal hard to interpret. A smoothed Capon algorithm is proposed in this paper to estimate the accurate path length of each wave packet. In the algorithm, frequency domain whitening is firstly used to obtain the transfer function in the bandwidth of the excitation pulse. Subsequently, wavenumber domain smoothing is employed to reduce the correlation between wave packets. Finally, the path lengths are determined by distance domain searching based on the Capon algorithm. Simulations are applied to optimize the number of smoothing times. Experiments are performed on an aluminum plate consisting of two simulated defects. The results demonstrate that spatial resolution is improved significantly by the proposed algorithm.

Thermal responses in a coronal loop maintained by wave heating mechanisms

NASA Astrophysics Data System (ADS)

Matsumoto, Takuma

2018-05-01

A full 3-dimensional compressible magnetohydrodynamic (MHD) simulation is conducted to investigate the thermal responses of a coronal loop to the dynamic dissipation processes of MHD waves. When the foot points of the loop are randomly and continuously forced, the MHD waves become excited and propagate upward. Then, 1-MK temperature corona is produced naturally as the wave energy dissipates. The excited wave packets become non-linear just above the magnetic canopy, and the wave energy cascades into smaller spatial scales. Moreover, collisions between counter-propagating Alfvén wave packets increase the heating rate, resulting in impulsive temperature increases. Our model demonstrates that the heating events in the wave-heated loops can be nanoflare-like in the sense that they are spatially localized and temporally intermittent.

A robust coding scheme for packet video

NASA Technical Reports Server (NTRS)

Chen, Y. C.; Sayood, Khalid; Nelson, D. J.

1991-01-01

We present a layered packet video coding algorithm based on a progressive transmission scheme. The algorithm provides good compression and can handle significant packet loss with graceful degradation in the reconstruction sequence. Simulation results for various conditions are presented.

A robust coding scheme for packet video

NASA Technical Reports Server (NTRS)

Chen, Yun-Chung; Sayood, Khalid; Nelson, Don J.

1992-01-01

A layered packet video coding algorithm based on a progressive transmission scheme is presented. The algorithm provides good compression and can handle significant packet loss with graceful degradation in the reconstruction sequence. Simulation results for various conditions are presented.

Controlled Quantum Packets

NASA Technical Reports Server (NTRS)

DeMartino, Salvatore; DeSiena, Silvio

1996-01-01

We look at time evolution of a physical system from the point of view of dynamical control theory. Normally we solve motion equation with a given external potential and we obtain time evolution. Standard examples are the trajectories in classical mechanics or the wave functions in Quantum Mechanics. In the control theory, we have the configurational variables of a physical system, we choose a velocity field and with a suited strategy we force the physical system to have a well defined evolution. The evolution of the system is the 'premium' that the controller receives if he has adopted the right strategy. The strategy is given by well suited laboratory devices. The control mechanisms are in many cases non linear; it is necessary, namely, a feedback mechanism to retain in time the selected evolution. Our aim is to introduce a scheme to obtain Quantum wave packets by control theory. The program is to choose the characteristics of a packet, that is, the equation of evolution for its centre and a controlled dispersion, and to give a building scheme from some initial state (for example a solution of stationary Schroedinger equation). It seems natural in this view to use stochastic approach to Quantum Mechanics, that is, Stochastic Mechanics [S.M.]. It is a quantization scheme different from ordinary ones only formally. This approach introduces in quantum theory the whole mathematical apparatus of stochastic control theory. Stochastic Mechanics, in our view, is more intuitive when we want to study all the classical-like problems. We apply our scheme to build two classes of quantum packets both derived generalizing some properties of coherent states.

Wave packet dynamics for a non-linear Schrödinger equation describing continuous position measurements

NASA Astrophysics Data System (ADS)

Zander, C.; Plastino, A. R.; Díaz-Alonso, J.

2015-11-01

We investigate time-dependent solutions for a non-linear Schrödinger equation recently proposed by Nassar and Miret-Artés (NM) to describe the continuous measurement of the position of a quantum particle (Nassar, 2013; Nassar and Miret-Artés, 2013). Here we extend these previous studies in two different directions. On the one hand, we incorporate a potential energy term in the NM equation and explore the corresponding wave packet dynamics, while in the previous works the analysis was restricted to the free-particle case. On the other hand, we investigate time-dependent solutions while previous studies focused on a stationary one. We obtain exact wave packet solutions for linear and quadratic potentials, and approximate solutions for the Morse potential. The free-particle case is also revisited from a time-dependent point of view. Our analysis of time-dependent solutions allows us to determine the stability properties of the stationary solution considered in Nassar (2013), Nassar and Miret-Artés (2013). On the basis of these results we reconsider the Bohmian approach to the NM equation, taking into account the fact that the evolution equation for the probability density ρ =| ψ | 2 is not a continuity equation. We show that the effect of the source term appearing in the evolution equation for ρ has to be explicitly taken into account when interpreting the NM equation from a Bohmian point of view.

Basis for paraxial surface-plasmon-polariton packets

NASA Astrophysics Data System (ADS)

Martinez-Herrero, Rosario; Manjavacas, Alejandro

2016-12-01

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

Time Dependent Channel Packet Calculation of Two Nucleon Scattering Matrix Elements

DTIC Science & Technology

2010-03-01

solutions, 46 ( ) ( )1 1 11 ( ) cos sinL L L L Lr Akr j kr krψ δ η δ= −   (3.70) Here, A is an arbitrary constant, Lδ is the phase shift...iv AFIT/DS/ENP/10-M03 Abstract A new approach to calculating nucleon-nucleon scattering matrix...elements using a proven atomic time-dependent wave packet technique is investigated. Using this technique, reactant and product wave packets containing

Performance Evaluation of Multihop Packet Radio Networks by Simulation

DTIC Science & Technology

1987-03-01

Multihop Packet Radio Networks," Proc. IEEE, Vol. 75, No. 1, January 1987. [15] 1. Gitman , "On the Capacity of Slotted ALOHA Networks and Some Design...Networks in the Presence of Noise," Proc. Infocom, Washington D. C., April 1985 [40] H. Frank, I. Gitman and R. Van Slyke, " Packet Radio System

Quantum solitonic wave-packet of a meso-scopic system in singularity free gravity

NASA Astrophysics Data System (ADS)

Buoninfante, Luca; Lambiase, Gaetano; Mazumdar, Anupam

2018-06-01

In this paper we will discuss how to localise a quantum wave-packet due to self-gravitating meso-scopic object by taking into account gravitational self-interaction in the Schrödinger equation beyond General Relativity. In particular, we will study soliton-like solutions in infinite derivative ghost free theories of gravity, which resolves the gravitational 1 / r singularity in the potential. We will show a unique feature that the quantum spread of such a gravitational system is larger than that of the Newtonian gravity, therefore enabling us a window of opportunity to test classical and quantum properties of such theories of gravity in the near future at a table-top experiment.

Femtosecond Electron Wave Packet Propagation and Diffraction: Towards Making the ``Molecular Movie"

NASA Astrophysics Data System (ADS)

Miller, R. J. Dwayne

2003-03-01

Time-resolved electron diffraction harbors great promise for achieving atomic resolution of the fastest chemical processes. The generation of sufficiently short electron pulses to achieve this real time view of a chemical reaction has been limited by problems in maintaining short electron pulses with realistic electron densities to the sample. The propagation dynamics of femtosecond electron packets in the drift region of a photoelectron gun are investigated with an N-body numerical simulation and mean-field model. This analyis shows that the redistribution of electrons inside the packet, arising from space-charge and dispersion contributions, changes the pulse envelope and leads to the development of a spatially linear axial velocity distribution. These results have been used in the design of femtosecond photoelectron guns with higher time resolution and novel electron-optical methods of pulse characterization that are approaching 100 fs timescales. Time-resolved diffraction studies with electron pulses of approximately 500 femtoseconds have focused on solid-liquid phase transitions under far from equilibrium conditions. This work gives a microscopic description of the melting process and illustrates the promise of atomically resolving transition state processes.

The Liouville equation for flavour evolution of neutrinos and neutrino wave packets

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

Hansen, Rasmus Sloth Lundkvist; Smirnov, Alexei Yu., E-mail: rasmus@mpi-hd.mpg.de, E-mail: smirnov@mpi-hd.mpg.de

We consider several aspects related to the form, derivation and applications of the Liouville equation (LE) for flavour evolution of neutrinos. To take into account the quantum nature of neutrinos we derive the evolution equation for the matrix of densities using wave packets instead of Wigner functions. The obtained equation differs from the standard LE by an additional term which is proportional to the difference of group velocities. We show that this term describes loss of the propagation coherence in the system. In absence of momentum changing collisions, the LE can be reduced to a single derivative equation over amore » trajectory coordinate. Additional time and spatial dependence may stem from initial (production) conditions. The transition from single neutrino evolution to the evolution of a neutrino gas is considered.« less

Fokker-Planck electron diffusion caused by an obliquely propagating electromagnetic wave packet of narrow bandwidth

NASA Technical Reports Server (NTRS)

Hizanidis, Kyriakos

1989-01-01

The relativistic motion of electrons in an intense electromagnetic wave packet propagating obliquely to a uniform magnetic field is analytically studied on the basis of the Fokker-Planck-Kolmogorov (FPK) approach. The wavepacket consists of circularly polarized electron-cyclotron waves. The dynamical system in question is shown to be reducible to one with three degrees of freedom. Within the framework of the Hamiltonian analysis the nonlinear diffusion tensor is derived, and it is shown that this tensor can be separated into zeroth-, first-, and second-order parts with respect to the relative bandwidth. The zeroth-order part describes diffusive acceleration along lines of constant unperturbed Hamiltonian. The second-order part, which corresponds to the longest time scale, describes diffusion across those lines. A possible transport theory is outlined on the basis of this separation of the time scales.

Time operators in stroboscopic wave-packet basis and the time scales in tunneling

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

Bokes, P.

2011-03-15

We demonstrate that the time operator that measures the time of arrival of a quantum particle into a chosen state can be defined as a self-adjoint quantum-mechanical operator using periodic boundary conditions and applied to wave functions in energy representation. The time becomes quantized into discrete eigenvalues; and the eigenstates of the time operator, i.e., the stroboscopic wave packets introduced recently [Phys. Rev. Lett. 101, 046402 (2008)], form an orthogonal system of states. The formalism provides simple physical interpretation of the time-measurement process and direct construction of normalized, positive definite probability distribution for the quantized values of the arrival time.more » The average value of the time is equal to the phase time but in general depends on the choice of zero time eigenstate, whereas the uncertainty of the average is related to the traversal time and is independent of this choice. The general formalism is applied to a particle tunneling through a resonant tunneling barrier in one dimension.« less

Stabilization and Structure of wave packets in Rydberg atoms ionized by a strong light field.

PubMed

Fedorov, M; Fedorov, S

1998-09-28

New features of the phenomenon of interference stabilization of Rydberg atoms are found to exist. The main of them are: (i) dynamical stabilization, which means that in case of pulses with a smooth envelope the time-dependent residual probability for an atom to survive in bound states remains almost constant in the middle part of a pulse (at the strongest fields); (ii) existence of the strong-field stabilization of the after-pulse residual probability in case of pulses longer than the classical Kepler period; and (iii) pulsation of the time-dependent Rydberg wave packet formed in the process of photoionization.

Evolution of Nonlinear Internal Waves in China Seas

NASA Technical Reports Server (NTRS)

Liu, Antony K.; Hsu, Ming-K.; Liang, Nai K.

1997-01-01

Synthetic Aperture Radar (SAR) images from ERS-I have been used to study the characteristics of internal waves of Taiwan in the East China Sea, and east of Hainan Island in the South China Sea. Rank-ordered packets of internal solitons propagating shoreward from the edge of the continental shelf were observed in the SAR images. Based on the assumption of a semidiurnal tidal origin, the wave speed can be estimated and is consistent with the internal wave theory. By using the SAR images and hydrographic data, internal waves of elevation have been identified in shallow water due to a thicker mixed layer as compared with the bottom layer on the continental shelf. The generation mechanism includes the influences of the tide and the Kuroshio intrusion across the continental shelf for the formations of elevation internal waves. The effects of water depth on the evolution of solitons and wave packets are modeled by nonlinear Kortweg-deVries (KdV) type equation and linked to satellite image observations. The numerical calculations of internal wave evolution on the continental shelf have been performed and compared with the SAR observations. For a case of depression waves in deep water, the solitons first disintegrate into dispersive wave trains and then evolve to a packet of elevation waves in the shallow water area after they pass through a turning point of approximately equal layer depths has been observed in the SAR image and simulated by numerical model.

SEQUENCING of TSUNAMI WAVES: Why the first wave is not always the largest?

NASA Astrophysics Data System (ADS)

Synolakis, C.; Okal, E.

2016-12-01

We discuss what contributes to the `sequencing' of tsunami waves in the far field, that is, to the distribution of the maximum sea surface amplitude inside the dominant wave packet constituting the primary arrival at a distant harbour. Based on simple models of sources for which analytical solutions are available, we show that, as range is increased, the wave pattern evolves from a regime of maximum amplitude in the first oscillation to one of delayed maximum, where the largest amplitude takes place during a subsequent oscillation. In the case of the simple, instantaneous uplift of a circular disk at the surface of an ocean of constant depth, the critical distance for transition between those patterns scales as r 30 /h2 where r0 is the radius of the disk and h the depth of the ocean. This behaviour is explained from simple arguments based on a model where sequencing results from frequency dispersion in the primary wave packet, as the width of its spectrum around its dominant period T0 becomes dispersed in time in an amount comparable to T0 , the latter being controlled by a combination of source size and ocean depth. The general concepts in this model are confirmed in the case of more realistic sources for tsunami excitation by a finite-time deformation of the ocean floor, as well as in real-life simulations of tsunamis excited by large subduction events, for which we find that the influence of fault width on the distribution of sequencing is more important than that of fault length. Finally, simulation of the major events of Chile (2010) and Japan (2011) at large arrays of virtual gauges in the Pacific Basin correctly predicts the majority of the sequencing patterns observed on DART buoys during these events. By providing insight into the evolution with time of wave amplitudes inside primary wave packets for far field tsunamis generated by large earthquakes, our results stress the importance, for civil defense authorities, of issuing warning and evacuation orders

Control of propagation of spatially localized polariton wave packets in a Bragg mirror with embedded quantum wells

NASA Astrophysics Data System (ADS)

Sedova, I. E.; Chestnov, I. Yu.; Arakelian, S. M.; Kavokin, A. V.; Sedov, E. S.

2018-01-01

We considered the nonlinear dynamics of Bragg polaritons in a specially designed stratified semiconductor structure with embedded quantum wells, which possesses a convex dispersion. The model for the ensemble of single periodically arranged quantum wells coupled with the Bragg photon fields has been developed. In particular, the generalized Gross-Pitaevskii equation with the non-parabolic dispersion has been obtained for the Bragg polariton wave function. We revealed a number of dynamical regimes for polariton wave packets resulting from competition of the convex dispersion and the repulsive nonlinearity effects. Among the regimes are spreading, breathing and soliton propagation. When the control parameters including the exciton-photon detuning, the matter-field coupling and the nonlinearity are manipulated, the dynamical regimes switch between themselves.

Controlling of the electromagnetic solitary waves generation in the wake of a two-color laser

NASA Astrophysics Data System (ADS)

Pan, K. Q.; Li, S. W.; Guo, L.; Yang, D.; Li, Z. C.; Zheng, C. Y.; Jiang, S. E.; Zhang, B. H.; He, X. T.

2018-05-01

Electromagnetic solitary waves generated by a two-color laser interaction with an underdense plasma are investigated. It is shown that, when the former wave packet of the two-color laser is intense enough, it will excite nonlinear wakefields and generate electron density cavities. The latter wave packets will beat with the nonlinear wakefield and generate both high-frequency and low-frequency components. When the peak density of the cavities exceeds the critical density of the low-frequency component, this part of the electromagnetic field will be trapped to generate electromagnetic solitary waves. By changing the laser and plasma parameters, we can control the wakefield generation, which will also control the generation of the solitary waves. One-dimensional particle-in-cell simulations are performed to prove the controlling of the solitary waves. The simulation results also show that solitary waves generated by higher laser intensities will become moving solitary waves. The two-dimensional particle-in-cell also shows the generation of the solitary waves. In the two-dimensional case, solitary waves are distributed in the transverse directions because of the filamentation instability.

Possibility to Probe Negative Values of a Wigner Function in Scattering of a Coherent Superposition of Electronic Wave Packets by Atoms.

PubMed

Karlovets, Dmitry V; Serbo, Valeriy G

2017-10-27

Within a plane-wave approximation in scattering, an incoming wave packet's Wigner function stays positive everywhere, which obscures such purely quantum phenomena as nonlocality and entanglement. With the advent of the electron microscopes with subnanometer-sized beams, one can enter a genuinely quantum regime where the latter effects become only moderately attenuated. Here we show how to probe negative values of the Wigner function in scattering of a coherent superposition of two Gaussian packets with a nonvanishing impact parameter between them (a Schrödinger's cat state) by atomic targets. For hydrogen in the ground 1s state, a small parameter of the problem, a ratio a/σ_{⊥} of the Bohr radius a to the beam width σ_{⊥}, is no longer vanishing. We predict an azimuthal asymmetry of the scattered electrons, which is found to be up to 10%, and argue that it can be reliably detected. The production of beams with the not-everywhere-positive Wigner functions and the probing of such quantum effects can open new perspectives for noninvasive electron microscopy, quantum tomography, particle physics, and so forth.

Ballistic pulse propagation in quantum wire waveguides: Toward localization and control of electron wave packets in space and time

NASA Astrophysics Data System (ADS)

Hayata, K.; Tsuji, Y.; Koshiba, M.

1992-10-01

A theoretical formulation of electron pulse propagation in quantum wire structures with mesoscopic scale cross sections is presented, assuming quantum ballistic transport of electron wave packets over a certain characteristic length. As typical mesoscopic structures for realizing coherent electron transmission, two traveling-wave configurations are considered: straight quantum wire waveguides and quantum wire bend structures (quantum whispering galleries). To estimate temporal features of the pulse during propagation, the walk off, the dispersion, and the pulse coherence lengths are defined as useful characteristic lengths. Numerical results are shown for ultrashort pulse propagation through rectangular wire waveguides. Effects due to an external electric field are discussed as well.

The dynamics and spectral characteristics of the GPS TEC wave packets excited by the solar terminator

NASA Astrophysics Data System (ADS)

Afraimovich, E. L.; Edemsky, I. K.; Voeykov, S. V.; Yasukevich, Y. V.; Zhivetiev, I. V.

2009-04-01

The great variety of solar terminator (ST) -linked phenomena in the atmosphere gave rise to a num¬ber of studies on the analysis of ionosphere parameter variations obtained by different ionosphere sounding methods. Main part of experimental data was obtained using methods for analyzing the spectrum of ionosphere parameter variations in separate local points. To identify ST-generated wave disturbances it is necessary to measure the dynamic and spectral characteristics of the wave disturbances and to compare it with spatial-temporal characteristics of ST. Using TEC measurements from the dense network of GPS sites GEONET (Japan), we have obtained the first GPS-TEC image of the space structure of medium-scale traveling wave packets (MS TWP) excited by the solar terminator. We use two known forms of the 2D GPS-TEC image for our presentation of the space structure of ST-generated MS TWP: 1) - the diagram "distance-time"; 2) - the 2D-space distribution of the values of filtered TEC series dI (λ, φ, t) on the latitude φ and longitude λ for each 30-sec TEC counts. We found that the time period and wave-length of ST-generated wave packets are about 10-20 min and 200-300 km, respectively. Dynamic images analysis of dI (λ, φ, t) gives precise estimation of velocity and azimuth of TWP wave front propagation. We use the method of determining velocity of traveling ionosphere disturbances (SADM-GPS), which take into account the relative moving of subionosphere points. We found that the velocity of the TWP phase front, traveling along GEONET sites, varies in accordance with the velocity of the ST line displacement. The space image of MS TWP manifests itself in pronounced anisotropy and high coherence over a long distance of about 2000 km. The TWP wave front extends along the ST line with the angular shift of about 20°. The hypothesis on the connection between the TWP generation and the solar terminator can be tested in the terminator local time (TLT) system: d

Determination of the effective transverse coherence of the neutron wave packet as employed in reflectivity investigations of condensed-matter structures. I. Measurements

NASA Astrophysics Data System (ADS)

Majkrzak, Charles F.; Metting, Christopher; Maranville, Brian B.; Dura, Joseph A.; Satija, Sushil; Udovic, Terrence; Berk, Norman F.

2014-03-01

The primary purpose of this investigation is to determine the effective coherent extent of the neutron wave packet transverse to its mean propagation vector k when it is prepared in a typical instrument used to study the structure of materials in thin film form via specular reflection. There are two principal reasons for doing so. One has to do with the fundamental physical interest in the characteristics of a free neutron as a quantum object, while the other is of a more practical nature, relating to the understanding of how to interpret elastic scattering data when the neutron is employed as a probe of condensed-matter structure on an atomic or nanometer scale. Knowing such a basic physical characteristic as the neutron's effective transverse coherence can dictate how to properly analyze specular reflectivity data obtained for material film structures possessing some amount of in-plane inhomogeneity. In this study we describe a means of measuring the effective transverse coherence length of the neutron wave packet by specular reflection from a series of diffraction gratings of different spacings. Complementary nonspecular measurements of the widths of grating reflections were also performed, which corroborate the specular results. (This paper principally describes measurements interpreted according to the theoretical picture presented in a companion paper.) Each grating was fabricated by lift-off photolithography patterning of a nickel film (approximately 1000 Å thick) formed by physical vapor deposition on a flat silicon crystal surface. The grating periods ranged from 10 μm (5 μm Ni stripe, 5 μm intervening space) to several hundred microns. The transverse coherence length, modeled as the width of the wave packet, was determined from an analysis of the specular reflectivity curves of the set of gratings.

A Versatile Applet to Explore the Wave Behaviour of Particles

ERIC Educational Resources Information Center

Fernandez Palop, J. I.

2009-01-01

A pedagogical tool that consists of a Java applet has been developed so that undergraduate students in physics can explore the wave behaviour of particles. The applet executes a simulation in which a two-dimensional wave packet moves towards a slit and an obstacle with variable widths. By changing three parameters, slit width, obstacle width and…

Packet loss mitigation for biomedical signals in healthcare telemetry.

PubMed

Garudadri, Harinath; Baheti, Pawan K

2009-01-01

In this work, we propose an effective application layer solution for packet loss mitigation in the context of Body Sensor Networks (BSN) and healthcare telemetry. Packet losses occur due to many reasons including excessive path loss, interference from other wireless systems, handoffs, congestion, system loading, etc. A call for action is in order, as packet losses can have extremely adverse impact on many healthcare applications relying on BAN and WAN technologies. Our approach for packet loss mitigation is based on Compressed Sensing (CS), an emerging signal processing concept, wherein significantly fewer sensor measurements than that suggested by Shannon/Nyquist sampling theorem can be used to recover signals with arbitrarily fine resolution. We present simulation results demonstrating graceful degradation of performance with increasing packet loss rate. We also compare the proposed approach with retransmissions. The CS based packet loss mitigation approach was found to maintain up to 99% beat-detection accuracy at packet loss rates of 20%, with a constant latency of less than 2.5 seconds.

Filtering for networked control systems with single/multiple measurement packets subject to multiple-step measurement delays and multiple packet dropouts

NASA Astrophysics Data System (ADS)

Moayedi, Maryam; Foo, Yung Kuan; Chai Soh, Yeng

2011-03-01

The minimum-variance filtering problem in networked control systems, where both random measurement transmission delays and packet dropouts may occur, is investigated in this article. Instead of following the many existing results that solve the problem by using probabilistic approaches based on the probabilities of the uncertainties occurring between the sensor and the filter, we propose a non-probabilistic approach by time-stamping the measurement packets. Both single-measurement and multiple measurement packets are studied. We also consider the case of burst arrivals, where more than one packet may arrive between the receiver's previous and current sampling times; the scenario where the control input is non-zero and subject to delays and packet dropouts is examined as well. It is shown that, in such a situation, the optimal state estimate would generally be dependent on the possible control input. Simulations are presented to demonstrate the performance of the various proposed filters.

Generation of attosecond electron packets via conical surface plasmon electron acceleration

PubMed Central

Greig, S. R.; Elezzabi, A. Y.

2016-01-01

We present a method for the generation of high kinetic energy attosecond electron packets via magnetostatic and aperture filtering of conical surface plasmon (SP) accelerated electrons. The conical SP waves are excited by coupling an ultrafast radially polarized laser beam to a conical silica lens coated with an Ag film. Electromagnetic and particle tracking models are employed to characterize the ultrafast electron packets. PMID:26764129

Influence of orbital symmetry on diffraction imaging with rescattering electron wave packets

DOE PAGES

Pullen, M. G.; Wolter, B.; Le, A. -T.; ...

2016-06-22

The ability to directly follow and time-resolve the rearrangement of the nuclei within molecules is a frontier of science that requires atomic spatial and few-femtosecond temporal resolutions. While laser-induced electron diffraction can meet these requirements, it was recently concluded that molecules with particular orbital symmetries (such as pg) cannot be imaged using purely backscattering electron wave packets without molecular alignment. Here, we demonstrate, in direct contradiction to these findings, that the orientation and shape of molecular orbitals presents no impediment for retrieving molecular structure with adequate sampling of the momentum transfer space. We overcome previous issues by showcasing retrieval ofmore » the structure of randomly oriented O 2 and C 2H 2 molecules, with π g and π u symmetries, respectively, and where their ionization probabilities do not maximize along their molecular axes. As a result, while this removes a serious bottleneck for laser-induced diffraction imaging, we find unexpectedly strong backscattering contributions from low-Z atoms.« less

Propagation of THz acoustic wave packets in GaN at room temperature

NASA Astrophysics Data System (ADS)

Maznev, A. A.; Hung, T.-C.; Yao, Y.-T.; Chou, T.-H.; Gandhi, J. S.; Lindsay, L.; Shin, H. D.; Stokes, D. W.; Forrest, R. L.; Bensaoula, A.; Sun, C.-K.; Nelson, K. A.

2018-02-01

We use femtosecond laser pulses to generate coherent longitudinal acoustic phonons at frequencies of 1-1.4 THz and study their propagation in GaN-based structures at room temperature. Two InGaN-GaN multiple-quantum-well (MQW) structures separated by a 2.3 μm-thick GaN spacer are used to simultaneously generate phonon wave packets with a central frequency determined by the period of the MQW and detect them after passing through the spacer. The measurements provide lower bounds for phonon lifetimes in GaN, which are still significantly lower than those from first principles predictions. The material Q-factor at 1 THz is found to be at least as high as 900. The measurements also demonstrate a partial specular reflection from the free surface of GaN at 1.4 THz. This work shows the potential of laser-based methods for THz range phonon spectroscopy and the promise for extending the viable frequency range of GaN-based acousto-electronic devices.

Five-wave-packet quantum error correction based on continuous-variable cluster entanglement

PubMed Central

Hao, Shuhong; Su, Xiaolong; Tian, Caixing; Xie, Changde; Peng, Kunchi

2015-01-01

Quantum error correction protects the quantum state against noise and decoherence in quantum communication and quantum computation, which enables one to perform fault-torrent quantum information processing. We experimentally demonstrate a quantum error correction scheme with a five-wave-packet code against a single stochastic error, the original theoretical model of which was firstly proposed by S. L. Braunstein and T. A. Walker. Five submodes of a continuous variable cluster entangled state of light are used for five encoding channels. Especially, in our encoding scheme the information of the input state is only distributed on three of the five channels and thus any error appearing in the remained two channels never affects the output state, i.e. the output quantum state is immune from the error in the two channels. The stochastic error on a single channel is corrected for both vacuum and squeezed input states and the achieved fidelities of the output states are beyond the corresponding classical limit. PMID:26498395

Sequencing of tsunami waves: why the first wave is not always the largest

NASA Astrophysics Data System (ADS)

Okal, Emile A.; Synolakis, Costas E.

2016-02-01

This paper examines the factors contributing to the `sequencing' of tsunami waves in the far field, that is, to the distribution of the maximum sea surface amplitude inside the dominant wave packet constituting the primary arrival at a distant harbour. Based on simple models of sources for which analytical solutions are available, we show that, as range is increased, the wave pattern evolves from a regime of maximum amplitude in the first oscillation to one of delayed maximum, where the largest amplitude takes place during a subsequent oscillation. In the case of the simple, instantaneous uplift of a circular disk at the surface of an ocean of constant depth, the critical distance for transition between those patterns scales as r_0^3 / h^2 where r0 is the radius of the disk and h the depth of the ocean. This behaviour is explained from simple arguments based on a model where sequencing results from frequency dispersion in the primary wave packet, as the width of its spectrum around its dominant period T0 becomes dispersed in time in an amount comparable to T0, the latter being controlled by a combination of source size and ocean depth. The general concepts in this model are confirmed in the case of more realistic sources for tsunami excitation by a finite-time deformation of the ocean floor, as well as in real-life simulations of tsunamis excited by large subduction events, for which we find that the influence of fault width on the distribution of sequencing is more important than that of fault length. Finally, simulation of the major events of Chile (2010) and Japan (2011) at large arrays of virtual gauges in the Pacific Basin correctly predicts the majority of the sequencing patterns observed on DART buoys during these events. By providing insight into the evolution with time of wave amplitudes inside primary wave packets for far field tsunamis generated by large earthquakes, our results stress the importance, for civil defense authorities, of issuing warning and

Delay-time distribution in the scattering of time-narrow wave packets (II)—quantum graphs

NASA Astrophysics Data System (ADS)

Smilansky, Uzy; Schanz, Holger

2018-02-01

We apply the framework developed in the preceding paper in this series (Smilansky 2017 J. Phys. A: Math. Theor. 50 215301) to compute the time-delay distribution in the scattering of ultra short radio frequency pulses on complex networks of transmission lines which are modeled by metric (quantum) graphs. We consider wave packets which are centered at high wave number and comprise many energy levels. In the limit of pulses of very short duration we compute upper and lower bounds to the actual time-delay distribution of the radiation emerging from the network using a simplified problem where time is replaced by the discrete count of vertex-scattering events. The classical limit of the time-delay distribution is also discussed and we show that for finite networks it decays exponentially, with a decay constant which depends on the graph connectivity and the distribution of its edge lengths. We illustrate and apply our theory to a simple model graph where an algebraic decay of the quantum time-delay distribution is established.

Random access with adaptive packet aggregation in LTE/LTE-A.

PubMed

Zhou, Kaijie; Nikaein, Navid

While random access presents a promising solution for efficient uplink channel access, the preamble collision rate can significantly increase when massive number of devices simultaneously access the channel. To address this issue and improve the reliability of the random access, an adaptive packet aggregation method is proposed. With the proposed method, a device does not trigger a random access for every single packet. Instead, it starts a random access when the number of aggregated packets reaches a given threshold. This method reduces the packet collision rate at the expense of an extra latency, which is used to accumulate multiple packets into a single transmission unit. Therefore, the tradeoff between packet loss rate and channel access latency has to be carefully selected. We use semi-Markov model to derive the packet loss rate and channel access latency as functions of packet aggregation number. Hence, the optimal amount of aggregated packets can be found, which keeps the loss rate below the desired value while minimizing the access latency. We also apply for the idea of packet aggregation for power saving, where a device aggregates as many packets as possible until the latency constraint is reached. Simulations are carried out to evaluate our methods. We find that the packet loss rate and/or power consumption are significantly reduced with the proposed method.

Electrostatic solitary waves generated by beam injection in LAPD

NASA Astrophysics Data System (ADS)

Chen, L.; Gekelman, W. N.; Lefebvre, B.; Kintner, P. M.; Pickett, J. S.; Pribyl, P.; Vincena, S. T.

2011-12-01

Spacecraft data have revealed that electrostatic solitary waves are ubiquitous in non-equilibrium collisionless space plasmas. These solitary waves are often the main constituents of the observed electrostatic turbulence. The ubiquitous presence of these solitary waves in space motivated laboratory studies on their generation and evolution in the Large Plasma Device (LAPD) at UCLA. In order to observe these structures, microprobes with scale sizes of order of the Debye length (30 microns) had to be built using Mems technology. A suprathermal electron beam was injected into the afterglow plasma, and solitary waves as well as nonlinear wave packets were measured. The solitary waves are interpreted as BGK electron holes based on their width, amplitude, and velocity characteristics. The ensuing turbulence, including the solitary waves and wave packets, exhibits a band dispersion relation with its central line consistent with the electrostatic whistler mode. One surprise brought by the laboratory experiments is that the electron holes were not generated through resonant two-stream instabilities, but likely through an instability due to parallel currents. The characteristics of the LAPD electron holes and those observed in space will be compared to motivate further theoretical, simulation, and experimental work.

Sampled-Data Consensus of Linear Multi-agent Systems With Packet Losses.

PubMed

Zhang, Wenbing; Tang, Yang; Huang, Tingwen; Kurths, Jurgen

In this paper, the consensus problem is studied for a class of multi-agent systems with sampled data and packet losses, where random and deterministic packet losses are considered, respectively. For random packet losses, a Bernoulli-distributed white sequence is used to describe packet dropouts among agents in a stochastic way. For deterministic packet losses, a switched system with stable and unstable subsystems is employed to model packet dropouts in a deterministic way. The purpose of this paper is to derive consensus criteria, such that linear multi-agent systems with sampled-data and packet losses can reach consensus. By means of the Lyapunov function approach and the decomposition method, the design problem of a distributed controller is solved in terms of convex optimization. The interplay among the allowable bound of the sampling interval, the probability of random packet losses, and the rate of deterministic packet losses are explicitly derived to characterize consensus conditions. The obtained criteria are closely related to the maximum eigenvalue of the Laplacian matrix versus the second minimum eigenvalue of the Laplacian matrix, which reveals the intrinsic effect of communication topologies on consensus performance. Finally, simulations are given to show the effectiveness of the proposed results.In this paper, the consensus problem is studied for a class of multi-agent systems with sampled data and packet losses, where random and deterministic packet losses are considered, respectively. For random packet losses, a Bernoulli-distributed white sequence is used to describe packet dropouts among agents in a stochastic way. For deterministic packet losses, a switched system with stable and unstable subsystems is employed to model packet dropouts in a deterministic way. The purpose of this paper is to derive consensus criteria, such that linear multi-agent systems with sampled-data and packet losses can reach consensus. By means of the Lyapunov function

Greedy data transportation scheme with hard packet deadlines for wireless ad hoc networks.

PubMed

Lee, HyungJune

2014-01-01

We present a greedy data transportation scheme with hard packet deadlines in ad hoc sensor networks of stationary nodes and multiple mobile nodes with scheduled trajectory path and arrival time. In the proposed routing strategy, each stationary ad hoc node en route decides whether to relay a shortest-path stationary node toward destination or a passing-by mobile node that will carry closer to destination. We aim to utilize mobile nodes to minimize the total routing cost as far as the selected route can satisfy the end-to-end packet deadline. We evaluate our proposed routing algorithm in terms of routing cost, packet delivery ratio, packet delivery time, and usability of mobile nodes based on network level simulations. Simulation results show that our proposed algorithm fully exploits the remaining time till packet deadline to turn into networking benefits of reducing the overall routing cost and improving packet delivery performance. Also, we demonstrate that the routing scheme guarantees packet delivery with hard deadlines, contributing to QoS improvement in various network services.

Greedy Data Transportation Scheme with Hard Packet Deadlines for Wireless Ad Hoc Networks

PubMed Central

Lee, HyungJune

2014-01-01

We present a greedy data transportation scheme with hard packet deadlines in ad hoc sensor networks of stationary nodes and multiple mobile nodes with scheduled trajectory path and arrival time. In the proposed routing strategy, each stationary ad hoc node en route decides whether to relay a shortest-path stationary node toward destination or a passing-by mobile node that will carry closer to destination. We aim to utilize mobile nodes to minimize the total routing cost as far as the selected route can satisfy the end-to-end packet deadline. We evaluate our proposed routing algorithm in terms of routing cost, packet delivery ratio, packet delivery time, and usability of mobile nodes based on network level simulations. Simulation results show that our proposed algorithm fully exploits the remaining time till packet deadline to turn into networking benefits of reducing the overall routing cost and improving packet delivery performance. Also, we demonstrate that the routing scheme guarantees packet delivery with hard deadlines, contributing to QoS improvement in various network services. PMID:25258736

A robust low-rate coding scheme for packet video

NASA Technical Reports Server (NTRS)

Chen, Y. C.; Sayood, Khalid; Nelson, D. J.; Arikan, E. (Editor)

1991-01-01

Due to the rapidly evolving field of image processing and networking, video information promises to be an important part of telecommunication systems. Although up to now video transmission has been transported mainly over circuit-switched networks, it is likely that packet-switched networks will dominate the communication world in the near future. Asynchronous transfer mode (ATM) techniques in broadband-ISDN can provide a flexible, independent and high performance environment for video communication. For this paper, the network simulator was used only as a channel in this simulation. Mixture blocking coding with progressive transmission (MBCPT) has been investigated for use over packet networks and has been found to provide high compression rate with good visual performance, robustness to packet loss, tractable integration with network mechanics and simplicity in parallel implementation.

'Superluminal paradox' in wave packet propagation and its quantum mechanical resolution

NASA Astrophysics Data System (ADS)

Sokolovski, D.; Akhmatskaya, E.

2013-12-01

We analyse in detail the reshaping mechanism leading to apparently 'superluminal' advancement of a wave packet traversing a classically forbidden region. In the coordinate representation, a barrier is shown to act as an effective beamsplitter, recombining envelopes of the freely propagating pulse with various spacial shifts. Causality ensures that none of the constituent envelopes are advanced with respect to free propagation, yet the resulting pulse is advanced due to a peculiar interference effect, similar to the one responsible for 'anomalous' values which occur in Aharonov's 'weak measurements'. In the momentum space, the effect is understood as a bandwidth phenomenon, where the incident pulse probes local, rather than global, analytical properties of the transmission amplitude T(p). The advancement is achieved when T(p) mimics locally an exponential behaviour, similar to the one occurring in Berry's 'superoscillations'. Seen in a broader quantum mechanical context, the 'paradox' is but a consequence of an attempt to obtain 'which way?' information without destroying the interference between the pathways of interest. This explains, to a large extent, the failure to adequately describe tunnelling in terms of a single 'tunnelling time'.

Extensible packet processing architecture

DOEpatents

Robertson, Perry J.; Hamlet, Jason R.; Pierson, Lyndon G.; Olsberg, Ronald R.; Chun, Guy D.

2013-08-20

A technique for distributed packet processing includes sequentially passing packets associated with packet flows between a plurality of processing engines along a flow through data bus linking the plurality of processing engines in series. At least one packet within a given packet flow is marked by a given processing engine to signify by the given processing engine to the other processing engines that the given processing engine has claimed the given packet flow for processing. A processing function is applied to each of the packet flows within the processing engines and the processed packets are output on a time-shared, arbitered data bus coupled to the plurality of processing engines.

Propagation of THz acoustic wave packets in GaN at room temperature

DOE PAGES

Maznev, A. A.; Hung, T.-C.; Yao, Y.-T.; ...

2018-02-05

We use femtosecond laser pulses to generate coherent longitudinal acoustic phonons at frequencies of 1–1.4 THz and study their propagation in GaN-based structures at room temperature. Two InGaN-GaN multiple-quantum-well (MQW) structures separated by a 2.3 μm-thick GaN spacer are used to simultaneously generate phonon wave packets with a central frequency determined by the period of the MQW and detect them after passing through the spacer. The measurements provide lower bounds for phonon lifetimes in GaN, which are still significantly lower than those from first principles predictions. The material Q-factor at 1 THz is found to be at least as highmore » as 900. The measurements also demonstrate a partial specular reflection from the free surface of GaN at 1.4 THz. This work shows the potential of laser-based methods for THz range phonon spectroscopy and the promise for extending the viable frequency range of GaN-based acousto-electronic devices.« less

Propagation of THz acoustic wave packets in GaN at room temperature

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

Maznev, A. A.; Hung, T.-C.; Yao, Y.-T.

We use femtosecond laser pulses to generate coherent longitudinal acoustic phonons at frequencies of 1–1.4 THz and study their propagation in GaN-based structures at room temperature. Two InGaN-GaN multiple-quantum-well (MQW) structures separated by a 2.3 μm-thick GaN spacer are used to simultaneously generate phonon wave packets with a central frequency determined by the period of the MQW and detect them after passing through the spacer. The measurements provide lower bounds for phonon lifetimes in GaN, which are still significantly lower than those from first principles predictions. The material Q-factor at 1 THz is found to be at least as highmore » as 900. The measurements also demonstrate a partial specular reflection from the free surface of GaN at 1.4 THz. This work shows the potential of laser-based methods for THz range phonon spectroscopy and the promise for extending the viable frequency range of GaN-based acousto-electronic devices.« less

Influence of wave-packet dynamics on the medium gain of an atomic system

NASA Astrophysics Data System (ADS)

Delagnes, J. C.; Bouchene, M. A.

2007-10-01

A sequence of two femtosecond pulses—a strong driving π -polarized pulse and a weak propagating σ -polarized pulse—excites resonantly the S1/2→P1/2 transition of an atomic system. Strong interference effects take place in the system between absorption and emission paths leading to a substantial amplification of the σ pulse. We study the influence of the fine structure on the medium gain when the contribution of the off-resonant P3/2 level is taken into account. A drastic reduction of the medium gain is obtained. This effect is explained within the bright-state dark-state formalism where the strong driving pulse creates a wave packet that can be trapped in a state—the bright state—leading to a significant reduction of the gain for the σ pulse. Finally, we also show that periodical gain dependence with the driving pulse energy exhibits a significant change in its period value (compared with expected Rabi oscillations).

Wave-packet approach to transport properties of carrier coupled with intermolecular and intramolecular vibrations of organic semiconductors

NASA Astrophysics Data System (ADS)

Ishii, Hiroyuki; Honma, Keisuke; Kobayashi, Nobuhiko; Hirose, Kenji

2012-06-01

We present a methodology to study the charge-transport properties of organic semiconductors by the time-dependent wave-packet diffusion method, taking the polaron effects into account. As an example, we investigate the transport properties of single-crystal pentacene organic semiconductors coupled with inter- and intramolecular vibrations within the mixed Holstein and Peierls model, which describes both hopping and bandlike transport behaviors due to small and large polaron formations. Taking into account static disorders, which inevitably exist in the molecular crystals, we present the temperature dependence of charge-transport properties in competition among the thermal fluctuation of molecular motions, the polaron formation, and the static disorders.

Coherent and incoherent contributions to the carrier-envelope phase control of wave packet localization in quantum double wells

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

Hader, K.; Engel, V., E-mail: voen@phys-chemie.uni-wuerzburg.de

2014-05-14

We study laser excitation processes in a double well potential. The possibility to influence localization via the carrier-envelope phase (CEP) of a laser pulse is investigated for various situations which differ in the nature of the initial state prior to the laser interactions. In more detail, the CEP-dependence of asymmetries in the case where initially the system is described by localized wave packets, eigenstates, or incoherent mixtures are calculated and interpreted within time-dependent perturbation theory. It is investigated which contributions to the asymmetry exist and how they can be modified to reveal a more or less pronounced CEP-effect.

Coherent and incoherent contributions to the carrier-envelope phase control of wave packet localization in quantum double wells.

PubMed

Hader, K; Engel, V

2014-05-14

We study laser excitation processes in a double well potential. The possibility to influence localization via the carrier-envelope phase (CEP) of a laser pulse is investigated for various situations which differ in the nature of the initial state prior to the laser interactions. In more detail, the CEP-dependence of asymmetries in the case where initially the system is described by localized wave packets, eigenstates, or incoherent mixtures are calculated and interpreted within time-dependent perturbation theory. It is investigated which contributions to the asymmetry exist and how they can be modified to reveal a more or less pronounced CEP-effect.

Wave packet and statistical quantum calculations for the He + NeH⁺ → HeH⁺ + Ne reaction on the ground electronic state.

PubMed

Koner, Debasish; Barrios, Lizandra; González-Lezana, Tomás; Panda, Aditya N

2014-09-21

A real wave packet based time-dependent method and a statistical quantum method have been used to study the He + NeH(+) (v, j) reaction with the reactant in various ro-vibrational states, on a recently calculated ab initio ground state potential energy surface. Both the wave packet and statistical quantum calculations were carried out within the centrifugal sudden approximation as well as using the exact Hamiltonian. Quantum reaction probabilities exhibit dense oscillatory pattern for smaller total angular momentum values, which is a signature of resonances in a complex forming mechanism for the title reaction. Significant differences, found between exact and approximate quantum reaction cross sections, highlight the importance of inclusion of Coriolis coupling in the calculations. Statistical results are in fairly good agreement with the exact quantum results, for ground ro-vibrational states of the reactant. Vibrational excitation greatly enhances the reaction cross sections, whereas rotational excitation has relatively small effect on the reaction. The nature of the reaction cross section curves is dependent on the initial vibrational state of the reactant and is typical of a late barrier type potential energy profile.

Description and Simulation of a Fast Packet Switch Architecture for Communication Satellites

NASA Technical Reports Server (NTRS)

Quintana, Jorge A.; Lizanich, Paul J.

1995-01-01

The NASA Lewis Research Center has been developing the architecture for a multichannel communications signal processing satellite (MCSPS) as part of a flexible, low-cost meshed-VSAT (very small aperture terminal) network. The MCSPS architecture is based on a multifrequency, time-division-multiple-access (MF-TDMA) uplink and a time-division multiplex (TDM) downlink. There are eight uplink MF-TDMA beams, and eight downlink TDM beams, with eight downlink dwells per beam. The information-switching processor, which decodes, stores, and transmits each packet of user data to the appropriate downlink dwell onboard the satellite, has been fully described by using VHSIC (Very High Speed Integrated-Circuit) Hardware Description Language (VHDL). This VHDL code, which was developed in-house to simulate the information switching processor, showed that the architecture is both feasible and viable. This paper describes a shared-memory-per-beam architecture, its VHDL implementation, and the simulation efforts.

Two-dimensional numerical simulations of shoaling internal solitary waves at the ASIAEX site in the South China Sea

NASA Astrophysics Data System (ADS)

Lamb, K. G.; Warn-Varnas, A.

2015-05-01

The interaction of barotropic tides with Luzon Strait topography generates some of the world's largest internal solitary waves which eventually shoal and dissipate on the western side of the northern South China Sea. Two-dimensional numerical simulations of the shoaling of a single internal solitary wave at the site of the Asian Seas International Acoustic Experiment (ASIAEX) have been undertaken in order to investigate the sensitivity of the shoaling process to the stratification and the underlying bathymetry and to explore the influence of rotation. The bulk of the simulations are inviscid; however, exploratory simulations using a vertical eddy-viscosity confined to a near bottom layer, along with a no-slip boundary condition, suggest that viscous effects may become important in water shallower than about 200 m. A shoaling solitary wave fissions into several waves. At depths of 200-300 m the front of the leading waves become nearly parallel to the bottom and develop a very steep back as has been observed. The leading waves are followed by waves of elevation (pedestals) that are conjugate to the waves of depression ahead and behind them. Horizontal resolutions of at least 50 m are required to simulate these well. Wave breaking was found to occur behind the second or third of the leading solitary waves, never at the back of the leading wave. Comparisons of the shoaling of waves started at depths of 1000 and 3000 m show significant differences and the shoaling waves can be significantly non-adiabatic even at depths greater than 2000 m. When waves reach a depth of 200 m, their amplitudes can be more than 50% larger than the largest possible solitary wave at that depth. The shoaling behaviour is sensitive to the presence of small-scale features in the bathymetry: a 200 m high bump at 700 m depth can result in the generation of many mode-two waves and of higher mode waves. Sensitivity to the stratification is considered by using three stratifications based on summer

Integrated Model for Performance Analysis of All-Optical Multihop Packet Switches

NASA Astrophysics Data System (ADS)

Jeong, Han-You; Seo, Seung-Woo

2000-09-01

The overall performance of an all-optical packet switching system is usually determined by two criteria, i.e., switching latency and packet loss rate. In some real-time applications, however, in which packets arriving later than a timeout period are discarded as loss, the packet loss rate becomes the most dominant criterion for system performance. Here we focus on evaluating the performance of all-optical packet switches in terms of the packet loss rate, which normally arises from the insufficient hardware or the degradation of an optical signal. Considering both aspects, we propose what we believe is a new analysis model for the packet loss rate that reflects the complicated interactions between physical impairments and system-level parameters. On the basis of the estimation model for signal quality degradation in a multihop path we construct an equivalent analysis model of a switching network for evaluating an average bit error rate. With the model constructed we then propose an integrated model for estimating the packet loss rate in three architectural examples of multihop packet switches, each of which is based on a different switching concept. We also derive the bounds on the packet loss rate induced by bit errors. Finally, it is verified through simulation studies that our analysis model accurately predicts system performance.

Local Dynamics of Baroclinic Waves in the Martian Atmosphere

NASA Astrophysics Data System (ADS)

Kavulich, M. J.; Szunyogh, I.; Gyarmati, G.; Wilson, R.

2010-12-01

In this presentation, the spatio-temporal evolution of baroclinic waves in the GFDL Mars GCM is investigated. The study employs diagnostic techniques that were developed to analyze the life cycles of baroclinic waves in the terrestrial atmosphere. These techniques include a Hilbert-transform-based method to extract the packets of Rossby wave envelopes at the jet level, the eddy kinetic energy equation for the full atmospheric column, and ensemble-based diagnostics. The results show that, similar to the terrestrial atmosphere, coherent westward-propagating wave packets can be detected in the Martian atmosphere. These wave packets are composed of waves of wavenumber 2 through 5, in contrast to the wavenumber 4 through 9 waves that contribute the upper-tropospheric wave packets of the terrestrial atmosphere. Additionally, as in the terrestrial atmosphere, the dominant part of the eddy kinetic energy is generated in regions of baroclinic energy conversion, which are strongly localized in both space and time. Implications of the results for predictability of the state of the Martian atmosphere are also discussed.

An Efficient Conflict Detection Algorithm for Packet Filters

NASA Astrophysics Data System (ADS)

Lee, Chun-Liang; Lin, Guan-Yu; Chen, Yaw-Chung

Packet classification is essential for supporting advanced network services such as firewalls, quality-of-service (QoS), virtual private networks (VPN), and policy-based routing. The rules that routers use to classify packets are called packet filters. If two or more filters overlap, a conflict occurs and leads to ambiguity in packet classification. This study proposes an algorithm that can efficiently detect and resolve filter conflicts using tuple based search. The time complexity of the proposed algorithm is O(nW+s), and the space complexity is O(nW), where n is the number of filters, W is the number of bits in a header field, and s is the number of conflicts. This study uses the synthetic filter databases generated by ClassBench to evaluate the proposed algorithm. Simulation results show that the proposed algorithm can achieve better performance than existing conflict detection algorithms both in time and space, particularly for databases with large numbers of conflicts.

Acoustic mode coupling induced by shallow water nonlinear internal waves: sensitivity to environmental conditions and space-time scales of internal waves.

PubMed

Colosi, John A

2008-09-01

While many results have been intuited from numerical simulation studies, the precise connections between shallow-water acoustic variability and the space-time scales of nonlinear internal waves (NLIWs) as well as the background environmental conditions have not been clearly established analytically. Two-dimensional coupled mode propagation through NLIWs is examined using a perturbation series solution in which each order n is associated with nth-order multiple scattering. Importantly, the perturbation solution gives resonance conditions that pick out specific NLIW scales that cause coupling, and seabed attenuation is demonstrated to broaden these resonances, fundamentally changing the coupling behavior at low frequency. Sound-speed inhomogeneities caused by internal solitary waves (ISWs) are primarily considered and the dependence of mode coupling on ISW amplitude, range width, depth structure, location relative to the source, and packet characteristics are delineated as a function of acoustic frequency. In addition, it is seen that significant energy transfer to modes with initially low or zero energy involves at least a second order scattering process. Under moderate scattering conditions, comparisons of first order, single scattering theoretical predictions to direct numerical simulation demonstrate the accuracy of the approach for acoustic frequencies upto 400 Hz and for single as well as multiple ISW wave packets.

Simulation of Detecting Damage in Composite Stiffened Panel Using Lamb Waves

NASA Technical Reports Server (NTRS)

Wang, John T.; Ross, Richard W.; Huang, Guo L.; Yuan, Fuh G.

2013-01-01

Lamb wave damage detection in a composite stiffened panel is simulated by performing explicit transient dynamic finite element analyses and using signal imaging techniques. This virtual test process does not need to use real structures, actuators/sensors, or laboratory equipment. Quasi-isotropic laminates are used for the stiffened panels. Two types of damage are studied. One type is a damage in the skin bay and the other type is a debond between the stiffener flange and the skin. Innovative approaches for identifying the damage location and imaging the damage were developed. The damage location is identified by finding the intersection of the damage locus and the path of the time reversal wave packet re-emitted from the sensor nodes. The damage locus is a circle that envelops the potential damage locations. Its center is at the actuator location and its radius is computed by multiplying the group velocity by the time of flight to damage. To create a damage image for estimating the size of damage, a group of nodes in the neighborhood of the damage location is identified for applying an image condition. The image condition, computed at a finite element node, is the zero-lag cross-correlation (ZLCC) of the time-reversed incident wave signal and the time reversal wave signal from the sensor nodes. This damage imaging process is computationally efficient since only the ZLCC values of a small amount of nodes in the neighborhood of the identified damage location are computed instead of those of the full model.

A Gaussian Wave Packet Propagation Approach to Vibrationally Resolved Optical Spectra at Non-Zero Temperatures.

PubMed

Reddy, Ch Sridhar; Prasad, M Durga

2016-04-28

An effective time dependent approach based on a method that is similar to the Gaussian wave packet propagation (GWP) technique of Heller is developed for the computation of vibrationally resolved electronic spectra at finite temperatures in the harmonic, Franck-Condon/Hertzberg-Teller approximations. Since the vibrational thermal density matrix of the ground electronic surface and the time evolution operator on that surface commute, it is possible to write the spectrum generating correlation function as a trace of the time evolved doorway state. In the stated approximations, the doorway state is a superposition of the harmonic oscillator zero and one quantum eigenfunctions and thus can be propagated by the GWP. The algorithm has an O(N(3)) dependence on the number of vibrational modes. An application to pyrene absorption spectrum at two temperatures is presented as a proof of the concept.

Packet telemetry and packet telecommand - The new generation of spacecraft data handling techniques

NASA Technical Reports Server (NTRS)

Hooke, A. J.

1983-01-01

Because of rising costs and reduced reliability of spacecraft and ground network hardware and software customization, standardization Packet Telemetry and Packet Telecommand concepts are emerging as viable alternatives. Autonomous packets of data, within each concept, which are created within ground and space application processes through the use of formatting techniques, are switched end-to-end through the space data network to their destination application processes through the use of standard transfer protocols. This process may result in facilitating a high degree of automation and interoperability because of completely mission-independent-designed intermediate data networks. The adoption of an international guideline for future space telemetry formatting of the Packet Telemetry concept, and the advancement of the NASA-ESA Working Group's Packet Telecommand concept to a level of maturity parallel to the of Packet Telemetry are the goals of the Consultative Committee for Space Data Systems. Both the Packet Telemetry and Packet Telecommand concepts are reviewed.

Experience with the EURECA Packet Telemetry and Packet Telecommand system

NASA Technical Reports Server (NTRS)

Sorensen, Erik Mose; Ferri, Paolo

1994-01-01

The European Retrieval Carrier (EURECA) was launched on its first flight on the 31st of July 1992 and retrieved on the 29th of June 1993. EURECA is characterized by several new on-board features, most notably Packet telemetry, and a partial implementation of packet telecommanding, the first ESA packetised spacecraft. Today more than one year after the retrieval the data from the EURECA mission has to a large extent been analysed and we can present some of the interesting results. This paper concentrates on the implementation and operational experience with the EURECA Packet Telemetry and Packet Telecommanding. We already discovered during the design of the ground system that the use of packet telemetry has major impact on the overall design and that processing of packet telemetry may have significant effect on the computer loading and sizing. During the mission a number of problems were identified with the on-board implementation resulting in very strange anomalous behaviors. Many of these problems directly violated basic assumptions for the design of the ground segment adding to the strange behavior. The paper shows that the design of a telemetry packet system should be flexible enough to allow a rapid configuration of the telemetry processing in order to adapt it to the new situation in case of an on-board failure. The experience gained with the EURECA mission control should be used to improve ground systems for future missions.

A scheme for synchronizing clocks connected by a packet communication network

NASA Astrophysics Data System (ADS)

dos Santos, R. V.; Monteiro, L. H. A.

2012-07-01

Consider a communication system in which a transmitter equipment sends fixed-size packets of data at a uniform rate to a receiver equipment. Consider also that these equipments are connected by a packet-switched network, which introduces a random delay to each packet. Here we propose an adaptive clock recovery scheme able of synchronizing the frequencies and the phases of these devices, within specified limits of precision. This scheme for achieving frequency and phase synchronization is based on measurements of the packet arrival times at the receiver, which are used to control the dynamics of a digital phase-locked loop. The scheme performance is evaluated via numerical simulations performed by using realistic parameter values.

Interconnecting network for switching data packets and method for switching data packets

DOEpatents

Benner, Alan Frederic; Minkenberg, Cyriel Johan Agnes; Stunkel, Craig Brian

2010-05-25

The interconnecting network for switching data packets, having data and flow control information, comprises a local packet switch element (S1) with local input buffers (I(1,1) . . . I(1,y)) for buffering the incoming data packets, a remote packet switch element (S2) with remote input buffers (I(2,1) . . . I(2,y)) for buffering the incoming data packets, and data lines (L) for interconnecting the local and the remote packet switch elements (S1, S2). The interconnecting network further comprises a local and a remote arbiter (A1, A2) which are connected via control lines (CL) to the input buffers (I(1,1) . . . I(1,y), I(2,1) . . . I(2,y)), and which are formed such that they can provide that the flow control information is transmitted via the data lines (L) and the control lines (CL).

Dynamics of wave packets in two-dimensional random systems with anisotropic disorder.

PubMed

Samelsohn, Gregory; Gruzdev, Eugene

2008-09-01

A theoretical model is proposed to describe narrowband pulse dynamics in two-dimensional systems with arbitrary correlated disorder. In anisotropic systems with elongated cigarlike inhomogeneities, fast propagation is predicted in the direction across the structure where the wave is exponentially localized and tunneling of evanescent modes plays a dominant role in typical realizations. Along the structure, where the wave is channeled as in a waveguide, the motion of the wave energy is relatively slow. Numerical simulations performed for ultra-wide-band pulses show that even at the initial stage of wave evolution, the radiation diffuses predominantly in the direction along the major axis of the correlation ellipse. Spectral analysis of the results relates the long tail of the wave observed in the transverse direction to a number of frequency domain "lucky shots" associated with the long-living resonant modes localized inside the sample.

Fast and local non-linear evolution of steep wave-groups on deep water: A comparison of approximate models to fully non-linear simulations

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

Adcock, T. A. A.; Taylor, P. H.

2016-01-15

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 whichmore » 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.« less

Monte Carlo wave-packet approach to trace nuclear dynamics in molecular excited states by XUV-pump-IR-probe spectroscopy

NASA Astrophysics Data System (ADS)

Jing, Qingli; Bello, Roger Y.; Martín, Fernando; Palacios, Alicia; Madsen, Lars Bojer

2018-04-01

Recent research interests have been raised in uncovering and controlling ultrafast dynamics in excited neutral molecules. In this work we generalize the Monte Carlo wave packet (MCWP) approach to XUV-pump-IR-probe schemes to simulate the process of dissociative double ionization of H2 where singly excited states in H2 are involved. The XUV pulse is chosen to resonantly excite the initial ground state of H2 to the lowest excited electronic state of 1Σu + symmetry in H2 within the Franck-Condon region. The delayed intense IR pulse couples the excited states of 1Σu + symmetry with the nearby excited states of 1Σg + symmetry. It also induces the first ionization from H2 to H2 + and the second ionization from H2 + to H++H+. To reduce the computational costs in the MCWP approach, a sampling method is proposed to determine in time the dominant ionization events from H2 to H2+. By conducting a trajectory analysis, which is a unique possibility within the MCWP approach, the origins of the characteristic features in the nuclear kinetic energy release spectra are identified for delays ranging from 0 to 140 fs and the nuclear dynamics in the singly excited states in H2 is mapped out.

Dynamics of wave packets in two-dimensional random systems with anisotropic disorder

NASA Astrophysics Data System (ADS)

Samelsohn, Gregory; Gruzdev, Eugene

2008-09-01

A theoretical model is proposed to describe narrowband pulse dynamics in two-dimensional systems with arbitrary correlated disorder. In anisotropic systems with elongated cigarlike inhomogeneities, fast propagation is predicted in the direction across the structure where the wave is exponentially localized and tunneling of evanescent modes plays a dominant role in typical realizations. Along the structure, where the wave is channeled as in a waveguide, the motion of the wave energy is relatively slow. Numerical simulations performed for ultra-wide-band pulses show that even at the initial stage of wave evolution, the radiation diffuses predominantly in the direction along the major axis of the correlation ellipse. Spectral analysis of the results relates the long tail of the wave observed in the transverse direction to a number of frequency domain “lucky shots” associated with the long-living resonant modes localized inside the sample.

Simulation of the elementary evolution operator with the motional states of an ion in an anharmonic trap

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

Santos, Ludovic; Vaeck, Nathalie; Justum, Yves

2015-04-07

Following a recent proposal of L. Wang and D. Babikov [J. Chem. Phys. 137, 064301 (2012)], we theoretically illustrate the possibility of using the motional states of a Cd{sup +} ion trapped in a slightly anharmonic potential to simulate the single-particle time-dependent Schrödinger equation. The simulated wave packet is discretized on a spatial grid and the grid points are mapped on the ion motional states which define the qubit network. The localization probability at each grid point is obtained from the population in the corresponding motional state. The quantum gate is the elementary evolution operator corresponding to the time-dependent Schrödingermore » equation of the simulated system. The corresponding matrix can be estimated by any numerical algorithm. The radio-frequency field which is able to drive this unitary transformation among the qubit states of the ion is obtained by multi-target optimal control theory. The ion is assumed to be cooled in the ground motional state, and the preliminary step consists in initializing the qubits with the amplitudes of the initial simulated wave packet. The time evolution of the localization probability at the grids points is then obtained by successive applications of the gate and reading out the motional state population. The gate field is always identical for a given simulated potential, only the field preparing the initial wave packet has to be optimized for different simulations. We check the stability of the simulation against decoherence due to fluctuating electric fields in the trap electrodes by applying dissipative Lindblad dynamics.« less

Coherent electronic wave packet motion in C(60) controlled by the waveform and polarization of few-cycle laser fields.

PubMed

Li, H; Mignolet, B; Wachter, G; Skruszewicz, S; Zherebtsov, S; Süssmann, F; Kessel, A; Trushin, S A; Kling, Nora G; Kübel, M; Ahn, B; Kim, D; Ben-Itzhak, I; Cocke, C L; Fennel, T; Tiggesbäumker, J; Meiwes-Broer, K-H; Lemell, C; Burgdörfer, J; Levine, R D; Remacle, F; Kling, M F

2015-03-27

Strong laser fields can be used to trigger an ultrafast molecular response that involves electronic excitation and ionization dynamics. Here, we report on the experimental control of the spatial localization of the electronic excitation in the C_{60} fullerene exerted by an intense few-cycle (4 fs) pulse at 720 nm. The control is achieved by tailoring the carrier-envelope phase and the polarization of the laser pulse. We find that the maxima and minima of the photoemission-asymmetry parameter along the laser-polarization axis are synchronized with the localization of the coherent electronic wave packet at around the time of ionization.

Numerical study on the mechanism of active interfacial debonding detection for rectangular CFSTs based on wavelet packet analysis with piezoceramics

NASA Astrophysics Data System (ADS)

Xu, Bin; Chen, Hongbing; Xia, Song

2017-03-01

In recent years, Piezoelectric Lead Zirconate Titanate (PZT) based active interfacial debonding defect detection approach for concrete-filled steel tubular (CFST) columns has been proposed and validated experimentally. In order to investigate the mechanism of the PZT based interfacial debonding detection approach, a multi-physics coupling finite element model (FEM) composed of surface-mounted PZT actuator, embedded PZT sensor and a rectangular CFST column is constructed to numerically simulate the stress wave propagation induced by the surface-mounted PZT actuator under different excitation signals with different frequency and amplitude. The measurements of the embedded PZT sensor in concrete core of the CFST columns with different interfacial debonding defect lengths and depths are determined numerically with transient dynamic analysis. The linearity between the PZT response and the input amplitude, the effect of different frequency and measurement distance are discussed and the stress wave fields of CFST members without and with interface debonding defects are compared. Then, the response of the embedded PZT in concrete core is analyzed with wavelet packet analysis. The root mean square deviation (RMSD) of wavelet packet energy spectrum of the PZT measurement is employed as an evaluation index for the interfacial debonding detection. The results showed that the defined index under continuous sinusoidal and sweep frequency signals changes with the interfacial defects length and depth and is capable of effectively identifying the interfacial debonding defect between the concrete core and the steel tubular. Moreover, the index under sweep frequency signal is more sensitive to the interfacial debonding. The simulation results indicate that the interfacial debonding defect leads to the changes in the propagation path, travel time and the magnitude of stress waves. The simulation results meet the findings from the previous experimental study by the authors and help

Analysis of the packet formation process in packet-switched networks

NASA Astrophysics Data System (ADS)

Meditch, J. S.

Two new queueing system models for the packet formation process in packet-switched telecommunication networks are developed, and their applications in process stability, performance analysis, and optimization studies are illustrated. The first, an M/M/1 queueing system characterization of the process, is a highly aggregated model which is useful for preliminary studies. The second, a marked extension of an earlier M/G/1 model, permits one to investigate stability, performance characteristics, and design of the packet formation process in terms of the details of processor architecture, and hardware and software implementations with processor structure and as many parameters as desired as variables. The two new models together with the earlier M/G/1 characterization span the spectrum of modeling complexity for the packet formation process from basic to advanced.

Heralded wave packet manipulation and storage of a frequency-converted pair photon at telecom wavelength

NASA Astrophysics Data System (ADS)

Kroh, Tim; Ahlrichs, Andreas; Sprenger, Benjamin; Benson, Oliver

2017-09-01

Future quantum networks require a hybrid platform of dissimilar quantum systems. Within the platform, joint quantum states have to be mediated either by single photons, photon pairs or entangled photon pairs. The photon wavelength has to lie within the telecommunication band to enable long-distance fibre transmission. In addition, the temporal shape of the photons needs to be tailored to efficiently match the involved quantum systems. Altogether, this requires the efficient coherent wavelength-conversion of arbitrarily shaped single-photon wave packets. Here, we demonstrate the heralded temporal filtering of single photons as well as the synchronisation of state manipulation and detection as key elements in a typical experiment, besides of delaying a photon in a long fibre. All three are realised by utilising commercial telecommunication fibre-optical components which will permit the transition of quantum networks from the lab to real-world applications. The combination of these renders a temporally filtering single-photon storage in a fast switchable fibre loop possible.

Rogue-wave bullets in a composite (2+1)D nonlinear medium.

PubMed

Chen, Shihua; Soto-Crespo, Jose M; Baronio, Fabio; Grelu, Philippe; Mihalache, Dumitru

2016-07-11

We show that nonlinear wave packets localized in two dimensions with characteristic rogue wave profiles can propagate in a third dimension with significant stability. This unique behavior makes these waves analogous to light bullets, with the additional feature that they propagate on a finite background. Bulletlike rogue-wave singlet and triplet are derived analytically from a composite (2+1)D nonlinear wave equation. The latter can be interpreted as the combination of two integrable (1+1)D models expressed in different dimensions, namely, the Hirota equation and the complex modified Korteweg-de Vries equation. Numerical simulations confirm that the generation of rogue-wave bullets can be observed in the presence of spontaneous modulation instability activated by quantum noise.

Identification of ground motion features for high-tech facility under far field seismic waves using wavelet packet transform

NASA Astrophysics Data System (ADS)

Huang, Shieh-Kung; Loh, Chin-Hsiung; Chen, Chin-Tsun

2016-04-01

Seismic records collected from earthquake with large magnitude and far distance may contain long period seismic waves which have small amplitude but with dominant period up to 10 sec. For a general situation, the long period seismic waves will not endanger the safety of the structural system or cause any uncomfortable for human activity. On the contrary, for those far distant earthquakes, this type of seismic waves may cause a glitch or, furthermore, breakdown to some important equipments/facilities (such as the high-precision facilities in high-tech Fab) and eventually damage the interests of company if the amplitude becomes significant. The previous study showed that the ground motion features such as time-variant dominant frequencies extracted using moving window singular spectrum analysis (MWSSA) and amplitude characteristics of long-period waves identified from slope change of ground motion Arias Intensity can efficiently indicate the damage severity to the high-precision facilities. However, embedding a large hankel matrix to extract long period seismic waves make the MWSSA become a time-consumed process. In this study, the seismic ground motion data collected from broadband seismometer network located in Taiwan were used (with epicenter distance over 1000 km). To monitor the significant long-period waves, the low frequency components of these seismic ground motion data are extracted using wavelet packet transform (WPT) to obtain wavelet coefficients and the wavelet entropy of coefficients are used to identify the amplitude characteristics of long-period waves. The proposed method is a timesaving process compared to MWSSA and can be easily implemented for real-time detection. Comparison and discussion on this method among these different seismic events and the damage severity to the high-precision facilities in high-tech Fab is made.

Retrieval of charge mobility from apparent charge packet movements in LDPE thin films

NASA Astrophysics Data System (ADS)

Meng, Jia; Zhang, Yewen; Holé, Stéphane; Zheng, Feihu; An, Zhenlian

2017-03-01

The charge packet phenomenon observed in polyethylene materials has been reported extensively during the last decades. To explain its movement, Negative Differential Mobility (NDM) theory is a competitive model among several proposed mechanisms. However, as a key concept of this theory, a sufficiently acute relationship between charge mobility and electric field has never been reported until now, which makes it hard to precisely describe the migration of charge packets with this theory. Based on the substantial negative-charge packet observations with a sufficiently by wide electric field range from 15 kV/mm to 50 kV/mm, the present contribution successfully retrieved the negative-charge mobility from the apparent charge packet movements, which reveals a much closer relationship between the NDM theory and charge packet migrations. Back simulations of charge packets with the retrieved charge mobility offer a good agreement with the experimental data.

Rapid Monte Carlo Simulation of Gravitational Wave Galaxies

NASA Astrophysics Data System (ADS)

Breivik, Katelyn; Larson, Shane L.

2015-01-01

With the detection of gravitational waves on the horizon, astrophysical catalogs produced by gravitational wave observatories can be used to characterize the populations of sources and validate different galactic population models. Efforts to simulate gravitational wave catalogs and source populations generally focus on population synthesis models that require extensive time and computational power to produce a single simulated galaxy. Monte Carlo simulations of gravitational wave source populations can also be used to generate observation catalogs from the gravitational wave source population. Monte Carlo simulations have the advantes of flexibility and speed, enabling rapid galactic realizations as a function of galactic binary parameters with less time and compuational resources required. We present a Monte Carlo method for rapid galactic simulations of gravitational wave binary populations.

Denoising in digital speckle pattern interferometry using wave atoms.

PubMed

Federico, Alejandro; Kaufmann, Guillermo H

2007-05-15

We present an effective method for speckle noise removal in digital speckle pattern interferometry, which is based on a wave-atom thresholding technique. Wave atoms are a variant of 2D wavelet packets with a parabolic scaling relation and improve the sparse representation of fringe patterns when compared with traditional expansions. The performance of the denoising method is analyzed by using computer-simulated fringes, and the results are compared with those produced by wavelet and curvelet thresholding techniques. An application of the proposed method to reduce speckle noise in experimental data is also presented.

Vorticity Transport and Wave Emission in the Protoplanetary Nebula

NASA Technical Reports Server (NTRS)

Davis, S. S.; DeVincenzi, Donald (Technical Monitor)

2001-01-01

Higher order numerical algorithms (4th order in time, 3rd order in space) are applied to the Euler/Energy equations and are used to examine vorticity transport and wave motion in a non-self gravitating, initially isentropic Keplerian disk. In this talk we will examine the response of the nebula to an isolated vortex with a circulation about equal to the rotation rate of Jupiter. The vortex is located on the 4 AU circle and the nebula is simulated from 1 to 24 AU. We show that the vortex emits pressure-supported density and Rossby-type wave packets before it decays within a few orbits. The acoustic density waves evolve into weak (non entropy preserving) shock waves that propagate over the entire disk. The Rossby waves remain in the vicinity of the initial vortex disturbance, but are rapidly damped. Temporal frequencies and spatial wavenumbers are derived using the simulation data and compared with analytical dispersion relations from the linearized Euler/Energy equations.

Vorticity Transport and Wave Emission In A Protoplanetary Disk

NASA Technical Reports Server (NTRS)

Davis, S. S.; Davis, Sanford (Technical Monitor)

2002-01-01

Higher order numerical algorithms (4th order in time, 3rd order in space) are applied to the Euler equations and are used to examine vorticity transport and wave motion in a non-self gravitating, initially isentropic Keplerian disk. In this talk we will examine the response of the disk to an isolated vortex with a circulation about equal to the rotation rate of Jupiter. The vortex is located on the 4 AU circle and the nebula is simulated from 1 to 24 AU. We show that the vortex emits pressure-supported density and Rossby-type wave packets before it decays within a few orbits. The acoustic density waves evolve into weak (non entropy preserving) shock waves that propagate over the entire disk. The Rossby waves remain in the vicinity of the initial vortex disturbance, but are rapidly damped. Temporal frequencies and spatial wavenumbers are derived from the nonlinear simulation data and correlated with analytical dispersion relations from the linearized Euler and energy equations.

In situ accurate determination of the zero time delay between two independent ultrashort laser pulses by observing the oscillation of an atomic excited wave packet.

PubMed

Zhang, Qun; Hepburn, John W

2008-08-15

We propose a novel method that uses the oscillation of an atomic excited wave packet observed through a pump-probe technique to accurately determine the zero time delay between a pair of ultrashort laser pulses. This physically based approach provides an easy fix for the intractable problem of synchronizing two different femtosecond laser pulses in a practical experimental environment, especially where an in situ time zero measurement with high accuracy is required.

Packet flow monitoring tool and method

DOEpatents

Thiede, David R [Richland, WA

2009-07-14

A system and method for converting packet streams into session summaries. Session summaries are a group of packets each having a common source and destination internet protocol (IP) address, and, if present in the packets, common ports. The system first captures packets from a transport layer of a network of computer systems, then decodes the packets captured to determine the destination IP address and the source IP address. The system then identifies packets having common destination IP addresses and source IP addresses, then writes the decoded packets to an allocated memory structure as session summaries in a queue.

Formation of wave packets in the Ostrovsky equation for both normal and anomalous dispersion

PubMed Central

Grimshaw, Roger; Stepanyants, Yury; Alias, Azwani

2016-01-01

It is well known that the Ostrovsky equation with normal dispersion does not support steady solitary waves. An initial Korteweg–de Vries solitary wave decays adiabatically through the radiation of long waves and is eventually replaced by an envelope solitary wave whose carrier wave and envelope move with different velocities (phase and group velocities correspondingly). Here, we examine the same initial condition for the Ostrovsky equation with anomalous dispersion, when the wave frequency increases with wavenumber in the limit of very short waves. The essential difference is that now there exists a steady solitary wave solution (Ostrovsky soliton), which in the small-amplitude limit can be described asymptotically through the solitary wave solution of a nonlinear Schrödinger equation, based at that wavenumber where the phase and group velocities coincide. Long-time numerical simulations show that the emergence of this steady envelope solitary wave is a very robust feature. The initial Korteweg–de Vries solitary wave transforms rapidly to this envelope solitary wave in a seemingly non-adiabatic manner. The amplitude of the Ostrovsky soliton strongly correlates with the initial Korteweg–de Vries solitary wave. PMID:26997887

Hierarchical trie packet classification algorithm based on expectation-maximization clustering

PubMed Central

Bi, Xia-an; Zhao, Junxia

2017-01-01

With the development of computer network bandwidth, packet classification algorithms which are able to deal with large-scale rule sets are in urgent need. Among the existing algorithms, researches on packet classification algorithms based on hierarchical trie have become an important packet classification research branch because of their widely practical use. Although hierarchical trie is beneficial to save large storage space, it has several shortcomings such as the existence of backtracking and empty nodes. This paper proposes a new packet classification algorithm, Hierarchical Trie Algorithm Based on Expectation-Maximization Clustering (HTEMC). Firstly, this paper uses the formalization method to deal with the packet classification problem by means of mapping the rules and data packets into a two-dimensional space. Secondly, this paper uses expectation-maximization algorithm to cluster the rules based on their aggregate characteristics, and thereby diversified clusters are formed. Thirdly, this paper proposes a hierarchical trie based on the results of expectation-maximization clustering. Finally, this paper respectively conducts simulation experiments and real-environment experiments to compare the performances of our algorithm with other typical algorithms, and analyzes the results of the experiments. The hierarchical trie structure in our algorithm not only adopts trie path compression to eliminate backtracking, but also solves the problem of low efficiency of trie updates, which greatly improves the performance of the algorithm. PMID:28704476

Hierarchical trie packet classification algorithm based on expectation-maximization clustering.

PubMed

Bi, Xia-An; Zhao, Junxia

2017-01-01

With the development of computer network bandwidth, packet classification algorithms which are able to deal with large-scale rule sets are in urgent need. Among the existing algorithms, researches on packet classification algorithms based on hierarchical trie have become an important packet classification research branch because of their widely practical use. Although hierarchical trie is beneficial to save large storage space, it has several shortcomings such as the existence of backtracking and empty nodes. This paper proposes a new packet classification algorithm, Hierarchical Trie Algorithm Based on Expectation-Maximization Clustering (HTEMC). Firstly, this paper uses the formalization method to deal with the packet classification problem by means of mapping the rules and data packets into a two-dimensional space. Secondly, this paper uses expectation-maximization algorithm to cluster the rules based on their aggregate characteristics, and thereby diversified clusters are formed. Thirdly, this paper proposes a hierarchical trie based on the results of expectation-maximization clustering. Finally, this paper respectively conducts simulation experiments and real-environment experiments to compare the performances of our algorithm with other typical algorithms, and analyzes the results of the experiments. The hierarchical trie structure in our algorithm not only adopts trie path compression to eliminate backtracking, but also solves the problem of low efficiency of trie updates, which greatly improves the performance of the algorithm.

Nonparaxial wave beams and packets with general astigmatism

NASA Astrophysics Data System (ADS)

Kiselev, A. P.; Plachenov, A. B.; Chamorro-Posada, P.

2012-04-01

We present exact solutions of the wave equation involving an arbitrary wave form with a phase closely similar to the general astigmatic phase of paraxial wave optics. Special choices of the wave form allow general astigmatic beamlike and pulselike waves with a Gaussian-type unrestricted localization in space and time. These solutions are generalizations of the known Bateman-type waves obtained from the connection existing between beamlike solutions of the paraxial parabolic equation and relatively undistorted wave solutions of the wave equation. As a technical tool, we present a full description of parametrizations of 2×2 symmetric matrices with positive imaginary part, which arise in the theory of Gaussian beams.

Ocean Wave Simulation Based on Wind Field

PubMed Central

2016-01-01

Ocean wave simulation has a wide range of applications in movies, video games and training systems. Wind force is the main energy resource for generating ocean waves, which are the result of the interaction between wind and the ocean surface. While numerous methods to handle simulating oceans and other fluid phenomena have undergone rapid development during the past years in the field of computer graphic, few of them consider to construct ocean surface height field from the perspective of wind force driving ocean waves. We introduce wind force to the construction of the ocean surface height field through applying wind field data and wind-driven wave particles. Continual and realistic ocean waves result from the overlap of wind-driven wave particles, and a strategy was proposed to control these discrete wave particles and simulate an endless ocean surface. The results showed that the new method is capable of obtaining a realistic ocean scene under the influence of wind fields at real time rates. PMID:26808718

Ocean Wave Simulation Based on Wind Field.

PubMed

Li, Zhongyi; Wang, Hao

2016-01-01

Ocean wave simulation has a wide range of applications in movies, video games and training systems. Wind force is the main energy resource for generating ocean waves, which are the result of the interaction between wind and the ocean surface. While numerous methods to handle simulating oceans and other fluid phenomena have undergone rapid development during the past years in the field of computer graphic, few of them consider to construct ocean surface height field from the perspective of wind force driving ocean waves. We introduce wind force to the construction of the ocean surface height field through applying wind field data and wind-driven wave particles. Continual and realistic ocean waves result from the overlap of wind-driven wave particles, and a strategy was proposed to control these discrete wave particles and simulate an endless ocean surface. The results showed that the new method is capable of obtaining a realistic ocean scene under the influence of wind fields at real time rates.

Effects of reactant rotational excitation on H + O2--> OH + O reaction rate constant: quantum wave packet, quasi-classical trajectory and phase space theory calculations.

PubMed

Lin, Shi Ying; Guo, Hua; Lendvay, György; Xie, Daiqian

2009-06-21

We examine the impact of initial rotational excitation on the reactivity of the H + O(2)--> OH + O reaction. Accurate Chebyshev wave packet calculations have been carried out for the upsilon(i) = 0, j(i) = 9 initial state of O(2) and the J = 50 partial wave. In addition, we present Gaussian-weighted quasi-classical trajectory and phase space theory calculations of the integral cross section and thermal rate constant for the title reaction. These theoretical results suggest that the initial rotational excitation significantly enhances reactivity with an amount comparable to the effect of initial vibrational state excitation. The inclusion of internally excited reactants is shown to improve the agreement with experimental rate constant.

Charge transport calculations by a wave-packet dynamical approach using maximally localized Wannier functions based on density functional theory: Application to high-mobility organic semiconductors

NASA Astrophysics Data System (ADS)

Ishii, Hiroyuki; Kobayashi, Nobuhiko; Hirose, Kenji

2017-01-01

We present a wave-packet dynamical approach to charge transport using maximally localized Wannier functions based on density functional theory including van der Waals interactions. We apply it to the transport properties of pentacene and rubrene single crystals and show the temperature-dependent natures from bandlike to thermally activated behaviors as a function of the magnitude of external static disorder. We compare the results with those obtained by the conventional band and hopping models and experiments.

Charge mobility retrieval approach from apparent charge packet movements based on the negative differential resistance theory.

PubMed

Meng, Jia; Zhang, Yewen; Holé, Stéphane; Zheng, Feihu; An, Zhenlian

2018-04-12

Space charge migration characteristics play an important role in the evaluation of polymer insulation performance. However, an accurate description of charge carrier mobility in several typical insulating polymers such as polyethylene, polypropylene is currently not available. Recently, with the observation of a series of negative charge packet movements associated with the negative differential resistance characteristic of charge mobility in LDPE films, the extraction of charge mobility from the apparent charge packet movement has been attempted using appropriate methods. Based on the previous report of the successful derivation of charge mobility from experimental results using numerical methods, the present research improves the derivation accuracy and describes the details of the charge mobility derivation procedure. Back simulation results under several typical polarizing fields using the derived charge mobility are exhibited. The results indicate that both the NDR theory and the simulation models for the polyethylene materials are reasonable. A significant migration velocity difference between the charge carrier and the charge packet is observed. Back simulations of the charge packet under several typical polarizing fields using the obtained E-v curve show good agreement with the experimental results. The charge packet shapes during the migrations were also found to vary with the polarizing field.

Wave energy analysis based on simulation wave data in the China Sea

NASA Astrophysics Data System (ADS)

Gao, Zhan-sheng; Qian, Yu-hao; Sui, Yu-wei; Chen, Xuan; Zhang, Da

2018-05-01

In the current world, where human beings are severely plagued by environmental problems and energy crisis, the full and reasonable utilization of marine new energy resources will contribute to alleviating the energy crisis, contributing to global energy-saving, emission reduction and environmental protection, thus to promote sustainable development. In this study, we firstly simulated a 10-year (1991-2000) 6-hourly wave data of the China Sea, by using the Simulating WAves Nearshore (SWAN) wave model nested with WAVEWATCH-III (WW3) wave model forced with Cross-Calibrated, Multi-Platform (CCMP) wind data. Considering the value size and stability of the wave energy density, we analyzed the overall characteristics of the China Sea wave energy with using the simulation wave data. Results show that: (1) The wave energy density in January and October is distinctly higher than that in April and July. The large center of annual average Wave energy density is located in the north of the South China Sea (of about 12-16 kW/m). (2) Synthetically considering the value size and stability of the wave energy density and stability, the energy-rich area is found to be located in the north region of the South China Sea.

Radiology/Imaging. Clinical Rotation. Instructor's Packet and Student Study Packet.

ERIC Educational Resources Information Center

Texas Univ., Austin. Extension Instruction and Materials Center.

The instructor's packet, the first of two packets, is one of a series of materials designed to help students who are investigating the activities within a radiology department or considering any of the imaging technologies as a career. The material is designed to relate training experience to information studied in the classroom. This packet…

Scattering of matter waves in spatially inhomogeneous environments

DOE PAGES

Tsitoura, F.; Krüger, P.; Kevrekidis, P. G.; ...

2015-03-30

In this article, we study scattering of quasi-one-dimensional matter waves at an interface of two spatial domains, one with repulsive and one with attractive interatomic interactions. It is shown that the incidence of a Gaussian wave packet from the repulsive to the attractive region gives rise to generation of a soliton train. More specifically, the number of emergent solitons can be controlled, e.g., by the variation of the amplitude or the width of the incoming wave packet. Furthermore, we study the reflectivity of a soliton incident from the attractive region to the repulsive one. We find the reflection coefficient numericallymore » and employ analytical methods, which treat the soliton as a particle (for moderate and large amplitudes) or a quasilinear wave packet (for small amplitudes), to determine the critical soliton momentum (as a function of the soliton amplitude) for which total reflection is observed.« less

Monitoring and Indentification Packet in Wireless With Deep Packet Inspection Method

NASA Astrophysics Data System (ADS)

Fali Oklilas, Ahmad; Tasmi

2017-04-01

Layer 2 and Layer 3 are used to make a process of network monitoring, but with the development of applications on the network such as the p2p file sharing, VoIP, encrypted, and many applications that already use the same port, it would require a system that can classify network traffics, not only based on port number classification. This paper reports the implementation of the deep packet inspection method to analyse data packets based on the packet header and payload to be used in packet data classification. If each application can be grouped based on the application layer, then we can determine the pattern of internet users and also to perform network management of computer science department. In this study, a prototype wireless network and applications SSO were developed to detect the active user. The focus is on the ability of open DPI and nDPI in detecting the payload of an application and the results are elaborated in this paper.

Sliding Mode Control for Discrete-Time Systems With Markovian Packet Dropouts.

PubMed

Song, Heran; Chen, Shih-Chi; Yam, Yeung

2017-11-01

This paper presents the design of a sliding mode controller for networked control systems subject to successive Markovian packet dropouts. This paper adopts the Gilbert-Elliott channel model to describe the temporal correlation among packet losses, and proposes an update scheme to select the assumed available states for use in a sliding mode control law. A technique used in the theory of discrete-time Markov jump linear systems is applied to tackle the effect of the packet losses. This involves introducing a couple of Lyapunov functions dependent on the indicator functions of the instantaneous packet loss, and proving that the sliding mode controller is able to drive the system state trajectories into the neighborhood of the designed integral sliding surface in mean-square sense given that the corresponding Lyapunov inequalities are satisfied. The system is guaranteed thereafter to remain inside the neighborhood of the sliding surface. Simulated case studies are presented to illustrate the effectiveness of the control law.

Packet Fragmentation and Reassembly in Molecular Communication.

PubMed

Furubayashi, Taro; Nakano, Tadashi; Eckford, Andrew; Okaie, Yutaka; Yomo, Tetsuya

2016-04-01

This paper describes packet fragmentation and reassembly to achieve reliable molecular communication among bionanomachines. In the molecular communication described in this paper, a sender bionanomachine performs packet fragmentation, dividing a large molecular message into smaller pieces and embedding into smaller molecular packets, so that molecular packets have higher diffusivity to reach the receiver bionanomachine. The receiver bionanomachine then performs packet reassembly to retrieve the original molecular message from a set of molecular packets that it receives. To examine the effect of packet fragmentation and reassembly, we develop analytical models and conduct numerical experiments. Numerical results show that packet fragmentation and reassembly can improve the message delivery performance. Numerical results also indicate that packet fragmentation and reassembly may degrade the performance in the presence of drift in the environment.

Cebuano Language Packet.

ERIC Educational Resources Information Center

Peace Corps, Manila (Philippines).

The materials in this packet were designed for the rapid Cebuano language training of Peace Corps volunteers, focusing on daily communication needs in this context. The packet contains: lists of common phrases, expressions, and vocabulary on a variety of topics related to Peace Corps work; a list of core competencies for specific topics…

Threatened and Endangered Species: Tour Packet.

ERIC Educational Resources Information Center

Coats, Victoria; Samia, Cory

This resource unit contains a teacher information packet and a middle school student activity packet to be used in creating a threatened and endangered species unit. The packet of student activities is designed to help maximize a field trip to the zoo and build on students' zoo experience in the classroom. The teacher information packet covers the…

Transition from Propagating Polariton Solitons to a Standing Wave Condensate Induced by Interactions

NASA Astrophysics Data System (ADS)

Sich, M.; Chana, J. K.; Egorov, O. A.; Sigurdsson, H.; Shelykh, I. A.; Skryabin, D. V.; Walker, P. M.; Clarke, E.; Royall, B.; Skolnick, M. S.; Krizhanovskii, D. N.

2018-04-01

We explore phase transitions of polariton wave packets, first, to a soliton and then to a standing wave polariton condensate in a multimode microwire system, mediated by nonlinear polariton interactions. At low excitation density, we observe ballistic propagation of the multimode polariton wave packets arising from the interference between different transverse modes. With increasing excitation density, the wave packets transform into single-mode bright solitons due to effects of both intermodal and intramodal polariton-polariton scattering. Further increase of the excitation density increases thermalization speed, leading to relaxation of the polariton density from a solitonic spectrum distribution in momentum space down to low momenta, with the resultant formation of a nonequilibrium condensate manifested by a standing wave pattern across the whole sample.

Transition from Propagating Polariton Solitons to a Standing Wave Condensate Induced by Interactions.

PubMed

Sich, M; Chana, J K; Egorov, O A; Sigurdsson, H; Shelykh, I A; Skryabin, D V; Walker, P M; Clarke, E; Royall, B; Skolnick, M S; Krizhanovskii, D N

2018-04-20

We explore phase transitions of polariton wave packets, first, to a soliton and then to a standing wave polariton condensate in a multimode microwire system, mediated by nonlinear polariton interactions. At low excitation density, we observe ballistic propagation of the multimode polariton wave packets arising from the interference between different transverse modes. With increasing excitation density, the wave packets transform into single-mode bright solitons due to effects of both intermodal and intramodal polariton-polariton scattering. Further increase of the excitation density increases thermalization speed, leading to relaxation of the polariton density from a solitonic spectrum distribution in momentum space down to low momenta, with the resultant formation of a nonequilibrium condensate manifested by a standing wave pattern across the whole sample.

Investigation of dissociative electron attachment to 2'-deoxycytidine-3'-monophosphate using DFT method and time dependent wave packet approach

NASA Astrophysics Data System (ADS)

Bhowmick, Somnath; B, Renjith; Mishra, Manoj K.; Sarma, Manabendra

2012-08-01

Effect of electron correlation on single strand breaks (SSBs) induced by low energy electron (LEE) has been investigated in a fragment excised from a DNA, viz., 2'-deoxycytidine-3'-monophosphate [3'-dCMPH] molecule in gas phase at DFT-B3LYP/6-31+G(d) accuracy level and using local complex potential based time dependent wave packet (LCP-TDWP) approach. The results obtained, in conjunction with our earlier investigation, show the possibility of SSB at very low energy (0.15 eV) where the LEE transfers from π* to σ* resonance state which resembles a SN2 type mechanism. In addition, for the first time, an indication of quantum mechanical tunneling in strand breaking is seen from the highest anionic bound vibrational state (χ5), which may have a substantial role during DNA damage.

Nonlinear optical waves with the second Painleve transcendent shape of envelope in Kerr media

NASA Astrophysics Data System (ADS)

Shcherbakov, Alexandre S.; Tepichin Rodriguez, Eduardo; Sanchez Sanchez, Mauro

2004-05-01

Nonlinear optical wave packets with the second Painleve transcendent shape of envelope are revealed in Kerr media, manifesting weakly focusing cubic nonlinearity, square-law dispersion, and linear losses. When the state of nonlinear optical transmission is realized, two possible types of boundary conditions turn out to be satisfied for these wave packets. The propagation of initially unchirped optical wave packets under consideration could be supported by lossless medium in both normal and anomalous dispersion regimes. At the same time initially chirped optical waves with the second Painleve transcendent shape in low-loss medium and need matching the magnitude of optical losses by the dispersion and nonlinear properties of that medium.

Robust state preparation in quantum simulations of Dirac dynamics

NASA Astrophysics Data System (ADS)

Song, Xue-Ke; Deng, Fu-Guo; Lamata, Lucas; Muga, J. G.

2017-02-01

A nonrelativistic system such as an ultracold trapped ion may perform a quantum simulation of a Dirac equation dynamics under specific conditions. The resulting Hamiltonian and dynamics are highly controllable, but the coupling between momentum and internal levels poses some difficulties to manipulate the internal states accurately in wave packets. We use invariants of motion to inverse engineer robust population inversion processes with a homogeneous, time-dependent simulated electric field. This exemplifies the usefulness of inverse-engineering techniques to improve the performance of quantum simulation protocols.

Energy-saving scheme based on downstream packet scheduling in ethernet passive optical networks

NASA Astrophysics Data System (ADS)

Zhang, Lincong; Liu, Yejun; Guo, Lei; Gong, Xiaoxue

2013-03-01

With increasing network sizes, the energy consumption of Passive Optical Networks (PONs) has grown significantly. Therefore, it is important to design effective energy-saving schemes in PONs. Generally, energy-saving schemes have focused on sleeping the low-loaded Optical Network Units (ONUs), which tends to bring large packet delays. Further, the traditional ONU sleep modes are not capable of sleeping the transmitter and receiver independently, though they are not required to transmit or receive packets. Clearly, this approach contributes to wasted energy. Thus, in this paper, we propose an Energy-Saving scheme that is based on downstream Packet Scheduling (ESPS) in Ethernet PON (EPON). First, we design both an algorithm and a rule for downstream packet scheduling at the inter- and intra-ONU levels, respectively, to reduce the downstream packet delay. After that, we propose a hybrid sleep mode that contains not only ONU deep sleep mode but also independent sleep modes for the transmitter and the receiver. This ensures that the energy consumed by the ONUs is minimal. To realize the hybrid sleep mode, a modified GATE control message is designed that involves 10 time points for sleep processes. In ESPS, the 10 time points are calculated according to the allocated bandwidths in both the upstream and the downstream. The simulation results show that ESPS outperforms traditional Upstream Centric Scheduling (UCS) scheme in terms of energy consumption and the average delay for both real-time and non-real-time packets downstream. The simulation results also show that the average energy consumption of each ONU in larger-sized networks is less than that in smaller-sized networks; hence, our ESPS is better suited for larger-sized networks.

Quantum revival for elastic waves in thin plate

NASA Astrophysics Data System (ADS)

Dubois, Marc; Lefebvre, Gautier; Sebbah, Patrick

2017-05-01

Quantum revival is described as the time-periodic reconstruction of a wave packet initially localized in space and time. This effect is expected in finite-size systems which exhibit commensurable discrete spectrum such as the infinite quantum well. Here, we report on the experimental observation of full and fractional quantum revival for classical waves in a two dimensional cavity. We consider flexural waves propagating in thin plates, as their quadratic dispersion at low frequencies mimics the dispersion relation of quantum systems governed by Schrödinger equation. Time-dependent excitation and measurement are performed at ultrasonic frequencies and reveal a periodic reconstruction of the initial elastic wave packet.

Deep Packet/Flow Analysis using GPUs

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

Gong, Qian; Wu, Wenji; DeMar, Phil

Deep packet inspection (DPI) faces severe performance challenges in high-speed networks (40/100 GE) as it requires a large amount of raw computing power and high I/O throughputs. Recently, researchers have tentatively used GPUs to address the above issues and boost the performance of DPI. Typically, DPI applications involve highly complex operations in both per-packet and per-flow data level, often in real-time. The parallel architecture of GPUs fits exceptionally well for per-packet network traffic processing. However, for stateful network protocols such as TCP, their data stream need to be reconstructed in a per-flow level to deliver a consistent content analysis. Sincemore » the flow-centric operations are naturally antiparallel and often require large memory space for buffering out-of-sequence packets, they can be problematic for GPUs, whose memory is normally limited to several gigabytes. In this work, we present a highly efficient GPU-based deep packet/flow analysis framework. The proposed design includes a purely GPU-implemented flow tracking and TCP stream reassembly. Instead of buffering and waiting for TCP packets to become in sequence, our framework process the packets in batch and uses a deterministic finite automaton (DFA) with prefix-/suffix- tree method to detect patterns across out-of-sequence packets that happen to be located in different batches. In conclusion, evaluation shows that our code can reassemble and forward tens of millions of packets per second and conduct a stateful signature-based deep packet inspection at 55 Gbit/s using an NVIDIA K40 GPU.« less

Following coherent multichannel nuclear wave packets in pump-probe studies of O2 with ultrashort laser pulses

NASA Astrophysics Data System (ADS)

Xue, Shan; Du, Hongchuan; Hu, Bitao; Lin, C. D.; Le, Anh-Thu

2018-04-01

We reexamine the recent pump-probe experiment with O2 using short intense infrared laser pulses theoretically. Using parameters that closely mimic the experimental conditions and taking into account the angle-dependent population redistribution due to resonant coupling between the relevant states, we show that the observed kinetic energy release spectra, including the energy-dependent structure and the quantum beat frequencies, can be accurately reproduced. Our results reveal additional important channels that were missed earlier. In particular, the strong contributions from O2+a 4Πu and b 4Σg- states lead to the possibility of observing the interchannel beating. We further demonstrate that, by varying the laser parameters, the coherent nuclear wave-packet motions on different potential energy surfaces (PESs) can be probed and the properties of the PES can be examined. Future experiments with different wavelength lasers are proposed for better probing and controlling nuclear dynamics on different PESs.

Seismic Wave Propagation

NASA Astrophysics Data System (ADS)

Wu, Xianyun; Wu, Ru-Shan

A seismic wave is a mechanical disturbance or energy packet that can propagate from point to point in the Earth. Seismic waves can be generated by a sudden release of energy such as an earthquake, volcanic eruption, or chemical explosion. There are several types of seismic waves, often classified as body waves, which propagate through the volume of the Earth, and surface waves, which travel along the surface of the Earth. Compressional and shear waves are the two main types of body wave and Rayleigh and Love waves are the most common forms of surface wave.

Simulation of wave interactions with MHD

NASA Astrophysics Data System (ADS)

Batchelor, D.; Alba, C.; Bateman, G.; Bernholdt, D.; Berry, L.; Bonoli, P.; Bramley, R.; Breslau, J.; Chance, M.; Chen, J.; Choi, M.; Elwasif, W.; Fu, G.; Harvey, R.; Jaeger, E.; Jardin, S.; Jenkins, T.; Keyes, D.; Klasky, S.; Kruger, S.; Ku, L.; Lynch, V.; McCune, D.; Ramos, J.; Schissel, D.; Schnack, D.; Wright, J.

2008-07-01

The broad scientific objectives of the SWIM (Simulation 01 Wave Interaction with MHD) project are twofold: (1) improve our understanding of interactions that both radio frequency (RF) wave and particle sources have on extended-MHD phenomena, and to substantially improve our capability for predicting and optimizing the performance of burning plasmas in devices such as ITER: and (2) develop an integrated computational system for treating multiphysics phenomena with the required flexibility and extensibility to serve as a prototype for the Fusion Simulation Project. The Integrated Plasma Simulator (IPS) has been implemented. Presented here are initial physics results on RP effects on MHD instabilities in tokamaks as well as simulation results for tokamak discharge evolution using the IPS.

Dynamics of Quasi-Electrostatic Whistler waves in Earth's Radiation belts

NASA Astrophysics Data System (ADS)

Goyal, R.; Sharma, R. P.; Gupta, D. N.

2017-12-01

A numerical model is proposed to study the dynamics of high amplitude quasi-electrostatic whistler waves propagating near resonance cone angle and their interaction with finite frequency kinetic Alfvén waves (KAWs) in Earth's radiation belts. The quasi-electrostatic character of whistlers is narrated by dynamics of wave propagating near resonance cone. A high amplitude whistler wave packet is obtained using the present analysis which has also been observed by S/WAVES instrument onboard STEREO. The numerical simulation technique employed to study the dynamics, leads to localization (channelling) of waves as well as turbulent spectrum suggesting the transfer of wave energy over a range of frequencies. The turbulent spectrum also indicates the presence of quasi-electrostatic whistlers and density fluctuations associated with KAW in radiation belts plasma. The ponderomotive force of pump quasi-electrostatic whistlers (high frequency) is used to excite relatively much lower frequency waves (KAWs). The wave localization and steeper spectra could be responsible for particle energization or heating in radiation belts.

The effect of plasma inhomogeneities on (i) radio emission generation by non-gyrotropic electron beams and (ii) particle acceleration by Langmuir waves

NASA Astrophysics Data System (ADS)

Tsiklauri, D.

2014-12-01

Extensive particle-in-cell simulations of fast electron beams injected in a background magnetised plasma with a decreasing density profile were carried out. These simulations were intended to further shed light on a newly proposed mechanism for the generation of electromagnetic waves in type III solar radio bursts [1]. Here recent progress in an alternative to the plasma emission model using Particle-In-Cell, self-consistent electromagnetic wave emission simulations of solar type III radio bursts will be presented. In particular, (i) Fourier space drift (refraction) of non-gyrotropic electron beam-generated wave packets, caused by the density gradient [1,2], (ii) parameter space investigation of numerical runs [3], (iii) concurrent generation of whistler waves [4] and a separate problem of (iv) electron acceleration by Langmuir waves in a background magnetised plasma with an increasing density profile [5] will be discussed. In all considered cases the density inhomogeneity-induced wave refraction plays a crucial role. In the case of non-gyrotropic electron beam, the wave refaction transforms the generated wave packets from standing into freely escaping EM radiation. In the case of electron acceleration by Langmuir waves, a positive density gradient in the direction of wave propagation causes a decrease in the wavenumber, and hence a higher phase velocity vph=ω/k. The k-shifted wave is then subject to absorption by a faster electron by wave-particle interaction. The overall effect is an increased number of high energy electrons in the energy spectrum. [1] D. Tsiklauri, Phys. Plasmas 18, 052903 (2011) [2] H. Schmitz, D. Tsiklauri, Phys. Plasmas 20, 062903 (2013) [3] R. Pechhacker, D. Tsiklauri, Phys. Plasmas 19, 112903 (2012) [4] M. Skender, D. Tsiklauri, Phys. Plasmas 21, 042904 (2014) [5] R. Pechhacker, D. Tsiklauri, Phys. Plasmas 21, 012903 (2014)

Simulations of Seismic Wave Propagation on Mars

DOE PAGES

Bozdağ, Ebru; Ruan, Youyi; Metthez, Nathan; ...

2017-03-23

In this paper, we present global and regional synthetic seismograms computed for 1D and 3D Mars models based on the spectral-element method. For global simulations, we implemented a radially-symmetric Mars model with a 110 km thick crust. For this 1D model, we successfully benchmarked the 3D seismic wave propagation solver SPECFEM3D_GLOBE against the 2D axisymmetric wave propagation solver AxiSEM at periods down to 10 s. We also present higher-resolution body-wave simulations with AxiSEM down to 1 s in a model with a more complex 1D crust, revealing wave propagation effects that would have been difficult to interpret based on raymore » theory. For 3D global simulations based on SPECFEM3D_GLOBE, we superimposed 3D crustal thickness variations capturing the distinct crustal dichotomy between Mars’ northern and southern hemispheres, as well as topography, ellipticity, gravity, and rotation. The global simulations clearly indicate that the 3D crust speeds up body waves compared to the reference 1D model, whereas it significantly changes surface waveforms and their dispersive character depending on its thickness. We also perform regional simulations with the solver SES3D based on 3D crustal models derived from surface composition, thereby addressing the effects of various distinct crustal features down to 2 s. The regional simulations confirm the strong effects of crustal variations on waveforms. Finally, we conclude that the numerical tools are ready for examining more scenarios, including various other seismic models and sources.« less

Simulations of Seismic Wave Propagation on Mars

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

Bozdağ, Ebru; Ruan, Youyi; Metthez, Nathan

In this paper, we present global and regional synthetic seismograms computed for 1D and 3D Mars models based on the spectral-element method. For global simulations, we implemented a radially-symmetric Mars model with a 110 km thick crust. For this 1D model, we successfully benchmarked the 3D seismic wave propagation solver SPECFEM3D_GLOBE against the 2D axisymmetric wave propagation solver AxiSEM at periods down to 10 s. We also present higher-resolution body-wave simulations with AxiSEM down to 1 s in a model with a more complex 1D crust, revealing wave propagation effects that would have been difficult to interpret based on raymore » theory. For 3D global simulations based on SPECFEM3D_GLOBE, we superimposed 3D crustal thickness variations capturing the distinct crustal dichotomy between Mars’ northern and southern hemispheres, as well as topography, ellipticity, gravity, and rotation. The global simulations clearly indicate that the 3D crust speeds up body waves compared to the reference 1D model, whereas it significantly changes surface waveforms and their dispersive character depending on its thickness. We also perform regional simulations with the solver SES3D based on 3D crustal models derived from surface composition, thereby addressing the effects of various distinct crustal features down to 2 s. The regional simulations confirm the strong effects of crustal variations on waveforms. Finally, we conclude that the numerical tools are ready for examining more scenarios, including various other seismic models and sources.« less

Advanced computational simulations of water waves interacting with wave energy converters

NASA Astrophysics Data System (ADS)

Pathak, Ashish; Freniere, Cole; Raessi, Mehdi

2017-03-01

Wave energy converter (WEC) devices harness the renewable ocean wave energy and convert it into useful forms of energy, e.g. mechanical or electrical. This paper presents an advanced 3D computational framework to study the interaction between water waves and WEC devices. The computational tool solves the full Navier-Stokes equations and considers all important effects impacting the device performance. To enable large-scale simulations in fast turnaround times, the computational solver was developed in an MPI parallel framework. A fast multigrid preconditioned solver is introduced to solve the computationally expensive pressure Poisson equation. The computational solver was applied to two surface-piercing WEC geometries: bottom-hinged cylinder and flap. Their numerically simulated response was validated against experimental data. Additional simulations were conducted to investigate the applicability of Froude scaling in predicting full-scale WEC response from the model experiments.

Effect of wave localization on plasma instabilities

NASA Astrophysics Data System (ADS)

Levedahl, William Kirk

1987-10-01

The Anderson model of wave localization in random media is involved to study the effect of solar wind density turbulence on plasma processes associated with the solar type III radio burst. ISEE-3 satellite data indicate that a possible model for the type III process is the parametric decay of Langmuir waves excited by solar flare electron streams into daughter electromagnetic and ion acoustic waves. The threshold for this instability, however, is much higher than observed Langmuir wave levels because of rapid wave convection of the transverse electromagnetic daughter wave in the case where the solar wind is assumed homogeneous. Langmuir and transverse waves near critical density satisfy the Ioffe-Reigel criteria for wave localization in the solar wind with observed density fluctuations -1 percent. Numerical simulations of wave propagation in random media confirm the localization length predictions of Escande and Souillard for stationary density fluctations. For mobile density fluctuations localized wave packets spread at the propagation velocity of the density fluctuations rather than the group velocity of the waves. Computer simulations using a linearized hybrid code show that an electron beam will excite localized Langmuir waves in a plasma with density turbulence. An action principle approach is used to develop a theory of non-linear wave processes when waves are localized. A theory of resonant particles diffusion by localized waves is developed to explain the saturation of the beam-plasma instability. It is argued that localization of electromagnetic waves will allow the instability threshold to be exceeded for the parametric decay discussed above.

Advanced radiometric and interferometric milimeter-wave scene simulations

NASA Technical Reports Server (NTRS)

Hauss, B. I.; Moffa, P. J.; Steele, W. G.; Agravante, H.; Davidheiser, R.; Samec, T.; Young, S. K.

1993-01-01

Smart munitions and weapons utilize various imaging sensors (including passive IR, active and passive millimeter-wave, and visible wavebands) to detect/identify targets at short standoff ranges and in varied terrain backgrounds. In order to design and evaluate these sensors under a variety of conditions, a high-fidelity scene simulation capability is necessary. Such a capability for passive millimeter-wave scene simulation exists at TRW. TRW's Advanced Radiometric Millimeter-Wave Scene Simulation (ARMSS) code is a rigorous, benchmarked, end-to-end passive millimeter-wave scene simulation code for interpreting millimeter-wave data, establishing scene signatures and evaluating sensor performance. In passive millimeter-wave imaging, resolution is limited due to wavelength and aperture size. Where high resolution is required, the utility of passive millimeter-wave imaging is confined to short ranges. Recent developments in interferometry have made possible high resolution applications on military platforms. Interferometry or synthetic aperture radiometry allows the creation of a high resolution image with a sparsely filled aperture. Borrowing from research work in radio astronomy, we have developed and tested at TRW scene reconstruction algorithms that allow the recovery of the scene from a relatively small number of spatial frequency components. In this paper, the TRW modeling capability is described and numerical results are presented.

Theoretical and experimental evidence of non-symmetric doubly localized rogue waves.

PubMed

He, Jingsong; Guo, Lijuan; Zhang, Yongshuai; Chabchoub, Amin

2014-11-08

We present determinant expressions for vector rogue wave (RW) solutions of the Manakov system, a two-component coupled nonlinear Schrödinger (NLS) equation. As a special case, we generate a family of exact and non-symmetric RW solutions of the NLS equation up to third order, localized in both space and time. The derived non-symmetric doubly localized second-order solution is generated experimentally in a water wave flume for deep-water conditions. Experimental results, confirming the characteristic non-symmetric pattern of the solution, are in very good agreement with theory as well as with numerical simulations, based on the modified NLS equation, known to model accurately the dynamics of weakly nonlinear wave packets in deep water.

Method and Apparatus for Processing UDP Data Packets

NASA Technical Reports Server (NTRS)

Murphy, Brandon M. (Inventor)

2017-01-01

A method and apparatus for processing a plurality of data packets. A data packet is received. A determination is made as to whether a portion of the data packet follows a selected digital recorder standard protocol based on a header of the data packet. Raw data in the data packet is converted into human-readable information in response to a determination that the portion of the data packet follows the selected digital recorder standard protocol.

Multi-Media Instructional Packets.

ERIC Educational Resources Information Center

Brophy, John W.

This is a collection of multi-media packets for each of the following business subjects: (1) Introduction to Business; (2) Principles of Marketing; (3) Principles of Advertising; (4) Principles of Retailing/Merchandising; and (5) Principles of Salesmanship. Each packet includes information regarding: (1) most relevant textbooks; (2) Suggested…

Dynamic Simulation of a Wave Rotor Topped Turboshaft Engine

NASA Technical Reports Server (NTRS)

Greendyke, R. B.; Paxson, D. E.; Schobeiri, M. T.

1997-01-01

The dynamic behavior of a wave rotor topped turboshaft engine is examined using a numerical simulation. The simulation utilizes an explicit, one-dimensional, multi-passage, CFD based wave rotor code in combination with an implicit, one-dimensional, component level dynamic engine simulation code. Transient responses to rapid fuel flow rate changes and compressor inlet pressure changes are simulated and compared with those of a similarly sized, untopped, turboshaft engine. Results indicate that the wave rotor topped engine responds in a stable, and rapid manner. Furthermore, during certain transient operations, the wave rotor actually tends to enhance engine stability. In particular, there is no tendency toward surge in the compressor of the wave rotor topped engine during rapid acceleration. In fact, the compressor actually moves slightly away from the surge line during this transient. This behavior is precisely the opposite to that of an untopped engine. The simulation is described. Issues associated with integrating CFD and component level codes are discussed. Results from several transient simulations are presented and discussed.

Equatorial waves in some CMIP5 coupled models (with stratosphere)

NASA Astrophysics Data System (ADS)

Maury, Pauline; Lott, François; Guez, Lionel

2013-04-01

The Kelvin and the Rossby Gravity Waves (RGWs) packets that dominate the day to day variability in the low equatorial stratosphere (50hPa) are analyzed in 7 ESMs that participate to CMIP5 and that include a well resolved stratosphere. The results are compared to ERAI. Two models are also used to quantify better (i) the impact of the QBO on these waves (MPI-P and MPI-MR), and (ii) the impact of convection (IPSL-CM5A and CM5B). In the stratosphere all models present quite coherent Kelvin waves and RGWs packets, which is good think since these waves dominate the day to day variability in the low stratosphere. The errors on these freely propagating waves seem therefore less pronounced then the differences seen by others on the convectively coupled waves in the troposphere. The difference between the models nevertheless stay very large, the models with a QBO have more pronounced waves, and represent better their life-cycle (this is particularly true for the RGWs). The sensitivity to the convection of the rather slow waves analysed here is not as pronounced as was found in the past for may be faster waves, but is nevertheless confirmed when we look at the same model with two drastically different convection parameterization. In the same spirit, the sensitivity of the RGWs to the QBO is confirmed by comparing almost the same model runs, one with a QBO and one without. Having a QBO nevertheless does not guarantee that the waves are realistic in all respects, as shows for instance the Temperature signature due to the RGWs in the UKMO model. There also seems to have an issue when the resolution changes drastically, the MRI model behaving quite differently from the other models when it comes to the simulations of these equatorial waves.

Internal Ocean Waves

NASA Image and Video Library

2006-07-17

The false-color VNIR image from NASA Terra spacecraft was acquired off the island of Tsushima in the Korea Strait shows the signatures of several internal wave packets, indicating a northern propagation direction.

Heat waves over Central Europe in regional climate model simulations

NASA Astrophysics Data System (ADS)

Lhotka, Ondřej; Kyselý, Jan

2014-05-01

Regional climate models (RCMs) have become a powerful tool for exploring impacts of global climate change on a regional scale. The aim of the study is to evaluate the capability of RCMs to reproduce characteristics of major heat waves over Central Europe in their simulations of the recent climate (1961-2000), with a focus on the most severe and longest Central European heat wave that occurred in 1994. We analyzed 7 RCM simulations with a high resolution (0.22°) from the ENSEMBLES project, driven by the ERA-40 reanalysis. In observed data (the E-OBS 9.0 dataset), heat waves were defined on the basis of deviations of daily maximum temperature (Tmax) from the 95% quantile of summer Tmax distribution in grid points over Central Europe. The same methodology was applied in the RCM simulations; we used corresponding 95% quantiles (calculated for each RCM and grid point) in order to remove the bias of modelled Tmax. While climatological characteristics of heat waves are reproduced reasonably well in the RCM ensemble, we found major deficiencies in simulating heat waves in individual years. For example, METNOHIRHAM simulated very severe heat waves in 1996, when no heat wave was observed. Focusing on the major 1994 heat wave, considerable differences in simulated temperature patterns were found among the RCMs. The differences in the temperature patterns were clearly linked to the simulated amount of precipitation during this event. The 1994 heat wave was almost absent in all RCMs that did not capture the observed precipitation deficit, while it was by far most pronounced in KNMI-RACMO that simulated virtually no precipitation over Central Europe during the 15-day period of the heat wave. By contrast to precipitation, values of evaporative fraction in the RCMs were not linked to severity of the simulated 1994 heat wave. This suggests a possible major contribution of other factors such as cloud cover and associated downward shortwave radiation. Therefore, a more detailed

Recognition of the optical packet header for two channels utilizing the parallel reservoir computing based on a semiconductor ring laser

NASA Astrophysics Data System (ADS)

Bao, Xiurong; Zhao, Qingchun; Yin, Hongxi; Qin, Jie

2018-05-01

In this paper, an all-optical parallel reservoir computing (RC) system with two channels for the optical packet header recognition is proposed and simulated, which is based on a semiconductor ring laser (SRL) with the characteristic of bidirectional light paths. The parallel optical loops are built through the cross-feedback of the bidirectional light paths where every optical loop can independently recognize each injected optical packet header. Two input signals are mapped and recognized simultaneously by training all-optical parallel reservoir, which is attributed to the nonlinear states in the laser. The recognition of optical packet headers for two channels from 4 bits to 32 bits is implemented through the simulation optimizing system parameters and therefore, the optimal recognition error ratio is 0. Since this structure can combine with the wavelength division multiplexing (WDM) optical packet switching network, the wavelength of each channel of optical packet headers for recognition can be different, and a better recognition result can be obtained.

Analysis of Measured and Simulated Supraglottal Acoustic Waves.

PubMed

Fraile, Rubén; Evdokimova, Vera V; Evgrafova, Karina V; Godino-Llorente, Juan I; Skrelin, Pavel A

2016-09-01

To date, although much attention has been paid to the estimation and modeling of the voice source (ie, the glottal airflow volume velocity), the measurement and characterization of the supraglottal pressure wave have been much less studied. Some previous results have unveiled that the supraglottal pressure wave has some spectral resonances similar to those of the voice pressure wave. This makes the supraglottal wave partially intelligible. Although the explanation for such effect seems to be clearly related to the reflected pressure wave traveling upstream along the vocal tract, the influence that nonlinear source-filter interaction has on it is not as clear. This article provides an insight into this issue by comparing the acoustic analyses of measured and simulated supraglottal and voice waves. Simulations have been performed using a high-dimensional discrete vocal fold model. Results of such comparative analysis indicate that spectral resonances in the supraglottal wave are mainly caused by the regressive pressure wave that travels upstream along the vocal tract and not by source-tract interaction. On the contrary and according to simulation results, source-tract interaction has a role in the loss of intelligibility that happens in the supraglottal wave with respect to the voice wave. This loss of intelligibility mainly corresponds to spectral differences for frequencies above 1500 Hz. Copyright © 2016 The Voice Foundation. Published by Elsevier Inc. All rights reserved.

78 FR 63228 - Determination That Potassium Citrate, 10 Milliequivalents/Packet and 20 Milliequivalents/Packet...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-10-23

... approved. ANDA applicants do not have to repeat the extensive clinical testing otherwise necessary to gain... mEq/packet and 20 mEq/packet, is the subject of NDA 19-647, held by Nova-K LLC, and initially...

Numerical simulations of internal wave generation by convection in water.

PubMed

Lecoanet, Daniel; Le Bars, Michael; Burns, Keaton J; Vasil, Geoffrey M; Brown, Benjamin P; Quataert, Eliot; Oishi, Jeffrey S

2015-06-01

Water's density maximum at 4°C makes it well suited to study internal gravity wave excitation by convection: an increasing temperature profile is unstable to convection below 4°C, but stably stratified above 4°C. We present numerical simulations of a waterlike fluid near its density maximum in a two-dimensional domain. We successfully model the damping of waves in the simulations using linear theory, provided we do not take the weak damping limit typically used in the literature. To isolate the physical mechanism exciting internal waves, we use the spectral code dedalus to run several simplified model simulations of our more detailed simulation. We use data from the full simulation as source terms in two simplified models of internal-wave excitation by convection: bulk excitation by convective Reynolds stresses, and interface forcing via the mechanical oscillator effect. We find excellent agreement between the waves generated in the full simulation and the simplified simulation implementing the bulk excitation mechanism. The interface forcing simulations overexcite high-frequency waves because they assume the excitation is by the "impulsive" penetration of plumes, which spreads energy to high frequencies. However, we find that the real excitation is instead by the "sweeping" motion of plumes parallel to the interface. Our results imply that the bulk excitation mechanism is a very accurate heuristic for internal-wave generation by convection.

Simulations of Seismic Wave Propagation on Mars

NASA Astrophysics Data System (ADS)

Bozdağ, Ebru; Ruan, Youyi; Metthez, Nathan; Khan, Amir; Leng, Kuangdai; van Driel, Martin; Wieczorek, Mark; Rivoldini, Attilio; Larmat, Carène S.; Giardini, Domenico; Tromp, Jeroen; Lognonné, Philippe; Banerdt, Bruce W.

2017-10-01

We present global and regional synthetic seismograms computed for 1D and 3D Mars models based on the spectral-element method. For global simulations, we implemented a radially-symmetric Mars model with a 110 km thick crust (Sohl and Spohn in J. Geophys. Res., Planets 102(E1):1613-1635, 1997). For this 1D model, we successfully benchmarked the 3D seismic wave propagation solver SPECFEM3D_GLOBE (Komatitsch and Tromp in Geophys. J. Int. 149(2):390-412, 2002a; 150(1):303-318, 2002b) against the 2D axisymmetric wave propagation solver AxiSEM (Nissen-Meyer et al. in Solid Earth 5(1):425-445, 2014) at periods down to 10 s. We also present higher-resolution body-wave simulations with AxiSEM down to 1 s in a model with a more complex 1D crust, revealing wave propagation effects that would have been difficult to interpret based on ray theory. For 3D global simulations based on SPECFEM3D_GLOBE, we superimposed 3D crustal thickness variations capturing the distinct crustal dichotomy between Mars' northern and southern hemispheres, as well as topography, ellipticity, gravity, and rotation. The global simulations clearly indicate that the 3D crust speeds up body waves compared to the reference 1D model, whereas it significantly changes surface waveforms and their dispersive character depending on its thickness. We also perform regional simulations with the solver SES3D (Fichtner et al. Geophys. J. Int. 179:1703-1725, 2009) based on 3D crustal models derived from surface composition, thereby addressing the effects of various distinct crustal features down to 2 s. The regional simulations confirm the strong effects of crustal variations on waveforms. We conclude that the numerical tools are ready for examining more scenarios, including various other seismic models and sources.

[KIND Worksheet Packet: Wild Animals (Junior).

ERIC Educational Resources Information Center

National Association for Humane and Environmental Education, East Haddam, CT.

This packet is the junior part of a series of worksheet packets available at both junior (grades 3-4) and senior (grades 5-6) levels that covers a variety of humane and environmental topics. Each packet includes 10 worksheets, all of which originally appeared in past issues of the annual teaching magazine "KIND (Kids in Nature's Defense)…

[KIND Worksheet Packet: Wild Animals (Senior).

ERIC Educational Resources Information Center

National Association for Humane and Environmental Education, East Haddam, CT.

This packet is the senior part of a series of worksheet packets available at both junior (grades 3-4) and senior (grades 5-6) levels that covers a variety of humane and environmental topics. Each packet includes 10 worksheets, all of which originally appeared in past issues of the annual teaching magazine "KIND (Kids in Nature's Defense)…

On-board closed-loop congestion control for satellite based packet switching networks

NASA Technical Reports Server (NTRS)

Chu, Pong P.; Ivancic, William D.; Kim, Heechul

1993-01-01

NASA LeRC is currently investigating a satellite architecture that incorporates on-board packet switching capability. Because of the statistical nature of packet switching, arrival traffic may fluctuate and thus it is necessary to integrate congestion control mechanism as part of the on-board processing unit. This study focuses on the closed-loop reactive control. We investigate the impact of the long propagation delay on the performance and propose a scheme to overcome the problem. The scheme uses a global feedback signal to regulate the packet arrival rate of ground stations. In this scheme, the satellite continuously broadcasts the status of its output buffer and the ground stations respond by selectively discarding packets or by tagging the excessive packets as low-priority. The two schemes are evaluated by theoretical queuing analysis and simulation. The former is used to analyze the simplified model and to determine the basic trends and bounds, and the later is used to assess the performance of a more realistic system and to evaluate the effectiveness of more sophisticated control schemes. The results show that the long propagation delay makes the closed-loop congestion control less responsive. The broadcasted information can only be used to extract statistical information. The discarding scheme needs carefully-chosen status information and reduction function, and normally requires a significant amount of ground discarding to reduce the on-board packet loss probability. The tagging scheme is more effective since it tolerates more uncertainties and allows a larger margin of error in status information. It can protect the high-priority packets from excessive loss and fully utilize the downlink bandwidth at the same time.

Picture of the global field of quasi-monochromatic gravity waves observed by stratospheric balloons and MST radars

NASA Technical Reports Server (NTRS)

Yamanaka, M. D.

1989-01-01

In MAP observations, it was found that: (1) gravity waves in selected or filtered portions of data are fit for monochromatic structures, whereas (2) those in fully continuous and resolved observations take universal continuous spectra. It is possible to explain (2) by dispersion of quasi-monochromatic (or slowly varying) wave packets observed locally as (1), since the medium atmosphere is unsteady and nonuniform. Complete verification of the wave-mean flow interactions by tracking individual wave packets seems hopeless, because the wave induced flow cannot be distinguished from the basic flow independent of the waves. Instead, the primitive picture is looked at before MAP, that is, the atmosphere is just like an entertainment stage illuminated by cocktail lights of quasi-monochromatic gravity waves. The wave parameters are regarded as functions of time and spatial coordinates. The observational evidences (1) and (2) suggest that the wave parameter field is rather homogeneous, which can be explained by interference of quasi-monochromatic wave packets.

About the Nature of a Coherence of Light Waves

NASA Astrophysics Data System (ADS)

Demyaneko, P. O.; Zinkovskiy, Y. F.; Savenko, Y. V.

motion. So, the light is a photons flux: both light wave and light electromagnetic field consist of final number of photons. At that, it is important to remember that in any light source along with spontaneous mechanism it also operates a mechanism of induced radiation, generating identical (coherent) quantums. Due to it, there is radiated a partially coherent flux, consisting of large or small groups of quantums ("quantum packets"), from any light source. In limits of a separate packet its component quantums are coherent, because all of them are originated by one quantum which has appeared spontaneously, which induced occurrence of other quantums of this packet, passing by other excited atoms. The representation about quantum packets gives clear physical explanation to concept of "light waves zugs". Quantum packet is that "zug of waves". "Quality" of a light source (in sense of its coherence) is determined by sizes of quantum packets -- the larger they the more qualitative source, radiating them. There are understandable a better coherence of a gas light sources: the atoms in gas are arranged on large distances and do not hinder for spontaneously generated light quantum to overcome without absorption or dispersion that large distance, challenging on it an induced radiation of other excited atoms. The low coherence of glow-discharge tubes is stipulated by that the radiation in them goes only from surface layer of atoms and the requirements for development of the mechanism of induced radiation are unfavorable. It is also obvious the high coherence of a laser radiation due to a positive optical back coupling. The coherent quantums of one quantum packet exist a long time inside the resonator; they are reproducing there during all this time. Due to this the lasers are capable to generate multi-km quantum packets ("zugs"). By the way, it could not to explain "by emissive opportunities" of one atom. It is understandable a division of quantum packets on semi transparent mirrors

Theoretical and experimental evidence of non-symmetric doubly localized rogue waves

PubMed Central

He, Jingsong; Guo, Lijuan; Zhang, Yongshuai; Chabchoub, Amin

2014-01-01

We present determinant expressions for vector rogue wave (RW) solutions of the Manakov system, a two-component coupled nonlinear Schrödinger (NLS) equation. As a special case, we generate a family of exact and non-symmetric RW solutions of the NLS equation up to third order, localized in both space and time. The derived non-symmetric doubly localized second-order solution is generated experimentally in a water wave flume for deep-water conditions. Experimental results, confirming the characteristic non-symmetric pattern of the solution, are in very good agreement with theory as well as with numerical simulations, based on the modified NLS equation, known to model accurately the dynamics of weakly nonlinear wave packets in deep water. PMID:25383023

Fractional conductance oscillations in quantum rings: wave packet picture of transport in a few-electron system.

PubMed

Chwiej, T; Szafran, B

2013-04-17

We study electron transfer across a two-terminal quantum ring using a time-dependent description of the scattering process. For the considered scattering event the quantum ring is initially charged with one or two electrons, with another electron incident to the ring from the input channel. We study the electron transfer probability (T) as a function of the external magnetic field. We determine the periodicity of T for a varied number of electrons confined within the ring. For that purpose we develop a method to describe the wave packet dynamics for a few electrons participating in the scattering process, taking into full account the electron-electron correlations. We find that electron transfer across the quantum ring initially charged by a single electron acquires a distinct periodicity of half of the magnetic flux quantum (Φ0/2), corresponding to the formation of a transient two-electron state inside the ring. In the case of a three-electron scattering problem with two electrons initially occupying the ring, a period of Φ0/3 for T is formed in the limit of thin channels. The effect of disorder present in the confinement potential of the ring is also discussed.

Manipulating acoustic wave reflection by a nonlinear elastic metasurface

NASA Astrophysics Data System (ADS)

Guo, Xinxin; Gusev, Vitalyi E.; Bertoldi, Katia; Tournat, Vincent

2018-03-01

The acoustic wave reflection properties of a nonlinear elastic metasurface, derived from resonant nonlinear elastic elements, are theoretically and numerically studied. The metasurface is composed of a two degree-of-freedom mass-spring system with quadratic elastic nonlinearity. The possibility of converting, during the reflection process, most of the fundamental incoming wave energy into the second harmonic wave is shown, both theoretically and numerically, by means of a proper design of the nonlinear metasurface. The theoretical results from the harmonic balance method for a monochromatic source are compared with time domain simulations for a wave packet source. This protocol allows analyzing the dynamics of the nonlinear reflection process in the metasurface as well as exploring the limits of the operating frequency bandwidth. The reported methodology can be applied to a wide variety of nonlinear metasurfaces, thus possibly extending the family of exotic nonlinear reflection processes.

Simulated GOLD Observations of Atmospheric Waves

NASA Astrophysics Data System (ADS)

Correira, J.; Evans, J. S.; Lumpe, J. D.; Rusch, D. W.; Chandran, A.; Eastes, R.; Codrescu, M.

2016-12-01

The Global-scale Observations of the Limb and Disk (GOLD) mission will measure structures in the Earth's airglow layer due to dynamical forcing by vertically and horizontally propagating waves. These measurements focus on global-scale structures, including compositional and temperature responses resulting from dynamical forcing. Daytime observations of far-UV emissions by GOLD will be used to generate two-dimensional maps of the ratio of atomic oxygen and molecular nitrogen column densities (ΣO/N2 ) as well as neutral temperature that provide signatures of large-scale spatial structure. In this presentation, we use simulations to demonstrate GOLD's capability to deduce periodicities and spatial dimensions of large-scale waves from the spatial and temporal evolution observed in composition and temperature maps. Our simulations include sophisticated forward modeling of the upper atmospheric airglow that properly accounts for anisotropy in neutral and ion composition, temperature, and solar illumination. Neutral densities and temperatures used in the simulations are obtained from global circulation and climatology models that have been perturbed by propagating waves with a range of amplitudes, periods, and sources of excitation. Modeling of airglow emission and predictions of ΣO/N2 and neutral temperatures are performed with the Atmospheric Ultraviolet Radiance Integrated Code (AURIC) and associated derived product algorithms. Predicted structure in ΣO/N2 and neutral temperature due to dynamical forcing by propagating waves is compared to existing observations. Realistic GOLD Level 2 data products are generated from simulated airglow emission using algorithm code that will be implemented operationally at the GOLD Science Data Center.

A Practical Terrestrial Packet Radio Network.

DTIC Science & Technology

1983-11-01

12 Howard Frank, Israel Gitman and Richard Van Slyke , "Packet Radio System--Network Considerations," AFIPS Conference Proceedings, Anaheim, 1975...p, 1396. 33 Howard Frank, Israel Gitman and Richard Van Slyke, "Packet Radio System--Network Considerations," AFIPS...44, 1975 NCC, Anaheim, pp. 233-242. J 149 I : Frank, Howard, Israel Gitman and Richard Van Slyke, "Packet Radio System — Network

Converging Oceaniac Internal Waves, Somalia, Africa

NASA Image and Video Library

1988-10-03

The arculate fronts of these apparently converging internal waves off the northeast coast of Somalia (11.5N, 51.5E) probably were produced by interaction with two parallel submarine canyons off the Horn of Africa. Internal waves are packets of tidally generated waves traveling within the ocean at varying depths and are not detectable by any surface disturbance.

Evidence for four- and three-wave interactions in solar type III radio emissions

NASA Astrophysics Data System (ADS)

Thejappa, G.; MacDowall, R. J.; Bergamo, M.

2013-08-01

The high time resolution observations obtained by the STEREO/WAVES experiment show that in the source regions of solar type III radio bursts, Langmuir waves often occur as intense localized wave packets with short durations of only few ms. One of these wave packets shows that it is a three-dimensional field structure with WLneTe ~ 10-3, where WL is the peak energy density, and ne and Te are the electron density and temperature, respectively. For this wave packet, the conditions of the oscillating two-stream instability (OTSI) and supersonic collapse are satisfied within the error range of determination of main parameters. The density cavity, observed during this wave packet indicates that its depth, width and temporal coincidence are consistent with those of a caviton, generated by the ponderomotive force of the collapsing wave packet. The spectrum of each of the parallel and perpendicular components of the wave packet contains a primary peak at fpe, two secondary peaks at fpe ± fS and a low-frequency enhancement below fS, which, as indicated by the frequency and wave number resonance conditions, and the fast Fourier transform (FFT)-based tricoherence spectral peak at (fpe, fpe, fpe + fS, fpe - fS), are coupled to each other by the OTSI type of four-wave interaction (fpe is the local electron plasma frequency and fS is the frequency of ion sound waves). In addition to the primary peak at fpe, each of these spectra also contains a peak at 2fpe, which as indicated by the frequency and wave number resonance conditions, and the wavelet-based bicoherence spectral peak at (fpe, fpe), appears to correspond to the second harmonic electromagnetic waves generated as a result of coalescence of oppositely propagating sidebands excited by the OTSI. Thus, these observations for

Numerical simulations of merging black holes for gravitational-wave astronomy

NASA Astrophysics Data System (ADS)

Lovelace, Geoffrey

2014-03-01

Gravitational waves from merging binary black holes (BBHs) are among the most promising sources for current and future gravitational-wave detectors. Accurate models of these waves are necessary to maximize the number of detections and our knowledge of the waves' sources; near the time of merger, the waves can only be computed using numerical-relativity simulations. For optimal application to gravitational-wave astronomy, BBH simulations must achieve sufficient accuracy and length, and all relevant regions of the BBH parameter space must be covered. While great progress toward these goals has been made in the almost nine years since BBH simulations became possible, considerable challenges remain. In this talk, I will discuss current efforts to meet these challenges, and I will present recent BBH simulations produced using the Spectral Einstein Code, including a catalog of publicly available gravitational waveforms [black-holes.org/waveforms]. I will also discuss simulations of merging black holes with high mass ratios and with spins nearly as fast as possible, the most challenging regions of the BBH parameter space.

Delta function excitation of waves in the earth's ionosphere

NASA Technical Reports Server (NTRS)

Vidmar, R. J.; Crawford, F. W.; Harker, K. J.

1983-01-01

Excitation of the earth's ionosphere by delta function current sheets is considered, and the temporal and spatial evolution of wave packets is analyzed for a two-component collisional F2 layer. Approximations of an inverse Fourier-Laplace transform via saddle point methods provide plots of typical wave packets. These illustrate cold plasma wave theory and may be used as a diagnostic tool since it is possible to relate specific features, e.g., the frequency of a modulation envelope, to plasma parameters such as the electron cyclotron frequency. It is also possible to deduce the propagation path length and orientation of a remote radio beacon.

Drift Wave Simulation in Toroidal Geometry.

NASA Astrophysics Data System (ADS)

Lebrun, Maurice Joseph, III

1988-12-01

The drift wave, a general category of plasma behavior arising from a plasma inhomogeneity, is studied using the particle simulation method. In slab geometry, the drift wave (or universal mode) is stabilized by any finite amount of magnetic shear. In toroidal geometry, however, the coupling of the poloidal harmonics gives rise to a new branch of drift wave eigenmodes called the toroidicity -induced mode, which is predicted to be unstable in some regimes. The drift wave in a toroidal system is intrinsically three-dimensional, and is sensitive to the handling of the parallel electron dynamics, the (nearly) perpendicular wave dynamics, and the radial variation of magnetic field vector (shear). A simulation study must therefore be kinetic in nature, motivating the extension of particle simulation techniques to complex geometries. From this effort a three dimensional particle code in a toroidal coordinate system has been developed and applied to the toroidal drift wave problem. The code uses an (r,theta,phi) -type coordinate system, and a nonuniform radial grid that increases resolution near the mode-rational surfaces. Full ion dynamics and electron guiding center dynamics are employed. Further, the algorithm incorporates a straightforward limiting process to cylindrical geometry and slab geometry, enabling comparison to the theoretical results in these regimes. Simulations of the density-driven modes in toroidal geometry retain a single toroidal mode number (n = 9). In this regime, the poloidal harmonics are expected to be strongly coupled, giving rise to the marginally unstable toroidicity-induced drift mode. Analysis of the simulation data reveals a strong, low-frequency response that peaks near each mode rational surface. Further, the characteristic oscillation frequencies persist from one mode rational surface to the next, which identifies them as multiple harmonics of the toroidicity-induced mode. The lowest harmonic occurs at a frequency of omega/ omega^{*} ~ 0

Gravity Wave Interactions with Fine Structures in the Mesosphere and Lower Thermosphere

NASA Astrophysics Data System (ADS)

Mixa, Tyler; Fritts, David; Bossert, Katrina; Laughman, Brian; Wang, Ling; Lund, Thomas; Kantha, Lakshmi

2017-04-01

An anelastic numerical model is used to probe the influences of fine layering structures on gravity wave propagation in the Mesosphere and Lower Thermosphere (MLT). Recent lidar observations confirm the presence of persistent layered structures in the MLT that have sharp stratification and vertical scales below 1km. Gravity waves propagating through finely layered environments can excite and modulate the evolution of small scale instabilities that redefine the layering structure in these regions. Such layers in turn filter the outgoing wave spectra, promote ducting or reflection, hasten the onset of self-acceleration dynamics, and encourage wave/mean-flow interactions via energy and momentum transport. Using high resolution simulations of a localized gravity wave packet in a deep atmosphere, we identify the relative impacts of various wave and mean flow parameters to improve our understanding of these dynamics and complement recent state-of-the-art observations.

Ultrasound shear wave simulation based on nonlinear wave propagation and Wigner-Ville Distribution analysis

NASA Astrophysics Data System (ADS)

Bidari, Pooya Sobhe; Alirezaie, Javad; Tavakkoli, Jahan

2017-03-01

This paper presents a method for modeling and simulation of shear wave generation from a nonlinear Acoustic Radiation Force Impulse (ARFI) that is considered as a distributed force applied at the focal region of a HIFU transducer radiating in nonlinear regime. The shear wave propagation is simulated by solving the Navier's equation from the distributed nonlinear ARFI as the source of the shear wave. Then, the Wigner-Ville Distribution (WVD) as a time-frequency analysis method is used to detect the shear wave at different local points in the region of interest. The WVD results in an estimation of the shear wave time of arrival, its mean frequency and local attenuation which can be utilized to estimate medium's shear modulus and shear viscosity using the Voigt model.

Drift wave turbulence simulations in LAPD

NASA Astrophysics Data System (ADS)

Popovich, P.; Umansky, M.; Carter, T. A.; Auerbach, D. W.; Friedman, B.; Schaffner, D.; Vincena, S.

2009-11-01

We present numerical simulations of turbulence in LAPD plasmas using the 3D electromagnetic code BOUT (BOUndary Turbulence). BOUT solves a system of fluid moment equations in a general toroidal equlibrium geometry near the plasma boundary. The underlying assumptions for the validity of the fluid model are well satisfied for drift waves in LAPD plasmas (typical plasma parameters ne˜1x10^12cm-3, Te˜10eV, and B ˜1kG), which makes BOUT a perfect tool for simulating LAPD. We have adapted BOUT for the cylindrical geometry of LAPD and have extended the model to include the background flows required for simulations of recent bias-driven rotation experiments. We have successfully verified the code for several linear instabilities, including resistive drift waves, Kelvin-Helmholtz and rotation-driven interchange. We will discuss first non-linear simulations and quasi-stationary solutions with self-consistent plasma flows and saturated density profiles.

Trade Related Reading Packets for Disabled Readers.

ERIC Educational Resources Information Center

Davis, Beverly; Woodruff, Nancy S.

Six trade-related reading packets for disabled readers are provided for these trades: assemblers, baking, building maintenance, data entry, interior landscaping, and warehousing. Each packet stresses from 9 to 14 skills. Those skills common to most packets include context clues, fact or opinion, details, following directions, main idea,…

Influence of nonlinear interactions on the development of instability in hydrodynamic wave systems

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

Romanova, N. N.; Chkhetiani, O. G., E-mail: ochkheti@mx.iki.rssi.ru, E-mail: ochkheti@gmail.ru; Yakushkin, I. G.

2016-05-15

The problem of the development of shear instability in a three-layer medium simulating the flow of a stratified incompressible fluid is considered. The hydrodynamic equations are solved by expanding the Hamiltonian in a small parameter. The equations for three interacting waves, one of which is unstable, have been derived and solved numerically. The three-wave interaction is shown to stabilize the instability. Various regimes of the system’s dynamics, including the stochastic ones dependent on one of the invariants in the problem, can arise in this case. It is pointed out that the instability development scenario considered differs from the previously consideredmore » scenario of a different type, where the three-wave interaction does not stabilize the instability. The interaction of wave packets is considered briefly.« less

Dolphin "packet" use during long-range echolocation tasks.

PubMed

Finneran, James J

2013-03-01

When echolocating, dolphins typically emit a single broadband "click," then wait to receive the echo before emitting another click. However, previous studies have shown that during long-range echolocation tasks, they may instead emit a burst, or "packet," of several clicks, then wait for the packet of echoes to return before emitting another packet of clicks. The reasons for the use of packets are unknown. In this study, packet use was examined by having trained bottlenose dolphins perform long-range echolocation tasks. The tasks featured "phantom" echoes produced by capturing the dolphin's outgoing echolocation clicks, convolving the clicks with an impulse response to create an echo waveform, and then broadcasting the delayed, scaled echo to the dolphin. Dolphins were trained to report the presence of phantom echoes or a change in phantom echoes. Target range varied from 25 to 800 m. At ranges below 75 m, the dolphins rarely used packets. As the range increased beyond 75 m, two of the three dolphins increasingly produced packets, while the third dolphin instead utilized very high click repetition rates. The use of click packets appeared to be governed more by echo delay (target range) than echo amplitude.

Observations and Simulations of the Impact of Wave-Current Interaction on Wave Direction in the Surf Zone

NASA Astrophysics Data System (ADS)

Hopkins, Julia; Elgar, Steve; Raubenheimer, Britt

2017-04-01

Accurately characterizing the interaction of waves and currents can improve predictions of wave propagation and subsequent sediment transport in the nearshore. Along the southern shoreline of Martha's Vineyard, MA, waves propagate across strong tidal currents as they shoal, providing an ideal environment for investigating wave-current interaction. Wave directions and mean currents observed for two 1-month-long periods in 7- and 2-m water depths along 11 km of the Martha's Vineyard shoreline have strong tidal modulations. Wave directions shift by as much as 70 degrees over a tidal cycle in 7 m depth, and by as much as 25 degrees in 2 m depth. The magnitude of the tidal modulations in the wave field decreases alongshore to the west, consistent with the observed decrease in tidal currents from 2.1 to 0.2 m/s. The observations are reproduced accurately by a numerical model (SWAN and Deflt3D-FLOW) that simulates waves and currents over the observed bathymetry. Model simulations with and without wave-current interaction and tidal depth changes demonstrate that the observed tidal modulations of the wave field primarily are caused by wave-current interaction and not by tidal changes to water depths over the nearby complex shoals. Sediment transport estimates from simulated wave conditions using a range of tidal currents and offshore wave fields indicate that the modulation of the wave field at Martha's Vineyard can impact the direction of wave-induced alongshore sediment transport, sometimes driving transport opposing the direction of the offshore incident wave field. As such, the observations and model simulations suggest the importance of wave-current interaction to tidally averaged transport in mixed-energy wave-and-current nearshore environments. Supported by ASD(R&E), NSF, NOAA (Sea Grant), and ONR.

Relationship Between the Parameters of the Linear and Nonlinear Wave Generation Stages in a Magnetospheric Cyclotron Maser in the Backward-Wave Oscillator Regime

NASA Astrophysics Data System (ADS)

Demekhov, A. G.

2017-03-01

By using numerical simulations we generalize certain relationships between the parameters of quasimonochromatic whistler-mode waves generated at the linear and nonlinear stages of the cyclotron instability in the backward-wave oscillator regime. One of these relationships is between the wave amplitude at the nonlinear stage and the linear growth rate of the cyclotron instability. It was obtained analytically by V.Yu.Trakhtengerts (1984) for a uniform medium under the assumption of constant frequency and amplitude of the generated wave. We show that a similar relationship also holds for the signals generated in a nonuniform magnetic field and having a discrete structure in the form of short wave packets (elements) with fast frequency drift inside each element. We also generalize the formula for the linear growth rate of absolute cyclotron instability in a nonuniform medium and analyze the relationship between the frequency drift rate in the discrete elements and the wave amplitude. These relationships are important for analyzing the links between the parameters of chorus emissions in the Earth's and planetary magnetospheres and the characteristics of the energetic charged particles generating these signals.

TCP Packet Trace Analysis. M.S. Thesis

NASA Technical Reports Server (NTRS)

Shepard, Timothy J.

1991-01-01

Examination of a trace of packets collected from the network is often the only method available for diagnosing protocol performance problems in computer networks. This thesis explores the use of packet traces to diagnose performance problems of the transport protocol TCP. Unfortunately, manual examination of these traces can be so tedious that effective analysis is not possible. The primary contribution of this thesis is a graphical method of displaying the packet trace which greatly reduce, the tediousness of examining a packet trace. The graphical method is demonstrated by the examination of some packet traces of typical TCP connections. The performance of two different implementations of TCP sending data across a particular network path is compared. Traces many thousands of packets long are used to demonstrate how effectively the graphical method simplifies examination of long complicated traces. In the comparison of the two TCP implementations, the burstiness of the TCP transmitter appeared to be related to the achieved throughput. A method of quantifying this burstiness is presented and its possible relevance to understanding the performance of TCP is discussed.

Effect of wave localization on plasma instabilities. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Levedahl, William Kirk

1987-01-01

The Anderson model of wave localization in random media is involved to study the effect of solar wind density turbulence on plasma processes associated with the solar type III radio burst. ISEE-3 satellite data indicate that a possible model for the type III process is the parametric decay of Langmuir waves excited by solar flare electron streams into daughter electromagnetic and ion acoustic waves. The threshold for this instability, however, is much higher than observed Langmuir wave levels because of rapid wave convection of the transverse electromagnetic daughter wave in the case where the solar wind is assumed homogeneous. Langmuir and transverse waves near critical density satisfy the Ioffe-Reigel criteria for wave localization in the solar wind with observed density fluctuations -1 percent. Numerical simulations of wave propagation in random media confirm the localization length predictions of Escande and Souillard for stationary density fluctations. For mobile density fluctuations localized wave packets spread at the propagation velocity of the density fluctuations rather than the group velocity of the waves. Computer simulations using a linearized hybrid code show that an electron beam will excite localized Langmuir waves in a plasma with density turbulence. An action principle approach is used to develop a theory of non-linear wave processes when waves are localized. A theory of resonant particles diffusion by localized waves is developed to explain the saturation of the beam-plasma instability. It is argued that localization of electromagnetic waves will allow the instability threshold to be exceeded for the parametric decay discussed above.

Vocational and Industrial Arts Packets.

ERIC Educational Resources Information Center

Maine Audubon Society, Falmouth.

This book is a teacher's guide to energy alternatives. It is divided into seven informational packets on the following topics: parabolic solar concentrators, solar flat plate collectors, wood as fuel, heat loss, bio-gas, wind, and water. Each packet contains background information for the teachers and learning activities for the students. The…

Packets Distributing Evolutionary Algorithm Based on PSO for Ad Hoc Network

NASA Astrophysics Data System (ADS)

Xu, Xiao-Feng

2018-03-01

Wireless communication network has such features as limited bandwidth, changeful channel and dynamic topology, etc. Ad hoc network has lots of difficulties in accessing control, bandwidth distribution, resource assign and congestion control. Therefore, a wireless packets distributing Evolutionary algorithm based on PSO (DPSO)for Ad Hoc Network is proposed. Firstly, parameters impact on performance of network are analyzed and researched to obtain network performance effective function. Secondly, the improved PSO Evolutionary Algorithm is used to solve the optimization problem from local to global in the process of network packets distributing. The simulation results show that the algorithm can ensure fairness and timeliness of network transmission, as well as improve ad hoc network resource integrated utilization efficiency.

Dynamically reconfigurable optical packet switch (DROPS)

NASA Astrophysics Data System (ADS)

Huang, Chi-Heng; Chou, Hsu-Feng; Bowers, John E.; Toudeh-Fallah, Farzam; Gyurek, Russ

2006-12-01

A novel Dynamically Reconfigurable Optical Packet Switch (DROPS) that combines both spectral and spatial switching capabilities is proposed and experimentally demonstrated for the first time. Compared with an Arrayed Waveguide Grating Router (AWGR), the added spatial switching capability provided by the microelectromechanical systems (MEMS) enables dynamically reconfigurable routing that is not possible with an AWGR alone. This methodology has several advantages over an AWGR including scalability, additional degrees of freedom in routing a packet from an ingress port to an egress port and more flexibility in path or line card recovery. The experimental demonstration implemented with 10-Gb/s packets shows that the added spatial switching does not degrade the bit-error-rate performance, indicating the promising potential of DROPS as a versatile and ultra-high capacity switch for optical packet-switched networks.

One-Dimensional Full Wave Simulation of Equatorial Magnetosonic Wave Propagation in an Inhomogeneous Magnetosphere

NASA Astrophysics Data System (ADS)

Liu, Xu; Chen, Lunjin; Yang, Lixia; Xia, Zhiyang; Malaspina, David M.

2018-01-01

The effect of the plasmapause on equatorially radially propagating fast magnetosonic (MS) waves in the Earth's dipole magnetic field is studied by using finite difference time domain method. We run 1-D simulation for three different density profiles: (1) no plasmapause, (2) with a plasmapause, and (3) with a plasmapause accompanied with fine-scale density irregularity. We find that (1) without plasmapause the radially inward propagating MS wave can reach ionosphere and continuously propagate to lower altitude if no damping mechanism is considered. The wave properties follow the cold plasma dispersion relation locally along its trajectory. (2) For simulation with a plasmapause with a scale length of 0.006 RE compared to wavelength, only a small fraction of the MS wave power is reflected by the plasmapause. WKB approximation is generally valid for such plasmapause. (3) The multiple fine-scale density irregularities near the outer edge of plasmapause can effectively block the MS wave propagation, resulting in a terminating boundary for MS waves near the plasmapause.

Environment Resource Packets Get Wide Use

ERIC Educational Resources Information Center

Chemical and Engineering News, 1974

1974-01-01

Announces the availability of the resource packet entitled "Noise Pollution," the third in the series prepared by the University of Maryland, and the main topics which will be covered in the remaining three packets. (CC)

Packet Traffic Dynamics Near Onset of Congestion in Data Communication Network Model

NASA Astrophysics Data System (ADS)

Lawniczak, A. T.; Tang, X.

2006-05-01

The dominant technology of data communication networks is the Packet Switching Network (PSN). It is a complex technology organized as various hierarchical layers according to the International Standard Organization (ISO) Open Systems Interconnect (OSI) Reference Model. The Network Layer of the ISO OSI Reference Model is responsible for delivering packets from their sources to their destinations and for dealing with congestion if it arises in a network. Thus, we focus on this layer and present an abstraction of the Network Layer of the ISO OSI Reference Model. Using this abstraction we investigate how onset of traffic congestion is affected for various routing algorithms by changes in network connection topology. We study how aggregate measures of network performance depend on network connection topology and routing. We explore packets traffic spatio-temporal dynamics near the phase transition point from free flow to congestion for various network connection topologies and routing algorithms. We consider static and adaptive routings. We present selected simulation results.

Tropical Animal Tour Packet. Metro.

ERIC Educational Resources Information Center

Metro Washington Park Zoo, Portland, OR. Educational Services Div.

This packet is designed to assist teachers in creating a tropical animals lesson plan that centers around a visit to the zoo. A teacher packet is divided into eight parts: (1) goals and objectives; (2) what to expect at the zoo; (3) student activities (preparatory activities, on-site activities, and follow-up activities); (4) background…

Speech transport for packet telephony and voice over IP

NASA Astrophysics Data System (ADS)

Baker, Maurice R.

1999-11-01

Recent advances in packet switching, internetworking, and digital signal processing technologies have converged to allow realizable practical implementations of packet telephony systems. This paper provides a tutorial on transmission engineering for packet telephony covering the topics of speech coding/decoding, speech packetization, packet data network transport, and impairments which may negatively impact end-to-end system quality. Particular emphasis is placed upon Voice over Internet Protocol given the current popularity and ubiquity of IP transport.

On the stability of lumps and wave collapse in water waves.

PubMed

Akylas, T R; Cho, Yeunwoo

2008-08-13

In the classical water-wave problem, fully localized nonlinear waves of permanent form, commonly referred to as lumps, are possible only if both gravity and surface tension are present. While much attention has been paid to shallow-water lumps, which are generalizations of Korteweg-de Vries solitary waves, the present study is concerned with a distinct class of gravity-capillary lumps recently found on water of finite or infinite depth. In the near linear limit, these lumps resemble locally confined wave packets with envelope and wave crests moving at the same speed, and they can be approximated in terms of a particular steady solution (ground state) of an elliptic equation system of the Benney-Roskes-Davey-Stewartson (BRDS) type, which governs the coupled evolution of the envelope along with the induced mean flow. According to the BRDS equations, however, initial conditions above a certain threshold develop a singularity in finite time, known as wave collapse, due to nonlinear focusing; the ground state, in fact, being exactly at the threshold for collapse suggests that the newly discovered lumps are unstable. In an effort to understand the role of this singularity in the dynamics of lumps, here we consider the fifth-order Kadomtsev-Petviashvili equation, a model for weakly nonlinear gravity-capillary waves on water of finite depth when the Bond number is close to one-third, which also admits lumps of the wave packet type. It is found that an exchange of stability occurs at a certain finite wave steepness, lumps being unstable below but stable above this critical value. As a result, a small-amplitude lump, which is linearly unstable and according to the BRDS equations would be prone to wave collapse, depending on the perturbation, either decays into dispersive waves or evolves into an oscillatory state near a finite-amplitude stable lump.

Digital core based transmitted ultrasonic wave simulation and velocity accuracy analysis

NASA Astrophysics Data System (ADS)

Zhu, Wei; Shan, Rui

2016-06-01

Transmitted ultrasonic wave simulation (TUWS) in a digital core is one of the important elements of digital rock physics and is used to study wave propagation in porous cores and calculate equivalent velocity. When simulating wave propagates in a 3D digital core, two additional layers are attached to its two surfaces vertical to the wave-direction and one planar wave source and two receiver-arrays are properly installed. After source excitation, the two receivers then record incident and transmitted waves of the digital rock. Wave propagating velocity, which is the velocity of the digital core, is computed by the picked peak-time difference between the two recorded waves. To evaluate the accuracy of TUWS, a digital core is fully saturated with gas, oil, and water to calculate the corresponding velocities. The velocities increase with decreasing wave frequencies in the simulation frequency band, and this is considered to be the result of scattering. When the pore fluids are varied from gas to oil and finally to water, the velocity-variation characteristics between the different frequencies are similar, thereby approximately following the variation law of velocities obtained from linear elastic statics simulation (LESS), although their absolute values are different. However, LESS has been widely used. The results of this paper show that the transmission ultrasonic simulation has high relative precision.

A Multi-Agent Framework for Packet Routing in Wireless Sensor Networks

PubMed Central

Ye, Dayon; Zhang, Minji; Yang, Yu

2015-01-01

Wireless sensor networks (WSNs) have been widely investigated in recent years. One of the fundamental issues in WSNs is packet routing, because in many application domains, packets have to be routed from source nodes to destination nodes as soon and as energy efficiently as possible. To address this issue, a large number of routing approaches have been proposed. Although every existing routing approach has advantages, they also have some disadvantages. In this paper, a multi-agent framework is proposed that can assist existing routing approaches to improve their routing performance. This framework enables each sensor node to build a cooperative neighbour set based on past routing experience. Such cooperative neighbours, in turn, can help the sensor to effectively relay packets in the future. This framework is independent of existing routing approaches and can be used to assist many existing routing approaches. Simulation results demonstrate the good performance of this framework in terms of four metrics: average delivery latency, successful delivery ratio, number of live nodes and total sensing coverage. PMID:25928063

Large Amplitude Whistler Waves and Electron Acceleration in the Earth's Radiation Belts: A Review of STEREO and Wind Observations

NASA Technical Reports Server (NTRS)

Cattell, Cynthia; Breneman, A.; Goetz, K.; Kellogg, P.; Kersten, K.; Wygant, J.; Wilson, L. B., III; Looper, Mark D.; Blake, J. Bernard; Roth, I.

2012-01-01

One of the critical problems for understanding the dynamics of Earth's radiation belts is determining the physical processes that energize and scatter relativistic electrons. We review measurements from the Wind/Waves and STEREO S/Waves waveform capture instruments of large amplitude whistler-mode waves. These observations have provided strong evidence that large amplitude (100s mV/m) whistler-mode waves are common during magnetically active periods. The large amplitude whistlers have characteristics that are different from typical chorus. They are usually nondispersive and obliquely propagating, with a large longitudinal electric field and significant parallel electric field. We will also review comparisons of STEREO and Wind wave observations with SAMPEX observations of electron microbursts. Simulations show that the waves can result in energization by many MeV and/or scattering by large angles during a single wave packet encounter due to coherent, nonlinear processes including trapping. The experimental observations combined with simulations suggest that quasilinear theoretical models of electron energization and scattering via small-amplitude waves, with timescales of hours to days, may be inadequate for understanding radiation belt dynamics.

Photonic integrated circuit optical buffer for packet-switched networks.

PubMed

Burmeister, Emily F; Mack, John P; Poulsen, Henrik N; Masanović, Milan L; Stamenić, Biljana; Blumenthal, Daniel J; Bowers, John E

2009-04-13

A chip-scale optical buffer performs autonomous contention resolution for 40-byte packets with 99% packet recovery. The buffer consists of a fast, InP-based 2 x 2 optical switch and a silica-on-silicon low loss delay loop. The buffer is demonstrated in recirculating operation, but may be reconfigured in feed-forward operation for longer packet lengths. The recirculating buffer provides packet storage in integer multiples of the delay length of 12.86 ns up to 64.3 ns with 98% packet recovery. The buffer is used to resolve contention between two 40 Gb/s packet streams using multiple photonic chip optical buffers.

A Genetic Algorithm for the Generation of Packetization Masks for Robust Image Communication

PubMed Central

Zapata-Quiñones, Katherine; Duran-Faundez, Cristian; Gutiérrez, Gilberto; Lecuire, Vincent; Arredondo-Flores, Christopher; Jara-Lipán, Hugo

2017-01-01

Image interleaving has proven to be an effective solution to provide the robustness of image communication systems when resource limitations make reliable protocols unsuitable (e.g., in wireless camera sensor networks); however, the search for optimal interleaving patterns is scarcely tackled in the literature. In 2008, Rombaut et al. presented an interesting approach introducing a packetization mask generator based in Simulated Annealing (SA), including a cost function, which allows assessing the suitability of a packetization pattern, avoiding extensive simulations. In this work, we present a complementary study about the non-trivial problem of generating optimal packetization patterns. We propose a genetic algorithm, as an alternative to the cited work, adopting the mentioned cost function, then comparing it to the SA approach and a torus automorphism interleaver. In addition, we engage the validation of the cost function and provide results attempting to conclude about its implication in the quality of reconstructed images. Several scenarios based on visual sensor networks applications were tested in a computer application. Results in terms of the selected cost function and image quality metric PSNR show that our algorithm presents similar results to the other approaches. Finally, we discuss the obtained results and comment about open research challenges. PMID:28452934

Time-optimum packet scheduling for many-to-one routing in wireless sensor networks

USGS Publications Warehouse

Song, W.-Z.; Yuan, F.; LaHuser, R.

2007-01-01

This paper studies the WSN application scenario with periodical traffic from all sensors to a sink. We present a time-optimum and energy-efficient packet scheduling algorithm and its distributed implementation. We first give a general many-to-one packet scheduling algorithm for wireless networks, and then prove that it is time-optimum and costs max(2N(u1) - 1, N(u 0) -1) time slots, assuming each node reports one unit of data in each round. Here N(u0) is the total number of sensors, while N(u 1) denotes the number of sensors in a sink's largest branch subtree. With a few adjustments, we then show that our algorithm also achieves time-optimum scheduling in heterogeneous scenarios, where each sensor reports a heterogeneous amount of data in each round. Then we give a distributed implementation to let each node calculate its duty-cycle locally and maximize efficiency globally. In this packet scheduling algorithm, each node goes to sleep whenever it is not transceiving, so that the energy waste of idle listening is also eliminated. Finally, simulations are conducted to evaluate network performance using the Qualnet simulator. Among other contributions, our study also identifies the maximum reporting frequency that a deployed sensor network can handle. ??2006 IEEE.

Time-optimum packet scheduling for many-to-one routing in wireless sensor networks

USGS Publications Warehouse

Song, W.-Z.; Yuan, F.; LaHusen, R.; Shirazi, B.

2007-01-01

This paper studies the wireless sensor networks (WSN) application scenario with periodical traffic from all sensors to a sink. We present a time-optimum and energy-efficient packet scheduling algorithm and its distributed implementation. We first give a general many-to-one packet scheduling algorithm for wireless networks, and then prove that it is time-optimum and costs [image omitted], N(u0)-1) time slots, assuming each node reports one unit of data in each round. Here [image omitted] is the total number of sensors, while [image omitted] denotes the number of sensors in a sink's largest branch subtree. With a few adjustments, we then show that our algorithm also achieves time-optimum scheduling in heterogeneous scenarios, where each sensor reports a heterogeneous amount of data in each round. Then we give a distributed implementation to let each node calculate its duty-cycle locally and maximize efficiency globally. In this packet-scheduling algorithm, each node goes to sleep whenever it is not transceiving, so that the energy waste of idle listening is also mitigated. Finally, simulations are conducted to evaluate network performance using the Qualnet simulator. Among other contributions, our study also identifies the maximum reporting frequency that a deployed sensor network can handle.

Biobeam—Multiplexed wave-optical simulations of light-sheet microscopy

PubMed Central

Weigert, Martin; Bundschuh, Sebastian T.

2018-01-01

Sample-induced image-degradation remains an intricate wave-optical problem in light-sheet microscopy. Here we present biobeam, an open-source software package that enables simulation of operational light-sheet microscopes by combining data from 105–106 multiplexed and GPU-accelerated point-spread-function calculations. The wave-optical nature of these simulations leads to the faithful reproduction of spatially varying aberrations, diffraction artifacts, geometric image distortions, adaptive optics, and emergent wave-optical phenomena, and renders image-formation in light-sheet microscopy computationally tractable. PMID:29652879

Two-dimensional simulation of quantum reflection

NASA Astrophysics Data System (ADS)

Galiffi, Emanuele; Sünderhauf, Christoph; DeKieviet, Maarten; Wimberger, Sandro

2017-05-01

A propagation method for the scattering of a quantum wave packet from a potential surface is presented. It is used to model the quantum reflection of single atoms from a corrugated (metallic) surface. Our numerical procedure works well in two spatial dimensions requiring only reasonable amounts of memory and computing time. The effects of the surface corrugation on the reflectivity are investigated via simulations with a paradigm potential. These indicate that our approach should allow for future tests of realistic, effective potentials obtained from theory in a quantitative comparison to experimental data.

Ingestion of Laundry Detergent Packets in Children.

PubMed

Shah, Lindsey Wilson

2016-08-01

Ingestion of laundry detergent packets is an important threat to young children. Because of their developmental stage, toddlers are prone to place these small, colorful packets in their mouths. The packets can easily burst, sending a large volume of viscous, alkaline liquid throughout the oropharynx. Ingestion causes major toxic effects, including depression of the central nervous system, metabolic acidosis, respiratory distress, and dysphagia. Critical care nurses should anticipate these clinical effects and facilitate prompt intervention. Increased understanding of the risks and clinical effects of ingestion of laundry detergent packets will better prepare critical care nurses to provide care for these children. (Critical Care Nurse 2016; 36[4]:70-75). ©2016 American Association of Critical-Care Nurses.

Direct Numerical Simulations of Small-Scale Gravity Wave Instability Dynamics in Variable Stratification and Shear

NASA Astrophysics Data System (ADS)

Mixa, T.; Fritts, D. C.; Laughman, B.; Wang, L.; Kantha, L. H.

2015-12-01

Multiple observations provide compelling evidence that gravity wave dissipation events often occur in multi-scale environments having highly-structured wind and stability profiles extending from the stable boundary layer into the mesosphere and lower thermosphere. Such events tend to be highly localized and thus yield local energy and momentum deposition and efficient secondary gravity wave generation expected to have strong influences at higher altitudes [e.g., Fritts et al., 2013; Baumgarten and Fritts, 2014]. Lidars, radars, and airglow imagers typically cannot achieve the spatial resolution needed to fully quantify these small-scale instability dynamics. Hence, we employ high-resolution modeling to explore these dynamics in representative environments. Specifically, we describe numerical studies of gravity wave packets impinging on a sheet of high stratification and shear and the resulting instabilities and impacts on the gravity wave amplitude and momentum flux for various flow and gravity wave parameters. References: Baumgarten, Gerd, and David C. Fritts (2014). Quantifying Kelvin-Helmholtz instability dynamics observed in noctilucent clouds: 1. Methods and observations. Journal of Geophysical Research: Atmospheres, 119.15, 9324-9337. Fritts, D. C., Wang, L., & Werne, J. A. (2013). Gravity wave-fine structure interactions. Part I: Influences of fine structure form and orientation on flow evolution and instability. Journal of the Atmospheric Sciences, 70(12), 3710-3734.

A novel lost packets recovery scheme based on visual secret sharing

NASA Astrophysics Data System (ADS)

Lu, Kun; Shan, Hong; Li, Zhi; Niu, Zhao

2017-08-01

In this paper, a novel lost packets recovery scheme which encrypts the effective parts of an original packet into two shadow packets based on (2, 2)-threshold XOR-based visual Secret Sharing (VSS) is proposed. The two shadow packets used as watermarks would be embedded into two normal data packets with digital watermarking embedding technology and then sent from one sensor node to another. Each shadow packet would reveal no information of the original packet, which can improve the security of original packet delivery greatly. The two shadow packets which can be extracted from the received two normal data packets delivered from a sensor node can recover the original packet lossless based on XOR-based VSS. The Performance analysis present that the proposed scheme provides essential services as long as possible in the presence of selective forwarding attack. The proposed scheme would not increase the amount of additional traffic, namely, lower energy consumption, which is suitable for Wireless Sensor Network (WSN).

Probing the ionization wave packet and recollision dynamics with an elliptically polarized strong laser field in the nondipole regime

NASA Astrophysics Data System (ADS)

Maurer, J.; Willenberg, B.; Daněk, J.; Mayer, B. W.; Phillips, C. R.; Gallmann, L.; Klaiber, M.; Hatsagortsyan, K. Z.; Keitel, C. H.; Keller, U.

2018-01-01

We explore ionization and rescattering in strong mid-infrared laser fields in the nondipole regime over the full range of polarization ellipticity. In three-dimensional photoelectron momentum distributions (3D PMDs) measured with velocity map imaging spectroscopy, we observe the appearance of a sharp ridge structure along the major polarization axis. Within a certain range of ellipticity, the electrons in this ridge are clearly separated from the two lobes that commonly appear in the PMD with elliptically polarized laser fields. In contrast to the well-known lobes of direct electrons, the sharp ridge is created by Coulomb focusing of the softly recolliding electrons. These ridge electrons are directly related to a counterintuitive shift of the PMD peak opposite to the laser beam propagation direction when the dipole approximation breaks down. The ellipticity-dependent 3D PMDs give access to different ionization and recollision dynamics with appropriate filters in the momentum space. For example, we can extract information about the spread of the initial wave packet and the Coulomb momentum transfer of the rescattering electrons.

Comparison between wavelet and wavelet packet transform features for classification of faults in distribution system

NASA Astrophysics Data System (ADS)

Arvind, Pratul

2012-11-01

The ability to identify and classify all ten types of faults in a distribution system is an important task for protection engineers. Unlike transmission system, distribution systems have a complex configuration and are subjected to frequent faults. In the present work, an algorithm has been developed for identifying all ten types of faults in a distribution system by collecting current samples at the substation end. The samples are subjected to wavelet packet transform and artificial neural network in order to yield better classification results. A comparison of results between wavelet transform and wavelet packet transform is also presented thereby justifying the feature extracted from wavelet packet transform yields promising results. It should also be noted that current samples are collected after simulating a 25kv distribution system in PSCAD software.

Event-triggered resilient filtering with stochastic uncertainties and successive packet dropouts via variance-constrained approach

NASA Astrophysics Data System (ADS)

Jia, Chaoqing; Hu, Jun; Chen, Dongyan; Liu, Yurong; Alsaadi, Fuad E.

2018-07-01

In this paper, we discuss the event-triggered resilient filtering problem for a class of time-varying systems subject to stochastic uncertainties and successive packet dropouts. The event-triggered mechanism is employed with hope to reduce the communication burden and save network resources. The stochastic uncertainties are considered to describe the modelling errors and the phenomenon of successive packet dropouts is characterized by a random variable obeying the Bernoulli distribution. The aim of the paper is to provide a resilient event-based filtering approach for addressed time-varying systems such that, for all stochastic uncertainties, successive packet dropouts and filter gain perturbation, an optimized upper bound of the filtering error covariance is obtained by designing the filter gain. Finally, simulations are provided to demonstrate the effectiveness of the proposed robust optimal filtering strategy.

Simulation of wave propagation in three-dimensional random media

NASA Technical Reports Server (NTRS)

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

1993-01-01

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

Observation of Relativistic Electron Microbursts in Conjunction with Intense Radiation Belt Whistler-Mode Waves

NASA Technical Reports Server (NTRS)

Kersten, K.; Cattell, C. A.; Breneman, A.; Goetz, K.; Kellogg, P. J.; Wygant, J. R.; Wilson, L. B., III; Blake, J. B.; Looper, M. D.; Roth, I.

2011-01-01

We present multi-satellite observations of large amplitude radiation belt whistler-mode waves and relativistic electron precipitation. On separate occasions during the Wind petal orbits and STEREO phasing orbits, Wind and STEREO recorded intense whistler-mode waves in the outer nightside equatorial radiation belt with peak-to-peak amplitudes exceeding 300 mV/m. During these intervals of intense wave activity, SAMPEX recorded relativistic electron microbursts in near magnetic conjunction with Wind and STEREO. This evidence of microburst precipitation occurring at the same time and at nearly the same magnetic local time and L-shell with a bursty temporal structure similar to that of the observed large amplitude wave packets suggests a causal connection between the two phenomena. Simulation studies corroborate this idea, showing that nonlinear wave.particle interactions may result in rapid energization and scattering on timescales comparable to those of the impulsive relativistic electron precipitation.

3D Ultrasonic Wave Simulations for Structural Health Monitoring

NASA Technical Reports Server (NTRS)

Campbell, Leckey Cara A/; Miler, Corey A.; Hinders, Mark K.

2011-01-01

Structural health monitoring (SHM) for the detection of damage in aerospace materials is an important area of research at NASA. Ultrasonic guided Lamb waves are a promising SHM damage detection technique since the waves can propagate long distances. For complicated flaw geometries experimental signals can be difficult to interpret. High performance computing can now handle full 3-dimensional (3D) simulations of elastic wave propagation in materials. We have developed and implemented parallel 3D elastodynamic finite integration technique (3D EFIT) code to investigate ultrasound scattering from flaws in materials. EFIT results have been compared to experimental data and the simulations provide unique insight into details of the wave behavior. This type of insight is useful for developing optimized experimental SHM techniques. 3D EFIT can also be expanded to model wave propagation and scattering in anisotropic composite materials.

Your Paycheck. Cooperative Work Experience Learning Activity Packet: Series on Job Entry and Adjustment; Packet Five.

ERIC Educational Resources Information Center

Herschbach, Dennis R.; And Others

This student booklet is fifth in an illustrated series of eleven learning activity packets for use in teaching job hunting and application procedures and the management of wages to secondary students. Two units are included in this packet: the first describing the various ways of being paid: salary (including overtime and compensatory time),…

Packet utilisation definitions for the ESA XMM mission

NASA Technical Reports Server (NTRS)

Nye, H. R.

1994-01-01

XMM, ESA's X-Ray Multi-Mirror satellite, due for launch at the end of 1999 will be the first ESA scientific spacecraft to implement the ESA packet telecommand and telemetry standards and will be the first ESOC-controlled science mission to take advantage of the new flight control system infrastructure development (based on object-oriented design and distributed-system architecture) due for deployment in 1995. The implementation of the packet standards is well defined at packet transport level. However, the standard relevant to the application level (the ESA Packet Utilization Standard) covers a wide range of on-board 'services' applicable in varying degrees to the needs of XMM. In defining which parts of the ESA PUS to implement, the XMM project first considered the mission objectives and the derived operations concept and went on to identify a minimum set of packet definitions compatible with these aspects. This paper sets the scene as above and then describes the services needed for XMM and the telecommand and telemetry packet types necessary to support each service.

Simulation of femtosecond two-dimensional electronic spectra of conical intersections

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

Krčmář, Jindřich; Gelin, Maxim F.; Domcke, Wolfgang

2015-08-21

We have simulated femtosecond two-dimensional (2D) electronic spectra for an excited-state conical intersection using the wave-function version of the equation-of-motion phase-matching approach. We show that 2D spectra at fixed values of the waiting time provide information on the structure of the vibronic eigenstates of the conical intersection, while the evolution of the spectra with the waiting time reveals predominantly ground-state wave-packet dynamics. The results show that 2D spectra of conical intersection systems differ significantly from those obtained for chromophores with well separated excited-state potential-energy surfaces. The spectral signatures which can be attributed to conical intersections are discussed.

Development of FullWave : Hot Plasma RF Simulation Tool

NASA Astrophysics Data System (ADS)

Svidzinski, Vladimir; Kim, Jin-Soo; Spencer, J. Andrew; Zhao, Liangji; Galkin, Sergei

2017-10-01

Full wave simulation tool, modeling RF fields in hot inhomogeneous magnetized plasma, is being developed. The wave equations with linearized hot plasma dielectric response are solved in configuration space on adaptive cloud of computational points. The nonlocal hot plasma dielectric response is formulated in configuration space without limiting approximations by calculating the plasma conductivity kernel based on the solution of the linearized Vlasov equation in inhomogeneous magnetic field. This approach allows for better resolution of plasma resonances, antenna structures and complex boundaries. The formulation of FullWave and preliminary results will be presented: construction of the finite differences for approximation of derivatives on adaptive cloud of computational points; model and results of nonlocal conductivity kernel calculation in tokamak geometry; results of 2-D full wave simulations in the cold plasma model in tokamak geometry using the formulated approach; results of self-consistent calculations of hot plasma dielectric response and RF fields in 1-D mirror magnetic field; preliminary results of self-consistent simulations of 2-D RF fields in tokamak using the calculated hot plasma conductivity kernel; development of iterative solver for wave equations. Work is supported by the U.S. DOE SBIR program.

A propagation method with adaptive mesh grid based on wave characteristics for wave optics simulation

NASA Astrophysics Data System (ADS)

Tang, Qiuyan; Wang, Jing; Lv, Pin; Sun, Quan

2015-10-01

Propagation simulation method and choosing mesh grid are both very important to get the correct propagation results in wave optics simulation. A new angular spectrum propagation method with alterable mesh grid based on the traditional angular spectrum method and the direct FFT method is introduced. With this method, the sampling space after propagation is not limited to propagation methods no more, but freely alterable. However, choosing mesh grid on target board influences the validity of simulation results directly. So an adaptive mesh choosing method based on wave characteristics is proposed with the introduced propagation method. We can calculate appropriate mesh grids on target board to get satisfying results. And for complex initial wave field or propagation through inhomogeneous media, we can also calculate and set the mesh grid rationally according to above method. Finally, though comparing with theoretical results, it's shown that the simulation result with the proposed method coinciding with theory. And by comparing with the traditional angular spectrum method and the direct FFT method, it's known that the proposed method is able to adapt to a wider range of Fresnel number conditions. That is to say, the method can simulate propagation results efficiently and correctly with propagation distance of almost zero to infinity. So it can provide better support for more wave propagation applications such as atmospheric optics, laser propagation and so on.

Adaptive Learning and Pruning Using Periodic Packet for Fast Invariance Extraction and Recognition

NASA Astrophysics Data System (ADS)

Chang, Sheng-Jiang; Zhang, Bian-Li; Lin, Lie; Xiong, Tao; Shen, Jin-Yuan

2005-02-01

A new learning scheme using a periodic packet as the neuronal activation function is proposed for invariance extraction and recognition of handwritten digits. Simulation results show that the proposed network can extract the invariant feature effectively and improve both the convergence and the recognition rate.

The effect of plasma inhomogeneities on (i) radio emission generation by non-gyrotropic electron beams and (ii) particle acceleration by Langmuir waves

NASA Astrophysics Data System (ADS)

Tsiklauri, David

2015-04-01

Extensive particle-in-cell simulations of fast electron beams injected in a background magnetised plasma with a decreasing density profile were carried out. These simulations were intended to further shed light on a newly proposed mechanism for the generation of electromagnetic waves in type III solar radio bursts [1]. Here recent progress in an alternative to the plasma emission model using Particle-In-Cell, self-consistent electromagnetic wave emission simulations of solar type III radio bursts will be presented. In particular, (i) Fourier space drift (refraction) of non-gyrotropic electron beam-generated wave packets, caused by the density gradient [1,2], (ii) parameter space investigation of numerical runs [3], (iii) concurrent generation of whistler waves [4] and a separate problem of (iv) electron acceleration by Langmuir waves in a background magnetised plasma with an increasing density profile [5] will be discussed. In all considered cases the density inhomogeneity-induced wave refraction plays a crucial role. In the case of non-gyrotropic electron beam, the wave refraction transforms the generated wave packets from standing into freely escaping EM radiation. In the case of electron acceleration by Langmuir waves, a positive density gradient in the direction of wave propagation causes a decrease in the wavenumber, and hence a higher phase velocity vph = ω/k. The k-shifted wave is then subject to absorption by a faster electron by wave-particle interaction. The overall effect is an increased number of high energy electrons in the energy spectrum. [1] D. Tsiklauri, Phys. Plasmas 18, 052903 (2011); http://dx.doi.org/10.1063/1.3590928 [2] H. Schmitz, D. Tsiklauri, Phys. Plasmas 20, 062903 (2013); http://dx.doi.org/10.1063/1.4812453 [3] R. Pechhacker, D. Tsiklauri, Phys. Plasmas 19, 112903 (2012); http://dx.doi.org/10.1063/1.4768429 [4] M. Skender, D. Tsiklauri, Phys. Plasmas 21, 042904 (2014); http://dx.doi.org/10.1063/1.4871723 [5] R. Pechhacker, D. Tsiklauri

Simulation of wave propagation in three-dimensional random media

NASA Astrophysics Data System (ADS)

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

1995-04-01

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

Hybrid Packet-Pheromone-Based Probabilistic Routing for Mobile Ad Hoc Networks

NASA Astrophysics Data System (ADS)

Kashkouli Nejad, Keyvan; Shawish, Ahmed; Jiang, Xiaohong; Horiguchi, Susumu

Ad-Hoc networks are collections of mobile nodes communicating using wireless media without any fixed infrastructure. Minimal configuration and quick deployment make Ad-Hoc networks suitable for emergency situations like natural disasters or military conflicts. The current Ad-Hoc networks can only support either high mobility or high transmission rate at a time because they employ static approaches in their routing schemes. However, due to the continuous expansion of the Ad-Hoc network size, node-mobility and transmission rate, the development of new adaptive and dynamic routing schemes has become crucial. In this paper we propose a new routing scheme to support high transmission rates and high node-mobility simultaneously in a big Ad-Hoc network, by combining a new proposed packet-pheromone-based approach with the Hint Based Probabilistic Protocol (HBPP) for congestion avoidance with dynamic path selection in packet forwarding process. Because of using the available feedback information, the proposed algorithm does not introduce any additional overhead. The extensive simulation-based analysis conducted in this paper indicates that the proposed algorithm offers small packet-latency and achieves a significantly higher delivery probability in comparison with the available Hint-Based Probabilistic Protocol (HBPP).

Design of a bounded wave EMP (Electromagnetic Pulse) simulator

NASA Astrophysics Data System (ADS)

Sevat, P. A. A.

1989-06-01

Electromagnetic Pulse (EMP) simulators are used to simulate the EMP generated by a nuclear weapon and to harden equipment against the effects of EMP. At present, DREO has a 1 m EMP simulator for testing computer terminal size equipment. To develop the R and D capability for testing larger objects, such as a helicopter, a much bigger threat level facility is required. This report concerns the design of a bounded wave EMP simulator suitable for testing large size equipment. Different types of simulators are described and their pros and cons are discussed. A bounded wave parallel plate type simulator is chosen for it's efficiency and the least environmental impact. Detailed designs are given for 6 m and 10 m parallel plate type wire grid simulators. Electromagnetic fields inside and outside the simulators are computed. Preliminary specifications for a pulse generator required for the simulator are also given. Finally, the electromagnetic fields radiated from the simulator are computed and discussed.

Computational study of nonlinear plasma waves. [plasma simulation model applied to electrostatic waves in collisionless plasma

NASA Technical Reports Server (NTRS)

Matsuda, Y.

1974-01-01

A low-noise plasma simulation model is developed and applied to a series of linear and nonlinear problems associated with electrostatic wave propagation in a one-dimensional, collisionless, Maxwellian plasma, in the absence of magnetic field. It is demonstrated that use of the hybrid simulation model allows economical studies to be carried out in both the linear and nonlinear regimes with better quantitative results, for comparable computing time, than can be obtained by conventional particle simulation models, or direct solution of the Vlasov equation. The characteristics of the hybrid simulation model itself are first investigated, and it is shown to be capable of verifying the theoretical linear dispersion relation at wave energy levels as low as .000001 of the plasma thermal energy. Having established the validity of the hybrid simulation model, it is then used to study the nonlinear dynamics of monochromatic wave, sideband instability due to trapped particles, and satellite growth.

Development of optical packet and circuit integrated ring network testbed.

PubMed

Furukawa, Hideaki; Harai, Hiroaki; Miyazawa, Takaya; Shinada, Satoshi; Kawasaki, Wataru; Wada, Naoya

2011-12-12

We developed novel integrated optical packet and circuit switch-node equipment. Compared with our previous equipment, a polarization-independent 4 × 4 semiconductor optical amplifier switch subsystem, gain-controlled optical amplifiers, and one 100 Gbps optical packet transponder and seven 10 Gbps optical path transponders with 10 Gigabit Ethernet (10GbE) client-interfaces were newly installed in the present system. The switch and amplifiers can provide more stable operation without equipment adjustments for the frequent polarization-rotations and dynamic packet-rate changes of optical packets. We constructed an optical packet and circuit integrated ring network testbed consisting of two switch nodes for accelerating network development, and we demonstrated 66 km fiber transmission and switching operation of multiplexed 14-wavelength 10 Gbps optical paths and 100 Gbps optical packets encapsulating 10GbE frames. Error-free (frame error rate < 1×10(-4)) operation was achieved with optical packets of various packet lengths and packet rates, and stable operation of the network testbed was confirmed. In addition, 4K uncompressed video streaming over OPS links was successfully demonstrated. © 2011 Optical Society of America

Wireless Avionics Packet to Support Fault Tolerance for Flight Applications

NASA Technical Reports Server (NTRS)

Block, Gary L.; Whitaker, William D.; Dillon, James W.; Lux, James P.; Ahmad, Mohammad

2009-01-01

In this protocol and packet format, data traffic is monitored by all network interfaces to determine the health of transmitter and subsystems. When failures are detected, the network inter face applies its recover y policies to provide continued service despite the presence of faults. The protocol, packet format, and inter face are independent of the data link technology used. The current demonstration system supports both commercial off-the-shelf wireless connections and wired Ethernet connections. Other technologies such as 1553 or serial data links can be used for the network backbone. The Wireless Avionics packet is divided into three parts: a header, a data payload, and a checksum. The header has the following components: magic number, version, quality of service, time to live, sending transceiver, function code, payload length, source Application Data Interface (ADI) address, destination ADI address, sending node address, target node address, and a sequence number. The magic number is used to identify WAV packets, and allows the packet format to be updated in the future. The quality of service field allows routing decisions to be made based on this value and can be used to route critical management data over a dedicated channel. The time to live value is used to discard misrouted packets while the source transceiver is updated at each hop. This information is used to monitor the health of each transceiver in the network. To identify the packet type, the function code is used. Besides having a regular data packet, the system supports diagnostic packets for fault detection and isolation. The payload length specifies the number of data bytes in the payload, and this supports variable-length packets in the network. The source ADI is the address of the originating interface. This can be used by the destination application to identify the originating source of the packet where the address consists of a subnet, subsystem class within the subnet, a subsystem unit

STEREO observations of insitu waves in the vicinity of interplanetary shocks

NASA Astrophysics Data System (ADS)

Golla, T.; MacDowall, R. J.

2017-12-01

We present the high time resolution observations of the in situ waves obtained by the time domain sampler (TDS) of the WAVES experiment on the STEREO spacecraft in the vicinity of typical quasi-perpendicular super-critical interplanetary shocks. We show that often Langmuir waves occur as coherent one dimensional magnetic field aligned wave packets in the upstream regions and persist over large distances. The characteristics of these wave packets are consistent with those of Langmuir solitons formed as a result of oscillatting two stream instability (OTSI). Very intense high frequency waves which are completely different from Langmuir waves occur in the transition regions. These waves occur as very incoherent emissions and exhibit broad fundamental and second harmonic spectral peaks. We identify these waves as electron acoustic waves excited by the electron beams in the transition regions. We also show that very intense low frequency ion sound waves occur in the downstream regions. We discuss the implications of these observations on the theories of (1) strong Langmuir turbulence, (2) beam stabilization, (3) emission mechanisms of solar type II radio bursts, (4) wave-particle interactions responsible for collisionless dissipation, and (5) heating of the downstream plasmas.

Energy Conservation Activity Packet, Grade 3.

ERIC Educational Resources Information Center

Bakke, Ruth

This activity packet for grade 3 is one of a series developed in response to the concern for energy conservation. It contains activities that stress an energy conservation ethic and includes many values clarification activities for grade three. The packet is divided into two parts and provides the teacher with background information, concepts and…

Gravity wave generation from jets and fronts: idealized and real-case simulations

NASA Astrophysics Data System (ADS)

Plougonven, Riwal; Arsac, Antonin; Hertzog, Albert; Guez, Lionel; Vial, François

2010-05-01

The generation of gravity waves from jets and fronts remains an outstanding issue in the dynamics of the atmosphere. It is important to explain and quantify this emission because of the several impacts of these waves, in particular the induced momentum fluxes towards the middle atmosphere, and their contribution to turbulence and mixing, e.g. in the region of the tropopause. Yet, the mechanisms at the origin of these waves have been difficult to identify, the fundamental reason for this being the separation between the time scales of balanced motions and gravity waves. Recent simulations of idealized baroclinic life cycles and of dipoles have provided insights into the mechanisms determining the characteristics and the amplitude of gravity waves emitted by jets. It has been shown in particular that the environmental strain and shear play a crucial role in determining the characteristics and location of the emitted waves, emphasizing jet exit regions for the appearance of coherent low-frequency waves. It has also been shown how advection of relatively small-scales allow to overcome the separation of time scales alluded to above. Recent results, remaining open questions and ongoing work on these idealized simulations will be briefly summarized. Nevertheless, unavoidable shortcomings of such idealized simulations include the sensitivity of the emitted waves to model setup (resolution, diffusion, parameterizations) and uncertainty regarding the realism of this aspect of the simulations. Hence, it is necessary to compare simulations with observations in order to assess their relevance. Such comparison has been undertaken using the dataset from the Vorcore campaign (Sept. 2005 - Feb. 2006, Hertzog, J. Atmos. Ocean. Techno. 2007) during which 27 superpressure balloons drifted as quasi-Lagrangian tracers in the lower stratosphere above Antarctica and the Southern Ocean. High-resolution simulations (dx = 20 km) have been carried out using the Weather Research and Forecast

Getting a Raise. Cooperative Work Experience Learning Activity Packet: Series on Job Entry and Adjustment; Packet Seven.

ERIC Educational Resources Information Center

Herschbach, Dennis R.; And Others

This student booklet is seventh in an illustrated series of eleven learning activity packets for use in teaching job hunting and application procedures and the management of wages to secondary students. Two units are included in this packet, one explaining the differences between periodic and merit pay increases and between flat amount and…

Simulating Freak Waves in the Ocean with CFD Modeling

NASA Astrophysics Data System (ADS)

Manolidis, M.; Orzech, M.; Simeonov, J.

2017-12-01

Rogue, or freak, waves constitute an active topic of research within the world scientific community, as various maritime authorities around the globe seek to better understand and more accurately assess the risks that the occurrence of such phenomena entail. Several experimental studies have shed some light on the mechanics of rogue wave formation. In our work we numerically simulate the formation of such waves in oceanic conditions by means of Computational Fluid Dynamics (CFD) software. For this purpose we implement the NHWAVE and OpenFOAM software packages. Both are non-hydrostatic, turbulent flow solvers, but NHWAVE implements a shock-capturing scheme at the free surface-interface, while OpenFOAM utilizes the Volume Of Fluid (VOF) method. NHWAVE has been shown to accurately reproduce highly nonlinear surface wave phenomena, such as soliton propagation and wave shoaling. We conducted a range of tests simulating rogue wave formation and horizontally varying currents to evaluate and compare the capabilities of the two software packages. Then we used each model to investigate the effect of ocean currents and current gradients on the formation of rogue waves. We present preliminary results.

Guided waves in anisotropic and quasi-isotropic aerospace composites: three-dimensional simulation and experiment.

PubMed

Leckey, Cara A C; Rogge, Matthew D; Raymond Parker, F

2014-01-01

Three-dimensional (3D) elastic wave simulations can be used to investigate and optimize nondestructive evaluation (NDE) and structural health monitoring (SHM) ultrasonic damage detection techniques for aerospace materials. 3D anisotropic elastodynamic finite integration technique (EFIT) has been implemented for ultrasonic waves in carbon fiber reinforced polymer (CFRP) composite laminates. This paper describes 3D EFIT simulations of guided wave propagation in undamaged and damaged anisotropic and quasi-isotropic composite plates. Comparisons are made between simulations of guided waves in undamaged anisotropic composite plates and both experimental laser Doppler vibrometer (LDV) wavefield data and dispersion curves. Time domain and wavenumber domain comparisons are described. Wave interaction with complex geometry delamination damage is then simulated to investigate how simulation tools incorporating realistic damage geometries can aid in the understanding of wave interaction with CFRP damage. In order to move beyond simplistic assumptions of damage geometry, volumetric delamination data acquired via X-ray microfocus computed tomography is directly incorporated into the simulation. Simulated guided wave interaction with the complex geometry delamination is compared to experimental LDV time domain data and 3D wave interaction with the volumetric damage is discussed. Published by Elsevier B.V.

Numerical Simulation of Coronal Waves Interacting with Coronal Holes. III. Dependence on Initial Amplitude of the Incoming Wave

NASA Astrophysics Data System (ADS)

Piantschitsch, Isabell; Vršnak, Bojan; Hanslmeier, Arnold; Lemmerer, Birgit; Veronig, Astrid; Hernandez-Perez, Aaron; Čalogović, Jaša

2018-06-01

We performed 2.5D magnetohydrodynamic (MHD) simulations showing the propagation of fast-mode MHD waves of different initial amplitudes and their interaction with a coronal hole (CH), using our newly developed numerical code. We find that this interaction results in, first, the formation of reflected, traversing, and transmitted waves (collectively, secondary waves) and, second, in the appearance of stationary features at the CH boundary. Moreover, we observe a density depletion that is moving in the opposite direction of the incoming wave. We find a correlation between the initial amplitude of the incoming wave and the amplitudes of the secondary waves as well as the peak values of the stationary features. Additionally, we compare the phase speed of the secondary waves and the lifetime of the stationary features to observations. Both effects obtained in the simulation, the evolution of secondary waves, as well as the formation of stationary fronts at the CH boundary, strongly support the theory that coronal waves are fast-mode MHD waves.

Observationally constrained modeling of sound in curved ocean internal waves: examination of deep ducting and surface ducting at short range.

PubMed

Duda, Timothy F; Lin, Ying-Tsong; Reeder, D Benjamin

2011-09-01

A study of 400 Hz sound focusing and ducting effects in a packet of curved nonlinear internal waves in shallow water is presented. Sound propagation roughly along the crests of the waves is simulated with a three-dimensional parabolic equation computational code, and the results are compared to measured propagation along fixed 3 and 6 km source/receiver paths. The measurements were made on the shelf of the South China Sea northeast of Tung-Sha Island. Construction of the time-varying three-dimensional sound-speed fields used in the modeling simulations was guided by environmental data collected concurrently with the acoustic data. Computed three-dimensional propagation results compare well with field observations. The simulations allow identification of time-dependent sound forward scattering and ducting processes within the curved internal gravity waves. Strong acoustic intensity enhancement was observed during passage of high-amplitude nonlinear waves over the source/receiver paths, and is replicated in the model. The waves were typical of the region (35 m vertical displacement). Two types of ducting are found in the model, which occur asynchronously. One type is three-dimensional modal trapping in deep ducts within the wave crests (shallow thermocline zones). The second type is surface ducting within the wave troughs (deep thermocline zones). © 2011 Acoustical Society of America

Initial Simulations of RF Waves in Hot Plasmas Using the FullWave Code

NASA Astrophysics Data System (ADS)

Zhao, Liangji; Svidzinski, Vladimir; Spencer, Andrew; Kim, Jin-Soo

2017-10-01

FullWave is a simulation tool that models RF fields in hot inhomogeneous magnetized plasmas. The wave equations with linearized hot plasma dielectric response are solved in configuration space on adaptive cloud of computational points. The nonlocal hot plasma dielectric response is formulated by calculating the plasma conductivity kernel based on the solution of the linearized Vlasov equation in inhomogeneous magnetic field. In an rf field, the hot plasma dielectric response is limited to the distance of a few particles' Larmor radii, near the magnetic field line passing through the test point. The localization of the hot plasma dielectric response results in a sparse matrix of the problem thus significantly reduces the size of the problem and makes the simulations faster. We will present the initial results of modeling of rf waves using the Fullwave code, including calculation of nonlocal conductivity kernel in 2D Tokamak geometry; the interpolation of conductivity kernel from test points to adaptive cloud of computational points; and the results of self-consistent simulations of 2D rf fields using calculated hot plasma conductivity kernel in a tokamak plasma with reduced parameters. Work supported by the US DOE ``SBIR program.

Adaptive UEP and Packet Size Assignment for Scalable Video Transmission over Burst-Error Channels

NASA Astrophysics Data System (ADS)

Lee, Chen-Wei; Yang, Chu-Sing; Su, Yih-Ching

2006-12-01

This work proposes an adaptive unequal error protection (UEP) and packet size assignment scheme for scalable video transmission over a burst-error channel. An analytic model is developed to evaluate the impact of channel bit error rate on the quality of streaming scalable video. A video transmission scheme, which combines the adaptive assignment of packet size with unequal error protection to increase the end-to-end video quality, is proposed. Several distinct scalable video transmission schemes over burst-error channel have been compared, and the simulation results reveal that the proposed transmission schemes can react to varying channel conditions with less and smoother quality degradation.

A packet data compressor

NASA Technical Reports Server (NTRS)

Grunes, Mitchell R.; Choi, Junho

1995-01-01

We are in the preliminary stages of creating an operational system for losslessly compressing packet data streams. The end goal is to reduce costs. Real world constraints include transmission in the presence of error, tradeoffs between the costs of compression and the costs of transmission and storage, and imperfect knowledge of the data streams to be transmitted. The overall method is to bring together packets of similar type, split the data into bit fields, and test a large number of compression algorithms. Preliminary results are very encouraging, typically offering compression factors substantially higher than those obtained with simpler generic byte stream compressors, such as Unix Compress and HA 0.98.

106-17 Telemetry Standards Chapter 7 Packet Telemetry Downlink

DTIC Science & Technology

2017-07-31

Acronyms IP Internet Protocol IPv4 Internet Protocol, Version 4 IPv6 Internet Protocol, Version 6 LLP low-latency PTDP MAC media access control...o 4’b0101: PT Internet Protocol (IP) Packet o 4’b0110: PT Chapter 24 TmNSMessage Packet o 4’b0111 – 4’b1111: Reserved • Fragment (bits 17 – 16...packet is defined as a free -running 12-bit counter. The PT test counter packet shall consist of one 12-bit word and shall be encoded as one 24-bit

Numerical study of interfacial solitary waves propagating under an elastic sheet

PubMed Central

Wang, Zhan; Părău, Emilian I.; Milewski, Paul A.; Vanden-Broeck, Jean-Marc

2014-01-01

Steady solitary and generalized solitary waves of a two-fluid problem where the upper layer is under a flexible elastic sheet are considered as a model for internal waves under an ice-covered ocean. The fluid consists of two layers of constant densities, separated by an interface. The elastic sheet resists bending forces and is mathematically described by a fully nonlinear thin shell model. Fully localized solitary waves are computed via a boundary integral method. Progression along the various branches of solutions shows that barotropic (i.e. surface modes) wave-packet solitary wave branches end with the free surface approaching the interface. On the other hand, the limiting configurations of long baroclinic (i.e. internal) solitary waves are characterized by an infinite broadening in the horizontal direction. Baroclinic wave-packet modes also exist for a large range of amplitudes and generalized solitary waves are computed in a case of a long internal mode in resonance with surface modes. In contrast to the pure gravity case (i.e without an elastic cover), these generalized solitary waves exhibit new Wilton-ripple-like periodic trains in the far field. PMID:25104909

Packet Controller For Wireless Headset

NASA Technical Reports Server (NTRS)

Christensen, Kurt K.; Swanson, Richard J.

1993-01-01

Packet-message controller implements communications protocol of network of wireless headsets. Designed for headset application, readily adapted to other uses; slight modification enables controller to implement Integrated Services Digital Network (ISDN) X.25 protocol, giving far-reaching applications in telecommunications. Circuit converts continuous voice signals into digital packets of data and vice versa. Operates in master or slave mode. Controller reduced to single complementary metal oxide/semiconductor integrated-circuit chip. Occupies minimal space in headset and consumes little power, extending life of headset battery.

Quantum mechanics of neutrino oscillations - hand waving for pedestrians.

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

Lipkin, H. J.

1998-12-22

Why Hand Waving? All calculations in books describe oscillations in time. But real experiments don't measure time. Hand waving is used to convert the results of a ''gedanken time experiment'' to the result of a real experiment measuring oscillations in space. Right hand waving gives the right answer; wrong hand waving gives the wrong answer. Many papers use wrong handwaving to get wrong answers. This talk explains how to do it right and also answers the following questions: (1) A neutrino which is a mixture of two mass eigenstates is emitted with muon in the decay of a pion atmore » rest. This is a ''missing mass experiment'' where the muon energy determines the neutrino mass. Why are the two mass states coherent? (2) A neutrino which is a mixture of two mass eigenstates is emitted at time t=0. The two mass eigenstates move with different velocities and arrive at the detector at different times. Why are the two mass states coherent? (3) A neutrino is a mixture of two overlapping wave packets with different masses moving with different velocities. Will the wave packets eventually separate? If yes, when?« less

Equatorial waves simulated by the NCAR community climate model

NASA Technical Reports Server (NTRS)

Cheng, Xinhua; Chen, Tsing-Chang

1988-01-01

The equatorial planetary waves simulated by the NCAR CCM1 general circulation model were investigated in terms of space-time spectral analysis (Kao, 1968; Hayashi, 1971, 1973) and energetic analysis (Hayashi, 1980). These analyses are particularly applied to grid-point data on latitude circles. In order to test some physical factors which may affect the generation of tropical transient planetary waves, three different model simulations with the CCM1 (the control, the no-mountain, and the no-cloud experiments) were analyzed.

Accounting Clerk Guide, Exercise and Worksheet Packet--Part I.

ERIC Educational Resources Information Center

Foster, Brian; And Others

The exercise and worksheet packet is part of an eight volume unit for grades 10, 11, and 12, designed for individualized progression in preparing students for entry into the occupation of accounting clerk. The exercise and worksheet packet contains a copy of every worksheet in the learner packet for lessons 1 through 11 so that the instructor can…

Instrument for measurement of vacuum in sealed thin wall packets

DOEpatents

Kollie, T.G.; Thacker, L.H.; Fine, H.A.

1993-10-05

An instrument is described for the measurement of vacuum within sealed packets, the packets having a wall sufficiently thin that it can be deformed by the application of an external vacuum to small area thereof. The instrument has a detector head for placement against the deformable wall of the packet to apply the vacuum in a controlled manner to accomplish a limited deformation or lift of the wall, with this deformation or lift monitored by the application of light as via a bifurcated light pipe. Retro-reflected light through the light pipe is monitored with a photo detector. An abrupt change (e.g., a decrease) of retro-reflected light signals the wall movement such that the value of the vacuum applied through the head to achieve this initiation of movement is equal to the vacuum within the packet. In a preferred embodiment a vacuum reference plate is placed beneath the packet to ensure that no deformation occurs on the reverse surface of the packet. A packet production line model is also described. 3 figures.

Instrument for measurement of vacuum in sealed thin wall packets

DOEpatents

Kollie, Thomas G.; Thacker, Louis H.; Fine, H. Alan

1993-01-01

An instrument for the measurement of vacuum within sealed packets 12, the packets 12 having a wall 14 sufficiently thin that it can be deformed by the application of an external vacuum to small area thereof. The instrument has a detector head 18 for placement against the deformable wall 14 of the packet to apply the vacuum in a controlled manner to accomplish a limited deformation or lift of the wall 14, with this deformation or lift monitored by the application of light as via a bifurcated light pipe 20. Retro-reflected light through the light pipe is monitored with a photo detector 26. An abrupt change (e.g., a decrease) of retro-reflected light signals the wall movement such that the value of the vacuum applied through the head 18 to achieve this initiation of movement is equal to the vacuum Within the packet 12. In a preferred embodiment a vacuum reference plate 44 is placed beneath the packet 12 to ensure that no deformation occurs on the reverse surface 16 of the packet. A packet production line model is also described.

Determination of detonation wave boundary angles via hydrocode simulations using CREST

NASA Astrophysics Data System (ADS)

Whitworth, N. J.; Childs, M.

2017-01-01

A key input parameter to Detonation Shock Dynamics models is the angle that the propagating detonation wave makes with the charge edge. This is commonly referred to as the boundary angle, and is a property of the explosive/confiner material combination. Such angles can be determined: (i) experimentally from measured detonation wave-shapes, (ii) theoretically, or (iii) via hydrocode simulations using a reactive burn model. Of these approaches: (i) is difficult because of resolution, (ii) breaks down for certain configurations, while (iii) requires a well validated model. In this paper, the CREST reactive burn model, which has previously been successful in modelling a wide range of explosive phenomena, is used to simulate recent Detonation Confinement Sandwich Tests conducted at LANL using the insensitive high explosive PBX 9502. Simulated detonation wave-shapes in PBX 9502 for a number of different confiner materials and combinations closely match those recorded from the experiments. Boundary angles were subsequently extracted from the simulated results via a wave-shape analysis toolkit. The results shown demonstrate the usefulness of CREST in determining detonation wave boundary angles for a range of explosive/confiner material combinations.

Photodissociation of water. II. Wave packet calculations for the photofragmentation of H2O and D2O in the B˜ band

NASA Astrophysics Data System (ADS)

van Harrevelt, Rob; van Hemert, Marc C.

2000-04-01

A complete three-dimensional quantum mechanical description of the photodissociation of water in the B˜ band, starting from its rotational ground state, is presented. In order to include B˜-X˜ vibronic coupling and the B˜-Ã Renner-Teller coupling, diabatic electronic states have been constructed from adiabatic electronic states and matrix elements of the electronic angular momentum operators, following the procedure developed by A. J. Dobbyn and P. J. Knowles [Mol. Phys. 91, 1107 (1997)], using the ab initio results discussed in the preceding paper. The dynamics is studied using wave packet methods, and the evolution of the time-dependent wave function is discussed in detail. Results for the H2O and D2O absorption spectra, OH(A)/OH(X) and OD(A)/OD(X) branching ratios, and rovibrational distributions of the OH and OD fragments are presented and compared with available experimental data. The present theoretical results agree at least qualitatively with the experiments. The calculations show that the absorption spectrum and the product state distributions are strongly influenced by long-lived resonances on the adiabatic B˜ state. It is also shown that molecular rotation plays an important role in the photofragmentation process, due to both the Renner-Teller B˜-X˜ mixing, and the strong effect of out-of-plane molecular rotations (K>0) on the dynamics at near linear HOH and HHO geometries.

Disk Operating System--DOS. Teacher Packet. Learning Activity Packets.

ERIC Educational Resources Information Center

Oklahoma State Dept. of Vocational and Technical Education, Stillwater. Curriculum and Instructional Materials Center.

The Learning Activity Packets (LAPs) contained in this manual are designed to assist the beginning user in understanding DOS (Disk Operating System). LAPs will not work with any version below DOS Version 3.0 and do not address the enhanced features of versions 4.0 or higher. These elementary activities cover only the DOS commands necessary to…

Design and application of discrete wavelet packet transform based multiresolution controller for liquid level system.

PubMed

Paul, Rimi; Sengupta, Anindita

2017-11-01

A new controller based on discrete wavelet packet transform (DWPT) for liquid level system (LLS) has been presented here. This controller generates control signal using node coefficients of the error signal which interprets many implicit phenomena such as process dynamics, measurement noise and effect of external disturbances. Through simulation results on LLS problem, this controller is shown to perform faster than both the discrete wavelet transform based controller and conventional proportional integral controller. Also, it is more efficient in terms of its ability to provide better noise rejection. To overcome the wind up phenomenon by considering the saturation due to presence of actuator, anti-wind up technique is applied to the conventional PI controller and compared to the wavelet packet transform based controller. In this case also, packet controller is found better than the other ones. This similar work has been extended for analogous first order RC plant as well as second order plant also. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.

Quasi-light storage for optical data packets.

PubMed

Schneider, Thomas; Preußler, Stefan

2014-02-06

Today's telecommunication is based on optical packets which transmit the information in optical fiber networks around the world. Currently, the processing of the signals is done in the electrical domain. Direct storage in the optical domain would avoid the transfer of the packets to the electrical and back to the optical domain in every network node and, therefore, increase the speed and possibly reduce the energy consumption of telecommunications. However, light consists of photons which propagate with the speed of light in vacuum. Thus, the storage of light is a big challenge. There exist some methods to slow down the speed of the light, or to store it in excitations of a medium. However, these methods cannot be used for the storage of optical data packets used in telecommunications networks. Here we show how the time-frequency-coherence, which holds for every signal and therefore for optical packets as well, can be exploited to build an optical memory. We will review the background and show in detail and through examples, how a frequency comb can be used for the copying of an optical packet which enters the memory. One of these time domain copies is then extracted from the memory by a time domain switch. We will show this method for intensity as well as for phase modulated signals.

Simulation of wind wave growth with reference source functions

NASA Astrophysics Data System (ADS)

Badulin, Sergei I.; Zakharov, Vladimir E.; Pushkarev, Andrei N.

2013-04-01

We present results of extensive simulations of wind wave growth with the so-called reference source function in the right-hand side of the Hasselmann equation written as follows First, we use Webb's algorithm [8] for calculating the exact nonlinear transfer function Snl. Second, we consider a family of wind input functions in accordance with recent consideration [9] ( )s S = ?(k)N , ?(k) = ? ? ?- f (?). in k 0 ?0 in (2) Function fin(?) describes dependence on angle ?. Parameters in (2) are tunable and determine magnitude (parameters ?0, ?0) and wave growth rate s [9]. Exponent s plays a key role in this study being responsible for reference scenarios of wave growth: s = 4-3 gives linear growth of wave momentum, s = 2 - linear growth of wave energy and s = 8-3 - constant rate of wave action growth. Note, the values are close to ones of conventional parameterizations of wave growth rates (e.g. s = 1 for [7] and s = 2 for [5]). Dissipation function Sdiss is chosen as one providing the Phillips spectrum E(?) ~ ?5 at high frequency range [3] (parameter ?diss fixes a dissipation scale of wind waves) Sdiss = Cdissμ4w?N (k)θ(? - ?diss) (3) Here frequency-dependent wave steepness μ2w = E(?,?)?5-g2 makes this function to be heavily nonlinear and provides a remarkable property of stationary solutions at high frequencies: the dissipation coefficient Cdiss should keep certain value to provide the observed power-law tails close to the Phillips spectrum E(?) ~ ?-5. Our recent estimates [3] give Cdiss ? 2.0. The Hasselmann equation (1) with the new functions Sin, Sdiss (2,3) has a family of self-similar solutions of the same form as previously studied models [1,3,9] and proposes a solid basis for further theoretical and numerical study of wave evolution under action of all the physical mechanisms: wind input, wave dissipation and nonlinear transfer. Simulations of duration- and fetch-limited wind wave growth have been carried out within the above model setup to check its

Optical Kerr spatiotemporal dark extreme waves

NASA Astrophysics Data System (ADS)

Wabnitz, Stefan; Kodama, Yuji; Baronio, Fabio

2018-02-01

We study the existence and propagation of multidimensional dark non-diffractive and non-dispersive spatiotemporal optical wave-packets in nonlinear Kerr media. We report analytically and confirm numerically the properties of spatiotemporal dark lines, X solitary waves and lump solutions of the (2 + 1)D nonlinear Schr odinger equation (NLSE). Dark lines, X waves and lumps represent holes of light on a continuous wave background. These solitary waves are derived by exploiting the connection between the (2 + 1)D NLSE and a well-known equation of hydrodynamics, namely the (2+1)D Kadomtsev-Petviashvili (KP) equation. This finding opens a novel path for the excitation and control of spatiotemporal optical solitary and rogue waves, of hydrodynamic nature.

Sports Medicine. Clinical Rotation. Instructor's Packet and Student Study Packet.

ERIC Educational Resources Information Center

Texas Univ., Austin. Extension Instruction and Materials Center.

The materials in this packet are for a course designed to provide individualized classroom study for a specific area of clinical rotation--sports medicine. The instructor's manual describes the learning objectives together with a list of reference materials that should be provided for completion of the student worksheets, and lists suggested…

A multi-ring optical packet and circuit integrated network with optical buffering.

PubMed

Furukawa, Hideaki; Shinada, Satoshi; Miyazawa, Takaya; Harai, Hiroaki; Kawasaki, Wataru; Saito, Tatsuhiko; Matsunaga, Koji; Toyozumi, Tatuya; Wada, Naoya

2012-12-17

We newly developed a 3 × 3 integrated optical packet and circuit switch-node. Optical buffers and burst-mode erbium-doped fiber amplifiers with the gain flatness are installed in the 3 × 3 switch-node. The optical buffer can prevent packet collisions and decrease packet loss. We constructed a multi-ring optical packet and circuit integrated network testbed connecting two single-ring networks and a client network by the 3 × 3 switch-node. For the first time, we demonstrated 244 km fiber transmission and 5-node hopping of multiplexed 14-wavelength 10 Gbps optical paths and 100 Gbps optical packets encapsulating 10 Gigabit Ethernet frames on the testbed. Error-free (frame error rate < 1 × 10(-4)) operation was achieved with optical packets of various packet lengths. In addition, successful avoidance of packet collisions by optical buffers was confirmed.

Peri-Elastodynamic Simulations of Guided Ultrasonic Waves in Plate-Like Structure with Surface Mounted PZT.

PubMed

Patra, Subir; Ahmed, Hossain; Banerjee, Sourav

2018-01-18

Peridynamic based elastodynamic computation tool named Peri-elastodynamics is proposed herein to simulate the three-dimensional (3D) Lamb wave modes in materials for the first time. Peri-elastodynamics is a nonlocal meshless approach which is a scale-independent generalized technique to visualize the acoustic and ultrasonic waves in plate-like structure, micro-electro-mechanical systems (MEMS) and nanodevices for their respective characterization. In this article, the characteristics of the fundamental Lamb wave modes are simulated in a sample plate-like structure. Lamb wave modes are generated using a surface mounted piezoelectric (PZT) transducer which is actuated from the top surface. The proposed generalized Peri-elastodynamics method is not only capable of simulating two dimensional (2D) in plane wave under plane strain condition formulated previously but also capable of accurately simulating the out of plane Symmetric and Antisymmetric Lamb wave modes in plate like structures in 3D. For structural health monitoring (SHM) of plate-like structures and nondestructive evaluation (NDE) of MEMS devices, it is necessary to simulate the 3D wave-damage interaction scenarios and visualize the different wave features due to damages. Hence, in addition, to simulating the guided ultrasonic wave modes in pristine material, Lamb waves were also simulated in a damaged plate. The accuracy of the proposed technique is verified by comparing the modes generated in the plate and the mode shapes across the thickness of the plate with theoretical wave analysis.

A Bibliography of Packet Radio Literature.

DTIC Science & Technology

1984-03-01

r r* C.C.4. W . . . . . . . . .. . . . Gafni, E. and D. Bertsekas, "Distributed Algorithms for Generating Loop-Free Routes in Networks with Frequently...December 1980). Leiner, B., K. Klemba, and J. Tornow , "Packet Radio Networking," Computer World, pp. 26-37, 30, (September 27, 1982). Liu, J...34Distributed Routing and Relay Management in Mobile Packet Radio Networks," Proceedings IEEE COMPCON Fall 󈨔, p. 235-243 (1980). MacGregor, W ., J. Westcott, and

Dance Theatre of Harlem--Theater Activity Packet.

ERIC Educational Resources Information Center

New York City Board of Education, Brooklyn, NY. Div. of Curriculum and Instruction.

Intended to complement the New York City communication arts curriculum, this packet introduces young students, guided by the classroom teacher, to a dress rehearsal performance of the Dance Theatre of Harlem ballet company. The packet is one of a series in the "Early Stages" program, a joint effort of the Mayor's Office of Film, Theater…

Field Experiments on Real-Time 1-Gbps High-Speed Packet Transmission in MIMO-OFDM Broadband Packet Radio Access

NASA Astrophysics Data System (ADS)

Taoka, Hidekazu; Higuchi, Kenichi; Sawahashi, Mamoru

This paper presents experimental results in real propagation channel environments of real-time 1-Gbps packet transmission using antenna-dependent adaptive modulation and channel coding (AMC) with 4-by-4 MIMO multiplexing in the downlink Orthogonal Frequency Division Multiplexing (OFDM) radio access. In the experiment, Maximum Likelihood Detection employing QR decomposition and the M-algorithm (QRM-MLD) with adaptive selection of the surviving symbol replica candidates (ASESS) is employed to achieve such a high data rate at a lower received signal-to-interference plus background noise power ratio (SINR). The field experiments, which are conducted at the average moving speed of 30km/h, show that real-time packet transmission of greater than 1Gbps in a 100-MHz channel bandwidth (i.e., 10bits/second/Hz) is achieved at the average received SINR of approximately 13.5dB using 16QAM modulation and turbo coding with the coding rate of 8/9. Furthermore, we show that the measured throughput of greater than 1Gbps is achieved at the probability of approximately 98% in a measurement course, where the maximum distance from the cell site was approximately 300m with the respective transmitter and receiver antenna separation of 1.5m and 40cm with the total transmission power of 10W. The results also clarify that the minimum required receiver antenna spacing is approximately 10cm (1.5 carrier wave length) to suppress the loss in the required received SINR at 1-Gbps throughput to within 1dB compared to that assuming the fading correlation between antennas of zero both under non-line-of-sight (NLOS) and line-of-sight (LOS) conditions.

Packetized video on MAGNET

NASA Astrophysics Data System (ADS)

Lazar, Aurel A.; White, John S.

1986-11-01

Theoretical analysis of an ILAN model of MAGNET, an integrated network testbed developed at Columbia University, shows that the bandwidth freed up by video and voice calls during periods of little movement in the images and silence periods in the speech signals could be utilized efficiently for graphics and data transmission. Based on these investigations, an architecture supporting adaptive protocols that are dynamically controlled by the requirements of a fluctuating load and changing user environment has been advanced. To further analyze the behavior of the network, a real-time packetized video system has been implemented. This system is embedded in the real time multimedia workstation EDDY that integrates video, voice and data traffic flows. Protocols supporting variable bandwidth, constant quality packetized video transport are descibed in detail.

Current-induced instability of domain walls in cylindrical nanowires

NASA Astrophysics Data System (ADS)

Wang, Weiwei; Zhang, Zhaoyang; Pepper, Ryan A.; Mu, Congpu; Zhou, Yan; Fangohr, Hans

2018-01-01

We study the current-driven domain wall (DW) motion in cylindrical nanowires using micromagnetic simulations by implementing the Landau-Lifshitz-Gilbert equation with nonlocal spin-transfer torque in a finite difference micromagnetic package. We find that in the presence of DW, Gaussian wave packets (spin waves) will be generated when the charge current is suddenly applied to the system. This effect is excluded when using the local spin-transfer torque. The existence of spin waves emission indicates that transverse domain walls can not move arbitrarily fast in cylindrical nanowires although they are free from the Walker limit. We establish an upper velocity limit for DW motion by analyzing the stability of Gaussian wave packets using the local spin-transfer torque. Micromagnetic simulations show that the stable region obtained by using nonlocal spin-transfer torque is smaller than that by using its local counterpart. This limitation is essential for multiple DWs since the instability of Gaussian wave packets will break the structure of multiple DWs.

Nonlinear heating of ions by electron cyclotron frequency waves

NASA Astrophysics Data System (ADS)

Zestanakis, P. A.; Hizanidis, K.; Ram, A. K.; Kominis, Y.

2010-11-01

We study the nonlinear interaction of ions with electron cyclotron (EC) wave packets in a magnetized plasma. Previous studies have shown that such interactions with high frequency electrostatic lower hybrid waves can lead to coherent energization of ions. It requires the frequency bandwidth of the wave packet to be broader than the ion cyclotron frequency [1,2]. For the electromagnetic high frequency EC waves we have developed a more general theory, based on the Lie transform canonical perturbation method [3,4]. We apply the theory to the case of two overlapping EC beams. The wave frequency of each beam is assumed to be frequency modulated with a modulation bandwidth comparable to the ion cyclotron frequency. We present results for both X-mode and O-mode and illustrate the conditions for ion energization. [4pt] [1] D. Benisti, A. K. Ram, and A. Bers, Phys. Plasmas 5, 3224 (1998). [0pt] [2] A. K. Ram, A. Bers, and D. Benisti , J. Geophys. Res. 103, 9431 (1998). [0pt] [3] J.R. Cary and A.N. Kaufman, Phys. Fluids 24, 1238 (1981). [0pt] [4] R.L. Dewar, J. Phys A-Math. Gen 9, 2043 (1976).

A ray tracing model of gravity wave propagation and breakdown in the middle atmosphere

NASA Technical Reports Server (NTRS)

Schoeberl, M. R.

1985-01-01

Gravity wave ray tracing and wave packet theory is used to parameterize wave breaking in the mesosphere. Rays are tracked by solving the group velocity equations, and the interaction with the basic state is determined by considering the evolution of the packet wave action density. The ray tracing approach has a number of advantages over the steady state parameterization as the effects of gravity wave focussing and refraction, local dissipation, and wave response to rapid changes in the mean flow are more realistically considered; however, if steady state conditions prevail, the method gives identical results. The ray tracing algorithm is tested using both interactive and noninteractive models of the basic state. In the interactive model, gravity wave interaction with the polar night jet on a beta-plane is considered. The algorithm produces realistic polar night jet closure for weak topographic forcing of gravity waves. Planetary scale waves forced by local transfer of wave action into the basic flow in turn transfer their wave action into the zonal mean flow. Highly refracted rays are also found not to contribute greatly to the climatology of the mesosphere, as their wave action is severely reduced by dissipation during their lateral travel.

Study on ambient noise generated from breaking waves simulated by a wave maker in a tank

NASA Astrophysics Data System (ADS)

Wei, Ruey-Chang; Chan, Hsiang-Chih

2002-11-01

This paper studies ambient noise in the surf zone that was simulated by a piston-type wave maker in a tank. The experiment analyzed the bubbles of a breaking wave by using a hydrophone to receive the acoustic signal, and the images of bubbles were recorded by a digital video camera to observe the distribution of the bubbles. The slope of the simulated seabed is 1:5, and the dimensions of the water tank are 35 m x1 m x1.2 m. The studied parameters of ambient noise generated by breaking wave bubbles were wave height, period, and water depth. Short-time Fourier transform was applied to obtain the acoustic spectrum of bubbles, MATLAB programs were used to calculate mean sound pressure level, and determine the number of bubbles. Bubbles with resonant frequency from 0.5 to 10 kHz were studied, counted from peaks in the spectrum. The number of bubbles generated by breaking waves could be estimated by the bubbles energy distributions. The sound pressure level of ambient noise was highly related to the wave height and period, with correlation coefficient 0.7.

Acoustic multipath arrivals in the horizontal plane due to approaching nonlinear internal waves.

PubMed

Badiey, Mohsen; Katsnelson, Boris G; Lin, Ying-Tsong; Lynch, James F

2011-04-01

Simultaneous measurements of acoustic wave transmissions and a nonlinear internal wave packet approaching an along-shelf acoustic path during the Shallow Water 2006 experiment are reported. The incoming internal wave packet acts as a moving frontal layer reflecting (or refracting) sound in the horizontal plane. Received acoustic signals are filtered into acoustic normal mode arrivals. It is shown that a horizontal multipath interference is produced. This has previously been called a horizontal Lloyd's mirror. The interference between the direct path and the refracted path depends on the mode number and frequency of the acoustic signal. A mechanism for the multipath interference is shown. Preliminary modeling results of this dynamic interaction using vertical modes and horizontal parabolic equation models are in good agreement with the observed data.

Accounting Clerk Guide, Test Packet--Part I.

ERIC Educational Resources Information Center

Foster, Brian; And Others

The test packet is part of an eight volume unit for grades 10, 11, and 12, designed for individualized progression in preparing students for entry into the occupation of accounting clerk. The test packet contains both pretests and post-tests for lessons 1 through 12. The unit is concerned with the basic accounting theory found in the accounting…

On resonant coupling of acoustic waves and gravity waves

NASA Astrophysics Data System (ADS)

Millet, Christophe

2017-11-01

Acoustic propagation in the atmosphere is often modeled using modes that are confined within waveguides causing the sound to propagate through multiple paths to the receiver. On the other hand, direct observations in the lower stratosphere show that the gravity wave field is intermittent, and is often dominated by rather well defined large-amplitude wave packets. In the present work, we use normal modes to describe both the gravity wave field and the acoustic field. The gravity wave spectrum is obtained by launching few monochromatic waves whose properties are chosen stochastically to mimic the intermittency. Owing to the disparity of the gravity and acoustic length scales, the interactions between the gravity wave field and each of the acoustic modes can be described using a multiple-scale analysis. The appropriate amplitude evolution equation for the acoustic field involves certain random terms that can be directly related to the gravity wave sources. We will show that the cumulative effect of gravity wave breakings makes the sensitivity of ground-based acoustic signals large, in that small changes in the gravity wave parameterization can create or destroy specific acoustic features.

On Maximizing the Throughput of Packet Transmission under Energy Constraints.

PubMed

Wu, Weiwei; Dai, Guangli; Li, Yan; Shan, Feng

2018-06-23

More and more Internet of Things (IoT) wireless devices have been providing ubiquitous services over the recent years. Since most of these devices are powered by batteries, a fundamental trade-off to be addressed is the depleted energy and the achieved data throughput in wireless data transmission. By exploiting the rate-adaptive capacities of wireless devices, most existing works on energy-efficient data transmission try to design rate-adaptive transmission policies to maximize the amount of transmitted data bits under the energy constraints of devices. Such solutions, however, cannot apply to scenarios where data packets have respective deadlines and only integrally transmitted data packets contribute. Thus, this paper introduces a notion of weighted throughput, which measures how much total value of data packets are successfully and integrally transmitted before their own deadlines. By designing efficient rate-adaptive transmission policies, this paper aims to make the best use of the energy and maximize the weighted throughput. What is more challenging but with practical significance, we consider the fading effect of wireless channels in both offline and online scenarios. In the offline scenario, we develop an optimal algorithm that computes the optimal solution in pseudo-polynomial time, which is the best possible solution as the problem undertaken is NP-hard. In the online scenario, we propose an efficient heuristic algorithm based on optimal properties derived for the optimal offline solution. Simulation results validate the efficiency of the proposed algorithm.

Time-dependent quantum wave packet calculation for nonadiabatic F(2P3/2,2P1/2)+H2 reaction

NASA Astrophysics Data System (ADS)

Zhang, Yan; Xie, Ting-Xian; Han, Ke-Li; Zhang, John Z. H.

2003-12-01

In this paper we present a time-dependent quantum wave packet calculation for the reaction of F(2P3/2,2P1/2)+H2 on the Alexander-Stark-Werner potential energy surface. The reaction probabilities and the integral cross sections for the reaction of F(2P3/2,2P1/2)+H2 (v=j=0) are computed using time-dependent quantum methods with the centrifugal sudden approximate. The results are compared with recent time-independent quantum calculations. The two-surface reaction probability for the initial ground spin-orbit state of J=0.5 is similar to the time-independent result obtained by Alexander et al. [J. Chem. Phys. 113, 11084 (2000)]. Our calculation also shows that electronic coupling has a relatively minor effect on the reactivity from the 2P3/2 state but a non-negligible one from the 2P1/2 state. By comparison with exact time-independent calculations, it is found that the Coriolis coupling plays a relatively minor role. In addition, most of the reactivity of the excited state of fluorine atom results from the spin-orbit coupling.

The Long Life Ration Packet (LLRP)

DTIC Science & Technology

1991-02-18

entree, a cereal bar, a cookie component, a candy component, an instant beverage and an accessory packet. It weighs less than one pound for an...which may be eaten as is or rapidly reconstituted with either hot or cold water; other low moisture ready-to-eat foods and several instant beverage... instant beverage and accessory packet. 0 Field testing of prototype LRP scheduled for 4Q90 using Fort Drum IRP troops. 0 In-Process Review for acceptance of

RF wave simulation for cold edge plasmas using the MFEM library

NASA Astrophysics Data System (ADS)

Shiraiwa, S.; Wright, J. C.; Bonoli, P. T.; Kolev, T.; Stowell, M.

2017-10-01

A newly developed generic electro-magnetic (EM) simulation tool for modeling RF wave propagation in SOL plasmas is presented. The primary motivation of this development is to extend the domain partitioning approach for incorporating arbitrarily shaped SOL plasmas and antenna to the TORIC core ICRF solver, which was previously demonstrated in the 2D geometry [S. Shiraiwa, et. al., "HISTORIC: extending core ICRF wave simulation to include realistic SOL plasmas", Nucl. Fusion in press], to larger and more complicated simulations by including a 3D realistic antenna and integrating RF rectified sheath potential model. Such an extension requires a scalable high fidelity 3D edge plasma wave simulation. We used the MFEM [http://mfem.org], open source scalable C++ finite element method library, and developed a Python wrapper for MFEM (PyMFEM), and then a radio frequency (RF) wave physics module in Python. This approach allows for building a physics layer rapidly, while separating the physics implementation being apart from the numerical FEM implementation. An interactive modeling interface was built on pScope [S Shiraiwa, et. al. Fusion Eng. Des. 112, 835] to work with an RF simulation model in a complicated geometry.

Simulation of Guided Wave Interaction with In-Plane Fiber Waviness

NASA Technical Reports Server (NTRS)

Leckey, Cara A. C.; Juarez, Peter D.

2016-01-01

Reducing the timeline for certification of composite materials and enabling the expanded use of advanced composite materials for aerospace applications are two primary goals of NASA's Advanced Composites Project (ACP). A key a technical challenge area for accomplishing these goals is the development of rapid composite inspection methods with improved defect characterization capabilities. Ongoing work at NASA Langley is focused on expanding ultrasonic simulation capabilities for composite materials. Simulation tools can be used to guide the development of optimal inspection methods. Custom code based on elastodynamic finite integration technique is currently being developed and implemented to study ultrasonic wave interaction with manufacturing defects, such as in-plane fiber waviness (marcelling). This paper describes details of validation comparisons performed to enable simulation of guided wave propagation in composites containing fiber waviness. Simulation results for guided wave interaction with in-plane fiber waviness are also discussed. The results show that the wavefield is affected by the presence of waviness on both the surface containing fiber waviness, as well as the opposite surface to the location of waviness.

Simulation of guided wave interaction with in-plane fiber waviness

NASA Astrophysics Data System (ADS)

Leckey, Cara A. C.; Juarez, Peter D.

2017-02-01

Reducing the timeline for certification of composite materials and enabling the expanded use of advanced composite materials for aerospace applications are two primary goals of NASA's Advanced Composites Project (ACP). A key a technical challenge area for accomplishing these goals is the development of rapid composite inspection methods with improved defect characterization capabilities. Ongoing work at NASA Langley is focused on expanding ultrasonic simulation capabilities for composite materials. Simulation tools can be used to guide the development of optimal inspection methods. Custom code based on elastodynamic finite integration technique is currently being developed and implemented to study ultrasonic wave interaction with manufacturing defects, such as in-plane fiber waviness (marcelling). This paper describes details of validation comparisons performed to enable simulation of guided wave propagation in composites containing fiber waviness. Simulation results for guided wave interaction with in-plane fiber waviness are also discussed. The results show that the wavefield is affected by the presence of waviness on both the surface containing fiber waviness, as well as the opposite surface to the location of waviness.

Parametric decay of current-driven Langmuir oscillations and wave packet formation in plateau plasmas: Relevance to type III bursts

NASA Astrophysics Data System (ADS)

Sauer, K.; Malaspina, D.; Pulupa, M.

2016-12-01

Instead of starting with an unstable electron beam, our focus is directed on the nonlinear response of Langmuir oscillations which are driven after beam stabilization by the still persisting current of the (stable) two-electron plasma. The velocity distribution function of the second population forms a plateau with weak damping over a more or less extended wave number range k. As shown by PIC simulations, this so-called plateau plasma drives primarily Langmuir oscillations at the plasma frequency ωe with k=0 over long times without remarkable change of the distribution function. The Langmuir oscillations, however, act as pump wave for parametric decay by which an electron-acoustic wave slightly below ωe and a counter-streaming ion-acoustic wave are generated. Both high-frequency waves have nearly the same amplitude which is simply given by the product of plateau density and velocity. Beating of these two wave types leads to pronounced Langmuir amplitude modulation, in good agreement with solar wind and foreshock WIND observations where waveforms and electron distribution functions have simultaneously been analyzed.

Simulation studies on the standing and traveling wave thermoacoustic prime movers

NASA Astrophysics Data System (ADS)

Skaria, Mathew; Rasheed, K. K. Abdul; Shafi, K. A.; Kasthurirengan, S.; Behera, Upendra

2014-01-01

Thermoacoustic systems have been a focus of recent research due to its structural simplicity, high reliability due to absence of moving parts, and can be driven by low grade energy such as fuel, gas, solar energy, waste heat etc. There has been extensive research on both standing wave and traveling wave systems. Towards the development of such systems, simulations can be carried out by several methods such as (a) solving the energy equation, (b) enthalpy flow model, (c) DeltaEC, a free software available from LANL, USA (d) Computational Fluid Dynamics (CFD) etc. We present here the simulation studies of standing wave and traveling wave thermoacoustic prime movers using CFD and DeltaEC. The CFD analysis is carried out using Fluent 6.3.26, incorporating the necessary boundary conditions with different working fluids at different operating pressures. The results obtained by CFD are compared with those obtained using DeltaEC. Also, the CFD simulation of the thermoacoustically driven refrigerator is presented.

Simulation studies on the standing and traveling wave thermoacoustic prime movers

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

Skaria, Mathew; Rasheed, K. K. Abdul; Shafi, K. A.

Thermoacoustic systems have been a focus of recent research due to its structural simplicity, high reliability due to absence of moving parts, and can be driven by low grade energy such as fuel, gas, solar energy, waste heat etc. There has been extensive research on both standing wave and traveling wave systems. Towards the development of such systems, simulations can be carried out by several methods such as (a) solving the energy equation, (b) enthalpy flow model, (c) DeltaEC, a free software available from LANL, USA (d) Computational Fluid Dynamics (CFD) etc. We present here the simulation studies of standingmore » wave and traveling wave thermoacoustic prime movers using CFD and DeltaEC. The CFD analysis is carried out using Fluent 6.3.26, incorporating the necessary boundary conditions with different working fluids at different operating pressures. The results obtained by CFD are compared with those obtained using DeltaEC. Also, the CFD simulation of the thermoacoustically driven refrigerator is presented.« less

Magneto-acoustic wave energy in sunspots: observations and numerical simulations

NASA Astrophysics Data System (ADS)

Felipe, T.; Khomenko, E.; Collados, M.; Beck, C.

2011-11-01

We have reproduced some sunspot wave signatures obtained from spectropolarimetric observations through 3D MHD numericalsimulations. The results of the simulations arecompared with the oscillations observed simultaneously at different heights from the SiI lambda10827Å line, HeI lambda10830Å line, the CaII H core and the FeI blends at the wings of the CaII H line. The simulations show a remarkable agreement with the observations, and we have used them to quantify the energy contribution of the magneto-acoustic waves to the chromospheric heating in sunspots. Our findings indicate that the energy supplied by these waves is 5-10 times lower than the amount needed to balance the chromospheric radiative losses.

Packetized Video On MAGNET

NASA Astrophysics Data System (ADS)

Lazar, Aurel A.; White, John S.

1987-07-01

Theoretical analysis of integrated local area network model of MAGNET, an integrated network testbed developed at Columbia University, shows that the bandwidth freed up during video and voice calls during periods of little movement in the images and periods of silence in the speech signals could be utilized efficiently for graphics and data transmission. Based on these investigations, an architecture supporting adaptive protocols that are dynamicaly controlled by the requirements of a fluctuating load and changing user environment has been advanced. To further analyze the behavior of the network, a real-time packetized video system has been implemented. This system is embedded in the real-time multimedia workstation EDDY, which integrates video, voice, and data traffic flows. Protocols supporting variable-bandwidth, fixed-quality packetized video transport are described in detail.

Statistics of Gaussian packets on metric and decorated graphs.

PubMed

Chernyshev, V L; Shafarevich, A I

2014-01-28

We study a semiclassical asymptotics of the Cauchy problem for a time-dependent Schrödinger equation on metric and decorated graphs with a localized initial function. A decorated graph is a topological space obtained from a graph via replacing vertices with smooth Riemannian manifolds. The main term of an asymptotic solution at an arbitrary finite time is a sum of Gaussian packets and generalized Gaussian packets (localized near a certain set of codimension one). We study the number of packets as time tends to infinity. We prove that under certain assumptions this number grows in time as a polynomial and packets fill the graph uniformly. We discuss a simple example of the opposite situation: in this case, a numerical experiment shows a subexponential growth.

Simulating Responses of Gravitational-Wave Instrumentation

NASA Technical Reports Server (NTRS)

Armstrong, John; Edlund, Jeffrey; Vallisneri. Michele

2006-01-01

Synthetic LISA is a computer program for simulating the responses of the instrumentation of the NASA/ESA Laser Interferometer Space Antenna (LISA) mission, the purpose of which is to detect and study gravitational waves. Synthetic LISA generates synthetic time series of the LISA fundamental noises, as filtered through all the time-delay-interferometry (TDI) observables. (TDI is a method of canceling phase noise in temporally varying unequal-arm interferometers.) Synthetic LISA provides a streamlined module to compute the TDI responses to gravitational waves, according to a full model of TDI (including the motion of the LISA array and the temporal and directional dependence of the arm lengths). Synthetic LISA is written in the C++ programming language as a modular package that accommodates the addition of code for specific gravitational wave sources or for new noise models. In addition, time series for waves and noises can be easily loaded from disk storage or electronic memory. The package includes a Python-language interface for easy, interactive steering and scripting. Through Python, Synthetic LISA can read and write data files in Flexible Image Transport System (FITS), which is a commonly used astronomical data format.

Estimation of the Kelvin wave contribution to the semiannual oscillation

NASA Technical Reports Server (NTRS)

Hitchman, Matthew H.; Leovy, Conway B.

1988-01-01

Daily temperature data acquired during the Limb Infrared Monitor of the Stratosphere experiment are used to study the behavior of Kelvin waves in the equatorial middle atmosphere. It is suggested that Kelvin wave packets of different zonal wave numbers propagate separately and may be forced separately. Two Kelvin wave regimes were identified during the October 1978 to May 1979 data period. Most of the properties of the observed waves are shown to be consistent with slowly-varying theory. Results suggest that gravity waves may contribute significantly to the equatorial stratopause semiannual oscillation.

106-17 Telemetry Standards Recorder Data Packet Format Standard Chapter 11

DTIC Science & Technology

2017-07-01

11.2.2 PCM Data Packets ..................................................................................... 11-11 11.2.3 Time Data Packets...11-95 11.2.15 Ethernet Data Packets ................................................................................ 11-97 11.2.16 Time Space...4 Time ............................................................ 11-10 Figure 11-5. Secondary Header IEEE 1588 Time

Adaptive packet switch with an optical core (demonstrator)

NASA Astrophysics Data System (ADS)

Abdo, Ahmad; Bishtein, Vadim; Clark, Stewart A.; Dicorato, Pino; Lu, David T.; Paredes, Sofia A.; Taebi, Sareh; Hall, Trevor J.

2004-11-01

A three-stage opto-electronic packet switch architecture is described consisting of a reconfigurable optical centre stage surrounded by two electronic buffering stages partitioned into sectors to ease memory contention. A Flexible Bandwidth Provision (FBP) algorithm, implemented on a soft-core processor, is used to change the configuration of the input sectors and optical centre stage to set up internal paths that will provide variable bandwidth to serve the traffic. The switch is modeled by a bipartite graph built from a service matrix, which is a function of the arriving traffic. The bipartite graph is decomposed by solving an edge-colouring problem and the resulting permutations are used to configure the switch. Simulation results show that this architecture exhibits a dramatic reduction of complexity and increased potential for scalability, at the price of only a modest spatial speed-up k, 1packet switch is implemented on separate programmable logic devices forming electronic "islands" interconnected by photonics technology. The demonstrator design has 8 inputs and 8 outputs with reconfigurable central stage crossbars. Each sector is a 4x4 sub-switch implemented on a single FPGA with shared buffer memory. Communication among entities is performed through a high speed 10 Mbps link.

Observation and simulation of the ionosphere disturbance waves triggered by rocket exhausts

NASA Astrophysics Data System (ADS)

Lin, Charles C. H.; Chen, Chia-Hung; Matsumura, Mitsuru; Lin, Jia-Ting; Kakinami, Yoshihiro

2017-08-01

Observations and theoretical modeling of the ionospheric disturbance waves generated by rocket launches are investigated. During the rocket passage, time rate change of total electron content (rTEC) enhancement with the V-shape shock wave signature is commonly observed, followed by acoustic wave disturbances and region of negative rTEC centered along the trajectory. Ten to fifteen min after the rocket passage, delayed disturbance waves appeared and propagated along direction normal to the V-shape wavefronts. These observation features appeared most prominently in the 2016 North Korea rocket launch showing a very distinct V-shape rTEC enhancement over enormous areas along the southeast flight trajectory despite that it was also appeared in the 2009 North Korea rocket launch with the eastward flight trajectory. Numerical simulations using the physical-based nonlinear and nonhydrostatic coupled model of neutral atmosphere and ionosphere reproduce promised results in qualitative agreement with the characteristics of ionospheric disturbance waves observed in the 2009 event by considering the released energy of the rocket exhaust as the disturbance source. Simulations reproduce the shock wave signature of electron density enhancement, acoustic wave disturbances, the electron density depletion due to the rocket-induced pressure bulge, and the delayed disturbance waves. The pressure bulge results in outward neutral wind flows carrying neutrals and plasma away from it and leading to electron density depletions. Simulations further show, for the first time, that the delayed disturbance waves are produced by the surface reflection of the earlier arrival acoustic wave disturbances.

Simulating wave-turbulence on thin elastic plates with arbitrary boundary conditions

NASA Astrophysics Data System (ADS)

van Rees, Wim M.; Mahadevan, L.

2016-11-01

The statistical characteristics of interacting waves are described by the theory of wave turbulence, with the study of deep water gravity wave turbulence serving as a paradigmatic physical example. Here we consider the elastic analog of this problem in the context of flexural waves arising from vibrations of a thin elastic plate. Such flexural waves generate the unique sounds of so-called thunder machines used in orchestras - thin metal plates that make a thunder-like sound when forcefully shaken. Wave turbulence in elastic plates is typically investigated numerically using spectral simulations with periodic boundary conditions, which are not very realistic. We will present the results of numerical simulations of the dynamics of thin elastic plates in physical space, with arbitrary shapes, boundary conditions, anisotropy and inhomogeneity, and show first results on wave turbulence beyond the conventionally studied rectangular plates. Finally, motivated by a possible method to measure ice-sheet thicknesses in the open ocean, we will further discuss the behavior of a vibrating plate when floating on an inviscid fluid.

Adaptive Packet Combining Scheme in Three State Channel Model

NASA Astrophysics Data System (ADS)

Saring, Yang; Bulo, Yaka; Bhunia, Chandan Tilak

2018-01-01

The two popular techniques of packet combining based error correction schemes are: Packet Combining (PC) scheme and Aggressive Packet Combining (APC) scheme. PC scheme and APC scheme have their own merits and demerits; PC scheme has better throughput than APC scheme, but suffers from higher packet error rate than APC scheme. The wireless channel state changes all the time. Because of this random and time varying nature of wireless channel, individual application of SR ARQ scheme, PC scheme and APC scheme can't give desired levels of throughput. Better throughput can be achieved if appropriate transmission scheme is used based on the condition of channel. Based on this approach, adaptive packet combining scheme has been proposed to achieve better throughput. The proposed scheme adapts to the channel condition to carry out transmission using PC scheme, APC scheme and SR ARQ scheme to achieve better throughput. Experimentally, it was observed that the error correction capability and throughput of the proposed scheme was significantly better than that of SR ARQ scheme, PC scheme and APC scheme.

Numerical Simulations of Shock Wave Refraction at Inclined Gas Contact Discontinuity

ERIC Educational Resources Information Center

Bulat, Pavel V.; Volkov, Konstantin N.

2016-01-01

When a shock wave interacts with a contact discontinuity, there may appear a reflected rarefaction wave, a deflected contact discontinuity and a refracted supersonic shock. The numerical simulation of shock wave refraction at a plane contact discontinuity separating gases with different densities is performed. Euler equations describing inviscid…

Time-dependent wave-packet quantum dynamics study of the Ne + D2(+) (v0 = 0-2, j0 = 0) → NeD(+) + D reaction: including the coriolis coupling.

PubMed

Yao, Cui-Xia; Zhang, Pei-Yu

2014-07-10

The dynamics of the Ne + D2(+) (v0 = 0-2, j0 = 0) → NeD(+) + D reaction has been investigated in detail by using an accurate time-dependent wave-packet method on the ground 1(2)A' potential energy surface. Comparisons between the Coriolis coupling results and the centrifugal-sudden ones reveal that Coriolis coupling effect can influence reaction dynamics of the NeD2(+) system. Integral cross sections have been evaluated for the Ne + D2(+) reaction and its isotopic variant Ne + H2(+), and a considerable intermolecular isotopic effect has been found. Also obvious is the great enhancement of the reactivity due to the reagent vibrational excitation. Besides, a comparison with previous theoretical results is also presented and discussed.

Learn about Seabirds. Teaching Packet, Grades 4-6.

ERIC Educational Resources Information Center

Fish and Wildlife Service (Dept. of Interior), Anchorage, AK.

This teaching packet is designed to teach Alaskan students in grades 4-6 about Alaska's seabird populations, the worldwide significance of seabirds, and the environmental conditions to which seabirds are sensitive. The packet includes a curriculum guide (containing a teacher's background story and 12 teaching activities), a separately published…

Internally driven inertial waves in geodynamo simulations

NASA Astrophysics Data System (ADS)

Ranjan, A.; Davidson, P. A.; Christensen, U. R.; Wicht, J.

2018-05-01

Inertial waves are oscillations in a rotating fluid, such as the Earth's outer core, which result from the restoring action of the Coriolis force. In an earlier work, it was argued by Davidson that inertial waves launched near the equatorial regions could be important for the α2 dynamo mechanism, as they can maintain a helicity distribution which is negative (positive) in the north (south). Here, we identify such internally driven inertial waves, triggered by buoyant anomalies in the equatorial regions in a strongly forced geodynamo simulation. Using the time derivative of vertical velocity, ∂uz/∂t, as a diagnostic for traveling wave fronts, we find that the horizontal movement in the buoyancy field near the equator is well correlated with a corresponding movement of the fluid far from the equator. Moreover, the azimuthally averaged spectrum of ∂uz/∂t lies in the inertial wave frequency range. We also test the dispersion properties of the waves by computing the spectral energy as a function of frequency, ϖ, and the dispersion angle, θ. Our results suggest that the columnar flow in the rotation-dominated core, which is an important ingredient for the maintenance of a dipolar magnetic field, is maintained despite the chaotic evolution of the buoyancy field on a fast timescale by internally driven inertial waves.

Numerical Simulations of Upstream Propagating Solitary Waves and Wave Breaking In A Stratified Fjord

NASA Astrophysics Data System (ADS)

Stastna, M.; Peltier, W. R.

In this talk we will discuss ongoing numerical modeling of the flow of a stratified fluid over large scale topography motivated by observations in Knight Inlet, a fjord in British Columbia, Canada. After briefly surveying the work done on the topic in the past we will discuss our latest set of simulations in which we have observed the gener- ation and breaking of three different types of nonlinear internal waves in the lee of the sill topography. The first type of wave observed is a large lee wave in the weakly strat- ified main portion of the water column, The second is an upward propagating internal wave forced by topography that breaks in the strong, near-surface pycnocline. The third is a train of upstream propagating solitary waves that, in certain circumstances, form as breaking waves consisting of a nearly solitary wave envelope and a highly unsteady core near the surface. Time premitting, we will comment on the implications of these results for our long term goal of quantifying tidally driven mixing in Knight Inlet.

Graphene oxide as sensitive layer in Love-wave surface acoustic wave sensors for the detection of chemical warfare agent simulants.

PubMed

Sayago, Isabel; Matatagui, Daniel; Fernández, María Jesús; Fontecha, José Luis; Jurewicz, Izabela; Garriga, Rosa; Muñoz, Edgar

2016-02-01

A Love-wave device with graphene oxide (GO) as sensitive layer has been developed for the detection of chemical warfare agent (CWA) simulants. Sensitive films were fabricated by airbrushing GO dispersions onto Love-wave devices. The resulting Love-wave sensors detected very low CWA simulant concentrations in synthetic air at room temperature (as low as 0.2 ppm for dimethyl-methylphosphonate, DMMP, a simulant of sarin nerve gas, and 0.75 ppm for dipropylene glycol monomethyl ether, DPGME, a simulant of nitrogen mustard). High responses to DMMP and DPGME were obtained with sensitivities of 3087 and 760 Hz/ppm respectively. Very low limit of detection (LOD) values (9 and 40 ppb for DMMP and DPGME, respectively) were calculated from the achieved experimental data. The sensor exhibited outstanding sensitivity, good linearity and repeatability to all simulants tested. The detection mechanism is here explained in terms of hydrogen bonding formation between the tested CWA simulants and GO. Copyright © 2015 Elsevier B.V. All rights reserved.

Simulating Seismic Wave Propagation in Viscoelastic Media with an Irregular Free Surface

NASA Astrophysics Data System (ADS)

Liu, Xiaobo; Chen, Jingyi; Zhao, Zhencong; Lan, Haiqiang; Liu, Fuping

2018-05-01

In seismic numerical simulations of wave propagation, it is very important for us to consider surface topography and attenuation, which both have large effects (e.g., wave diffractions, conversion, amplitude/phase change) on seismic imaging and inversion. An irregular free surface provides significant information for interpreting the characteristics of seismic wave propagation in areas with rugged or rapidly varying topography, and viscoelastic media are a better representation of the earth's properties than acoustic/elastic media. In this study, we develop an approach for seismic wavefield simulation in 2D viscoelastic isotropic media with an irregular free surface. Based on the boundary-conforming grid method, the 2D time-domain second-order viscoelastic isotropic equations and irregular free surface boundary conditions are transferred from a Cartesian coordinate system to a curvilinear coordinate system. Finite difference operators with second-order accuracy are applied to discretize the viscoelastic wave equations and the irregular free surface in the curvilinear coordinate system. In addition, we select the convolutional perfectly matched layer boundary condition in order to effectively suppress artificial reflections from the edges of the model. The snapshot and seismogram results from numerical tests show that our algorithm successfully simulates seismic wavefields (e.g., P-wave, Rayleigh wave and converted waves) in viscoelastic isotropic media with an irregular free surface.

Instrument for measurement of vacuum in sealed thin wall packets

DOEpatents

Kollie, T.G.; Thacker, L.H.; Fine, H.A.

1995-04-18

An instrument is disclosed for the measurement of vacuum within sealed packets, the packets having a wall that it can be deformed by the application of an external dynamic vacuum to an area thereof. The instrument has a detector head for placement against the deformable wall of the packet to apply the vacuum in a controlled manner to accomplish a limited deformation or lift of the wall with this deformation or lift monitored by the application of light as via a bifurcated light pipe. Retro-reflected light through the light pipe is monitored with a photo detector. A change (e.g., a decrease) of retro-reflected light signals the wall movement such that the value of the dynamic vacuum applied through the head be to achieve this initiation of movement is equal to the vacuum within the packet. In a preferred embodiment a vacuum plate is placed beneath the packet to ensure that no deformation occurs on the reverse surface of the packet. A vacuum can be applied to a recess in this vacuum plate, the value of which can be used to calibrate the vacuum transducer in the detector head. 4 figs.

The ESA standard for telemetry and telecommand packet utilisation: PUS

NASA Technical Reports Server (NTRS)

Kaufeler, Jean-Francois

1994-01-01

ESA has developed standards for packet telemetry and telecommand, which are derived from the recommendations of the Inter-Agency Consultative Committee for Space Data Systems (CCSDS). These standards are now mandatory for future ESA programs as well as for many programs currently under development. However, while these packet standards address the end-to-end transfer of telemetry and telecommand data between applications on the ground and Application Processes on-board, they leave open the internal structure or content of the packets. This paper presents the ESA Packet Utilization Standard (PUS) which addresses this very subject and, as such, serves to extend and complement the ESA packet standards. The goal of the PUS is to be applicable to future ESA missions in all application areas (Telecommunications, Science, Earth Resources, microgravity, etc.). The production of the PUS falls under the responsibility of the ESA Committee for Operations and EGSE Standards (COES).

Continuing Development of California State Packet Radio Project.

ERIC Educational Resources Information Center

Brownrigg, Edwin

1992-01-01

Provides background on the California State Library Packet Radio project, which will use packet radios to deploy a wireless, high-speed, wide-area network of 600 nodes, including 100 libraries, in the San Francisco Bay Area. Project goals and objectives, plan of operation, equipment, and evaluation plans are summarized. (MES)

Shear wave elastography using Wigner-Ville distribution: a simulated multilayer media study.