Magnetization reversal using excitation of collective modes in nanodot matrices
Elyasi, Mehrdad; Bhatia, Charanjit S.; Yang, Hyunsoo
2015-01-01
The large arrays of magnetic dots are the building blocks of magnonic crystals and the emerging bit patterned media for future recording technology. In order to fully utilize the functionalities of high density magnetic nanodots, a method for the selective reversal of a single nanodot in a matrix of dots is desired. We have proposed a method for magnetization reversal of a single nanodot with microwave excitation in a matrix of magneto-statically interacting dots. The method is based on the excitation of collective modes and the spatial anomaly in the microwave power absorption. We perform numerical simulations to demonstrate the possibility of switching a single dot from any initial state of a 3 by 3 matrix of dots, and develop a theoretical model for the phenomena. We discuss the applicability of the proposed method for introducing defect modes in magnonic crystals as well as for future magnetic recording. PMID:25601554
The collective excitation of g-modes in the sun
NASA Technical Reports Server (NTRS)
Wolff, C. L.
1980-01-01
Oscillations of the solar interior (linear g-modes) may be strongly driven by the collective influence of all the modes upon the nuclear reactions in the core. This heretofore neglected effect could couple the modes, reduce the effective amplitudes near the center, and spatially concentrate most of the oscillation energy into just a portion of the radiative interior. If operating at sufficient strength, this can reverse the conventional conclusion, drawn from single mode calculations, that almost all solar g-modes are damped. Furthermore, it would put the theory into rough harmony with three otherwise troubling observations: (1) the 'low' neutrino flux measured by Davis (1978), (2) the high correspondence found by Wolff (1976) between recurrence periods in solar activity and the rotational beat periods of g-modes, and (3) the fluctuations in the sun's diameter which imply g-mode activity at high angular harmonics (Hill and Caudell 1979). A nonlinear expression is derived for the local rate of work done on an array of oscillation modes by the nuclear reactions. Three additional tests of the model are suggested.
Collective excitations of atoms and field modes in coupled cavities
NASA Astrophysics Data System (ADS)
Enaki, Nicolae A.; Bazgan, Sergiu
2014-04-01
The exact solution for the system formed from two or three q-bits doped in coupled cavities is discussed. The problem of indistinguishability between the excited radiators and the photons is analyzed using the intrinsic symmetry of the system. It is demonstrated that the solution is drastically simplified when the radiators and photons are considered as new polariton excitations. The exact solution of the Schrödinger equation is obtained for single and two excitations in each cavity considering the indistinguishability principle. This approach opens new possibilities for the interpretation of quantum entangled states in comparison with the traditional distinct situation (see e.g. Napoli and Messina 2001 Fortschr. Phys. 49 1059; Enaki and Bazgan 2013 Phys. Scr. T153 014022) due to the decrease in the number of degrees of freedom in the system. Considering that the energy of coupling between the radiators and the photons is larger than that of the coupling with an external vacuum field, we have found the master equation for the dumping of collective excitations. The time dependence of the population for new dressed quasi-levels of energy is obtained by solving the master equation analytically and numerically.
Collective excitations in quantum Hall liquid crystals: Single-mode approximation calculations
Lapilli, Cintia M.; Wexler, Carlos
2006-02-15
A variety of recent experiments probing the low-temperature transport properties of quantum Hall systems have suggested an interpretation in terms of liquid crystalline mesophases dubbed quantum Hall liquid crystals. The single mode approximation (SMA) has been a useful tool for the determination of the excitation spectra of various systems such as phonons in {sup 4}He and in the fractional quantum Hall effect. In this paper we calculate (via the SMA) the spectrum of collective excitations in a quantum Hall liquid crystal by considering nematic, tetratic, and hexatic generalizations of Laughlin's trial wave function having twofold, fourfold, and sixfold broken rotational symmetry, respectively. In the limit of zero wave vector q the dispersion of these modes is singular, with a gap that is dependent on the direction along which q=0 is approached for nematic and tetratic liquid crystalline states, but remains regular in the hexatic state, as permitted by the fourth order wave-vector dependence of the (projected) oscillator strength and static structure factor.
NASA Astrophysics Data System (ADS)
Bahrami, A.; Tavares, P. E. S.; Fritsch, A. R.; Tonin, Y. R.; Telles, G. D.; Bagnato, V. S.; Henn, E. A. L.
2015-07-01
We investigate the momentum distribution of a Bose-Einstein condensate (BEC) under the effect of an external small oscillatory perturbation. The condensate is perturbed, and we let it evolve in-trap after which we perform standard time-of-flight absorption imaging. The momentum distribution is extracted and analyzed as a function of the in-trap free evolution time. We show that the momentum distribution has its features varying periodically with the same frequency as the quadrupolar mode displayed by the atomic gas. We discuss the consequences of this finding for the study of turbulent atomic BECs.
Competition between collective and noncollective excitation modes at high spin in Ba124
NASA Astrophysics Data System (ADS)
Al-Khatib, A.; Singh, A. K.; Hübel, H.; Bringel, P.; Bürger, A.; Domscheit, J.; Neußer-Neffgen, A.; Schönwaßer, G.; Hagemann, G. B.; Hansen, C. Ronn; Herskind, B.; Sletten, G.; Wilson, J. N.; Timár, J.; Algora, A.; Dombrádi, Zs.; Gál, J.; Kalinka, G.; Molnár, J.; Nyakó, B. M.; Sohler, D.; Zolnai, L.; Clark, R. M.; Cromaz, M.; Fallon, P.; Lee, I. Y.; Macchiavelli, A. O.; Ward, D.; Amro, H.; Ma, W. C.; Kmiecik, M.; Maj, A.; Styczen, J.; Zuber, K.; Hauschild, K.; Korichi, A.; Lopez-Martens, A.; Roccaz, J.; Siem, S.; Hannachi, F.; Scheurer, J. N.; Bednarczyk, P.; Byrski, Th.; Curien, D.; Dorvaux, O.; Duchêne, G.; Gall, B.; Khalfallah, F.; Piqueras, I.; Robin, J.; Görgen, A.; Juhász, K.; Patel, S. B.; Evans, A. O.; Rainovski, G.; Benzoni, G.; Bracco, A.; Camera, F.; Leoni, S.; Mason, P.; Million, B.; Paleni, A.; Sacchi, R.; Wieland, O.; Petrache, C. M.; Petrache, D.; Rana, G. La; Moro, R.; De Angelis, G.; Lisle, J. C.; Cederwall, B.; Lagergren, K.; Lieder, R. M.; Podsvirova, E.; Gast, W.; Jäger, H.; Redon, N.
2006-07-01
High-spin states in Ba124 were investigated in two experiments using the Ni64(Ni64, 4n)Ba124 reaction at three different beam energies. In-beam γ-ray coincidences were measured with the Euroball and Gammasphere detector arrays. In the experiment with Euroball, the CsI detector array Diamant was employed to discriminate against charged-particle channels. Six new rotational bands were observed in Ba124, and previously known bands were extended to higher spins. One of the bands shows a transition from collective to noncollective behavior at high spins. Configuration assignments are suggested on the basis of comparison with cranked shell model and cranked Nilsson-Strutinsky calculations.
Collective excitations in neutron-star crusts
NASA Astrophysics Data System (ADS)
Chamel, N.; Page, D.; Reddy, S.
2016-01-01
We explore the spectrum of low-energy collective excitations in the crust of a neutron star, especially in the inner region where neutron-proton clusters are immersed in a sea of superfluid neutrons. The speeds of the different modes are calculated systematically from the nuclear energy density functional theory using a Skyrme functional fitted to essentially all experimental atomic mass data.
Collective excitations in itinerant spiral magnets
Kampf, A.P.
1996-01-01
We investigate the coupled charge and spin collective excitations in the spiral phases of the two-dimensional Hubbard model using a generalized random-phase approximation. Already for small doping the spin-wave excitations are strongly renormalized due to low-energy particle-hole excitations. Besides the three Goldstone modes of the spiral state the dynamical susceptibility reveals an extra zero mode for low doping and strong coupling values signaling an intrinsic instability of the homogeneous spiral state. In addition, near-zero modes are found in the vicinity of the spiral pitch wave number for out-of-plane spin fluctuations. Their origin is found to be the near degeneracy with staggered noncoplanar spiral states which, however, are not the lowest energy Hartree-Fock solutions among the homogeneous spiral states. {copyright} {ital 1996 The American Physical Society.}
Gilson, Erik P.; Davidson, Ronald C.; Efthimion, Philip C.; Majeski, Richard; Startsev, Edward A.; Wang, Hua; Koppell, Stewart; Talley, Matthew
2013-05-15
Transverse dipole and quadrupole modes have been excited in a one-component cesium ion plasma trapped in the Paul Trap Simulator Experiment (PTSX) in order to characterize their properties and understand the effect of their excitation on equivalent long-distance beam propagation. The PTSX device is a compact laboratory Paul trap that simulates the transverse dynamics of a long, intense charge bunch propagating through an alternating-gradient transport system by putting the physicist in the beam's frame of reference. A pair of arbitrary function generators was used to apply trapping voltage waveform perturbations with a range of frequencies and, by changing which electrodes were driven with the perturbation, with either a dipole or quadrupole spatial structure. The results presented in this paper explore the dependence of the perturbation voltage's effect on the perturbation duration and amplitude. Perturbations were also applied that simulate the effect of random lattice errors that exist in an accelerator with quadrupole magnets that are misaligned or have variance in their field strength. The experimental results quantify the growth in the equivalent transverse beam emittance that occurs due to the applied noise and demonstrate that the random lattice errors interact with the trapped plasma through the plasma's internal collective modes. Coherent periodic perturbations were applied to simulate the effects of magnet errors in circular machines such as storage rings. The trapped one component plasma is strongly affected when the perturbation frequency is commensurate with a plasma mode frequency. The experimental results, which help to understand the physics of quiescent intense beam propagation over large distances, are compared with analytic models.
Collective Excitations in Electron-Hole Bilayers
Kalman, G. J.; Hartmann, P.; Donko, Z.; Golden, K. I.
2007-06-08
We report a combined analytic and molecular dynamics analysis of the collective mode spectrum of a bipolar (electron-hole) bilayer in the strong coupling classical limit. A robust, isotropic energy gap is identified in the out-of-phase spectra, generated by the combined effect of correlations and of the excitation of the bound dipoles. In the in-phase spectra we identify longitudinal and transverse acoustic modes wholly maintained by correlations. Strong nonlinear generation of higher harmonics of the fundamental dipole oscillation frequency and the transfer of harmonics between different modes is observed.
Collective charge excitations along cell membranes
NASA Astrophysics Data System (ADS)
Manousakis, E.
2005-07-01
A significant part of the thin layers of counter-ions adjacent to the exterior and interior surfaces of a cell membrane form quasi-two-dimensional (2D) layers of mobile charge. Collective charge density oscillations, known as plasmon modes, in these 2D charged systems of counter-ions are predicted in the present paper. This is based on a calculation of the self-consistent response of this system to a fast electric field fluctuation. The possibility that the membrane channels might be using these excitations to carry out fast communication is suggested and experiments are proposed to reveal the existence of such excitations.
Mitigation of mode instabilities by dynamic excitation of fiber modes
NASA Astrophysics Data System (ADS)
Otto, Hans-Jürgen; Jauregui, Cesar; Stutzki, Fabian; Jansen, Florian; Limpert, Jens; Tünnermann, Andreas
2013-03-01
By dynamically varying the power content of the excited fiber modes of the main amplifier of a fiber-based MOPA system at high average output power levels, it was possible to mitigate mode instabilities to a large extent. In order to achieve the excitation variation, we used an acousto-optic deflector in front of the Yb-doped rod-type fiber. Therewith, it was possible to significantly increase both the average and the instantaneous minimum power content of the fundamental mode. This, consequently, led to a substantial improvement of the beam quality and pointing stability at power levels well beyond the threshold of mode instabilities.
Fletcher, Daniel A.; Kino, Gordon S.
2002-11-05
A lens system including a collection lens and a microlens spaced from the collection lens adjacent the region to be observed. The diameter of the observablel region depends substantially on the radius of the microlens.
Mode Selective Excitation Using Coherent Control Spectroscopy
Singh, Ajay K.; Konradi, Jakow; Materny, Arnulf; Sarkar, Sisir K.
2008-11-14
Femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) gives access to ultrafast molecular dynamics. However, femtosecond laser pulses are spectrally broad and therefore coherently excite several molecular modes. While the temporal resolution is high, usually no mode-selective excitation is possible. This paper demonstrates the feasibility of selectively exciting specific molecular vibrations in solution phase with shaped fs laser excitation using a feedback-controlled optimization technique guided by an evolutionary algorithm. This approach is also used to obtain molecule-specific CARS spectra from a mixture of different substances. The optimized phase structures of the fs pulses are characterized to get insight into the control process. Possible applications of the spectrum control are discussed.
Interchange mode excited by trapped energetic ions
Nishimura, Seiya
2015-07-15
The kinetic energy principle describing the interaction between ideal magnetohydrodynamic (MHD) modes with trapped energetic ions is revised. A model is proposed on the basis of the reduced ideal MHD equations for background plasmas and the bounce-averaged drift-kinetic equation for trapped energetic ions. The model is applicable to large-aspect-ratio toroidal devices. Specifically, the effect of trapped energetic ions on the interchange mode in helical systems is analyzed. Results show that the interchange mode is excited by trapped energetic ions, even if the equilibrium states are stable to the ideal interchange mode. The energetic-ion-induced branch of the interchange mode might be associated with the fishbone mode in helical systems.
NASA Astrophysics Data System (ADS)
Gayen, Saurabh; Behera, Surjyo; Bose, Shyamalendu
2006-03-01
The Raman spectra of a single-wall carbon nanotube (SWNT) consist of three types of modes; (i) the high frequency G-mode arising out of tangential oscillations of carbon atoms, (ii) D-mode due to the defects in the nanotube and (iii) the low frequency radial breathing mode (RBM) resulting out of radial oscillations of the carbon atoms. In this paper we theoretically investigate the effects of collective oscillations of electrons (plasmons) on the G and RBM modes in the Raman spectra of a filled and unfilled metallic SWNT. Inclusion of plasmon and the filling (rattler) atom produces four peaks in the Raman spectra in general. The positions and relative strengths of the Raman peaks [1] depend upon phonon frequencies of the nanotube and that of the filling atoms, the plasmon frequency, the strength of the electron-phonon interaction, strength of the interactions between the nanotube phonons and rattler phonon and radius of the nanotube [2]. Usually the intensity of the G-mode is higher than that of RBM. For heavier filling atoms the frequency of the rattler phonon is lower in value, which may broaden the peak to such an extent that it may disappear in the background spectrum altogether. 1.S.M. Bose et al., Physica B 351, 129 (2004) 2. S.M. Bose, S.Gayen and S. Behera, Phys. Rev. B 72, 153402 (2005).
Atmospheric Excitation of Planetary Normal Modes
NASA Technical Reports Server (NTRS)
Tanimoto, Toshiro
2001-01-01
The objectives of this study were to: (1) understand the phenomenon of continuous free oscillations of the Earth and (2) examine the idea of using this phenomenon for planetary seismology. We first describe the results on (1) and present our evaluations of the idea (2) in the final section. In 1997, after almost forty years since the initial attempt by Benioff et al, continuous free oscillations of the Earth were discovered. Spheroidal fundamental modes between 2 and 7 millihertz are excited continuously with acceleration amplitudes of about 0.3-0.5 nanogals. The signal is now commonly found in virtually all data recorded by STS-1 type broadband seismometers at quiet sites. Seasonal variation in amplitude and the existence of two coupled modes between the atmosphere and the solid Earth support that these oscillations are excited by the atmosphere. Stochastic excitation due to atmospheric turbulence is a favored mechanism, providing a good match between theory and data. The atmosphere has ample energy to support this theory because excitation of these modes require only 500-10000 W whereas the atmosphere contains about 117 W of kinetic energy. An application of this phenomenon includes planetary seismology, because other planets may be oscillating due to atmospheric excitation. The interior structure of planets could be learned by determining the eigenfrequencies in the continuous free oscillations. It is especially attractive to pursue this idea for tectonically quiet planets, since quakes may be too infrequent to be recorded by seismic instruments.
NASA Technical Reports Server (NTRS)
Goldreich, Peter; Murray, Norman; Kumar, Pawan
1994-01-01
We investigate the rates at which energy is supplied to individual p-modes as a function of their frequencies nu and angular degrees l. The observationally determined rates are compared with those calculated on the hypothesis that the modes are stochastically excited by turbulent convection. The observationally determined excitation rate is assumed to be equal to the product of the mode's energy E and its (radian) line width Gamma. We obtain E from the mode's mean square surface velocity with the aid of its velocity eigenfuction. We assume that Gamma measures the mode's energy decay rate, even though quasi-elastic scattering may dominate true absorption. At fixed l, E(Gamma) arises as nu(exp 7) at low nu, reaches a peak at nu approximately equal 3.5 mHz, and then declines as nu(exp 4.4) at higher nu . At fixed nu, E(Gamma) exhibits a slow decline with increasing l. To calculate energy input rates, P(sub alpha), we rely on the mixing-length model of turbulent convection. We find entropy fluctuations to be about an order of magnitude more effective than the Reynolds stress in exciting p-modes . The calculated P(sub alpha) mimic the nu(exp 7) dependence of E(Gamma) at low nu and the nu(exp -4.4) dependence at high nu. The break of 11.4 powers in the nu-dependence of E(Gamma) across its peak is attributed to a combination of (1) the reflection of high-frequency acoustic waves just below the photosphere where the scale height drops precipitously and (2) the absence of energy-bearing eddies with short enough correlation times to excite high-frequency modes. Two parameters associated with the eddy correlation time are required to match the location and shape of the break. The appropriate values of these parameters, while not unnatural, are poorly constrained by theory. The calculated P(sub alpha) can also be made to fit the magnitude of E(Gamma) with a reasonable value for the eddy aspect ratio. Our resutls suggest a possible explanation for the decline of mode energy
Collective excitations in soft-sphere fluids.
Bryk, Taras; Gorelli, Federico; Ruocco, Giancarlo; Santoro, Mario; Scopigno, Tullio
2014-10-01
Despite that the thermodynamic distinction between a liquid and the corresponding gas ceases to exist at the critical point, it has been recently shown that reminiscence of gaslike and liquidlike behavior can be identified in the supercritical fluid region, encoded in the behavior of hypersonic waves dispersion. By using a combination of molecular dynamics simulations and calculations within the approach of generalized collective modes, we provide an accurate determination of the dispersion of longitudinal and transverse collective excitations in soft-sphere fluids. Specifically, we address the decreasing rigidity upon density reduction along an isothermal line, showing that the positive sound dispersion, an excess of sound velocity over the hydrodynamic limit typical for dense liquids, displays a nonmonotonic density dependence strictly correlated to that of thermal diffusivity and kinematic viscosity. This allows rationalizing recent observation parting the supercritical state based on the Widom line, i.e., the extension of the coexistence line. Remarkably, we show here that the extremals of transport properties such as thermal diffusivity and kinematic viscosity provide a robust definition for the boundary between liquidlike and gaslike regions, even in those systems without a liquid-gas binodal line. Finally, we discuss these findings in comparison with recent results for Lennard-Jones model fluid and with the notion of the "rigid-nonrigid" fluid separation lines. PMID:25375488
Collective dynamical skyrmion excitations in a magnonic crystal
NASA Astrophysics Data System (ADS)
Mruczkiewicz, M.; Gruszecki, P.; Zelent, M.; Krawczyk, M.
2016-05-01
We investigate theoretically the magnetization dynamics in a skyrmion magnonic crystal. Collective excitations are studied in a chain of touching ferromagnetic nanodots in a skyrmion magnetic configuration. The determined dispersion relation of coupled skyrmions shows a periodic dependence on the wave vector, a characteristic feature of the band structure in magnonic crystals. By spatial analysis of the magnetization amplitude in the magnonic bands we identify the excited modes as breathing and clockwise gyrotropic dynamic skyrmions. Propagating with a negative and positive group velocity, respectively, these high- and low-frequency excitations can be further explored theoretically and experimentally for fundamental properties and technological applications in spintronics and magnonics.
Nuclear collective excitations: A relativistic density functional approach
NASA Astrophysics Data System (ADS)
Piekarewicz, J.
2015-08-01
Density functional theory provides the most promising, and likely unique, microscopic framework to describe nuclear systems ranging from finite nuclei to neutron stars. Properly optimized energy density functionals define a new paradigm in nuclear theory where predictive capability is possible and uncertainty quantification is demanded. Moreover, density functional theory offers a consistent approach to the linear response of the nuclear ground state. In this paper, we review the fundamental role played by nuclear collective modes in uncovering novel excitations and in guiding the optimization of the density functional. Indeed, without collective excitations the determination of the density functional remains incomplete. Without collective excitations, the equation of state of neutron-rich matter continues to be poorly constrained. We conclude with a discussion of some of the remaining challenges in this field and propose a path forward to address these challenges.
Collective excitations in layered organic conductors
NASA Astrophysics Data System (ADS)
Bonačić Lošić, Ž.; Bjeliš, A.; Županović, P.
2010-06-01
We apply the dielectric formalism within random phase approximation (RPA) and G0W0 approximation to the tight-binding multi-band systems with the three-dimensional long-range Coulomb interaction in order to calculate the one-particle spectral function for TTF-TCNQ, and to investigate dielectric properties of quasi-two-dimensional conductor ‧-(BEDT-TTF)2SF5CH2CF2SO3. In the model with two one-dimensional electron bands per donor and acceptor chains, appropriate for TTF-TCNQ, the RPA dielectric response comprises a low energy collective mode due to the strong coupling between the plasmon and the dipolar modes, together with the mode at order of magnitude higher energies. The first mode is responsible for the absence of low-energy quasi-particles and the appearance of broad dispersion at low energies in the spectral function. The wide structure at higher energies is due the second mode. These results are in the qualitative agreement with the ARPES data. In the model with two conducting bands, one one-dimensional and the other two-dimensional, which can be applied to ‧-(BEDT-TTF)2SF5CH2CF2SO3, the coupling between the plasmon and the dipolar mode leads to the appearance of the low energy collective mode perpendicular to the stacks, while the low energy dipolar mode persists along the stacks, as is observed in optical measurements.
Selective mode excitation in hollow-core photonic crystal fiber
NASA Astrophysics Data System (ADS)
Galea, A. D.; Couny, F.; Coupland, S.; Roberts, P. J.; Sabert, H.; Knight, J. C.; Birks, T. A.; Russell, Philip St. J.
2005-04-01
Modes are selectively excited by launching light through the cladding from the side into a hollow-core photonic crystal fiber. Measuring the total output power at the end of the fiber as a function of the angle of incidence of the exciting laser beam provides a powerful diagnostic for characterizing the cladding bandgap. Furthermore, various types of modes on either side of the bandgap are excited individually, and their near-field images are obtained.
Collective Modes in a Quantum Solid
NASA Astrophysics Data System (ADS)
Gazit, Snir; Podolsky, Daniel; Nonne, Heloise; Auerbach, Assa; Arovas, Daniel P.
2016-08-01
We provide a theoretical explanation for the optical modes observed in inelastic neutron scattering on the bcc solid phase of helium 4 [T. Markovich et al., Phys. Rev. Lett. 88, 195301 (2002)]. We argue that these excitations are amplitude (Higgs) modes associated with fluctuations of the crystal order parameter within the unit cell. We present an analysis of the modes based on an effective Ginzburg-Landau model, classify them according to their symmetry properties, and compute their signature in inelastic neutron scattering experiments. In addition, we calculate the dynamical structure factor by means of an ab intio quantum Monte Carlo simulation and find a finite frequency excitation at zero relative momentum.
Low-Energy Dipole Modes of Excitation Below the Neutron Separation Energy
Tonchev, A. P.; Howell, C. R.; Tornow, W.; Angell, C.; Boswell, M.; Karwowski, H. J.; Kelley, J. H.; Tsoneva, N.
2006-03-13
The nuclear resonance fluorescence experiments have been performed at the High Intensity Gamma Source (HI{gamma}S) on 138Ba nuclei using four 60% efficient HPGe detectors. Excitation energies, spin, parities, and decay branching ratios were measured for the low-energy dipole modes of excitations. Experimental results on the parity measurement below the neutron separation energy shows that all dipole states in this energy region exhibit E1 excitation. These results are consistent with theoretical prediction of the collective isoscalar nature of this low-energy mode of excitation.
Nuclear collective excitations in a two-phase coexistence region
Aguirre, R. M.; De Paoli, A. L.
2011-04-15
The relation between collective modes and phase transitions in nuclear matter is examined. The dispersion relations for the low-lying excitations in a linear approach are evaluated within a Landau-Fermi liquid scheme by assuming coexisting phases in thermodynamical equilibrium. Temperature and isospin composition are used as relevant parameters. The in-medium nuclear interaction is provided by a recently proposed density functional model. The low density liquid-gas phase transition is taken as a typical situation for examination. We found significative modifications in the energy spectrum, within a certain range of temperatures and isospin asymmetry, due to the separation of matter into independent phases. The influence of the electromagnetic interaction over the dispersion relation of these collective excitations is also examined.
Magnetotail dynamics excited by the streaming tearing mode
NASA Technical Reports Server (NTRS)
Sato, T.; Walker, R. J.
1982-01-01
Magnetotail reconnection in the presence of plasma streaming parallel to the neutral sheet is modeled. The tearing mode is excited much more violently in the case with parallel plasma flow in the plasma sheet than in the case with no flow. The flow patterns for the nonlinear resistive tearing mode and the streaming tearing mode are much more complex than those for the linear tearing mode. Flow vortices are observed in both cases.
Excitation of inertial modes in an experimental spherical Couette flow.
Rieutord, Michel; Triana, Santiago Andrés; Zimmerman, Daniel S; Lathrop, Daniel P
2012-08-01
Spherical Couette flow (flow between concentric rotating spheres) is one of flows under consideration for the laboratory magnetic dynamos. Recent experiments have shown that such flows may excite Coriolis restored inertial modes. The present work aims to better understand the properties of the observed modes and the nature of their excitation. Using numerical solutions describing forced inertial modes of a uniformly rotating fluid inside a spherical shell, we first identify the observed oscillations of the Couette flow with nonaxisymmetric, retrograde, equatorially antisymmetric inertial modes, confirming first attempts using a full sphere model. Although the model has no differential rotation, identification is possible because a large fraction of the fluid in a spherical Couette flow rotates rigidly. From the observed sequence of the excited modes appearing when the inner sphere is slowed down by step, we identify a critical Rossby number associated with a given mode, below which it is excited. The matching between this critical number and the one derived from the phase velocity of the numerically computed modes shows that these modes are excited by an instability likely driven by the critical layer that develops in the shear layer, staying along the tangent cylinder of the inner sphere. PMID:23005851
Collective excitations and dust particles in space
NASA Technical Reports Server (NTRS)
Gilra, D. P.
1972-01-01
It is shown that observed bands at 2200 A and in the 10 micron region are most probably due to collective excitations of dust particles. The following specific conclusions are drawn: (1) the 2200 A interstellar band is very likely due to graphite particles; (2) these graphite particles should be very small, approximately spherical, and should have no coating whatsoever; (3) the identification of circumstellar and interstellar silicates from the observations in the 10 micron region does not seem to be correct; (4) very valuable information about the shape of the circumstellar and interstellar dust particles can be obtained directly from observations; and (5) narrow band polarization measurements in the spectral regions of these bands will be very helpful in determining the shape of the particles.
Cavity modes and their excitations in elliptical plasmonic patch nanoantennas.
Chakrabarty, Ayan; Wang, Feng; Minkowski, Fred; Sun, Kai; Wei, Qi-Huo
2012-05-21
We present experimental and theoretical studies of two dimensional periodic arrays of elliptical plasmonic patch nanoantennas. Experimental and simulation results demonstrate that the azimuthal symmetry breaking of the metal patches leads to the occurrence of even and odd resonant cavity modes and the excitation geometries dependent on their modal symmetries. We show that the cavity modes can be described by the product of radial and angular Mathieu functions with excellent agreements with both simulations and experiments. The effects of the patch periodicity on the excitation of the surface plasmon and its coupling with the cavity modes are also discussed. PMID:22714147
Necessary conditions for mode interactions in parametrically excited waves.
Epstein, T; Fineberg, J
2008-04-01
We study the spatial and temporal structure of nonlinear states formed by parametrically excited waves on a fluid surface (Faraday instability), in a highly dissipative regime. Short-time dynamics reveal that 3-wave interactions between different spatial modes are only observed when the modes' peak values occur simultaneously. The temporal structure of each mode is functionally described by the Hill's equation and is unaffected by which nonlinear interaction is dominant. PMID:18517955
Collective Modes in a Quantum Solid.
Gazit, Snir; Podolsky, Daniel; Nonne, Heloise; Auerbach, Assa; Arovas, Daniel P
2016-08-19
We provide a theoretical explanation for the optical modes observed in inelastic neutron scattering on the bcc solid phase of helium 4 [T. Markovich et al., Phys. Rev. Lett. 88, 195301 (2002)]. We argue that these excitations are amplitude (Higgs) modes associated with fluctuations of the crystal order parameter within the unit cell. We present an analysis of the modes based on an effective Ginzburg-Landau model, classify them according to their symmetry properties, and compute their signature in inelastic neutron scattering experiments. In addition, we calculate the dynamical structure factor by means of an ab intio quantum Monte Carlo simulation and find a finite frequency excitation at zero relative momentum. PMID:27588863
Collective charge excitation in low dimensional organic salts
NASA Astrophysics Data System (ADS)
Naka, Makoto; Ishihara, Sumio
2013-03-01
Electronic ferroelectricity is known as phenomena where electric polarization is attributed to the charge order without inversion symmetry. This is seen in some transition metal oxides, e.g. LuFe2O4, and charge transfer salts. Quasi 2-dimesional organic salt kappa-(ET)2Cu2(CN)3\\ is one of the electronic ferroelectricities. Two ET molecules construct a dimer and are arranged on a triangular lattice. Recently, it is reported that a dielectric anomaly is experimentally observed around 30K. An origin of this dielectric anomaly is thought to be an ?electronic? dipole generated by a localized hole in one side of the ET molecules in dimers. Motivated by the experimental results, we study charge dynamics in dimer-Mott insulating system with internal charge degree of freedom in a dimer. We adopt the three kinds of models, extended Hubbard model, V-t model and its effective pseudo-spin model. We analyze these models by utilizing the exact diagonalization method and spin wave approximation, and focus on the collective charge excitation. In the ground state, paraelectric dimer-Mott phase and ferroelectric charge ordered phase compete with each other. We find the low-energy intra-dimer charge excitations which show a strong light polarization dependence. The collective excitation mode which is observable by light being parallel to the electric polarization shows a softening and a remarkable frequency dispersion around the phase boundary. This collective charge excitation of the ?electronic? dipole explains the recently observed peak structure in optical conductivity for the THz region.
Gravitational Effects on Collective Modes of Superfluid Shells
NASA Astrophysics Data System (ADS)
Padavić, Karmela; Sun, Kuei; Lannert, Courtney; Vishveshwara, Smitha
We study the effects of gravity on collective excitations of shell-shaped Bose-Einstein condensates (BECs). Superfluid shells are of general interest as examples of hollow geometries that can be produced in ultracold atoms in bubble-trap potentials or optical lattices. Our approach to analyzing superfluid shells is based on a Gross-Pitaevskii mean field theory and hydrodynamic equations derived from it. Considering a spherically symmetric BEC in general, there are distinct collective excitation spectra for the cases of a fully filled sphere and a very thin shell. Furthermore, an adiabatic change in the potential producing a slow transition from one geometry to the other shows a characteristic evolution. Given that in most realistic experimental conditions gravity cannot be neglected we investigate its effects on the equilibrium profile and the collective modes in the very thin shell limit. We analytically obtain the full excitation spectrum for the thin shell geometry and account for gravity perturbatively at length and energy scales that describe a stable matter-wave bubble. We find that gravity breaks spherical symmetry of the equilibrium density profile and affects the collective excitations by coupling adjacent modes in the angular direction.
Collective oscillations and coupled modes in confined microfluidic droplet arrays
NASA Astrophysics Data System (ADS)
Schiller, Ulf D.; Fleury, Jean-Baptiste; Seemann, Ralf; Gompper, Gerhard
Microfluidic droplets have a wide range of applications ranging from analytic assays in cellular biology to controlled mixing in chemical engineering. Ensembles of microfluidic droplets are interesting model systems for non-equilibrium many-body phenomena. When flowing in a microchannel, trains of droplets can form microfluidic crystals whose dynamics are governed by long-range hydrodynamic interactions and boundary effects. In this contribution, excitation mechanisms for collective waves in dense and confined microfluidic droplet arrays are investigated by experiments and computer simulations. We demonstrate that distinct modes can be excited by creating specific `defect' patterns in flowing droplet trains. While longitudinal modes exhibit a short-lived cascade of pairs of laterally displacing droplets, transversely excited modes form propagating waves that behave like microfluidic phonons. We show that the confinement induces a coupling between longitudinal and transverse modes. We also investigate the life time of the collective oscillations and discuss possible mechanisms for the onset of instabilities. Our results demonstrate that microfluidic phonons can exhibit effects beyond the linear theory, which can be studied particularly well in dense and confined systems. This work was supported by Deutsche Forschungsgemeinschaft under Grant No. SE 1118/4.
Higher order mode excitations in gyro-amplifiers
NASA Astrophysics Data System (ADS)
Nguyen, K. T.; Calame, J. P.; Danly, B. G.; Levush, B.; Garven, M.; Antonsen, T.
2001-05-01
In gyro-devices, a nonlinear output taper is often employed as the transition from the near cutoff radius of the interaction circuit to a much larger output waveguide. The tapers are usually designed to avoid passive mode conversion, and thus do not consider the effect of a bunched beam. However, recent simulations with the self-consistent MAGY code [Botton et al., IEEE Trans. Plasma Sci. 26, 882 (1998)] indicate that higher order mode interactions with the bunched electron beam can substantially compromise the mode purity of the rf output. The interaction in the taper region is traveling wave in nature, and is strongly dependent on the residual beam bunching characteristics resulting from the upstream operating mode interaction. An experiment has been performed to quantify the rf output mode content from a Ka-band gyroklystron. The agreement between salient theoretical and measured rf output characteristics confirms the existence of higher order mode excitation in output tapers as predicted by theory.
Magnetic antenna excitation of whistler modes. II. Antenna arrays
Stenzel, R. L.; Urrutia, J. M.
2014-12-15
The excitation of whistler modes from magnetic loop antennas has been investigated experimentally. The field topology of the excited wave driven by a single loop antenna has been measured for different loop orientations with respect to the uniform background field. The fields from two or more antennas at different locations are then created by superposition of the single-loop data. It is shown that an antenna array can produce nearly plane waves which cannot be achieved with single antennas. By applying a phase shift along the array, oblique wave propagation is obtained. This allows a meaningful comparison with plane wave theory. The Gendrin mode and oblique cyclotron resonance are demonstrated. Wave helicity and polarization in space and time are demonstrated and distinguished from the magnetic helicity of the wave field. The superposition of two oblique plane whistler modes produces in a “whistler waveguide” mode whose polarization and helicity properties are explained. The results show that single point measurements cannot properly establish the wave character of wave packets. The laboratory observations are relevant for excitation and detection of whistler modes in space plasmas.
Higher Order Mode Excitations in Gyro-amplifiers
NASA Astrophysics Data System (ADS)
Nguyen, Khanh
2000-10-01
A key element in the design of gyro-amplifier RF structures is the minimization of unwanted modes. For example, a nonlinear output taper is often employed in the transition from the near cutoff radius of the interacting circuit to a much larger output waveguide, which also serves as the collector. The taper designs are usually done without considering the effect of a bunched beam. However, recent simulations [1] with the self-consistent MAGY code [2] reveal that higher order mode interactions with the bunched electron beam can substantially compromise the mode purity of the RF output. The interaction in the taper region is that of a travelling-wave type and is strongly dependent on the beam bunching characteristics resulting from previous interaction with the operating mode in the interacting circuit. Subsequent to this prediction, an experiment was performed to measure the RF output mode content from a Ka-band gyro-klystron at the Naval Research Laboratory. The agreement between salient theoretical and measured RF output characteristics confirms the existence higher order mode excitation in output tapers as predicted by theory. Another example of the need to employ self-consistent theoretical model in the design of gyro-amplifier RF structures is the phenomenon of beam-induced RF excitation in drift sections, which are cutoff to the operating mode and are used to separate cavities in gyroklystron amplifiers. This non-resonant RF excitation is at the drive frequency and the RF field structure is that of the operating mode. The RF amplitude is found to scale linearly with the bunched beam current. The presence of RF in the drift section has important thermal implications in the design and use of lossy dielectrics in drift-sections, especially for high-average power devices. [1] K. Nguyen, et al., IEEE Trans. Plasma Science, in press 2000. [2] M. Botton, et al., IEEE Trans. Plasma Science, V.26, p.882, June 1998.
Inspection of bonded composites using selectively excited ultrasonic modes
NASA Astrophysics Data System (ADS)
Krauss, Gordon Gustav
Improved methods of nondestructive testing (NDT) of multi-layered composites are vital for fundamental research in composites fabrication and performance. Fast, accurate NDT methods can also be used to predict catastrophic in-use failure and to reduce costly rejects during the manufacture of composite parts. Commercial normal incidence inspection techniques have generally yielded reliable detection of large areas of delamination and damage. They fail, however, to detect defects within thin bonded regions, such as disbonds, debonds, kissing bonds, and porosity. We have developed and studied a nondestructive testing technique designed to be sensitive to flaws in the bond area of adhesively bonded anisotropic materials. The technique utilizes specific ultrasonic modes which are selected through a priori modeling of the composite as a single anisotropic elastic layer. The displacement and stress profiles of the modes within the fluid loaded layer are evaluated. A propagating mode that is predicted to be highly sensitive to the bond area is then utilized in the inspection. The inspection is carried out with an apparatus designed and constructed to excite and detect the selected ultrasonic mode. The apparatus uses transducers oriented at the theoretically optimal incident angle to excite the desired mode, using a tone burst between 0.5 and 10.0 MHz. We monitor with a second transducer changes in the amplitude of the leaky component of the mode propagating in the plate. By using this apparatus we have experimentally distinguished changes in the bond areas of adhesively bonded aluminum plates and carbon-epoxy composite plates of unidirectional and quasi-isotropic lay-up, The radiated leaky wave amplitudes from poorly bonded plates were less than 50% of those from corresponding well bonded plates. We observed no significant changes in the amplitudes of normal incidence pulse-echo signals for these specimens. These results demonstrate that selective mode excitation can
On fast radial propagation of parametrically excited geodesic acoustic mode
Qiu, Z.; Chen, L.; Zonca, F.
2015-04-15
The spatial and temporal evolution of parametrically excited geodesic acoustic mode (GAM) initial pulse is investigated both analytically and numerically. Our results show that the nonlinearly excited GAM propagates at a group velocity which is, typically, much larger than that due to finite ion Larmor radius as predicted by the linear theory. The nonlinear dispersion relation of GAM driven by a finite amplitude drift wave pump is also derived, showing a nonlinear frequency increment of GAM. Further implications of these findings for interpreting experimental observations are also discussed.
Exotic modes of excitation in proton rich nuclei
Paar, N.
2011-11-30
The framework of relativistic energy density functional has been applied in description of excitation phenomena in nuclei close to the proton drip line. In particular, low-lying dipole excitations have been studied using relativistic quasiparticle random phase approximation, based on effective Lagrangians with density dependent meson nucleon couplings. In the isovector dipole channel, the occurrence of pronounced low-lying dipole peaks is predicted, corresponding to the proton pygmy dipole resonance. Since this exotic mode still awaits its experimental confirmation, systematic calculations have been conducted within a pool of neutron deficient nuclei, in order to identify the best possible candidates for measurements.
Spin-wave modes and their intense excitation effects in Skyrmion crystals.
Mochizuki, Masahito
2012-01-01
We theoretically study spin-wave modes and their intense excitations activated by microwave magnetic fields in the Skyrmion-crystal phase of insulating magnets by numerically analyzing a two-dimensional spin model using the Landau-Lifshitz-Gilbert equation. Two peaks of spin-wave resonances with frequencies of ∼1 GHz are found for in-plane ac magnetic field where distribution of the out-of-plane spin components circulates around each Skyrmion core. Directions of the circulations are opposite between these two modes, and hence the spectra exhibit a salient dependence on the circular polarization of irradiating microwave. A breathing-type mode is also found for an out-of-plane ac magnetic field. By intensively exciting these collective modes, melting of the Skyrmion crystal accompanied by a redshift of the resonant frequency is achieved within nanoseconds. PMID:22304290
Micromagnetic study of excitation modes of an artificial skyrmion crystal
NASA Astrophysics Data System (ADS)
Miao, B. F.; Wen, Y.; Yan, M.; Sun, L.; Cao, R. X.; Wu, D.; You, B.; Jiang, Z. S.; Ding, H. F.
2015-11-01
We present a micromagnetic study on the eigen excitations of an artificial skyrmion crystal, which has been experimentally confirmed to be stable at room temperature without the need of any Dzyaloshinsky-Moriya interaction (DMI). Three in-plane rotational modes and one breathing-type mode are identified. We find the intrinsic origin of the dynamics of skyrmion crystal is the nontrivial magnetic texture instead of DMI. And the rotational direction of a skyrmion is solely determined by the sign of the skyrmion number, irrespective of its circulation sense, evidencing the topological nature of the magnetic skyrmion.
Asymmetric excitation of surface plasmons by dark mode coupling.
Zhang, Xueqian; Xu, Quan; Li, Quan; Xu, Yuehong; Gu, Jianqiang; Tian, Zhen; Ouyang, Chunmei; Liu, Yongmin; Zhang, Shuang; Zhang, Xixiang; Han, Jiaguang; Zhang, Weili
2016-02-01
Control over surface plasmons (SPs) is essential in a variety of cutting-edge applications, such as highly integrated photonic signal processing systems, deep-subwavelength lasing, high-resolution imaging, and ultrasensitive biomedical detection. Recently, asymmetric excitation of SPs has attracted enormous interest. In free space, the analog of electromagnetically induced transparency (EIT) in metamaterials has been widely investigated to uniquely manipulate the electromagnetic waves. In the near field, we show that the dark mode coupling mechanism of the classical EIT effect enables an exotic and straightforward excitation of SPs in a metasurface system. This leads to not only resonant excitation of asymmetric SPs but also controllable exotic SP focusing by the use of the Huygens-Fresnel principle. Our experimental findings manifest the potential of developing plasmonic metadevices with unique functionalities. PMID:26989777
Asymmetric excitation of surface plasmons by dark mode coupling
Zhang, Xueqian; Xu, Quan; Li, Quan; Xu, Yuehong; Gu, Jianqiang; Tian, Zhen; Ouyang, Chunmei; Liu, Yongmin; Zhang, Shuang; Zhang, Xixiang; Han, Jiaguang; Zhang, Weili
2016-01-01
Control over surface plasmons (SPs) is essential in a variety of cutting-edge applications, such as highly integrated photonic signal processing systems, deep-subwavelength lasing, high-resolution imaging, and ultrasensitive biomedical detection. Recently, asymmetric excitation of SPs has attracted enormous interest. In free space, the analog of electromagnetically induced transparency (EIT) in metamaterials has been widely investigated to uniquely manipulate the electromagnetic waves. In the near field, we show that the dark mode coupling mechanism of the classical EIT effect enables an exotic and straightforward excitation of SPs in a metasurface system. This leads to not only resonant excitation of asymmetric SPs but also controllable exotic SP focusing by the use of the Huygens-Fresnel principle. Our experimental findings manifest the potential of developing plasmonic metadevices with unique functionalities. PMID:26989777
Are Resonant Helioseimic Modes Excited by Solar Flares?
NASA Astrophysics Data System (ADS)
Leibacher, John W.; Baudin, Frédéric; Rabello Soares, Maria Cristina
2016-05-01
We critically examine reports that flares have been observed to excite resonant p-modes by:-looking in detail at the results of the ring-diagram analysis in terms of duty cycle and center-to-limb variation of ring-diagram power.-applying the same analysis to the Halloween flare using GONG and MDI data.-assessing the stability in terms of oscillation power of both instruments.
KIC 8164262: A Heartbeat Star with a Resonantly Excited Mode
NASA Astrophysics Data System (ADS)
Hambleton, Kelly Marie; Kurtz, Donald Wayne; thompson, susan; Fuller, Jim
2015-08-01
With the advent of high precision photometry from the Kepler satellite, a new layer of interesting and astounding astronomical objects has been revealed: heartbeat stars are an example of such objects. Heartbeat stars are eccentric ellipsoidal variables that undergo strong tidal interactions at the time of closest approach, when the stars are almost in contact. The consequence of these interactions is not only the deformation and mutual irradiation of the stars at periastron, but in many of these objects (~20%) we observe tidally induced pulsations. Tidally induced pulsations are pulsations driven by the tidal forcing of the binary star companion. They can be easily distinguished from other pulsations as they occur at precise multiples of the orbital frequency. Moreover, we have identified several objects where the tidally excited modes are undergoing resonance. This occurs when the tidal forces are in resonance with an eigenfrequency of one of the stellar components. In this paper we present KIC 8164262, a prime example of a heartbeat star with a resonantly excited mode. We provide the results of spectral modelling combined with extensive binary light and radial velocity curve modelling, generated using PHOEBE and MCMC. We further discuss why resonant locking, which has been theorised as the mechanism that keeps a system in resonance, is likely acting on this system. Finally, we describe the theoretical implications of tidally induced and resonantly excited modes, and their effects on binary star evolution.
Collective modes in the fluxonium qubit
NASA Astrophysics Data System (ADS)
Catelani, Gianluigi; Viola, Giovanni
2015-03-01
In the fluxonium qubit, an array comprising a large number of identical Josephson junctions form a so-called superinductance. The superinductance is connected to a junction - the phase slip element - with a smaller Josephson energy and a different charging energy. We investigate the effects of unavoidable capacitive couplings to ground as well as non-linearities of the superinductance: they both introduce interactions between the low-energy qubit degree of freedom and higher-energy collective modes of the circuit. We also consider the role of the additional capacitances that are used to couple the qubit to a resonator for driving and read-out. We show that the interactions with the collective modes can affect not only the spectrum of the qubit but also its coherence. Work supported in part by the EU under REA Grant Agreement No. CIG-618258.
Interpretation of the nonlinear mode excitation in the ITER gyrotron
Nusinovich, G. S.; Sinitsyn, O. V.
2007-11-15
This study was motivated by an interesting physical effect observed in experiments with a 1 MW, 170 GHz, continuous-wave gyrotron developed at the Japan Atomic Energy Agency for plasma heating and current drive in ITER [see, e.g., Fusion Eng. Des. 55, issues 2-3 (2001)]. In these experiments, the gyrotron switching from a parasitic mode to the operating one was observed with the increase in external magnetic field in the region of hard self-excitation of the operating mode where it cannot be excited from the noise level in the absence of other modes. Below, the theory describing this effect is developed. The switching mechanism caused by merging and disappearance of two (one stable and another unstable) equilibrium states with nonzero amplitudes of both modes is proposed. It is found that the present theory can correctly interpret experimental results qualitatively, but the lack of experimental data does not let the authors carry out some simulations more adequate to experimental conditions.
Collective excitation spectra of transitional even nuclei
Quentin, P. Paris-11 Univ., 91 - Orsay . Centre de Spectrometrie Nucleaire et de Spectrometrie de Masse); Deloncle, I.; Libert, J. . Centre de Spectrometrie Nucleaire et de Spectrometrie de Masse); Sauvage, J. . Inst. de Physique Nucleaire)
1990-11-06
This talk is dealing with the nuclear low energy collective motion as described in the context of microscopic versions of the Bohr Hamiltonian. Two different ways of building microscopically Bohr collective Hamiltonians will be sketched; one within the framework of the Generator Coordinate Method, the other using the Adiabatic Time-Dependent Hartree-Fock-Boholyubov approximation. A sample of recent results will be presented which pertains to the description of transitional even nuclei and to the newly revisited phenomenon of superdeformation at low spin.
Variety of c-Axis Collective Excitations in Layered Multigap Superconductors
NASA Astrophysics Data System (ADS)
Ota, Yukihiro; Machida, Masahiko; Koyama, Tomio
2011-04-01
We present a dynamical theory for the phase differences along a stacked direction of intrinsic Josephson junctions (IJJ’s) in layered multigap superconductors, motivated by the discovery of highly anisotropic iron-based superconductors with thick perovskite-type blocking layers. The dynamical equations describing ac and dc intrinsic Josephson effects peculiar to multigap IJJ’s are derived, and collective Leggett mode excitations in addition to the Josephson plasma established in single-gap IJJ’s are predicted. The dispersion relations of their collective modes are explicitly displayed, and the remarkable peculiarity of the Leggett mode is demonstrated.
Search for intrinsic collective excitations in {sup 152}Sm
Kulp, W. D.; Wood, J. L.; Allmond, J. M.; Garrett, P. E.; Wu, C. Y.; Cline, D.; Hayes, A. B.; Hua, H.; Teng, R.; Bandyopadhyay, D.; Choudry, S. N.; McEllistrem, M. T.; McKay, C. J.; Orce, J. N.; Dashdorj, D.; Mynk, M. G.; Yates, S. W.
2008-06-15
The 685 keV excitation energy of the first excited 0{sup +} state in {sup 152}Sm makes it an attractive candidate to explore expected two-phonon excitations at low energy. Multiple-step Coulomb excitation and inelastic neutron scattering studies of {sup 152}Sm are used to probe the E2 collectivity of excited 0{sup +} states in this 'soft' nucleus and the results are compared with model predictions. No candidates for two-phonon K{sup {pi}}=0{sup +}quadrupole vibrational states are found. A 2{sup +},K=2 state with strong E2 decay to the first excited K{sup {pi}}=0{sup +} band and a probable 3{sup +} band member are established.
Collective modes in asymmetric ultracold Fermi systems
Gubankova, Elena; Mannarelli, Massimo; Sharma, Rishi
2010-09-15
We derive the long wavelength effective action for the collective modes in systems of fermions interacting via a short-range s-wave attraction, featuring unequal chemical potentials for the two fermionic species (asymmetric systems). As a consequence of the attractive interaction, fermions form a condensate that spontaneously breaks the U(1) symmetry associated with total number conservation. Therefore at sufficiently small temperatures and asymmetries, the system is a superfluid. We reproduce previous results for the stability conditions of the system as a function of the four-fermion coupling and asymmetry. We obtain these results analyzing the coefficients of the low energy effective Lagrangian of the modes describing fluctuations in the magnitude (Higgs mode) and in the phase (Nambu-Goldstone, or Anderson-Bogoliubov, mode) of the difermion condensate. We find that for certain values of parameters, the mass of the Higgs mode decreases with increasing mismatch between the chemical potentials of the two populations, if we keep the scattering length and the gap parameter constant. Furthermore, we find that the energy cost for creating a position dependent fluctuation of the condensate is constant in the gapped region and increases in the gapless region. These two features may lead to experimentally detectable effects. As an example, we argue that if the superfluid is put in rotation, the square of the radius of the outer core of a vortex should sharply increase on increasing the asymmetry, when we pass through the relevant region in the gapless superfluid phase. Finally, by gauging the global U(1) symmetry, we relate the coefficients of the effective Lagrangian of the Nambu-Goldstone mode with the screening masses of the gauge field.
Collective and noncollective excitations in 122Te
NASA Astrophysics Data System (ADS)
Nag, Somnath; Singh, A. K.; Ragnarsson, I.; Hübel, H.; Al-Khatib, A.; Bringel, P.; Engelhardt, C.; Neußer-Neffgen, A.; Hagemann, G. B.; Herskind, B.; Sletten, G.; Carpenter, M. P.; Janssens, R. V. F.; Khoo, T. L.; Lauritsen, T.; Clark, R. M.; Fallon, P.; Benzoni, G.; Bracco, A.; Camera, F.; Chowdhury, P.
2013-10-01
High-spin states in 122Te were populated in the reaction 82Se(48Ca, α4n)122Te at a beam energy of 200 MeV and γ-ray coincidences were measured with the Gammasphere spectrometer. The previously known level scheme was extended to considerably higher spin. Maximally aligned states and several high-energy transitions feeding into some of these levels were observed. In addition, seven collective high-spin bands were discovered for the first time in this nucleus. The experimental results are compared with cranked Nilsson-Strutinsky model calculations and possible configuration assignments to the new high-spin structures are discussed.
Analysis of excitation and collection geometries for planar waveguide immunosensors
NASA Astrophysics Data System (ADS)
Christensen, Douglas A.; Dyer, Shellee; Fowers, David; Herron, James N.
1993-05-01
We demonstrate the use of a two-channel flowcell for fluorescent immunoassays. The flowcell contains a planar silica waveguide for evanescent excitation of the fluorophores, and the planar waveguide surface provides the solid support for immobilization of the antibodies. The detection system is composed of a grating spectrometer and a CCD camera for spectral characterization of the emitted signals. Two methods of sensing have been studied: a displacement-type technique and a sandwich-type assay. The sensitivity achieved for measuring concentrations of HCG by the sandwich method is sub-picomolar. Also, we have experimentally compared the signal strengths for two alternative ways of excitation and collection, and determine that waveguide excitation/side collection has some practical advantages over side excitation/waveguide collection.
Grating assisted optical waveguide coupler to excite individual modes of a multi-mode waveguide
NASA Astrophysics Data System (ADS)
Bremer, K.; Lochmann, S.; Roth, B.
2015-12-01
Spatial division multiplexing (SDM) in the form of mode division multiplexing (MDM) in multi-mode (MM) waveguides is currently explored to overcome the capacity limitation of single-mode (SM) waveguides in data transmission technology. In this work a new approach towards mode selective optical waveguide couplers to multiplex and demultiplex individual modes of MM waveguides is presented. We discuss a grating assisted mode selective optical waveguide coupler and evaluate numerically its coupling efficiency. The approach relies on a grating structure in a SM waveguide which is used to excite individual modes of an adjacent unmodified MM waveguide via evanescent field coupling. The simulations verify that by using the grating structure and tailoring the grating period, light from the SM waveguide can be coupled selectively into the fundamental mode or any higher-order mode of a MM waveguide with high efficiency and low crosstalk to adjacent mode-channels. The results indicate the potential of the grating assisted waveguide coupler approach for future applications in on-chip photonic networks and the (de)multiplexing of individual modes of MM waveguides.
Excitation of Slow-Modes in Network Magnetic Elements
NASA Astrophysics Data System (ADS)
Kato, Y.; Steiner, O.; Steffen, M.; Suematsu, Y.
2012-05-01
From radiation magnetohydrodynamic (RMHD) simulations of the solar atmosphere we have found a new mechanism for the excitation of longitudinal slow modes within magnetic flux concentrations. It is found that the convective downdrafts in the immediate surroundings of magnetic elements are responsible for the excitation of slow modes. The coupling between the external downdraft and the plasma motion internal to the flux concentration is mediated by the inertial forces of the downdraft that act on the magnetic flux concentration. These forces pump the internal atmosphere in the downward direction, which entails a fast downflow in the photospheric and chromospheric layers of the magnetic element. Subsequent to the transient pumping phase, the atmosphere rebounds, causing a slow mode traveling along the magnetic flux concentration in the upward direction and developing into a shock wave in chromospheric heights, possibly capable of producing some kind of dynamic fibril. This event occurs recurrently. We compare the power spectra of the temperature and velocity of the flux-sheet atmosphere to the corresponding spectra of the unmagnetized atmosphere.
Thermally excited modes in a pure electron plasma.
Anderegg, F; Shiga, N; Danielson, J R; Dubin, D H E; Driscoll, C F; Gould, R W
2003-03-21
Thermally excited plasma modes are observed in near-thermal-equilibrium pure electron plasmas over a temperature range of 0.05
Electron plasma dynamics during autoresonant excitation of the diocotron mode
Baker, C. J. Danielson, J. R. Hurst, N. C. Surko, C. M.
2015-02-15
Chirped-frequency autoresonant excitation of the diocotron mode is used to move electron plasmas confined in a Penning-Malmberg trap across the magnetic field for advanced plasma and antimatter applications. Plasmas of 10{sup 8} electrons, with radii small compared to that of the confining electrodes, can be moved from the magnetic axis to ≥90% of the electrode radius with near unit efficiency and reliable angular positioning. Translations of ≥70% of the wall radius are possible for a wider range of plasma parameters. Details of this process, including phase and displacement oscillations in the plasma response and plasma expansion, are discussed, as well as possible extensions of the technique.
Exotic modes of excitation in deformed neutron-rich nuclei
Yoshida, Kenichi
2011-05-06
Low-lying dipole excitation mode in neutron-rich Mg isotopes close to the drip line is investigated in the framework of the Hartree-Fock-Bogoliubov and the quasiparticle random-phase approximation employing the Skyrme and the pairing energy-density functionals. It is found that the low-lying dipole-strength distribution splits into the K{sup {pi}} = 0{sup -} and 1{sup -} components due to the nuclear deformation. The low-lying dipole strength increases as the neutron drip-line is approached.
Fast excitation of geodesic acoustic mode by energetic particle beams
Cao, Jintao; Qiu, Zhiyong; Zonca, Fulvio
2015-12-15
A new mechanism for geodesic acoustic mode (GAM) excitation by a not fully slowed down energetic particle (EP) beam is analyzed to explain experimental observations in Large Helical Device. It is shown that the positive velocity space gradient near the lower-energy end of the EP distribution function can strongly drive the GAM unstable. The new features of this EP-induced GAM (EGAM) are: (1) no instability threshold in the pitch angle; (2) the EGAM frequency can be higher than the local GAM frequency; and (3) the instability growth rate is much larger than that driven by a fully slowed down EP beam.
High energy components and collective modes in thermonuclear plasmas
Coppi, B.; Cowley, S.; Detragiache, P.; Kulsrud, R.; Pegoraro, F.
1986-02-01
The theory of a class of collective modes of a thermonuclear magnetically confined plasma, with frequencies in the range of the ion cyclotron frequency and of its harmonics, is presented. These modes can be excited by their resonant cyclotron interaction with a plasma component of relatively high energy particles characterized by a strongly anisotropic distribution in velocity space. Normal modes that are spatially localized by the inhomogeneity of the plasma density are found. This ensures that the energy gained by their resonant interaction is not convected away. The mode spatial localization can be significantly altered by the magnetic field inhomogeneity for a given class of plasma density profiles. Special attention is devoted to the case of a spin polarized plasma, where the charged products of fusion reactions are anisotropically distributed. We show that for the mode of polarization that enhances nuclear reaction rates the tritium will be rapidly depolarized to toroidal configurations with relatively mild gradients of the confining magnetic field. 18 refs., 9 figs.
Large angular scale CMB anisotropy from an excited initial mode
NASA Astrophysics Data System (ADS)
Sojasi, A.; Mohsenzadeh, M.; Yusofi, E.
2016-07-01
According to inflationary cosmology, the CMB anisotropy gives an opportunity to test predictions of new physics hypotheses. The initial state of quantum fluctuations is one of the important options at high energy scale, as it can affect observables such as the CMB power spectrum. In this study a quasi-de Sitter inflationary background with approximate de Sitter mode function built over the Bunch-Davies mode is applied to investigate the scale-dependency of the CMB anisotropy. The recent Planck constraint on spectral index motivated us to examine the effect of a new excited mode function (instead of pure de Sitter mode) on the CMB anisotropy at large angular scales. In so doing, it is found that the angular scale-invariance in the CMB temperature fluctuations is broken and in the limit ℓ < 200 a tiny deviation appears. Also, it is shown that the power spectrum of CMB anisotropy is dependent on a free parameter with mass dimension H << M * < M p and on the slow-roll parameter ɛ. Supported by the Islamic Azad University, Rasht Branch, Rasht, Iran
NASA Astrophysics Data System (ADS)
Margulis, Vl. A.; Makarov, S. V.; Piterimova, T. V.; Gaiduk, E. A.
2003-05-01
Using a mean-field approximation, we have developed a systematic treatment of collective electronic modes in a semiconductor superlattice (SL) in the presence of strong electric and magnetic fields parallel to the SL axis. The spectrum of collective modes with zero wavevector along the SL axis is shown to consist of a principle magnetoplasmon mode and an infinite set of Bernstein-like modes. For non-zero wavevector along the SL axis, in addition to the cyclotron modes, extra collective modes are found at the frequencies \\vert Nω_c± Mω_s\\vert, which we call cyclotron-Stark modes (ω_c and ω_s are respectively the cyclotron and Stark frequencies, N and M are integer numbers). The frequencies of the modes propagating in “oblique” direction with respect to the SL axis show oscillatory behavior as a function of electric field strength. All the modes considered have very weak spatial dispersion and they are not Landau damped. The specific predictions made for the dispersion relations of the collective excitations should be observable in resonant Raman scattering experiments.
Influence of collective effects on lifetimes of condensed excited states
NASA Technical Reports Server (NTRS)
Zmuidzinas, Jonas Stasys
1987-01-01
The possibility that collective effects may dramatically influence autoionization-limited lifetimes of condensed excited states is investigated in the context of a two-band model of an insulator in a strong magnetic field. Two different mechanisms for suppressing autoionization are discussed which may prevent the potentially catastrophic destruction of the excited state. Under appropriate circumstances, the residual low-density Auger electrons may be confined in a superconducting state and paired by excitonic fluctuations in the conduction band.
Bryk, Taras; Wax, J-F
2016-05-21
Using a combination of ab initio molecular dynamics and several fit models for dynamic structure of liquid metals, we explore an issue of possible manifestation of non-acoustic collective excitations in longitudinal dynamics having liquid Na as a case study. A model with two damped harmonic oscillators (DHOs) in time domain is used for analysis of the density-density time correlation functions. Another similar model with two propagating contributions and three lowest exact sum rules is considered, as well as an extended hydrodynamic model known as thermo-viscoelastic one which permits two types of propagating modes outside the hydrodynamic region to be used for comparison with ab initio obtained time correlation functions and calculations of dispersions of collective excitations. Our results do not support recent suggestions that, even in simple liquid metals, non-hydrodynamics transverse excitations contribute to the longitudinal collective dynamics and can be detected as a DHO-like spectral shape at their transverse frequency. We found that the thermo-viscoelastic dynamic model permits perfect description of the density-density and current-current time correlation functions of the liquid Na in a wide range of wave numbers, which implies that the origin of the non-hydrodynamic collective excitations contributing to longitudinal dynamics can be short-wavelength heat waves. PMID:27208952
NASA Astrophysics Data System (ADS)
Bryk, Taras; Wax, J.-F.
2016-05-01
Using a combination of ab initio molecular dynamics and several fit models for dynamic structure of liquid metals, we explore an issue of possible manifestation of non-acoustic collective excitations in longitudinal dynamics having liquid Na as a case study. A model with two damped harmonic oscillators (DHOs) in time domain is used for analysis of the density-density time correlation functions. Another similar model with two propagating contributions and three lowest exact sum rules is considered, as well as an extended hydrodynamic model known as thermo-viscoelastic one which permits two types of propagating modes outside the hydrodynamic region to be used for comparison with ab initio obtained time correlation functions and calculations of dispersions of collective excitations. Our results do not support recent suggestions that, even in simple liquid metals, non-hydrodynamics transverse excitations contribute to the longitudinal collective dynamics and can be detected as a DHO-like spectral shape at their transverse frequency. We found that the thermo-viscoelastic dynamic model permits perfect description of the density-density and current-current time correlation functions of the liquid Na in a wide range of wave numbers, which implies that the origin of the non-hydrodynamic collective excitations contributing to longitudinal dynamics can be short-wavelength heat waves.
Suppression of higher mode excitation in a high gain relativistic klystron amplifier
NASA Astrophysics Data System (ADS)
Wu, Y.; Xu, Z.; Jin, X.; Li, Z. H.; Tang, C. X.
2012-02-01
Suppressing higher mode excitation is very important in the high gain relativistic klystron amplifier because higher mode can seriously degrade klystron performance and cause pulse shortening. The mechanism of higher mode self-excitation is explored in the PIC simulation, and it is shown the coupling between cavities is the main cause of higher mode self-excitation. The coupling forms the positive feedback loop for higher mode to be excited just like that in the oscillator circuit. The formula for startup current of higher mode self-excitation is developed based on the coupling between cavities. And the corresponding methods are taken to avoid higher mode self-excitation. Finally, mode control is realized in the RKA with output power up to 1.02 GW when driven power is only few kilowatts.
Collective excitations in liquid CD4: Neutron scattering and molecular-dynamics simulations
NASA Astrophysics Data System (ADS)
Guarini, E.; Bafile, U.; Barocchi, F.; Demmel, F.; Formisano, F.; Sampoli, M.; Venturi, G.
2005-12-01
We have investigated the dynamic structure factor S(Q,ω) of liquid CD4 at T = 97.7 K in the wave vector range 2 <= Q/nm-1 <= 15 by means of neutron scattering and molecular-dynamics simulation, in order to study the centre-of-mass collective dynamics. The agreement between the experimental spectra and those simulated using a recent ab initio based intermolecular potential is good, particularly at low Q. Underdamped collective excitations, detected in the whole experimental Q-range, characterize the dynamics of liquid CD4 as markedly different from that of other molecular liquids. Also, the energy and damping of collective excitations in methane are shown to differ considerably, even at the lowest measured Q-values, from those of linearized hydrodynamic modes. An empirical relation, able to reconcile the different wave vector ranges of mode propagation observed in disparate liquids, is investigated.
Dynamics of the collective modes of an inhomogeneous spin ensemble in a cavity
Wesenberg, Janus H.; Kurucz, Zoltan; Moelmer, Klaus
2011-02-15
We study the excitation dynamics of an inhomogeneously broadened spin ensemble coupled to a single cavity mode. The collective excitations of the spin ensemble can be described in terms of generalized spin waves, and, in the absence of the cavity, the free evolution of the spin ensemble can be described as a drift in the wavenumber without dispersion. In this article we show that the dynamics in the presence of coupling to the cavity mode can be described solely by a modified time evolution of the wavenumbers. In particular, we show that collective excitations with a well-defined wavenumber pass without dispersion from negative to positive-valued wavenumbers without populating the zero wavenumber spin wave mode. The results are relevant for multimode collective quantum memories where qubits are encoded in different spin waves.
Collective excitations on a surface of topological insulator
2012-01-01
We study collective excitations in a helical electron liquid on a surface of three-dimensional topological insulator. Electron in helical liquid obeys Dirac-like equation for massless particles and direction of its spin is strictly determined by its momentum. Due to this spin-momentum locking, collective excitations in the system manifest themselves as coupled charge- and spin-density waves. We develop quantum field-theoretical description of spin-plasmons in helical liquid and study their properties and internal structure. Value of spin polarization arising in the system with excited spin-plasmons is calculated. We also consider the scattering of spin-plasmons on magnetic and nonmagnetic impurities and external potentials, and show that the scattering occurs mainly into two side lobes. Analogies with Dirac electron gas in graphene are discussed. PACS: 73.20.Mf; 73.22.Lp; 75.25.Dk. PMID:22376744
Excitation of external kink mode by trapped energetic particles
NASA Astrophysics Data System (ADS)
Guo, S. C.; Xu, X. Y.; Liu, Y. Q.; Wang, Z. R.
2016-05-01
An unstable fishbone-like non-resonant external kink mode (FLEM) is numerically found to be driven by the precessional drift motion of trapped energetic particles (EPs) in both reversed-field pinch (RFP) and tokamak plasmas, even under the ideal wall boundary condition. In the presence of a sufficiently large fraction of trapped energetic ions in high beta plasmas, the FLEM instability may occur. The excitation condition is discussed in detail. The frequency of the FLEM is linked to the precessional drift frequency of EPs, and varies with the plasma flow speed. Therefore, it is usually much higher than that of the typical resistive wall mode (RWM). In general, the growth rate of FLEM does not depend on the wall resistivity. However, the wall position can significantly affect the mode’s property. The drift kinetic effects from thermal particles (mainly due to the transit resonance of passing particles) play a stabilizing role on FLEMs. In the presence of EPs, the FLEM and the RWM can co-exist or even couple to each other, depending on the plasma parameters. The FLEM instabilities in RFP and tokamaks have rather similar physics nature, although certain sub-dominant characters appear differently in the two configurations.
Minola, M; Dellea, G; Gretarsson, H; Peng, Y Y; Lu, Y; Porras, J; Loew, T; Yakhou, F; Brookes, N B; Huang, Y B; Pelliciari, J; Schmitt, T; Ghiringhelli, G; Keimer, B; Braicovich, L; Le Tacon, M
2015-05-29
We used resonant inelastic x-ray scattering (RIXS) with and without analysis of the scattered photon polarization, to study dispersive spin excitations in the high temperature superconductor YBa_{2}Cu_{3}O_{6+x} over a wide range of doping levels (0.1≤x≤1). The excitation profiles were carefully monitored as the incident photon energy was detuned from the resonant condition, and the spin excitation energy was found to be independent of detuning for all x. These findings demonstrate that the largest fraction of the spin-flip RIXS profiles in doped cuprates arises from magnetic collective modes, rather than from incoherent particle-hole excitations as recently suggested theoretically [Benjamin et al. Phys. Rev. Lett. 112, 247002 (2014)]. Implications for the theoretical description of the electron system in the cuprates are discussed. PMID:26066453
Collective spin excitation in finite size array of patterned magnonic crystals
NASA Astrophysics Data System (ADS)
Piao, H.-G.; Shim, J.-H.; Pan, L.; Yu, S.-C.; Kim, D.-H.
2016-04-01
We explore further details of the collectively excited spin wave mode in finite arrays of elliptically shaped ferromagnetic nanoelements as two-dimensional magnonic crystals by means of micromagnetic simulations. Under a pulsed magnetic driving field, collective spin wave modes were intensively investigated with variation of nanoelement dimensions and interelement separation as structural parameters of the magnonic crystal as well as changing the applied bias magnetic field. Via observing and analyzing the dynamic behavior of collective spin wave modes, we have found that the dynamic behavior strongly depends on the bias magnetic field with a quasi-linear dependency. The quasi-linear dependency of spin wave frequency transition can be achieved to a high sensitivity of the pT/Hz level. By modulating the magnonic crystal lattice structures and the bias magnetic field, the spin wave dynamic behavior is tunable which might be a promising property for a future magnonic crystal application and multifunctional sensors.
Experimental studies of collective excitations of a BEC in light-induced gauge fields
NASA Astrophysics Data System (ADS)
Li, Chuan-Hsun; Niffenegger, Robert; Blasing, David; Olson, Abraham; Chen, Yong P.
2015-05-01
We present our experimental studies of collective modes including spin dipole mode and scissors mode of a 87Rb Bose-Einstein condensate (BEC) in the presence of Raman light-induced gauge fields and synthetic spin-orbit coupling (SOC). By Raman dressing the mf spin states within the F =1 manifold, we engineer atoms' energy-momentum dispersion to create synthetic SOC, and spin dependent synthetic electric and magnetic fields. We have used spin dependent synthetic electric fields to make two BECs with different spins oscillate and collide in the optical trap. We have studied the effects of SOC on both the momentum damping and thermalization behaviors of the BECs when undergoing such spin dipole oscillations. We have also used spatially dependent synthetic electric fields to excite the scissors mode, which has been used as a probe for superfluidity. We have investigated the effects of the synthetic gauge fields and SOC on the measured scissors mode.
Excitation of ultrasharp trapped-mode resonances in mirror-symmetric metamaterials
NASA Astrophysics Data System (ADS)
Yang, Shengyan; Liu, Zhe; Xia, Xiaoxiang; E, Yiwen; Tang, Chengchun; Wang, Yujin; Li, Junjie; Wang, Li; Gu, Changzhi
2016-06-01
We experimentally demonstrate a metamaterial structure composed of two mirror-symmetric joint split ring resonators (JSRRs) that support extremely sharp trapped-mode resonance with a large modulation depth in the terahertz region. Contrary to the regular mirror-arranged SRR arrays in which both the subradiant inductive-capacitive (LC) resonance and quadrupole-mode resonance can be excited, our designed structure features a metallic microstrip bridging the adjacent SRRs, which leads to the emergence of an otherwise inaccessible ultrahigh-quality-factor resonance. The ultrasharp resonance occurs near the Wood-Rayleigh anomaly frequency, and the underlying mechanism can be attributed to the strong coupling between the in-plane propagating collective lattice surface mode originating from the array periodicity and localized surface plasmon resonance in mirror-symmetric coupled JSRRs, which dramatically reduces radiative damping. The ultrasharp resonance shows great potential for multifunctional applications such as plasmonic switching, low-power nonlinear processing, and chemical and biological sensing.
Collective excitations in Na2IrO3.
Igarashi, Jun-Ichi; Nagao, Tatsuya
2016-01-20
We study the collective excitations of Na2IrO3 in an itinerant electron approach. We consider a multi-orbital tight-binding model with the electron transfer between the Ir 5d states mediated via oxygen 2p states and the direct d-d transfer on a honeycomb lattice. The one electron energy as well as the ground state energy are investigated within the Hartree-Fock approximation. When the direct d-d transfer is weak, we obtain nearly flat energy bands due to the formation of quasimolecular orbitals, and the ground state exhibits the zigzag spin order. The evaluation of the density-density correlation function within the random phase approximation shows that the collective excitations emerge as bound states. For an appropriate value of the direct d-d transfer, some of them are concentrated in the energy region ω<50 meV(magnetic excitations) while the others lie in the energy region ω>350 meV (excitonic excitations). This behaviour is consistent with the resonant inelastic x-ray scattering spectra. We also show that the larger values of the direct d-d transfer are unfavourable in order to explain the observed aspects of Na2IrO3 such as the ordering pattern of the ground state and the excitation spectrum. These findings may indicate that the direct d-d transfer is suppressed by the structural distortions in the view of excitation spectroscopy, as having been pointed out in the ab initio calculation. PMID:26683496
Collective excitations in Na2IrO3
NASA Astrophysics Data System (ADS)
Igarashi, Jun-Ichi; Nagao, Tatsuya
2016-01-01
We study the collective excitations of Na2IrO3 in an itinerant electron approach. We consider a multi-orbital tight-binding model with the electron transfer between the Ir 5d states mediated via oxygen 2p states and the direct d-d transfer on a honeycomb lattice. The one-electron energy as well as the ground state energy are investigated within the Hartree-Fock approximation. When the direct d-d transfer is weak, we obtain nearly flat energy bands due to the formation of quasimolecular orbitals, and the ground state exhibits the zigzag spin order. The evaluation of the density-density correlation function within the random phase approximation shows that the collective excitations emerge as bound states. For an appropriate value of the direct d-d transfer, some of them are concentrated in the energy region ω <50 meV (magnetic excitations) while the others lie in the energy region ω >350 meV (excitonic excitations). This behaviour is consistent with the resonant inelastic x-ray scattering spectra. We also show that the larger values of the direct d-d transfer are unfavourable in order to explain the observed aspects of Na2IrO3 such as the ordering pattern of the ground state and the excitation spectrum. These findings may indicate that the direct d-d transfer is suppressed by the structural distortions in the view of excitation spectroscopy, as having been pointed out in the ab initio calculation.
Retardation effects on collective excitations in correlated superlattices
NASA Astrophysics Data System (ADS)
Golden, Kenneth I.; Kalman, G.; Miao, Limin; Snapp, Robert R.
1998-04-01
The authors analyze the effects of electrodynamic retardation on the collective modes in an unmagnetized infinite superlattice modeled as an array of parallel two-dimensional plasma layers embedded in a dielectric substrate. The present work concentrates for the most part on correlated semiconductor superlattices, although the model is equally well suited to metallic superlattices consisting of an alternating array of thin metal layers and thick insulator slabs (e.g., 50 Å Al layers and 500 Å Al2O3 slabs). The analysis is based on the transverse magnetic (TM) and transverse electric (TE) dispersion relations recently formulated by the authors in the retarded quasilocalized charge approximation (RQLCA) [K. I. Golden, G. Kalman, L. Miao, and R. R. Snapp, Phys. Rev. B 55, 16 349 (1997)]. In the nonretarded limit, the QLCA mode structure consists of (i) an isolated in-phase plasmon mode, (ii) a band of gapped plasmons, (iii) an in-phase acoustic shear mode, and (iv) a band of gapped shear modes. This paper presents numerical and approximate analytical solutions of the long-wavelength RQLCA dispersion relations for the collective modes (i)-(iv) all the way down to very small wave numbers where retardation effects can be especially pronounced. Additionally, this work presents insightful approximate analytical formulas for the electromagnetic mode frequencies and gap widths, which add to the literature on the infinite sequences of TM- and TE-polarized electromagnetic bands. Some noteworthy effects that emerge from this study are as follows: (a) The appearance of ultralow frequency shear modes arising from the combined effect of retardation and strong coulomb interactions; the quasilocalization basis of the theory suggests that these modes can propagate when the two-dimensional plasma layers are in a crystalline phase. (b) A negative random-phase approximation shift in the bulk-plasma frequency induced by electrodynamic retardation; this effect can be appreciable in
Observation of the first excited transverse mode in guided matter waves.
Dall, R G; Hodgman, S S; Manning, A G; Truscott, A G
2011-04-01
In direct analogy to the textbook example of light guided in a few-mode fiber (FMF), we report the observation of the first excited mode of an optically guided atomic beam. We selectively excite the atomic analog of the LP₀₁ optical mode by controlling the energy distribution of ultracold atoms loaded into the guide, resulting in a modal structure dominated by a 47(2)% population in the first excited transverse mode. The ability to guide lower-order modes has been essential to demonstrating optical effects such as multimode interferometry, slow light, and entanglement, and an atomic analog to a FMF may lead to similarly useful applications. PMID:21479006
Magnetic antenna excitation of whistler modes. I. Basic properties
Urrutia, J. M.; Stenzel, R. L.
2014-12-15
Properties of magnetic loop antennas for exciting electron whistler modes have been investigated in a large laboratory plasma. The parameter regime is that of large plasma frequency compared to the cyclotron frequency and signal frequency below half the cyclotron frequency. The antenna diameter is smaller than the wavelength. Different directions of the loop antenna relative to the background magnetic field have been measured for small amplitude waves. The differences in the topology of the wave magnetic field are shown from measurements of the three field components in three spatial directions. The helicity of the wave magnetic field and of the hodogram of the magnetic vector in space and time are clarified. The superposition of wave fields is used to investigate the properties of two antennas for small amplitude waves. Standing whistler waves are produced by propagating two wave packets in opposite directions. Directional radiation is obtained with two phased loops separated by a quarter wavelength. Rotating antenna fields, produced with phased orthogonal loops at the same location, do not produce directionality. The concept of superposition is extended in a Paper II to generate antenna arrays for whistlers. These produce nearly plane waves, whose propagation angle can be varied by the phase shifting the currents in the array elements. Focusing of whistlers is possible. These results are important for designing antennas on spacecraft or diagnosing and heating of laboratory plasmas.
Higgs amplitude mode in the BCS superconductors Nb1-xTi(x)N induced by terahertz pulse excitation.
Matsunaga, Ryusuke; Hamada, Yuki I; Makise, Kazumasa; Uzawa, Yoshinori; Terai, Hirotaka; Wang, Zhen; Shimano, Ryo
2013-08-01
Ultrafast responses of BCS superconductor Nb(1-x)Ti(x)N films in a nonadiabatic excitation regime were investigated by using terahertz (THz) pump-THz probe spectroscopy. After an instantaneous excitation with the monocycle THz pump pulse, a transient oscillation emerges in the electromagnetic response in the BCS gap energy region. The oscillation frequency coincides with the asymptotic value of the BCS gap energy, indicating the appearance of the theoretically anticipated collective amplitude mode of the order parameter, namely the Higgs amplitude mode. Our result opens a new pathway to the ultrafast manipulation of the superconducting order parameter by optical means. PMID:23952432
Sensitivity of nonlinear photoionization to resonance substructure in collective excitation
Mazza, T.; Karamatskou, A.; Ilchen, M.; Bakhtiarzadeh, S.; Rafipoor, A. J.; O'Keeffe, P.; Kelly, T. J.; Walsh, N.; Costello, J. T.; Meyer, M.; Santra, R.
2015-01-01
Collective behaviour is a characteristic feature in many-body systems, important for developments in fields such as magnetism, superconductivity, photonics and electronics. Recently, there has been increasing interest in the optically nonlinear response of collective excitations. Here we demonstrate how the nonlinear interaction of a many-body system with intense XUV radiation can be used as an effective probe for characterizing otherwise unresolved features of its collective response. Resonant photoionization of atomic xenon was chosen as a case study. The excellent agreement between experiment and theory strongly supports the prediction that two distinct poles underlie the giant dipole resonance. Our results pave the way towards a deeper understanding of collective behaviour in atoms, molecules and solid-state systems using nonlinear spectroscopic techniques enabled by modern short-wavelength light sources. PMID:25854939
Sensitivity of nonlinear photoionization to resonance substructure in collective excitation
Mazza, T.; Karamatskou, A.; Ilchen, M.; Bakhtiarzadeh, S.; Rafipoor, A. J.; O’Keeffe, P.; Kelly, T. J.; Walsh, N.; Costello, J. T.; Meyer, M.; Santra, R.
2015-04-09
Collective behaviour is a characteristic feature in many-body systems, important for developments in fields such as magnetism, superconductivity, photonics and electronics. Recently, there has been increasing interest in the optically nonlinear response of collective excitations. Here we demonstrate how the nonlinear interaction of a many-body system with intense XUV radiation can be used as an effective probe for characterizing otherwise unresolved features of its collective response. Resonant photoionization of atomic xenon was chosen as a case study. The excellent agreement between experiment and theory strongly supports the prediction that two distinct poles underlie the giant dipole resonance. Our results pave the way towards a deeper understanding of collective behaviour in atoms, molecules and solid-state systems using nonlinear spectroscopic techniques enabled by modern short-wavelength light sources.
Sensitivity of nonlinear photoionization to resonance substructure in collective excitation
Mazza, T.; Karamatskou, A.; Ilchen, M.; Bakhtiarzadeh, S.; Rafipoor, A. J.; O’Keeffe, P.; Kelly, T. J.; Walsh, N.; Costello, J. T.; Meyer, M.; et al
2015-04-09
Collective behaviour is a characteristic feature in many-body systems, important for developments in fields such as magnetism, superconductivity, photonics and electronics. Recently, there has been increasing interest in the optically nonlinear response of collective excitations. Here we demonstrate how the nonlinear interaction of a many-body system with intense XUV radiation can be used as an effective probe for characterizing otherwise unresolved features of its collective response. Resonant photoionization of atomic xenon was chosen as a case study. The excellent agreement between experiment and theory strongly supports the prediction that two distinct poles underlie the giant dipole resonance. Our results pavemore » the way towards a deeper understanding of collective behaviour in atoms, molecules and solid-state systems using nonlinear spectroscopic techniques enabled by modern short-wavelength light sources.« less
NASA Astrophysics Data System (ADS)
Ekardt, W.
1987-09-01
The wave-vector dispersion of collective modes in small particles is investigated within the time-dependent local-density approximation as applied to a self-consistent jellium particle. It is shown that the dispersion of the volume plasmons can be understood from that in an infinite electron gas. For a given multipole an optimum wave vector exists for the quasiresonant excitation of the volume mode but not for the surface mode. It is pointed out that-for the volume modes-the hydrodynamic approximation gives a reasonable first guess for the relation between frequencies and size-quantized wave vectors.
Wave modes of collective vortex gyration in dipolar-coupled-dot-array magnonic crystals
Han, Dong-Soo; Vogel, Andreas; Jung, Hyunsung; Lee, Ki-Suk; Weigand, Markus; Stoll, Hermann; Schütz, Gisela; Fischer, Peter; Meier, Guido; Kim, Sang-Koog
2013-01-01
Lattice vibration modes are collective excitations in periodic arrays of atoms or molecules. These modes determine novel transport properties in solid crystals. Analogously, in periodical arrangements of magnetic vortex-state disks, collective vortex motions have been predicted. Here, we experimentally observe wave modes of collective vortex gyration in one-dimensional (1D) periodic arrays of magnetic disks using time-resolved scanning transmission x-ray microscopy. The observed modes are interpreted based on micromagnetic simulation and numerical calculation of coupled Thiele equations. Dispersion of the modes is found to be strongly affected by both vortex polarization and chirality ordering, as revealed by the explicit analytical form of 1D infinite arrays. A thorough understanding thereof is fundamental both for lattice vibrations and vortex dynamics, which we demonstrate for 1D magnonic crystals. Such magnetic disk arrays with vortex-state ordering, referred to as magnetic metastructure, offer potential implementation into information processing devices. PMID:23877284
Wave modes of collective vortex gyration in dipolar-coupled-dot-array magnonic crystals.
Han, Dong-Soo; Vogel, Andreas; Jung, Hyunsung; Lee, Ki-Suk; Weigand, Markus; Stoll, Hermann; Schütz, Gisela; Fischer, Peter; Meier, Guido; Kim, Sang-Koog
2013-01-01
Lattice vibration modes are collective excitations in periodic arrays of atoms or molecules. These modes determine novel transport properties in solid crystals. Analogously, in periodical arrangements of magnetic vortex-state disks, collective vortex motions have been predicted. Here, we experimentally observe wave modes of collective vortex gyration in one-dimensional (1D) periodic arrays of magnetic disks using time-resolved scanning transmission x-ray microscopy. The observed modes are interpreted based on micromagnetic simulation and numerical calculation of coupled Thiele equations. Dispersion of the modes is found to be strongly affected by both vortex polarization and chirality ordering, as revealed by the explicit analytical form of 1D infinite arrays. A thorough understanding thereof is fundamental both for lattice vibrations and vortex dynamics, which we demonstrate for 1D magnonic crystals. Such magnetic disk arrays with vortex-state ordering, referred to as magnetic metastructure, offer potential implementation into information processing devices. PMID:23877284
Collective excitations in a superfluid of color-flavor locked quark matter
NASA Astrophysics Data System (ADS)
Fukushima, Kenji; Iida, Kei
2005-04-01
We investigate collective excitations coupled with baryon density in a system of massless three-flavor quarks in the collisionless regime. By using the Nambu Jona-Lasinio (NJL) model in the mean-field approximation, we field-theoretically derive the spectra both for the normal and color-flavor locked (CFL) superfluid phases at zero temperature. In the normal phase, we obtain usual zero sound as a low-lying collective mode in the particle-hole (vector) channel. In the CFL phase, the nature of collective excitations varies in a way dependent on whether the excitation energy, ω, is larger or smaller than the threshold given by twice the pairing gap Δ, at which pair excitations with nonzero total momentum become allowed to break up into two quasiparticles. For ω≪2Δ, a phonon corresponding to fluctuations in the U(1) phase of Δ appears as a sharp peak in the particle-particle (“H”) channel. We reproduce the property known from low-energy effective theories that this mode propagates at a velocity of vH=1/√(3) in the low momentum regime; the decay constant fH obtained in the NJL model is identical with the QCD result obtained in the mean-field approximation. We also find that, as the momentum of the phonon increases, the excitation energy goes up and asymptotically approaches ω=2Δ. Above the threshold for pair excitations (ω>2Δ), zero sound manifests itself in the vector channel. By locating the zero sound pole of the vector propagator in the complex energy plane, we investigate the attenuation and energy dispersion relation of zero sound. In the long wavelength limit, the phonon mode, the only low-lying excitation, has its spectral weight in the H channel alone, while the spectral function vanishes in the vector channel. This is due to nontrivial mixing between the H and vector channels in the superfluid medium. We finally extend our study to the case of nonzero temperature. We demonstrate how Landau damping smears the phonon peak in the finite
Collective magneto-polariton excitation in a terahertz photonic cavity
NASA Astrophysics Data System (ADS)
Zhang, Qi; Lou, Minhan; Li, Xinwei; Chabanov, Andrey; Reno, John; Pan, Wei; Watson, John; Manfra, Michael; Kono, Junichiro
Collective excitations in solids offer new opportunities for quantum optical studies. Many-body interactions inherent to condensed matter systems can lead to novel phenomena that cannot be achieved in traditional atomic systems. Here, we report collective ultrastrong light-matter coupling in a two-dimensional electron gas in a high- Q terahertz photonic-crystal cavity in a magnetic field. We directly observed time-domain vacuum Rabi oscillations, whose frequency was found to be proportional to the square root of N (where N is the carrier density), evidence for the collective nature of ultrastrong coupling. In addition, a small but definite blue shift due to the diamagnetic term in the Hamiltonian was observed for the polariton frequencies, which is another signature of ultrastrong light-matter coupling. Furthermore, the high- Q cavity suppressed the superradiant decay of cyclotron resonance, which resulted in unprecedentedly narrow intrinsic cyclotron resonance linewidths (~5.6 GHz at 2 K). Our method is also applicable to many classes of strongly correlated systems with collective many-body excitations in the terahertz range, opening a door to the fascinating physics of terahertz many-body cavity QED.
Local excitation and collection in polymeric fluorescent microstructures
NASA Astrophysics Data System (ADS)
Henrique, Franciele Renata; Mendonca, Cleber Renato
2016-04-01
Integrated photonics has gained attention in recent years due to its wide range of applications which span from biology to optical communications. The use of polymer-based platforms for photonic devices is of great interest because organic compounds can be easily incorporated to polymers, enabling modifications to the system physical properties. The two-photon polymerization technique has emerged as an interesting tool for the production of three-dimensional polymeric microstructures. However, for their further incorporation in photonic devices it is necessary to develop methods to perform optical excitation and signal collection on such microstructures. With such purpose, we demonstrate approaches to perform local excitation and collection in polymeric microstructures doped with fluorescent dyes, employing tapered fibers. The obtained results indicate that fiber tapers are suitable to couple light in and out of fluorescent polymeric microstructures, paving the way for their incorporation in photonic devices. We also show that microstructures doped with more than one dye can be used as built-in broadband light sources to photonic circuits and their emission spectrum can be tuned by the right choice of the excitation position.
Charge-exchange modes of excitation in deformed neutron-rich nuclei
Yoshida, Kenichi
2015-10-15
Gamow-Teller (GT) mode of excitation and β-decay properties of deformed neutron-rich even-N Zr isotopes are investigated in a self-consistent Skyrme energy-density-functional approach, in which the Hartree-Fock-Bogoliubov equation is solved in the coordinate space and the proton-neutron Quasiparticle-RPA equation is solved in the quasiparticle basis. It is found that a stronger collectivity is generated for the GT giant resonance as an increase in the neutron number. Furthermore, we find that the T = 0 pairing enhances the low-lying GT strengths cooperatively with the T = 1 pairing correlation depending on the microscopic structure of the low-lying mode and the shell structure around the Fermi levels, and that the enhanced strength shortens the β-decay half-lives by at most an order of magnitude.
NASA Astrophysics Data System (ADS)
Lisenkov, Ivan; Tyberkevych, Vasyl; Nikitov, Sergey; Slavin, Andrei
2016-06-01
A general theory of collective spin-wave edge modes in semi-infinite and finite periodic arrays of magnetic nanodots having uniform dynamic magnetization (macrospin approximation) is developed. The theory is formulated using a formalism of multivectors of magnetization dynamics, which allows one to study edge modes in arrays having arbitrarily complex primitive cells and lattice structure. The developed formalism can describe spin-wave edge modes localized both at the physical edges of the array and at the internal "domain walls" separating the array regions existing in different static magnetization states. Using a perturbation theory, in the framework of the developed formalism, it is possible to calculate damping of the edge modes and to describe their excitation by external variable magnetic fields. The theory is illustrated on the following practically important examples: (i) calculation of the FMR absorption in a finite nanodot array having the shape of a right triangle; (ii) calculation of the spectra of nonreciprocal spin-wave edge modes, including the modes at the physical edges of an array and modes at the domain walls inside the array; and (iii) study of the influence of the domain wall modes on the FMR spectrum of an array existing in a nonideal chessboard antiferromagnetic ground state.
Collective Excitations in InAs Well Intersubband Transitions
NASA Technical Reports Server (NTRS)
Li, Jian-Zhong; Ning, Cun-Zheng
2003-01-01
Intersubband transitions in semiconductor quantum well are studied using a density matrix theory that goes beyond the Hartree-Fock approximation by including the full second order electron-electron scattering terms in the polarization equation for the first time. Even though the spectral features remain qualitatively similar to the results obtained with dephasing rate approximation, significant quantitative changes result from such a more detailed treatment of dephasing. More specifically, we show how the interplay of the two fundamental collective excitations, the Fermi-edge singularity and the intersubband plasmon, leads to significant changes in lineshape as the electron density varies.
Phase velocity spectrum analysis for a time delay comb transducer for guided wave mode excitation
Quarry, M J; Rose, J L
2000-09-26
A theoretical model for the analysis of ultrasonic guided wave mode excitation of a comb transducer with time delay features was developed. Time delay characteristics are included via a Fourier transform into the frequency domain. The phase velocity spectrum can be used to determine the mode excitation on the phase velocity dispersion curves for a given structure. Experimental and theoretical results demonstrate the tuning of guided wave modes using a time delay comb transducer.
Planar Defect Modes Excited at the Band Edge of Three-dimensional Photonic Crystals
NASA Astrophysics Data System (ADS)
Iida, Masaru; Tani, Masahiko; Sakai, Kiyomi; Watanabe, Masayoshi; Kitahara, Hideaki; Tohme, Takuya; Wada Takeda, Mitsuo
2004-09-01
We experimentally and numerically studied planar defect modes excited at band-edge resonant mode frequencies in three-dimensional photonic crystals. We identified the observed peaks as the defect modes using the spectrum calculated at the defect layer. The spectrum also clarifies the difference between these modes and ordinary band-edge resonant modes. The calculated spatial distribution of the electric field in the defect modes shows that the defect modes have a characteristic field concentration in the band-edge resonant mode.
Collective excitations in 2D hard-disc fluid.
Huerta, Adrian; Bryk, Taras; Trokhymchuk, Andrij
2015-07-01
Collective dynamics of a two-dimensional (2D) hard-disc fluid was studied by molecular dynamics simulations in the range of packing fractions that covers states up to the freezing. Some striking features concerning collective excitations in this system were observed. In particular, the short-wavelength shear waves while being absent at low packing fractions were observed in the range of high packing fractions, just before the freezing transition in a 2D hard-disc fluid. In contrast, the so-called "positive sound dispersion" typically observed in dense Lennard-Jones-like fluids, was not detected for the 2D hard-disc fluid. The ratio of specific heats in the 2D hard-disc fluid shows a monotonic increase with density approaching the freezing, resembling in this way the similar behavior in the vicinity of the Widom line in the case of supercritical fluids. PMID:25595625
Strong interaction between electrons and collective excitations in the multiband superconductor MgB2
Mou, Daixiang; Jiang, Rui; Taufour, Valentin; Flint, Rebecca; Bud'ko, S. L.; Canfield, P. C.; Wen, J. S.; Xu, Z. J.; Gu, Genda; Kaminski, Adam
2015-04-08
We use a tunable laser angle-resolved photoemission spectroscopy to study the electronic properties of the prototypical multiband BCS superconductor MgB2. Our data reveal a strong renormalization of the dispersion (kink) at ~65meV, which is caused by the coupling of electrons to the E2g phonon mode. In contrast to cuprates, the 65 meV kink in MgB2 does not change significantly across Tc. More interestingly, we observe strong coupling to a second, lower energy collective mode at a binding energy of 10 meV. As a result, this excitation vanishes above Tc and is likely a signature of the elusive Leggett mode.
Dhakal, Ashim; Raza, Ali; Peyskens, Frédéric; Subramanian, Ananth Z; Clemmen, Stéphane; Le Thomas, Nicolas; Baets, Roel
2015-10-19
We develop and experimentally verify a theoretical model for the total efficiency η0 of evanescent excitation and subsequent collection of spontaneous Raman signals by the fundamental quasi-TE and quasi-TM modes of a generic photonic channel waveguide. Single-mode silicon nitride (Si3N4) slot and strip waveguides of different dimensions are used in the experimental study. Our theoretical model is validated by the correspondence between the experimental and theoretical absolute values within the experimental errors. We extend our theoretical model to silicon-on-insulator (SOI) and titanium dioxide (TiO2) channel waveguides and study η0 as a function of index contrast, polarization of the mode and the geometry of the waveguides. We report nearly 2.5 (4 and 5) times larger η0 for the fundamental quasi-TM mode when compared to η0 for the fundamental quasi-TE mode of a typical Si3N4 (TiO2 and SOI) strip waveguide. η0 for the fundamental quasi-TE mode of a typical Si3N4, (TiO2 and SOI) slot waveguide is about 7 (22 and 90) times larger when compared to η0 for the fundamental quasi-TE mode of a strip waveguide of the similar dimensions. We attribute the observed enhancement to the higher electric field discontinuity present in high index contrast waveguides. PMID:26480401
Collective spin excitations in 2D paramagnet with dipole interaction
NASA Astrophysics Data System (ADS)
Tsiberkin, Kirill
2016-02-01
The collective spin excitations in the unbounded 2D paramagnetic system with dipole interactions are studied. The model Hamiltonian includes Zeeman energy and dipole interaction energy, while the exchange vanishes. The system is placed into a constant uniform magnetic field which is orthogonal to the lattice plane. It provides the equilibrium state with spin ordering along the field direction, and the saturation is reached at zero temperature. We consider the deviations of spin magnetic moments from its equilibrium position along the external field. The Holstein-Primakoff representation is applied to spin operators in low-temperature approximation. When the interaction between the spin waves is negligible and only two-magnon terms are taken into account, the Hamiltonian diagonalisation is possible. We obtain the dispersion relation for spin waves in the square and hexagonal honeycomb lattice. Bose-Einstein statistics determine the average number of spin deviations, and total system magnetization. The lattice structure does not influence on magnetization at the long-wavelength limit. The dependencies of the relative magnetization and longitudinal susceptibility on temperature and external field intensity are found. The internal energy and specific heat of the Bose gas of spin waves are calculated. The collective spin excitations play a significant role in the properties of the paramagnetic system at low temperature and strong external magnetic field.
User-friendly software for modeling collective spin wave excitations
NASA Astrophysics Data System (ADS)
Hahn, Steven; Peterson, Peter; Fishman, Randy; Ehlers, Georg
There exists a great need for user-friendly, integrated software that assists in the scientific analysis of collective spin wave excitations measured with inelastic neutron scattering. SpinWaveGenie is a C + + software library that simplifies the modeling of collective spin wave excitations, allowing scientists to analyze neutron scattering data with sophisticated models fast and efficiently. Furthermore, one can calculate the four-dimensional scattering function S(Q,E) to directly compare and fit calculations to experimental measurements. Its generality has been both enhanced and verified through successful modeling of a wide array of magnetic materials. Recently, we have spent considerable effort transforming SpinWaveGenie from an early prototype to a high quality free open source software package for the scientific community. S.E.H. acknowledges support by the Laboratory's Director's fund, ORNL. Work was sponsored by the Division of Scientific User Facilities, Office of Basic Energy Sciences, US Department of Energy, under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC.
NASA Astrophysics Data System (ADS)
Zocher, E.
1987-12-01
A multiport hybrid mode exciter with axial mode feed, generating each of the two orthogonally polarized sum and difference radiation patterns was developed. The modes TE11, TE11*, TE01, TM01 excited by mode couplers in different sections of the circular main waveguide are transferred using a conical corrugated transition to hybrid modes HE11, HE11* and to the classical modes of the TE01 and the TM02 type in the next cylindrical corrugated waveguide section. These modes are radiated by a conical corrugated horn. The principles applied for the design of mode couplers and feed networks are illustrated. Using theoretical results, the dimensioning of the corrugated waveguide components with reduced disturbing modes is explained. The measured radiation patterns show good rotational symmetry, low sidelobes and very small cross polarization levels.
Collective modes in a uniform Fermi gas with Feshbach resonances
Huang, Beibing; Wan, Shaolong
2007-05-15
The collective modes in a uniform fermionic atomic gas with Feshbach resonance are investigated with the path integral method in the frame of a fermion-boson model Hamiltonian. We mainly concentrated on the long-wavelength and low-frequency limits at T=0 K and got an analytical expression for the collective modes across the whole BCS-Bose-Einstein condensate (BEC) crossover. We completely recover the Anderson-Bogoliubov modes in the BCS limit and the Bogoliubov modes of the bosonic systems in the BEC limit. The numerical results show that there exists a continuous interpolation for sound velocity between BCS and BEC limits.
NASA Astrophysics Data System (ADS)
Kozich, V.; Szyc, Ł.; Nibbering, E. T. J.; Werncke, W.; Elsaesser, T.
2009-04-01
Vibrational relaxation after spectrally selective excitation within the NH stretching band of adenine-thymine base pairs in DNA oligomers was studied by subpicosecond infrared-pump/anti-Stokes Raman-probe spectroscopy. The decay of the different NH stretching vibrations populates distinct accepting modes in the NH bending range with a rise time of 0.6 ps that is close to the NH stretching decay times. The population of thymine fingerprint modes after excitation of the adenine antisymmetric NH 2 stretching mode points to an ultrafast excitation transfer to the thymine NH stretching vibration before relaxation. The nonequilibrium fingerprint populations decay on a time scale of several picoseconds.
Critical quadrupole fluctuations and collective modes in iron pnictide superconductors
NASA Astrophysics Data System (ADS)
Thorsmølle, V. K.; Khodas, M.; Yin, Z. P.; Zhang, Chenglin; Carr, S. V.; Dai, Pengcheng; Blumberg, G.
2016-02-01
The multiband nature of iron pnictides gives rise to a rich temperature-doping phase diagram of competing orders and a plethora of collective phenomena. At low dopings, the tetragonal-to-orthorhombic structural transition is closely followed by a spin-density-wave transition both being in close proximity to the superconducting phase. A key question is the nature of high-Tc superconductivity and its relation to orbital ordering and magnetism. Here we study the NaFe1 -xCoxAs superconductor using polarization-resolved Raman spectroscopy. The Raman susceptibility displays critical enhancement of nonsymmetric charge fluctuations across the entire phase diagram, which are precursors to a d -wave Pomeranchuk instability at temperature θ (x ) . The charge fluctuations are interpreted in terms of quadrupole interorbital excitations in which the electron and hole Fermi surfaces breathe in-phase. Below Tc, the critical fluctuations acquire coherence and undergo a metamorphosis into a coherent in-gap mode of extraordinary strength.
NASA Astrophysics Data System (ADS)
Qi, Zhongqiang; Au, Francis T. K.
2016-04-01
The vibration mode shapes are often used to identify damage of bridges because the mode shapes are not only important modal properties but also sensitive to damage. However, the key issue is how to conveniently obtain the mode shapes of a bridge in service. Traditional methods invariably require installation of instruments on the bridge for collection of dynamic responses for constructing mode shapes, which are both costly and inconvenient. Therefore a method is developed to construct the mode shapes of simply supported bridges based on Hilbert Transform using only vehicle acceleration response for identification of the location of damage. Firstly, an algorithm is devised to construct the mode shapes by using the dynamic responses extracted from a moving vehicle under impact excitation. Then, based on these intermediate results, the coordinate modal assurance criterion in conjunction with suitable wavelets is used to identify the location of damage. Compared with the traditional methods, the proposed method uses only the information from the moving vehicle. Moreover, additional impact excitation on the vehicle helps to excite the bridge. This helps to improve the accuracy by overcoming the adverse effects of measurement noise and road surface roughness, which leads to high accuracy of damage detection. To verify the feasibility of the proposed method, some numerical studies have been carried out to investigate the effects of measurement noise, road surface roughness and multiple locations of damage on the accuracy of results.
Higher Order Parametric Excitation Modes for Spaceborne Quadrupole Mass Spectrometers
NASA Technical Reports Server (NTRS)
Gershman, D. J.; Block, B. P.; Rubin, M.; Benna, M.; Mahaffy, P. R.; Zurbuchen, T. H.
2011-01-01
This paper describes a technique to significantly improve upon the mass peak shape and mass resolution of spaceborne quadrupole mass spectrometers (QMSs) through higher order auxiliary excitation of the quadrupole field. Using a novel multiresonant tank circuit, additional frequency components can be used to drive modulating voltages on the quadrupole rods in a practical manner, suitable for both improved commercial applications and spaceflight instruments. Auxiliary excitation at frequencies near twice that of the fundamental quadrupole RF frequency provides the advantages of previously studied parametric excitation techniques, but with the added benefit of increased sensed excitation amplitude dynamic range and the ability to operate voltage scan lines through the center of upper stability islands. Using a field programmable gate array, the amplitudes and frequencies of all QMS signals are digitally generated and managed, providing a robust and stable voltage control system. These techniques are experimentally verified through an interface with a commercial Pfeiffer QMG422 quadrupole rod system.When operating through the center of a stability island formed from higher order auxiliary excitation, approximately 50% and 400% improvements in 1% mass resolution and peak stability were measured, respectively, when compared with traditional QMS operation. Although tested with a circular rod system, the presented techniques have the potential to improve the performance of both circular and hyperbolic rod geometry QMS sensors.
Higher order parametric excitation modes for spaceborne quadrupole mass spectrometers
Gershman, D. J.; Block, B. P.; Rubin, M.; Zurbuchen, T. H.; Benna, M.; Mahaffy, P. R.
2011-12-15
This paper describes a technique to significantly improve upon the mass peak shape and mass resolution of spaceborne quadrupole mass spectrometers (QMSs) through higher order auxiliary excitation of the quadrupole field. Using a novel multiresonant tank circuit, additional frequency components can be used to drive modulating voltages on the quadrupole rods in a practical manner, suitable for both improved commercial applications and spaceflight instruments. Auxiliary excitation at frequencies near twice that of the fundamental quadrupole RF frequency provides the advantages of previously studied parametric excitation techniques, but with the added benefit of increased sensed excitation amplitude dynamic range and the ability to operate voltage scan lines through the center of upper stability islands. Using a field programmable gate array, the amplitudes and frequencies of all QMS signals are digitally generated and managed, providing a robust and stable voltage control system. These techniques are experimentally verified through an interface with a commercial Pfeiffer QMG422 quadrupole rod system. When operating through the center of a stability island formed from higher order auxiliary excitation, approximately 50% and 400% improvements in 1% mass resolution and peak stability were measured, respectively, when compared with traditional QMS operation. Although tested with a circular rod system, the presented techniques have the potential to improve the performance of both circular and hyperbolic rod geometry QMS sensors.
NASA Astrophysics Data System (ADS)
DeBock, M. F. M.; Classen, I. G. J.; Busch, C.; Jaspers, R. J. E.; Koslowski, H. R.; Unterberg, B.; TEXTOR Team
2008-01-01
For fusion reactors, based on the principle of magnetic confinement, it is important to avoid so-called magnetic islands or tearing modes. They reduce confinement and can be the cause of major disruptions. One class of magnetic islands is that of the perturbation field driven modes. This perturbation field can, for example, be the intrinsic error field. Theoretical work predicts a strong relationship between plasma rotation and the excitation of perturbation field modes. Experimentally, the theory on mode excitation and plasma rotation has been confirmed on several tokamaks. In those experiments, however, the control over the plasma rotation velocity and direction, and over the externally applied perturbation field was limited. In this paper experiments are presented that were carried out at the TEXTOR tokamak. Two tangential neutral beam injectors and a set of helical perturbation coils, called the dynamic ergodic divertor (DED), provide control over both the plasma rotation and the external perturbation field in TEXTOR. This made it possible to set up a series of experiments to test the theory on mode excitation and plasma rotation in detail. The perturbation field induced by the DED not only excites magnetic islands, it also sets up a layer near the plasma boundary where the magnetic field is stochastic. It will be shown that this stochastic field alters both the rotational response of the plasma on the perturbation field and the threshold for mode excitation. It therefore has to be included in an extended theory on mode excitation.
Interplay of Collective Excitations in Quantum Well Intersubband Resonances
NASA Technical Reports Server (NTRS)
Li, Jian-Zhong; Ning, C. Z.
2003-01-01
Intersubband resonances in a semiconductor quantum well (QW) display some of the most fascinating features involving various collective excitations such as Fermi-edge singularity (FES) and intersubband plasmon (ISP). Using a density matrix approach, we treated many-body effects such as depolarization, vertex correction, and self-energy consistently for a two-subband system. We found a systematic change in resonance spectra from FES-dominated to ISP-dominated features, as QW- width or electron density is varied. Such an interplay between FES and ISP significantly changes both line shape and peak position of the absorption spectrum. In particular, we found that a cancellation of FES and ISP undresses the resonant responses and recovers the single-particle features of absorption for semiconductors with a strong nonparabolicity such as InAs, leading to a dramatic broadening of the absorption spectrum.
Collective mode at Lifshitz transition in iron-pnictide superconductors.
Rodriguez, J P
2016-09-21
We obtain the exact low-energy spectrum of two mobile holes in a t-J model for an isolated layer in an iron-pnictide superconductor. The minimum d xz and d yz orbitals per iron atom are included, with no hybridization between the two. After tuning the Hund coupling to a putative quantum critical point (QCP) that separates a commensurate spin-density wave from a hidden-order antiferromagnet at half filling, we find an s-wave hole-pair groundstate and a d-wave hole-pair excited state. Near the QCP, both alternate in sign between hole Fermi surface pockets at the Brillouin zone center and emergent electron Fermi surface pockets at momenta that correspond to commensurate spin-density waves (cSDW). The dependence of the energy splitting with increasing Hund coupling yields evidence for a true QCP in the thermodynamic limit near the putative one, at which the s-wave and d-wave Cooper pairs are degenerate. A collective s-to-d-wave oscillation of the macroscopic superconductor that couples to orthorhombic shear strain is also identified. Its resonant frequency is predicted to collapse to zero at the QCP in the limit of low hole concentration. This implies degeneracy of Cooper pairs with s, d and [Formula: see text] symmetry in the corresponding quantum critical state. We argue that the critical state describes Cooper pairs in hole-doped iron superconductors at the Lifshitz transition, where electron bands first rise above the Fermi level. We thereby predict that the s-to-d-wave collective mode observed by Raman spectroscopy in Ba1-x K x Fe2As2 at optimal doping should also be observed at higher doping near the Lifshitz transition. PMID:27419913
Collective mode at Lifshitz transition in iron-pnictide superconductors
NASA Astrophysics Data System (ADS)
Rodriguez, J. P.
2016-09-01
We obtain the exact low-energy spectrum of two mobile holes in a t-J model for an isolated layer in an iron-pnictide superconductor. The minimum d xz and d yz orbitals per iron atom are included, with no hybridization between the two. After tuning the Hund coupling to a putative quantum critical point (QCP) that separates a commensurate spin-density wave from a hidden-order antiferromagnet at half filling, we find an s-wave hole-pair groundstate and a d-wave hole-pair excited state. Near the QCP, both alternate in sign between hole Fermi surface pockets at the Brillouin zone center and emergent electron Fermi surface pockets at momenta that correspond to commensurate spin-density waves (cSDW). The dependence of the energy splitting with increasing Hund coupling yields evidence for a true QCP in the thermodynamic limit near the putative one, at which the s-wave and d-wave Cooper pairs are degenerate. A collective s-to-d-wave oscillation of the macroscopic superconductor that couples to orthorhombic shear strain is also identified. Its resonant frequency is predicted to collapse to zero at the QCP in the limit of low hole concentration. This implies degeneracy of Cooper pairs with s, d and s+\\text{i}d symmetry in the corresponding quantum critical state. We argue that the critical state describes Cooper pairs in hole-doped iron superconductors at the Lifshitz transition, where electron bands first rise above the Fermi level. We thereby predict that the s-to-d-wave collective mode observed by Raman spectroscopy in Ba1‑x K x Fe2As2 at optimal doping should also be observed at higher doping near the Lifshitz transition.
Selective excitation of higher order modes in hollow-core PCF via prism-coupling.
Trabold, Barbara M; Novoa, David; Abdolvand, Amir; Russell, Philip St J
2014-07-01
Prism-coupling through the microstructured cladding is used to selectively excite individual higher order modes in hollow-core photonic crystal fibers (PCFs). Mode selection is achieved by varying the angle between the incoming beam and the fiber axis, in order to match the axial wavevector component to that of the desired mode. The technique allows accurate measurement of the effective indices and transmission losses of modes of arbitrary order, even those with highly complex transverse field distributions that would be extremely difficult to excite by conventional endfire coupling. PMID:24978724
Wu, Feng
2016-06-01
We present a quantum mechanical study of mode-specific tunneling upon fundamental excitation in malonaldehyde with a multidimensional theory that utilizes the saddle-point normal coordinates. We find that a ring-deformation normal mode is as essential as the well-known imaginary-frequency normal mode in the multidimensional investigation. The changes in tunneling splittings upon fundamental excitation are calculated. The results are competitive with those from a recently developed mixed classical-quantum method. Moreover, the results are qualitatively consistent with experiment for about half of all the modes. PMID:27192182
Characterization of superconducting radiofrequency breakdown by two-mode excitation
Eremeev, Grigory V.; Palczewski, Ari D.
2014-01-14
We show that thermal and magnetic contributions to the breakdown of superconductivity in radiofrequency (RF) fields can be separated by applying two RF modes simultaneously to a superconducting surface. We develop a simple model that illustrates how mode-mixing RF data can be related to properties of the superconductor. Within our model the data can be described by a single parameter, which can be derived either from RF or thermometry data. Our RF and thermometry data are in good agreement with the model. We propose to use mode-mixing technique to decouple thermal and magnetic effects on RF breakdown of superconductors.
NASA Astrophysics Data System (ADS)
Sedelnikova, O. V.; Bulusheva, L. G.; Asanov, I. P.; Yushina, I. V.; Okotrub, A. V.
2014-04-01
Effect of corrugation of hexagonal carbon network on the collective electron excitations has been studied using optical absorption and X-ray photoelectron spectroscopy in conjunction with density functional theory calculations. Onion-like carbon (OLC) was taken as a material, where graphitic mantle enveloping agglomerates of multi-shell fullerenes is strongly curved. Experiments showed that positions of π and π + σ plasmon modes as well as π → π* absorption peak are substantially redshifted for OLC as compared with those of highly ordered pyrolytic graphite and thermally exfoliated graphite consisted of planar sheets. This effect was reproduced in behavior of dielectric functions of rippled graphite models calculated within the random phase approximation. We conclude that the energy of electron excitations in graphitic materials could be precisely tuned by a simple bending of hexagonal network without change of topology. Moreover, our investigation suggests that in such materials optical exciton can transfer energy to plasmon non-radiatively.
Sedelnikova, O. V. Bulusheva, L. G.; Okotrub, A. V.; Asanov, I. P.; Yushina, I. V.
2014-04-21
Effect of corrugation of hexagonal carbon network on the collective electron excitations has been studied using optical absorption and X-ray photoelectron spectroscopy in conjunction with density functional theory calculations. Onion-like carbon (OLC) was taken as a material, where graphitic mantle enveloping agglomerates of multi-shell fullerenes is strongly curved. Experiments showed that positions of π and π + σ plasmon modes as well as π → π* absorption peak are substantially redshifted for OLC as compared with those of highly ordered pyrolytic graphite and thermally exfoliated graphite consisted of planar sheets. This effect was reproduced in behavior of dielectric functions of rippled graphite models calculated within the random phase approximation. We conclude that the energy of electron excitations in graphitic materials could be precisely tuned by a simple bending of hexagonal network without change of topology. Moreover, our investigation suggests that in such materials optical exciton can transfer energy to plasmon non-radiatively.
Nonlinear excitation of subcritical fast ion-driven modes
NASA Astrophysics Data System (ADS)
Lesur, M.; Itoh, K.; Ido, T.; Itoh, S.-I.; Kosuga, Y.; Sasaki, M.; Inagaki, S.; Osakabe, M.; Ogawa, K.; Shimizu, A.; Ida, K.; the LHD experiment group
2016-05-01
In collisionless plasma, it is known that linearly stable modes can be destabilized (subcritically) by the presence of structures in phase-space. The growth of such structures is a nonlinear, kinetic mechanism, which provides a channel for free-energy extraction, different from conventional inverse Landau damping. However, such nonlinear growth requires the presence of a seed structure with a relatively large threshold in amplitude. We demonstrate that, in the presence of another, linearly unstable (supercritical) mode, wave–wave coupling can provide a seed, which can lead to subcritical instability by either one of two mechanisms. Both mechanisms hinge on a collaboration between fluid nonlinearity and kinetic nonlinearity. If collisional velocity diffusion is low enough, the seed provided by the supercritical mode overcomes the threshold for nonlinear growth of phase-space structure. Then, the supercritical mode triggers the conventional subcritical instability. If collisional velocity diffusion is too large, the seed is significantly below the threshold, but can still grow by a sustained collaboration between fluid and kinetic nonlinearities. Both of these subcritical instabilities can be triggered, even when the frequency of the supercritical mode is rapidly sweeping. These results were obtained by modeling the subcritical mode kinetically, and the impact of the supercritical mode by simple wave–wave coupling equations. This model is applied to bursty onset of geodesic acoustic modes in an LHD experiment. The model recovers several key features such as relative amplitude, timescales, and phase relations. It suggests that the strongest bursts are subcritical instabilities, with sustained collaboration between fluid and kinetic nonlinearities.
Excitation of collective modes in a quantum flute
NASA Astrophysics Data System (ADS)
Torfason, Kristinn; Manolescu, Andrei; Molodoveanu, Valeriu; Gudmundsson, Vidar
2012-06-01
We use a generalized master equation (GME) formalism to describe the nonequilibrium time-dependent transport of Coulomb interacting electrons through a short quantum wire connected to semi-infinite biased leads. The contact strength between the leads and the wire is modulated by out-of-phase time-dependent potentials that simulate a turnstile device. We explore this setup by keeping the contact with one lead at a fixed location at one end of the wire, whereas the contact with the other lead is placed on various sites along the length of the wire. We study the propagation of sinusoidal and rectangular pulses. We find that the current profiles in both leads depend not only on the shape of the pulses, but also on the position of the second contact. The current reflects standing waves created by the contact potentials, like in a wind musical instrument (for example, a flute), but occurring on the background of the equilibrium charge distribution. The number of electrons in our quantum “flute” device varies between two and three. We find that for rectangular pulses the currents in the leads may flow against the bias for short time intervals, due to the higher harmonics of the charge response. The GME is solved numerically in small time steps without resorting to the traditional Markov and rotating wave approximations. The Coulomb interaction between the electrons in the sample is included via the exact diagonalization method. The system (leads plus sample wire) is described by a lattice model.
Observation of beam-excited dipole modes in traveling wave accelerator structures
Vetter, A.M.; Adamski, J.L.; Gallagher, W.J.
1985-10-01
Beamline tests on a series of waveguide models have recently been completed at the Boeing Radiation Effects Laboratory. The purpose of these tests has been to study beam excitation of the dipole modes which participate in regenerative and cumulative beam breakup processes in RF linac waveguides. Cell excitation patterns, dependence on transverse beam displacement from the axis, and comparative excitation levels in waveguides of different design were measured.
NASA Astrophysics Data System (ADS)
Kumar, Shailesh; Lausen, Jens L.; Garcia-Ortiz, Cesar E.; Andersen, Sebastian K. H.; Roberts, Alexander S.; Radko, Ilya P.; Smith, Cameron L. C.; Kristensen, Anders; Bozhevolnyi, Sergey I.
2016-02-01
Nitrogen-vacancy (NV) centers in diamonds are interesting due to their remarkable characteristics that are well suited to applications in quantum-information processing and magnetic field sensing, as well as representing stable fluorescent sources. Multiple NV centers in nanodiamonds (NDs) are especially useful as biological fluorophores due to their chemical neutrality, brightness and room-temperature photostability. Furthermore, NDs containing multiple NV centers also have potential in high-precision magnetic field and temperature sensing. Coupling NV centers to propagating surface plasmon polariton (SPP) modes gives a base for lab-on-a-chip sensing devices, allows enhanced fluorescence emission and collection which can further enhance the precision of NV-based sensors. Here, we investigate coupling of multiple NV centers in individual NDs to the SPP modes supported by silver surfaces protected by thin dielectric layers and by gold V-grooves (VGs) produced via the self-terminated silicon etching. In the first case, we concentrate on monitoring differences in fluorescence spectra obtained from a source ND, which is illuminated by a pump laser, and from a scattering ND illuminated only by the fluorescence-excited SPP radiation. In the second case, we observe changes in the average NV lifetime when the same ND is characterized outside and inside a VG. Fluorescence emission from the VG terminations is also observed, which confirms the NV coupling to the VG-supported SPP modes.
Dynamical aspects of phonon-phonon coupling in collective mode damping
NASA Astrophysics Data System (ADS)
Cataldo, H. M.; Hernández, E. S.; Dorso, C. O.
1987-04-01
We present an extension of the Quantal Brownian Motion (QBM) model of vibration damping that incorporates phonon-phonon or phonon-(two-particle-two-hole) interactions as sources of dissipative evolution of the excited mode. Starting from the Schrödinger-on Neumann equation of motion, a reduction procedure combined with the proper approximations leads to coupled, nonlinear master equations for the density vectors of the separate oscillators. The fermionic heat bath remains equilibrated at temperature T. The evolution of the phonon system is numerically analyzed under different initial conditions that simulate excitation of one or more collective vibrations, for several strengths of mode-mode coupling. It is found that in the majority of cases the system reaches statistical equilibrium with relaxation times that can be extracted from the numerical treatment.
Minimizing the Excitation of Parasitic Modes of Vibration in Slender Power Ultrasonic Devices
NASA Astrophysics Data System (ADS)
Mathieson, A.; Lucas, M.
The design of slender power ultrasonic devices can often be challenging due to the excitation of parasitic modes of vibration during operation. The excitation of these modes is known to manifest from behaviors such as modal coupling which if not controlled or designed out of the system can, under operational conditions, lead to poor device performance and device failure. However, a report published by the authors has indicted that the excitation of these modes of vibration could be minimized through device design, specifically careful location of the piezoceramic stack. This paper illustrates that it is possible, through piezoceramic stack position, to minimize modal coupling between a parasitic mode and the tuned longitudinal mode of vibration for slender ultrasonic devices.
Excitation of surface modes by electron beam in semi-bounded quantum plasma
Mohamed, B. F.; Elbasha, N. M.
2015-10-15
The excitation of the TM surface modes due to the interaction of electron beam with a semi-bounded quantum magnetized plasma is investigated. The generated current and the perturbed densities of the electron beam and plasma are obtained. The wave equation that describes the excited fields has been solved to obtain the dispersion relation for these modes. It is found that the quantum effects play important role for frequencies less and bigger than plasma frequency such that the phase velocity of modes increases with increasing the quantum effects compared to the classical case. It has also been displayed that in the absence of external magnetic field, the surface modes appear in the all regions of the wavelength while they have been only excited for high wavenumber in the presence of the magnetic field. Besides, it has been shown that the dispersion curves of the modes depend essentially on the density ratio of beam and plasma.
Yang Xuefeng; Cui Jian; Zhang Yuan; Liu Yue
2012-07-15
The dispersion relations of the externally and thermally (naturally) excited dust lattice modes (both longitudinal and transverse) in two-dimensional Debye-Yukawa complex plasma crystals are investigated. The dispersion relations are calculated numerically by taking the neutral gas damping effects into account and the numerical results are in agreement with the experimental data given by Nunomura et al.[Phys. Rev. E 65, 066402 (2002)]. It is found that for the mode excited by an external disturbance with a real frequency, the dispersion properties are changed at a critical frequency near where the group velocity of the mode goes to zero. Therefore, the high frequency branch with negative dispersion cannot be reached. In contrast, for the thermally excited mode, the dispersion curve can extend all the way to the negative dispersion region, while a 'cut-off' wave number exists at the long wavelength end of the dispersion in the transverse mode.
Collective modes at a surface of a topological insulator
NASA Astrophysics Data System (ADS)
Wu, Jhih-Sheng; Fogler, M. M.; Basov, D. N.
2015-03-01
We investigate hybrid plasmon-phonon modes of a polar topological insulator that originate from interaction among the quasiparticles of surface and bulk states, and also optical phonons. As an example, we study electron-doped Bi2Se3. We analyze the dispersion of the collective modes of this compound for (i) a bulk sample with a depletion layer created by acceptor adsorbates on the surface and (ii) a thin film. In the first case, we show that a depletion layer gives rise to two energy-momentum regions, where the surface states dominate the collective modes over the bulk carriers. In a thin film, the phonons are more prominent than the bulk carriers. The anisotropy of the phonon response makes the thin film behaves as a waveguide. We discuss how these various collective modes can be detected by scanning near-field optical microscopy. Supported by ONR and UCOP.
Nonlinear dynamics and collective excitations in layered superconducting structures
NASA Astrophysics Data System (ADS)
Zel'Tser, A. S.; Kivshar', Iu. S.; Soboleva, T. K.
1991-06-01
Nonlinear excitations in layered superconducting structures representing a system of interacting extended Josephson junctions are investigated theoretically. The possibility of the propagation of dynamic supersolitons, localized vortex lattice density excitations, in such a system is demonstrated. Particular attention is given to soliton excitations of two types: kinks and envelope solitons. The relaxation of dynamic kinks is investigated numerically.
Instability of insulating states in optical lattices due to collective phonon excitations
NASA Astrophysics Data System (ADS)
Yukalov, V. I.; Ziegler, K.
2015-02-01
The effect of collective phonon excitations on the properties of cold atoms in optical lattices is investigated. These phonon excitations are collective excitations, whose appearance is caused by intersite atomic interactions correlating the atoms, and they do not arise without such interactions. These collective excitations should not be confused with lattice vibrations produced by an external force. No such force is assumed. But the considered phonons are purely self-organized collective excitations, characterizing atomic oscillations around lattice sites, due to intersite atomic interactions. It is shown that these excitations can essentially influence the possibility of atoms' being localized. The states that would be insulating in the absence of phonon excitations can become delocalized when these excitations are taken into account. This concerns long-range as well as local atomic interactions. To characterize the region of stability, the Lindemann criterion is used.
Correlation between excitation of Alfven modes and degradation of ICRF heating efficiency in TFTR
Bernabei, S.; Chang, Z.; Darrow, D.
1997-05-01
Alfven modes are excited by energetic ions in TFTR during intense minority ICRF heating. There is a clear threshold in rf power above which the modes are destabilized. The net effect of these modes is the increase of the fast ion losses, with an associated saturation of the ion tail energy and of the efficiency of the heating. Typically, several modes are excited with progressive n-numbers, with frequencies in the neighborhood of 200 kHz. Results suggest that Energetic Particle Modes (EPM), mostly unseen by the Mirnov coils, are generated near the center and are responsible for the ion losses. Stronger global TAE modes, which are destabilized by the stream of displaced fast ions, appear responsible only for minor losses.
Bochkova, Elena; Burokur, Shah Nawaz; de Lustrac, André; Lupu, Anatole
2016-01-15
We provide evidence for the mechanism of direct dark mode excitation in a metasurface composed of bi-layered Z-shaped enantiomeric meta-atoms. The electromagnetic behavior of the structure is investigated through both numerical simulations and experimental measurements in the microwave domain. We demonstrate direct field coupling excitation of second higher order electric mode under normal incidence based only on symmetry matching conditions. The proposed approach provides a better flexibility in engineering dark mode resonances that do not rely on hybridization mechanism and presents important advantages for multi-spectral sensor applications. PMID:26766727
The energy flux of MHD wave modes excited by realistic photospheric drivers
NASA Astrophysics Data System (ADS)
Fedun, Viktor; Von Fay-Siebenburgen, Erdélyi Robert; Mumford, Stuart
The mechanism(s) responsible for solar coronal heating are still an unresolved and challenging task. In the framework of 3D numerical modelling of MHD wave excitation and propagation in the strongly stratified solar atmosphere we analyse the mode coupling and estimate the wave energy partition which can be supplied to the upper layers of the solar atmosphere by locally decomposed slow, fast and Alfven modes. These waves are excited by a number of realistic photospheric drivers which are mimicking the random granular buffeting, the coherent global solar oscillations and swirly motion observed in e.g. magnetic bright points. Based on a self-similar approach, a realistic magnetic flux tubes configuration is constructed and implemented in the VALIIIC model of the solar atmosphere. A novel method for decomposing the velocity perturbations into parallel, perpendicular and azimuthal components in 3D geometry is developed using field lines to trace a volume of constant energy flux. This method is used to identify the excited wave modes propagating upwards from the photosphere and to compute the percentage energy contribution of each mode. We have found, that for all cases where torsional motion is present, the main contribution to the flux (60%) is by Alfven wave. In the case of the vertical driver it is found to mainly excite the fast- and slow-sausage modes and a horizontal driver primarily excites the slow kink mode.
Mode-locked solid state lasers using diode laser excitation
Holtom, Gary R.
2012-03-06
A mode-locked laser employs a coupled-polarization scheme for efficient longitudinal pumping by reshaped laser diode bars. One or more dielectric polarizers are configured to reflect a pumping wavelength having a first polarization and to reflect a lasing wavelength having a second polarization. An asymmetric cavity provides relatively large beam spot sizes in gain medium to permit efficient coupling to a volume pumped by a laser diode bar. The cavity can include a collimation region with a controlled beam spot size for insertion of a saturable absorber and dispersion components. Beam spot size is selected to provide stable mode locking based on Kerr lensing. Pulse durations of less than 100 fs can be achieved in Yb:KGW.
Symmetry breaking induced excitations of dark plasmonic modes in multilayer graphene ribbons.
Dai, Y Y; Chen, A; Xia, Y Y; Han, D Z; Liu, X H; Shi, L; Zi, J
2016-09-01
Multilayer graphene can support multiple plasmon bands. If structured into graphene ribbons, they can support multiple localized plasmonic modes with interesting optical properties. However, not all such plasmonic modes can be excited directly due to the constrains of the structural symmetry. We show by numerical simulations that by breaking the symmetry all plasmonic modes can be excited. We discuss the general principles and properties of two-layer graphene ribbons and then extend to multilayer graphene ribbons. In multilayer graphene ribbons with different ribbon widths, a tunable broadband absorption can be attained due to the excitations of all plasmonic modes. Our results suggest that these symmetry-broken multilayer graphene ribbons could offer more degrees of freedom in designing photonic devices. PMID:27607610
Low-Energy Electron Impact Excitation of the (010) Bending Mode of CO2
NASA Technical Reports Server (NTRS)
Huo, Winifred M.; Langhoff, Stephen R. (Technical Monitor)
1996-01-01
Low-energy electron impact excitation of the fundamental modes of CO2 has been extensively studied, both experimentally and theoretically. Much attention has been paid to the virtual state feature in the the (100) mode excitation and the (sup 2)II(sub upsilon) resonance feature around 3.8 eV, which is observable in all three fundamental modes. For the excitation of the (010) mode away from the resonance region, the Born dipole approximation was generally considered adequate. The present study employs the Born dipole approximation to treat the long range interaction and the Schwinger multichannel method for the short range interaction. The roles of the two interaction potentials will be compared.
NASA Astrophysics Data System (ADS)
Stepanov, E. A.; van Loon, E. G. C. P.; Katanin, A. A.; Lichtenstein, A. I.; Katsnelson, M. I.; Rubtsov, A. N.
2016-01-01
We propose an efficient dual boson scheme, which extends the dynamical mean-field theory paradigm to collective excitations in correlated systems. The theory is fully self-consistent both on the one- and on the two-particle level, thus describing the formation of collective modes as well as the renormalization of electronic and bosonic spectra on equal footing. The method employs an effective impurity model comprising both fermionic and bosonic hybridization functions. Only single- and two-electron Green's functions of the reference problem enter the theory, due to the optimal choice of the self-consistency condition for the effective bosonic bath. We show that the theory is naturally described by a dual Luttinger-Ward functional and obeys the relevant conservation laws.
Aiba, N.; Hirota, M.
2015-08-15
In a rotating toroidal plasma surrounded by a resistive wall, it is shown that linear magnetohydrodynamic (MHD) instabilities can be excited by interplay between the resistive wall mode (RWM) and stable ideal MHD modes, where the RWM can couple with not only a stable external kink mode but also various stable Alfvén eigenmodes that abound in a toroidal plasma. The RWM growth rate is shown to peak repeatedly as the rotation frequency reaches specific values for which the frequencies of the ideal MHD modes are Doppler-shifted to the small RWM frequency. Such destabilization can be observed even when the RWM in a static plasma is stable. A dispersion relation clarifies that the unstable mode changes from the RWM to the ideal MHD mode destabilized by wall resistivity when the rotation frequency passes through these specific values. The unstable mode is excited at these rotation frequencies even though plasma rotation also tends to stabilize the RWM from the combination of the continuum damping and the ion Landau damping.
N-mode coherence in collective neutrino oscillations
Raffelt, Georg G.
2011-05-15
We study two-flavor neutrino oscillations in a homogeneous and isotropic ensemble under the influence of neutrino-neutrino interactions. For any density there exist forms of collective oscillations that show self-maintained coherence. They can be classified by a number N of linearly independent functions that describe all neutrino modes as linear superpositions. What is more, the dynamics is equivalent to another ensemble with the same effective density, consisting of N modes with discrete energies E{sub i} with i=1,...,N. We use this equivalence to derive the analytic solution for two-mode (bimodal) coherence, relevant for spectral-split formation in supernova neutrinos.
Crossover of collective modes and positive sound dispersion in supercritical state.
Fomin, Yu D; Ryzhov, V N; Tsiok, E N; Brazhkin, V V; Trachenko, K
2016-11-01
Supercritical state has been viewed as an intermediate state between gases and liquids with largely unknown physical properties. Here, we address the important ability of supercritical fluids to sustain collective excitations. We directly study propagating modes on the basis of correlation functions calculated in molecular dynamics simulations and find that the supercritical system sustains propagating solid-like transverse modes below the Frenkel line but not above where there is one longitudinal mode only. Important thermodynamic implications of this finding are discussed. We directly detect positive sound dispersion (PSD) below the Frenkel line where transverse modes are operative and quantitatively explain its magnitude on the basis of transverse and longitudinal velocities. PSD disappears above the Frenkel line which therefore demarcates the supercritical phase diagram into two areas where PSD does and does not operate. PMID:27603524
Coexisting single-particle and collective excitations in 70As
NASA Astrophysics Data System (ADS)
Haring-Kaye, R. A.; Elder, R. M.; Döring, J.; Tabor, S. L.; Volya, A.; Allegro, P. R. P.; Bender, P. C.; Medina, N. H.; Morrow, S. I.; Oliviera, J. R. B.; Tripathi, V.
2015-10-01
High-spin states in 70As were studied using the 55Mn(18O,3 n ) fusion-evaporation reaction at a beam energy of 50 MeV. Prompt γ -γ coincidences were measured using the Florida State University Compton-suppressed Ge array consisting of three Clover detectors and seven single-crystal detectors. A reinvestigation of the known level scheme resulted in the addition of 32 new transitions and the rearrangement of 10 others. The high-spin decay pattern of yrast negative-parity states was modified and enhanced extensively. Spins were assigned based on directional correlation of oriented nuclei ratios. Lifetimes of seven excited states were measured using the Doppler-shift attenuation method. The B (E 2 ) rates inferred from the lifetimes of states in the yrast positive-parity band imply substantial collectivity, in agreement with the results of previous studies. Substantial signature splitting and large alternations in the B (M 1 ) strengths were observed in this band as well, supporting the interpretation of an aligned π g9 /2⊗ν g9 /2 intrinsic configuration for this structure beginning at the lowest 9+ state. Large-scale shell-model calculations performed for 70As reproduce the relative energy differences between adjacent levels and the B (M 1 ) rates in the yrast positive-parity band rather well, but underestimate the B (E 2 ) strengths. The g9 /2 orbital occupancies for the lowest 9+ state predicted by the shell-model calculations provide additional evidence of a stretched π g9 /2⊗ν g9 /2 configuration for this state.
Collective excitations in doped two-leg quantum spin ladders
NASA Astrophysics Data System (ADS)
Blumberg, Girsh
2004-03-01
Investigation of the charge and spin dynamics of spin 1/2 quasi one-dimensional Sr_14Cu_24O_41 ladder compound has attracting attention because of the critical nature of its magnetic ground state and the relevance to the phase diagram of the high-Tc superconductors. Understanding the competition between the insulating states at low hole concentrations and superconducting pairing at higher hole densities has emerged as a key feature of the problem in cuprates. We use ultra-low frequency Raman spectroscopy as well as linear and nonlinear electrical response over about 10 decades of frequency to identify the insulating state of self-doped Sr_14Cu_24O_41 ladders as a weakly pinned, sliding spin/charge density wave with non-linear conductivity and a giant dielectric response (ɛ1 10^6) that persists to remarkably high temperatures [1]. We also performed structural studies in the density wave state by anomalous X-ray diffraction at the O K- and Cu L- edges. At sharp resonance with O K- pre-edge we observed peak that corresponds to commensurate with the lattice charge density modulation with period of five ladder steps. Intriguingly, the density wave peak intensity drops rapidly when excitation energy is detuned from the pre-edge resonance suggesting that the lattice does not respond to the charge modulation and therefore the density modulation is driven by anti-ferromagnetic interactions. Similar density wave correlations were found in ladders with higher hole concentration that show metallic-like conductivity and are superconducting under pressure. Our results demonstrate that the superconducting state in cuprates is competing with a crystalline charge ordered state and suggest that the transport in metallic ladders, which is similar to transport in underdoped high-Tc cuprates, is driven by a collective electronic response [2]. 1. G. Blumberg et al, Science 297, 584 (2002). 2. A. Gozar et al, PRL91, 087401 (2003); PRL87, 197202 (2001).
Phase diagram and collective excitations in an excitonic insulator from an orbital physics viewpoint
NASA Astrophysics Data System (ADS)
Nasu, Joji; Watanabe, Tsutomu; Naka, Makoto; Ishihara, Sumio
2016-05-01
An excitonic-insulating system is studied from a viewpoint of the orbital physics in strongly correlated electron systems. An effective model Hamiltonian for low-energy electronic states is derived from the two-orbital Hubbard model with a finite-energy difference corresponding to the crystalline-field splitting. The effective model is represented by the spin operators and the pseudospin operators for the spin-state degrees of freedom. The ground-state phase diagram is analyzed by the mean-field approximation. In addition to the low-spin state and high-spin state phases, two kinds of the excitonic-insulating phases emerge as a consequence of the competition between the crystalline-field effect and the Hund coupling. Transitions to the excitonic phases are classified to an Ising-type transition resulted from a spontaneous breaking of the Z2 symmetry. Magnetic structures in the two excitonic-insulating phases are different from each other: an antiferromagnetic order and a spin nematic order. Collective excitations in each phase are examined using the generalized spin-wave approximation. Characteristics in the Goldstone modes in the excitonic-insulating phases are studied through the calculations of the dynamical correlation functions for the spins and pseudospin operators. Both the transverse and longitudinal spin excitation modes are active in the two excitonic-insulating phases in contrast to the low-spin state and high-spin state phases. Relationships of the present results to the perovskite cobalt oxides are discussed.
Morozov, V.G.; Mukhai, A.N.
1988-10-01
Long-wave collective oscillations in a system of parametric spin waves of a ferromagnet are studied on the basis of the kinetic equations for the Wigner distribution functions of the magnons. A study is made of the linear response of the magnetization m to a change in the internal field h (in the case of deviation of a packet of parametric waves from a stationary state), and boundary-value problem for finding the eigenfrequencies of the collective modes in a sample of finite volume is formulated. It is shown that allowance for the influence of the boundary conditions leads to discreteness of the frequency spectrum of the collective modes in the region of wave numbers q of the order of the reciprocal sample dimension L/sup /minus/1/. For a spherical sample, expressions are obtained for the discrete frequencies of long-wave collective modes corresponding to oscillations with longitudinal component h/sub z/ of the internal field that does not depend on the coordinate z. Criteria for stability of stationary states of the ferromagnet with respect to the excitation of auto-oscillations are obtained.
Mugarza, Aitor; Shimizu, Tomoko K.; Ogletree, D. Frank; Salmeron, Miquel
2009-05-07
Tunneling electrons in a scanning tunneling microscope were used to excite specific vibrational quantum states of adsorbed water and hydroxyl molecules on a Ru(0 0 0 1) surface. The excited molecules relaxed by transfer of energy to lower energy modes, resulting in diffusion, dissociation, desorption, and surface-tip transfer processes. Diffusion of H{sub 2}O molecules could be induced by excitation of the O-H stretch vibration mode at 445 meV. Isolated molecules required excitation of one single quantum while molecules bonded to a C atom required at least two quanta. Dissociation of single H{sub 2}O molecules into H and OH required electron energies of 1 eV or higher while dissociation of OH required at least 2 eV electrons. In contrast, water molecules forming part of a cluster could be dissociated with electron energies of 0.5 eV.
NASA Astrophysics Data System (ADS)
Bryk, Taras; Ruocco, G.; Scopigno, T.; Seitsonen, Ari P.
2015-09-01
Unlike phonons in crystals, the collective excitations in liquids cannot be treated as propagation of harmonic displacements of atoms around stable local energy minima. The viscoelasticity of liquids, reflected in transition from the adiabatic to elastic high-frequency speed of sound and in absence of the long-wavelength transverse excitations, results in dispersions of longitudinal (L) and transverse (T) collective excitations essentially different from the typical phonon ones. Practically, nothing is known about the effect of high pressure on the dispersion of collective excitations in liquids, which causes strong changes in liquid structure. Here dispersions of L and T collective excitations in liquid Li in the range of pressures up to 186 GPa were studied by ab initio simulations. Two methodologies for dispersion calculations were used: direct estimation from the peak positions of the L/T current spectral functions and simulation-based calculations of wavenumber-dependent collective eigenmodes. It is found that at ambient pressure, the longitudinal and transverse dynamics are well separated, while at high pressures, the transverse current spectral functions, density of vibrational states, and dispersions of collective excitations yield evidence of two types of propagating modes that contribute strongly to transverse dynamics. Emergence of the unusually high-frequency transverse modes gives evidence of the breakdown of a regular viscoelastic theory of transverse dynamics, which is based on coupling of a single transverse propagating mode with shear relaxation. The explanation of the observed high-frequency shift above the viscoelastic value is given by the presence of another branch of collective excitations. With the pressure increasing, coupling between the two types of collective excitations is rationalized within a proposed extended viscoelastic model of transverse dynamics.
Bryk, Taras; Ruocco, G.; Scopigno, T.
2015-09-14
Unlike phonons in crystals, the collective excitations in liquids cannot be treated as propagation of harmonic displacements of atoms around stable local energy minima. The viscoelasticity of liquids, reflected in transition from the adiabatic to elastic high-frequency speed of sound and in absence of the long-wavelength transverse excitations, results in dispersions of longitudinal (L) and transverse (T) collective excitations essentially different from the typical phonon ones. Practically, nothing is known about the effect of high pressure on the dispersion of collective excitations in liquids, which causes strong changes in liquid structure. Here dispersions of L and T collective excitations in liquid Li in the range of pressures up to 186 GPa were studied by ab initio simulations. Two methodologies for dispersion calculations were used: direct estimation from the peak positions of the L/T current spectral functions and simulation-based calculations of wavenumber-dependent collective eigenmodes. It is found that at ambient pressure, the longitudinal and transverse dynamics are well separated, while at high pressures, the transverse current spectral functions, density of vibrational states, and dispersions of collective excitations yield evidence of two types of propagating modes that contribute strongly to transverse dynamics. Emergence of the unusually high-frequency transverse modes gives evidence of the breakdown of a regular viscoelastic theory of transverse dynamics, which is based on coupling of a single transverse propagating mode with shear relaxation. The explanation of the observed high-frequency shift above the viscoelastic value is given by the presence of another branch of collective excitations. With the pressure increasing, coupling between the two types of collective excitations is rationalized within a proposed extended viscoelastic model of transverse dynamics.
Plasma confinement regimes and collective modes characterizing them
Coppi, B.; Zhou, T.
2012-10-15
A unified theory is presented for the modes that are excited at the edge of the plasma column and are important signatures of the advanced confinement regimes into which magnetically confined plasmas can be driven. In particular, the so-called EDA H-Regime, the Elmy H-Regime, and the I-Regime are considered. The modes that are identified theoretically have characteristics that are consistent with or have anticipated those of the modes observed experimentally for each of the investigated regimes. The phase velocities, the produced transport processes, the frequencies, the wavelengths, and the consistency with the direction of spontaneous rotation are the factors considered for comparison with the relevant experiments. The quasi-coherent mode [I. Cziegler, Ph.D. dissertation, Massachusetts Institute of Technology, Cambridge, MA, 2011] that is present in the EDA H-Regime has a phase velocity in the direction of the ion diamagnetic velocity in the plasma reference frame. Consequently, this is identified as a ballooning mode near finite Larmor radius marginal stability involving the effects of transverse ion viscosity and other dissipative effects. In this regime, impurities are driven outward by the combined effects of the local temperature gradients of the impurities and their thermal conductivity, while in the Elmy H-Regime impurities are driven toward the center of the plasma column. In the I-Regimes, the excited 'Heavy Particle' modes [B. Coppi and T. Zhou, Phys. Plasmas 19, 012302 (2012); Phys. Lett. A 375, 2916 (2011)] are not of the ballooning kind and are shown to expel the impurities toward the plasma edge in the presence of significant fluctuations. These modes can have a finite frequency of oscillation with a phase velocity in the direction of the electron diamagnetic velocity or they can be nearly purely growing, explaining why there are I-Regimes where fluctuations are not observed. Instead, the modes considered for the Elmy H-Regime are of the ballooning
Elliptically polarized modes for the unidirectional excitation of surface plasmon polaritons.
Compaijen, Paul J; Malyshev, Victor A; Knoester, Jasper
2016-02-22
We propose a new method for the directional excitation of surface plasmon polaritons by a metal nanoparticle antenna, based on the elliptical polarization of the normal modes of the antenna when it is in close proximity to a metallic substrate. The proposed theoretical model allows for the full characterization of the modes, giving the dipole configuration, frequency and lifetime. As a proof of principle, we have performed calculations for a dimer antenna and we report that surface plasmon polaritons can be excited in a given direction with an intensity of more than two orders of magnitude larger than in the opposite direction. Furthermore, using the fact that the response to any excitation can be written as a superposition of the normal modes, we show that this directionality can easily be accessed by exciting the system with a local source or a plane wave. Lastly, exploiting the interference between the normal modes, the directionality can be switched for a specific excitation. We envision the proposed mechanism to be a very useful tool for the design of antennas in layered media. PMID:26907039
Nanoscale spintronic oscillators based on the excitation of confined soliton modes
NASA Astrophysics Data System (ADS)
Finocchio, G.; Puliafito, V.; Komineas, S.; Torres, L.; Ozatay, O.; Hauet, T.; Azzerboni, B.
2013-10-01
This paper demonstrates how to excite complex soliton modes in nanomagnets with perpendicular to plane magnetic anisotropy driven by the non-uniform injection of a spin-polarized current. We addressed the study toward two different scenarios, in the first the excitation of two rotating bubble/antibubble pairs is predicted, in the second one, by means of the topological density, we characterized the dissipative droplet recently measured as single constrained bubble/antibubble pair. Our results are important for the theoretical understanding of how to control the spatial structure of soliton modes for application in spintronics, magnonics, and domain wall devices.
Bijnen, R. M. W. van; Parker, N. G.; Kokkelmans, S. J. J. M. F.; Martin, A. M.; O'Dell, D. H. J.
2010-09-15
We present a general method for obtaining the exact static solutions and collective excitation frequencies of a trapped Bose-Einstein condensate (BEC) with dipolar atomic interactions in the Thomas-Fermi regime. The method incorporates analytic expressions for the dipolar potential of an arbitrary polynomial density profile, thereby reducing the problem of handling nonlocal dipolar interactions to the solution of algebraic equations. We comprehensively map out the static solutions and excitation modes, including non-cylindrically-symmetric traps, and also the case of negative scattering length where dipolar interactions stabilize an otherwise unstable condensate. The dynamical stability of the excitation modes gives insight into the onset of collapse of a dipolar BEC. We find that global collapse is consistently mediated by an anisotropic quadrupolar collective mode, although there are two trapping regimes in which the BEC is stable against quadrupole fluctuations even as the ratio of the dipolar to s-wave interactions becomes infinite. Motivated by the possibility of a fragmented condensate in a dipolar Bose gas due to the partially attractive interactions, we pay special attention to the scissors modes, which can provide a signature of superfluidity, and identify a long-range restoring force which is peculiar to dipolar systems. As part of the supporting material for this paper we provide the computer program used to make the calculations, including a graphical user interface.
Local mode excitation and direct unimolecular reaction rate measurements in tetramethyldioxetane
Cannon, B.D.; Crim, F.F.
1981-08-15
Direct excitation of overtone vibrations combined with time-resolved detection of product chemiluminescence produces both overtone vibration excitation spectra and directly measured unimolecular decay rates of tetramethyldioxetane. The spectra show increasingly pure local mode character in higher vibrational levels and exhibit splittings which arise from nonequivalent sites occupied by methyl hydrogens. The temporal evolution of the signal reflects the unimolecular decomposition rate of the highly vibrationally excited molecule, and comparing the observed behavior to Rice--Ramsperger--Kassel--Marcus theory calculations shows that they adequately describe the decomposition if properly averaged over the thermal vibrational energy content of the molecule.
DE-1 and COSMOS 1809 observations of lower hybrid waves excited by VLF whistler mode waves
Bell, T.F.; Inan, U.S.; Lauben, D.; Sonwalkar, V.S.; Helliwell, R.A.; Sobolev, Ya.P.; Chmyrev, V.M.; Gonzalez, S.
1994-04-15
Past work demonstrates that strong lower hybrid (LH) waves can be excited by electromagnetic whistler mode waves throughout large regions of the topside ionosphere and magnetosphere. The effects of the excited LH waves upon the suprathermal ion population in the topside ionosphere and magnetosphere depend upon the distribution of LH wave amplitude with wavelength {lambda}. The present work reports plasma wave data from the DE-1 and COSMOS 1809 spacecraft which suggests that the excited LH wave spectrum has components for which {lambda} {le} 3.5 m when excitation occurs at a frequency roughly equal to the lower hybrid resonance frequency. This wavelength limit is a factor of {approximately} 3 below that reported in past work and suggests that the excited LH waves can interact with suprathermal H{sup +} ions with energy {le} 6 eV. This finding supports recent work concerning the heating of suprathermal ions above thunderstorm cells. 19 refs., 3 figs.
DE-1 and COSMOS 1809 observations of lower hybrid waves excited by VLF whistler mode waves
NASA Technical Reports Server (NTRS)
Bell, T. F; Inan, U. S.; Lauben, D.; Sonwalkar, V. S.; Helliwell, R. A.; Sobolev, Ya. P.; Chmyrev, V. M.; Gonzalez, S.
1994-01-01
Past work demostrates that strong lower hybrid (LH) waves can be excited by electromagnetic whistler mode waves throughout large regions of the topside ionosphere and magnetosphere. The effects of the excited LH waves upon the suprathermal ion population in the topside ionosphere and magnetosphere depend upon the distribution of LH wave amplitude with wavelength lambda. The present work reports plasma wave data from the DE-1 and COSMOS 1809 spacecraft which suggests that the excited LH wave spectrum has components for which lambda less than or equal to 3.5 m when excitation occurs at a frequency roughly equal to the local lower hybrid resonance frequency. This wavelength limit is a factor of approximately 3 below that reported in past work and suggests that the excited LH waves can interact with suprathermal H(+) ions with energy less than or equal to 6 eV. This finding supports recent work concerning the heating of suprathermal ions above thunderstorm cells.
NASA Astrophysics Data System (ADS)
Bryk, Taras; Mryglod, Ihor; Scopigno, Tullio; Ruocco, Giancarlo; Gorelli, Federico; Santoro, Mario
2010-07-01
The approach of generalized collective modes is applied to the study of dispersion curves of collective excitations along isothermal lines of supercritical pure Lennard-Jones fluid. An effect of structural relaxation and other nonhydrodynamic relaxation processes on the dispersion law is discussed. A simple analytical expression for the dispersion law in the long-wavelength region of acoustic excitations is obtained within a three-variable viscoelastic model of generalized hydrodynamics. It is shown that the deviation from the linear dependence in the long-wavelength region can be either "positive" or "negative" depending on the ratio between the high-frequency (elastic) and isothermal speed of sound. An effect of thermal fluctuations on positive and negative dispersion is estimated from the analytical solution of a five-variable thermoviscoelastic model that generalizes the results of the viscoelastic treatment. Numerical results are reported for a Lennard-Jones supercritical fluid along two isothermal lines T∗=1.71,4.78 with different densities and discussed along the theoretical expressions derived.
Direct observation of dynamic modes excited in a magnetic insulator by pure spin current
Demidov, V. E.; Evelt, M.; Bessonov, V.; Demokritov, S. O.; Prieto, J. L.; Muñoz, M.; Ben Youssef, J.; Naletov, V. V.; de Loubens, G.; Klein, O.; Collet, M.; Bortolotti, P.; Cros, V.; Anane, A.
2016-01-01
Excitation of magnetization dynamics by pure spin currents has been recently recognized as an enabling mechanism for spintronics and magnonics, which allows implementation of spin-torque devices based on low-damping insulating magnetic materials. Here we report the first spatially-resolved study of the dynamic modes excited by pure spin current in nanometer-thick microscopic insulating Yttrium Iron Garnet disks. We show that these modes exhibit nonlinear self-broadening preventing the formation of the self-localized magnetic bullet, which plays a crucial role in the stabilization of the single-mode magnetization oscillations in all-metallic systems. This peculiarity associated with the efficient nonlinear mode coupling in low-damping materials can be among the main factors governing the interaction of pure spin currents with the dynamic magnetization in high-quality magnetic insulators. PMID:27608533
Direct observation of dynamic modes excited in a magnetic insulator by pure spin current.
Demidov, V E; Evelt, M; Bessonov, V; Demokritov, S O; Prieto, J L; Muñoz, M; Ben Youssef, J; Naletov, V V; de Loubens, G; Klein, O; Collet, M; Bortolotti, P; Cros, V; Anane, A
2016-01-01
Excitation of magnetization dynamics by pure spin currents has been recently recognized as an enabling mechanism for spintronics and magnonics, which allows implementation of spin-torque devices based on low-damping insulating magnetic materials. Here we report the first spatially-resolved study of the dynamic modes excited by pure spin current in nanometer-thick microscopic insulating Yttrium Iron Garnet disks. We show that these modes exhibit nonlinear self-broadening preventing the formation of the self-localized magnetic bullet, which plays a crucial role in the stabilization of the single-mode magnetization oscillations in all-metallic systems. This peculiarity associated with the efficient nonlinear mode coupling in low-damping materials can be among the main factors governing the interaction of pure spin currents with the dynamic magnetization in high-quality magnetic insulators. PMID:27608533
Resonance Excitation of Longitudinal High Order Modes in Project X Linac
Khabiboulline, T.N.; Sukhanov, A.AUTHOR = Awida, M.; Gonin, I.; Lunin, A.AUTHOR = Solyak, N.; Yakovlev, V.; /Fermilab
2012-05-01
Results of simulation of power loss due to excitation of longitudinal high order modes (HOMs) in the accelerating superconducting RF system of CW linac of Project X are presented. Beam structures corresponding to the various modes of Project X operation are considered: CW regime for 3 GeV physics program; pulsed mode for neutrino experiments; and pulsed regime, when Project X linac operates as a driver for Neutrino Factory/Muon Collider. Power loss and associated heat load due to resonance excitation of longitudinal HOMs are shown to be small in all modes of operation. Conclusion is made that HOM couplers can be removed from the design of superconducting RF cavities of Project X linac.
NASA Technical Reports Server (NTRS)
Warren, Gary
1988-01-01
The SOS code is used to compute the resonance modes (frequency-domain information) of sample devices and separately to compute the transient behavior of the same devices. A code, DOT, is created to compute appropriate dot products of the time-domain and frequency-domain results. The transient behavior of individual modes in the device is then plotted. Modes in a coupled-cavity traveling-wave tube (CCTWT) section excited beam in separate simulations are analyzed. Mode energy vs. time and mode phase vs. time are computed and it is determined whether the transient waves are forward or backward waves for each case. Finally, the hot-test mode frequencies of the CCTWT section are computed.
NASA Astrophysics Data System (ADS)
Gubbiotti, G.; Tacchi, S.; Madami, M.; Carlotti, G.; Yang, Z.; Ding, J.; Adeyeye, A. O.; Kostylev, M.
2016-05-01
In the developing field of magnonics, it is very important to achieve tailoring of spin wave propagation by both a proper combination of materials with different magnetic properties and their nanostructuring on the submicrometric scale. With this in mind, we have exploited deep ultraviolet lithography, in combination with the tilted shadow deposition technique, to fabricate arrays of closely spaced bilayer nanowires (NWs), with separation d =100 nm and periodicity a =440 nm , having bottom and top layers made of permalloy and iron, respectively. The NWs have either a "rectangular" cross section (bottom and upper layers of equal width) or an "L-shaped" cross section (upper layer of half width). The frequency dispersion of collective spin wave excitations in the above bilayered NW arrays has been measured by the Brillouin light-scattering technique while sweeping the wave vector perpendicularly to the wire length over three Brillouin zones of the reciprocal space. For the rectangular NWs, the lowest-frequency fundamental mode, characterized by a quasiuniform profile of the amplitude of the dynamic magnetization across the NW width, exhibits a sizable and periodic frequency dispersion. A similar dispersive mode is also present in L-shaped NWs, but the mode amplitude is concentrated in the thin side of the NWs. The width and the center frequency of the magnonic band associated with the above fundamental modes have been analyzed, showing that both can be tuned by varying the external applied field. Moreover, for the L-shaped NWs it is shown that there is also a second dispersive mode, at higher frequency, characterized by an amplitude concentrated in the thick side of the NW. These experimental results have been quantitatively reproduced by an original numerical model that includes a two-dimensional Green's function description of the dipole field of the dynamic magnetization and interlayer exchange coupling between the layers.
NASA Astrophysics Data System (ADS)
Beltran Madrigal, Josslyn; Berthel, Martin; Gardillou, Florent; Tellez Limon, Ricardo; Couteau, Christophe; Barbier, Denis; Drezet, Aurelien; Salas-Montiel, Rafael; Huant, Serge; Blaize, Sylvain; Geng, Wei
2015-10-01
Several works have already shown that the excitation of plasmonic structures through waveguides enables a strong light confinement and low propagation losses [1]. This kind of excitation is currently exploited in areas such as biosensing [2], nanocircuits[3] and spectroscopy[4]. The efficient excitation of surface plasmon modes (SPP) with guided modes supported by high-index-contrast waveguides, such as silicon-on-insulator waveguides, had already been shown [1,5]. However, the use of weakconfined guided modes of a glass ion exchanged waveguide as a SPP excitation source represents a technological challenge, because the mismatch between the size of their respective electromagnetic modes is so high that the resultant coupling loss is unacceptable for practical applications. In this work, we describe how an adiabatic taper structure formed by an intermediate high-index-contrast layer placed between a plasmonic structure and an ion-exchanged waveguide decreases the mismatch between effective indices, size, and shape of the guided modes. This hybrid structure concentrates the electromagnetic energy from the micrometer to the nanometer scale with low coupling losses to radiative modes. The electromagnetic mode confined to the high-index-contrast waveguide then works as an efficient source of SPP supported by metallic nanostructures placed on its surface. We theoretically studied the modal properties and field distribution along the adiabatic coupler structure. In addition, we fabricated a high-index-contrast waveguide by electron beam lithography and thermal evaporation on top of an ion-exchanged waveguide on glass. This structure was characterized with the use of near field scanning optical microscopy (NSOM). Numerical simulations were compared with the experimental results. [1] N. Djaker, R. Hostein, E. Devaux, T. W. Ebbesen, and H. Rigneault, and J. Wenger, J. Phys. Chem. C 114, 16250 (2010). [2] P. Debackere, S. Scheerlinck, P. Bienstman, R. Baets, Opt. Express 14
The Photoresponse of Atomic Nuclei: Collective Excitations and Photodissociation
NASA Astrophysics Data System (ADS)
Zilges, A.; Babilon, M.; van den Berg, A. M.; Galaviz, D.; Hasper, J.; Harakeh, M. N.; Lindenberg, K.; Müller, S.; Ramspeck, K.; Savran, D.; Sonnabend, K.; Volz, S.; Wörtche, H. J.; Zarza, M.
2006-04-01
The dipole strength distribution of atomic nuclei below the particle threshold has been investigated systematically in photon scattering experiments. A concentration of electric dipole strength around 7 MeV exhausting up to 1% of the Energy Weighted Sum Rule has been observed in all nuclei studied so far. The detailed structure of these excitations and the connection to a resonance-like concentration of E1 strength above the threshold found in neutron-rich radioactive nuclei is still not understood. The latest strength measurements and new experiments with hadrons to study the isospin character of the excitations are discussed.
Selective mode excitation in finite size plasma crystals by diffusely reflected laser light
Schablinski, Jan; Block, Dietmar
2015-02-15
The possibility to use diffuse reflections of a laser beam to exert a force on levitating dust particles is studied experimentally. Measurements and theoretical predictions are found to be in good agreement. Further, the method is applied to test the selective excitation of breathing-like modes in finite dust clusters.
Using Fast Neutrons to Study Collective Nuclear Excitations
NASA Astrophysics Data System (ADS)
Yates, S. W.
2013-03-01
For many years, the inelastic scattering of accelerator-produced fast neutrons has been used at the University of Kentucky to study nuclei which have been described as vibrational Recent data which have emerged from studies with this reaction and from other probes is reviewed, and conclusions about the applicability of the vibrational phonon description for multiphonon quadrupole and octupole excitations are given.
Isomeric States and Collective Excitations of Heaviest Nuclei
NASA Astrophysics Data System (ADS)
Adamian, G. G.; Antonenko, N. V.; Jolos, R. V.; Kuzmina, A. N.; Malov, L. A.; Shirikova, N. Yu.; Sushkov, A. V.
2013-03-01
The isotopic dependence of two-quasiparticle isomeric states in Fm and No is treated. An α-decay chain through the isomeric states of super-heavy nuclei is demonstrated. The excitation energies and the structure of the low lying states with Kπ = 0‒ 1‒ 2‒ are calculated with the quasiparticle phonon model.
Novel Piezoelectric Fiber Transducers for Mode Selective Excitation and Detection of Lamb Waves
NASA Astrophysics Data System (ADS)
Koehler, B.; Frankenstein, B.; Schubert, F.; Barth, M.
2009-03-01
One of the most widely applied methods for Structural Health Monitoring of plate like structures, shells and tubes is based on the transmission and reception of guided elastic waves. But, dispersion of various wave modes leads to complex signals which are difficult to interpret. Piezoelectric fiber patches (PFP) have been developed which can be used to excite and detect Lamb waves. These are of low thickness having the potential to be integrated into structures. This paper deals with a novel method to excite PFP. By this method a Lamb modes can be both excited and detected selectively. In addition, also directivity can be realized. These sensors can be used to simplify the interpretation of the acoustic signals considerably.
Injection locking of an electronic maser in the hard excitation mode
Yakunina, K. A.; Kuznetsov, A. P.; Ryskin, N. M.
2015-11-15
The phenomenon of hard excitation is natural for many electronic oscillators. In particular, in a gyrotron, a maximal efficiency is often attained in the hard excitation regime. In this paper, we study the injection-locking phenomena using two models of an electronic maser in the hard excitation mode. First, bifurcation analysis is performed for the quasilinear model described by ordinary differential equations for the slow amplitude and phase. Two main scenarios of transition to the injection-locked mode are described, which are generalizations of the well-known phase-locking and suppression mechanisms. The results obtained for the quasilinear model are confirmed by numerical simulations of a gyrotron with fixed Gaussian structure of the RF field.
Injection locking of an electronic maser in the hard excitation mode
NASA Astrophysics Data System (ADS)
Yakunina, K. A.; Kuznetsov, A. P.; Ryskin, N. M.
2015-11-01
The phenomenon of hard excitation is natural for many electronic oscillators. In particular, in a gyrotron, a maximal efficiency is often attained in the hard excitation regime. In this paper, we study the injection-locking phenomena using two models of an electronic maser in the hard excitation mode. First, bifurcation analysis is performed for the quasilinear model described by ordinary differential equations for the slow amplitude and phase. Two main scenarios of transition to the injection-locked mode are described, which are generalizations of the well-known phase-locking and suppression mechanisms. The results obtained for the quasilinear model are confirmed by numerical simulations of a gyrotron with fixed Gaussian structure of the RF field.
Zhou, Yanyan; Luan, Feng; Gu, Bobo; Yu, Xia
2015-02-23
Metallic diffraction grating coupler is investigated for controlled excitation of whispering gallery modes (WGMs) of different radial orders. Based on effective mode index calculations and finite difference time domain method, it is found that higher radial order WGMs can be separated from the fundamental modes by sending them into the opposite propagation direction. By phase-matching designs, the metallic diffraction grating provides extra freedom to switch propagation directions, and is able to selectively enhance or suppress different radial-order WGMs. Such structure offers a simple and practical configuration for various WGM applications including liquid sensing, band pass filtering and fiber lasers. PMID:25836534
Collective modes in three-dimensional magnonic vortex crystals
Hänze, Max; Adolff, Christian F.; Schulte, Benedikt; Möller, Jan; Weigand, Markus; Meier, Guido
2016-01-01
Collective modes in three-dimensional crystals of stacked permalloy disks with magnetic vortices are investigated by ferromagnetic resonance spectroscopy and scanning transmission X-ray microscopy. The size of the arrangements is increased step by step to identify the different contributions to the interaction between the vortices. These contributions are the key requirement to understand complex dynamics of three dimensional vortex crystals. Both vertical and horizontal coupling determine the collective modes. In-plane dipoles strongly influence the interaction between the disks in the stacks and lead to polarity-dependent resonance frequencies. Weaker contributions discern arrangements with different polarities and circularities that result from the lateral coupling of the stacks and the interaction of the core regions inside a stack. All three contributions are identified in the experiments and are explained in a rigid particle model. PMID:26932833
Collective modes in three-dimensional magnonic vortex crystals
NASA Astrophysics Data System (ADS)
Hänze, Max; Adolff, Christian F.; Schulte, Benedikt; Möller, Jan; Weigand, Markus; Meier, Guido
2016-03-01
Collective modes in three-dimensional crystals of stacked permalloy disks with magnetic vortices are investigated by ferromagnetic resonance spectroscopy and scanning transmission X-ray microscopy. The size of the arrangements is increased step by step to identify the different contributions to the interaction between the vortices. These contributions are the key requirement to understand complex dynamics of three dimensional vortex crystals. Both vertical and horizontal coupling determine the collective modes. In-plane dipoles strongly influence the interaction between the disks in the stacks and lead to polarity-dependent resonance frequencies. Weaker contributions discern arrangements with different polarities and circularities that result from the lateral coupling of the stacks and the interaction of the core regions inside a stack. All three contributions are identified in the experiments and are explained in a rigid particle model.
Collective modes in light nuclei from first principles.
Dytrych, T; Launey, K D; Draayer, J P; Maris, P; Vary, J P; Saule, E; Catalyurek, U; Sosonkina, M; Langr, D; Caprio, M A
2013-12-20
Results for ab initio no-core shell model calculations in a symmetry-adapted SU(3)-based coupling scheme demonstrate that collective modes in light nuclei emerge from first principles. The low-lying states of 6Li, 8Be, and 6He are shown to exhibit orderly patterns that favor spatial configurations with strong quadrupole deformation and complementary low intrinsic spin values, a picture that is consistent with the nuclear symplectic model. The results also suggest a pragmatic path forward to accommodate deformation-driven collective features in ab initio analyses when they dominate the nuclear landscape. PMID:24483740
Emerging modes of collective cell migration induced by geometrical constraints
Vedula, Sri Ram Krishna; Leong, Man Chun; Lai, Tan Lei; Hersen, Pascal; Kabla, Alexandre J.; Lim, Chwee Teck; Ladoux, Benoît
2012-01-01
The role of geometrical confinement on collective cell migration has been recognized but has not been elucidated yet. Here, we show that the geometrical properties of the environment regulate the formation of collective cell migration patterns through cell–cell interactions. Using microfabrication techniques to allow epithelial cell sheets to migrate into strips whose width was varied from one up to several cell diameters, we identified the modes of collective migration in response to geometrical constraints. We observed that a decrease in the width of the strips is accompanied by an overall increase in the speed of the migrating cell sheet. Moreover, large-scale vortices over tens of cell lengths appeared in the wide strips whereas a contraction-elongation type of motion is observed in the narrow strips. Velocity fields and traction force signatures within the cellular population revealed migration modes with alternative pulling and/or pushing mechanisms that depend on extrinsic constraints. Force transmission through intercellular contacts plays a key role in this process because the disruption of cell–cell junctions abolishes directed collective migration and passive cell–cell adhesions tend to move the cells uniformly together independent of the geometry. Altogether, these findings not only demonstrate the existence of patterns of collective cell migration depending on external constraints but also provide a mechanical explanation for how large-scale interactions through cell–cell junctions can feed back to regulate the organization of migrating tissues. PMID:22814373
Wexler, Adam D; Drusová, Sandra; Woisetschläger, Jakob; Fuchs, Elmar C
2016-06-28
In this experiment liquid water is subject to an inhomogeneous electric field (∇(2)Ea≈ 10(10) V m(2)) using a high voltage (20 kV) point-plane electrode system. Using interferometry it was found that the application of a strong electric field gradient to water generates local changes in the refractive index of the liquid, polarizes the surface and creates a downward moving electro-convective jet. A maximum temperature difference of 1 °C is measured in the immediate vicinity of the point electrode. Raman spectroscopy performed on water reveals an enhancement of the vibrational collective modes (3250 cm(-1)) as well as an increase in the local mode (3490 cm(-1)) energy. This bimodal enhancement indicates that the spectral changes are not due to temperature changes. The intense field gradient thus establishes an excited subpopulation of vibrational oscillators far from thermal equilibrium. Delocalization of the collective vibrational mode spatially expands this excited population beyond the microscale. Hindered rotational freedom due to electric field pinning of molecular dipoles retards the heat flow and generates a chemical potential gradient. These changes are responsible for the observed changes in the refractive index and temperature. It is demonstrated that polar liquids can thus support local non-equilibrium thermodynamic transient states critical to biochemical and environmental processes. PMID:27253197
Collective Bulk and Edge Modes through the Quantum Phase Transition in Graphene at ν = 0
NASA Astrophysics Data System (ADS)
Murthy, Ganpathy; Shimshoni, Efrat; Fertig, Herbert
Undoped graphene in a strong, tilted magnetic field exhibits a radical change in conduction upon changing the tilt-angle, which can be attributed to a quantum phase transition from a canted antiferromagnetic (CAF) to a ferromagnetic (FM) bulk state at filling factor ν = 0 . This behavior signifies a change in the nature of the collective ground state and excitations across the transition. Using the time-dependent Hartree-Fock approximation, we study the collective neutral (particle-hole) excitations in the two phases, both in the bulk and on the edge of the system. The CAF has gapless neutral modes in the bulk, whereas the FM state supports only gapped modes in its bulk. At the edge, however, only the FM state supports gapless charge-carrying states. Linear response functions are computed to elucidate their sensitivity to the various modes. The response functions demonstrate that the two phases can be distinguished by the evolution of a local charge pulse at the edge. NSF 1066293 (Aspen), US-Israel BSF 2012120 (GM, EF,HAF), ISF 231/14 (ES), NSF-DMR 1306897 (GM), NSF-DMR 1506460 (HAF).
Collective Modes in Strongly Coupled Electronic Bilayer Liquids
Kalman, G.; Valtchinov, V.; Valtchinov, V.; Golden, K.I.
1999-04-01
We present the first reliable calculation of the collective mode structure of a strongly coupled electronic bilayer. The calculation is based on a classical model through the 3rd frequency-moment-sum rule preserving quasi-localized-charge approximation, using the recently calculated hypernetted-chain pair correlation functions. The out-of-phase spectrum shows an energy gap at k=0 and the absence of a previously conjectured dynamical instability. {copyright} {ital 1999} {ital The American Physical Society}
Discrete excitation of mode pulses using a diode-pumped solid-state digital laser
NASA Astrophysics Data System (ADS)
Ngcobo, Sandile; Bell, Teboho
2016-03-01
In this paper, we experimentally demonstrate novel method of generating discrete excitation of on-demand Lagaurre-Gaussian (LG) mode pulses, in a diode pumped solid-state digital laser. The digital laser comprises of an intra-cavity spatial light modulator (SLM) that acts as an end-mirror of the resonator for uploading digital holograms, for the selection of discrete LG modes and controlling the quality facto, Q of the resonator. Discrete excitation of LG mode pulses of azimuthal-order l of 0, 1, 2, with zero radial-order (p = 0) were generated. Pulses of duration 200 ms and intensities as high as 1 mW with repetition speed of 60 Hz were produced at 1 um wavelength. The maximum peak power-conversion efficiency measured was 1.3%.
Travel Mode Detection with Varying Smartphone Data Collection Frequencies.
Shafique, Muhammad Awais; Hato, Eiji
2016-01-01
Smartphones are becoming increasingly popular day-by-day. Modern smartphones are more than just calling devices. They incorporate a number of high-end sensors that provide many new dimensions to smartphone experience. The use of smartphones, however, can be extended from the usual telecommunication field to applications in other specialized fields including transportation. Sensors embedded in the smartphones like GPS, accelerometer and gyroscope can collect data passively, which in turn can be processed to infer the travel mode of the smartphone user. This will solve most of the shortcomings associated with conventional travel survey methods including biased response, no response, erroneous time recording, etc. The current study uses the sensors' data collected by smartphones to extract nine features for classification. Variables including data frequency, moving window size and proportion of data to be used for training, are dealt with to achieve better results. Random forest is used to classify the smartphone data among six modes. An overall accuracy of 99.96% is achieved, with no mode less than 99.8% for data collected at 10 Hz frequency. The accuracy is observed to decrease with decrease in data frequency, but at the same time the computation time also decreases. PMID:27213380
Travel Mode Detection with Varying Smartphone Data Collection Frequencies
Shafique, Muhammad Awais; Hato, Eiji
2016-01-01
Smartphones are becoming increasingly popular day-by-day. Modern smartphones are more than just calling devices. They incorporate a number of high-end sensors that provide many new dimensions to smartphone experience. The use of smartphones, however, can be extended from the usual telecommunication field to applications in other specialized fields including transportation. Sensors embedded in the smartphones like GPS, accelerometer and gyroscope can collect data passively, which in turn can be processed to infer the travel mode of the smartphone user. This will solve most of the shortcomings associated with conventional travel survey methods including biased response, no response, erroneous time recording, etc. The current study uses the sensors’ data collected by smartphones to extract nine features for classification. Variables including data frequency, moving window size and proportion of data to be used for training, are dealt with to achieve better results. Random forest is used to classify the smartphone data among six modes. An overall accuracy of 99.96% is achieved, with no mode less than 99.8% for data collected at 10 Hz frequency. The accuracy is observed to decrease with decrease in data frequency, but at the same time the computation time also decreases. PMID:27213380
Excitation of (2,1) neoclassical tearing modes by mode coupling with (1,1) internal mode in EAST
NASA Astrophysics Data System (ADS)
Shi, Tonghui; Wan, Baonian; Shen, Biao; Sun, Youwen; Qian, Jinping; Hu, Liqun; Gong, Xianzu; Liu, Guangjun; Luo, Zhengping; Zhong, Guoqiang; Xu, Liqing; Zhang, Jizong; Lin, Shiyao; Jie, Yinxian; Wang, Fudi; Lv, Bo; the EAST Team
2013-05-01
Neoclassical tearing modes (NTM) are observed in discharges with auxiliary heating LH+ICRF and LH only during H-mode in EAST. The m/n = 2/1 NTM is triggered by strongly coupling with an m/n = 1/1 internal mode. Here, LH and ICRF are the abbreviations of lower hybrid resonance heating and ion cyclotron resonance frequency heating, respectively. The mode number of the NTM is m/n = 2/1, where m is the poloidal mode number and n is the toroidal mode number. Just before the triggering of NTMs, an m/n = 1/1 internal mode appears in the soft x-ray emission at plasma centre when the intensity of hard x-ray (IHX) reaches a critical value. The mode, characterized by frequency chirping in the spectrum, may be related to suprathermal electrons produced by LH. The saturated magnetic island width wsat of the NTM is strongly correlated with poloidal βp. Normalized βN,onset and the magnetic island critical width wcrit increase with electron temperature Te.
Electron pair escape from fullerene cage via collective modes
Schüler, Michael; Pavlyukh, Yaroslav; Bolognesi, Paolo; Avaldi, Lorenzo; Berakdar, Jamal
2016-01-01
Experiment and theory evidence a new pathway for correlated two-electron release from many-body compounds following collective excitation by a single photon. Using nonequilibrium Green’s function approach we trace plasmon oscillations as the key ingredient of the effective electron-electron interaction that governs the correlated pair emission in a dynamic many-body environment. Results from a full ab initio implementation for C60 fullerene are in line with experimental observations. The findings endorse the correlated two-electron photoemission as a powerful tool to access electronic correlation in complex systems. PMID:27086559
Electron pair escape from fullerene cage via collective modes
NASA Astrophysics Data System (ADS)
Schüler, Michael; Pavlyukh, Yaroslav; Bolognesi, Paolo; Avaldi, Lorenzo; Berakdar, Jamal
2016-04-01
Experiment and theory evidence a new pathway for correlated two-electron release from many-body compounds following collective excitation by a single photon. Using nonequilibrium Green’s function approach we trace plasmon oscillations as the key ingredient of the effective electron-electron interaction that governs the correlated pair emission in a dynamic many-body environment. Results from a full ab initio implementation for C60 fullerene are in line with experimental observations. The findings endorse the correlated two-electron photoemission as a powerful tool to access electronic correlation in complex systems.
Exotic modes of excitation and weak interaction rates at finite temperature
Paar, N.
2011-10-28
The interplay of isospin asymmetry and finite temperature in nuclei plays an important role on properties of nuclear excitations and weak interaction rates in stellar environment. Recently a fully self-consistent microscopic framework, based on Hartree-Fock plus random phase approximation using Skyrme functionals, has been introduced for description of excitations and weak-interaction cross sections at finite temperature. Another self-consistent framework involving nuclei at finite temperature has also been developed within relativistic mean field theory using effective Lagrangians with density dependent meson-nucleon vertex functions. Nuclear excitations are studied using finite temperature random phase approximation for the range of temperatures T = 0-2 MeV, as well as in nuclei far from stability. In the focus of research are the structure properties of exotic modes of excitation (e.g. pygmy dipole resonances) and charge-exchange modes (e.g. Gamow-Teller resonances and forbidden transitions). It is shown that finite temperature effects include novel low-energy multipole excitations and modifications of the Gamow-Teller transition spectra. Using a representative set of Skyrme functionals, as well as covariant energy density functional with DD-ME2 parameterization, both theory frameworks have been applied in calculations of electron-capture cross sections relevant in the stage of supernova precollapse.
Collective hypersonic excitations in strongly multiple scattering colloids.
Still, T; Gantzounis, G; Kiefer, D; Hellmann, G; Sainidou, R; Fytas, G; Stefanou, N
2011-04-29
Unprecedented low-dispersion high-frequency acoustic excitations are observed in dense suspensions of elastically hard colloids. The experimental phononic band structure for SiO(2) particles with different sizes and volume fractions is well represented by rigorous full-elastodynamic multiple-scattering calculations. The slow phonons, which do not relate to particle resonances, are localized in the surrounding liquid medium and stem from coherent multiple scattering that becomes strong in the close-packing regime. Such rich phonon-matter interactions in nanostructures, being still unexplored, can open new opportunities in phononics. PMID:21635048
Development of collective structures over noncollective excitations in 139Nd
NASA Astrophysics Data System (ADS)
Bhowal, S.; Gangopadhyay, G.; Petrache, C. M.; Ragnarsson, I.; Singh, A. K.; Bhattacharya, S.; Hübel, H.; Neußer-Neffgen, A.; Al-Khatib, A.; Bringel, P.; Bürger, A.; Nenoff, N.; Schönwaßer, G.; Hagemann, G. B.; Herskind, B.; Jensen, D. R.; Sletten, G.; Fallon, P.; Görgen, A.; Bednarczyk, P.; Curien, D.; Korichi, A.; Lopez-Martens, A.; Rao, B. V. T.; Reddy, T. S.; Singh, Nirmal
2011-08-01
High-spin states in 139Nd were investigated using the reaction 96Zr(48Ca,5n) at a beam energy of 195 MeV and γ-ray coincidences were acquired with the Euroball spectrometer. Apart from several dipole bands at medium excitation energy, three quadrupole bands have been observed at high spin. Linking transitions connecting two of the high-spin bands to low-energy states have been observed. Calculations based on the cranked-Nilsson-Strutinsky formalism have been used to assign configurations for the high-spin quadrupole bands.
Flute mode waves near the lower hybrid frequency excited by ion rings in velocity space
NASA Technical Reports Server (NTRS)
Cattell, C.; Hudson, M.
1982-01-01
Discrete emissions at the lower hybrid frequency are often seen on the S3-3 satellite. Simultaneous observation of perpendicularly heated ions suggests that these ions may provide the free energy necessary to drive the instability. Studies of the dispersion relation for flute modes excited by warm ion rings in velocity space show that waves are excited with real frequencies near the lower hybrid frequency and with growth rates ranging from about 0.01 to 1 times the ion cyclotron frequency. Numerical results are therefore consistent with the possibility that the observed ions are the free energy source for the observed waves.
Nusinovich, Gregory S.; Pu, Ruifeng; Granatstein, Victor L.
2015-07-06
In recent years, there was an active development of high-power, sub-terahertz (sub-THz) gyrotrons for numerous applications. For example, a 0.67 THz gyrotron delivering more than 200 kW with about 20% efficiency was developed. This record high efficiency was achieved because the gyrotron operated in a high-order TE{sub 31,8}-mode with the power of ohmic losses less than 10% of the power of outgoing radiation. That gyrotron operated at the fundamental cyclotron resonance, and a high magnetic field of about 27 T was created by a pulse solenoid. For numerous applications, it is beneficial to use gyrotrons at cyclotron harmonics which can operate in available cryomagnets with fields not exceeding 15 T. However, typically, the gyrotron operation at harmonics faces severe competition from parasitic modes at the fundamental resonance. In the present paper, we consider a similar 0.67 THz gyrotron designed for operation in the same TE{sub 31,8}-mode, but at the second harmonic. We focus on two nonlinear effects typical for interaction between the fundamental and second harmonic modes, viz., the mode suppression and the nonlinear excitation of the mode at the fundamental harmonic by the second harmonic oscillations. Our study includes both the analytical theory and numerical simulations performed with the self-consistent code MAGY. The simulations show that stable second harmonic operation in the TE{sub 31,8} mode is possible with only modest sacrifice of efficiency and power.
Collective modes in the color flavor-locked phase.
Anglani, R.; Mannarelli, M.; Ruggieri, M.
2011-05-17
We study the low-energy effective action for some collective modes of the color flavor-locked (CFL) phase of QCD. This phase of matter has long been known to be a superfluid because by picking a phase its order parameter breaks the quark-number U(1){sub B} symmetry spontaneously. We consider the modes describing fluctuations in the magnitude of the condensate, namely the Higgs mode, and in the phase of the condensate, namely the Nambu-Goldstone (NG) (or Anderson-Bogoliubov) mode associated with the breaking of U(1){sub B}. By employing as microscopic theory the Nambu-Jona-Lasinio model, we reproduce known results for the Lagrangian of the NG field to the leading order in the chemical potential and extend such results evaluating corrections due to the gap parameter. Moreover, we determine the interaction terms between the Higgs and the NG field. This study paves the way for a more reliable study of various dissipative processes in rotating compact stars with a quark matter core in the CFL phase.
Excitation of unstable TAEs and stable n=0 modes in Alcator C-Mod
NASA Astrophysics Data System (ADS)
Sears, J.; Bader, A.; Parker, R. R.; Kramer, G. J.
2009-11-01
Toroidicity-induced Alfv'en Eigenmodes (TAEs) are weakly damped MHD modes in tokamak plasmas. The modes occur at discrete frequencies near φTAE=vA/2qR, ( vA=B/√μ0ρ ) in a gap of the continuous spectrum of Alfv'en waves. Unstable TAEs are excited by ICRF heating of at least 3.5 MW in Alcator C-Mod L-mode plasmas. These unstable modes have toroidal mode numbers in the range of n=-6 to n=6. In contrast, stable resonant modes that are observed in these plasmas at similar and lower ICRF powers by the Active MHD diagnostic in the TAE frequency range commonly have toroidal mode numbers of n=0, which precludes a TAE or EAE identity. The origin of these modes is explored with the NOVA-K code, and the destabilizing role of the energetic hydrogen tail as measured by the Neutral Particle Analyzer is presented.
Magnetic stochasticity and transport due to nonlinearly excited subdominant microtearing modes
Hatch, D. R.; Jenko, F.; Doerk, H.; Pueschel, M. J.; Terry, P. W.; Nevins, W. M.
2013-01-15
Subdominant, linearly stable microtearing modes are identified as the main mechanism for the development of magnetic stochasticity and transport in gyrokinetic simulations of electromagnetic ion temperature gradient driven plasma microturbulence. The linear eigenmode spectrum is examined in order to identify and characterize modes with tearing parity. Connections are demonstrated between microtearing modes and the nonlinear fluctuations that are responsible for the magnetic stochasticity and electromagnetic transport, and nonlinear coupling with zonal modes is identified as the salient nonlinear excitation mechanism. A simple model is presented, which relates the electromagnetic transport to the electrostatic transport. These results may provide a paradigm for the mechanisms responsible for electromagnetic stochasticity and transport, which can be examined in a broader range of scenarios and parameter regimes.
Normal-mode splitting with large collective cooperativity
Tuchman, A. K.; Long, R.; Vrijsen, G.; Boudet, J.; Lee, J.; Kasevich, M. A.
2006-11-15
We report the observation of normal-mode splitting of the atom-cavity dressed states in both the fluorescence and transmission spectra for large atom number and observe subnatural linewidths in this regime. We also implement a method of utilizing the normal-mode splitting to observe Rabi oscillations on the {sup 87}Rb ground state hyperfine clock transition. We demonstrate a large collective cooperativity, C=1.2x10{sup 4}, which, in combination with large atom number, N{approx}2x10{sup 5}, offers the potential to realize an absolute phase sensitivity better than that achieved by state-of-the-art atomic fountain clocks or inertial sensors operating near the quantum projection noise limit.
M = +1, ± 1 and ± 2 mode helicon wave excitation.
NASA Astrophysics Data System (ADS)
Kim, J.-H.; Yun, S.-M.; Chang, H.-Y.
1996-11-01
The characteristics of M=+1, ± 1 and ± 2 modes helicon wave excited using a solenoid antenna, Nagoya type III and quadrupole antenna respectively are first investigated. The solenoid antenna is constructed by winding a copper cable on a quartz discharge tube. Two dimensional cross-field measurements of ArII optical emission induced by hot electrons are made to investigate RF power deposition: Components of the wave magnetic field measured with a single-turn, coaxial magnetic probe were compared with the field patterns computed for M=+1, ± 1 and ± 2 modes. The M=+1 mode plasma produced by the solenoid antenna has a cylindrical high intensity plasma column, which center is empty. This cylindrical high intensity column results from the rotation of the cross-sectional electric field pattern (right hand circularly polarization). The radial plasma density profile has a peak at r=2.5cm with axisymmetry. It has been found that the radial profile of the plasma density is in good agreement with the computed power deposition profile. The radial profiles of the wave magnetic field are in good agreement with computations. The plasma excited by Nagoya type III antenna has two high intensity columns which results from the linear combination of M=+1 and -1 modes (i.e. plane polarization). The radial plasma density profile is in good agreement with emission intensity profile of ArII line (488nm). The plasma excited by quadrupole antenna has four high intensity columns which results from the linear combination of M=+2 and -2 modes (i.e. plane polarization). In the M=± 2 modes, the radial plasma density profile is also in good agreement with emission intensity profile of ArII line.
NASA Astrophysics Data System (ADS)
He, H. D.; Dong, J. Q.; Fu, G. Y.; Zheng, G. Y.; Sheng, Z. M.; Long, Y. X.; He, Z. X.; Jiang, H. B.; Shen, Y.; Wang, L. F.
2010-08-01
The internal kink (fishbone) modes, driven by barely passing energetic ions (EIs), are numerically studied with the spatial distribution of the EIs taking into account. It is found that the modes with frequencies comparable to the toroidal precession frequencies are excited by resonant interaction with the EIs. Positive and negative density gradient dominating cases, corresponding to off- and near-axis depositions of neutral beam injection (NBI), respectively, are analyzed in detail. The most interesting and important feature of the modes is that there exists a second stable regime in higher βh (=pressure of EIs/toroidal magnetic pressure) range, and the modes may only be excited by the barely passing EIs in a region of βth1<βh<βth2 (βth is threshold or critical beta of EIs). Besides, the unstable modes require minimum density gradients and minimum radial positions of NBI deposition. The physics mechanism for the existence of the second stable regime is discussed. The results may provide a means of reducing or even preventing the loss of NBI energetic ions and increasing the heating efficiency by adjusting the pitch angle and driving the system into the second stable regime fast enough.
Tuning a material's properties through the excitation of localized defect modes
NASA Astrophysics Data System (ADS)
Serra Garcia, Marc; Lydon, Joseph; Daraio, Chiara
2015-03-01
Technological applications such as acoustic super-lenses and vibration mitigation devices require materials with extreme mechanical properties (Very high, zero, or negative stiffness). These properties can be achieved through buckling instabilities, local resonances and phase transitions, mechanisms that are limited to particular frequencies, strains or temperatures. In this talk I will present an alternative mechanism to tune the stiffness of a lattice. The mechanism is based on the excitation of a nonlinear localized defect mode. The oscillation of the defect mode affects the bulk properties of the lattice. This is due to the thermal expansion of the defect mode and the nonlinear coupling between the mode amplitude and the strain of the lattice. Due to the singular properties of nonlinear systems near bifurcation points, the lattice can achieve an arbitrarily large stiffness. It is possible to select point of the force-displacement relation that is being tuned by selecting the defect's excitation frequency and amplitude. Depending on the nonlinear interaction potential at the defect site, the stiffness can be tuned to extremely positive or extremely negative values. While our theoretical and experimental results have been obtained in a granular crystal, the analysis suggests that an equivalent effect should be present in other lattices with localized modes and nonlinearity.
Spontaneous emission from an excited atom in the presence of N atoms and M modes
NASA Astrophysics Data System (ADS)
Cummings, F. W.
1985-05-01
The spontaneous emission of an excited two-level atom into a system of N nonexcited atoms of the same type (with N much greater than 1) in the presence of M electromagnetic-field modes is investigated analytically, applying the Hamiltonian formulation of Dicke (1954) studied by Jaynes and Cummings (1963), Tavis and Cummings (1968), and Buley and Cummings (1964). It is shown that the trapping of radiation in the system seen when one EM mode is present does not persist as M approaches N. The feasibility of an experimental verification of these phenomena is discussed.
Evolution of l-photon excited thermo vacuum state in a single-mode damping channel
NASA Astrophysics Data System (ADS)
He, Rui; Fan, Hong-Yi
2016-01-01
In this paper, we investigate how a kind of non-Gaussian states (l-photon excited thermo vacuum state Cla†l|0(β)>) evolves in a single-mode damping channel. We find that it evolves into a Laguerre-polynomial-weighted real-fictitious squeezed thermo vacuum state, which exhibits strong decoherence and its original nonclassicality fades. In particular, when l = 0, in this damping process the thermo squeezing effect decreases while the fictitious-mode vacuum becomes chaotic. In overcoming the difficulty of calculation, we employ the summation method within ordered product of operators, a new generating function formula about two-variable Hermite polynomials is derived.
Coherent phonon spectroscopy of non-fully symmetric modes using resonant terahertz excitation
Huber, T. Huber, L.; Johnson, S. L.; Ranke, M.; Ferrer, A.
2015-08-31
We use intense terahertz (THz) frequency electromagnetic pulses generated via optical rectification in an organic crystal to drive vibrational lattice modes in single crystal Tellurium. The coherent modes are detected by measuring the polarization changes of femtosecond laser pulses reflecting from the sample surface, resulting in a phase-resolved detection of the coherent lattice motion. We compare the data to a model of Lorentz oscillators driven by the near-single-cycle broadband THz pulse. The demonstrated technique of optically probed coherent phonon spectroscopy with THz frequency excitation could prove to be a viable alternative to other time-resolved spectroscopic methods like standard THz time domain spectroscopy.
Monopole Modes of Excitation in Deformed Neutron-rich Mg Isotopes
Yoshida, Kenichi
2009-08-26
The giant monopole resonance (GMR) and the low-frequency mode of monopole excitation in neutron-rich magnesium isotopes close to the drip line are investigated by means of the deformed Hartree-Fock-Bogoliubov and quasiparticle random-phase approximations. It is found that the GMR has a two-peak structure due to the deformation. The lower-energy resonance is generated associated with the coupling to the K{sup p}i = 0{sup +} component of the giant quadrupole resonance. Besides the GMR, we obtain the soft K{sup p}i = 0{sup +} mode below the neutron emission threshold energy.
Coherent phonon spectroscopy of non-fully symmetric modes using resonant terahertz excitation
NASA Astrophysics Data System (ADS)
Huber, T.; Ranke, M.; Ferrer, A.; Huber, L.; Johnson, S. L.
2015-08-01
We use intense terahertz (THz) frequency electromagnetic pulses generated via optical rectification in an organic crystal to drive vibrational lattice modes in single crystal Tellurium. The coherent modes are detected by measuring the polarization changes of femtosecond laser pulses reflecting from the sample surface, resulting in a phase-resolved detection of the coherent lattice motion. We compare the data to a model of Lorentz oscillators driven by the near-single-cycle broadband THz pulse. The demonstrated technique of optically probed coherent phonon spectroscopy with THz frequency excitation could prove to be a viable alternative to other time-resolved spectroscopic methods like standard THz time domain spectroscopy.
NASA Technical Reports Server (NTRS)
Prasad, C. B.; Mei, Chuh
1987-01-01
Multiple-mode nonlinear analysis is carried out for beams subjected to acoustic excitation. Effects of both nonlinear damping and large-deflection are included in the analysis in an attempt to explain the experimental phenomena of aircraft panels excited at high sound pressure levels; that is the broadening of the strain response peaks and the increase of modal frequency. An amplitude dependent nonlinear damping model is used in the anlaysis to study the effects and interactions of multiple modes, nonlinear stiffness and nonlinear damping on the random response of beams. Mean square maximum deflection, mean square maximum strain, and spectral density function of maximum strain for simple supported and clamped beams are obtained. It is shown analytically that nonlinear damping contributes significantly to the broadening of the response peak and to the mean square deflection and strain.
Spontaneous excitation of geodesic acoustic mode by toroidal Alfvén eigenmodes
NASA Astrophysics Data System (ADS)
Qiu, Zhiyong; Chen, Liu; Zonca, Fulvio
2013-02-01
Spontaneous nonlinear excitation of geodesic acoustic mode (GAM) by toroidal Alfvén eigenmodes (TAE) is studied within the framework of gyrokinetic theory. The dispersion relation for the parametric decays of a pump TAE mode into a TAE lower sideband and a GAM is derived. It is shown that, in the ideal MHD first stability region, the condition for spontaneous excitation of GAM by TAEs is ω20 > V2A/(4q2R20), in which, ω0 is the pump TAE real frequency, V A is the Alfvén speed, q is the safety factor and R0 is the torus major radius. The corresponding threshold condition is also derived and suggests the decay process as an effective saturation mechanism for TAE.
Intermediate energy electron impact excitation of composite vibrational modes in phenol
Neves, R. F. C.; Jones, D. B.; Lopes, M. C. A.; Nixon, K. L.; Oliveira, E. M. de; Lima, M. A. P.; Costa, R. F. da; Varella, M. T. do N.; Bettega, M. H. F.; Silva, G. B. da; Brunger, M. J.
2015-05-21
We report differential cross section results from an experimental investigation into the electron impact excitation of a number of the low-lying composite (unresolved) vibrational modes in phenol (C{sub 6}H{sub 5}OH). The measurements were carried out at incident electron energies in the range 15–40 eV and for scattered-electron angles in the range 10–90°. The energy resolution of those measurements was typically ∼80 meV. Calculations, using the GAMESS code, were also undertaken with a B3LYP/aug-cc-pVDZ level model chemistry, in order to enable us to assign vibrational modes to the features observed in our energy loss spectra. To the best of our knowledge, the present cross sections are the first to be reported for vibrational excitation of the C{sub 6}H{sub 5}OH molecule by electron impact.
Markers of pathological excitability derived from principal dynamic modes of hippocampal neurons
NASA Astrophysics Data System (ADS)
Kang, Eunji E.; Zalay, Osbert C.; Serletis, Demitre; Carlen, Peter L.; Bardakjian, Berj L.
2012-10-01
Transformation of principal dynamic modes (PDMs) under epileptogenic conditions was investigated by computing the Volterra kernels in a rodent epilepsy model derived from a mouse whole hippocampal preparation, where epileptogenesis was induced by altering the concentrations of Mg2 + and K+ of the perfusate for different levels of excitability. Both integrating and differentiating PDMs were present in the neuronal dynamics, and both of them increased in absolute magnitude for increased excitability levels. However, the integrating PDMs dominated at all levels of excitability in terms of their relative contributions to the overall response, whereas the dominant frequency responses of the differentiating PDMs were shifted to higher ranges under epileptogenic conditions, from ripple activities (75-200 Hz) to fast ripple activities (200-500 Hz).
Markers of pathological excitability derived from principal dynamic modes of hippocampal neurons.
Kang, Eunji E; Zalay, Osbert C; Serletis, Demitre; Carlen, Peter L; Bardakjian, Berj L
2012-10-01
Transformation of principal dynamic modes (PDMs) under epileptogenic conditions was investigated by computing the Volterra kernels in a rodent epilepsy model derived from a mouse whole hippocampal preparation, where epileptogenesis was induced by altering the concentrations of Mg(2 +) and K(+) of the perfusate for different levels of excitability. Both integrating and differentiating PDMs were present in the neuronal dynamics, and both of them increased in absolute magnitude for increased excitability levels. However, the integrating PDMs dominated at all levels of excitability in terms of their relative contributions to the overall response, whereas the dominant frequency responses of the differentiating PDMs were shifted to higher ranges under epileptogenic conditions, from ripple activities (75-200 Hz) to fast ripple activities (200-500 Hz). PMID:22871606
Asymptotic persistence of collective modes in shear flows
Mahajan, S.M. |; Rogava, A.D. |
1998-03-31
A new nonasymptotic method is presented that reveals an unexpected richness in the spectrum of fluctuations sustained by a shear flow with nontrivial arbitrary mean kinematics. The vigor of the method is illustrated by analyzing a two-dimensional, compressible hydrodynamic shear flow. The temporal evolution of perturbations spans a wide range of nonexponential behavior from growth-cum oscillations to monotonic growth. The principal characteristic of the revealed exotic collective modes in their asymptotic persistence. {open_quotes}Echoing{close_quotes} as well as unstable (including parametrically-driven) solutions are displayed. Further areas of application, for both the method and the new physics, are outlined.
NASA Technical Reports Server (NTRS)
Tanaka, Motohiko; Sato, Tetsuya; Hasegawa, A.
1989-01-01
The excitation of the kinetic Alfven wave by resonant mode conversion and longitudinal heating of the plasma by the kinetic Alfven wave were demonstrated on the basis of a macroscale particle simulation. The longitudinal electron current was shown to be cancelled by the ions. The kinetic Alfven wave produced an ordered motion of the plasma particles in the wave propagation direction. The electrons were pushed forward along the ambient magnetic field by absorbing the kinetic Alfven wave through the Landau resonance.
Mode Locking of Spin Waves Excited by Direct Currents in Microwave Nano-oscillators
NASA Astrophysics Data System (ADS)
Rezende, S. M.; de Aguiar, F. M.; Rodríguez-Suárez, R. L.; Azevedo, A.
2007-02-01
A spin-wave theory is presented which explains the frequency pulling and mode locking observed when two closely spaced spin-transfer nanometer-scale oscillators with slightly different frequencies are separately driven in the same magnetic thin film by spin-polarized carriers at high direct-current densities. The theory confirms recent experimental evidence that the origin of the phenomena lies in the nonlinear interaction between two overlapping spin waves excited in the magnetic nanostructure.
Noncontact excitation of guided waves (A0 mode) using an electromagnetic acoustic transducer (EMAT)
NASA Astrophysics Data System (ADS)
Fromme, Paul
2016-02-01
Fatigue damage can develop in aircraft structures at locations of stress concentration, such as fasteners, and has to be detected before reaching a critical size to ensure safe aircraft operation. Guided ultrasonic waves offer an efficient method for the detection and characterization of such defects in large aerospace structures. Electromagnetic acoustic transducers (EMAT) for the noncontact excitation of guided ultrasonic waves were developed. The transducer development for the specific excitation of the A0 Lamb wave mode with an out-of-plane Lorentz force is explained. The achieved radial and angular dependency of the excited guided wave pulses were measured using a noncontact laser interferometer. Based on the induced eddy currents in the plate a theoretical model was developed. The application of the developed transducers for defect detection in aluminum components using fully noncontact guided wave measurements was demonstrated. Excitation of the A0 Lamb wave mode was achieved using the developed EMAT transducer and the guided wave propagation and scattering was measured using a noncontact laser interferometer.
Collective, stochastic and nonequilibrium behavior of highly excited hadronic matter
Carruthers, P.
1983-01-01
We discuss selected problems concerning the dynamic and stochasticc behavior of highly excited matter, particularly the QCD plasma. For the latter we consider the equation of state, kinetics, quasiparticles, flow properties and possible chaos and turbulence. The promise of phase space distribution functions for covariant transport and kinetic theory is stressed. The possibility and implications of a stochastic bag are spelled out. A simplified space-time model of hadronic collisions is pursued, with applications to A-A collisions and other matters. The domain wall between hadronic and plasma phase is of potential importance: its thickness and relation to surface tension are noticed. Finally we reviewed the recently developed stochastic cell model of multiparticle distributions and KNO scaling. This topic leads to the notion that fractal dimensions are involved in a rather general dynamical context. We speculate that various scaling phenomena are independent of the full dynamical structure, depending only on a general stochastic framework having to do with simple maps and strange attractors. 42 references.
Damping of confined excitation modes of one-dimensional condensates in an optical lattice
NASA Astrophysics Data System (ADS)
Trallero-Giner, C.; Santiago-Pérez, Darío G.; Chung, Ming-Chiang; Marques, G. E.; Cipolatti, R.
2015-10-01
We study the damping of the collective excitations of Bose-Einstein condensates in a harmonic trap potential loaded in an optical lattice. In the presence of a confining potential the system is inhomogeneous and the collective excitations are characterized by a set of discrete confined phononlike excitations. We derive a general convenient analytical description for the damping rate, which takes into account the trapping potential and the optical lattice for the Landau and Beliaev processes at any temperature T . At high temperature or weak spatial confinement, we show that both mechanisms display a linear dependence on T . In the quantum limit, we find that the Landau damping is exponentially suppressed at low temperatures and the total damping is independent of T . Our theoretical predictions for the damping rate under the thermal regime is in complete correspondence with the experimental values reported for the one-dimensional (1D) condensate of sodium atoms. We show that the laser intensity can tune the collision process, allowing a resonant effect for the condensate lifetime. Also, we study the influence of the attractive or repulsive nonlinear terms on the decay rate of the collective excitations. A general expression for the renormalized Goldstone frequency is obtained as a function of the 1D nonlinear self-interaction parameter, laser intensity, and temperature.
The radiation performance of offset reflector antennas with horn feeds excited by high order modes
NASA Astrophysics Data System (ADS)
Thielen, Herbert
1988-07-01
The physical reasons for alignment errors in the antenna tracking of asymmetric reflector systems were investigated. The radiation behavior of offset reflector antennas, employing higher-order modes was theoretically and experimentally analyzed. In the case of TE21-mode excitation, a cross-polarization component is produced in single-reflector antennas due to feed tilt which is considerably larger than with the communication mode (TE11 or HE11 mode). In the case of circular polarization, this causes a null shift amounting to 1/10 or 1/5 of the half-power beam width of the main lobe. No null shift exists for the TM01- and TE01-modes. When the TE21-mode is used, the cross-polarization component is considerably smaller for dual-offset than for single-reflector antennas. In the case of ground station antennas where beam-waveguides consisting of two reflectors are used, a similar performance is obtained as for single-reflector antennas.
Direct excitation of TE11 mode in a relativistic backward wave oscillator
NASA Astrophysics Data System (ADS)
Xiao, Renzhen; Zhang, Yuchuan; Li, Jiawei; Song, Zhimin; Sun, Jun
2016-02-01
A relativistic backward wave oscillator for directly generating TE11 mode is proposed. An axially asymmetric slow wave structure and a sectioned annular cathode are introduced to suppress the TM01 mode and excite the TE11 mode. A pre-modulation dual-cavity, which allows part of the backward power to propagate into the diode region, is adopted to optimize the electron beam bunch, indicating that the conventional design principle that the diode region and the beam-wave interaction region should be isolated can be broken to increase the interaction efficiency. Particle-in-cell simulations show that when the diode voltage is 780 kV, and beam current is 6.1 kA, a microwave with power of 2.0 GW, and frequency of 9.25 GHz can be obtained, corresponding to an efficiency of 42%. Furthermore, the main output mode is TE11 mode, and the power of the cross-polarized mode is less than 10% within the calculation time of 50 ns.
Detection of elliptical polarization and mode splitting in discrete Schumann resonance excitations
NASA Technical Reports Server (NTRS)
Sentman, D. D.
1989-01-01
Elliptical polarization and mode splitting have been detected in the magnetic component of discrete, well defined Schumann resonance excitations. These ELF excitations, which are large electromagnetic transients of approximately 1 s duration, are called Q-bursts and typically occur every few minutes. They are believed to be the signature of the impulsive excitation of the earth-ionosphere cavity by ultra-large lightning currents. In this paper the magnetic polarization and spectral characteristics of four large Q-bursts are examined in detail using a new analysis technique. Two events display right-hand polarization and two display left-hand polarization. The theoretical polarization properties of the central and side multiplets of the Schumann resonances are used to define a local orthogonal coordinate system in the measurement frame in which these components may be separated. Maximum entropy spectrums computed separately for what are identified to be the central and side multiplets in this coordinate system show distinctly different eigenfrequencies for the lowest mode near 7.5 Hz. For the limited number of cases examined the magnitude of the line splitting detected using this technique is roughly 1.4-1.8 Hz, larger by nearly a factor of two than theoretical or observed values of the splitting previously reported. The frequencies of the side multiplets may lie either above or below the frequency of the central multiplet.
Collective Excitations of Bose-Einstein Condensates In Isotropic and Slightly Anisotropic Traps
NASA Astrophysics Data System (ADS)
Barentine, Andrew; Lobser, Dan; Lewandowski, Heather; Cornell, Eric
2014-05-01
Boltzmann proved that the monopole mode of a thermal gas in an isotropic, harmonic and 3D trap is undamped. Bose-Einstein Condensates (BECs) are not classical gases and their weakly interacting nature causes damping at finite temperature in a 3D monopole mode. The large parameter space of the TOP (Time-averaged Orbiting Potential) trap allows for precise control of the trap geometry. Exciting a monopole mode in a BEC as well as its canonical thermal cloud in the hydrodynamic regime will allow us to investigate damping effects in isotropic and slightly anisotropic traps. Funding : NSF,NIST,ONR
Superfluidity and collective modes in Rashba spin–orbit coupled Fermi gases
He, Lianyi; Huang, Xu-Guang
2013-10-15
We present a theoretical study of the superfluidity and the corresponding collective modes in two-component atomic Fermi gases with s-wave attraction and synthetic Rashba spin–orbit coupling. The general effective action for the collective modes is derived from the functional path integral formalism. By tuning the spin–orbit coupling from weak to strong, the system undergoes a crossover from an ordinary BCS/BEC superfluid to a Bose–Einstein condensate of rashbons. We show that the properties of the superfluid density and the Anderson–Bogoliubov mode manifest this crossover. At large spin–orbit coupling, the superfluid density and the sound velocity become independent of the strength of the s-wave attraction. The two-body interaction among the rashbons is also determined. When a Zeeman field is turned on, the system undergoes quantum phase transitions to some exotic superfluid phases which are topologically nontrivial. For the two-dimensional system, the nonanalyticities of the thermodynamic functions and the sound velocity across the phase transition are related to the bulk gapless fermionic excitation which causes infrared singularities. The superfluid density and the sound velocity behave nonmonotonically: they are suppressed by the Zeeman field in the normal superfluid phase, but get enhanced in the topological superfluid phase. The three-dimensional system is also studied. -- Highlights: •The general effective action for Rashba spin–orbit coupled Fermi superfluids is derived. •The evolution of the collective modes manifests the BCS/BEC-rashbon crossover. •The superfluid properties are universal at large spin–orbit coupling. •The sound velocity behaves nonanalytically across the quantum phase transition.
Two modes of a plasma jet excited by a direct current voltage
NASA Astrophysics Data System (ADS)
Li, Xuechen; Zhang, Panpan; Bao, Wenting; Jia, Pengying; Chu, Jingdi
2016-04-01
A plasma jet excited by a direct current voltage is developed to generate a diffuse plasma plume by blowing atmospheric pressure argon. Results show that the plume discharge operates in a single-pulsed mode or a continuous one depending on the applied voltage. For the single-pulsed mode, the discharge frequency increases with increasing the applied voltage or the air concentration, while it keeps almost constant with increasing the argon flow rate. The discharge dynamics at the breakdown stage indicate that the light emission propagates along the gas flow at a velocity in the order of 104 m s-1. The spatially resolved emission intensity at the afterglow stage of the pulsed discharge manifests a stratification into dark and bright luminous regions along the gas flow. For the continuous mode, however, the emission intensity gradually decreases along the gas flow. It is found that the continuous discharge is in a Townsend discharge regime judged from both the positive slope of the voltage-current curve and the small current density on the cathode surface. Based on optical emission spectroscopy, excited electron temperature and gas temperature of the plasma plume are obtained by a Boltzmann plot and fitting the spectra of OH radicals, respectively.
NASA Astrophysics Data System (ADS)
Bell, T. F.; Inan, U. S.; Platino, M.; Pickett, J. S.; Kossey, P. A.; Kennedy, E. J.
2004-03-01
We report new observations from the CLUSTER spacecraft of strong excitation of lower hybrid (LH) waves by electromagnetic (EM) whistler mode waves at altitudes >=20,000 km outside the plasmasphere. Previous observations of this phenomenon occurred at altitudes <=7000 km. The excitation mechanism appears to be linear mode coupling in the presence of small scale plasma density irregularities. These observations provide strong evidence that EM whistler mode waves are continuously transformed into LH waves as the whistler mode waves propagate at high altitudes beyond L ~ 4. This may explain the lack of lightning generated whistlers observed in this same region of space.
Flight and analytical investigations of a structural mode excitation system on the YF-12A airplane
NASA Technical Reports Server (NTRS)
Goforth, E. A.; Murphy, R. C.; Beranek, J. A.; Davis, R. A.
1987-01-01
A structural excitation system, using an oscillating canard vane to generate force, was mounted on the forebody of the YF-12A airplane. The canard vane was used to excite the airframe structural modes during flight in the subsonic, transonic, and supersonic regimes. Structural modal responses generated by the canard vane forces were measured at the flight test conditions by airframe-mounted accelerometers. Correlations of analytical and experimental aeroelastic results were made. Doublet lattice, steady state double lattice with uniform lag, Mach box, and piston theory all produced acceptable analytical aerodynamic results within the restrictions that apply to each. In general, the aerodynamic theory methods, carefully applied, were found to predict the dynamic behavior of the YF-12A aircraft adequately.
Entanglement spectrum and entangled modes of highly excited states in random XX spin chains
NASA Astrophysics Data System (ADS)
Pouranvari, Mohammad; Yang, Kun
We examine the newly developed real space renormalization group method of finding excited eigenstate (RSRG-X) of the XX spin-1/2 chain, from entanglement perspectives. Eigenmodes of the entanglement Hamiltonian, especially the maximally entangled mode (that contributes the most to the entanglement entropy) and corresponding entanglement energies are studied and compared with predictions of RSRG-X. Our numerical results demonstrate the accuracy of the RSRG-X method in the strong disorder limit, and quantify its error when applied to weak disorder regime. Overall, our results validate the RSRG-X method qualitatively, but as in the case of real space renormalization group method for the ground state (RSRG) there are quantitative errors for weaker randomness, and also such error grows with increasing temperature/excitation energy density.
Collective modes and thermodynamics of the liquid state
NASA Astrophysics Data System (ADS)
Trachenko, K.; Brazhkin, V. V.
2016-01-01
Strongly interacting, dynamically disordered and with no small parameter, liquids took a theoretical status between gases and solids with the historical tradition of hydrodynamic description as the starting point. We review different approaches to liquids as well as recent experimental and theoretical work, and propose that liquids do not need classifying in terms of their proximity to gases and solids or any categorizing for that matter. Instead, they are a unique system in their own class with a notably mixed dynamical state in contrast to pure dynamical states of solids and gases. We start with explaining how the first-principles approach to liquids is an intractable, exponentially complex problem of coupled non-linear oscillators with bifurcations. This is followed by a reduction of the problem based on liquid relaxation time τ representing non-perturbative treatment of strong interactions. On the basis of τ, solid-like high-frequency modes are predicted and we review related recent experiments. We demonstrate how the propagation of these modes can be derived by generalizing either hydrodynamic or elasticity equations. We comment on the historical trend to approach liquids using hydrodynamics and compare it to an alternative solid-like approach. We subsequently discuss how collective modes evolve with temperature and how this evolution affects liquid energy and heat capacity as well as other properties such as fast sound. Here, our emphasis is on understanding experimental data in real, rather than model, liquids. Highlighting the dominant role of solid-like high-frequency modes for liquid energy and heat capacity, we review a wide range of liquids: subcritical low-viscous liquids, supercritical state with two different dynamical and thermodynamic regimes separated by the Frenkel line, highly-viscous liquids in the glass transformation range and liquid-glass transition. We subsequently discuss the fairly recent area of liquid-liquid phase transitions, the
Collective modes and thermodynamics of the liquid state.
Trachenko, K; Brazhkin, V V
2016-01-01
Strongly interacting, dynamically disordered and with no small parameter, liquids took a theoretical status between gases and solids with the historical tradition of hydrodynamic description as the starting point. We review different approaches to liquids as well as recent experimental and theoretical work, and propose that liquids do not need classifying in terms of their proximity to gases and solids or any categorizing for that matter. Instead, they are a unique system in their own class with a notably mixed dynamical state in contrast to pure dynamical states of solids and gases. We start with explaining how the first-principles approach to liquids is an intractable, exponentially complex problem of coupled non-linear oscillators with bifurcations. This is followed by a reduction of the problem based on liquid relaxation time τ representing non-perturbative treatment of strong interactions. On the basis of τ, solid-like high-frequency modes are predicted and we review related recent experiments. We demonstrate how the propagation of these modes can be derived by generalizing either hydrodynamic or elasticity equations. We comment on the historical trend to approach liquids using hydrodynamics and compare it to an alternative solid-like approach. We subsequently discuss how collective modes evolve with temperature and how this evolution affects liquid energy and heat capacity as well as other properties such as fast sound. Here, our emphasis is on understanding experimental data in real, rather than model, liquids. Highlighting the dominant role of solid-like high-frequency modes for liquid energy and heat capacity, we review a wide range of liquids: subcritical low-viscous liquids, supercritical state with two different dynamical and thermodynamic regimes separated by the Frenkel line, highly-viscous liquids in the glass transformation range and liquid-glass transition. We subsequently discuss the fairly recent area of liquid-liquid phase transitions, the
Unpaired Majorana modes in Josephson-Junction Arrays with gapless bulk excitations
Pino, M.; Tsvelik, A.; Ioffe, L. B.
2015-11-06
In this study, the search for Majorana bound states in solid-state physics has been limited to materials that display a gap in their bulk spectrum. We show that such unpaired states appear in certain quasi-one-dimensional Josephson-junction arrays with gapless bulk excitations. The bulk modes mediate a coupling between Majorana bound states via the Ruderman-Kittel-Yosida-Kasuya mechanism. As a consequence, the lowest energy doublet acquires a finite energy difference. For a realistic set of parameters this energy splitting remains much smaller than the energy of the bulk eigenstates even for short chains of length L~10.
Gyrotron with a sectioned cavity based on excitation of a far-from-cutoff operating mode
NASA Astrophysics Data System (ADS)
Bandurkin, I. V.; Kalynov, Yu. K.; Osharin, I. V.; Savilov, A. V.
2016-01-01
A typical problem of weakly relativistic low-power gyrotrons (especially in the case of operation at high cyclotron harmonics) is the use of long cavities ensuring extremely high diffraction Q-factors for the operating near-cutoff waves. As a result, a great share of the rf power radiated by electrons is spent in Ohmic losses. In this paper, we propose to use a sectioned cavity with π-shifts of the wave phase between sections. In such a cavity, a far-from-cutoff axial mode of the operating cavity having a decreased diffraction Q-factor is excited by the electron beam in a gyrotron-like regime.
Unpaired Majorana Modes in Josephson-Junction Arrays with Gapless Bulk Excitations
NASA Astrophysics Data System (ADS)
Pino, M.; Tsvelik, A. M.; Ioffe, L. B.
2015-11-01
The search for Majorana bound states in solid-state physics has been limited to materials that display a gap in their bulk spectrum. We show that such unpaired states appear in certain quasi-one-dimensional Josephson-junction arrays with gapless bulk excitations. The bulk modes mediate a coupling between Majorana bound states via the Ruderman-Kittel-Yosida-Kasuya mechanism. As a consequence, the lowest energy doublet acquires a finite energy difference. For a realistic set of parameters this energy splitting remains much smaller than the energy of the bulk eigenstates even for short chains of length L ˜10 .
Unpaired Majorana Modes in Josephson-Junction Arrays with Gapless Bulk Excitations.
Pino, M; Tsvelik, A M; Ioffe, L B
2015-11-01
The search for Majorana bound states in solid-state physics has been limited to materials that display a gap in their bulk spectrum. We show that such unpaired states appear in certain quasi-one-dimensional Josephson-junction arrays with gapless bulk excitations. The bulk modes mediate a coupling between Majorana bound states via the Ruderman-Kittel-Yosida-Kasuya mechanism. As a consequence, the lowest energy doublet acquires a finite energy difference. For a realistic set of parameters this energy splitting remains much smaller than the energy of the bulk eigenstates even for short chains of length L∼10. PMID:26588406
Selective excitation of high-Q resonant modes in a bottle/quasi-cylindrical microresonator
NASA Astrophysics Data System (ADS)
Dong, Yongchao; Jin, Xueying; Wang, Keyi
2016-08-01
We fabricate a bottle/quasi-cylindrical microresonator by using a fusion splicer. This method does not require a real-time control of the translation stages and can easily fabricate a resonator with expected size and shape. Selective excitation of whispering gallery modes (WGMs) in the resonator is realized with a fiber taper coupled at various positions of the resonator along the bottle axis. Most importantly, we obtain a clean and regular spectrum with very high quality factor (Q) modes up to 3.1×107 in the quasi-cylindrical region of the resonator. Moreover, we package the coupling system into a whole device that can be moved freely. The vibration performance tests of the packaged device show that the coupling system with the taper coupled at the quasi-cylindrical region has a remarkable anti-vibration ability. The portability and robustness of the device make it attractive in practical applications.
Nonlinear excitation of polariton cavity modes in ZnO single nanocombs.
Capeluto, M G; Grinblat, G; Tirado, M; Comedi, D; Bragas, A V
2014-03-10
Tunable second harmonic (SH) polaritons have been efficiently generated in ZnO nanocombs, when the material is excited close to half of the band-gap. The nonlinear signal couples to the nanocavity modes, and, as a result, Fabry-Pérot resonances with high Q factors of about 500 are detected. Due to the low effective volume of the confined modes, matter-light interaction is very much enhanced. This effect lowers the velocity of the SH polariton in the material by 50 times, and increases the SH confinement inside the nanocavity due to this higher refractive index. We also show that the SH phase-matching condition is achieved through LO-phonon mediation. Finally, birrefringence of the crystal produces a strong SH intensity dependence on the input polarization, with a high polarization contrast, which could be used as a mechanism for light switching in the nanoscale. PMID:24663874
Slow-Mode Oscillations of Hot Loops Excited at Flaring Footpoints
NASA Astrophysics Data System (ADS)
Wang, T.; Liu, W.; Ofman, L.; Davila, J.
2012-05-01
The analysis of a hot loop oscillation event using SOHO/SUMER, GOES SXI, and RHESSI observations is presented. Damped Doppler shift oscillations were detected in the Fe xix line by SUMER, and interpreted as a fundamental standing slow mode. The evolution of soft X-ray emission from GOES/SXI and hard X-ray sources from RHESSI suggests that the oscillations of a large loop are triggered by a small flare, which may be produced by interaction (local reconnection) of this large loop with a small loop at its footpoint. This study provides clear evidence supporting our early conjecture that the slow-mode standing waves in hot coronal loops are excited by impulsive heating (small or microflares) at the loop's footpoint.
NASA Technical Reports Server (NTRS)
Bell, T. F.; Ngo, H. D.
1990-01-01
This paper presents a theoretical model for electrostatic lower hybrid waves excited by electromagnetic whistler mode waves propagating in regions of the magnetosphere and the topside ionosphere, where small-scale magnetic-field-aligned plasma density irregularities are thought to exist. In this model, the electrostatic waves are excited by linear mode coupling as the incident electromagnetic whistler mode waves scatter from the magnetic-field-aligned plasma density irregularities. Results indicate that high-amplitude short-wavelength (5 to 100 m) quasi-electrostatic whistler mode waves can be excited when electromagnetic whistler mode waves scatter from small-scale planar magnetic-field-aligned plasma density irregularities in the topside ionosphere and magnetosphere.
NASA Astrophysics Data System (ADS)
Gadzuk, J. W.
1998-09-01
The phenomenon of breathing mode excitation or bound-state wavepacket squeezing and spreading driven by a time-dependent oscillator frequency (due to either a transient force constant or mass) is considered here. An easily implemented theory of stimulated wavepacket dynamics for near-harmonic systems is presented which describes a variety of generic time dependences such as single sudden excitation, double switching (excitation/time delay/de-excitation) and decaying initially excited states which characterize many processes in spectroscopy, pump-probe control in intramolecular dynamics, and femtochemistry. The model is used as the theoretical basis for understanding such diverse phenomena as quantum excitation due to temporary neutron capture, stimulated bond-breaking resulting in delocalization, desorption, or dissociation, and breathing mode excitation of ultracold atoms trapped in optical lattices. Whilst the first two examples are speculative, results for transient wavepacket dynamics of the occupied excited optical lattice are in accord with recent experimental observations reported by the NIST Laser Cooling Group. Emphasis on the inherent theoretical simplicity and the multidisciplinary aspects of near-harmonic breathing mode excitation, as exemplified by the specific realizations considered here, has been a major intent of this topical review.
The Blazhko Effect and Additional Excited Modes in RR Lyrae Stars
NASA Astrophysics Data System (ADS)
Benkő, J. M.; Szabó, R.
2015-08-01
Recent photometric space missions, such as CoRoT and Kepler, revealed that many RR Lyrae stars pulsate—beyond their main radial pulsation mode—in low-amplitude modes. Space data seem to indicate a clear trend that, namely, overtone (RRc) stars and modulated fundamental (RRab) RR Lyrae stars ubiquitously show additional modes, while non-Blazhko RRab stars never do. Two Kepler stars (V350 Lyr and KIC 7021124), however, apparently seemed to break this rule: they were classified as non-Blazhko RRab stars showing additional modes. We processed Kepler pixel photometric data of these stars. We detected a small amplitude (but significant) Blazhko effect for both stars by using the resulting light curves and O-C diagrams. This finding strengthens the apparent connection between the Blazhko effect and the excitation of additional modes. In addition, it yields a potential tool for detecting Blazhko stars through the additional frequency patterns, even if we have only short but accurate time series observations. V350 Lyr shows the smallest amplitude multiperiodic Blazhko effect ever detected.
NASA Astrophysics Data System (ADS)
Xiao, Bo; Antonsen, Thomas; Ott, Edward; Anlage, Steven; Ma, Tzuhsuan; Shvets, Gennady
Electronic chiral edge states in Quantum Hall Effect systems has attracted a lot of attention in recent years because of its unique directionality and robustness against scattering from disorder. Its electromagnetic counterpart can be found in photonic crystals, which is a material with periodic dielectric constant. Here we present the experimental results demonstrating the unidirectional edge mode inside a bi-anisotropic meta-waveguide (BMW) structure. It is a parallel plate waveguide with metal rods placed in a hexagonal lattice. Half of the rods are attached to the top plate while the other half are attached to the bottom plate creating a domain wall. The edge mode is excited by two loop antennas placed perpendicular to each other within one wavelength, generating a rotating magnetic dipole that couples to the left or right-going mode. The transmission measurement are taken along the BMW boundary and shows high transmission only around the edge, thus confirming the presence of an edge mode. We also demonstrated that very high directivity can be achieved when the input amplitude and phase of the two loop antennas are tuned properly This work is funded by the ONR under Grants No. N00014130474 and N000141512134, and the Center for Nanophysics and Advanced Materials (CNAM).
On the importance of collective excitations for thermal transport in graphene
Gill-Comeau, Maxime; Lewis, Laurent J.
2015-05-11
We use equilibrium molecular dynamics (MD) simulations to study heat transport in bulk single-layer graphene. Through a modal analysis of the MD trajectories employing a time-domain formulation, we find that collective excitations involving flexural acoustic (ZA) phonons, which have been neglected in the previous MD studies, actually dominate the heat flow, generating as much as 78% of the flux. These collective excitations are, however, much less significant if the atomic displacements are constrained in the lattice plane. Although relaxation is slow, we find graphene to be a regular (non-anomalous) heat conductor for sample sizes of order 40 μm and more.
NASA Astrophysics Data System (ADS)
Grujic, Katarina; Hole, J. Patrick; Hellesø, Olav Gaute; Wilkinson, James S.
2006-02-01
Optical microsphere resonators, with their exceptionally low optical losses and high Q-factors, are attracting a lot of interest in integrated optics and related fields. Not being accessible by free-space beams, whispering gallery modes (WGM) of a microsphere resonator require near-field coupler devices. Efficient evanescent coupling has been demonstrated previously by using thin tapered fibres, fibre half-block couplers, angle-polished fibres and bulk prisms. In this work, we demonstrate WGM excitation in microspheres, from 8 to 15 μm in diameter, by using an integrated optics channel waveguide. Light from a tunable laser was coupled into a single mode K + ion-exchanged channel waveguide formed in BK7 glass substrate. Dry borosilicate glass microspheres were dispersed on the substrate surface. Polystyrene microspheres were suspended in electrolyte water solution and confined in a closed cell on top of the waveguide. The light was coupled to the particles sitting on the waveguide surface. The scattered light was observed through the microscope. As the laser wavelength was tuned, the observed images were recorded with a CCD camera. WGM excitation was observed through the increased scattered light intensity at certain wavelengths. In the case of glass microspheres and a Ti:Sapphire tunable laser, the obtained resonance quality (Q-) factors were about 400. The resonances observed in polystyrene microspheres using a tunable diode laser had lower Q-factors and were deteriorating with decreasing particle size.
NASA Astrophysics Data System (ADS)
Hohl, Andreas; Tergeist, Mathias; Oueslati, Hatem; Jain, Jayesh R.; Herbig, Christian; Ostermeyer, Georg-Peter; Reckmann, Hanno
2015-04-01
Drilling system applications are subject to torsional vibrations that are induced by self-excitation mechanisms. A common mechanism is a falling characteristic of contact or cutting forces with respect to the relative velocity between the bit and the formation. To mitigate the effects of this mechanism, it is important to identify modes that are the most likely to be excited. However, in complex structures the identification of critical mode shapes is no trivial task. This paper discusses a criterion derived to identify critical torsional modes in drilling systems that are prone to self-excitation. Basic assumptions are a falling (velocity-weakening) characteristic of the contact forces and only one contributing mode. Multiple contact forces along the structure can be considered with different contact characteristics. Contributing parameters are angular eigenfrequency, deflection of the mode shape at the contact points, modal damping of the examined mode, and the slope of the characteristic of the contact forces at the operating point. In a case study of a drilling system the derived criterion is tested. The case study focuses on torsional vibrations excited by cutting forces observed in field measurements with high amplitudes and accelerations. The corresponding modes are localized to the so-called bottomhole assembly (BHA) at the end of the drilling system. Numerical results from a finite element analysis are compared to downhole measurements to verify the critical modes that are identified with the criterion. In addition, mass and stiffness changes along the structure are intentionally induced to beneficially influence mode shapes. Results indicate that reducing the mode shape at the source of vibration (bit) decreases the excitability of this mode shape.
Collective Excitations of Bose-Einstein Condensates In Isotropic and Slightly Anisotropic Traps
NASA Astrophysics Data System (ADS)
Barentine, Andrew; Lobser, Dan; Lewandowski, Heather; Cornell, Eric
2014-03-01
Boltzmann proved that the monopole mode of a thermal gas in an isotropic, harmonic and 3D trap is undamped. Bose-Einstein Condensates (BECs) are not classical gases and their weakly interacting nature causes damping in a 3D monopole mode. The large parameter space of the TOP (Time-averaged Orbiting Potential) trap allows for precise control of the trap geometry. Exciting a monopole mode in a BEC as well as its canonical thermal cloud allows us to investigate damping effects in isotropic and slightly anisotropic traps for both hydrodynamic and collisionless regimes. We also hope to achieve a greater understanding of the frequency shifts due to anharmonicity in the trap in order to apply this to our research on quasi-2D monopole modes. Funding: NSF, NIST, ONR
Motobayashi, Kenta; Kim, Yousoo; Arafune, Ryuichi; Ohara, Michiaki; Ueba, Hiromu; Kawai, Maki
2014-05-21
We present a novel reaction mechanism for a single adsorbed molecule that proceeds via simultaneous excitation of two different vibrational modes excited by inelastic tunneling electrons from a scanning tunneling microscope. Specifically, we analyze the dissociation of a single dimethyl disulfide (DMDS, (CH{sub 3}S){sub 2}) molecule on Cu(111) by using a versatile theoretical method, which permits us to simulate reaction rates as a function of sample bias voltage. The reaction is induced by the excitation of C-H stretch and S-S stretch modes by a two-electron process at low positive bias voltages. However, at increased voltages, the dissociation becomes a single-electron process that excites a combination mode of these stretches, where excitation of the C-H stretch is the energy source and excitation of the S-S stretch mode enhances the anharmonic coupling rate. A much smaller dissociation yield (few orders of magnitude) at negative bias voltages is understood in terms of the projected density of states of a single DMDS on Cu(111), which reflects resonant excitation through the molecular orbitals.
Collective excitations of the hybrid atomic-molecular Bose-Einstein condensates
Gupta, Moumita; Dastidar, Krishna Rai
2010-06-15
We investigate the low-energy excitations of the spherically and axially trapped atomic Bose-Einstein condensate coupled to a molecular Bose gas by coherent Raman transitions. We apply the sum-rule approach of many-body response theory to derive the low-lying collective excitation frequencies of the hybrid atom-molecular system. The atomic and molecular ground-state densities obtained in Gross-Pitaevskii and modified Gross-Pitaevskii (including the higher order Lee-Huang-Yang term in interatomic interaction) approaches are used to find out the individual energy components and hence the excitation frequencies. We obtain different excitation energies for different angular momenta and study their characteristic dependence on the effective Raman detuning, the scattering length for atom-atom interaction, and the intensities of the coupling lasers. We show that the inclusion of the higher-order nonlinear interatomic interaction in modified Gross-Pitaevskii approach introduces significant corrections to the ground-state properties and the excitation frequencies both for axially and spherically trapped coupled {sup 87}Rb condensate system with the increase in the s-wave scattering length (for peak gas-parameter {>=}10{sup -3}). It has been shown that the excitation frequencies decrease with the increase in the effective Raman detuning as well as the s-wave scattering length, whereas excitation frequencies increase with the increase in the atom-molecular coupling strength. The frequencies in modified Gross-Pitaevskii approximation exhibit an upward trend after a certain value of scattering length and also largely deviate from the Gross-Pitaevskii results with the increase in s-wave scattering length. The strong dependence of excitation frequencies on the laser intensities used for Raman transitions manifests the role of atom-molecular coupling strength on the control of collective excitations. The collective excitation frequencies for the hybrid atom-molecular BEC differ
Bernabei, S.; Chang, Z.; Darrow, D.; Fredrickson, E.D.; Fu, G.Y.; Hoang, G.T.; Hosea, J.C.; Majeski, R.; Phillips, C.K.; Rogers, J.H.; Schilling, G.; Wilson, J.R.
1997-04-01
Alfv{acute e}n modes are excited by energetic ions in TFTR during intense minority ICRF heating. There is a clear threshold in rf power above which the modes are distabilized. The net effect of these modes is the increase of the fast ion losses, with an associated saturation of the ion tail energy and of the efficiency of the heating. Typically, several modes are excited with progressive n-numbers, with frequencies in the neighborhood of 200 kHz. Results suggest that Energetic Particle Modes (EPM), mostly unseen by the Mirnov coils, are generated near the center and are responsible for the ion losses. Stronger global TAE modes, which are destabilized by the stream of displaced fast ions, appear responsible only for minor losses. {copyright} {ital 1997 American Institute of Physics.}
Study of Collective Dipole Excitations below the Giant Dipole Resonance at HI{gamma}S
Tonchev, A. P.; Howell, C. R.; Tornow, W.; Angell, C.; Boswell, M.; Karwowski, H. J.; Chyzh, A.; Kelley, J. H.; Tsoneva, N.; Wu, Y. K.
2007-02-26
The High-Intensity Gamma-ray Source utilizing intra-cavity back-scattering of free electron laser photons from relativistic electrons allows one to produce a unique beam of high-flux gamma rays with 100% polarization and selectable energy and energy resolution which is ideal for low-energy {gamma}-ray scattering experiments. Nuclear resonance fluorescence experiments have been performed on N=82 nuclei. High sensitivity studies of E1 and M1 excitations at energies close to the neutron emission threshold have been performed. The method allows the determination of excitation energies, spin, parities, and decay branching ratios of the pygmy dipole mode of excitation. The observations are compared with calculations using statistical and quasi-particle random-phase approximations.
NASA Astrophysics Data System (ADS)
Chen, Cheng-Chien; van Veenendaal, Michel; Devereaux, Thomas P.; Wohlfeld, Krzysztof
2015-04-01
Using a combined analytical and numerical approach, we study the collective spin and orbital excitations in a spin-orbital chain under a crystal field. Irrespective of the crystal-field strength, these excitations can be universally described by fractionalized fermions. The fractionalization phenomenon persists and contrasts strikingly with the case of a spin chain, where fractionalized spinons cannot be individually observed but confined to form magnons in a strong magnetic field. In the spin-orbital chain, each of the fractional quasiparticles carries both spin and orbital quantum numbers, and the two variables are always entangled in the collective excitations. Our result further shows that the recently reported separation phenomenon occurs when crystal fields fully polarize the orbital degrees of freedom. In this case, however, the spinon and orbiton dynamics are decoupled solely because of a redefinition of the spin and orbital quantum numbers.
NASA Astrophysics Data System (ADS)
Bell, T. F.; Inan, U. S.; Platino, M.; Pickett, J.; Kossey, P. A.; Kennedy, E. J.
2003-12-01
We report new observations from the CLUSTER spacecraft of strong excitation of lower hybrid waves by electromagnetic whistler mode waves at altitudes of roughly 20,000 km outside the plasmasphere. Previous observations of this phenomenon have been limited to altitudes less than 7000 km. The excitation mechanism appears to be linear mode coupling in the presence of small scale plasma density irregularities. The wavelengths of the excited lower hybrid waves, as deduced from their doppler shifts, appear to lie in the 15 - 1500 m range. These observations provide strong evidence that electromagnetic whistler mode waves are continuously transformed into lower hybrid waves as the whistler mode waves propagate at high altitudes beyond L = 4. This finding may explain the lack of lightning generated whistlers observed in this same region of space.
NASA Astrophysics Data System (ADS)
Liu, Joseph T. C.; Lee, Keseok
2013-11-01
Experiments of Asai, et al. (2011) confirm earlier experiments of Sato & Okada (1966), Peterson & Hama (1976) that, for sufficiently slender axisymmetric bodies of revolution placed in a stream parallel to the axes, only convectively unstable modes exist. However, in the downstream nonlinear region, the present theoretical/computational work shows that the imposition of the most unstable helical modes results in the generation of a stationary harmonic-helical mode that persists downstream. This is elucidated from energy transfer mechanism from the mean flow and inter-mode energy transfer via triad interactions. While absolute unstable modes behind bluff bodies of revolution are a natural occurrence according to the linear theory, the presence of such modes behind very slender bodies of revolution is a consequence of downstream nonlinear interactions between the excited helical modes.
Enhanced Third Harmonic Generation in Single Germanium Nanodisks Excited at the Anapole Mode.
Grinblat, Gustavo; Li, Yi; Nielsen, Michael P; Oulton, Rupert F; Maier, Stefan A
2016-07-13
We present an all-dielectric germanium nanosystem exhibiting a strong third order nonlinear response and efficient third harmonic generation in the optical regime. A thin germanium nanodisk shows a pronounced valley in its scattering cross section at the dark anapole mode, while the electric field energy inside the disk is maximized due to high confinement within the dielectric. We investigate the dependence of the third harmonic signal on disk size and pump wavelength to reveal the nature of the anapole mode. Each germanium nanodisk generates a high effective third order susceptibility of χ((3)) = 4.3 × 10(-9) esu, corresponding to an associated third harmonic conversion efficiency of 0.0001% at an excitation wavelength of 1650 nm, which is 4 orders of magnitude greater than the case of an unstructured germanium reference film. Furthermore, the nonlinear conversion via the anapole mode outperforms that via the radiative dipolar resonances by about 1 order of magnitude, which is consistent with our numerical simulations. These findings open new possibilities for the optimization of upconversion processes on the nanoscale through the appropriate engineering of suitable dielectric materials. PMID:27331867
Mid-infrared Otto excitation of transverse electric modes in doped graphene
NASA Astrophysics Data System (ADS)
Ramos-Mendieta, F.
2015-04-01
We have studied numerically the excitation of surface modes of transverse electric polarization in doped graphene. Using the prism-based Otto configuration, the electromagnetic resonances were found within ultra-tiny angular windows of width of order of Δ θ i = 10-3 degrees or lower, beyond the critical angle where evanescent fields are already available. We obtained absorption peaks of angular position strongly dependent on the prism-graphene separation d, which is larger than dc, the cutoff prism-graphene separation. We prove numerically that dc depends on the graphene parameters and can be written as d c = α / 2 , where α ( ω ) is the decay length of the electromagnetic field of the modes. With doping levels of Fermi energy 0.2 eV ≤ μ ≤ 0.3 eV, we found resonances within the range of 80-145 THz. The numerical calculations show the mayor role played by the graphene losses that, indeed, can obliterate the mode resonance.
g-MODE EXCITATION DURING THE PRE-EXPLOSIVE SIMMERING OF TYPE Ia SUPERNOVAE
Piro, Anthony L.
2011-09-01
Prior to the explosive burning of a white dwarf (WD) that makes a Type Ia supernova (SN Ia), the star 'simmers' for {approx}10{sup 3} yr in a convecting, carbon-burning region. I estimate the excitation of g-modes by convection during this phase and explore their possible effect on the WD. As these modes propagate from the core of the WD toward its surface, their amplitudes grow with decreasing density. Once the modes reach nonlinear amplitudes, they break and deposit their energy into a shell of mass {approx}10{sup -4} M{sub sun}. This raises the surface temperature by {approx}4 x 10{sup 8} K, which is sufficient to ignite a layer of helium, as is expected to exist for some SN Ia scenarios. This predominantly synthesizes {sup 40}Ca, but some amount of {sup 28}Si, {sup 32}S, and {sup 44}Ti may also be present. These ashes are expanded out with the subsequent explosion up to velocities of {approx}20, 000 km s{sup -1}, which may explain the high velocity features (HVFs) seen in many SNe Ia. The appearance of HVFs would therefore be a useful discriminant for determining between progenitors, since a flammable helium-rich layer will not be present for accretion from a C/O WD as in a merger scenario. I also discuss the implications of {sup 44}Ti production.
NASA Astrophysics Data System (ADS)
Filinov, A.
2016-07-01
A two-component, two-dimensional (2D) dipolar bosonic system in the bilayer geometry is considered. By performing quantum Monte Carlo simulations in a wide range of layer spacings we analyze in detail the pair correlation functions, the static response function, and the kinetic and interaction energies. By reducing the layer spacing we observe a transition from weakly to strongly bound dimer states. The transition is accompanied by the onset of short-range correlations, suppression of the superfluid response, and rotonization of the excitation spectrum. A dispersion law and a dynamic structure factor for the in-phase (symmetric) and out-of-phase (antisymmetric) collective modes during the dimerization is studied in detail with the stochastic reconstruction method and the method of moments. The antisymmetric mode spectrum is most strongly influenced by suppression of the inlayer superfluidity (specified by the superfluid fraction γs=ρs/ρ ). In a pure superfluid (normal fluid) phase, only an acoustic [optical (gapped)] mode is recovered. In a partially superfluid phase, both are present simultaneously, and the dispersion splits into two branches corresponding to a normal and a superfluid component. The spectral weight of the acoustic mode scales linearly with γs. This weight transfers to the optical branch when γs is reduced due to formation of dimer states. In summary, we demonstrate how the interlayer dimerization in dipolar bilayers can be uniquely identified by static and dynamic properties.
G. Ciovati; P. Kneisel
2005-05-01
Simultaneous excitation of both modes has been carried out on a CEBAF single cell cavity. The cavity has two beam pipe side-ports for each mode for input and pick-up couplers. Coupling to the TE011 mode is done by magnetic loop couplers while for the TM010 mode coaxial antennas are used. Simultaneous excitation of both TM and TE modes has been proposed recently for superconducting photoinjector applications to take advantage of the accelerating electric field of the TM mode, combined with the focusing magnetic field of the TE mode. The TE011 mode has the property of having zero surface electric field, surface magnetic field orthogonal to the one in the TM010 mode and concentrated in the iris/wall regions of the cavity. The presence of both modes in the cavity at the same time can also be used to investigate the so-called high field Q-drop in the TM010 mode. This paper will present some preliminary result on the test of the single cell cavity at 2 K.
Beta decay properties of the collective scissors mode 1+-states in 50Cr
NASA Astrophysics Data System (ADS)
Zenginerler, Zemine; Yakut, Hakan; Kuliev, Ali Akbar; Guliyev, Ekber
2014-03-01
The beta decay properties of collective IπK = 1+1 states in doubly even deformed 50Cr nucleus are investigated in the framework of the random-phase approximation (RPA). The model Hamiltonian includes restoring rotational invariance of the deformed single particle Hamiltonian forces and the spin-spin interactions. The present investigation demonstrates an advantage the rotational invariant model (R-QRPA) over the rotational non-invariant model (RN-QRPA). For a more complete comparison with the experimental data, we calculate to the log ft values as well as the energies and B(M1) value of the excited 1+-states. The calculated energy spectrum of 50Cr nucleus demonstrates a very rich ft strength structure in accordance to experiment. The agreement between the calculated energy spectrum and the logft values of the scissors mode excitations with the available experimental data is quite good. One of the authors (Z.Z) would like to acknowledge that this work is performed of the Fellowship No:2219 under the TUBITAK-TURKEY.
NASA Astrophysics Data System (ADS)
Rigo, E.; Aparicio, F. J.; Vanacharla, M. R.; Larcheri, S.; Guider, R.; Han, B.; Pucker, G.; Pavesi, L.
2014-03-01
A silicon oxynitride channel waveguide based evanescent-field optical transducer is presented for lab-on-chip application. The optical biosensor detects luminescent bioanalytes infiltrated within a reactor well realized across the waveguide. As a main novelty, the sensing mechanism proposed makes use of the evanescent-field propagating in the waveguide to both excite and to collect the fluorescent signal. To understand the chip behavior, its design and collection efficiency were analyzed by finite-difference time-domain simulations in comparison with similar structures differing in the bioreactor thickness and therefore in the excitation and collection mechanisms. It is demonstrated that the best efficiency and performance are reached for the proposed dual evanescent field approach. Characterization of the optical losses and fluorescence measurements from a dye solution infiltrated in the bioreactor well validate the proposed working concept.
Huysmans, G.T.A.; Kerner, W.; Borba, D.; Holties, H.A.; Goedbloed, J.P.
1995-05-01
The active excitation of global Alfven modes using the saddle coils in the Joint European Torus (JET) [{ital Plasma} {ital Physics} {ital and} {ital Controlled} {ital Nuclear} {ital Fusion} {ital Research} 1984, Proceedings of the 10th International Conference, London (International Atomic Energy Agency, Vienna, 1985), Vol. 1, p. 11] as the external antenna, will provide information on the damping of global modes without the need to drive the modes unstable. For the modeling of the Alfven mode excitation, the toroidal resistive magnetohydrodynamics (MHD) code CASTOR (Complex Alfven Spectrum in TORoidal geometry) [18{ital th} {ital EPS} {ital Conference} {ital On} {ital Controlled} {ital Fusion} {ital and} {ital Plasma} {ital Physics}, Berlin, 1991, edited by P. Bachmann and D. C. Robinson (The European Physical Society, Petit-Lancy, 1991), Vol. 15, Part IV, p. 89] has been extended to calculate the response to an external antenna. The excitation of a high-performance, high beta JET discharge is studied numerically. In particular, the influence of a finite pressure is investigated. Weakly damped low-{ital n} global modes do exist in the gaps in the continuous spectrum at high beta. A pressure-driven global mode is found due to the interaction of Alfven and slow modes. Its frequency scales solely with the plasma temperature, not like a pure Alfven mode with a density and magnetic field.
Excitation of kinetic geodesic acoustic modes by drift waves in nonuniform plasmas
Qiu, Z.; Chen, L.; Zonca, F.
2014-02-15
Effects of system nonuniformities and kinetic dispersiveness on the spontaneous excitation of Geodesic Acoustic Mode (GAM) by Drift Wave (DW) turbulence are investigated based on nonlinear gyrokinetic theory. The coupled nonlinear equations describing parametric decay of DW into GAM and DW lower sideband are derived and then solved both analytically and numerically to investigate the effects on the parametric decay process due to system nonuniformities, such as nonuniform diamagnetic frequency, finite radial envelope of DW pump, and kinetic dispersiveness. It is found that the parametric decay process is a convective instability for typical tokamak parameters when finite group velocities of DW and GAM associated with kinetic dispersiveness and finite radial envelope are taken into account. When, however, nonuniformity of diamagnetic frequency is taken into account, the parametric decay process becomes, time asymptotically, a quasi-exponentially growing absolute instability.