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.
Probing the neutron skin thickness in collective modes of excitation
NASA Astrophysics Data System (ADS)
Paar, N.; Horvat, A.
2014-03-01
Nuclear collective motion provides valuable constraint on the size of neutron-skin thickness and the properties of nuclear matter symmetry energy. By employing relativistic nuclear energy density functional (RNEDF) and covariance analysis related to χ2 fitting of the model parameters, relevant observables are identified for dipole excitations, which strongly correlate with the neutron-skin thickness (rnp), symmetry energy at saturation density (J) and slope of the symmetry energy (L). Using the RNEDF framework and experimental data on pygmy dipole strength (68Ni, 132Sn, 208Pb) and dipole polarizability (208Pb), it is shown how the values of J, and L, and rnp are constrained. The isotopic dependence of moments associated to dipole excitations in 116-136Sn shows that the low-energy dipole strength and polarizability in neutron-rich nuclei display strong sensitivity to the symmetry energy parameter J, more pronounced than in isotopes with moderate neutron-to-proton number ratios.
Near Gap Excitation of Collective Modes in a Charge Density Wave
NASA Astrophysics Data System (ADS)
Leuenberger, Dominik; Sobota, Jonathan; Yang, Shuolong; Kemper, Alexander; Giraldo, Paula; Moore, Rob; Fisher, Ian; Kirchmann, Patrick; Devereaux, Thomas; Shen, Zhi-Xun
2015-03-01
We present time- and angle-resolved photoemission spectroscopy (trARPES) measurements on the charge density wave system's (CDW) CeTe3. Optical excitation transiently populates the unoccupied band structure and reveals a CDW gap size of 2 Δ = 0 . 59 eV. In addition, the occupied Te- 5 p band dispersion is coherently modified by three collective modes. First, the spatial polarization of the modes is analyzed by fits of a transient model dispersion and DFT frozen phonon calculations. We thereby demonstrate how the rich information from trARPES allows identification of collective modes and their spatial polarization, which explains the mode-dependent coupling to charge order. Second, the exciting photon energy hν was gradually lowered towards 2 Δ , at constant optical excitation density. The coherent response of the amplitude mode deviates from the optical conductivity, which is dominated by direct interband transitions between the lower and upper CDW bands. The measured hν -dependence can be reproduced by a calculated joint density of states for optical transition between bands with different orbital character. This finding suggests, that the coherent response of the CDW amplitude mode is dominated by photo-doping of the charge ordering located in the Te-planes.
Three-mode resonant coupling of collective excitations in a Bose-Einstein condensate
Ma Yongli; Huang, Guoxiang; Hu Bambi
2005-04-01
We make a systematic study of the resonant mode coupling of the collective excitations at zero temperature in a Bose-Einstein condensate (BEC). (i) Based on the Gross-Pitaevskii equation we derive a set of nonlinearly coupled envelope equations for a three-mode resonant interaction (TMRI) by means of a method of multiple scales. (ii) We calculate the coupling matrix elements for the TMRI and show that the divergence appearing in previous studies can be eliminated completely by using a Fetter-like variational approximation for the ground-state wave function of the condensate. (iii) We provide the selection rules in mode-mode interaction processes [including TMRI and second-harmonic generation (SHG)] according to the symmetry of the excitations. (iv) By solving the nonlinearly coupled envelope equations we obtain divergence-free nonlinear amplitudes for the TMRI and SHG processes and show that our theoretical results on the shape oscillations of the condensate agree well with the experimental ones. We suggest also an experiment to check the theoretical prediction of the present study on the TMRI of collective excitations in a BEC.
Loading of a Bose-Einstein condensate into an optical lattice: The excitation of collective modes
NASA Astrophysics Data System (ADS)
Plata, J.
2004-03-01
The dynamics of a Bose-Einstein condensate in a harmonic trap with a nonadiabatically loaded optical lattice is studied analytically. As the global effect of the optical potential can be described in terms of a renormalized interaction coupling constant and of an effective mass in the laser direction, a fast loading can be understood as a sudden change of those characteristic parameters. In this approach, a standard scaling transformation is applied to study the resulting dynamics, in particular, the generation of collective modes. The relevance of the excited modes to the interference patterns obtained after free expansion is analyzed. The applicability of trap-frequency adjustments as a strategy for suppressing the loading induced excitations is discussed.
NASA Astrophysics Data System (ADS)
Okuducu, Ş.; Akti, N. N.; Saraç, H.; Bölükdemir, M. H.; Tel, E.
In this study the nuclear energy level density based on nuclear collective excitation mechanism has been identified in terms of the low-lying collective level bands near the neutron binding energy. Nuclear level density parameters of some light deformed medical radionuclides used widely in medical applications have been calculated by using different collective excitation modes of observed nuclear spectra. The calculated parameters have been used successfully in estimation of the neutron-capture cross section basic data for the production of new medical radionuclides. The investigated radionuclides have been considered in the region of mass number 40collective coupled state bands of the interest radionuclides. The present calculated results have been compared with the compiled values from the literatures for s-wave neutron resonance data.
Elementary excitations and a collective mode in hcp sup 4 He
Lengua, G.A.; Goodkind, J.M. )
1990-06-01
We have measured the velocity and attenuation of sound at 10, 30, and 50 MHz in solid {sup 4}He at higher purity, lower density, and lower acoustic power than have been measured previously. At 10 MHz the velocity varies as T{sup 4}, as would be expected for a very high quality crystal with remarkable low dislocation density. The temperature dependence of the attenuation reveals coupling to thermally activated excitations that are consistent with vacancies measured in other work. However, in our work the activation energy is {approximately}0.7 K so that their concentration is sufficiently high to require Bose statistics. At 30 and 50 MHz, an unexpected, additional resonant behavior was observed.
Multimode optical fibers: steady state mode exciter.
Ikeda, M; Sugimura, A; Ikegami, T
1976-09-01
The steady state mode power distribution of the multimode graded index fiber was measured. A simple and effective steady state mode exciter was fabricated by an etching technique. Its insertion loss was 0.5 dB for an injection laser. Deviation in transmission characteristics of multimode graded index fibers can be avoided by using the steady state mode exciter.
Statistical dynamo theory: Mode excitation.
Hoyng, P
2009-04-01
We compute statistical properties of the lowest-order multipole coefficients of the magnetic field generated by a dynamo of arbitrary shape. To this end we expand the field in a complete biorthogonal set of base functions, viz. B= summation operator_{k}a;{k}(t)b;{k}(r) . The properties of these biorthogonal function sets are treated in detail. We consider a linear problem and the statistical properties of the fluid flow are supposed to be given. The turbulent convection may have an arbitrary distribution of spatial scales. The time evolution of the expansion coefficients a;{k} is governed by a stochastic differential equation from which we infer their averages a;{k} , autocorrelation functions a;{k}(t)a;{k *}(t+tau) , and an equation for the cross correlations a;{k}a;{l *} . The eigenfunctions of the dynamo equation (with eigenvalues lambda_{k} ) turn out to be a preferred set in terms of which our results assume their simplest form. The magnetic field of the dynamo is shown to consist of transiently excited eigenmodes whose frequency and coherence time is given by Ilambda_{k} and -1/Rlambda_{k} , respectively. The relative rms excitation level of the eigenmodes, and hence the distribution of magnetic energy over spatial scales, is determined by linear theory. An expression is derived for |a;{k}|;{2}/|a;{0}|;{2} in case the fundamental mode b;{0} has a dominant amplitude, and we outline how this expression may be evaluated. It is estimated that |a;{k}|;{2}/|a;{0}|;{2} approximately 1/N , where N is the number of convective cells in the dynamo. We show that the old problem of a short correlation time (or first-order smoothing approximation) has been partially eliminated. Finally we prove that for a simple statistically steady dynamo with finite resistivity all eigenvalues obey Rlambda_{k}<0 .
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.
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.
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.
Interchange mode excited by trapped energetic ions
NASA Astrophysics Data System (ADS)
Nishimura, Seiya
2015-07-01
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.
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 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).
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
NASA Astrophysics Data System (ADS)
Alakhaly, Galal Ahmed; Dey, Bishwajyoti
2015-05-01
We have studied the dynamic evolution of the collective excitations in Bose-Einstein condensates in a deep optical lattice with tunable three-body interactions. Their dynamics is governed by a high order discrete nonlinear Schrödinger equation (DNLSE). The dynamical phase diagram of the system is obtained using the variational method. The dynamical evolution shows very interesting features. The discrete breather phase totally disappears in the regime where the three-body interaction completely dominates over the two-body interaction. The soliton phase in this particular regime exists only when the soliton line approaches the critical line in the phase diagram. When weak two-body interactions are reintroduced into this regime, the discrete breather solutions reappear, but occupies a very small domain in the phase space. Likewise, in this regime, the soliton as well as the discrete breather phases completely disappear if the signs of the two-and three-body interactions are opposite. We have analysed the causes of this unusual dynamical evolution of the collective excitations of the Bose-Einstein condensate with tunable interactions. We have also performed direct numerical simulations of the governing DNLS equation to show the existence of the discrete soliton solution as predicted by the variational calculations, and also to check the long term stability of the soliton solution.
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.
Collective excitations in soft-sphere fluids
NASA Astrophysics Data System (ADS)
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.
Hong-Ou-Mandel Interference between Two Deterministic Collective Excitations in an Atomic Ensemble.
Li, Jun; Zhou, Ming-Ti; Jing, Bo; Wang, Xu-Jie; Yang, Sheng-Jun; Jiang, Xiao; Mølmer, Klaus; Bao, Xiao-Hui; Pan, Jian-Wei
2016-10-28
We demonstrate deterministic generation of two distinct collective excitations in one atomic ensemble, and we realize the Hong-Ou-Mandel interference between them. Using Rydberg blockade we create single collective excitations in two different Zeeman levels, and we use stimulated Raman transitions to perform a beam-splitter operation between the excited atomic modes. By converting the atomic excitations into photons, the two-excitation interference is measured by photon coincidence detection with a visibility of 0.89(6). The Hong-Ou-Mandel interference witnesses an entangled NOON state of the collective atomic excitations, and we demonstrate its two times enhanced sensitivity to a magnetic field compared with a single excitation. Our work implements a minimal instance of boson sampling and paves the way for further multimode and multiexcitation studies with collective excitations of atomic ensembles.
Hong-Ou-Mandel Interference between Two Deterministic Collective Excitations in an Atomic Ensemble
NASA Astrophysics Data System (ADS)
Li, Jun; Zhou, Ming-Ti; Jing, Bo; Wang, Xu-Jie; Yang, Sheng-Jun; Jiang, Xiao; Mølmer, Klaus; Bao, Xiao-Hui; Pan, Jian-Wei
2016-10-01
We demonstrate deterministic generation of two distinct collective excitations in one atomic ensemble, and we realize the Hong-Ou-Mandel interference between them. Using Rydberg blockade we create single collective excitations in two different Zeeman levels, and we use stimulated Raman transitions to perform a beam-splitter operation between the excited atomic modes. By converting the atomic excitations into photons, the two-excitation interference is measured by photon coincidence detection with a visibility of 0.89(6). The Hong-Ou-Mandel interference witnesses an entangled NOON state of the collective atomic excitations, and we demonstrate its two times enhanced sensitivity to a magnetic field compared with a single excitation. Our work implements a minimal instance of boson sampling and paves the way for further multimode and multiexcitation studies with collective excitations of atomic ensembles.
Ab initio study of collective excitations in a disparate mass molten salt.
Bryk, Taras; Klevets, Ivan
2012-12-14
Ab initio molecular dynamics simulations and the approach of generalized collective modes are applied for calculations of spectra of longitudinal and transverse collective excitations in molten LiBr. Dispersion and damping of low- and high-frequency branches of collective excitations as well as wave-number dependent relaxing modes were calculated. The main mode contributions to partial, total, and concentration dynamic structure factors were estimated in a wide region of wave numbers. A role of polarization effects is discussed from comparison of mode contributions to concentration dynamic structure factors calculated for molten LiBr from ab initio and classical rigid ion simulations.
Correlation and Collective Modes in Narrow Band Materials.
1982-05-25
explanation of the shielding is that the surface electrons couple and form a Bose condensate .16 It is also possible that this phase is superconducting. Other...experiments indicate that an exciton gas formed in Cu20 by laser excitation obeys Bose - Einstein statistics. 1 7 Since Cu 0 is a semiconducting...or conduction bands. For these systems one must often consider the effects of excitation structure and localized collective modes to understand the
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.
Fishbone mode excitation in the ion kinetic regime
Shi, B.; Sui, G. |
1997-08-01
By solving the dispersion relation in the ion kinetic regime, it is found that the threshold of the plasma beta value for exciting the ion-fishbone mode is lowered. Thus, for most of the present-day tokamaks where the Bussac criterion [Bussac {ital et al.}, Phys. Rev. Lett. {bold 35}, 1638 (1975)] is not satisfied, it will still be possible to excite the ion-fishbone mode. {copyright} {ital 1997 American Institute of Physics.}
Collective excitations and viscosity in liquid Bi
NASA Astrophysics Data System (ADS)
Ropo, Matti; Akola, Jaakko; Jones, R. O.
2016-11-01
The analysis of extensive density functional/molecular dynamics simulations (over 500 atoms, up to 100 ps) of liquid bismuth at four temperatures between 573 K and 1023 K has provided details of the dynamical structure factors, the dispersion of longitudinal and transverse collective modes, and related properties (power spectrum, viscosity, and sound velocity). Agreement with available inelastic x-ray and neutron scattering data and with previous simulations is generally very good. The results show that density functional/molecular dynamics simulations can give dynamical information of good quality without the use of fitting functions, even at long wavelengths.
Evanescent optical fluorescence excitation: the role of photonic mode density
NASA Astrophysics Data System (ADS)
Menges, Bernhard; Sato, Akihiro; Knoll, Wolfgang
2007-04-01
In this paper we will discuss a few basic concepts concerning the use of evanescent optical fields for the excitation of fluorescent chromophores placed near the interface. The observation of enhanced fluorescence from chromophores excited by surface plasmon and waveguide modes will be presented and discussed. We attribute the enhancement to the near-field interaction between the chromophores and the increased photonic mode density by surface plasmon and waveguide modes. We determined limits of detection (LOD) of DNA hybridisation using the same sensor architecture by surface plasmon fluorescence spectroscopy (SPFS) and optical waveguide fluorescence spectroscopy (OWFS). Both SPFS and OWFS techniques have the same detection principle using an enhanced electromagnetic field to excite fluorophores and make it possible to monitor DNA hybridisation in real-time with high sensitivity. The relative photonic mode density of each mode was calculated under the resonance condition, and these values are reflected in the LOD values.
Decay modes of the excited pseudoscalar glueball
NASA Astrophysics Data System (ADS)
Eshraim, Walaa I.; Schramm, Stefan
2017-01-01
We study three different chiral Lagrangians that describe the two- and three-body decays of an excited pseudoscalar glueball, JP C=0*-+ , into light mesons and charmonium states as well as into a scalar and pseudoscalar glueball. We compute the decay channels for an excited pseudoscalar glueball with a mass of 3.7 GeV and consider a ground-state pseudoscalar glueball of mass 2.6 GeV, following predictions from lattice QCD simulations. These states and channels are in reach of the ongoing BESIII experiment and the PANDA experiments at the upcoming FAIR facility experiment. We present the resulting decay branching ratios with a parameter-free prediction.
Collective excitation of a trapped Bose-Einstein condensate with spin-orbit coupling
NASA Astrophysics Data System (ADS)
Chen, Li; Pu, Han; Yu, Zeng-Qiang; Zhang, Yunbo
2017-03-01
We investigate the collective excitations of a Raman-induced spin-orbit coupled Bose-Einstein condensate confined in a quasi-one-dimensional harmonic trap using the Bogoliubov method. By tuning the Raman coupling strength, three phases of the system can be identified. By calculating the transition strength, we are able to classify various excitation modes that are experimentally relevant. We show that the three quantum phases possess distinct features in their collective excitation properties. In particular, the spin dipole and the spin breathing modes can be used to clearly map out the phase boundaries. We confirm these predictions by direct numerical simulations of the quench dynamics that excites the relevant collective modes.
Taher, Aymen Belhadj; Di Bin, Philippe; Bahloul, Faouzi; Tartaret-Josnière, Etienne; Jossent, Mathieu; Février, Sébastien; Attia, Rabah
2016-01-25
We propose a new technique to selectively excite the fundamental mode in a few mode fiber (FMF). This method of excitation is made from a single mode fiber (SMF) which is inserted facing the FMF into an air-silica microstructured cane before the assembly is adiabatically tapered. We study theoretically and numerically this method by calculating the effective indices of the propagated modes, their amplitudes along the taper and the adiabaticity criteria, showing the ability to achieve an excellent selective excitation of the fundamental mode in the FMF with negligible loss. We experimentally demonstrate that the proposed solution provides a successful mode conversion and allows an almost excellent fundamental mode excitation in the FMF (representing 99.8% of the total power).
Signature of nonadiabatic coupling in excited-state vibrational modes.
Soler, Miguel A; Nelson, Tammie; Roitberg, Adrian E; Tretiak, Sergei; Fernandez-Alberti, Sebastian
2014-11-13
Using analytical excited-state gradients, vibrational normal modes have been calculated at the minimum of the electronic excited-state potential energy surfaces for a set of extended conjugated molecules with different coupling between them. Molecular model systems composed of units of polyphenylene ethynylene (PPE), polyphenylenevinylene (PPV), and naphthacene/pentacene (NP) have been considered. In all cases except the NP model, the influence of the nonadiabatic coupling on the excited-state equilibrium normal modes is revealed as a unique highest frequency adiabatic vibrational mode that overlaps with the coupling vector. This feature is removed by using a locally diabatic representation in which the effect of NA interaction is removed. Comparison of the original adiabatic modes with a set of vibrational modes computed in the locally diabatic representation demonstrates that the effect of nonadiabaticity is confined to only a few modes. This suggests that the nonadiabatic character of a molecular system may be detected spectroscopically by identifying these unique state-specific high frequency vibrational modes.
Extremely confined gap surface-plasmon modes excited by electrons
NASA Astrophysics Data System (ADS)
Raza, Søren; Stenger, Nicolas; Pors, Anders; Holmgaard, Tobias; Kadkhodazadeh, Shima; Wagner, Jakob B.; Pedersen, Kjeld; Wubs, Martijn; Bozhevolnyi, Sergey I.; Mortensen, N. Asger
2014-06-01
High-spatial and energy resolution electron energy-loss spectroscopy (EELS) can be used for detailed characterization of localized and propagating surface-plasmon excitations in metal nanostructures, giving insight into fundamental physical phenomena and various plasmonic effects. Here, applying EELS to ultra-sharp convex grooves in gold, we directly probe extremely confined gap surface-plasmon (GSP) modes excited by swift electrons in nanometre-wide gaps. We reveal the resonance behaviour associated with the excitation of the antisymmetric GSP mode for extremely small gap widths, down to ~5 nm. We argue that excitation of this mode, featuring very strong absorption, has a crucial role in experimental realizations of non-resonant light absorption by ultra-sharp convex grooves with fabrication-induced asymmetry. The occurrence of the antisymmetric GSP mode along with the fundamental GSP mode exploited in plasmonic waveguides with extreme light confinement is a very important factor that should be taken into account in the design of nanoplasmonic circuits and devices.
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.
Excitation of parasitic modes in gyrotrons with fast voltage rise
Nusinovich, G. S.; Antonsen, T. M. Jr.; Vlasov, A. N.; Lohr, J.; Danly, B. G.; Hogge, J.-P.
2008-10-15
Megawatt-class, long-pulse and continuous-wave gyrotrons operate in high-order modes in order to handle the thermal losses in the resonators. The spectral density of neighboring modes in these devices is high; consequently during the beam voltage rise parasitic modes can be excited. If such gyrotrons are used in plasma experiments, these parasites can be dangerous for the receiving channels of numerous diagnostic tools. It is shown that in gyrotrons utilizing diode-type magnetron injection guns the shortening of the voltage rise time to about one microsecond can practically eliminate excitation of parasitic modes even in devices with a 2 MW power level. Some means for realizing such rise times in high-voltage modulators which can be used for megawatt-class gyrotrons are discussed. It is also shown that allowable beam voltage overshoot in such gyrotrons is about 2.5%.
Search for intrinsic collective excitations in Sm152
NASA Astrophysics Data System (ADS)
Kulp, W. D.; Wood, J. L.; Garrett, P. E.; Wu, C. Y.; Cline, D.; Allmond, J. M.; Bandyopadhyay, D.; Dashdorj, D.; Choudry, S. N.; Hayes, A. B.; Hua, H.; Mynk, M. G.; McEllistrem, M. T.; McKay, C. J.; Orce, J. N.; Teng, R.; Yates, S. W.
2008-06-01
The 685 keV excitation energy of the first excited 0+ state in Sm152 makes it an attractive candidate to explore expected two-phonon excitations at low energy. Multiple-step Coulomb excitation and inelastic neutron scattering studies of Sm152 are used to probe the E2 collectivity of excited 0+ states in this “soft” nucleus and the results are compared with model predictions. No candidates for two-phonon Kπ=0+quadrupole vibrational states are found. A 2+,K=2 state with strong E2 decay to the first excited Kπ=0+ band and a probable 3+ band member are established.
Excitation of leaky modes in a system of coupled waveguides
Usievich, B A; Nurligareev, J Kh; Sychugov, V A; Golant, K M
2007-06-30
A system of coupled single-mode waveguides with the number M of guided modes lower than the number N of single-mode waveguides is studied. Leaky modes in this system are investigated in detail. It is shown, in particular, that these modes can be excited by light incident on the side surface of the system when the reflection coefficient vanishes. It is found that the angular dependence of the coefficient of reflection from the side surface of the system can be used to refine the dispersion curve for leaky modes. It is shown that light incident at a grazing angle can propagate in the system in the direction considerably different from the propagation direction of a beam incident from a substrate, even in the case of a small difference in the refractive indices. (fiber and integrated optics)
Roundabout relaxation: collective excitation requires a detour to equilibrium.
Morita, Hidetoshi; Kaneko, Kunihiko
2005-03-04
Relaxation to equilibrium after strong and collective excitation is studied by using a Hamiltonian dynamical system of a one-dimensional XY model. After an excitation of a domain of K elements, the excitation is concentrated to fewer elements, which are made farther away from equilibrium, and the excitation intensity increases logarithmically with K. Equilibrium is reached only after taking this roundabout route, with the time for relaxation diverging asymptotically as Kgamma with gamma approximately 4.2.
Roundabout Relaxation: Collective Excitation Requires a Detour to Equilibrium
NASA Astrophysics Data System (ADS)
Morita, Hidetoshi; Kaneko, Kunihiko
2005-03-01
Relaxation to equilibrium after strong and collective excitation is studied by using a Hamiltonian dynamical system of a one-dimensional XY model. After an excitation of a domain of K elements, the excitation is concentrated to fewer elements, which are made farther away from equilibrium, and the excitation intensity increases logarithmically with K. Equilibrium is reached only after taking this roundabout route, with the time for relaxation diverging asymptotically as Kγ with γ≈4.2.
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.
Two-Mode Excited Entangled Coherent State: Nonclassicality and Entanglement
NASA Astrophysics Data System (ADS)
Zhang, Hao-Liang; Wu, Jia-Ni; Liu, Cun-Jin; Hu, Yin-Quan; Hu, Li-Yun
2017-03-01
Two-mode excited entangled coherent states (TME-ECSs) are introduced by operating repeatedly the photon-excited operator on the ECSs. It is shown that the normalization constant is related to the product of two Laguerre polynomials. The influence of the operation on nonclassical behaviour of the ECSs is investigated in terms of cross-correlation function, anti-bunching effect and the negativity of Wigner function, which show that nonclassical properties can be enhanced. In addition, inseparability properties of the TME-ECSs are discussed by using Bell inequality and concurrence. It is found that the degree of quantum entanglement of even ECSs increases with the increase of the total excited photon number, and the violation of Bell inequality can be present for both even and odd case only when the total excited photon numbers are even and odd, respectively.
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.
Magnetic antenna excitation of whistler modes. II. Antenna arrays
NASA Astrophysics Data System (ADS)
Stenzel, R. L.; Urrutia, J. M.
2014-12-01
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.
Collective excitations of spherical semiconductor nanoparticles
NASA Astrophysics Data System (ADS)
Moradi, Afshin
2016-10-01
In this article, we study the dispersion properties of bulk and surface electrostatic oscillations of a spherical quantum electron-hole semiconductor plasma as a simple model of a semiconductor nanoparticle. We derive general dispersion relation for both bulk and surface modes, using quantum hydrodynamic theory (including the electrons and holes quantum recoil effects, quantum statistical pressures of the plasma species, as well as exchange and correlation effects) in conjunction with Poisson’s equation and appropriate boundary conditions. We show that for the arbitrary value of angular quantum number {\\ell }≥slant 1 there are only two surface plasmon modes, but two infinite series of bulk modes for {\\ell }≥slant 0 that owe their existence to the curvature of the interface. We use the typical values of GaAs semiconductor to compute the bulk and surface mode frequencies for different value of {\\ell }.
Measurement of collective excitations in a spin-orbit-coupled Bose-Einstein condensate
NASA Astrophysics Data System (ADS)
Khamehchi, M. A.; Zhang, Yongping; Hamner, Chris; Busch, Thomas; Engels, Peter
2014-12-01
We measure the collective excitation spectrum of a spin-orbit-coupled Bose-Einstein condensate using Bragg spectroscopy. The spin-orbit coupling is generated by Raman dressing of atomic hyperfine states. When the Raman detuning is reduced, mode softening at a finite momentum is revealed, which provides insight into a supersolid-like phase transition. We find that for the parameters of our system, this softening stops at a finite excitation gap and is symmetric under a sign change of the Raman detuning. Finally, using a moving barrier that is swept through the BEC, we also show the effect of the collective excitation on the fluid dynamics.
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
The quest for novel modes of excitation in exotic nuclei
NASA Astrophysics Data System (ADS)
Paar, N.
2010-06-01
This paper provides an insight into several open problems in the quest for novel modes of excitation in nuclei with isospin asymmetry, deformation and finite-temperature characteristics in stellar environments. Major unsolved problems include the nature of pygmy dipole resonances, the quest for various multipole and spin-isospin excitations both in neutron-rich and proton drip-line nuclei mainly driven by loosely bound nucleons, excitations in unstable deformed nuclei and evolution of their properties with the shape phase transition. Exotic modes of excitation in nuclei at finite temperatures characteristic of supernova evolution present open problems with a possible impact in modeling astrophysically relevant weak interaction rates. All these issues challenge self-consistent many-body theory frameworks at the frontiers of on-going research, including nuclear energy density functionals, both phenomenological and constrained by the strong interaction physics of QCD, models based on low-momentum two-nucleon interaction Vlow-k and correlated realistic nucleon-nucleon interaction VUCOM, supplemented by three-body force, as well as two-nucleon and three-nucleon interactions derived from the chiral effective field theory. Joined theoretical and experimental efforts, including research with radioactive isotope beams, are needed to provide insight into dynamical properties of nuclei away from the valley of stability, involving the interplay of isospin asymmetry, deformation and finite temperature.
Vibrationally mode-specific excitation in molecular photoionization
NASA Astrophysics Data System (ADS)
Poliakoff, Erwin
2003-05-01
Recent measurements on the photoionization of polyatomic molecules demonstrate that excitations of nominally forbidden vibrations are surprisingly intense, and that their energy dependences elucidate why they are occurring. The unifying theme underscored by these results is that the continuum photoelectron exerts tremendous influence on which vibrations are excited and the degree of excitation. These data are generated via high resolution photoelectron spectroscopy coupled with high brightness synchrotron radiation. Results are presented on the linear triatomic systems CO_2, CS_2, and N_2O. For these molecules, all vibrational modes are excited. Moreover, the energy dependences for the alternative vibrational modes exhibit dramatic differences, which are attributed to the degree and type of localization experienced by the continuum photoelectron in the molecular framework. And while the electronic structures of these molecules are very similar, they behave very differently from each other, even over a very broad energy range. Theoretical results by Prof. R.R. Lucchese will be discussed, and the comparison with experiment helps to illustrate the state of our understanding of these phenomena. In addition to the linear triatomics, preliminary results will be reported on BF_3, as well as a van der Waals dimer, Ar_2.
Collective π -electronic excitations in BN double-walled nanotubes
NASA Astrophysics Data System (ADS)
Margulis, Vl. A.; Muryumin, E. E.; Gaiduk, E. A.
2008-07-01
We report a systematic theoretical study of the collective π -electronic excitations in boron nitride double-walled nanotubes (BN-DWNTs). For simplicity, it is assumed that both shells (inner and outer) of such tubes have a zigzag achiral structure. Taking into account intershell Coulomb coupling and neglecting intershell electron tunneling, we introduce the effective dynamic-dielectric-response function of the BN-DWNTs, which depends on frequency ω , wave number q , and angular momentum L . An explicit expression for this function is derived within the random-phase approximation using standard many-body techniques based on the Green’s function method. Numerical results are presented for the wave-number dispersion and damping of the π -plasmon modes with different L ’s, demonstrating a unified picture of the π -plasmon-energy variation with q for the BN-DWNTs of different diameters. According to this picture, the spectrum of the π plasmons, which are shown to be long lived and hence well-defined collective electronic excitations in the BN-DWNTs, consists of a set of nonintersecting upward-dispersed branches, which are well separated in their energies at small values of q , but which tend to merge with increasing q . Each of the branches corresponds to one and only one value of the angular momentum L=0,1,2,… and none of the branches starts from q=0 . The present calculations also show that the π plasmons in the BN-DWNTs can exist even at those q values at which the π -plasmon modes are not supported by either of the nanotube shells alone. It is found that the threshold value of the wavelength, at which the L=0 π -plasmon dispersion curve in the BN-DWNTs makes its start, is redshifted as compared to that in the inner and outer nanotube shells if they are considered separately. The most important features of our calculated results seem to be consistent, more or less reasonable, with those derived from the recent electron
Few-body collective excitations beyond Kohn's theorem in quantum Hall systems
NASA Astrophysics Data System (ADS)
Wooten, R. E.; Yan, B.; Greene, Chris H.
2017-01-01
A relative coordinate breathing mode in the quantum Hall system is predicted to exist with different behavior under either Coulomb or dipole-dipole interactions. While Kohn's theorem [W. Kohn, Phys. Rev. 123, 1242 (1961), 10.1103/PhysRev.123.1242] predicts that any relative coordinate interaction will fail to alter the center-of-mass energy spectrum, it can affect excitations in the relative coordinates. One such collective excitation, which we call the hyperradial breathing mode, emerges naturally from a few-body, hyperspherical representation of the problem and depends on the interparticle interactions, the ground state wave function, and the number of particles participating in the excitation. Possible observations of this excitation will be discussed in the context of both conventional quantum Hall experiments and cold, rotating atomic simulations.
Propagation of collective modes in non-overlapping dipolar Bose-Einstein Condensates
NASA Astrophysics Data System (ADS)
Gallemi, A.; Guilleumas, M.; Mayol, R.; Pi, M.
2014-04-01
We investigate long-range effects of the dipolar interaction in Bose-Einstein condensates by solving the time-dependent 3D Gross-Pitaevskii equation. We study the propagation of excitations between non-overlapping condensates when a collective mode is excited in one of the condensates. We obtain the frequency shifts due to the long-range character of the dipolar coupling for the bilayer and also the trilayer system when the dipolar mode is excited in one condensate. The propagation of the monopolar and quadrupolar modes are also investigated. The coupled-pendulum model is proposed to qualitatively explain the long range effects of the dipolar coupling.
Infra red active modes due to coupling of cyclotron excitation and LO phonons in polar semiconductor
NASA Astrophysics Data System (ADS)
Agrawal, Ratna; Dubey, Swati; Ghosh, S.
2013-06-01
Effects of free carrier concentration, external magnetic field and Callen effective charge on infra red active modes in a polar semiconductor have been analytically investigated using simple harmonic oscillator model. Callen effective charge considerably enhances reflectivity and shifts minima towards lower values of energy. Presence of magnetic field leads towards the coupling of collective cyclotron excitations with LO phonon giving rise to maximum reflectivity whereas cyclotron resonance absorption results into minimum reflectivity.
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.
Radial structures and nonlinear excitation of geodesic acoustic modes
NASA Astrophysics Data System (ADS)
Zonca, F.; Chen, L.
2008-08-01
Geodesic acoustic modes (GAM) are shown to constitute a continuous spectrum due to radial inhomogeneities. The importance and theoretical as well as experimental implications of this fact are discussed in this work. The existence of a singular layer causes GAM to mode convert to short-wavelength kinetic GAM (KGAM) via finite ion Larmor radii; analogous to kinetic Alfvén waves (KAW). Furthermore, it is shown that KGAM can be nonlinearly excited by drift-wave (DW) turbulence via 3-wave parametric interactions, and the resultant driven-dissipative nonlinear system exhibits typical prey-predator self-regulatory dynamics, consistent with recent experimental observations on HL-2A. The degeneracy of GAM/KGAM with beta-induced Alfvén eigenmodes (BAE) is demonstrated and discussed, with emphasis on its important role in the complex self-organized behaviors of burning plasmas.
Nonlinear terahertz coherent excitation of vibrational modes of liquids.
Allodi, Marco A; Finneran, Ian A; Blake, Geoffrey A
2015-12-21
We report the first coherent excitation of intramolecular vibrational modes via the nonlinear interaction of a TeraHertz (THz) light field with molecular liquids. A terahertz-terahertz-Raman pulse sequence prepares the coherences with a broadband, high-energy, (sub)picosecond terahertz pulse, that are then measured in a terahertz Kerr effect spectrometer via phase-sensitive, heterodyne detection with an optical pulse. The spectrometer reported here has broader terahertz frequency coverage, and an increased sensitivity relative to previously reported terahertz Kerr effect experiments. Vibrational coherences are observed in liquid diiodomethane at 3.66 THz (122 cm(-1)), and in carbon tetrachloride at 6.50 THz (217 cm(-1)), in exact agreement with literature values of those intramolecular modes. This work opens the door to 2D spectroscopies, nonlinear in terahertz field, that can study the dynamics of condensed-phase molecular systems, as well as coherent control at terahertz frequencies.
Nonlinear terahertz coherent excitation of vibrational modes of liquids
NASA Astrophysics Data System (ADS)
Allodi, Marco A.; Finneran, Ian A.; Blake, Geoffrey A.
2015-12-01
We report the first coherent excitation of intramolecular vibrational modes via the nonlinear interaction of a TeraHertz (THz) light field with molecular liquids. A terahertz-terahertz-Raman pulse sequence prepares the coherences with a broadband, high-energy, (sub)picosecond terahertz pulse, that are then measured in a terahertz Kerr effect spectrometer via phase-sensitive, heterodyne detection with an optical pulse. The spectrometer reported here has broader terahertz frequency coverage, and an increased sensitivity relative to previously reported terahertz Kerr effect experiments. Vibrational coherences are observed in liquid diiodomethane at 3.66 THz (122 cm-1), and in carbon tetrachloride at 6.50 THz (217 cm-1), in exact agreement with literature values of those intramolecular modes. This work opens the door to 2D spectroscopies, nonlinear in terahertz field, that can study the dynamics of condensed-phase molecular systems, as well as coherent control at terahertz frequencies.
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
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 edge modes in fractional quantum Hall systems
NASA Astrophysics Data System (ADS)
Nguyen, Hoang K.; Joglekar, Yogesh N.; Murthy, Ganpathy
2004-07-01
Over the past few years one of us (Murthy) in collaboration with Shankar has developed an extended Hamiltonian formalism capable of describing the ground-state and low-energy excitations in the fractional quantum Hall regime. The Hamiltonian, expressed in terms of composite fermion operators, incorporates all the nonperturbative features of the fractional Hall regime, so that conventional many-body approximations such as Hartree-Fock and time-dependent Hartree-Fock are applicable. We apply this formalism to develop a microscopic theory of the collective edge modes in fractional quantum Hall regime. We present the results for edge mode dispersions at principal filling factors ν=1/3 , 1/5 , and 2/5 for systems with unreconstructed edges. The primary advantage of the method is that one works in the thermodynamic limit right from the beginning, thus avoiding the finite-size effects which ultimately limit exact diagonalization studies.
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.
Quasiparticle Coherence, Collective Modes, and Competing Order in Cuprate Superconductors
NASA Astrophysics Data System (ADS)
Hinton, James Patrick
In recent years, the study of cuprate superconductors has been dominated by the investigation of normal state properties. Of particular interest is the nature of interactions between superconductivity and other incipient orders which emerge above the superconducting transition temperature, Tc. The discovery of charge density wave (CDW) correlations in YBa2Cu3O6+x (YBCO) and HgBa2CuO 4+d (Hg-1201) has established that some form of charge order is ubiquitous in the cuprates. In this work, we explore the non-equilibrium dynamics of systems which sit near the boundary between superconductivity and competing orders. Ultrafast pump-probe spectroscopy is ideally suited to the study of competing order. Exciting the sample with an optical pulse perturbs the system from equilibrium, altering the balance between the co-existing orders. The return to equilibrium is then monitored by a time-delayed probe pulse, revealing multiple decay processes as well as collective excitations. We first apply this technique to Hg-1201, conducting a detailed study of the phase diagram. At temperatures near Tc, the pump pulse induces a non-equilibrium quasiparticle population. At Tc we observe a doping-dependent peak in the relaxation time of these quasiparticles which we associate with a divergence in the coherence time of the fluctuating CDW. Using heterodyne probing in the transient grating geometry, we are able to disentangle the transient reflectivity components associated with superconductivity and the pseudogap, domonstrating competition across the phase diagram. We also discuss the observation of a sharp transition in the nature of the pseudogap signal at ˜ 11% doping. In YBCO, we explore the temperature and doping dependence of coherent oscillations excited by the pump pulse. We associate these oscillations with the excitation of the CDW amplitude mode, and model their temperature dependence within the framework of a Landau model of competing orders. We conclude with an investigation
Crossover from skin mode to proton-neutron mode in E1 excitations of neutron-rich nuclei
NASA Astrophysics Data System (ADS)
Nakada, H.; Inakura, T.; Sawai, H.
2013-03-01
The character of the low-energy E1 excitations is investigated by analyzing transition densities obtained from the RPA calculations in the doubly magic nuclei. We propose a decomposition method of the E1 excitations into the pn mode (i.e., oscillation between protons and neutrons) and the skin mode (i.e., oscillation of the neutron skin against the inner core) via the transition densities, by which their mixing is handled in a straightforward manner. Crossover behavior of the E1 excitations is found, from the skin mode at low energy to the pn mode at higher energy. The ratio of the skin-mode strength to the full strength turns out to be insensitive to the nuclides and to the effective interactions in the energy region of the crossover. Depending on the excitation energy, the observed low-energy E1 excitations are not necessarily dominated by the skin mode, as exemplified for 90Zr.
Excitation of the symmetry forbidden bending mode in molecular photoionization
NASA Astrophysics Data System (ADS)
Miller, J. Scott; Poliakoff, E. D.; Miller, Thomas F.; Natalense, Alexandra P. P.; Lucchese, Robert R.
2001-03-01
We present results on the energy dependence of the vibrational branching ratio for the bending mode in CO2 3σu-1 photoionization. Specifically, we determine the v+=(0,1,0)/v+=(0,0,0) intensity ratio by detecting dispersed fluorescence from the electronically excited photoions. The results exhibit large deviations over a very wide energy range, 18
NASA Astrophysics Data System (ADS)
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.
2015-05-01
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 YBa2Cu3O6 +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.
Radial structures and nonlinear excitation of Geodesic Acoustic Modes
NASA Astrophysics Data System (ADS)
Chen, Liu; Zonca, Fulvio
2007-11-01
In this paper, we show that GAMs constitute a continuous spectrum due to radial inhomogeneities. The existence of singular layer, thus, suggests linear mode conversion to short-wavelength kinetic GAM (KGAM) via finite ion Larmor radii. This result is demonstrated by derivations of the GAM mode structure and dispersion relation in the singular layer. At the lowest order in krρi, with kr the radial wave vector and ρi the ion Larmor radius, the well known kinetic dispersion relation of GAM is recovered. At the next relevant order, O(kr^2ρi^2), we show that KGAM propagates in the low-temperature and/or high safety-factor domain; i.e., typically, radially outward, and a corresponding damping rate is derived. In this work, we also show that, while KGAM is linearly stable due to ion Landau damping, it can be nonlinearly excited by finite-amplitude DW turbulence via 3-wave parametric interactions. The resultant 3-wave system exhibits the typical prey-predator self-regulatory dynamics.
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.
Neutron star structure and collective excitations of finite nuclei
NASA Astrophysics Data System (ADS)
Paar, N.; Moustakidis, Ch. C.; Marketin, T.; Vretenar, D.; Lalazissis, G. A.
2014-07-01
A method is introduced that establishes relations between properties of collective excitations in finite nuclei and the phase transition density nt and pressure Pt at the inner edge separating the liquid core and the solid crust of a neutron star. A theoretical framework that includes the thermodynamic method, relativistic nuclear energy density functionals, and the quasiparticle random-phase approximation is employed in a self-consistent calculation of (nt,Pt) and collective excitations in nuclei. Covariance analysis shows that properties of charge-exchange dipole transitions, isovector giant dipole and quadrupole resonances, and pygmy dipole transitions are correlated with the core-crust transition density and pressure. A set of relativistic nuclear energy density functionals, characterized by systematic variation of the density dependence of the symmetry energy of nuclear matter, is used to constrain possible values for (nt,Pt). By comparing the calculated excitation energies of giant resonances, energy-weighted pygmy dipole strength, and dipole polarizability with available data, we obtain the weighted average values: nt=0.0955±0.0007 fm-3 and Pt=0.59±0.05 MeV fm-3. This approach crucially depends on experimental results for collective excitations in nuclei and, therefore, accurate measurements are necessary to further constrain the structure of the crust of neutron stars.
Asymmetry of collective excitations in electron- and hole-doped cuprate superconductors
NASA Astrophysics Data System (ADS)
Lee, W. S.; Lee, J. J.; Nowadnick, E. A.; Gerber, S.; Tabis, W.; Huang, S. W.; Strocov, V. N.; Motoyama, E. M.; Yu, G.; Moritz, B.; Huang, H. Y.; Wang, R. P.; Huang, Y. B.; Wu, W. B.; Chen, C. T.; Huang, D. J.; Greven, M.; Schmitt, T.; Shen, Z. X.; Devereaux, T. P.
2014-11-01
High-temperature superconductivity emerges on doping holes or electrons into antiferromagnetic copper oxides. The large energy scale of magnetic excitations, for example, compared with phonon energies, is thought to drive superconductivity with high transition temperatures (Tc). Comparing high-energy magnetic excitations of hole- and electron-doped superconductors provides an opportunity to test this hypothesis. Here, we use resonant inelastic X-ray scattering at the Cu L3-edge to reveal collective excitations in the electron-doped cuprate Nd2-xCexCuO4. Surprisingly, magnetic excitations harden significantly across the antiferromagnetic high-temperature superconductivity phase boundary despite short-ranged antiferromagnetic correlations, in contrast to the hole-doped cuprates. Furthermore, we find an unexpected branch of collective modes in superconducting compounds, absent in hole-doped cuprates. These modes emanate from the zone centre and possess a higher temperature scale than Tc, signalling a distinct quantum phase. Despite their differences, the persistence of magnetic excitations and the existence of a distinct quantum phase are apparently universal in both hole- and electron-doped cuprates.
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.
NASA Astrophysics Data System (ADS)
Murotani, Yuta; Tsuji, Naoto; Aoki, Hideo
2017-03-01
We theoretically investigate coherent optical excitations of collective modes in two-band BCS superconductors, which accommodate two Higgs modes and one Leggett mode corresponding, respectively, to the amplitude and relative-phase oscillations of the superconducting order parameters associated with the two bands. We find, based on a mean-field analysis, that each collective mode can be resonantly excited through a nonlinear light-matter coupling when the doubled frequency of the driving field coincides with the frequency of the corresponding mode. Among the two Higgs modes, the higher-energy one exhibits a sharp resonance with light, while the lower-energy mode has a broadened resonance width. The Leggett mode is found to be resonantly induced by a homogeneous ac electric field because the leading nonlinear effect generates a potential offset between the two bands that couples to the relative phase of the order parameters. The resonance for the Leggett mode becomes sharper with increasing temperature. All of these light-induced collective modes along with density fluctuations contribute to the third-harmonic generation. We also predict an experimental possibility of optical detection of the Leggett mode.
Direct dark mode excitation by symmetry matching of a single-particle-based metasurface
NASA Astrophysics Data System (ADS)
Burokur, Shah Nawaz; Lupu, Anatole; de Lustrac, André
2015-01-01
This paper provides evidence for a direct dark mode excitation mechanism in a metasurface structure. The dark mode excitation mechanism is entirely determined by structures' symmetry and does not depend on near-field coupling between elements. In our examples, we consider single-element based metasurface composed of two V antennas connected in an antisymmetric arrangement. Both experimental and modeling results show an efficient excitation of magnetic dipolar mode in such structures. The direct dark mode excitation mechanism provides a design that is more robust with respect to technology imperfections. The considered approach opens promising perspectives for new types of nanostructure designs and greatly relaxes fabrication constraints for the optical domain.
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.
Plasmon mode excitation and photoluminescence enhancement on silver nanoring
NASA Astrophysics Data System (ADS)
Kuchmizhak, Aleksandr A.; Gurbatov, Stanislav O.; Kulchin, Yuri N.; Vitrik, Oleg B.
2015-12-01
We demonstrate a simple and high-performance laser-assisted technique for silver nanoring fabrication, which includes the ablation of the Ag film by focused nanosecond pulses and subsequent reactive ion polishing. The nanoring diameter and thickness can be controlled by optimizing both the pulse energy and the metal film thickness at laser ablation step, while the subsequent reactive ion polishing provides the ability to fabricate the nanoring with desirable height. Scattering patterns of s-polarized collimated laser beam obliquely illuminating the nanoring demonstrate the focal spot inside the nanoring shifted from its center at a distance of ~0.57Rring. Five-fold enhancement of the photoluminescence signal from the Rhodamine 6G organic dye near the Ag nanoring was demonstrated. This enhancement was attributed to the increase of the electromagnetic field amplitude near the nanoring surface arising from excitation of the multipole plasmon modes traveling along the nanoring. This assumption was confirmed by dark-field back-scattering spectrum of the nanoring measured under white-light illumination, as well as by supporting finite-difference time-domain simulations.
Magnetic antenna excitation of whistler modes. I. Basic properties
NASA Astrophysics Data System (ADS)
Urrutia, J. M.; Stenzel, R. L.
2014-12-01
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.
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.; ...
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
Sensitivity of nonlinear photoionization to resonance substructure in collective excitation
NASA Astrophysics Data System (ADS)
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.
2015-04-01
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.
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.
Collective excitations in a superfluid of color-flavor locked quark matter
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, {omega}, is larger or smaller than the threshold given by twice the pairing gap {delta}, at which pair excitations with nonzero total momentum become allowed to break up into two quasiparticles. For {omega}<<2{delta}, a phonon corresponding to fluctuations in the U(1) phase of {delta} 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 v{sub H}=1/{radical}(3) in the low momentum regime; the decay constant f{sub H} 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 {omega}=2{delta}. Above the threshold for pair excitations ({omega}>2{delta}), 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
Collective modes in multi-Weyl semimetals
Ahn, Seongjin; Hwang, E. H.; Min, Hongki
2016-01-01
We investigate collective modes in three dimensional (3D) gapless multi-Weyl semimetals with anisotropic energy band dispersions (i.e., with a positive integer J). For comparison, we also consider the gapless semimetals with the isotropic band dispersions (i.e. E ~ kJ). We calculate analytically long-wavelength plasma frequencies incorporating interband transitions and chiral properties of carriers. For both the isotropic and anisotropic cases, we find that interband transitions and chirality lead to the depolarization shift of plasma frequencies. For the isotropic parabolic band dispersion the long-wavelength plasmons do not decay via Landau damping, while for the higher-order band dispersions the long-wavelength plasmons experience damping below a critical density. For systems with the anisotropic dispersion the density dependence of the long-wavelength plasma frequency along the direction of non-linear dispersion behaves like that of the isotropic linear band model, while along the direction of linear dispersion it behaves like that of the isotropic non-linear model. Plasmons along both directions remain undamped over a broad range of densities due to the chirality induced depolarization shift. Our results provide a comprehensive picture of how band dispersion and chirality affect plasmon behaviors in 3D gapless chiral systems with the arbitrary band dispersion. PMID:27687770
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.
Mode-selective phonon excitation in gallium nitride using mid-infrared free-electron laser
NASA Astrophysics Data System (ADS)
Kagaya, Muneyuki; Yoshida, Kyohei; Zen, Heishun; Hachiya, Kan; Sagawa, Takashi; Ohgaki, Hideaki
2017-02-01
The single-phonon mode was selectively excited in a solid-state sample. A mid-infrared free-electron laser, which was tuned to the target phonon mode, was irradiated onto a crystal cooled to a cryogenic temperature, where modes other than the intended excitation were suppressed. An A 1(LO) vibrational mode excitation on GaN(0001) face was demonstrated. Anti-Stokes Raman scattering was used to observe the excited vibrational mode, and the appearance and disappearance of the scattering band at the target wavenumber were confirmed to correspond to on and off switching of the pump free-electron laser and were fixed to the sample vibrational mode. The sum-frequency generation signals of the pump and probe lasers overlapped the Raman signals and followed the wavenumber shift of the pump laser.
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
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.
A new class of collective excitations: Exciton strings
NASA Astrophysics Data System (ADS)
Mazumdar, S.; Guo, F.; Meissner, K.; Fluegel, B.; Peyghambarian, N.
1996-06-01
Optical excitation in a strongly neutral quasi-one-dimensional mixed-stack charge-transfer solid results in an exciton state, in which the electron and the hole are bound by electrostatic Coulomb interactions that are large compared to the one-electron hopping. We present a joint theoretical-experimental demonstration of a new class of collective excitations, multiexcitons or exciton strings, consisting of a string of several (more than two) bound excitons, in a prototype neutral charge-transfer solid. The stability of the multiexciton states arise from the combined effects of one dimensionality and strong Coulomb interactions. Theoretically, we show that in narrow band one-dimensional semiconductors with long range Coulomb interactions, the occurrence of stable 2-exciton string (biexciton) necessarily implies stable higher multiexcitons. Experimentally, evidence for the multiexciton strings is demonstrated by femtosecond pump-probe spectroscopy of anthracene pyromellitic acid dianhydride. Excellent qualitative agreement is found between the calculated and the measured differential transmission spectra. Photoinduced absorptions to the 2-exciton string at low pump intensity and to the 3-exciton string at high pump intensity are observed, in agreement with the theory of excited state absorption. The 2-exciton string is confirmed also by a direct two-photon absorption measurement. The binding energies of the 2-exciton and the 3-exciton strings are obtained from the experimental data. The larger binding energy of the 3-exciton is in agreement with theory.
Strong interaction between electrons and collective excitations in the multiband superconductor MgB2
Mou, Daixiang; Jiang, Rui; Taufour, Valentin; ...
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.
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)
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.
NASA Astrophysics Data System (ADS)
Ullrich, C. A.; Vignale, G.
1998-09-01
It is well known that high-frequency collective excitations in electronic systems are not Landau damped, i.e., they cannot decay effectively into single particle-hole pairs. The leading damping mechanism in this regime is instead provided by dynamical exchange and correlation effects, such as multipair production. These effects are not captured by the widely used adiabatic local-density approximation (ALDA), which accounts for Landau damping only. In the recently developed time-dependent current density-functional formalism [G. Vignale, C. A. Ullrich, and S. Conti, Phys. Rev. Lett. 79, 4878 (1997)], exchange and correlation enter as viscoelastic stresses in the electron fluid, causing an additional damping that is not contained in the ALDA. We use this theory to derive an explicit formula for the linewidth of collective electronic excitations that are not Landau damped. The formula is then applied to calculate the linewidth of collective modes in two-dimensional (2D) quantum strips. In comparison with the corresponding modes in the homogeneous 2D electron gas, we find an order-of-magnitude enhancement of the linewidth due to the nonuniformity of the system.
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.
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.
Optimization of orthotropic distributed-mode loudspeaker using attached masses and multi-exciters.
Lu, Guochao; Shen, Yong; Liu, Ziyun
2012-02-01
Based on the orthotropic model of the plate, the method to optimize the sound response of the distributed-mode loudspeaker (DML) using the attached masses and the multi-exciters has been investigated. The attached masses method will rebuild the modes distribution of the plate, based on which multi-exciter method will smooth the sound response. The results indicate that the method can be used to optimize the sound response of the DML.
Magnetic antenna excitation of whistler modes. III. Group and phase velocities of wave packets
NASA Astrophysics Data System (ADS)
Urrutia, J. M.; Stenzel, R. L.
2015-07-01
The properties of whistler modes excited by single and multiple magnetic loop antennas have been investigated in a large laboratory plasma. A single loop excites a wavepacket, but an array of loops across the ambient magnetic field B0 excites approximate plane whistler modes. The single loop data are measured. The array patterns are obtained by linear superposition of experimental data shifted in space and time, which is valid in a uniform plasma and magnetic field for small amplitude waves. Phasing the array changes the angle of wave propagation. The antennas are excited by an rf tone burst whose propagating envelope and oscillations yield group and phase velocities. A single loop antenna with dipole moment across B0 excites wave packets whose topology resembles m = 1 helicon modes, but without radial boundaries. The phase surfaces are conical with propagation characteristics of Gendrin modes. The cones form near the antenna with comparable parallel and perpendicular phase velocities. A physical model for the wave excitation is given. When a wave burst is applied to a phased antenna array, the wave front propagates both along the array and into the plasma forming a "whistler wing" at the front. These laboratory observations may be relevant for excitation and detection of whistler modes in space plasmas.
Nonlinear excitation of long-wavelength modes in Hall plasmas
NASA Astrophysics Data System (ADS)
Lakhin, V. P.; Ilgisonis, V. I.; Smolyakov, A. I.; Sorokina, E. A.
2016-10-01
Hall plasmas with magnetized electrons and unmagnetized ions exhibit a wide range of small scale fluctuations in the lower-hybrid frequency range as well as low-frequency large scale modes. Modulational instability of lower-hybrid frequency modes is investigated in this work for typical conditions in Hall plasma devices such as magnetrons and Hall thrusters. In these conditions, the dispersion of the waves in the lower-hybrid frequency range propagating perpendicular to the external magnetic field is due to the gradients of the magnetic field and the plasma density. It is shown that such lower-hybrid modes are unstable with respect to the secondary instability of the large scale quasimode perturbations. It is suggested that the large scale slow coherent modes observed in a number of Hall plasma devices may be explained as a result of such secondary instabilities.
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.
Response functions and spectrum of collective excitations of fractional-quantum-Hall-effect systems
NASA Astrophysics Data System (ADS)
Lopez, Ana; Fradkin, Eduardo
1993-03-01
We calculate the electromagnetic response functions of a fractional-quantum-Hall-effect (FQHE) system within the framework of the fermion Chern-Simons theory for the FQHE, which we developed before. Our results are valid in a semiclassical expansion around the average-field approximation (AFA). We reexamine the AFA and the role of fluctuations. We argue that, order-by-order in the semiclassical expansion, the response functions obey the correct symmetry properties required by Galilean and gauge invariance and by the incompressibility of the fluid. In particular, we find that the low-momentum limit of the semiclassical approximation to the response functions is exact and that it saturates the f-sum rule. We obtain the spectrum of collective excitations of FQHE systems in the low-momentum limit. We find a rich spectrum of modes which includes a host of quasiparticle-quasihole bound states and, in general, two collective modes coalescing at the cyclotron frequency. The Hall conductance is obtained from the current-density correlation function, and it has the correct value already at the semiclassical level. We applied these results to the problem of the screening of external charges and fluxes by the electron fluid, and obtained asymptotic expressions of the charge and current-density profiles, for different types of interactions. Finally, we reconsider the anyon superfluid within our scheme and derive the spectrum of collective modes for interacting hard-core bosons and semions. In addition to the gapless phase mode, we find a set of gapped collective modes.
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.
Study of p-mode excitation and damping rate variations from IRIS++ observations
NASA Astrophysics Data System (ADS)
Salabert, D.; Jiménez-Reyes, S. J.; Tomczyk, S.
2003-09-01
11 years of low degree helioseismic data collected by the IRIS++ network (International Research of the Interior of the Sun) have been analyzed. The epoch covered (mid-1989 to end-1999) spans the maximum and the falling phase of solar cycle 22 and the rising phase of the current solar cycle 23. Annual timeseries with an overlap of 6 months are used to study the variations with solar activity of the p-mode frequencies nu n,l, heights Hn,l, and linewidths Gamma n,l, taking into account the effects of the window function. These are used to infer variations in the velocity power
Excitation of higher order modes in optical fibers with parabolic index profile.
Chen, C L
1988-06-01
A large number of modes can be supported by multimode fibers. There are applications where higher order modes are preferred. Microbend intensity sensors are good examples. The sensitivity of these sensors is greatly increased if higher order modes are excited. In this work, a simple method to excite higher order modes preferentially is suggested. It consists of thin-film gratings deposited directly onto the fiber end. By controlling the film thickness or transparency of the grating structure, a desired transmission coefficient T(r,Phi) is synthesized. The desired mode can be excited preferentially by incident Gaussian beams without the aid of additional optical components. Binary intensity and binary phase gratings have been studied. Numerical investigation reveals that the phase gratings are more effective for the preferential excitation of higher order modes than the intensity gratings. In fact, by using binary phase gratings and in optimal excitation conditions as much as 81.1, 76.9, 74.6, 73.3, and 72.3% of the power in the incoming, linearly polarized, fundamental Gaussian beam can be converted to LP(02), LP(03), LP(04), LP(05), and LP(06) modes, respectively, excluding Fresnel loss.
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.
NASA Astrophysics Data System (ADS)
Clary, David C.; Meijer, Anthony J. H. M.
2002-06-01
Quantum dynamical calculations have been carried out on the excitation of the torsional vibrations of a protein by collision with a solvent molecule. This energy transfer process represents the first step in the unfolding of the protein. The method developed for this purpose is the torsional close coupling, infinite order sudden approximation. Both time-independent and time dependent methods are used to solve the scattering problem and individual excitation of all the torsional modes of the protein is treated. The method is applied to the excitation of the HIV protein gp41 colliding with a water molecule. This protein has 1101 atoms, 56 amino acids, and 452 torsional modes. A major mode-selective effect is found in the computations: it is much easier to excite backbone torsions than sidechain torsions in the protein. In addition, resonances arise in the collisional process and these complexes involve temporary trapping of the water molecule inside the pockets of the protein.
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.
Collective Modes and Colored Noise as Beam-Halo Amplifiers
Bohn, Courtlandt L
2004-08-06
As illustrated herein, collective modes and colored noise conspire to produce beam halo with much larger amplitude than could be generated by either phenomenon separately. Collective modes are inherent to nonequilibrium beams with space charge. Colored noise arises from unavoidable machine transitions and/or errors that influence the internal space-charge force. Lowest-order radial eigenmodes calculated self-consistently for a direct-current, cylindrically symmetric, warm-fluid Kapchinskij-Vladimirskij equilibrium serve to model the collective modes. Even with weak space charge, small-amplitude collective modes, and weak noise strength, a pronounced halo is seen to develop if these phenomena act on the beam over a sufficiently long time, such as in a synchrotron or storage ring.
Probing the Collective Modes of Spherical Shell-Shaped Condensates with Quench Numerics
NASA Astrophysics Data System (ADS)
Yang, Frances; Sun, Kuei; Padavic, Karmela; Vishveshwara, Smitha; Lannert, Courtney
2015-03-01
We explore the collective modes of Bose-Einstein condensates by numerical solution of the Gross-Pitaevskii equation with an external ``bubble trap'' potential (Vtrap =√{(r2 - Δ) 2 / 4 -Ω2 }) that can be continuously tuned between a thin spherical shell-shaped condensate (at large Δ) and an ordinary spherical condensate in a harmonic trap (at Δ = Ω = 0). We excite the condensate's collective modes by making a small sudden change to the trapping potential and analyzing the subsequent time evolution of the condensate wavefunction. We observe the evolution of the frequency of the low-lying collective modes between the limits of a thin-shell condensate and a filled-spherical condensate. Work supported by the National Science Foundation under Award DMR-1243574.
Mode-locked solid state lasers using diode laser excitation
Holtom, Gary R [Boston, MA
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.
Resonant mode characterisation of a cylindrical Helmholtz cavity excited by a shear layer.
Bennett, Gareth J; Stephens, David B; Rodriguez Verdugo, Francisco
2017-01-01
This paper investigates the interaction between the shear-layer over a circular cavity with a relatively small opening and the flow-excited acoustic response of the volume within to shear-layer instability modes. Within the fluid-resonant category of cavity oscillation, most research has been conducted on rectangular geometries: generally restricted to longitudinal standing waves, or when cylindrical: to Helmholtz resonance. In practical situations, however, where the cavity is subject to a range of flow speeds, many different resonant mode types may be excited. The current work presents a cylindrical cavity design where Helmholtz oscillation, longitudinal resonance, and azimuthal acoustic modes may all be excited upon varying the flow speed. Experiments performed show how lock-on between each of the three fluid-resonances and shear-layer instability modes can be generated. A circumferential array of microphones flush-mounted with the internal surface of the cavity wall was used to decompose the acoustic pressure field into acoustic modes and has verified the excitation of higher order azimuthal modes by the shear-layer. For azimuthal modes especially, the location of the cavity opening affects the pressure response. A numerical solution is validated and provides additional insight and will be applied to more complex aeronautical and automotive geometries in the future.
Upper hybrid wave excitation due to O-mode interaction with density gradient in the ionosphere
Antani, S.N.; Kaup, D.J.; Rao, N.N.
1995-12-31
It has been well recognized that upper hybrid (UH) waves play a key role in various wave processes occurring in the upper hybrid resonance (UHR) region of the ionosphere leading to the observed stimulated electromagnetic emissions (SEE) during artificial heating by ordinary mode (O-mode) electromagnetic waves. Hence it is important to investigate how the UH waves get excited from the incident O-mode. It has been generally suggested that the UH waves are excited by O-mode interaction with nonuniform ionospheric plasma. For instance, direct conversion of the O-mode into UH waves due to pre-existing short scale irregularities was reported earlier. Here the authors consider the role of large-scale, smooth density gradient in exciting the UH waves from the O-mode. The model used is that of a driven harmonic oscillator in which the source term arises from the O-mode interaction with local density gradient. For a slab model with density gradient in the x-direction, and the geomagnetic field in the z-direction, they obtain an inhomogeneous fourth order ordinary differential equation governing the UH wave excitation. This equation has been analyzed in the vicinity of the UHR. The pertinent solutions will be presented and discussed for the typical parameters of heating experiments.
NASA Astrophysics Data System (ADS)
Nogajewski, K.; Łusakowski, J.; Knap, W.; Popov, V. V.; Teppe, F.; Rumyantsev, S. L.; Shur, M. S.
2011-11-01
Magnetotransport and magnetooptics investigations of plasmon excitations in large-area grating-gate terahertz modulators based on AlGaN/GaN high-electron-mobility transistors with different grating-gate duty cycle are reported. We demonstrate that the effect of the gate potential on the ungated region extends beyond the conventional fringing effect distance, ranging over 250-350 nm instead of expected 26-30 nm. This phenomenon enables excitation of the localized gated magnetoplasmon modes only if the inter-finger spacing in the grating gate exceeds 350 nm. For narrower slits, only the collective gated magnetoplasmon modes extending over the entire period of the structure can be excited.
Numerical and experimental study of a compressive-mode energy harvester under random excitations
NASA Astrophysics Data System (ADS)
Li, H. T.; Yang, Z.; Zu, J.; Qin, W. Y.
2017-03-01
Piezoelectric energy harvester working in compressive mode has shown outstanding performance under harmonic excitation. However, it is still not clear if the compressive-mode energy harvester can sustain its superiority under random excitations. This paper presents a theoretical and experimental study on a nonlinear compressive-mode piezoelectric energy harvester under random excitations. First, a comprehensive distributed parameter electro-elastic model is developed using the extended Hamilton’s principle and the Euler–Bernoulli beam theory. The embedded force amplification effect of the flexural motion is analytically predicted. Then, the model is numerically solved under random excitations. Strong nonlinear responses was observed in both mechanical and electrical responses. Furthermore, a prototype was fabricated and tested. The experimental data show a good agreement with the model estimations under different level excitations and resistances. The results under random excitation demonstrate that the compressive-mode energy harvester significantly outperforms the state-of-the-art systems in terms of output voltage and normalized power density. If the optimal resistance is chosen in the harvesting circuit, the root mean square power of the prototype will reach three times higher than that of the counterparts.
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.
Volkovich, Roie; Härtle, Rainer; Thoss, Michael; Peskin, Uri
2011-08-28
We show that individual vibrational modes in single-molecule junctions with asymmetric molecule-lead coupling can be selectively excited by applying an external bias voltage. Thereby, a non-statistical distribution of vibrational energy can be generated, that is, a mode with a higher frequency can be stronger excited than a mode with a lower frequency. This is of particular interest in the context of mode-selective chemistry, where one aims to break specific (not necessarily the weakest) chemical bond in a molecule. Such mode-selective vibrational excitation is demonstrated for two generic model systems representing asymmetric molecular junctions and/or scanning tunneling microscopy experiments. To this end, we employ two complementary theoretical approaches, a nonequilibrium Green's function approach and a master equation approach. The comparison of both methods reveals good agreement in describing resonant electron transport through a single-molecule contact, where differences between the approaches highlight the role of non-resonant transport processes, in particular co-tunneling and off-resonant electron-hole pair creation processes.
Excitation of geodesic acoustic modes by external fields.
Hallatschek, K; McKee, G R
2012-12-14
It is planned to use external magnetic perturbations at acoustic frequencies at the DIII-D tokamak to attempt to drive geodesic acoustic modes (GAM) to modify the turbulent transport. We show that this might not only be possible--despite the well-known electrostatic nature of the GAMs--but might be a viable and efficient method to generate GAMs in magnetically confined plasmas, by developing an elegant analytic method which allows us to couple numerical dynamic equilibrium calculations with massively parallel non-Boussinesq turbulence code runs and yields practical estimates of the effectivity of the method.
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.
Plasma undulator excited by high-order mode lasers
NASA Astrophysics Data System (ADS)
Wang, Jingwei; Rykovanov, Sergey
2016-10-01
A laser-created plasma undulator together with a laser-plasma accelerator makes it possible to construct an economical and extremely compact XFEL. However, the spectrum spread of the radiation from the current plasma undulators is too large for XFELs, because of the different values of strength parameters. The phase slippage between the electrons and the wakefield also limits the number of the electron oscillation cycles, thus reduces the performance of XFEL. Here we proposed a phase-locked plasma undulator created by high-order mode lasers. The modulating field is uniform along the transverse direction by choosing appropriate laser intensities of the modes, which enables all the electrons oscillate with the same strength parameter. The plasma density is tapered to lock the phase between the electrons and the wakefield, which signally increases the oscillation cycles. As a result, X-ray radiation with high brightness and narrow bandwidth is generated by injecting a high-energy electron beam into the novel plasma undulator. The beam loading limit indicates that the current of the electron beam could be hundreds of Ampere. These properties imply that such a plasma undulator may have great potential in compact XFELs. This work was supported by the Helmholtz Association (Young Investigator's Group No. VH-NG-1037).
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 and the nature of Mott transition in undoped gapped graphene.
Jafari, S A
2012-08-01
The particle-hole continuum (PHC) for massive Dirac fermions provides an unprecedented opportunity for the formation of two collective split-off states, one in the singlet and the other in the triplet (spin-1) channel, when the short-range interactions are added to the undoped system. Both states are close in energy and are separated from the continuum of free particle-hole excitations by an energy scale of the order of the gap parameter Δ. They both disperse linearly with two different velocities, reminiscent of spin-charge separation in Luttinger liquids. When the strength of Hubbard interactions is stronger than a critical value, the velocity of singlet excitation, which we interpret as a charge composite boson, becomes zero and renders the system a Mott insulator. Beyond this critical point the low-energy sector is left with a linearly dispersing triplet mode-a characteristic of a Mott insulator. The velocity of the triplet mode at the Mott criticality is twice the velocity of the underlying Dirac fermions. The phase transition line in the space of U and Δ is in qualitative agreement with our previous dynamical mean field theory calculations.
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.
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.
A study of quasi-mode parametric excitations in lower-hybrid heating of tokamak plasmas
NASA Astrophysics Data System (ADS)
Villalon, E.; Bers, A.
1980-03-01
A detailed linear and non-linear analysis of quasi-mode parametric excitations, relevant to experiments in supplementary heating of tokamak plasmas, is presented. The linear analysis includes the full ion-cyclotron harmonic quasi-mode spectrum, while the nonlinear one, considering depletion of the pump electric field, is applied to the recent Alcator A heating experiment. The quasi-mode excitations are studied independently for the plasma edge and the main bulk of the plasma, and for the two typical regimes in overall density. It is concluded that the excited spectrum has a frequency close to the initial pump frequency, while the wave-number spectrum may be different from the initial linear spectrum.
NASA Astrophysics Data System (ADS)
Tamaru, S.; Bain, J. A.; van de Veerdonk, R. J. M.; Crawford, T. M.; Covington, M.; Kryder, M. H.
2004-09-01
This work presents experimental results of magnetostatic mode excitation using scanning Kerr microscopy under continuous sinusoidal excitation in the microwave frequency range. This technique was applied to 100nm thick permalloy coupons excited in two different ways. In the first experiment, the uniform (Kittel) mode was excited at frequencies in 2.24-8.00GHz . The resonant condition was effectively described with the conventional Kittel mode equation. The LLG damping parameter α increased significantly with decreasing bias field. It was confirmed that this increase was caused by multidomain structure and ripple domains formed under weak bias fields, as suggested by other studies. In the second experiment, propagating magnetostatic mode surface waves were excited. They showed an exponential amplitude decay and a linear phase variation with distance from the drive field source, consistent with a decaying plane wave. The Damon-Eshbach (DE) model was extended to include a finite energy damping and used to analyze the results. It was found that the wave number and the decay constant were reasonably well described by the extended DE model. In contrast to the first experiment, no significant variation of α with frequency or bias field was seen in this second experiment, where spatial inhomogeneities in the magnetization are less significant.
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)
Tarana, Michal; Houfek, Karel; Horáček, Jiří; Fabrikant, Ilya I.
2011-11-01
We present a study of dissociative electron attachment and vibrational excitation processes in electron collisions with the CF3Cl molecule. The calculations are based on the two-dimensional nuclear dynamics including the C-Cl symmetric stretch coordinate and the CF3 symmetric deformation (umbrella) coordinate. The complex potential energy surfaces are calculated using the ab initio R-matrix method. The results for dissociative attachment and vibrational excitation of the umbrella mode agree quite well with experiment whereas the cross section for excitation of the C-Cl symmetric stretch vibrations is about a factor-of-three too low in comparison with experimental data.
Crossover of collective modes and positive sound dispersion in supercritical state
NASA Astrophysics Data System (ADS)
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.
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
2016-11-02
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.
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.
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
Collective modes of a spin-orbit-coupled Bose-Einstein condensate: A hydrodynamic approach
NASA Astrophysics Data System (ADS)
Zheng, Wei; Li, Zhibing
2012-05-01
We studied the collective modes of a Bose-Einstein condensate (BEC) with spin-orbit coupling. We developed the hydrodynamic equations for spin-orbit coupled BECs and used them to study collective modes in the plane-wave phase and large Rabi coupling regime for both a uniform BEC and a BEC in a harmonic trap. In the homogeneous situation, we obtained energy spectra of elementary excitations and found that the spin-orbit coupling can increase the effective mass of the atoms, which will suppress the sound velocity. The spin-orbit coupling can also change the spin mixing, which will modify the interaction energy, and may lead to an enhancement of sound velocity. The competition between these two effects gives the behavior of sound velocity. In a harmonic trap, we found that the dipole mode and the breathing mode are coupled together in the plane-wave phase, and these two modes have a π/2 phase difference, because the spin-orbit coupling and the interaction are not invariant under spin rotation. However, in the large Rabi coupling regime, the dipole mode and the breathing mode are decoupled due to the symmetry restriction.
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.
Dhakal, Ashim; Subramanian, Ananth Z; Wuytens, Pieter; Peyskens, Frédéric; Le Thomas, Nicolas; Baets, Roel
2014-07-01
We experimentally demonstrate the use of high contrast, CMOS-compatible integrated photonic waveguides for Raman spectroscopy. We also derive the dependence of collected Raman power with the waveguide parameters and experimentally verify the derived relations. Isopropyl alcohol (IPA) is evanescently excited and detected using single-mode silicon-nitride strip waveguides. We analyze the measured signal strength of pure IPA corresponding to an 819 cm⁻¹ Raman peak due to in-phase C-C-O stretch vibration for several waveguide lengths and deduce a pump power to Raman signal conversion efficiency on the waveguide to be at least 10⁻¹¹ per cm.
Incompressible Modes Excited by Supersonic Shear in Boundary Layers: Acoustic CFS Instability
NASA Astrophysics Data System (ADS)
Belyaev, Mikhail A.
2017-02-01
We present an instability for exciting incompressible modes (e.g., gravity or Rossby modes) at the surface of a star accreting through a boundary layer. The instability excites a stellar mode by sourcing an acoustic wave in the disk at the boundary layer, which carries a flux of energy and angular momentum with the opposite sign as the energy and angular momentum density of the stellar mode. We call this instability the acoustic Chandrasekhar–Friedman–Schutz (CFS) instability, because of the direct analogy to the CFS instability for exciting modes on a rotating star by emission of energy in the form of gravitational waves. However, the acoustic CFS instability differs from its gravitational wave counterpart in that the fluid medium in which the acoustic wave propagates (i.e., the accretion disk) typically rotates faster than the star in which the incompressible mode is sourced. For this reason, the instability can operate even for a non-rotating star in the presence of an accretion disk. We discuss applications of our results to high-frequency quasi-periodic oscillations in accreting black hole and neutron star systems and dwarf nova oscillations in cataclysmic variables.
Real-time observation of collective excitations in photoemission
NASA Astrophysics Data System (ADS)
Lemell, C.; Neppl, S.; Wachter, G.; Tőkési, K.; Ernstorfer, R.; Feulner, P.; Kienberger, R.; Burgdörfer, J.
2015-06-01
Ejection of an electron by absorption of an extreme ultraviolet (xuv) photon probes the many-electron response of a solid well beyond the single-particle picture. Photoemission spectra feature complex correlation satellite structures signifying the simultaneous excitation of single or multiple plasmons. The time delay of the plasmon satellites relative to the main line can be resolved in attosecond streaking experiments. Time-resolved photoemission thus provides the key to discriminate between intrinsic and extrinsic plasmon excitation. We demonstrate the determination of the branching ratio between intrinsic and extrinsic plasmon generation for simple metals.
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
Radiation efficiency for exciting whistler modes of electric and magnetic antennas: a comparison
NASA Astrophysics Data System (ADS)
Urrutia, J. M.; Stenzel, R. L.
2016-10-01
Low frequency whistler modes (ω <ωc / 2) are excited in a large uniform laboratory plasma with electric dipoles and magnetic loop antennas oriented perpendicular to the ambient magnetic field. The antennas are driven under identical plasma conditions with short pulses from the same rf source so as to avoid nonlinear effects. The wave propagation and rf field topology are measured with rf probes. As expected, a magnetic loop antenna excites much stronger whistler modes than an electric dipole antenna. This is because the dipole electric field is shielded by sheaths and its current is a small displacement current compared to the conduction current of a closed loop antenna. A power ratio of Ploop /Pdipole = 8000 has been observed. The radiation resistances have also been obtained from first principles (Rrad =Prad /Irms2), but cannot be compared since the currents are vastly different. It is interesting to note that the electric dipole excites a wave whose topology resembles that of an m = 1 helicon mode. The loop has an elongated shape of the same length as the electric dipole (15 cm) and excites an m = 0 mode. These results are relevant to whistler wave injections experiments into space plasmas. Work supported by NSF/DOE.
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.
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.
Multi-Mode Excitation and Data Reduction for Fatigue Crack Characterization in Conducting Plates
NASA Technical Reports Server (NTRS)
Wincheski, B.; Namkung, M.; Fulton, J. P.; Clendenin, C. G.
1992-01-01
Advances in the technique of fatigue crack characterization by resonant modal analysis have been achieved through a new excitation mechanism and data reduction of multiple resonance modes. A non-contacting electromagnetic device is used to apply a time varying Lorentz force to thin conducting sheets. The frequency and direction of the Lorentz force are such that resonance modes are generated in the test sample. By comparing the change in frequency between distinct resonant modes of a sample, detecting and sizing of fatigue cracks are achieved and frequency shifts caused by boundary condition changes can be discriminated against. Finite element modeling has been performed to verify experimental results.
Nonlinear mode coupling and resonant excitations in two-component Bose-Einstein condensates.
Xue, Ju-Kui; Li, Guan-Qiang; Zhang, Ai-Xia; Peng, Ping
2008-01-01
Nonlinear excitations in two-component Bose-Einstein condensates (BECs) described by two coupled Gross-Pitaevskii equations are investigated analytically and numerically. The beating phenomenon, the higher-harmonic generation, and the mixing of the excited modes are revealed by both variational approximation and numerical method. The strong excitations induced by the parametric resonance are also studied by time-periodic modulation for the intercomponent interaction. The resonance conditions in terms of the modulation frequency and the strength of intercomponent interaction are obtained analytically, which are confirmed by numerical method. Direct numerical simulations show that, when the resonance takes place, periodic phase separation and multisoliton configurations (including soliton trains, soliton pairs, and multidomain walls) can be excited. In particular, we demonstrate a method for formation of multisoliton configurations through parametric resonance in two-component BECs.
Paillet, Frederick L.; Cheng, C.H.; Meredith, J.A.
1987-01-01
Existing techniques for the quantitative interpretation of waveform data have been based on one of two fundamental approaches: (1) simultaneous identification of compressional and shear velocities; and (2) least-squares minimization of the difference between experimental waveforms and synthetic seismograms. Techniques based on the first approach do not always work, and those based on the second seem too numerically cumbersome for routine application during data processing. An alternative approach is tested here, in which synthetic waveforms are used to predict relative mode excitation in the composite waveform. Synthetic waveforms are generated for a series of lithologies ranging from hard, crystalline rocks (Vp equals 6. 0 km/sec. and Poisson's ratio equals 0. 20) to soft, argillaceous sediments (Vp equals 1. 8 km/sec. and Poisson's ratio equals 0. 40). The series of waveforms illustrates a continuous change within this range of rock properties. Mode energy within characteristic velocity windows is computed for each of the modes in the set of synthetic waveforms. The results indicate that there is a consistent variation in mode excitation in lithology space that can be used to construct a unique relationship between relative mode excitation and lithology.
Collective excitation of Rydberg-atom ensembles beyond the superatom model.
Gärttner, Martin; Whitlock, Shannon; Schönleber, David W; Evers, Jörg
2014-12-05
In an ensemble of laser-driven atoms involving strongly interacting Rydberg states, the steady-state excitation probability is usually substantially suppressed. In contrast, here we identify a regime in which the Rydberg excited fraction is enhanced by the interaction. This effect is associated with the buildup of many-body coherences induced by coherent multiphoton excitations between collective states. The excitation enhancement should be observable under currently existing experimental conditions and may serve as a direct probe for the presence of coherent multiphoton dynamics involving collective quantum states.
EXCITATION OF SLOW MODES IN NETWORK MAGNETIC ELEMENTS THROUGH MAGNETIC PUMPING
Kato, Yoshiaki; Steiner, Oskar; Steffen, Matthias; Suematsu, Yoshinori
2011-04-01
From radiation magnetohydrodynamic simulations of the solar atmosphere, we find a new mechanism for the excitation of longitudinal slow modes within magnetic flux concentrations. We find 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, in conjunction with the downward movement, pump the internal atmosphere in the downward direction, which entails a fast downdraft 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. It develops into a shock wave in chromospheric heights, possibly capable of producing some kind of dynamic fibril. We propose an observational detection of this process.
Quantum dot based detections of propagating plasmonic modes excited by bowtie antennas
NASA Astrophysics Data System (ADS)
Wen, Jing; Wang, Kang; Feng, Hui; Lv, Yating; Chen, Jiannong; Zhang, Dawei
2017-03-01
Propagating plasmonic modes excited by bowtie apertures based on emissions from a layer of CdSe/ZnS quantum dots are experimentally detected. The mode distributions with a cladding of 20 nm thick Al2O3 film in between the silver and the quantum dot layers are more homogenous compared to the uncoated structure. The variation discipline of the effective indexes and the decay lengths of the plasmonic modes are discussed for various refractive indexes and thicknesses of the cladding. The three dimensional field distributions of the structure are simulated and the plasmonic fields are only excited in and around the cladding layer on top of the silver film. Such quantum dots based detection methods are promising tools for simultaneous imaging of near field optical distributions in integrated plasmonic nano-circuits.
LETTER TO THE EDITOR: Collective modes of tri-nuclear molecules of the type 96Sr+ 10Be+ 146Ba
NASA Astrophysics Data System (ADS)
Hess, P. O.; Scheid, W.; Greiner, W.; Hamilton, J. H.
1999-12-01
The collective modes of the tri-nuclear molecule 96Sr+ 10Be+ 146Ba, observed in recent cold fission decay of 252Cf into three clusters, are theoretically investigated. The main excitations are rotations, the butterfly and belly-dancer modes and icons/Journals/Common/beta" ALT="beta" ALIGN="TOP"/>- and icons/Journals/Common/gamma" ALT="gamma" ALIGN="TOP"/>-vibrations. Due to the presence of the Be nucleus, butterfly excitation energies are shifted up to 2 MeV. There are only a few collective states below 1 MeV which are not rotational. The first rotational level of spin 2+ lies at an energy of about 6 keV. Proposals of how these collective modes may be measured are suggested.
Thermal conductivity of graphene and graphite: collective excitations and mean free paths.
Fugallo, Giorgia; Cepellotti, Andrea; Paulatto, Lorenzo; Lazzeri, Michele; Marzari, Nicola; Mauri, Francesco
2014-11-12
We characterize the thermal conductivity of graphite, monolayer graphene, graphane, fluorographane, and bilayer graphene, solving exactly the Boltzmann transport equation for phonons, with phonon-phonon collision rates obtained from density functional perturbation theory. For graphite, the results are found to be in excellent agreement with experiments; notably, the thermal conductivity is 1 order of magnitude larger than what found by solving the Boltzmann equation in the single mode approximation, commonly used to describe heat transport. For graphene, we point out that a meaningful value of intrinsic thermal conductivity at room temperature can be obtained only for sample sizes of the order of 1 mm, something not considered previously. This unusual requirement is because collective phonon excitations, and not single phonons, are the main heat carriers in these materials; these excitations are characterized by mean free paths of the order of hundreds of micrometers. As a result, even Fourier's law becomes questionable in typical sample sizes, because its statistical nature makes it applicable only in the thermodynamic limit to systems larger than a few mean free paths. Finally, we discuss the effects of isotopic disorder, strain, and chemical functionalization on thermal performance. Only chemical functionalization is found to play an important role, decreasing the conductivity by a factor of 2 in hydrogenated graphene, and by 1 order of magnitude in fluorogenated graphene.
NASA Astrophysics Data System (ADS)
Roy, Khokan; Kayal, Surajit; Ariese, Freek; Beeby, Andrew; Umapathy, Siva
2017-02-01
Femtosecond transient absorption (fs-TA) and Ultrafast Raman Loss Spectroscopy (URLS) have been applied to reveal the excited state dynamics of bis(phenylethynyl)benzene (BPEB), a model system for one-dimensional molecular wires that have numerous applications in opto-electronics. It is known from the literature that in the ground state BPEB has a low torsional barrier, resulting in a mixed population of rotamers in solution at room temperature. For the excited state this torsional barrier had been calculated to be much higher. Our femtosecond TA measurements show a multi-exponential behaviour, related to the complex structural dynamics in the excited electronic state. Time-resolved, excited state URLS studies in different solvents reveal mode-dependent kinetics and picosecond vibrational relaxation dynamics of high frequency vibrations. After excitation, a gradual increase in intensity is observed for all Raman bands, which reflects the structural reorganization of Franck-Condon excited, non-planar rotamers to a planar conformation. It is argued that this excited state planarization is also responsible for its high fluorescence quantum yield. The time dependent peak positions of high frequency vibrations provide additional information: a rapid, sub-picosecond decrease in peak frequency, followed by a slower increase, indicates the extent of conjugation during different phases of excited state relaxation. The CC triple (-C≡C-) bond responds somewhat faster to structural reorganization than the CC double (>C=C<) bonds. This study deepens our understanding of the excited state of BPEB and analogous linear pi-conjugated systems and may thus contribute to the advancement of polymeric "molecular wires."
Roy, Khokan; Kayal, Surajit; Ariese, Freek; Beeby, Andrew; Umapathy, Siva
2017-02-14
Femtosecond transient absorption (fs-TA) and Ultrafast Raman Loss Spectroscopy (URLS) have been applied to reveal the excited state dynamics of bis(phenylethynyl)benzene (BPEB), a model system for one-dimensional molecular wires that have numerous applications in opto-electronics. It is known from the literature that in the ground state BPEB has a low torsional barrier, resulting in a mixed population of rotamers in solution at room temperature. For the excited state this torsional barrier had been calculated to be much higher. Our femtosecond TA measurements show a multi-exponential behaviour, related to the complex structural dynamics in the excited electronic state. Time-resolved, excited state URLS studies in different solvents reveal mode-dependent kinetics and picosecond vibrational relaxation dynamics of high frequency vibrations. After excitation, a gradual increase in intensity is observed for all Raman bands, which reflects the structural reorganization of Franck-Condon excited, non-planar rotamers to a planar conformation. It is argued that this excited state planarization is also responsible for its high fluorescence quantum yield. The time dependent peak positions of high frequency vibrations provide additional information: a rapid, sub-picosecond decrease in peak frequency, followed by a slower increase, indicates the extent of conjugation during different phases of excited state relaxation. The CC triple (-C≡C-) bond responds somewhat faster to structural reorganization than the CC double (>C=C<) bonds. This study deepens our understanding of the excited state of BPEB and analogous linear pi-conjugated systems and may thus contribute to the advancement of polymeric "molecular wires."
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.
Collective and quasiparticle excitations in superdeformed {sup 190}Hg
Wilson, A.N.; Timar, J.; Sharpey-Schafer, J.F.; Crowell, B.; Carpenter, M.P.; Janssens, R.V.; Blumenthal, D.J.; Ahmad, I.; Astier, A.; Azaiez, F.; Bergstroem, M.; Ducroux, L.; Gall, B.J.; Hannachi, F.; Khoo, T.L.; Korichi, A.; Lauritsen, T.; Lopez-Martens, A.; Meyer, M.; Nisius, D.; Paul, E.S.; Porquet, M.G.; Redon, N.; Wilson, J.N.; Nakatsukasa, T. ||||||
1996-08-01
Superdeformed (SD) states of {sup 190}Hg have been studied with the Eurogam Phase 2 {gamma}-ray spectrometer using the {sup 160}Gd({sup 34}S,4{ital n}) reaction. Two new excited SD bands have been found and identified as belonging to this nucleus, bringing the total number of SD bands in {sup 190}Hg to 4. One of the new bands has a dynamic moment of inertia that is very similar to that of the yrast SD band of {sup 190}Hg and most other SD bands in the {ital A}{approximately}190 region. In contrast, the other band has a dynamic moment of inertia which is mainly constant as a function of rotational frequency and exhibits a dramatic increase at the lowest frequencies. The observed dynamic moments of inertia are compared with the results of random phase approximation calculations based on the cranked shell model. Finally, the known excited SD band has been extended towards lower frequencies and new transitions have been found linking this band to the yrast SD band. The extracted {ital B}({ital E}1) values of the new linking transitions give further support for the possible octupole vibrational character of this band. {copyright} {ital 1996 The American Physical Society.}
Collective and quasiparticle excitations in superformed Hg-190.
Wilson, A. N.; Timar, J.; Sharpey-Schafer, J. F.; Crowell, B.; Carpenter, M. P.; Janssens, R. V. F.; Blumenthal, D. J.; Ahmad, I.; Astier, A.; Azaiez, F.; Bergstrom, M.; Ducroux, L.; Gall, B. J. P.; Hannachi, F.; Khoo, T. L.; Korichi, A.; Lauritsen, T.; Lopez-Martens, A.; Meyer, M.; Nisius, D.; Paul, E. S.; Porquet, M. G.; Redon, N.; Wilson, J. N.; Nakatsukasa, T.; Physics; Univ. of Liverpool; Univ. of Liverpool; Centre de Recherches Nucleaires; Inst. de Physique Nucleaire Lyon; I.P.N.; Inst. of Physique Nucleaire Lyon; C.S.N.S.M.; AECL
1996-08-01
Superdeformed (SD) states of {sup 190}Hg have been studied with the Eurogam Phase 2 {gamma}-ray spectrometer using the {sup 160}Gd({sup 34}S,4n) reaction. Two new excited SD bands have been found and identified as belonging to this nucleus, bringing the total number of SD bands in {sup 190}Hg to 4. One of the new bands has a dynamic moment of inertia that is very similar to that of the yrast SD band of {sup 190}Hg and most other SD bands in the A{approx}190 region. In contrast, the other band has a dynamic moment of inertia which is mainly constant as a function of rotational frequency and exhibits a dramatic increase at the lowest frequencies. The observed dynamic moments of inertia are compared with the results of random phase approximation calculations based on the cranked shell model. Finally, the known excited SD band has been extended towards lower frequencies and new transitions have been found linking this band to the yrast SD band. The extracted B(E1) values of the new linking transitions give further support for the possible octupole vibrational character of this band.
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.
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.
NASA Astrophysics Data System (ADS)
Coppi, B.
2017-03-01
The radiation emission from Shining Black Holes is most frequently observed to have nonthermal features. It is therefore appropriate to consider relevant collective processes in plasmas surrounding black holes that contain high energy particles with nonthermal distributions in momentum space. A fluid description with significant temperature anisotropies is the simplest relevant approach. These anisotropies are shown to have a critical influence on: (a) the existence and characteristics of stationary plasma and field ring configurations, (b) the excitation of "thermo-gravitational modes" driven by temperature anisotropies and gradients that involve gravity and rotation, (c) the generation of magnetic fields over macroscopic scale distances, and (d) the transport of angular momentum.
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
He, H. D.; Zheng, G. Y.; Long, Y. X.; He, Z. X.; Jiang, H. B.; Shen, Y.; Wang, L. F.; Dong, J. Q.; Fu, G. Y.; Sheng, Z. M.
2010-08-15
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 {beta}{sub h} (=pressure of EIs/toroidal magnetic pressure) range, and the modes may only be excited by the barely passing EIs in a region of {beta}{sub th1}<{beta}{sub h}<{beta}{sub th2} ({beta}{sub th} 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.
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.
Investigation of quantum dot passively mode-locked lasers with excited-state transition.
Cheng, Hsu-Chieh; Lee, Chien-Ping
2013-11-04
Monolithic passively mode-locked quantum dot lasers with excited-state transition were investigated in a broad operating range without ground-state lasing. Optical and electrical characteristics of these mode locked lasers were studied in detail at different levels of injection current and absorber bias. Very different behaviors in the evolution of the hysteresis, the optical spectra and the evolution of repetition frequency were observed between our lasers and conventional quantum dot lasers with ground-state transition. Possible mechanisms behind these observed phenomena were proposed and discussed. A minimum pulse width of 3.3 ps and an externally compressed pulse width of 0.78 ps were obtained.
Comparison of electric dipole and magnetic loop antennas for exciting whistler modes
NASA Astrophysics Data System (ADS)
Stenzel, R. L.; Urrutia, J. M.
2016-08-01
The excitation of low frequency whistler modes from different antennas has been investigated experimentally in a large laboratory plasma. One antenna consists of a linear electric dipole oriented across the uniform ambient magnetic field B0. The other antenna is an elongated loop with dipole moment parallel to B0. Both antennas are driven by the same rf generator which produces a rf burst well below the electron cyclotron frequency. The antenna currents as well as the wave magnetic fields from each antenna are measured. Both the antenna currents and the wave fields of the loop antenna exceed that of the electric dipole by two orders of magnitude. The conclusion is that loop antennas are far superior to dipole antennas for exciting large amplitude whistler modes, a result important for active wave experiments in space plasmas.
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; de Oliveira, E M; da Costa, R F; Varella, M T do N; Bettega, M H F; Lima, M A P; da Silva, G B; 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 (C6H5OH). 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 C6H5OH molecule by electron impact.
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
Numerical study of the quasinormal mode excitation of Kerr black holes
Dorband, Ernst Nils; Diener, Peter; Tiglio, Manuel; Berti, Emanuele; Schnetter, Erik
2006-10-15
We present numerical results from three-dimensional evolutions of scalar perturbations of Kerr black holes. Our simulations make use of a high-order accurate multiblock code which naturally allows for adapted grids and smooth inner (excision) and outer boundaries. We focus on the quasinormal ringing phase, presenting a systematic method for extraction of the quasinormal mode frequencies and amplitudes and comparing our results against perturbation theory. The detection of a single mode in a ringdown waveform allows for a measurement of the mass and spin of a black hole; a multimode detection would allow a test of the Kerr nature of the source. Since the possibility of a multimode detection depends on the relative mode amplitude, we study this topic in some detail. The amplitude of each mode depends exponentially on the starting time of the quasinormal regime, which is not defined unambiguously. We show that this time-shift problem can be circumvented by looking at appropriately chosen relative mode amplitudes. From our simulations we extract the quasinormal frequencies and the relative and absolute amplitudes of corotating and counterrotating modes (including overtones in the corotating case). We study the dependence of these amplitudes on the shape of the initial perturbation, the angular dependence of the mode, and the black hole spin, comparing against results from perturbation theory in the so-called asymptotic approximation. We also compare the quasinormal frequencies from our numerical simulations with predictions from perturbation theory, finding excellent agreement. For rapidly rotating black holes (of spin j=0.98) we can extract the quasinormal frequencies of not only the fundamental mode, but also of the first two overtones. Finally we study under what conditions the relative amplitude between given pairs of modes gets maximally excited and present a quantitative analysis of rotational mode-mode coupling. The main conclusions and techniques of our
Long-range quantum Ising spin glasses at t=0: gapless collective excitations and universality.
Andreanov, A; Müller, M
2012-10-26
We solve the Sherrington-Kirkpatrick model in a transverse field Γ deep in its quantum glass phase at zero temperature. We show that the glass phase is critical everywhere, exhibiting collective excitations with a gapless Ohmic spectral function. Using an effective potential approach, we interpret the latter as arising from disordered collective excitations behaving like weakly coupled, underdamped oscillators. For a small transverse field Γ, the low-frequency spectrum takes a form independent of the fluctuation strength Γ.
Long-Range Quantum Ising Spin Glasses at T=0: Gapless Collective Excitations and Universality
NASA Astrophysics Data System (ADS)
Andreanov, A.; Müller, M.
2012-10-01
We solve the Sherrington-Kirkpatrick model in a transverse field Γ deep in its quantum glass phase at zero temperature. We show that the glass phase is critical everywhere, exhibiting collective excitations with a gapless Ohmic spectral function. Using an effective potential approach, we interpret the latter as arising from disordered collective excitations behaving like weakly coupled, underdamped oscillators. For a small transverse field Γ, the low-frequency spectrum takes a form independent of the fluctuation strength Γ.
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.
Chavez-Pirson, A; Chu, S T
1999-01-01
We solve numerically the three-dimensional vector form of Maxwell's equation for the situation of near-field excitation and collection of luminescence from a single quantum dot, using a scanning near-field optical fibre probe with subwavelength resolution. We highlight the importance of polarization-dependent effects in both the near-field excitation and collection processes. Applying a finite-difference time domain method, we calculate the complete vector fields emerging from a realistic probe structure which is in close proximity to a semiconductor surface. We model the photoluminescence from the quantum dot in terms of electric dipoles of different polarization directions, and determine the near-field luminescence images of the dot captured by the same probe. We show that a collimating effect in the high index semiconductor significantly improves the spatial resolution in the excitation-collection mode. We find that the spatial resolution, image shape and collection efficiency of near-field luminescence imaging strongly depend on the polarization direction as represented by the orientation of the radiating electric dipoles inside the quantum dot.
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.
Excitation of Single-Mode Lamb Waves at High-Frequency-Thickness Products.
Khalili, Pouyan; Cawley, Peter
2016-02-01
Guided wave inspection is used extensively in petrochemical plants to check for defects such as corrosion. Long-range low-frequency inspection can be used to detect relatively large defects, while higher frequency inspection provides improved sensitivity to small defects, but the presence of multiple dispersive modes makes it difficult to implement. This paper investigates the possibility of exciting a single-mode Lamb wave with low dispersion at a frequency thickness of around 20 MHz-mm. It is shown by finite element (FE) analysis backed up by experiments that a signal dominated by the A1 mode can be generated, even in a region where many modes have similar phase velocities. The A1 mode has relatively little motion at the plate surface which means that only a small reflection is generated at features such as T-joints; this is verified numerically. It is also expected that it will be relatively unaffected by surface roughness or attenuative coatings. These features are very similar to those of the higher order mode cluster (HOMC) reported by other authors, and it is shown that the A1 mode shape is very similar to the deflected shape reported in HOMC.
Dantan, A.; Marler, J. P.; Albert, M.; Guenot, D.; Drewsen, M.
2010-09-03
We report on a novel noninvasive method to determine the normal mode frequencies of ion Coulomb crystals in traps based on the resonance enhanced collective coupling between the electronic states of the ions and an optical cavity field at the single photon level. Excitations of the normal modes are observed through a Doppler broadening of the resonance. An excellent agreement with the predictions of a zero-temperature uniformly charged liquid plasma model is found. The technique opens up for investigations of the heating and damping of cold plasma modes, as well as the coupling between them.
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.
Single-particle and collective excitations in 62Ni
NASA Astrophysics Data System (ADS)
Albers, M.; Zhu, S.; Ayangeakaa, A. D.; Janssens, R. V. F.; Gellanki, J.; Ragnarsson, I.; Alcorta, M.; Baugher, T.; Bertone, P. F.; Carpenter, M. P.; Chiara, C. J.; Chowdhury, P.; David, H. M.; Deacon, A. N.; DiGiovine, B.; Gade, A.; Hoffman, C. R.; Kondev, F. G.; Lauritsen, T.; Lister, C. J.; McCutchan, E. A.; Nair, C.; Rogers, A. M.; Seweryniak, D.
2016-09-01
Background: Level sequences of rotational character have been observed in several nuclei in the A =60 mass region. The importance of the deformation-driving π f7 /2 and ν g9 /2 orbitals on the onset of nuclear deformation is stressed. Purpose: A measurement was performed in order to identify collective rotational structures in the relatively neutron-rich 62Ni isotope. Method: The 26Mg(48Ca,2 α 4 n γ )62Ni complex reaction at beam energies between 275 and 320 MeV was utilized. Reaction products were identified in mass (A ) and charge (Z ) with the fragment mass analyzer (FMA) and γ rays were detected with the Gammasphere array. Results: Two collective bands, built upon states of single-particle character, were identified and sizable deformation was assigned to both sequences based on the measured transitional quadrupole moments, herewith quantifying the deformation at high spin. Conclusions: Based on cranked Nilsson-Strutinsky calculations and comparisons with deformed bands in the A =60 mass region, the two rotational bands are understood as being associated with configurations involving multiple f7 /2 protons and g9 /2 neutrons, driving the nucleus to sizable prolate deformation.
Model for Quasinormal Mode Excitation by a Particle Plunging into a Black Hole
NASA Astrophysics Data System (ADS)
Mark, Zachary; Zimmerman, Aaron; Yang, Huan; Chen, Yanbei
2016-03-01
It is known that the late time gravitational waveform produced by a particle plunging into a Kerr black hole is well described by a sum of quasinormal modes. However it is not yet understood how the early part of the waveform gives way to the quasinormal mode description, which diverges at early times, nor how the inhomogenous part of the waveform contributes. Motivated by, we offer a model for quasinormal mode excitation by a particle plunging into a Schwarzschild black hole. To develop our model we study approximations to the Regge-Wheeler equation that allow for a closed-form expression for the frequency-domain Green's function, which we use to isolate the component of the waveform that should be identified with quasinormal ringing. Our description of quasinormal ringing does not diverge at early times and reveals that quasinormal ringing should be understood in analogy with a damped harmonic oscillator experiencing a transient driving source.
Collective amplitude mode fluctuations in a flat band superconductor formed at a semimetal surface
NASA Astrophysics Data System (ADS)
Kauppila, V. J.; Hyart, T.; Heikkilä, T. T.
2016-01-01
We study the fluctuations of the amplitude (i.e., the Higgs-Anderson) mode in a superconducting system of coupled Dirac particles proposed as a model for possible surface or interface superconductivity in rhombohedral graphite. This system also serves as a generic model of a topological semimetal with an interaction-driven transition on its surface. We show that the absence of Fermi energy and vanishing of the excitation gap of the collective amplitude mode in the model leads to a large fluctuation contribution to thermodynamic quantities, such as the heat capacity. As a consequence, the mean-field theory becomes inaccurate, indicating that the interactions lead to a strongly correlated state. We also present a microscopic derivation of the Ginzburg-Landau theory corresponding to this model.
Low-frequency Raman modes and electronic excitations in atomically thin MoS2 films
NASA Astrophysics Data System (ADS)
Zeng, Hualing; Zhu, Bairen; Liu, Kai; Fan, Jiahe; Cui, Xiaodong; Zhang, Q. M.
2012-12-01
Atomically thin MoS2 crystals have been recognized as quasi-two-dimensional semiconductors with remarkable physical properties. We report our Raman scattering measurements on multilayer and monolayer MoS2, especially in the low-frequency range (<50 cm-1). We find two low-frequency Raman modes with a contrasting thickness dependence. When increasing the number of MoS2 layers, one mode shows a significant increase in frequency while the other decreases following a 1/N (N denotes the number of unit layers) trend. With the aid of first-principles calculations we assign the former as the shear mode E2g2. The latter is distinguished as the compression vibrational mode, similar to the surface vibration of other epitaxial thin films. The opposite evolution of the two modes with thickness demonstrates vibrational modes in an atomically thin crystal as well as a more precise way to characterize the thickness of atomically thin MoS2 films. In addition, we observe a broad feature around 38 cm-1(5 meV) which is visible only under near-resonance excitation and pinned at a fixed energy, independent of thickness. We interpret the feature as an electronic Raman scattering associated with the spin-orbit coupling induced splitting in a conduction band at K points in their Brillouin zone.
Role of cavity degeneracy for high-order mode excitation in end-pumped solid-state lasers.
Barré, Nicolas; Romanelli, Marco; Brunel, Marc
2014-02-15
The possibility of exciting laser modes such as Laguerre-Gaussian (LG) or Ince-Gaussian (IG) modes is discussed on the basis of a gain-matching integral. We reach the conclusion that, using tight pumping and away from degeneracy regions, only the IG(n,n)(e) modes can be excited. Furthermore, pure high-order modes with circular or elliptical nodal lines can never be excited. Only an approximation of such modes, which we call quasi-IG or quasi-LG modes, can be observed and only when the cavity is partially degenerate. We provide experimental results in perfect agreement with the theory and discuss the exact nature of the profiles observed at degeneracy in our experiments and elsewhere in the literature.
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.
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.
Single-particle and collective excitations in Ni62
Albers, M.; Zhu, S.; Ayangeakaa, A. D.; ...
2016-09-01
In this study, level sequences of rotational character have been observed in several nuclei in the A = 60 mass region. The importance of the deformation-driving πf7/2 and νg9/2 orbitals on the onset of nuclear deformation is stressed. A measurement was performed in order to identify collective rotational structures in the relatively neutron-rich 62Ni isotope. Here, the 26Mg(48Ca,2α4nγ)62Ni complex reaction at beam energies between 275 and 320 MeV was utilized. Reaction products were identified in mass (A) and charge (Z) with the fragment mass analyzer (FMA) and γ rays were detected with the Gammasphere array. As a result, two collectivemore » bands, built upon states of single-particle character, were identified and sizable deformation was assigned to both sequences based on the measured transitional quadrupole moments, herewith quantifying the deformation at high spin. In conclusion, based on cranked Nilsson-Strutinsky calculations and comparisons with deformed bands in the A = 60 mass region, the two rotational bands are understood as being associated with configurations involving multiple f7/2 protons and g9/2 neutrons, driving the nucleus to sizable prolate deformation.« less
NASA Astrophysics Data System (ADS)
Daniel, Timothy; Fortuner, Auberry; Abawi, Ahmad; Kirsteins, Ivars; Marston, Philip
2016-11-01
The modulated radiation pressure (MRP) of ultrasound has been widely used to selectively excite low frequency modes of fluid objects. We previously used MRP to excite less compliant metallic object in water including the low frequency modes of a circular metal plate in water. A larger focused ultrasonic transducer allows us to drive modes of larger more-realistic targets. In our experiments solid targets are suspended by strings or supported on sand and the modulated ultrasound is focused on the target's surface. Target sound emissions were recorded and a laser vibrometer was used to measure the surface velocity of the target to give the magnitude of the target response. The source transducer was driven with a doublesideband suppressed carrier voltage as in. By varying the modulation frequency and monitoring target response, resonant frequencies can be measured and compared to finite element models. We also demonstrate the radiation torque of a focused first-order acoustic vortex beam associated with power absorption in the Stokes layer adjacent to a sphere. Funded by ONR.
Photonic crystal fiber modal interferometer based on thin-core-fiber mode exciter.
Miao, Yinping; Ma, Xixi; Wu, Jixuan; Song, Binbin; Zhang, Hao; Liu, Bo; Yao, Jianquan
2015-11-10
A thin-core-fiber excited photonic crystal fiber modal interferometer has been proposed and experimentally demonstrated. By employing a thin-core fiber as the mode exciter, both of the core and cladding modes propagate in the photonic crystal fiber and interfere with each other. The experimental results show that the transmission dips corresponding to different-order modes have various strain responses with opposite shift directions. The strain sensitivity could be improved to 58.57 pm/με for the applied strain from 0 to 491 με by utilizing the wavelength interval between the dips with opposite shift directions. Moreover, due to the pure silica property of the employed photonic crystal fiber, the proposed fiber modal interferometer exhibits a low-temperature sensitivity of about 0.56 pm/°C within a temperature range from 26.4°C (room temperature) to 70°C. Additionally, the proposed fiber modal interferometer has several advantages, such as good stability, compact structure, and simple fabrication. Therefore, it is more applicable for strain measurement with reducing temperature cross-sensitivity.
Persistence of well-defined collective excitations in a molten transition metal.
Bermejo, F. J.; Saboungi, M. L.; Price, D. L.; Alvarez, M.; Roessli, B.; Cabrillo, C.; Ivanov, A.; Materials Science Division; Consejo Superior de Investigaciones Cientificas; Paul Scherrer Inst.; Inst. Laue Langevin
2000-07-02
Well-defined microscopic collective excitations are found in liquid Ni at 1763 K by means of inelastic neutron scattering. Such excitations are supported by the liquid despite an anharmonic character of its thermodynamic functions. Consideration of the detailed shape of the interionic pair potential provides a way to understand why atomic motions at microscopic scales behave in a way much closer to the alkali metals than to the liquefied rare gases.
NASA Astrophysics Data System (ADS)
Min, Fuhong; Wang, Yaoda; Peng, Guangya; Wang, Enrong; Auth, Jane A.
2016-08-01
The bifurcation and Lyapunov exponent for a single-machine-infinite bus system with excitation model are carried out by varying the mechanical power, generator damping factor and the exciter gain, from which periodic motions, chaos and the divergence of system are observed respectively. From given parameters and different initial conditions, the coexisting motions are developed in power system. The dynamic behaviors in power system may switch freely between the coexisting motions, which will bring huge security menace to protection operation. Especially, the angle divergences due to the break of stable chaotic oscillation are found which causes the instability of power system. Finally, a new adaptive backstepping sliding mode controller is designed which aims to eliminate the angle divergences and make the power system run in stable orbits. Numerical simulations are illustrated to verify the effectivity of the proposed method.
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.
Gyrotron with a sectioned cavity based on excitation of a far-from-cutoff operating mode
Bandurkin, I. V.; Kalynov, Yu. K.; Osharin, I. V.; Savilov, A. V.
2016-01-15
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
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.
NASA Astrophysics Data System (ADS)
Tas, Murat; Tanatar, B.
2008-09-01
We calculate the collective excitation modes of strongly coupled bilayer charged Bose systems. We employ the dielectric matrix formulation to study the correlation effects within the random-phase approximation (RPA), the self consistent field approximation Singwi, Tosi, Land, and Sjölander (STLS), and the quasilocalized charge approximation (QLCA), which satisfies the third-frequency-moment (⟨ω3⟩) sum rule. We find that the QLCA predicts a long-wavelength correlation-induced energy gap in the out-of-phase plasmon mode, similar to the situation in electronic bilayer systems. The energy gap and the plasmon density of states are studied as a function of interlayer separation and coupling parameter rs . The results should be helpful for experimental investigations.
Superfluidity and collective modes in Rashba spin-orbit coupled Fermi gases
NASA Astrophysics Data System (ADS)
He, Lianyi; Huang, Xu-Guang
2013-10-01
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.
Fountaine, Katherine T; Kendall, Christian G; Atwater, Harry A
2014-05-05
We report design methods for achieving near-unity broadband light absorption in sparse nanowire arrays, illustrated by results for visible absorption in GaAs nanowires on Si substrates. Sparse (<5% fill fraction) nanowire arrays achieve near unity absorption at wire resonant wavelengths due to coupling into 'leaky' radial waveguide modes of individual wires and wire-wire scattering processes. From a detailed conceptual development of radial mode resonant absorption, we demonstrate two specific geometric design approaches to achieve near unity broadband light absorption in sparse nanowire arrays: (i) introducing multiple wire radii within a small unit cell array to increase the number of resonant wavelengths, yielding a 15% absorption enhancement relative to a uniform nanowire array and (ii) tapering of nanowires to introduce a continuum of diameters and thus resonant wavelengths excited within a single wire, yielding an 18% absorption enhancement over a uniform nanowire array.
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.
Debnath, P. K.; Chakrabarti, Barnali
2010-10-15
We study the instability of collective excitations of a three-dimensional Bose-Einstein condensate with repulsive and attractive interactions in a shallow trap designed as a quadratic plus a quartic potential. By using a correlated many-body theory, we determine the excitation modes and probe the critical behavior of collective modes, having a crucial dependence on the anharmonic parameter. We examine the power-law behavior of monopole frequency near criticality. In Gross-Pitaevskii variational treatment [Phys. Rev. Lett. 80, 1576 (1998)] the power-law exponent is determined as one-fourth power of (1-(A/A{sub cr})), A is the number of condensate atoms and A{sub cr} is the critical number near collapse. We observe that the power-law exponent becomes (1/6) in our calculation for the pure harmonic trap and it becomes (1/7), for traps with a small anharmonic distortion. However for large anharmonicity the power law breaks down.
NASA Astrophysics Data System (ADS)
Debnath, P. K.; Chakrabarti, Barnali
2010-10-01
We study the instability of collective excitations of a three-dimensional Bose-Einstein condensate with repulsive and attractive interactions in a shallow trap designed as a quadratic plus a quartic potential. By using a correlated many-body theory, we determine the excitation modes and probe the critical behavior of collective modes, having a crucial dependence on the anharmonic parameter. We examine the power-law behavior of monopole frequency near criticality. In Gross-Pitaevskii variational treatment [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.80.1576 80, 1576 (1998)] the power-law exponent is determined as one-fourth power of (1-(A)/(Acr)), A is the number of condensate atoms and Acr is the critical number near collapse. We observe that the power-law exponent becomes (1)/(6) in our calculation for the pure harmonic trap and it becomes (1)/(7), for traps with a small anharmonic distortion. However for large anharmonicity the power law breaks down.
Instability modes excited by natural screech tones in a supersonic rectangular jet
NASA Technical Reports Server (NTRS)
Raman, Ganesh; Rice, Edward J.
1993-01-01
The evolution of hydrodynamic instability modes self-excited by harmonically related natural screech tones was experimentally investigated. A convergent rectangular nozzle with an aspect ratio of 9.63 was used to produce a supersonic shock containing jet. Measurements in the flow-field were made using standard hot-film probes positioned only in the subsonic (outer) portions of the flow. The hydrodynamic instability mode observed in the shear layer at the screech frequency was observed to be antisymmetric (sinuous) about the smaller dimension of the jet, whereas its harmonic was observed to be symmetric (varicose). In addition, the near-field noise measurements indicated that the radiated screech tone noise was out of phase on either side of the small jet dimension whereas its harmonic was in phase over the same region. To our knowledge such an observation on the nature of the harmonic has thus far gone unreported and therefore is the focus of the present work. The hydrodynamic instability modes occurring at the screech frequency and its harmonic satisfied the conditions for resonance. Detailed measurements of the coherent wave evolution in the streamwise and spanwise directions indicated that strong spanwise variations were present beyond x/h = 8. Details of the screech noise radiated by the coherent instability modes are also presented in this paper.
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).
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.
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
Control of the electronic phase of a manganite by mode-selective vibrational excitation.
Rini, Matteo; Tobey, Ra'anan; Dean, Nicky; Itatani, Jiro; Tomioka, Yasuhide; Tokura, Yoshinori; Schoenlein, Robert W; Cavalleri, Andrea
2007-09-06
Controlling a phase of matter by coherently manipulating specific vibrational modes has long been an attractive (yet elusive) goal for ultrafast science. Solids with strongly correlated electrons, in which even subtle crystallographic distortions can result in colossal changes of the electronic and magnetic properties, could be directed between competing phases by such selective vibrational excitation. In this way, the dynamics of the electronic ground state of the system become accessible, and new insight into the underlying physics might be gained. Here we report the ultrafast switching of the electronic phase of a magnetoresistive manganite via direct excitation of a phonon mode at 71 meV (17 THz). A prompt, five-order-of-magnitude drop in resistivity is observed, associated with a non-equilibrium transition from the stable insulating phase to a metastable metallic phase. In contrast with light-induced and current-driven phase transitions, the vibrationally driven bandgap collapse observed here is not related to hot-carrier injection and is uniquely attributed to a large-amplitude Mn-O distortion. This corresponds to a perturbation of the perovskite-structure tolerance factor, which in turn controls the electronic bandwidth via inter-site orbital overlap. Phase control by coherent manipulation of selected metal-oxygen phonons should find extensive application in other complex solids--notably in copper oxide superconductors, in which the role of Cu-O vibrations on the electronic properties is currently controversial.
NASA Astrophysics Data System (ADS)
Xiao, Bo; Lai, Kueifu; Yu, Yang; Ma, Tzuhsuan; Shvets, Gennady; Anlage, Steven M.
2016-11-01
Photonic topological insulators are an interesting class of materials whose photonic band structure can have a band gap in the bulk while supporting topologically protected unidirectional edge modes. Recent studies on bianisotropic metamaterials that emulate the electronic quantum spin Hall effect using its electromagnetic analog are examples of such systems with a relatively simple and elegant design. In this paper, we present a rotating magnetic dipole antenna, composed of two perpendicularly oriented coils, that can efficiently excite the unidirectional topologically protected surface waves in the bianisotropic metawaveguide (BMW) structure recently realized by T. Ma et al. [Phys. Rev. Lett. 114, 127401 (2015), 10.1103/PhysRevLett.114.127401] despite the fact that the BMW medium does not break time-reversal invariance. In addition to achieving a high directivity, the antenna can be tuned continuously to excite reflectionless edge modes in the two opposite directions at various amplitude ratios. We demonstrate its performance through experiments and compare the results to simulation results.
NASA Astrophysics Data System (ADS)
Kong, D. F.; Liu, A. D.; Lan, T.; Yu, C. X.; Cheng, J.; Qiu, Z. Y.; Zhao, H. L.; Shen, H. G.; Yan, L. W.; Dong, J. Q.; Xu, M.; Zhao, K. J.; Duan, X. R.; Liu, Y.; Chen, R.; Zhang, S. B.; Sun, X.; Xie, J. L.; Li, H.; Liu, W. D.
2017-04-01
Coexisting dual kinetic geodesic acoustic modes (KGAMs) with similar characteristics have been observed with Langmuir probe arrays in the edge plasma of HL-2A tokamak with low density Ohmic discharge. The dual KGAMs are named a low-frequency GAM (LFGAM) and a high-frequency GAM (HFGAM), respectively. By changing the line averaged density from 1.0× {{10}19}~{{\\text{m}}-3} to 0.7× {{10}19}~{{\\text{m}}-3} , the study of n e and T e profiles indicate that collision damping rate plays a crucial role on exciting of dual KGAMs, especially for the higher frequency branch (HFGAM). With the application of modulating techniques, we provide direct proof that nonlinear interactions between GAMs and ambient turbulence (AT) show great difference at different radial positions. At the exciting position of GAM, the amplitude modulation of AT is dominant, indicating that GAM is generated in the energy-conserving triad interaction. After the exciting of GAMs, they will propagate both inward and outward. During the propagation, the phase modulation of AT is dominant, GAMs can rarely gain energy from AT, yet they can give back-reactions on AT through shearing effect.
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.
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, (CH3S)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 magnetic excitations of C4-symmetric magnetic states in iron-based superconductors
NASA Astrophysics Data System (ADS)
Scherer, Daniel D.; Eremin, Ilya; Andersen, Brian M.
2016-11-01
We study the collective magnetic excitations of the recently discovered C4-symmetric spin-density-wave states of iron-based superconductors with particular emphasis on their orbital character based on an itinerant multiorbital approach. This is important since the C4-symmetric spin-density-wave states exist only at moderate interaction strengths where damping effects from a coupling to the continuum of particle-hole excitations strongly modify the shape of the excitation spectra compared to predictions based on a local moment picture. We uncover a distinct orbital polarization inherent to magnetic excitations in C4-symmetric states, which provide a route to identify the different commensurate magnetic states appearing in the continuously updated phase diagram of the iron-pnictide family.
Hamiltonian theory of the FQHE edge: Collective modes
NASA Astrophysics Data System (ADS)
Nguyen, Hoang; Joglekar, Yogesh; Murthy, Ganpathy
2003-03-01
We study the collective modes of the fractional quantum Hall edge states using the Hamiltonian formalism [1]. While most theoretical approaches start with an effective bosonic theory [2] in which all fermions are integrated out (an exception is the approach based on Chern-Simons theory [3]), the Hamiltonian theory treats the composite fermions as fully interacting. We obtain the gapless edge-modes using a conserving approximation which respects the constraints [4]. The implications of our study to the tunneling experiments into the edge of a fractional quantum Hall system [5] are discussed. [1] R.Shankar and G.Murthy, Phys.Rev.Lett. 79, 4437 (1997). [2] X.-G.Wen, Phys.Rev.Lett. 64, 2206 (1990); D.-H.Lee and X.-G.Wen, cond-mat/9809160; A.Lopez and E.Fradkin, Phys.Rev.B 59, 15323 (1999); U. Zulicke and A.H.MacDonald, Phys.Rev.B 60, 1837 (1999); V.J.Goldman and E.V.Tsiper, Phys.Rev.Lett. 86, 5841 (2001); S.S.Mandal and J.K.Jain, Phys.Rev.Lett. 89, 096801 (2002). [3] L.S.Levitov, A.V.Shytov, and B.I.Halperin, Phys. Rev. B 64, 075322 (2001). [4] N. Read, Phys.Rev.B 58, 16262 (1998); G. Murthy, Phys.Rev.B 64, 195310 (2001). [5] A.M.Chang et.al., Phys.Rev.Lett. 86, 143 (2000).
Collective modes at the fractional quantum Hall edge
NASA Astrophysics Data System (ADS)
Joglekar, Yogesh; Murthy, Ganpathy
2002-03-01
The fractional quantum Hall edge has been a continuing source of new ideas [1] and experimental results [2] for some time. Most theoretical approaches start with an effective bosonic theory [1] in which all fermions have been integrated out (an exception is the approach based on Chern-Simons theory [3]). Our approach is based on the lowest Landau level Hamiltonian theory of the FQHE [4]. In this theory, composite fermions are fully interacting, and We obtain the collective modes using a conserving approximation which respects the constraints. We present the edge-mode dispersions for various simple fractions. 1. X.-G.Wen, Phys. Rev. Lett. 64, 2206 (1990); A.Lopez and E.Fradkin, Phys. Rev. B 59, 15323 (1999); U. Zulicke and A.H.MacDonald, Phys. Rev. B 60, 2837 (1999); D.-H.Lee and X.-G.Wen, cond-mat/9809160. 2. A.M.Chang et al, Phys. Rev. Lett. 86, 143 (2000). 3. L.S.Levitov, A.V.Shytov, and B.I.Halperin, Phys. Rev. B 64, 075322 (2001). 4. R. Shankar and G. Murthy, Phys. Rev. Lett. 79, 4437 (1997).
NASA Astrophysics Data System (ADS)
Li, Biaobin; Lu, Yalin; He, Zhigang; Li, Weiwei; Jia, Qika; Wang, Lin
2017-02-01
The cylindrical dielectric loaded waveguide (DLW) supports a discrete set of modes, which can be excited by electron beam passing through the structure, and the high-order modes can be the harmonics of the fundamental one by properly choosing the parameters of the DLW. By using a train of electron bunches, repeated at the fundamental frequency of the DLW, as the driving source, coherent and simultaneous excitation of multi-modes can be expected. With this proposed scheme, multi-color narrow-band THz radiation with high pulse power and high frequency can be obtained simultaneously.
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.
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
Two-dimensional collective Hamiltonian for chiral and wobbling modes
NASA Astrophysics Data System (ADS)
Chen, Q. B.; Zhang, S. Q.; Zhao, P. W.; Jolos, R. V.; Meng, J.
2016-10-01
A two-dimensional collective Hamiltonian (2DCH) on both azimuth and polar motions in triaxial nuclei is proposed to investigate the chiral and wobbling modes. In the 2DCH, the collective potential and the mass parameters are determined from three-dimensional tilted axis cranking (TAC) calculations. The broken chiral and signature symmetries in the TAC solutions are restored by the 2DCH. The validity of the 2DCH is illustrated with a triaxial rotor (γ =-30∘ ) coupling to one h11 /2 proton particle and one h11 /2 neutron hole. By diagonalizing the 2DCH, the angular momenta and energy spectra are obtained. These results agree with the exact solutions of the particle rotor model (PRM) at high rotational frequencies. However, at low frequencies, the energies given by the 2DCH are larger than those by the PRM due to the underestimation of the mass parameters. In addition, with increasing angular momentum, the transitions from the chiral vibration to chiral rotation and further to longitudinal wobbling motion have been presented in the 2DCH.
Two-Dimensional Collective Hamiltonian for Chiral and Wobbling Modes
Chen, Q. B.; Zhang, S. Q.; Zhao, P. W.; ...
2016-10-03
Here, a two-dimensional collective Hamiltonian (2DCH) on both azimuth and polar motions in triaxial nuclei is proposed to investigate the chiral and wobbling modes. In the 2DCH, the collective potential and the mass parameters are determined from three-dimensional tilted axis cranking (TAC) calculations. The broken chiral and signature symmetries in the TAC solutions are restored by the 2DCH. The validity of the 2DCH is illustrated with a triaxial rotor (γ= -30°) coupling to one h11/2 proton particle and one h11/2 neutron hole. By diagonalizing the 2DCH, the angular momenta and energy spectra are obtained. These results agree with the exactmore » solutions of the particle rotor model (PRM) at high rotational frequencies. However, at low frequencies, the energies given by the 2DCH are larger than those by the PRM due to the underestimation of the mass parameters. In addition, with increasing angular momentum, the transitions from the chiral vibration to chiral rotation and further to longitudinal wobbling motion have been presented in the 2DCH.« less
Two-Dimensional Collective Hamiltonian for Chiral and Wobbling Modes
Chen, Q. B.; Zhang, S. Q.; Zhao, P. W.; Jolos, R. V.; Meng, J.
2016-10-03
Here, a two-dimensional collective Hamiltonian (2DCH) on both azimuth and polar motions in triaxial nuclei is proposed to investigate the chiral and wobbling modes. In the 2DCH, the collective potential and the mass parameters are determined from three-dimensional tilted axis cranking (TAC) calculations. The broken chiral and signature symmetries in the TAC solutions are restored by the 2DCH. The validity of the 2DCH is illustrated with a triaxial rotor (γ= -30°) coupling to one h_{11/2} proton particle and one h_{11/2} neutron hole. By diagonalizing the 2DCH, the angular momenta and energy spectra are obtained. These results agree with the exact solutions of the particle rotor model (PRM) at high rotational frequencies. However, at low frequencies, the energies given by the 2DCH are larger than those by the PRM due to the underestimation of the mass parameters. In addition, with increasing angular momentum, the transitions from the chiral vibration to chiral rotation and further to longitudinal wobbling motion have been presented in the 2DCH.
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.
Tang, Sai Chun; Clement, Gregory T
2008-02-01
The aim of this study is to evaluate the feasibility of using harmonic cancellation for a therapeutic ultrasound transducer excited by a switched-mode power converter without an additional output filter. A switching waveform without the third harmonic was created by cascading two switched-mode power inverter modules at which their output waveforms were pi/3 phase shifted from each other. A PSPICE simulation model for the power converter output stage was developed. The simulated results were in good agreement with the measurement. The waveform and harmonic contents of the acoustic pressure generated by a 1-MHz, self-focused piezoelectric transducer with and without harmonic cancellation have been evaluated. Measured results indicated that the acoustic third harmonicto- fundamental ratio at the focus was small (-48 dB) with harmonic cancellation, compared to that without harmonic cancellation (-20 dB). The measured acoustic levels of the fifth harmonic for both cases with and without harmonic cancellation also were small (-46 dB) compared to the fundamental. This study shows that it is viable to drive a piezoelectric ultrasound transducer using a switched-mode power converter without the requirement of an additional output filter in many high-intensity focused ultrasound (HIFU) applications.
NASA Astrophysics Data System (ADS)
Asgari-Targhi, M.; Coppi, B.
2016-10-01
The radiation emission from Shining Black Holes is most frequently observed to have non-thermal features. It is therefore appropriate to consider relevant collective processes of plasmas surrounding black holes that contain high energy particles with non-thermal distributions in momentum space. For simplicity we use a fluid description considering the case where significant temperature anisotropies are present. These anisotropies are shown to have a critical influence on: a) the existence and characteristics of stationary plasma and field configurations; b) the excitation of magneto-gravitational modes driven by temperature anisotropies and differential rotation; c) the generation of magnetic fields over macroscopic scale distances; d) the outward transport of angular momentum. Sponsored in part by the U.S. D.O.E.
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.
Magnetochromic sensing and size-dependent collective excitations in iron oxide nanoparticles
NASA Astrophysics Data System (ADS)
O'Neal, Kenneth R.; Patete, Jonathan M.; Chen, Peng; Nanavati, Ruhani; Holinsworth, Brian S.; Smith, Jacqueline M.; Marques, Carlos; Simonson, Jack W.; Aronson, Meigan C.; McGill, Stephen A.; Wong, Stanislaus S.; Musfeldt, Janice L.
2017-03-01
We combine optical and magneto-optical spectroscopies with complementary vibrational and magnetic property measurements to reveal finite length scale effects in nanoscale α -Fe2O3 . Analysis of the d -to-d on-site excitations uncovers enhanced color contrast at particle sizes below approximately 75 nm due to size-induced changes in spin-charge coupling that are suppressed again below the superparamagnetic limit. These findings provide a general strategy for amplifying magnetochromism in α -Fe2O3 and other iron-containing nanomaterials that may be useful for advanced sensing applications. We also unravel the size dependence of collective excitations in this iconic antiferromagnet.
Gravitational Waves from F-modes Excited by the Inspiral of Highly Eccentric Neutron Star Binaries
NASA Astrophysics Data System (ADS)
Chirenti, Cecilia; Gold, Roman; Miller, M. Coleman
2017-03-01
As gravitational wave instrumentation becomes more sensitive, it is interesting to speculate about subtle effects that could be analyzed using upcoming generations of detectors. One such effect that has great potential for revealing the properties of very dense matter is fluid oscillations of neutron stars. These have been found in numerical simulations of the hypermassive remnants of double neutron star mergers and of highly eccentric neutron star orbits. Here we focus on the latter and sketch out some ideas for the production, gravitational-wave detection, and analysis of neutron star oscillations. These events will be rare (perhaps up to several tens per year could be detected using third-generation detectors such as the Einstein Telescope or the Cosmic Explorer), but they would have unique diagnostic power for the analysis of cold, catalyzed, dense matter. Furthermore, these systems are unusual in that analysis of the tidally excited f-modes of the stars could yield simultaneous measurements of their masses, moments of inertia, and tidal Love numbers, using the frequency, damping time, and amplitude of the modes. They would thus present a nearly unique opportunity to test the I-Love-Q relation observationally. The analysis of such events will require significant further work in nuclear physics and general relativistic nonlinear mode coupling, and thus we discuss further directions that will need to be pursued. For example, we note that for nearly grazing encounters, numerical simulations show that the energy delivered to the f-modes may be up to two orders of magnitude greater than predicted in the linear theory.
NASA Astrophysics Data System (ADS)
Rauscher, E. A.; van Bise, W. L.
2001-10-01
SPECIFIC PLASMA IONOSPHERIC EXCITATIONS MODES IN THE IONOSPHERE PRODUCED BY SPACE VEHICLE LAUNCH AND RE ENTRY AND NATURAL PHENOMENA We have examined both experimentally and theoretically the formation and excitation of highly well defined specific wave forms of plasma excitation in the D, E, F(1) and F(2) and sometimes G layers of the earth?s ionosphere. In our formal study period from October 1989 until December 1996, we measured 41 distinct events out of a possible 73 events utilizing ground based sensitive T1050 magnetometers. In five cases more than two to three stations were displayed and detected the same ionospheric excitations. Sometimes background noise was high and dominated the signals, but under good measurement conditions signals appeared to be 50 to 70 dbm over the background noise floor. Specific frequencies of the D-layer appeared around 5.2 to 6.52 Hz and E layer excitations were from 10.48 to 12.8 Hz. Sometimes an F double peak appeared around 15 to 17 Hz as excited by space shuttle activity and delta rockets and in several cases, large scale volcanism. A theoretical model has been developed which describes sustained long duration and long range coherent plasma excitation modes which occur when the ionospheric layers are shock excited. Alfven-like velocities of propogation are calculated in these ionospheric layer. Some Schumann resonates were observed from 7 to 8 Hz.
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.
NASA Astrophysics Data System (ADS)
Schaefer, H.; Kabanov, V. V.; Demsar, J.
2014-01-01
The interplay between the electronic and structural subsystems has strong implications on the character of collective excitations in cooperative systems. Their detailed understanding can provide important information on the coupling mechanisms and coupling strengths in such systems. With the recent developments in femtosecond time-resolved optical probes, numerous advantages with respect to conventional time-integrated probes have been put forward. Owing to their high dynamic range, high-frequency resolution, fast data acquisition, and an inherent access to phases of coherent excitations, they provide direct access to the interplay between various degrees of freedom. In this paper, we present a detailed analysis of time-resolved optical data on blue bronzes (K0.3MoO3 and Rb0.3MoO3), prototype quasi-one-dimensional charge-density wave (CDW) systems. Numerous coherent (Raman active) modes appear upon the phase transition into the CDW state. We analyze the temperature dependence of mode frequencies, their damping times, as well as their oscillator strengths and phases using the time-dependent Ginzburg-Landau model. We demonstrate that these low-temperature modes are a result of linear coupling between the Fermi surface nesting driven modulation of the conduction electron density and the normal-state phonons at the CDW wave vector, and determine their coupling strengths. Moreover, we are able to identify the nature of excitation of these coupled modes, as well as the nature of the probing mechanisms in this type of experiments. We demonstrate that in incommensurate CDW systems, femtosecond optical excitation initially suppresses the electronic density modulation, while the reflectivity changes at frequencies far above the CDW induced gap in the single-particle excitation spectrum are governed by the modulation of interband transitions caused by lattice motion. This approach can be readily extended to more complex systems with spatially modulated ground states.
Magnetic antenna excitation of whistler modes. IV. Receiving antennas and reciprocity
Stenzel, R. L. Urrutia, J. M.
2015-07-15
Antenna radiation patterns are an important property of antennas. Reciprocity holds in free space and the radiation patterns for exciting and receiving antennas are the same. In anisotropic plasmas, radiation patterns are complicated by the fact that group and phase velocities differ and certain wave properties like helicity depend on the direction of wave propagation with respect to the background magnetic field B{sub 0}. Interference and wave focusing effects are different than in free space. Reciprocity does not necessarily hold in a magnetized plasma. The present work considers the properties of various magnetic antennas used for receiving whistler modes. It is based on experimental data from exciting low frequency whistler modes in a large uniform laboratory plasma. By superposition of linear waves from different antennas, the radiation patterns of antenna arrays are derived. Plane waves are generated and used to determine receiving radiation patterns of different receiving antennas. Antenna arrays have radiation patterns with narrow lobes, whose angular position can be varied by physical rotation or electronic phase shifting. Reciprocity applies to broadside antenna arrays but not to end fire arrays which can have asymmetric lobes with respect to B{sub 0}. The effect of a relative motion between an antenna and the plasma has been modeled by the propagation of a short wave packet moving along a linear antenna array. An antenna moving across B{sub 0} has a radiation pattern characterized by an oscillatory “whistler wing.” A receiving antenna in motion can detect any plane wave within the group velocity resonance cone. The radiation pattern also depends on loop size relative to the wavelength. Motional effects prevent reciprocity. The concept of the radiation pattern loses its significance for wave packets since the received signal does not only depend on the antenna but also on the properties of the wave packet. The present results are of fundamental
Magnetic antenna excitation of whistler modes. IV. Receiving antennas and reciprocity
NASA Astrophysics Data System (ADS)
Stenzel, R. L.; Urrutia, J. M.
2015-07-01
Antenna radiation patterns are an important property of antennas. Reciprocity holds in free space and the radiation patterns for exciting and receiving antennas are the same. In anisotropic plasmas, radiation patterns are complicated by the fact that group and phase velocities differ and certain wave properties like helicity depend on the direction of wave propagation with respect to the background magnetic field B0. Interference and wave focusing effects are different than in free space. Reciprocity does not necessarily hold in a magnetized plasma. The present work considers the properties of various magnetic antennas used for receiving whistler modes. It is based on experimental data from exciting low frequency whistler modes in a large uniform laboratory plasma. By superposition of linear waves from different antennas, the radiation patterns of antenna arrays are derived. Plane waves are generated and used to determine receiving radiation patterns of different receiving antennas. Antenna arrays have radiation patterns with narrow lobes, whose angular position can be varied by physical rotation or electronic phase shifting. Reciprocity applies to broadside antenna arrays but not to end fire arrays which can have asymmetric lobes with respect to B0. The effect of a relative motion between an antenna and the plasma has been modeled by the propagation of a short wave packet moving along a linear antenna array. An antenna moving across B0 has a radiation pattern characterized by an oscillatory "whistler wing." A receiving antenna in motion can detect any plane wave within the group velocity resonance cone. The radiation pattern also depends on loop size relative to the wavelength. Motional effects prevent reciprocity. The concept of the radiation pattern loses its significance for wave packets since the received signal does not only depend on the antenna but also on the properties of the wave packet. The present results are of fundamental interest and of relevance to
Dong, Zheng-Gao; Liu, Hui; Xu, Ming-Xiang; Li, Tao; Wang, Shu-Ming; Cao, Jing-Xiao; Zhu, Shi-Ning; Zhang, X
2010-10-11
An otherwise dark magnetic dipole resonance in a split-ring resonator can be excited electrically with a Fano-type profile once the symmetric environment for this resonator is broken with respect to the polarized electric-field direction of incident waves. When this asymmetrically induced narrow resonance coincides with a broad dipolar resonance at an identical frequency regime, the metamaterial analogue of electromagnetically-induced transparency (EIT) window can be formed. We demonstrate that this environmental-asymmetry condition can be introduced dielectrically as well as plasmonically, either resonantly or nonresonantly, which indicates the plasmon coupling between different resonant modes is not responsible for the dark mode excitation. Thus, this result should contribute to the physical understanding on dark-mode excitation pathway for EIT-like phenomenon in plasmonic metamaterials.
NASA Astrophysics Data System (ADS)
Ye, Jinwu
2005-03-01
We study the interlayer coherent incompressible phase in trilayer quantum Hall systems (TLQH) at total filling factor νT=1 from three approaches: Mutual composite fermion (MCF), composite boson (CB), and wave function approach. Just like in bilayer quantum Hall system, CB approach is superior than MCF approach in studying TLQH with broken symmetry. The Hall and Hall drag resistivities are found to be quantized at h/e2 . Two neutral gapless modes with linear dispersion relations are identified and the ratio of the two velocities is close to 3 . The excitation spectra are classified into two classes, charge neutral bosonic two-body bound states and charge ±1 fermionic three-body bound states. In general, there are two two-body Kosterlize-Thouless (KT) transition temperatures and one three-body KT transition. The charge ±1 three-body fermionic bound states may be the main dissipation source of transport measurements. The broken symmetry in terms of SU (3) algebra is studied. The structure of excitons and their flowing patterns are given. The coupling between the two Goldstone modes will lead to the broadening in the zero-bias peak in the interlayer correlated tunnelings of the TLQH. Several interesting features unique to TLQH are outlined. Limitations of the CB approach are also pointed out.
Coronal Seismology of Flare-Excited Standing Slow-Mode Waves Observed by SDO/AIA
NASA Astrophysics Data System (ADS)
Wang, Tongjiang; Ofman, Leon; Davila, Joseph M.
2016-05-01
Flare-excited longitudinal intensity oscillations in hot flaring loops have been recently detected by SDO/AIA in 94 and 131 Å bandpasses. Based on the interpretation in terms of a slow-mode wave, quantitative evidence of thermal conduction suppression in hot (>9 MK) loops has been obtained for the first time from measurements of the polytropic index and phase shift between the temperature and density perturbations (Wang et al. 2015, ApJL, 811, L13). This result has significant implications in two aspects. One is that the thermal conduction suppression suggests the need of greatly enhanced compressive viscosity to interpret the observed strong wave damping. The other is that the conduction suppression provides a reasonable mechanism for explaining the long-duration events where the thermal plasma is sustained well beyond the duration of impulsive hard X-ray bursts in many flares, for a time much longer than expected by the classical Spitzer conductive cooling. In this study, we model the observed standing slow-mode wave in Wang et al. (2015) using a 1D nonlinear MHD code. With the seismology-derived transport coefficients for thermal conduction and compressive viscosity, we successfully simulate the oscillation period and damping time of the observed waves. Based on the parametric study of the effect of thermal conduction suppression and viscosity enhancement on the observables, we discuss the inversion scheme for determining the energy transport coefficients by coronal seismology.
Excitability, mixed-mode oscillations and transition to chaos in a stochastic ice ages model
NASA Astrophysics Data System (ADS)
Alexandrov, D. V.; Bashkirtseva, I. A.; Ryashko, L. B.
2017-03-01
Motivated by an important geophysical significance, we consider the influence of stochastic forcing on a simple three-dimensional climate model previously derived by Saltzman and Sutera. A nonlinear dynamical system governing three physical variables, the bulk ocean temperature, continental and marine ice masses, is analyzed in deterministic and stochastic cases. It is shown that the attractor of deterministic model is either a stable equilibrium or a limit cycle. We demonstrate that the process of continental ice melting occurs with a noise-dependent time delay as compared with marine ice melting. The paleoclimate cyclicity which is near 100 ky in a wide range of model parameters abruptly increases in the vicinity of a bifurcation point and depends on the noise intensity. In a zone of stable equilibria, the 3D climate model under consideration is extremely excitable. Even for a weak random noise, the stochastic trajectories demonstrate a transition from small- to large-amplitude stochastic oscillations (SLASO). In a zone of stable cycles, SLASO transitions are analyzed too. We show that such stochastic transitions play an important role in the formation of a mixed-mode paleoclimate scenario. This mixed-mode dynamics with the intermittency of large- and small-amplitude stochastic oscillations and coherence resonance are investigated via analysis of interspike intervals. A tendency of dynamic paleoclimate to abrupt and rapid glaciations and deglaciations as well as its transition from order to chaos with increasing noise are shown.
Patel, Vishesha; Malinovsky, Vladimir S.; Malinovskaya, Svetlana
2010-06-15
Coherent anti-Stokes Raman scattering (CARS) microscopy has been a major tool of investigation of biological structures as it contains the vibrational signature of molecules. A quantum control method based on chirped pulse adiabatic passage was recently proposed for selective excitation of a predetermined vibrational mode in CARS microscopy [Malinovskaya and Malinovsky, Opt. Lett. 32, 707 (2007)]. The method utilizes the chirp sign variation at the peak pulse amplitude and gives a robust adiabatic excitation of the desired vibrational mode. Using this method, we investigate the impact of coupling between vibrational modes in molecules on controllability of excitation of the CARS signal. We analyze two models of two coupled two-level systems (TLSs) having slightly different transitional frequencies. The first model, featuring degenerate ground states of the TLSs, gives robust adiabatic excitation and maximum coherence in the resonant TLS for positive value of the chirp. In the second model, implying nondegenerate ground states in the TLSs, a population distribution is observed in both TLSs, resulting in a lack of selectivity of excitation and low coherence. It is shown that the relative phase and coupling between the TLSs play an important role in optimizing coherence in the desired vibrational mode and suppressing unwanted transitions in CARS microscopy.
Qu, J Y; Huang, Z; Hua, J
2000-07-01
We present an imaging technique for the correction of geometrical effects in fluorescence measurement of optically thick, turbid media such as human tissue. Specifically, we use the cross-polarization method to reject specular reflection and enhance the diffusive backscattering of polarized fluorescence excitation light from the turbid media. We correct the nonuniformity of the image field caused by the excitation-and-collection geometry of a fluorescence imaging system by normalizing the fluorescence image to the cross-polarized reflection image. The ratio image provides a map of relative fluorescence yield, defined as the ratio of emerging fluorescence power to incident excitation, over the surface of an imaged homogeneous turbid medium when fluorescence excitation-and-collection geometries vary in a wide range. We investigate the mechanism of ratio imaging by using Monte Carlo modeling. Our findings show that this technique could have a potential use in the detection of early cancer, which usually starts from a superficial layer of tissue, based on the contrast in the tissue fluorescence of an early lesion and of the surrounding normal tissue.
Lee, Jae Sung; Han, Sanghoon; Shirdel, Javid; Koo, Sukmo; Sadiq, Diyar; Lienau, Christoph; Park, Namkyoo
2011-06-20
We compare single- and double-sided excitation methods of adiabatic surface plasmon polariton (SPP) wave superfocusing for scattering-type metallic near-field scanning optical microscopy (s-NSOM). Using the results of full 3D finite difference time domain analyses, the differences in field enhancement factors are explained and reveal the mode selectivity of a conical NSOM tip for adiabatic SPP superfocusing. Exploiting the mode-symmetric nature of the tip further, we also show that it is possible to selectively confine either the electric or magnetic field at the NSOM tip apex, by simply adjusting the relative phase between the SPP waves in the double-sided excitation approach.
Collective 2+ 1 excitations in 206Po and 208,210Rn
NASA Astrophysics Data System (ADS)
Grahn, T.; Pakarinen, J.; Jokiniemi, L.; Albers, M.; Auranen, K.; Bauer, C.; Bernards, C.; Blazhev, A.; Butler, P. A.; Bönig, S.; Damyanova, A.; De Coster, T.; De Witte, H.; Elseviers, J.; Gaffney, L. P.; Huyse, M.; Herzáň, A.; Jakobsson, U.; Julin, R.; Kesteloot, N.; Konki, J.; Kröll, Th.; Lewandowski, L.; Moschner, K.; Peura, P.; Pfeiffer, M.; Radeck, D.; Rahkila, P.; Rapisarda, E.; Reiter, P.; Reynders, K.; Rudiger, M.; Salsac, M.-D.; Sambi, S.; Scheck, M.; Seidlitz, M.; Siebeck, B.; Steinbach, T.; Stolze, S.; Suhonen, J.; Thoele, P.; Thürauf, M.; Warr, N.; Van Duppen, P.; Venhart, M.; Vermeulen, M. J.; Werner, V.; Veselsky, M.; Vogt, A.; Wrzosek-Lipska, K.; Zielińska, M.
2016-11-01
In the present study, B(E2; 2+1→ 0+1) values have been measured in the 208,210Rn and 206Po nuclei through Coulomb excitation of re-accelerated radioactive beams in inverse kinematics at CERN-ISOLDE. These nuclei have been proposed to lie in, or at the boundary of the region where the seniority scheme should persist. However, contributions from collective excitations are likely to be present when moving away from the N=126 closed shell. Such an effect is confirmed by the observed increased collectivity of the 2+1→ 0+1 transitions. Experimental results have been interpreted with the aid of theoretical studies carried out within the BCS-based QRPA framework.
NASA Astrophysics Data System (ADS)
Loon Lee, Kean; Proukakis, Nick P.
2016-11-01
The non-equilibrium dynamics of trapped ultracold atomic gases, or mixtures thereof, is an extremely rich subject. Despite 20 years of studies, and remarkable progress mainly on the experimental front, numerous open question remain, related to the growth, relaxation and thermalisation of such systems, and there is still no universally accepted theory for their theoretical description. In this paper we discuss one of the state-of-the-art kinetic approaches, which gives an intuitive picture of the physical processes happening at the microscopic scale, being broadly applicable both below and above the critical region (but not within the critical region itself, where fluctuations become dominant and symmetry breaking takes place). Specifically, the ‘Zaremba-Nikuni-Griffin’ (ZNG) scheme provides a self-consistent description of the coupling between the condensate and the thermal atoms, including the collisions between these two subsystems. It has been successfully tested against experiments in various settings, including investigation of collective modes (e.g. monopole, dipole and quadrupole modes), dissipation of topological excitations (solitons and vortices) as well as surface evaporative cooling. Here, we show that the ZNG model can capture two important aspects of non-equilibrium dynamics for both single-component and two-component BECs: the Kohn mode (the undamped dipole oscillation independent of interactions and temperature) and (re)thermalisation leading to condensate growth following sudden evaporation. Our simulations, performed in a spherically symmetric trap reveal (i) an interesting two-stage dynamics and the emergence of a prominent monopole mode in the evaporative cooling of a single-component Bose gas, and (ii) the long thermalisation time associated with the sympathetic cooling of a realistic two-component mixture. Related open questions arise about the mechanisms and the nature of thermalisation in such systems, where further controlled
NASA Astrophysics Data System (ADS)
Crawford, T. M.; Covington, M.; Parker, G. J.
2003-01-01
We measure quantized spin waves excited by a spatially inhomogeneous pulsed magnetic field in patterned NiFe thin films by inductive detection of the dynamic magnetization. When anisotropy and numerically calculated demagnetizing fields are included in the magnetostatic Damon Eshbach spin-wave dispersion relation, the predicted mode frequencies agree closely with measurements. Micromagnetic calculations predict the correct mode frequencies and agree remarkably well with time-domain measurements.
Quadrupole collectivity beyond N = 28: intermediate-energy Coulomb excitation of (47,48)Ar.
Winkler, R; Gade, A; Baugher, T; Bazin, D; Brown, B A; Glasmacher, T; Grinyer, G F; Meharchand, R; McDaniel, S; Ratkiewicz, A; Weisshaar, D
2012-05-04
We report on the first experimental study of quadrupole collectivity in the very neutron-rich nuclei (47,48)Ar using intermediate-energy Coulomb excitation. These nuclei are located along the path from doubly magic Ca to collective S and Si isotopes, a critical region of shell evolution and structural change. The deduced B(E2) transition strengths are confronted with large-scale shell-model calculations in the sdpf shell using the state-of-the-art SDPF-Uand EPQQM effective interactions. The comparison between experiment and theory indicates that a shell-model description of Ar isotopes around N=28 remains a challenge.
Quadrupole Collectivity beyond N=28: Intermediate-Energy Coulomb Excitation of Ar47,48
NASA Astrophysics Data System (ADS)
Winkler, R.; Gade, A.; Baugher, T.; Bazin, D.; Brown, B. A.; Glasmacher, T.; Grinyer, G. F.; Meharchand, R.; McDaniel, S.; Ratkiewicz, A.; Weisshaar, D.
2012-05-01
We report on the first experimental study of quadrupole collectivity in the very neutron-rich nuclei Ar47,48 using intermediate-energy Coulomb excitation. These nuclei are located along the path from doubly magic Ca to collective S and Si isotopes, a critical region of shell evolution and structural change. The deduced B(E2) transition strengths are confronted with large-scale shell-model calculations in the sdpf shell using the state-of-the-art SDPF-Uand EPQQM effective interactions. The comparison between experiment and theory indicates that a shell-model description of Ar isotopes around N=28 remains a challenge.
Collective excitations of 96Ru by means of (p ,p'γ ) experiments
NASA Astrophysics Data System (ADS)
Hennig, A.; Ahn, T.; Anagnostatou, V.; Blazhev, A.; Cooper, N.; Derya, V.; Elvers, M.; Endres, J.; Goddard, P.; Heinz, A.; Hughes, R. O.; Ilie, G.; Mineva, M. N.; Petkov, P.; Pickstone, S. G.; Pietralla, N.; Radeck, D.; Ross, T. J.; Savran, D.; Spieker, M.; Werner, V.; Zilges, A.
2015-12-01
Background: One-phonon mixed-symmetry quadrupole excitations are a well-known feature of near-spherical, vibrational nuclei. Their interpretation as a fundamental building block of vibrational structures is supported by the identification of multiphonon states resulting from a coupling of fully-symmetric and mixed-symmetric quadrupole phonons. In addition, the observation of strong M 1 transitions between low-lying 3- and 4+ states has been interpreted as an evidence for one-phonon mixed-symmetry excitations of octupole and hexadecapole character. Purpose: The aim of the present study is to identify collective one- and two-phonon excitations in the heaviest stable N =52 isotone 96Ru based on a measurement of absolute M 1 , E 1 , and E 2 transition strengths. Methods: Inelastic proton-scattering experiments have been performed at the Wright Nuclear Structure Laboratory (WNSL), Yale University, and the Institute for Nuclear Physics (IKP), University of Cologne. From the acquired proton-γ and γ γ coincidence data we deduced spins of excited states, γ -decay branching ratios, and multipole mixing ratios, as well as lifetimes of excited states via the Doppler-shift attenuation method (DSAM). Results: Based on the new experimental data on absolute transition strengths, we identified the 2+ and 3+ members of the two-phonon mixed-symmetry quintuplet (21,ms +⊗21,s +) . Furthermore, we observed strong M 1 transitions between low-lying 3- and 4+ states suggesting one-phonon symmetric and mixed-symmetric octupole and hexadecapole components in their wave functions, respectively. The experimental results are compared to s d g -IBM-2 and shell-model calculations. Conclusions: Both the s d g -IBM-2 and the shell-model calculations are able to describe key features of mixed-symmetry excitations of 96Ru. Moreover, they support the one-phonon mixed-symmetry hexadecapole assignment of the experimental 42+ state.
Emergence of an excitonic collective mode in the dilute electron gas
NASA Astrophysics Data System (ADS)
Takada, Yasutami
2016-12-01
By comparing two expressions for the polarization function Π (q ,i ω ) given in terms of two different local-field factors, G+(q ,i ω ) and Gs(q ,i ω ) , we have derived the kinetic-energy-fluctuation (or sixth-power) sum rule for the momentum distribution function n (p ) in the three-dimensional electron gas. With use of this sum rule, together with the total-number (or second-power) and the kinetic-energy (or fourth-power) sum rules, we have obtained n (p ) in the low-density electron gas at negative compressibility (namely, rs>5.25 with rs being the conventional density parameter) up to rs≈22 by improving on the interpolation scheme due to Gori-Giorge and Ziesche proposed in 2002. The obtained results for n (p ) combined with the improved form for Gs(q ,ω +i 0+) are employed to calculate the dynamical structure factor S (q ,ω ) to reveal that a giant peak, even bigger than the plasmon peak, originating from an excitonic collective mode made of electron-hole pair excitations, emerges in the low-ω region at |q | near 2 pF (pF: the Fermi wave number). Connected with this mode, we have discovered a singular point in the retarded dielectric function at ω =0 and |q | ≈2 pF .
NASA Astrophysics Data System (ADS)
Pitchappa, Prakash; Manjappa, Manukumara; Ho, Chong Pei; Singh, Ranjan; Singh, Navab; Lee, Chengkuo
2016-11-01
We report experimental results of the active switching of electromagnetically induced transparency (EIT) analogue by controlling the dark mode excitation pathways in a microelectromechanical system based tri-atomic metamolecule, operating in the terahertz spectral region. The tri-atomic metamolecule consists of two bright cut wire resonators (CWRs) on either side of the dark split ring resonators (SRRs). Each of the CWRs can independently excite the dark inductive-capacitive resonance mode of the SRRs through inductive coupling, and this allows for the dual pathways of dark mode excitation. The CWRs are made movable along the out-of-plane direction and electrically isolated to achieve selective reconfiguration. Hence, by controlling the physical position of these CWRs, the excitation pathways can be actively reconfigured. This enables the strong excitation of EIT analogue at 0.65 THz, only when one of the pathways is made accessible. Moreover, the transparency peak is completely modulated when both pathways are made either inaccessible or equally accessible. The proposed approach of realizing independent control of constituent resonators in a multi-resonator coupled system, enables the realization of efficient slow light devices and tunable high-Q resonators in terahertz spectral region.
PHOTOEMISSION AS A PROBE OF THE COLLECTIVE EXCITATIONS IN CONDENSED MATTER SYSTEMS.
JOHNSON, P.D.; VALLA, T.
2006-08-01
New developments in instrumentation have recently allowed photoemission measurements to be performed with very high energy and momentum resolution.[1] This has allowed detailed studies of the self-energy corrections to the lifetime and mass renormalization of excitations in the vicinity of the Fermi level. These developments come at an opportune time. Indeed the discovery of high temperature superconductivity in the cuprates and related systems is presenting a range of challenges for condensed matter physics.[2] Does the mechanism of high T{sub c} superconductivity represent new physics? Do we need to go beyond Landau's concept of the Fermi liquid?[3] What, if any, is the evidence for the presence or absence of quasiparticles in the excitation spectra of these complex oxides? The energy resolution of the new instruments is comparable to or better than the energy or temperature scale of superconductivity and the energy of many collective excitations. As such, photoemission has again become recognized as an important probe of condensed matter. Studies of the high T{sub c} superconductors and related materials are aided by the observation that they are two dimensional. To understand this, we note that the photoemission process results in both an excited photoelectron and a photohole in the final state. Thus the experimentally measured photoemission peak is broadened to a width reflecting contributions from both the finite lifetime of the photohole and the momentum broadening of the outgoing photoelectron.
NASA Astrophysics Data System (ADS)
Shinohara, S.; Tanikawa, T.; Motomura, T.
2014-09-01
A flat type, segmented multi-loop antenna was developed in the Tokai Helicon Device, built for producing high-density helicon plasma, with a diameter of 20 cm and an axial length of 100 cm. This antenna, composed of azimuthally splitting segments located on four different radial positions, i.e., r = 2.8, 4.8, 6.8, and 8.8 cm, can excite the azimuthal mode number m of 0, ±1, and ±2 by a proper choice of antenna feeder parts just on the rear side of the antenna. Power dependencies of the electron density ne were investigated with a radio frequency (rf) power less than 3 kW (excitation frequency ranged from 8 to 20 MHz) by the use of various types of antenna segments, and ne up to ˜5 × 1012 cm-3 was obtained after the density jump from inductively coupled plasma to helicon discharges. Radial density profiles of m = 0 and ±1 modes with low and high rf powers were measured. For the cases of these modes after the density jump, the excited mode structures derived from the magnetic probe measurements were consistent with those expected from theory on helicon waves excited in the plasma.
Shinohara, S.; Tanikawa, T.; Motomura, T.
2014-09-15
A flat type, segmented multi-loop antenna was developed in the Tokai Helicon Device, built for producing high-density helicon plasma, with a diameter of 20 cm and an axial length of 100 cm. This antenna, composed of azimuthally splitting segments located on four different radial positions, i.e., r = 2.8, 4.8, 6.8, and 8.8 cm, can excite the azimuthal mode number m of 0, ±1, and ±2 by a proper choice of antenna feeder parts just on the rear side of the antenna. Power dependencies of the electron density n{sub e} were investigated with a radio frequency (rf) power less than 3 kW (excitation frequency ranged from 8 to 20 MHz) by the use of various types of antenna segments, and n{sub e} up to ∼5 × 10{sup 12} cm{sup −3} was obtained after the density jump from inductively coupled plasma to helicon discharges. Radial density profiles of m = 0 and ±1 modes with low and high rf powers were measured. For the cases of these modes after the density jump, the excited mode structures derived from the magnetic probe measurements were consistent with those expected from theory on helicon waves excited in the plasma.
Shinohara, S; Tanikawa, T; Motomura, T
2014-09-01
A flat type, segmented multi-loop antenna was developed in the Tokai Helicon Device, built for producing high-density helicon plasma, with a diameter of 20 cm and an axial length of 100 cm. This antenna, composed of azimuthally splitting segments located on four different radial positions, i.e., r = 2.8, 4.8, 6.8, and 8.8 cm, can excite the azimuthal mode number m of 0, ±1, and ±2 by a proper choice of antenna feeder parts just on the rear side of the antenna. Power dependencies of the electron density ne were investigated with a radio frequency (rf) power less than 3 kW (excitation frequency ranged from 8 to 20 MHz) by the use of various types of antenna segments, and n(e) up to ~5 × 10(12) cm(-3) was obtained after the density jump from inductively coupled plasma to helicon discharges. Radial density profiles of m = 0 and ±1 modes with low and high rf powers were measured. For the cases of these modes after the density jump, the excited mode structures derived from the magnetic probe measurements were consistent with those expected from theory on helicon waves excited in the plasma.
NASA Technical Reports Server (NTRS)
Merchant, D. H.; Gates, R. M.; Straayer, J. W.
1975-01-01
The effect of localized structural damping on the excitability of higher-order large space telescope spacecraft modes is investigated. A preprocessor computer program is developed to incorporate Voigt structural joint damping models in a finite-element dynamic model. A postprocessor computer program is developed to select critical modes for low-frequency attitude control problems and for higher-frequency fine-stabilization problems. The selection is accomplished by ranking the flexible modes based on coefficients for rate gyro, position gyro, and optical sensor, and on image-plane motions due to sinusoidal or random PSD force and torque inputs.
Eremeev, Grigory; Geng, Rongli; Palczewski, Ari
2011-07-01
We have studied thermal breakdown in several multicell superconducting radiofrequency cavity by simultaneous excitation of two TM{sub 010} passband modes. Unlike measurements done in the past, which indicated a clear thermal nature of the breakdown, our measurements present a more complex picture with interplay of both thermal and magnetic effects. JLab LG-1 that we studied was limited at 40.5 MV/m, corresponding to B{sub peak} = 173 mT, in 8{pi}/9 mode. Dual mode measurements on this quench indicate that this quench is not purely magnetic, and so we conclude that this field is not the fundamental limit in SRF cavities.
NASA Astrophysics Data System (ADS)
Chen, Tsun-Hsu; Wang, Hsin-Hu; Hsu, Yu-Hsiang; Lee, Chih-Kung
2016-03-01
In comparison to more developed optical method for microparticle manipulation like optical tweezers, an optopiezoelectric actuating system could provide force output that is several orders higher. Taking advantages of photoconductive materials, the concept of integrating a virtual electrode in a distributed opto-piezoelectric actuators was developed for real-time in-situ spatial tailoring for vast varieties of applications in biochips, smart structures, etc. In this study, photoconductive material titanium oxide phthalocyanine (TiOPc) was used as the active ingredient to enable the virtual electrode in an opto-piezoelectric material based distributed actuator. By illuminating light of proper wavelength and enough intensity onto TiOPc photoconductive material, the effective impedance of the illuminated portion of TiOPc could drop significantly. The contributions of using additives in the TiOPc photoconductive electrode to adjust the electrical properties was investigated for optimization. Further, the two-mode excited linear ultrasonic motor was also studied and the feasibility to integrate the TiOPc photoconductive electrode was discussed. The flexibility provided by this newly developed system could potential deliver versatile performance in biochip applications.
Magnetochromic sensing and size-dependent collective excitations in iron oxide nanoparticles
O'Neal, Kenneth R.; Patete, Jonathan M.; Chen, Peng; ...
2017-03-10
We combine optical and magneto-optical spectroscopies with complementary vibrational and magnetic property measurements to reveal finite length scale effects in nanoscale α–Fe2O3. Analysis of the d-to-d on-site excitations uncovers enhanced color contrast at particle sizes below approximately 75 nm due to size-induced changes in spin-charge coupling that are suppressed again below the superparamagnetic limit. These findings provide a general strategy for amplifying magnetochromism in α–Fe2O3 and other iron-containing nanomaterials that may be useful for advanced sensing applications. Lastly, we also unravel the size dependence of collective excitations in this iconic antiferromagnet.
High-energy collective electronic excitations in free-standing single-layer graphene
NASA Astrophysics Data System (ADS)
Wachsmuth, P.; Hambach, R.; Kinyanjui, M. K.; Guzzo, M.; Benner, G.; Kaiser, U.
2013-08-01
In this joint experimental and theoretical work, we investigate collective electronic excitations (plasmons) in free-standing, single-layer graphene. The energy- and momentum-dependent electron energy-loss function was measured up to 50eV along two independent in-plane symmetry directions (ΓM and ΓK) over the first Brillouin zone by momentum-resolved electron energy-loss spectroscopy in a transmission electron microscope. We compare our experimental results with corresponding time-dependent density-functional theory calculations. For finite momentum transfers, good agreement with experiments is found if crystal local-field effects are taken into account. In the limit of small and vanishing momentum transfers, we discuss differences between calculations and the experimentally obtained electron energy-loss functions of graphene due to a finite momentum resolution and out-of-plane excitations.
NASA Astrophysics Data System (ADS)
Yashkir, O. V.; Yashkir, Yu N.
1987-06-01
A theoretical investigation is made of nonlinear excitation of planar waveguide modes at frequencies ω when external plane optical waves of frequency ω1 are incident on the waveguide surface. The general formulas for the efficiency of the excitation of modes by a monochromatic wave are obtained and analyzed for the case of self-interaction of the ω = ω1 + ω1 - ω1 type and by a biharmonic wave in the case of generation of the difference frequency ω = ω1 - ω1'. The efficiency of parametric conversion of waveguide modes ω accompanied by an increase of the frequency to the range ω' is considered for the case when the sum frequency ω + ω1 = ω1' is generated. The numerical method developed by the authors is used to analyze the characteristic features of these processes in some specific cases.
NASA Astrophysics Data System (ADS)
Satoh, Kazuhiro
1989-08-01
Numerical studies are made out the behavior of a random neural network in which each neuron is coupled to a certain number of randomly chosen neurons. Such a random-net serves as a simple model for an elemental sub-network of the cortex. Neurons are regarded as binary decision elements, and they synchronously update their values in discrete time steps according to a deterministic equation (the McCulloch-Pitts model). It is found that each random-net containing one hundred neurons has only a few kinds of characteristic modes of excitation. Periods of these modes are usually less than ten steps when the number of connections per neuron is two to five. For the random-net containing one thousand neurons, an excited mode is practically aperiodic. When the refractory period is introduced, however, a nearly periodic oscillation takes place in the activity of the network.
Shelke, Amit; Kundu, Tribikram; Amjad, Umar; Hahn, Katrin; Grill, Wolfgang
2011-03-01
Selective modes of guided Lamb waves are generated in a laminated aluminum plate for damage detection using a broadband piezoelectric transducer structured with a rigid electrode. Appropriate excitation frequencies and modes for inspection are selected from theoretical and experimental dispersion curves. Dispersion curves are obtained experimentally by short time Fourier transform of the transient signals. Sensitivity of antisymmetric and symmetric modes for delamination detection are investigated. The antisymmetric mode is found to be more reliable for delamination detection. Unlike other studies, in which the attenuation of the propagating waves is related to the extent of the internal damage, in this investigation, the changes in the time-of-flight (TOF) of guided Lamb waves are related to the damage progression. The mode conversion phenomenon of Lamb waves during progressive delamination is investigated. Close matching between the theoretical and experimentally derived dispersion curves and TOF assures the reliability of the results presented here.
NASA Astrophysics Data System (ADS)
Kushwaha, Manvir S.
2013-04-01
intersubband single-particle as well as collective excitations], the loss functions for the IES and the Raman intensity for the ILS. We observe that it is the collective (plasmon) excitations that largely contribute to the predominant peaks in the energy-loss and the Raman spectra. The inductive reasoning is that the IES can be a potential alternative of the overused ILS for investigating collective excitations in quantum wires. We trust that this research work shall be useful to all - from novice to expert and from theorist to experimentalist - who believe in the power of traditional science.
Mode Control and Tunability in Rf-Excited Carbon - Waveguide Lasers.
NASA Astrophysics Data System (ADS)
Hill, Christopher Alexander
Available from UMI in association with The British Library. The first chapter describes some uses and advantages of the CO_2 waveguide laser, with a brief historical review. The rest of the thesis, apart from routine accounts of apparatus and summaries of parts of the literature, reports several pieces of original work. These have aimed mainly at a better understanding of waveguide laser models and at applying them in detail to real devices, with a general emphasis on the design of highly tunable cw CO_2 waveguide oscillators. Chapter 2 has a formal statement of passive waveguide transmission theory and suggests that some recent experimental work elsewhere can be explained by assuming that the wavefronts of EH_{1_{rm m} } guide modes are curved. Chapter 4 shows that the seminal paper on waveguide reflector EH_{11} coupling losses by Abrams (1972) contains an error which leads to predictions significantly different from those of Degnan and Hall (1973). It is resolved by introducing the correct phase shifts phi_{rm p }(z,R_{rm M} ) for the Laguerre-Gaussian beams reflected from a spherical mirror. The two methods of calculation (Gaussian -beam expansion and diffraction integral) are then seen to yield the same results. Also, chapter 4 contains a detailed review of published coupling loss theory for plane mirrors. Surprising errors and inconsistencies are revealed. Chapter 6 discusses the application of Rigrod -type modelling to waveguide gas lasers, especially those with significant distributed loss. It reports an attempt to characterize an rf-excited waveguide CO_2 laser whose waveguide losses are certainly significant. For another such laser (chapter 7) the dependence of gain on rf excitation frequency is confirmed. Chapter 8 develops a multimode model of a dual -Case I waveguide laser with one tilted mirror. This description fits many commercial lasers; if a diffraction grating is modelled as a lossy plane mirror with a wavelength-dependent tilt, it also fits many
Hamiltonian Lattice Studies of Pionic Collective Excitations in the Non-linear Sigma Model
NASA Astrophysics Data System (ADS)
Chin, Siu A.
2001-04-01
The latticization of the non-linear sigma model reduces a chiral meson field theory to an O(4) spin system with quantum fluctuations. By solving the resulting lattice Hamiltonian by Monte Carlo methods, the dynamics and thermodynamics of pions can be determined non-perturbatively. In particular, the mas gap of pionic collective excitations with quantum number of vector mesons can be determined as the chiral phase transition is approached. Results based on a newly discovered 4th order method of solving for the ground state of a quantum many-body Hamitonian will be presented.
Ichou, Farid; Schwarzenberg, Adrian; Lesage, Denis; Alves, Sandra; Junot, Christophe; Machuron-Mandard, Xavier; Tabet, Jean-Claude
2014-06-01
Reproducibility among different types of excitation modes is a major bottleneck in the field of tandem mass spectrometry library development in metabolomics. In this study, we specifically evaluated the influence of collision voltage and activation time parameters on tandem mass spectrometry spectra for various excitation modes [collision-induced dissociation (CID), pulsed Q dissociation (PQD) and higher-energy collision dissociation (HCD)] of Orbitrap-based instruments. For this purpose, internal energy deposition was probed using an approach based on Rice-Rampserger-Kassel-Marcus modeling with three thermometer compounds of different degree of freedom (69, 228 and 420) and a thermal model. This model treats consecutively the activation and decomposition steps, and the survival precursor ion populations are characterized by truncated Maxwell-Boltzmann internal energy distributions. This study demonstrates that the activation time has a significant impact on MS/MS spectra using the CID and PQD modes. The proposed model seems suitable to describe the multiple collision regime in the PQD and HCD modes. Linear relationships between mean internal energy and collision voltage are shown for the latter modes and the three thermometer molecules. These results suggest that a calibration based on the collision voltage should provide reproducible for PQD, HCD to be compared with CID in tandem in space instruments. However, an important signal loss is observed in PQD excitation mode whatever the mass of the studied compounds, which may affect not only parent ions but also fragment ions depending on the fragmentation parameters. A calibration approach for the CID mode based on the variation of activation time parameter is more appropriate than one based on collision voltage. In fact, the activation time parameter in CID induces a modification of the collisional regime and thus helps control the orientation of the fragmentation pathways (competitive or consecutive dissociations).
Multi-hop Whistler-Mode ELF/VLF Signals and Triggered Emissions Excited by the HAARP HF Heater
2004-12-28
Multi-hop whistler-mode ELF/VLF signals and triggered emissions excited by the HAARP HF heater U. S. Inan,1 M. Gol-kowski,1 D. L. Carpenter,1 N...accepted 24 November 2004; published 28 December 2004. [1] Modulated heating of the lower ionosphere with the HAARP HF heater is used to excite 1–2 kHz...are believed to be amplified, and are accompanied by triggered emissions. Simultaneous observations near (30 km) HAARP show 2-hop signals which travel
NASA Astrophysics Data System (ADS)
Wang, Xiang; Cannon, Patrick; Zhou, Chen; Honary, Farideh; Ni, Binbin; Zhao, Zhengyu
2016-04-01
Recent ionospheric modification experiments performed at Tromsø, Norway, have indicated that X-mode pump wave is capable of stimulating high-frequency enhanced plasma lines, which manifests the excitation of parametric instability. This paper investigates theoretically how the observation can be explained by the excitation of parametric instability driven by X-mode pump wave. The threshold of the parametric instability has been calculated for several recent experimental observations at Tromsø, illustrating that our derived equations for the excitation of parametric instability for X-mode heating can explain the experimental observations. According to our theoretical calculation, a minimum fraction of pump wave electric field needs to be directed along the geomagnetic field direction in order for the parametric instability threshold to be met. A full-wave finite difference time domain simulation has been performed to demonstrate that a small parallel component of pump wave electric field can be achieved during X-mode heating in the presence of inhomogeneous plasma.
NASA Astrophysics Data System (ADS)
White, W. B.; Dettinger, M. D.; Cayan, D. R.; White, Warren B.; Dettinger, Michael D.; Cayan, Daniel R.
Global average upper ocean temperatures anomalies of +/-0.05°K fluctuate in fixed phase with decadal signals in the Sun's irradiance of +/-0.5 Watts m-2 over the past 100 years (White et al., 1997), but its amplitude is 2 to 3 times that expected from the transient Stefan-Boltzmann radiation balance (White et al., 1988). Examining global patterns of upper ocean temperature and lower troposphere winds, we find the internal interannual mode of variability in Earth's ocean-atmosphere-terrestrial system with global-average upper ocean temperature anomalies of +/-0.05°K occurring naturally, independent of changing solar irradiance (White et al., 2000). Yet coherence and phase statistics indicate that the observed internal decadal mode in Earth's ocean -atmosphere terrestrial system is excited by the decadal signal in the Sun's irradiance. To understand the thermodynamics of this association we conduct a global-average upper ocean heat budget utilizing upper ocean temperatures from the SIO reanalysis and air-sea heat and momentum fluxes from the COADS reanalysis, finding the source of decadal global warming to be the reduction in trade wind intensity across the tropics, decreasing global average latent heat flux out of the ocean. We demonstrate that this reduction in trade wind intensity in the Pacific Ocean is governed by a delayed action oscillator mechanism in the ocean-atmosphere system differing little from that used to explain the El Niño-Southern Oscillation (Graham and White, 1988). We operate an intermediate coupled model of this delayed action oscillator, normally driven by white noise, by superimposing the Stefan-Boltzmann upper ocean temperature response to decadal changes in the Sun's irradiance. We find the latter, with weak amplitude of +/-0.02°K and non-random phase, is able to excite a decadal signal in this delayed action oscillator, yielding a damped resonance response of +/-0.1°K in the equatorial Pacific Ocean, with dissipation provided by
Fast color flow mode imaging using plane wave excitation and temporal encoding
NASA Astrophysics Data System (ADS)
Udesen, Jesper; Gran, Fredrik; Jensen, Jorgen A.
2005-04-01
In conventional ultrasound color flow mode imaging, a large number (~500) of pulses have to be emitted in order to form a complete velocity map. This lowers the frame-rate and temporal resolution. A method for color flow imaging in which a few (~10) pulses have to be emitted to form a complete velocity image is presented. The method is based on using a plane wave excitation with temporal encoding to compensate for the decreased SNR, resulting from the lack of focusing. The temporal encoding is done with a linear frequency modulated signal. To decrease lateral sidelobes, a Tukey window is used as apodization on the transmitting aperture. The data are beamformed along the direction of the flow, and the velocity is found by 1-D cross correlation of these data. First the method is evaluated in simulations using the Field II program. Secondly, the method is evaluated using the experimental scanner RASMUS and a 7 MHz linear array transducer, which scans a circulating flowrig. The velocity of the blood mimicking fluid in the flowrig is constant and parabolic, and the center of the scanned area is situated at a depth of 40 mm. A CFM image of the blood flow in the flowrig is estimated from two pulse emissions. At the axial center line of the CFM image, the velocity is estimated over the vessel with a mean relative standard deviation of 2.64% and a mean relative bias of 6.91%. At an axial line 5 mm to the right of the center of the CFM image, the velocity is estimated over the vessel with a relative standard deviation of 0.84% and a relative bias of 5.74%. Finally the method is tested on the common carotid artery of a healthy 33-year-old male.
LaForge, A. C.; Drabbels, M.; Brauer, N. B.; Coreno, M.; Devetta, M.; Di Fraia, M.; Finetti, P.; Grazioli, C.; Katzy, R.; Lyamayev, V.; Mazza, T.; Mudrich, M.; O'Keeffe, P.; Ovcharenko, Y.; Piseri, P.; Plekan, O.; Prince, K. C.; Richter, R.; Stranges, S.; Callegari, C.; Möller, T.; Stienkemeier, F.
2014-01-01
Free electron lasers (FELs) offer the unprecedented capability to study reaction dynamics and image the structure of complex systems. When multiple photons are absorbed in complex systems, a plasma-like state is formed where many atoms are ionized on a femtosecond timescale. If multiphoton absorption is resonantly-enhanced, the system becomes electronically-excited prior to plasma formation, with subsequent decay paths which have been scarcely investigated to date. Here, we show using helium nanodroplets as an example that these systems can decay by a new type of process, named collective autoionization. In addition, we show that this process is surprisingly efficient, leading to ion abundances much greater than that of direct single-photon ionization. This novel collective ionization process is expected to be important in many other complex systems, e.g. macromolecules and nanoparticles, exposed to high intensity radiation fields. PMID:24406316
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 MgB_{2}. Our data reveal a strong renormalization of the dispersion (kink) at ~65meV, which is caused by the coupling of electrons to the E_{2g} phonon mode. In contrast to cuprates, the 65 meV kink in MgB_{2} does not change significantly across T_{c}. 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 T_{c} and is likely a signature of the elusive Leggett mode.
Extracting Equation of State of a Trapped Gas from the Frequency of its Collective Excitations
NASA Astrophysics Data System (ADS)
Olchanyi, Maxim; Perrin, Hélène
2013-05-01
We address the question of a relationship between frequency of small collective excitations of an unknown trapped cold gas and its Equation of State (EoS). In particular, we compare the frequency-EoS relationship obtained using a nonlinear double amplitude-coordinate perturbative expansion [M. Olshanii, H. Perrin, V. Lorent, PRL 105, 095302 (2010)] with the formula resulting from a scaling variational anzats [G.E. Astrakharchik, R. Combescot, X. Leyronas, S. Stringari, PRL 95, 030404 (2005)] and show that for power-law EoS's, the two agree exactly. We further compare predictions of both methods with ab initio numerical results. We argue that the frequencies of collective excitations represent a new reliable second thermodynamical axis, to complement the existing one, based on density profiles [N. Navon, S. Nascimbène, F. Chevy, C. Salomon, Science 328, 729 (2010)]. Supported by ONR, NSF, and IFRAF. Laboratoire de physique des lasers is UMR 7538 of CNRS and Paris 13 University.
Ndao, Abdoulaye; Salut, Roland; Baida, Fadi I.; Belkhir, Abderrahmane
2013-11-18
We present here the fabrication and the optical characterization of slanted annular aperture arrays engraved into silver film. An experimental enhanced transmission based on the excitation of the cutoff-less plasmonic guided mode of the nano-waveguides (the transmission electron microscopy mode) is demonstrated and agrees well with the theoretical predicted results. By the way, even if it is less efficient (70% → 20%), an enhanced transmission can occur at larger wavelength value (720 nm–930 nm) compared to conventional annular aperture arrays structure by correctly setting the metal thickness.
Two-photon excited whispering-gallery mode ultraviolet laser from an individual ZnO microneedle
NASA Astrophysics Data System (ADS)
Zhu, G. P.; Xu, C. X.; Zhu, J.; Lv, C. G.; Cui, Y. P.
2009-02-01
Wurtzite structural ZnO microneedles with hexagonal cross section were fabricated by vapor-phase transport method and an individual microneedle was employed as a lasing microcavity. Under excitation of a femtosecond pulse laser with 800 nm wavelength, the ultraviolet (UV) laser emission was obtained, which presented narrow linewidth and high Q value. The UV emission, resonant mechanism, and laser mode characteristics were discussed in detail. The results demonstrated that the UV laser originated from the whispering-gallery mode induced by two-photon absorption assisted by Rabi oscillation.
NASA Technical Reports Server (NTRS)
Antoni, TH.; Jung, K.; Ehrhardt, H.; Chang, E. S.
1986-01-01
At 2 eV, the simultaneous rotational-vibrational cross sections for the fundamental modes are found to be well described by the Born formula with just long-range interactions. However, this result is not obtained for pure vibrational excitation (Q branch) in the Raman-active Fermi diads. At 3.8 eV, the infrared-active v2 and v3 cross sections agree with a previous theory incorporating resonant and direct scattering coherently. Measurements on the Raman-active v1 mode indicate that theories need to account for the Fermi resonance.
Crucial Role of Internal Collective Modes in Underdoped Cuprates
NASA Astrophysics Data System (ADS)
Mallik, Aabhaas V.; Yadav, Umesh K.; Medhi, Amal; Krishnamurthy, H. R.; Shenoy, Vijay B.
The enigmatic cuprate superconductors have attracted resurgent interest with several recent reports and discussions of competing orders in the underdoped side. Motivated by this, here we address the natural question of frailty of the d-wave superconducting state in underdoped cuprates. Using a combination of theoretical approaches we study a t - J like model. We report an - as yet unexplored - instability that is brought about by an ``internal'' fluctuation (anti-symmetric mode) of the d-wave state. This new theoretical result helps in understanding recent ARPES and STM studies. We also suggest further experiments to uncover this physics. Work supported by CSIR, UGC, DST and DAE.
Quantum Phase Transitions and Collective Modes in d-Wave Superconductors
NASA Astrophysics Data System (ADS)
Vojta, Matthias; Sachdev, Subir
Fluctuations near second-order quantum phase transitions in d-wave superconductors can cause strong damping of fermionic excitations, as observed in photoemission experiments. The damping of the gapless nodal quasiparticles can arise naturally in the quantum-critical region of a transition with an additional spin-singlet, zero momentum order parameter; we argue that the transition to a dx^2-y^2+ i dxy pairing state is the most likely possibility in this category. On the other hand, the gapped antinodal quasiparticles can be strongly damped by the coupling to antiferromagnetic spin fluctuations arising from the proximity to a Neel-ordered state. We review some aspects of the low-energy field theories for both transitions and the corresponding quantum-critical behavior.In addition, we discuss the spectral properties of the collective modes associated with the proximity to a superconductor with dx^2-y^2+ i dxy symmetry, and implications for experiments.
Shaw, Pankaj Kumar Sekar Iyengar, A. N.
2015-12-15
We report on the experimental observation of canard orbit and mixed mode oscillations (MMOs) in an excitable glow discharge plasma induced by an external magnetic field perturbation using a bar magnet. At a small value of magnetic field, small amplitude quasiperiodic oscillations were excited, and with the increase in the magnetic field, large amplitude oscillations were excited. Analyzing the experimental results, it seems that the magnetic field could be playing the role of noise for such nonlinear phenomena. It is observed that the noise level increases with the increase in magnetic field strength. The experimental results have also been corroborated by a numerical simulation using a FitzHugh-Nagumo like macroscopic model derived from the basic plasma equations and phenomenology, where the noise has been included to represent the internal plasma noise. This macroscopic model shows MMO in the vicinity of the canard point when an external noise is added.
Near-field techniques for probing collective modes of anisotropic superconducting thin films
NASA Astrophysics Data System (ADS)
Stinson, H. T.; Wu, J. S.; Jiang, B. Y.; Fei, Z.; Rodin, A. S.; Chapler, B.; McLeod, A. S.; Castro-Neto, A.; Lee, Y. S.; Fogler, M. M.; Basov, D. N.
2014-03-01
We propose the use of scattering-type scanning near-field optical microscopy (s-SNOM) to characterize the collective mode spectrum of anisotropic superconductors. To probe the dispersion of collective modes with large in-plane momenta, specifically surface plasmons and guided wave modes, we model the real-space interference patterns of modes launched by the sharp s-SNOM tip and their reflections off physical and electronic boundaries. In addition, we show that s-SNOM spectroscopy allows for a direct probe of the c-axis superfluid density in underdoped anisotropic superconductors with nanoscale spatial resolution.
Pang, Yong; Zhang, Xiaoliang; Xie, Zhentian; Wang, Chunsheng; Vigneron, Daniel B
2011-11-01
Double-tuned radio-frequency (RF) coils for heteronuclear mangentic resonance (MR) require sufficient electromagnetic isolation between the two resonators operating at two Larmor frequencies and independent tuning in order to attain highly efficient signal acquisition at each frequency. In this work, a novel method for double-tuned coil design at 7T based on the concept of common-mode differential-mode (CMDM) was developed and tested. Common mode (CM) and differential mode (DM) currents exist within two coupled parallel transmission lines, e.g., microstrip lines, yielding two different current distributions. The electromagnetic (EM) fields of the CM and DM are orthogonal to each other, and thus, the two modes are intrinsically EM decoupled. The modes can be tuned independently to desired frequencies, thus satisfying the requirement of dual-frequency MR applications. To demonstrate the feasibility and efficiency of the proposed CMDM technique, CMDM surface coils and volume coils using microstrip transmission line for (1)H and (13)C MRI/MRSI were designed, constructed, and tested at 7T. Bench test results showed that the isolations between the two frequency channels of the CMDM surface coil and volume coil were better than -30 and -25 dB, respectively. High quality MR phantom images were also obtained using the CMDM coils. The performance of the CMDM technique was validated through a comparison with the conventional two-pole design method at 7T. The proposed CMDM technique can be also implemented by using other coil techniques such as lumped element method, and can be applied to designing double-tuned parallel imaging coil arrays. Furthermore, if the two resonant modes of a CMDM coil were tuned to the same frequency, the CMDM coil becomes a quadrature coil due to the intrinsic orthogonal field distribution of CM and DM.
1986-11-01
Excitation of the Internal Vibrational Mode of a Diatomic Molecule Adsorbed on a Metal Surface m by ’ Andre Peremans, Jacques Darville , Jean-Marie...Andre Peremans, Jacques Darville , Jean-Marie Gilles and Thomas F. George 13. TYPE OF REPORT 13b. TIME COVERED 14. DATE OF REPORT (Yr. Mo.. Dayl As...ON A METAL SURFACE h Andr& Peremans , Jacques Darville and Jean-Marie Gilles _ _ _ _ Laboratoire de Spectroscopie Mol6culaire de Surface Accesnion
Collective-mode dynamics in a spin-orbit-coupled Bose-Einstein condensate
NASA Astrophysics Data System (ADS)
Chen, Zhu; Zhai, Hui
2012-10-01
Recently a spin-orbit-coupled Bose condensate has been realized experimentally using two-photon Raman coupling, and this condensate exhibits two distinct equilibrium phases known as the plane wave phase and the stripe phase at equilibrium. In this Rapid Communication we show that such condensate exhibits unique dynamic behaviors, which originate from interactions and are absent in a noninteracting system. In the plane wave phase, a dipole mode will induce a breathing mode in its perpendicular plane and vice versa. This is a cooperation effect between spin-velocity locking and spin-dependent interaction. While in the stripe phase, a breathing mode will induce the sliding mode of the density stripe along its perpendicular direction. This reflects the fact that the sliding mode is the gapless excitation in this phase due to spontaneous spatial translation symmetry breaking.
NASA Astrophysics Data System (ADS)
Stinson, H. T.; Wu, J. S.; Jiang, B. Y.; Fei, Z.; Rodin, A. S.; Chapler, B. C.; McLeod, A. S.; Castro Neto, A.; Lee, Y. S.; Fogler, M. M.; Basov, D. N.
2014-07-01
We investigate near-field infrared spectroscopy and superfluid polariton imaging experiments on conventional and unconventional superconductors. Our modeling shows that near-field spectroscopy can measure the magnitude of the superconducting energy gap in Bardeen-Cooper-Schrieffer-like superconductors with nanoscale spatial resolution. We demonstrate how the same technique can measure the c-axis plasma frequency, and thus the c-axis superfluid density, of layered unconventional superconductors with a similar spatial resolution. Our modeling also shows that near-field techniques can image superfluid surface mode interference patterns near physical and electronic boundaries. We describe how these images can be used to extract the collective mode dispersion of anisotropic superconductors with subdiffractional spatial resolution.
NASA Technical Reports Server (NTRS)
Kojima, H.; Matsumoto, H.; Omura, Y.; Tsurutani, B. T.
1989-01-01
An ion beam resonates with R-mode waves at a high-frequency RH mode and a low-frequency RL mode. The nonlinear evolution of ion beam-generated RH waves is studied here by one-dimensional hybrid computer experiments. Both wave-particle and subsequent wave-wave interactions are examined. The competing process among coexisting RH and RL mode beam instabilities and repeated decay instabilities triggered by the beam-excited RH mode waves is clarified. It is found that the quenching of the RH instability is not caused by a thermal spreading of the ion beam, but by the nonlinear wave-wave coupling process. The growing RH waves become unstable against the decay instability. This instability involves a backward-traveling RH electromagnetic wave and a forward-traveling longitudinal sound wave. The inverse cascading process is found to occur faster than the growth of the RL mode. Wave spectra decaying from the RH waves weaken as time elapses and the RL mode waves become dominant at the end of the computer experiment.
Photo-thermal quartz tuning fork excitation for dynamic mode atomic force microscope
Bontempi, Alexia; Teyssieux, Damien; Thiery, Laurent; Hermelin, Damien; Vairac, Pascal; Friedt, Jean-Michel
2014-10-13
A photo-thermal excitation of a Quartz Tuning Fork (QTF) for topographic studies is introduced. The non-invasive photo-thermal excitation presents practical advantages compared to QTF mechanical and electrical excitations, including the absence of the anti-resonance and its associated phase rotation. Comparison between our theoretical model and experiments validate that the optical transduction mechanism is a photo-thermal rather than photo-thermoacoustic phenomenon. Topographic maps in the context of near-field microscopy distance control have been achieved to demonstrate the performance of the system.
Goldstone Mode Induced by Skyrmions and Collective Modes in Disordered Quantum Hall Crystals
NASA Astrophysics Data System (ADS)
Kanazawa, I.
2015-10-01
We have proposed the effective Lagrangian density for the skyrmion-like solitons around the filling factor v ∼ 1, and have introduced the massless gauge field (Goldstone mode) induced by the hedgehog-like solitons. We have discussed the skyrmion glassy behaviour.
Collective modes in strongly correlated yukawa liquids: waves in dusty plasmas.
Kalman, G; Rosenberg, M; DeWitt, H E
2000-06-26
We determine the collective mode structure of a strongly correlated Yukawa fluid, with the purpose of analyzing wave propagation in a strongly coupled dusty plasma. We identify a longitudinal plasmon and a transverse shear mode. The dispersion is characterized by a low- k acoustic behavior, a frequency maximum well below the plasma frequency, and a high- k merging of the two modes around the Einstein frequency of localized oscillations. The damping effect of collisions between neutrals and dust grains is estimated.
Szilner, S.; Jelavic-Malenica, D.; Soic, N.; Corradi, L.; Fioretto, E.; Sahin, E.; Silvestri, R.; Stefanini, A. M.; Valiente-Dobon, J. J.; Haas, F.; Lebhertz, D.; Bouhelal, M.; Caurier, E.; Courtin, S.; Goasduff, A.; Nowacki, F.; Ur, C. A.; Beghini, S.; Farnea, E.
2011-07-15
New {gamma} transitions have been identified in argon isotopes in {sup 40}Ar + {sup 208}Pb multiple transfer reactions by exploiting, in a fragment-{gamma} measurement, the new generation of magnetic spectrometers based on trajectory reconstruction coupled to large {gamma} arrays. The coupling of single-particle degrees of freedom to nuclear vibration quanta was discussed. The interpretation of the newly observed states within a particle-phonon coupling picture was used to consistently follow, via their excitation energies, the evolution of collectivity in odd Ar isotopes. The proposed level schemes are supported by the results of sd-pf shell-model calculations, which have been also employed to evaluate the strength functions of the populated states.
NASA Astrophysics Data System (ADS)
Chen, Yong; Yan, Zhenya
2017-01-01
The effect of derivative nonlinearity and parity-time-symmetric (PT -symmetric) potentials on the wave propagation dynamics is explored in the derivative nonlinear Schrödinger equation, where the physically interesting Scarf-II and harmonic-Hermite-Gaussian potentials are chosen. We study numerically the regions of unbroken and broken linear PT -symmetric phases and find some stable bright solitons of this model in a wide range of potential parameters even though the corresponding linear PT -symmetric phases are broken. The semielastic interactions between particular bright solitons and exotic incident waves are illustrated such that we find that particular nonlinear modes almost keep their shapes after interactions even if the exotic incident waves have evidently been changed. Moreover, we exert the adiabatic switching on PT -symmetric potential parameters such that a stable nonlinear mode with the unbroken linear PT -symmetric phase can be excited to another stable nonlinear mode belonging to the broken linear PT -symmetric phase.
Long, Yongbing; Shen, Liang; Xu, Haitao; Deng, Haidong; Li, Yuanxing
2016-01-01
Graphene perfect absorbers with ultranarrow bandwidth are numerically proposed by employing a subwavelength dielectric grating to excite the guided-mode resonance of one-dimensional photonic crystals (1DPCs). Critical coupling of the guided-mode resonance of 1DPCs to graphene can produce perfect absorption with a ultranarrow bandwidth of 0.03 nm. The quality factor of the absorption peak reaches a ultrahigh value of 20000. It is also found that the resonant absorption peaks can be tuned by controlling the dispersion line of the guided mode and the period of the grating. When the parameters of the grating and the 1DPCs are suitably set, the perfect absorption peaks can be tuned to any randomly chosen wavelength in the visible wavelength range. PMID:27577721
Resonant and non-resonant internal kink modes excited by the energetic electrons on HL-2A tokamak
NASA Astrophysics Data System (ADS)
Yu, L. M.; Chen, W.; Jiang, M.; Shi, Z. B.; Ji, X. Q.; Ding, X. T.; Li, Y. G.; Ma, R. R.; Shi, P. W.; Song, S. D.; Yuan, B. S.; Zhou, Y.; Ma, R.; Song, X. M.; Dong, J. Q.; Xu, M.; Liu, Y.; Yan, L. W.; Yang, Q. W.; Xu, Y. H.; Duan, X. R.; HL-2A Team
2017-03-01
Strong resonant and non-resonant internal kink modes (abbreviated as RKs and NRKs, respectively), which are also called resonant and non-resonant fishbones, are observed on HL-2A tokamak with high-power ECRH + ECCD‑ (or ECRH) and ECRH + ECCD+, respectively. (‘Resonant’ derives from the existence of q = 1 surface (the resonant surface), and ‘non-resonant’ originates from the absence of q = 1 surface ({{q}\\text{min}}>1 ). ECCD+ and ECCD‑ mean the driving direction of energetic electrons is the same and opposite to plasma current, respectively.) RK has features of periodic strong bursting amplitude and rapid chirping-down frequency, but NRK usually has the saturated amplitude, slow changed or constant frequency and long-lasting time. The NRK excited by energetic electrons is found for the first time. The reversed q-profiles are formed, and q min decreases during plasma current ramp-up. The value of q min is slightly smaller and a bit bigger than unity for RK and NRK conditions, respectively. The internal kink mode (IKM) structures of RKs and NRKs are confirmed by the ECEI system. Although there are different current drive directions of ECCD for excitation of RK and NRK, they all propagate in electron diamagnetic directions in poloidal. The radial mode structures, frequency and growth rate for IKMs are obtained by solving the dispersion relationship. The NRK is stable when q min is larger than a certain value, and with the decreasing q min the frequency drops, but the growth rate almost keeps constant when {{q}\\text{min}}>1 . This result is in agreement with experimental observation. Studying IKMs excited by energetic electrons can provide important experimental experiences for ITER, because the NRKs may be excited by high-power non-inductive drive of ECCD or ECRH in the operation of hybrid scenarios.
NASA Astrophysics Data System (ADS)
Pei, Youbin; Xiang, Nong; Hu, Youjun; Todo, Y.; Li, Guoqiang; Shen, Wei; Xu, Liqing
2017-03-01
Kinetic-MagnetoHydroDynamic hybrid simulations are carried out to investigate fishbone modes excited by fast ions on the Experimental Advanced Superconducting Tokamak. The simulations use realistic equilibrium reconstructed from experiment data with the constraint of the q = 1 surface location (q is the safety factor). Anisotropic slowing down distribution is used to model the distribution of the fast ions from neutral beam injection. The resonance condition is used to identify the interaction between the fishbone mode and the fast ions, which shows that the fishbone mode is simultaneously in resonance with the bounce motion of the trapped particles and the transit motion of the passing particles. Both the passing and trapped particles are important in destabilizing the fishbone mode. The simulations show that the mode frequency chirps down as the mode reaches the nonlinear stage, during which there is a substantial flattening of the perpendicular pressure of fast ions, compared with that of the parallel pressure. For passing particles, the resonance remains within the q = 1 surface, while, for trapped particles, the resonant location moves out radially during the nonlinear evolution. In addition, parameter scanning is performed to examine the dependence of the linear frequency and growth rate of fishbones on the pressure and injection velocity of fast ions.
Renormalization of Collective Modes in Large-Scale Neural Dynamics
NASA Astrophysics Data System (ADS)
Moirogiannis, Dimitrios; Piro, Oreste; Magnasco, Marcelo O.
2017-03-01
The bulk of studies of coupled oscillators use, as is appropriate in Physics, a global coupling constant controlling all individual interactions. However, because as the coupling is increased, the number of relevant degrees of freedom also increases, this setting conflates the strength of the coupling with the effective dimensionality of the resulting dynamics. We propose a coupling more appropriate to neural circuitry, where synaptic strengths are under biological, activity-dependent control and where the coupling strength and the dimensionality can be controlled separately. Here we study a set of N→ ∞ strongly- and nonsymmetrically-coupled, dissipative, powered, rotational dynamical systems, and derive the equations of motion of the reduced system for dimensions 2 and 4. Our setting highlights the statistical structure of the eigenvectors of the connectivity matrix as the fundamental determinant of collective behavior, inheriting from this structure symmetries and singularities absent from the original microscopic dynamics.
Multiscale theory of collective and quasiparticle modes in quantum nanosystems.
Ortoleva, P; Iyengar, S S
2008-04-28
A quantum nanosystem (such as a quantum dot, nanowire, superconducting nanoparticle, or superfluid nanodroplet) involves widely separated characteristic lengths. These lengths range from the average nearest-neighbor distance between the constituent fermions or bosons, or the lattice spacing for a conducting metal, to the overall size of the quantum nanosystem (QN). This suggests the wave function has related distinct dependencies on the positions of the constituent fermions and bosons. We show how the separation of scales can be used to generate a multiscale perturbation scheme for solving the wave equation. Results for electrons or other fermions show that, to lowest order, the wave function factorizes into an antisymmetric (fermion) part and a symmetric (bosonlike) part. The former manifests the short-range/exclusion-principle behavior, while the latter corresponds to collective behaviors, such as plasmons, which have a boson character. When the constituents are bosons, multiscale analysis shows that, to lowest order, the wave function can also factorize into short- and long-scale parts. However, to ensure that the product wave function has overall symmetric particle label exchange behavior, there could, in principle, be states of the boson nanosystem where both the short- and long-scale factors are either boson- or fermionlike; the latter "dual fermion" states are, due to their exclusion-principle-like character, of high energy (i.e., single particle states cannot be multiply occupied). The multiscale perturbation analysis is used to argue for the existence of a coarse-grained wave equation for bosonlike collective behaviors. Quasiparticles, with effective mass and interactions, emerge naturally as consequences of the long-scale dynamics of the constituent particles. The multiscale framework holds promise for facilitating QN computer simulations and novel approximation schemes.
Solar seismology. II - The stochastic excitation of the solar p-modes by turbulent convection
NASA Technical Reports Server (NTRS)
Goldreich, P.; Keeley, D. A.
1977-01-01
We test the hypothesis that the solar p-modes are stabilized by damping due to turbulent viscosity in the convective zone. Starting from the assumption that the modes are stable, we calculate expectation values for the modal energies. We find that the interaction between a p-mode and the turbulent convection is such that the modal energy tends toward equipartition with the kinetic energy of turbulent eddies whose lifetimes are comparable to the modal period. From the calculated values of the modal energies, we compute rms surface velocity amplitudes. Our predicted rms surface velocities range from 0.01 cm/sec for the fundamental radial mode to 0.6 cm/sec for the radial mode whose period is approximately 5 minutes. The predicted surface velocities for the low order p-modes are much smaller than the velocities inferred from recent observations.
Kadhane, U; Misra, D; Singh, Y P; Tribedi, Lokesh C
2003-03-07
Projectile deexcitation Lyman x-ray emission following electron capture and K excitation has been studied in collisions of bare and Li-like sulphur ions (of energy 110 MeV) with fullerenes (C(60)/C(70)) and different gaseous targets. The intensity ratios of different Lyman x-ray lines in collisions with fullerenes are found to be substantially lower than those for the gas targets, both for capture and excitation. This has been explained in terms of a model based on "solidlike" effect, namely, wakefield induced stark mixing of the excited states populated via electron capture or K excitation: a collective phenomenon of plasmon excitation in the fullerenes under the influence of heavy, highly charged ions.
Effects of Berry Curvature on the Collective Modes of Ultracold Gases
NASA Astrophysics Data System (ADS)
Price, Hannah M.; Cooper, Nigel R.
2013-11-01
Topological energy bands have important geometrical properties described by the Berry curvature. We show that the Berry curvature changes the hydrodynamic equations of motion for a trapped Bose-Einstein condensate, and causes significant modifications to the collective mode frequencies. We illustrate our results for the case of two-dimensional Rashba spin-orbit coupling in a Zeeman field. Using an operator approach, we derive the effects of Berry curvature on the dipole mode in very general settings. We show that the sizes of these effects can be large and readily detected in experiment. Collective modes therefore provide a sensitive way to measure geometrical properties of energy bands.
Sokolov, V I; Marusin, N V; Molchanova, S I; Savelyev, A G; Khaydukov, E V; Panchenko, V Ya
2014-11-30
The problem of reflection of a TE-polarised Gaussian light beam from a layered structure under conditions of resonance excitation of waveguide modes using a total internal reflection prism is considered. Using the spectral approach we have derived the analytic expressions for the mode propagation lengths, widths and depths of m-lines (sharp and narrow dips in the angular dependence of the specular reflection coefficient), depending on the structure parameters. It is shown that in the case of weak coupling, when the propagation lengths l{sub m} of the waveguide modes are mainly determined by the extinction coefficient in the film, the depth of m-lines grows with the mode number m. In the case of strong coupling, when l{sub m} is determined mainly by the radiation of modes into the prism, the depth of m-lines decreases with increasing m. The change in the TE-polarised Gaussian beam shape after its reflection from the layered structure is studied, which is determined by the energy transfer from the incident beam into waveguide modes that propagate along the structure by the distance l{sub m}, are radiated in the direction of specular reflection and interfere with a part of the beam reflected from the working face of the prism. It is shown that this interference can lead to the field intensity oscillations near m-lines. The analysis of different methods for determining the parameters of thin-film structures is presented, including the measurement of mode angles θ{sub m} and the reflected beam shape. The methods are based on simultaneous excitation of a few waveguide modes in the film with a strongly focused monochromatic Gaussian beam, the waist width of which is much smaller than the propagation length of the modes. As an example of using these methods, the refractive index and the thickness of silicon monoxide film on silica substrate at the wavelength 633 nm are determined. (fibre and integrated-optical structures)
Castro Palacio, J C; Velazquez Abad, L; Lombardi, A; Aquilanti, V; Rubayo Soneíra, J
2007-05-07
Molecular dynamics simulations and both normal mode and hyperspherical mode analyses of NO-doped Kr solid are carried out in order to get insights into the structural relaxation of the medium upon electronic excitation of the NO molecule. A combined study is reported on the time evolution of the cage radius and on the density of vibrational states, according to the hyperspherical and normal mode analyses. For the hyperspherical modes, hyper-radial and grand angular contributions are considered. For the normal modes, radial and tangential contributions are examined. Results show that the first shell radius dynamics is driven by modes with frequencies at approximately 47 and approximately 15 cm-1. The first one is related to the ultrafast regime where a large part of the energy is transmitted to the lattice and the second one to relaxation and slow redistribution of the energy. The density of vibrational states gamma(omega) is characterized by a broad distribution of bands peaking around the frequencies of approximately 13, approximately 19, approximately 25, approximately 31, approximately 37, approximately 47, and approximately 103 cm-1 (very small band). The dominant modes in the relaxation process were at 14.89, 23.49, and 53.78 cm-1; they present the largest amplitudes and the greatest energy contributions. The mode at 14.89 cm-1 is present in both the fit of the first shell radius and in the hyper-radial kinetic energy spectrum and resulted the one with the largest amplitude, although could not be revealed by the total kinetic energy power spectrum.
Multiple hot-carrier collection in photo-excited graphene Moiré superlattices
Wu, Sanfeng; Wang, Lei; Lai, You; Shan, Wen-Yu; Aivazian, Grant; Zhang, Xian; Taniguchi, Takashi; Watanabe, Kenji; Xiao, Di; Dean, Cory; Hone, James; Li, Zhiqiang; Xu, Xiaodong
2016-01-01
In conventional light-harvesting devices, the absorption of a single photon only excites one electron, which sets the standard limit of power-conversion efficiency, such as the Shockley-Queisser limit. In principle, generating and harnessing multiple carriers per absorbed photon can improve efficiency and possibly overcome this limit. We report the observation of multiple hot-carrier collection in graphene/boron-nitride Moiré superlattice structures. A record-high zero-bias photoresponsivity of 0.3 A/W (equivalently, an external quantum efficiency exceeding 50%) is achieved using graphene’s photo-Nernst effect, which demonstrates a collection of at least five carriers per absorbed photon. We reveal that this effect arises from the enhanced Nernst coefficient through Lifshtiz transition at low-energy Van Hove singularities, which is an emergent phenomenon due to the formation of Moiré minibands. Our observation points to a new means for extremely efficient and flexible optoelectronics based on van der Waals heterostructures. PMID:27386538
Control of self-excitation mode in thermoacoustic system using heat phase adjuster
NASA Astrophysics Data System (ADS)
Kido, Aiko; Sakamoto, Shin-ichi; Taga, Kazusa; Watanabe, Yoshiaki
2016-07-01
The capability of a heat phase adjuster (HPA) to control the resonance mode in a loop-tube-type thermoacoustic system by locally heating the outside is experimentally investigated. It is shown that the HPA enables the resonance mode of the tube to shift to lower modes with higher thermoacoustic conversion efficiency, thus significantly enhancing the energy conversion efficiency. The transition of the resonance mode due to the stepwise change in the input electric power to the HPA is also investigated. As a result, it is demonstrated that the resonance mode changes with the temperature and a threshold exists for the HPA temperature at which the transition is induced. These results suggest the possibility of externally controlling a loop-tube-type thermoacoustic system.
NASA Astrophysics Data System (ADS)
Li, Xuechen; Niu, Dongying; Yin, Zengqian; Fang, Tongzhen; Wang, Long
2012-08-01
The characteristics of dielectric barrier discharge excited by a saw-tooth voltage are simulated in atmospheric pressure helium based on a one-dimensional fluid model. A stepped discharge is obtained per half voltage cycle with gas gap width less than 2 mm by the simulation, which is different to the pulsed discharge excited by a sinusoidal voltage. For the stepped discharge, the plateau duration increases with increasing the voltage amplitude and decreasing the gas gap. Therefore, uniform discharge with high temporal duty ratio can be realized with small gap through increasing the voltage amplitude. The maximal densities of both electron and ion appear near the anode and the electric field is almost uniformly distributed along the gap, which indicates that the stepped discharge belongs to a Townsend mode. In contrast to the stepped discharge with small gas gap, a pulsed discharge can be obtained with large gas gap. Through analyzing the spatial density distributions of electron and ion and the electric field, the pulsed discharge is in a glow mode. The voltage-current (V-I) characteristics are analyzed for the above mentioned discharges under different gas gaps, from which the different discharge modes are verified.
NASA Astrophysics Data System (ADS)
Labombard, B.; Golfinopoulos, T.; Parker, R.; Burke, W.; Leccacorvi, R.; Vieira, R.; Zaks, J.; Granetz, R.; Greenwald, M.; Marmar, E.; Porkolab, M.; Wolfe, S.; Woskov, P.; Wuktich, S.
2011-10-01
Experiments indicate that short wavelength, drift-Alfvenic turbulence largely sets the transport levels in the plasma edge: pressure gradients in L and H-mode are `clamped' at canonical values of the MHD parameter (αMHD) ; broadband and coherent fluctuations have strong magnetic signatures, with k⊥ρs ~ 0.1 being prominent. A quasi-coherent mode (50 kHz < f < 150 kHz, 1 < k⊥ < 2 cm-1) drives particle transport in C-Mod's EDA H-modes, making them steady-state without ELMs. With the idea of exciting, controlling or otherwise exploiting this transport behavior, we are developing a novel, high k⊥ antenna system to drive drift-Alfvenic modes at the outer midplane with k⊥ ~ 1.5 cm-1. A `shoelace' style winding is placed in close proximity to the last-closed flux surface. In principle, this scheme inductively drives parallel current fluctuations that mimic intrinsic plasma fluctuations but at larger amplitude. Details of the antenna system design, its planned modes of operation and initial results will be presented. Supported by USDoE award DE-FC02-99ER54512.
Enhanced modes excitation in photonic crystal fiber by long-period gratings for sensing application
NASA Astrophysics Data System (ADS)
Zheng, Shijie; Zhu, Yinian
2016-03-01
Evanescent-wave sensing platform is proposed by two interrogating schemes, core-cladding coupling and core-cladding-core coupling and re-coupling, in endlessly single-mode photonic crystal fiber (ESM-PCF) with long-period gratings (LPGs). The sensing characteristics are experimentally investigated by stress relaxation technique and point-by-point grating inscription via CO2 laser. It shows that the evanescent wave in cladding mode is significantly increased due to LPGs, compared with in core mode only. The introduced concept will further help explore the PCF evanescent-wave sensing and its applications.
Magnetostatic spin wave modes excitation in yttrium-iron-garnet film under various temperatures
NASA Astrophysics Data System (ADS)
Kaack, M.; Jun, S.; Nikitov, S. A.; Pelzl, J.
1999-09-01
Temperature-dependent magnetostatic spin wave modes spectra in a ferromagnetic thin film of yttrium-iron-garnet are investigated by means of conventional and photothermally modulated ferromagnetic resonance techniques. Values for the anisotropy field are derived from the evaluation of resonance spectra. In the wide range of temperature the resonance characteristics of spin wave modes spectra are consistent with the Damon-Eshbach theory. Close to the Curie temperature they, however, strongly deviate from the theoretical predictions.
Fishbone Mode Excited by Deeply Trapped Energetic Beam Ions in EAST
NASA Astrophysics Data System (ADS)
Zheng, Ting; Wu, Bin; Xu, Liqing; Hu, Chundong; Zang, Qing; Ding, Siye; Li, Yingying; Wu, Xingquan; Wang, Jinfang; Shen, Biao; Zhong, Guoqiang; Li, Hao; Shi, Tonghui; EAST Team
2016-06-01
This paper describes the fishbone mode phenomena during the injection of high-power neutral beams in EAST (Experimental Advanced Superconducting Tokamak). The features of the fishbone mode are presented. The change in frequency of the mode during a fishbone burst is from 1 kHz to 6 kHz. The nonlinear behavior of the fishbone mode is analyzed by using a prey-predator model, which is consistent with the experimental results. This model indicates that the periodic oscillations of the fishbone mode always occur near the critical value of fast ion beta. Furthermore, the neutral beam analysis for the discharge is done by using the NUBEAM module of the TRANSP code. According to the numerical simulation results and theoretical calculation, it can be concluded that the fishbone mode is driven by the deeply trapped energetic beam ions in EAST. supported by the National Magnetic Confinement Fusion Science Program of China (Nos. 2013GB101001, 2014DFG61950 and 2013GB112003) and National Natural Science Foundation of China (Nos. 11175211 and 11275233)
NASA Astrophysics Data System (ADS)
Braviner, Harry J.; Ogilvie, Gordon I.
2015-02-01
We model a tidally forced star or giant planet as a Maclaurin spheroid, decomposing the motion into the normal modes found by Bryan. We first describe the general prescription for this decomposition and the computation of the tidal power. Although this formalism is very general, forcing due to a companion on a misaligned, circular orbit is used to illustrate the theory. The tidal power is plotted for a variety of orbital radii, misalignment angles, and spheroid rotation rates. Our calculations are carried out including all modes of degree l ≤ 4, and the same degree of gravitational forcing. Remarkably, we find that for close orbits (a/R* ≈ 3) and rotational deformations that are typical of giant planets (e ≈ 0.4) the l = 4 component of the gravitational potential may significantly enhance the dissipation through resonance with surface gravity modes. There are also a large number of resonances with inertial modes, with the tidal power being locally enhanced by up to three orders of magnitude. For very close orbits (a/R* ≈ 3), the contribution to the power from the l = 4 modes is roughly the same magnitude as that due to the l = 3 modes.
High Energy Plasmas, General Relativity and Collective Modes in the Vicinity of Black Holes*
NASA Astrophysics Data System (ADS)
Coppi, B.
2009-05-01
Plasmas around black holes can take different equilibrium configurations^1 from those known from fluid theory as the vertical Lorentz compression due to plasma currents can overtake that of the gravitational force. In a disk with a ``seed'' magnetic field, axisymmetric modes as well as tri-dimensional spirals can be excited by the combined effects of the radial gradient of the plasma rotation frequency and of the plasma pressure gradient^2. The spirals' properties depend strongly on their vertical structure^3. Axisymmetric modes can produce vertical counter-flows of thermal energy and particles and be candidates for the origin of the winds emanating from disks in Active Galactic Nuclei (AGN's)^2. The excitation of radially localized density spirals corotating with the plasma near a black hole can provide an explanation for^4 the observed Quasi Periodic Oscillations (QPO's) of the X-ray emission from compact objects. Convective spiral modes^3 that are purely oscillatory in time and not localized radially can acquire their amplitudes from coupling to unstable modes and provide transport^3 of angular momentum toward the outer region of the disk structure.*Sponsored in part by the U.S. DOE. ^1B. Coppi and F. Rousseau, Ap. J., 641, 458 (2006). ^2B. Coppi, Europhys. Letters 82, 19001 (2008). ^3B. Coppi, MIT/LNS Report 08/08, submitted to A&A (2008). ^4B. Coppi and P. Rebusco, Paper P5.154, E.P.S. Conf. Pl. Phys. (Crete, 2008).
Surface Collective Modes in the Topological Insulators Bi2 Se3 and Bi0.5 Sb1.5 Te3 -xSex
NASA Astrophysics Data System (ADS)
Kogar, A.; Vig, S.; Thaler, A.; Wong, M. H.; Xiao, Y.; Reig-i-Plessis, D.; Cho, G. Y.; Valla, T.; Pan, Z.; Schneeloch, J.; Zhong, R.; Gu, G. D.; Hughes, T. L.; MacDougall, G. J.; Chiang, T.-C.; Abbamonte, P.
2015-12-01
We used low-energy, momentum-resolved inelastic electron scattering to study surface collective modes of the three-dimensional topological insulators Bi2 Se3 and Bi0.5 Sb1.5 Te3 -xSex . Our goal was to identify the "spin plasmon" predicted by Raghu and co-workers [Phys. Rev. Lett. 104, 116401 (2010)]. Instead, we found that the primary collective mode is a surface plasmon arising from the bulk, free carriers in these materials. This excitation dominates the spectral weight in the bosonic function of the surface χ"(q ,ω ) at THz energy scales, and is the most likely origin of a quasiparticle dispersion kink observed in previous photoemission experiments. Our study suggests that the spin plasmon may mix with this other surface mode, calling for a more nuanced understanding of optical experiments in which the spin plasmon is reported to play a role.
Español, Malena I; Rotstein, Horacio G
2015-06-01
The Oregonator is the simplest chemically plausible model for the Belousov-Zhabotinsky reaction. We investigate the response of the Oregonator to sinusoidal inputs with amplitudes and frequencies within plausible ranges. We focus on a regime where the unforced Oregonator is excitable (with no sustained oscillations). We use numerical simulations and dynamical systems tools to both characterize the response patterns and explain the underlying dynamic mechanisms.
Photo-excited charge carriers suppress sub-terahertz phonon mode in silicon at room temperature
Liao, Bolin; Maznev, A. A.; Nelson, Keith A.; Chen, Gang
2016-01-01
There is a growing interest in the mode-by-mode understanding of electron and phonon transport for improving energy conversion technologies, such as thermoelectrics and photovoltaics. Whereas remarkable progress has been made in probing phonon–phonon interactions, it has been a challenge to directly measure electron–phonon interactions at the single-mode level, especially their effect on phonon transport above cryogenic temperatures. Here we use three-pulse photoacoustic spectroscopy to investigate the damping of a single sub-terahertz coherent phonon mode by free charge carriers in silicon at room temperature. Building on conventional pump–probe photoacoustic spectroscopy, we introduce an additional laser pulse to optically generate charge carriers, and carefully design temporal sequence of the three pulses to unambiguously quantify the scattering rate of a single-phonon mode due to the electron–phonon interaction. Our results confirm predictions from first-principles simulations and indicate the importance of the often-neglected effect of electron–phonon interaction on phonon transport in doped semiconductors. PMID:27731406
Dynamical structure factors and excitation modes of the bilayer Heisenberg model
NASA Astrophysics Data System (ADS)
Lohöfer, M.; Coletta, T.; Joshi, D. G.; Assaad, F. F.; Vojta, M.; Wessel, S.; Mila, F.
2015-12-01
Using quantum Monte Carlo simulations along with higher-order spin-wave theory, bond-operator and strong-coupling expansions, we analyze the dynamical spin structure factor of the spin-half Heisenberg model on the square-lattice bilayer. We identify distinct contributions from the low-energy Goldstone modes in the magnetically ordered phase and the gapped triplon modes in the quantum disordered phase. In the antisymmetric (with respect to layer inversion) channel, the dynamical spin structure factor exhibits a continuous evolution of spectral features across the quantum phase transition, connecting the two types of modes. Instead, in the symmetric channel, we find a depletion of the spectral weight when moving from the ordered to the disordered phase. While the dynamical spin structure factor does not exhibit a well-defined distinct contribution from the amplitude (or Higgs) mode in the ordered phase, we identify an only marginally damped amplitude mode in the dynamical singlet structure factor, obtained from interlayer bond correlations, in the vicinity of the quantum critical point. These findings provide quantitative information in direct relation to possible neutron or light scattering experiments in a fundamental two-dimensional quantum-critical spin system.
Photo-excited charge carriers suppress sub-terahertz phonon mode in silicon at room temperature
NASA Astrophysics Data System (ADS)
Liao, Bolin; Maznev, A. A.; Nelson, Keith A.; Chen, Gang
2016-10-01
There is a growing interest in the mode-by-mode understanding of electron and phonon transport for improving energy conversion technologies, such as thermoelectrics and photovoltaics. Whereas remarkable progress has been made in probing phonon-phonon interactions, it has been a challenge to directly measure electron-phonon interactions at the single-mode level, especially their effect on phonon transport above cryogenic temperatures. Here we use three-pulse photoacoustic spectroscopy to investigate the damping of a single sub-terahertz coherent phonon mode by free charge carriers in silicon at room temperature. Building on conventional pump-probe photoacoustic spectroscopy, we introduce an additional laser pulse to optically generate charge carriers, and carefully design temporal sequence of the three pulses to unambiguously quantify the scattering rate of a single-phonon mode due to the electron-phonon interaction. Our results confirm predictions from first-principles simulations and indicate the importance of the often-neglected effect of electron-phonon interaction on phonon transport in doped semiconductors.
Baldini, Edoardo; Mann, Andreas; Borroni, Simone; Arrell, Christopher; van Mourik, Frank; Carbone, Fabrizio
2016-01-01
A femtosecond pump-probe setup is described that is optimised for broadband transient reflectivity experiments on solid samples over a wide temperature range. By combining high temporal resolution and a broad detection window, this apparatus can investigate the interplay between coherent collective modes and high-energy electronic excitations, which is a distinctive characteristic of correlated electron systems. Using a single-shot readout array detector at frame rates of 10 kHz allows resolving coherent oscillations with amplitudes <10−4. We demonstrate its operation on the charge-transfer insulator La2CuO4, revealing coherent phonons with frequencies up to 13 THz and providing access into their Raman matrix elements. PMID:27990455
Laboratory experiment on the excitation of whistler-mode chorus waves
NASA Astrophysics Data System (ADS)
An, Xin; van Compernolle, Bart; Bortnik, Jacob; Decyk, Viktor; Thorne, Richard
2016-10-01
Whistler-mode chorus waves play an important role in accelerating electrons to relativistic energies in the heart of the outer radiation belt, as well as in precipitating electrons to the atmosphere. An experiment in the Large Plasma Device at UCLA generates both broadband and discrete chirping whistler-mode emissions using a gyrating electron beam injected into a cold background plasma. The mode structure of these emissions is identified using a phase-correlation technique. The emission forms of the whistler waves depend on plasma density, beam density and magnetic field profiles. A kinetic simulation in accordance with the experiment shows an initial relaxation of the electron beam by Langmuir waves and subsequently growing whistler waves through cyclotron resonance and Landau resonance. The research was funded by the Department of Energy and the National Science Foundation by Grant DE-SC0010578 and was also funded by NASA Grant NNX16AG21G.
Multiple-mode excitation in spin-transfer nanocontacts with dynamic polarizer
NASA Astrophysics Data System (ADS)
Wang, N.; Wang, X. L.; Qin, W.; Yeung, S. H.; Kwok, D. T. K.; Wong, H. F.; Xue, Q.; Chu, P. K.; Leung, C. W.; Ruotolo, A.
2011-06-01
We report our study on the emission response of a magnetic nanocontact with dynamic polarizer in perpendicular magnetic field. In this configuration three modes are accessible, two of which correspond to the precessional motion of a vortex in one of the two ferromagnetic layers with the other working as a static polarizer. At high currents a third mode can be observed that is ascribed to the simultaneous precession of two vortices, one in each layer, with the other layer working as a dynamic polarizer.
Higher-harmonic collective modes in a trapped gas from second-order hydrodynamics
NASA Astrophysics Data System (ADS)
Lewis, W. E.; Romatschke, P.
2017-02-01
Utilizing a second-order hydrodynamics formalism, the dispersion relations for the frequencies and damping rates of collective oscillations as well as spatial structure of these modes up to the decapole oscillation in both two- and three- dimensional gas geometries are calculated. In addition to higher-order modes, the formalism also gives rise to purely damped ‘non-hydrodynamic’ modes. We calculate the amplitude of the various modes for both symmetric and asymmetric trap quenches, finding excellent agreement with an exact quantum mechanical calculation. We find that higher-order hydrodynamic modes are more sensitive to the value of shear viscosity, which may be of interest for the precision extraction of transport coefficients in Fermi gas systems.
Mitchell, Deborah G; Johnson, Alan M; Johnson, Jeremy A; Judd, Kortney A; Kim, Kilyoung; Mayhew, Maurine; Powell, Amber L; Sevy, Eric T
2008-02-14
Relaxation of highly vibrationally excited 1,2-, 1,3-, and 1,4-difluorobenzne (DFB) by collisions with carbon dioxide has been investigated using diode laser transient absorption spectroscopy. Vibrationally hot DFB (E' approximately 41,000 cm(-1)) was prepared by 248 nm excimer laser excitation followed by rapid radiationless relaxation to the ground electronic state. Collisions between hot DFB isomers and CO2 result in large amounts of rotational and translational energy transfer from the hot donors to the bath. The CO2 nascent rotational population distribution of the high-J (J = 58-80) tail of the 00(0)0 state was probed at short times following the excimer laser pulse to measure rate constants and probabilities for collisions populating these states. The amount of translational energy gained by CO2 during collisions was determined using Doppler spectroscopy to measure the width of the absorption line for each transition. The energy transfer probability distribution function, P(E,E'), for the large DeltaE tail was obtained by resorting the state-indexed energy transfer probabilities as a function of DeltaE. P(E,E') was fit to a biexponential function to determine the average energy transferred in a single DFB/CO2 collision and fit parameters describing the shape of P(E,E'). P(E,E') fit parameters for DFB/CO2 and the previously studied C6F6/CO2 system are compared to various donor molecular properties. A model based on Fermi's Golden Rule indicates that the shape of P(E,E') is primarily determined by the low-frequency out-of-plane donor vibrational modes. A fractional mode population analysis is performed, which suggests that for energy transfer from DFB and C6F6 to CO2 the two key donor vibrational modes from which energy leaks out of the donor into the bath are nu11 and nu16. These "gateway" modes are some of the same modes determined to be the most efficient energy transfer modes by quantum scattering studies of benzene/He collisions.
Nonlinear excitation of convective cells by interchange modes and spectrum cascade processes
Pavlenko, V.P.; Weiland, J.
1980-04-01
Convective cell formation due to interchange modes has been studied. The spectral cascade processes between such waves have been considered in the limit k/sub parallel/=0 where the influence of gravity is particularly strong. Possibilities for up conversion are found.
Libration induced stretching mode excitation for pump-probe spectroscopy in pure liquid water.
Amir, Wafa; Gallot, Guilhem; Hache, François
2004-10-22
We developed an experimental approach to study pure liquid water in the infrared and avoid thermal effects. This technique is based on libration induced stretching excitation of water molecules. A direct correspondence between frequencies within the libration and OH stretching bands is demonstrated. Energy diffusion is studied in pure liquid water by measuring wave packet dynamics of OH stretching vibrator with infrared femtosecond spectroscopy. Wave packet dynamics reveals ultrafast energy dynamics and reflects 130 fs intermolecular energy transfer between water vibrators. Energy diffusion is almost two orders of magnitude faster than self diffusion in water.
Yoshida, Kyohei; Hachiya, Kan; Okumura, Kensuke; Mishima, Kenta; Inukai, Motoharu; Torgasin, Konstantin; Omer, Mohamed; Sonobe, Taro; Zen, Heishun; Negm, Hani; Kii, Toshiteru; Masuda, Kai; Ohgaki, Hideaki
2013-10-28
Mode-selective phonon excitation by a mid-infrared laser (MIR-FEL) is demonstrated via anti-Stokes Raman scattering measurements of 6H-silicon carbide (SiC). Irradiation of SiC with MIR-FEL and a Nd-YAG laser at 14 K produced a peak where the Raman shift corresponds to a photon energy of 119 meV (10.4 μm). This phenomenon is induced by mode-selective phonon excitation through the irradiation of MIR-FEL, whose photon energy corresponds to the photon-absorption of a particular phonon mode.
Goehring, Jenny L; Neff, Donna L; Baudhuin, Jacquelyn L; Hughes, Michelle L
2014-08-01
This study compared pitch ranking, electrode discrimination, and electrically evoked compound action potential (ECAP) spatial excitation patterns for adjacent physical electrodes (PEs) and the corresponding dual electrodes (DEs) for newer-generation Cochlear devices (Cochlear Ltd., Macquarie, New South Wales, Australia). The first goal was to determine whether pitch ranking and electrode discrimination yield similar outcomes for PEs and DEs. The second goal was to determine if the amount of spatial separation among ECAP excitation patterns (separation index, Σ) between adjacent PEs and the PE-DE pairs can predict performance on the psychophysical tasks. Using non-adaptive procedures, 13 subjects completed pitch ranking and electrode discrimination for adjacent PEs and the corresponding PE-DE pairs (DE versus each flanking PE) from the basal, middle, and apical electrode regions. Analysis of d' scores indicated that pitch-ranking and electrode-discrimination scores were not significantly different, but rather produced similar levels of performance. As expected, accuracy was significantly better for the PE-PE comparison than either PE-DE comparison. Correlations of the psychophysical versus ECAP Σ measures were positive; however, not all test/region correlations were significant across the array. Thus, the ECAP separation index is not sensitive enough to predict performance on behavioral tasks of pitch ranking or electrode discrimination for adjacent PEs or corresponding DEs.
Monte Carlo calculations of diatomic molecule gas flows including rotational mode excitation
NASA Technical Reports Server (NTRS)
Yoshikawa, K. K.; Itikawa, Y.
1976-01-01
The direct simulation Monte Carlo method was used to solve the Boltzmann equation for flows of an internally excited nonequilibrium gas, namely, of rotationally excited homonuclear diatomic nitrogen. The semi-classical transition probability model of Itikawa was investigated for its ability to simulate flow fields far from equilibrium. The behavior of diatomic nitrogen was examined for several different nonequilibrium initial states that are subjected to uniform mean flow without boundary interactions. A sample of 1000 model molecules was observed as the gas relaxed to a steady state starting from three specified initial states. The initial states considered are: (1) complete equilibrium, (2) nonequilibrium, equipartition (all rotational energy states are assigned the mean energy level obtained at equilibrium with a Boltzmann distribution at the translational temperature), and (3) nonequipartition (the mean rotational energy is different from the equilibrium mean value with respect to the translational energy states). In all cases investigated the present model satisfactorily simulated the principal features of the relaxation effects in nonequilibrium flow of diatomic molecules.
NASA Astrophysics Data System (ADS)
Jiménez-Reyes, S. J.; García, R. A.; Jiménez, A.; Chaplin, W. J.
2003-09-01
We have used observations made by the Global Oscillations at Low Frequency (GOLF) and the Variability of Irradiance and Gravity Oscillations Sun Photometer (VIRGO/SPM) instruments on board the ESA/NASA Solar and Heliospheric Observatory satellite to study variations in the excitation and damping of low angular degree (low-l) solar p-modes on the rising phase of activity cycle 23. Our analysis includes a correction procedure that for the first time allows GOLF data to be ``treated'' as a single homogeneous set, thereby compensating for the change of operational configuration partway through the mission. Over the range 2.5<=ν<=3.5mHz, we uncover an increase in damping and decrease in mode power that is consistent with previous findings. Furthermore, an excellent level of agreement is found between the variations extracted from the GOLF and VIRGO/SPM data. We find no net long-term changes to the modal energy supply rate. However, an analysis of the residuals uncovers the presence of a quasi-periodic signature of period ~1.5 yr (most pronounced for SPM). While it is true that several workers claim to have uncovered similar periodicities in other phenomena related to the near-surface layers of the Sun here, we are at present more inclined to attribute our finding to an artifact of the mode-fitting procedure. We also uncover a significant change in the asymmetry of mode peaks in the GOLF data, as found in previous studies of much longer data sets. These assumed that the dominant contribution to this arose from the switch in operating configuration partway through the mission (which altered the depth in the solar atmosphere sampled by the instrument). However, our preliminary analysis of data collected over the 100 day period beginning 2002 November 19-when the instrument switched back to its original configuration-suggests that this change may have a solar cycle component.
Chen, Yong; Yan, Zhenya
2017-01-01
The effect of derivative nonlinearity and parity-time-symmetric (PT-symmetric) potentials on the wave propagation dynamics is explored in the derivative nonlinear Schrödinger equation, where the physically interesting Scarf-II and harmonic-Hermite-Gaussian potentials are chosen. We study numerically the regions of unbroken and broken linear PT-symmetric phases and find some stable bright solitons of this model in a wide range of potential parameters even though the corresponding linear PT-symmetric phases are broken. The semielastic interactions between particular bright solitons and exotic incident waves are illustrated such that we find that particular nonlinear modes almost keep their shapes after interactions even if the exotic incident waves have evidently been changed. Moreover, we exert the adiabatic switching on PT-symmetric potential parameters such that a stable nonlinear mode with the unbroken linear PT-symmetric phase can be excited to another stable nonlinear mode belonging to the broken linear PT-symmetric phase.
Qualitative analysis of collective mode frequency shifts in L-alanine using terahertz spectroscopy.
Taulbee, Anita R; Heuser, Justin A; Spendel, Wolfgang U; Pacey, Gilbert E
2009-04-01
We have observed collective mode frequency shifts in deuterium-substituted L-alanine, three of which have previously only been calculated. Terahertz (THz) absorbance spectra were acquired at room temperature in the spectral range of 66-90 cm(-1), or 2.0-2.7 THz, for L-alanine (L-Ala) and four L-Ala compounds in which hydrogen atoms (atomic mass = 1 amu) were substituted with deuterium atoms (atomic mass = 2 amu): L-Ala-2-d, L-Ala-3,3,3-d(3), L-Ala-2,3,3,3-d(4), and L-Ala-d(7). The absorbance maxima of two L-Ala collective modes in this spectral range were recorded for multiple spectral measurements of each compound, and the magnitude of each collective mode frequency shift due to increased mass of these specific atoms was evaluated for statistical significance. Calculations were performed which predict the THz absorbance frequencies based on the estimated reduced mass of the modes. The shifts in absorbance maxima were correlated with the location(s) of the substituted deuterium atom(s) in the L-alanine molecule, and the atoms contributing to the absorbing delocalized mode in the crystal structure were deduced using statistics described herein. The statistical analyses presented also indicate that the precision of the method allows reproducible frequency shifts as small as 1 cm(-1) or 0.03 THz to be observed and that these shifts are not random error in the measurement.
Saito, Teruo; Tatematsu, Yoshinori; Yamaguchi, Yuusuke; Ikeuchi, Shinji; Ogasawara, Shinya; Yamada, Naoki; Ikeda, Ryosuke; Ogawa, Isamu; Idehara, Toshitaka
2012-10-12
Dynamic mode interaction between fundamental and second-harmonic modes has been observed in high-power sub-terahertz gyrotrons [T. Notake et al., Phys. Rev. Lett. 103, 225002 (2009); T. Saito et al. Phys. Plasmas 19, 063106 (2012)]. Interaction takes place between a parasitic fundamental or first-harmonic (FH) mode and an operating second-harmonic (SH) mode, as well as among SH modes. In particular, nonlinear excitation of the parasitic FH mode in the hard self-excitation regime with assistance of a SH mode in the soft self-excitation regime was clearly observed. Moreover, both cases of stable two-mode oscillation and oscillation of the FH mode only were observed. These observations and theoretical analyses of the dynamic behavior of the mode interaction verify the nonlinear hard self-excitation of the FH mode.
A Switched-Mode Breast Coil for 7 T MRI Using Forced-Current Excitation
Bosshard, John C.; Rispoli, Joseph V.; Dimitrov, Ivan E.; Cheshkov, Sergey; McDougall, Mary Preston; Malloy, Craig; Wright, Steven M.
2015-01-01
In high-field magnetic resonance imaging, the radio frequency wavelength within the human body is comparable to anatomical dimensions, resulting in B1 inhomogeneity and nonuniform sensitivity patterns. Thus, this relatively short wavelength presents engineering challenges for RF coil design. In this study, a bilateral breast coil for 1H imaging at 7 T was designed and constructed using forced-current excitation. By forcing equal current through the coil elements, we reduce the effects of coupling between the elements to simplify tuning and to ensure a uniform field across both breasts. To combine the benefits of the higher power efficiency of a unilateral coil with the bilateral coverage of a bilateral coil, a switching circuit was implemented to allow the coil to be reconfigured for imaging the left, right, or both breasts. PMID:25706501
Coulomb excitations of monolayer germanene
NASA Astrophysics Data System (ADS)
Shih, Po-Hsin; Chiu, Yu-Huang; Wu, Jhao-Ying; Shyu, Feng-Lin; Lin, Ming-Fa
2017-01-01
The feature-rich electronic excitations of monolayer germanene lie in the significant spin-orbit coupling and the buckled structure. The collective and single-particle excitations are diversified by the magnitude and direction of transferred momentum, the Fermi energy and the gate voltage. There are four kinds of plasmon modes, according to the unique frequency- and momentum-dependent phase diagrams. They behave as two-dimensional acoustic modes at long wavelength. However, for the larger momenta, they might change into another kind of undamped plasmons, become the seriously suppressed modes in the heavy intraband e–h excitations, keep the same undamped plasmons, or decline and then vanish in the strong interband e–h excitations. Germanene, silicene and graphene are quite different from one another in the main features of the diverse plasmon modes.
Coulomb excitations of monolayer germanene
Shih, Po-Hsin; Chiu, Yu-Huang; Wu, Jhao-Ying; Shyu, Feng-Lin; Lin, Ming-Fa
2017-01-01
The feature-rich electronic excitations of monolayer germanene lie in the significant spin-orbit coupling and the buckled structure. The collective and single-particle excitations are diversified by the magnitude and direction of transferred momentum, the Fermi energy and the gate voltage. There are four kinds of plasmon modes, according to the unique frequency- and momentum-dependent phase diagrams. They behave as two-dimensional acoustic modes at long wavelength. However, for the larger momenta, they might change into another kind of undamped plasmons, become the seriously suppressed modes in the heavy intraband e–h excitations, keep the same undamped plasmons, or decline and then vanish in the strong interband e–h excitations. Germanene, silicene and graphene are quite different from one another in the main features of the diverse plasmon modes. PMID:28091555
Walther, M; Plochocka, P; Fischer, B; Helm, H; Uhd Jepsen, P
2002-01-01
We present well-resolved absorption spectra of biological molecules in the far-IR (FIR) spectral region recorded by terahertz time-domain spectroscopy (THz-TDS). As an illustrative example we discuss the absorption spectra of benzoic acid, its monosubstitutes salicylic acid (2-hydroxy-benzoic acid), 3- and 4-hydroxybenzoic acid, and aspirin (acetylsalicylic acid) in the spectral region between 18 and 150 cm(-1). The spectra exhibit distinct features originating from low-frequency vibrational modes caused by intra- or intermolecular collective motion and lattice modes. Due to the collective origin of the observed modes the absorption spectra are highly sensitive to the overall structure and configuration of the molecules, as well as their environment. The THz-TDS procedure can provide a direct fingerprint of the molecular structure or conformational state of a compound.
Heisenberg symmetry and collective modes of one dimensional unitary correlated fermions
NASA Astrophysics Data System (ADS)
Abhinav, Kumar; Chandrasekhar, B.; Vyas, Vivek M.; Panigrahi, Prasanta K.
2017-02-01
The correlated fermionic many-particle system, near infinite scattering length, reveals an underlying Heisenberg symmetry in one dimension, as compared to an SO (2 , 1) symmetry in two dimensions. This facilitates an exact map from the interacting to the non-interacting system, both with and without a harmonic trap, and explains the short-distance scaling behavior of the wave-function. Taking advantage of the phenomenological Calogero-Sutherland-type interaction, motivated by the density functional approach, we connect the ground-state energy shift, to many-body correlation effect. For the excited states, modes at integral values of the harmonic frequency ω are predicted in one dimension, in contrast to the breathing modes with frequency 2ω in two dimensions.
Collective behavior of Cr3 + ions in ruby revealed by whispering gallery modes
NASA Astrophysics Data System (ADS)
Bourhill, Jeremy; Goryachev, Maxim; Farr, Warrick G.; Tobar, Michael E.
2015-08-01
We present evidence for the collective action of Cr3 + ion impurities in a highly concentrated ruby crystal coupled to microwave whispering gallery modes (WGMs). The cylindrical geometry of the crystal allows the creation of superradiant or "spin-mode" doublets, with spatial structures similar to that of WGMs. The formation of these spin patterns allows us to observe directly different selection rules, namely, wave number and azimuthal phase matching. The demonstration is made via an avoided level crossing between spin and photon mode doublets as well as absence of coupling between spin modes of different wave numbers. The effect is observable due to strong spin-photon coupling (67 MHz) exceeding both spin ensemble and cavity losses as well as the photon doublet splitting. We demonstrate that a four harmonic oscillator model not only with coupling between photon resonances (0.43 MHz) but also with a spin doublet (73 MHz) is necessary to accurately describe these results.
Gilmore, Adam Matthew
2014-01-01
Contemporary spectrofluorimeters comprise exciting light sources, excitation and emission monochromators, and detectors that without correction yield data not conforming to an ideal spectral response. The correction of the spectral properties of the exciting and emission light paths first requires calibration of the wavelength and spectral accuracy. The exciting beam path can be corrected up to the sample position using a spectrally corrected reference detection system. The corrected reference response accounts for both the spectral intensity and drift of the exciting light source relative to emission and/or transmission detector responses. The emission detection path must also be corrected for the combined spectral bias of the sample compartment optics, emission monochromator, and detector. There are several crucial issues associated with both excitation and emission correction including the requirement to account for spectral band-pass and resolution, optical band-pass or neutral density filters, and the position and direction of polarizing elements in the light paths. In addition, secondary correction factors are described including (1) subtraction of the solvent's fluorescence background, (2) removal of Rayleigh and Raman scattering lines, as well as (3) correcting for sample concentration-dependent inner-filter effects. The importance of the National Institute of Standards and Technology (NIST) traceable calibration and correction protocols is explained in light of valid intra- and interlaboratory studies and effective spectral qualitative and quantitative analyses including multivariate spectral modeling.
Nonradiating and radiating modes excited by quantum emitters in open epsilon-near-zero cavities
Liberal, Iñigo; Engheta, Nader
2016-01-01
Controlling the emission and interaction properties of quantum emitters (QEs) embedded within an optical cavity is a key technique in engineering light-matter interactions at the nanoscale, as well as in the development of quantum information processing. State-of-the-art optical cavities are based on high quality factor photonic crystals and dielectric resonators. However, wealthier responses might be attainable with cavities carved in more exotic materials. We theoretically investigate the emission and interaction properties of QEs embedded in open epsilon-near-zero (ENZ) cavities. Using analytical methods and numerical simulations, we demonstrate that open ENZ cavities present the unique property of supporting nonradiating modes independently of the geometry of the external boundary of the cavity (shape, size, topology, etc.). Moreover, the possibility of switching between radiating and nonradiating modes enables a dynamic control of the emission by, and the interaction between, QEs. These phenomena provide unprecedented degrees of freedom in controlling and trapping fields within optical cavities, as well as in the design of cavity opto- and acoustomechanical systems. PMID:27819047
NASA Astrophysics Data System (ADS)
Mitra, Vramori; Prakash, N. Hari; Solomon, Infant; Megalingam, Mariammal; Sekar Iyengar, A. N.; Marwan, Norbert; Kurths, Jürgen; Sarma, Arun; Sarma, Bornali
2017-02-01
The typical phenomena of mixed mode oscillations and their associated nonlinear behaviors have been investigated in collisionless magnetized plasma oscillations in a DC glow discharge plasma system. Plasma is produced between a cylindrical mesh grid and a constricted anode. A spherical mesh grid of 80% optical transparency is kept inside a cylindrical grid to produce an inverted fireball. Three Langmuir probes are kept in the ambient plasma to measure the floating potential fluctuations at different positions of the chamber. It has been observed that under certain conditions of discharge voltages and magnetic fields, the mixed mode oscillation phenomena (MMOs) appears, and it shows a sequential alteration with the variation of the magnetic fields and probe positions. Low frequency instability has been observed consistently in various experimental conditions. The mechanisms of the low frequency instabilities along with the origin of the MMOs have been qualitatively explained. Extensive linear and nonlinear analysis using techniques such as fast Fourier transform, recurrence quantification analysis, and the well-known statistical computing, skewness, and kurtosis are carried out to explore the complex dynamics of the MMO appearing in the plasma oscillations under various discharge conditions and external magnetic fields.
η collective mode as A1 g Raman resonance in cuprate superconductors
NASA Astrophysics Data System (ADS)
Montiel, X.; Kloss, T.; Pépin, C.; Benhabib, S.; Gallais, Y.; Sacuto, A.
2016-01-01
We discuss the possible existence of a spin singlet excitation with charge ±2 (η mode) originating the A1 g Raman resonance in cuprate superconductors. This η mode relates the d -wave superconducting singlet pairing channel to a d -wave charge channel. We show that the η boson forms a particle-particle bound state below the 2 Δ threshold of the particle-hole continuum where Δ is the maximum d -wave gap. Within a generalized random phase approximation and Bethe-Salpeter approximation study, we find that this mode has energies similar to the resonance observed with inelastic neutron scattering below the superconducting (SC) coherent peak at 2 Δ in various SC cuprate compounds. We show that it is a very good candidate for the resonance observed in Raman scattering below the 2 Δ peak in the A1 g symmetry. Since the η mode sits in the S =0 channel, it may be observable via Raman, x-ray, or electron energy loss spectroscopy probes.
Selective excitation of Fabry-Perot or whispering-gallery mode-type lasing in GaN microrods
Baek, Hyeonjun; Hyun, Jerome K.; Chung, Kunook; Oh, Hongseok; Yi, Gyu-Chul
2014-11-17
Lasing from long semiconductor nanorods is dictated by Fabry-Perot (FP) resonances whereas that from large-diameter microrods is determined by whispering gallery modes (WGMs). Lengths and diameters intermediate between the two systems represent an important size regime for photonics and electronics, but have not been studied in detail. Here, we report on the detection of FP and WGM lasing emissions from a single GaN microrod, and demonstrate the ability to switch between the two lasing mechanisms by translating the excitation beam along the microrod. The competition between FP and WGM-type lasing was studied by finite-difference time-domain simulation and statistical analysis by measuring microrods of various diameters. Finally, control over the relative lasing intensities originating from either FPs or WGMs was demonstrated by tuning the polarization of the emission.
NASA Astrophysics Data System (ADS)
Miao, Hongchen; Huan, Qiang; Wang, Qiangzhong; Li, Faxin
2017-02-01
Excitation of single fundamental torsional wave T(0, 1) mode is of practical importance in inspecting or monitoring the structural integrity of pipelines, as T(0, 1) wave is the only non-dispersive mode in pipe-like structures. This work presents a piezoelectric ring array to excite and receive single T(0, 1) mode which is made up of a series of equally-spaced face-shear d24 PZT elements around the pipe. Firstly, we proposed that single T(0, 1) mode can be excited by the piezoelectric ring, when the number of d24 PZT elements is slightly greater than n, where F(n, 2) is the highest circumferential order flexural torsional mode within the frequency bandwidth of the drive signal. Then this proposed principle was confirmed by finite element simulations. Later, experimental testing was conducted on a 100 mm outer diameter, 3 mm thick aluminum pipe. Results show that the ring of 24 face-shear d24 PZT elements can suppress all the non-axisymmetric flexural modes at the excitation frequency of 150 kHz so that single T(0, 1) mode is generated. Moreover, such a piezoelectric ring transducer can also filter flexural modes and receive the T(0, 1) mode only at 150 kHz. Note that here the highest circumferential order flexural torsional mode within the frequency bandwidth is F(20, 2), so the experimental results are in good agreement with the proposed principle. The presented ring of face-shear d24 PZT elements is very suitable for severing as the T(0, 1) wave transducer in structural health monitoring system, as it is cost-effective and no external load is required for operation.
Choke Flange for High Power RF Components Excited by TE01 Mode
Yeremian, A.Dian; /SLAC
2009-12-11
A multifaceted program to study high gradient structures and properties of RF breakdown is under way at SLAC. This program includes testing of simplified versions of traveling wave and standing wave structures at 11.4 GHz. [Dolgashev] RF power is fed into these structures using a TE01 mode-launcher. An RF flange is used to connect the mode-launcher to the test-structure. The rf currents flow through either the stainless steel lip on the flange or, in an alternate assembly, through a copper gasket pressed between the same stainless steel lips. In a recent experiment with a single cell traveling wave structure, a flange with stainless steel lips was irreversibly damaged at RF power about 90 MW and {approx}100 ns pulse length. We suggest an alternative flange that does not rely on metal-to-metal contact in the rf power transfer region. The idea is to use an asymmetric choke flange, where the choke grove is cut into a conflate flange on the mode-launcher. The structures themselves will have a simpler, flat conflate flange with rounded corners on the vacuum side. The Vacuum seal is achieved with a Cu gasket between these two flanges above the RF region. We have designed a flange with a choke which is almost field free in the vacuum gasket region, whose technical specifications and RF properties are presented below. Design simulations were conducted using HFSS, a 3D finite element code that solves electromagnetic fields in complex structures. Figure 1 demonstrates the projected physical look of the choke flange, while the table next to it lists the critical parameters. The maximum electric field for in this geometry is on axis at 33.6MV/m for 100 MW input. The electric field near the gasket, meaning at the top of the choke gap is at 125kV/m or 1.25kV/cm. Figure 2 demonstrates the electric field strength profile in the geometry for 100 MW input power. The maximum magnetic field for in this geometry is near the pipe at 59kA/m for 100 MW input. The magnetic field at the
NASA Astrophysics Data System (ADS)
Tanner, Christian; Manca, Carine; Leutwyler, Samuel
2005-05-01
The excited-state hydrogen-atom transfer (ESHAT) reaction of the 7-hydroxyquinoline•(NH3)3 cluster involves a crossing from the initially excited π1π* to a π1σ* state. The nonadiabatic coupling between these states induces homolytic dissociation of the O-H bond and H-atom transfer to the closest NH3 molecule, forming a biradical structure denoted HT1, followed by two more Grotthus-type translocation steps along the ammonia wire. We investigate this reaction at the configuration interaction singles level, using a basis set with diffuse orbitals. Intrinsic reaction coordinate calculations of the enol→HT1 step predict that the H-atom transfer is preceded and followed by extensive twisting and bending of the ammonia wire, as well as large O -H⋯NH3 hydrogen bond contraction and expansion. The calculations also predict an excited-state proton transfer path involving synchronous proton motions; however, it lies 20-25kcal/mol above the ESHAT path. Higher singlet and triplet potential curves are calculated along the ESHAT reaction coordinate: Two singlet-triplet curve crossings occur within the HT1 product well and intersystem crossing to these Tn states branches the reaction back to the enol reactant side, decreasing the ESHAT yield. In fact, a product yield of ≈40% 7-ketoquinoline•(NH3)3 is experimentally observed. The vibrational mode selectivity of the enol→HT1 reaction step [C. Manca, C. Tanner, S. Coussan, A. Bach, and S. Leutwyler, J. Chem. Phys. 121, 2578 (2004)] is shown to be due to the large sensitivity of the diffuse πσ* state to vibrational displacements along the intermolecular coordinates.
NASA Astrophysics Data System (ADS)
Décanini, Yves; Folacci, Antoine; Ould El Hadj, Mohamed
2015-07-01
With the possibility of testing massive gravity in the context of black hole physics in mind, we consider the radiation produced by a particle plunging from slightly below the innermost stable circular orbit into a Schwarzschild black hole. In order to circumvent the difficulties associated with black hole perturbation theory in massive gravity, we use a toy model in which we replace the graviton field with a massive scalar field and consider a linear coupling between the particle and this field. We compute the waveform generated by the plunging particle and study its spectral content. This permits us to highlight and interpret some important effects occurring in the plunge regime which are not present for massless fields, such as (i) the decreasing and vanishing, as the mass parameter increases, of the signal amplitude generated when the particle moves on quasicircular orbits near the innermost stable circular orbit; and (ii) in addition to the excitation of the quasinormal modes, the excitation of the quasibound states of the black hole.
Allmond, James M
2016-01-01
The synthesis of Coulomb excitation and decay offers very practical advantages in the study of nuclear shapes and collectivity. For instance, Coulomb excitation is unique in its ability to measure the electric quadrupole moments, i.e., I2 ||M(E2)||I1 matrix elements, of excited, non-isomeric states in atomic nuclei, providing information on the intrinsic shape. However, the Coulomb excitation analysis and structural inter- pretation can be strongly dependent upon weak transitions or decay branches, which are often obscured by the Compton background. Transitions of particular interest are those low in energy and weak in intensity due to the E 5 attenuation factor. These weak decay branches can often be determined with high precision from -decay studies. Recently, 106Mo and 110Cd were studied by both Coulomb excitation and decay. Preliminary results of new weak decay branches following decay of 110mAg to 110Cd are presented; these results will challenge competing interpretations based on vibrations and configuration mixing.
NASA Astrophysics Data System (ADS)
Allmond, J. M.
2016-09-01
The synthesis of Coulomb excitation and β decay offers very practical advantages in the study of nuclear shapes and collectivity. For instance, Coulomb excitation is unique in its ability to measure the electric quadrupole moments, i.e., < I_2^π allel M(E2)allel I_1^π > matrix elements, of excited, non-isomeric states in atomic nuclei, providing information on the intrinsic shape. However, the Coulomb excitation analysis and structural interpretation can be strongly dependent upon weak transitions or decay branches, which are often obscured by the Compton background. Transitions of particular interest are those low in energy and weak in intensity due to the Eγ5 attenuation factor. These weak decay branches can often be determined with high precision from β-decay studies. Recently, 106Mo and 110Cd were studied by both Coulomb excitation and β decay. Preliminary results of new weak decay branches following β decay of 110mAg to 110Cd are presented; these results will challenge competing interpretations based on vibrations and configuration mixing.
Bonhommeau, David; Valero, Rosendo; Truhlar, Donald G.; Jasper, Ahren W.
2009-06-21
Using previously developed potential energy surfaces and their couplings, non-Born-Oppenheimer trajectory methods are used to study the state-selected photodissociation of ammonia, prepared with up to six quanta of vibrational excitation in the symmetric ({nu}{sub 1}) or antisymmetric ({nu}{sub 3}) stretching modes of NH{sub 3}(A-tilde). The predicted dynamics is mainly electronically nonadiabatic (that is, it produces ground electronic state amino radicals). The small probability of forming the excited-state amino radical is found, for low excitations, to increase with total energy and to be independent of whether the symmetric or antisymmetric stretch is excited; however some selectivity with respect to exciting the antisymmetric stretch is found when more than one quantum of excitation is added to the stretches, and more than 50% of the amino radical are found to be electronically excited when six quanta are placed in the antisymmetric stretch. These results are in contrast to the mechanism inferred in recent experimental work, where excitation of the antisymmetric stretch by a single quantum was found to produce significant amounts of excited-state products via adiabatic dissociation at total energies of about 7.0 eV. Both theory and experiment predict a broad range of translational energies for the departing H atoms when the symmetric stretch is excited, but the present simulations do not reproduce the experimental translational energy profiles when the antisymmetric stretch is excited. The sensitivity of the predicted results to several aspects of the calculation is considered in detail, and the analysis leads to insight into the nature of the dynamics that is responsible for mode selectivity.
Yang, Liping; Zhang, Lei; He, Jiansen; Tu, Chuanyi; Wang, Linghua; Peter, Hardi; Zhang, Shaohua; Feng, Xueshang
2015-02-20
The Atmospheric Imaging Assembly instrument on board the Solar Dynamics Observatory has directly imaged the fast-propagating magnetosonic waves (FMWs) successively propagating outward along coronal magnetic funnels. In this study we perform a numerical investigation of the excitation of FMWs in the interchange reconnection scenario, with footpoint shearing flow being used to energize the system and drive the reconnection. The modeling results show that as a result of magnetic reconnection, the plasma in the current sheet is heated up by Joule dissipation to ∼10 MK and is ejected rapidly, developing the hot outflows. Meanwhile, the current sheet is torn into plasmoids, which are shot quickly both upward and downward. When the plasmoids reach the outflow regions, they impact and collide with the ambient magnetic field there, which consecutively launches FMWs. The FMWs propagate outward divergently away from the impact regions, with a phase speed of the Alfvén speed of ∼1000 km s{sup –1}. In the k – ω diagram of the Fourier wave power, the FMWs display a broad frequency distribution with a straight ridge that represents the dispersion relation. With the WKB approximation, at the distance of 15 Mm from the wave source region, we estimate the energy flux of FMWs to be E ∼ 7.0 × 10{sup 6} erg cm{sup –2} s{sup –1}, which is ∼50 times smaller than the energy flux related to the tube-channeled reconnection outflow. These simulation results indicate that energetically and dynamically the outflow is far more important than the waves.
NASA Astrophysics Data System (ADS)
Yan, Zhenya; Wen, Zichao; Konotop, Vladimir V.
2015-08-01
We report branches of explicit expressions for nonlinear modes in parity-time (PT )-symmetric potentials of several types. For the single-well and double-well potentials the found solutions are two-parametric and appear to be stable even when the PT symmetry of respective underlying linear models is broken. Based on the examples of these solutions we describe an algorithm of excitation of a stable nonlinear mode in a model whose linear limit is unstable. The method is based on the adiabatic change of the control parameter driving the mode along a branch bifurcating from a stable linear mode. The suggested algorithm is confirmed by extensive numerical simulations.
Measurement of collective excitations in VO2 by resonant inelastic x-ray scattering
He, Haowei; Gray, A. X.; Granitzka, P.; ...
2016-10-15
Vanadium dioxide is of broad interest as a spin-1/2 electron system that realizes a metal-insulator transition near room temperature, due to a combination of strongly correlated and itinerant electron physics. Here, resonant inelastic x-ray scattering is used to measure the excitation spectrum of charge and spin degrees of freedom at the vanadium L edge under different polarization and temperature conditions, revealing excitations that differ greatly from those seen in optical measurements. Furthermore, these spectra encode the evolution of short-range energetics across the metal-insulator transition, including the low-temperature appearance of a strong candidate for the singlet-triplet excitation of a vanadium dimer.
NASA Technical Reports Server (NTRS)
Mcpeak, W. L.
1975-01-01
A new exciter switch assembly has been installed at the three DSN 64-m deep space stations. This assembly provides for switching Block III and Block IV exciters to either the high-power or 20-kW transmitters in either dual-carrier or single-carrier mode. In the dual-carrier mode, it provides for balancing the two drive signals from a single control panel located in the transmitter local control and remote control consoles. In addition to the improved switching capabilities, extensive monitoring of both the exciter switch assembly and Transmitter Subsystem is provided by the exciter switch monitor and display assemblies.
NASA Astrophysics Data System (ADS)
Fedorov, E.; Mazur, N.; Pilipenko, V.; Baddeley, L.
2016-11-01
The ionospheric Alfvén resonator (IAR) and fast magnetosonic (FMS) waveguide, which can trap the electromagnetic wave energy in the range from fractions of Hz to several Hz, are characteristic features of the upper ionosphere. Their role in the electromagnetic impulsive coupling between atmospheric discharge processes and the ionosphere can be elucidated with a proper model. The presented model is based on numerical solution of coupled wave equations for electromagnetic modes in the ionosphere and atmosphere in a realistic ionosphere modeled with the use of IRI (International Reference Ionosphere) vertical profiles. The geomagnetic field is supposed to be nearly vertical, so the model can be formally applied to high latitudes, though the main features of ground ULF structure will be qualitatively similar at middle latitudes as well. The modeling shows that during the lightning discharge a coupled wave system comprising IAR and MHD waveguide is excited. Using the model, the spatial structure, frequency spectra, and polarization parameters have been calculated at various distances from a vertical dipole. In the lightning proximity (about several hundred kilometer) only the lowest IAR harmonics are revealed in the radial magnetic component spectra. At distances >800 km the multiband spectral structure is formed predominantly by harmonics of FMS waveguide modes. The model predictions do not contradict the results of search coil magnetometer observations on Svalbard; however, the model validation demands more dedicated experimental studies.
NASA Astrophysics Data System (ADS)
Zheng, Gaige; Xu, Linhua; Zou, Xiujuan; Liu, Yuzhu
2017-02-01
We demonstrate the excitation of surface phonon polaritons (SPhPs) in the mid-infrared (mid-IR) Reststrahlen band (10.288 μm-12.563 μm) on patterned surfaces with silicon carbide (SiC) substrate and gold (Au) gratings. The very large negative permittivity of Au limits its applications in the mid-IR range, and to couple incident light to SPhPs modes, their momentum mismatch can be compensated by patterning Au grating onto the surface of SiC substrate. Samples were fabricated and characterized experimentally by Fourier transform infrared reflection (FTIR) spectroscopy. The optical properties were also simulated by the rigorous coupled wave analysis (RCWA) method. Reflection dips are observed for light polarized vertical to the grating lines (TM-polarized), which are attributed to the coupling of electromagnetic (EM) waves into the SPhP modes. In addition, we present small-volume index sensing with analyte specificity based on mid-IR SPhPs in the fabricated configuration.
Kumagai, Tsutaru Kishi, Tetsuo; Yano, Tetsuji
2015-03-21
Bubble-containing Nd{sup 3+}-doped tellurite glass microspheres were fabricated by localized laser heating technique to investigate their optical properties for use as microresonators. Fluorescence and excitation spectra measurements were performed by pumping with a tunable CW-Ti:Sapphire laser. The excitation spectra manifested several sharp peaks due to the conventional whispering gallery mode (WGM) when the pumping laser was irradiated to the edge part of the microsphere. However, when the excitation light was irradiated on the bubble position inside the microsphere, “non-WGM excitation” was induced, giving rise to numerous peaks at a broad wavelength range in the excitation spectra. Thus, efficient excitation was achieved over a wide wavelength range. Lasing threshold excited at the bubble position was much lower than that for the excitation at the edges of the microsphere. The lowest value of the laser threshold was 34 μW for a 4 μm sphere containing a 0.5 μm bubble. Efficiency of the excitation at the bubble position with broadband light was calculated to be 5 times higher than that for the edge of the microsphere. The bubble-containing microsphere enables efficient utilization of broadband light excitation from light-emitting diodes and solar light.
Dong, Shan; Zhang, Anmin; Liu, Kai; ...
2016-02-26
The recent renaissance of black phosphorus (BP) as a two-dimensional (2D) layered material has generated tremendous interest, but its unique structural characters underlying many of its outstanding properties still need elucidation. Here we report Raman measurements that reveal an ultralow-frequency collective compression mode (CCM) in BP, which is unprecedented among similar 2D layered materials. This novel CCM indicates an unusually strong interlayer coupling, and this result is quantitatively supported by a phonon frequency analysis and first-principles calculations. Moreover, the CCM and another branch of low-frequency Raman modes shift sensitively with changing number of layers, allowing an accurate determination of themore » thickness up to tens of atomic layers, which is considerably higher than previously achieved by using high-frequency Raman modes. Lastly, these findings offer fundamental insights and practical tools for further exploration of BP as a highly promising new 2D semiconductor.« less
Dong, Shan; Zhang, Anmin; Liu, Kai; Ji, Jianting; Ye, Y. G.; Luo, X. G.; Chen, X. H.; Ma, Xiaoli; Jie, Yinghao; Chen, Changfeng; Wang, Xiaoqun; Zhang, Qingming
2016-02-26
The recent renaissance of black phosphorus (BP) as a two-dimensional (2D) layered material has generated tremendous interest, but its unique structural characters underlying many of its outstanding properties still need elucidation. Here we report Raman measurements that reveal an ultralow-frequency collective compression mode (CCM) in BP, which is unprecedented among similar 2D layered materials. This novel CCM indicates an unusually strong interlayer coupling, and this result is quantitatively supported by a phonon frequency analysis and first-principles calculations. Moreover, the CCM and another branch of low-frequency Raman modes shift sensitively with changing number of layers, allowing an accurate determination of the thickness up to tens of atomic layers, which is considerably higher than previously achieved by using high-frequency Raman modes. Lastly, these findings offer fundamental insights and practical tools for further exploration of BP as a highly promising new 2D semiconductor.
NASA Astrophysics Data System (ADS)
Dong, Shan; Zhang, Anmin; Liu, Kai; Ji, Jianting; Ye, Y. G.; Luo, X. G.; Chen, X. H.; Ma, Xiaoli; Jie, Yinghao; Chen, Changfeng; Wang, Xiaoqun; Zhang, Qingming
2016-02-01
The recent renaissance of black phosphorus (BP) as a two-dimensional (2D) layered material has generated tremendous interest, but its unique structural characters underlying many of its outstanding properties still need elucidation. Here we report Raman measurements that reveal an ultralow-frequency collective compression mode (CCM) in BP, which is unprecedented among similar 2D layered materials. This novel CCM indicates an unusually strong interlayer coupling, and this result is quantitatively supported by a phonon frequency analysis and first-principles calculations. Moreover, the CCM and another branch of low-frequency Raman modes shift sensitively with changing number of layers, allowing an accurate determination of the thickness up to tens of atomic layers, which is considerably higher than previously achieved by using high-frequency Raman modes. These findings offer fundamental insights and practical tools for further exploration of BP as a highly promising new 2D semiconductor.
Tobing, Landobasa Y M; Zhang, Dao-Hua
2016-02-03
Aluminum is a promising candidate for light at the nanoscale in the ultraviolet (UV); however, the realization of magnetic resonance in the UV range remains challenging due to stringent dimensional requirements arising from the intrinsic loss caused by the interband transition. Here, the mode interaction with the aluminum interband transition and preferential excitation of the hybrid magnetic-electric mode, as discovered in ultrasmall Al resonators, are reported.
Ogasawara, S.; Kubo, S.; Nishiura, M.; Tanaka, K.; Shimozuma, T.; Yoshimura, Y.; Igami, H.; Takahashi, H.; Ito, S.; Takita, Y.; Kobayashi, S.; Mizuno, Y.; Okada, K.; Tatematsu, Y.; Saito, T.; Minami, R.; Kariya, T.; Imai, T.
2012-10-15
Collective Thomson scattering (CTS) diagnostic requires a strong probing beam to diagnose a bulk and fast ion distribution function in fusion plasmas. A mega-watt gyrotron for electron cyclotron resonance heating is used as a probing beam in the large helical device. Spurious mode oscillations are often observed during the turning on/off phase of the modulation. The frequency spectra of the 77-GHz gyrotron output power have been measured, and then one of the spurious modes, which interferes with the CTS receiver system, is identified as the TE{sub 17,6} mode at the frequency of 74.7 GHz. The mode competition calculation indicates that the increase of the magnetic field strength at the gyrotron resonator can avoid such a spurious mode and excite only the main TE{sub 18,6} mode. The spurious radiation at the 74.7 GHz is experimentally demonstrated to be suppressed in the stronger magnetic field than that optimized for the high-power operation.
Yusupov, R.V.; Mertelj, T.; Chu, J.-H.; Fisher, I.R.; Mihailovic, D.; /Stefan Inst., Ljubljana
2010-02-15
The coupling of phonons with collective modes and single-particle gap excitations associated with one (1d) and two-directional (2d) electronically-driven charge-density wave (CDW) ordering in metallic RTe{sub 3} is investigated as a function of rare-earth ion chemical pressure (R = Tb, Dy, Ho) using femtosecond pump-probe spectroscopy. From the T-dependence of the CDW gap {Delta}{sub CDW} and the amplitude mode (AM) we find that while the transition to a 1d-CDW ordered state at Tc1 initially proceeds in an exemplary mean-field (MF)-like fashion, below T{sub c1}, {Delta}{sub CDW} is depressed and departs from the MF behavior. The effect is apparently triggered by resonant mode-mixing of the amplitude mode (AM) with a totally symmetric phonon at 1.75 THz. At low temperatures, when the state evolves into a 2d-CDW ordered state at T{sub c2} in the DyTe{sub 3} and HoTe{sub 3}, additional much weaker mode mixing is evident but no soft mode is observed.
ERIC Educational Resources Information Center
Wright, Bradford L.
1975-01-01
Advocates the creation of swimming pool oscillations as part of a general investigation of mechanical oscillations. Presents the equations, procedure for deriving the slosh modes, and methods of period estimation for exciting swimming pool oscillations. (GS)
Band structure of collective modes and effective properties of binary magnonic crystals
NASA Astrophysics Data System (ADS)
Zivieri, R.; Malagò, P.; Giovannini, L.
2014-11-01
In this paper a theoretical study of the band structure of collective modes of binary ferromagnetic systems formed by a submicrometric periodic array of cylindrical cobalt nanodots partially or completely embedded into a permalloy ferromagnetic film is performed. The binary ferromagnetic systems studied are two-dimensional periodic, but they can be regarded as three-dimensional, since the magnetization is non uniform also along the z direction due to the contrast between the saturation magnetizations of the two ferromagnetic materials along the thickness. The dynamical matrix method, a finite-difference micromagnetic approach, formulated for studying the dynamics in one-component periodic ferromagnetic systems is generalized to ferromagnetic systems composed by F ferromagnetic materials. It is then applied to investigate the spin dynamics in four periodic binary ferromagnetic systems differing each other for the volume of cobalt dots and for the relative position of cobalt dots within the primitive cell. The dispersion curves of the most representative frequency modes are calculated for each system for an in-plane applied magnetic field perpendicular to the Bloch wave vector. The dependence of the dispersion curves on the cobalt quantity and position is discussed in terms of distribution of effective "surface magnetic charges" at the interface between the two ferromagnetic materials. The metamaterial properties in the propagative regime are also studied (1) by introducing an effective magnetization and effective "surface magnetic charges" (2) by describing the metamaterial wave dispersion of the most representative mode in each system within an effective medium approximation and in the dipole-exchange regime. It is also shown that the interchange between cobalt and permalloy does not necessarily lead to an interchange of the corresponding mode dispersion. Analogously to the case of electromagnetic waves in two-dimensional photonic crystals, the degree of
Xu, Z.; Fauchet, M.; Rella, C.W.
1995-12-31
Hydrogen in amorphous and crystalline silicon has been the topic of intense theoretical and experimental investigations for more than one decade. To better understand how the Si-H bonds interact with the Si matrix and how they can be broken, it would be useful to excite selectively these bonds and monitor the energy flow from the Si-H bonds into the bulk Si modes. One attractive way of exciting the Si-H modes selectively is with an infrared laser tuned to a Si-H vibrational mode. Unfortunately, up to now, this type of experiment had not been possible because of the lack of a laser producing intense, ultrashort pulses that are tunable in the mid infrared. In this presentation, we report the first measurement where a 1 picosecond long laser pulse was used to excite the Si-H stretching modes near 2000 cm{sup -1} and another identical laser pulse was used to measure the deexcitation from that specific vibrational mode. The laser was the Stanford free electron laser generating {approximately}1 ps-long pulses, tunable in the 5 {mu}m region and focussed to an intensity of {approximately}1 GW/cm{sup 2}. The pump-probe measurements were performed in transmission at room temperature on several 2 {mu}m thick a-Si:H films deposited on c-Si. Samples with predominant Si-H{sub 1} modes, predominant Si-H{sub n>1} modes and with a mixture of modes were prepared. The laser was tuned on resonance with either of these modes. Immediately after excitation, we observe a bleaching of the infrared absorption, which can be attributed to excitation of the Si-H mode. Beaching is expected since, as a result of anharmonicity, the detuning between the (E{sub 3} - E{sub 2}) resonance and the (E{sub 2} - E{sub 1}) resonance is larger than the laser bandwidth. Note that despite the anharmonicity, it should be possible to climb the vibrational ladder due to power broadening.
Nuclear collective motion with a coherent coupling interaction between quadrupole and octupole modes
NASA Astrophysics Data System (ADS)
Minkov, N.; Yotov, P.; Drenska, S.; Scheid, W.; Bonatsos, D.; Lenis, D.; Petrellis, D.
2006-04-01
A collective Hamiltonian for the rotation-vibration motion of nuclei is considered in which the axial quadrupole and octupole degrees of freedom are coupled through the centrifugal interaction. The potential of the system depends on the two deformation variables β2 and β3. The system is considered to oscillate between positive and negative β3 values by rounding an infinite potential core in the (β2,β3) plane with β2>0. By assuming a coherent contribution of the quadrupole and octupole oscillation modes in the collective motion, the energy spectrum is derived in an explicit analytic form, providing specific parity shift effects. On this basis several possible ways in the evolution of quadrupole-octupole collectivity are outlined. A particular application of the model to the energy levels and electric transition probabilities in alternating parity spectra of the nuclei Nd150, Sm152, Gd154, and Dy156 is presented.
Development of collective structures over noncollective excitations in {sup 139}Nd
Bhowal, S.; Gangopadhyay, G.; Petrache, C. M.; Ragnarsson, I.; Singh, A. K.; Bhattacharya, S.; Huebel, H.; Neusser-Neffgen, A.; Al-Khatib, A.; Bringel, P.; Buerger, A.; Nenoff, N.; Schoenwasser, G.; Hagemann, G. B.; Herskind, B.; Jensen, D. R.; Sletten, G.; Fallon, P.; Goergen, A.; Bednarczyk, P.
2011-08-15
High-spin states in {sup 139}Nd were investigated using the reaction {sup 96}Zr({sup 48}Ca,5n) at a beam energy of 195 MeV and {gamma}-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.
NASA Astrophysics Data System (ADS)
Liu, Li; Muckerman, James T.
1997-09-01
Vibrational eigenvalues with estimated errors <5×10-2 cm-1 and their corresponding eigenfunctions for J=0 5D (planar) acetylene modeled by the Halonen-Child-Carter potential-energy surface are obtained using an energy-shifted, imaginary-time Lanczos propagation of symmetry-adapted wave packets. A lower resolution (˜4 cm-1) vibrational eigenspectrum of the system is also calculated by the Fourier transform of the autocorrelation of an appropriate wave packet. The eigenvalues from both approaches are in excellent agreement. The wave function of the molecule is represented in a direct-product discrete variable representation (DVR) with nearly 300 000 grid points. Our results are compared with the previously reported theoretical and experimental values. We use our 69 computed eigenstates as a basis to perform an optimal control simulation of selective two-photon excitation of the symmetric CH-stretch mode with an infrared, linearly polarized, transform-limited, and subpicosecond-picosecond laser pulse. The resulting optimal laser pulses, which are then tested on the full DVR grid, fall within the capabilities of current powerful, subpicosecond, and tunable light sources.
Sokolov, V I; Marusin, N V; Panchenko, V Ya; Savelyev, A G; Seminogov, V N; Khaydukov, E V
2013-12-31
We propose a method for measuring simultaneously the refractive index n{sub f}, extinction coefficient m{sub f} and thickness H{sub f} of thin films. The method is based on the resonant excitation of waveguide modes in the film by a TE- or a TM-polarised laser beam in the geometry of frustrated total internal reflection. The values of n{sub f}, m{sub f} and H{sub f} are found by minimising the functional φ = [N{sup -1}Σ{sup N}{sub i=1}(R{sub exp}(θ{sub i}) – R{sub thr}(θ{sub i})){sup 2}]{sup 1/2}, where R{sub exp}(θ{sub i}) and R{sub thr}(θ{sub i}) are the experimental and theoretical coefficients of reflection of the light beam from the interface between the measuring prism and the film at an angle of incidence θ{sub i}. The errors in determining n{sub f}, m{sub f} and H{sub f} by this method are ±2 × 10{sup -4}, ±1 × 10{sup -3} and ±0.5%, respectively. (fiber and integrated optics)
Soleimani Meigooni, A.
1984-01-01
This work involves the measurement and analysis of neutron elastic and inelastic scattering cross section from /sup 12/C at incident neutron energies between 20 and 26 MeV. These data cover an energy range that has not previously been investigated with neutrons and where the direct interaction mechanism should be dominant. These energies are also of particular interest in the fields of radiation protection and radio-therapy. The objectives of the present work are to analyze excitation of the measured collective states in /sup 12/C and to develop an energy dependent optical model potential that can be used to calculate quantities of importance to neutron dosimetry at all energies between 20 and 100 MeV. In addition, a separate series of experiments was performed using a large sample (47.45 gm) at 22 and 24 MeV to investigate the weakly excited states above the 3/sub 1/..sqrt..(9.641 MeV) level in /sup 12/C. Differential cross sections for nine excited states in the first 15 MeV excitation of /sup 12/C were resolved and measured. New rotation-vibration formalisms were developed to be used with the code ECIS79 in order to analyze the collective motions of /sup 12/C. Excellent agreement between experimental data and theoretical calculation is obtained for (a) the ground state rotation band, (b) O/sub 2//sup +/ (7.655 MeV) state using ..beta..-vibration plus breathing mode, (c) the 1/sub 1//sup -/ (10.84 MeV) and 2/sub 1//sup -/ (11.83 MeV) states using K/sup ..pi../ = 1/sup -/ octupole vibration, and (d) the 3/sub 1//sup -/ (9.64 MeV) and 4/sub 1//sup -/ (13.35 MeV) states using K/sup ..pi../ = 3/sup -/ octupole vibration. An energy dependent optical model potential has been obtained that describes the present neutron scattering data, differential proton scattering data of higher energies and total neutron cross sections between 20 and 100 MeV.
NASA Astrophysics Data System (ADS)
Brand, Christian; Winkler, Andreas; Hess, Peter; Miklós, András; Bozóki, Zoltán; Sneider, János
1995-06-01
The pulsed excitation of acoustic resonances was studied with a continuously monitoring photoacoustic detector system. Acoustic waves were generated in C2H4/N 2 gas mixtures by light absorption of the pulses from a transversely excited atmospheric CO2 laser. The photoacoustic part consisted of high-Q cylindrical resonators (Q factor 820 for the first radial mode in N2) and two adjoining variable acoustic filter systems. The time-resolved signal was Fourier transformed to a frequency spectrum of high resolution. For the first radial mode a Lorentzian profile was fitted to the measured data. The outside noise suppression and the signal-to-noise ratio were investigated in a normal laboratory environment in the flow-through mode. The acoustic and electric filter system combined with the
Zhang Pei; Baboi, Nicoleta; Jones, Roger M.; Shinton, Ian R. R.; Flisgen, Thomas; Glock, Hans-Walter
2012-08-15
We investigate the feasibility of beam position diagnostics using higher order mode (HOM) signals excited by an electron beam in the third harmonic 3.9 GHz superconducting accelerating cavities at FLASH. After careful theoretical and experimental assessment of the HOM spectrum, three modal choices have been narrowed down to fulfill different diagnostics requirements. These are localized dipole beam-pipe modes, trapped cavity modes from the fifth dipole band, and propagating modes from the first two dipole bands. These modes are treated with various data analysis techniques: modal identification, direct linear regression (DLR), and singular value decomposition (SVD). Promising options for beam diagnostics are found from all three modal choices. This constitutes the first prediction, subsequently confirmed by experiments, of trapped HOMs in third harmonic cavities, and also the first direct comparison of DLR and SVD in the analysis of HOM-based beam diagnostics.
Zhang, Pei; Baboi, Nicoleta; Jones, Roger M; Shinton, Ian R R; Flisgen, Thomas; Glock, Hans-Walter
2012-08-01
We investigate the feasibility of beam position diagnostics using higher order mode (HOM) signals excited by an electron beam in the third harmonic 3.9 GHz superconducting accelerating cavities at FLASH. After careful theoretical and experimental assessment of the HOM spectrum, three modal choices have been narrowed down to fulfill different diagnostics requirements. These are localized dipole beam-pipe modes, trapped cavity modes from the fifth dipole band, and propagating modes from the first two dipole bands. These modes are treated with various data analysis techniques: modal identification, direct linear regression (DLR), and singular value decomposition (SVD). Promising options for beam diagnostics are found from all three modal choices. This constitutes the first prediction, subsequently confirmed by experiments, of trapped HOMs in third harmonic cavities, and also the first direct comparison of DLR and SVD in the analysis of HOM-based beam diagnostics.
Collective excitation of an electric dipole on a molecular dimer in an organic dimer-Mott insulator.
Itoh, K; Itoh, H; Naka, M; Saito, S; Hosako, I; Yoneyama, N; Ishihara, S; Sasaki, T; Iwai, S
2013-03-08
The terahertz response in 10-100 cm(-1) was investigated in an organic dimer-Mott (DM) insulator κ-(ET)(2)Cu(2)(CN)(3) that exhibits a relaxorlike dielectric anomaly. An ~30 cm(-1) band in the optical conductivity was attributable to collective excitation of the fluctuating intradimer electric dipoles that are formed by an electron correlation. We succeeded in observing photoinduced enhancement of this ~30 cm(-1) band, reflecting the growth of the electric dipole cluster in the DM phase. Such optical responses in κ-(ET)(2)Cu(2)(CN)(3) reflect an instability near the boundary between the DM-ferroelectric charge ordered phases.
NASA Astrophysics Data System (ADS)
Su, Nan
2017-03-01
I summarize recent developments in the hard-thermal-loop approach to QCD. I first discuss a finite-temperature and -density calculation of QCD thermodynamics at NNLO from the hard-thermal-loop perturbation theory. I then discuss a generalization of the hard-thermal-loop framework to the magnetic scale g2T, from which a novel non-Abelian massless mode is uncovered.
Salasnich, Luca; Malomed, Boris A; Toigo, Flavio
2014-10-01
We propose a possibility to simulate the exciton-polariton (EP) system in the lossless limit, which is not currently available in semiconductor microcavities, by means of a simple optical dual-core waveguide, with one core carrying the nonlinearity and operating close to the zero-group-velocity-dispersion point, and the other core being linear and dispersive. Both two-dimensional (2D) and one-dimensional (1D) EP systems may be emulated by means of this optical setting. In the framework of this system, we find that, while the uniform state corresponding to the lower branch of the nonlinear dispersion relation is stable against small perturbations, the upper branch is always subject to the modulational instability. The stability and instability are verified by direct simulations too. We analyze collective excitations on top of the stable lower-branch state, which include a Bogoliubov-like gapless mode and a gapped one. Analytical results are obtained for the corresponding sound velocity and energy gap. The effect of a uniform phase gradient (superflow) on the stability is considered too, with a conclusion that the lower-branch state becomes unstable above a critical wave number of the flux. Finally, we demonstrate that the stable 1D state may carry robust dark solitons.
Tuniz, Alessandro; Chemnitz, Mario; Dellith, Jan; Weidlich, Stefan; Schmidt, Markus A
2017-02-08
We propose and experimentally demonstrate a monolithic nanowire-enhanced fiber-based nanoprobe for the broadband delivery of light (550-730 nm) to a deep subwavelength scale using short-range surface plasmons. The geometry is formed by a step index fiber with an integrated gold nanowire in its core and a protruding gold nanotip with sub-10 nm apex radius. We present a novel coupling scheme to excite short-range surface plasmons, whereby the radially polarized hybrid mode propagating inside the nanowire section excites the plasmonic mode close to the fiber endface, which is in turn superfocused down to nanoscale dimensions at the tip apex. We show that in this all-integrated fiber-plasmonic coupling scheme the wire length can be orders of magnitude longer than the attenuation length of short-range plasmon polaritons, yielding a broadband plasmon excitation and reducing demands in fabrication. We observe that the scattered light in the far-field from the nanotip is axially polarized and preferentially excited by a radially polarized input, unambiguously revealing that it originates from a short-range plasmon propagating on the nanotip, in agreement with simulations. This novel excitation scheme will have important applications in near-field microscopy and nanophotonics and potentially offers significantly improved resolution compared to current delivery near-field probes.
Is it possible to enhance the nuclear Schiff moment by nuclear collective modes?
Auerbach, N. Dmitriev, V. F. Flambaum, V. V. Lisetskiy, A. Sen'kov, R. A. Zelevinsky, V. G.
2007-09-15
The nuclear Schiff moment is predicted to be enhanced in nuclei with static quadrupole and octupole deformation. The analogous suggestion of the enhanced contribution to the Schiff moment from the soft collective quadrupole and octupole vibrations in spherical nuclei is tested in the framework of the quasiparticle random phase approximation with separable quadrupole and octupole forces applied to the odd {sup 217-221}Ra and {sup 217-221}Rn isotopes. In this framework, we confirm the existence of the enhancement effect due to the soft modes, but only in the limit when the frequencies of quadrupole and octupole vibrations are close to zero.
Fingerprints of different interaction mechanisms on the collective modes in complex (dusty) plasmas
NASA Astrophysics Data System (ADS)
Khrapak, Sergey A.; Klumov, Boris A.; Thomas, Hubertus M.
2017-02-01
In this paper, we discuss the relations between the exact shape of interparticle interactions in complex (dusty) plasmas and the dispersion relation of the longitudinal collective mode. Several representative repulsive potentials, predicted previously theoretically, are chosen, and the corresponding dispersion relations are calculated using the quasi-crystalline approximation. Both weakly coupled and strongly coupled regimes are considered. It is shown that the long-wavelength portions of the dispersion curves can be sensitive to the long-range asymptote of the interaction potential. This can be used to discriminate between different interaction mechanisms operational in complex plasmas experimentally. Main requirements are briefly discussed.
Sesnic, S.; Kaita, R.; Kaye, S.; Okabayashi, M.; Takahashi, H.; Bell, R.E.; Bernabei, S.; Chance, M.S.; Hatcher, R.E.; Jardin, S.C.; Kessel, C.E.; Kugel, H.W.; LeBlanc, B.; Manickam, J.; Ono, M.; Paul, S.F.; Sauthoff, N.R.; Holland, A.; Asakura, N.; Duperrex, P.A.; Fonck, R.J.; Gammel, G.M.; Greene, G.J.; Jiang, T.W.; Levinton, F.M.; Powell, E.T.; Roberts, D.W.; Qin, Y.
1993-06-01
High-frequency pressure-driven modes have been observed in high-poloidal-{beta} discharges in the Princeton Beta Experiment-Modification (PBX-M). These modes are excited in a non-axisymmetric equilibrium characterized by a large, low frequency m{sub 1}=1/n{sub 1}=1 island, and they are capable of expelling fast ions. The modes reside on or very close to the q=1 surface, and have mode numbers with either m{sub h}=n{sub h} or (less probably) m{sub h}/n{sub h}=m{sub h}/(m{sub h}-1), with m{sub h} varying between 3 and 10. Occasionally, these modes are, simultaneously localized in the vicinity of the m{sub 1}=2/n{sub 1}=1 island. The high frequency modes near the q=1 surface also exhibit a ballooning character, being significantly stronger on the large major radius side of the plasma. When a large m{sub 1}=1/n{sub 1}=1 island is present the mode is poloidally localized in the immediate vicinity of the x-point of the island. The modes, which occur exclusively in high-{beta} discharges, appear to be driven by the plasma pressure or pressure gradient. They can thus be a manifestation of either a toroidicity-induced shear Alfven eigenmode (TAE) at q=(2m{sub h}+ 1)/2n{sub h}, a kinetic ballooning mode (KBM), or some other type of pressure-driven mode. Theory predicts that the TAE mode is a gap mode, but the high frequency modes in PBX-M are found exclusively on or in the immediate neighborhood of magnetic surfaces with low rational numbers.
Collective excitations of dipolar gases based on local tunneling in superlattices
NASA Astrophysics Data System (ADS)
Cao, Lushuai; Mistakidis, Simeon I.; Deng, Xing; Schmelcher, Peter
2017-01-01
The collective dynamics of a dipolar fermionic quantum gas confined in a one-dimensional double-well superlattice is explored. The fermionic gas resides in a paramagnetic-like ground state in the weak interaction regime, upon which a new type of collective dynamics is found when applying a local perturbation. This dynamics is composed of the local tunneling of fermions in separate supercells, and is a pure quantum effect, with no classical counterpart. Due to the presence of the dipolar interactions the local tunneling transports through the entire superlattice, giving rise to a collective dynamics. A well-defined momentum-energy dispersion relation is identified in the ab-initio simulations demonstrating the phonon-like behavior. The phonon-like characteristic is also confirmed by an analytical description of the dynamics within a semiclassical picture.
Tsekrekos, C P; Smink, R W; de Hon, B P; Tijhuis, A G; Koonen, A M
2007-04-02
Selective excitation of graded-index multimode fibers (GI-MMFs) with a single-mode fiber (SMF) has gained increased interest for telecommunication applications. It has been proposed as a way to enhance the transmission bandwidth of GI-MMF links and/or create parallel communication channels over the same GI-MMF. Although the effect of SMF excitation on the transmission bandwidth has been investigated, its impact on the near-field intensity pattern at the output face of the GI-MMF has not been systematically addressed. We have carried out an analysis of the near-field intensity pattern at the output face of silica-based GI-MMFs excited by a radially offset SMF. Simulation results exhibit all of the features displayed by experimental ones. It turns out that differential mode attenuation and delay, full intra-group mode mixing, and small deviations in the refractive index profile of the GI-MMF do not affect the overall shape of the near-field intensity, which is determined by the radial offset of the input SMF. This can be exploited in mode group diversity multiplexing links. The effect of defects in the refractive index profile, such as a central dip or peak, is also examined.
Kumar, D.; Barman, A.; Kłos, J. W.; Krawczyk, M.
2014-01-28
We present the observation of a complete bandgap and collective spin wave excitation in two-dimensional magnonic crystals comprised of arrays of nanoscale antidots and nanodots, respectively. Considering that the frequencies dealt with here fall in the microwave band, these findings can be used for the development of suitable magnonic metamaterials and spin wave based signal processing. We also present the application of a numerical procedure, to compute the dispersion relations of spin waves for any high symmetry direction in the first Brillouin zone. The results obtained from this procedure have been reproduced and verified by the well established plane wave method for an antidot lattice, when magnetization dynamics at antidot boundaries are pinned. The micromagnetic simulation based method can also be used to obtain iso–frequency contours of spin waves. Iso–frequency contours are analogous of the Fermi surfaces and hence, they have the potential to radicalize our understanding of spin wave dynamics. The physical origin of bands, partial and full magnonic bandgaps have been explained by plotting the spatial distribution of spin wave energy spectral density. Although, unfettered by rigid assumptions and approximations, which afflict most analytical methods used in the study of spin wave dynamics, micromagnetic simulations tend to be computationally demanding. Thus, the observation of collective spin wave excitation in the case of nanodot arrays, which can obviate the need to perform simulations, may also prove to be valuable.
Penedo, M. Hormeño, S.; Fernández-Martínez, I.; Luna, M.; Briones, F.; Raman, A.
2014-10-27
Recent developments in dynamic Atomic Force Microscopy where several eigenmodes are simultaneously excited in liquid media are proving to be an excellent tool in biological studies. Despite its relevance, the search for a reliable, efficient, and strong cantilever excitation method is still in progress. Herein, we present a theoretical modeling and experimental results of different actuation methods compatible with the operation of Atomic Force Microscopy in liquid environments: ideal acoustic, homogeneously distributed force, distributed applied torque (MAC Mode™), photothermal and magnetostrictive excitation. From the analysis of the results, it can be concluded that magnetostriction is the strongest and most efficient technique for higher eigenmode excitation when using soft cantilevers in liquid media.
Surface collective modes in the topological insulators Bi2Se3 and Bi0.5Sb1.5Te3-xSex
Kogar, A.; Gu, G.; Vig, S.; ...
2015-12-15
In this study, we used low-energy, momentum-resolved inelastic electron scattering to study surface collective modes of the three-dimensional topological insulators Bi2Se3 and Bi0.5Sb1.5Te3-xSex. Our goal was to identify the “spin plasmon” predicted by Raghu and co-workers [Phys. Rev. Lett. 104, 116401 (2010)]. Instead, we found that the primary collective mode is a surface plasmon arising from the bulk, free carriers in these materials. This excitation dominates the spectral weight in the bosonic function of the surface χ''(q,ω) at THz energy scales, and is the most likely origin of a quasiparticle dispersion kink observed in previous photoemission experiments. Our study suggestsmore » that the spin plasmon may mix with this other surface mode, calling for a more nuanced understanding of optical experiments in which the spin plasmon is reported to play a role.« less
Li, Xiaomin; Wang, Rui; Zhang, Fan; Zhou, Lei; Shen, Dengke; Yao, Chi; Zhao, Dongyuan
2013-12-18
Core/shell1/shell2/shell3 structured NaGdF4:Nd/NaYF4/NaGdF4:Nd,Yb,Er/NaYF4 nanocrystals were well designed and synthesized, each of the parts assume respective role and work together to achieve dual-mode upconverting (UC) and downconverting (DC) luminescence upon the low heat effect 800-nm excitation. Nd(3+), Yb(3+), Er(3+) tri-doped NaGdF4:Nd,Yb,Er UC layer [NIR (800 nm)-to-Visible (540 nm)] with a constitutional efficient 800 nm excitable property were achieved for the in-vitro bioimaging with low auto-fluorescence and photo-damage effects. Moreover, typical NIR (800 nm)-to-NIR (860-895 nm) DC luminescence of Nd(3+) has also been realized with this designed nanostructure. Due to the low heat effect, high penetration depth of the excitation and the high efficiency of the DC luminescence, the in-vivo high contrast DC imaging of a whole body nude mouse was achieved. We believe that such dual-mode luminescence NCs will open the door to engineering the excitation and emission wavelengths of NCs and will provide a new tool for a wide variety of applications in the fields of bioanalysis and biomedical.
NASA Astrophysics Data System (ADS)
Ahn, Kyo-Hoon; Lee, Kwan-Woo; Pickett, Warren E.
2015-09-01
NbP is one member of a new class of nodal loop semimetals characterized by the cooperative effects of spin-orbit coupling (SOC) and a lack of inversion center. Here transport and spectroscopic properties of NbP are evaluated using density functional theory methods. SOC together with the lack of inversion symmetry splits degeneracies, giving rise to "Russian doll nested" Fermi surfaces containing 4 ×10-4 electron (hole) carriers/f.u. Due to the modest SOC strength in Nb, the Fermi surfaces map out the Weyl nodal loops. Calculated structure around T*≈100 K in transport properties reproduces well the observed transport behavior only when SOC is included, attesting to the precision of the (delicate) calculations and the stoichiometry of the samples. Low-energy collective electron-hole excitations (plasmons) in the 20-60 meV range result from the nodal loop splitting.
Cowell, David M J; Smith, Peter R; Freear, Steven
2013-06-01
Switched-mode operation allows the miniaturization of excitation circuitry but suffers from high harmonic distortion. This paper presents a method of phase-inversion-based selective harmonic elimination (PI-SHE) and the use of multiple switching levels. PI-SHE is shown to enable multiples of any selected harmonic to be eliminated through controlled timing of the transition between different excitation voltage levels. Multiples of the third harmonic are shown to be eliminated in three-level tone waveforms. In addition, multiples of the fifth harmonic are shown to be eliminated using five-level tone waveforms. A method of calculating the expected amplitude of each harmonic is presented. The application of PI-SHE in linear frequency-modulated (LFM) excitation is proposed. A heuristic derivation of the spectral properties of multilevel switched LFM waveforms is presented. The performance of the proposed PI-SHE method is confirmed through experimental measurement of the harmonics present in an ultrasound wave using two, three, and five levels for both tone and LFM excitation. The proposed method of controlling harmonics through the use of multilevel switched excitation is especially suitable for applications in which portability, high channel counts, and precise harmonic control are required.
Numerical solution of the Boltzmann equation for the collective modes of trapped Fermi gases
Lepers, Thomas; Davesne, Dany; Chiacchiera, Silvia; Urban, Michael
2010-08-15
We numerically solve the Boltzmann equation for trapped fermions in the normal phase by using the test-particle method. After discussing a couple of tests in order to estimate the reliability of the method, we apply it to the description of collective modes in a spherical harmonic trap. The numerical results are compared with those obtained previously by taking moments of the Boltzmann equation. We find that the general shape of the response function is very similar in both methods, but the relaxation time obtained from the simulation is significantly longer than that predicted by the method of moments. It is shown that the result of the method of moments can be corrected by including fourth-order moments in addition to the usual second-order ones and that this method agrees very well with our numerical simulations.
Self consistent theories of superfluid density and collective modes in BCS-BEC
NASA Astrophysics Data System (ADS)
Boyack, Rufus; Anderson, Brandon; Wu, Chien-Te; Levin, Kathryn
Establishing fully self consistent and sum rule compatible response functions in strongly correlated Fermi superfluids has been a historically challenging subject. In this talk, we present recent progress pertaining to response functions in many-body Fermi systems. We note that even in strict BCS theory, the textbook derivation of density and current response functions in the gradient expansion breaks certain conservation laws such as the compressibility sum rule. To include additional contributions that preserve all expected conservation laws, we show how to exploit Ward identities within two different t-matrix schemes. In this way we address the density-density response (including collective modes) and the superfluid density. Finally, we characterize approximations made in the literature where some consistency requirements have been dropped.
Field-dependent Collective ESR Mode in YbRh2Si2
Petrovic, C.; Holanda, L.M.; Duque, J.G.S.; Bittar, E.M.; Adriano, C.; Pagliuso, P.G.; Rettori, C.; Hub, R.W.; Maquilon, S.; Fisk, Z.; Huber, D.L.; Oseroff, S.B.
2009-10-15
Electron spin resonance (ESR) experiments in YbRh{sub 2}Si{sub 2} Kondo lattice (T{sub K} {approx_equal} 25 K) at different field/frequencies (4.1 {le} v {le} 34.4 GHz) and H{sub {perpendicular}c} revealed: (i) a strong field dependent Yb{sup 3+} spin-lattice relaxation, (ii) a weak field and T-dependent effectiveg-value, (iii) a suppression of the ESR intensity beyond 15% of Lu-doping, and (iv) a strong sample and Lu-doping ({le}15%) dependence of the ESR data. These results suggest that the ESR signal in YbRh{sub 2}Si{sub 2} may be due to a coupled Yb{sup 3+}-conduction electron resonant collective mode with a subtle field-dependent spins dynamic.
NASA Technical Reports Server (NTRS)
Herbst, Eric; Winnewisser, G.; Yamada, K. M. T.; Defrees, D. J.; Mclean, A. D.
1989-01-01
A mechanism for the enhanced splitting detected in the millimeter-wave rotational spectra of the first excited S-S stretching state of HSSH (disulfane) has been studied. The mechanism, which involves a potential coupling between the first excited S-S stretching state and excited torsional states, has been investigated in part by the use of ab initio theory. Based on an ab initio potential surface, coupling matrix elements have been calculated, and the amount of splitting has then been estimated by second-order perturbation theory. The result, while not in quantitative agreement with the measured splitting, lends plausibility to the assumed mechanism.
Kushwaha, Manvir S
2011-09-28
We report on the theoretical investigation of the elementary electronic excitations in a quantum wire made up of vertically stacked self-assembled InAs/GaAs quantum dots. The length scales (of a few nanometers) involved in the experimental setups prompt us to consider an infinitely periodic system of two-dimensionally confined (InAs) quantum dot layers separated by GaAs spacers. The resultant quantum wire is characterized by a two-dimensional harmonic confining potential in the x-y plane and a periodic (Kronig-Penney) potential along the z (or the growth) direction within the tight-binding approximation. Since the wells and barriers are formed from two different materials, we employ the Bastard's boundary conditions in order to determine the eigenfunctions along the z direction. These wave functions are then used to generate the Wannier functions, which, in turn, constitute the legitimate Bloch functions that govern the electron dynamics along the direction of periodicity. Thus, the Bloch functions and the Hermite functions together characterize the whole system. We then make use of the Bohm-Pines' (full) random-phase approximation in order to derive a general nonlocal, dynamic dielectric function. Thus, developed theoretical framework is then specified to work within a (lowest miniband and) two-subband model that enables us to scrutinize the single-particle as well as collective responses of the system. We compute and discuss the behavior of the eigenfunctions, band-widths, density of states, Fermi energy, single-particle and collective excitations, and finally size up the importance of studying the inverse dielectric function in relation with the quantum transport phenomena. It is remarkable to notice how the variation in the barrier- and well-widths can allow us to tailor the excitation spectrum in the desired energy range. Given the advantage of the vertically stacked quantum dots over the planar ones and the foreseen applications in the single-electron devices
NASA Astrophysics Data System (ADS)
Golfinopoulos, Theodore
2013-10-01
Experiments indicate that short-wavelength, k⊥ρs ~ 0 . 1 , drift-Alfvénic turbulence plays an important role in C-Mod edge plasma transport. A Quasi-Coherent Mode (QCM, 50 < f < 150 kHz, k⊥ ~ 1 . 5 cm-1) regulates particle and impurity transport in C-Mod's EDA H-modes. A Weakly Coherent Mode (WCM, 150 < f < 500 kHz, k⊥ ~ 1 . 5 cm-1) plays a similar role in I-mode discharges, suppressing the formation of a density pedestal while maintaining a temperature pedestal. ELMs are not present in either confinement regime. With the idea of exciting, probing, and perhaps exploiting this transport behavior, we have developed a novel antenna system to excite drift-Alfvén-like modes at the outer midplane. A winding with a ``shoelace'' geometry is placed ~ 3 - 5 mm from the LCFS. The principal design parameters, k⊥ = 1 . 5 +/- 0 . 1 cm-1 and 45 < f < 300 kHz, match the QCM and WCM properties, so that the antenna induces parallel currents in the boundary plasma that mimic those observed for the intrinsic modes. Phase-locking to intrinsic modes is also accomplished via a custom circuit. The antenna produces perturbations in density and field comparable to amplitudes of the intrinsic QCM. The plasma response exhibits a resonance near the natural QCM frequency, which generally satisfies the drift wave dispersion relation. While a driven B~θ fluctuation is visible throughout the discharge, the driven ñe is only observed during H-mode, though it precedes the onset of the intrinsic QCM. Like the QCM, the driven mode propagates in the electron diamagnetic drift direction and is approximately field-aligned. Recent mirror probe measurements show the intrinsic QCM structure is predominantly drift-Alfvénic, and we might expect the same of the driven mode. However, the induced perturbation is not global, but is localized to field lines which map to the antenna, suggesting a damped response, and direct measurements of the damping rate indicate γ /ω0 ~ 5 %. If the antenna
Luong, Gloria; Charles, Susan T.; Rook, Karen S.; Reynolds, Chandra A.; Gatz, Margaret
2015-01-01
The current study investigated how participant aging may influence mode effects, wherein individuals report less negative and more positive psychosocial functioning with data collection modes that have greater (vs. less) direct contact with interviewers (e.g., in-person interviews vs. telephone interviews). Using two longitudinal datasets, the Later Life Study of Social Exchanges (LLSSE) and Swedish Adoption/Twin Study of Aging (SATSA), we tested how mode effects may vary with cohort (baseline age differences) and maturational development (longitudinal change). In Study 1, LLSSE participants (65–90 years old) completed in-person and telephone interviews assessing negative and positive aspects of psychosocial functioning across two years. The data collection mode with greater direct contact with interviewers (in-person interviews) was associated with reporting less negative and more positive psychosocial functioning compared to the mode with less direct contact (telephone interviews). These mode effects were more pronounced with older baseline age, but only for the negative psychosocial measures. Mode effects also became stronger over time for reports of negative affect. In Study 2, SATSA participants (38–86 years old) completed mailed questionnaires and questionnaires collected in-person that assessed depressive symptoms and positive affect across 18 years. Consistent with Study 1, participants reported fewer depressive symptoms and more positive affect with greater (vs. less) direct contact with interviewers (questionnaires collected in-person vs. mailed questionnaires). For reports of depressive symptoms, but not positive affect, mode effects were more pronounced with age and time. Together, the results underscore how mode effects may contribute to inconsistent findings in the socioemotional aging literature. PMID:25528065
Three-photon excitation in fluorescence microscopy
NASA Astrophysics Data System (ADS)
Hell, Stefan W.; Bahlmann, Karsten; Schrader, Martin; Soini, Aleksi; Malak, Henryk; Gryczynski, Ignacy; Lakowicz, Joseph R.
1996-01-01
We show experiments proving the feasibility of scanning fluorescence microscopy by three-photon excitation. Three-photon excitation fluorescence axial images are shown of polystyrene beads stained with the fluorophore 2,5- bis(4-biphenyl)oxazole (BBO). Three-photon excitation is performed at an excitation wavelength of 900 nm and with pulses of 130 fs duration provided by a mode-locked titanium-sapphire laser. Fluorescence is collected between 350 and 450 nm. The fluorescence image signal features a third-order dependence on the excitation power, also providing intrinsic 3-D imaging. The resolution of a three-photon excitation microscope is increased over that of a comparable two-photon excitation microscope.
Marler, J. P.; Surko, C. M.
2005-12-15
Absolute measurements are presented for the excitation of the {nu}{sub 3} vibrational mode in CF{sub 4} by positron and electron impact from 0.1 to 2 eV. To minimize systematic differences, these measurements were made using the same trap-based electron or positron beam, associated experimental apparatus, and procedures. Unlike other vibrational excitation cross sections studied to date, the near-threshold cross section for the {nu}{sub 3} vibrational mode in CF{sub 4} is similar, both in magnitude and shape, for positrons and electrons. Comparison of the cross sections with an analytic Born dipole model yields good agreement, while comparison of this model with other measured positron-impact vibrational cross sections indicates that the contribution of this long-range dipole coupling varies widely. The maximum value of the cross section in CF{sub 4} is the largest of any positron-impact vibrational excitation cross section measured to date. This provides a likely explanation of the observation that CF{sub 4} is very effective when used as a buffer gas to cool positron gases and plasmas.
NASA Astrophysics Data System (ADS)
Miao, Hongchen; Huan, Qiang; Li, Faxin
2016-11-01
The fundamental shear horizontal (SH0) wave in plate-like structures is of great importance in non-destructive testing (NDT) and structural health monitoring (SHM) as it is non-dispersive, while excitation or reception of SH0 waves using piezoelectrics is always a challenge. In this work, we firstly demonstrate via finite element simulations that face-shear piezoelectrics is superior to thickness-shear piezoelectrics in driving SH waves. Next, by using a newly defined face-shear d24 PZT wafer as an actuator and face-shear d36 PMN-PT wafers as sensors, pure SH0 wave was successfully excited in an aluminum plate from 130 to 180 kHz. Then, it was shown that the face-shear d24 PZT wafer could receive the SH0 wave only and filter the Lamb waves over a wide frequency range (120-230 kHz). The directionality of the excited SH0 wave was also investigated using face-shear d24 PZT wafers as both actuators and sensors. Results show that pure SH0 wave can be excited symmetrically along two orthogonal directions (0° and 90°) and the amplitude of the excited SH0 wave can keep over 90% of the maximum amplitude when the deviate angle is within 30°. This work could greatly promote the applications of SH0 wave in NDT and SHM.
Collective modes of a one-dimensional trapped Bose gas in the presence of the anomalous density
NASA Astrophysics Data System (ADS)
Boudjemâa, Abdelâali
2016-11-01
We study the collective modes of a one-dimensional harmonically trapped Bose-Einstein condensate in the presence of the anomalous density using the time-dependent Hartree-Fock-Bogoliubov theory. Within the hydrodynamic equations, we derive analytical expressions for the mode frequencies and the density fluctuations of the anomalous density which constitutes the minority component at very low temperature and feels an effective external potential exerted by the majority component, i.e., the condensate. On the other hand, we numerically examine the temperature dependence of the breathing mode oscillations of the condensate at finite temperature in the weak-coupling regime. At zero temperature, we compare our predictions with available experimental data, theoretical treatments, and Monte carlo simulations in all interaction regimes and the remaining hindrances are emphasized. We show that the anomalous correlations have a non-negligible role on the collective modes at both zero and finite temperatures.
Golfinopoulos, T.; LaBombard, B.; Parker, R. R.; Burke, W.; Davis, E.; Granetz, R.; Greenwald, M.; Irby, J.; Leccacorvi, R.; Marmar, E.; Parkin, W.; Porkolab, M.; Terry, J.; Vieira, R.; Wolfe, S.
2014-05-15
A novel “Shoelace” antenna has been used to inductively excite a short-wavelength edge fluctuation in a tokamak boundary layer for the first time. The principal design parameters, k{sub ⊥}=1.5±0.1 cm{sup −1} and 45
NASA Astrophysics Data System (ADS)
Gascoyne, A.; Jain, R.; Hindman, B. W.
2014-07-01
We consider damping and absorption of solar p modes due to their energy loss to magnetic tube waves that can freely carry energy out of the acoustic cavity. The coupling of p modes and sausage tube waves is studied in a model atmosphere composed of a polytropic interior above which lies an isothermal upper atmosphere. The sausage tube waves, excited by p modes, propagate along a magnetic fibril which is assumed to be a vertically aligned, stratified, thin magnetic flux tube. The deficit of p-mode energy is quantified through the damping rate, Γ, and absorption coefficient, α. The variation of Γ and α as a function of frequency and the tube's plasma properties is studied in detail. Previous similar studies have considered only a subphotospheric layer, modeled as a polytrope that has been truncated at the photosphere. Such studies have found that the resulting energy loss by the p modes is very sensitive to the upper boundary condition, which, due to the lack of an upper atmosphere, have been imposed in a somewhat ad hoc manner. The model presented here avoids such problems by using an isothermal layer to model the overlying atmosphere (chromosphere, and, consequently, allows us to analyze the propagation of p-mode-driven sausage waves above the photosphere. In this paper, we restrict our attention to frequencies below the acoustic cut off frequency. We demonstrate the importance of coupling all waves (acoustic, magnetic) in the subsurface solar atmosphere with the overlying atmosphere in order to accurately model the interaction of solar f and p modes with sausage tube waves. In calculating the absorption and damping of p modes, we find that for low frequencies, below ≈3.5 mHz, the isothermal atmosphere, for the two-region model, behaves like a stress-free boundary condition applied at the interface (z = -z 0).
Sabaeian, Mohammad; Rezaei, Hamidreza; Ghalambor-Dezfouli, Abdolmohammad
2017-02-01
Pulsed laser beam excitations are more commonly used in thermal lens spectroscopy (TLS) than continuous-wave (CW) ones, because CW excitations limit the measurement to linear absorption processes [J. Opt. A5, 256 (2003)]. In this work, we present a new and full analytical model for a single-pulsed laser excitation dual-beam mode-mismatched TLS for low absorption solid-state and liquid samples. Our model has been based on a new solution of time-dependent heat equation for a finite-radius cylindrical sample exposed to a single-pulsed excitation laser beam. For low absorbent samples, unlike previous models, all aberration terms associated in the thermal lens were taken into account in Fresnel integration. Besides, the model provides a full analytical mathematical expression for the temperature rise, normalized signal intensity, and Z-scan photothermal lens signal. The model was confirmed with experimental data of distilled deionized water with excellent agreement. Therefore, the model allows us to extract thermo-optical properties of samples in an analytical and more accurate way.
2012-01-01
RECS relies on actual records from energy suppliers to produce robust survey estimates of household energy consumption and expenditures. During the RECS Energy Supplier Survey (ESS), energy billing records are collected from the companies that supply electricity, natural gas, fuel oil/kerosene, and propane (LPG) to the interviewed households. As Federal agencies expand the use of administrative records to enhance, replace, or evaluate survey data, EIA has explored more flexible, reliable and efficient techniques to collect energy billing records. The ESS has historically been a mail-administered survey, but EIA introduced web data collection with the 2009 RECS ESS. In that survey, energy suppliers self-selected their reporting mode among several options: standardized paper form, on-line fillable form or spreadsheet, or failing all else, a nonstandard format of their choosing. In this paper, EIA describes where reporting mode appears to influence the data quality. We detail the reporting modes, the embedded and post-hoc quality control and consistency checks that were performed, the extent of detectable errors, and the methods used for correcting data errors. We explore by mode the levels of unit and item nonresponse, number of errors, and corrections made to the data. In summary, we find notable differences in data quality between modes and analyze where the benefits of offering these new modes outweigh the "costs".
Aremu, A S; Vijay, Ritesh; Adeleke, O O
2013-01-01
The use of hauled container system for municipal solid waste collection and transportation often results in socio-economic and environmental impacts which are linearly related to trip time. In this study, trip times for the conventional and exchange container mode of solid waste collection by the hauled container system were evaluated. A trip time model was developed for this evaluation through field studies. The model was applied on ten trips to collect solid waste bins and its transportation to disposal site in the city of Ilorin, Nigeria. The results of the model for both modes were compared and Showed that at 5 % significance level,.the trip time for the conventional mode was greater than the trip time for the exchange container mode. Also, the exchange container mode resulted in haul distance reduction by 3 to 15% and trip time reduction by 2.5 to 13 %. This reduction could help in improving logistics and also reduce the negative, impacts associated with collection operation.
Ground state, collective mode, phase soliton and vortex in multiband superconductors.
Lin, Shi-Zeng
2014-12-10
This article reviews theoretical and experimental work on the novel physics in multiband superconductors. Multiband superconductors are characterized by multiple superconducting energy gaps in different bands with interaction between Cooper pairs in these bands. The discovery of prominent multiband superconductors MgB2 and later iron-based superconductors, has triggered enormous interest in multiband superconductors. The most recently discovered superconductors exhibit multiband features. The multiband superconductors possess novel properties that are not shared with their single-band counterpart. Examples include: the time-reversal symmetry broken state in multiband superconductors with frustrated interband couplings; the collective oscillation of number of Cooper pairs between different bands, known as the Leggett mode; and the phase soliton and fractional vortex, which are the main focus of this review. This review presents a survey of a wide range of theoretical exploratory and experimental investigations of novel physics in multiband superconductors. A vast amount of information derived from these studies is shown to highlight unusual and unique properties of multiband superconductors and to reveal the challenges and opportunities in the research on the multiband superconductivity.
Sakong, Sung; Kratzer, Peter
2010-08-07
Density functional theory (DFT) calculations are used to determine the vibrational modes of hydrogen adsorbed on graphene in the low-coverage limit. Both the calculated adsorption energy of a H atom of 0.8 eV and calculated C-H stretch vibrational frequency of 2552 cm(-1) are unusually low for hydrocarbons, but in agreement with data from electron energy loss spectroscopy on hydrogenated graphite. The clustering of two adsorbed H atoms observed in scanning tunneling microscopy images shows its fingerprint also in our calculated spectra. The energetically preferred adsorption on different sublattices correlates with a blueshift of the C-H stretch vibrational modes in H adatom clusters. The C-H bending modes are calculated to be in the 1100 cm(-1) range, resonant with the graphene phonons. Moreover, we use our previously developed methods to calculate the relaxation of the C-H stretch mode via vibration-phonon interaction, using the Born-Oppenheimer surface for all local modes as obtained from the DFT calculations. The total decay rate of the H stretch into other H vibrations, thereby creating or annihilating one graphene phonon, is determined from Fermi's golden rule. Our calculations using the matrix elements derived from DFT calculations show that the lifetime of the H stretch mode on graphene is only several picoseconds, much shorter than on other semiconductor surfaces such as Ge(001) and Si(001).
NASA Astrophysics Data System (ADS)
Wu, Rukuan; Shi, Yu
2011-02-01
A mixture of two species of pseudospin-(1)/(2) Bose gases exhibits interesting interplay between spin and orbital degrees of freedom. Expectation values of various quantities of the collective spins of the two species play crucial roles in the Gross-Pitaevskii-like equations governing the four orbital wave functions in which Bose-Einstein condensation occurs. Consequently, the elementary excitations of these orbital wave functions reflect properties of the collective spins. When the coupling between the two collective spins is isotropic, the energy gap of the gapped orbital excitation peaks. There is a quantum phase transition in the ground state of the effective Hamiltonian of the two collective spins, which have previously been found to be maximally entangled.
Sergeicheva, E. G.; Sosin, S. S.; Prozorova, L. A.; ...
2017-01-18
We report on an electron spin resonance (ESR) study of a nearly one-dimensional (1D) spin-1/2 chain antiferromagnet, Sr2CuO3, with extremely weak magnetic ordering. The ESR spectra at T > TN, in the disordered Luttinger-spin-liquid phase, reveal nearly ideal Heisenberg-chain behavior with only a very small, field-independent linewidth, ~1/T. In the ordered state, below TN, we identify field-dependent antiferromagnetic resonance modes, which are well described by pseudo-Goldstone magnons in the model of a collinear biaxial antiferromagnet. Additionally, we observe a major resonant mode with unusual and strongly anisotropic properties, which is not anticipated by the conventional theory of Goldstone spin waves.more » Lastly, we propose that this unexpected magnetic excitation can be attributed to a field-independent magnon mode renormalized due to its interaction with the high-energy amplitude (Higgs) mode in the regime of weak spontaneous symmetry breaking.« less
Akimov, Yu A; Koh, W S; Ostrikov, K
2009-06-08
Recent research in the rapidly emerging field of plasmonics has shown the potential to significantly enhance light trapping inside thin-film solar cells by using metallic nanoparticles. In this article it is demonstrated the plasmon enhancement of optical absorption in amorphous silicon solar cells by using silver nanoparticles. Based on the analysis of the higher-order surface plasmon modes, it is shown how spectral positions of the surface plasmons affect the plasmonic enhancement of thin-film solar cells. By using the predictive 3D modeling, we investigate the effect of the higher-order modes on that enhancement. Finally, we suggest how to maximize the light trapping and optical absorption in the thin-film cell by optimizing the nanoparticle array parameters, which in turn can be used to fine tune the corresponding surface plasmon modes.
NASA Astrophysics Data System (ADS)
Verma, Kanika; Sajal, Vivek; Baliyan, Sweta; Kumar, Ravindra; Sharma, Navneet K.
2015-06-01
The stimulated Brillouin scattering (SBS) of nonresonant beat mode in the presence of static magnetic field is investigated in a plasma. Two counter-propagating lasers of frequencies ( ω 1 and ω 2 ) and wave vectors ( k 1 and k 2 ) drive a nonresonant space charge beat mode at the phase matching condition of frequency ω 0 ≈ ω 1 ˜ ω 2 and wave number k → 0 ≈ k → 1 + k → 2 . The driver wave parametrically excites a pair of ion acoustic wave ( ω , k → ) and a sideband electromagnetic wave ( ω 3 , k → 3 ) . The beat wave couples with the sideband electromagnetic wave to exert a nonlinear ponderomotive force at the frequency of ion acoustic wave. Density perturbations due to ion acoustic wave and ponderomotive force couple with the oscillatory motion of plasma electron due to velocity of beat wave to give rise to a nonlinear current (by feedback mechanism) responsible for the growth of sideband wave at resonance. The growth rate of SBS was reduced (from ˜ 10 12 s - 1 to 10 10 s - 1 ) by applying a transverse static magnetic field ˜ 90 T. The present study can be useful for the excitation of fast plasma waves (for the purpose of electron acceleration) by two counter-propagating laser beams.
Sun, Jin; Li, Guang; Liang, WanZhen
2015-07-14
A real-time time-dependent density functional theory coupled with the classical electrodynamics finite difference time domain technique is employed to systematically investigate the optical properties of hybrid systems composed of silver nanoparticles (NPs) and organic adsorbates. The results demonstrate that the molecular absorption spectra throughout the whole energy range can be enhanced by the surface plasmon resonance of Ag NPs; however, the absorption enhancement ratio (AER) for each absorption band differs significantly from the others, leading to the quite different spectral profiles of the hybrid complexes in contrast to those of isolated molecules or sole NPs. Detailed investigations reveal that the AER is sensitive to the energy gap between the molecular excitation and plasmon modes. As anticipated, two separate absorption bands, corresponding to the isolated molecules and sole NPs, have been observed at a large energy gap. When the energy gap approaches zero, the molecular excitation strongly couples with the plasmon mode to form the hybrid exciton band, which possesses the significantly enhanced absorption intensity, a red-shifted peak position, a surprising strongly asymmetric shape of the absorption band, and the nonlinear Fano effect. Furthermore, the dependence of surface localized fields and the scattering response functions (SRFs) on the geometrical parameters of NPs, the NP-molecule separation distance, and the external-field polarizations has also been depicted.
Samsonoff, Nathan; Ooms, Matthew D.; Sinton, David
2014-01-27
Excitation of photosynthetic biofilms using surface-confined evanescent light fields enables energy dense photobioreactors, while electrode-adhered biofilms can provide electricity directly. Here, we demonstrate concurrent light delivery and electron transport through a plasmonically excited metal film. Biofilms of cyanobacterium Synechococcus bacillaris on 50-nm gold films are excited via the Kretschmann configuration at λ = 670 nm. Cells show light/dark response to plasmonic excitation and grow denser biofilms, closer to the electrode surface, as compared to the direct irradiated case. Directly irradiated biofilms produced average electrical powers of 5.7 μW/m{sup 2} and plasmonically excited biofilms produced average electrical powers of 5.8 μW/m{sup 2}, with individual biofilms producing as much as 12 μW/m{sup 2}.
NASA Astrophysics Data System (ADS)
Samsonoff, Nathan; Ooms, Matthew D.; Sinton, David
2014-01-01
Excitation of photosynthetic biofilms using surface-confined evanescent light fields enables energy dense photobioreactors, while electrode-adhered biofilms can provide electricity directly. Here, we demonstrate concurrent light delivery and electron transport through a plasmonically excited metal film. Biofilms of cyanobacterium Synechococcus bacillaris on 50-nm gold films are excited via the Kretschmann configuration at λ = 670 nm. Cells show light/dark response to plasmonic excitation and grow denser biofilms, closer to the electrode surface, as compared to the direct irradiated case. Directly irradiated biofilms produced average electrical powers of 5.7 μW/m2 and plasmonically excited biofilms produced average electrical powers of 5.8 μW/m2, with individual biofilms producing as much as 12 μW/m2.
Collective edge modes near the onset of a graphene quantum spin Hall state
NASA Astrophysics Data System (ADS)
Murthy, Ganpathy; Shimshoni, Efrat; Fertig, H. A.
2014-12-01
Graphene subject to a strong, tilted magnetic field exhibits an insulator-metal transition tunable by tilt angle, attributed to the transition from a canted antiferromagnetic (CAF) to a ferromagnetic (FM) bulk state at filling factor ν =0 . We develop a theoretical description for the spin and valley edge textures in the two phases, and the implied evolution in the nature of edge modes through the transition. In particular, we show that the CAF has gapless neutral modes in the bulk, but supports gapped charged edge modes. At the transition to the FM state the charged edge modes become gapless and are smoothly connected to the helical edge modes of the FM state. Possible experimental consequences are discussed.
Agula, Justina; Barrett, Jennifer B; Tobi, Hilde
2015-09-01
Accurate data on young people's sexual behaviour and sexual health practice is essential to inform effective interventions and policy. However, little empirical evidence exists to support methodological design decisions in projects assessing young people's sexual health, especially in African contexts. This short report uses original empirical data collected in Ghana in 2012 to assess the effects of data collection mode and interviewer gender on young people's reporting of sexual health and access to supportive sexual health resources. The findings indicate that the effect of data collection mode may vary by gender, and there is no indication of an interviewer gender effect for males in this study. Preliminary results suggest that building strong rapport with research participants in this context may lead to reduced sexual health data quality. These findings merit further investigation and have direct implications for the design of projects measuring sexual health and related variables in Ghana.
NASA Astrophysics Data System (ADS)
Verma, Kanika; Sajal, Vivek; Kumar, Ravindra; Sharma, Navneet K.
2016-01-01
The decay instability of non-resonant beat mode is investigated in homogeneous, hot, and collision less plasma having transverse static magnetic field. Two counter-propagating X-mode lasers with frequency difference ω1˜ω2≥2 ωp and wave numbers k→ 1 and k→ 2 drive a non-resonant space charge beat wave at phase matching conditions of frequency ω0=ω1˜ω2 and wave numbers k→ 0=k→ 1+k→ 2 . The driven beat wave acts as a pump for decay instability and parametrically excites a pair of lower hybrid wave (ω,k → ) and sideband upper hybrid wave (ω3,k→ 3) propagating in sideward direction so that momentum remains conserved. The sideband wave couples with the driver beat wave to exert ponderomotive force on plasma electrons at frequency ω=ω0+ω3 . The oscillatory motion of plasma electrons due to ponderomotive force and lower hybrid wave causes density perturbation in plasma, which couples with oscillating beat mode by feedback mechanism and gives rise to a sideband wave at resonance. The maximum growth rate is achieved at scattering angels θs˜30 ° and θs˜150 ° . The growth rate becomes half by changing applied magnetic field from ˜90 T to ˜270 T . The suppression of decay instability can be beneficial for parametric excitation of fast plasma wave (coupled with slow plasma wave) by two counter-propagating lasers for electron acceleration.
NASA Astrophysics Data System (ADS)
Dorfman, S. E.; Carter, T. A.; Pribyl, P.; Tripathi, S.; Van Compernolle, B.; Vincena, S. T.; Sydora, R. D.
2013-12-01
Alfvén waves, a fundamental mode of magnetized plasmas, are ubiquitous in space plasmas. While the linear behavior of these waves has been extensively studied [1], non-linear effects are important in many real systems, including the solar corona and solar wind. In particular, a parametric decay process in which a large amplitude Alfvén wave decays into an ion acoustic wave and backward propagating Alfvén wave may play an important role in the coronal heating problem. Specifically, the decay of large-amplitude Alfvén waves propagating outward from the photosphere could lead to heating of the corona by the daughter ion acoustic modes [2]. As direct observational evidence of parametric decay is limited [3], laboratory experiments may play an important role in validating simple theoretical predictions and aiding in the interpretation of space measurements. Recent counter-propagating Alfvén wave experiments in the Large Plasma Device (LAPD) have recorded the first laboratory observation of the Alfvén-acoustic mode coupling at the heart of this parametric decay instability [4]. A resonance in the beat wave response produced by the two launched Alfvén waves is observed and is identified as a damped ion acoustic mode based on the measured dispersion relation. Other properties of the interaction including the spatial profile of the beat mode and response amplitude are also consistent with theoretical predictions for a three-wave interaction driven by a nonlinear ponderomotive force. Strong damping observed after the pump Alfvén waves are turned off is under investigation; a novel ion acoustic wave launcher is under development to launch the mode directly for damping studies. New experiments also aim to identify decay instabilities from a single large-amplitude Alfvén wave. In conjunction with these experiments, gyrokinetic simulation efforts are underway to scope out the relevant parameter space. [1] W. Gekelman, et. al., Phys. Plasmas 18, 055501 (2011). [2] F
Dorfman, S.; Carter, T. A.
2015-05-15
The nonlinear three-wave interaction process at the heart of the parametric decay process is studied by launching counter-propagating Alfvén waves from antennas placed at either end of the Large Plasma Device [W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)]. A resonance in the beat wave response produced by the two launched Alfvén waves is observed and is identified as a damped ion acoustic mode based on the measured dispersion relation. Other properties of the interaction including the spatial profile of the beat mode and response amplitude are also consistent with theoretical predictions for a three-wave interaction driven by a nonlinear ponderomotive force. A simple damped, driven oscillator model making use of the MHD equations well-predicts most of the observations, but the width of the resonance curve is still under investigation.
NASA Astrophysics Data System (ADS)
Yang, Jaehak; Kim, Junhoe; Kim, Bosung; Cho, Young-Jun; Lee, Jae-Hyeok; Kim, Sang-Koog
2016-07-01
We performed micromagnetic numerical calculations to explore a cylindrical nanotube's magnetization dynamics and domain-wall (DW) motions driven by eigen-circular-rotating magnetic fields of different frequencies. We discovered the presence of two different localized DW oscillations as well as asymmetric ferromagnetic resonance precession and azimuthal spin-wave modes at the corresponding resonant frequencies of the circular-rotating fields. Associated with these intrinsic modes, there exist very contrasting DW motions of different speed and propagation direction for a given DW chirality. The direction and speed of the DW propagation were found to be controllable according to the rotation sense and frequency of noncontact circular-rotating fields. Furthermore, spin-wave emissions from the moving DW were observed at a specific field frequency along with their Doppler effect. This work furthers the fundamental understanding of soft magnetic nanotubes' intrinsic dynamic modes and spin-wave emissions and offers an efficient means of manipulating the speed and direction of their DW propagations.
Individual and collective vibrational modes of nanostructures studied by picosecond ultrasonics.
Bienville, T; Robillard, J F; Belliard, L; Roch-Jeune, I; Devos, A; Perrin, B
2006-12-22
We report on picosecond ultrasonic measurements obtained on aluminum and platinum nanostructures with variable dot size and lateral periodicity which realized a 2D phononic crystal. Performing investigations at different resolution scales, we have identified individual modes of vibration depending on the dot size, and mode of vibration strongly correlated with the bi-dimensional organization. The platinum dots sputtered on an aluminum layer have shown a behavior of isolated oscillators without any coupling between neighbor elements in this phononic crystal. The frequency of such normal modes, extracted from time resolved measurements are in good agreement with 3D finite element simulations. In contrast, with aluminum dot systems where the coupling is more efficient we observe a complex spectrum of vibrational modes related to the band structure induced by the bi-dimensional patterning.
NASA Astrophysics Data System (ADS)
Avrutin, Evgenii A.; Arnold, John M.; Marsh, John H.
1996-04-01
A distributed time-domain model is used for a numerical analysis of the dynamics of a passively mode locked laser diode under external modulation at a frequency close to the round-trip frequency of the laser. The possible dynamical regimes of the laser are identified as synchronization locking, frequency mixing and chaotic dynamics, including a special case of quasi-locking. For the locked regime, steady-state parameters are defined, the crucial role of group-velocity dispersion in achieving locking demonstrated and stages of the locking dynamics and corresponding time constants identified.
Chenel, Aurélie; Mangaud, Etienne; Burghardt, Irene E-mail: chris@irsamc.ups-tlse.fr; Meier, Christoph E-mail: chris@irsamc.ups-tlse.fr; Desouter-Lecomte, Michèle E-mail: chris@irsamc.ups-tlse.fr
2014-01-28
Following the recent quantum dynamics investigation of the charge transfer at an oligothiophene-fullerene heterojunction by the multi-configuration time dependent Hartree method [H. Tamura, R. Martinazzo, M. Ruckenbauer and I. Burghardt, J. Chem. Phys. 137, 22A540 (2012)], we revisit the transfer process by a perturbative non-Markovian master equation treated by the time local auxiliary density matrix approach. We compare the efficiency of the spin-boson model calibrated by quantum chemistry with the effective mode representation. A collective mode is extracted from the spin-boson spectral density. It is weakly coupled to a residual bath of vibrational modes, allowing second-order dynamics. The electron transfer is analyzed for a sampling of inter-fragment distances showing the fine interplay of the electronic coupling and energy gap on the relaxation. The electronic coherence, expected to play a role in the process, is preserved during about 200 fs.
NASA Astrophysics Data System (ADS)
Heilman, A. L.; Gordon, M. J.
2016-06-01
A tip-enhanced near-field optical microscope with side-on and attenuated total reflectance (ATR) excitation and collection is described and used to demonstrate sub-diffraction-limited (super-resolution) optical and chemical characterization of surfaces. ATR illumination is combined with an Au optical antenna tip to show that (i) the tip can quantitatively transduce the optical near-field (evanescent waves) above the surface by scattering photons into the far-field, (ii) the ATR geometry enables excitation and characterization of surface plasmon polaritons (SPPs), whose associated optical fields are shown to enhance Raman scattering from a thin layer of copper phthalocyanine (CuPc), and (iii) SPPs can be used to plasmonically excite the tip for super-resolution chemical imaging of patterned CuPc via tip-enhanced Raman spectroscopy (TERS). ATR-illumination TERS is also quantitatively compared with the more conventional side-on illumination scheme. In both cases, spatial resolution was better than 40 nm and tip on/tip off Raman enhancement factors were >6500. Furthermore, ATR illumination was shown to provide similar Raman signal levels at lower "effective" pump powers due to additional optical energy delivered by SPPs to the active region in the tip-surface gap.
NASA Astrophysics Data System (ADS)
Bangert, U.; Pierce, W.; Boothroyd, C.; Pan, C.-T.; Gwilliam, R.
2016-06-01
Plasmons in the visible/UV energy regime have attracted great attention, especially in nano-materials, with regards to applications in opto-electronics and light harvesting; tailored enhancement of such plasmons is of particular interest for prospects in nano-plasmonics. This work demonstrates that it is possible, by adequate doping, to create excitations in the visible/UV regime in nano-carbon materials, i.e., carbon nanotubes and graphene, with choice of suitable ad-atoms and dopants, which are introduced directly into the lattice by low energy ion implantation or added via deposition by evaporation. Investigations as to whether these excitations are of collective nature, i.e., have plasmonic character, are carried out via DFT calculations and experiment-based extraction of the dielectric function. They give evidence of collective excitation behaviour for a number of the introduced impurity species, including K, Ag, B, N, and Pd. It is furthermore demonstrated that such excitations can be concentrated at nano-features, e.g., along nano-holes in graphene through metal atoms adhering to the edges of these holes.
Bangert, U.; Pierce, W.; Boothroyd, C.; Pan, C.-T.; Gwilliam, R.
2016-01-01
Plasmons in the visible/UV energy regime have attracted great attention, especially in nano-materials, with regards to applications in opto-electronics and light harvesting; tailored enhancement of such plasmons is of particular interest for prospects in nano-plasmonics. This work demonstrates that it is possible, by adequate doping, to create excitations in the visible/UV regime in nano-carbon materials, i.e., carbon nanotubes and graphene, with choice of suitable ad-atoms and dopants, which are introduced directly into the lattice by low energy ion implantation or added via deposition by evaporation. Investigations as to whether these excitations are of collective nature, i.e., have plasmonic character, are carried out via DFT calculations and experiment-based extraction of the dielectric function. They give evidence of collective excitation behaviour for a number of the introduced impurity species, including K, Ag, B, N, and Pd. It is furthermore demonstrated that such excitations can be concentrated at nano-features, e.g., along nano-holes in graphene through metal atoms adhering to the edges of these holes. PMID:27271352
Bangert, U; Pierce, W; Boothroyd, C; Pan, C-T; Gwilliam, R
2016-06-07
Plasmons in the visible/UV energy regime have attracted great attention, especially in nano-materials, with regards to applications in opto-electronics and light harvesting; tailored enhancement of such plasmons is of particular interest for prospects in nano-plasmonics. This work demonstrates that it is possible, by adequate doping, to create excitations in the visible/UV regime in nano-carbon materials, i.e., carbon nanotubes and graphene, with choice of suitable ad-atoms and dopants, which are introduced directly into the lattice by low energy ion implantation or added via deposition by evaporation. Investigations as to whether these excitations are of collective nature, i.e., have plasmonic character, are carried out via DFT calculations and experiment-based extraction of the dielectric function. They give evidence of collective excitation behaviour for a number of the introduced impurity species, including K, Ag, B, N, and Pd. It is furthermore demonstrated that such excitations can be concentrated at nano-features, e.g., along nano-holes in graphene through metal atoms adhering to the edges of these holes.
NASA Astrophysics Data System (ADS)
Schlank, Carter; James, Royce; Thayer, Nicholas; Sherman, Justin; Nolan, Stephen; Lopez, Michael
2012-10-01
Small helicon plasmas have been employed in various capacities from industry to spacecraft propulsion. At the Coast Guard Academy Plasma Lab (CGAPL), a small Helicon Plasma Experiment (HPX) is being developed to utilize the reputed high density (10^13 cm-3 and higher) at low pressure (.01 T) [1] Helicon Mode Plasmas. HPX will become a high temperature and density diagnostic development test-bed for future laboratory investigations in addition to becoming a tool for future spacecraft propulsion devices. HPX Plasmas are created by imparting directed energy into a Pyrex tube preloaded with Ar gas with fill pressures on the order of 10^4 mTorr utalizing a power supply and matching box can deliver up 250 W of power in a 20 MHz to 100 MHz frequency range. It has been demonstrated [1] that a uniform magnetic field in lower energy level plasmas can facilitate a decrease in inertial effects, which promotes energy conservation within the plasma and provids the necessary external energy in the plasma's magnetic field to reach the Helicon Mode. HPX employes an electromagnet to establish this uniform field. An acceleration coil, currently under construction, will be used to increase the plasma velocity to facilitate partcle and optical probing within the vacuum chamber for experimental analysis. Initial accuracy and calibration measurements of the relative magnetic fields created by both electromagnets will be reported.[0pt][1] K. Toki, et al., Thin Solid Films 506-507 (2005).
Ultrafast optical excitation of magnetic skyrmions
Ogawa, N.; Seki, S.; Tokura, Y.
2015-01-01
Magnetic skyrmions in an insulating chiral magnet Cu2OSeO3 were studied by all-optical spin wave spectroscopy. The spins in the conical and skyrmion phases were excited by the impulsive magnetic field from the inverse-Faraday effect, and resultant spin dynamics were detected by using time-resolved magneto-optics. Clear dispersions of the helimagnon were observed, which is accompanied by a distinct transition into the skyrmion phase, by sweeping temperature and magnetic field. In addition to the collective excitations of skyrmions, i.e., rotation and breathing modes, several spin precession modes were identified, which would be specific to optical excitation. The ultrafast, nonthermal, and local excitation of the spin systems by photons would lead to the efficient manipulation of nano-magnetic structures. PMID:25897634
NASA Astrophysics Data System (ADS)
Geng, Lijie; Ren, Deming; Zhao, Weijiang; Qu, Yanchen; Chen, Huiying; Du, Jun
2013-02-01
An efficient, compact pulsed D2O terahertz (THz) super-radiant laser pumped by a TEA (transversely excited atmospheric pressure) CO2 laser is presented. The pulse energy of the THz laser has been discussed as a function of CO2 laser pump energy, D2O gas pressure, and pump absorption. A pulse width of about 110 ns and the maximum pulse energy of about 1.3 mJ have been achieved at 385 μm, with pumping by a 378 mJ fundamental transverse mode TEA CO2 laser, and the photon conversion efficiency of 29% has been achieved. We have also studied the temporal behavior features such as the decay time, the full width at half-maximum, and the pulse broadening of the THz laser pulse compared with the pump pulse and the residual pump pulse at the optimum pressure.
He, Y. Z.; Bao, C. G.
2011-12-15
The response of spin-2 small condensates to an external magnetic field B is studied. The parameters of the interaction are considered as variable. The emphasis is placed on clarifying the modes of excitation caused by the quadratic Zeeman term. The theoretical method used is beyond the mean-field theory. A set of eigenstates with the U(5) superset of SO(5) superset of SO(3) symmetry is introduced to facilitate the analysis. To obtain a quantitative evaluation on the response, the fidelity susceptibility and the B-dependent average populations of spin components have been calculated. Mostly the particle number N=30 is assumed. The effect with a larger or smaller N is also considered. It was found that the sensitivity of the response depends strongly both on the interaction and on the inherent symmetry.
Verma, Kanika; Sajal, Vivek Kumar, Ravindra; Sharma, Navneet K.; Baliyan, Sweta
2015-06-15
The stimulated Brillouin scattering (SBS) of nonresonant beat mode in the presence of static magnetic field is investigated in a plasma. Two counter-propagating lasers of frequencies (ω{sub 1} and ω{sub 2}) and wave vectors (k{sub 1} and k{sub 2}) drive a nonresonant space charge beat mode at the phase matching condition of frequency ω{sub 0}≈ω{sub 1}∼ω{sub 2} and wave number k{sup →}{sub 0}≈k{sup →}{sub 1}+k{sup →}{sub 2}. The driver wave parametrically excites a pair of ion acoustic wave (ω,k{sup →}) and a sideband electromagnetic wave (ω{sub 3},k{sup →}{sub 3}). The beat wave couples with the sideband electromagnetic wave to exert a nonlinear ponderomotive force at the frequency of ion acoustic wave. Density perturbations due to ion acoustic wave and ponderomotive force couple with the oscillatory motion of plasma electron due to velocity of beat wave to give rise to a nonlinear current (by feedback mechanism) responsible for the growth of sideband wave at resonance. The growth rate of SBS was reduced (from ∼10{sup 12}s{sup −1} to 10{sup 10}s{sup −1}) by applying a transverse static magnetic field ∼90 T. The present study can be useful for the excitation of fast plasma waves (for the purpose of electron acceleration) by two counter-propagating laser beams.
Dong, Hang; Zhang, Wenyuan; Zhou, Li; Ma, Yongli
2015-01-01
We investigate the transition and damping of low-energy collective modes in a trapped unitary Fermi gas by solving the Boltzmann-Vlasov kinetic equation in a scaled form, which is combined with both the T-matrix fluctuation theory in normal phase and the mean-field theory in order phase. In order to connect the microscopic and kinetic descriptions of many-body Feshbach scattering, we adopt a phenomenological two-fluid physical approach, and derive the coupling constants in the order phase. By solving the Boltzmann-Vlasov steady-state equation in a variational form, we calculate two viscous relaxation rates with the collision probabilities of fermion’s scattering including fermions in the normal fluid and fermion pairs in the superfluid. Additionally, by considering the pairing and depairing of fermions, we get results of the frequency and damping of collective modes versus temperature and s-wave scattering length. Our theoretical results are in a remarkable agreement with the experimental data, particularly for the sharp transition between collisionless and hydrodynamic behaviour and strong damping between BCS and unitary limits near the phase transition. The sharp transition originates from the maximum of viscous relaxation rate caused by fermion-fermion pair collision at the phase transition point when the fermion depair, while the strong damping due to the fast varying of the frequency of collective modes from BCS limit to unitary limit. PMID:26522094
NASA Astrophysics Data System (ADS)
Fahy, Stephen; Murray, Eamonn
2015-03-01
Using first principles electronic structure methods, we calculate the induced force on the Eg (zone centre transverse optical) phonon mode in bismuth immediately after absorption of a ultrafast pulse of polarized light. To compare the results with recent ultra-fast, time-resolved x-ray diffraction experiments, we include the decay of the force due to carrier scattering, as measured in optical Raman scattering experiments, and simulate the optical absorption process, depth-dependent atomic driving forces, and x-ray diffraction in the experimental geometry. We find excellent agreement between the theoretical predictions and the observed oscillations of the x-ray diffraction signal, indicating that first-principles theory of optical absorption is well suited to the calculation of initial atomic driving forces in photo-excited materials following ultrafast excitation. This work is supported by Science Foundation Ireland (Grant No. 12/IA/1601) and EU Commission under the Marie Curie Incoming International Fellowships (Grant No. PIIF-GA-2012-329695).
Faigel, G.; Berman, L.E.; Grover, J.R.; Hastings, J.B.; Haustein, P.E.; Siddons, D.P. . Central Research Inst. for Physics; Brookhaven National Lab., Upton, NY )
1989-01-01
In this paper the time dependence of the coherent decay of nuclear excited state in an {alpha}-{sup 57}Fe{sub 2}O{sub 3} single crystal is presented. The experiment was carried out in diffraction geometry. A highly monocromatized and collimated beam of synchrotron radiation was used for the excitation of nuclear levels. Quantum beat spectra taken below and above the (7,7,7) pure nuclear reflection of hematite show a characteristic pattern corresponding to the magnetic and quadrupole hyperfine interactions. 16 refs., 1 fig.
Magdy S. Tawfik; Binh T. Pham; Vivek Agarwal; Nancy J. Lybeck
2011-09-01
Interest in implementing advanced Prognostic Health Management (PHM) systems in commercial nuclear power plants (NPPs) has increased rapidly in recent years, with an overarching goal of implementing of improving the safety, reliability, and economics/profitability of the aging nuclear fleet and extending their service life in the most cost-effective manner. The PHM system utilizes prognostic tools to estimate the remaining useful life (RUL) of a component or system of components based on current and predicted operating conditions. An effective implementation of the PHM system will anticipate and identify unique age-dependent degradation modes to provide early warning of emerging problems. Selection of the components and structures to be monitored is a crucial step for successful PHM implementation in NPPs. A selection framework is recommended for risk significant components (both safety-related and non-safety related) based on the Fussell-Vesely (F-V) Importance Measure and the Risk Achievement Worth (RAW) measure. For the selected components, a failure mode degradation library will be developed consisting of data corresponding to different failure/degradation modes. In lieu of constructing an expensive scaled test facility, several data sources are identified for populating the failure mode degradation library, including various national laboratories, universities, agencies, and industries.
NASA Astrophysics Data System (ADS)
Abbasi, Mustafa; Sadeghi, Yahya; Sobhanian, Samad; Asgarian, Mohammad Ali
2016-03-01
The electron Bernstein wave (EBW) is typically the only wave in the electron cyclotron (EC) range that can be applied in spherical tokamaks for heating and current drive (H&CD). Spherical tokamaks (STs) operate generally in high- β regimes, in which the usual EC ordinary (O) and extraordinary (X) modes are cut off. As it was recently investigated the existence of EBWs at nonlinear regime thus the next step would be the probable nonlinear phenomena study which are predicted to be occurred within the high levels of injected power. In this regard, parametric instabilities are considered as the major channels for losses at the X-B conversion. Hence, we have to consider their effects at the UHR region which can reduce the X-B conversion efficiency. In the case of EBW heating (EBH) at high power density, the nonlinear effects can arise. Particularly at the UHR position, the group velocity is strongly reduced, which creates a high energy density and subsequently a high amplitude electric field. Therefore, a part of the input wave can decay into daughter waves via parametric instability (PI). Thus, via the present research, the excitations of ion Bernstein waves as the dominant decay channels are investigated and also an estimate for the threshold power in terms of experimental parameters related to the fundamental mode of instability is proposed.
Cao, Gaoqing; He, Lianyi; Zhuang, Pengfei
2014-09-15
It is known that a constant magnetic field is a strong catalyst of dynamical chiral symmetry breaking in 2+1 dimensions, leading to generating dynamical fermion mass even at weakest attraction. In this work we investigate the collective modes associated with the dynamical chiral symmetry breaking in a constant magnetic field in the (2+1)-dimensional Nambu–Jona-Lasinio model with continuous U(1) chiral symmetry. We introduce a self-consistent scheme to evaluate the propagators of the collective modes at the leading order in 1/N. The contributions from the vacuum and from the magnetic field are separated such that we can employ the well-established regularization schememore » for the case of vanishing magnetic field. The same scheme can be applied to the study of the next-to-leading order correction in 1/N. We show that the sigma mode is always a lightly bound state with its mass being twice the dynamical fermion mass for arbitrary strength of the magnetic field. Since the dynamics of the collective modes is always 2+1 dimensional, the finite temperature transition should be of the Kosterlitz-Thouless (KT) type. We determine the KT transition temperature TKT as well as the mass melting temperature T* as a function of the magnetic field. It is found that the pseudogap domain TKT < T < T* is enlarged with increasing strength of the magnetic field. The influence of a chiral imbalance or axial chemical potential μ5 is also studied. We find that even a constant axial chemical potential μ5 can lead to inverse magnetic catalysis of the KT transition temperature in 2+1 dimensions. As a result, the inverse magnetic catalysis behavior is actually the de Haas–van Alphen oscillation induced by the interplay between the magnetic field and the Fermi surface.« less
Cao, Gaoqing; He, Lianyi; Zhuang, Pengfei
2014-09-15
It is known that a constant magnetic field is a strong catalyst of dynamical chiral symmetry breaking in 2+1 dimensions, leading to generating dynamical fermion mass even at weakest attraction. In this work we investigate the collective modes associated with the dynamical chiral symmetry breaking in a constant magnetic field in the (2+1)-dimensional Nambu–Jona-Lasinio model with continuous U(1) chiral symmetry. We introduce a self-consistent scheme to evaluate the propagators of the collective modes at the leading order in 1/N. The contributions from the vacuum and from the magnetic field are separated such that we can employ the well-established regularization scheme for the case of vanishing magnetic field. The same scheme can be applied to the study of the next-to-leading order correction in 1/N. We show that the sigma mode is always a lightly bound state with its mass being twice the dynamical fermion mass for arbitrary strength of the magnetic field. Since the dynamics of the collective modes is always 2+1 dimensional, the finite temperature transition should be of the Kosterlitz-Thouless (KT) type. We determine the KT transition temperature T_{KT} as well as the mass melting temperature T* as a function of the magnetic field. It is found that the pseudogap domain T_{KT} < T < T* is enlarged with increasing strength of the magnetic field. The influence of a chiral imbalance or axial chemical potential μ_{5} is also studied. We find that even a constant axial chemical potential μ5 can lead to inverse magnetic catalysis of the KT transition temperature in 2+1 dimensions. As a result, the inverse magnetic catalysis behavior is actually the de Haas–van Alphen oscillation induced by the interplay between the magnetic field and the Fermi surface.
The Hidden Order Gap and In-Gap Excitation Mode in URu2Si2 Revealed by Electronic Raman Scattering
NASA Astrophysics Data System (ADS)
Kung, Hsiang-Hsi; Baumbach, Ryan; Bauer, Eric; Mydosh, John A.; Zhang, Weilu; Thorsmølle, Verner K.; Haule, Kristjan; Blumberg, Girsh
2014-03-01
The heavy fermion compound URu2Si2 displays a phase transition into the so called ``hidden order'' state at THO = 17 . 5 K. Using polarized electronic Raman scattering, we show that the Raman response in the A2 g symmetry channel (D4 h): (1) at high temperatures can be described by a Drude-like continuum with the scattering rate decreasing from 46 cm-1 at 300 K to 16 cm-1 at 70 K (2) develops a low energy peak due to spectral weight transfer through Fano interference in the temperature range of 70-20 K (3) below THO develops a gap of about 55 cm-1 in the continuum, and a sharp in-gap mode centered at 14 cm-1. In addition, we show that the real part of the static Raman susceptibility in the A2 g symmetry is proportional to the c-axis static magnetic susceptibility above THO. The implication of these observations will be discussed in the talk. GB, HHK and VKT acknowledge support from DOE BES Award DE-SC0005463 and NSF award DMR-1104884. KH acknowledge support from NSF Career DMR-0746395. WZ acknowledge ICAM support (NSF-IMI grant DMR-0844115).
Bentivegna, Carolyn S; DeFelice, Chelsea R; Murphy, Wyatt R
2016-06-30
The impact of Hurricane Sandy (October 29, 2012) on PAH exposure was investigated in adult Atlantic menhaden (Brevoortia tyrannus) collected along the NJ coast. Collections were made in August, September and/or October of 2011, 2012 and 2013. PAHs were monitored in raw fish oil using excitation-emission matrix (EEM) spectroscopy. Results showed that raw fish oils had relatively high levels of high molecular weight, PAH-like compounds (173 to 24,421ng/mL) compared to values reported for bile in other species. EEM profiles resembled that of crude oil and excluded matrix interference by some common biological molecules that also fluoresce. Concentrations and EEM profiles varied by collection; however, collection ship, month, year and fish size did not account for the data. Replicates showed that fish from the same catch had similar PAH exposure. Overall, Hurricane Sandy did not alter body burdens of PAHs in raw fish oil of menhaden.
Exotic Orbital Modes in Nuclei
NASA Astrophysics Data System (ADS)
von Neumann-Cosel, P.
2003-06-01
Experimental evidence for two types of collective excitations in nuclei generated by orbital motion is discussed, viz. a magnetic quadrupole twist mode observed in 180° electron scattering experiments and a toroidal electric dipole mode. The latter may be a source of low-energy pygmy dipole resonances observed in many nuclei. This is discussed in detail for the example of 208Pb based on the recent finding of a resonance at particle threshold in a high-resolution (γ, γ') experiment.
Collective mode damping and viscosity in a 1D unitary Fermi gas
NASA Astrophysics Data System (ADS)
Punk, M.; Zwerger, W.
2006-08-01
We calculate the damping of the Bogoliubov Anderson mode in a one-dimensional (1D) two-component attractive Fermi gas for arbitrary coupling strength within a quantum hydrodynamic approach. Using the Bethe-ansatz solution of the 1D BCS-BEC crossover problem, we derive analytic results for the viscosity covering the full range from a Luther Emery liquid of weakly bound pairs to a Lieb Liniger gas of strongly bound bosonic dimers. At the unitarity point, the system is a Tonks Girardeau gas with a universal constant αζ = 0.38 in the viscosity ζ = αζplanck n for T = 0. For the trapped case, we calculate the Q-factor of the breathing mode and show that the damping provides a sensitive measure of temperature in 1D Fermi gases.
NASA Astrophysics Data System (ADS)
Intrator, T.; Myra, J. R.; D'Ippolito, D. A.
2003-07-01
Externally launched ion Bernstein wave (IBW) experiments have demonstrated localized electron heating, sheared flows and transport barriers in several tokamaks. Experiments in the tokamak fusion test reactor (TFTR) showed that IBW waves launched from low-field side IBW antennas could drive a velocity shear layer in the central plasma, but the power coupled to the IBW was not sufficient to achieve a transport barrier. This experiment raised important questions concerning where the radio-frequency (rf) power went and whether the anomalous loss channels are more important in larger machines. Recently, it was proposed that the power loss was due to a coaxial electron plasma wave (EPW) mode excited in the low density plasma halo near the vessel wall (Myra et al 2000 Phys. Plasmas 7 283). This mode could dissipate a significant power fraction by sheath and collisional mechanisms, fits more easily in larger machines like TFTR and has the phasing dependence observed in the experiments. Here we extend that work by demonstrating the existence and phasing dependence of the coaxial mode (CM) in a realistic rf coupling calculation. A three-dimensional finite-element electromagnetic code couples a detailed model of the antenna geometry with a plasma dielectric model that retains CM physics. Quantitative results show the dependence of the CM rf fields and power dissipation on the phasing of the multiple-strap array. Unlike conventional rf coupling codes, this paper enables the antenna limiters to be immersed in tenuous plasma, an important feature for correctly modelling parasitic coupling to the CM.
Wittgenstein running: neural mechanisms of collective intentionality and we-mode.
Becchio, Cristina; Bertone, Cesare
2004-03-01
In this paper we discuss the problem of the neural conditions of shared attitudes and intentions: which neural mechanisms underlie "we-mode" processes or serve as precursors to such processes? Neurophysiological and neuropsychological evidence suggests that in different areas of the brain neural representations are shared by several individuals. This situation, on the one hand, creates a potential problem for correct attribution. On the other hand, it may provide the conditions for shared attitudes and intentions.
Chiral Second-Sound Collective Modes at the Edge of 2D Systems with a Nontrivial Berry Curvature
NASA Astrophysics Data System (ADS)
Principi, Alessandro; Katsnelson, Mikhail I.; Levchenko, Alex
2017-01-01
We study the thermal transport in two-dimensional systems with a nontrivial Berry curvature texture. The physical realizations are many; for the sake of definiteness, we consider undoped graphene gapped by the presence of an aligned hexagonal-boron-nitride substrate. The same phenomenology applies, i.e., to surface states of 3D topological insulators in the presence of a uniform magnetization. We find that chiral valley-polarized second-sound collective modes propagate along the edges of the system. The localization length of the edge modes has a topological origin stemming from the anomalous velocity term in the quasiparticle current. At low temperature, the single-particle contribution to the transverse thermal conductance is exponentially suppressed, and only second-sound modes carry heat along the boundary. A sharp change in the behavior of the thermal Hall conductance, extracted from nonlocal measurements of the temperature along the edge, marks the onset of ballistic heat transport due to second-sound edge modes.
NASA Astrophysics Data System (ADS)
Werner, V.; Cooper, N.; Régis, J.-M.; Rudigier, M.; Williams, E.; Jolie, J.; Cakirli, R. B.; Casten, R. F.; Ahn, T.; Anagnostatou, V.; Berant, Z.; Bonett-Matiz, M.; Elvers, M.; Heinz, A.; Ilie, G.; Radeck, D.; Savran, D.; Smith, M. K.
2016-03-01
The B (E 2 ) excitation strength of the first excited 2+ state in even-even nuclei should directly correlate with the size of the valence space and maximize at mid-shell. A previously found saturation of B (E 2 ) strengths in well-deformed rotors at mid-shell is tested through high-precision measurements of the lifetimes of the lowest-lying 2+ states of the 168Hf and 174W rare earth isotopes. Measurements were performed using fast LaBr3 scintillation detectors. Combined with the recently remeasured B (E 2 ;21+→01+) values for Hf and W isotopes the new data remove discrepancies observed in the differentials of B (E 2 ) values for these isotopes.
NASA Astrophysics Data System (ADS)
Hayes, A. B.; Cline, D.; Moody, K. J.; Ragnarsson, I.; Wu, C. Y.; Becker, J. A.; Carpenter, M. P.; Carroll, J. J.; Gohlke, D.; Greene, J. P.; Hecht, A. A.; Janssens, R. V. F.; Karamian, S. A.; Lauritsen, T.; Lister, C. J.; Macri, R. A.; Propri, R.; Seweryniak, D.; Wang, X.; Wheeler, R.; Zhu, S.
2010-10-01
A 98% pure 242mAm (K=5-, t1/2=141 years) isomeric target was Coulomb excited with a 170.5-MeV Ar40 beam. The selectivity of Coulomb excitation, coupled with the sensitivity of Gammasphere plus CHICO, was sufficient to identify 46 new states up to spin 18ℏ in at least four rotational bands; 11 of these new states lie in the isomer band, 13 in a previously unknown yrast Kπ=6- rotational band, and 13 in a band tentatively identified as the predicted yrast Kπ=5+ band. The rotational bands based on the Kπ=5- isomer and the 6- bandhead were populated by Coulomb excitation with unexpectedly equal cross sections. The γ-ray yields are reproduced by Coulomb excitation calculations using a two-particle plus rotor model (PRM), implying nearly complete ΔK=1 mixing of the two almost-degenerate rotational bands, but recovering the Alaga rule for the unperturbed states. The degeneracy of the 5- and 6- bands allows for precise determination of the mixing interaction strength V, which approaches the strong-mixing limit; this agrees with the 50% attenuation of the Coriolis matrix element assumed in the model calculations. The fractional admixture of the IKπ=66- state in the nominal 65- isomer band state is measured within the PRM as 45.6-1.1+0.3%. The E2 and M1 strengths coupling the 5- and 6- bands are enhanced significantly by the mixing, while E1 and E2 couplings to other low-K bands are not measurably enhanced. The yields of the 5+ band are reproduced by an E3 strength of ≈15 W.u., competitive with the interband E2 strength. Alignments of the identified two-particle Nilsson states in Am242 are compared with the single-particle alignments in Am241.
NASA Astrophysics Data System (ADS)
Maslov, Dmitrii; Maiti, Saurabh
2015-03-01
We address the issue damping of spin collective modes in systems with spin orbit coupling in 2D. We show that these modes exist for arbitrary nature of spin-orbit coupling and are intrinsically damped even in the long wavelength limit. This damping is driven by electron-electron interactions and is unique to spin orbit coupled systems. Its origin is linked to an imperfect cancellation of the self energy and vertex contributions of the interaction. In the Fermi-liquid language, this is an effect arising from residual interaction between quasiparticles. This damping mechanism exists already at T=0 and without impurities and/or phonons. We also discuss the consequences of this damping for the experiment. This work was supported by the National Science Foundation via Grant NSF DMR-1308972.
Al-Subari, Karema; Al-Baddai, Saad; Tomé, Ana Maria; Volberg, Gregor; Hammwöhner, Rainer; Lang, Elmar W.
2015-01-01
We discuss a data-driven analysis of EEG data recorded during a combined EEG/fMRI study of visual processing during a contour integration task. The analysis is based on an ensemble empirical mode decomposition (EEMD) and discusses characteristic features of event related modes (ERMs) resulting from the decomposition. We identify clear differences in certain ERMs in response to contour vs noncontour Gabor stimuli mainly for response amplitudes peaking around 100 [ms] (called P100) and 200 [ms] (called N200) after stimulus onset, respectively. We observe early P100 and N200 responses at electrodes located in the occipital area of the brain, while late P100 and N200 responses appear at electrodes located in frontal brain areas. Signals at electrodes in central brain areas show bimodal early/late response signatures in certain ERMs. Head topographies clearly localize statistically significant response differences to both stimulus conditions. Our findings provide an independent proof of recent models which suggest that contour integration depends on distributed network activity within the brain. PMID:25910061
Surface Majorana fermions and bulk collective modes in superfluid 3He-B
NASA Astrophysics Data System (ADS)
Park, YeJe; Chung, Suk Bum; Maciejko, Joseph
2015-02-01
The theoretical study of topological superfluids and superconductors has so far been carried out largely as a translation of the theory of noninteracting topological insulators into the superfluid language, whereby one replaces electrons by Bogoliubov quasiparticles and single-particle band Hamiltonians by Bogoliubov-de Gennes Hamiltonians. Band insulators and superfluids are, however, fundamentally different: While the former exist in the absence of interparticle interactions, the latter are broken symmetry states that owe their very existence to such interactions. In particular, unlike the static energy gap of a band insulator, the gap in a superfluid is due to a dynamical order parameter that is subject to both thermal and quantum fluctuations. In this work, we explore the consequences of bulk quantum fluctuations of the order parameter in the B phase of superfluid 3He on the topologically protected Majorana surface states. Neglecting the high-energy amplitude modes, we find that one of the three spin-orbit Goldstone modes in 3He-B couples to the surface Majorana fermions. This coupling in turn induces an effective short-range two-body interaction between the Majorana fermions, with coupling constant inversely proportional to the strength of the nuclear dipole-dipole interaction in bulk 3He. A mean-field theory suggests that the surface Majorana fermions in 3He-B may be in the vicinity of a metastable gapped time-reversal-symmetry-breaking phase.
Di Donato, Mariangela; Ragnoni, Elena; Lapini, Andrea; Kardaś, Tomasz M; Ratajska-Gadomska, Boźena; Foggi, Paolo; Righini, Roberto
2015-05-07
Assigning the vibrational modes of molecules in the electronic excited state is often a difficult task. Here we show that combining two nonlinear spectroscopic techniques, transient 2D exchange infrared spectroscopy (T2D-IR-EXSY) and femtosecond stimulated Raman spectroscopy (FSRS), the contribution of the C═C and C═O modes in the excited-state vibrational spectra of trans-β-apo-8'-carotenal can be unambiguously identified. The experimental results reported in this work confirm a previously proposed assignment based on quantum-chemical calculations and further strengthen the role of an excited state with charge-transfer character in the relaxation pathway of carbonyl carotenoids. On a more general ground, our results highlight the potentiality of nonlinear spectroscopic methods based on the combined use of visible and infrared pulses to correlate structural and electronic changes in photoexcited molecules.
NASA Astrophysics Data System (ADS)
Li, Faxin; Miao, Hongchen
2016-10-01
The non-dispersive fundamental shear horizontal (SH0) wave is extremely useful in guided-wave-based inspection techniques. However, the generation or reception of the SH0 wave by using a piezoelectric transducer is always a challenge. In this work, first, we realized the apparent face-shear (d36) mode in PbZr1-xTixO3 (PZT) ceramics via two-dimensional antiparallel poling. Then, we demonstrated via finite element simulations that the apparent d36 mode PZT wafer can behave as both a SH0 wave actuator and a SH0 wave sensor. Next, by using the apparent d36 PZT wafer as an actuator and a face-shear d36 0.72[Pb(Mg1/3Nb2/3)O3]-0.28[PbTiO3] crystal as the sensor, almost a pure SH0 wave with a high signal-to-noise ratio was successfully excited in an aluminum plate from 180 kHz to 200 kHz. Later, experiments showed that the proposed apparent d36 PZT wafer can also serve as a sensor to detect the SH0 wave over a wide frequency range (160 kHz to 230 kHz). Finally, the amplitude directivity of the SH0 wave generated by the apparent d36 PZT wafer was also investigated. The wave amplitude reaches its maxima at the main direction (0° and 90°) and then decreases monotonically when the propagation direction deviates from the main directions, with the symmetric axis along the 45° direction. The proposed apparent d36 PZT wafer is very suitable for severing as SH0 wave actuators and sensors in structural health monitoring systems.
Owen, Robin L; Yorke, Briony A; Pearson, Arwen R
2012-05-01
During X-ray irradiation protein crystals radiate energy in the form of small amounts of visible light. This is known as X-ray-excited optical luminescence (XEOL). The XEOL of several proteins and their constituent amino acids has been characterized using the microspectrophotometers at the Swiss Light Source and Diamond Light Source. XEOL arises primarily from aromatic amino acids, but the effects of local environment and quenching within a crystal mean that the XEOL spectrum of a crystal is not the simple sum of the spectra of its constituent parts. Upon repeated exposure to X-rays XEOL spectra decay non-uniformly, suggesting that XEOL is sensitive to site-specific radiation damage. However, rates of XEOL decay were found not to correlate to decays in diffracting power, making XEOL of limited use as a metric for radiation damage to protein crystals.
Owen, Robin L.; Yorke, Briony A.; Pearson, Arwen R.
2012-01-01
During X-ray irradiation protein crystals radiate energy in the form of small amounts of visible light. This is known as X-ray-excited optical luminescence (XEOL). The XEOL of several proteins and their constituent amino acids has been characterized using the microspectrophotometers at the Swiss Light Source and Diamond Light Source. XEOL arises primarily from aromatic amino acids, but the effects of local environment and quenching within a crystal mean that the XEOL spectrum of a crystal is not the simple sum of the spectra of its constituent parts. Upon repeated exposure to X-rays XEOL spectra decay non-uniformly, suggesting that XEOL is sensitive to site-specific radiation damage. However, rates of XEOL decay were found not to correlate to decays in diffracting power, making XEOL of limited use as a metric for radiation damage to protein crystals. PMID:22525748
Plasmon excitations in two-dimensional atomic cluster systems
NASA Astrophysics Data System (ADS)
Yu, Yan-Qin; Yu, Ya-Bin; Xue, Hong-Jie; Wang, Ya-Xin; Chen, Jie
2016-09-01
Properties of plasmon excitations in two-dimensional (2D) atomic cluster systems are theoretically studied within an extended Hubbard model. The collective oscillation equations of charge, plasmon eigen-equations and the energy-absorption spectrum formula are presented. The calculated results show that different symmetries of plasmons exist in the cluster systems, and the symmetry of charge distribution in the plasmon resonance originate from the intrinsic symmetry of the corresponding eigen-plasmon modes, but not from the symmetry of applied external fields; however, the plasmon excitation with a certain polarization direction should be excited by the field in this direction, the dipole mode of plasmons can be excited by both uniform and non-uniform fields, but multipole ones cannot be excited by an uniform field. In addition, we show that for a given electron density, plasmon spectra are red-shifted with increasing size of the systems.
Coupling of Higgs and Leggett modes in non-equilibrium superconductors.
Krull, H; Bittner, N; Uhrig, G S; Manske, D; Schnyder, A P
2016-06-21
In equilibrium systems amplitude and phase collective modes are decoupled, as they are mutually orthogonal excitations. The direct detection of these Higgs and Leggett collective modes by linear-response measurements is not possible, because they do not couple directly to the electromagnetic field. In this work, using numerical exact simulations we show for the case of two-gap superconductors, that optical pump-probe experiments excite both Higgs and Leggett modes out of equilibrium. We find that this non-adiabatic excitation process introduces a strong interaction between the collective modes, which is absent in equilibrium. Moreover, we propose a type of pump-probe experiment, which allows to probe and coherently control the Higgs and Leggett modes, and thus the order parameter directly. These findings go beyond two-band superconductors and apply to general collective modes in quantum materials.
Coupling of Higgs and Leggett modes in non-equilibrium superconductors
Krull, H.; Bittner, N.; Uhrig, G. S.; Manske, D.; Schnyder, A. P.
2016-01-01
In equilibrium systems amplitude and phase collective modes are decoupled, as they are mutually orthogonal excitations. The direct detection of these Higgs and Leggett collective modes by linear-response measurements is not possible, because they do not couple directly to the electromagnetic field. In this work, using numerical exact simulations we show for the case of two-gap superconductors, that optical pump–probe experiments excite both Higgs and Leggett modes out of equilibrium. We find that this non-adiabatic excitation process introduces a strong interaction between the collective modes, which is absent in equilibrium. Moreover, we propose a type of pump–probe experiment, which allows to probe and coherently control the Higgs and Leggett modes, and thus the order parameter directly. These findings go beyond two-band superconductors and apply to general collective modes in quantum materials. PMID:27323887
Sharma, Rashmi S; Joy, Raechel C; Boushey, Carol J; Ferruzzi, Mario G; Leonov, Alexei P; McCrory, Megan A
2014-03-01
Para-aminobenzoic acid (PABA) has long been used as an objective measure to assess completeness of 24-hour urine collections. However, pharmaceutical-grade PABA for human ingestion is not available in the United States. An alternative, the potassium salt of PABA, aminobenzoate potassium, can be obtained for clinical use, although it has not yet been validated in this role. Both PABA and aminobenzoate potassium can be directly ingested in their tablet or capsule forms or added to food before consumption. Our aim was to investigate the effect of form (PABA vs aminobenzoate potassium) and administration mode (directly ingested as a tablet/capsule vs added to food) on urinary PABA recovery levels. Twenty healthy participants underwent 3 test days separated by two 24-hour wash-out periods. Three test conditions, one on each test day, were investigated in randomized order: PABA tablet, aminobenzoate potassium capsule, and PABA or aminobenzoate potassium in food. Ingestion of each dose was supervised and participants performed the 24-hour urine collections while free-living. The 24-hour urine collections were analyzed for PABA recovery (%R) levels using a colorimetric assay. Recoveries 85% to 110% were deemed complete and those >110% were reanalyzed by high pressure liquid chromatography and mass spectrometry. Only complete collections (>85%R) were included in analyses. The recovery for the PABA tablet, aminobenzoate potassium capsule, and PABA/aminobenzoate potassium in food were similar at 98.8%R±2.0%R, 95.1%R±2.3%R, and 93.2%R±2.1%R, respectively, and did not differ significantly. These results suggest that aminobenzoate potassium may be used as an alternative to PABA for assessing the completeness of 24-hour urine collections and to track compliance with consuming provided diets in community-dwelling studies.
Spin waves and magnetic excitations
Borovik-Romanov, A.S.; Sinha, S.K.
1988-01-01
This book describes both simple spin waves (magnons) and complicated excitations in magnetic systems. The following subjects are covered: - various methods of magnetic excitation investigations such as neutron scattering on magnetic excitations, spin-wave excitation by radio-frequency, power light scattering on magnons and magnetic excitation observation within the light-absorption spectrum; - oscillations of magnetic electron systems coupled with phonons, nuclear spin systems and localized impurity modes: - low-dimensional magnetics, amorphous magnetics and spin glasses.
NASA Astrophysics Data System (ADS)
Yue, Sheng-Ying; Zhang, Xiaoliang; Qin, Guangzhao; Yang, Jiayue; Hu, Ming
2016-09-01
The past few years have witnessed a rapid evolution of hybrid organic-inorganic perovskite solar cells as an unprecedented photovoltaic technology with both relatively low cost and high-power conversion. The fascinating physical and chemical properties of perovskites are benefited from their unique crystal structures represented by the general chemical formula A M X3 , where the A cations occupy the hollows formed by the M X3 octahedra and thus balance the charge of the entire network. Despite a vast amount of theoretical and experimental investigations have been dedicated to the structural stability, electrical, and optical properties of hybrid halide perovskite materials in relation to their applications in solar cells, the thermal transport property, another critical parameter to the design and optimization of relevant solar cell modules, receives less attention. In this paper, we evaluate the lattice thermal conductivity of a representative methylammonium lead triiodide perovskite (CH3NH3PbI3 ) with direct nonequilibrium ab initio molecular dynamics simulation. Resorting to full first-principles calculations, we illustrate the details of the mysterious vibration of the methylammonium cluster (CH3NH3+ ) and present an unambiguous picture of how the organic cluster interacting with the inorganic cage and how the collective motions of the organic cluster drags the thermal transport, which provide fundamental understanding of the ultralow thermal conductivity of CH3NH3PbI3 . We also reveal the strongly localized phonons associated with the internal motions of the CH3NH3+ cluster, which contribute little to the total thermal conductivity. The importance of the CH3NH3+ cluster to the structural instability is also discussed in terms of the unconventional dispersion curves by freezing the partial freedoms of the organic cluster. These results provide more quantitative description of organic-inorganic interaction and coupling dynamics from accurate first
NASA Astrophysics Data System (ADS)
Seto, Daichi; Nikka, Ren; Nishio, Shogo; Taguchi, Yoshihiro; Saiki, Toshiharu; Nagasaka, Yuji
2017-01-01
A nanoscale thermometry method called fluorescence near-field optics thermal nanoscopy (Fluor-NOTN) has been developed using near-field fluorescence imaging. This method can detect local temperature distributions with a nanoscale spatial resolution by measuring the fluorescence lifetimes of Cd/Se quantum dots (QDs) as a temperature probe. To increase the sensitivity of Fluor-NOTN, time-correlated single-photon counting (TCSPC) was introduced with a triple-tapered fusion-spliced near-field (TFN) optical fiber probe. This highly sensitive technique for measuring the fluorescence lifetime of QDs enabled the detection of low-level light signals with a picosecond time resolution at high-precision in an illumination-collection mode for Fluor-NOTN. The feasibility of this proposed method was experimentally verified by measuring the temperature dependence of the fluorescence lifetimes of the QDs by Fluor-NOTN using TCSPC with a TFN optical fiber probe with an aperture of 70 nm.
Yuzefovsky, A I; Lonardo, R F; Michel, R G
1995-07-01
A single 90 degrees off-axis ellipsoidal mirror fragment was used in a dispersive detection system for electrothermal atomization laser-excited atomic fluorescence spectrometry. The performance of the new optical arrangement was compared with those of optical arrangements that employed a plane mirror in combination with biconvex or plano-convex lenses. All the optical arrangements collected fluorescence in a scheme called front surface illustration. BEAM-4, an optical ray tracing program, was used for calculations of spatial ray distributions and optical collection efficiency for the various optical configurations. Experimentally, the best collection efficiency was obtained by use of the ellipsoidal mirror, in qualitative agreement with simulations done by use of the BEAM-4 software. The best detection limit for cobalt with the new optical arrangement was 20 fg, which was a factor of 5 better than that obtained with conventional optical arrangements with otherwise the same instrumentation. The signal-to-background ratio and the fluorescence collection efficiency were also studied as a function of position of the optical components for the various optical arrangements. For both cobalt and phosphorus, the signal-to-background ratio with the new optical arrangement remained stable within 10-20% during +/- 8 mm shifts in the position of the detection system from the focal plane of the optics. Overall, the new optical arrangement offered high collection efficiency, excellent sensitivity, and facile optical alignment due to efficient spatial separation between the fluorescence signal and the background radiation. The advantages of the new optical arrangement were particularly important during measurements in the presence of high levels of blackbody radiation.
NASA Astrophysics Data System (ADS)
Louchart, C.; Obertelli, A.; Görgen, A.; Korten, W.; Bazzacco, D.; Birkenbach, B.; Bruyneel, B.; Clément, E.; Coleman-Smith, P. J.; Corradi, L.; Curien, D.; de Angelis, G.; de France, G.; Delaroche, J.-P.; Dewald, A.; Didierjean, F.; Doncel, M.; Duchêne, G.; Eberth, J.; Erduran, M. N.; Farnea, E.; Finck, C.; Fioretto, E.; Fransen, C.; Gadea, A.; Girod, M.; Gottardo, A.; Grebosz, J.; Habermann, T.; Hackstein, M.; Huyuk, T.; Jolie, J.; Judson, D.; Jungclaus, A.; Karkour, N.; Klupp, S.; Krücken, R.; Kusoglu, A.; Lenzi, S. M.; Libert, J.; Ljungvall, J.; Lunardi, S.; Maron, G.; Menegazzo, R.; Mengoni, D.; Michelagnoli, C.; Million, B.; Molini, P.; Möller, O.; Montagnoli, G.; Montanari, D.; Napoli, D. R.; Orlandi, R.; Pollarolo, G.; Prieto, A.; Pullia, A.; Quintana, B.; Recchia, F.; Reiter, P.; Rosso, D.; Rother, W.; Sahin, E.; Salsac, M.-D.; Scarlassara, F.; Schlarb, M.; Siem, S.; Singh, P. P.; Söderström, P.-A.; Stefanini, A. M.; Stézowski, O.; Sulignano, B.; Szilner, S.; Theisen, Ch.; Ur, C. A.; Valiente-Dobón, J. J.; Zielinska, M.
2013-05-01
Background: Neutron-rich nuclei with protons in the fp shell show an onset of collectivity around N=40. Spectroscopic information is required to understand the underlying mechanism and to determine the relevant terms of the nucleon-nucleon interaction that are responsible for the evolution of the shell structure in this mass region.Methods: We report on the lifetime measurement of the first 2+ and 4+ states in 70,72,74Zn and the first 6+ state in 72Zn using the recoil distance Doppler shift method. The experiment was carried out at the INFN Laboratory of Legnaro with the AGATA demonstrator, first phase of the Advanced Gamma Tracking Array of highly segmented, high-purity germanium detectors coupled to the PRISMA magnetic spectrometer. The excited states of the nuclei of interest were populated in the deep inelastic scattering of a 76Ge beam impinging on a 238U target.Results: The maximum of collectivity along the chain of Zn isotopes is observed for 72Zn at N=42. An unexpectedly long lifetime of 20-5.2+1.8 ps was measured for the 4+ state in 74Zn.Conclusions: Our results lead to small values of the B(E2;41+→21+)/B(E2;21+→01+) ratio for 72,74Zn, suggesting a significant noncollective contribution to these excitations. These experimental results are not reproduced by state-of-the-art microscopic models and call for lifetime measurements beyond the first 2+ state in heavy zinc and nickel isotopes.
Quasinormal modes of near extremal black branes
NASA Astrophysics Data System (ADS)
Starinets, Andrei O.
2002-12-01
We find quasinormal modes of near extremal black branes by solving a singular boundary value problem for the Heun equation. The corresponding eigenvalues determine the dispersion law for the collective excitations in the dual strongly coupled N=4 supersymmetric Yang-Mills theory at finite temperature.
Super-radiant mode in InAs—monolayer–based Bragg structures
Pozina, G.; Kaliteevski, M. A.; Nikitina, E. V.; Denisov, D. V.; Polyakov, N. K.; Pirogov, E. V.; Goray, L. I.; Gubaydullin, A. R.; Ivanov, K. A.; Kaliteevskaya, N. A.; Egorov, A. Yu.; Clark, S. J.
2015-01-01
We report direct experimental evidence of the collective super-radiant mode in Bragg structure containing 60 InAs monolayer-based quantum wells (QWs) periodically arranged in GaAs matrix. Time-resolved photoluminescence measurements reveal an appearance of the additional super-radiant mode, originated from coherent collective interaction of QWs. This mode demonstrates a super-linear dependence of the intensity and radiative decay rate on the excitation power. The super-radiant mode is not manifested in the case if only a small number of QWs is excited. PMID:26456523
NASA Astrophysics Data System (ADS)
Griv, Evgeny; Kharchenko, Nina V.; Piskunov, Anatoly E.; Hou, Li-Gang; Jiang, Ing-Guey
2015-10-01
Measurements of great importance of photometric/trigonometric distances and velocities have recently done for 2859 open clusters and 103 masers associated with young high-mass stars in the disc of our Galaxy by Kharchenko et al. and Reid et al. We use these new high-precision data to determine the spectrum of Lin-Shu-type density waves in the system. The kinematics of 472 clusters and 65 masers selected within 4 kpc from the Sun is analysed on the assumption that the Galaxy is subject to moderately unstable, tightly-wound, small-amplitude density waves. For a given number of spiral arms, several minima of a least-squares estimator S of measured and predicted line-of-sight velocities of both clusters and masers with respect to the pitch angle p and the phase of the wave at the Sun's location are apparent from our calculation as |p| increases from 1° to 20°. The appearance of the minima of S is explained in terms of a number of discrete spiral modes of collective oscillations developing in the solar vicinity as suggested analytically by Lau, Lin & Mark, Bertin & Mark, Lau & Bertin and others in the late 1970s.
Franzosi, Roberto; Penna, Vittorio
2003-04-01
The dynamics of the three coupled bosonic wells (trimer) containing N bosons is investigated within a standard (mean-field) semiclassical picture based on the coherent-state method. Various periodic solutions (configured as pi-like, dimerlike, and vortex states) representing collective modes are obtained analytically when the fixed points of trimer dynamics are identified on the N=const submanifold in the phase space. Hyperbolic, maximum and minimum points are recognized in the fixed-point set by studying the Hessian signature of the trimer Hamiltonian. The system dynamics in the neighborhood of periodic orbits (associated with fixed points) is studied via numeric integration of trimer motion equations, thus revealing a diffused chaotic behavior (not excluding the presence of regular orbits), macroscopic effects of population inversion, and self-trapping. In particular, the behavior of orbits with initial conditions close to the dimerlike periodic orbits shows how the self-trapping effect of dimerlike integrable subregimes is destroyed by the presence of chaos.
NASA Astrophysics Data System (ADS)
Prudil, Z.; Smolec, R.; Skarka, M.; Netzel, H.
2017-03-01
We report the discovery of a new group of double-periodic stars in the OGLE Galactic bulge photometry. In 38 stars identified as fundamental-mode RR Lyrae and four classified as first-overtone RR Lyrae, we detected an additional shorter periodicity. The periods of the dominant variability in the newly discovered group are 0.28 < PD < 0.41 d. Period ratios (0.68-0.72) are smaller than the period ratios of the Galactic bulge RRd stars. The typical amplitude ratio (of the additional to the dominant periodicity) is 20 per cent for the stars identified as fundamental-mode RR Lyrae and 50 per cent for stars classified as first-overtone RR Lyrae. 10 stars from our sample exhibit equidistant peaks in the frequency spectrum, which suggests the Blazhko-type modulation of the main pulsation frequency and/or additional periodicity. The Fourier coefficients R21 and R31 are some of the lowest among fundamental-mode RR Lyrae stars, but among the highest for the first-overtone pulsators. For the phase Fourier coefficients φ21 and φ31, our stars lie between RRab and RRc stars. The stars discussed were compared with radial linear pulsation models. Their position in the Petersen diagram cannot be reproduced by assuming that two radial modes are excited and their physical parameters are like those characteristic of RR Lyrae stars. The non-radial-mode scenario also faces difficulties. We conclude that the dominant variability is most likely due to pulsation in the radial fundamental mode, which applies to stars classified as first-overtone mode pulsators. At this point, we cannot explain the nature of the additional periodicity. Even more, the classification of the stars as RR Lyrae should be treated as tentative.
Low-Energy Excitation Spectra in the Excitonic Phase of Cobalt Oxides
NASA Astrophysics Data System (ADS)
Yamaguchi, Tomoki; Sugimoto, Koudai; Ohta, Yukinori
2017-04-01
We study the excitonic phase and low-energy excitation spectra of perovskite cobalt oxides. Constructing the five-orbital Hubbard model defined on the three-dimensional cubic lattice for the 3d bands of Pr0.5Ca0.5CoO3, we calculate the excitonic susceptibility in the normal state in the random-phase approximation (RPA) to show the presence of the instability toward excitonic condensation. On the basis of the excitonic ground state with a magnetic multipole obtained in the mean-field approximation, we calculate the dynamical susceptibility of the excitonic phase in the RPA and find that there appear a gapless collective excitation in the spin-transverse mode (Goldstone mode) and a gapful collective excitation in the spin-longitudinal mode (Higgs mode). The experimental relevance of our results is discussed.
Enhanced charge excitations in electron-doped cuprates by resonant inelastic x-ray scattering
NASA Astrophysics Data System (ADS)
Tohyama, Takami; Tsutsui, Kenji; Mori, Michiyasu; Sota, Shigetoshi; Yunoki, Seiji
2015-07-01
Resonant inelastic x-ray scattering (RIXS) tuned for the Cu L edge is a possible tool to detect charge excitations in cuprate superconductors. We theoretically investigate the possibility for observing a collective charge excitation by the RIXS. The RIXS process via the intermediate state inevitably makes the spectral weight of charge excitation stronger in electron doping than in hole doping. Electron-hole asymmetry also appears in the dynamical charge structure factor, showing a new enhanced small-momentum low-energy mode in electron doping. These facts indicate a possibility of detecting the new charge mode by RIXS in electron-doped systems.
NASA Astrophysics Data System (ADS)
Pietanza, L. D.; Colonna, G.; D'Ammando, G.; Capitelli, M.
2017-01-01
A time-dependent self-consistent model based on the coupling of the Boltzmann equation for the electron energy distribution function (EEDF) with the non-equilibrium vibrational kinetics of the asymmetric mode, as well as a simplified global model, have been implemented for a pure CO2 plasma. The simplified time-dependent global model takes into account dissociation and ionization as well as the reverse of these processes. It also takes into account the excitation/de-excitation of an electronic excited state at 10.5 eV. The model has been applied to describe the discharge and post-discharge conditions typically met in an atmospheric-pressure dielectric barrier discharge (DBD) and in a moderate-pressure microwave discharge. The reported results show the strong coupling between the excited state and the electron energy distribution kinetics due to superelastic (vibrational and electronic) collisions. Moreover, the dissociation rate from a pure vibrational mechanism can become competitive with the corresponding rate from the direct electron impact mechanism at high values of vibrational temperature.
Off-axis fishbone-like instability and excitation of resistive wall modes in JT-60U and DIII-D
Okabayashi, M.; Solomon, W. M.; Budny, R. V.; Manickam, J.; Matsunaga, G.; Takechi, M.; Asakura, N.; Shinohara, K.; Grassie, J. S. de; Strait, E. J.; Jackson, G. L.; La Haye, R. J.; Heidbrink, W. W.; Zhu, Y. B.; In, Y.; Liu, Y. Q.
2011-05-15
An energetic-particle (EP)-driven ''off-axis-fishbone-like mode (OFM)'' often triggers a resistive wall mode (RWM) in JT-60U and DIII-D devices, preventing long-duration high-{beta}{sub N} discharges. In these experiments, the EPs are energetic ions (70-85 keV) injected by neutral beams to produce high-pressure plasmas. EP-driven bursting events reduce the EP density and the plasma rotation simultaneously. These changes are significant in high-{beta}{sub N} low-rotation plasmas, where the RWM stability is predicted to be strongly influenced by the EP precession drift resonance and by the plasma rotation near the q=2 surface (kinetic effects). Analysis of these effects on stability with a self-consistent perturbation to the mode structure using the MARS-K code showed that the impact of EP losses and rotation drop is sufficient to destabilize the RWM in low-rotation plasmas, when the plasma rotation normalized by Alfven frequency is only a few tenths of a percent near the q=2 surface. The OFM characteristics are very similar in JT-60U and DIII-D, including nonlinear mode evolution. The modes grow initially like a classical fishbone, and then the mode structure becomes strongly distorted. The dynamic response of the OFM to an applied n=1 external field indicates that the mode retains its external kink character. These comparative studies suggest that an energetic particle-driven 'off-axis-fishbone-like mode' is a new EP-driven branch of the external kink mode in wall-stabilized plasmas, analogous to the relationship of the classical fishbone branch to the internal kink mode.
Off-axis fishbone-like instability and excitation of resistive wall modes in JT-60U and DIII-Da)
NASA Astrophysics Data System (ADS)
Okabayashi, M.; Matsunaga, G.; deGrassie, J. S.; Heidbrink, W. W.; In, Y.; Liu, Y. Q.; Reimerdes, H.; Solomon, W. M.; Strait, E. J.; Takechi, M.; Asakura, N.; Budny, R. V.; Jackson, G. L.; Hanson, J. M.; La Haye, R. J.; Lanctot, M. J.; Manickam, J.; Shinohara, K.; Zhu, Y. B.
2011-05-01
An energetic-particle (EP)-driven "off-axis-fishbone-like mode (OFM)" often triggers a resistive wall mode (RWM) in JT-60U and DIII-D devices, preventing long-duration high-βN discharges. In these experiments, the EPs are energetic ions (70-85 keV) injected by neutral beams to produce high-pressure plasmas. EP-driven bursting events reduce the EP density and the plasma rotation simultaneously. These changes are significant in high-βN low-rotation plasmas, where the RWM stability is predicted to be strongly influenced by the EP precession drift resonance and by the plasma rotation near the q =2 surface (kinetic effects). Analysis of these effects on stability with a self-consistent perturbation to the mode structure using the MARS-K code showed that the impact of EP losses and rotation drop is sufficient to destabilize the RWM in low-rotation plasmas, when the plasma rotation normalized by Alfvén frequency is only a few tenths of a percent near the q =2 surface. The OFM characteristics are very similar in JT-60U and DIII-D, including nonlinear mode evolution. The modes grow initially like a classical fishbone, and then the mode structure becomes strongly distorted. The dynamic response of the OFM to an applied n =1 external field indicates that the mode retains its external kink character. These comparative studies suggest that an energetic particle-driven "off-axis-fishbone-like mode" is a new EP-driven branch of the external kink mode in wall-stabilized plasmas, analogous to the relationship of the classical fishbone branch to the internal kink mode.
Detwiler, Jillian T; Criscione, Charles D
2011-09-01
Cryptic aspects of parasite population biology, e.g., mating systems, are increasingly being inferred from polymorphic and co-dominant genetic markers such as microsatellite loci. Underlying the use of such co-dominant markers is the assumption of Mendelian inheritance. The failure to meet this assumption can lead to artifactual statistics and erroneous population inferences. Here, we illustrate the importance of testing the Mendelian segregation and assortment of genetic markers and demonstrate how field-collected samples can be utilised for this purpose. To examine the reproductive mode and mating system of hermaphroditic parasites, we developed microsatellites for the cestode, Oochoristica javaensis. Among loci, we found a bimodal distribution of F(IS) (a fixation index that quantifies the deviation from Hardy-Weinberg equilibrium within subpopulations) values where loci were either highly negative (close to -1) or highly positive (∼0.8). By conducting tests of Mendelian segregation from natural crosses, we determined that loci with negative F(IS) values were in fact duplicated loci that were amplified by a single primer pair. Genetic crosses also provided linkage data and indicated that the duplicated loci most likely arose via tandem duplications rather than whole genome/chromosome duplications. By correcting for the duplicated loci, we were able to correctly infer that O. javaensis has sexual reproduction, but the mating system is highly inbred. To assist others in testing Mendelian segregation and independent assortment from natural samples, we discuss the benefits and limitations, and provide guidelines for particular parasite systems amenable to the methods employed here.
Barr, Paul J; Forcino, Rachel C; Thompson, Rachel; Ozanne, Elissa M; Arend, Roger; Castaldo, Molly Ganger; O'Malley, A James; Elwyn, Glyn
2017-01-01
Background Shared decision-making (SDM) has become a policy priority, yet its implementation is not routinely assessed. To address this gap we tested the delivery of CollaboRATE, a 3-item patient reported experience measure of SDM, via multiple survey modes. Objective To assess CollaboRATE response rates and respondent characteristics across different modes of administration, impact of mode and patient characteristics on SDM performance and cost of administration per response in a real-world primary care practice. Design Observational study design, with repeated assessment of SDM performance using CollaboRATE in a primary care clinic over 15 months of data collection. Different modes of administration were introduced sequentially including paper, patient portal, interactive voice response (IVR) call, text message and tablet computer. Participants Consecutive patients ≥18 years, or parents/guardians of patients <18 years, visiting participating primary care clinicians. Main measures CollaboRATE assesses three core SDM tasks: (1) explanation about health issues, (2) elicitation of patient preferences and (3) integration of patient preferences into decisions. Responses to each item range from 0 (no effort was made) to 9 (every effort was made). CollaboRATE scores are calculated as the proportion of participants who report a score of nine on each of the three CollaboRATE questions. Key results Scores were sensitive to mode effects: the paper mode had the highest average score (81%) and IVR had the lowest (61%). However, relative clinician performance rankings were stable across the different data collection modes used. Tablet computers administered by research staff had the highest response rate (41%), although this approach was costly. Clinic staff giving paper surveys to patients as they left the clinic had the lowest response rate (12%). Conclusions CollaboRATE can be introduced using multiple modes of survey delivery while producing consistent clinician
NASA Astrophysics Data System (ADS)
Nikumb, S. K.; Seguin, H. J. J.; Seguin, V. A.; Presakarchuk, D.
1988-10-01
The incorporation of a gating signal into the trigger circuit of a photoinitiated, impulse-enhanced, electrically excited (PIE) laser system has permitted high-power, pulsed operation of a normally cw CO2 discharge. The 40 liter gain medium has been run at repetition rates approaching 1 kHz utilizing this approach. Plasma uniformity and stability have been significantly enhanced, such that a factor of two increase in electrical power deposition into the excited volume has been achieved. Results suggest that pulsed performance considerably in excess of that achievable under cw operating conditions can be realized through the adoption of this simple modification to the PIE ionization process.
Bray, James William [Niskayuna, NY; Garces, Luis Jose [Niskayuna, NY
2012-03-13
The disclosed technology is a cryogenic static exciter. The cryogenic static exciter is connected to a synchronous electric machine that has a field winding. The synchronous electric machine is cooled via a refrigerator or cryogen like liquid nitrogen. The static exciter is in communication with the field winding and is operating at ambient temperature. The static exciter receives cooling from a refrigerator or cryogen source, which may also service the synchronous machine, to selected areas of the static exciter and the cooling selectively reduces the operating temperature of the selected areas of the static exciter.
NASA Astrophysics Data System (ADS)
Munzar, D.; Chaloupka, J.; Bernhard, C.; Dubroka, A.; Vašátko, J.
2010-12-01
The low-temperature spectra of the c-axis infrared conductivity of bilayer high-Tc cuprate superconductors (HTCS) exhibit two superconductivity-induced modes [Li Yu et al., Phys. Rev. Lett. 100 (2008) 177004; and references therein]. Both can be understood in terms of a microscopic theory developed recently [J. Chaloupka, C. Bernhard, D. Munzar, Phys. Rev. B 79 (2009) 184513]. Here we summarize the elements of the theory and report on the temperature dependence (TD) of the low-energy mode and of the total optical spectral weight (SW). The calculated TD of the mode is consistent with experiment but the trends of the SW are not.
Cavalier, J.; Lemoine, N.; Bonhomme, G.; Tsikata, S.; Honore, C.; Gresillon, D.
2012-08-15
The effect of the collective light scattering diagnostic transfer function is considered in the context of the dispersion relation of the unstable E Multiplication-Sign B mode previously reported. This transfer function is found to have a contribution to the measured frequencies and mode amplitudes which is more or less significant depending on the measurement wavenumbers and angles. After deconvolution, the experimental data are found to be possibly compatible with the idea that the mode frequency in the jet frame (after subtraction of the Doppler effect due to the plasma motion along the thruster axis) is independent of the orientation of the wave vector in the plane orthogonal to the local magnetic field.
NASA Technical Reports Server (NTRS)
Hall, David G.; Heidelberg, Laurence; Konno, Kevin
1993-01-01
The rotating microphone measurement technique and data analysis procedures are documented which are used to determine circumferential and radial acoustic mode content in the inlet of the Advanced Ducted Propeller (ADP) model. Circumferential acoustic mode levels were measured at a series of radial locations using the Doppler frequency shift produced by a rotating inlet microphone probe. Radial mode content was then computed using a least squares curve fit with the measured radial distribution for each circumferential mode. The rotating microphone technique is superior to fixed-probe techniques because it results in minimal interference with the acoustic modes generated by rotor-stator interaction. This effort represents the first experimental implementation of a measuring technique developed by T. G. Sofrin. Testing was performed in the NASA Lewis Low Speed Anechoic Wind Tunnel at a simulated takeoff condition of Mach 0.2. The design is included of the data analysis software and the performance of the rotating rake apparatus. The effect of experiment errors is also discussed.
NASA Technical Reports Server (NTRS)
Hall, David G.; Heidelberg, Laurence; Konno, Kevin
1993-01-01
The rotating microphone measurement technique and data analysis procedures are documented which are used to determine circumferential and radial acoustic mode content in the inlet of the Advanced Ducted Propeller (ADP) model. Circumferential acoustic mode levels were measured at a series of radial locations using the Doppler frequency shift produced by a rotating inlet microphone probe. Radial mode content was then computed using a least squares curve fit with the measured radial distribution for each circumferential mode. The rotating microphone technique is superior to fixed-probe techniques because it results in minimal interference with the acoustic modes generated by rotor-stator interaction. This effort represents the first experimental implementation of a measuring technique developed by T. G. Sofrin. Testing was performed in the NASA Lewis Low Speed Anechoic Wind Tunnel at a simulated takeoff condition of Mach 0.2. The design is included of the data analysis software and the performance of the rotating rake apparatus. The effect of experiment errors is also discussed.
Park, G Barratt; Baraban, Joshua H; Field, Robert W
2014-10-07
A full-dimensional Franck-Condon calculation has been applied to the Ã (1)Au-X̃ 1Σg+ transition in acetylene in the harmonic normal mode basis. Details of the calculation are discussed in Part I of this series. To our knowledge, this is the first full-dimensional Franck-Condon calculation on a tetra-atomic molecule undergoing a linear-to-bent geometry change. In the current work, the vibrational intensity factors for levels involving excitation in ungerade vibrational modes are evaluated. Because the Franck-Condon integral accumulates away from the linear geometry, we have been able to treat the out-of-plane component of trans bend (ν4('')) in the linear X̃ state in the rotational part of the problem, restoring the χ Euler angle and the a-axis Eckart conditions. A consequence of the Eckart conditions is that the out-of-plane component of ν4('') does not participate in the vibrational overlap integral. This affects the structure of the coordinate transformation and the symmetry of the vibrational wavefunctions used in the overlap integral, and results in propensity rules involving the bending modes of the X̃ state that were not previously understood. We explain the origin of some of the unexpected propensities observed in IR-UV laser-induced fluorescence spectra, and we calculate emission intensities from bending levels of the Ã state into bending levels of the X̃ state, using normal bending mode and local bending mode basis sets. Our calculations also reveal Franck-Condon propensities for the Cartesian components of the cis bend (ν5('')), and we predict that the best Ã-state vibrational levels for populating X̃-state levels with large amplitude bending motion localized in a single C-H bond (the acetylene↔vinylidene isomerization coordinate) involve a high degree of excitation in ν6(') (cis-bend). Mode ν4(') (torsion) populates levels with large amplitude counter-rotational motion of the two hydrogen atoms.
Plasmon excitations in sodium atomic planes: a time-dependent density functional theory study.
Wang, Bao-Ji; Xu, Yuehua; Ke, San-Huang
2012-08-07
The collective electronic excitation in planar sodium clusters is studied by time-dependent density functional theory calculations. The formation and development of the resonances in photoabsorption spectra are investigated in terms of the shape and size of the two-dimensional (2D) systems. The nature of these resonances is revealed by the frequency-resolved induced charge densities present on a real-space grid. For long double chains, the excitation is similar to that in long single atomic chains, showing longitudinal modes, end and central transverse modes. However, for 2D planes consisting of (n × n) atoms with n being up to 16, new 2D characteristic modes emerge regardless of the symmetries considered. For in-plane excitations, besides the equivalent end mode, mixed modes with contrary polarity occur. The relation between the frequency of the primary modes and the system size is similar to the case of a 2D electron gas but with a correction due to the realistic atomic structure. For excitations perpendicular to the plane there are corner, side center, bulk center, and circuit modes. Our calculation reveals the importance of dimensionality for plasmon excitation and how it evolves from 1D to 2D.
1981-08-01
8217 INCLUDING THE EFFECTS OF HIGHER "ORDER MODES Syracuse University Yehuda Leviatan Arlon T. Adams APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED] C9 2...GRANT NUMSERf() Yecthuda Leviatan Arlon T. Adams F30602-79-C-0011 9. PERNORMING ORGANIZATION NAME ANO ADDRESS 10. PROGRAM ELEMENT, PROJECT, TASK
CNO cycle: ”Soft E1” mode of the 17Ne excitation in the 17Ne+γ → 15O+2p reaction
NASA Astrophysics Data System (ADS)
Parfenova, Yu L.; Grigorenko, L. V.; Egorova, I. A.; Shulgina, N. B.; Zhukov, M. V.
2016-01-01
The 15O(2p, γ)17Ne reaction is studied using the time-reversed reaction of the17Ne E1 Coulomb dissociation on lead target in the context of nuclear astrophysics. Looking for the relation between the data on the Coulomb excitation and the astrophysical 2p-capture rate, one faces problem to extract the Coulomb E1 strength function from the measured Coulex cross section. We use a number of phenomenological approaches to estimate influence of such processes as Coulomb-nuclear interference, populations of states with different Jπ, etc. We calculate the 17Ne+2p astrophysical capture rate and compare the results with different calculations.
Sharipov, Sh.; Ermamatov, M. J. Bayimbetova, J. K.
2008-02-15
The properties of excited states of two deformable odd nuclei are investigated within the nonadiabatic model previously developed by the present authors. The results of relevant calculations are compared with available experimental data.
Relaxation of a hot-electron-two-mode-phonon system in highly excited CdS1-xSex crystals
NASA Astrophysics Data System (ADS)
Žukauskas, A.; Juršėnas, S.
1995-02-01
An investigation of the electron-hole-plasma effective-temperature relaxation in highly excited CdS1-xSex mixed crystals is presented. The slow (~100-ps) relaxation stage, attributed to the depopulation of the fragments (decay products) of the initially produced nonequilibrium LO phonons, is examined with variation of the alloy composition. The relevant relaxation time dependence on x exhibiting a remarkable drop at small CdSe mole fractions is analyzed in terms of a two-route energy relaxation model considering hot-carrier plasma and two generations of nonequilibrium phonons each originating from both pure constituents of the alloy. The disorder-enhanced cross relaxation between two sublattices of the alloy is inferred to account for the experimental results.
Measurement of collective excitations in ${\text{VO}}_{2}$ by resonant inelastic x-ray scattering
He, Haowei; Gray, A. X.; Granitzka, P.; Jeong, J. W.; Aetukuri, N. P.; Kukreja, R.; Miao, Lin; Breitweiser, S. Alexander; Wu, Jinpeng; Huang, Y. B.; Olalde-Velasco, P.; Pelliciari, J.; Schlotter, W. F.; Arenholz, E.; Schmitt, T.; Samant, M. G.; Parkin, S. S. P.; Dürr, H. A.; Wray, L. Andrew
2016-10-15
Vanadium dioxide is of broad interest as a spin-1/2 electron system that realizes a metal-insulator transition near room temperature, due to a combination of strongly correlated and itinerant electron physics. Here, resonant inelastic x-ray scattering is used to measure the excitation spectrum of charge and spin degrees of freedom at the vanadium L edge under different polarization and temperature conditions, revealing excitations that differ greatly from those seen in optical measurements. Furthermore, these spectra encode the evolution of short-range energetics across the metal-insulator transition, including the low-temperature appearance of a strong candidate for the singlet-triplet excitation of a vanadium dimer.
NASA Astrophysics Data System (ADS)
Levshov, Dmitry I.; Avramenko, Marina V.; Than, Xuan-Tinh; Michel, Thierry; Arenal, Raul; Paillet, Matthieu; Rybkovskiy, Dmitry V.; Osadchy, Alexander V.; Rochal, Sergei B.; Yuzyuk, Yuri I.; Sauvajol, Jean-Louis
2016-01-01
Radial breathing modes (RBMs) are widely used for the atomic structure characterization and index assignment of single-walled carbon nanotubes (SWNTs) from resonant Raman spectroscopy. However, for double-walled carbon nanotubes (DWNTs), the use of conventional ωRBM(d) formulas is complicated due to the van der Waals interaction between the layers, which strongly affects the frequencies of radial modes and leads to new collective vibrations. This paper presents an alternative way to theoretically study the collective radial breathing-like modes (RBLMs) of DWNTs and to account for interlayer interaction, namely the continuous two-dimensional membrane theory. We obtain an analytical ωRBLM(do,di) relation, being the equivalent of the conventional ωRBM(d) expressions, established for SWNTs. We compare our theoretical predictions with Raman data, measured on individual index-identified suspended DWNTs, and find a good agreement between experiment and theory. Moreover, we show that the interlayer coupling in individual DWNTs strongly depends on the interlayer distance, which is manifested in the frequency shifts of the RBLMs with respect to the RBMs of the individual inner and outer tubes. In terms of characterization, this means that the combination of Raman spectroscopy data and predictions of continuous membrane theory may give additional criteria for the index identification of DWNTs, namely the interlayer distance.
Korolyuk, A.; Kinnunen, J. J.; Toermae, P.
2011-09-15
We consider the density response of a trapped two-component Fermi gas. Combining the Bogoliubov-deGennes method with the random phase approximation allows the study of both collective and single-particle excitations. Calculating the density response across a wide range of interactions, we observe a crossover from a weakly interacting pair vibration mode to a strongly interacting Goldstone mode. The crossover is associated with a depressed collective mode frequency and an increased damping rate, in agreement with density response experiments performed in strongly interacting atomic gases.
NASA Astrophysics Data System (ADS)
Kumar, R.; Mehta, D. S.; Saraswati, S.; Shakher, C.
2012-02-01
Apart from commonly employed target-specific labeling/adsorption of antibodies over Au-NPs surface for the creation of localized aggregates, an alternative approach using optical tweezers (OT) driven by hybrid-TEM*11 mode has been devised and exploited for in vitro detection of Ehrlich ascites carcinoma cells (EAC) relying on enhanced scattering. Intra-cavity generated spatially featured asymmetric (SFA) laser beam (λ = 532 nm) has effected simultaneous trapping of mice-EAC cells and in-situ crowd/assembly of incubated Au-NPs/small gold nano-aggregates (created from two or more individual Au-NPs). Relatively larger focus spot created by tightly focused SFA beam than frequently employed Gaussian-mode in OT has offered an extended working area and hence dilute heating has taken care of EAC cells. GNA improves significantly the sensitivity of diagnostics relying on scattered light and the safety and efficacy of therapeutic nanotechnologies for the diseases of cancer and vascular system in medicine.
NASA Astrophysics Data System (ADS)
Sherman, Justin; Azzari, Phillip; Crilly, P. B.; Duke-Tinson, Omar; James, Royce W.; Karama, Jackson; Page, E. J.; Schlank, Carter; Zuniga, Jonathan
2014-10-01
CGAPL is conducting small investigations in plasma physics and magneto-hydrodynamics buoy positioning. For data management, we are developing capability to analyze/digitize data with a National Instruments Data Acquisition board, 2 MS/s sampling rate (long time scale), and an Express Octopus card, 125 MS/s sampling rate (short scale). Sampling at 12 bits precision, we use LabVIEW as a programing language; GUIs will control variables in 1 or more concurrent runs and monitor of diagnostics. HPX utilizes high density (1013 cm3 up), low pressure (.01 T) Ar gas (fill pressure: on 104 mTorr order). Helicon/W Mode plasmas become a diagnostics test-bed for other investigations and a tool for future spacecraft propulsion devices. Plasmas created by directing energy into gas-filled Pyrex tube; power supply and matching box, up to 250 W power in 20-100 MHz frequencies, provide energy to ignite. Uniform magnetic field needed to reach the W-Mode. We employ an electromagnet to B-field while an acceleration coil positions plasma in vacuum chamber, facilitating analysis. Initial field requirements and accuracy calibration have been completed. Progress on development and implementation of probes and DAQ/GUI system will be reported. Supported by U.S. DEPS Grant [HEL-JTO] PRWJFY13.
Chen, Yulin; Iyo, Akira; Yang, Wanli; Ino, Akihiro; Arita, M; Johnston, Steve; Eisaki, Hiroshi; Namatame, H; Taniguchi, M; Devereaux, Thomas P; Hussain, Zahid; Shen, Z-X
2009-07-17
Low energy ultrahigh momentum resolution angle resolved photoemission spectroscopy study on four-layer self-doped high Tc superconductor Ba2Ca3Cu4O8F2 (F0234) revealed fine structure in the band dispersion, identifying the unconventional association of hole and electron doping with the inner and outer CuO2 layers, respectively. For the states originating from two inequivalent CuO2 layers, different energy scales are observed in dispersion kinks associated with the collective mode coupling, with the larger energy scale found in the electron (n-) doped state which also has stronger coupling strength. Given the earlier finding that the superconducting gap is substantially larger along the n-type Fermi surface, our observations connect the mode coupling energy and strength with magnitude of the pairing gap.
Chen, Yulin; Iyo, Akira; Yang, Wanli; Ino, Akihiro; Arita, M.; Johnston, Steve; Eisaki, Hiroshi; Namatame, H.; Taniguchi, M.; Devereaux, Thomas P.; Hussain, Zahid; Shen, Z.-X.; /SLAC /Stanford U., Phys. Dept.
2011-08-12
Low energy ultrahigh momentum resolution angle resolved photoemission spectroscopy study on four-layer self-doped high T{sub c} superconductor Ba{sub 2}Ca{sub 3}Cu{sub 4}O{sub 8}F{sub 2} (F0234) revealed fine structure in the band dispersion, identifying the unconventional association of hole and electron doping with the inner and outer CuO{sub 2} layers, respectively. For the states originating from two inequivalent CuO{sub 2} layers, different energy scales are observed in dispersion kinks associated with the collective mode coupling, with the larger energy scale found in the electron (n-) doped state which also has stronger coupling strength. Given the earlier finding that the superconducting gap is substantially larger along the n-type Fermi surface, our observations connect the mode coupling energy and strength with magnitude of the pairing gap.
An ASAP treatment of vibrationally excited S2O: The ν3 mode and the ν3 + ν2 - ν2 hot band
NASA Astrophysics Data System (ADS)
Thorwirth, S.; Martin-Drumel, M. A.; Endres, C. P.; Salomon, T.; Zingsheim, O.; van Wijngaarden, J.; Pirali, O.; Gruet, S.; Lewen, F.; Schlemmer, S.; McCarthy, M. C.
2016-01-01
The fundamental S-S stretching mode ν3 of disulfur monoxide, S2O, located at 679 cm-1, has been investigated using Fourier-transform far-infrared spectroscopy at the SOLEIL synchrotron facility. A spectroscopic analysis has been performed using an Automated Spectral Assignment Procedure (ASAP) which permits accurate determination of more than 2000 energy levels from ν3. In addition, the ν3 + ν2 - ν2 hot band was observed for the first time and some 500 corresponding energy levels were assigned. The high-resolution synchrotron study was complemented with pure rotational spectra of S2O in the (v1, v2, v3) = (0, 0, 1) vibrational state observed in the frequency range from 250 to 280 GHz using a long-path absorption cell. From these combined measurements, extensive molecular parameter sets have been determined and precise band centers have been derived for both vibrational bands.
Spagnolo, V.; Patimisco, P.; Borri, Simone; Scamarcio, G.; Bernacki, Bruce E.; Kriesel, J.M.
2012-10-23
A sensitive spectroscopic sensor based on a hollow-core fiber-coupled quantum cascade laser (QCL) emitting at 10.54 µm and quartz enhanced photoacoustic spectroscopy (QEPAS) technique is reported. The design and realization of mid-infrared fiber and coupler optics has ensured single-mode QCL beam delivery to the QEPAS sensor . The collimation optics was designed to produce a laser beam of significantly reduced beam size and waist so as to prevent illumination of the quartz tuning fork and micro-resonator tubes. SF6 was selected as the target gas. A minimum detection sensitivity of 50 parts per trillion in 1 s was achieved with a QCL power of 18 mW, corresponding to a normalized noise-equivalent absorption of 2.7x10-10 W•cm-1/Hz1/2.
Spagnolo, Vincenzo; Patimisco, Pietro; Borri, Simone; Scamarcio, Gaetano; Bernacki, Bruce E; Kriesel, Jason
2012-11-01
A sensitive spectroscopic sensor based on a hollow-core fiber-coupled quantum cascade laser (QCL) emitting at 10.54 μm and quartz enhanced photoacoustic spectroscopy (QEPAS) technique is reported. The design and realization of mid-IR fiber and coupler optics has ensured single-mode QCL beam delivery to the QEPAS sensor. The collimation optics was designed to produce a laser beam of significantly reduced beam size and waist so as to prevent illumination of the quartz tuning fork and microresonator tubes. SF(6) was selected as the target gas. A minimum detection sensitivity of 50 parts per trillion in 1 s was achieved with a QCL power of 18 mW, corresponding to a normalized noise-equivalent absorption of 2.7×10(-10) W·cm(-1)/Hz(1/2).
NASA Astrophysics Data System (ADS)
Okabayashi, M.
2010-11-01
Advanced tokamak experiments in JT-60U [1] and DIII-D [2] have revealed that in high-beta q(0)>1 plasmas, where the resistive wall modes (RWMs) are predicted to be stable by kinetic effects of energetic particles, plasma rotation and a nearby conducting wall, off-axis fishbone-like instabilities often trigger RWMs. The rapid growth of these RWMs prevents high performance operation. The off-axis fishbone-like instability has some similarities to the classic m/n=1/1 internal fishbone instability in terms of its initial frequency near the energetic ion precession frequency, downward frequency-chirping, and a neutron rate drop of ˜20% during each burst. However, there are several unique non-ideal-MHD features in the off-axis fishbone-like instability. The waveform time behavior has strong non-sinusoidal distortion from the q˜2 area to the edge, synchronized with bursting energetic particle losses, while the plasma rotation is rapidly reduced within a few milliseconds. Based on experimental observations the following hypothesis emerges. In plasmas where rotation and kinetic effects are usually sufficient to stabilize the RWM, energetic particles can drive the fishbone instability of several kHz (larger than the inverse of the resistive wall time constant). The reduction of kinetic stabilization due to the resulting energetic particle loss and rapid decrease of plasma rotation makes the plasma more vulnerable to the near-zero frequency RWM. The impact on RWM stability by the off-axis fishbone with its radial and toroidal distortion of the mode structure is assessed by comparing the JT-60U/DIII-D results with theoretical predictions. 6pt [1] G. Matsunaga et al., Phys. Rev. Lett. 103, 045001. (2009). [2] M. Okabayashi et al., Nucl. Fusion 49 (2009) 125003.
Light plasmon mode in the CFL phase
Malekzadeh, H.; Rischke, Dirk H.
2007-02-27
The self-energies and the spectral densities of longitudinal and transverse gluons at zero temperature in the color-flavor-locked (CFL) phase are calculated. There appears a collective excitation, a light plasmon, at energies smaller than two times the gap parameter and momenta smaller than about eight times the gap. The minimum in the dispersion relation of this mode at some nonzero value of momentum corresponds to the van Hove singularity.
Cooperative entangled effects between the cavity mode components of Raman process
NASA Astrophysics Data System (ADS)
Enaki, Nicolae A.
2016-12-01
The cooperative excitation and absorption of light into three cavity modes (pump, Stokes and anti-Stokes), stimulated by excited radiators, is studied as bound entangled states of the photon subsystem. The three modes collective Roman emission and its connection with entangled state is defined introducing the cooperative description between photons of cavity modes. In the case, when the scattering rates in the Stokes and anti-Stokes modes coincide, the SU(2) and SU(1,1) symmetries are applied for a simple description of these cooperative processes. The possibilities to realize this effect in the free space is proposed, replacing the cavity modes with dipole active excited atoms in tow-quantum interaction with dipole-forbidden transitions of D atom. The statistical properties and detection method are proposed using the information entropy and atomic correlation functions.
Intriguing triple-mode RR Lyrae star with period doubling
NASA Astrophysics Data System (ADS)
Smolec, R.; Soszyński, I.; Udalski, A.; Szymański, M. K.; Pietrukowicz, P.; Skowron, J.; Kozłowski, S.; Poleski, R.; Moskalik, P.; Skowron, D.; Pietrzyński, G.; Wyrzykowski, Ł.; Ulaczyk, K.; Mróz, P.
2015-03-01
We report the discovery of an intriguing triple-mode RR Lyrae star found in the Optical Gravitational Lensing Experiment (OGLE) Galactic bulge collection, OGLE-BLG-RRLYR-24137. In the OGLE catalogue, the star was identified as RRd star - double-mode pulsator, pulsating simultaneously in the fundamental and in the first overtone modes. We find that third mode is excited and firmly detect its period doubling. Period ratios are not far from that expected for triple-mode - fundamental, first and third overtone - pulsation. Unfortunately, we cannot reproduce period ratios of the three modes with a consistent set of pulsation models. Therefore the other interpretation, that additional mode is non-radial, is also likely.
Whitmire, S E; Wolpert, D; Markelz, A G; Hillebrecht, J R; Galan, J; Birge, R R
2003-08-01
Far infrared (FIR) spectral measurements of wild-type (WT) and D96N mutant bacteriorhodopsin thin films have been carried out using terahertz time domain spectroscopy as a function of hydration, temperature, and conformational state. The results are compared to calculated spectra generated via normal mode analyses using CHARMM. We find that the FIR absorbance is slowly increasing with frequency and without strong narrow features over the range of 2-60 cm(-1) and up to a resolution of 0.17 cm(-1). The broad absorption shifts in frequency with decreasing temperature as expected with a strongly anharmonic potential and in agreement with neutron inelastic scattering results. Decreasing hydration shifts the absorption to higher frequencies, possibly resulting from decreased coupling mediated by the interior water molecules. Ground-state FIR absorbances have nearly identical frequency dependence, with the mutant having less optical density than the WT. In the M state, the FIR absorbance of the WT increases whereas there is no change for D96N. These results represent the first measurement of FIR absorbance change as a function of conformational state.
Vibrational excitation induces double reaction.
Huang, Kai; Leung, Lydie; Lim, Tingbin; Ning, Zhanyu; Polanyi, John C
2014-12-23
Electron-induced reaction at metal surfaces is currently the subject of extensive study. Here, we broaden the range of experimentation to a comparison of vibrational excitation with electronic excitation, for reaction of the same molecule at the same clean metal surface. In a previous study of electron-induced reaction by scanning tunneling microscopy (STM), we examined the dynamics of the concurrent breaking of the two C-I bonds of ortho-diiodobenzene physisorbed on Cu(110). The energy of the incident electron was near the electronic excitation threshold of E0=1.0 eV required to induce this single-electron process. STM has been employed in the present work to study the reaction dynamics at the substantially lower incident electron energies of 0.3 eV, well below the electronic excitation threshold. The observed increase in reaction rate with current was found to be fourth-order, indicative of multistep reagent vibrational excitation, in contrast to the first-order rate dependence found earlier for electronic excitation. The change in mode of excitation was accompanied by altered reaction dynamics, evidenced by a different pattern of binding of the chemisorbed products to the copper surface. We have modeled these altered reaction dynamics by exciting normal modes of vibration that distort the C-I bonds of the physisorbed reagent. Using the same ab initio ground potential-energy surface as in the prior work on electronic excitation, but with only vibrational excitation of the physisorbed reagent in the asymmetric stretch mode of C-I bonds, we obtained the observed alteration in reaction dynamics.
Energy transport in metal nanoparticle chains via sub-radiant plasmon modes.
Willingham, Britain; Link, Stephan
2011-03-28
We investigate the propagation of surface plasmon polaritons through coupling of light to sub-radiant dipole modes in finite chains of Ag nanoparticles. End excitation of collections of closely spaced particles reveals a band of sub-radiant modes whereby the decay of surface plasmon polaritons due to radiative losses is minimized. We show that excitation of any of these sub-radiant modes results in the most efficient energy transfer throughout the optical spectrum, with smaller interparticle separations resulting in the longest propagation.
Kogar, A.; Gu, G.; Vig, S.; Thaler, A.; Wong, M. H.; Xiao, Y.; Reig-i-Plessis, D.; Cho, G. Y.; Valla, T.; Pan, Z.; Schneeloch, J.; Zhong, R.; Hughes, T. L.; MacDougall, G. J.; Chiang, T. -C.; Abbamonte, P.
2015-12-15
In this study, we used low-energy, momentum-resolved inelastic electron scattering to study surface collective modes of the three-dimensional topological insulators Bi_{2}Se_{3} and Bi_{0.5}Sb_{1.5}Te_{3-x}Se_{x}. Our goal was to identify the “spin plasmon” predicted by Raghu and co-workers [Phys. Rev. Lett. 104, 116401 (2010)]. Instead, we found that the primary collective mode is a surface plasmon arising from the bulk, free carriers in these materials. This excitation dominates the spectral weight in the bosonic function of the surface χ''(q,ω) at THz energy scales, and is the most likely origin of a quasiparticle dispersion kink observed in previous photoemission experiments. Our study suggests that the spin plasmon may mix with this other surface mode, calling for a more nuanced understanding of optical experiments in which the spin plasmon is reported to play a role.
A dual mode breath sampler for the collection of the end-tidal and dead space fractions.
Salvo, P; Ferrari, C; Persia, R; Ghimenti, S; Lomonaco, T; Bellagambi, F; Di Francesco, F
2015-06-01
This work presents a breath sampler prototype automatically collecting end-tidal (single and multiple breaths) or dead space air fractions (multiple breaths). This result is achieved by real time measurements of the CO2 partial pressure and airflow during the expiratory and inspiratory phases. Suitable algorithms, used to control a solenoid valve, guarantee that a Nalophan(®) bag is filled with the selected breath fraction even if the subject under test hyperventilates. The breath sampler has low pressure drop (<0.5 kPa) and uses inert or disposable components to avoid bacteriological risk for the patients and contamination of the breath samples. A fully customisable software interface allows a real time control of the hardware and software status. The performances of the breath sampler were evaluated by comparing (a) the CO2 partial pressure calculated during the sampling with the CO2 pressure measured off-line within the Nalophan(®) bag; (b) the concentrations of four selected volatile organic compounds in dead space, end-tidal and mixed breath fractions. Results showed negligible deviations between calculated and off-line CO2 pressure values and the distributions of the selected compounds into dead space, end-tidal and mixed breath fractions were in agreement with their chemical-physical properties.
Terahertz plasmonic excitations in Bi2Se3 topological insulator.
Autore, M; Di Pietro, P; Di Gaspare, A; D'Apuzzo, F; Giorgianni, F; Brahlek, Matthew; Koirala, Nikesh; Oh, Seangshik; Lupi, S
2017-05-10
After the discovery of Dirac electrons in condensed matter physics, more specifically in graphene and its derivatives, their potentialities in the fields of plasmonics and photonics have been readily recognized, leading to a plethora of applications in active and tunable optical devices. Massless Dirac carriers have been further found in three-dimensional topological insulators. These exotic quantum systems have an insulating gap in the bulk and intrinsic Dirac metallic states at any surface, sustaining not only single-particle excitations but also plasmonic collective modes. In this paper we will review the plasmon excitations in different microstructures patterned on Bi2Se3 topological insulator thin films as measured by terahertz spectroscopy. We discuss the dependence of the plasmon absorption versus the microstructure shape, wavevector, and magnetic field. Finally we will discuss the topological protection of both the Dirac single-particle and plasmon excitations.
Shreif, Zeina; Ortoleva, Peter
2011-03-14
Examples of quantum nanosystems are graphene nanoribbons, molecular wires, and superconducting nanoparticles. The objective of the multiscale theory presented here is to provide a new perspective on the coupling of processes across scales in space and time underlying the dynamics of these systems. The long range objective for this multiscale approach is to serve as an efficient computational algorithm. Long space-time dynamics is derived using a perturbation expansion in the ratio ɛ of the nearest-neighbor distance to a nanometer-scale characteristic length and a theorem on the equivalence of long time-averages and expectation values. This dynamics is shown to satisfy a coarse-grained wave equation (CGWE) which takes a Schrödinger-like form with modified masses and interactions. The scaling of space and time is determined by the orders of magnitude of various contributions to the N-body potential. If the spatial scale of the coarse-graining is too large, the CGWE would imply an unbounded growth of gradients; if it is too short, the system's size would display uncontrolled growth inappropriate for the bound states of interest, i.e., collective motion or migration within a stable nanoassembly. The balance of these two extremes removes arbitrariness in the choice of the scaling of space-time. Since the long-scale dynamics of each Fermion involves its interaction with many others, we hypothesize that the solutions of the CGWE have mean-field character to good approximation, i.e., can be factorized into single-particle functions. This leads to a coarse-grained mean-field approximation that is distinct in character from traditional Hartree-Fock theory. A variational principle is used to derive equations for the single-particle functions. This theme is developed and used to derive an equation for low-lying disturbances from the ground state corresponding to long wavelength density disturbances or long-scale migration. An algorithm for the efficient simulation of
List mode multichannel analyzer
Archer, Daniel E.; Luke, S. John; Mauger, G. Joseph; Riot, Vincent J.; Knapp, David A.
2007-08-07
A digital list mode multichannel analyzer (MCA) built around a programmable FPGA device for onboard data analysis and on-the-fly modification of system detection/operating parameters, and capable of collecting and processing data in very small time bins (<1 millisecond) when used in histogramming mode, or in list mode as a list mode MCA.
Mode-mode fiber interferometer with impact localization ability
NASA Astrophysics Data System (ADS)
Kotov, Oleg; Chapalo, Ivan
2016-04-01
In this publication we investigate distributed mode-mode fiber interferometer (MFI) with ability of external impact localization. It is based on bidirectional continuous selective excitation of multimode fiber (MMF) with increasing of launched modes quantity along the MMF from excitation point to the opposite end of fiber. Two photo detection systems register output signals from both directions. MFI output signal characteristics such as amplitude and spectrum width depend on excited modes quantity at the point of perturbation. Thus, every fiber point is characterized by two opposite direction signal parameters. Calculating these parameters' values makes it possible to localize the segment subjected by external impact. Experimental MFI setup include 3 MMF segments with 2 mode controllers among them which increase excited modes number from segment to segment. During the experiment, every MMF segment was subjected by arbitrary external perturbations and output signals were analyzed. Obtained results confirmed the ability of localization.
Noguchi, T.; Hayashi, H. Univ. of Tokyo ); Tasumi, M. ); Atkinson, G.H. Hebrew Univ., Jerusalem )
1991-04-18
Picosecond time-resolved resonance Raman spectra in the C{double bond}C stretching region are presented for {beta}-carotene and two of its derivatives, {beta}-apo-8{prime}-carotenal and ethyl {beta}-apo-8{prime}-carotenoate. The solvent effects on the Franck-Condon-active a{sub g} C{double bond}C stretching mode in the {sup 1}A{sub g}{sup {minus}} ground state (S{sub 0}) and the 2{sup 1}A{sub g}{sup {minus}} excited state (S{sub 1}) of each carotenoid are described. The C{double bond}C stretching frequencies in S{sub 1} are affected by the solvent and show a correlation with the absorption maxima of the S{sub 2} ({sup 1}B{sub u}{sup +}) {l arrow} S{sub 0} transition, while those in S{sub 0} are not significantly affected. These results are interpreted in terms of the vibronic coupling among the S{sub 0}, S{sub 1}, and S{sub 2} electronic states, the solvent effect on the energy of the S{sub 1} and S{sub 2} states, and the structures of carotenoid molecules.
Mode pumping experiments on biomolecules
Austin, R.H.; Erramilli, S.; Xie, A.; Schramm, A.
1995-12-31
We will explore several aspects of protein dynamics and energy transfer that can be explored by using the intense, picosecond, tunable mid-IR output of the FEL. In order of appearance they are: (1) Saturation recovery and inter-level coupling of the low temperature amide-I band in acetanilide. This is a continuation of earlier experiments to test soliton models in crystalline hydrogen bonded solids. In this experiment we utilize the sub-picosecond time resolution and low repetition rate of the Stanford SCLA FEL to do both T{sub 1} and T{sub 2} relaxation measurements at 1650 cm{sup -1}. (2) Probing the influence of collective dynamics in sensory rhodopsin. In this experiment we use the FIR output of the Stanford FIREFLY FEL to determine the lifetime of collective modes in the photo-active protein sensory rhodopsin, and begin experiments on the influence of collective modes on retinal reaction dynamics. (3) Probing the transition states of enzymes. This experiment, in the initial stages, attempts to use the intense IR output of the FEL to probe and influence the reaction path of a transition state analog for the protein nucleoside hydrolase. The transition state of the inosine substrate is believed to have critical modes softened by the protein so that bond-breaking paths show absorption at approximately 800 cm{sup -1}. A form of action spectrum using FEL excitation will be used to probe this state.
Mode-selective control of the crystal lattice.
Först, M; Mankowsky, R; Cavalleri, A
2015-02-17
CONSPECTUS: Driving phase changes by selective optical excitation of specific vibrational modes in molecular and condensed phase systems has long been a grand goal for laser science. However, phase control has to date primarily been achieved by using coherent light fields generated by femtosecond pulsed lasers at near-infrared or visible wavelengths. This field is now being advanced by progress in generating intense femtosecond pulses in the mid-infrared, which can be tuned into resonance with infrared-active crystal lattice modes of a solid. Selective vibrational excitation is particularly interesting in complex oxides with strong electronic correlations, where even subtle modulations of the crystallographic structure can lead to colossal changes of the electronic and magnetic properties. In this Account, we summarize recent efforts to control the collective phase state in solids through mode-selective lattice excitation. The key aspect of the underlying physics is the nonlinear coupling of the resonantly driven phonon to other (Raman-active) modes due to lattice anharmonicities, theoretically discussed as ionic Raman scattering in the 1970s. Such nonlinear phononic excitation leads to rectification of a directly excited infrared-active mode and to a net displacement of the crystal along the coordinate of all anharmonically coupled modes. We present the theoretical basis and the experimental demonstration of this phenomenon, using femtosecond optical spectroscopy and ultrafast X-ray diffraction at a free electron laser. The observed nonlinear lattice dynamics is shown to drive electronic and magnetic phase transitions in many complex oxides, including insulator-metal transitions, charge/orbital order melting and magnetic switching in manganites. Furthermore, we show that the selective vibrational excitation can drive high-TC cuprates into a transient structure with enhanced superconductivity. The combination of nonlinear phononics with ultrafast crystallography at